ANNUAL REVIEW
Protective Coati ngs HOWARD L. GERHART
EARL E. PARKER
The regular additions t o existing families of polymers by imaginative synthesis and evol utionary modification and the detailed understanding of such polymers through the application of techniques of physics and physical chemistry, as a means t o formulate coatings with optimum properties, are the 4
E Y,
two technological forces at work
i
enlarging the horizons of the coatings industry. The Jettmar technique ( 7 I C ) j n d s a Benard cell in cross section. The transport of clear vehicle upzward from the depth to the surface of a j l m is easily recognized: (1) pattern ofj7ol'o.l at cell boundary, ( 2 ) pigment-rich inner zone, and (3)pigment starved surface
42
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Structural steel is protected with an epoxy resin-bitumen system f o long ~ term maintenance-free service in both salt and fresh water in the movable locks along the west coast of Holland which will controljoods from the sea
COURTESY RIdKBWATERSTAAT, D E N HAAO (FEDERAL WATER COMMISSION. T H E
HAOUE)
n excellent traditional recitation of segmented A references to worldwide literature in coatings technology is available (5911). The presentation is divided into 14 categories written in the style characteristic of library card files-Le., generally without editorial comment or summary. The procedure is especially useful for the detection of discoveries filed in countries which publish typical patent claims at an early date. The intention of this review is to spot stirrings or trends; to answer the question “What’s happening in polymer coatings?” ; to supply generalized and particular background in story form. It is not intended to provide an encyclopedic documentation, or to recite all the modifications available in raw materials. Possibly the best objective service to the chemical and engineering profession is annually to locate the most comprehensive review articles as a basis for cataloging and .updating the state of the science. I n a discipline where the craft seems to overpower the science, this can bring order to the confusion of essential details which characterize the work of coatings technologists. The review is written for two types of readers: those active in the coatings profession who already know most of the progress but can benefit by systemized comment; those working in somewhat related fields who desire an occasional instant updating for generalized purposes in “the other man’s technology.” A fitting example of a complete subject review is the case of two assessments in the field of thermosetting acrylic resins which the authors consider to define the technical status and which need no further abstraction (504 69A).
A
B
An indication of precision in the study of surface weathering on painted panels. In A an unexposedjlm pigmented with titanium dioxide shows ( I ) the pigment comfortably covered with the enveloping vehicle. In B the sameJilm after artijicial weathering is degraded ( 2 ) to a packed layer of unsupForted pigmented particles
VOL. 5 9
NO. 8
AUGUST 1967
43
In the case of “electrophoretic paints” (more properly, electrodeposited films), a single comprehensive analytical treatment is not available. One can only recite a list of repom or practices which, in a subtle or sbmewhat concealed way, reveals that there are now available coatings based on the following generic resin classes: esterified polyols, maleinized oils, epoxy esters, poly(acrylates), and alkyd-melamine. In all technology, a t a certain period during the early years of commercial use, one must accept a plateau in which gems may have the same interest as diamonds. Though no new and dramatic results are reported, there is w u r a n c e that the predictions of the past have been fulfilled, and progress is marked by the degree to which the several installations of electrocoating tanks on an international scale are now in foolproof operation. The extensive biographic section shown below testifies that these process and property improvements have been accomplished : 4 - p r i m i n g , onecoat systems -simplified feed systems -tolerance for pigments -wet adhesion -saponification and detergent resistance -electrodeposited top coats on primed surfaces -increased throw power and filmbuild -assurance of adequate cornmion protection
2A
IIA
21A
34A
53A
67A
3A
72A
23A
35A
55A
68A
5A
13A
25A
36A
56A
75A
4
74A
26A
37A
58A
76A
4
15A
29A
38A
64A
78A
4
18A
37A
39A
65A
79A
4
19A
32A
41A
66A
80A
In the coatings industry with annual domestic sales
SYNTHETIC RESINS
of $2.375 biuion, science has
now caught up with the craft. Two technological forces are a t work in pushing the horizons of the industry of coatings science: (a) The regular additions to existing families of polymers by imaginative synthesis and evolutionary modification (b) The detailed understanding of such polymem through the application of techniques of physics and physical chemistry a8 a means to formulate coatings with optimum properties 44
INDUSTRIAL AND ENGINEERING CHEMISTRY
Polyeden
The advent of new types of polyesters in the coatings field has led to some contusion in nomenclature. The types of interest can be classified as follows: (1) alkyd resins, (2) polyester polyols, (3) polyester polyacids, (4) linear polyesters (polymeric plasticizm), and (5) unsaturated polyester (polyester-styreneresins). Examples are shown in Figure 1.
Coatings based on alkyd resins continue to hold their own year after year in spite of ever-increasing competition from other materials (77A). The use of nonvolatile acrylate or methacrylate monomers added as solvents in alkyd resin formulations has added a new dimension to alkyd resin formulations. These monomers coreact with the resin and are permanently incorporated into the film. Monofunctional monomers such as lauryl methacrylate were found to plasticize the film while difunctional monomers such as ethylene glycol dimethacrylate were found to harden it. In both cases, the throughdry of the film was improved even in the absence of lead driers ( 4 4 . Lactic acid has been recommended as an ingredient for alkyd resins for the reduction of viscosity and improvement in pigment dispersion properties. This approach can be used in highly reactive systems to control viscosity and to make novel resins of very short oil length (87A). The glycerolysis rate of drying oils was found to be favored by high iodine number and low acid number and retarded by high acid number and low iodine value (2OA). Polyester polyols (frequently named “oil free alkyds”) constitute an exciting future growth area in polyester technology. These products vary from essentially linear polyesters to conventional alkyd resins made with nondrying oils. Figure 2 shows how polyester polyols can be cross-linked by reacting them with hexamethoxymethyl melamine (3oA), urea formaldehyde resins, melamine formaldehyde resins, or thermoaetting acrylics (514. Coatings prepared from polyester polyols have a light color, excellent hardnesa a t a given flexibility, good *stance to yellowing, and superior adhesion to metals. Improved resistance to saponification and chemical attack is obtained by the use of polyols or acids carrying methyl01 groups or carboxyl groups on completely substituted carbon atoms. Polyesters from sueh materials are far more difficult to hydrolyze than conventional polyesters and provide films with superior chemical resistance. Neopentyl glycol (76A,6ZA) and the glycidyl ester of 9 to 11 carbon atom branched chain acids (574have been used with particular success in this respect. These polyesters are compatible with a wide variety of other thermoplastic and can be used to modify their properties. An interesting use of polyester polyacids is as a curing agent for epoxidized oils (Figure 3). Carboxyl terminated polyesters, where the acid is tetrachlorophthalic or chlorendic, are capable of curing epoxidized oils rapidly a t room temperature. Films of this type have shown better gloss retention, better color retention, and less chalking than moisture cured urethanes or conventional catalyzed epoxies. T h e durability was almost equal to a baked alkyd melamine system @A).
I
Resins for Water Based Coatings
Currently the major types of latices used in trade sales coatings are poly(viny1 acetate) and poly(acry1ates). Poly(viny1 acetate) has the greatest share of the present market and much effort is being expended in attempts to keep it in a strong position (77A). Copolymers of vinyl acetate and vinyl esters of branched chain fatty acids of 9 to 11 carbon atoms have improved properties over latices prepared from vinyl acetate homopolymer. Good latex stability, superior resistance to scrubbing, dilute acids and alkalies, and improved exterior weathering are claimed (43A). The adhesion of outdoor emulsion paints over a highly chalked surface is often poor. Formulation with a n alkyd resin is commonly used to eliminate this difficulty. Modifications as high as 75% alkyd resin were found to give improved performance (49A). Latices containing copolymers of vinyl acetate with ethylene (45A), acrylic monomers, maleate esters, and vinyl Chloride have been introduced and are vying with more conventional latices for a share of the market. The new latex is claimed to have superior flexibility, durability, and potentially reasonable cost (77A). Copolymers of vinyl chloride with acrylic monomers have finally entered the water based exterior house paint market. These copolymers have an advantage over competitive materials in durability. Tables I and I1 show some of the physical properties of one vinyl chloride-acrylic copolymer in comparison with three of the current commercial types ( 7 A ) . A 100% acrylic emulsion for exterior wood and masonry paints has been introduced. I t has high resistance to chalking, reduced dirt pick-up, greater latitude in the use of pigment and extenders plus good resistance to grain cracking, and excellent adhesion over old weathered surfaces. An emulsifiable polyurethane resin improves the adhesion of emulsion paints to highly chalked surfaces when used in 20 to 25y0 of the total resin solids in the paints (77A). Sheetz has proposed a new theory to explain the mechanism of latex film formation. The relationship between wet sintering and capillarity and diffusion was investigated (73A). The success of electrocoating has generated a great deal of effort in the preparation of water soluble coatings. This work has been reviewed by Hagen (23A) and also by MacLean (444). Water soluble butadiene copolymers have been described by Oelsner (524). Prepolymers prepared from epoxidized linseed oil and fumaric acid can be deposited from aqueous solution and cured to form tough resinous films (56A). Water soluble alkyd resins prepared from tris-hydroxymethylaminomethane have been described. Epoxy resin esters can be solubilized by maleinization or phthalic acid half ester formation and used as vehicles for electrodeposition (9A, 57A). Transparent, water resistant, curable epoxy acetals and resins are possible from monoepoxy acetals and polyepoxy acetals by polymerization in the presence 46
INDUSTRIAL A N D ENGINEERING CHEMISTRY
I TABLE I . CRACKING RESISTANCE OF SELFPRIMED PAINTS (2570 PVC) AFTER 16 MONTHS OUTDOOR AGING Latex type Rating A. Vinyl chloride-acrylic copolymer 10 C. Styrene-acrylic copolymer 5 B. 10070 Acrylic 7 D. Vinvl acetate homouolvmer 8 10 = no cracking 1 = completely cracked
Thermosetting Acrylics
The use of fast curing thermosetting acrylics for automotive, appliance, metal strip, and can coatings is flourishing. Currently, thermosetting acrylics can be classified under acrylic-melamine, acrylic-epoxy, acrylamide, and acrylic-alkyd types. All of these crosslink by polycondensation reactions ( 6 2 A ) . Vinyl cyclic acetals are a new type of monomer which cross-link through autooxidation. Acrylic monomers containing the metadioxane ring produce polymers with unusually high softening points that cross-link by peroxide or ionic mechanisms. Two of these monomers are: 0
It
CH,= C -C-
I
CH3
I. R = H
/CH20\
OCH,rC l'CH2-0 CH3
c,
R =R
11. R = CH3
The CR2 group appears to be involved in the crosslinking reaction since the polymer of Compound I crosslinked much faster than the polymer of Compound I1 under the influence of either peroxide or anhydrous acid (47A). Other novel monomers contain cyclic carbonate, bicyclic phosphate, bicyclic phosphite, spiroacetal, oxazoline, and quaternary ammonium groups (50A). Thermosetting acrylic resins have been improved by copolymerization with unsaturated polyester resins. Saturated polyester resins used as controls were incompatible and gave poor results (72%). Lewis has studied the efficiency of the cross-linking of thermosetting acrylic resins by bisamide formation, transesterification, formal formation, and transformalation. H e determined the cross-linking density by a novel linear constrained film swelling ratio method and found that all four mechanisms were about equally effective (40A).
TABLE II. Latex type (see Table I ) Tensile strength yo Elongation Tensile strength, 200 hr. in Fade-0-Meter yo Elongation, 200 hr. in Fade-0-Meter yo Swelling in water (24 hr.) Moisture vapor transmission, grams/100 sq. in./24 hr. Visual observations during Fade-0-Meter exposure
PHYSICAL PROPERTIES OF CLEAR F I L M
A
B
c
1885 490 2300
2135
1095 560
370 2.05 0.9 Stiff, slightly brittle at 1400 hr.
Fusion Coatings
There has been a great deal of commercial interest in application methods that provide a thick film in one operation. This concept has both the advantage of reducing labor costs by reducing the number of passes and also eliminating the use of hazardous solvents. The coating of metal parts with finely divided polymers is called fusion coating. I n fluid bed coating, the metal part is preheated and passed through a fluidized bed of the polymer. I n electrostatic bed coating and electrostatic spray, the coating is applied electrically, and it is not necessary to preheat the metal part. A further variation is flock spraying in which the powdered polymer is sprayed onto a preheated metal part. Epoxies, vinyls, polyethylene, polyamides, cellulose acetate butyrate, poly (methacrylate), poly(viny1 acetate), poly(propylene), and poly(styrene) have all been used for this purpose. Film thicknesses up to 60 mils are feasible (47A). Fluorocarbon polymers in the form of poly(viny1 fluoride) and poly(viny1idene fluoride) are similar to fusion coatings except that they are normally applied from suspension. Since they have excellent outdoor weatherability (up to 30 years), they are now entering the exterior siding market. I t has been estimated that these polymers may capture up to 25% of the exterior siding market by 1970 ( 7 7 A ) . High Energy Activation
Electron curing is a procedure which may revolutionize certain segments of the coating industry. I t is possible to cure materials that normally have to be baked for fairly long times in as little as 3 seconds at room temperature. Electron curing should be especially effective for the coating of heat sensitive materials such as wood, rubber, and plastics. It is claimed that chemical bonds form between the paint and the base material so that the coatings are less likely to blister or peel. T h e process is stated to be mare economical to operate than conventional processes requiring conveyor lines
595 1800
D 725 910
1350 60 2.04
400 2.10 6.3 Shrinking at 220 hr. complete a t 360 hr.
1.8 shrinkage, very slightly yellow at 340 hr., brittle 1020 hr.
...
...
2.38 6.3 ,
.,
and drying ovens. Although many types of -vehicles can be used for electron curing, it is desirable to tailor them specifically for this purpose. The principal disadvantage is reaching recessed areas (75A). A novel method for coating metals with very thin pinhole-free films utilizes a glow discharge. T h e discharge ionizes the monomer vapor and causes it to polymerize on the substrate. Almost any carbon containing gas can be polymerized including methane. Films as thin as 0.02 mil are essentially free from pinholes. Protective coatings for metals and primers for both metallic and nonmetallic substrates are of particular interest. The films are more uniform in thickness than conventionally applied coatings. This method has generated a great deal of interest in strip coating, fabric treatment, and the surfacing of plastics (77A). The regular need to improve the adhesion between successive coats of applied films may receive an assist from the process designated “Casing” (cross-linking by activated species of inert gases). Low cohesive strength surfaces are flooded with electronically excited gases, such as helium, krypton, neon, xenon, and argon. T h e metastable and ionic’gases, in contact with certain polymers, abstract hydrogen atoms to form polymer radicals a t or near the surface of the polymer. Such radicals interact to form cross-links and unsaturated groups without scission of the polymer chain in the case of polyethylene. T h e surface cohesive strength is much increased through the formation of a dense gel matrix. Activated oxygen, hydrogen, and nitrogen are likewise effective and sometimes improve the wettability of the surface (27A, 28A). New Polymers
Polyxylenols are prepared according to the following equation :
VOL. 5 9
NO. 8 A U G U S T 1 9 6 7
47
R in the above equation can be methyl or partially or entirely allyl. The allyl containing material can be cured to infusible insoluble coatings by exposure to air, even a t room temperature. The polymers are remarkably soluble in common organic solvents and produce clear hard adhesive films (63A). A new type of epoxy monomer can be prepared according to the following equation : (CH,),C=O
/o + C1-CH,-C-OCH,CH=CH,
-
+ NaOCZH5
These monomers can be polymerized through the allyl group and cross-linked through the epoxy group (544, 82A). A natural oil of possible interest extracted from the plant Euphorbia lagascae contains fatty acids which are 60% epoxidized (QA).
FORMULATION CONCEPTS Designed Experimentation
The formulation of paints is essentially a craft having the goals of maximizing contributions for each ingredient. Traditionally, the technique used to develop product improvements begins by examining the ingredients of an established, seasoned formulation followed by changing the type and ratio of one (out of a possible 10 to 25) raw material. Examination of the “new” formula may involve testing in use or accelerated failure and frequently long term exposure. This typical randomness is usually supported by prior experience and some intuition. One of the sophisticated changes in this procedure is current practice of formulation by computer. A service of particular merit is available through the publication of a computer program by a raw material supplier (7B). Written in Fortran language, proper raw material constants are fed as input to generate these typical readouts on a formula bulked to 100 gallons:
Silicate Coatings
NASA has developed a new family of heat-resistant easy-to-apply satellite paints based on potassium silicate. These coatings air cure and are capable of resisting temperatures as high as 2000’ C. The cured coatings are washable, have fairly good hardness and abrasion resistance, and are resistant to ultraviolet radiation in a high vacuum. The basic system consists of potassium silicate with titanium dioxide, aluminum oxide, or zinc oxide fillers. The addition of boric acid increases the water resistance and hardness, and aluminum hydroxide is used to keep the filler in suspension and improve handling characteristics. I t has been suggested that these coatings might be suitable for interior and exterior house paints. However, the production of satisfactory material is tricky, and the directions available from NASA are not complete and the attempts to follow them so far have not been completely successful ( 3 3 A ) . High Build Coatings
High build coatings are defined as those having a minimum of 3 mils dry thickness per application. I t has been established that from 5 to 8 mils of dry film thickness are required for a mild chemical environment. More severe environments require greater thicknesses for satisfactory resistance. Since high build coatings require high solids as well as a higher concentration of pigment, special formulations are required. The pigment to binder ratio must be optimized to give a tight, nonporous, and chemically resistant film. The solvent system must be engineered to give a fast dry as well as a flaw-free film. Ideally, high build coatings should be easily sprayed without the necessity of reduction with additional solvent. Since the applied films are thicker than normal, they must be thixotropic to prevent sagging. They should have excellent adhesion to the substrate without the need for a primer. Vinyls, epoxies, coal tar epoxides, and chlorinated rubbers have been used most successfully in this field ( 4 8 4 60A). 48
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Pigment-to-binder ratio % Vol. solids Total gal. each ingredient Total cost PVC Cost/sq. ft./mil, theoretical
% Solids Total lb. each ingredient Cost each ingredient Wt. yo of binder for each ingredient s q . ft./gal./mil, theoretical
The time tested randomized approach to the permutations of resins is also threatened by sophistication. The type of approach represented by a joint universityindustry cooperative study of Hunter and Hoff (6B) is already in general use. There are hints that the values inherent in relatively simple utilization of factorial and fractional factorial design reduce the tedium and improve the effectiveness of studies in resin improvements. The large number of interdependent variables necessary to produce a given formulation justify the extraordinary effort required to draw conclusions concerning the properties of particulate matter (2B). Ten conclusions were drawn from a study having the objective of elucidating the phenomenon of pigment dispersion. An industry sponsored program to predict long term durability from short term tests sponsored at the IIT Research Institute relies upon stress/strain and creep measurements of films. The rate of deterioration of the unsupported films in ozone is expressed in terms of work-to-failure which equates measured mechanical properties and time of exposure to ozone (4B). Anti plasticizers
An antiplasticizer is a chemical which at concentrations up to 30% increases the tensile strength and modulus of a polymer and decreases the elongation. The T , is depressed to a lesser degree than is the case for an equal ratio of a plasticizer. Though the present utilization of the principle may not be extensive in coatings, the understanding of possibilities and limitations is important to formulators in specific instances.
The enhancement of physical properties of polycarbonate films was significant as studied by Jackson and Caldwell (7B). These characteristics are defined for antiplasticizers used in a polycarbonate film: -Polar atoms or groups, such as sulfur, oxygen, halogen, and nitrogen -A high degree of structural stiffness or rigidity through cyclic compounds, sulfones, and multiring systems -High T , values (above -50’ C.) for the noncrystalline antiplasticizers as an indication of rigidity -Bulky, polar, thick molecules having the above properties are not antiplasticizing A measure of the thickness taken from physical models has given the hint that bulky additives push the polymer chains so far apart that the attractive forces between chains are reduced to the point where the system exhibits plasticization characteristics. One dimension of 5.5 A. in a t least 65% of the length of the molecule is average for the ‘(anti)’ property. Having defined the requisite character of the antiplasticizing molecule, Jackson and Caldwell advanced the understanding by studying the nature of polymers which can be antiplasticized. Film properties were determined. The antiplasticizable polymers must have rigid, stiff chains and contain polar groups. The mechanism may be attributed to a reduction in free volume of the polymer, interaction between polar groups of polymer and additive, and a stiffening due to the rigid antiplasticizer molecules adjacent to the polar groups of the polymer. 3-D Solubility
A recurring problem for the coatings chemist is to predict accurately the solubility of resins and polyblends in organic solvents. From previous experience, he can associate the polymer in question with other similar polymers. The intuitive approach in this craft is time honored. A new foundation has been set whereby the solubility characteristics of polymers can be plotted on contour maps in which the solubility parameter and dipole moment are matched on the X and Y axes, respectively, and hydrogen bonding values are plotted on contour lines. Since the contour represents the border line between solubility and insolubility, the area inside the closed system gives a representation of solvent properties necessary for resin compatibility. With the threedimensional plots available, it is possible to visualize the relationships of any of 100 commercially available solvents, latent solvents, or diluents, plus mixtures of these to each other and to the polymer under consideration. Thus, the formulator is supplied with an instant readout of solvency for a particular polymer and, in addition, has graphic evidence of dilution ratios for any solvent. I n general experience, a courageous decision must be made to justify diverting time for the development of such precise solubility data for new vehicles. The prediction is made that the introduction of new resins in the future will presuppose the availability of similar plots (3B, 5B).
PERFORMANCE MEASUREMENT When we consider that an organic polymer has a coefficient of expansion of an order of magnitude equal to 50 times that of a normal metal substrate with high mechanical parameters (10 X 10+ for coatings and for steel) and allow for the expecplastics us. 0.2 X tation of excellent adhesion at all times, it is remarkable that a coating on steel can endure in the real world. The mechanical and thermal stresses of nonrigid polymeric materials were examined by Thor Smith (26C). H e undertook to analyze the stress-strain time-temperature relationships for polymers to establish failure criteria with a view of deriving a constitutive equation for deformations up to rupture. This is a classical study which provides methods to characterize ultimate properties of amorphous and crystalline elastomers-whether cross-linked or not. Aspeck has continued his important study of critical pigment packing which he pioneered (with M . Van Loo) before 1950 (ZC). He is concerned with the knowledge, albeit beneficial, that tensile strength of a pigmented film below the critical pigment volume concentration (CPVC) is greater than the value for the unpigmented cast film. The question: Is this attributed to interaction or reinforcement? The answer derives from a measurement of values at a range of strain rates where the magnitude of the tensile value is strongly dependent upon the speed of strain application and the test temperature. An equation is derived to predict the tensile strength of a coatings system at any PVC, based on the parameters of the vehicle system, pigment content, and knowledge of CPVC. The concept is fortified with a pictorial representation of the way in which strain rate affects ultimate properties of bulk polymers. At the instant stress is applied, the coil polymer molecule reacts so that each segment helps support the stress. With increasing time, the chains elongate with fewer segments to hold the stress in any given cross section. Finally, only a relatively few segments will support the load. From this, “the faster the molecule is stressed, the more chains will participate in the action and the As byhigher. . . will be the tensile strength.” products, the study yielded additional insight into the influence upon CPVC of ( u ) pigment particle size and size distribution, ( b ) degree of dispersion in case of solution vehicles, (c) polymer particle size in dispersed vehicles. By extension, one can extrapolate results in coatings to filled plastics and to the elusive reason for the strength of adhesion in thin films. The durability of coatings is of major concern and consequently continues to receive a great deal of attention. As coatings have improved in quality, the time required for critical durability evaluation has continued to increase. One method of overcoming this is the use of the so-called “dew cycle” Weather-0-Meter. The use of this instrument greatly speeded up the breakdown nf paint films, and results are correlated with actual Florida exposures (27C). Exposure to an atmosphere of ammonia or to elevated temperatures as a method of VOL. 5 9
NO. 8
AUGUST 1967
49
accelerated yellowing did not correlate with outdoor tests in London ( E ) . Ten volatile products have been identified as photodegradation products of films irradiated with a xenon arc or a mercury arc. Carbon dioxide was the most abundant product. Others were carbon monoxide, methane, acetone, formic acid, methanol, ethylene, acetylene, hydrogen chloride, and water. Alkyd, vinyl, and epoxy-type films were studied (7OC). A plot of tensile strength us. time of exposure offered a good possibility for predicting absolute durability. This method correlated well with a wide variety of air drying and baking finishes. Joining this method with accelerated weathering machines has relevance with outdoor exposure (22C). Weathering or heating of latex films increased their water absorption when they contained certain surfactants. Low molecular weight water soluble surfactants gave the poorest results (8C). The current desire to know the ultimate exterior durability for baked industrial coatings applied to wood, aluminum, and galvanized steel challenges the talents of analyst and soothsayer alike. The substantial capacity of poly (fluorocarbons), siliconized polyesters, thermosetting acrylics, to name three acknowledged candidates, to endure against gross failure by cracking, checking, and flaking is regularly confirmed. h4ore tenuous is the extrapolation of color change over an extended period from short term tests. This problem is confounded by the observation that a highly durable clear film such as poly(viny1idene fluoride) in the pigmented condition can, under some circumstances, change color after 1 2 months of Florida exposure. There is no firm assurance that a film which has resisted chalking for years may not follow a n exponential rate of pigment erosion once the process has begun. I t is well understood that certain oxides, notably titanium dioxide, can, by being changed to a metastable state of higher valence, stabilize by oxidizing the surrounding ~ e h i c l e . This is the reason that short wavelength sunlight radiation causes pigment release from the surface. “Finger tests” of incipient and progressive chalking are hardly adequate for the new expectations of service life in the facc of the desire for a warranty of 20 years on coatings applied to metals and wood used in residential and industrial structures. .4t an early stage in the weathering process, Saris (21C) gained an idea of the incidence of deterioration by the use of the replica technique. This contribution is an advance in examining the identical point of a test panel a t repeated intervals during the progression of exposure changes. The authors submit that one of the ablest investigators, W. Jettmar, by his refined techniques in microscopy and interpretations of photographs, has introduced a procedure for direct examination of weathered films with a new dimension of importance ( 7 I C ) . FYhereas most analytical assessments of degradation are limited by examinations of the top surface, he studied the changing conditions within the film. Ultrathin sections are taken a t right angles to the surface. As a prelude to the ab0~7e,Jettmar (by private com50
INDUSTRIAL A N D ENGINEERING CHEMISTRY
munication) earlier studied the weathering of flocculated and nonflocculated pigments by optical and electromicroscopic photography of microtome sections embedded in poly(methacr) late). The appreciation of the possibility for visualizing phase chaiiges and the separation of pigment from vehicle matrix led to the later work. The investigation of weathering effects on pigmented coatings was demonstrated by a description of the dificult and tedious techniques using ultrathin sections taken a t right angles to the surface ( 7 7C). Contrasts are made between the exposed and unexposed 0.03- to 0.1-p sections using light and electron microscopes. The examinations are made with the microtome sections embedded in methylmethacrylate or epoxy blocks, and the teclinique reveals substantially more than the traditional top surface examinations. The exposed surface need not be disturbed, as it is observed “unidimensionally.” The interpretation of weathering effects can be made by observing the phase relationships beneath the surface. Another in\ estigator ( I 7 C ) has turned to the study of cross-sectioned films by coating the test film with an epoxy casting resin. The entire panel, including the substrate, is sectioned and polished perpendicular to the painted surface. This provides a common sense method to study corrosion in terms of the nature of the primer and the distribution of tlie paint on the substrate. By use of unsupported films, a different approach was directed to predicting exterior durability from short term laboratory tests. This objectil e was tested b) means of a plot of stress-strain measurements to deterinine the point at which inversion of tensile strength occurs, followed by a study of the slope of tensile strength degradation beyond that point. This concept of durability as measured on accelerated weathering machines gives good correlation with exterior exposure (23C). Coatings technologists in most instances are forced or are willing to accept lack of knowledge about the actual distribution of pigments and fillers throughout the organic matrix of the deposited film. The reason: Very rarelj- is there enough concern to make a microscopic examination. This is excused upon the acknowledgment that the primary function of a pigmcnt is to produce a n aesthetic effect on the top surface and that the particulate matter (pigment or inert substance) has relatively less reinforcing action than, for example, tlie filling of vulcanized rubber with carbon black. In the latter case, the property enhancement is an order of magnitude whereas the “filler effect” frequently diminishes film strengths or at best increases them by a low order. Reegen has studied the peel strength of polyurethane coatings on aluminum. Modification with epoxy resins, chlorinated paraffins, and sulfonamide-formaldehyde resins was found to increase the peel strength. Fatty
H. L. Gerhart is Director, Research and DevelopDejartment, Coatings and Resins Division, Pittsburgh Glass Co., and E. E . Parker is a Scientist at the SpringP a . , laboratories oJ the Coatings arid Resins Di‘uision of Industries.
AUTHORS
ment Plate dale, PPG
acids were detrimental. The more flexible types of isocyanates, as well as partially isotactic polyols, improved the peel strength (2OC). Moisture cured urethanes are less sensitive to substrate and surface preparation than any other system studied, are less susceptible to intercoat adhesion failure, and they adhere reasonably well to weathered surfaces. Oil modified polyether urethanes were superior to other modified urethane varnishes that were tested (24C). A new method using the Brabender Plasti-Corder has been developed to show the difference between good and poor dispersing media. The flow characteristics of pigment in a vehicle during various stages of dispersion were measured. I n the case of alkyd resins the dispersing efficiency decreased as the oil length decreased (9C). Jones has evaluated the varnish holding properties of 1 6 different woods ( I 2 C ) . A polishing machine for the evaluation of the polishing properties of automotive finishes has been developed (16C). The mechanism of protective film formation on wood has been studied. A method for determining the penetration of vehicles into the wood has been developed ( I S C ) . The Zeiss goniophotometer has been recommended for gloss measurements (I&). The temperature of industrial structures has been related to the color and type of coating ( 79C). The performance of asphalt in coatings has been related to their water absorption behavior and also to their infrared structure ( 7 8 2 , 25C). All decorative coatings and a substantial ratio of protective types are concerned with the functions of color. Thanks to Fred W. Billmeyer, Jr., and Max Saltzman, the world has just been given a new basic text on color technology (5C). One of the authors previously published on accuracy and caution in color measurement (3C, 4C). An extension of the subject from the United Kingdom with excellent references has appeared ( I C ) . A quartz crystal microbalance has been used on very thin (0.5 p.) elastomer films to detect weight changes due to oxidation. This method provides a more accurate definition of the aging mechanism, a more precise measurement of the factors affecting aging, and a substantially reduced test time. The sensitivity of the microbalance is in excess of 10-9 gram (7C). The penetration of liquids and pigments into wood can be observed advantageously by the use of an x-ray projection microscope. The x-ray method permits a greater depth of field than the use of light microscopy. I t can be observed that when pigmented liquids are used to coat wood that the liquid penetrates further into the wood than the pigment ( I 3 C ) .
PIGMENTS AND DISPERSION The use of high productivity equipment in paint manufacture has placed a priority upon the modification of pigment surfaces to provide ease of dispersion. Carr has assessed the difficulties of assigning a texture index to this problem ( 4 0 ) . This study is a valuable contribution for both the pigment chemist and the persons concerned with obtaining ultimate dispersion. In later publica-
tions, comments are made on the technique with reference to the interpretation of measurements and to methods of establishing numerical ratings of texture ( 6 D ) . The pigment-vehicle interface is the subject of constant study and is well documented by the Paint Research Institute of The Netherlands (80)for the adsorption of water vapor, stearic acid, stearyl alcohol, and alkyd resins on titanium dioxide. A portion of this 160-page report in the Dutch language will soon appear in English translation (Journal of Oil and Colour Chemists’ Association, late 1967). The details which influence certain factors in the efficiency of dispersion have been published ( 9 D ) . The optimum formulation of mill pastes for present plant equipment is responding to scientific design. There is an awareness of the rheological conditions during dispersion (70, I I D ) . I n dispersion theory, probably the most significant advance is the work on the effect of particle size, shape, and composition of pigments on their absorption and scattering efficiencies. The work reported so far, coming mainly from Germany, is at the ground breaking level. Theories are being developed to correlate the Mie theory of light scattering to the Kubelka-Munk relationship and to explain the absorption scattering relationships of colored pigments. Not only are theoretical concepts being studied, but the practical and useful aspects of these relationships are being evaluated ( 7 5 0 ) . Efforts in texture improvement of organic pigments have led to revised surface treatments for phthalocyanine types. As a result, soft textured phthalo pigments are now available. I n addition, improvements in resistance to crystallization and flocculation have been attained through systematic studies of substitute products, condensation reactions, conditioning procedures, and finishing operations ( I 9 D ) Along with the trend toward high productivity and speed, a method for measuring the “apparent” density of organic pigments by displacement of liquids has been proposed by Beresford and Brack ( 2 0 ) . The true density of organic pigments can only be measured by displacement of helium. This is tedious and requires high vacuum apparatus with careful temperature control. Also, since pigment particles are dispersed in liquids and not gases, the apparent density would be of more interest. I t is reported that the apparent density technique is reliable to better than 0.5y0,which is adequate for all normal applications. With emphasis on the scientific approach, areas of paint technology which previously were neglected are now being investigated. The results of a study conducted by Honigmann ( 7 2 0 ) on the crystal properties of organic pigments indicate that organic pigments show their optimum tinctorial properties over a particle size range of 0.05 to 1 p . Blue pigments show optimum properties in the lower part of this range while red pigments show optimum properties in the upper region. The hiding power and lightfastness increase with increasing particle size within the range given, whereas the final color strength increases with decreasing particle size. The shades of the pigments undergo continuous VOL. 5 9
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change with variations of the particle size. In general, red and green pigments with small particles are bluish within the range referred to, while the same pigments with larger particles are yellowish. Blue pigments with small particles have a reddish shade whereas blue pigment? with large particles have a greenish shade. A great deal of progress has been made within the past decade on modiCcation of TiO, pigments ( 3 0 ) . Many experiments, such as those reported by Bleclita and Lavicka have contributed to this progress. Their study concerned the influence of sodium and potassium salt additions to hydrated Ti02 before calcination at 850’ to 1000’ C. They concluded that the cation of the impregnation salt has the main influence on tlie quality of the calcinate, whereas the anion has a srcondary influence, and that the potassium salts (chloride and sulfate) are negative rutilization catalysts while the sodium salts (chloride and sulfate) are positive. Also, the influence of sodium and potassium salts on the tinting strength of the calcinate at tlie optimum temperature is a function of the amount of impregnation salt. Finally, at a given impregnation level, potassium salts result in a calcination of higher tinting strength than sodium salts. Probably two of the most important characteristics of carbon black pigments, in regard to paint application, are jetness of tone and dispersibility. The significance of particle size distribution in relation to jetness and undertone has been presented by Scott (180). H e also reported that chemical modification of the black pigment surface has produced comparatively low surface area pigments with a high concentration of acidic complexes giving improved dispersibility and stability. Scott’s comprehensi\-e report included the results of other experiments which indicate that the amount of dispersing agent needed to give stability in the mill paste is affected by surface area. Likewise, the pigment-to-binder ratio necessary to give stability is affected by surface area. The minimum requirement of ionic dispersing agent is influenced by tlie concentration of acidic oxygen on the carbon black surface. Oil absorption is governed by the superficial surface area independent of porosity. The subjects of toxicity and safet)- measures have gained prominence in recent years. Chatfield (5D)has suggested that aluminum pigmented wood primers be used as substitutes for the con\-entional white lead-red lead primers on both hard and soft woods. I n addition to being nontoxic, the aluminum primers would have better flow properties. TVild (270) proposed that manganese powder replace zinc dust in anticorrosive welding primers. Since manganese has a reduced volatility under welding conditions, it could be used to replace zinc dust in localities where zinc has been prohibited because of the resulting fumes. Under marine conditions, however, primers based on manganese will blister and perform poorly compared to zinc-rich primers. O n the other hand, the use of zinc pigments in “nonwelding” primers has reached a significant stage in their developnient according to Atkinson ( I D ) . The zincrich paints are well established as effective anticorrosive 52
INDUSTRIAL AND ENGINEERING C H E M I S T R Y
materials, and consideration is now being given to increasing their usefulness. Atkinson reported that the incorporation of inert extenders will offer more economical, but still effective, formulations. Zinc primer formulated for flexibility will open a new field of application since the primer can then be applied before fabrication. Exposure studies comparing conventional leafing aluminum pastes with the combination of leafing aluminum pastes and strontium chromate were conducted by Dowel1 (1OD). The results indicate that color retention and film integrity of the combination are superior to the conventional pastes. This is illustrated in different vehicles and on panels with various surface preparations. Equally important is the improvement in rust inhibition and resulting increased film life. Innovations in colored pigments were reported during 1966. Molybdate orange and chrome yellow, encapsulated with a heavy coating of silica, were introduced (730). Their prime application is in plastics where heat resistance is an important feature. Translucent dry powders composed of titanium dioxide coated micas were offered ( 7 4 0 ) . The appearance is best visualized by describing them as hybrids of metallic and pearl pigments. The new “Afflairs” are claimed to be more brilliant than the prototype. A series of stable bronze pigments for plastics has been developed ( 7 6 0 ) . I t is claimed that the new pigments will resist the darkening caused by heat and sulfide fumes, as well as resist greening caused by salt water exposure. Fine particle extenders are a practical means to add hiding to dry films. This subject has been exhausted in an encyclopedic documentation wherein eight extenders (0.1- to 1 - p ultimate particle size) are detailed in two types of latex paint and a semigloss enamel. The performance is influenced more by vehicle demand than any other single property. No single extender is completely satisfactory in each type of paint examined a t a range of PVC lelTels, but certain hydrated silicates provide better overall performance than other types. I n latex paints, the viscosity is independent of the oil absorption of fine particle extenders. The property showing. the greatest variation from one particle extender to another is tint efficiency. Some extenders actually decrease tint efficiency when used with lower oil absorption Ti02. I n evaluating tint efficiency or tint strength of a pignientation in a flat paint, it would be hazardous to evaluate either tint efficiency or dry hiding alone since these are obviously related. In one instance, the relationship between stain removal and oil absorption shows two surprising features, First, oil absorption has a minimum effect on stain removal, suggesting that fine particle extender oil absorption has little effect on the porosity of the paint film, and second, tlie stain reinoval is improved over that of a control containing no fine particle extender. Brightness is not a function of oil absorption or the dry brightness but is related to tint efficiency ( 7 7 0 ) . Fixing upon the property of zinc oxide to improve tint retention and mildew resistance in paint films, the American Zinc Institute has updated the facts concerning a current cooperative program ( Z O O ) .
Titanium pigments have come a long way since the initial development in the 1930’s of a coprecipitated combination of titanium dioxide and barium sulfate which carved out a niche for itself in the paint industry as a replacement for lithopone. Irnprovements in titanium pigments are still appearing. I t is perhaps paradoxical that the earliest recognized deficiency of titanium dioxide-its poor chalk resistance-should have become one of the last frontiers for these improvements. This is not to say that titanium pigments of truly excellent exterior durability, compared to their predecessors, have not been a staple commodity for some time, but it is also a fact that very significant improvements in this area have recently come from the research centers of the white pigment industry. I t is generally recognized that various levels of silica and alumina treatments are capable of varying the chalk resistance of titanium dioxide in a paint system. Not quite so general is the appreciation that untreated titanium dioxide actually contributes to the breakdown of organic films in which it is dispersed because of the pigment’s photoreaction by ultraviolet light and the simultaneous oxidation of adjacent organic binder. All improvements in chalk resistance of titanium pigments have therefore been based upon the inhibition of this reduction-oxidation cycle by occupying the reactive sites on the crystal surfaces and--up until very recentlyhave teen characterized by increasing amounts of treatment. Gloss retention, on the other hand, is dependent upon fine particle size and good dispersion a t any given level of chalk resistance and is generally more apt to be reduced than improved by increased levels of treatment-although alumina is often felt to aid dispersion. Some of the traditional methods of applying treatments have been about as efficient as spraying paint on a wire fence. Furthermore, the more treatment that is applied in a n attempt to compensate for the “overspray effect,” the greater the probability that it will cement adjacent pigment particles together, causing loss of hiding power and tinctorial strength due to a large effective particle size. As a consequence, conventional chalk resistant pigments have been deficient in strength, yellow in undertone, and poor in gloss retention when compared with finer particle size products. The adoption of a n entirely new concept of the treatment process has enabled production of a high durability pigment with maximum strength, blue tone, and with high initial gloss and gloss retention. Recommended for critical automotive and coil coating formulations, this pigment was piloted and commercially produced in Europe on a sulfate base several years in advance of its introduction in this country on a chloride base. So extensive is the manufacturer’s experience with the new concept that a written warranty is said to be available covering its performance. Still another new “high durability” product is available by following the higher-level-of-treatment route to stabilize the titanium dioxide crystal. Designated “encapsulated with treatment,’’ this pigment does not possess the high tinting strength or excellent gloss of the
previously described product, although this is also produced by the chloride process. Chalk resistance appears to have been improved compared with previous grades, but not gloss retention. A final new product in the “high durability” category has been offered by a third producer with claims of higher strength and bluer tone than conventional chalk resistant pigments. Manufactured by the sulfate process, this pigment, just recently introduced, would appear to have departed from the old idea that a high level of treatment is essential for maximum durability. Since the possession of exterior durability does not reduce the usefulness of a pigment for interior finishes, the combination of properties offered by a t least two of these new products suggests the possibility of inventory simplification-inasmuch as the optical properties of hiding power, brightness, and gloss are a t near maximum levels.
ANALYTICAL TECHNIQUES The sophisticated instrumentation of the analytical and polymer chemist is commonplace in coatings technology. Zorll has made electron micrographs of particle arrangements in pigmented films. T h e alignment of the particles depends on the method of application and affects the mechanical properties of the film (79E). A torsion pendulum has been used to measure the sheer modulus and the logarithmic decrement of free films. Coatings of different end use types show different mechanical behavior. The temperature of the transition region often determines the suitability of a vehicle for a given application. I n cross-linking, the presence of plasticizers and degradation by ultraviolet light can be detected by this method (75E). The Sward rocker hardness actually is a function of the modulus of the elasticity of films. The rocker hardness obtained is a sensitive function of the temperature (ZE). Vapor phase chromatography of coatings materials has received a great deal of attention. It can be used for the determination of residual monomers in poly(viny1 acetate) and copolymer latices. Speed and accuracy are greatly improved over previously available methods (4E). Vapor phase chromatography can be used to establish the purity of raw materials and for the identification of components of mixtures. Polymers themselves can be identified by chromatography of pyrolysis products. Since vapor phase chromatography can be used for the separation of glycerides and the resolution of isomers, it can be of value for the elucidation of the mechanism of oxidation of oils and film formation (5E, 7 E ) . Mass spectrometry has been recommended for paint research, particularly in conjunction with gas and thin layer chromatography (78E). Alkyd resins can be fractionated by gel permeation chromatography. Polymers up to a number average molecular weight of 20,000 can be studied. The vapor phase osmometer is a particularly valuable companion instrument (70E). A method based on infrared spectroscopy has been developed for the determination of styrene in butadieneVOL. 5 9
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styrene copolymers. An infrared method is recommended for the determination of phthalic anhydride or isophthalic acid and nitrocellulose in dried lacquer films (7E, 76E). Nuclear magnetic resonance serves for structure determination of vehicles, molecular weight determinations, and reactions of epoxy resins (77E). A new gel strength tester for thixotropic materials has been developed (72E). The derivatograph has been used to study the properties of epoxy films (9E). A torsional braid apparatus has been used to study the cross-linking of acrylic systems with hexamethoxymetliyl melamine. It was found that hexamethoxymethyl inelaminc was a more efficient cross-linker, giving better flexibility at equivalent hardnesses than other amine resin systems tested ( 8 E ) . A simplified instrument for the routine measurement of viscosity of paint has been developed. This cone and plate viscometer is fast, easy to clean, and can work with small samples a t a high shear rate (72E). A machine for performing the crosscut adhesion test has been devised (74E). Jacobsen has described two new instruments for the measurement ofthe degree of chalking of paint films (6E). New methods for measuring the permeability of paint f i l m to water in either direction have been developed. T h e test works on weathered or unweathered films ( 7 7E, 73E). Radiochemical techniques of coating analysis have long been used to measure film thickness, continuity, and uniformity. The porosity of thin films can be measured either by autoradiographic or diffusion methods. Radioisotopes have proved to be a valuable tool in the study of surface forces and dimensions where data have been collected which strongly suggest that the adhesion of commercial coatings to metals is due to hydrogen bonding. This was demonstrated by the use of tritiated water on a number of metal surfaces. The efficiency of^ rust preventives can be estimated by the use of radiochemical procedures (3E).
COR ROSlON PROTECTION The 1966 FATIPEC Congress devoted substantial effort to update the status of paints in their protective function. The reports ranged through every experience of corrosion protection, and the bound volume of collected papers is a good current publication in this field. A documentation of 20 )-ears’ experience in the protection of water immersed structural steel in the Swiss utility industry concludes that a 0.2-mm. zinc metallic layer or a coat of zinc-rich paint, covered with 0.15 mm. of bituminous surface, is the preferred system. Swiss investigators have defined a scale which specifies the degree of care of the surface preparation for steel surfaces prepared for anticorrosive painting. I n this study, they conclude that in the instance of scraped and wire brushed rusted steel, red lead in oil is the preferred primer with red lead alkyd showing promising results and being preferred over zinc chromate alkyd. O n blasted surfaces, zinc chromate alkyd gave better results than iron oxide, but again red lead primers are used ( 7 F ) . British investigators consider that the ultimate goal of 54
INDUSTRIAL AND ENGINEERING
CHEMISTRY
a protcctive coating for iron and steel can be in excess of 20 years. This is based upon field experiments using rather conventional systems. The documentation includes details from the “British Standard Code of Practice for the Protection of Iron and Steel Structurcs from Corrosion,” including inspection procedures for the control of paint film continuity and thickness on cleaned surfaces. 4 summary of paint film thickness nieasurement instruments is given as well. Especially useful is the stress placed upon proper surface preparation of new steel and the appeal to apply the prime coat immediately after descaling and blasting (71;). Dutch investigators distinguish betwecn the corrosivc effects at immersion conditions as against those of the same substance in gas phase, and create a case for more research involving the understanding of the corrosi\,e process at a high relative humidity but below 10070 (IOF). Corrosion inhibitors in the form of after treatment of phosphate coatings are reviewed (72F). A substantial list of organic dichromates was examined ( 7 6 F ) , and those having a high degree of corrosion inhibition to metal priming paints were identified. Several are superior to zinc potassium chromate. An objective of this program is the development of effective dicliromate soluble in paint veliicles. Polish investigators (74F) approached the effectiveness of organic polar corrosion inhibitors through the concept of permselectivity-. Measurements of resistance and capacitance are employed to denote changes in protective coatings properties und,er the influencc of electrolyte solution. Triethanolamine oleate in alkyd resins is used as the anionic active agent. Pompowski et al. conclude that it is misleading to equate increased coating resistivity and decreased electrochemical capacitance with anticorrosive effectiveness. -4 report of investigations in Germany calls attention to the effectiveness of calcium hydroxide as an inhibitor in nonsaponifiable vehicles ( 2 F ) . One of the authorities (8F), concentrating on the coating of galvanized steel, reported a thorough summary on his extensive studies in the Ketherlands. Eijnsbergeti has tabulated the explanations of 15 types of failure. This work calls attention to the greater interest in calcium orthoplumbate pigmentations in Europe than is the case in the U.S.A. With the promised availability of tlic identical products through Canadian sources, we can expect domestic activity to be accelerated. In Europe and especially in the United Kingdom, primers for steel and hot-dip galvanized iron are regularly formulated with calcium plumbate a t a level of 50 to 70y0volume concentrations for maintenance protection. A booklet is available which documents case histories of forrnulations exposed to aggressive atmospheres abroad (L5F). Proof of practical performance is presented (61;) for noncross-linking polymer emulsions as protective coatings for steel. The author did not offer an explanation for the lack of rusting of iron in contact with the emulsion, but the report substantiates the recent important advance in the utilization of latex based maintenance finishes. Another case ( 9 F ) in support of the water
systems in paint for corrosion prevention is presented as a need for readily available ionic reactions to interrupt the chain of equations leading to the formation of rust. Emulsions containing benzidene hexacyanoferrate are chosen because of the latter’s reactivity with sulfate ions and ferric ions. T h e suitability of emulsion paints as anticorrosive topcoats is reported (7727) on the basis of weathering tests conducted over a 10-year period. When alkyd resin or linseed oil primers are used, aqueous emulsion paints are given a full blessing-especially when the primers contain lead pigments. The purpose of the work was to settle the argument in favor of the advantages of emulsion coatings over linseed oil topcoats. Swiss investigators, as reported by Meyer ( 7 3 F ) , fixed upon the ability of hydroxy, amine, and carboxy groups to react with metal surfaces, especially phosphated steel Containing water of crystallization. Definite chemical bonds with the phosphated surface have been identified. Adhesion is improved by the deliberate introduction of carboxylic groups in the vehicle resin. Reactive pigments containing water of hydration formulated into carboxylic resins provide the means for enhanced adhesion and rust inhibition. The vehicle studied is nitrocellulose plasticized with higher acid alkyds. These are formulated with hydrated zinc phosphate and lead phoshate. The thesis of this paper was that hydrated pigments formulated into vehicles containing carboxylic groups give the best adhesion and rust inhibition. Adhesion as a determinant of coatings performance offers possibly the best opportunity for getting the most out of any good anticorrosive film. British investigators a t the Paint Research Institute have both advanced and enlivened this theme. For example, urea alkyd and melamine alkyd resins applied to solvent cleaned metal surfaces can show a large percentage of clean detachment, whereas thermosetting acrylics free of alkyd components offer distinctly better service. The interpretation : The free fatty acids and low molecular weight half-esters in the alkyds are the weak moiety, whereas the acid groups in thermosetting acrylics are attached to the polymer. Not surprisingly, extraction of the lower molecular weight acidic and hydroxyl fraction from the alkyd offers a marked improvement in adhesion. The evidence is building that except for mechanically weak or highly reactive substrates, strong adhesion is a normal expectation for any kind of paint. T o quote: “Defective adhesion>frequently localized is associated with an interfacial layer of weak material (in the resin vehicle) rather than with a n intrinsic inability for a n adhesive force to develop between the substrate proper and the binder in the paint film.” In practice, most metal substrates will carry some organic contaminant, possibly in less than a complete monolayer. To secure strong adhesion, this contaminant must be removed. One radical and successful approach is to remove it by taking off a sizable surface layer from the metal. Another approach is to include in the paint molecules which are likely to replace the contaminant on the surface and will not themselves
interfere with adhesion. I n many newer vehicles, no strongly absorbing molecules are present-hence the need for higher standards of surface preparation. As a principle, a built-in safety factor must be designed. One component recommended is a long chain or complex polymer having free carboxyl groups and the ability, after adsorption on a surface, to react with or become mechanically linked with the main body of the film forming material (@). The 850 specimens of sprayed metallic zinc or aluminum were tested with 25 different primers a t five atmospheric sites plus a full immersion in fresh water. The comprehensive program offers a wide selection of successful products (3F). A stubborn problem in metal protection is filiform corrosion. Possibly because it occurs as a n occasional surprise with unpredictable incidence and severity, the prevention is not fully assured under new circumstances. While strong suspicion rests with the prehistory of the metal surface, the solution and prevention rest heavily with the coatings technologist. T o support the case that the matter is interdisciplinary, the role of oxygencarbon dioxide concentration was defined. O n steel, filiform corrosion was inhibited by carbon dioxide a t concentrations exceeding 570 and accelerated by elevating the oxygen ratio to 5%. With increased concern a t the observation of the problem on aluminum, the fight for complete understanding has just begun. A meritorious basic work on the formation and growth of zinc phosphate coatings is not intended to solve filiform corrosion tendencies but is notable for the practical difficulties of obtaining uniform surface pretreatment in real world practices (75F). REFERENCES Introduction a n d Synthetic Resins (1A) Antlfinger, G. J., Park, J. E., Anthony, J. C., B. F. Goodrich Co. Technical Report. (2A) Austin, R. O., Schmidt, D. C., Odom, H. C., J . Paint Technol. 91-5. (3A) Bardin, P. C., Ind. Finishing (Indianapolis) 42 (9), 22-4, 26, 28, 30, 32 (1966). (4A) Barrett, K. E. J., Lambourne, R., J . O i l Colour Chemists’ Assoc. 49, 443-63 (1966). (SA) Barry, E. F., Prod. Finishing (Cincinnati) 30 (12), 50-7 (1966). (6A) Braun, L. M., Ind. Finishing (Indianapolis) 43 ( Z ) , 22-30 (1967). (7A) Brewer G. E. F., Horsch, M. E., Madarasz, M . F., J . Paint Technol. 38, 452-5 ’(1966). (8A) Brewer, G. E. F., Strosberg, G. G., Madejczyk, L. A., Hines, R. F., Ihid., pp. 449-51. (9A) Brushwell, William,Am.PaintJ. 50 (44), 103, 106, 111-13 (1966). (10A) Burnside, G. L., Brewer, G. E. F., J.Paint Technol. 38, 96-100 (1966). (11A) Burnside, G. L., Brewer, G. E. F. Madejczyk L. A,, Wiedmayer, L. W., Am. SOC.of Mech. Engrs., P a p e r 66-MD-45, 5 pp,, i966. (12A) Burnside, G. L., Brewer, G. E. F., Strosberg, G. G., Igras, R. A., J . Paint Techno/. 38, 101-4 (1966). (13A) Burnside, G. L., Strosberg, G. G., Brewer, G . E. F., Pant Varnish Prod. 55 (12), 53-4, 59-60, 62,64, 66 (1966). (14A) Chem. Eng. News 44 (48), 54-5 (1966). (15A) Deibert, R. J., J. Paint Technol. 38, 421-3 (1966). (16A) Edwards D. L Finney, D. C., Von Bramer, P. T., P ~ i n tVarnish Prod. 5 6 ( 9 ) , 44-5, 4718 (19;;). (17A) Errico, Anthony, Ibid., 57 (l), 33-7 (1967). (18A) Fox, Leonard, Jubilee, Benjamin, Am. Paint J . 5 2 (28), 60-2 (1967). (19A) Freeman, D . B., Burden, P., Trans. Inst. MetalFinishing 44, 71-7 (1966). (20A) Ghanem, N . A., El-Mohsen, F. F. Abd, J . Oil Colour Chemists’ Assoc. 49. 490-9 (1966). (21A) Gladstone, J. R., Can. Paint Finishing 40 (a), 25-7, 63-4 (1966). (22A) Graver, R. B., J. Point Techno/. 39, 71-7 (1967). (23A) Hagen, J. W., Ibid., 98, 436-9 (1966). (24A) Ihid. (25A) Hagan, J. W., Paint Varnish Prod. 55 (9), 47-8, 50, 52 (1965). (26A) Hagan, J. W., Orttung, F. W., Chow, S. W., Ibid., 57 (4), 48-55 (1967) (27A) Hansen, R. H., et al., J . Polymer Sci. A3, 2205-14 (1965).
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(28A) Hansen, R . H., Schonhorn, H., Polymer Letters 4, 203-209 (1966). (29A) Haughney, J. P., Insulation 12 (5), 55-9 (1966). (30A) Hensley, M‘.L., Paint Varnish Prod. 5 6 ( l l ) , 68-9 (1966). (31.4) Holzinger, Franz, Paint Technol. 30 (81, 20-4, 26-32; (9), 26-32 (1966). (32A) Hutchinson, C. O., Prod. Finishing (Cincinnati) 31 (61, 50-7 (1967). (33.4) I n d . Res. 8 ( 8 ) , 49 (1966). (3411) Kays, William T., J . Paint Technol. 38, 440-2 (1966). (35A) Koch, R . L.: Zbid., pp. 443-8. (36A) Kock, Erhard, Mater. Design Eng. 64 (4), 70-5 (1966). (37A) Landon, G., Paint Technol. 30 (9), 42-7 (1966). (38.4) Landon, G., Ashton, I. H., J . Oil Colour Chemists’ Asroc. 49, 202-21 (1966). (39A) LeBras, L. R., J . Paint Technol. 38, 85-90 (1966). (40A) Lewis, S. N., Zbid., pp. 667-74. (41A) Maass, 1%’.B., Am. PnintJ. 51 (21), 38, 40, 42, 46, 48 (1966). (42A) Zbid., 5 2 (31), 58-60, 62, 64-5 (1967). (43A) McIntosh, A., Reader, C. E. L., J . Oil Colour Chemists’ Assoc. 49, 525-42 (1966). , Paint Manuf. 30 (9),51-3 (1966). (45A) Ibid., 36 ( 9 ) , 61-2 (1966). (46A) Maisch, Waldemar, Znd.-Lackier-Betrieb 33, 299-313 (1965). (47A) Mantell, G. J., Rankin, D., Galiano, F. R . , J . Appl. Polymer Sci. 9, 3625-33 (1965). (48A) Manter, 0. D., Am. Puint Contractor, Znd. M a i n . Point. Sect. 6 (2), 28-32 (June 1966). (49A) Merkel, K . W., J . Paint Technol. 38, 543-55 (1966). (50A) Miranda: T. J., Zbid., pp. 469-77. (51A) Naumann, tV. G., Paint Varnish Prod. 56 ( 8 ) , 35-6, 38, 40, 43 (1966). (52A) Oelsner, E., Farbe Lack 72, 876-80 (1966). (53A) Olsen, D . A., J . Paint Technol. 38, 429-35 (1966). (54A) Paint M a n u f . 36 (51, 41 (1966). (55A) Paint, Oil Colour J . 150 (3549), 792-3 (1966). (56A) Ibid., 151 (3560). pp. 30-2. (57A) Zbid., (3563), pp.177-8. (58A) Paint Technol. 30 ( l l ) , 19-22 (1966). ( 5 9 4 ) Paint Vnr. Prod. 7967 Buyers’Guide57 ( 3 , p t . 2), 26-135 (1967). (GOA) Parker, H . E., J . Point Terhnol. 38, 357-61 (1966). (61A) Phillips, Benjamin, Starcher, P. S. ( t o Union Carbide Gorp.), IJ. S. Patent 3,158,590 (Nov. 24, 1964). (62A) Preuss, Harold, Metal Finishing 65 (1 ), 69-72 (1967). (63.4) Price, C . C., J . Paint Technol. 38, 705509 (1966). (64A) Prod. Finishing (London) 19 (Z), 62-4 (1966). (65A) Ibid., (lo), pp. 52-7. (66A) Ibid., (11), pp. 54-61. (67A) Ibid., (12), pp. 56-7. (68A) Zbid., 20 (l), 62-3 (1967). (69A) Robinson, P. V., Winter, K., J. Oil Coiour Chemists’ Assoc. 50, 25-47 (1967). (70A) Saifullin, R . S ., Zaitseva, L. V., Pomt Technol. 30 ( I ) , 20-2 (1966). (71A) Sandford, J. E., Iron Age 194 ( 3 ) , 75-7 (1964). (72.4) Sekmakas, Kazys, Stancl, R . F.! J. Paint Technol. 38, 217-26 (1966). (73A) Sheetz, D . P., J.A p p l . PoijmerSci. 9, 3759-73 (1965). (74A) Solomon, D. H.: Hopwood, J. J., J . Oil Colour Chemists’ Assoc. 50, 306-21 (I 967). (75A) Steel (Cleaeiand) 158 (7), 42-3 (1966). (76A) Ibid., 159 (13), 46-7 (1966). (77A) Sreinhebel, Fred, Znd. Finishing (Indianapolcs) 42 ( 6 ) ,30-2 (1966). (78A) Strauch, D., Paint Techno/. 31 (2), 34-40 (1967). (79A) Sullivan, hf. R . , J . Paint Techno/. 38, 424-8 (1966). (80A) Tasker, L., Taylor, J. R . , J . Ozl Colour Chemiits’ Assoc. 49, 756-69 (1966). (81A) Touchin, H.,F.A.T.I.P.E.C., 7th Congr., Vichy, 1964, pp. 170-5. (82.4) Warson Henr Parsons, R . J., Simmonds, L . A . (to Vinyl Products, Ltd.1, Brit. Patent 995,72$’(June 23, 1965). Formulation Concepts (1E) i l m . Paint J.51 (35), 18, 20 (1967). (2B) Brownlie, Gavin, Furaus, G. C., J.Paint Techno/. 38, 113-22 (1966). (3B) Crowley, J . D., Teague, G. S., Lowe, J. I V . , Ibid., 39, 19-27 (1967). (4B) Gutfreund, K u r t , Ibid., pp. 732-9. (5B) H a n s m , C. M . , Itid., pp. 104-17. (6E) Hunter, W. G., Hoff, M .E., IND.E N G .CHEM. 59 (3), 43-8 (1967). (7B) Jackson? W. J., Caldwell, J. R A m . Chem. Soc., Din. Ort. Coatings Plastics Chem. Preprints 2 6 (21, 160-79 (1966j:
(14C) Loof, Heinz, J . Paint Techno/. 38, 632-9 (1966). (15C) Loon, J. van, J. Oil Colow Chemists’ Assoc. 49, 844-67 (1966). (16C) Monk, C. J. H., Adamson, D. W., Ibid., pp. 390-9.
(17C) Moree, J. C., F.A.T.Z.P.E.C., 8th Congr., T h e Hague, 1966, pp. 277-81. (18C) O’Brien, H. C., I N D .E N G .CHEM.58 (61, 45-54 (1966). (19C) Paintindm 1 6 (51, 34 (1966). (2OC) Reegen, S. L., J . Appl. Polymer Sci. IO, 1217-59 (1966). (21C) Saris, H. J . A . , F.A.T.Z.P.E.C., 8th Congr.,TheHague, 1966, pp. 490-6. (22C) Schurr, G. G., Hay, T. K., V a n Loo, Maurice, J. Paint Tecirnol. 38, 591-9 (1966). (23‘2) Ibid. (24C) Skreckoski, Gerald, Bailey, h l . E., Kane, A . J., Eerger, S. E., Itid., pp. 45661. . ~ .
(25C) Smith, C. D., Schuetz, C. C., Hodgson, R . S., Iim. ENC. CXEM.PROD. RES. DEVELOP.5, 153-61 (1966). (26‘2) Smith,T. L., A m . Chem. Soc., Diu. Org. Coatings Plastics Ciiem. Preprints 26 (2), 1-11 (1966). (27C) Stieg, F. B., J . Paint Technol. 38, 29-36 (1966) Pigments a n d Dispersion (1D) Atkinson, G . D . , J . Ozl CviouiCliernists’iissoc. 49, 137-49 (1966). (2D) Beresford, J., Brack, R . E., Ibid., pp. 150-8. (3D) Blechta, V., LaviEka. M., Ibid., pp. 195-201. (4D) Carr, W., Ibid., pp. 831-43. (5D) Chatfield, H . W., Paint Techno/. 30 (41, 25-7 (1966). (6D) Growl, V. T., Bulletr, T. R., J . Oil Colour Chernisfr’ Arzoc. 50, 82-6 (1967). (7D) Daniel, F. K., J . Paint Technol. 38, 534-42 (1966). (8D) Doorgeest, T., “ T h e Dispersion of Pigments in Alkyd Resin Solution,” Paint Research Institute T.N.O., Postbox 203, Delft, Netherlands. (9D) Doorgeesr,T., F.A.T.Z.P.E.C.,7th Congr., Vichy, 1964,pp. 314-19. (10D) Dowell, R . B., Am. PnintJ. 50 (43), 94-105 (1966). ( l l D ) Hanan, S. E., Bukowski, R . L., J.Paint Technol. 38, 527-33 (1966). (12D) Honigmann, Bertold, Ibid.,pp. 77-84. (13D) Iler, R. K . (to E. I. du Pont de Nemours and Co., Inc.), U. S. Patcnt 2,885,366 (May 5? 1959). (14D) Klenke, E . F., Stratton, A . J., Ibid., 3,087,827 (April 30, 1963); Linton, H. R . , Zbid., 3,087,828 (April 30, 1963). (15D) Maikowski, M. A , , Nassenstein, M., V d z , H . G., Papers presented at thc Meeting of the Deutsche Bunsen-Gesellschaft, Frankfurr a m hlain-Hb;chst, 1966. (16D) Neitlich, N. W., Plastics W o r l d 24 (61, 57-9 (1966). (17D) Ritter, H . S., Blose, W . A , , Dembski, T. A,, J . Paint Tedinol. 38, 509-26 (1966). (18D) Scott, Ii.,J . O i l Colour Chemists’ Assoc. 49, 559-75 (1966). (19D) TVagener, A. P., Am. Ink AfaXpr 44 ( 6 ) , 67-71 (1966). (20D) Werrhan, S., Paint Varnish Prod. 56 (IO), 33-40 (1966). (21D) Wild, G. L. E., Paint Techno/. 30 ( 8 ) , 9-16 (1966).
Analytical Techniques
(1E) Adams, hi. L., Keiser, J . R . , J . Paint Techno/. 38, 163-7 (1966). (2E) Cass, R . A . , Zbid., pp. 281-4. (3E) Coe, G. R . , J.Oil Colour Chemists’ Assoc. 50, 297--305 (1967). (4E) Fossick, G. N., Tompsett, A . J., Ibid., 49, 477-89 (1966). (5E) Hakcn, J. K., Ibid., pp. 993-1002. Paint Varnish Prod. 56 (IO), 51-4 (1966). (6E) Jacobsen, A . F,., (7E) Kelly, J. S., J . Paint Technol. 38, 302-7 (1966). (8E) Koral, J. Ii,,Petropoulos, J . C., Ibid., pp, 600-9. (9E) Kovacs, L., Rohonczy-Talas, E., Paint Techno/. 30 (lo), 30--2, 34-6, 38, 40 (1966). ( 1 OF,) Ixsnini, D. G., J . Paint Techno/. 38, 498-507 (1966). (11E) Lowrey, E. J . , Broome, T. T.: Ibid., pp. 227-49. (12E) Monk, C. J. H., Hartridge, L. S., J. O i l Calour Ciiernirtr’ ASJGC. 49, 576-80 (1966). (13E) Paint .?-lonuf. 36 ( 7 ) , 50-2 (1966). (14E) Petri, E. A , , A m . Paint J . 51 (14), 98, 100 (1966). J.Parnt 7’echnoi. 38, 263-8 (1966). ( l 5 E ) Picrce, P. E., Holsworth, R. M., (16E) Post, hi. A , , Ibid., pp. 336-42. (17E) Rybicka, S. M., Reu. Current Lit. Paini Allied Ind. (Lotidon) 38, 847-54 (1965). (18E) Ibid., 39, 87-91 (1966). (19E) Zorll, U., Forbe Lack 72, 733 42 (1966). Corrosion Protection
Performance Measurement (1C) Adams, 3. h l . , J.O i l Colour Chemists’ Asroc. 50, 59-71 (1967). (ZC) Aspeck, TV. K.: Am. Chem. Soc., Diu. Org. Coatings Plastics Chem. Preprints 26
(2), 13-30 (1966). ( 3 C ) Billmeyer: Fred h‘., 08,. Dig., Federation Soc. Paint Technol. 34, 1333-42 (1962). (4C) Ibid., J.Opt. Sot. A m . 55, 707-17 (1965). (5C) Billmeyer, F. W,, Saltzman, Max, “Principles of Color Technology,” Interscience, New York, 1966. (6C) Chaplin, C . A,, Fish, R . A , , J . Oil Colour Chemists’ Asioc. 49, 749-55 (1966). (7C) Fischer, 1%‘.F.. King, W.H . , Am. Chem. SOC.,Div. Rubber Chem., P a p e r 31, Montreal Meeting: M a y 4. 1967. (8C) Fox, Leonard, Burns, E. J., Am. Paint J . 50 (33), 68-70,72 (1966). ( 9 C ) Hanan, S . E,, Pukowski, R . L., J . Paint Techno/. 38, 527-33 (1966). (1OC) Hearst, Peter J., Ibid., 39, 119-27 (1967). F.A.T.I.P.E.C., 8 t h Congr., T h e Hague, 1966, pp. 497-503. (11C) Jettmar, W., (12C) Jones, K . L., J.OilColout Chemzsts’ Assoc. 49, 314-39 (1966). (13C) Jongbloed, W. L., Jutte, S. M . , F.A.T.I.P.E.C., 8th Congr., T h e Hague, 1966, pp. 306-11.
56
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
(1F) Anderson, B., Ekwall, G.: F.A.T.Z.P.E.C., 8th Congr., T h e Haguc, 1966, pp. 45-57. (2F) Berger, \V., Zbid., pp. 299-305. (3F) Bonner, P. E., IYatkins, K. O., Ibid., pp. 385-94. (4F) Bullett, T. R . , I’rossrr, J. I..,Ibid., pp. 374-81. (SF) “Caldox Case Histories,” Associated Lead hlanufacturcrs, L t d . , 1,ondon. (6F) Disselhoff, H., F.A.T.I.P.E.C., 8th Congr., T h e Haguc, 1966, pp. 338-43. (7F) Dunkley, F. G., Ibid., pp. 75-88. (8F) Eijnsbergen, J. F. 11. van, Zbid., pp. 323-30. (9F) Kiihn, M., Ibid., p p , 344-5. (10F) Laar, J. A . W.van, Ibid., p p . 263-76. (11F) Lehmann, H., Wiisrefeld, H., Ibid., pp. 346654. (12F) hiachu, I$’., Ibid., pp. 286-8. (13F) hleyer, G., Ibid., pp. 359-65. (14F) Pumpowski, T., Klenowicz, Z . , Jakobs: J., Janusz, TV., Zbid., pp. 294-8. (15F) Slahough, W. H., Chan. E. J., Paint ?Pchno/. 30, 417-20 (1966). (16F) Vessey, C. A , , Harris, A . S . . P.A.T.I.P.E.C., 8th Congr., T h e Haguc, 1966, pp. 289-93.
