February, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
plastic is shielded from any possible contact with gasoline or cleaning fluids-for example, instrument pointers and dials. Hundrpds of safety solvents are sold over the country and all of them will change styrene polymers into a gummy mass on contact. Gasoline has less effect. We have been assured that there is a good chance that this weakness will be overcome, and if such is the case, styrene can become a great competitor for the clear or light colored plastics. Molded phenolics are used in places where brittleness is not too great a factor and where darker colors or painted parts can be successfully used. Phenolics are also used as inserts for the brighter thermoplastics. Urea-formaldehyde plastics were probably the first light colored plastics to be employed in the automotive industry, but were originally discarded because they could not be injection-molded and were not available in the depth of color that we now desire. These resins are now available in a good
239
range of colors and are only awaiting new methods for economically molding thermosetting plastics. Cellulose nitrate, the old timer of thermoplastics, still finds important usage in the automotive industry. Its heat resistance is comparatively good and i t is available in an excellent range of colors. It is used in instrument and clock dials, and until recently we were careful not to use it in places where i t might come in contact with a careless match or cigaret. Only quite recently have nitrate samples been flameproofed to such an extent that they can be used almost anywhere on the interior of the automobile. However, they still exhibit extreme dimensional changes with moisture and heat. Thus, the engineer should be thoroughly familiar with the characteristics of the plastic material before recommending its use on any definite part of an automobile. Until such time as a perfect plastic is developed, i t will be necessary to use a variety of plastics in the automotive industry.
R. C. KRUEGER, L. W. SCHAEFER, AND J. S . LONG Jonas-Dabney Company, Louisville, Ky.
Pimpling results where adhesion, usually of primer to metal, is overcome by the resultant of the swelling forces induced by absorption of water by the three-coat system. Pimpling is often localized to areas or even tiny spots where adhesion is poor or to areas where the merging of the three coats (primer, surfacer, and enamel) produces some local condition or irregularity. Pimpling is a result depending upon primary factors-permeability, swelling, and adhesion. Each of these depends on variablese. g., ad$esion on the nature of the surface and its preparation, and nature of primer vehicle. Permeability and swelling depend on film thickness, composition of material, both vehicle and pigment, with special emphasis on particle size, pigment volume concentration, temperature of baking, final film structure, etc. Tables show the influence of a number of such factors.
EARCH of the literature failed to reveal any data on pimpling of baked enamel systems. Some papers on blistering of house paint Nms were found, and the primary underlying factors of permeability and swelling are covered. Several articles are especially pertinent (1, 8, 4-7). This paper deals primarily with variables in the design of surfacers in baked enamel systems, especially automotive types. Reference is made, however, to other variables, such as the importance of preparation of surface to receive the primer and to variables in the primer and enamel. The whole matter of pimpling of these systems and the design of systems to minimize pimpling involve a large number of interrelated variables. A few tables are given to show the influence of the factors when vaned one at a time. It should be noted in the design of a surfacer or primer that a change in one variable or factor will involve changes in others or in the system as a whole.
S
The design of a surfacer, primer, or enamel coat and the resulting system requires consideration of the large number of interdependent variables. In general, fine pigment particle size and fine grinding are important in primers and surfacers. The advantages of oleoresinous vehicles seem to outweigh their disadvantages to a greater extent than do the advantages of alkyds outweigh their disadvantages. Phenol-modified alkyds combine some features of each. What might in general be called “film structure” is an important variable. The pigment, through its particle size, directly affects the film structure. This covers the general idea of relatively fine pigment particles and preferably uniformly fine ones strongly attracted to and thoroughly wet by the vehicle so that a structure is produced having strong cohesive forces.
Systematic variation of the interrelated factors has enabled us to draw certain conclusions and t o present a theoretical picture of the mechanism of pimpling. We found such a guide helpful in showing how to compensate or adjust for any variables entering the picture from some consideration encountered in practice on the line. Despite large quantities of data already in hand, we feel that much additional work is warranted to afford security in this important field. The studies along this line are being continued in our laboratories. We have brought together measurements on the permesbility, swelling, and pimpling of the films made from the same coating materials a t the same time under as controlled conditions as practicable, and studied the resultant data for correlations.
Materials and Methods Primers, surfacers, and enamels were made up from commercial pigments and vehicles, including both oleoresinous
240
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
and alkyds. The pigments were dispersed in the vehicles in all cases in small laboratory steel ball mills containing 3 pounds of 3/16-inch steel balls per pint of paint. I n general, grinding or dispersion was continued for 96 hours. I n other cases (Table VII) grinding time was varied. A few samples of products marketed by other companies and of factory production samples of our own plants were included a t times t o give constant tie-in to practical results being obtained on the assembly lines. All films for permeability, swelling, and pimpling tests were run in duplicate, and in some cases the results were checked by two operators in different laboratories. Care was taken in the handling of the films to get no fingerprints on the film, since foreign matter, such as body oil, has a definite effect on the speed of failure. If any prints were noticed, the panel or film was discarded. It is felt that the errors inherent in the methods used are small enough so that they do not reverse decisions or factors being studied, and that more elaborate methods can therefore wait for higher state of development of our knowledge of the dependent variables of these systems. PREPARATION OF PANELS. All panels used in this study were automotive.steel except in the metal and metal treatment series (Table 111). The automotive steel panels were all prepared by the following systems: 1. New panels were washed thoroughly in dirty naphtha solvent and rinsed in clean naphtha solvent to remove all grease. 2. Old panels were washed in a hydrochloric acid bath to remove all rust, then in water, and then washed in naphtha to remove any grease. 3. All panels were sanded lightly to get uniform smoothness over the panel surface. 4. All panels were marked with metal dies to ensure recordings. 5. After marking, all panels were washed in a bath containing one part solvent naphtha and one part ethyl alcohol containing 1 pint of ammonium hydroxide to 5 gallons of the naphtha-alcohol mixture. The panels were then dried with clean cheesecloth without being touched by the hand so as to have no fingerprints or body grease on the anels. 6 . All panels as prepared for the pimptng test were prepared by s ray coating, the schedule being as follows: a. Epray application of the primer with one pass giving the approximate film solids thickness of 0.5 mil (0.012 mm.). The primer was baked in an air-circulating oven at 121.1' C. for 1.5 hours. The primer was heavily water-sanded with 400-mesh paper to get uniform smoothness. b. Spray application of the surfacer with two passes, allowing 10 minutes between applications. The surfacer was sprayed to give a film thickness of 1.5 mils (0.037 mm.). The surfacer was baked in an air-circulated oven at 121.1' C. for 1 hour. The surfacer was wet-sanded lightly with 400-mesh paper to give maximum smoothness with minimum scratches. c . Spray application of the enamel with two passes, allowing 10 minutes between applications. The enamel was sprayed to get a film-solids thickness of approximately 1 mil (0.025 mm.). The enamel-sprayed panels were baked in an air-circulated oven at 121.1' C. for 1 hour. A 24-hour period was allowed before immersion in the water bath for the pimpling test.
Measurements SWELLING.The procedure used in the determination of the swelling of films is as follows: The films were applied to tincoated panels (3 inches X 4 inches) with 5 3-mil (0.076-mm.) Bird W applicator and baked in an air-circulating oven at whatever temperature the film is normally baked at in the system. All of the panel edges were coated with a thin brush coat of the material being tested in order to prevent rusting at the edges. After baking, the panels were weighed and submerged in a constant-temperature bath a t 40.5' C. (105" F.) for 4 days. They were removed, wiped dry, and weighed each day for 4 days. After the last weighing they were baked at 121.1' C. (250' F.) for 1 hour to drive off the water absorbed during the swelling test and weighed again. The difference in weights before and after baking gives the amount of solids lost from the film in the immersion period.
Vol. 33, No. 2
Calculations were made to volume per cent in order t o better visualize the degree to which swelling may affect the failure of the automotive system. PERMEABILITY. Films for ermeability measurement were prepared by the a plication orthe paint on smooth tin-coated anels with a 3-miy(0.076-mm.) Bird film applicator. This wet as applied a t 0.076-mm. thickness when baked gave a dry film thickness of approximately 0.040 mm. which is near the 0.037 mm. used in spray application. Unless a variation in thickness was desired, all films were therefore applied with the 0.076-mm. applicator to get maximum uniformity for comparisons of permeability with pimpling. All films were baked the same as in the system application; i. e., the primers were baked in an air-circulating oven at 121.1' C. for 1.5 hours, surfacers at 121.1' C. for 1 hour, and enamels at 121.1' C. for 1 hour. The films were removed from the tin-coated panels by floating them off in a mercury bath. After being removed from the panels, the films were wiped free from mercury and cut to fit the Payne cups. Before clamping the films in the cup, all films were measured for thickness with an Ames thickness gage graduated in 0.0001 mm. Measurements were taken a t six different places over the film, and an average was taken to get an accurate film thickness measurement. Eight cubic centimeters of the water were put in the cups, and the films clamped firmly to ensure no water loss except through the films. Weighings were made on an analytical balance, and the cups inverted and placed in a desiccator with P z O for ~ the desiccant. Weighings were made every 24 hours for 7 days, but calculations as used in comparison with pimpling and swelling were made only from the average of the first 4 days so as to have figures which would compare directly with pimpling results. Permeabilities are ex ressed as milligrams of water diffusing through 1 sq. cm. area o?O.O40-mm. thickness in24 hoursat 25' C. (77' F.). Since the amount of water diffusing through a film is inversely proportional to the film thickness (S), care was taken to get dry films close t o the 1.57-mil (0.040-mm.) thickness characteristic of general spray practice. Calculations were made to correct the permeability to 0.040 mm. in all cases, but these corrections were small because the films were kept as laid down relatively close to 0.040 mm. Permeability measurements were all made in duplicate.
km
Pimpling
All panels were prepared according to the method given under Preparation of Panels. The panels were examined after every 24 hours, and any failure was recorded according to the types of failure shown in Figure 1. After baking, the panels were immersed in a n electrically controlled constant-temperature bath, 4 X 1:5 X 2 feet deep, maintained at 40.5' C. (105" F.) * 1' C. A slow stream of tap water circulated through the apparatus and flowed out an overflow. The stream was sufficient to keep the water clean. The bath was agitated by bubbling air through it at all times. Immersion in the constant-temperature bath was discontinued a t 120 hours unless there was no failure, in which case immersion was continued until some failure was noted. TABLE I. WATERVAPORus. LIQUIDWATERCONTACT (25" C.) lhIateria1 Black automotive enamel
Method Used Liquid u,ater contact
Pigment vol. concn. 7.7270, film solids 32.80%
Water vapor
Film Thickness, hfm. Permeability 0.039 13.52 0.041 11.33 0.059 5.72 0,054 3.73 0.068 3.72 0.074 2.24
In the literature on the permeability of paint a m s to water, permeability was determined by vapor contact; that is, the Payne cups were allowed to stand upright with the films not in direct contact with liquid water in the cups. To correlate our permeability tests to the pimpling tests which are immersion tests, we inverted the cups so as to have the water in direct contact with the film.
INDUSTRIAL AHD ENGINEERING CHEMISTRY
February, 1941
241
Table I gives the permeability of the films at various film thickness for both liquid water and water vapor. The permeability to liquid water is greater in the case of this pigmented enamel; also, a difference in film thickness causes a greater percentage difference in permeability in the case of liquid water contact.
TABLE 11. PERMEABILITY OF FILMS AT 25'
c.
Film System 1
250 1.563 1.675 1.074 1.995 3.320 2.171
System 2 System 3
AND AT
43.3" C.
Permeability 4 3 . 3 0 c. 27.810 27.770 5 3 . 0 0 (weak spots) Film broke Film broke Film broke
M i croscopic
Hazy
lacrosco~~ic
Macroscooic General
ClusteA
-.
7 >
/
I
C
I
Systems 1, 2, and 3 (Table 11) represent three different three-coat automotive systems in which the primer and enamel are the same and in which three different surfacers have been used. Since the pimpling tests were run at 43.3" C. (110" F.), i t would be desirable t o run all permeabilities a t 43.3" C., but experimental difficulties are great. As shown by Table 11, films break too often under the heavier permeability loads and the greater vapor pressure in the cup.
TABLE 111. EFFECT OF DIFFERENT METALSAND METALTREATMENT ON PIMPIJNG AND WRINKLING Metal or Treatment Automotive steel untreatdd
Surfacer* 24-hr 4 1 None 2 None 3
Type of Failur48-hr 72-hr 96-hr None
4b6
45* 6 None
459 6 None
5: 7 None
1 2 3
None None None
None None None
None None None
Trace5 None None
5?7
Brass
1
None None None
3.5 None None
4i5
4$5
4,3fjba
None
None
None
1
None None None
None None None
None None None
None None None
5 None None
1
None None None
5,2 5 2 N&e
5 5 5,7
5 5 5,7
5 7 5: 7 5,7
None None None
None None None
2,5 2 None
Z35 None
2, 5, 8 2, 7 None
2 3
4, w 2.3 None
4,6,W 3,5 None
4,6,W 4,b None
4,6,W 4i5
4,6,W 4g5
1 2 3
4 2,3 None
6 4 5 NAne
6 2 4 5 r\ioie
6 2.4.5 None
6 2,4,5 None
1 2 3
4 None None
0 3 3
0 5
6
6 6 5
6 6 6
1 2 3
None None None
None None
3 2, w None
4 ,3W None
"3" None
1 2 3
None None None
None None None
W,2 None None
W,3 None None
None None
Metal treatment 3b
1 2 3
None None None
W None None
2,W None None
2.3, W 5 None
2,3,W 5 None
Metal treatment 4b
1
Copper Tin-coated steel
Stainless steel
2 3 2 3
1 2
3 Zinc
Smooth glass
Sand-blasted glass Metal treatment 1b
Metal treatment 2 b
1
7
w.3
None None W W W None None None None None None None None None None 0 Surfacers 1, 2, and 3 were selected as representing three different types previous work on which had indicated 1 t o be very unsatisfactory 3 t o b; satisfactory, and 2 to be intermediate between 1 and 3, when they &ere used aver a primer on untreated automotive steel b Metal treatments 1, 2, 3 and 4 are commercial metal treatments of the phosphate type 2 3
S
* '
I
.
Medium at Random
/
Medium '
General
' %
Erupt ion s of Oxidized Metal, Scattered
Eruptions of Oxidized
Metal, GiPneral
W-Wrinkling All panels haze in the bath in 24 hours ahd are not marked as such in any table unless t h e hazing returns after wiping or does not wipe off at all. FIGURE 1. TYPES OF FAILURE
120-hr
Aluminum
2 3
\ '
I n this series attempts were made to use single films such
as surfacer films, but breakage occurred within the first 24 hours of test, and even the films of the three-coat system were not strong enough in most cases to withstand the strain at 43.3" C. Rise of temperature from 25" to 43.3' C. increased the permeability at least sixteen fold.
Effect of Metals and Metal Treatments on Pimpling and Wrinkling The results in Table I11 show that the type of metal or metal treatment does have an important effect on the ultimate speed of failure. Generally, the metal treatments showed an improvement over the untreated automotive steel; some treatments gave outstanding results. Variation in the type of metal s-howed marked variatiens. Zinc and zinc-containing metals gave poor results, copper and aluminum gave better results. Stainless steel showed some improvement over automotive steel. Glass or sandblasted glass are poor. Table I11 shows widely different results with the same material on the different surfaces, and indicates the importance of adhesion as a factor in pimpling.
Comparison of Alkyd and Oleoresinous Systems INFLUENCE OF VEHICLE.Surfacer vehicle variation (Table IV-A) has a great effect on the speed of failure of the automotive system. This table shows that the degree of permeability and the volume of swelling, individually and collectively, affect the degree of pimpling failure. Our study indicates that, generally, are superior to alkyd resin solutions in However, the number les involved-e. g., type of oil, type of resin, oil len of bddying during the Cook, drier content, etc.-and the further dependence of the pig-
INDUSTRIAL A N D ENGINEERING CHEMISTRY
242
Vol. 33, No. 2
OF ALKYDAND OLEORESINOUS SYSTEMS TABLE IV. COMPARISON
Filmah
,Surfacer Sanding
Surfacer Holdout
Type of Failurc 72-hr.
I
48-hr.
24-hr.
A.
120-hr.
Pimpling Failure, Hr.
Permeabilityc
Swelling, Val. %
None None None
None None Kone
192 216 264
7.87 5.13 5.54
5.32 15.75 9.34
None None 6
None None 6
None
216 168
?One
6.53 22.80 26.98
15.55 23.60 36.40
5 Bad W Trace W,3
6 Very bad W W, 5
6 VBW, 3
VBW, 3
9.32 13.83 4.28
56.68 62.47 86.40
5
6 None
6 2
6 2, 3
6 2, 3
...
...
14.60 14.78
76.92 13.78
None None None None 3 3
None None None ;, 3
None None 3 2, 3, 5 6 6
216 192
2.72 4.48 13.56 2.19 3.90 19.90
12.40 13.13 14.15 70.90 00.95 34.78
5-18 S-20 9-23
Good Good Good
Good Good Good
None None None
None Iione None
S-25 S-51 S-49
Good Good Good
Good Good Good
None None 3
None None 5
27-50 s-45 S-13
Good Good Fair
Good Good Fair
w
3
S-16 s-8
Very good Good
Poor Good
5-40 S-43 S-44 5-46 s-47 5-48
Good Good Good Good Good Good
Good Good Good Good Good Good
None None
B.
-
Influence of Vehicle None None None
96-hr.
5
-
6
w, 5
W,6
Influence of Vehicle Oil Length None None None None 3 3 2, 3, 5 2, 3, 5 6 6 6 6
... ... ... ...
-
...
... ... ...
-
a Pigment' Ca and Mg carbonates and silicates, 92.8%: TiOz, 5.45; lampblack 1.75. pi ment volume oonoentration: 42.75% b S-18 S-20 S-23 phenolic resin tung oil varnish: 5-25 natural resin, tung'oil v&nisf. 5-51 phenolic resin linseed oil Garnish; S-49 perilla oil (45%') moiified alkyd with variatidn in type of dibasic acid: 5-50 = perilla oil (60%) modifieh alkyd with variation i i glyceride: 5-45 = linseed-tung oil ( 4 5 T ) modified alkyd: S-13 = dehydrated castor oil (45%) modified alkyd; S-16 = maleic alkyd, linseed oil modified (45%); 5-8 = phenol modified tung oil 45 O).alkyd: S-40 = henolic resin, tung oil yarnish 10-gal. length: 5-43 = same, 20-gal. length: 5-44 = same, 30-gal. length; 5-46 = perilla oil alkyd a t 4 0 z o 1 1 modification; E-47 = same a t 50% pi1 modification; S-48 = same a t 60% oil modification. e Mg.HzO/sq. cm./24 hours/0.040-mm. film thickness.
ment and pigment wetting on vehicle variations make it inipracticable to lay down a specification to be followed. We have gotten excellent results, for example, with dissimilar resin types, and also a range of good t o poor with resins within a type or by cooking variations. There is considerable variation in pimpling results, with changes in formulation in both the oleoresinous varnishes and alkyd solutions. Table IV-A shows that the degree of permeability and the volume of swelling go hand in hand in controlling pimpling failure. There seems to be an optimum range for both permeability and swelling, with a maximum point which varies as either one or both increase. INFLUENCE OF VEHICLEOIL LENGTH. I n Table IV-B (as in A ) an outstanding difference is seen between alkyd and oleoresinous vehicles; the oleoresinous varnishes shorn superiority over alkyd resin solutions in water immersion tests. The variation of the percentage of oil in the vehicle has a different effect in the oleoresinous vehicle from that in the alkyd. Permeability and swelling figures (Table IV-B) indicate that in the case of the oleoresinous varnish, although increase in oil length does not greatly affect the swelling, it does affect the permeability and thus the speed of pimpling failure. It is apparent that, a t least with the resin used, the oil is nearly as nonswelling as the resin. I n the case of the alkyd, the oil swells least. Increase in oil modification in the alkyd affects the permeability considerably, but the smelling is so high that the failure appears t o be directly related to the high degree of swelling.
Variation of the type of oil in the same alkyd vehicle formula (Table V) shows a definite effect on pimpling, swelling, and permeability. Although the apparent difference in pimpling results is not great, it is visible. Water permeability and volume percentage of water swelling (Table V) seem to be in direct ratio to pimpling results; i. e., as the permeability, swelling, or both increase, the degree of pimpling increases.
a
7
6
h
5
i
B
8E'
c
3
z I
10
20
SO
Pigment Volume
40
50
Concentration
FIGURE 2. PERMEABILITY us. PIQMENT VOLUMECONCENTRATION
OF TYPEOF OIL IN ALKYDVEHICLES TABLEV. IXFLUEKCE
Influence of Type of Oil i n Alkyd Vehicles
8
Surfacer. s-10 s-1 1 67-12 S-13 S-14 5-15 5-17
Vehicleb LX4550 PerX4550 FX4550 DX4550 SoyX4550 TX4550 OitX4550
-Type 24-hr. 48-hr. None 3 None None None 3 None 3 None 3 W W W W
of Failure72-hr. 96-hr. 5 tjb7 3 5 5,7 5 5,7 5 5, 7 3,W 3,W 3, W 3, W
120-hr. 6,7 6 6,7 6.7 6,7 3,W 3,W
Permeability 27.24 10,57 32.67 18.72 5.25 7.69 9.48
Swelling, Vol. % 23.93 26.40 21.00 19.91 26.63 12.54 10.66
a Pigment: Ca and AIg carbonate and silicates, 92.S'%; TiOz, 5 4 5 ; lampblack, 1.75; pigment volume concentration: 42.75%. The primer and enamel were constant throughout thia series. b LX4550 = linseed oil modified alkyd. PerX4550 = perilla oil modified alkyd' FX4550 = fish oil modified alkyd; DX4550 = dAhydrated castor oil modified alkyd; SoiX4j50 = soybean oil modified alkyd: TX4550 = tung oil modified alkyd: OitX4550 = oiticica oil modified alkyd. All resin solutions were a t 45% modification and 50% solids.
February, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
F ( X 100) OF VARIOUSTYPES OF FAILURE FIGIJRIO 3. PHOTOGRAPHS
This study indicates that, a t least in the modification used, the oils follow this order of excellence (decreasing) : tung and oiticica, perilla, dehydrated castor, soybean, linseed, fish.
Effect of Pigment Volume Concentration
243
G ( X 100)
show any correlation with pimpling in this series, using these vehicles and pigment; however, Table V shows t h a t pigment, even in small quantities, increases the swelling by as much as seven fold over that of the clear vehicle. The degree of dispersion of the surfacer is a factor in the durability of the automotive system in the pimpling tests. The effect is shown in three ways in Table VII. The holdout of the enamel by the surfacer, the permeability, and the degree of pimpling are all affected. This phase of the study indicates that the poorer the dispersion, the more easily water can get into the system, and the more easily adhesion can be overcome and lead to pimpling.
I n preparing the surfacer in this study, a master grind of paste was made a t 55 per cent pigment volume concentration and reduced with resin solution to get the desired percentage of pigment; thus fineness of grind and ratio of the several pigments to one another remained the same. Table VI shows pimpling, permeability, and swelling results. It indicates: (a) permeability is in direct proportion to pimpling; (b) percentage of pigment has a direct effect on pimpling; (c) pigment percentage directly affects sanding and holdout. It isapparent that there TABLE VI. EFFECT OF PIGMENT VOLUMECONCENTRATION is an optimum range in pigPigment Vol. Swelling, ment volume concentration Conon., Surfacer Surfacer Type of Failure PermeaVol. Filma % Sanding Holdout 24-hr. 48-hr. 72-hr. 136-hr. 120-hr. bilitvb olb above or below which unS-35c 0 Very poor Good None Slight W W 3 w 3 w 3.24 4.77 desirable results obtain. A 10 Very poor Good None None Slight W Slight W SligdtW.3 3.0 30.82 S-36d 5-37d 22 Very poor Good None None 2 3 3 2.95 30.52 pigment volume concen5-38d 32 Poor Good None None None 2 2 2.28 33.80 tration of 35 to 42 per cent S-3W 38 Fair Good None None None None None 1.38 37.50 seems to be the range in * S-40d 42 Good Good None None None None None 1.96 33.78 3 3 3, 5 2.18 34.65 S-41d 46 Good Fair None which the best results obS-42d 52 Fair poor None 3" 4 3.6 3. 6 42.40 31.60 tain (Figure 2); below it a I n the pimpling tests the primer ughout and only the surfacer was chan e d . there is poor sanding and the primer was a commercial iron ox was a carbon black-alkyd-urea-forrna?de: hyde enamel. pimpling, and above there b No primer or enamel was used in t and swelling tests. c Phenol modified alkyd. is poor holdout and bad d Same phenol xrie&%d-alkyd as Spimpling. lampblack, 1.75. Swelling results do not
-
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
244
~
--
~
~
~~
~
O F DISPERsION TABLE VII. INFLUENCE O F DEQREE
Materiala s-59 23-60 S-61 S-63
Time of Grind, Hr. 24 48 72 96
Type of Failur24-hr. 48-hr. 72-hr. 96-hr. None TraceW W , 2 W,3 None None None 2, W None None None 2 None None None None
120-hr. W,2,3 W.3 3 2
Permeability 94.75 77.00 66.18 38.72
Swelling, Vol. % ' 29.12 30.25 33 31 33.78
-SurfacerSanding Holdout Good Poor Good Fair Good Good Good Good
a Pigment: C a and Mg, carbonate and silicates, 92.8%; TiOz, 5.45: lampblack, 1.75; vehicle: fied alkyd a t 45% linseed oil modification; pigment volume concentration: 42.75Y0.
phenol modi-
TABLE VIII. INFLUENCE OF TYPEOF PIGMENT Film5 S-58 S-62 S-33 S-4 S-31 5-57 S-34 5-52 S-64 S-1 S-7 5-53 5-32 5-28
Sanding Good Very good Fair Fair Good Good Good Good Good Good Good Good Good Fair
Particle Size Micrdns 24-hr. 5 None 5 None None 0.5-0.0 None 5 5 None 5 ' -' 'Nbne 10 None None 7 5 None 16 None 10-12 None 20 None 20 W 22 W
Holdout Good Good Very good Fair Good Good Good Fair Good Fair Good Poor Poor Very poor
Type of Failur48-hr. 72-hr. 96-hr. None None None None None None None None 2 W W W None None 2 1 1 2 None None 2 W W 2 W,3 None Nn:e 2 2 3 4 3 4 4,6 WW,3 W,5 W.3 W 3 W,4 W W:3 W,3
120-hr. None None 2 W 3 3 3 W,5 3 4 4,6 W.6 W,4 W,3
Permea- Swelling, %.Sol. in bility Vol. % Pigment 0.689 18.72 0.41 6.32 17.11 0.06 9.80 9.16 0.09 20.46 3.80 0.22 26.97 7.92 0.12 19.12 15.52 0.41 39.37 9.09 0.30 14.66 12.94 0.49 14.78 33.78 0.41 16.67 14.02 0.64 79.20 7.08 0.13 37.40 0.54 56.15 41.78 0.52 21.35 38.30 0.25 42.73
Vol. 33, No. 2
The pigment particles apparently are stepping stones for water in passing through the paint film, and the coarser the particles, the faster the water may travel through the film. It is logical that soluble salts in the pigments would aid the water in passing through a film but most commercial pigments have an almost n e g l i g i b l e a m o u n t of water-soluble salts. This factor, therefore, would not have a major effect on pimpling failure.
Comparison of Primer, Surfacer, and Enamel
Table IX was developed primarily to show the physical properties of the individual parts of the system and their possible effects on the system. Not much importance can be attached to the results on the automotive TABLEIX. COMPARISON OF PRIMER, SURFACER, AND ENAMEL primer because in actual Film spray application it is apSpray ------Type -------erof ul iaF Thickness, PermeaSwelling, Film Coatso 24-hr. 48-hr. 72-hr. 96-hr. 120-hr. Mm.b bility Vol. % plied so that after sanding Autqmotive 1 None None None None None 0.011 78.14 39.63 it will have a thickness of primer 2 None None 3 3 3 0.025 40.56 45.48 3 None 3 4 4 P-10 4 0.049 24.60 47.00 only 0.5 mil (0.0127 mm.) ; Surfacer 1 None None None None None 0.030 2.39 7.30 at t h i s t h i c k n e s s t h e None 5-334 2 None None None None 0.064 0.92 7.55 permeability is so great 3 None None None None None 0.066 0.89 9.16 that it acts almost as a Surfacer 1 0.103 19.41 35.32 rust spots Immersion discontinued after 6rst s-2sa sieve, and measurements 2 Verybad Same 24 hrs. 0.108 20.89 38.76 3 Same [ J All thinner films broke 38.30 are inaccurate and diffiin preparation cult to make. We believe Automotive 1 None None None None None 0.013 53.28 7.48 that the primary function enamel 2 None None Trace2 2 2 0.014 44.20 5.92 E-l/ 3 None 3 2 4 4 0.019 36.66 9.9s of the primer is to act as 0.029 13.66 .... a bond coat for the system 0.067 2.93 .... to the metal, and because P-I, s-33, None None None None None ... ... .... E-1 of its thinness it does not P-l,S-28, .. W w W,2 w,3 W,3,5 ... ... .... 1-1 play so important a part Panels for pimpling tests were prepared with 1, 2, and 3 coats of the primer, surfacer, and enamel alone b y bakin pimpling resistance as i n g between each coat. do t h e surfacer and b These film thickness measurements were the thickness measurements of the films used in permeability measurements and have no connection with either swelling or pim ling tests. enamel. c Iron oxide igment 40%: oleoresinous solids, 22: s o c e n t 38. d Carbon ant?TiOz pigments 43.5%: phenol-modified alkyd resin solids 20.0. solvent 36 5 P e r m e a b i l i t y figures e AI, and Mg silicates and Ti&, 36.0%' phenol-modified alkyd resin solids 2y.O. solvent k i . 0 . were not obtained on the f Pigment volume concentration, 7.72%; pigment, carbon and iron blue; \;ohm; of film-{orming solids, 32.80%; vehicle, oil modified alkyd. systems using surfacers 8-33 and 8-28 because of the difficulty of applying each coat uniformly; however, the trends indiInfluence of Type of Pigment cated that the permeability of the system is dependent on the The type of pigment has an important effect on the repermeability of the least permeable film. sults obtained with the automotive system. In making these The pimpling, Permeability, and swelling results with surcomparisons, a wide variation was made in types of pigment. facer 8-33 alone, in comparison with the same results on Pimpling, swelling, and permeability results varied more enamel 23-1, indicate that it should be a strong member in a khan in any of the other series throughout the study. system since there was no pimpling in 120 hours in the water As Table VI11 shows, the original particle size has an imbath, and both swelling and permeability were low. This was portant part to play in the ultimate results. It is indicated shown to be true when it was used in the system, since no that, as the particle size increases, permeability and swelling failure was observed after 120 hours in the bath. have a chance to increase with a proportional increase in the Surfacer 8-28 should give bad failure in the system since it speed of pimpling failure. would be a weak part, as shown by its early failure in allowPigment variations were made only in the surfacer. primer and enamel were constant throughout the test. Surfacer pigment volume concentration was 42.75%: sukfacer vehicle was phenol modified alkyd a t 45% oil modification. Pigment variations were as follows: s - 5 8 = treated C a and Mg carbonates and silicates: 27-62 = mineral black: 5-33 = carbon and TiOz: S-4 = micronized mica; 5-31 = slate flour. S-57 = treated Ca and Mg talc: 5-52 = fine asbestine: 9-61 = Ca and Mg ckrbonates and silicates. S-1 = carbonates and silicates: 8-34 Al, Ca, and M g silicates and iron oxide, 5-7 = kaolin. S-53 asbestine. S-32 = A1 and Mg silicates. '5-23 = ooarse mica. The pigment as contained in the surfacer; had approximatel; 7.2% of the following additioAa1 hiding pigment: Ti02 75.70%, lampblack 24.30%. Q
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
February, 1941
ing rust to form on immersion. Its permeability and swelling are very high and are an added indication of weakness. This appears to be true, as shown when it is used in the system. The results given in Table IX indicate that to have an automotive system which will stand water immersion without pimpling, each member must be similar in permeability and swelling.
TABLE X. INFLUENCE OF BAKING TEMPERATURE Baking Temp., O F. 200 250 300
24-hr. None None None
48-hr. 1 None None
Type of Failurc 72-hr. 96-hr. 1,2 $3 None None None
120-hr. 1.4 3 Trace2
Table X indicates that baking temperature has a definite effect on the speed of pimpling failure. The films obtained at the higher temperatures had greater resistance t o pimpling. The three films were built up of primer P-1, surfacer 5-65, and enamel 8-1, and were as nearly identical as possible in all factors except temperature of baking, as indicated.
TABLE XI.
INFLUENCE OF PRIMER VARIATION”
Type of Failure Primerb 24-hr. 48-hr. 72-hr. 96-hr. 120-hr. P-2 None 2 3 4 6 P-3 None None 2 3 4 P-4 None None 2 2.3 2, 5 P-5 None None 2 3 5 P-6 None None 3 5 3,5 P-7 None None 3 6 3.5 P-8 None 2 3 4 6 a The surfacer and enamel on all panels were the same. Surfacer 5-8: pigment = Ca and Mg carbonates and silicates 9 2 . 8 7 Ti02 5.45 lampblack 1.75; vehicle = phenol modified alkyd at 45% &seed oil rdodification. Enamel E-1: pigment volume concentration, 7.72% ; pigment. oarbon,and iron blue; volume of film-forming solids, 32.80%; vehicle, oil modified alkyd. b P-2 = iron oxide-long oil oleoresinous primer; P-3 = zinc chromate-iron oxide-long oil oleoresinous primer; P-4 = red lead-oil primer’ P-5 = zinc chromate-iron oxide-short oil oleoresinous primer; P-6 = TiOklampblackasbestine oleoresinous primer; P-7 = 20-gal. tung oil phenolic varnish (unpigmented) ; P-8 = zinc chromate-iron oxide-long oil alkyd primer.
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The primary reason for studying the problem presented here was to find measurable correlative factors for determining the rate of pimpling of the automotive system. Since it was felt that the greatest variation in formulation and the greatest variation in results would be obtained by studying the surfacer, the greatest amount of work was done on it. Of the several variations studied, some had major effects on pimpling failure. The variations made were as follows: type of vehicle, type of oil, vehicle oil length, type of pigment, degree of dispersion, pigment volume concentration, type of metal and metal treatment, baking temperature, type of primer. Each variable in turn brought out factors which could be correlated to pimpling. Since pimpling is primarily caused by water getting into the system and destroying the bond between films or between the film and metal, the important factor to measure was the amount of water that would get through the film, or the degreeof. pemwb2ity. *Indirect connection with permeability would be the percentage of swelling resulting from the water as it went through the film. Through the correlation of the three factors-permeability, swelling, and pimpling-it was ‘possible to find the weak points in each series. This brought out three major points which are of value in preparing an automotive surfacer: (a) A fine, well dispersed pigment is an aid to retard pimpling; (b) a vehicle which swells little is an aid to retard pimpling; ( c ) there is an optimum pigment vehicle concentration range within which pimpling resistance is improved.
Literature Cited (1) Blom, A. V.. J. Oil & Colour C h m . Assoc., 22, 104 (1939). (2) Buser, K., Farbeu. Luck, 1932,256. (3) Paint & Varnish Production Clubs. N e w York Production Club, “Permeability Measurements”, p. 76 (1937). (4) Rinse, J., and Wiebols, W. H. G., IND.ENG.CREM.,29, 1149 (1937). ( 5 ) Wagner, H., Furben-Ztg., 36,1214 (1931). (6) Zbid., 38, 266 (1932). (7) Wray, IND.ENG.CREW,25,842 (1933).
We believe that the primary function of the primer is to act as a coat bonding the system to the metal. Because of its thinness it does not play so important a part as the surfacer or enamel in keeping water out. Table XI shows some results i n primer variation which, despite considerable differences in composition, are quite close in the rate of pimpling failure. The small variations in results may be interpreted as a variation in adhesion to the metal.
Discussion Figure 3, A and B, shows systems which have been in the constant-temperature bath 120 hours; the failure is type 6 (Figure 1). C is an enlargement of a pimple which falls in the class of type 6. D and E are enlargements of types 7 and 8. There is no pimpling in this type of failure; however, at these points there seems to be a pin point or pore which acts as a channel permitting oxidized metal to appear on the enamel surface, and we have called this type of failure “erup tion of oxidized metals’’ (usually rust). F and G are enlarged oross sections of two automotive systems, the only variant being the type of pigment in the surfacer or intermediate coat. The surfacer in F has an average pigment particle size of 0.5 micron, and the surfacer in G, of 22 microns with the oversine particles as large as 45 microns. F and G show the effect particle size can have on permeability and wrinkling.
COLUMNSFOR RECOVFIRY OF EXCESS PEXTU-EAND DICHLOROPENTAPI’PIISOLATION, IS THE PESTANE CHLORINATION DEPARTMENT OF TFLE SHARPLES SOLVENTS CORPORATIOX (See papera of McBee et al., pages 176-188)
