June, 1933
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
COMMERCIAL APPLICATIOKS ANODEPROCESS RUBBERARTICLES. Many relatively thin rubber articles, such as balloons and gloves, have long been made by the repeated dipping of forms into rubber cement. This method often requires several hours to build up the necessary thickness of deposits, and has other disadvantages such as fire and health hazards, limitations in compounding and curing ingredients, and inferior chemical and physical properties. Thin articles can also be made by repeated dipping in latex, but such a multiple dip method also has marked disadvantages, such as the formation of striations and layers, separation of the layers under stress, the entrapment of air, and slow rates of thickness building. For example, it would require a number of individual dips and a like number of drying intervals to produce inch in thickness. With the anode process, on the other hand, homogeneous deposits free from defects are produced in one application, and the time required for most articles is measured in seconds and minutes rather than in hours. Anode rubber has extraordinary strength and durability. Tensile and elongation data such as 5900 pounds per square inch a t 970 per cent elongation and 6700 pounds a t 925 per cent are characteristic of anode compounds but are most difficult to obtain with masticated rubber. Remarkably high tear resistance is exhibited by anode rubber stocks all the way from the uncured state to the point of optimum cure. It has good resistance to wear, abrasion, and corrosive chemicals. The water absorption can be controlled to a value comparable with that of good masticated rubber and very much less than that of gum-dipped rubber. Rubber products that are a t present being manufactured by the anode process include gloves, balloons, drug sundries,
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fountain pen sacs, bathing caps, rubber overshoes, and many specialties. ARTICLESCOVERED WITR ANODEPROCESS RUBBER. Ror many years engineers have been specifying rubber-lined tanks and other types of rubber-covered equipment for resistance to severe corrosive conditions and for other specific uses. However, the application of rubber coatings by hand (paperhanging method) is too expensive for wide use on Emall oddshaped articles. Xow the anode process has ushered in a new era in which articles of countless shapes and sizes can be efficiently and inexpensively covered with adherent coatings of soft and hard rubber. A high degree of adhesion to metal and many types of nonmetal surfaces can be obtained through the use of Vulcalock (a rubber isomer of remarkable adhesive properties) which can be applied to article surfaces by anode process deposition from water dispersions or by dipping in solvent solutions. dnode soft and hard rubber coatings are used for such varied purposes as resistance to corrosive chemicals; resistance to wear and abrasion; insulation against electricity, heat, sound, and vibration; and for specific applications. ACKNOWLEDGMENT The author extends his thanks to R. W. Albright, general manager of American Anode, Inc., for permission to publish this paper. He also wishes to acknowledge the many contributions of Andrew Szegvari of American Anode, Inc., to anode process technology; the pioneering efforts of Paul Klein of the Hungarian Rubber Goods Company, and S. E. Sheppard and L. W. Eberlin of the Eastman Kodak Company; and the technical contributions of American Anode licensees. RECEIVEDJanuary 19, 1933.
Alkyd Resins as Bonding Materials A. G. HOVEY General Electric Company, Schenectady, N. Y.
T
H E quest for suitable adhesives is probably one of the oldest problems of civilized man. Today certain whole industries depend upon adhesives, and yet so often the contempt of executives is shown by the exclamation, “A sticker? Why anyone can make a sticker!” To those who have been assigned the problem of formulating adhesives for commercial purposes, however, it is apparent that there is not only many a slip between choice of adhesives and production of finished articles, but also that there is no such thing as a “universal sticker.” One adhesive cannot work equally well on materials so different in nature as rubber, celluloid, glass, and molded materials, and so differently affected by solvents. It is too much to expect the same quick set between smooth, tight, dense surfaces, such as glass or molded articles, as may be obtained between rough, porous surfaces, such as cloth,. paper, or unglazed porcelain. For smooth surfaces, penetration and wetting are of prime importance, whereas these properties are of secondary importance for porous surfaces. However, too much penetration of porous material is undesirable because the adhesive will soak in, leaving little binder on the surface. It is also necessary to consider the conditions under which the finished article is to operate, as well as the conditions allowed in manufacture. For example, there are surprisingly few adhesives which set rapidly enough to allow pasting a fair-sized strip of rubber upon vertical walls without having the strip
fall off of its own weight after being apparently stuck. A universal adhesive has so many chances to come to grief that any household cement or office glue is in danger of losing its reputation because of the number of jobs it will not do instead of gaining a reputation for the large number of jobs it will doall because of the unexpected variety of chemical and physical abuse which will be demanded of it. Aside from the convenience of having one standard material to purchase, control, and become accustomed to, the real reason a universal adhesive is sought is to take advantage of low cost by large production. However, the amount of adhesive used in manufacturing is usually small in comparison with the amount of material upon which the adhesive is used, so that while certain industries, such as the manufacture of windshields, may find the cost of adhesive a large and important item, the cost of adhesive used is in most cases so small in proportion to the value added in manufacture that a satisfactory adhesive would still be profitable even if the cost were many times higher. Consequently, adhesives are made for the job instead of making the job work with a universal adhesive, since there is so much more required of an adhesive than just sticking. HISTORYOF ALRYDRESINADHESIVE Perhaps the outstanding feature of the alkyd resins from the time of their discovery has been tackiness with subsequent
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I N D U S T R I A L A N D E N G I N E E R I N G C H E ?VII S T R Y
adhesion to practically all materials. Another indication of their usefulness where the need of adhesion was imperative was given by the high degree of penetration of fibrous materials and by the good wetting action on surfaces. Although certain alkyd resins were described in chemical literature long ago, and in patents by Callahan ( d ) , Arsem (f), Dawson (5),and Howell (9) as good adhesives and as forming adherent tough films on metal, nevertheless it was not until after the World War and the advent of cheaper phthalic anhydride that alkyd resins were seriously considered for commercial purposes. As soon as the cost of the alkyd resins began to approach that of the natural resins, it became apparent that the synthetic products had the following advantages over the natural: (1) control in manufacture and in formulation; (2) uniformity as opposed to chance variation; and (3) freedom from impurities, adulterants, and dirt which constitute an undesirable menace to electrical insulation.
Vol. 25, No. 6
lin itself is not an adhesive and when dried out becomes quite brittle, relatively large amounts may be used with alkyd resins without ill effects to produce the much desired quicksetting properties. Plasticizers, such as dibutyl phthalate, tricresyl phosphate, camphor, and the like, may be added to prevent embrittlement of the nitrocellulose component of cements, but permanent adhesion is obtained by having a substantial proportion of alkyd resin present. For such a quick-setting cement, the following formula is recommended: Modified alkyd resin 35% s o h of l/a eec. nitrocellulose Solvent Plasticizer
Parta by weight 11-20
64-73 11-2 1 4-8
On a dry basis, 11 to 20 per cent of modified alkyd resin may be used with such proportions as 22 to 26 per cent of low-viscosity nitrocellulose of the type known as second ALKYDRESINADHESIVES IN INSULATIOX cotton. While it is not necessary to use low-viscosity nitroThe alkyd resins were first used in the manufacture of cellulose for all cements, it is advantageous to do so because of composite mica articles for electrical insulation. Up to the the higher solid content, since the cement may thus be prepresent time the substitution of synthetic products of the pared in a concentrated form which gives less shrinkage phenolic condensation type for natural resins has been unsuc- upon drying out than would be the case if the solid content cessful because this type of resin carbonizes readily under an were lower. I n preparation of such a cement, alkyd resins of arc, and because of the lack of adhesion. When the phthalic the type modified by drying oils and their acids are used. An adhesive of this type which was originally developed anhydride-glycerol resin in acetone solution is used as a binder for mica products under the procedure outlined in a for special use in assembling radio parts where fast airpatent of Barringer and Peterson (S), the adhesion of the drying is demanded, has found additional use on small coils, alkyd resin to the mica is found to be excellent and so tena- for labeling, for pattern shop work, and for general office and cious that the cemented mica articles ring when struck as factory adhesive work where a quick set and lasting bond are though made of steel. While a t first all the mica parts using needed which must not be affected by changes in humidity alkyd resin as a binder were heated in a press to effect the and which will not be a tempting food for parasites. While curing of the resin, it was later discovered by Peterson (1%’) a universal adhesive is out of the question, this one covers a that improved results could be obtained by carrying out the wide variety of usefulness. first part of the hardening reaction under such conditions that the escape of volatile matter is facilitated, and subsequently OTHERAPPLICATIONS IN INDUSTRY by pressing during the latter part of the curing. In the attaching of bases to incandescent lamps and to large The substitution of the clear light-colored alkyd resin for the dark-colored binders which had previously been used for vacuum tubes, alkyd resins have played a useful part. A bonding mica also improved greatly the appearance of articles paste, consisting of resin, solvent, and inorganic filler, is made of composite mica, and stimulated its use for lamp placed in the base, the lamp is inserted in the base, and heat is applied to volatilize the solvent and to cure the resin. shades and other objets d’art. Mica sheets of permanent flexibility had not been possible, Considerable advancement was given to lamp-basing by the using the old natural brittle resins as a binder; however, using discovery of Wright (16) that the process of heat-curing of the technic just described for the production of rigid mica alkyd resins was hastened by the addition of certain dehydrat(substituting for the phthalic anhydride-glycerol resin a modi- ing catalysts. Among these catalysts, zinc oxide is particufied alkyd resin in which a part of the phthalic anhydride has larly effective because of its availability and light color. been replaced by fatty acids of oils with or without the addi- A white cement made from glycerol-phthalic anhydride resin, tion of oils themselves or other plasticizers), it has been pos- zinc oxide, and white inorganic filler increased the reflecting sible to produce tough, permanently flexible mica sheets. power and improved the adhesion to the glass. This imThe same adhesive is used on slot tube work and for pasting provement was particularly welcome in the case of surgical lamps which are intended for insertion within the human sheet fiber and mica to form several composite insulations. The usefulness of alkyd resins as bonding material for pur- body. A new application of certain alkyd resins has been found poses of electrical insulation has not been limited to mica products, but that is the typical example of their utility, (8) for holding a thin layer of heat-resisting inorganic insulasince it is quite difficult to obtain adhesion to mica. A special tion which in itself is not flexible or very adhesive, such as flexible resin in which part of the phthalic anhydride is re- oxidized aluminum, to a wire until this conductor is bent placed by linseed fatty acids has been successfully used for into the desired shape, such as a coil. Wuen the coil is wound, the alkyd resin, which has been holding the heatattaching asbestos to copper wire. resistant insulation on the wire during bending, may be removed by solvent or by heating to 390-400° C.; then a QUICK-SETTING CEMENT FOR GENERAL USE final application of rigid inorganic insulation may be applied. I n order to accelerate the air-drying properties of the alkyd For removal by heating, those resins which are unmodified resins and to cut down on the penetration of fabrics and by drying oils and their acids are preferred. Another new development in which alkyd resin is used as fibrous or porous materials, which for some purposes become objectionable because of the increased stiffness and larger a binder is for foundry sand (6). The difficulty of slag formaamount of resin absorbed, it is often advantageous to incor- tion in cores is taken care of by the volatilization of the alkyd porate nitrocellulose with an alkyd resin. Although pyroxy- resin which leaves no carbonaceous residue.
June, 1933
I N D U S T R I A L A N D E N G N E E R I N G C H E M I S T 1%Y
The alkyd resins liave a usefulness a8 a binder for molding materials and as a plastic, the merits of which have recently been described by Wright (2::). The value of the adhesion to metals of alkyd resin coating compositions has been known for some time and descrilred by Kienle ( I O ) , Ferguson (7), and Harringer (8).
not be expected to be 100 per cent efficient for all the materials; it should, however, he a reliable guide.
soL\rEX'rLEsSCEMENTS
The above uses of alkyd resin as a bonding material have iiirolved the use of solvent. There are, however, many places where resiii in solid form is useful, and others where solvent is not wanted. For example, a high-vacuum cement to be used for sealing leaks in a glass system must have a miniinurn of volatile material. Certain of tlie alkyd resins, especially glycol phthalate described by Sager and Kennedy (1)and by Kienle and Ifovey ( l l ) ,are useful as a vacuumscaling cement, not only because a lower amount of rolatile matter permits tlie obtaining of a better vacuum, but also because a better f l i i ~results without Iraviing to overheat c.racked glass or "ring seals," and because of the excellent penetration, power of wetting glass, transparency: and light color. The lieat-convertible alkyd resins when used without solvent as thcrnroplastic bonding materials offer the additional advantages of curing, increased strength, and increased inertness. Filler may be incorporated tu economize on resin. As with lamp-basing cements, dehydrating catalysts, such as sinr oxide, may be nsrd to liasten the cure. This type of solvcntless cement, prepared by nrilling in the fillers a.nd catalyst a t a low temperature and tlrcn applying and curing at a higher temperature, gives more promise of becoming useful wliere there is so much space to be filled between the art.icles to be cemented that an adlresive requiring solvent is not practical. I n attempting to prepare composite molded insulation from paper, linen, or cotton cloth, or other sheets of cellulose material by using under heat and pressure the A stage (fusible and soluble) of certain alkyd resins, it was found that the intimate mixture of alkyd resin and cellnlose fiber under the conditions of combined heat and pressure resulted in weakening of the cellulose fibers. At ordinary pressures, horn-ercr, varnished cloth may be prepared from alkyd resin varnish without injury to the fibers through baking. It was subsequently found by Rolilfs (19) that it was possible to mold composite insulation from alkyd resin and cellulose sheet materials by using B stage resin binder. Tlie B stage resin is intermediate between the A and C stages, though not so definite as either of them, and, while substantially insoluble hut fusible, is capable of absorbing solvent and becornine tackv. It is then Dossible to heat and convert to the c stage. " Excellent tbermodastic tams and mountinp tissues may be prepared by coating paper tape or sheet with alkyd resin eerrrcnt and allowing the cement to dry before rolling up the treated paper. When ready to use, the dry tape or tissue may 1~ pressed on the desired spot by a hot flat iron. These, hoaerer, have not been in production up t o the preseiit t.inre.
BLENDING If necessary, the alkyd resins may by one method or another be made compatible with or blended with almost all of t,he plastic materials used as adhesives either with or without solvent. The following table indicatos n,hich of the generally uscd methods may be expected to work. It must be born in mind that there are many typcs of alkyd resins a8 described in the literature, as well as much variation in t h e natural materials with which they are to be blended, and this list must
615
-1. 2.
3.
4. 5.
1 . 2. 3. 4 1 2 3 4 1: 2: 3: 4 3, 4 1. 3 1, :I. 4 ii with B hydroearbonruliihie resin 5 3, 5 1, 2, 3, 4 3, 4 if resin i~ of hydroceibonroioblc type Casrio 3. 5 Chiole 3, 4 Rubber iat,er 3. 5 Nitrooell"k>se 3. 4 Pine tar 1 , 2 , 3. 4 Censda balaarn 1. 2. 3. 4 Dryinp, oil8 1. 2, 3. 4. 5 Pbenolio type of r e ~ i ~ 1. 3 . 4 urea resina 1. 3, 5 Vinyl Bretate 3. 4 Paraeurnaions resina 1. 2 . 3. 4 Cooking with other insrlrdienla in preyerstion oiaikydieain uumplex. Siinpie heat-blending. Hot miring on rollers in dough mixers. or in B,snbur mixers Dissolving both in a iamrnon eolvent OT in miscible sofvant8. ' Using B water sdutiun of ammonia or triet,hanolamine.
The alkyd resins are, therefore, ail iinportant class of bonding materials with a wide variety of applications already in use as well as many more in development and under consideration. With the availability of new and better raw materials, more orih~naland judicious formulation, and the increased interest on the part of the consumers of adhesives, the properties of alkyd resin adhesives are being improved day by day. LITERATURE CITED (1) AMW, U. S. Patent 1,0!JX,i7i (1914). (2) Barrinrer, s. Patent 1,772,713 (1930). (3) Barringer and Peterson. U. S. l'htmts S,hhY,094 (1928); l,G19.-
u.
692 (1Y27). (4) Callnhan,
U S Patent 1,0!)1,G27 (1914):
.
~,
.
1,091,782 (1914);
PLLL'n.1. Oii, Cham. Xiz.. 83, S o . 22, 17 (1932). 1.842,!17o (1rm)). (9) H o ~ v e l l IJ. , S. Patent 1,098,728 (1914). (IO) Kicnle %miFsrauaon, IUD. Ex". SHEX.. 21, :349 (19'9). (11) Kienle iurd HOTW, 1.Am. C h e m Soc., 52. 3630-.46 (19YU) ( l a ) Pot,ormn, L'. S. Put,eet 1,619,758 (1927). (13) RohlL, U. S. Patcnt 1.866 (14) Basor and Kennedy, Physi (16) Wright.
