United States Patent Office Patented June 13, 1972
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3,669,716 United States Patent Office Patented June 13, 1972 2 3,669,716 ester resin coatings of predetermined substantial thick HIGH ENERGY CURING OF PHOTOPOLYMERIZ. ness which are mar-resistant, scratch-resistant and sol ABLE NONAR NHBTED POLYESTER RESN vent-resistant. COATNGS Alex C. Key, Walnut Creek, Calif., and Mary G. Brodie, A further object is to provide a new and improved Chicago, Ill., assignors to The Sherwin-Williams Com method for producing polyester resin coatings of the type pany, Cleveland, Ohio described quickly and without excessive heating. No Drawing. Continuation-in-part of application Ser. No. A more specific object is to produce wooden panels 701,023, Dec. 5, 1967, now Patent No. 3,511,687, coated with coatings 1 to 12 mils thick which are mar which is a continuation-in-part of application Ser. No. resistant, scratch-resistant and solvent-resistant. Other ob 360,359, Apr. 16, 1964. This application May 11, 1970, O jects will appear hereinafter. Ser. No. 36,414 The portion of the term of the patent subsequent to BRIEF SUMMARY OF THE INVENTION May 12, 1987, has been disclaimed int, C, B44d 1/50 In accordance with the invention it has been found U.S. C. 17-62 16 Claims that new and improved results in the coatings art can 5 be obatined in preparing coatings having a thickness of 1 to 12 mils (0.001 to 0.012 inch) by forming such ABSTRACT OF THE DISCLOSURE coatings on a substrate from photopolymerizable nonair Photopolymerizable nonair inhibited polyester resin inhibited polyester resins, preferably containing a photo coatings having a thickness of 1 to 12 mils (0.001 to Sensitizer, and curing such resins by subjecting them to 0.012 inch), preferably containing a photosensitizer, are 20 light waves within the range of 1850 to 4000 angstroms. cured by subjecting them to light waves within the range The process is useful in forming coatings on metal, wood of 1850 to 4000 angstroms. The process is useful in form or other substrate but is especially valuable for producing ing coatings on metal, wood or other substrate but is cured resinous coatings on wood, e.g., plywood panels. especially valuable for producing cured resinous coatings on Wood, e.g., plywood panel. 25 DETALED DESCRIPTION OF THE INVENTION The resins which are effective for the purpose of this invention are all characterized by the fact that they are This application is a continuation-in-part of United not inhibited by air or oxygen. They can also be described States application Ser. No. 701,023 filed Dec. 5, 1967, now 30 as air drying polyesters. These resins, because of their U.S. Pat. 3,511,687, which is a continuation-in-part of chemical composition, are capable of achieving good sur United States application Ser. No. 360,350 filed April 16, face cure in the presence of air or oxygen. Examples of 1964, now abandoned. the chemical types involved include allyl ether resins, BACKGROUND OF THE INVENTION benzyl ether resins, tetrahydrophthalic anhydride resins, Infusible polyester resins are formed by curing a com 35 endomethylene tetrahydrophthalic anhydride resins, cyclo position comprising one or more polymers of polycarboxy pentadiene modified resins, acetal resins, polyalkylene Organic compounds and polyhydroxy organic compounds fumarate resins where there are at least three ethylene together with a monomer containing ethylenic unsatura groups, and tetrahydrofurfuryl resins. tion, usually styrene. Thus, a general type of polyester The nonair inhibited polyesters employed in the prac 40 tice of this invention can also be described as air drying resin might be made by reacting propylene glycol, maleic unsaturated polyesters. Air drying unsaturated polyesters anhydride, phthalic anhydride and styrene. The styrene which are employed in this invention to produce polyester acts as a solvent and also copolymerizes when the resin coatings are especially modified to prevent air inhibition is cured. This type of polyester resin, however, is air of cure. inhibited and is unsuitable for the practice of the present 45 invention. Various groups can be introduced into the polyester A basic deterrent to the use of polyesters in the coatings most of which are subject to auto-oxidation and thus field has been the difficulty of obtaining practical cure actively prevent the inhibiting action of atmospheric oxy rates at low temperatures, particularly as required in fin gen which is normally dissolved at the surface of poly ishing wood and other heat sensitive substrates. ester coatings exposed to air. Examples of groups which Catalyst systems employing peroxides with inhibitors 50 may be introduced into the polyester formulation include and stabilizers to prevent permature gelling of polyester aliphatic, cycloaliphatic and aromatic ethers, e.g., tri finishes have been developed in the prior art. Practical methylol propane (TMP) diallyl ether, tetrahydrofurfuryl catalyst systems have been a compromise between pot alcohol, dioxane, dicyclopentyl ethers, TMP monobenzyl life and curing time. Catalysts have been developed for 55 ether, and triethylene glycol; acetal type structures; cyclo curing both at room temperature and under low tem hexene type compounds, e.g. tetrahydrophthalic anhydride, perature baking conditions. and endomethylene tetrahydrophthalic anhydride; dicy clopentadiene derivatives such as 8-oxytricyclodecene-4- OBJECTS (5,2,1,0), and tricyclodecane-(5,2,1,026) dimethylol; One of the objects of the present invention is to provide and by direct modification with cyclopentadiene or dicy a new and improved method for producing cured poly 80 clopentadiene. 3,669,716 3 4. Allyl ethers useful in the preparation of unsaturated rolidone, divinyl spirobi, trially citrate, ethylene glycol polyesters for the purpose of incorporating allyl substit dimethacrylate, etc. uent groups in the polyester molecule include monohydric The following are examples of preferred constituents and/or polyhydric ether derivatives of polyhydric alcohols for providing reactive sites in the polymer: trimethylol and allyl glycidyl ether. These compounds may be sub 5 propane diallyl ether; trimethylolpropane monoallyl ether; stituted for from 5 to 50% of the glycol equivalents in an dially pentaerythritol; allyl glycidyl ether; allyl glycerol unsaturated polyester formulation depending to a certain ether; allyloxy propanol; pentaerythritol dibenzyl ether; extent upon the number of allyl groups per mole of the TMP monobenzyl ether; triethylene glycol or higher particular allyl ether(s) used. homologues; tetrahydrofurfuryl alcohol; dioxane; acetal The dicarboxylic acid component of this type of for O made from 1,2,6-hexane-triol and formaldehyde, 2-vinyl mulation may be characterized by a maximum ratio of 1,3-dioxolane (hexanetriol and acrolein) and diallylidene unsaturated to saturated acid of 95 to 5 and a minimum pentaerythritol; dicyclopentadiene; endomethylene tetra ratio of 10 to 90 with a preferred range of between 75 to hydrophthalic anhydride; TCD Alcohol E (8-oxytricyclo 25 and 25 to 75, respectively. The strongest cured films decene-4-(5,2,1,026); TCD Alcohol DM tricyclodecane are obtained when the unsaturated acid content is greater 15 (5,2,1,026) dimethylol; and tetrahydrophthalic anhydride. than 50% of the total dicarboxylic acid component of Conventional catalyst systems are for the most part the polyester. inoperable to cure polyester resins at low temperatures Dicarboxylic acids illustrative of those often used in because it is impossible to obtain a cure at room tem preparing unsaturated polyesters suitable for the purposes perature. Catalysts most frequently used to effect the heat of this invention include maleic acid, fumaric acid, maleic conversion of unsaturated polyester resins consist mainly anhydride, etc. Though fumaric acid is, perhaps, pre of peroxide initiators. Peroxide initiators include benzoyl ferred, other dicarboxylic acids substituted therefor in peroxide; 2,4-dichlorobenzoyl peroxide; methyl ethyl ke whole or in part include itaconic acid, citraconic acid, tone peroxide; cyclohexanone peroxide; cumene hydro mesaconic acid, aconitic acid and the other less common peroxide; bis(para-bromobenzoyl) peroxide; bis(phthalyl) dicarboxylic acids as mentioned in the polyester art. 25 peroxide; bis(acetyl) peroxide; tertiary-butyl hydroper Other dicarboxylic acids can be used in partial replace oxide; ethyl peroxydicarbonate; di-isopropylene OZonide; ment for the unsaturated class described above, and in peracetic acid, etc. cluded are phthalic anhydride, phthalic acid, Nadic an Other additives may be and normally are included with hydride, tetrahydrophthalic anhydride, adipic acid, azelaic the initiator to increase pot life of unsaturated polyesters acid, etc. 30 by inhibiting polymerization. One class of agents called Aromatic dicarboxylic acids and those of even greater retardants' accomplishes this end by inhibiting or Sup acid functionality (e.g., mellitic anhydride), though con pressing free-radical formation. Illustrative of such re taining double bonds in the nucleus, do not undergo ad tardants are alpha methyl styrene and aromatic nitro dition reactions as do the preferred class of dicarboxylic compounds. A second class of agents, illustratively qui acids (fumaric). From the above and the state of the art, 35 nones and salts of substituted hydrazines, often referred it is clear that mixtures of polyfunctional acids or their to as “stabilizers” are preferred over "retardants' be anhydrides are often employed to produce unsaturated cause the former