Patent Publication Number: US-4318837-A

Title: Adhesive for wood and vinyl

Description:
This invention relates to an adhesive. More particularly, this invention relates to an adhesive for laminating wood to vinyl polymers or resins. 
     It has been desirable to adhere vinyl resin parts or films to wood to protect the wood and also to give the wood certain desirable aesthetic effects, as vinyl film can have printed thereon any design effect. Unfortunately, difficulty has been experienced in obtaining good hot strength and adhesion between the vinyl part and the wood and also the adhesives useful for adhering vinyl to wood have tended to have a very short pot life and therefore could not be made and utilized for relatively long times. 
     The adhesive of this invention comprises a fluid blend of 100 parts of a saturated polyester composed of the condensation product of an organic dicarboxylic acid or anhydride with a glycol to obtain a molecular weight of 10,000 to 30,000 with the preferred range being 15,000 to 26,000, five to 150 parts of an unsaturated polyester obtained by condensing an unsaturated acid or anhydride such as malaic or fumaric, either alone or in conjunction with 0 to 70 percent by weight of isophthalic acid with a simple glycol, or preferably bis phenol A to obtain a condensate of 10,000 to 30,000 molecular weight and 5 to 15 parts of an organic polyisocyanate, preferably of the polymeric type. The fluidity of the above blend is primarily a function of the molecular weight of the polyester used and the amount of solvent. Suitable solvents are the ketones such as acetone, methyl ethyl ketone, isopropyl butyl ketone and blends of these ketones with toluene and xylene. Sufficient solvent, usually five to 20 percent, is used to permit the adhesive to be readily applied by spraying or painting. 
    
    
     The nature of this invention more readily may be seen and understood along with its advantages by reference to the following example, wherein all parts and percentages are by weight. 
     EXAMPLE 
     Five parts of the polyester obtained by condensation of 50 parts isophthalic acid and 50 parts fumaric acid with sufficient bisphenol A to give a molecular weight of 20,000 were blended with 100 parts of a saturated polyester obtained by condensing 50 parts ethylene glycol, 50 parts neopentyl glycol with sufficient terephthalic acid to obtain a condensate having a molecular weight of 20,000. To this blend of saturated and unsaturated polyesters 10 parts of a polymeric polyisocyanate made by phosgenation of the acid rearrangement product of aniline and formaldehyde was added and thoroughly mixed to give the adhesive. This adhesive hereinafter called &#34;modified adhesive&#34;, has a pot life in excess of 48 hours and was utilized to coat a piece of wood and then a vinyl chloride film was spread over the wood and pressed into tight relationship to form a laminate. A control adhesive was prepared by replacing the unsaturated polyester with the saturated polyester in the above recipe. This control adhesive was used to prepare a laminate in the manner described above and the 90°  peel strength in pounds per inch was determined on the two specimens. The peel strength on these specimens are shown for the time intervals indicated in the table below: 
     
         ______________________________________                                    
         90° PEEL STRENGTHS, LBS/INCH                              
Time, in hours                                                            
           Initial  2         24   168    336                             
______________________________________                                    
Adhesive used,                                                            
           6.0 lb/in                                                      
                    10.0      vinyl                                       
                                   vinyl  vinyl                           
control             lb/in     tear tear   tear                            
Modified   7.0 lb/in                                                      
                    14-15     vinyl                                       
                                   vinyl  vinyl                           
                    lb/in     tear tear   tear                            
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     This modified adhesive gave superior peel strength initially as well as after two hours. 
     If the adhesive of the above modified adhesive is replaced with Adhesive A, similar good adhesion is obtainable. Adhesive A can be made by mixing 5 to 25 parts of polyester of ethylene glycol, 50/50 isophthalate-fumarate of about 18,000 to 25,000 molecular weight with 100 parts of ethylene terephthalate of 16,000 to 24,000 molecular weight and 7 to 12 parts of a commercial polymethylene polyphenylisocyanate or a similar polyisocyanate. 
     The saturated polyesters useful in this invention can be illustrated by the following formula: ##STR1## where m, n and t are integers representing the number of --CH 2  -- groups in glycol and acid respectively. The saturated polyesters can be homo or copolyesters. 
     Representative of the copolyesters usable in the above example are those containing units from ethylene glycol and units from neopenthyl glycol in the ratio of 56/44 and units from terephthalic acid and sebacic acid in the ratio of 71/29. 
     The example illustrates the invention with respect to the use of a specific copolyester of sebacid acid, terephthalic acid, ethylene glycol and neopentyl glycol. Such resins of a range of compositions can be used. For example, the ethylene glycol units can range from 40 to 60 percent of the total glycol units, the neopentyl glycol units can range from 60 to 40 percent of the total, the terephthalic acid units can range from 20 to 75 percent of the total acid units and the sebacic acid units can range from 80 to 25 percent of the total acid units. 
     Other copolyester resins can be used in place of the ethylene glycol-neopentyl glycol-terephthalate sebacate copolyester used in the example. Representative examples of such copolyesters are ethylene-neopentyl terephthalate isophthalate isophthalate copolyesters in which the ratio of ethylene glycol units to neopentyl glycol units is in the range of 40/60 to 60/40 and the terephthalic acid units and isophthalic acid units in the copolyester are present in the range of 95/5 to 50/50 and tetramethylene-terephthalate isophthalate sebacate copolyesters in which the units of the acids are present in the range of 20 to 50 of terephthalic units to 5 to 50 is isophthalic units and 50 to 20 percent of sebacic units. 
     The unsaturated polyesters are of essentially the same structure as the saturated polyesters except part or all of the saturated organic acids have been replaced with unsaturated organic acids or anhydrides such as malaic or fumaric and related unsaturated acids. 
     Typical polyisocyanates suitable for the purposes of the present invention include, among others, 1,5-naphthalene diisocyanate, 4,4&#39;-diphenyl diisocyanate, 4,4&#39;-diphenylene methane diisocyanate, p-phenylene diisocyanate, 2,4-tolylene diisocyanate, 4,4&#39;,4&#34;-triphenyl methane triisocyanate, 4,4&#39;-tolidine diisocyanate, dianisidine diisocyanate, hexamethylene diisocyanate, r,r&#39;-diisocyanate of diphenyl ether and mixtures thereof. 
     The polymeric polyisocyanates such as the one obtained by phosgenation of acid rearrangement product of reaction of aldehydes and aromatic amines such as formaldehyde amd aniline are most preferred and are referred to generically as poly aryl polyisocyanate and are available commercially as polymethylene polyphenylisocyanate. 
     The vinyl resins or fims useful in this invention are well known and comprise polyvinyl chloride or copolymers of vinyl chloride and vinyl acetate or vinylidene chloride. Where high flexibility is desired usually the vinyl resin is plasticized with from 10 to 150 parts per hundred of the normal vinyl resin plasticizers. 
     While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.