CA1136792A - Pre-mixed catalyzed vinyl acetate co-polymer adhesive composition - Google Patents

Abstract

A pre-mixed adhesive composition comprised of a vinyl acetate co-polymer emulsion including a cross-linking catalyst and a cross-linking inhibitor providing a good cured water resistant Type II bond and extended shelf life so that the adhesive composition will not gel over an extended period of time and will therefore be usable for direct gluing application to semi-porous and porous substrates.

Description

31 ~367~2 This is a continuation-in-part of my co-pending application, Serial No. 671,269, filed ~larch 29, 1976, now patent ~lo. 4,0~5,074 and relates to cross-linkable vinyl acetate co-polymer emulsions containing a curing or cross-linking agent for use as an adhesive for porous and semi-porous materials.
Heretofore, gluing operations using cross-linkable vinyl acetate polymer emulsions required the mixing of the emulsion with a catalyst, i.e. a curing or cross-linking 10 agent prior to application to the substrates to be glued in pressing equipment, as, for exam~le, in the Armour et al patent No. 3,563,851. Because the cross-linking of the resin occurs over a relatively short period of time after addition of the catalyst, the mix gels over that relatively short period of time and therefore cannot then be employed as a workable adhesive.
The primary object of this invention is to provide an adhesive emulsion comprising a co-polymerized cross-linkable vinyl acetate resin, a cross-linking catalyst and ~0 and cross-linking inhibitor, which adhesive provides a cured water resistant Type II bond and possesses increased shelf life and can therefore be used over a relatively long period of time for direct application to porous and semi-porous substrates for gluing in appropriate pressing equipment.
Another object of the invention is to provide an adhesive composition comprising a cross-linkable vinyl acetate co-polymer resin emulsion, an acidic inorganic metal salt cross-linking catalyst and a basic organic cross-linking inhibitor, which adhesive composition provides a 30 Type II water resistant bond and possesses a shelf life considerably extended over the shelf life of a mixture of the resin emulsion and catalyst alone.

, 1 ~

1~36792 Another object of the invention is to provide an adhesive composition of the character described which possesses a shelf life increased over that of the composi-tion without the inhibitor and a shear strength of at least 50 psi using a one-half hour boil test following the pro-cedure set forth in ASTM D~1151-72 The foregoing objects are obtained by providing an aqueous resin emulsion containing vinyl acetate co-pol~merized with N-alkylol derivatives of amides of alpha, beta-unsaturated carboxylic acids, such as N-methylol acrylamide, a protective hydrocolloid emulsifier such as polyvinyl alcohol or cellulosic dispersing agents, e. g.
hydroxethyethylcellulose, carboxymethylcellulose, etc., a cross-linking catalyst in the form of an acid metal salt such as aluminum chloride, aluminum nitra~e, chromic chloride and chromic nitrate, and a cross-linking inhibitor in the form of an amine such as ammonia, the alkyl and alkanol amines, e.g. mono, di and triethylamine and mono, di and triethanolamine.

The resin emulsion is made by polymerization techniques known in the art using free radical or re-dox catalysts. A monomer mixture of about 90-98% by weight of vinyl acetate and about 2-10% by weight of an N-alkylol derivative of an amide of an alpha, beta-unsaturated carboxylic acid is refluxed at about 60-90C
with agitation in an aqueous medium containing in addition to the monomer mixture 3-6% of a hydrocolloid by weight of the monomer mixture, the free radical or redox ~36~g2 polymerization catalysts, a deEoamer and an emulsifier. The reaction is carried on for about 3 to 6 hours and the resultant aqueous resin emulsion has a solids content of about 4n-60% .
At present, this resin emulsion is used as a two-part adhesive for admixture with an acidic metal cross-linking c~talyst solution such as AlC13, Al (N03) 3r CrCl3 and Cr(NO3)3 at the site where application of the adhesive in appro~riate pressing equipment is to be carried out. The resin emulsion per se can be stored at room temperature for at leas-t 3 months, but once the same is admixed with the cross-linking catalyst the mix has a considerably reduced shelf or pot life. Over a range of 1.0 to 12.0 parts by weight of the catalyst solution per 100 parts by weiqht of the resin emulsion, where the acidic salt concentration of the catalyst solution is about 0.21 gram moles ~er 100 gms catalyst solution, the shelf life varies from about 1 day to about 8g days. This mix yields a Type II water resistant bond as defined in Federal ~pecification M~-A-188b, November 8, 1960 entitled "Adhesive;

2~ Urea-Resin-Type (Liquid and Powder)", which is herein incorporated by reference.
In accordance with the instant invention, the resin emulsion includes about 0.0032 to 0.025 ~ram moles per 100 grams of emulsion of an acidic metal salt catalyst and a cross-linking inhibitor in sufficient ~amount and concentration to at least increase, and preferably double, the shelf life of the resin emulsion plus catalyst alone and provide a bond whose shear strength is at least 50 psi when subjected to a preconditioning for one day and one-half hour boil test as set forth ln par. ~.l and condition 16 respectively of ASTM

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D-1151-72, which is herein incorporated by reference.
The acidic metal salt cross-linking agent is preferably added to -the resin emulsion in the form of a solution containing ahout 0.21 ~ram moles of the catalyst per lOn grams of the catalyst solution. Said catalyst solution is added to the resin emulsion in an amount of about 1.5 to 12.0 parts by weight of the catalyst solution to 100 parts by weight of the resin emulsion. Thus, there is present in the resin emulsion about 0.0032 to 0.025 gram moles of the catalvst per 100 ~rams of resin emulsion ~he cross-linking inhibitor is present in the resin emulsion in an efective amount up to a maximum mole ratio of inhibitor to catalyst of about 0.7 to 1.7.
The preferred adhesive composition includes a resin emulsion (RE) comprising a monomer mixture of about 90-98%
vinyl acetate (VA) and about 2-10% N-methylol acrylaminde (NM~), by ~eight,polymeri~ed with the use of a redox or free radical type catalyst system in an aqueous medium containing about 5 polyvinyl alcohol, in the manner described hereinbefore, the 0 solids content of the resulta.r.t emulsion being a~out 50~ by weigh~. The resin emulsion is white, has a pH of 4.3 to 5.0, a viscosity of 3000-41,000 cps (25C) and a specific gravity of about 1.09. To this resin emulsion is added an aqueous solution of aluminum chloride in an amount o about 1.5 to 12.0 parts by ~eight of the aluminum chloride solution to 100 parts by weight of the resin emulsion, said aluminum chloride solution containing about 0.21 gram moles AlC13/100 gms solution, thus providinq 0.0032 to 0.025 gram moles of AlC13 per 100 grams of resin emulsion, and triethanolamine ~L36'7~Z~

tTEoA) in a mole ratio of TEOA/AlC13 up to about 0.7 to 1.7 as a maximum. To obtain an adhesive composition which will possess a shelf life which is increaseA over that of the resin emulsion plus catalyst alone and also possess a cured water resistance bond of at least 50 psi in a one-half hour boil test, the minimum TEOA/AlC13 mole ratio is about o.l to o.2.
A most practical adhesive is one in which the weight ratio of VA
to NMA is in the range of 95/S to 98/~.
The following are illustrative but non-limitative examples in table form of the adhesive compositions of the instant invention, control compositions and comparative results as to shelf life and shear strength.

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The procedures used in testing the control and instant adhesive compositions o~ the Table were as follows. The test samples were prepared in accordance with ASTM D-906-64 (ReapProved 1970), herein incorporated ~y reference, and applied to the blrch test panels at a glue spread rate of 40 lh./1000 sq. ft. single glue line, assembly time of one minute, a press temperature of 121C, a press time of ~hree minutes and a pressure of 150 psi.
The one-half hour boil test was carried out in accordance with ASTM D-1151-72 using a preconditioning under par. 4.1 of one day and condition 16, i.e. immersion in boiling water for one-half hour and determining the average strength arter exposure in accordance with par. 5.2.1.

The 2-cycle boil test was carried out in accordance with Commercial Standard CS35-61, Hardwood Plywood, published by U.S. Dept. of Commerce, Sup. of Docs., Washington 25, D.C., which is herein incorporated by reference, par. 5.4.2 thereof.

The ~8 hour soak test is carried out in accordance with the procedure of ASTM D-1151-72, condition 6, wherein the ~o specimen is immersed in water at a temperature o~ 23C for 48 hours and then subjected to the shear strength test.
The shelf or pot life end point is taken as the time at which the adhesive composition gels to the point tha-t it will no longer flow from the container. The sample is not agitated during the total test period and the container is tightly capped so that no skin is formed.

The instant adhesi~e composi-tlon is directly applicable to semi-porous and porous substra~es, such as hard-woods, softwoods, hardboard, particle board, high pressure laminates and similar materials in appropriate pressing equip-ment in open assembly time up to about five minutes and closed assembly time up to about twenty minutes. The adhesive is primarily applicable to hot press (pressures of about 25-200 psi) or hi~h frequency cure although it will produce an effective Type II water resistant hond when pressed at room temperature (25C) for about 40 minutes. The press time will vary depending on the type of press, method of cure, temperature, spread rate, assembly time and type of substrates being bonded.

Claims (13)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A pre-mixed catalyzed adhesive composition comprised of (a) an aqueous cross-linkable vinyl acetate resin emulsion including polymerized vinyl acetate, in which the polymerized vinyl acetate is made from a monomer mixture of about 90-98% vinyl acetate and about 2-10% of an N-alkylol derivative of an amide of an alpha, beta-unsaturated carboxylic acid in a aqueous medium containing about 3-6% by weight of a hydrocolloid selected from the group consisting of polyvinyl alcohol, hydroxyethylcellulose and carboxymethylcellulose, by weight of the monomer mixture, (b) an acidic metal-salt cross-linking catalyst selected from the group consisting of aluminum chloride, aluminum nitrate, chromic chloride and chromic nitrate in an amount of about 0.0032 to 0.025 gram moles per 100 grams of the resin emulsion, and (c) a cross-linking inhibitor selected from the group consisting of ammonia, alkyl amines and alkylol amines wherein the mole ratio of the cross-linking inhibitor to catalyst ranges from a minimum of about 0.1 to 0.2 to a maximum of about 0.7 to 1.7.

2. The adhesive composition of claim 1 wherein the N-alkylol derivative of an amide of an alpha, beta-unsaturated carboxylic acid is N-methylol acrylamide.

3. The adhesive composition of claim 1 wherein the hydrocolloid is polyvinyl alcohol.

4. The adhesive composition of claim 1 wherein the catalyst is aluminum chloride.

5. The adhesive composition of claim 1 wherein the inhibitor is triethanolamine.

6. A pre-mixed catalyzed adhesive composition comprised of (a) an aqueous cross-linkable vinyl acetate resin emulsion including polymerized vinyl acetate, in which the polymerized vinyl acetate is made from a monomer mixture of about 95-98% vinyl acetate and about 2-5% of an N-alkylol derivative of an amide of an alpha, beta-unsatur-ated carboxylic acid in an aqueous medium containing about 3-6% by weight of a hydrocolloid selected from the group consisting of polyvinyl alcohol, hydroxyethlcellulose and carboxymethylcellulose, by weight of the monomer mixture, (b) an acidic metal salt cross-linking catalyst selected from the group consisting of aluminum chloride, aluminum nitrate, chromic chloride and chromic nitrate in an amount of about 0.0032 to 0.025 gram moles per 100 grams of the resin emulsion, and (c) a cross-linking inhibitor selected from the group consisting of ammonia, alkyl amines and alkylol amines wherein the mole ratio of the cross-linking inhibitor to catalyst ranges from a minimum of about 0.1 to 0.2 to a maximum of about 0.7 to 1.7.

7. A pre-mixed catalyzed adhesive composition comprised of (a) an aqueous cross-linkable vinyl acetate resin emulsion including polymerized vinyl acetate, in which the polymerized vinyl acetate is made for a monomer mixture of about 95-98% vinyl acetate and about 2-5% of N-methylol acrylamide in an aqueous medium containing about 3-6% of polyvinyl alcohol, by weight of the monomer mixture, (b) aluminum chloride as a cross-linking catalyst in an amount of about 0.0032 to 0.025 gram moles per 100 grams of the resin emulsion and (c) triethanolamine as a cross-linking inhibitor in a mole ratio of the triethanolamine to aluminum chloride in the range from a minimum of about 0.1 to 0.2 to a maximum of about 0.7 to 1.7.

8. A structure comprising two substrates bonded together by the adhesive composition of claim 1 in a cured condition.

9. A structure comprising two substrates bonded together by the adhesive composition of claim 6 in a cured condition.

10. A structure comprising two substrates bonded together by the adhesive composition of claim 7 in a cured condition.

11. A pre-mixed catalyzed adhesive composition comprised of (a) an aqueous cross-linkable vinyl acetate resin emulsion including polymerized vinyl acetate, in which the polymerized vinyl acetate is made from a monomer mix-ture of about 90-98% vinyl acetate and about 2-10% of N-methylol acrylamide in an aqueous medium containing about 3-6% of polyvinyl alcohol, by weight of the monomer, (b) aluminum chloride as a cross-linking catalyst in an amount of about 0.0032 to 0.025 gram moles per 100 grams of the resin emulsion and (c) triethanolamine as a cross-linking inhibitor in a mole ratio of the triethanolamine to aluminum chloride in the range from a minimum of about 0.1 to 0.2 to a maximum of about 0.7 to 1.7.

12. A pre-mixed catalyzed adhesive composition comprised of (a) an aqueous cross-linkable vinyl acetate resin emulsion of co-polymerized vinyl acetate, in which the co-polymerized vinyl acetate is made from a monomer mixture of about 95-98% vinyl acetate and about 2-5% of an N-alkylol derivative of an amide of an alpha, beta-unsaturated carboxylic acid in an aqueous medium containing about 3-6% by weight of a hydrocolloid selected from the group consisting of polyvinyl alcohol, hydroxyethylcellulose and carboxymethylcellulose, by weight of the monomer mixture, (b) an inorganic acid metal salt cross-linking catalyst selected from the group consisting of aluminum chloride, aluminum nitrate, chromic chloride and chromic nitrate in an amount of about 0.0032 to 0.025 gram moles per 100 grams of the resin emulstion, and (c) a cross-linking non-volatile alkanol amine inhibitor wherein the mole ratio of the cross-linking inhibitor to catalyst ranges from a minimum of about 0.1 to 0.2 to a maximum of about 0.7 to 1.7.

13. The adhesive composition of claim 12 wherein the non-volatile alkanol amine inhibitor is selected from the group consisting of mono, di and tri ethanolamine.