WO2000015695A1

WO2000015695A1 - Primer composition and method of use thereof

Info

Publication number: WO2000015695A1
Application number: PCT/US1999/021022
Authority: WO
Inventors: Peter Gottschalk
Original assignee: H.B. Fuller Licensing & Financing, Inc.
Priority date: 1998-09-14
Filing date: 1999-09-14
Publication date: 2000-03-23

Abstract

The present invention relates to a primer composition comprising an organic acid in alcohol, methyl ethyl ketone, ethyl acetate, water or mixtures thereof to improve the bonding of the solvent based adhesive to polyamide substrate. The invention also relates to a method of using the primer composition to improve the adhesion properties of the polyamide substrate.

Description

PRIMER COMPOSITION AND METHOD OF USE THEREOF

Field Of The Invention

The present invention generally relates to a method of improving the adhesion of a coating or adhesive to surfaces of a polymeric material. More particularly, the present- invention relates to a method for improving the adhesion properties of a polyamide substrate to solvent-based adhesive using a primer composition comprising an organic acid in alcohol, water, methyl ethyl ketone, ethyl acetate or mixtures thereof. The treated substrate exhibits highly improved adhesion properties. Another aspect of the invention is an article of manufacture comprising a plurality of substrates utilizing the primer composition in association with a solvent based polyurethane adhesive.

Background Of The Invention

Traditionally, the adhesive bonding of polyamide substrates, particularly nylon has been a difficult task, requiring either a great deal of surface preparation and/or use of highly specialized adhesive formulations to improve the bonding of the substrates. By treating nylon in accordance with the method of the present invention, a substrate is formed which has very good surface and adhesion properties.

Nylon, despite its relatively high surface energy, is difficult to bond due to its crystalline nature that prevents much interpenetration of adhesive polymers. It also tends to be quite smooth limiting the contribution from mechanical interlocking in adhesion.

Previous strategies to improve adhesion to nylon consists of treating nylon with hydroxylated aromatic compounds such as phenol, resorcinol, hydroxynaphthalene, etc.

These compounds disrupt the strong hydrogen bonding within nylon and soften the surface. Adhesives, particularly with solvent based adhesives, can better penetrate into the surface resulting in strong bonds due to interpenetration of polymer chains.

However, the hydroxylated aromatics tend to be quite toxic and dark in color, the dark coloration being the result of small amounts of quinoid species formed from air oxidation. Various methods of treating substrates with certain materials in order to enhance the attachment of the substrate to a solvent based adhesive have been suggested. Richard C. Snogren, Handbook Of Surface Preparation, 191 , Palmerton Publishing Co., Inc., describes solvent treating nylon with isopropyl alcohol (page 79 & 348). Additionally, the types of processes used for surface preparation include active chemicals which alter the surface physically and chemically to make it receptive to __ bonding (e.g., acid and alkali).

Nylon to nylon bonding can be obtained using a water or alcohol based system containing phenol, resorcinol or calcium chloride as outlined in SPI Plastics, 5th Ed., pp.710-711 (1991). Such systems can be used as primers for other adhesive systems. However, they suffer from the introduction of a large amount of water which limits adhesion and bond durability and the use of highly toxic materials such as phenol.

Alternative water based primers have been developed as primers. For example, JP 76116296 discloses phenol-formaldehyde resin in dilute aqueous ammonia for bonding a polyurethane coating to nylon fabric. Abu-Isa, U.S. 3,607,353 discloses improving adhesion between a metal coating and a nylon surface by treating the nylon surface with an aqueous solution of iodine and iodide ion followed by an aqueous rinse and a second rinse using an aqueous solution of an oxidant such as thiosulfate.

Solvent based primers typically contain hydroxylated aromatic compounds or resins. JP 7003060 discloses a primer formulation consisting of chlorinated polyolefin, novolak resin and acrylic monomers in aromatic solvents.

Magistro et al, U.S.5, 178,938 discloses the use of aromatic mono-, di-, or tri- hydroxy compounds alone or containing peel strength improving additives such as titanium, zirconium or silicone based compounds having at least one functional group of -OH, -SH, -NH2, phosphorous or combinations thereof as a primer for solvent based polyurethane adhesives. The presence of hydroxylated aromatics and aromatic solvents render these primers a health hazard. Other alternative solvent based systems have also been disclosed. Inouye et al., U.S. 5,112,682 discloses a solvent based primer consisting of dyes and pigments, particularly, azine dye and a complex mixture of partial hydrolyzates of organosilicon compounds. Donermeyer et al., U.S. 4,443,519 discloses the use of polyisocyanate primer which must be moisture cured prior to adhesive application. In an attempt to develop a surface treating method which is simple and speedy as compared to conventional methods and significantly less toxic and hazardous to use, the present inventor made intensive studies and as a result of these studies, a method was developed to provide a means of conditioning and enhancing the surfaces of chemically inert organic materials so as to render them receptive to bonding, dyeing, cementing, and coating agents and which the prior art references fail to disclose or teach.

Summary Of The Invention

The present invention is directed to a primer composition for improving the bonding of solvent based polyurethane adhesive to polyamide substrates, the primer composition comprising: i) at least one acid selected from the group consisting of C,-C₈ linear or branched alkanoic acid, C,-C₈ linear or branched hydroxyalkanoic acid, aromatic acid, alkanoic acid and mixtures thereof; ii) at least one solvent selected from the group consisting of water, alcohol, methyl ethyl ketone, ethyl acetate and mixtures thereof. Another aspect of the present invention is directed to a method of bonding a plurality of substrates together with a solvent-based adhesive formulation comprising the steps of: a) providing a primer composition comprising: i) at least one organic acid selected from the group consisting of C

C₈ linear or branched alkanoic acid, C_rC₈ linear or branched hydroxyalkanoic acid, aromatic acid, alkenoic acid and mixtures thereof; and ii) at least one solvent selected from the group consisting of water, alcohol, methyl ethyl ketone, ethyl acetate and mixtures thereof. b) applying to at least one portion of a surface of a first substrate a layer of the primer composition; c) drying the at least one portion of a surface of the first substrate to form a primed first substrate; d) applying onto the dried substrate at least one organic solvent based adhesive, allowing the solvent to evaporate and heating at about 50°C to about 70°C ; e) contacting and bonding the adhesive coated surface portion of the first substrate with at least a portion of the surface of a second substrate coated with said adhesive and heating at about 50°C to about 70°C. __

A further aspect of the invention is to provide a bonded assembly comprising at least a pair of substrates adhesively bonded wherein the polyamide substrate is treated with a primer composition comprising: i) at least one organic acid selected from the group consisting of C,-C₈ linear or branched alkanoic acid, C,-C₈ linear or branched hydroxyalkanoic acid, aromatic acid, alkanoic acid and mixtures thereof; and ii) at least one solvent selected from the group consisting of water, alcohol, methyl ethyl ketone, ethyl acetate and mixtures thereof. Another aspect of the present invention is to provide a primer composition comprising: i) at least one organic acid selected from the group consisting of C,-C₈ linear or branched alkanoic acid, C,-C₈ linear or branched hydroxyalkanoic acid, aromatic acid, alkanoic acid and mixtures thereof; and ii) at least one alcohol selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, methyl ethyl ketone, ethyl acetate and mixtures thereof; and optionally water. A further aspect of the present invention is to provide highly improved surface and adhesion properties of a polyamide substrate to solvent based adhesives without discoloration of the substrate.

These and other aspects of the present invention would be apparent to one of ordinary skill in the art from the following detailed description illustrating the preferred embodiments of the invention. Brief Description Of Figures

Figure 1 illustrates a comparison of peel values of an untreated Nylon 6 control and Nylon 6 treated with dilute solutions of acetic acid, propionic acid, hexanoic acid, benzoic acid, gly colic acid, lactic acid, hydroxycaproic acid, salicylic acid, 3- hydroxybutyric acid and 2-tetrahydrofuroic acid. The acids were dissolved in __ isopropanol at 10% by weight.

Figure 2 illustrates a comparison of peel values of an untreated Nylon 6 control and Nylon 6 and 12 treated with dilute solutions of acetic acid, propionic acid, hexanoic acid, benzoic acid, glycolic acid, lactic acid, hydroxycaproic acid, salicylic acid, 3- hydroxybutyric acid and 2-tetrahydrofuroic acid. The acids were dissolved in isopropanol at 10% by weight.

Detailed Description Of The Invention

The present invention is directed to a method for improving the bonding of solvent based polyurethane adhesives to polyamide substrates, using a primer composition.

The polyamide substrate, particularly nylon, having utility in the present invention is formed by conventional methods which are well known to the art and to the literature, several of which are outlined below. It is understood that the various nylon substrates discussed below are merely examples of suitable nylon substrates having utility in the present invention, but that other nylon substrates could be utilized in the present invention without affecting the concept thereof.

Nylons are synthetic polymers that contain an amide group, -CONH-, as a recurring part of the chain. There are some exceptions. For example, although polyalpha-amino acids, such as synthetic proteins, meet this specification, they are not identified as nylons. Another class of polyamide resins that are not nylons is based on dimerized vegetable oil acids and polyamines such as ethylene diamine or diethylene triamine. These are relatively low in molecular weight (about 2000 to 10,000), are more soluble and flexible than nylons, and they vary from liquids to low-melting-point solids. Nylons are made from (a) diamines and dibasic acids, (b) omega-amino acids, or

(c) lactams. Nylons are identified by numbers corresponding to the number of carbon atoms in the monomers (diamine first) for (a). Nylon 6/6 is the reaction product of hexamethylene diamine and adipic acid, poly(hexamethylene adipamide, H[NH(CH₂)₆ NHCO(CH₂)₄CO]_nOH; nylon 11, poly(l 1-aminoundeconoic acids), is prepared from 11- aminoundeconoic acid; and nylon 6, polycaprolactam, is preferred from epsilon- caprolactam. Nylon 6/12 is made from hexamethylene diamine and the 12-carbon acid,_ dodecanedioic acid, or HOOC (CH₂)₁₀COOH. The molecular weights of nylons range from about 11,000 to 34,000. They usually are semicrystalline polymers with melting points in the range of about 350°F (177°C) to 570°F (299°C).

Other commercial nylons that may be useful in the practice of this invention are 6/9, 6/10, 7, 8, 10, 11, 12, 13 and the recently introduced 4/6 and 12/12. The more carbon atoms, that is, the lower the concentration of amide groups, the lower the melting point, so long as the nylons in which the amides are separated by an even number of carbon atoms melt higher than those of similar amide concentration with an odd number of carbon atoms. The organic acid in the primer formulation is present in an amount of from about

5% to about 50% by weight based on the total weight of organic acids and polar solvent, preferably about 10% to about 40% by weight, most preferably about 15% to about 35% by weight.

The organic acid employed in the preparation of the primer composition includes at least one organic acid selected from the group consisting of C,-C₈ linear or branched alkanoic acid, C,-C₈ linear or branched hydroxyalkanoic acid, aromatic acid, alkanoic acid and mixtures thereof. Examples include acetic acid, glycolic acid, propionic acid, lactic acid, hexanoic acid, hydroxy-caproic acid, benzoic acid, maleic acid, salicylic acid, 3 -hydroxybutyric acid, 2-tetrahydrofuroic acid, fumaric acid and mixtures thereof. Preferred organic acids are acids which are liquid at room temperature and contain oxygen substitution on the carbon α to the carboxylic acid moiety. A more preferable organic acid is lactic acid.

Suitable solvents include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, methyl ethyl ketone, ethyl acetate and mixtures thereof. Optionally, water is used as the solvent. A preferable solvent is isopropanol.

Suitable polyamide substrates include nylon 6, nylon 6/6, nylon 6/10, nylon 7, nylon 8, nylon 10, nylon 11, nylon 12, and nylon 13. Preferred polyamide substrate is nylon 6/6, more preferably nylon 6. The form of polyamide substrate includes textile fiber, woven or non-woven, film, sheet, filament, particles and flakes. The second substrate is selected from the group consisting of rubber materials, textiles and plastic materials. Plastic materials include vinyl polymer, polyvinylaromatic polymer, _ polyolefm polymer, polyacrylate polymer, polycarbonate polymer and polyester polymer.

Suitable solvent based polyurethane adhesive include those typically used in footwear manufacturing such as Ultraflex® 4320 commercially available from H.B. Fuller Company. Other solvent based polyurethane adhesives include those generally formulated as contact adhesives by dissolving polyurethane resins in solvent blends.

In the present invention, the organic acid is dissolved in alcohol or water and then applied as a thin coating as, for example by spraying, knife coating, brushing, rolling, dipping or immersing the substrate in the primer composition or by other methods known and techniques known in the art in an amount sufficient to wet, desirably to wet uniformly, the surface of the polyamide substrate prior to coating with a solvent based adhesive. After evaporation of the primer, the adhesive is applied and the polyurethane adhesive coated nylon substrate is bonded to the surface of a second substrate. The primer provides highly improved surface and adhesion properties of the polyamide substrate to solvent based adhesive without visual discoloration of the substrate.

The substrates are coated with adhesive and heat activated at a temperature of about 50°C to about 70°C, then pressed together for about 5 to about 15 seconds at about 10 to about 60 psi. The polyamide substrate can be bonded by means of the adhesive to a large number of different types of surfaces, and these can for instance be plastic materials, wood, paper, metal, and woven or non-woven textile fabrics. Plastic materials can be sheets or films or in the form of other shapes, and can, if desired be expanded materials. Suitable materials include vinyl polymers, such as polyvinyl chloride, polyvinylidene, chloride, or a copolymer of vinyl chloride; a polyvinylaromatic plastic, such as polystyrene; a polyacrylate, such as methyl polymethacrylate; or a polyolefm such as polyethylene or polypropylene. Excellent results are obtained with polyvinyl chloride (PVC) both in a dense and an expanded form.

The amount of the primer composition which is applied to the surfaces which are to be bonded together only need be an amount sufficient to wet the surfaces with a film of the primer composition. __

The present invention illustrates the use of organic acids to improve the adhesion of solvent based adhesives to nylon. Various amounts of acids dissolved in isopropyl alcohol or mixtures of isopropyl alcohol and water can be applied to nylon. After evaporation of solvent, and after a solvent wipe to clean off precipitated acid from the surface (for acids that are solid at room temperature), the adhesive can be applied. In this case, a solvent based adhesive is applied (Ultraflex® from H.B.Fuller) and the solvent evaporated. Another substrate such as canvas or SBR (surface chlorination required for good adhesion) is also coated with adhesive and allowed to become tack free. The adhesive on these substrates are heat reactivated at about 50°C to about 70°C, then pressed together for about 15 seconds at 50 psi. Peel tests are conducted 3-5 days after bonding. The advantage of the primer composition is that it is relatively non-hazardous and does not provide discoloration of the polyamide substrate, and significantly improves bond strength.

Included within the scope of the present invention is a method for adhering shoe sole components by treating the nylon components with a primer composition. The solvent based adhesive is applied to both soles and uppers, dried, activated by heat treatment, and bonded by hot pressing the two adhesive-coated surfaces together.

The following specific examples are provided to better assist the reader in the various aspects of practicing the present invention. As these specific examples are merely illustrative, nothing in the following descriptions should be construed as limiting the invention in any way.

EXAMPLES Example 1 Treatment of Nylon 6 with 20% Lactic acid/isopropanol

A 1" x 6" Nylon 6 substrate such as Gorlon®, commercially available from EMS Chemie, was lightly brushed with various % acid in commercial grade anhydrous isopropanol. The isopropanol was allowed to evaporate for 15 minutes at room temperature. The nylon substrate was coated with the solvent based adhesive (Ultraflex® 4320) and the solvent allowed to evaporate for over 30 minutes at ambient temperature. The adhesive was similarly applied to a strip of SBR such as BRS® 1000 .. (1/8" thick) which had previously been surface treated with 2% trichlorisocyanuric acid in ethyl acetate. The adhesive surfaces were heated to 60°C - 70°C using IR lamps then pressed together for 15 seconds at 50 psi. Peel tests (180°) were conducted at about 3-5 days after bonding.

The results of the Peel tests as shown in Table I demonstrate that the adhesion increased by at least 8% to 20% as compared to the untreated substrate. The untreated substrate control was wiped with isopropanol/water.

TABLE I

In order to determine the stability of the primer composition when applied to the substrate and then coated with solvent based adhesives, peel tests were conducted at various time intervals after application of the primer: lactic acid/isopropanol/water at a ratio of 26:70:4. TABLE II

From the above Table II, primer effectiveness decreases with time, but good bond strengths were still attained at 48 hours after primer application. Example 2

Bonds were prepared as described in Example 1 using Nylon 6 and canvas. Acids were dissolved in isopropanol at 10% by weight and applied to Nylon 6 as described in Example 1. Peels were conducted at an angle of 90 degrees. The data demonstrate significant improvement in peel values, particularly for acids containing a hydroxy or ether linkage on the carbon α to the carboxylic acid moiety. See Figure 1.

Example 3

Bonds were prepared as described in Example 1 using Nylon 6, 12 and canvas. Acids were dissolved in isopropanol at 10% by weight and applied to Nylon 6, 12 as described in Example 1. Peels were conducted at an angle of 90 degrees. The data demonstrates significant improvement in peel values. All acids were comparably effective. See Figure 2.

The examples have been depicted solely for the purpose of exemplification and are not intended to restrict the scope or embodiments of the invention. The invention is further illustrated with reference to the claims that follow thereto.

Claims

1. A primer composition for improving the adhesion property of a polyamide substrate to solvent based adhesive comprising: a) at least one organic acid selected from the group consisting of C,-C₈ linear or branched alkanoic acid, C,-C₈ linear or branched __ hydroxyalkanoic acid, aromatic acid, alkanoic acid and mixtures thereof; and b) at least one solvent selected from the group consisting of methyl ethyl ketone, ethyl acetate, water, alcohol and mixtures thereof.

2. The primer composition according to Claim 1 wherein at least one of the polyamide substrate is selected from the group consisting of nylon 4, nylon 6, nylon 6/6, nylon 6/10, nylon 7, nylon 8, nylon 10, nylon 11, nylon 12, nylon 13 and mixtures thereof.

3. The primer composition according to Claim 1 wherein the alcohol is selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n- butanol, isobutanol and mixtures thereof.

4. The primer composition according to Claim 1 or 3 wherein the organic acid is selected from the group consisting of acetic acid, glycolic acid, propionic acid, lactic acid, hexanoic acid, hydroxy-caproic acid,benzoic acid, maleic acid, salicylic acid, 3 -hydroxybutyric acid, 2-tetrahydrofuroic acid, fumaric acid and mixtures thereof;

5. The primer composition according to Claim 1 or 3 wherein the organic acid is present in an amount of from about 5% to about 50% by weight.

6. The primer composition according to Claim 1 or 3 wherein the organic acid is an acid containing a hydroxy or ether linkage on the carbon ╬▒ to the carboxylic acid moiety.

7. A method of bonding a plurality of substrates together with a solvent-based adhesive formulation comprising the steps of: a) providing a primer composition comprising: i) at least one organic acid selected from the group consisting of C,-C₈ linear or branched alkanoic acid, C,-C₈ linear or branched ΓÇö hydroxyalkanoic acid, aromatic acid, alkenoic acid and mixtures thereof; and ii) at least one solvent selected from the group consisting of water, methyl ethyl ketone, ethyl acetate, alcohol and mixtures thereof. b) applying a layer of the primer composition to at least one portion of a surface of a first substrate; c) drying the at least one portion of a surface of the first substrate to form a primed first substrate; d) applying onto the dried substrate at least one organic solvent based adhesive, allowing the solvent to evaporate and heating at about 50┬░C to about 70┬░C; e) contacting and bonding the adhesive coated surface portion of the first substrate with at least a portion of the surface of a second substrate coated with said adhesive and heating at about 50┬░C to about 70┬░C.

8. The method according to Claim 7 wherein said bonded substrates are treated using heat and pressure.

9. The method according to Claim 7 or 8 wherein the bonded substrates are treated at a temperature of about 50┬░C to about 70┬░C.

10. The method according to Claim 7 wherein the organic acid is selected from the group consisting of acetic acid, glycolic acid, propionic acid, lactic acid, hexanoic acid, hydroxy-caproic acid, benzoic acid, maleic acid, salicylic acid, 3- hydroxybutyric acid, 2- tetrahydrofuroic acid, fumaric acid and mixtures thereof.

11. The method according to Claim 7 or 10 wherein the amount of organic acid is present in an amount of from about 5% to about 50% by weight.

12. The method according to Claim 7 or 10 wherein the organic acid is an acid containing a hydroxy or ether linkage on the carbon ╬▒ to the carboxylic acid ΓÇö moiety.

13. The method according to Claim 7 or 8 wherein the primer is applied to the first substrate by brushing, dipping, flow coating or spraying.

14. The method according to Claim 7 or 8 wherein the primer is applied by immersing the substrate in a solution of the primer composition.

15. The method according to Claim 7 or 8 wherein at least one of said substrate is a polyamide substrate.

16. The method according to Claim 15 wherein at least one of said polyamide substrate is a member selected from the group consisting of nylon 4, nylon 6, nylon 6/6, nylon 6/10, nylon 7, nylon 8, nylon 10, nylon 11, nylon 12, nylon 13 and mixtures thereof.

17. The method according to Claim 7 or 8 wherein the alcohol is selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and mixtures thereof.

18. The method according to Claim 7 or 8 wherein the solvent based adhesive is polyurethane based adhesive.

19. The method according to Claim 7 or 8 wherein the second substrate is selected from the group consisting of rubber materials, textile and plastic materials.

20. The method according to Claim 7 or 8 wherein the second substrate is selected from the group consisting of vinyl polymer, polyvinylaromatic polymer, polyolefm polymer, polyacrylate polymer, polycarbonate polymer and polyester polymer. ΓÇö

21. A bonded assembly comprising at least a pair of substrates adhesively bonded wherein at least one of the substrates is treated with a primer composition comprising: i) at least one organic acid selected from the group consisting of C,-C₈ linear or branched alkanoic acid, C,-C₈ linear or branched hydroxyalkanoic acid, aromatic acid, alkenoic acid and mixtures thereof; and ii) at least one solvent selected from the group consisting of methyl ethyl ketone, ethyl acetate, water, alcohol and mixtures thereof.

22. The bonded assembly according to Claim 21 wherein at least one of said substrate is a polyamide substrate.

23. The bonded assembly according to Claim 21 or 22 wherein at least one of said substrates is a polyamide substrate member selected from the group consisting of nylon 4, nylon 6, nylon 6/6, nylon 6/10, nylon 7, nylon 8, nylon 10, nylon 11, nylon 12, nylon 13 and mixtures thereof.

24. The bonded assembly according to Claim 21 or 22 wherein the organic acid is selected from the group consisting of acetic acid, glycolic acid, propionic acid, lactic acid, hexanoic acid, hydroxy-caproic acid, benzoic acid, maleic acid, salicylic acid, 3 -hydroxybutyric acid, 2-tetrahydrofuroic acid, fumaric acid and mixtures thereof;

25. An article of manufacture comprising at least one substrate treated with a primer composition and coated with a solvent based adhesive, said primer composition comprising: a) at least one organic acid selected from the group consisting of C,-C₈ linear or branched alkanoic acid, C,-C₈ linear or branched hydroxyalkanoic acid, aromatic acid, alkenoic acid and mixtures thereof; and ΓÇö b) at least one solvent selected from the group consisting of ethyl acetate, methyl ethyl ketone, water, alcohol and mixtures thereof.

26. The article according to Claim 25 wherein the substrate is a polyamide substrate.

27. The article according to Claim 25 or 26 wherein at least one of said substrates is a polyamide substrate member selected from the group consisting of nylon 4, nylon 6, nylon 6/6, nylon 6/10, nylon 7, nylon 8, nylon 10, nylon 11, nylon 12, nylon 13 and mixtures threof.

28. The article according to Claim 25 or 26 wherein the alcohol is selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and mixtures thereof.