CA1228438A - Grafted styrene-butadiene latex for adhesion of rubber to organic textile materials - Google Patents

Abstract

GRAFTED STYRENE-BUTADIENE LATEX FOR ADHESION OF RUBBER
TO ORGANIC TEXTILE MATERIALS

Abstract of the Disclosure A textile to rubber coating composition compris-ing A) resorcinol-formaldehyde resin and B) a rubber latex having grafted thereon 1) acrylamide, 2) an alkylacrylamide 3) a tertiary nitrogen monomer or 4) a mixture thereof and a method of adhering textile to rubber therewith.

Description

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GRAFTED STYRENE-BUTADIENE LATEX FOR ADHESION OF RUBBER
TO ORGANIC TEXTILE MATERIALS
The present inventions relates to a coating come position useful in the adhesion of a textile material to rubber and to the process for effecting the adhesion. More particularly, this invention relates to such composition and process wherein the rubber employed is previously modified by grafting thereon a polymer comprising a nitrogen- containing monomer.
It is conventional practice in the rubber in-dozier Jo adhere rubber to textile fibers, glass fibers, brass-coated steel wires and the like, the latter generally being in the form of cords. The so-called "insight" method comprises ye ~-Grmation of an adhesive resin at the rubber-cord interface. This method is used primarily with brass-coated steel wire in the fabrication of steel-belted radial tires. A second method, the so-called dip-coating method is used with textile fibers, including epoxy-isocyanate pro-treated and chlorinated-phenol pretreated polyester fibers, and glass fibers. The present invention relates to it provements in the latter method.
Conventional dip-coating is conducted by coating the cords or fibers with a composition comprising a rubber latex and a phenol-formaldehyde resin before embedding them in the rubber stock prior to vulcanization. The most widely used rubber latex is a butadiene~styrene-vinylpyridine ton-polymer latex. The resin is usually a resorcinol-formal-Dodd resin. This combination is the so-called "RFL" system (resorcinol-ormaldehyde latex).

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- 2 - 1109-71~9 Although the conventional RFL system provides good rubber to cord adhesion, it possesses certain drawbacks. The rubber latex is usually limited to a terpolymer derived from butadiene, styrenes and vinylpyridine monomers, which requires about 10-15 weigh-t percent of expensive vinylpyridine monomer.
This particular rubber limited -the RFL method to the specific terpolymer specified and does no-t permit the use of other rubbery polymers. It would be highly desirable, therefore, if a rubber latex could be provided for this application which eliminated the Lo requirement for vinyl pardon monomer and enabled effective use to be made of other readily available rubbery polymer latex compositions. The provision for such a rubber latex would fulfill a long felt need and constitute a significant advance in the art.
In accordance with the present invention, there is provided an aqueous dispersion, useful as a coating composition for the adhesion of a textile material to rubber, comprising (A) a resorcinol-formaldehyde resin solution and (B) a rubber latex selected from natural rubber latex, butadiene-s-tyrene latex and polyisoprene latex, said rubber in said latex having grafted thereon repeating units derived from monomers selected from (1) acrylamide; I a tertiary nitrogen containing monomer; (3) come binations thereof; and (~) combinations of at least one thereof with N-monosubs-ti-tuted acrylamides wherein the substi-tuent is an alkali of 1 to 12 carbon atoms or an alkoxymethyl group in which the alkyd group contains 1 to 12 carbon atoms, wherein said grafted rubber contains at least about 3 weight percent based on the weight o-f rubber of nitrogen containing monomer.

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- 3 - 1109-7189 There is also provided a process for increasing the adhesion of a textile material to rubber, which comprises dip-coating said textile material with an aqueous dispersion, useful as a coating composition for -the adhesion of a textile material to rubber, comprising (A) a resorcinol-formaldehyde resin solution and (B) a rubber latex selected from natural rubber latex, butadiene-styrene latex and polyisoprene latex, said rubber in said latex having grafted thereon repeating units derived from monomers selected from (1) acrylamide; (2) a -tertiary Lo nitrogen-containing monomer; (3) combinations -thereof; and (4) combinations of at least one thereof with ~-monosubsti-tuted acrylamides wherein the substituent is an alkyd of 1 to 12 carbon atoms or an alkoxymethyl group in which the alkyd group contains 1 to 12 carbon atoms, wherein said grafted rubber contains at least about 3 weight percent based on the weight of rubber of nitrogen-containing monomer placing said treated textile material in intimate contact with a vulcanizable rubber composition to which said textile material is -to be bonded, and vulcanizing the composition.
The composition and process of the present invention have advantages over the conventional RFL system and provide equal or better rubber to cord adhesion. The grafting procedure is adaptable to any of a large number of commercially available diene-containing rubber lattices. Accordingly, such compositions can readily be subjected to grafting to provide useful rubber lattices for use in the present invention, thus increasing its versatility.

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As indicated, the composition of the present invention comprises a resorcinol-formaldehyde resin solution and a grafted rubber latex in combination as a dip-coating for tire cords of textile materials.
The resorcinol-formaldehyde resin solution used in the present invention is the same as that used in the conventional RFL system. It is commercially available as a reaction product of the two components or it may be prepared as described in the accompanying examples.

The rubber latex used in the conventional RFL system contains 15-20 weight percent styrenes 70 weight percent butadiene and 10-15 weight percent vinylpyridine. In the percent invention butadiene-styrene copolymer lattices containing up to about 50 weight percent styrenes may be used in the preparation of the grafted rubber latex. Although butadiene-styrene copolymer lattices are preferred, other rubber lattices are also useful.
These include natural rubber latex, polybutadiene latex, ply-isoprene latex, butadiene-acrylonitrile copolymer latex, and the like.
The preferred grafting monomer for modifying the rubber in the rubber latex is acrylamide. However, N-monosubstituted acrylamides are also useful. Examples of N-mono-substituted acrylamides which may be used include those having the general formulas:

CH2=CH-C-NHR and CH2=CH-C-NHCH2OR

(I) (II) ,.. ..

- pa -1109~7189 wherein R is an alkyd group of 1 to 12 carbon atoms. Represent-live compounds include N-butylacrylamide, N-pentylacrylamide, N-hexylacrylamide, N-(2-ethyl-hexyl) acrylamide, N~dodecylacryl-aside and the like and N-methoxymethylacrylamide, N-ethoxyme-thyl-acrylamide, N-butoxymethylacrylamide and the like.
It is not necessary to use acrylamide as the sole rafting monomer in preparing the grafted rubber. Thus, it is possible to use one or more monomers in addition to the acrylamide provided that the copolymer graft obtained contains at least about Lo 3 weigh-t percent of a nitrogen-containing monomer, based on -the weight of dry rubber solids in the latex. Suitable comonomers include, for example, methacrylamide, methylacrylate, e-thylacrylate, butyl-acrylate, methylmethacrylate, ethylmethacrylate and the like.
As an alternative to acrylamide it is also possible to employ vinyl monomers containing a tertiary nitrogen atom. Vinyl monomers containing a tertiary nitrogen atom include for example, vinylimidazole, N,N-dimethylaminoethylmethacrylate, N,N-diethyl-aminoethylacrylate, N,N-dimethylaminoethylacrylate, N,N-diethyl-aminoethylacrylamide, N,N-diethylaminoethylmethacrylamide, N,N-dimethylaminoethylacrylamide, and the like.

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Copolymers thereof which may include acrylamide and N-monosubstituted acrylamides as well as non nitrogen containing comonomers described above are also useful, pro-voided the nitrogen-containing monomer comprises at least about 3 weight percent, based on the weight of dry rubber solids.
The grafted rubbers may be prepared by convent tonal graft polymerization techniques. For example, the grafted rubbers may be prepared in a manner which produces a high percentage of grafting on the surface of the rubber particles in the latex. For this purpose, any redo initiator system used should consist of two parts, one being soluble in the oil phase which tends to remain dispersed with the latex particles and the other being highly water soluble so as to stay within the aqueous phase. Either of the oxidation and reduction components may be in the oil phase while the other is in the aqueous phase. Most of the grafted elastomers rubbery polymers) have been prepared using cumin hydra-peroxide as the oil soluble oxidation component, but any peroxide or hydroperoxide may be used. Similarly, polyamides have been used as the water soluble reducing agent, but any other water soluble reducing agent may be used. In general, however, the oxidation component may be water soluble, for example, hydrogen peroxide, and the reduction component may be oil soluble, such as oil soluble polyamides. As a matter of principle, any redo initiator system that it composed of a water soluble component and an oil soluble component may be used. Ferrous sulfate, in small amounts, promotes the redo activity of the hydroperoxide-polyamine system. Other known promoters may be used In general, at least about 3 weight percent of the nitrogen-containing monomer, based on the dry weight of the rubber latex solids, bound on the surface of the latex particles as grafted polymer, is sufficient to provide the desired level of adhesion.
The amount of acrylamide, N-monosubstituted acrylamide, or vinyl monomer containing a tertiary nitrogen atom contained in the grafted rubber may vary, provided the graft contains at least about 3 weight percent of tube vitro-gen-containing monomer to provide effective adhesion.
The textile material which may be treated in accordance with the present invention include nylon, polyp ester fiber (both isocyanate-epoxy and chlorinated phenol pretreated, glass fiber, aromatic polyamide fiber, and the like. Nylon and polyester fibers are preferred.
The rubber stock to which the coated fibers are bonded include those commonly used in the manufacture of tires, such as natural rubber, styrene-butadiene rubber (SIR), polybutadiene rubber, polyisoprene rubber, neoprene, Boyle rubber, butadiene-acrylonitrile rubber (NOR), ethylene-propylene-diene rubber (EPDM), and the like.
In carrying out the process of the present invent lion, the textile material is dip-coated with conventional amounts of the composition of the present invention, then placed in intimate contact with the rubber stock to which it is to be bonded in accordance with conventional procedures, and the resulting composition of coated textile material and rubber stock is then vulcanized according to conventional procedures.
The invention is more fully illustrated in the following non-limiting examples wherein all parts and per-cent ages are by weight unless otherwise specified.
Example l Acrylamide (2.8 parts is added to 40 milliliters (ml) of a 40% solids content butadiene/styrene latex (75/25) which is diluted with 40 ml of water. Cumin hydroperoxide (0.57 parts) is then added and the mixture is stirred for 3-

4 hours to permit the cumin hydroperoxide to swell into the latex particles. A trace amount of ferrous sulfate and tetraethylene pent amine (1.7 ml of a 10% aqueous solution) are then added and the reaction mixture is stirred at room temperature for about 12 hours. Analyses of the isolated graft polymer shows that 1.05 parts ~6.56% based on dry rubber solids) of acrylamide is bound to the butadiene-styrene rubber of the latex.
Example To 623 parts of water are added 23 parts of resorcinol, 26 parts of 37% aqueous formaldehyde and 2.0 parts of 10% sodium hydroxide solution. The mixture i allowed to age for 4 to 6 hours before use.
Example 3 The resorcinol-formaldehyde resin solution of Example 2 (21.3 parts, 1.065 parts of resin) is added to 30.5 parts (5.75 parts of rubber solids) of the latex of Example 1. The composition is aged for about 12~15 hours before further use.
Example 4 Nylon cords (2 ply, 1260 denier) are fed through the dip composition of Example 3. Pickup is controlled in the range of 6-7%. The dipped cords are dried at 425F. for about 1 minute in an oven.
The rubber composition to which the dipped cords are bonded has the following components:
Component Parts Natural rubber 70 Styrene/butadiene rubber (23.5/76.5) 30 Carbon Black 30 Zinc Oxide 5 Starkey Acid 2 Processing Oil 4 Accelerator 1.13 Sulfur 2 Note: (1) = N-oxydiethylene benzothiazole-2-sulfonamide The H-Test (ASTM D 2138-72), which is used to measure the adhesive strength of the rubber-cord bond, is designed to measure the force required to pull a cord, in the direction of its axis, from a strip of rubber in which it is embedded. The property measured is a shearing force acting at the cord-rubber interface. The test specimen consists of two end-strips of rubber with an interconnecting cord, no-symboling the letter H. Each specimen has a single cord which is embedded in the center of each of the two end-strips of rubber weaken are 1/4 x 1 inches (approximately). The specie miens are vulcanized for 18-20 minutes at 307F. and then aged for at least 16 hours at 23 20C. prior to testing. Data S are recorded as pounds of pull (lobs. force) to separate the cord from the cord-strips, or in Newtons (10 Newtons = 2.25 lobs. force).
Example 5 The dipped nylon curds of Example 4, along with similar cords coated with the standard RFL system, are embedded into the above-described rubber composition and vulcanized as described in the H-Test description. The adhesive strength is determined according to ASTM D2138-72.
Data are as follows:
H-Test (lobs. force) Cords of Example 5 39.3 2.99 Standard RFL cords average 35-39 Example 6 Following the procedure of Example 1, a graft polymer is prepared using 1.0 parts of acrylamide instead of 2.8 parts. Analysis of the graft polymer shows that 0.74 parts of acrylamide (4.62% based on the weight of dry rubber solids) is bound to the rubber particles of the latex. When the adhesion is determined as described in Example 5, a force of 35.4 + 3.7 pounds is required to separate the cord from the rubber end-strips.
Exam~les-7-9 Following the procedure of Example 1, graft polyp mews in separate runs are prepared using other monomers in place of acrylamide. In Example 7, vinylimidazole (4 parts) is used as the monomer. In Example 8, the monomer is NUN-diethylaminoethyl-methacrylate I parts) and in Example 9 the monomer is N(isobutoxymethyl)-acrylamide (1 part. When these grafted rubber are tested for adhesion as described, I similar results are obtained.

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Examples 10 13 Following the procedure of Example 4, other cords are dip-coated as described. In Example lo the cords are isocyanate-epoxy pretreated polyester fiber. In Example 11, the cords are chlorinated phenol pretreated polyester cords.
When these cords are processed as in Example S and tested by the H-test, similar results are obtained.
Example 14 (Comparative) 20 ml. of SIR latex is mixed with 20 ml. of a 7%
aqueous solution of polyacrylamide (my = 49,000). A sample of 30.5 ml of this solution is mixed with 21.3 ml. of RF
solution. Nylon cord are dip coated as described in Example 4 and vulcanized with the rubber stock as in Example 5. An adhesive strength of 21.5 + 3.0 pounds is obtained, thus-treating that the acrylamide must be grafted onto the rubber latex before good adhesion is obtained.
Example 15 Following the procedure of Example l, 1.8 parts of acrylamide and 1 part of methylmethacrylate are used in place of 2.8 parts of acrylamide. When evaluated as described in Examples 3, 4 and 5, similar results are obtained.
Example 16 Following the procedure of Example 1, 1 part of acrylamide and 1.8 parts of N,Nl-diethylaminoethylmethacryl-ate are used in place of 2.8 parts of acrylamide. When evaluated as described in Examples 3,4 and 5, similar results are obtained.
In further examples wherein other rubber stocks are employed, similar adhesion is shown by textile material dip-coated with the composition of the invention.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An aqueous dispersion, useful as a coating composition for the adhesion of a textile material to rubber, comprising (A) a resorcinol-formaldehyde resin solution and (B) a rubber latex selected from natural rubber latex, butadiene-styrene latex and polyisoprene latex, said rubber in said latex having grafter thereon repeating units derived from monomers selected from (1) acrylamide; (2) a tertiary nitrogen-containing monomer; (3) com-binations thereof; and (4) combinations of at least one thereof with N-monosubstituted acrylamides wherein the substituent is an alkyl of 1 to 12 carbon atoms or an alkoxymethyl group in which the alkyl group contains 1 to 12 carbon atoms, wherein said grafted rubber contains at least about 3 weight percent based on the weight of rubber of nitrogen-containing monomer.

2. The dispersion of claim 1 wherein said rubber latex is a butadiene-styrene copolymer latex.

3. The dispersion of claim 1 wherein said monomer is acryl-amide.

4. The dispersion of claim 2 wherein said monomer is acryl-amide.

5. The dispersion of claim 1 wherein said monomer is a tertiary nitrogen-containing monomer.

6. The dispersion of claim 5 wherein said tertiary nitro-gen-containing monomer is vinylimidazole.

7. A process for increasing the adhesion of a textile material to rubber which comprises dip-coating said textile material with the aqueous dispersion of claim 1, placing said treated textile material in intimate contact with a vulcanizable rubber composition to which said textile material is to be bonded, and vulcanizing the composition.

8. The process of claim 7 wherein said aqueous dispersion is a butadiene-styrene copolymer latex grafted with acrylamide.

9. The process of claim 7 wherein said aqueous dispersion is a butadiene-styrene copolymer latex grafted with a tertiary nitrogen-containing monomer.

10. The process of claim 7 wherein said vulcanizable rubber composition comprises natural rubber.