GB2048275A - Tire cord adhesives - Google Patents

Abstract

Vulcanizable rubber compositions providing excellent bonding of textile or metal reinforcing fibers thereto comprise a rubber, a filler material an N-(methylated or alkoxy methylolated) melamine and a bisphenol. Best results are achieved when a high surface area activated silica is also incorporated. The melamine compound and the bisphenol may be added separately during the making up of the composition, or the bisphenol may be dissolved in the melamine compound prior to mixing with the rubber.

Description

SPECIFICATION Tire cord adhesives The invention relates to a vulcanizable rubber composition which forms an adhesive bond with a tire cord material.

Automobile tires and the like are usually reinforced with textile fibers in cord form, or increasingly..

with steel wire and with glass cords. In all such instances, the reinforcing material must be firmly bonded to the rubber. This is so whether the fiber is natural, synthetic or metallic or whether the rubber is natural or synthetic.

U.S. Patent 3,586,735 discloses the use of Bisphenol A in a resin which is added to rubber.

U.S. Patent 4,092,455 discloses useful vulcanizable rubber compositions providing excellent bonding of textile or metal reinforcing fibers thereto which comprises a rubber, a filler material, an N (substituted oxymethyl) melamine and a compound selected from 1,1 '-methylenebis(2-naphthol), 2,2'- methylenebis( 1 -naphthol), mixtures thereof, 1,1 '-thiobis(2-naphthol), 2,2'-thiobis(1-naphthol) and mixtures thereof, 4,4'-methylenebis(l -naphthol) and 4,4'-thiobis( 1 -naphthol).

The bisnaphthol compounds useful according to this patent are known. It is preferable to use the methylenebis(2-naphthol) and thiobis(2-naphthol) compounds since beta naphthol is more readily available than alpha naphthol; however, as indicated, either of the alpha naphthol derivatives or mixtures thereof with their beta naphthol analogs, are useful as methylene, or formaldehyde acceptors in the tire cord adhesion system described herein.

According to the patent, the N-(substituted oxymethyl) melamines which serve as the methylene donors when combined with the bisnaphthol compounds have the following general formula:

wherein X is hydrogen or lower alkyl (1-8 carbons); R, R1, R2, R3, and R4are individually hydrogen, lower alkyl having from 1 to 8 carbon atoms or the group --CHH-,OX, wherein X is as defined above.

Specific illustrative species include hexakis(methoxymethyl) melamine, N,N',N"-trimethyl N,N',N"- trimethylolmelamine, hexamethylolmelamine, N,N',N"-trimethylol melamine, N-methylolmelamine, N,N'-dimethylolmelamine, N,N',N"-tris(methoxymethyl) melamine, and N,N',N"-tributyl-N,N',N"- trimethylolmelamine. A preferred methylene donor is hexakis(methoxymethyl) melamine.

The N-methylol derivatives of melamine are prepared by known methods by reacting melamine with 1 to 6 molar equivalents of formaldehyde. Although N-(substituted oxymethyl) melamines are the preferred methylene donors, others such as hexamethylenetetramine, N-(substituted oxymethyl) ureas, N-(substituted oxymethyl) imidazolidines, N-(substituted oxymethyl)-hydantoins may also be useful.

The use of both resorcinol and the naphthol derivatives in tire adhesives have inherent disadvantages. Both are very expensive and with both there is the question of availability in the quantities required by the tire industry, assuming the tire industry switched to the naphthols. The present invention as claimed seeks to provide a remedy to the stability cost and availability problem inherent in the prior art materials.

The advantages offered by the present invention are mainly that 4,4'-isopropylidenediphenol is both cheap and is in plentiful supply and relatively stable as compared to resorcinol formaldehyde resoles. The melamine derivatives useful in the practice of the present invention include those disclosed in U.S. Patent 4,092,455.

The bisphenols useful in the practice of the present invention are those of the formula:

where one X1 per phenyl group is hydroxyl and the remaining are hydrogen; R5 and R6 are hydrogen or a lower alkyl having one to three carbon atoms; and R7, R8, Rg, and Rlo are hydrogen or a lower (C1-8) alkyl group. The preferred bisphenols contemplated are 4,4'-isopropylidene diphenol, 3,4'isopropylidene diphenol and 3,3'-isopropylidene diphenol.Other bisphenols inc!ude 4,4"-methylene diphenol, 3,4'-methylene diphenol, 3,3'-methylene diphenol, 4,4'-ethylidene diphenol, 3,4'-ethylidene diphenol, 3,3'-ethylidene diphenol and similar bisphenols substituted with methyi or ethyl groups in the 3 or 3' positions.

Particularly useful reinforcing materials found to form strong adhesive bonds to rubber in accordance with the invention are glass and brass-plated steel wire.

The rubber being bonded to the reinforcing material may be any rubber used in the manufacture of automobile tires, drive belts, conveyor belts or pressure hose. these include natural rubber, synthetic diene rubbers, such as polybutadiene or polyisoprene, ethylene-propylene terpolymer rubbers (EPDM), butadiene, styrene copolymer rubbers (SBR), butadiene acrylonitrile copolymer rubbers (N BR), chloroprene rubber, or chlorosulfonated polyethylene, or mixtures thereof.

The rubber vulcanizate which is bonded to the textile fiber or steel wire by in situ resin formation may contain conventional compounding ingredients such as carbon black, antioxidants, sulfur, zinc oxide, accelerators, high surface area activated silica (including mixtures thereof with carbon black), processing and softening oils, and the like.

A reaction product or mixture of the N-(substituted oxymethyl) melamine and the bisphenol compound may typicaily be incorporated into the rubber vulcanizate in an amount of from about 0.5 to12 parts per hundred of rubber, preferably 1 to 5 parts per hundred of rubber. The ratio of the melamine to the bisphenol is preferably from 1:1 to 10:1. The melamine and bisphenol can also be added to the rubber vulcanizate separately.

For optimum adhesion of the reinforcing cord material, whether glass fiber or steel, to rubber it has been found desirable to incorporate a high surface area activated silica into the vulcanizate composition.

When used, the silica is preferably added in an amount of from about 2 to 20 parts per hundred of rubber, preferably about 8 to 1 5 parts per hundred of rubber.

A preferred method of making the rubber vulcanizate is to mix the rubber, carbon black, zinc oxide, lubricants, the bisphenol containing compound and the like, in a Banbury mixer at a temperature of about 1 500C. The resulting masterbatch is then compounded on a standard two-roll rubber mill with sulfur, accelerators, silica, and the N-(substituted oxymethyl) melamine compound. The vulcanizable composition is shaped, placed in contact with the reinforcing material, i.e., glass fiber or steel wire, and vulcanized.

The following examples are provided for illustrative purposes and may include particular features of the invention. However, the examples should not be construed as limiting the invention, many variations of which are possible without departing from the spirit or scope thereof.

1. Materials a. 4,4'-isopropylidenediphenol (Bisphenol A) This material was practical grade Eastman Organical Chemicals, melting point 1 56-1 580C.

b. Hexamethoxymethylmelamine (HMMM) This material was furnished by the American Cyanamid Company as Cymel 303 (Coating Resins Department) and Cyrez 963 (Elastomers and Polymer Additives Department). It is a clear, viscous liquid with the following properties: Table I Properties of Cymel 303 (Cyrez 963) Non-volatile, % 98.0 min.

Ash,% 0.01 max.

Free formaldehyde, % 0.50 max.

Color, Gardner 1963 2 max.

Pounds/gallon, approx. 10.0 Kilograms/liter 1.198 Viscosity, Gardner-Holdt, 250C X-Z2 Flash point 1800C It is also available as a solid powder, 60% active on 40% inactive carrier, but more expensive in that form.

c. Conventional rubber and compounding materials were used. PPG glass cord, style 145 was used for most glass cord tests. The cord coated with a conventional resorcinol formaldehyde resin, vinyl pyridine-butadiene-styrene latex.

2. Preparation of "Bonding Agent BAC" BAC is Bisphenol A (4,4'-isopropylidenediphenol) dissolved in hexamethoxymethylmelamine (Cymel 303, Cyrez 963). A mixture of 78 parts Cyrez 963 and 22 parts Bisphenol A were stored at 790C and agitated periodically. Complete solution was affected after about 20 hours of this procedure.

The product remains a viscous liquid after one year room temperature storage.

3. Physical Testing Standard ASTM physical test methods were used. Wire adhesion was determined by ASTM D2229 which describes the jig used for determining pull-out force on the Instron tester. A modified slot jig was used that gives more reproducible but lower adhesion values than the "hole" jig used by many laboratories.

Adhesion data are given in relative values. Since this study was conducted on relatively small laboratory batches and over a considerable time period, considerable variation in absolute values were encountered. Comparison between different masterbatches was avoided.

4. Rubber Compound Table II shows the basic rubber compound used in this work. Adhesion promotors were added on the mill together with sulfur and accelerators. All parts and percentages throughout this application are by weight.

Table II Rubber Compound Used In Adhesion Tests Material Weight NR (Natural Rubber) 46.50 Endor (peptizing agent zinc salt of pentachlorothiophenol 0.14 SBR 1500 (styrene butadiene rubber) 38.50 Duragen 1203 (cis polybutadiene rubber) 15.00 FEF (N-550) (carbon black) 60.00 (45.00) HiSil 215 (silica) 0 (15.00) BLE (antioxidant reaction product of diphenylamine and acetone 2.00 Philrich #5 (compounding oil) 5.00 Zinc oxide 3.00 Stearic Acid 1.50 Banbury masterbatch added at RT, 5 min., stock drops at 2850F (1400C).

Material Weight Santocure (n-cyclohexyl 2-benzothiazole sulfenamide) 1.20 Crystex (sulfur) 3.00 Rubber mill addition Results and Discussion 1. Chemistry The following ether exchange reaction is postulated.

Me -- Melamine

In contrast to resorcinol, Bisphenol A has four equivalent reactive positions; resorcinol has two equivalent and one position between the OH groups (position 2) that may have different reactivity, depending on the catalyst and the reaction conditions.

For the preparation of "Bonding Agent BAC," optimum conditions should be chosen, where an optimum amount of the exchange reaction will take place to avoid crystallization of the unreacted Bisphenol A. Under those conditions any residual small amount of formaldehyde present in the HMMM should also have reacted. Bisphenol A is less reactive with formaldehyde than resorcinol. Its reactivity should be comparable to phenol or p-cresol.

If the reaction is driven too far, viscosity will be excessive, making compounding mixing difficult.

2. Effect of Bisphenol A/HMMM Ratio On Adhesion to Steel and Glass Cord Table Ill shows the effect of HMMM in the compound with and without silica reinforcement. In the presence of silica modulus is slightly increased by the additive. Steel adhesion is only slightly decreased by this additive.

Table Ill Effect of HMMM On Adhesion Additive None 4.1 HMMM None 4.1 HMMM Reinforcement 60 FEF 60 FEF 45 FEF 45 FEF 15 HiSil 233 15 HiSil 233 Rubber Properties Cure. min./3200F (1600C) 12 17 20 100% Modulus, psi (MPa) 720 (5.0) 590(4.1) 400 (2.76) 460 (3.2) 300% Modulus, psi (MPa) 2700(18.7) 2250(15.5) 1720(12.0) 1900(13.1) Tensile psi (MPa) 2750 (19.0) 2750 (19.0) 2500 (17.3) 3000 (20.7) Shore A 61 68 67 68 Relative Adhesion to Steel Tire Cord (%) RT 100 91 100 93 2500F(1210C) 100 92 100 96 Table IV shows the effect of the concentration of Bisphenol A in HMMM in the presence of SiO2 (HiSil 21 5). At the levels studied, curing is somewhat slowed and adhesion to steel and glass cord is improved.Most of our work was done with the 22% solution to make comparisons with other bonding agents more convenient.

Table IV Variation of Bisphenol A Concentration In Bonding Agent* % Bisphenol A in Bonding Agent None 1 5 22 30 Rubber Properties Cure 45 min./ 2870F (141 0C) 300% Modulus, psi (MPa) 2150(14.8) 1975(13.6) 1850(12.8) 1800(12.4) Tensile, psi (MPa) 2950 (20.3) 3050 (21.0) 2950 (20.3) 2950 (20.3) Elongation, % 420 470 500 500 Shore A 65 69 67 68 Relative Adhesion** To Wire RT 100 128 122 132 2500F(1210C) 100 129 119 111 To Glass RT 100 110 112 115 2500F(1210C) 100 115 110 103 *AII compounds contain 1 5 pphr HiSil 21 5 **,,No additive" values are considered 100% in each column. Adhesion pads were cured at 3150F (1 570C). Without promotor: 20 min., all others 25 min. at which time the cure had leveled out (Monsanto Rheometer).Bonding Agent contents is 4.7 pphr.

3. Effect of Bonding Agent BAC Level and HiSil 215 This study indicates an optimum in adhesion around the 4.7 pphr level of the bonding agent (Table V).

Table V Effect of Bonding Agent Level* Bonding Agent BAC, pphr 0 3.4 4.7 6.0 Rubber Properties Cure 45 min./ 2870F (141 0C) 300% Modulus, psi (MPa) 1825 (12.6) 1850 (12.7) 1725(11.9) 1750(12.1) Tensile, psi (MPa) 2825 (19.5) 3150(26.7) 2925 (20.2) 3900 (20.0) Elongation, % 450 520 520 520 Shore A 64 67 68 69 Relative Adhesion Cure, min. @ 3150F(1600C) 20 25 25 25 Steel RT 100 104 125 100 2500F 100 121 127 110 Glass RT 100 112 119 110 2500F 100 104 112 111 *Contains 45 FEF/15 HiSil 21 5 reinforcement Data in Table VI indicate the importance of finely divided silica (HiSil 215) in the rubber compound for attaining maximum adhesion to steel cord. The glass cord adhesion showed less improvement by the presence of HiSil 21 5.

Table Vl Effect of HiSil 215 on Cord Adhesion* Reinforcement, pphr FEF 60 45 HiSi1215 0 15 Rubber Properties Cure 45 min./2870F (141 C) 300% Modulus, psi (MPa) 2425 (16.7) 1800 (12.4) Tensile, psi (MPa) 2925 (26.2) 2975 (20.5) Elongation, % 380 470 Shore A 69 67 Relative Adhesion** Steel RT 100 158 2500F (121 0C) 100 138 Glass RT 100 106 2500F (121 0C) 100 112 *Compounds contain 4.7 pphr Bonding Agent BAC **Adhesion samples were cured 25 min./315 F (1 570C) Data in Table VII indicate performance on steel and glass in the presence of HiSil 21 5.

Table VII Bonding Agent None BAC Rubber Properties Cure 45 min./2870F (141 0C) 300% Modulus, psi (MPa) 1825 (12.6) 1725 (11.9) Tensile, psi (MPa) 2825 (19.5) 2925 (20.2) Elongation, % 450 520 Shore A 64 68 Relative Adhesion Cure#315 F(158 C), min. 20 25 Steel RT 100 126 2500F (121 0C) 100 127 Glass RT 100 119 250 F(121 C) 100 111 *All compounds contain 45 FEF/1 5 HiSil 215; 4.7 pphr of the bonding agent was used.

Claims (4)

1. A vulcanizable rubber composition comprising rubber, filler material, and an effective adhesion promoting amount of an N-(substituted oxymethyi) melamine having the general formula:

and a bisphenol of the formula:

wherein X is hydrogen or lower (C1-C8) alkyl; R, Fl1, R2, R3 and R4 are individually hydrogen, lower (C1-C8) alkyl or the group --CH2,OX, X being as defined hereinabove, one X1 per phenyl group is hydroxyl and the remaining are hydrogen, R5 and R6 are hydrogen or a lower alkyl having one to three carbon atoms, and R, R8, R9 and Rio are hydrogen or a lower (C1-C8) alkyl group; or a reaction product of said melamine and bis-phenol derivative.

2. A composition according to claim 1 also including activated silica.

3. A composition according to claim 1 substantially as any herein described in the Examples.

4. A composition according to any one of claims 1 to 3 vulcanized and bonded to a rubber reinforcement.