CS266998B1 - Means for increasing rubber adhesion to reinforcing materials - Google Patents

Abstract

The solution relates to a composition for increasing the adhesion of rubber to reinforcing materials, in particular steel cord, which consists of 10 to 30% by weight of beta-naphthol, 40 to 80% by weight of precipitated silicic acid, 10 to 30% by weight of 0.0-dialkyl copper phosphate and optionally also 10 to 20% by weight of hexamethylenetetramine. The composition can be used in the production of rubber products reinforced with steel cord.

Description

The invention relates to a composition for increasing the adhesion to reinforcing materials, in particular a steel cord, based on beta-naphthol, precipitated silicic acid, copper dialkyl phosphate and, if appropriate, hexamethylenetetramine.

The development of the production and use of tires and other rubber products reinforced with steel cord is arousing increased interest in the adhesive properties of steel cord. To improve the adhesive properties, the steel cord is brassed. According to previous knowledge, the adhesion between the brass layer and the rubber occurs due to the formation of a thin film of copper sulfide on the surface of the brass in the initial stage of vulcanization. This film has good adhesive and cohesive properties and, in addition, is porous, so that the molecules of the vulcanizing rubber penetrate into it. However, the action of water, oxygen, sodium chloride and other agents leads to corrosion of the brassed steel cord (and galvanized steel rope in the case of conveyor belts) and thus reduces the adhesion of the rubber-steel cord system, which negatively affects the life of the product. For these reasons, the adhesion of the brassier himself, resp. galvanized steel cord to rubber is insufficient.

In order to improve the adhesion of the treated cord, various adhesives are added to the deposited rubber mixtures of the steel cords, which increase the adhesion of the rubber-steel cord system. corrosion resistance of the steel cord and prevents adhesion destruction. The result of such interventions is an increased service life of the products. They are used as adhesives! phenol-formaldehyde resins (US 4,236,564), cresol-formaldehyde resins, resorcinol-formaldehyde condensates, triazine derivatives (GB 1,575,516) and in particular transition metal compounds from the group of inorganic salts (EP 26,294), organic acid salts (US 4,340,515) and complex compounds especially cobalt and nickel (US 4,137,359). An organometallic adhesive based on a cobalt-boron compound of the general formula has found a significant practical application:

B (O-Co-X) ₃ where X is a monocarboxylic acid residue containing 7 to 11 C atoms (DE 2 921 289), which is much more efficient compared to simple cobalt compounds and ensures good adhesion of different types of vulcanized rubbers to the steel cord.

In practice, combined adhesive systems are also used, which most often consist of the already mentioned organic cobalt compounds and the so-called RHS system consisting of resorcinol (R), hexamethylenetetramine (H) and precipitated silicic acid (S). During vulcanization, resorcinol is reacted with hexamethylenetetramine (or another methylene group donor, e.g., hexamethoxymethylmelamine) to form resorcinol formaldehyde resins (U.S. Pat. No. 4,057,529). In the literature (Nichols M. J., Ohm R. F. - Adhesives Age 19, 1976, No. 7, pp. 25-30) beta-naphthol is mentioned as a possible replacement for resorcinol in the RHS system as an acceptor of the methylene group resp. formaldehyde, which is formed by the reaction of hexamethylenetetramine with water at elevated temperatures.

A significant disadvantage of said adhesive systems is, in the first place, the high prices of cobalt compounds. When used in the increased doses required to achieve the desired degree of adhesion, the resistance of the vulcanizate to thermal aging deteriorates and they bloom on the surface of the rubber composition, thereby reducing the ready-to-use tackiness of the composition. The disadvantages of resorcinol lie mainly in its unfavorable hygienic-toxicological properties (irritating to the skin, eyes, causes dermatosis), insufficient dispersion in the rubber mixture and the fact that it is a deficient raw material.

These disadvantages are eliminated by a composition for increasing the adhesion of rubber to reinforcing materials, in particular a steel cord, according to the invention, the essence of which consists in that the composition contains 10 to 30% by weight of beta-naphthol, 40 to 80% by weight of precipitated silicic acid, 10 to 30% by weight. %, Ο, Ο-dialkyl copper phosphate of formula I

CS 266 998 Bl

2 where R and R are the same or different and denote! linear or branched C 1 to C 6 alkyl or cyclohexyl, and optionally also 10 to 20% by weight of hexamethylenetramine.

Cu / 1 /

A composition for increasing the adhesion of rubber to the reinforcing materials of the present invention can be prepared by adding beta-naphthol and optionally hexamethylenetetramine to precipitated silicic acid in a mixing chamber heated to 130 ° C, stirring constantly and mixing Ο, Ο-dialkylphosphate of formula 1. into the mixture thus prepared. Precipitated silicic acid serves as a carrier for the active ingredients of the composition and at the same time contributes to their increased joint adhesive effect.

The composition according to the invention is added to the rubber mixture in an amount of 8 to 12 parts by weight per 100 parts by weight of rubber. In case the composition according to the invention does not contain hexamethylenetetramine, it can be added to the rubber mixture separately in an amount of 0.8 to 1.6 parts by weight per 100 parts by weight of rubber.

The advantage of the rubber adhesion promoter according to the invention over known adhesives and adhesive systems is, inter alia, that it provides a high degree of adhesion to the rubber-steel cord system at a significantly lower cost, while significantly reducing the corrosion of the steel cord and thus decrease in adhesion, which is reflected in the longer life of the products. Such a degree of effect cannot be achieved even with increased doses of the individual components of the composition according to the invention, used alone. The use of the composition according to the invention also considerably simplifies the technology for the preparation of rubber mixtures, in particular the weighing of components.

The composition according to the invention is well miscible in rubber compounds based on both natural and synthetic rubbers and is compatible with other rubber additives used in practice, such as accelerators, vulcanizing agents, plasticizers, fillers, antidegradants, etc. It can be used in the production of rubber products reinforced with steel cord such as tires, conveyor belts and others.

The following example illustrates but does not limit the scope of the invention.

Example

A rubber premix of the following composition was used in the experiments:

Component Parts by weight natural rubber100 stearic acid1,5 zinc oxide10 carbon black, type N-33065 plasticizer2

N-isopropyl-N'-phenyl-p-phenylene-1 diamine-phenyl-beta-naphthylamine1

180.5

The vulcanization system and the tested adhesives were mixed into said premix according to the following schedule:

CS 266 998 Bl

Component _____ Mixture number, parts by weight

1 2 3 4 5 6 7 8 premix 180.5 180.5 180.5 180.5 180.5 180.5 180.5 180.5 N-oxydiethylene-2-benzothiazolesulfenamide 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 sulfur 3 3 3 3 3 . 3 3 3 adhesive according to DE 2 921 289 - 1.2 - 1.2 - - - - resorcinol - - 1.5 1.5 - - - - hexamethylenetetramine - - 1 1 0.8 - 0.9 1.6 precipitated silicic acid - 5 5 - - - - PCBS-1 - - - - 12 - - - PCHBS-2 - - - - - ' • 9 - - PCBS-3 - - - - - - 8 - PCBS-4 - - - - - - - 10

Composition of PCBS-1: 10% by weight of β, β-dibutylphosphate of copper% by weight of beta-naphthol% by weight of precipitated silicic acid

Composition of PCHBS-2: 18% by weight of copper 0,0-di- (2-ethylhexyl) phosphate% by weight of beta-naphthol% by weight of precipitated silicic acid% by weight of hexamethylenetetramine

Composition of PCBS-3: 20% by weight of O-2-ethylhexyl / -O-cyclohexylphosphate 20% by weight of beta-naphthol% by weight of precipitated silicic acid

Composition PCBS-4: 30% by weight of β, β-dioctadecylphosphate of copper% by weight of beta-naphthol% by weight of precipitated silicic acid

After determining the vulcanization characteristics of the mixture on a Monsanto Rheometer at 145 ° C, test specimens were prepared by vulcanization at 145 ° C. The adhesion of the vulcanizates to the brassed steel cord 7x4x0.22 mm + 1x0.15 mm was measured according to ON 62 1465. The essence of the method is to measure the force required to pull out the cord pressed into the rubber test specimen at a depth of 25 mm. The degree of rubber coverage of the torn-out part of the cord was also monitored, which complements the picture of the nature of the joint defect.

The resistance of the vulcanisate and the cord to the effects occurring when using rubber products reinforced with steel cord was tested under the following conditions:

(a) test piece with pressed cords, immersed in 10% sodium chloride solution for 24 h at 20 ° C,

b) a test piece melted for 24 hours at a temperature of 80 ° C and a relative humidity of 95%,

c) thermal stress of the test specimen for 7 days at 100 ° C,

d) 10 times repeated 45% compression deformation of the test specimen.

The measured values are summarized in the following table.

CS 266 998 Bl

Table

Mixture number

1 2 '3 4 5 6 7 8 Vulcanization characteristics processing security, 5.25 5.0 3.6 3.65 3.8 3.95 3.7 3.9 t / min / optimal vulcanization time ₍ , 15.5 17.75 16.0 15.75 18.0 17.2 17.1 16.9 ^t 90, ^{/ min /} Physico-mechanical properties , t _{0 9} θ 145 ° C / vulcanizate strength, (MPa) 24.9 24.8 23.5 22.4 23.4 23.8 24.0 23.3 ductility (%) 315 320 310 285 305 310 320 300 after aging for 5 days at 90 ° G: vulcanizate strength (MPa) 18.1 14.7 15.0 14.9 16.2 16.9 16.8 16.3 ductility (%) 150 125 130 130 145 140 150 140 Adhesion, / N / 25 mm / 24 hours after pressing 860 1 140 940 1 320 1 340 1 370 1 335 1 380 after aging under the conditions: ’ a) 455 475 560 755 850 970 905 840 b) 690 765 730 895 900 985 940 895 c) 610 685 670 795 800 970 795 670 d) 510 600 590 620 635 670 640 625 Degree of surface coverage kordu qumou, (%) before aging 65 85 80 95 95 100 95 100 after aging in conditions: a) 25 35 40 65 65 70 65 70 b) 45 55 50 60 65 70 65 70 c) 40 50 50 55 60 60 65 55 d) 20 40 40 45 45 50 45 45

OBJECT OF THE INVENTION

Claims (2)

OBJECT OF THE INVENTION A composition for increasing the adhesion of rubber to reinforcing materials, in particular steel cord, based on beta-naphthol and precipitated silicic acid, characterized in that it contains 10 to 30% by weight of meta-naphthol, 40 to 80% by weight of precipitated silicic acid and in addition 80 to 30% by weight of β, β-dialkyl copper phosphate of the formula I. Cu Wherein R 1 and R 2 are the same or different and represent linear or branched (1) to C ₁₀ alkyl 10 or cyclohexyl. 2. A composition according to claim 1, characterized by the addition of hexamethylenetetramine in an amount 10 to 20% by weight.