Adhesive Mixtures for Uncured Rubbers

Abstract

The present invention relates to adhesive mixtures containing resorcinol and/or resorcinol esters, melamine formaldehyde ethers and sulfenamide derivatives and also silica for use in rubbers, to the production thereof, to vulcanizates and composite articles produced therefrom and to the use thereof.

Claims

1. An adhesive mixture containing resorcinol and/or resorcinol ester of formula (I) ##STR00007## wherein all radicals R.sup.1 are identical or different and represent hydrogen, a straight-chain or branched C.sub.1-C.sub.18-alkyl radical or a phenyl radical, and at least one melamine formaldehyde ether of formula (II) ##STR00008## wherein all radicals R.sup.2 are identical or different and represent hydrogen or a straight-chain or branched C.sub.1-C.sub.4-alkyl radical or a phenyl radical, wherein not more than 5 R.sup.2 radicals represent hydrogen and/or polymers of melamine formaldehyde ethers of formula (II), at least one sulfenamide of formula (III) ##STR00009## where x=0 or 1 and z=1 or 2, wherein the sum of z and x=2 and y=1-4, and at least one silica-based filler.

2. The adhesive mixture according to claim 1 wherein the sulfenamide of formula (III) is a compound in which x=0, y=1 and z=2.

3. The adhesive mixture according to claim 1 wherein the total proportion of resorcinol and/or resorcinol esters of formula (I), melamine formaldehyde ethers of formula (II) and/or polymers of melamine formaldehyde ethers of formula (II) is 20-80% by weight and the proportion of sulfenamide of formula (III) is 0.1-10% by weight based on the total adhesive mixture.

4. The adhesive mixture according to claim 1 wherein the mixture further comprises natural and/or synthetic rubbers.

5. A process for producing the adhesive mixture according to claim 4, comprising treating the silica-based filler initially with melamine formaldehyde ether(s) of formula (II) and/or polymers of melamine formaldehyde ethers of formula (II) and subsequently with resorcinol and/or resorcinol ester(s) of formula (I) or treating the silica-based filler simultaneously with melamine formaldehyde ether(s) of formula (II) and/or polymers of melamine formaldehyde ethers of formula (II) and resorcinol ester(s) of formula (I) or treating the silica-based filler initially simultaneously with resorcinol ester(s) of formula (I) and subsequently with melamine formaldehyde ether(s) of formula (II) and/or polymers of melamine formaldehyde ethers of formula (II) or treating the silica-based filler with a mixture of melamine formaldehyde ether(s) of formula (II) and/or polymers of melamine formaldehyde ethers of formula (II) and resorcinol ester(s) of formula (I) or mixing resorcinol esters of formula (I) and melamine formaldehyde ethers of formula (II) and/or polymers of melamine formaldehyde ethers of formula (II) with the silica-based filler separately whereby mixtures are formed and the mixtures are subsequently combined and said filler is subsequently added to the rubber with the sulfenamide of formula (III).

6. (canceled)

7. A vulcanizate obtainable by vulcanization of adhesive mixture as claimed in claim 4 at blend temperatures of 100° C. to 200° C.

8. A process for producing vulcanizates as claimed in claim 7, comprising vulcanizing an adhesive mixture as claimed in claim 4 at blend temperatures of 100° C. to 200° C.

9. A composite article containing vulcanizates as claimed in claim 7.

10. The composite article as claimed in claim 9, wherein said composite article is selected from tires, conveyor belts, belts of all kinds, V-belts, reinforced hoses, fire hoses and coated fabrics.

11. The adhesive mixture according to claim 1 wherein R1 comprises methyl or stearyl.

12. The adhesive mixture according to claim 1 wherein R2 is hydrogen or methyl.

13. The adhesive mixture according to claim 1 wherein not more than one R2 radical is hydrogen.

14. The adhesive mixture according to claim 1 wherein the filler is precipitated silica or pyrogenic silica.

15. The adhesive mixture according to claim 1 wherein the total proportion of resorcinol and/or resorcinol esters of formula (I), melamine formaldehyde ethers of formula (II) and/or polymers of melamine formaldehyde ethers of formula (II) is 25-55% by weight and the proportion of sulfenamide of formula (III) is 0.1-10% by weight based on the total adhesive mixture.

16. The adhesive mixture according to claim 1 wherein the mixture further comprises natural rubber and/or synthetic rubbers selected from the group of polybutadiene, butadiene/C.sub.1-C.sub.4-alkyl acrylate copolymer, polychloroprene, polyisoprene, styrene/butadiene copolymers with styrene contents of 1-60% by weight, isobutylene/isoprene copolymers, butadiene/acrylonitrile copolymers with acrylonitrile contents of 5-60% by weight, partially hydrogenated and fully hydrogenated NBR rubber and ethylene/propylene/diene copolymers and mixtures thereof.

Description

WORKING EXAMPLES

Examples for Production of Adhesive Systems

[0084] The reference mixture and rubber mixtures 1 and 2 were produced as follows:

TABLE-US-00001 TABLE 1 Adhesive mixture 1 Adhesive mixture 2 (inv.) (inv.) Silica CAS No. 7631-86-9 12.7 12.7 Melamine formaldehyde ether of formula (II) where 4.6 4.6 R.sup.2 = hydrogen (4x) and methyl (2x), on silica (50%) Resorcinol and stearic acid (2:1) 3.4 3.4 Benzothiazylsulfenamide of formula (III) where x = 0.7 0.9 0, y = 1 and z = 2 (DBzBS)

[0085] For production of the rubber mixtures 1 and 2 the silica was initially admixed with melamine formaldehyde ether of formula (II) and subsequently treated with resorcinol and stearic acid, wherein the usage amounts and the reactants are as reported in table 1. These mixtures were subsequently each admixed with the sulfenamide of formula (III).

Production of Rubber Mixture from the Adhesive Mixtures 1 and 2

[0086] In an internal mixer natural rubber was consecutively admixed with the adhesive mixture 1/adhesive mixture 2 and subsequently carbon black and mineral oil. The input materials and usage amounts are apparent from table 2. The internal mixer had a temperature <90° C. and the residence time of the adhesive components was less than 5 minutes.

[0087] Subsequently, depending on the mixture either dicyclohexylbenzothiazylsulfenamide/sulfur for the reference or the benzothiazylsulfenamide of formula (III) where x=0, y=1 and z=2, sulfur and the other constituents for the rubber mixtures 1 or 2 were incorporated in the amounts reported in table 2 on the mixing mill.

[0088] The mixing mill had a temperature of less than 40° C. The resulting milled sheets were used for measurement of tear propagation resistance and rebound elasticity.

[0089] The internal mixer had a temperature <90° C. The residence time of the adhesive components was less than 5 minutes.

[0090] A further portion of the mixtures was vulcanized in an electric heating press. The crosslinking temperature was T=150° C. and the press pressure was p=100 bar. The crosslinking time was t=3180 seconds at a conversion of t95.

TABLE-US-00002 TABLE 2 Rubber formulation Reference Rubber Rubber according to mixture 1 mixture 2 EP-A-2960278 (inv.) (inv.) TSR natural rubber 100 100 100 Carbon black 50 50 50 Silica CAS No. 7631-86-9 12.7 12.7 12.7 Mineral oil 4 4 4 Zinc oxide 8 8 8 Melamine formaldehyde ether of formula (II) where 4.6 4.6 4.6 R.sup.2 = hydrogen (4x) and methyl (2x), on filler (50%) Resorcinol and stearic acid (2:1) 3.4 3.4 3.4 SULFUR 4.5 4.5 4.5 Dicyclohexylbenzothiazylsulfenamide (pa) 0.7 Benzothiazylsulfenamide of formula (III) where 0.7 0.9 x = 0, y = 1 and z = 2 (DBzBS) inv. = inventive pa = prior art
Quantities reported in phr (parts by weight per 100 parts of rubber)

TABLE-US-00003 Trade name Produced/marketed by Natural rubber TSR/RSS 3 DEFO 700 Handelshaus Weber & Schaer Carbon black CORAX N 326 Degussa-Evonik GmbH Silica VULKASIL S LANXESS Deutschland GmbH Polymerized 2,2,4-trimethyl- VULKANOX HS/LG LANXESS Deutschland GmbH 1,2-dihydroquinoline Zinc oxide ZINKOXYD AKTIV LANXESS Deutschland GmbH Sulfur MAHLSCHWEFEL 90/95 Solvay Deutschland GmbH CHANCEL Mineral oil TUDALEN 1849-TE Hansen&Rosenthal KG Dicyclohexylbenzothiazyl- VULKACIT DZ/EGC LANXESS Deutschland GmbH sulfenamide DBzBS LANXESS Deutschland Melamine formaldehyde COHEDUR A250 LANXESS Deutschland GmbH ether as condensation product from melamine, formaldehyde, methanol on filler (50%) Resorcinol and stearic acid COHEDUR RS LANXESS Deutschland GmbH (2:1)

[0091] The following methods of measurement were used to determine the properties of rubber mixture/vulcanizates:

Scorch Performance (Scorch Time t3 and t5):

[0092] The same test can moreover be used as described above to measure the scorch performance of a mixture. The selected temperature was 130° C. The rotor was run until, after passing through a minimum, the torque value increased to 5 Mooney units above the minimum value (t5). The greater the value (units of seconds), the slower the scorching of the mixture. In practice, a scorch time of more than 300 seconds is usually advantageous, but should be less than 1000 seconds, accounting for processing consistency and time spent.

Tear Propagation Resistance (According to DIN 53515):

[0093] The force with which a vulcanizate damaged by a cut opposes tear propagation is referred to as the tear propagation resistance. It was expressed in N/mm and determined using a tensile test machine according to the “Graves angle test” (DIN 53515) method.

Determination of Rebound Elasticity was Carried Out According to DIN 53512.

[0094] The measured results for the mixtures are summarized in table 3.

TABLE-US-00004 TABLE 3 Summary of results Rubber Rubber formulation formulation Parameter Unit DIN Reference 1 2 Mooney scorch for 130° C. (t3) sec DIN 53523-4 753 876 830 Mooney scorch for 130° C. (t5) sec DIN 53523-4 841 997 941 Tear propagation resistance N/mm 53515 41.7 45.2 45.9 Rebound resilience at 23° C. % 53512 40 40 41

[0095] Table 4 shows the results of the crosslink node structure analysis at identical molar accelerator concentration in natural rubber (tmax, 150° C.; 1.7 phr sulfur).

TABLE-US-00005 TABLE 4 Parameter Unit Reference Rubber formulation 1 Monosulfidic crosslink nodes % 4 12 Disulfidic crosslink nodes % 38 34 Polysulfidic crosslink nodes % 58 55

[0096] Crosslink node structure analysis by the thiol-amine method (Saville and Watson; 1967) is based on selective cleavage of the different sulfur bridges by various reagents. Distinguishing the three types of crosslink nodes from one another requires two thiols of different selectivity. The cleavage of exclusively polysulfidic sulfur bridges was effected using a 0.5 molar solution of i-propanethiol and piperidine in n-heptane. A 1 molar solution of n-hexanethiol and piperidine in n-heptane was used to cleave di- and polysulfidic crosslink nodes at the same time. The monosulfidic bonds did not react with the employed reagents within the decomposition times.

[0097] At a conversion of 100% (tmax) the crosslink node structure analysis of the DCBS system for the vulcanizate according to the invention resulted in primarily polysulfidic crosslink points (58%) and a proportion of 38% for the disulfidic crosslink nodes and 4% for the monosulfidic crosslink nodes.

[0098] Surprisingly, the DBzBS (N,N-dibenzyl-2-benzothiazylsulfenamide) also forms few monosulfidic crosslink points and a comparably large number of di- and polysulfidic crosslink nodes.

[0099] The noticeably longer scorch time of DBBS compared to DCBS (see table 3) slows down the vulcanization and thus the formation of the sulfur bridges between the individual rubber chains and the rubber can therefore readily anchor to the metal alloy via Cu-Sx-C bridges. This guarantees safe use of DBBS as a vulcanization accelerator in tire manufacture.

[0100] The results of the measurements show that the adhesive mixture according to the invention exhibits a significant improvement in scorch performance (long scorch time at 130° C.). This has the particular advantage that the flow time of the mixture leaves a sufficient margin for reaction of the formaldehyde elimination/for resin formation in order that the bond may be realized.

[0101] Furthermore, physical properties such as rebound elasticity and tear propagation resistance were improved while maintaining comparable further physical parameters, such as 300 modulus and tensile strength.