WO2010017673A1

WO2010017673A1 - Resorcinol and m-aminophenol derivatives blends in rubber compounding applications

Info

Publication number: WO2010017673A1
Application number: PCT/CN2008/071951
Authority: WO
Inventors: Quanhai Yang; Xin Chen; Qiang Chen
Original assignee: Sino Legend (Zhangjiagang) Chemical Co., Ltd
Priority date: 2008-08-12
Filing date: 2008-08-12
Publication date: 2010-02-18

Abstract

This invention is related to an improved vulcanization rubber composition comprising (i) a rubber component selected from natural and synthetic rubber; and (ii) a methylene donor; and (iii) a blend containing resorcinol and m-aminophenol derivative type material as the methylene acceptor. This resorcinol and m-aminophenol derivative blend can be prepared by melt blending of resorcinol with one or more derivative of m-aminophenol compound. The methylene acceptor compound of this invention has a lower melting point and also, showed much improved rubber compound cure, tensile and steel cord adhesion properties than resorcinol.

Description

RESORCINOL AND m-AMINOPHENOL DERIVATIVES BLENDS IN RUBBER COMPOUNDING APPLICATIONS

Technical Field This invention relates to rubber field, and in particular, to an improved vulcanization rubber composition and the uses thereof.

Background of the Invention

In the manufacture of reinforced rubber products, such as tires and hoses, various reinforcing materials have been used to enhance the strength of rubber articles. These reinforcing materials, in general, are made of rayon, nylon, polyester, steel wire and glass fibers. The steel wire used in these applications is primarily coated with brass or zinc. A primary requirement for effective reinforcement is that these reinforcing materials tightly bonded to rubber. Maximum reinforcement of the rubber or rubber compound is achieved when maximum adhesion is produced between the rubber and reinforcing element. Good adhesion is difficult to achieve where, for example in automobile tires, the article is subject to continuous flexing and exposure to high temperature during use. High initial adhesion could be obtained by providing good mechanical contact between the rubber and wire during the cure but, upon aging and use of the article, the adhesive bond is often weakened or lost completely, which results in premature failure. In order to prevent this, adhesion promoters are often used which can maintain a high level of adhesion between rubber or rubber compounds and metal.

The conventional method of promoting adhesion between rubber and brass or zinc coated steel wire is the use of a two part adhesive system, namely the methylene acceptor and methylene donor system. Historically, resorcinol has been used as the methylene acceptor and hexamethylene tetramine (Hexa) and hexamethoxymethyl melamine (HMMM) as the methylene donor compounds to promote adhesion between the steel wire or cords and rubber or rubber compounds. During the vulcanization process, methylene donor compounds released formaldehyde and reacted with resorcinol and formed an in-situ resorcinol- formaldehyde (RF) network structures. The formation of such RF network during rubber vulcanization improved the cured rubber physical, mechanical and adhesion properties.

Resorcinol has been widely in the manufacture of reinforced rubber articles because it is effective in enhancing hardness and dynamic modulus of elasticity of a rubber, toughening the rubber, reducing loss factor of a vulcanized rubber during a dynamic transformation and reducing heat build-up. Resorcinol (Molecular weight 110; Melting point 110 ⁰C) is a small molecular organic compound and therefore, can be uniformly distributed among the rubber molecules during compounding with rubber, resulting in an uncured rubber mixture that exhibits very low viscosity. This results in greater ease of processing and extrusion of the uncured rubber compounds.

Though resorcinol provides excellent physical, mechanical and steel cord adhesion properties in the uncured and cured rubber products, fuming associated with resorcinol at rubber processing temperatures always caused problems, particularly with loss of product. With respect to rubber manufacture, the incorporation of resorcinol in the rubber mixture leads to extensive smoking and fuming, since the mixing is carried out at relatively high temperatures and in particular the free resorcinol escapes into the atmosphere to a large extent. In the un-modified state, resorcinol is excessively volatile or fuming due to its sublimation property. Because of this, slight variations in the rubber processing temperature (normally higher temperatures) can result in variations in the amount of resorcinol distributed in rubber compounds. When the fuming of resorcinol appears, the adhesion and mechanical properties of rubber compounds become uneven, which could result in a remarkable decrease in quality of the rubber articles.

To reduce the fuming of resorcinol, resorcinol derivatives, resorcinol - formaldehyde (RF), alkyl-resorcinol - formaldehyde and aralkyl-resorcinol - formaldehyde resins have been developed and employed in rubber compounding applications, such as tires. These modified resorcinol derivatives and resins provided cured rubber or rubber compounds with enhanced mechanical and un-aged and aged adhesion properties. When the resorcinol is modified by derivatization or resins, the molecular weights of these modified compounds are generally higher. The use of such higher molecular weight compounds normally results in processing problems in rubber compounds. Higher mixing temperatures are often required to blend them effectively in rubbers. Compared to resorcinol, higher resin loadings are often required to achieve similar physical and mechanical properties in the cured rubber compounds.

In general, the cure rate of rubber compounds is severely affected by the use of these modified resorcinolic resins in the place of resorcinol in rubber compounds. When the resorcinol is derivatized by attaching functional groups either to the benzene ring or hydroxyl groups, the reactivity of the resulting resorcinolic derivatives towards the methylene donor compounds is greatly reduced or altered. The high reactivity of resorcinol towards conventional methylene donors such as formaldehyde, hexamethylenetetraamine (HEXA or HMTA) and hexamethoxymethylmelamine (HMMM), etc., is due to the presence of three reactive sites_.on the resorcinol molecule. The presence of two hydroxyl groups, meta with respect to each other, on the molecule further enhances the reactivity of the molecule towards methylene donors. When the resorcinol structure is altered by chemical reactions, its reactivity is considerably reduced. For example, substitutions at the 2, 4 or 6 positions of the benzene ring reduce the number of reactive sites for methylene donor interaction. Similarly, the monoether or monoester derivatives of resorcinol have reduced reactivity towards methylene donor compounds as compared to pure resorcinol.

The network formation during rubber curing is more effective with phenolic methylene acceptor compounds having meta-substitution than with other compounds due to their high reactivity towards methylene donors. Though modifications to resorcinol molecule are expected to lower the fuming characteristics of resorcinol, they also affect the networking efficiency during the rubber compound curing. Increased reactivity of resorcinolic derivatives is expected to speed up the network formation during rubber vulcanization, which ultimately enhances the physical and mechanical properties of the cured rubber.

It is advantageous to use meta substituted phenolic compounds in the rubber compounding application due to their high reactivity and networking efficiency. In this aspect, other meta substituted phenolic derivatives such as m-aminophenol (M. Pt : 123 ⁰C and M. Wt: 109) and phloroglucinol (M. Pt: 218 - 221 ⁰C and M. Wt: 162 for dihydrate) could also be employed in rubber compounds. M-Aminophenol is about 5 to 10 times more reactive and phloroglucinol is at-least about 25 times more reactive than resorcinol. But the use of phloroglucinol and m-aminophenol in rubber compounding formulations is limited due to their high cost and melting points. Therefore, the most commonly employed methylene acceptor is resorcinol, due to its comparatively low cost and high reactivity.

Summary of Invention

The objective of this invention is to develop resorcinol containing methylene acceptor system that can at least maintain or exceed the reactivity of resorcinol towards the methylene donor compounds. In order to achieve this objective, it was aimed to develop highly reactive methylene acceptor compounds, exhibiting reactivity either equal to or better than resorcinol, by melt blending resorcinol with another meta-substituted phenolic derivative such as m- aminophenol and its derivatives. The blends containing resorcinol exhibits lower melting points than resorcinol itself, and therefore could be mixed with rubber compounds at relatively lower temperatures and lower the fuming problems associated with resorcinol. These methylene acceptor systems are capable of enhancing the cure, mechanical and bonding properties of vulcanizable rubber compositions. The rubber compounds based on this invention could be useful in the manufacture of pneumatic tires, hoses and belts. The present invention also finds utility in, for example, metal-rubber articles such as motor mounts, cutless bearings, torsilastic springs, power belts, printing rolls, metal wire reinforced or braided hose, electrical deicers and shoe heels.

In the first aspect of the invetion, it is provided an improved vulcanization rubber composition comprising (i) a rubber component selected from natural and synthetic rubber; and (ii) a methylene donor; and (iii) a blend containing resorcinol and m-aminophenol derivative type material as the methylene acceptor, which can be prepared by melt blending of resorcinol with another meta-substituted phenolic derivative comprising the following chemical structure:

wherein R, Ri and R₂ can be independently hydrogen; hydroxyl; acetyl; benzoyl; alkyl such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, octyl, nonyl, decyl, dodecyl and pentadecyl; 2-hydroxyethyl, 2-hydroxypropyl and 2 -hydroxy butyl; cyclopentyl, cyclohexyl and cycloheptyl; aryl such as phenyl and substituted phenyls; and aralkyl such as benzyl or alkylaryl such as alkylphenyls.

In a preferred embodiment, the methylene acceptor blend composition comprises a mixture consisting of resorcinol and m-aminophenol.

In a preferred embodiment, the methylene acceptor blend compound can be prepared by melt blending of resorcinol with m-aminophenol or its derivatives.

In a preferred embodiment, the meta-substituted phenolic derivative that can be used to prepare the methylene acceptor blend can be selected from the group comprising m- aminophenol, N-methyl-m-aminophenol, N,N-dimethyl-m-aminophenol, N-ethyl- aminophenol, N,N-diethyl-m-aminophenol, N-butyl-m-aminophenol, N,N-dibutyl-m- aminophenol, 3-amino-5-methylphenol, 3-N-methylamino-5-methylphenol, 3-amino-5- ethylphenol, 3-N-methylamino-5-ethylphenol, N,N-dimethyl-3-amino-5-methylphenol, N- methyl-3-amino-5-propylphenol, 3-hydroxy diphenylamine, 3 -hydroxy-4' -methyl - diphenylamine, 3 -hydroxy-2 ' -methyl-diphenylamine, 3 -hydroxy -4 ' -methoxy-diphenylamine, 3 -hydroxy -N-naphthyl-aniline, 2-chloro-3'-hydroxy-diphenylamine and 3-hydroxy-3'- methoxy-4' -methyl-diphenylamine.

In a preferred embodiment, the rubber component can be any cis-l,4-polyisoprene (natural or synthetic), polybutadiene, polychloroprene and the copolymers of isoprene and butadiene, copolymers of acrylonitrile and butadiene, copolymers of acrylonitrile and isoprene, copolymers of styrene, butadiene and isoprene, isobutylene rubber (butyl) and ethylene-propylene rubber (EPDM), copolymers of styrene and butadiene and blends.

In a preferred embodiment, the methylene donors suitable for use include hexamethylenetetramine, hexaethoxymethylmelamine, hexamethoxymethylmelamine, 2- nitro-2 -methyl -1- propanol (NMP), trioxane and polymers of formaldehyde such as paraformaldehyde.

In a preferred embodiment, the vulcanization rubber compound prepared may also include additives such as sulfur, accelerator, carbon black, cobalt salts, stearic acid, silica, sulfur, zinc oxide, fillers, antioxidants and softening oils.

In a preferred embodiment, the meta-substituted phenolic compound used in the preparation of methylene acceptor can be selected from the group consisting of m- aminophenol, N-methyl-m-aminophenol, N, N-dimethyl-m-aminophenol, N, N-diethyl-m- aminophenol and 3-hydroxy diphenylamine, 3 -hydroxy -4' -methyl-diphenylamine, 3-hydroxy- 2 '-methyl-diphenylamine and 3 -hydroxy-4' -methoxy-diphenylamine. In a preferred embodiment, the methylene acceptor blend contains resorcinol.

In a preferred embodiment, the weight ratio of the components resorcinol: m- aminophenol is preferably in the range of 99:1 to 1:99 and, in particular from 85:15 to 15: 85.

In the second aspect of the invention, it is provided the use of the improved vulcanizable rubber composition of the invention in the preparation of composite products, including tires, power belts, conveyor belts, printing rolls, rubber shoe heels and soles, rubber wringers, automobile floor mats, mud flaps for trucks, ball mill liners, tubings, fan belts, conveyor belts, and the like.

Description of Drawings

Figure 1 shows the melting point behavior of resorcinol, m-aminophenol and the blend compositions.

Detailed Description of the Current Invention

According to the current invention, highly reactive and lower melting resorcinol based methylene acceptor systems capable of enhancing the cure, physical and mechanical properties of the uncured and cured vulcanizable rubber compositions are obtained by melt blending of resorcinol with the compound represented by the following formula (a):

wherein R, Ri and R₂ groups can be independently hydrogen; hydroxyl; acetyl; benzoyl; alkyl such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, octyl, nonyl, decyl, dodecyl and pentadecyl; 2 -hydroxy ethy, 2-hydroxypropyl and 2 -hydroxy butyl; cyclopentyl, cyclohexyl and cycloheptyl; aryl such as phenyl and substituted phenyls; and aralkyl such as benzyl or alkylaryl such as alkylphenyls.

One aspect of the current invention is to provide rubber compounds having enhanced physical, mechanical and cord adhesion properties.

Another aspect of the present invention is to provide a method for making rubber compounds having improved physical and mechanical properties.

Resorcinol blends containing the chemical structure (a) can be employed as the methylene acceptors in rubber compounds useful in the production of pneumatic tires, hoses and belts. Therefore, according to the current invention, there is provided an improved vulcanization rubber composition comprising (i) a rubber component selected from natural and synthetic rubber; and (ii) a methylene donor; and (iii) a resorcinol and m-aminophenol derivative blend as the methylene acceptor.

The rubber component of the current invention can be any cis-l,4-polyisoprene (natural or synthetic), polybutadiene, polychloroprene and the copolymers of isoprene and butadiene, copolymers of acrylonitrile and butadiene, copolymers of acrylonitrile and isoprene, copolymers of styrene, butadiene and isoprene, isobutylene rubber (butyl) and ethylene- propylene rubber (EPDM), copolymers of styrene and butadiene and blends.

In preferred embodiments of the present invention, the methylene acceptor compounds can be obtained by melt blending of resorcinol and m-aminophenol derivatives represented by the following formula (a):

wherein R, Ri and R₂ group can be independently hydrogen; hydroxyl; acetyl; benzoyl; alkyl such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, octyl, nonyl, decyl, dodecyl and pentadecyl; 2 -hydroxy ethy, 2-hydroxypropyl and 2 -hydroxy butyl; cyclopentyl, cyclohexyl and cycloheptyl; aryl such as phenyl and substituted phenyls; and aralkyl such as benzyl or alkylaryl such as alkylphenyls. Compounds represented by formula (a) includes, but not limited to, m-aminophenol, N- methyl-m-aminophenol, N,N-dimethyl-m-aminophenol, N-ethyl-aminophenol, N,N-diethyl- m-aminophenol, N-butyl-m-aminophenol, N,N-dibutyl-m-aminophenol, 3-amino-5- methylphenol, 3-N-methylamino-5-methylphenol, 3-amino-5-ethylphenol, 3-N-methylamino- 5-ethylphenol, N,N-dimethyl-3-amino-5-methylphenol, N-methyl-3-amino-5-propylphenol, 3 -hydroxy diphenylamine, 3-hydroxy-4'-methyl-diphenylamine, 3-hydroxy-2'-methyl- diphenylamine, 3-hydroxy-4'-methoxy-diphenylamine, 3 -hydroxy -N-naphthyl-aniline, 2- chloro-3 '-hydroxy-diphenylamine and 3-hydroxy-3 '-methoxy-4'-methyl-diphenylamine.

Above all, m-aminophenol, N-methyl-m-aminophenol, N, N-dimethyl-m-aminophenol,

N, N-diethyl-m-aminophenol and 3 -hydroxy diphenylamine can preferably be used.

The vulcanizable rubber compositions of the present invention may contain one or more methylene donor. The term "methylene donor" is intended to mean a compound capable of generating formaldehyde on heating and reacting with methylene acceptor blends of resorcinol and m-aminophenol derivatives and generate the cross linked network structure in the rubber compounds. Examples of methylene donors which are suitable for use in the present invention include hexamethylenetetramine, hexaethoxymethylmelamine, hexamethoxymethylmelamine, 2-nitro-2 -methyl -1- propanol (NMP), trioxane and polymers of formaldehyde such as paraformaldehyde.

In the process of making the blends suitable to use as the methylene acceptors of this invention, resorcinol and m-aminophenol or its derivatives can be melt blended at a weight ratio in the range of about 99: 1 to about 1 :99. The blend compositions may contain resorcinol and at least one or more m-aminophenol derivatives. Depending upon the ratios, the physical property, such as the melting or softening points, of the blends could vary.

These blends can be prepared by any methods known to the persons skilled in the art. In general, blends can be prepared either by the solution or molten methods. When the blends are prepared by the solution method, two or more organic chemical compounds are dissolved in suitable solvent first, and then remove the solvent completely either by evaporation or distillation. In the absence of a solvent, the blends can be conveniently prepared by melt blending the organic chemicals at elevated temperature conditions. Blends containing various proportions of resorcinol could be prepared and used in various applications. The concentration of resorcinol and m-aminophenol derivatives in these blends depends on the desired melting points and properties required for the particular applications. The rubber compounds properties will also vary depending upon the loading and compositions of resorcinol and m-aminophenol derivatives blends.

The weight ratio of methylene donor to methylene acceptor used in the rubber compound may vary. But, generally, the weight ratio will range from about 1 : 10 to about 10:1. Preferably, the weight ratio ranges from about 1 :5 to 5:1.

The vulcanization rubber compound of the current invention may also include additives such as carbon black, cobalt salts, stearic acid, silica, sulfur, zinc oxide, fillers, antioxidants and softening oils. Particulate fillers such as silica, carbon black, clays, talc, calcium carbonate, silicates have been generally used as reinforcing materials for rubbers to improve their physical and mechanical properties such as modulus, tensile strength, abrasion, tear properties, and dynamic properties

The vulcanization of the rubber compound is normally conducted in the presence of a sulfur vulcanizing agent. Examples of suitable sulfur vulcanizing agents include elemental sulfur (free sulfur) or sulfur donating vulcanizing agents, for example, an amine disulfide, polymeric polysulfide or sulfur olefin adducts. Preferably, the sulfur vulcanizing agent is elemental sulfur. As known to those skilled in the art, sulfur vulcanizing agents are used in an amount ranging from about 0.5 to 10 phr.

Accelerators are conventionally used to control the time and/or temperature required for vulcanization and to improve the properties of the vulcanizate. Suitable types of accelerators that may be used include amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates and xanthates. Preferably, the primary accelerator is a sulfenamide. If a secondary accelerator is used, the secondary accelerator is preferably a guanidine, dithiocarbamate or thiuram compound.

The additives of the invention can be added into rubber compositions by coventional means and methods for the known additives, such as methoxymethylmelamine (HMMM) for example. A usual method for mixing rubber compounds is by mixing in a Banbury mixer. In one typical method, additives which are not reactive are blended first into the rubber at temperatures up to about 150 ⁰C in the Banbury. Vulcanizing agents, accelerator, and adhesion promoters are added in a second and third mixing steps at temperatures from about 90 ⁰C to about 150 ⁰C

The current invention is further directed to a vulcanizable rubber composition having improvements in physical and mechanical properties such as tensile modulus and strength, hardness, scorch safety, cure time, dynamic storage modulus (G'), tan δ (hysteresis) and steel cord adhesion properties.

The vulcanizable rubber mixtures according to the invention can be prepared, processed and vulcanized by known methods. They are highly suitable for the manufacture of industrial rubber articles, preferably of those containing reinforcing supports based on steel cord or textile fiber. The steel cords are not limited in particular, and include known steel cords such as bare steel cords, brass-plated steel cords and zinc-plated steel cords.

The rubber compounds containing resorcinol and m-aminophenol derivative blend type products may be used in the preparation of composite products including tires, power belts, conveyor belts, printing rolls, rubber shoe heels and soles, rubber wringers, automobile floor mats, mud flaps for trucks, ball mill liners, tubings, fan belts, conveyor belts and the like. Preferably, the rubber vulcanizates are used in wire coat stocks, carcass ply or overlay compounds for tires.

The present invention will be illustrated with reference to the following examples, which are only given for the purpose of illustration and are not to be interpreted as limiting. The percents and parts are based on weight unless indicated otherwise.

Example 1

General Procedure for the Preparation Resorcinol and m-Aminophenol Blends Into a 250-mL three necked round bottomed flask fitted with a mechanical stirrer, thermometer and reflux condenser, weigh and transfer the known quantities of resorcinol (M. Pt = 110 ⁰C) and m-aminophenol (M. Pt = 123 ⁰C) into flask. The contents of the flask were externally heated to completely melt them. The blend mixture normally melts at 120 - 130 ⁰C in about 15 - 30 minutes. After the complete melting of the blend mixture, it was stirred for about 15 - 30 minutes. Then it was discharged from the flask, cooled and the solidified solid blend was stored. The melting point of the blend was determined by the capillary tube method.

The blend compositions of various blends prepared from the melt blending of resorcinol and m-aminophenol and their melting points are summarized in the following Table 1.

Table 1

A plot showing the melting point behavior of resorcinol, m-aminophenol and the blend compositions are presented in Figure 1.

As can be seen from Figure 1, the melting point of resorcinol could be considerably lowered by blending resorcinol with another reactive methylene acceptor compound like m- aminophenol. With the use of lower melting methylene acceptor compounds, the blend compositions could be mixed at lower rubber processing temperatures and uniformly distributed in the rubber compounds to achieve the maximum performance. Theoretically, it may be possible that fuming of resorcinol could be reduced, if not eliminated, if the blends are used in the place of pure resorcinol in rubber compounds.

Example 2

When resorcinol, resorcinol based derivatives and resins are used in rubber compounds, during rubber compound mixing, fuming of resorcinol can be observed. This is due to the volatile or sublimation nature of resorcinol and is present as an un-reacted monomer in the derivatives and resins. In order to determine the volatility of a material, thermo gravimetric analysis (TGA) data is obtained. Table 2 shows the thermo gravimetric analysis results of resorcinol, m-aminophenol and their blends

From the Table 2 results, it is obvious that the blends of this invention showed lower weight losses, and therefore expected to be less volatile at elevated temperatures than the commercially available pure resorcinol Due to reduced weight losses at the rubber processing temperatures, the use of blends, in the place of resorcinol, could provide improved performances during the mixing of rubber compounds

Example 3

The natural rubber compounds used for testing were prepared in three stages

The rubber master batch was mixed in the first stage to about 150 ⁰C in a Banbury mixer In a second stage, a methylene acceptor, with the inclusion of a cobalt salt was then mixed into an appropriate amount of the master batch on the Banbury mixer at about 145 ⁰C The insoluble sulfur, accelerator and appropriate amount of HMMM were mixed in the third stage at about 90 - 100 ⁰C The test compounds were conditioned overnight in a constant temperature room at about 23 ⁰C and 50% relative humidity The compounds were then tested for rheometer cure, shaped and optimum cured at 150 ⁰C for the evaluation of mechanical properties

Cure properties were measured with an Alpha Technology MDR 2000 Rheometer at 150 ⁰C, 1° arc and 1 67 Hz according to ASTMD 5289 and ISO 6502 test methods

In such an oscillating disc rheometer, compounded rubber samples are subjected to an oscillating shearing action of constant amplitude The torque of the oscillating disc embedded in the stock required to oscillate the rotor at the vulcanization temperature is measured The values obtained from this cure test are very significant since changes in the rubber or the compounding recipe are very readily detected In general, it is advantageous to have rubber compositions with fast cure rates.

From the Table 3 results, it is obvious that rubber composition containing the blends of this invention showed faster cure (T90) and higher cure rate index than resorcinol. The cure time (T90) for resorcinol is 13.12 minutes with 1.5 phr loading. This cure time was reduced to 9.53 minutes with 1.0 phr loading of the resorcinol - m-aminophenol blend (55:45 ratios). Decreasing the cure time of rubber compounds could be highly beneficial to the tire manufacturing processes. Therefore, the tire production rate could be increased by the use of the rubber compositions of this invention.

Example 4

The rubber composition, cure and scorch properties are presented in Table 4.

Compared to resorcinol, higher loading of the blends (2 phr) produced rubber compounds having faster cure (shorter T90) and scorchy (shorter Ts5) properties. When the blend loading was reduced to 1.0 phr, the rubber compositions showed better scorch and cure properties than resorcinol. This suggests, with the use of blends in place of resorcinol, the methylene acceptor loading in the rubber compounds could be reduced to as much as 50 % and still could achieve faster cure and similar scorch properties like resorcinol. From the Table 4, it is obvious that the rubber compositions showed good cure rate and scorch properties could be prepared and used with reduced levels of methylene acceptor blends of this invention than resorcinol.

Example 5

Table 5 illustrates the cure, scorch and Mooney viscosity properties determined using the non-silica rubber composition.

Due to very high reactivity, m-aminophenol showed faster cure (T90) and scorchier (Ts5) properties than the resorcinol and blends When the m-aminophenol content is increased from 20 to 70 weight percent in the blends, the cure time (T90) and scorch time (Ts5) were decreased

Example 6

The unaged and aged tensile and adhesion properties of the rubber compositions of this invention are presented in Table 6

When the rubber articles are reinforced, a high initial adhesion must be obtained between the rubber composition and the reinforcement, such as steel metal, and then be retained after thermal aging to ensure the extended life and good performance of the rubber article Referring to Table 6 and specifically to composition containing the resorcinol - MAP blends, the initial adhesion values were higher than resorcinol After the thermal, steam and humidity aging, high levels of adhesion were achieved From these test results, it is obvious that the adhesive bond between rubber compound and steel cord has been remarkably improved by the addition of blends of this invention Compared to resorcinol, the blends containing rubber compounds showed a marked improvement in tensile strength properties Example 7

In this example, the Rubber Process Analyzer (RPA) 2000 was used to determine dynamic mechanical properties.

The RPA 2000 is capable of testing uncured or cured rubber with a high degree of repeatability and reproducibility. The tests and subtests available include frequency sweeps at constant temperature and strain, curing at constant temperature and frequency, strain sweeps at constant temperature and frequency and temperature sweeps at constant strain and frequency. The accuracy and precision of the instrument allows reproducible detection of changes in the compounded sample. The values reported for the storage modulus, (G') and tan delta (δ) are obtained from a strain sweep and frequency sweep at 60 ⁰C on the cured samples. The data is presented in Table 7.

This data clearly demonstrates that the blends of this invention show good dynamic modulus properties in the cured rubber compounds.

Example 8

Following the preparative details illustrated in Example 1, blend samples of resorcinol (M. Pt = 110 ⁰C) and 3-diethylamino phenol (M. Pt = 78 ⁰C) were also prepared and tested in rubber compounds. Two blends were prepared at 50:50 and 70:30 weight ratios of resorcinol and 3-diethylamino phenol (3-DEAP). Both of these blend samples appeared as highly viscous liquids. The cure, tensile and steel cords adhesion properties obtained on the rubber compositions containing these blends are shown in Table 8.

The vulcanized rubber obtained from the rubber composition containing blends of this invention not only exhibits improved tensile strength but, also, exhibits much improved unaged, heat, steam, humidity and salt water aged adhesion properties, which indicates excellent cured rubber compound properties. Accordingly, a rubber product having excellent rubber strength properties can be obtained by applying the rubber composition of the present invention to a rubber material to be reinforced with steel cord or other reinforcing materials.

Whereas the particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention.

Claims

1. An improved vulcanization rubber composition comprising (i) a rubber component selected from natural and synthetic rubber; and (ii) a methylene donor; and (iii) a blend containing resorcinol and m-aminophenol derivative type material as the methylene acceptor, which can be prepared by melt blending of resorcinol with another meta-substituted phenolic derivative comprising the following chemical structure:

wherein R, Ri and R₂ can be independently hydrogen; hydroxyl; acetyl; benzoyl; alkyl such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, octyl, nonyl, decyl, dodecyl and pentadecyl; 2-hydroxyethyl,

2-hydroxypropyl and 2-hydroxybutyl; cyclopentyl, cyclohexyl and cycloheptyl; aryl such as phenyl and substituted phenyls; and aralkyl such as benzyl or alkylaryl such as alkylphenyls.

2. The improved rubber composition of Claim 1 wherein the methylene acceptor blend composition comprising a mixture consisting of resorcinol and m-aminophenol.

3. The improved rubber composition of Claim 1 wherein the methylene acceptor blend compound can be prepared by melt blending of resorcinol with m-aminophenol or its derivatives.

4. The improved rubber composition of Claim 1 wherein the meta-substituted phenolic derivative that can be used to prepare the methylene acceptor blend is selected from the group comprising m-aminophenol, N-methyl-m-aminophenol, N,N-dimethyl-m- aminophenol, N-ethyl-aminophenol, N,N-diethyl-m-aminophenol, N-butyl-m- aminophenol, N,N-dibutyl-m-aminophenol, 3-amino-5-methylphenol, 3 -N- methylamino-5-methylphenol, 3-amino-5-ethylphenol, 3-N-methylamino-5- ethylphenol, N,N-dimethyl-3 -amino-5 -methylphenol, N-methyl-3 -amino-5 - propylphenol, 3 -hydroxy diphenylamine, 3-hydroxy-4'-methyl-diphenylamine, 3- hydroxy-2'-methyl-diphenylamine, 3-hydroxy-4'-methoxy-diphenylamine, 3- hydroxy-N-naphthyl-aniline, 2-chloro-3'-hydroxy-diphenylamine and 3-hydroxy-3'- methoxy-4'-methyl-diphenylamine.

5. The improved rubber composition of Claim 1 wherein the rubber component can be any cis-l,4-polyisoprene (natural or synthetic), polybutadiene, polychloroprene and the copolymers of isoprene and butadiene, copolymers of acrylonitrile and butadiene, copolymers of acrylonitrile and isoprene, copolymers of styrene, butadiene and isoprene, isobutylene rubber (butyl) and ethylene-propylene rubber (EPDM), copolymers of styrene and butadiene and blends.

6. The improved rubber compound of Claim 1 wherein the methylene donors suitable for use include hexamethylenetetramine, hexaethoxymethylmelamine, hexamethoxymethylmelamine, 2-nitro-2 -methyl -1- propanol (NMP), trioxane and polymers of formaldehyde such as paraformaldehyde.

7. The improved vulcanizable rubber composition of Claim 1 wherein the vulcanization rubber compound prepared may also include additives such as sulfur, accelerator, carbon black, cobalt salts, stearic acid, silica, sulfur, zinc oxide, fillers, antioxidants and softening oils.

8. The improved vulcanizable rubber composition of Claim 1 wherein the meta- substituted phenolic compound used in the preparation of methylene acceptor can be selected from the group consisting of m-aminophenol, N-methyl-m-aminophenol, N, N-dimethyl-m-aminophenol, N, N-diethyl -m-aminophenol and 3 -hydroxy diphenylamine, 3-hydroxy-4'-methyl-diphenylamine, 3 -hydroxy-2' -methyl - diphenylamine and 3-hydroxy-4'-methoxy-diphenylamine.

9. The improved vulcanizable rubber composition of Claim 1 wherein the methylene acceptor blend contains resorcinol.

10. The improved vulcanizable rubber composition of Claim 1 wherein the weight ratio of the components resorcinol: m-aminophenol is preferably in the range of 99:1 to 1 :99 and, in particular from 85:15 to 15: 85.

11. The use of the improved vulcanizable rubber composition of Claim 1 in the preparation of composite products, including tires, power belts, conveyor belts, printing rolls, rubber shoe heels and soles, rubber wringers, automobile floor mats, mud flaps for trucks, ball mill liners, tubings, fan belts, conveyor belts, and the like.