WO2000061673A1

WO2000061673A1 - The elimination of cobalt salts in rubber formulations using modified melamine resins

Info

Publication number: WO2000061673A1
Application number: PCT/US2000/007436
Authority: WO
Inventors: Charles M. Hoff, Jr.; John Colin Brogan
Original assignee: Cytec Technology Corp.
Priority date: 1999-04-14
Filing date: 2000-03-21
Publication date: 2000-10-19
Also published as: AU3904600A

Abstract

Substantially cobalt-free and cobalt-free vulcanizable rubber compositions having an uncured rubber; vulcanizing agent, and an additive selected from the group consisting of a self-condensing alkylated triazine resin having high imino and/or methylol functionality, an oligomer of a self-condensing alkylated triazine resin having high imino and/or methylol functionality, and mixtures thereof.

Description

THE ELIMINATION OF COBALT SALTS IN FORMULATIONS USING MODIFIED MELAMINE RESINS

FIELD OF THE INVENTION

This invention relates to rubber compositions having excellent rubber toughness, tire sidewall reinforcement and/or adhesion to tire cords employing high imino and/or methylol functional self-condensing alkylated triazine resin additives in the substantial absence of cobalt and resorcinol and resorcinol equivalent coreactants.

BACKGROUND OF THE INVENTION

Automobile tires, as well as other rubber articles, such as hoses, conveyor belts, transmission belts, and the like, are typically reinforced with cords, formed from metal wires or natural, synthetic, or metallic fibers. Rubber additives for improving adhesion of vulcanized rubber to brass coated steel cords and polyaramide or polyester cord include the combination of hexamethoxymethylmelamine or hexamethylenetetramine with resorcinol, a resorcinol equivalent, and/or a cobalt compound, such as cobalt naphthenate or stearate. Those combinations of organic compounds are quite effective for the purpose, but the use of resorcinol presents malodorous and possibly toxic hazards during rubber processing due to excessive filming of resorcinol, and cobalt is a heavy metal, which raises issues of toxicity and waste disposal.

Resorcinol-free vulcanizable rubber compositions are known. For example, U.S. Patent No. 5,298,539 discloses vulcanizable rubber compositions containing uncured rubber, a vulcanizing agent and at least one additive selected from the group consisting of derivatives of melamine, acetoguanamine, benzoguanamine, cyclohexylguanamine and glycoluril monomer and oligomers of these monomers. These derivatives are substituted on average at two or more positions on the monomer or each unit of the oligomer with vinyl terminated radicals and the composition is free of resorcinol. Another manner of eliminating resorcinol from vulcanizable rubber compositions has relied on the use of alternative coreactants. U.S. Patent No. 4,038,220 describes a vulcanizable rubber composition which comprises a rubber, a filler material, N- (substituted oxymethyl)melamine and at least one of α or β naphthol. This reference employs the monohydric phenols, α or β naphthol, as methylene acceptors in the resin forming reaction during vulcanization in the absence of resorcinol. The use of resorcinol-formaldehyde resin to replace resorcinol in vulcanizable rubber compositions is also known. A. Peterson, et. al., "Resorcinol Bonding Systems For Steel Cord Adhesion", Rubber World (August 1984).

In addition, U.S. Patent No. 5,792,805 discloses vulcanizable rubber compositions containing a self-condensing alkylated triazine resin and a cobalt salt, which provides improved cord adhesion without the need for resorcinol.

However, a continuing need exists for vulcanizable rubber compositions containing commercially available cost effective additives that improve the adhesion of vulcanized rubber to tire cords and improve rubber toughness without the use of resorcinol or cobalt. The present invention provides such compositions.

SUMMARY OF THE INVENTION

The present invention is directed to a cobalt free and substantially cobalt free vulcanizable rubber composition comprising (a) an uncured rubber, (b) a self-condensing alkylated triazine resin having high imino and/or methylol functionality represented by the formula (I)

wherein Z is selected from the group consisting of -N(R) (CH₂OR^l), aryl having 6 to 10 carbon atoms, alkyl having 1 to 20 carbon atoms and an acetyl group, each R^l is independently selected from the group consisting of hydrogen or an alkyl group having 1 to 12 carbon atoms and each R is independently selected from the group consisting of hydrogen and -CH₂OR^l, wherein R^l is as previously described, provided that at least one R is hydrogen or -CH₂OH and at least one R¹ is selected from the alkyl group; and (c) a vulcanizing agent, such as, e.g., sulfur. The vulcanizing agent is preferably present in an amount of from about 4 to about 8 parts per hundred ("phr") based on 100 parts of uncured rubber. Optionally, the compositions of the invention may also comprise a metal compound, such as zinc oxide.

Z is preferably -N(R) (CH₂OR'), phenyl, methyl or cyclόhexyl. Most preferably, Z is -N(R) (CH₂OR^l), ue_^, a melamine derivative. Preferably, at least 2, more preferably at least 3 of the R groups of triazine resin are hydrogen and/or -CH₂OH. It is also preferred that at least one, more preferably at least two of the R¹ groups are a lower alkyl group having 1 to 6 carbon atoms, most preferably methyl or butyl. Most preferably, R is hydrogen and R¹ is a mixture of hydrogen and methyl.

Preferably, at least two R groups independently selected from the group consisting of hydrogen and -CH₂OH, at least one R¹ group is a lower alkyl group having 1 to 6 carbon atoms. More preferably, Z is N(R) (CH₂OR'), each R group is independently selected from the group consisting of hydrogen and -CH₂OH, each R¹ group is lower alkyl having 1 to 6 carbon atoms, and the additive is selected from the group consisting of derivatives of melamine, benzoguanamine, cyclohexylguanamine, acetoguanamine and oligomers thereof. The additive may also be a mixture of triazine (i) and oligomer (ii). Uncured rubbers useful in the invention include natural rubber and synthetic rubbers, such as butadiene-styrene copolymers, polyisoprene, polybutadiene, polychloroprene, nitrile and ethylene propylene copolymers, terpolymer rubbers, acrylo and fluoro elastomers, block copolymer rubbers.

The self-condensing alkylated triazine resin employed in this invention can also be an oligomer of the triazine resin of Formula I or a mixture of the monomeric triazine and the oligomers thereof. Oligomers of this invention include dimers, trimers, tetramers and the like of the triazine compound of Formula I. Generally, such oligomers are joined by a methylene radical or the radical -CH₂OCH₂- with at least one R group of the oligomer being hydrogen. In a preferred embodiment, the substantially cobalt free vulcanizable rubber composition of the invention comprises (a) an uncured rubber; (b) an additive, present in an amount sufficient to improve adhesion of the uncured rubber to a substrate upon curing, the additive selected from the group consisting of (i) a self-condensing alkylated triazine resin having high imino and/or methylol functionality represented by the formula (II)

(ii) an oligomer of (i), and (iii) a mixture of (i) and (ii), wheie each R¹ is independently selected from an alkyl group having 1 to 6 carbon atoms and each R is independently selected from the group consisting of hydrogen and -CH₂OR², wherein R² is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, provided that at least one of R or R² is hydrogen. Preferably, R¹ is methyl or butyl, and al least two R groups independently selected from the group consisting of hydrogen and -CH₂OH. More preferably at least two R groups are -CH₂OH. Typically, the degree of polymerization of said additive is in a range from about 1.5 to about.3. A typical cobalt-free vulcanizable rubber composition according to the invention comprises from about 0.2 to about 10 parts by weight of the additive per 100 parts of the composition, and may be in the form of a dry flowable powder or a liquid. The compositions of the invention may also comprise a support, which is typically silica, calcium silicate or a mixture thereof.

DETAILED DESCRIPTION OF THE INVENTION As used herein, the term "substantially cobalt-free" refers to compositions that do not contain an effective amount of a cobalt based adhesion composition, but may contain amounts of such compositions that do not appreciably improve the adhesion of rubber to a cord material. A substantially cobalt free composition in accordance with the invention preferably contains cobalt naphthenate or stearate in an amount of no more than about 0.75 percent by weight of rubber. In addition, as used herein, the term "cobalt-free" refers to any composition that is free of any cobalt l ased adhesion composition, other than the trace amounts that may occur as an impurity. Also, as used herein, the term "uncured rubber" refers to a rubber composition that has not been subjected to a time and temperature profile sufficient to achieve at least 80 percent of the maximum torque.

The present invention is directed to cobalt-free and substantially cobalt-free vulcanizable rubber compositions that comprises an uncured rubber, a vulcanizing agent, and a self-condensing alkylated triazine resin, having high imino and/or methylol functionality, represented by formula (I)

wherein Z is selected from the group consisting of -N(R) (CH₂OR^l), aryl having 6 to 10 carbon atoms, alkyl having 1 to 20 carbon atoms and an acetyl group, each R¹ is independently selected from the group consisting of hydrogen or an alkyl group having 1 to 12 carbon atoms and each R is independently selected from the group consisting of hydrogen and -CH₂OR', wherein R¹ is as previously described, provided that at least one R is hydrogen or -CH₂OH and at least one R¹ is selected from the alkyl group; and (c) a vulcanizing agent, which is preferably present in an amount of from about 4 to about 8 parts per hundred ("phr") based on 100 parts of uncured rubber, where, as used herein, "phr" is interchangeable with percent by weight of cured or uncured rubber. The self-condensing alkylated triazine resin is present in an amount sufficient to provide acceptable adhesion to wire, as determined by ASTM test D-2229-93, typically in the range of from about 0.2 to about 10 parts per 100 parts of the composition.. Z is preferably -N(R) (CH₂OR^*), phenyl, methyl or cyclohexyl. Most preferably, Z is -N(R) (CH₂OR'), e_^, a melamine derivative. Preferably, at least 2, more preferably at least 3 of the R groups of triazine resin are hydrogen and or -CH₂OH. It is also preferred that at least one, more preferably at least two of the R¹ groups are a lower alkyl group having 1 to 6 carbon atoms, most preferably methyl or butyl. Most preferably, R is hydrogen and R¹ is a mixture of hydrogen and methyl.

The substantially cobalt- free vulcanizable rubber compositions of this invention advantageously employ the self-condensing alkylated triazine resins having high imino and/or methylol functionality represented by formula I without the need of cobalt based adhesion compositions , resorcinol, or resorcinol equivalents, and, thus, may be referred to as one-component ("o-c") resins. It is believed in prior art compositions, that the alkoxymethylmelamines or hydroxymethyl melamine in rubber compositions formed a network through reaction with resorcinol to improve tire cord adhesion. Without being bound to theory, it is believed in the present invention that the high reactivity of the self-condensing alkylated triazine resins having high imino and/or methylol functionality allows those resins to self-condense and form a network to improve tire cord adhesion and/or sidewall reinforcement in the vulcanized rubber obtained from the substantially cobalt- free vulcanizable compositions of the present invention without the need of resorcinol as a coreactant. Moreover, the self-condensing alkylated triazine resins provide sufficient adhesion, so that cobalt based adhesion enhancers are not required, and, thus, can be eliminated.

High imino alkylated triazine resins for use in the substantially cobalt-free vulcanizable rubber compositions of this invention are available commercially. Typical commercially available high imino alkylated triazine resins, which are available from Cytec Industries, Inc., include, without limitation: 1. A high imino methoxymethyl melamine- formaldehyde resin having

3.8 units of combined formaldehyde and 2.8 units of methyl groups per unit of melamine (MF_{3 g}Me_{2 8}), 34 molar % NH, 56 molar % methylation, 10 molar % methylol and a degree of polymerization of 1.8;

2. A high imino mixed methoxymethyl/hutoxymethyl melamine- formaldehyde resin having 3.8 units of combined formaldehyde, 1.7 units of methyl groups and 1.6 units of n-butyl groups per unit of melamine (MF_{3 g}Me, ₇Bu, _j), 31 molar % NH, 34 molar % methoxy, 32 molar % n-butoxy; 3 molar % methylol and a degree of polymerization of 2.3;

3. A high imino methoxymethyl melamine-formaldehyde resin having

4.0 units of combined formaldehyde and 2.8 units of methyl groups per unit of melamine (-vD oMe-. _g), 30 molar % NH, 58 molar % methylation, 12 molar % methylol and a degree of polymerization of 2.3;

4. A high imino methoxymethyl melamine-formaldehyde resin having 4.4 units of combined formaldehyde and 3.3 units of methyl groups per unit of melamine (MF₄₄Me₃₃), 22 molar % NH, 66 molar % methylation, 18 molar % methylol and a degree of polymerization of 1.75; and

5. A high imino butoxy methyl melamine-formaldehyde resin having

4.1 units of combined formaldehyde and 2.7 units of n-butyl groups per unit of melamine (MF₄ ,Bu₂₇), 26 molar % NH, 58 molar % butylation, 16 molar % methyol and a degree of polymerization of 2.7. Methylol functional alkylated triazine resins for use in the substantially cobalt-free vulcanizable rubber compositions of this invention are also available commercially. Typical commercially available methylol functional alkylated triazine resins available from Cytec Industries, Inc., include, without limitation:

1. A methoxymethyl-methylol functional melamine resin having 4.9 units of combined formaldehyde and 2.4 units of methyl groups per unit of melamine

(MF₄₉Me₂₄), 12 molar % NH, 48 molar % methyl, 40 molar % methylol and a degree of polymerization of 2.0; and

2. A methoxymethyl-methylol functional melamine resin having 5.3 units of combined formaldehyde and 3.3 units of methyl groups per unit of melamine (MF₅₃,Me₃₃), 4 molar NH, 66 molar % methylation, 30 molar % methylol and a degree of polymerization of 2.5.

An exemplary commercially available self-condensing alkylated triazine resin having both high imino and methylol functionality available from Cytec Industries,

Inc., is a partially methylated melamine-formaldehyde resin having 3.6 units of combined formaldehyde and 2.0 units of methyl groups per unit of melamine

38 molar

% NH, 40 molar % methyl, 22 molar % methylol and a degree of polymerization of 1.8. As noted above, the self-condensing alkylated triazine resins of this invention having high imino and/or methylol functionality can be oligomeric. Such oligomers can be represented by the formula

wherein p is 2 to 10, L is methylene or the radical -CH₂OCH₂- and Z and R are described as above. Generally, the self-condensing alkylated triazine resins of this invention are mixtures of monomers and oligomers having a degree of polymerization, i.e., the average number of triazine units per molecule, of less than 3.0. Typically, the degree of polymerization of the triazine resins of this invention is in a range from about 1.5 to.3.0. The self-condensing alkylated triazine resins having high imino and/or methylol functionality are employed as adhesion promoting additives in the present invention by addition to substantially cobalt-free vulcanizable rubber compositions in amounts in the range from about 0.2 to 10 parts by weight per 100 parts of rubber (hereinafter "phr"). However, any amount of the self-condensing alkylated triazine having high imino and/or methylol functionality may be used that provides the vulcanized rubber composition with the desired tire cord adhesion and rubber toughness properties.

The self-condensing alkylated triazines may be employed in the substantially cobalt-free vulcanizable compositions of this invention in the form of liquids, solids or as dry powders on a support. Preferably, the self-condensing alkylated triazine resin having high imino and/or methylol functionality is on a support selected from the group consisting of silica, calcium silicate or the like. Generally, an amount of resin is mixed with the support in a ratio to provide a dry flowable powder, 70% by weight resin to 30% by weight support.

The self-condensing alkylated triazine resins having high imino and/or methylol functionality can be mixed with a support by heating the resin to a temperature in the range from about 50° to about 75 °C and slowly charging the heated resin to a Hobart mixer containing the support while mixing at low speed. The mixture is then agitated for an additional 5 to 10 minutes. If the resin contains solvent then the mixture may be dried in an oven at about 50°C. Calcium silicate and silica based supports are commercially available under the tradenames MICROCEL®-E or H1SIL® SC-72 from World Minerals, Inc., (Lompoc, California) and PPG Industries (Pittsburgh, Pennsylvania), respectively.

Generally, if a support is used, the resin is present in an amount from about 55 to about 85, more preferably about 65 to about 75 percent by weight of the combined resin and support.

The principal components of the substantially cobalt- free vulcanizable rubber compositions comprise rubber, which may be natural rubber or synthetic rubber, or a mixture ofnatural and synthetic rubbers, and a vulcanizing agent such as sulfur. Rubbers such as butadiene-styrene copolymers, polyisoprene, polybutadiene, polychloroprene, nitrile and ethylene propylene copolymers, terpolymer rubbers, acrylo and fluoro elastomers, block copolymer rubbers and the like can be used. Other conventional additives for rubber compositions may be included in rubber compositions of the present invention, such as carbon black, silica, zinc oxide, stearic acid, antioxidants, vulcanizing accelerators, and the like in preferred rubber compositions according to the present invention. The high imino alkylated adhesion promoting additives employed in this invention can be used in rubber compositions which also contain hydroxymethylmelamines or alkoxymethylmelamines or the like, but in a substantial absence of resorcinol or its equivalent. Equivalents of resorcinol are compounds that can be used instead of resorcinol as methylene-acceptors in rubber compositions. Some resorcinol equivalents are described, for example, in U.S. Patent No. 4,605,696.

A typical prior art vulcanizable rubber wire skim coat formulation of the prior art and the typical ranges of the components of such formulations are set forth below in Table I.

= enzo azy - - - u y su enam e CBS = Benzothiazyl-2-cyclohexyl sulfenamide

HMMM = Hexamethoxymethylmelamine

The hexamethoxymethylmelamine of the wire skim coat formulations given in Table I can be replaced or combined with self-condensing alkylated triazine resins having high imino and/or methylol functionality and the cobalt naphthenate and resorcinol removed to provide the substantially cobalt-free vulcanizable rubber composition of this invention. The self-condensing alkylated triazine resins having high imino and/or methylol functionality employed in this invention can be added into rubber compositions by conventional means and methods for the addition of melamine additives in rubber compositions, such as for hydroxymemlymelamines or methoxymethylmelamines. A well known method for mixing rubber compounds is by mixing in a B anbury mixer. In one typical method, additives which are not reactive are blended first into the rubber at temperatures up to about 140°C in the Banbury mixer. Vulcanizing agents, accelerators and adhesion promoters arc added in a second mixing step al temperatures from about 90° to 100°C. Such methods of preparation, are well within the knowledge of those skilled in the art.

EXAMPLES

The following non-limiting examples are merely illustrative of the preferred embodiments of the present invention, and are not to be construed as limiting the invention, the scope of which is defined by the appended claims.

A resorcinol and cobalt free wire coat master batch for forming substantially cobalt-free vulcanizable rubber compositions useful for precoating tire wires was prepared with the ingredients listed in Table II.

TABLE II

Various wire coat compositions were then formed by adding additional components to portions of the master batch to allow the testing and comparison of the resorcinol and cobalt free compositions with compositions containing cobalt and resorcinol. The components added to the master batch with the total parts of each composition are provided in Table III. Compositions 1 and 2 are controls, containing HMMM and various levels of cobalt naphthenate, composition 3 is similar to compositions 1 and 2, but is cobalt free, compositions 4, 4A, 4B, 6, 7, 10, 11, and 13 each contain a self-condensing alkylated triazine resins having high imino and or methylol functionality and various levels of cobalt, _Q and compositions 5, 8, and 12 each contain a self-condensing alkylated triazine resins having high imino and/or methylol functionality, and are cobalt free. The compositions were then tested to compare the compositions of the invention with those containing cobalt.

5

Samples of the compositions listed in Table III were subjected to rheometer tests using an oscillating disk rheometer in accordance with ASTM D-2084 to determine the minimum torque, maximum torque, scorch time, and the cure time to 90 percent of the maximum torque for each composition. The results are provided in Table IV.

5

TABLE IV

10

15

20

Rheometer Scorch Test

Rheometer scorch values for all samples in this study were approximately equal.

25

Rheometer Cure Test

Rheometer cure rates ("T90") varied depending on the type of resin involved and the amount of cobalt level present in each formulation. In general the presence of cobalt tends to produce a faster curing compound. Reducing cobalt levels in the controls 30 increased the time to 90 percent torque with a difference between full cobalt and no cobalt of almost 4.0 minutes. Removing the cobalt from the compositions containing C138L increased the T90 by 7minutes, but reducing level of C138L slightly increased the T90 by 1.5 minutes. Reducing the cobalt levels in the compositions containing C138M increased the cure time from 17.9 minutes for full cobalt to 30.2 minutes for no cobalt. Aging the 35 C138M resin gave an increase in T90 of about 30 seconds over the fresh sample. Reducing cobalt levels for the C132M compositions increased cure times from 20.4 minutes for full cobalt to 35.1 minutes for no cobalt. Reducing cobalt by half and C132M by Va, and increasing the accelerator by 15 percent increased T90 by almost 4.5 minutes in sample 13 when compared to sample 11.

The compositions listed in Table III were also tested for their tensile properties and hardness, and subjected to the DeMattia test in accordance with ASTM D813-95. The results of those test are given in Table V.

TABLE V

* Tensile modulus at 200 percent elongation; sample failed at less than 300 percent.

Reduced cobalt levels produced increased tensile values which varied from slight in the control samples to significant in the self condensing resins of the invention, which do not require the resorcinol. All self condensing resin samples, whether with or without cobalt, gave higher tensile values than the controls. Reduced cobalt levels produced increased tensile values which varied from slight (control) to significant (self condensing resins). Reducing the cobalt level of the controls had a slight positive affect on tensile strength, as did the removal of cobalt in the C138L compositions. However, a reduction in the level of C138L had no affect on the tensile value. Reducing cobalt levels gave a significant positive directional improvement in the tensile strength of C138M compositions, and the fresh and aged C138M samples were equal in tensile strength. Reducing the cobalt level also gave improved tensile strength in the C132M compositions. Reducing cobalt by half and C132M by a third, and increasing the amount of accelerator by 15 percent gave higher tensile strength values when compared to the control. Modulus Test

All self condensing resin samples, whether with or without cobalt, had equal to slightly lower modulus values compared to the control. In general, reducing cobalt in the self condensing resins gave mixed results ranging from a slight decrease with C132M to no affect with C138M to a slight improvement with C138L. Reducing cobalt with the control samples slightly decreased the modulus. Removing the cobalt from the C138L samples improved the modulus from 19 to 21.4 Mpa, but a reduced level of C138L had no affect on modulus. For the C138M samples, reducing the level of cobalt had no affect on modulus, and aged and fresh C138M samples had equal modulus. However, reducing the cobalt level in the C132M samples slightly reduced the modulus. Reducing cobalt by half and C132M by a third, and increasing the and accelerator by 15 percent gave essentially the same modulus for sample 13 as that obtained for sample 11.

DeMattia Crack Growth Test

All self condensing resins had higher DeMattia results than the control. In all cases the data showed that reducing or eliminating cobalt tended to greatly improve the DeMattia Crack Growth resistance. Reducing cobalt in the controls had no affect on the results in the DeMattia test. However, reducing the cobalt level in the C138L samples improved the DeMattia results by about 25 percent, and reducing the level of C138L resin gave mixed results, so that no trends were observed in either direction. Reducing the cobalt level in the C138M samples provided greatly improved results, such that the difference between full cobalt and no cobalt was 56 percent, although aged C138M gave slightly lower, but insignificant, DeMattia results than the fresh sample. Reducing the cobalt level in the C132M compositions also provided a 58 percent improvement in DeMattia results, while reducing cobalt by one half and C132M by a third with a 15 percent increase in accelerator giving a 38 percent improvement over the sample 11 control compound.

Shore A Durometer Hardness While all self condensing resins had similar hardness values to the control, each time cobalt was eliminated, the hardness dropped between 2 and 3 points compared to the control compound for the series. Reducing the cobalt in the controls results in a slight drop in hardness. However, removing the cobalt level in the C138L compositions causes a 2 point drop in hardness, but reducing the level of C138L had no affect on hardness. Reducing the cobalt level in the C138M compositions caused a 3 point drop in hardness from full cobalt to no cobalt with the aged C138M having an identical hardness value to that of the fresh sample. Reducing the cobalt level also caused a 2 point drop in the hardness of the C132M compositions, and reducing cobalt by a half and C132M by a third, and increasing the accelerator by 15 percent provided a 2 point drop in hardness compared to sample 1 1 control compound.

Aged and unaged samples of the materials listed in Table III were subjected to adhesion tests, and the results are given in Table VI.

TABLE VI

Original (Unaeed') Adhesion Test and Wire Coverage

All Self condensing compounds had much higher adhesion than the controls. Self condensing compound 4-B, 7, and 11 had the highest pull-out values of all, which were all significantly higher than the control. In the self condensing compounds, reducing cobalt levels didn't significantly cause any severe drop-ofFin pull-out values. Reducing the cobalt levels in the controls gave insignificantly lower adhesion results, but reducing the cobalt level had no affect on the adhesion of the unaged C138L compositions, and reducing the level of C138L resin gave a slight improvement in the adhesion. Reducing the level of cobalt in the C138M compositions gave mixed results with half the original cobalt (7) level giving the highest adhesion, followed by no cobalt (8), and the aged C138M composition gave slightly higher adhesion than the fresh sample (6). Reducing the cobalt level of the C132M samples gave insignificantly lower adhesion. Reducing cobalt by half and C132M by a third, and increasing the amount of accelerator by 15 percent did not significantly raise or lower the adhesion compared to the control (11).

All samples were judged to have wire coverage ratings of 100 percent. In no case did the reduction or elimination of cobalt cause any visible change in the wire coverages.

Heat Aeed Adhesion and Wire Coverage Tests

The highest adhesion levels for samples heat aged for five days at 90°C were obtained with the C138M without cobalt, sample 8, and sample 12, the C132M without cobalt. The self condensing resins had pull-out values that were slightly lower or slightly higher than the HMMM controls. In all cases where cobalt was eliminated, those compounds exhibited improved, i.e., higher adhesion, than the corresponding control for the particular compound involved. The sample 1 control had a much lower adhesion than all of the other compounds in the series, but may be an anomalous result, as the same formulation with Vi cobalt (2) and no cobalt (3) provide much higher adhesion. Reducing the cobalt in the C138L compositions gave slightly higher heat aged adhesion, and reducing levels of C138L had no significant affect on heat aged adhesion. Eliminating cobalt entirely in C138M gave much higher results than the normal cobalt loading (6) or one half cobalt (7), and aged C138M gave equal adhesion to the fresh sample (6). Eliminating cobalt in the C132M compositions also provided higher adhesion. All self condensing resins had wire coverage values equal to or greater than the control. Cobalt reduction and/or elimination produced slightly better wire coverage ratings in the heat aging test. Reducing the cobalt level in the controls and in the C138L compositions caused a slight improvement in heat aged wire coverage, but reducing the level of C138L did not affect wire coverage. Reducing the cobalt level in the C138M compositions also provided a slight improvement in adhesion, and aged C138M was equal to the fresh sample. Eliminating the cobalt caused no decrease in wire coverage in the C132M samples.

7-Dav Humidity Aging Test and Wire Coverage

All samples in this series, which were aged for seven days at 98 percent relative humidity and 80°C, had higher pull-out values than those in the heat aging series.

In all cases except C132M (11), the self condensing resins had equal or greater pull-out compared to the HMMM control. As was the case with the heat aging data, the highest pull-out values were obtained with the C138M with no cobalt (8) and the C132M with no cobalt (12). In no case, did the elimination of cobalt cause any serious drop-off in wire pull-out values. For the first time, reducing the level of C138L had a noticeable lowering affect on wire adhesion. Reducing cobalt in the control or the C138L samples had no affect on humidity adhesion. However, reducing the level of C138L resin had no affect at the initial reduction level (4-A); but caused poorer adhesion at the lowest level (4-B). Reducing cobalt levels in the C138M samples gave improved adhesion from full cobalt loading (6) to no cobalt loading (8), and aged C138M had an adhesion that is identical to that of the fresh sample (6). Eliminating the cobalt gave a 24 percent improvement in the C132M samples. All samples in this series generally had lower wire coverage ratings than in the heat aging study. Wire coverage ratings for the HMMM control and the self condensing resins were about equal, regardless of cobalt levels, i.e. reducing or eliminating cobalt did not seriously affect wire coverage. The one exception was C132M resin. This resin was the most sensitive to cobalt presence. With the normal cobalt loading (sample 11), wire coverage was barely detectable. Eliminating the cobalt from this sample altogether (sample 12) produced the highest wire coverage rating of all the samples. Reducing the level of C138L (4-A, 4-B) also produced a dramatic reduction in wire coverage compared to the control (4), which had the highest level of resin C138L. Reducing or eliminating cobalt caused no change in wire coverage in the control samples or in the C138M samples, but reducing cobalt in the C138L samples caused a slight decrease in wire coverage. Reducing levels of C138L caused a dramatic decrease in coverages from 70 to 20, and the coverage for the aged C138M sample was 20 points lower coverage than the fresh sample (50 vs 70). Eliminating cobalt caused a dramatic improvement in C132 resin samples, improving from 20 for full cobalt to 90 rating for no cobalt.

21 -Dav Humidity Aping and Wire Coverage In all cases, the self condensing resins C138L, C138M, and C132M had higher pull-out adhesion than the HMMM control after 21 days at 98 percent relative humidity and 80°C. As was the case in the heat aging and the 7-day humidity aging, the highest pull-out values belonged to samples (8) C138M and (12) C132M with no cobalt present. Likewise, as in the case of the 7-day humidity test, in no case did the reduction of cobalt cause a serious drop-off in wire adhesion values. Again, lowering the part level of C138L resin in formulations 4-A and 4-B caused a significant drop-off in wire adhesion pull-out values. Reducing the cobalt by half in the control samples gave a slight directional improvement in 21 -day humidity; but eliminating cobalt brought pull-out values back to the level observed with full cobalt loading, indicating that no significant overall change took place in the samples. Reducing cobalt levels in the C138L samples gave a slight loss of adhesion that was judged to be insignificant. Reducing the level of C138L gave a significant downward trend in adhesion, but reducing cobalt level from full loading (6) to half loading (7) in the C138M samples caused a slight drop-off in adhesion. The complete elimination the cobalt in the C138M samples gave a dramatic increase in adhesion over the full loading (6) or half loading (7), and aged C138M provided a increase in adhesion over the fresh sample (6). Reducing cobalt level in the C132M samples from full cobalt (11) to no cobalt (12) improved adhesion slightly.

Most samples in this series had lower wire coverage ratings than the 7-day humidity series. Exceptions were samples 8, 10, and 11, which were slightly higher. Wire coverage ratings for the HMMM control and the self condensing resins tended to be fairly equal with the exception of samples 9 and 13, regardless of cobalt level. Again, this indicates a negligible contribution by cobalt to wire coverage. Samples 8 (C138M/no cobalt) and 12 (C132M/no cobalt) showed marked improvements over their counterparts with full cobalt levels. Again, reducing the level of C138L resin produced a dramatic reduction in wire coverage compared to the control (4).

Claims

THE CLAIMS What is claimed is:

1. A substantially cobalt-free vulcanizable rubber composition comprising:

(a) an uncured rubber;

(b) an additive, present in an amount sufficient to improve adhesion of the uncured rubber to a substrate upon curing, the additive selected from the group consisting of (0 a self-condensing alkylated triazine resin having high imino and/or methylol functionality represented by the formula (I)

(ii) an oligomer of (i), and

(iii) a mixture of (i) and (ii) wherein Z is selected from the group consisting of -N(R) (CH₂OR^l), aryl having 6 to 10 carbon atoms, alkyl having 1 to 20 carbon atoms and an acetyl group, each R¹ is independently selected from the group consisting of hydrogen or an alkyl group having 1 to 12 carbon atoms, and each R is independently selected from the group consisting of hydrogen and -CH₂OR', wherein R' is as previously described, provided that at least one R is hydrogen or -CH₂OH and at least one R¹ is selected from the alkyl group; and

(c) a vulcanizing agent in an amount sufficient to cure the uncured rubber.

2. The substantially cobalt-free vulcanizable rubber composition according to claim 1, wherein at least two R groups are each independently selected from the group consisting of hydrogen and -CH₂OH.

3. The substantially cobalt- free vulcanizable rubber composition according to claim 2, wherein at least one R¹ group is a lower alkyl group having 1 to 6 carbon atoms.

4. The substantially cobalt-free vulcanizable rubber composition according to claim 3, wherein the additive is selected from the group consisting of derivatives of melamine, benzoguanamine, cyclohexylguanamine, acetoguanamine and oligomers thereof.

5. The substantially cobalt-free vulcanizable rubber composition according to claim 3, wherein Z is N(R) (CH₂OR').

6. The substantially cobalt-free vulcanizable rubber composition according to claim 5, wherein each R is independently selected from the group consisting of hydrogen and -CH₂OH.

7. The substantially cobalt-free vulcanizable rubber composition according to claim 6, wherein each R¹ group is lower alkyl having 1 to 6 carbon atoms.

8. The substantially cobalt-free vulcanizable rubber composition according to claim 1, wherein the additive is the oligomer (ii).

9. The substantially cobalt-free vulcanizable rubber composition according to claim I, wherein the additive is a mixture of triazine (i) and the oligomer (ii).

10. T e substantially cobalt-free vulcanizable rubber composition according to claim 1, wherein the uncured rubber is a natural rubber or synthetic rubber.

11. The substantially cobalt-free vulcanizable rubber composition according to claim 10, wherein the uncured rubber is selected from the group consisting of butadiene-styrene copolymers, polyisoprene, polybutadiene, polychloroprene, nitrile and ethylene propylene copolymers, terpolymer rubbers, acrylo and fluoro elastomers, block copolymer rubbers.

12. The substantially cobalt- free vulcanizable rubber composition according to claim 1 , wherein the vulcanizing agent is sulfur.

13. The substantially cobalt- free vulcanizable rubber composition according to claim 1, further comprising a metal compound.

14. The substantially cobalt-free vulcanizable rubber composition according to claim 13, wherein the metal compound is zinc oxide.

15. The substantially cobalt-free vulcanizable rubber composition according to claim 1, wherein the additive is in the form of a dry flowable powder.

16. The substantially cobalt-free vulcanizable rubber composition according to claim 1, wherein the additive is in the form of a liquid.

17. The substantially cobalt-free vulcanizable rubber composition according to claim 1, wherein the additive further comprises a support selected from the group consisting of silica, calcium silicate and mixtures thereof.

18. The substantially cobalt-free vulcanizable rubber composition according to claim 1, wherein the composition comprises from about 0.2 to about 10 parts by weight of the additive per 100 parts of the composition.

19. The substantially cobalt-free vulcanizable rubber composition according to claim 1, wherein the composition comprises no more than about 0.75 percent by weight cobalt naphthenate.

20. The substantially cobalt-free vulcanizable rubber composition according to claim 1, wherein the composition is cobalt free.

1. The substantially cobalt-free vulcanizable rubber composition according to claim 1, wherein the vulcanizing agent is present in an amount of from about 4 to about 8 parts per 100 parts of uncured rubber.

22. A substantially cobalt free vulcanizable rubber composition comprising:

(a) an uncured rubber;

(b) an additive, present in an amount sufficient to improve adhesion of the uncured rubber to a substrate upon curing, the additive selected from the group consisting of (i) a self-condensing alkylated triazine resin having high imino and/or methylol functionality represented by the formula (II)

(ii) an oligomer of (i), and (ϋi) a mixture of (i) and (ii) wherein each R^l is independently selected from an alkyl group having 1 to 6 carbon atoms and each R is independently selected from the group consisting of hydrogen and -CH₂OR², wherein R² is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, provided that at least one of R or R² is hydrogen.