Adhesion promoting systems for rubber compositions

Abstract

An adhesion promoting system for a rubber composition, wherein the system comprises a novolac resin prepared by reacting aldehyde A1 with a phenolic compound, and an organic manganese salt.

Description

Technical Field

[0001] The present invention relates to the field of adhesion promoting systems for rubber compositions. The present invention also relates to a rubber composition comprising an adhesion promoting system, a method of making a rubber article and a method of using the adhesion promoting system. Background Art

[0002] In the conventional manufacture of various rubber products such as automobile tires and conveyor belts, reinforcement materials such as metal or synthetic fibers are often used to improve their performance. In order to ensure the long-term performance of these reinforced rubber products, it is of utmost importance to provide adequate adhesion between the reinforcement materials and the rubber-based composition used to manufacture the rubber products. The most common solution to ensure such adequate adhesion is to introduce an adhesion promoter into the base rubber composition.

[0003] In this context, various adhesion promoters have been used in the art, including adhesion promoters based on so-called resorcinol novolacs as described in EP0440036A1 (Hesse et al.), or adhesion promoters based on resorcinol itself as described in US4148769A (Swarts et al.). As is well-known in the art, the use of resorcinol can cause health and environmental problems, in particular due to the evaporation of resorcinol under rubber processing conditions. In addition, adhesion promoters based on resorcinol are prone to premature aging, in particular under conditions of high temperature and / or high humidity. Adhesion promoters that do not contain resorcinol are described in EP0473948A2 (Singh et al.) and EP0827971A1 (Burkhart et al.). The adhesion promoters described in these references either lead to a slow vulcanization rate of the corresponding rubber blend or to undesirable smoke generation during rubber processing.

[0004] Other adhesion promoters known to improve the adhesion between reinforcement materials and rubber compositions are the use of cobalt salts. However, cobalt compounds are classified as potential human carcinogens and therefore have serious toxicity and environmental issues. In addition, the use of cobalt compounds is often associated with unstable supply chains and limited supply, which inevitably leads to higher costs. Patent application EP3636700A1 (Özkütükcü et al.) describes a rubber composition that is said to provide enhanced curing and adhesion properties, and the composition utilizes a very special zinc composition, which is called an active zinc composition and has a specific surface area in a very specific range. The special specifications of the required active zinc composition and the delicate process for obtaining it inevitably increase the overall technical complexity and the associated manufacturing costs.

[0005] Without questioning the technical advantages of the solutions known in the art, there is still a need for an adhesion promoting system for rubber compositions which at least partially overcomes the above-mentioned drawbacks. SUMMARY OF THE INVENTION

[0006] According to one aspect, the present invention relates to an adhesion promoting system for a rubber composition, wherein the system comprises a novolac resin and an organic manganese salt, the novolac resin being prepared by reacting an aldehyde A1 with a phenolic compound.

[0007] According to another aspect, the present invention relates to a rubber composition comprising the adhesion promoting system as described above and a rubber component.

[0008] In another aspect of the present invention, there is provided a method for manufacturing a rubber product, comprising the following steps:

[0009] a) providing an adhesion promoting system as described above;

[0010] b) adding the adhesion promoting system to the rubber component, thereby forming a rubber composition as described above; and

[0011] c) Optionally, vulcanizing or crosslinking or curing the rubber composition.

[0012] According to another aspect, the present invention relates to a method of using an adhesion promoting system as described above to promote adhesion between a rubber composition and a reinforcing agent in contact therewith. DETAILED DESCRIPTION OF THE INVENTION

[0014] According to a first aspect, the present invention relates to an adhesion promoting system for a rubber composition, wherein the system comprises a novolac resin prepared by reacting an aldehyde A1 with a phenolic compound, and wherein the adhesion promoting system further comprises an organic manganese salt.

[0015] In the context of the present invention, it has surprisingly been found that the adhesion promoting system as described above is particularly suitable for enhancing the adhesion properties of rubber compositions, in particular to reinforcing agents which are usually in contact with rubber compositions in conventional engineering rubber products.

[0016] It has also been found that the adhesion promoting system of the present invention can provide excellent adhesion properties to rubber compositions even under extreme conditions such as high temperature and high humidity. This is a particularly surprising finding because manganese salts are well known to be highly hygroscopic. Therefore, it would be intuitively expected that the use of manganese salts would result in poor adhesion properties under high humidity conditions, especially in combination with excessively high temperature conditions.

[0017] In addition, it has been found that the adhesion promoting system described herein can maintain the excellent mechanical properties and characteristics of the cured (or vulcanized) rubber composition, such as stiffness, hardness, flexibility or structural strength. More surprisingly, it has also been found that the adhesion promoting system maintains the outstanding characteristics related to the curing and processability of the rubber composition (such as curing speed, mixing and compounding performance, fluidity, extrudability, applicability, coating or molding) in the uncured (or unvulcanized) state.

[0018] Without being bound by theory, it is believed that these excellent properties and performance attributes are due, among other things, to the use of a specific combination of (a) a novolac resin prepared by reacting an aldehyde A1 with a phenolic compound, and (b) an organic manganese salt. Still without being bound by theory, it is believed that this specific combination of components together contributes to providing the rubber composition with favorable rheological properties (particularly viscosity properties) combined with excellent curing (or vulcanization) properties.

[0019] The adhesion promoting system described above also has one or more of the following advantageous advantages: (i) a simple and cost-effective manufacturing method based on readily available starting materials and a minimum of manufacturing steps; (ii) a simple formulation and a wide range of uses; (iii) relatively safe handling due to the use of small amounts of materials or products that may be harmful to humans or may cause environmental issues; and (iv) the ability to use metal-based salts with a stable and frictionless supply chain.

[0020] In the context of the present invention, a technically and economically viable alternative to the use of cobalt and cobalt salts as adhesion promoters for rubber compositions has been found. The use of organic manganese salts as described herein not only avoids the ESH (Environmental Safety and Health) issues typically associated with cobalt, but also significantly improves cost efficiency, considering that the cost of cobalt ore is 14 times higher than that of manganese ore.

[0021] Thus, the adhesion promoting system of the present invention is well suited for the manufacture of conventional reinforced engineered rubber products, such as pneumatic tires or conveyor belts, including automated industrial production lines for rubber products.

[0022] In the context of the present invention, the expression "organomanganese salt" is intended to mean a salt comprising a manganese cation and an organic anion, wherein the organic anion is in particular the conjugate base of an organic acid comprising at least one carbon-hydrogen covalent bond.

[0023] The adhesion-promoting system of the invention comprises as a first component a novolac resin which is prepared by reacting an aldehyde A1 with a phenolic compound.

[0024] The novolac resins used herein are not particularly limited as long as they are prepared by reacting aldehyde A1 with a phenol compound. Suitable novolac resins for use herein can be easily identified by those skilled in the art based on the disclosure of the present invention.

[0025] Advantageous aldehydes A1 for preparing the novolak resins are aliphatic monoaldehydes having one aldehyde group -CHO and 1 to 10 carbon atoms, which are preferably saturated.

[0026] In an advantageous aspect, the aldehyde A1 used herein is selected from formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, and any mixture thereof. In a particularly advantageous aspect, the aldehyde A1 used herein is selected from formaldehyde.

[0027] Virtually all phenolic compounds having at least one active hydrogen atom on the aromatic nucleus and at least one phenolic hydroxyl group (thus at least monofunctional in terms of reactivity with aldehydes) are suitable for preparing the novolac resins used herein. These include mononuclear or polynuclear phenolic compounds, which may be monofunctional, difunctional or trifunctional, or have a higher functionality in terms of reactivity with, for example, formaldehyde. The hydrogen atoms reactive toward aldehydes are those which are located in the ortho or para position on the aromatic nucleus relative to the hydroxyl group or another substituent having a +I and / or +M effect.

[0028] Suitable phenolic compounds for preparing novolac resins are mononuclear and polynuclear hydroxy-aromatic compounds which may have one hydroxyl group (monophenol) or more than one hydroxyl group (polyphenol) and which are optionally substituted by straight-chain, branched or cyclic alkyl groups having 1 to 20 carbon atoms, by oxyalkyl groups or halogen atoms and in which at least one active hydrogen atom is bonded to one of the aromatic nuclei. These phenolic compounds can be used alone or in mixtures. Phenol itself, the various cresol and xylenol isomers, isomers of ethylphenol, isomers of propylphenol or isopropylphenol and para- or ortho-substituted alkylphenols having up to 18, in particular up to 15, carbon atoms in the side chain can advantageously be used. Phenols substituted by olefinically unsaturated groups, for example o- or p-vinylphenol or p-isopropenylphenol, and phenolic substances reacted with dicyclopentadiene (DCPD) and / or styrene and / or rosin can also be used.

[0029] Polynuclear monophenolic compounds such as the isomeric hydroxynaphthalenes, which may optionally be substituted as described above, and mononuclear polyphenols such as catechol, resorcinol, hydroquinone, pyrogallol and phloroglucinol may also be suitably used.

[0030] Alternatively, polynuclear polyphenolic compounds such as diphenolylmethane, diphenolylethane, diphenolylpropane (bisphenol A) and isomers of bishydroxy aromatic compounds may be suitably used, wherein the aromatic structures are linked by direct bonds or vinyl, ether, carbonyl, sulfonyl, carbonyloxy or formamide groups, such as dihydroxybiphenyl, dihydroxystilbene, dihydroxydiphenyl ether, dihydroxybenzophenone, dihydroxydiphenyl sulfone, dihydroxyphenylbenzoate and dihydroxybenzanilide, which are optionally substituted with alkyl or alkoxy or halogen atoms as described above. Other polyhydroxy polynuclear phenolic compounds such as isomeric dihydroxynaphthalene and trihydroxy and polyhydroxy hydroxyaromatic compounds may also be suitably used to prepare the novolac resins used herein.

[0031] According to an advantageous aspect of the present invention, the phenolic compound used herein is selected from phenol, cresol, resorcinol, monoalkylphenol, and any mixture thereof. According to a particularly advantageous aspect, the phenolic compound used in the present invention is selected from (or includes) phenol.

[0032] In a typical aspect, the novolac resin used herein is prepared by reacting aldehyde A1 with a phenolic compound and further with an acid (catalyst). Suitable acids for use herein are not particularly limited and are advantageously strong mineral acids and / or acidic derivatives thereof, in particular sulfuric acid, hydrogen sulfates (in particular hydrogen sulfates of alkali metals or ammonium), half esters of sulfuric acid with aliphatic alcohols having 1 to 20 carbon atoms, phosphoric acid, hydrochloric acid, or organic acids, such as alkanesulfonic acids and arylsulfonic acids having 1 to 20 carbon atoms, in particular p-toluenesulfonic acid, and aliphatic monocarboxylic acids and dicarboxylic acids having 1 to 20 carbon atoms, such as chloroacetic acid, trifluoroacetic acid and in particular oxalic acid dihydrate. Lewis acids such as aluminum trichloride, zinc chloride and tin chloride as well as boron trifluoride and its etherates are also suitable.

[0033] In an advantageous aspect, the acid used herein is selected from oxalic acid, maleic anhydride, dodecylbenzenesulfonic acid, p-toluenesulfonic acid, and any mixture thereof. Preferably, the acid is selected from oxalic acid and p-toluenesulfonic acid.

[0034] The novolac resins used in the present invention can be prepared using conventional techniques and methods known to those skilled in the art. Exemplary preparation methods are described in, for example, GB 1448374 A (Hesse et al.).

[0035] According to another advantageous aspect, the adhesion promoting system of the invention further comprises a urethane (carbamate)-aldehyde resin, which is prepared in particular by condensing aldehyde A2 with an alkyl urethane. It has been found that such an adhesion promoting system can provide a further enhanced adhesion promoting effect to the rubber composition, in particular to the reinforcing agent.

[0036] The urethane-aldehyde resin used herein is not particularly limited and can be easily identified by those skilled in the art according to the present invention. In a typical aspect, the urethane-aldehyde resin is prepared by acid-catalyzed condensation of aldehyde A2 with alkyl urethane, optionally in the presence of a catalyst.

[0037] Aldehydes A2 suitable for the synthesis of urethane-aldehyde resins may be selected from the same compounds as listed under A1 in the context of the preparation of novolac resins described above.

[0038] In an advantageous aspect, the aldehyde A2 used herein is selected from formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, and any mixture thereof. In a particularly advantageous aspect, the aldehyde A2 used herein is selected to be formaldehyde.

[0039] The alkyl urethane used in the synthesis of the urethane-aldehyde resin includes, but is not limited to, monoalkyl urethane or alkylene bisurethane.

[0040] In an advantageous aspect, the alkyl urethane used to prepare the urethane-aldehyde resin is a monoalkyl urethane, which is particularly selected from ethyl urethane (ethyl carbamate), butyl urethane (butyl carbamate), 2-ethylhexyl urethane (2-ethylhexyl carbamate), decyl urethane (decyl carbamate), and any mixture thereof.

[0041] The urethane-aldehyde resin used in the present invention can be prepared by conventional techniques and methods known to those skilled in the art. Exemplary preparation methods are described in, for example, EP2432810A1 (Schafer et al.).

[0042] The adhesion promoting system of the present invention also comprises an organic manganese salt. The organic manganese salts used herein are not particularly limited as long as they comprise an organic anion. Suitable organic manganese salts for use herein can be readily identified by those skilled in the art based on the present invention.

[0043] In this context, inorganic manganese salts, such as manganese oxide, manganese sulfate, manganese bromide, manganese carbonate, manganese chloride or manganese nitrate, are not organic manganese salts in the sense of the present invention.

[0044] In typical aspects, the organomanganese salts used herein comprise an organic anion that is the conjugate base of an organic acid comprising at least one carbon-hydrogen covalent bond.

[0045] Advantageously, the organic manganese salts used in the present invention are manganese salts of carboxylic acids, particularly manganese salts of aliphatic or alicyclic carboxylic acids having 2-30 carbon atoms, 2-25 carbon atoms, 2-20 carbon atoms, 4-20 carbon atoms, or even 6-20 carbon atoms.

[0046] More advantageously, the organic manganese salt is a manganese salt of a monocarboxylic acid or a dicarboxylic acid, in particular a manganese salt of a monocarboxylic acid.

[0047] According to an advantageous aspect, the organic manganese salt used herein is chosen from the manganese salts of fatty acids and manganese salts of (saturated and unsaturated) aliphatic or alicyclic carboxylic acids having in particular 6 to 30 carbon atoms.

[0048] Preferably, the organic manganese salt is selected from manganese hexanoate, manganese heptanoate, manganese octanoate, manganese 2-ethylhexanoate, manganese nonanoate, manganese decanoate, manganese neodecanoate, manganese dodecanoate, manganese hexadecanoate, manganese octadecanoate, manganese oleate, manganese linoleate, manganese cyclohexanebutyrate, manganese naphthenate, and any mixture thereof.

[0049] Manganese salts of saturated aliphatic or alicyclic monocarboxylic acids having, in particular, 6 to 30 carbon atoms are particularly beneficial because they have no (or at least limited) adverse effects during the crosslinking or vulcanization of the rubber composition. In addition, it is believed that these specific manganese salts not only provide favorable miscibility characteristics with the entire rubber composition, but also further enhance the adhesion properties between the rubber composition and the reinforcing agent by further promoting the dispersion of the organic salt near the reinforcing agent or the adsorption of the organic manganese salt on the surface of the reinforcing agent.

[0050] More preferably, the organic manganese salt is selected from manganese hexanoate, manganese 2-ethylhexanoate, manganese neodecanoate, manganese hexadecanoate, manganese octadecanoate, manganese oleate, manganese linoleate, manganese cyclohexanebutyrate, and any mixture thereof.

[0051] In a particularly preferred aspect of the present invention, the organic manganese salt is selected from manganese 2-ethylhexanoate, manganese neodecanoate, manganese octadecanoate, and any mixture thereof.

[0052] The organic manganese salt used in the present invention can be prepared by using conventional techniques and methods known to those skilled in the art. An exemplary general manufacturing method is to react an organic acid (especially a carboxylic acid) with manganese oxide, manganese hydroxide or manganese carbonate. Another exemplary general production method includes: a) reacting an organic acid (especially a carboxylic acid) with sodium hydroxide to obtain a sodium salt of the organic acid, and then b) reacting the sodium salt of the organic acid with manganese chloride.

[0053] Alternatively, the organomanganese salts used herein can be purchased from conventional chemical suppliers.

[0054] The composition of the adhesion-promoting system, in particular the respective contents of novolac resin and organic manganese salt present in the system, can vary within wide ranges depending on the targeted properties and applications.

[0055] According to an advantageous aspect, the adhesion promoting system comprises:

[0056] a) 5-35 wt%, 5-30 wt%, 7-25 wt%, 10-20 wt% or even 10-15 wt% of an organic manganese salt, and

[0057] b) 65-95wt%, 70-95wt%, 75-93wt%, 80-90wt% or even 85-90wt% of a novolac resin;

[0058] The wt % is based on the total weight of the adhesion promoting system.

[0059] The adhesion promoting system of the present invention may also be in various forms and may be used or incorporated into conventional rubber compositions according to various techniques or configurations.

[0060] In one exemplary aspect, the adhesion promoting system described herein can be in the form of a split system, wherein the novolac resin and the organomanganese salt are provided as physically distinct entities, and thus can be separately introduced into a conventional rubber composition using any suitable order.

[0061] The advantage of the split-flow system is that it allows for more flexibility and adjustability in the steps of introducing the novolac resin and the organomanganese salt into a conventional rubber composition, and further provides more formulation flexibility.

[0062] In a further advantageous aspect, the adhesion promoting system is in the form of a (pre)mixture of the novolac resin and the organomanganese salt. The advantage of the (pre)mixture system is that it provides a ready-to-use adhesion promoting composition that can be conveniently introduced into a conventional rubber composition with only one step of addition.

[0063] Without being bound by theory, it is believed that the (pre)mixture system provides enhanced compatibility and miscibility of the organic manganese salt in the rubber composition compared to the introduction of the organic manganese salt alone. It is further believed that this favorable property will ultimately translate into enhanced adhesion between the rubber composition and the reinforcing agent.

[0064] According to a particular aspect in which the adhesion promoting system is in the form of a (pre)mixture of the novolac resin and the organic manganese salt, the (pre)mixture may advantageously be in the form of a dispersion in which the organic manganese salt is dispersed in the novolac resin. In addition, commercially available organic manganese salts are usually in the form of a dispersion in a hydrocarbon solvent.

[0065] According to a more advantageous aspect, the (pre)mixture is in the form of a blend, wherein the organic manganese salt is blended with the novolac resin. The blend form is believed to further improve the compatibility and miscibility of the organic manganese salt and the novolac resin in the rubber composition.

[0066] In addition, the blend can provide an adhesion promoting system in solid form, and it is substantially free of hydrocarbon solvents in which commercially available organomanganese salts are usually dispersed. Adhesion promoting systems in the form of solid blends are particularly beneficial in typical industrial manufacturing of rubber products. Exemplary solid blends used herein can generally be in the form of particles, beads or flakes.

[0067] The composition of the blend, in particular the respective contents of the novolac resin and the organic manganese salt present in the system, can vary within wide ranges depending on the targeted properties and applications.

[0068] According to an advantageous aspect, the weight ratio of the novolac resin to the organic manganese salt in the blend is 5:95-35:65, 7:93-25:75, or even 10:90-15:85.

[0069] The premix of the novolac resin and the organomanganese salt can be prepared according to techniques and methods known to those skilled in the art. An exemplary method of preparation is to add the novolac resin to the organomanganese salt (usually in the form of a dispersion in a hydrocarbon solvent) and heat the reaction mixture until the novolac resin melts. The mixture is then thoroughly homogenized by stirring and the residual solvent is removed under reduced pressure.

[0070] According to another aspect, the present invention relates to a rubber composition comprising the adhesion promoting system as described above and a rubber component.

[0071] There is no particular restriction on the rubber component used in this article. In fact, any rubber component known in the art can be used in the context of the present invention. The rubber component suitable for use in this article can be easily identified by those skilled in the art according to the disclosure of the present invention. The exemplary rubber component used in this article is described in detail in, for example, EP2432810A1 (Schafer et al.). The particularly suitable rubber component used in the present invention is a sulfur crosslinkable rubber component or a rubber component that can be vulcanized with sulfur.

[0072] In a typical aspect, the rubber component used in the rubber composition is selected from natural rubber, polyisoprene (IR), polybutadiene, styrene / butadiene rubber (SBR), acrylonitrile rubber, butyl rubber, ethylene / propylene / diene terpolymer rubber (EPDM), and any mixture thereof.

[0073] The content of the adhesion promoting system in the rubber composition can vary within wide ranges depending on the targeted properties and applications.

[0074] According to an advantageous aspect, the rubber composition comprises 0.5-15.0 phr, 0.5-12.0 phr, 0.5-10.0 phr, 1.0-8.0 phr, 1.0-6.0 phr, 1.0-5.0 phr, 1.5-5.0 phr, 1.5-4.5 phr or even 2.0-4.0 phr of the adhesion promoting system, based on 100 parts by mass of the rubber component.

[0075] As for the content of the organic manganese salt, in particular the content of manganese metal, it has been found that, although their content in the entire rubber composition can vary within a wide range, controlling their respective contents in the rubber composition is beneficial for optimizing properties, in particular in terms of adhesion properties.

[0076] In an advantageous aspect, the rubber composition comprises not more than 2.00 phr, not more than 1.80 phr, not more than 1.60 phr, not more than 1.50 phr, not more than 1.40 phr, not more than 1.20 phr, not more than 1.00 phr, not more than 0.80 phr, not more than 0.70 phr, not more than 0.60 phr, not more than 0.50 phr, not more than 0.40 phr, not more than 0.35 phr or even not more than 0.30 phr of the organic manganese salt, based on 100 parts by mass of the rubber component.

[0077] In another advantageous aspect, the rubber composition comprises 0.10-2.00 phr, 0.10-1.60 phr, 0.15-1.40 phr, 0.15-1.20 phr, 0.20-1.00 phr, 0.20-0.90 phr, 0.20-0.85 phr, 0.20-0.80 phr, 0.20-0.70 phr, 0.20-0.60 phr, 0.25-0.50 phr, 0.25-0.40 phr or even 0.25-0.35 phr of the organic manganese salt, based on 100 parts by mass of the rubber component.

[0078] In yet another advantageous aspect, the rubber composition comprises no more than 0.25 phr, no more than 0.22 phr, no more than 0.20 phr, no more than 0.18 phr, no more than 0.16 phr, no more than 0.14 phr, no more than 0.12 phr, no more than 0.10 phr, no more than 0.09 phr, no more than 0.08 phr, no more than 0.07 phr, no more than 0.06 phr or even no more than 0.05 phr of manganese metal, based on 100 parts by mass of the rubber component.

[0079] In yet another advantageous aspect, the rubber composition comprises 0.020-0.200 phr, 0.025-0.180 phr, 0.030-0.160 phr, 0.030-0.140 phr, 0.035-0.120 phr, 0.040-0.120 phr, 0.040-0.110 phr, 0.045-0.105 phr, 0.050-0.100 phr, 0.050-0.090 phr, 0.050-0.080 phr, 0.050-0.070 phr or even 0.050-0.060 phr of manganese metal, based on 100 parts by mass of the rubber component.

[0080] In the context of the present invention, it has been found that organic manganese salt contents, particularly manganese metal contents, in the rubber composition outside the ranges detailed above often result in unsatisfactory properties, particularly in terms of adhesion between the rubber composition and the reinforcing agent.

[0081] According to a typical aspect, the rubber composition used herein also includes a reinforcing agent. The reinforcing agent used herein is not particularly limited. In fact, any reinforcing agent known in the art can be used in the context of the present invention. The reinforcing agent suitable for use in this article can be easily identified by those skilled in the art according to the present invention. The exemplary reinforcing agent used herein has been described in detail in, for example, EP2432810A1 (Schafer et al.).

[0082] Advantageously, the reinforcing agent used herein is particularly selected from reinforcing fibers, reinforcing filaments, reinforcing threads, reinforcing cords, and any combination thereof.

[0083] More advantageously, the reinforcing agent comprises a material selected from the group consisting of metals (particularly steel), polymers, ceramics, textiles, composite materials, and any combination thereof.

[0084] It will be apparent to those skilled in the art that the rubber composition used herein can include other additives commonly used in the art. Suitable conventional additives include but are not limited to vulcanizing agents or cross-linking agents or curing agents, filler materials, ageing agents, antioxidants, tackifiers, mineral oils, plasticizers, processing aids, and any mixture thereof. Other additives used herein have sufficient examples in, for example, EP2432810A1 (Schafer et al.).

[0085] According to an advantageous aspect, the rubber composition of the present invention also comprises a vulcanizing agent or a crosslinking agent or a curing agent, a filler material, an additive, and any mixture thereof. Preferably, the vulcanizing agent or a crosslinking agent or a curing agent used herein comprises sulfur and / or a sulfur donor, which is optionally combined with an accelerator and / or an activator.

[0086] The rubber compositions described herein may be prepared, processed and crosslinked (or vulcanized) according to techniques and methods generally known to those skilled in the art, such as using internal mixers, kneaders or mixing rolls.

[0087] The adhesion promoting system and rubber composition of the present invention are well suited for making conventional reinforced engineered rubber products.

[0088] Thus, according to another aspect, the present invention relates to a preparation comprising the rubber composition as described above. Exemplary articles include, but are not limited to, pneumatic vehicle tires, conveyor belts, drive belts, pressure hoses, and gaskets.

[0089] Advantageously, the article of the invention is an engineered rubber article, in particular an engineered rubber article, more particularly a pneumatic vehicle tire or a conveyor belt.

[0090] According to another aspect, the present invention relates to a method for producing an adhesion promoting system in the form of a blend as described above, wherein the method comprises the steps of: a) preparing a novolac, adding a novolac resin to an organic manganese salt (optionally in the form of a dispersion in an organic solvent), thereby forming a reaction mixture, b) heating the reaction mixture until the novolac resin is (completely) melted, c) homogenizing the mixture by stirring, and d) optionally, removing any residual solvent.

[0091] The present invention also relates to a process for producing an adhesion-promoting system as described above, wherein the process comprises the step of preparing a novolac resin by reacting an aldehyde A1 with a phenolic compound in the presence of a urethane-aldehyde resin.

[0092] The present invention also relates to a method for producing a rubber composition as described above, wherein the method comprises the step of adding an adhesion promoting system as described above to the rubber component.

[0093] In another aspect of the present invention, there is provided a method for manufacturing a rubber product, comprising the following steps:

[0094] a) providing an adhesion promoting system as described above;

[0095] b) adding the adhesion promoting system to the rubber component, thereby forming a rubber composition as described above; and

[0096] c) Optionally, vulcanizing or crosslinking or curing the rubber composition.

[0097] According to another aspect, the invention relates to a method for promoting adhesion between a rubber composition and a reinforcing agent in contact with the rubber composition using an adhesion promoting system as described above, wherein the reinforcing agent is particularly selected from reinforcing fibers, reinforcing filaments, reinforcing cords, and any combination thereof.

[0098] The invention also relates to a method for using an adhesion-promoting system as described above in the manufacture of a rubber article, in particular selected from pneumatic vehicle tires and conveyor belts.

[0099] The present invention also relates to a method for promoting adhesion between a rubber composition and a reinforcing agent in contact with said rubber composition, comprising the step of introducing into the rubber composition an adhesion promoting system as described above. Example

[0100] The present invention is further illustrated by the following examples. These examples are for illustrative purposes only and are not intended to limit the scope of the claims.

[0101] Test Method

[0102] Evaluation of adhesion performance (tensile test according to ASTM D2229)

[0103] Preparation of test pieces for adhesive performance testing (Examples 1-4 and Examples C1-C2)

[0104] Rubber composition is heat treated by double test rollers to prepare a rubber sheet with a width of 100 mm, a thickness of 6 mm and a length of 400 mm. Two rubber sheets with a width of 12.5 mm, a thickness of 6 mm and a length of 200 mm are cut from the rubber sheet. 3*0.24 / 9*0.225 HT copper-plated (Cu63.5%, Zn 36.5%) steel wire ropes derived from Kiswire are sandwiched between the above-mentioned two rubber sheets and vulcanized at about 150°C to prepare the rubber composition test piece adhered with steel wire ropes.

[0105] Preparation of test pieces for adhesive performance testing (Example 5-Example 6)

[0106] The rubber composition was heat treated by double test rollers to prepare a rubber sheet with a width of 100 mm, a thickness of 3 mm and a length of 90 mm. Two rubber sheets with a width of 10 mm, a thickness of 3 mm and a length of 90 mm were cut from the rubber sheet. A 2*2*0.25HT copper-plated (Cu65%, Zn35%) steel wire rope from Bakaert was sandwiched between the two rubber sheets and vulcanized at about 150°C to prepare a rubber composition test piece adhered with a steel wire rope.

[0107] Evaluation method of adhesive properties (Examples 1 to 4 and Examples C1 to C2)

[0108] Using the above test piece, a tensile test was performed according to the method of ASTM D2229, and the adhesion between the rubber and the steel wire rope was measured. For the measurement of the adhesion, the following three types of measurements were performed.

[0109] Initial adhesion: A test piece was prepared by vulcanization under the above-mentioned vulcanization conditions and measured after 24 hours.

[0110] Adhesion after wet heat aging test: The test piece vulcanized under the above-mentioned vulcanization conditions was subjected to wet heat aging at 95° C. and 100% relative humidity (RH) for 7 days, and then the adhesion was measured.

[0111] Adhesion after long-term wet heat aging test: The test piece vulcanized under the above-mentioned vulcanization conditions was subjected to wet heat aging at 95° C. and 100% RH for 14 days, and then the adhesion was measured.

[0112] Evaluation method of adhesive properties (Example 5-Example 6)

[0113] Using the above test piece, a tensile test was performed according to the method of ASTM D2229, and the adhesion between the rubber and the steel wire rope was measured. For the measurement of the adhesion, the following three types of measurements were performed.

[0114] Initial adhesion: A test piece was prepared by vulcanization under the above-mentioned vulcanization conditions and measured after 24 hours.

[0115] Adhesion after wet heat aging test: Water immersion aging was performed by immersing the test piece vulcanized under the above-mentioned vulcanization conditions in hot water at 95° C. for 7 days, and then the adhesion was measured.

[0116] Adhesion after long-term wet heat aging test: Water immersion aging was performed by immersing the test piece vulcanized under the above-mentioned vulcanization conditions in hot water at 95°C for 14 days, and then the adhesion was measured.

[0117] raw material

[0118] The raw materials used in the embodiment are as follows:

[0119] Manganese 2-ethylhexanoate, available from Borchers as 60 wt% in hydrocarbon under the trade name Octa-Soligen Manganese 10HS.

[0120] Manganese neodecanoate, available from Borchers as 60 wt% in hydrocarbon under the trade name Deca Manganese 8.

[0121] Cobalt stearate (20.5%), available from Borchers under the trade name Manobond 740C.

[0122] MnO2, a manganese oxide salt, is commercially available from Nantong Runfeng Chemical Co. under the trade name MnO2.

[0123] ALNOVOL® PN 320, a clearcoat phenolic resin, is available from allnex GmbH, Germany.

[0124] Natural rubber SVR grade, available from HB Chemical under the trade name SVR 3L.

[0125] Carbon black grade N326, available from Cabot under the trade name Regal 300.

[0126] Stearic acid, available under the trade name SA 1801 from PT. SUMI ASIH.

[0127] Silica, available from Evonik under the trade name Ultrasil VN3.

[0128] TMQ, antioxidant, polymeric 2,2,4-trimethyl-1,1-dihydroquinoline, available from China Sunsine Chemical Holdings Ltd. under the trade name TMQ.

[0129] Oil, process oil, available from Orgkhim Biochemical Holding under the trade name Norman-346.

[0130] ZnO, zinc oxide, is commercially available from Zink US (Changshu) Metal Co. under the trade name Zinc Oxide 210P.

[0131] HMMM, hexamethoxymethylmelamine, is commercially available from allnex under the trade name Cyrez® 964.

[0132] Sulfur, sulfur powder, is available from Eastman Chemical Company under the trade name HDOT 20.

[0133] DCBS, N,N-dicyclohexyl-2-benzothiazolesulfonamide, is commercially available from China Sunsine Chemical Holdings Ltd. under the trade name DCBS.

[0134] TBBS, N-tert-butylbenzothiazolesulfonamide, is commercially available from China Sunsine Chemical Holdings Ltd. under the trade name TBBS.

[0135] Example 1: Preparation of a blend of manganese 2-ethylhexanoate and novolac resin (blend 1)

[0136] Manganese 2-ethylhexanoate (74.2 g, 60% in hydrocarbon) was placed in a four-necked round-bottom flask (1 L). Subsequently, novolac (PN320, 400.0 g) was added and the mixture was heated to 170° C. under protective gas (N2). Once the novolac was melted, the mixture was homogenized by stirring (2 hours) and the solvent was removed under reduced pressure (15 mbar, 1.5 hours, 170° C.), thereby forming a material with a melt viscosity of about 11060 mPa.s, a capillary viscosity of about 1110 mPa.s and a melting point of about 90° C.

[0137] Example 2: Preparation of a blend of manganese neodecanoate and novolac resin (blend 2)

[0138] Manganese neodecanoate (474.0 g, 60% in hydrocarbon) was placed in a four-necked round-bottom flask (6 L). Subsequently, novolac (PN320, 2930.2 g) was added and the mixture was heated to 145° C. under protective gas (N2). Once the novolac was melted, the mixture was homogenized by stirring (2 hours) and the solvent was removed under reduced pressure (15 mbar, 1 hour, 145-160° C.), forming a material with a melt viscosity of about 8585 mPa.s, a capillary viscosity of about 1391 mPa.s and a melting point of about 87° C.

[0139] Example 3: Base Rubber Matrix

[0140] To test the effect of the adhesion promoting system of the present invention in a vulcanizable rubber blend, a base rubber mixture was prepared by thoroughly mixing the components listed in Table 1 below in a kneader at about 140°C.

[0141] Table 1: Basic rubber compounds

[0142] Example 4: Exemplary Rubber Compositions

[0143] The following exemplary rubber compositions were prepared by adding the following additional materials (in parts per hundred parts of rubber) to separate portions of a base rubber mixture during kneading, each of which contained exactly 100 phr of natural rubber, in the order of the rows shown in Table 2 below. Comparative Example C1 contained cobalt stearate as an organic metal salt, and Comparative Example C2 contained an inorganic manganese salt. In the rubber composition of Example 5, a manganese salt and a novolac resin were incorporated into the base rubber mixture in the form of a blend obtained by the steps detailed in Example 1. In other exemplary rubber compositions, the two components were introduced separately into the base rubber mixture.

[0144] Table 2: Exemplary Rubber Compositions

[0145] [1] The values ​​shown in Table 2 correspond to the respective metal contents (in phr).

[0146] [2] The manganese salt and the novolac resin are introduced into the base rubber mixture in the form of a blend.

[0147] Adhesion performance

[0148] Table 3: Results of the adhesion test

[0149] From the results shown in Table 3, it can be seen that the adhesion promoting system of the present invention (see Examples 1-4 in particular) when used in a rubber composition provides excellent adhesion to copper-plated steel cords even under harsh humid aging conditions. These adhesion results are very similar to those obtained using the comparative cobalt salt (Example C1). In contrast, it can be seen that the adhesion results obtained using the inorganic manganese salt are inferior (by more than 10%) to the adhesion results obtained using the adhesion promoting system of the present invention (see Example 4).

[0150] It can also be seen that when the manganese salt and the novolac resin are introduced into the rubber mixture in the form of a blend (see Example 5), the obtained adhesion performance results are improved (by about 10%) compared to the adhesion performance results obtained using a similar composition but these components are added to the rubber mixture separately (see Example 6).

Claims

1. An adhesion promoting system for a rubber composition, wherein the system comprises a novolac resin and an organic manganese salt, wherein the novolac resin is prepared by reacting an aldehyde A1 with a phenolic compound.

2. The system according to claim 1, wherein the organic manganese salt is a manganese salt of a carboxylic acid, in particular a manganese salt of an aliphatic or alicyclic carboxylic acid having 2-30 carbon atoms, 2-25 carbon atoms, 2-20 carbon atoms, 4-20 carbon atoms, or even 6-20 carbon atoms.

3. The system according to claim 1 or 2, wherein the organic manganese salt is selected from manganese hexanoate, manganese 2-ethylhexanoate, manganese neodecanoate, manganese hexadecanoate, manganese octadecanoate, manganese oleate, manganese linoleate, manganese cyclohexanebutyrate, manganese naphthenate, and any mixture thereof.

4. A system according to any one of the preceding claims, comprising: a) 5-35 wt%, 5-30 wt%, 7-25 wt%, 10-20 wt% or even 10-15 wt% of said organic manganese salt, and b) 65-95wt%, 70-95wt%, 75-93wt%, 80-90wt% or even 85-90wt% of the novolac resin; The wt% is based on the total weight of the system.

5. The system according to any one of the preceding claims, wherein the aldehyde A1 is selected from formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, glyoxal, and any mixtures thereof.

6. The system according to any one of the preceding claims, wherein the phenolic compound is selected from the group consisting of monophenolic compounds, polyphenolic compounds, and any mixtures thereof.

7. The system according to any one of the preceding claims, wherein the novolac resin is prepared by reacting an aldehyde with a phenolic compound and further with an acid.

8. The system according to any one of the preceding claims, in the form of a (pre)mixture of the novolac resin and the organomanganese salt.

9. The system according to claim 8, wherein the (pre)mixture is in the form of a blend, wherein the organomanganese salt is blended with the novolac resin.

10. A rubber composition comprising the adhesion promoting system according to any one of claims 1 to 9 and a rubber component.

11. The composition of claim 10, comprising no more than 0.25 phr, no more than 0.22 phr, no more than 0.20 phr, no more than 0.18 phr, no more than 0.16 phr, no more than 0.14 phr, no more than 0.12 phr, no more than 0.10 phr, no more than 0.09 phr, no more than 0.08 phr, no more than 0.07 phr, no more than 0.06 phr or even no more than 0.05 phr of manganese metal based on 100 parts by mass of the rubber component.

12. The composition of claim 10 or 11, comprising 0.020-0.200 phr, 0.025-0.180 phr, 0.030-0.160 phr, 0.030-0.140 phr, 0.035-0.120 phr, 0.040-0.120 phr, 0.040-0.110 phr, 0.045-0.105 phr, 0.050-0.100 phr, 0.050-0.090 phr, 0.050-0.080 phr, 0.050-0.070 phr, or even 0.050-0.060 phr of manganese metal, based on 100 parts by mass of the rubber component.

13. The composition according to any one of claims 10 to 12, further comprising a reinforcing agent, wherein the reinforcing agent is especially selected from reinforcing fibers, reinforcing filaments, reinforcing threads, reinforcing cords, and any combination thereof.

14. A method for manufacturing a rubber product, comprising the steps of: a) providing an adhesion promoting system as claimed in any one of claims 1 to 9; b) adding the adhesion promoting system to a rubber component to form the rubber composition of any one of claims 10 to 13; and c) Optionally, vulcanizing or crosslinking or curing the rubber composition.

15. A method of promoting adhesion between a rubber composition and a reinforcing agent in contact with the rubber composition using the adhesion promoting system of any one of claims 1 to 9, wherein the reinforcing agent is particularly selected from reinforcing fibers, reinforcing filaments, reinforcing cords, and any combination thereof.

Images