JPH04161441A - Rubber composition - Google Patents

Abstract

PURPOSE:To provide a rubber composition having excellent mechanical properties, oil resistance, cold resistance, etc., by adding a crosslinking agent to a rubbery polymer which is prepared by emulsion-polymerizing monomers in the presence of a nonionic surfactant as an emulsifier and contains a small amount of metals. CONSTITUTION:0.1-5 pts.wt., preferably 0.1-3 pts.wt., of a crosslinking agent (e.g. an alkyl phenol.formaldehyde resin) is added to 100 pts.wt. of a rubbery polymer (e.g. acrylonitrile-butadiene copolymer), the rubber polymer being prepared by emulsion-polymerizing a kind or more of monomers in the presence of a kind or more of nonionic surfactants (e.g. polyoxyethylene alkyl ether) at a temperature below the clouding point of the surfactant and subsequently heating the prepared polymer latex at a temperature above the clouding point for the coagulation of the latex.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a rubber composition prepared by blending a crosslinking agent with a rubbery polymer with a low metal content obtained by emulsion polymerization.

[Prior Art] Conventionally, monomers that are almost insoluble in water are dispersed as small particles in an aqueous phase using an emulsifier such as soap or a surfactant.
It has been widely practiced to carry out emulsion polymerization to obtain polymers using water-soluble polymerization initiators such as potassium belloxonisulfate, hydrogen peroxide, and α-cumyl hydroperoxide.

For example, styrene-butadiene rubber (
In order to obtain SBR), i) emulsion polymerization by so-called hot rubber formulation or cold rubber formulation (polymerization step), ii) recovery step of recovering the monomer under reduced pressure or by vacuum steam distillation), and iii) further polymer latex. An electrolyte such as saline is added to cream it, and then a coagulant such as dilute sulfuric acid is added to separate it into porous crumb and serum (serum) in which the rubber components are aggregated, and the crumb is washed and separated (separation process). iV) A method is adopted in which the crumb is finally dried (drying process).

[Problem to be solved by the invention 1 As described above, in conventional emulsion polymerization, anionic activators containing alkali metals such as potassium and sodium as counterions are generally widely used as emulsifiers, and Metal compounds such as sodium chloride and calcium chloride are also used as coagulants in the process of separating the combined latex.

For this reason, these metal ions always remain in the polymer, and they can hardly be removed even when the polymer latex is coagulated and washed with water, and cannot be removed using normal emulsion polymerization - polymer production using a coagulant. It is extremely difficult to reduce the metal content by this method.

Therefore, when a crosslinked product is obtained using a polymer obtained by ordinary emulsion polymerization and used as a metal sealing material, there is a problem of metal corrosion. In addition, the type and amount of metal compounds contained in the polymer not only change the crosslinking rate but also affect the properties of the crosslinked rubber. This was a major technical challenge for each rubber company.

In recent years, there has been a remarkable movement toward high-speed crosslinking for the purpose of improving productivity in crosslinked rubber applications, but with conventional technology, it has not been possible to find materials that have a high crosslinking speed and an excellent balance of physical properties. It was extremely difficult.

The present invention was made against the background of the above-mentioned conventional technical problems, and uses a nonionic activator that does not inherently contain metal ions in emulsion polymerization, does not use a coagulant, and takes advantage of the characteristics of the activator. The present invention aims to provide a crosslinked rubber composition which has a high crosslinking rate and excellent crosslinked rubber properties by obtaining a polymer containing almost no metal ions, blending a crosslinking agent with the polymer, and crosslinking the polymer.

Means for Solving Problems C] That is, the present invention uses at least one nonionic activator as an emulsifier when obtaining a polymer by emulsion polymerization, and emulsion polymerization is carried out at a temperature below the cloud point of the nonionic activator. The present invention relates to a rubber composition obtained by blending a crosslinking agent into a rubber-like polymer obtained by coagulating the obtained polymer latex by heating it to a temperature equal to or higher than the clouding point.

The polymer obtained by emulsion polymerization of the present invention is not particularly limited, but includes acrylonitrile-butadiene copolymer (N
BR), styrene-butadiene copolymer (SBR), polychloroprene (CR), acrylic rubber, and modified polymers obtained by adding functional groups such as carboxyl groups, amino groups, epoxy groups, and hydroxyl groups to these.

Among the polymers, acrylonitrile-butadiene copolymers and styrene-butadiene copolymers are preferred, and acrylonitrile-butadiene copolymers are more preferred. The acrylonitrile-butadiene copolymer composition preferably has an acrylonitrile content of 10 to 50% by weight based on the total amount of monomers charged. If the amount of acrylonitrile is less than 10% by weight, the oil resistance, which is a characteristic of acrylonitrile-butadiene rubber, will be poor, and if it exceeds 50% by weight, the rubber elasticity will be poor. As for the styrene-butadiene copolymer composition, the amount of styrene is 15 to 5 of the total amount of monomers charged.
The amount of styrene is preferably 0% by weight, and if the amount of styrene is less than 15% by weight, the mechanical strength will be poor, and if it exceeds 50% by weight, the rubber elasticity will be poor.

The Mooney viscosity (ML (101+40°C)) of the rubbery polymer is preferably 20 to 120. If it is less than 20, the mechanical strength will be poor, and if it exceeds 120, the processability will be poor.

The nonionic surfactant used as an emulsifier in the emulsion polymerization of the present invention is one that does not ionize in an aqueous solution among substances that exhibit significant surface activity at low concentrations.

When an aqueous solution of a nonionic surfactant is heated, the temperature at which it first becomes cloudy is called the clouding point, and is a unique phenomenon that occurs in an aqueous solution of a nonionic surfactant.

Thermodynamically, the cloud point is defined as the lower critical solution temperature (LCS
Corresponds to T).

Therefore, when the temperature of a nonionic activator aqueous solution with a certain composition is increased, a phenomenon of cloudiness-phase separation appears above the point where it intersects with the LC8T curve, that is, at a temperature above the cloud point, and the system that was a homogeneous phase changes to water. It separates into two phases: a phase and an activator phase.

This phenomenon can be said to be a decrease in the concentration of the nonionic activator in the aqueous phase, in other words, the activator has become poorly soluble in water, and this phenomenon is characteristic of nonionic activators.

In this way, at temperatures above the cloud point, nonionic surfactants become poorly soluble in water and lose their activity as surfactants. This corresponds to the separation step of lowering the polymer latex and coagulating the polymer latex.

That is, when emulsion polymerization is carried out using a nonionic activator as an emulsifier, coagulation can be performed without using a coagulant by utilizing the phenomenon of clouding point.

However, although the cloud point of the nonionic surfactant aqueous solution does not necessarily match the cloud point of the polymerization solution in emulsion polymerization or the coagulation temperature of the polymer latex, there is a correlation between the former and latter temperatures, and in the present invention, The cloud point is used as a guideline for temperature or solidification temperature.

As the nonionic surfactant used in the present invention, one type or a combination of two or more of the compounds exemplified above may be used, and the nonionic surfactant is appropriately selected depending on the emulsion polymerization conditions.

For example, when the emulsion polymerization temperature is low, a nonionic activator with a low clouding point may be used, and when the polymerization temperature is high, a nonionic activator with a high clouding point may be used. Particularly preferred are nonionic activators with a cloud point of 40 to 120°C.

In addition, as a method for obtaining a polymer from polymer latex, a nonionic activator with a lower clouding point than the nonionic activator used as an emulsifier, an electrolyte, alcohol, fatty acid, etc. is added to the polymer latex, and then heated and solidified. You can also use the method.

In addition to the method of carrying out emulsion polymerization using the above-mentioned nonionic surfactant alone, the following method can also be used.

(i) After performing emulsion polymerization using an anionic and/or cationic activator and a nonionic activator as an emulsifier, a nonionic activator with a lower clouding point than the nonionic activator used as an emulsifier is added. and then heated to solidify.

(11) A method of carrying out emulsion polymerization using an anionic and/or cationic activator as an emulsifier, then adding a nonionic activator and an electrolyte, and then heating.

In this way, a polymer latex is obtained by emulsion polymerization at a temperature below the cloud point of the nonionic surfactant, and after normal monomer recovery, the polymer latex is heated to a temperature above the cloud point of the nonionic surfactant. When heated, the non-ionic activator phase separates, so that it can be coagulated without the use of a coagulant.

To specifically explain the emulsion polymerization applied to the present invention, first, in the emulsion polymerization, general polymerization agents are used in addition to nonionic activators, and in this case, as much as possible, they do not contain metal compounds such as alkali metals. It is effective to use However, since these drugs are used in very small amounts, this does not pose much of a problem.

Polymerization is performed using a polymerization initiator such as peroxide, redox compound, azo compound, persulfate, etc.
This may be carried out by a conventional emulsion polymerization method.

In addition, a molecular weight regulator or the like may be used if necessary. Furthermore, any monomer species that can be emulsion polymerized can be used, and there are no restrictions on the molecular weight that can be obtained.

The nonionic activator used in the emulsion polymerization of the present invention includes:
Examples include polyoxyethylene alkyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene oxypropylene block polymer, alkylsulfinyl alcohol, and fatty acid monoglyceride.

Among the emulsifiers that can be used as necessary during emulsion polymerization, examples of anionic activators include soap, funnel oil, emulsified oil, alkylnaphthalene sulfonate, dodecylbenzenesulfonate, oleate,
Alkylbenzene sulfonates, dialkyl sulfosuccinates, lignin sulfonates, alcohol ethoxy sulfates, secondary alkanesulfonates, α-olefin sulfonic acids, tamol, etc. are used as cationic activators, such as alkyl trimethyl ammonium salts, dialkyl dimethyl Examples include ammonium salts, alkylpyridinium salts, and alkylbenzyldimethylammonium salts.

Further, there are no restrictions on the monomers used in the present invention, and radically polymerizable monomers capable of emulsion polymerization can be copolymerized by homopolymerization or by combining them as necessary.

To give specific monomer names, conjugated dienes include butadiene, dimethylbutadiene, isoprene, chloroprene, and derivatives thereof, and (meth)acrylic acid esters include methyl (meth)acrylate, (meth)acrylic acid. Ethyl, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, lauryl (meth)acrylate, polyethylene glycol (meth)acrylate,
Epoxy (meth)acrylate, hydroxyalkyl (meth)acrylate, etc. obtained by reacting polypropylene glycol (meth)acrylate, diglycidyl ether of bisphenol A, diglycidyl ether of glycol, etc. with (meth)acrylic acid, hydroxyalkyl (meth)acrylate, etc. ) Urethane (meth)acrylate obtained by the reaction of acrylate and polyisocyanate, unsaturated hydrocarbons other than those mentioned above include olefins such as ethylene, propylene, ■-butene, 2-butene, isobutene, and 1-pentene, styrene, Examples include aromatic vinyls such as methylstyrene, and nitro compounds such as acrylonitrile and methacrylonitrile. Furthermore, monomers having functional groups can also be used if necessary.

For example, when the functional group is a carboxyl group, (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, β-(meth)acryloxyethyl succinate, β-(meth)acryloxyethyl maleate, β-phthalate -Unsaturated acids such as (meth)acryloxyethyl, hexahydrophthalic acid, and β-(meth)acryloxyethyl, and unsaturated acids such as maleic anhydride and succinic anhydride when the functional group is an acid anhydride group. Anhydride, if the functional group is an epoxy group, glycidyl (
meth) acrylate, allyl glycidyl ether, etc., and dimethylamino (meth) when the functional group is an amino group.
acrylate, diethylaminoethyl (meth)acrylate, etc.; when the functional group is an amide group, use (meth)acrylamide, dimethyl (meth)acrylamide, etc.; when the functional group is a hydroxyl group, use hydroxyethyl (meth)acrylate, hydroxypropyl ( When the functional group is an isocyanate group, use vinyl isocyanate, isocyanate ethyl (meth)acrylate, p-styryl isocyanate, etc., and when the functional group is a phosphoric acid group, use (meth)acryloxyethyl phosphate, etc. be able to.

In addition, compounds having multiple polymerizable double bonds in the molecule, such as crosslinking monomers divinylbenzene, divinyl ether, diallyl phthalate, ethylene glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate, may be mentioned. I can do it.

The emulsion polymerization is carried out in an oxygen-free reactor at a temperature below the cloud point of the nonionic activator used.

Monomers, nonionic activators, molecular weight regulators, polymerization initiators, etc. may be added in their entirety before the start of the reaction, or added in arbitrary portions after the start of the reaction, and conditions such as temperature and stirring may be changed during the reaction. can be changed arbitrarily. However, the polymerization temperature must be maintained at a temperature below the cloud point of the nonionic activator used.

The polymerization method may be either continuous or batchwise.

After recovering the monomers from the polymer latex thus obtained under reduced pressure or by ordinary monomer recovery means such as steam distillation, the latex is collected at a temperature above the clouding point of the nonionic activator (solidification temperature). ), the nonionic active phase undergoes phase separation, resulting in instantaneous precipitation of the polymer, which can be separated. Heating may be done in batches in a container, or it may be heated continuously.

Note that if the solidification temperature exceeds 100° C., a pressure device is also required in addition to a heating device.

After coagulation, the separated polymer is washed with water and dried to obtain a product polymer.

The thus obtained polymer obtained by the emulsion polymerization method of the present invention contains extremely small amounts of metal ions such as alkali metals and alkaline earth metals, compared to polymers obtained by ordinary emulsion polymerization. be.

There are no particular restrictions on the crosslinking agent to be added to the obtained rubbery polymer, and any of those commonly used for producing crosslinked rubbers may be used, and the crosslinking agent can be selected depending on the polymer or purpose.

Specifically, in addition to sulfur, examples of crosslinking agents containing sulfur include sulfur chloride, morpholine disulfide, tetramethylthiuram disulfide, and benzothiazoles. Oximes and nitroso compounds include p-quinonedioxime, p,p'-dibenzoylquinonedioxime, polyp-dinitrobenzene, N-(2
-methyl-2-nitropropyl) 4-nitrosoaniline and the like.

Examples of polyamines include hexamethylenediamine, triethylenetetramine, hexamethylenediamine carbamate, ethylenediamine carbamate, triethylenediamine, and the like. , as organic peroxides, t-butyl hydroperoxide, cumene hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, 2.5-dimethyl-t-butylperoxyhexane, 2.5-dimethyl-t- Examples include butylperoxyhexine, 1,3-bis(t-butylperoxyisopropyl)benzene, p-chlorobenzoylperoxide, t-butylperoxybenzoate, t-butylperoxyisopropyl carbonate, t-butylbenzoate, and the like.

Examples of resin crosslinking agents include alkylphenol formaldehyde resins.

Other examples include ammonium benzoates, polyfunctional (meth)acrylate monomers, bismaleimides, and triazines.

These crosslinking agents can be used alone or in combination, and can also be used in combination with various chemicals generally called crosslinking accelerators.

The amount of crosslinking agent blended into the rubber composition of the present invention is 0.00% per 100 parts by weight of the rubbery polymer. 1 to 5 parts by weight,
Preferably it is 0.1 to 3 parts by weight.

If it is less than 0.1 part by weight, crosslinking will be insufficient and mechanical strength will be weak. On the other hand, if the amount is 5 parts by weight or more, the elongation of the resulting crosslinked rubber composition is low and it is difficult to use it.

In addition, in the rubber composition of the present invention, in addition to the rubbery polymer and crosslinking agent that are essential components, ordinary rubber compounding agents such as carbon black, process oil, and crosslinking accelerator may be added as necessary. It can be kneaded using a conventional mixer such as a Banbury mixer and then cross-linked.

[Function] The present invention uses a nonionic activator that essentially does not contain metal ions as an emulsifier during emulsion polymerization, performs emulsion polymerization at a temperature below the cloud point of the activator, and uses the resulting polymer latex. Heating to a temperature above the cloud point causes phase separation of the nonionic activator phase, thus separating the polymer without the use of a coagulant, resulting in a polymer essentially free of metal ions, which can be used A rubber composition is obtained.

[Examples] Next, Examples of the present invention will be shown, but the present invention is not limited by these Examples unless the gist thereof is exceeded.

The physical properties of the rubber composition of the present invention were mainly determined according to JIS K-6301; mechanical properties were determined by a tensile test and a bending test; oil resistance was determined by an immersion test using JIS No. 3 oil; and cold resistance was determined by a low-temperature embrittlement test. and evaluated by Gehman torsion test.

Example 1 Using the emulsion polymerization recipe shown below, emulsion polymerization was carried out at 20° C. in an autoclave with an internal volume of 201 cm.

Emulsion polymerization recipe (1 part heavy) Butadiene; 65 Acrylonitrile, 35 Water; 220 Polyoxyethylene,; 1 Emulgen 920 manufactured by Kao Soap ■, cloud point 82°C After reaching a polymerization conversion rate of 90%, 0.2 parts by weight of hydroxylamine sulfate was added per 100 parts by weight of monomer,
Polymerization was stopped. Then heated to about 70'C under reduced pressure.
After recovering the residual monomer by steam evaporation, 2 parts by weight of alkylated phenol was added as an anti-aging agent, and the polymer latex was then placed in a pressure can and heated to 110°C to coagulate the latex. . The produced crumbs were taken out, washed with water, and dried under reduced pressure at 50°C to obtain samples for evaluation. The obtained copolymer was designated as Polymer I, and the polymerization results are summarized in Table-1.

Next, the obtained copolymer was kneaded in a Banbury mixer according to the formulation shown in Table 2 to obtain a rubber composition, which was then crosslinked at 160°C for 20 minutes. Table 3 shows the results of evaluating the physical properties of the obtained crosslinked product.

Example 2.3 Polymerization was carried out in the same manner as in Example 1, except that the types and amounts of the charged chemicals were changed as shown in Table 1, to obtain polymers (1) and (2).

The polymerization results are summarized in Table-1.

Using the obtained copolymer, a rubber composition was obtained in the same manner as in Example 1 and evaluated.

The results are shown in Table-3.

Comparative Example 1 Emulsion polymerization was carried out in the same manner as in Example 1 using the emulsion polymerization recipe shown below.

Emulsion polymerization recipe Butadiene: 65 Acrylonitrile; 35 Water, 220 Dodecylbenzene, 4 Sodium sulfonate, Tertiary dodecyl mercaptan; 0.4 Ammonium persulfate, 0.25 Cyanoethylated diethanol, 0.15 Amine To the resulting copolymer latex After adding an anti-aging agent in the same manner as in Example 1, the mixture was coagulated using a 1% aqueous calcium chloride solution, washed with water and dried to obtain a polymer (2). The polymerization results are summarized in Table-1.

Using the obtained rubbery copolymer, a rubber composition was obtained and evaluated in the same manner as in Example 1.

The results are shown in Table-3.

Comparative Example 2.3 Polymerization was carried out in the same manner as in Comparative Example 1, except that the types and amounts of the charged chemicals were changed as shown in Table 1, to obtain polymers (1) and (2).

The polymerization results are summarized in Table-1.

Using the obtained copolymer, a rubber composition was obtained in the same manner as in Example 1 and evaluated.

The results are shown in Table-3.

As is clear from comparisons of Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3, the rubber composition of the present invention exhibits the following characteristics. .

(1) It has excellent mechanical properties, especially good bending fatigue resistance.

(2) Excellent balance between oil resistance and cold resistance.

(3) Excellent wear resistance.

(4) Excellent rebound resilience.

Margins below [Effects of the Invention] The rubber composition of the present invention crosslinks quickly and has excellent bending resistance, a balance between oil resistance and cold resistance, and abrasion resistance. It can be used in fields where crosslinked rubber has traditionally been widely used.

[Brief explanation of drawings]

FIG. 1 shows a diagram of the crosslinking behavior of Example 1 and Comparative Example 1 measured using a JSR Curelastometer. It can be seen that Example 1 has a faster crosslinking rate and a sharper rise than Comparative Example 1. Patent applicant: Japan Synthetic Rubber Co., Ltd. r5ZJ ~ 1 hour (minute)

Claims (1)

[Claims] (1) Using at least one nonionic activator as an emulsifier, emulsion polymerization of monomers is carried out at a temperature below the cloud point of the nonionic activator, and then the obtained polymer latex is A rubber composition made by blending a crosslinking agent into a rubber-like polymer obtained by coagulating it by heating to a high temperature.