JPS6317097B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rubber composition containing type A zeolite as a vulcanizing agent, and an object of the present invention is to provide a rubber composition that exhibits excellent physical performance, especially when white carbon is not used as a filler. It is. In general, both natural rubber and various synthetic rubbers cannot be used as raw materials to produce practical rubber products, and after mastication is performed to give the rubber appropriate plasticity, various compounding agents, such as fillers, etc.
Rubber products with various necessary properties are manufactured by mixing softeners, anti-aging agents, vulcanization accelerators, vulcanizing agents, vulcanization aids, etc., followed by molding and vulcanization. Among these compounding agents, fillers are fine powder substances that are added in large amounts to increase the tensile strength, tear strength, abrasion resistance, etc. of rubber products, or to achieve the purpose of increasing the amount. . However, on the other hand, if excessive weight is added, the hardness of the rubber composition will increase and the elongation will be significantly reduced, so there is a limit to the amount added. Therefore, in order to obtain a rubber with high elongation and low hardness, it is necessary to reduce the amount of filler added or use a filler with less filling effect, but this also affects the tensile strength and tear strength. It was difficult to achieve both of these physical properties. Softeners improve the processability of rubber and smooth the surface of products, and various oils are used. Anti-aging agents are additives used to prevent vulcanized rubber from becoming viscous, hardening, and cracking over a long period of time.
Various types are used depending on the purpose, such as sunlight crack resistance and ozone crack resistance. On the other hand, the vulcanizing agent imparts a three-dimensional network structure to the rubber upon heating, and sulfur is often used. In addition, when cross-linking rubber using sulfur, the vulcanization accelerator is an effective agent for quickly forming a three-dimensional network structure at a relatively low temperature.
Various compounds such as thiazole type, guanidine type, thiuram type, dithioate type and others are used. When such an organic vulcanization accelerator is used, zinc white is always added as a vulcanization aid. The role of zinc white in this case is primarily to accelerate vulcanization by reacting with the vulcanization accelerator to produce a more active vulcanization accelerator, zinc salt, but it also It is thought that it is also involved in promoting vulcanization by neutralizing hydrogen sulfide and other acidic substances produced, or by exerting a depolymerization effect on rubber molecules as a so-called quick peptizer. In particular, when using strong vulcanization accelerators such as M, DM, and TT, it is impossible to reach even half of the standard vulcanization state that you are aiming for without zinc white as a vulcanization aid. Almost impossible to vulcanize. For this reason, zinc white as a vulcanization aid is often blended as an essential component at around 5 parts by weight per 100 parts by weight of raw rubber. Of course, zinc white mixed into rubber is useful not only as a vulcanization aid as mentioned above, but also as a coloring effect as a white pigment, a heat dissipation effect based on good thermal conductivity, and a slight filling effect. It is believed that In this way, zinc white for rubber plays an important role as a vulcanization aid, but on the other hand, as it becomes increasingly clear that compounds of the heavy metal zinc are generally quite toxic to the human body, It has become important to reduce the blending ratio of zinc white as much as possible in order to maintain a safe working environment for handling it and to ensure its safety as a rubber product. On the other hand, several proposals have been made regarding rubber compositions containing zeolite as a means of accelerating vulcanization (Japanese Patent Publication No. 5989, No. 36-598,
No. 12442, Special Publication No. 38-6631, Special Publication No. 47-18082
issue). However, in all of these, the vulcanization accelerator is made by adsorbing and supporting special chemicals on activated zeolite, which acts as a molecular sieve, and the conventional zinc white is used as a vulcanization aid to produce specific rubbers such as chloroprene rubber and butyl rubber. It is a mixture that does not directly use type A zeolite, and its purpose, mode of implementation, effects, etc. are all different from the contents of the present invention. The present inventors have carried out various experimental studies with the aim of reducing the amount of heavy metal zinc compounds harmful to the human body as much as possible and obtaining a rubber composition with excellent performance. The present invention was completed based on the discovery that it has an excellent function as an auxiliary agent and can replace most of the conventional zinc white for rubber in many rubber compositions. That is, the present invention provides a rubber composition obtained by mixing raw rubber with rubber compounding agents such as a filler other than white carbon, a vulcanizing agent, a vulcanization aid, a vulcanization accelerator, and a softening agent. 0.5 to 7 parts by weight of fine A-type zeolite, which has a rounded spherical or cubic shape with primary particles of 5 μm or less, and 0.1 to 2 parts by weight of a zinc compound as ZnO, and The present invention relates to a rubber composition characterized in that the total amount is 3 to 6 parts by weight. The A-type zeolite used in the present invention has _the general formula (1.0±0.2) _M2O・_Al2O3・(1.9±0.5) _SiO2・
An aluminosilicate represented by nH ₂ O (where M represents a monovalent cation, an equivalent polyvalent cation, or a partially substituted product thereof, and the value of n is 0 to 6.0), It has a specific cubic system crystal structure that can be distinguished from other various zeolites and silicates by the method of X-ray diffraction. M is Na,
A material containing K, Ca, Mg, etc. or two or more thereof can be used. Such zeolite has a primary particle diameter of 0.1 to 5 μm, preferably 0.5 to 5 μm.
It is a powder consisting of fine particles of 3 μm, and this particle size is an average particle size based on an observation measurement method using an electron microscope. The particle state of type A zeolite is generally cubic fine particles, but in the present invention, for example, spherical or cubic angular particles manufactured by JP-A No. 56-59618 and JP-A No. 57-3713 are used. It uses fine particles that have a rounded shape and a sharp particle size distribution. Such particles have good dispersibility in the raw rubber composition and can easily perform their functions. Next, compounding agents to be added to the raw rubber to improve various properties of the rubber, such as fillers, vulcanizing agents, vulcanization accelerators, vulcanization aids, softeners, anti-aging agents, Plasticizers etc. are used. First, fillers include fillers other than white carbon, such as carbon black, calcium carbonate, inorganic fillers such as clay, sulfuric acid, barium, and magnesium carbonate, high styrene resin, ligsin, and phenolic resin. Examples include organic fillers. Vulcanizing agents are substances that cross-link and mix raw rubber molecules to form a three-dimensional network structure, and sulfur is often used, but other agents include organic peroxides,
One or more of quinone dioxime, mercaptoimidazoline, modified phenolic resin, lead monoxide, lead trioxide, tin chloride, zinc white, etc. are used, and as vulcanization aids, zinc white and other basic zinc carbonate, water are used. Zinc compounds such as zinc oxide or zinc stearate are used. Examples of the vulcanization accelerator include guanidines, thiazoles, thiurams, dithioates, imidazolines, and aldehyde ammonias. Other dispersants such as stearic acid and naphthenic acid,
Process oil, pine tar vegetable oil, mineral oil, coumaron resin, hydrogenated rosin, softening agents such as pitch and wax, phthalate esters, aliphatic dibasic acid esters, phosphoric acid esters, fatty acid esters, epoxidized soybean oil Plasticizers such as white sub,
Processing aids such as Kurosabu, binders, anti-aging agents, pigments, foaming agents, etc. are used as necessary. Note that the raw material rubber that can be applied in the present invention is not particularly limited, and includes, for example, natural rubber, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), polybutadiene rubber (BR), and ethylene. - Various natural or synthetic rubbers such as propylene rubber (EPPM) and chloroprene rubber (CR) are representative, and they may be blended rubbers consisting of two or more types. Methods of using type A theolite in the present invention include (1) a method in which it is added alone when kneading raw rubber and various coordinating agents on a roller, (2) a method in which it is added alone as a raw material rubber, a filler, and a vulcanization accelerator. agent, zinc white,
Various methods are possible, such as adding and mixing in advance to one or more other raw materials or compounding agents such as stearic acid, and kneading this with the other raw materials or compounding agents as in a conventional method. The vulcanizable composition obtained by such kneading becomes a vulcanized rubber composition through various steps similar to conventional methods such as compression, extrusion, molding, and vulcanization. In this case, the amount of A-type zeolite to be blended will vary depending on the type and composition of the raw rubber and rubber compounding agent, especially when a zinc compound is used in combination, but
Generally, a practical vulcanization rate can be obtained by adding 0.5 to 7 parts by weight per 100 parts by weight of raw rubber.
When it is less than 0.5 part by weight, the effect is insufficient,
On the other hand, although it is possible to set the amount to 7 parts by weight or more, the effect does not increase in proportion to the amount blended. The zinc compound used in combination with the A-type zeolite is 0.1 to 2 ZnO based on 100 parts by weight of raw rubber.
parts by weight, and their total amount is in the range of 3 to 6 parts by weight. The present invention is characterized in that it is used in combination with A-type zeolite and a small amount of zinc compound, and this combination produces a kind of synergistic effect that improves the vulcanization rate and tensile strength of the vulcanizate. Since the zinc compound can be increased compared to the case of a single zinc compound, a characteristic rubber composition can be obtained. Furthermore, when the entire amount of the conventional zinc compound such as zinc white is replaced with A-type zeolite, the tensile strength of the vulcanized rubber decreases slightly, but the elongation increases markedly, and a rubber with a certain characteristic can be obtained. In this way, according to the present invention, most of the zinc white, which was conventionally considered indispensable for rubber compounding, can be replaced with non-toxic type A zeolite.
It becomes possible to maintain a safe working environment during rubber processing and to ensure the safety of rubber products. Although the details of the mechanism of action of type A zeolite in the present invention are not necessarily clear, in general, type A zeolite has strong activity against moisture and various compounds due to its unique crystal structure and chemical components, and is highly active against rubber compositions. In the composition, rubber molecules, vulcanizing agents, vulcanization accelerators, activators,
By acting as a type of depolymerization agent, adsorbent, acid neutralizer for moisture, etc., or a type of solid catalyst for crosslinking reactions, it exhibits an effect equal to or greater than zinc white, which is a conventional vulcanization aid. considered to be a thing. Type A zeolite is relatively inexpensive compared to zinc white, has almost no toxicity to the human body, is tasteless and odorless, and does not color or contaminate rubber, so it can be used as a vulcanization aid for various rubbers. However, it is particularly suitable for rubbers used in food and hygiene-related applications. The present invention will be specifically described below with reference to Examples. Example 1 Styrene butadiene rubber (SBR) is used as a raw material rubber, and various rubber compounding agents are blended together with sodium A-type zeolite as shown in Table 1, and the rubber composition can be vulcanized by kneading under the following conditions. I got it. For comparison, a rubber composition was obtained by carrying out the same treatment without adding type A zeolite. When the vulcanizability of these compositions was measured using a culastometer, the results shown in Table 1 were obtained.

[Table] Next, these unvulcanized compositions were prepared by a conventional method.
Regarding the rubber composition obtained by vulcanization at 150°C,
When physical performance was measured under the following conditions, the results shown in Table 2 were obtained.

[Table] The vulcanization degree test was conducted as follows. Kneading roll: Dimensions: 20.3 cm x 45.7 cm (8 x 18 inches) Number of revolutions: 18 rpm Rotation ratio: 1.18 Surface temperature: 50 ± 5°C Vulcanization conditions: 150°C x minutes Evaluation method Test piece: JIS No. 3 dumbbell tester: Shotspur type Tensile testing machine (capacity 50Kgf) Test method: Compliant with JIS K6301 Example 2 Styrene-butadiene rubber (SBR) with calcium-substituted type A zeolite or magnesium-substituted A
A vulcanizable rubber composition was obtained by blending various rubber compounding agents with type zeolite as shown in Table 3 in the same manner as in Example 1.
Vulcanization was performed at ℃ to obtain a rubber composition.

【table】

[Table] The rubber compositions obtained in Examples 2-1 and 2-2 had high tensile strength and elongation, even though the zinc content was significantly lower than that of the comparative example. Ta.

Claims (1)

[Claims] 1 Filler other than white carbon in raw rubber,
In a rubber composition formed by mixing rubber compounding agents such as a vulcanizing agent, a vulcanization accelerator, and a softening agent, the primary particles have a spherical or cubic shape with rounded corners based on 100 parts by weight of the raw rubber. 0.5 to 7 parts by weight of fine A-type zeolite of 5 μm or less and a zinc compound are ZnO
0.1 to 2 parts by weight, and the total amount thereof is 3 to 6 parts by weight. 2. The rubber composition according to claim 1, wherein the A-type zeolite is a sodium, calcium, or magnesium A-type zeolite.