JPS6253015B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to rubber compositions. More specifically, the present invention relates to a rubber composition containing zinc-substituted type A zeolite as a vulcanization aid. In general, both natural rubber and various synthetic rubbers cannot be used as raw materials to produce practical rubber products, so they are first masticated to give the rubber an appropriate plasticity, and then mixed with various compounding agents, such as fillers, etc.
By mixing softeners, anti-aging agents, vulcanization accelerators, vulcanizing agents, vulcanization aids, etc., and then molding and vulcanizing, it has the necessary properties such as strength, elongation, hardness, and durability. rubber products are manufactured. Among these compounding agents, fillers are inert substances in the form of fine powder, and are often added in large amounts comparable to the amount of raw rubber to improve the tensile strength, tear strength, abrasion resistance, etc. of the rubber composition. It is intended to increase or increase the amount of food. However, on the other hand, if it is added in an excessive amount, 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 used at around 5 parts by weight (3 parts by weight) per 100 parts by weight of raw rubber.
(6 parts by weight). In addition to acting as a vulcanization aid as mentioned above, zinc white added to rubber is also useful in terms of coloring effect as a white pigment, heat dissipation effect based on good thermal conductivity, and 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. The present inventors have (1) obtained a rubber composition with high elongation and low hardness without reducing the filler compounding ratio, and (2) obtained a rubber composition with a low content of zinc, which is toxic to the human body. As a result of various experimental studies aimed at achieving this purpose, we have found that zinc-substituted type A zeolite has the function as an optimal vulcanization aid to achieve this purpose, and has a high tensile strength in many rubber compositions. , provide a vulcanized rubber that has high elongation and low hardness while maintaining tear strength etc., and can replace most or all of conventional zinc white for rubber, and therefore a rubber composition with a low zinc content. They discovered that a product can be obtained and completed the present invention. That is, the present invention relates to a rubber composition obtained by mixing raw rubber with rubber compounding agents such as a filler, a vulcanizing agent, a vulcanization accelerator, a softening agent, and an anti-aging agent, and vulcanizing the mixture. The present invention relates to a rubber composition comprising: The zinc-substituted type A zeolite used in the present invention is roughly [xZnO・(1-x)M ₂ O・Al ₂ O ₃・zSiO ₂・
nH ₂ O] (where M is a monovalent cation or an equivalent amount of each valent cation), the value of x is 0.1 to 1, and the value of n is Values range from 0 to 5.0. It is usually obtained by replacing part or all of the sodium component of Na-A type zeolite with zinc through an ion exchange reaction with an aqueous zinc salt solution. According to X-ray diffraction, the crystal structure of such zinc-substituted type A zeolite belongs to the cubic system, and the value of the lattice constant a ₀ is 12.08 to 12.31 Å. In particular, the zinc-substituted type A zeolite used in the present invention has a spherical or cubic zeolite with rounded corners, and has a primary particle size of 0.1 based on electron microscopy.
It is preferable to use sodium A type zeolite having a diameter of 5 to 5 μm as the application raw material, and to contact it with an aqueous zinc salt solution for ion exchange. Zinc-substituted type A zeolite also has the same skeletal shape as the original zeolite, and is similarly fine and rounded. However, since sodium A-type zeolite has a cubic crystal structure and is cubic in most cases, it goes without saying that such a shape can also be used as a raw material. Next, in rubber compounding agents, the fillers are mainly carbon black, white carbon, and calcium carbonate, as well as inorganic fillers such as clay, barium sulfate, and magnesium carbonate, and organic fillers such as high styrene resin, ligsin, and phenolic resin. Examples include drugs. Vulcanizing agents are substances that crosslink raw rubber molecules to form a three-dimensional network structure, and in many cases sulfur is 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 zinc white is mainly used as the vulcanization aid. Examples of vulcanization accelerators include guanidines,
Examples include thiazoles, thiurams, dithioates, imidazolines, and aldehyde ammonias. In addition, dispersants such as stearic acid and naphthenic acid, process oils, pine tar vegetable oil, mineral oil, coumaron resin, softeners such as hydrogenated rosin, pitch, and wax, phthalate esters, aliphatic dibasic acid esters, phosphorus Acid esters, fatty acid esters, plasticizers such as epoxidized soybean oil, processing aids such as white sub and black sub, binders, anti-aging agents, pigments, blowing 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 (EPDM) and chloroprene rubber (CR) are representative, and they may also be blended rubbers consisting of two or more types. The zinc-substituted type A zeolite is used in the present invention (1) when it is added alone when kneading raw rubber and various compounding agents on a roller, (2) as raw rubber, filler, and vulcanization accelerator. 1 or 2 other agents such as zinc white, stearic acid, etc.
Various methods are possible, such as a method in which it is added in advance to more than one raw material or compounding agent, and then kneaded with other compounding agents or raw materials according to a conventional method. The rubber 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 zinc-substituted type A zeolite varies depending on the raw material rubber used and the types and amounts of various compounding agents, but generally it is at least 0.2 parts by weight per 100 parts by weight of raw rubber. It is necessary. When the amount is less than 0.2 parts by weight, the effect is insufficient, and in most cases, practical effects can be obtained by adding 0.5 parts by weight to 7.5 parts by weight. Furthermore
Although it is possible to add more than 7.5 parts by weight, the effect does not increase in proportion to the amount blended. In addition, if the entire amount of zinc white in a conventional rubber composition is replaced with zinc-substituted type A zeolite, the tensile strength of the vulcanized rubber may decrease slightly, but in many cases ZnO is added to 100 parts by weight of raw rubber. By using about 0.2 parts by weight of zinc white or other zinc compounds together with zinc-substituted type A zeolite, a kind of additive effect is exhibited, which improves the vulcanization rate and tensile strength of the vulcanizate compared to conventional zinc white formulations. can be increased even more than in the case of According to the present invention, it is possible to exhibit the characteristics of significantly increasing the elongation of the vulcanized rubber composition and reducing the hardness without reducing the blending ratio of the filler. Furthermore, especially when an increase in elongation or a decrease in hardness is not required, it is possible to obtain a more economical rubber composition by increasing the blending ratio of an inexpensive filler. Furthermore, according to the present invention, by replacing most or all of the zinc white, which was conventionally considered indispensable for rubber compounding, with zinc-substituted type A zeolite with a low zinc content, the working environment during rubber processing can be improved. It becomes possible to maintain safety and improve the safety of rubber products. Although the details of the mechanism of action of the zinc-substituted type A zeolite in the present invention are not necessarily clear, the zinc-substituted type A zeolite is susceptible to moisture, rubber molecules, vulcanization accelerators, etc. due to its unique crystal structure and chemical components. It has strong activity against substances and always exists as insoluble solid particles in rubber compositions, so during kneading and vulcanization, rubber molecules, vulcanizing agents, vulcanization accelerators, activators, and water in the composition are By acting as a kind of depolymerization agent, adsorbent, acid neutralizer, or a kind of solid catalyst for crosslinking reactions, it exhibits unique effects different from conventional zinc white and sodium A-type zeolite. it is conceivable that. The characteristics of the vulcanized rubber, which has high elongation and low hardness that can be obtained by using zinc-substituted type A zeolite, can be achieved by using an equivalent amount of sodium A-type zeolite and zinc white instead of zinc-substituted type A zeolite. will not come true. Zinc-substituted type A zeolite is relatively inexpensive compared to zinc white, and its zinc content is about 1/2
In addition to being small at less than 5, there are
Since it contains Zn ⁺⁺ , it has a strong binding force, and since there is virtually no contamination due to the release of Zn ⁺⁺ relative to the content, it is less toxic to the human body, is tasteless and odorless, and does not color or contaminate rubber. Therefore, the rubber composition according to the present invention is particularly suitable for rubbers characterized by high elongation and low hardness, and rubbers for food and hygiene-related uses. The rubber composition of the present invention will be explained below with reference to Examples. Example 1 Using styrene butadiene rubber (SBR) as a raw material rubber, various rubber compounding agents were blended with zinc-substituted type A zeolite as shown in Table 1,
A vulcanizable rubber composition was obtained by kneading by the method shown below. For comparison, a rubber composition was obtained by performing the same treatment without adding the zeolite. When the vulcanizability of these compositions was measured using a culastometer, the results shown in Table 1 were obtained.

【table】

[Table] Next, these unvulcanized compositions were prepared by a conventional method.
Regarding the rubber composition obtained by vulcanization at 150°C,
The results of measuring physical performance using the method shown below are
Shown in the table.

[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 Testing machine: Shotspur type Tensile testing machine (capacity 50Kgf) Test method: Compliant with JIS K6301 Example 2 Styrene butadiene rubber (SBR) was used as the raw material rubber, and zinc-substituted type A zeolite and various rubber compounding agents were compounded as shown in Table 3. A vulcanizable rubber composition was obtained in the same manner as in Example 1. For comparison, a rubber composition was obtained by performing the same treatment without adding zeolite. The vulcanizability of these compositions was measured using a culastometer, and the results shown in Table 3 were obtained.

[Table] Next, these unvulcanized compositions were prepared by a conventional method.
Regarding the rubber composition obtained by vulcanization at 150°C,
The physical performance was measured in the same manner as in Example 1, and the values shown in Table 4 were obtained.

[Table] Example 3 Zinc substitution A in styrene butadiene rubber (SBR)
A vulcanizable rubber composition was obtained by blending various rubber compounding agents with type zeolite as shown in Table 5 in the same manner as in Example 1.
Vulcanization was performed at ℃ to obtain a rubber composition.

【table】

It is the same as that in [Table].
The rubber compositions obtained in Examples 1 and 3-2 had a lower zinc content but significantly higher elongation and lower hardness than those obtained in Comparative Examples.

Claims (1)

[Claims] 1. In a rubber composition formed by mixing raw rubber with rubber compounding agents such as fillers, vulcanizing agents, vulcanization accelerators, softeners, and anti-aging agents, zinc-substituted type A zeolite is blended. Characteristic rubber composition.