JP2001335653A - Rubber foaming composition using industrial waste rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-weight and soft rubber foaming composition in which a natural rubber used for removing impurities in a closed kneading machine, is used as a main rubber material, and its production method. SOLUTION: This rubber composition is produced out of the natural rubber, which is used for removing impurities in a closed kneading machine, as the main rubber material. The main rubber material, in which ML(1+4) at 100 deg.C is 20 to 40, is blended with a sulfonyl hydrazide foaming agent of 3 to 5 pts.wt. as a foaming agent, a sulfenic amide vulcanization accelerator of 0.5 to 3 pts.wt. and sulfur of 0.5 to 10 pts.wt. to the above main rubber material 100 pts.wt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition using industrial waste rubber as a main rubber, and more particularly to a rubber composition used for desorption of impurities in a closed kneader and adjusted to a predetermined Mooney viscosity. The present invention relates to a lightweight and soft rubber foam composition using unvulcanized natural rubber as a main rubber.

[0002]

2. Description of the Related Art Conventionally, in a rubber production process, a raw rubber and a compounding agent are kneaded to form a compounded rubber, and the compounded rubber is molded into a predetermined shape to obtain a crosslinked rubber. Among these operations, kneading is an operation method for imparting plasticity to the raw rubber and mixing with the compounding agent.

[0003] As an apparatus used for this kneading, an open roll and a closed kneader can be cited, but the closed kneader is mainly used in terms of mass productivity and work environment. The closed kneader includes a Banbury-type kneader, a pressure kneader or an intermix, etc., but due to the property of the closed type, the compounding agent used earlier remains inside even after the kneaded rubber is taken out, This has a problem that it adversely affects the rubber to be kneaded next as an impurity. In particular, in recent years in which rubber products are required to have higher functionality, the mixing of impurities has a great influence on the rubber compounding design, which leads to a reduction in product performance.

[0004] Therefore, it has been customary practice to knead the raw material rubber into a closed kneader and then masticate it to remove impurities in the closed kneader.
This rubber can be used repeatedly, but after a certain number of uses, the molecular chains are cut by mechanical force, and the Mooney viscosity is reduced, so that the rubber sticks in the kneader and becomes unusable. The rubber with reduced Mooney viscosity has an unspecified amount of various types of compounding agents such as fillers, vulcanizing agents, vulcanization accelerators, antioxidants, plasticizers, etc. It was discarded in an unvulcanized state without being performed.

[0005]

However, in recent years, rubber recycling is highly expected from the viewpoints of preserving the global environment and depleting fossil fuels expected in the future. Since the impurity removing operation is performed at every kneading, the present inventors pay attention to the fact that the amount of waste of the impurity removing rubber reaches an enormous amount, and try to utilize the waste.

[0006]

That is, the invention of claim 1 of the present application resides in a rubber foam composition using a rubber to which impurities in a closed kneader that has been conventionally discarded are desorbed. The rubber to which this impurity has been desorbed is described in detail in ML _{(1 + 4)} at 100 ° C.
Is 20 to 40, and by setting the Mooney viscosity in the above range, a rubber foam composition having good foaming can be provided.

According to a second aspect of the present invention, in the rubber foamed composition according to the first aspect, the main rubber is prepared by adding natural rubber to a closed kneader to which impurities are adhered, masticating and removing impurities. At this point, the cycle of removing natural rubber from the internal mixer is repeated at least once,
Is a natural rubber whose ML _{(1 + 4)} is adjusted to 20-40.

[0008] The invention of claim 3 of the present application is directed to claim 1 or 2
In the rubber foam composition described above, sulfur having a long vulcanization induction period is added as a vulcanizing agent.

According to a fourth aspect of the present invention, in the rubber foamed composition according to the first, second or third aspect, the foaming agent is a sulfonyl hydrazide foaming agent which is harmless to a decomposition gas.

The invention of claim 5 of the present application is directed to claims 1, 2, 3
Alternatively, in the rubber foamed composition according to 4, a slow-acting vulcanization accelerator is added.

[0011] The invention of claim 6 of the present application provides claims 1, 2, and
In the rubber foamed composition according to 3, 4, or 5, the slow-acting vulcanization accelerator is a sulfenamide-based vulcanization accelerator.

[0012] The invention according to claim 7 of the present invention relates to a rubber foamed composition mainly composed of a rubber to which impurities are removed in an internal mixer, wherein the main rubber is an internal mixer to which the impurities are attached. A cycle in which natural rubber is charged, masticated and the natural rubber is removed from the internal mixer at the time of removing impurities is repeated at least once, and M at 100 ° C.
L _{(1 + 4)} is a natural rubber adjusted to 20 to 40, and sulfonyl.
3 to 5 parts by weight of a hydrazide-based blowing agent, 0.5 to 3 parts by weight of a sulfenamide-based vulcanization accelerator as a vulcanization accelerator, and 0.5 to 10 parts by weight of sulfur as a crosslinking agent are added.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The rubber used for desorption of impurities in a closed kneader can be used as long as it can be kneaded with a closed kneader. Use natural rubber which has excellent ability. When used for desorption, no compounding agent is basically added to natural rubber.
This is because the use of the rubber to which the compounding agent is added cannot achieve the original purpose of removing impurities in the internal mixer. However, if the Mooney viscosity decreases to some extent, the plasticity becomes high and it becomes difficult to handle, so that a filler such as carbon black may be added.

The above rubber is masticated with an internal mixer. By this kneading operation, impurities adhering to the inside of the internal mixer are removed by the rubber, kneaded into the rubber, and desorbed. The kneading conditions vary depending on the capacity and shape of the kneader, the amount of adhered impurities, and the like. Therefore, optimal conditions such as temperature, time, filling rate, and rotor speed should be selected according to the situation.

Further, as the number of times of use of the rubber increases, the molecular chain is cut and the Mooney viscosity decreases. As a result of the study by the present inventors, it is preferable to use the ML _{(1 + 4)} at 100 ° C. until the ML _{(1 + 4)} becomes 20 to 40. When the ML _{(1 + 4)} is less than 20, the rubber is stuck in the internal mixer and the recovery becomes difficult. On the other hand, when the ML _{(1 + 4)} exceeds 40, foaming becomes insufficient due to high viscosity. Sufficient light weight and flexibility cannot be obtained. However, ML _{(1 + 4)} is JIS
According to the test method of K6300, the Mooney viscosity was obtained by preheating the sample for 1 minute, rotating the L-shaped rotor at 2 revolutions per minute, and measuring the torque applied to the shaft after 4 minutes.

The ML _{(1 + 4)} at 100 ° C. is 20 to ₄
The rubber foamed composition according to the present invention is provided by utilizing the rubber used until it reaches zero. In addition, the rubber foam composition according to the present invention includes a short fiber, a filler, a plasticizer, an antioxidant, a vulcanization accelerator, a foaming agent and a vulcanization such as sulfur or an organic peroxide which can be generally used for rubber. It is possible to appropriately add a compounding agent such as an agent. However, various compounding agents, that is, impurities are mixed in the rubber, and a vulcanizing agent and a vulcanization accelerator are also contained therein, and the vulcanization rate tends to be high. Therefore, when using a foaming agent, sulfur crosslinking with a relatively long vulcanization induction period is preferred.

As the short fibers, organic fibers such as polyester, polyamide, aramid, nylon, vinylon, rayon, and cotton are used. The aramid fiber is specifically an aramid having an aromatic ring in the molecular structure, for example, trade names such as Conex, Nonex, Kevlar, Technora, Twaron and the like. The length of the short fiber is 0.1 to 10 mm, and the diameter of the elementary fiber is preferably several μm to several tens μm, and the addition amount thereof is 2 to 30 parts by weight based on 100 parts by weight of rubber.

Examples of the plasticizer include a mineral oil-based plasticizer, a vegetable oil-based plasticizer, a synthetic plasticizer, and the like. Specifically, paraffin-based oil, aromatic oil, naphthenic oil, coal tar, stearic acid and The salt, rapeseed oil, palm oil, coconut oil, pine tar, rosin, factice, phenol aldehyde resin, low melting point styrene resin, liquid rubber, dioctyl phthalate, dioctyl sebacate, etc., and one or more of these are used can do.

The foaming agent is roughly classified into an inorganic foaming agent and an organic foaming agent. Examples of the inorganic foaming agent include sodium bicarbonate and ammonium bicarbonate. Examples of the organic foaming agent include N-nitroso compounds, sulfonyl hydrazides, azo compounds and the like, and more specifically, P, P′-oxybis (benzenesulfonyl hydrazide), azodicarbonamide, dinitrosopentamethylenetetramine and the like. used. Among them, it is preferable to use a sulfonyl-hydrazide-based blowing agent which has a relatively small effect of accelerating vulcanization and has no harmful decomposition gas. The amount of rubber added is 100
It is preferably 3 to 5 parts by weight based on parts by weight. If the amount is less than 3 parts by weight, sufficient foaming cannot be obtained, and weight reduction and softening cannot be achieved. On the other hand, if it exceeds 5 parts by weight, foaming becomes excessive, and deformation occurs during molding.

It is possible to use organic peroxides as crosslinking agents. As the organic peroxide, specifically, di-
t-butyl peroxide, dicumyl peroxide,
t-butylcumyl peroxide, 1.1-t-butylperoxy-3.3.5-trimethylcyclohexane,
2.5-di-methyl-2.5-di (t-butylperoxy) hexane, 2.5-di-methyl-2.5-di (t-
Butylperoxy) hexane-3, bis (t-butylperoxydi-isopropyl)) benzene, 2.5-di-methyl-2.5-di (benzoylperoxy) hexane, t-
Butylperoxybenzoate, t-butylperoxy-2
-Ethyl-hexyl carbonate and the like are used. The compounding amount is preferably 0.1 to 100 parts by weight of rubber.
2 to 10 parts by weight. If the amount is less than 0.2 parts by weight, crosslinking is not sufficiently performed, and if it exceeds 10 parts by weight, sufficient elasticity cannot be obtained.

Known co-crosslinking agents (TAIC, TAC, maleimide, quinone dioxime, trimethylolpropane trimethacrylate, sulfur, etc.) and the like may be used in combination in order to increase the crosslinking efficiency with organic peroxides.

Examples of the vulcanization accelerator include guanidine-based, thiuram-based, dithiocarbamate-based, thiazole-based, and sulfenamide-based organic vulcanization accelerators. More specifically, N-cyclohexylbenzothiazylsulfenamide, N, N-diethyl-2-benzothiazylsulfenamide, 2-mercaptobenzothiazole,
-Mercaptothiazoline, 2-mercaptoimidazoline, diphenyl guanidine, triphenyl guanidine, thiohydropyridine, Zn-dimethyl dithiocarbamate, Zn-diethyl dithiocarbamate, tetramethylthiuram monosulfide, tetramethylthiuram disulfide, etc. can give. These vulcanization accelerators may be used alone or in combination of two or more. However, when adding a foaming agent to the rubber, it is preferable to add a vulcanization accelerator having a slow-acting effect. Specifically, it is preferable to use a sulfenamide vulcanization accelerator. As described above, since the rubber contains a compounding agent such as a vulcanizing agent or a vulcanization accelerator among impurities,
Vulcanization tends to be faster. However, by using a sulfenamide-based vulcanization accelerator, it is possible to prevent a rapid increase in viscosity that occurs with the start of vulcanization, maintain a long vulcanization induction period, and use a sulfonyl / hydrazide-based blowing agent. The effect of lowering the decomposition temperature of the foaming agent is obtained. The addition amount is suitably 0.5 to 3 parts by weight. If the amount is less than 0.5 part by weight, sufficient vulcanization induction time cannot be obtained, resulting in insufficient foaming. If the amount exceeds 3 parts by weight, the vulcanization reaction is inhibited. It is also possible to use scorch retarders such as phthalic anhydride and N-cyclohexylthiophthalimide.

As the filler, besides inorganic fillers such as silica, clay and calcium carbonate, there are organic fillers such as resin and cork powder. In particular, carbon black is added to improve the reinforcing property. Is desirable.

In order to improve the dispersibility of the filler,
A coupling agent may be used. Specifically, vinyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycoxypropyltrimethoxysilane, 3-aminopropylpropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis- (3-
Examples thereof include silane coupling agents such as (triethoxysilyl) propyl) tetrasulfide and N, N'-bis (2-methyl-2-nitropropyl) -1,6-diaminohexane.

Since natural rubber is a diene rubber having a double bond in its main chain, it is susceptible to aging such as thermal oxidation, ozone deterioration, and fatigue deterioration. Therefore, it is desirable to add an antioxidant. The antioxidant is not limited, but amine antioxidants such as amine ketone, diallylamine, p-phenylenediamine, phenolic antioxidants such as monophenol, polyphenol and hydroquinone, sulfur compounds, phosphites, tributyl Secondary aging inhibitors such as thiourea, and waxes for preventing ozone deterioration can be used.

The rubber may contain an elastomer component other than the rubber. Specifically, hydrogenated nitrile rubber, ethylene-α-olefin elastomer, chloroprene rubber, chlorosulfurized polyethylene, alkylated chlorosulfurized polyethylene, natural rubber, styrene / butadiene rubber, or olefin, ester, or urethane thermoplastic elastomer Etc. can be blended.

The means for kneading the rubber and the compounding agent is not limited, and may be kneaded by any suitable means and method such as a Banbury mixer, a roll, a kneader, and an extruder. The vulcanization method is also not limited, and vulcanization is performed by a known method using a vulcanizing apparatus such as a mold heating, a hot air heating, a rotary drum vulcanizer, and an injection molding machine.

[0028]

Next, the effects of the present invention will be described more specifically with reference to examples and comparative examples. Examples 1 to 6 and Comparative Examples 1 to 3 The compounding ingredients shown in Table 1 were added to each of the impurity-desorbed natural rubbers used until reaching the Mooney viscosity shown in Table 2, and kneaded with a Banbury mixer. In addition, about the foaming agent, the predetermined amount shown in Table 2 was added. The obtained rubber composition was rolled and vulcanized at 150 ° C. for 20 minutes.

[0029]

[Table 1]

With respect to the obtained vulcanized foamed rubber sheet, foam moldability was evaluated, and specific gravity and hardness were measured. For the measurement of the maximum impact value, the vulcanized sheet was 2 m thick.
After fixing on a plywood (skin material) of m, a metal ball having a load of 120 g and a diameter of 30 mm was dropped from a height of 10 cm. The impact level transmitted to the lower plate through the vulcanized sheet was measured by an acceleration pickup attached to the plywood, and analyzed by a high-speed Fourier transform analyzer (FFT analyzer) to measure the maximum impact value. The results are also shown in Table 2.

[0031]

[Table 2]

From the results shown in Table 2 above, 10
The rubber foam composition using the desorbing rubber having an ML _{(1 + 4)} of 20 to 40 at 0 ° C. is lightweight and soft,
Comparative Examples 1 and 2 in which the ML _{(1 + 4)} at 00 ° C. is out of the above range are high in both hardness and specific gravity. Further, in the example in which the sulfenamide-based vulcanization accelerator was added, foaming was good and the formability was excellent as compared with Example 2 in which the thiazole-based vulcanization accelerator was added. However, in Example 6 in which 6 parts by weight of the foaming agent was added, foaming was excessive, and although the specific gravity and hardness were low, the moldability was poor. In Comparative Example 3, in which no foaming agent was added, both the specific gravity and the hardness were high, and the desired physical properties could not be obtained.

[0033]

As described above, according to the invention of the present invention, it is possible to effectively use industrial waste rubber, and to provide a lightweight and soft rubber foam composition and a method for producing the same. The use of a sulfonyl / hydrazide-based blowing agent is more preferable from an environmental point of view, and the addition of a specific vulcanization accelerator makes the foaming property excellent.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 7/00 C08L 7/00 // C08L 7:00 7:00 F term (Reference) 4F074 AA06 AB00 BA17 BA18 BB01 BB05 BB27 BB29 CA21 CA22 CC27X 4F301 AA04 AB01 BA22 CA04 CA09 CA32 CA71 4J002 AC011 DA048 EV216 EV277 FD148 FD157 FD326

Claims (7)

[Claims] 1. A rubber foam composition containing a rubber as a main material to which impurities in an internal mixer are removed, wherein the main rubber is 10%.
A rubber foam composition characterized by being a natural rubber having a ML _{(1 + 4)} of 20 to 40 at 0 ° C. 2. The main rubber is (a) natural rubber is charged into an internal mixer kneaded with impurities, and (b) masticated,
(C) When the impurities are desorbed, the natural rubber is taken out of the internal mixer, and the cycle of (a) to (c) is repeated at least once, and the ML _{(1 + 4)} at 100 ° C.
The rubber foam composition according to claim 1, wherein the rubber foam composition is a natural rubber whose is adjusted to 20 to 40. 3. The rubber foam composition according to claim 1, wherein sulfur is added as a vulcanizing agent. 4. The rubber foam composition according to claim 1, wherein the foaming agent is a sulfonyl hydrazide foaming agent. 5. The rubber foam composition according to claim 1, wherein a slow-acting vulcanization accelerator is added. 6. The rubber foam composition according to claim 1, wherein the slow-acting vulcanization accelerator is a sulfenamide vulcanization accelerator. 7. A rubber foamed composition mainly composed of a rubber to which impurities have been desorbed in an internal mixer, (a) natural rubber is charged into an internal mixer to which impurities are attached, and B) masticating, and (c) removing the natural rubber from the internal kneading machine when the impurities are desorbed.
By repeating the cycle of (c) at least once or more, 1
A natural rubber whose ML _{(1 + 4)} at 00 ° C is adjusted to 20 to 40, and 3 to 5 parts by weight of a sulfonyl / hydrazide foaming agent as a foaming agent is added to 100 parts by weight of the rubber. As a sulfur accelerator, a sulfenamide-based vulcanization accelerator of 0.5
1 to 3 parts by weight, and 0.5 to 10 parts by weight of sulfur as a crosslinking agent.