JPH06329838A - Rubber composition - Google Patents

Abstract

PURPOSE:To provide a rubber composition low in Mooney viscosity, good in processability, needless for mastication, high in producibility, thus useful as a material for tires, containing natural rubber deproteinized so as to be a specified level or lower in the total nitrogen content. CONSTITUTION:The objective rubber composition containing natural rubber deproteinized so as to be <=0.1 (pref. <=0.05)wt.% in the total nitrogen content as an index of the amount of protein. The deproteinized natural rubber can preferably be obtained by adding a protease (pref. derived from bacteria) or a specific kind of bacteria to a latex.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a rubber composition containing natural rubber.

[0002]

2. Description of the Related Art Natural rubber is used in many fields from industrial products such as tires, belts and rolls to sports products such as tennis balls. Generally, a rubber product is repeatedly compressed-recovered-expanded during use, and energy loss is accumulated to generate heat. This heat promotes fatigue of the rubber and shortens the life of the rubber product. The larger the energy loss represented by the loss tangent tan δ, the larger the heat generation. For example, in the case of tires, rolling resistance is ta at 50 to 70 ° C.
It is empirically known that it depends on the size of n δ,
If tan δ is large, not only heat generation will increase, but also rolling resistance will increase and the fuel efficiency of the vehicle will deteriorate. In the case of a race tire or a high-performance high-grip tire, it is particularly required that the tread has a large tan δ, but in the case of a fuel-saving tire tread, it is desirable that the tan δ be small as described above.

Natural rubber is superior in mechanical properties to synthetic rubber and has a small tan δ, and as described above, it is widely used in tires, industrial products, sports products and the like. However, in recent years, performance requirements for various rubber materials have become more and more stringent, and it has become necessary to further improve the performance of natural rubber having excellent heat generation properties and mechanical properties. That is, it has better mechanical properties, smaller exothermicity, and the like. In the case of a rubber composition for a fuel-efficient tire, low heat build-up property as well as good wet grip are required. The wet grip depends on the size of tan δ at 0 ° C, and the larger the value, the better the wet grip.

[0004] Conventionally, in a rubber composition in which a natural rubber and a synthetic rubber are blended, attempts have been made to improve the heat generation property by improving the synthetic rubber. In the field of tires, at the same time as improving heat generation, attempts are being made to improve grip when wet. Also, with regard to physical properties of general rubber, for example, tensile strength, tear resistance, etc., there is a limit to the effect only by improving synthetic rubber, and pure natural rubber compositions are completely improved except that they rely on compounding agents such as reinforcing agents. There is no clue.

Further, raw natural rubber (rubber used as a raw material) has a problem in that it has poor processability and productivity during production. Generally, in the manufacturing process of a rubber product, there are a kneading process in which various additives are added to raw rubber to knead the rubber, and a calendering process or an extruding process in which the kneaded rubber is formed into a sheet shape. The elasticity and plasticity of the rubber material greatly affect its workability and work efficiency. The elasticity and plasticity of an unvulcanized rubber material is usually represented by the Mooney viscosity. The higher the Mooney viscosity, the higher the elasticity of the rubber and the lower the plasticity, and the lower the Mooney viscosity, the lower the elasticity and the higher the plasticity of the rubber. There is a tendency.

[0006] Raw natural rubber has a very high Mooney viscosity because of its high molecular weight, and therefore has high elasticity and low plasticity. For this reason, it is difficult to sufficiently mix the additives in the kneading step, and in the calendering and extruding steps, the torque is increased, the processing speed is reduced, and the productivity is deteriorated. Further, when the torque is large, the energy is accumulated in the rubber and causes the rubber to generate heat, which may cause burning of the rubber.

Therefore, it is general to carry out mastication prior to the kneading step. When mastication is carried out, the elasticity of the rubber is reduced and the rubber is plasticized to facilitate the processing operation after the kneading step. Mastication is an operation that applies mechanical shearing force to rubber before adding additives to loosen molecular coagulation and cut molecular chains to lower the molecular weight. May also use a disintegrant). But,
There is a problem that productivity is reduced by the addition of the mastication process.

When a softening agent such as oil is added, the Mooney viscosity becomes small. However, since the softening agent is easily extracted from the rubber material even after vulcanization, if used in a large amount, it may exude (bleed) to the surface of the product after vulcanization and may adversely affect strength etc. , It may not be used depending on the application. It is known that natural rubber is cured during storage to increase the Mooney viscosity, and a viscosity stabilizing rubber (for example, SMR-CV) has been developed to prevent this. However, this viscosity-stabilized rubber contains hydroxylamine hydrochloride as an additive for stabilization,
Further, in some cases, it is necessary to add castor oil, and therefore these chemicals may remain in the rubber product after vulcanization, which may adversely affect the strength and the like and may not be usable depending on the application. Further, since a step of adding these additives is added, there is a problem that productivity is lowered.

The present invention has been made in view of the above circumstances, and is to further improve a natural rubber excellent in mechanical properties and exothermicity as compared with synthetic rubber, that is, to have higher strength and tear resistance. It is an object of the present invention to provide a rubber composition which is large in size, low in exothermic property, low in Mooney viscosity and excellent in processability and therefore does not require mastication and is excellent in productivity.

Another object of the present invention is to use this rubber composition as a material for tires to reduce rolling resistance, suppress heat generation and increase grip when wet.

[0011]

Means and Actions for Solving the Problems In order to solve the above problems, the present inventors have made various studies on a new modification technique of natural rubber. As a result, it is possible to remove the protein originally contained in natural rubber as much as possible at 50 to 70 ° C.
Of tan δ at 0 ℃, improvement of tan δ at 0 ℃, high strength,
It was found that it is effective for improving the tear resistance and for improving the workability and productivity by decreasing the Mooney viscosity.

Natural rubber that has been subjected to deproteinization is known, and grade products such as crepe H, crepe G and crepe CD are actually on the market. In addition, these deproteinized natural rubbers are actually used in rubber compositions. However, the above effects have not been obtained with conventional deproteinized natural rubber. When the present inventors examined the cause of this, it was found that the conventional deproteinized natural rubber was not sufficiently deproteinized.

It is generally said that the protein content of natural rubber can be represented by 6.3 times the total nitrogen content measured by the Kjeldahl method. According to a study conducted by the present inventors, fresh natural rubber latex (field latex) has a total nitrogen content of about 0.5-.
0.8 wt%, commercially available purified latex and raw rubber (smoked sheet rubber) have a total nitrogen content of about 0.3 wt%
That was all. Although the amount of protein contained in conventional commercially available deproteinized natural rubber is significantly reduced, the total nitrogen content is 0.11% by weight even in the crepe CD containing the least amount of protein, indicating insufficient deproteinization. It was

Therefore, the present inventors have found that the total nitrogen content is 0.
As a result of trying to use a natural rubber that has been highly deproteinized so as to be 1% by weight or less, ta at 50 to 70 ° C.
We succeeded in producing a rubber composition effective in decreasing n δ, increasing tan δ at 0 ° C., increasing strength, improving tear resistance, and decreasing Mooney viscosity, and completed the present invention. It was That is, natural rubber highly deproteinized to have a total nitrogen content of 0.1% by weight or less has a small tan δ at 50 to 70 ° C. and a tan at 0 ° C. as compared with ordinary natural rubber. It has a large δ, a high strength, a large tear resistance, and a low Mooney viscosity.

Therefore, the rubber composition of the present invention is characterized by containing deproteinized natural rubber such that the total nitrogen content as an index of protein amount is 0.1% by weight or less. The natural rubber used in the rubber composition of the present invention, which has been deproteinized until the total nitrogen content is 0.1% by weight or less, and various conventionally known deproteinized natural rubbers (crepe rubbers) are different from each other. It is also clear from the following confirmation test conducted by the present inventors.

That is, various commercially available conventional crepe rubbers are dried.
Dissolve the dried product in toluene, and infra red this by the transmission method.
The line spectra were measured and found to be 328
0 cm ^-1Absorption was observed. This absorption of proteins in gum
Absorption caused by polypeptide binding
Dried latex before deproteinization
Or, it is also found in RSS No. 3 rubber.

On the other hand, used in the rubber composition of the present invention,
Natural rubber deproteinized so that the total nitrogen content is 0.1 wt% or less has almost no absorption at 3280 cm ⁻¹ , and especially the total nitrogen content is 0.02 wt% or less. The deproteinized natural rubber shows no absorption at 3280 cm ^-1 . This is because, as described later, the protein, that is, the polypeptide bond was decomposed by treating the natural rubber with a proteolytic enzyme and various surfactants.

The natural rubber used in the rubber composition of the present invention has a total nitrogen content of 0.1% by weight in the rubber as described above.
The protein was deproteinized to the following levels, but the more the protein was removed, the better the tan δ characteristics (small at high temperature, large at low temperature) and improved processability and productivity (lower Mooney viscosity). , High tear resistance and high tensile strength are developed. Therefore, the lower the total nitrogen content in the rubber, the better. Even within the above range, it is preferably 0.05% by weight or less, and more preferably 0.02% by weight or less.

The total nitrogen content used in the present invention is 0.
Examples of natural rubber deproteinized to 1% by weight or less include “natural rubber vol. 6, No. 8, 274-281 (19
74) ”, improved deproteinized natural rubber (total nitrogen content is 0.06% by weight) and the like.
Particularly, those produced by the method previously proposed by the present applicants to decompose the protein by adding proteolytic enzyme or bacteria to the latex or repeatedly washing with a surfactant such as soap are preferable. What is used, especially what was manufactured by the method of treating with a proteolytic enzyme and a surfactant simultaneously or sequentially is used more suitably (Japanese Patent Application No. 4-208754-Japanese Patent Application No. 4754/1975).
-208758). Washing with a surfactant may be performed by centrifugation or the like. The rubber component is isolated by centrifuging the latex once or several times after the above treatment.

The proteolytic enzyme used in the above treatment is not particularly limited, and is derived from bacteria, filamentous fungi,
Any yeast-derived one may be used, but among these, it is preferable to use a bacterial-derived protease. Further, as the surfactant, for example, an anionic surfactant and / or a nonionic surfactant can be used. Examples of the anionic surfactant include carboxylic acid-based surfactants, sulfonic acid-based surfactants, sulfate ester-based surfactants, and phosphoric acid ester-based surfactants.

The latex as a raw material may be either a fresh field latex obtained from a natural rubber tree or a commercially available ammonia-treated latex. Especially, when the latter is used, the green strength (raw rubber) of natural rubber is used. (Strength) is improved, winding around a roll is improved, and workability is further improved. In the rubber composition of the present invention, as the main rubber component, the natural rubber deproteinized so that the total nitrogen content is 0.1% by weight or less can be used alone. However, ordinary natural rubber that has not been deproteinized, commercially available deproteinized natural rubber having a total nitrogen content of more than 0.1% by weight, or various synthetic rubbers (styrene-butadiene rubber, butadiene rubber, etc.) Can also be used in combination with the above deproteinized natural rubber.

Other components that constitute the rubber composition of the present invention together with the above rubber component include sulfur, organic sulfur compounds,
Vulcanizing agents or crosslinking agents such as organic peroxides, metal oxides, polyamines, polyisocyanates, modified phenolic resins;
Vulcanization accelerators such as aldehyde-amines, dithiocarbanates, guanidines, thiazoles and thiurams; vulcanization accelerator aids such as metal oxides and fatty acids; various antioxidants;
Examples include reinforcing agents such as carbon black and white carbon; fillers; tackifiers; plasticizers; softeners; peptizers; coloring agents; lubricants.

The rubber composition of the present invention can be used particularly as a material for products that are subjected to repeated compression and extension. Examples thereof include industrial products such as tires, rubber belts, rubber rolls, bladders, and fenders, and sports products such as tennis balls, basketballs, soccer balls, and volleyballs. In the tire, it can be used as a material for all components constituting a rubber tire, such as treads, sidewalls, plies, beads, etc., and each of the above components is, in the same manner as the conventional one, in an optimal mixing ratio according to each component. Be compounded.

The rubber composition of the present invention thus obtained is
Tan δ at 50-70 ° C. as described in the examples below.
It has excellent effects of improving the productivity by lowering the viscosity, increasing the strength, improving the tear resistance, and decreasing the Mooney viscosity.
Further, when this material is used as a tire, it has an advantage that it has a low heat buildup and also has an excellent grip when wet.

[0025]

EXAMPLES The present invention will be described below based on examples, but the constitution of the present invention is not limited to the following examples. Example 1 (Preparation of Raw Rubber) To a commercially available high ammonia latex [produced by Guthrie Co., Malaysia], a 1% aqueous solution of a nonionic surfactant [trademark Emulgen 810 produced by Kao Corporation] was added to bring the rubber concentration to 8%. It was adjusted and centrifuged for 30 minutes at a rotation speed of 11,000 rpm.

Next, the creamy fraction produced by centrifugation was dispersed in a 1% aqueous solution of Emulgen 810 to adjust the rubber concentration to 8%, and then again.
It was centrifuged for 30 minutes at a rotation speed of 11,000 rpm. After repeating this operation once again, the obtained creamy fraction was dispersed in distilled water to prepare a deproteinized rubber latex having a solid rubber content of 60%.

Next, the deproteinized rubber latex is frozen,
After coagulation, water was removed to dry the raw rubber. When the total nitrogen content in the obtained raw rubber was measured by the Kjeldahl method, it was 0.04% by weight. (Production of rubber composition) Based on 100 parts by weight of the raw rubber,
The following components were blended and kneaded to produce a rubber composition.

Component Weight Part Furnace Black (ISAF ^{* 1} ) 50 Styrene 3 Zinc oxide (ZnO) 3 Anti-aging agent 13 1 Anti-aging agent RD (TMQ ^{* 2} ) 1 Sulfur 1.5 Vulcanization accelerator NS 0. 75 * 1: Intermediate super abrasion furnace black * 2: Polymer of 2,2,4-trimethyl-1,2-dihidroquinone Example 2 (Preparation of raw rubber) Commercially available high ammonia latex [solid rubber content manufactured by Guthrie Co., Malaysia] 62.0%],
It was diluted with a 0.12% sodium naphthenate aqueous solution to a solid rubber content of 10% by weight, and sodium dihydrogen phosphate was added to adjust the pH to 9.2. And rubber 10
g, proteolytic enzyme (Alcalase 2.0M)
Was added at a rate of 0.87 g, and the pH was readjusted to 9.2, and then maintained at 37 ° C. for 24 hours.

Next, the latex which has been subjected to the enzyme treatment is
Nonionic surfactant [Product name Emulgen 8 manufactured by Kao Corporation
The rubber concentration was adjusted to 8% by adding 1% aqueous solution of 10] and centrifuged at a rotation speed of 11,000 rpm for 30 minutes. Next, the creamy fraction produced by centrifugation was dispersed in a 1% aqueous solution of Emulgen 810 to adjust the rubber concentration to 8%, and then, again,
Centrifugation was carried out for 30 minutes at a rotation speed of 000 rpm. After repeating this operation once again, the obtained creamy fraction was dispersed in distilled water to prepare a deproteinized rubber latex having a solid rubber content of 60%.

Next, the deproteinized rubber latex is frozen,
After coagulation, water was removed to dry the raw rubber. When the total nitrogen content in the obtained raw rubber was measured by the Kjeldahl method, it was 0.015% by weight. (Production of Rubber Composition) A rubber composition was produced in the same manner as in Example 1 except that 100 parts by weight of the raw rubber was used.

Example 3 Similar to Example 1 except that 100 parts by weight of raw rubber having a total nitrogen content of 0.09% by weight, which was produced in the same manner as in (Preparation of raw rubber) of Example 1, was used. Then, a rubber composition was produced. Example 4 In the same manner as in Example 1 except that 100 parts by weight of raw rubber produced in the same manner as in (Preparation of raw rubber) in Example 2 and having a total nitrogen content of 0.009% by weight was used. A rubber composition was produced.

Example 5 The same as Example 1 except that 100 parts by weight of raw rubber having a total nitrogen content of 0.02% by weight, which was produced in the same manner as in (Preparation of raw rubber) of Example 2, was used. Then, a rubber composition was produced. Comparative Example 1 A rubber composition was produced in the same manner as in Example 1 except that 100 parts by weight of pale crepe, which belonged to the cleanest class among commercially available solid rubbers, was used as it was without deproteinization. Total nitrogen content of solid rubber is 0.46% by weight
Met.

Comparative Example 2 Similar to Example 1 except that 100 parts by weight of raw rubber having a total nitrogen content of 0.11% by weight, which was produced in the same manner as in (Preparation of raw rubber) of Example 1, was used. Then, a rubber composition was produced. Comparative Examples 3-5 The total nitrogen content used in Example 2 is 0.015% by weight.
The rubber compositions of Comparative Examples 3 to 5 were produced in the same manner as in Example 2 except that 100 parts by weight of the following raw material rubbers were used instead of 100 parts by weight of the raw rubber.

Comparative Example 3: Air-dried high ammonia latex Comparative Example 4: SMR-CV (Standard Malaysian Rubber-
CV) Comparative Example 5: Natural rubber (RSS3) masticated by adding a deflocculating agent Tensile Strength Test The rubber compositions prepared in the above Examples and Comparative Examples were subjected to 140 ° C. and 20 minutes, respectively. After press vulcanizing under the conditions, JI
Third of SK 6301 "Vulcanized rubber physical test method"
The initial tensile strength T _B [MPa] and the elongation E _B (%) were obtained according to the test method described in the section “Tensile test”. Further, the vulcanized sample was left at 100 ° C. for 48 hours, and then the same measurement was performed to obtain the tensile strength T _B [MPa] and the elongation E _B (%) after aging.

Tear Strength Test Each of the rubber compositions prepared in each Example and Comparative Example was tested as 1
After press vulcanization at 40 ° C for 20 minutes, JIS
K 6301 in accordance with the Shosai test method in Section 9, "tear test" in the "vulcanized rubber physical test method", the tear strength T _R
[KN / m] was determined.

Measurement of loss tangent tan δ The rubber compositions prepared in each of the examples and comparative examples were measured in 1
After press vulcanization at 40 ° C. for 20 minutes, a JIS K test was performed using a viscoelasticity measurement tester (manufactured by Iwamoto Manufacturing Co., Ltd.).
The loss tangent tan δ was measured according to the test method described in 6394 “Dynamic property test method for vulcanized rubber”. The measurement conditions were a frequency of 10 Hz, a temperature of 70 ° C. and 0 ° C.

Measurement of Mooney Viscosity and Scorch Time The Mooney viscosity ML _{1 + 4} (130 ° C.) of the rubber compositions prepared in each of the Examples and Comparative Examples was measured according to JIS K 6300 “Unvulcanized Rubber Physical Test Method”. The measurement was carried out according to the test method described in Section 4, "Moonie viscosity test". Scorch time (minutes) is 5 points, 10 points and 90
I made the machine automatically read the time until the point was raised.

Hardness Measurement The rubber compositions prepared in each of the examples and comparative examples were each
After press vulcanization at 40 ° C for 20 minutes, JIS
The initial spring hardness H _S was determined according to the test method described in Section 5 “Hardness test” of K6301 “Vulcanized rubber physical test method”. Also, 100% of the vulcanized sample
After leaving at 48 ° C. for 48 hours, the same measurement was performed to determine the spring hardness H _S after aging.

Abrasion amount measurement The rubber compositions prepared in each Example and Comparative Example were each
After press vulcanization at 40 ° C. for 20 minutes, according to the method specified in BS standard 903 partA9 C method, using an Akron abrasion tester, familiar running for 500 revolutions, AKRON abrasion loss after 500 revolutions of this test [Cc] was measured.

The above results are shown in Table 1. The above results
Tables 1 and 2 show the total nitrogen content values measured by the Kjeldahl method in the raw rubbers used in the rubber compositions of Examples and Comparative Examples.

[0041]

[Table 1]

[0042]

[Table 2]

As is clear from the results of Tables 1 and 2, Examples 1 to 5 having the constitution of the present invention are all Mooney as compared with Comparative Examples 1 to 5 using other conventional raw material rubbers. Since the viscosity was low, and in particular, the Mooney viscosity was lower than that of Comparative Example 5 in which mastication was once performed, it was found that the workability was improved and the productivity was excellent as mastication was unnecessary.
Example 1 in which the total nitrogen content is 0.1% by weight or less
5 Both, total nitrogen content of a high strength T _B tensile compared to Comparative Example 1-5 in which more than 0.1 wt%, yet it has been found that tear resistance is large.

[0044] Any Further Examples 1 to 5 also, small decrease and increase the amount of spring type hardness H _S elongation E _B due to aging, From this, it was confirmed that those not easily aged. Further, in all of Examples 1 to 5, since the results of the abrasion test are similar to those of the conventional ones, it was found that they can be sufficiently used as tire rubbers.

All Examples 1 to 5 are Comparative Examples 1 to 1.
Since tan δ at 70 ° C. is smaller than that of No. 5, it was also found that a rubber tire with low energy loss and low rolling resistance can be manufactured. It was also found that Examples 1 to 5 have the same or higher tan δ at 0 ° C. as compared with Comparative Examples 1 to 5, and thus are rubber tires having good wet grip.

Further, when the results of the respective examples were compared and examined, it was confirmed that the lower the total nitrogen content, the more desirable the result.

[0047]

Since the rubber composition of the present invention is constituted as described above, the rubber composition at 50 to 70 ° C. is higher than the conventional one.
It has a small tan δ and is superior in terms of heat generation and rolling resistance reduction. It has high strength, high tear resistance, and has a lower Mooney viscosity than that of masticated material, so it has good workability and does not require mastication and is immediately productive. It has excellent characteristics that have never been seen. Further, when this material is used as a material for tires, there is a feature that heat generation is small, rolling resistance is reduced, and wet grip is excellent.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Naoya Ichikawa 41, Shimizu, Uozumi-cho, Akashi-shi, Hyogo 1 Sumitomo Rubber Fish Dormitory (72) Inventor Yuichi Hioki 1293-7 Wakuyama, Wakayama Prefecture 1293-7 (72) Invention Shoji Hayashi 133-5 Enohara, Wakayama City, Wakayama Prefecture

Claims (4)

[Claims] 1. A rubber composition comprising a natural rubber deproteinized so that the total nitrogen content as an index of protein amount is 0.1% by weight or less. 2. The rubber composition according to claim 1, wherein the total nitrogen content of the deproteinized natural rubber is 0.05% by weight or less. 3. The rubber composition according to claim 1, wherein the total nitrogen content of the deproteinized natural rubber is 0.02% by weight or less. 4. The rubber composition according to claim 1, which is a tire material.