JPH05301994A - Rubber compounding composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition useful for tire, etc., having excellent strength, lightness, wet skid properties by blending a rubber composition consisting essentially of natural rubber with a given amount of microbial cellulose. CONSTITUTION:(A) A rubber composition consisting essentially of natural rubber is blended with (B) 0.5-25 pts.wt. calculated as dried material of microbial cellulose obtained by standing culture to give the objective composition.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to improving the strength of rubber compositions.

[0002]

2. Description of the Related Art A conventional rubber composition is mainly composed of a diene-based synthetic rubber. For example, a rubber composition having an oil resistance and an ozone resistance is a rubber composition comprising an acrylonitrile-butadiene copolymer rubber and a vinyl chloride resin. It is used.

To reduce the weight of tires, light and strong fine fibers are required. Currently, about 5% of carbon black is blended and the tire is heavy. Carbon black is not a strong structure because it has a series of granular particles.

It has been conventionally known that low rolling resistance is indispensable in order to realize energy saving, which is a social demand under high price oil in recent years, in terms of tire performance, but generally low rolling resistance is required. It has been considered that a rubber material exhibiting resistance has a poor road gripping ability on a wet road surface, that is, a so-called wet skid property, and the performances of the two are contradictory. Heretofore, a method of blending a diene-based synthetic rubber with an emulsifier such as an alkali amide salt of succinic acid (JP-A-59-59).
-45340), tin, silicon, and diene synthetic rubber (Japanese Patent Laid-Open No. 58-122939), which is a polymer containing a bond between a metal and carbon of germanium in its molecular chain, and a nonmetallic fiber (average fiber length). There is a tread rubber composition for studless tires (Japanese Patent Laid-Open No. 3-152140) containing 30 to 4000 microns and an average diameter of 10 to 35 microns. However, the strength has not been improved.

[0005]

An object of the present invention is to provide a rubber composition having excellent strength.

[0006]

[Means for Solving the Problems] According to the present invention, a conventional rubber composition is prepared by converting microbial cellulose (hereinafter abbreviated as microbial cellulose) obtained by static culture in the composition into a dried product. The rubber compounding composition is characterized in that it contains 0.5 to 25 parts by weight of the composition. They have found that the composition has excellent strength and completed the present invention. The present invention will be described in detail below.

The molding process of a rubber material is generally performed as follows. To the raw rubber that was first masticated and softened,
A product is obtained by kneading carbon, oil, an antioxidant and the like, further lowering the temperature and kneading sulfur, and then pressurizing and enclosing in a predetermined mold and press-heating at a temperature of about 150 ° C. for a certain period of time.

The amount of sulfur mixed in the raw rubber as a crosslinking agent varies depending on the type and amount of the vulcanization accelerator, and also varies depending on vulcanization conditions such as temperature and time. At this time, there are monosulfide bridges having one sulfur atom (S) that acts as a crosslinking point, disulfide bridges having two S2 crosslinking points, and polysulfide bridges composed of many S. There is also intramolecular crosslinking. On the other hand, when an organic peroxide is used as the cross-linking agent, a C-C cross-link in which different carbon atoms (C) in the rubber molecular chain are directly bonded to each other is obtained. For example, polysulfide crosslinked rubber is excellent in bending fatigue resistance, crack resistance, wear resistance, etc., but is not good in creep resistance, stress relaxation resistance, etc. On the other hand, the shortest C-C crosslinked rubber is the opposite, and is inferior in flex fatigue resistance but excellent in creep resistance. It is known that S-crosslinking and S-S-crosslinking show intermediate properties between these.
In contrast to such conventional rubber materials, thermoplastic elastomers and liquid elastomers have recently received attention as rubber materials having excellent processability. A thermoplastic elastomer is a combination of a resin part that easily forms a hard block such as a crystal structure or an aggregated structure in one molecular chain and a part that is made of a conventional rubber component that makes it difficult to form a hard block together. It is a high-polymer material. The liquid elastomer is a rubber obtained by reacting a liquid polymer having a molecular weight of 3,000 to 6000 with a hydroxyl group or a carboxyl group at its molecular end with a polyfunctional chain extender or binder. say.

For example, in the tread composition of a tire, various tread patterns are applied in a portion which is in direct contact with the road surface, depending on the purpose of use and the conditions thereof, to provide the effect of traction force, braking force and skid prevention. The rubber material used here is called a tread, and a compounding mainly considering wear resistance, fracture resistance, skid resistance and the like is used. Generally, butadiene rubber (hereinafter referred to as BR) has better wear resistance than styrene-butadiene rubber (hereinafter referred to as SBR) under severe operating conditions, so the tread composition should be mainly BR composition for large tires. Used by blending SBR. On the other hand, SBR is mainly used for small tires. Since SBR generates more heat than BR, SBR is not suitable for places where heat generation is important. But conversely,
This property of large heat generation may be used as a measure to increase skid resistance and prevent noise during running.

The vulcanization system containing the tread is required to have a flat vulcanizability so that the physical properties do not change so much even if it is overvulcanized. Usually sulfenamides, thiazoles alone,
Alternatively, it is sulfur vulcanization using a vulcanization accelerator such as a combination of both.

On the other hand, the microbial cellulose used in the present invention is a very thin ribbon (which is said to have a width or a diameter of 100 nm or less) made of cellulose having extremely high crystallinity and uniaxial orientation in the produced state. It has a network-like structure in which fibers are intertwined intricately, and this structure contains a large amount of liquid in the voids inside,
Its appearance is gel-like. The liquid component contained in the voids in the microbial cellulose structure, such as water, exists as free water and is easily squeezed out when an external force is applied. Since it is composed of a large number of ribbon-shaped fibers having extremely high crystallinity, it can withstand external forces such as tension even in a wet state. Microbial cellulose does not differ in primary structure from cellulose of plant-derived cotton, wood pulp, etc., but so-called higher-order structure such as the network described above is not found in plant-derived cellulose. Therefore, it is peculiar to microbial cellulose, and therefore exhibits various properties such as strength even though it is in a gel form.

Microbial cellulose, when produced, appears to be in the form of a gel. That is, the microbial cellulose is composed of thin fibers as described above, and contains 95% or more by weight of the liquid component of the liquid component in the voids between the fibers. The liquid component is not bound in the voids in a molecular state like general polymer gels. For example, when the liquid component is water, most of it exists as free water in the gelled microbial cellulose,
It is possible to squeeze out the liquid component by simply pinching it with your finger. In addition, microbial cellulose is characterized by being composed of α-cellulose having high crystallinity, having extremely strong surface orientation, and having extremely high strength.

The microbial cellulose obtained in such a gel form can be obtained by static culture as a production method. However, on the other hand, the microbial cellulose obtained by stirring culture is not gel-like but pellet-like.

Microbial cellulose includes those containing cellulose and a heteropolysaccharide having cellulose as a main chain and β,
Including glucan such as α. In the case of a heteropolysaccharide, the constituent components other than cellulose include hexoses such as mannose, fructose, galactose, xylose, arabinose, rhamnose and uronic acid, pentasaccharides and organic acids. There are celluloses in which these polysaccharides exist as a single substance, and there are celluloses in which two or more types of polysaccharides are mixed.

Microorganisms that produce such microbial cellulose are not particularly limited, and for example, acetobacter
Pasteurianus (Asetobacter pasturianus) ATCC10
821, FERM P-12884, the same aceti (A.acet
i), A. ransens, Sarcina ventriculi, Bacterium xyloi-des, Pseudomonas spp, Agrobacterium spp, Rhizobium spp, and the like.

For the production and accumulation of microbial cellulose,
A general method for culturing ordinary bacteria using the above-mentioned microorganism may be followed. That is, it is added to a normal nutrient medium containing a carbon source, a nitrogen source, inorganic salts, and other organic trace nutrients such as amino acids and vitamins at 20 ° C.
The static culture may be carried out by controlling the temperature to 40 ° C. The microbial cellulose produced in this manner is microbial cells or
Since it contains the medium components, it may be washed according to the application.
The washing may be performed with a dilute alkali, a dilute acid, an organic solvent, hot water or the like alone or in combination. Microbial cellulose with Waring blender 10,000 rpm 5-9
It may be pulverized for 0 minutes, preferably 10 to 30 minutes.
It is possible to carry out disaggregation in this way to produce disaggregated products, but the degree of disaggregation depends on JAPAN TAPPI
o. It can be measured by the method described in 52-89.

In order to develop the rubber composition, especially the tire tensile strength, the apparent fiber width measured by this method is 1 micron or less, the fiber length is 30 micron or less in weight average fiber length, and 25 micron in number average fiber length. The following are preferred. When the weight average fiber length is larger than 30 μm or when the number average fiber length is larger than 25 μm, the strength effect is not observed when compounded in the rubber composition as compared with the usual case.

Microbial cellulose obtained by stationary culture with stirring was disaggregated with a Waring blender to obtain a dissociated product having a length of 30.
About 40% of micron or more particles were obtained in the agitation culture, and 10% or less in the static culture. Therefore, microbial cellulose obtained by static culture is preferable for the purpose of the present invention.

The disaggregated product of the above-mentioned microbial cellulose can be used after being naturally dried or after being replaced with a solvent such as acetone or acetonitrile and then dried by a method such as air drying. The dried product may be added and kneaded at the time of mastication of raw rubber such as SBR and BR.

The rubber compounding composition of the present invention is obtained by converting microbial cellulose into a dry matter in the rubber composition,
It has been discovered that the inclusion of 5 to 25 parts by weight is superior in strength to conventional rubber compositions.

Test Method 1 Strength Test The tensile test was carried out at 25 degrees according to JIS K6301.

Test method 2 Weight ratio of rubber composition It was determined from the weight / volume ratio.

[0023]

EXAMPLES The present invention will be specifically described below based on examples.

Preparation of Microbial Cellulose (A) Obtained by Static Culture As a microbial cellulose production medium, fructose 4
0.0 g / l, corn steep liquor 50 ml / l,
Ammonium sulfate 3.0 g / l, 1 potassium phosphate 1.
0 g / l, magnesium sulfate heptahydrate 1.0 g / l, phytic acid 100 mg / l, ammonium ferric citrate 15 m
g / l, calcium chloride 15 mg / l, ammonium molybdate 1 mg / l, zinc sulfate heptahydrate 2 mg / l, manganese sulfate tetrahydrate 1 mg / l, copper sulfate pentahydrate 0.02 m
g / l, nicotinic acid 0.5 mg / l, pyridoxine hydrochloride 0.5 mg / l, thiamine hydrochloride 0.5 mg / l, calcium pantothenate 0.2 mg / l, riboflavin 0.2 mg / l, folic acid 0.02 mg / L, biotin 0.
The composition used was 02 mg / l, yeast extract 100 mg / l, and malto extract 100 mg / l (pH 5.0). After autoclaving the medium at 120 ° C. for 20 minutes, 1 × 10 4 Acetobacter aceti subsp. Xylinum (ATCC 10820) /
The mixture was inoculated at a concentration of ml, 150 ml of the mixture of the medium and the bacterial solution was placed in a large glass Petri dish (inner diameter 20 × 5 cm), and static culture was carried out at 30 ° C. for 14 days. After culturing, the microbial cellulose gel produced from the culture solution was washed with a 1% alkaline solution and tap water until the pH became neutral, and the microbial cellulose gel was washed with a Waring blender at 10,000 rpm for 15 minutes. went. The disaggregated product was replaced with twice the amount of acetone as the dissociated product for 3 hours, and the dissociated product was mixed with 6 times.
It was prepared by placing it in a 00 mesh sieve and air-drying at room temperature for 2 days.

Preparation of Microbial Cellulose (B) Obtained by Shaking Culture 400 ml of the above-mentioned medium was put into a 1 L stirring culture tank to carry out main culture. The culture temperature of the main culture was 30 ° C., the stirring speed was 400 rpm, and the aeration rate was 1 VVM. Pelletized microbial cellulose obtained 48 hours after the culture was prepared by the above method.

Examples 1-6 Preparation of rubber composition (unit is parts by weight) SBR-1712 83 BR 40 carbon black 40 zinc white 3 stearic acid 1.5 anti-aging agent AW 2 (Ethoxy-dihydro)
-Methyl-phosphite) Paraffin wax 3 Process oil 18 Vulcanization accelerator 1 Sulfur 1.8 Microbial cellulose (A) 0.5-25 The above zinc white, vulcanization accelerator, and additives other than sulfur are added to a Banbury mixer (TOYOSEI). -Made by KI), and then the remaining additives such as zinc white were added and kneaded by a kneading roll machine (TOYOSEIKI). Press vulcanization condition 145
It was carried out at ℃ for 22 minutes to produce a rubber having a thickness of 3 mm. The results of the physical properties of these rubber compounding compositions are shown in Table 1.

Comparative Example 1-4 A rubber compounding composition was obtained in the same manner as in Example, and the results of its physical properties are shown in Table 1.

[0028]

[Table 1]

[0029]

The rubber compound composition of the present invention is a useful technique which is superior in strength and weight reduction of rubber as compared with the conventional rubber composition.

Claims (1)

[Claims] 1. In a rubber composition containing natural rubber as a main component, the composition contains 0.5 to 25 parts by weight of microbial cellulose obtained by static culture in the composition, converted to a dried product. A rubber compounding composition comprising: