JPH0570659B2 - - Google Patents

Description

[Detailed description of the invention]

Technical field to which the invention relates The present invention relates to a pneumatic tire,
More specifically, the present invention relates to a pneumatic tire using a rubber composition whose processability and physical properties are improved by blending a calcium carbonate-based composite pigment into at least a portion of the rubber material in the tread portion of the tire. Conventional technology Fine particle silicic acid and silicates have been called white carbon because they have reinforcing properties second only to carbon black. In the tire industry, rubber materials containing white carbon have been used as white sidewalls, and steel cords and silicates have been used as white carbon. In order to satisfy requirements such as adhesion to rubber, cut resistance, and chipping resistance, large tires for rough roads are known in which treads are formed from a rubber composition that is especially blended with carbon black. However, since the silanol groups on the particle surface of white carbon are hygroscopic and at the same time adsorb polar substances, in the case of rubber containing white carbon, the white carbon may form an adsorption engagement with the rubber. Or, due to the cohesive force of white carbon, they coagulate together,
As a result, the viscosity when unvulcanized becomes high, which significantly impairs processability such as kneading and extrusion, and the dispersion is poor, making it unsatisfactory as a rubber material for tires. For this reason, a method has been proposed to prevent the adsorption of silanol groups in advance by adding polar substances such as organic bases and alcohols, so-called activators, to white carbon compounded rubber, thereby suppressing the increase in viscosity and improving processability. However, these activators have the disadvantage that they deteriorate the physical properties after vulcanization, especially the heat generation properties, so such rubber compositions are rarely used in pneumatic tires. That is the reality. On the other hand, calcium carbonate is known as a white filler other than white carbon, and has a particle size of 0.03~
There are fine cubic synthetic products with a particle diameter of 0.5 μm and a BET specific surface area of 6 to 50 m ² /g, and amorphous heavy products with a particle size of 2 to 10 μm and a BET specific surface area of 0.5 to 4 m ² /g.
Because its reinforcing properties are significantly inferior to that of white carbon, it has not been used much in the tire industry other than as a filler. DISCLOSURE OF THE INVENTION However, the BET specific surface area of 60 m ² /g or more and 70
Calcium carbonate-based composite pigments with linseed oil absorption of more than 100 g/ml have extremely excellent reinforcing properties, and by blending them in a specific amount, a rubber composition with excellent processability as a rubber material can be obtained and is inexpensive. Therefore, it was confirmed that by using a rubber material blended with such a calcium carbonate-based composite pigment, a pneumatic tire having characteristics equivalent to or better than conventional pneumatic tires could be obtained more easily and at a lower cost. I have achieved this. Therefore, in the pneumatic tire of the present invention, at least a portion of the rubber material constituting the tire contains 60 m ² /g per 100 parts by weight of natural rubber and/or synthetic rubber.
The present invention is characterized by using a rubber composition containing 5 to 100 parts by weight of a calcium carbonate composite pigment having a BET specific surface area of 70 ml/100 g or more and a linseed oil absorption of 70 ml/100 g or more. As described above, in the pneumatic tire of the present invention, at least a portion of the rubber material in the tread portion constituting the tire is made of a rubber composition blended with the specified amount of the calcium carbonate-based composite pigment. The rubber component may be natural rubber alone or natural rubber and synthetic rubber, and the synthetic rubber may be any rubber conventionally used in tires, such as styrene-butadiene rubber, synthetic polyisoprene rubber, polybutadiene rubber, and ethylene propylene rubber. Or butyl rubber etc.
These can be used alone or in combination. Further, these synthetic rubbers may be used in a blend with natural rubber. The calcium carbonate composite pigment used in the present invention has a BET specific surface area of 60 m ² /g or more, preferably 70 m ² /g or more, and 70 ml/100 g or more, preferably 100 ml/100 g or more, more preferably 120 m 2 /g or more.
It has a linseed oil absorption amount of ml/100g or more. This composite pigment has ultrafine particles with a diameter of 0.01 to 0.02 μm linearly bonded in a chain with a length of 0.05 to 1.00 μm, and exhibits suitable reinforcing properties within this range. The method for producing such a composite pigment is to use an aqueous solution of a water-soluble metal salt that forms a colloidal metal oxide, such as a sulfate or acetate of zinc, or a solution of these and sulfuric acid,
Add acetic acid or other mixed solution at a ratio of 0.02 to 0.10 mol to 1 mol of calcium hydroxide, so that the injection is completed within 3% of the carbonation rate (CaCO ₃ weight/Ca(OH) ₂ weight x 100 (%)). Then, it is mixed into carbon dioxide gas in a spray state and reacted. Furthermore, when the carbonation rate reaches 80%, soluble silicic acid, such as an alkali silicate, such as sodium silicate or silicate sol, is added as required to continue the carbonation reaction. A calcium carbonate pigment complexed with silicic acid and/or zinc in a chain shape of ~0.02 μm×0.05 to 1.00 μm in length is obtained. Here, by treating with soluble silicic acid, calcium silicate particles exhibit the effect of being more easily dispersed in the rubber in the form of fine primary particles due to their non-agglomerating properties, and zinc can obtain the desired chain-like particles. It is necessary for In the present invention, the calcium carbonate pigment is preferably blended in an amount of 5 to 100 parts by weight, particularly 5 to 30 parts by weight for diamond treads, based on 100 parts by weight of rubber. If the above pigment is less than 5 parts by weight, cut resistance and chipping resistance will not be improved when used in tire treads, which is not preferable, whereas if it exceeds 100 parts by weight, reinforcing properties will deteriorate and heat generation properties will also worsen. It is not desirable because it In the present invention, in addition to the above-mentioned calcium carbonate pigments, inorganic pigments and organic pigments such as carbon black, clay, heavy calcium carbonate, light calcium carbonate, or white carbon as required are further blended to form carbon black, especially carbon black. Preferably specific surface area ( _N2SA ) 80-120 by nitrogen adsorption method
m ² /g, dibutyl phthalate (DBP) oil absorption 90
It is preferable to use ~130 ml/100 g of highly reinforcing carbon black, usually in an amount of 20 to 80 parts by weight. If it is less than 20 parts by weight, no reinforcing effect can be obtained, and if it exceeds 80 parts by weight, heat generation properties will deteriorate, which is not preferable. In the present invention, the rubber composition in which the calcium carbonate-based composite pigment is blended includes vulcanizing agents, vulcanization accelerators, vulcanization accelerators, anti-aging agents, softeners, etc. that are usually blended in rubber compositions for tires. The following compounding agents are appropriately blended within the usual blending range and used as a rubber material for tire tread. EXAMPLES OF THE INVENTION The present invention will now be described in detail with reference to examples. Example 1 Four types of rubber compositions, Nos. 1 to 4, were prepared by kneading the components according to the formulation contents (parts by weight) shown in Table 1, and the Mooney viscosity of these rubber compositions was measured. Furthermore, after vulcanizing these rubber compositions in a press at 145°C for 40 minutes, the tensile strength, elongation, and modulus were measured. The impact resistance cut test and toread appearance test were also evaluated. The obtained results are also listed in Table 1. The evaluation methods for the impact resistance cut test and toread appearance test are as follows. Impact Resistance Cut Test The rubber composition after vulcanization was scratched by striking it with a steel blade from a certain height using a pendulum type impact cut tester, and the depth of the cut was indicated. Tradition appearance test A 1000-20, 14-ply bias structure pneumatic tire for trucks and buses was made by dividing the tread into four parts and using the rubber composition shown in Table 1. After driving for 2000km while applying sudden braking, the number of large cuts (scratches with a depth of 5 mm ^or more), small cuts (scratches with a depth of 1 to less than 5 mm), and chips (25 mm 2) per 100 cm ² of the tored surface
The number of pieces of rubber scraped off) was evaluated.

【table】

[Table] Example 2 Four types of rubber compositions Nos. 5 to 8 were prepared by kneading the respective compounding components according to the compounding contents (parts by weight) shown in Table 2, and Examples were prepared for these rubber compositions. The performance was evaluated in the same manner as in 1, and the obtained results are also listed in Table 2.

【table】

[Table] Effects of the Invention The tire of the present invention has a tread portion that constitutes the tire made of a rubber material consisting of a rubber composition in which a specific amount of the above-mentioned calcium carbonate-based composite pigment is blended with natural rubber alone or with natural rubber and synthetic rubber. As is clear from the results in Tables 1 and 2 of Examples, in addition to improved reinforcing properties, easier workability, and lower cost, by forming at least a part of the rubber material in It is clear that the rubber composition used in the present invention has significantly superior reinforcing properties compared to conventional rubber compositions containing calcium carbonate, and has significantly superior processability compared to rubber compositions containing white carbon. The tire of the present invention, in which the tread is formed using this rubber material, has the advantage of improved running performance on rough roads due to the improved reinforcing properties of the rubber.

Claims (1)

[Claims] 1. At least a portion of the rubber material in the tread portion constituting the tire has a BET specific surface area of 60 m ² /g or more and a linseed oil absorption of 70 ml / 100 g or more based on 100 parts by weight of natural rubber or natural rubber and synthetic rubber. A pneumatic tire characterized by using a rubber composition containing 5 to 100 parts by weight of a calcium carbonate-based composite pigment.