JPH07228726A - Foamable rubber composition for tire - Google Patents

Abstract

PURPOSE:To obtain a foamable rubber composition which foams homogeneously by mixing a rubber ingredient with given amounts of a foaming agent and an inert filler having a specific maximum average width. CONSTITUTION:100 pts.wt. rubber ingredient is mixed with 0.1-10 pts.wt. foaming agent, e.g. dinitrosopentamethylenetetramine, 1-50 pts.wt. inert filler having a maximum average width of 0.1-100mum and selected from silica, alumina, lime, etc., and other additive(s) including a curing agent, a curing accelerator, an auxiliary accelerator, an oil extender, a softener, and an antioxidant to obtain the title composition which foams highly homogeneously. The composition is foamed by hot pressing in a given manner to obtain a foamed rubber regulated with respect to the number and average diameter of the resulting closed cells.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber foam composition for tires having excellent foaming uniformity, and more specifically, for tread rubbers for tires, rubbers for sidewalls, rubbers for inner liners, etc. The present invention relates to a foamed rubber composition for a tire, which can improve the dynamic performance of a tire obtained by using the foamed rubber, the riding comfort of the tire, and the soundproofness against the sound outside and inside the vehicle.

[0002]

2. Description of the Related Art Rubber foams have various physical characteristics such as sound insulation, vibration absorption, lightness and surface roughness, and have been rapidly used for tire members in recent years. . As a method of expressing a foamed material in a rubber member of a tire, a method of controlling a vulcanization temperature and a pressure by dispersing a foaming agent in a rubber composition is generally used.

[0003]

[Problems to be Solved by the Invention] However, today,
It is known that the number of closed cells in the foam and the uniformity of the average diameter greatly affect various tire performances (for example, JP-A-62-283001 and JP-A-63-9040).
No. 2), there is a possibility that various problems may occur in terms of durability, quality safety, etc., simply by using foamed rubber.

For example, in terms of durability, when a portion of the foamed rubber in which the number of closed cells and the average diameter thereof are remarkably increased is generated, the strain of the portion is increased, which eventually leads to breakage and a predetermined durability cannot be obtained. However, there was a problem that there was concern about safety.

On the contrary, if the number of closed cells and the average diameter of the foamed rubber are remarkably reduced, there is a problem that the performance expected by the foamed rubber cannot be obtained.

Therefore, it is necessary to control the number of closed cells and the average diameter of the foamed rubber to ensure the uniformity of foaming.
It is extremely important in obtaining the required performances. However, conventionally, such control has not been sufficient. That is, as a conventional control method, an appropriate amount of a foaming aid is blended or a foaming agent is selected so that foaming starts favorably within the temperature and pressure ranges required for vulcanization during tire production. Attempts have been made, but under the present circumstances, it cannot be said that the above controls are sufficiently performed.

Therefore, an object of the present invention is to control the number and the average diameter of the closed cells of the foam developed during vulcanization of rubber.
It is intended to provide a foamed rubber composition for a tire having excellent foaming uniformity.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that when a foam rubber composition was blended with an inert filler of a predetermined size, excellent foam uniformity was obtained. Therefore, the present invention has been completed and the present invention has been completed.

That is, the foamed rubber composition for tires of the present invention is characterized by being blended with an inert filler having a maximum average width of 0.1 to 100 μm.

In the present invention, it is preferable that 0.1 to 10 parts by weight of the foaming agent and 1 to 50 parts by weight of the above-mentioned inert filler are mixed with 100 parts by weight of the rubber component.

As the above-mentioned inert filler, glass, silica (SiO ₂ ), alumina (Ai ₂ O ₃ ), lime (Ca
O), magnesium oxide (MgO), ceramics, talc, clay, lower carbon black having a surface area of 30 m ² / g or less, wood powder, cork powder, mica, nylon fiber, polyester fiber, aramid fiber, and the like. Is a powder of silica, alumina, lime, magnesium oxide.

Next, examples of the foaming agent according to the present invention include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, aromatic sulfonyl hydrazide compounds such as benzenesulfonyl hydrazide, toluenesulfonyl hydrazide, Oxybis-benzenesulfonyl hydrazide and the like can be used. In order to form a foamed rubber using such a foaming agent, these may be added to a rubber compound containing the above-mentioned inert filler and heated and pressed according to a usual tire manufacturing method.

In the rubber composition according to the present invention, in addition to the above foaming agent, an oil extender such as aromatic process oil and naphthenic process oil, a softening agent such as carbon black and spindle oil, an antiaging agent, and a vulcanization agent. It goes without saying that rubber accelerators such as accelerators, vulcanization accelerating aids such as stearic acid and zinc white, and vulcanizing agents can be compounded within the usual ranges.

[0014]

In the present invention, the added maximum average width of 0.
The inert filler of 1 to 100 μ acts as a core of each closed cell during vulcanization of the rubber, which makes it possible to maintain the uniformity of foaming. If the maximum average width is less than 0.1 μ, the effect of uniforming the foam diameter is small and it is unsuitable as a core of closed cells exhibiting excellent foaming uniformity. On the other hand, 100μ
When it exceeds, the durability of the rubber such as abrasion resistance and fracture resistance is deteriorated. It is preferable that the inert filler is hard and circular, and has a uniform particle size in order to function well as the core. The maximum average width is the diameter of the inert filler when it is in the form of particles, and the length when it is fibrous.

A suitable amount of such an inert filler to be blended is in the range of 1 to 50 parts by weight with respect to 100 parts by weight of the rubber component, but this is less than 1 part by weight as in the case of the above-mentioned maximum average width. This is because the effect of making the foam diameter uniform is small, and when it exceeds 50 parts by weight, the durability of the rubber such as abrasion resistance and fracture resistance is deteriorated.

The preferred amount of the foaming agent is 10 for the rubber component.
It is 0.1 to 10 parts by weight with respect to 0 parts by weight, but depending on the type of the foaming agent, if it is less than 0.1 parts by weight, the foaming itself will be insufficient and the desired performance effect will be obtained. On the other hand, if it exceeds 10 parts by weight, the durability of the rubber such as abrasion resistance and fracture resistance will be deteriorated.

[0017]

EXAMPLES Next, the present invention will be specifically described based on examples. A rubber composition was prepared according to the formulation (parts by weight) shown in Table 1 below. In the table, dinitrosopentamethylenetetramine was used as the foaming agent, and industrial calcium oxide having a maximum average width of 10 to 50 μ by the mesh method was used as the inert filler. The obtained rubber composition was vulcanized at ordinary temperature and pressure during tire production to obtain foamed rubber. The foaming ratio and foaming diameter distribution of the foamed rubber were evaluated as follows.

The foaming rate foaming rate V _S is represented by the following formula _{V S = {(ρ 0 -ρ} g) / (ρ l -ρ g) -1} × 100 (%) (1), ρ l is , Density of foam rubber (g / cm ³ ), ρ
₀ is the density (g / cm ³ ) of the solid phase portion of the foamed rubber, ρ
_g is the density (g / cm ³ ) of the gas part in the bubbles of the foamed rubber
Is.

The foamed rubber is composed of a rubber solid phase portion and a cavity (closed cell) formed by the rubber solid phase portion, that is, a gas portion in the bubble. Since the density of the gas part is extremely small, almost close to zero, and extremely small with respect to the density of the rubber solid phase part, the formula (1) is

It becomes almost equal to V _S = (ρ ₀ / ρ _l −1) × 100 (%) (2).

Then, the test foamed rubber was made into a thin piece having a thickness of 2 mm, left for one week after vulcanization to be stabilized, and then the density was measured. In addition, the density of the tread of the non-foamed rubber (solid phase rubber) was measured. The measurement was performed, and the foaming rate Vs was obtained using the formula (2).

Foam Diameter Distribution The foam diameter was measured by observing a cross section of a sample of the above-mentioned test foam rubber with a microscope. At this time, 10 μm or less was cut and the bubble diameter of 500 closed cells was measured to obtain the standard deviation value. The narrower the foam diameter distribution, the smaller the percentage and the better the foam uniformity. The results obtained are also shown in Table 1 below.

[0023]

[Table 1]

[0024]

As described above, in the foamed rubber composition for a tire of the present invention, the foamed rubber having excellent foaming uniformity in which the number of closed cells and the average diameter are controlled can be obtained. Therefore, in tire rubber for tread, rubber for sidewalls, rubber for inner liner, etc., good exercise performance of tires obtained by using foamed rubber, vibration ride comfort, soundproofness against outside and inside sounds, It can be further improved.

Claims (2)

[Claims] 1. A foamed rubber composition for a tire, comprising an inert filler having a maximum average width of 0.1 to 100 μm. 2. A rubber composition comprising 100 parts by weight of a foaming agent in an amount of 0.1 to 10 parts by weight and said inert filler in an amount of 1 to 50 parts by weight.
The foamed rubber composition for a tire according to claim 1, wherein the foamed rubber composition is blended in parts by weight.