JPH07292154A - Plasticizer for rubber - Google Patents

Abstract

PURPOSE:To obtain a plasticizer for rubber, having excellent compatibility with rubber and improved balance of permanence and freeze resistance and to provide a rubber composition for a tread for studless tire, having excellent freeze resistance/permanence. CONSTITUTION:This plasticizer for rubber comprises an ester which comprises a 3-9C polyhydric alcohol containing three or more hydroxyl groups in one molecule, a 2-12C aliphatic polyfunctional carboxylic acid and a 8-24C aliphatic monofunctional carboxylic acid, has 700-2,500 molecular weight and substantially not contains a hydroxyl group. 100 pts.wt. of rubber is mixed with 5-150 pts.wt. of the plasticizer and 30-100 pts.wt. of carbon black to give the objective rubber composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasticizer for rubber, and more particularly to a plasticizer for rubber in which cold resistance, heat resistance and durability such as non-migration property are improved in a well-balanced manner.

[0002]

2. Description of the Related Art Conventionally, rubber products have a low temperature flexibility,
For the purpose of improving so-called cold resistance such as low temperature impact resistance,
In many cases, various ester plasticizers are mixed. For example, Japanese Examined Patent Publication (Kokoku) No. 2-38104 discloses unsaturated fatty acid esters of hydroxy compounds, and JP-A-62-253641.
The publications each describe blending a neopentyl type polyol ester. In addition, there is a tread application for winter tires (studless tires) as a rubber composition that requires particularly cold resistance and durability, and dioctyl sebacate and / or dioctyl sebacate are used to maintain flexibility at low temperatures (improve cold resistance). Using an ester plasticizer such as trimethylolpropane oleate is disclosed in JP-A-59-206.
No. 208, JP-A No. 1-113444, and the like.

[0003]

However, in the ester compound as described above, the plasticizer is volatilized from the rubber product after molding probably due to its small molecular weight, or the resin compound is transferred to the contacted resin or the like, so that it is long. When it is used for a period of time, it has a drawback that the flexibility of the rubber is lowered, that is, the durability is poor.

On the other hand, if the molecular weight of the ester compound is increased in order to improve the durability, the cold resistance is deteriorated. That is, an object of the present invention is to provide a plasticizer for rubber which is excellent in compatibility with rubber and has a good balance between durability and cold resistance, and another object of the present invention is to provide cold resistance and durability. It is an object of the present invention to provide a rubber composition having excellent properties, which is particularly suitable for a tread of a studless tire.

[0005]

Means for Solving the Problems The inventors of the present invention have made earnest studies to find a plasticizer having good compatibility with rubber, excellent cold resistance and durability, and capable of retaining the flexibility of rubber for a long period of time. As a result of repeated studies, it was found that an ester of a polyhydric alcohol, an aliphatic polyhydric carboxylic acid and an aliphatic monohydric carboxylic acid having a specific structure satisfies the above requirements, and the present invention has been completed.

That is, the gist of the present invention is a polyhydric alcohol having 3 to 9 carbon atoms and 3 or more hydroxyl groups in one molecule, an aliphatic polycarboxylic acid having 2 to 12 carbon atoms, and 8 to 2 carbon atoms.
The molecular weight of the aliphatic monovalent carboxylic acid of 4 is 700 to 25
And a plasticizer for rubber consisting of an ester having substantially no hydroxyl group. Hereinafter, the present invention will be described in detail.

The rubber plasticizer of the present invention is an ester of the above-mentioned specific polyhydric alcohol and a specific aliphatic polycarboxylic acid or aliphatic monovalent carboxylic acid having a specific structure. The first constituent element of the ester used in the present invention has 3 to 9 carbon atoms.
The polyhydric alcohol having 3 or more hydroxyl groups in one molecule is not particularly limited, but a polyhydric alcohol having 3 to 6 hydroxyl groups is preferably used. Examples of such polyhydric alcohols include trimethylolethane,
Trimethylolpropane, glycerin, 3-methyl-
1,3,5-pentanetriol, pentaerythritol, diglycerin, erythritol, triglycerin,
Examples thereof include sorbitol and dipentaerythritol. Among them, the above polyhydric alcohols having 3 to 6 carbon atoms are preferably used, and glycerin and trimethylolpropane are particularly preferable. You may use these polyhydric alcohols individually or in mixture of 2 or more types.

The aliphatic polycarboxylic acid having 2 to 12 carbon atoms, which is the second constituent element of the ester used in the present invention, is not particularly limited, and examples thereof include maleic acid, fumaric acid, adipic acid and azelaic acid. , Sebacic acid, dodecanedioic acid and the like. Among them, those having 6 to 10 carbon atoms, particularly adipic acid, are excellent in balance of performance and availability. This aliphatic polycarboxylic acid component may also be used as a mixture of two or more kinds.

The aliphatic monovalent carboxylic acid having 8 to 24 carbon atoms, which is the third constituent element of the ester used in the present invention, may be saturated or unsaturated,
For example, caprylic acid, nonanoic acid, capric acid, lauric acid, myristic acid, myristoleic acid, palmitic acid,
Examples thereof include stearic acid, oleic acid, linoleic acid, ricinoleic acid, ricinoleic acid, linolenic acid, and behenic acid. Among them, those having 14 to 22 carbon atoms are preferable. From the viewpoint of cold resistance, it is preferable to use unsaturated monovalent fatty acids such as oleic acid and linoleic acid. This aliphatic monovalent carboxylic acid component can also be used as a mixture of two or more kinds.

As the ester used in the present invention, those having a molecular weight in the range of 700 to 2500 are used. When the molecular weight is less than 700, the volatility becomes high and the durability is lowered, while when the molecular weight exceeds 2500, the flexibility of the rubber product is insufficient especially at low temperatures. The ester used in the present invention is prepared by charging the above-mentioned polyhydric alcohol, aliphatic polyvalent carboxylic acid and aliphatic monovalent carboxylic acid according to the composition ratio of the objective, and by a generally known esterification method. It can be obtained by esterification.

The term "ester having substantially no hydroxyl group" as used in the present invention means one having less than 1 hydroxyl group in one molecule of ester. The number of the hydroxyl groups is preferably 0.8 or less, more preferably 0.5 or less. 1 hydroxyl group
An ester having one or more molecules in the molecule has low compatibility with rubber, and is easily spouted during processing or after commercialization.

Such an ester having substantially no hydroxyl group has the same composition as the charge composition at the time of ester synthesis so that the number of moles of the hydroxyl group and the carboxyl group to be reacted with the hydroxyl group are the same, and the reaction solution is determined at the end of the reaction. It can be obtained by examining the acid value and confirming that the esterification is sufficiently advanced. The number of hydroxyl groups in one molecule is the molecular weight (M) corresponding to a molecular formula derived from one having the smallest number of moles among the ester constituents as 1, and the hydroxyl value (O) measured according to JIS K 6751 for this ester.
HV) can be obtained from the following equation.

[0013]

[Equation 1]

It should be noted that it is effective to prevent the formation of high molecular weight ester due to excessive condensation by taking into consideration the reaction temperature of the esterification so as not to volatilize the charged components.
The plasticizer for rubber of the present invention comprising the above ester is a natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), nitrile-butadiene rubber (N).
BR), chloroprene rubber (CR), ethylene propylene rubber (EPM and EPDM), butyl rubber (II
R), acrylic rubber (ACM), etc. can be applied regardless of the type of rubber.

The rubber composition of the present invention is obtained by adding 5 to 150 parts by weight to 100 parts by weight of the rubber component, and further blending 30 to 100 parts by weight of carbon black and kneading. You can The amount of each component at this time is preferably 20 to 70 parts by weight of the plasticizer with respect to 100 parts by weight of the rubber component in terms of low temperature flexibility and abrasion resistance of the product, and carbon black is 30 to 30 parts by weight. 70
The parts by weight is preferable in terms of simultaneously satisfying low temperature flexibility and physical properties (strength) and wear resistance. Of course, in addition to the above-mentioned essential components, this rubber composition also contains other compounding agents usually used in rubber compositions, such as vulcanizing agents and vulcanization accelerators.
A filler, a softening agent, an antiaging agent, a processing aid and the like can be added if necessary.

Since this rubber composition has little volatilization and migration of the plasticizer, it can maintain flexibility for a long period of time and has little hardness increase at low temperatures. For example, when it is used in a tire tread, it can be used on a good ice and snow. It has braking performance and can suppress deterioration of performance during use and storage, and is particularly suitable for studless tires. The rubber composition of the present invention is a usual rubber kneading equipment such as a mill roll, a Banbury mixer,
It can be produced by kneading the above-mentioned components with a kneader blender or the like.

[0017]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to the following examples without departing from the gist thereof. Example of plasticizer synthesis trimethylolpropane 268g (2.0mol), adipic acid 142g (1.0mol), and oleic acid 11
To a mixture of 30 g (4.0 mol), 0.43 g of tetraisopropyl titanate (0.03 wt% of theoretical ester yield) was added as a catalyst, and the reaction temperature was 22 under nitrogen atmosphere.
An esterification reaction was performed at 0 ° C. for 10 hours to obtain a plasticizer ester (Sample-1). The sheet for measuring and evaluating the physical properties of the sheet was prepared based on the following formulation.

[0018]

[Table 1] SBR (SBR 1500: manufactured by Nippon Synthetic Rubber Co., Ltd.) 100 parts by weight carbon black (HAF: manufactured by Mitsubishi Kasei Co., Ltd.) 50 Zinc Hua No. 1 5 Stearic acid 1 Sulfur yellow 1.75 Vulcanization accelerator (CZ: Ouchi Shinko Co., Ltd.) 1.25 Vulcanization accelerator (TT: same as above) 0.25 Plasticizer 30

The plasticizers used in the evaluation are as shown in Table-1. Of these, Samples-2, -6 and -7 have the above-mentioned plasticization so as to have the compositions shown in the table. It was synthesized in the same manner as in the agent synthesis example. Other samples used were commercial products. Based on the above composition, a rubber composition was prepared by kneading with a Banbury mixer, and this was sheeted using a mill roll. Then, press vulcanization was performed to obtain a sheet for evaluation (thickness: 2 mm). The press vulcanization was carried out at a pressure of 200 kg / cm ² at 150 ° C. for 20 minutes. Using the obtained sheet, tensile properties, heat resistance, and cold resistance were measured according to the following methods.

[0020]

[Table 2] Tensile physical properties: According to JIS K 6301 (tensile test). Hardness: According to JIS K 6301 (hardness test).
(Spring type hardness test A type) Heat resistance test: According to JIS K 6301 (aging test) (100 ° C. × 72 hours). Volatility: The evaluation sheet was placed in activated carbon and placed in an oven at 120 ° C to measure the weight change. Cold resistance: (low temperature torsion test) according to JIS K 6745. (Dynamic viscoelasticity test) Measure the elastic modulus with a viscoelasticity measuring device,
The elastic moduli at low temperature were compared. Transferability: A sheet containing a plasticizer and a sheet not containing a plasticizer were superposed, a load (108 g / cm ² ) was applied from above, and the sheet was allowed to stand in an oven at 80 ° C. for a predetermined period of time. The weight change of the existing sheet was measured and compared. The test results are summarized in Table 2-1 to Table -2-2.

[0021]

[Table 3] *) DOP: di-2-ethylhexyl phthalate DOA: di-2-ethylhexyl adipate

[0022]

[Table 4]

[0023]

[Table 5]

It can be seen that the esters of the examples have the following characteristics. Good heat resistance. (The hardness change and the mass change are smaller than those of the plasticizers of Comparative Examples 1 to 4. At the same level as Comparative Example 5.) Volatility is low. (It is superior to any comparative example.) Low migration property. (Better than any of the comparative examples.) Excellent in cold resistance. (It shows low-temperature torsion test results and dynamic viscoelasticity data equivalent to DOP, which is a standard plasticizer, although it does not reach DOA, which is generally said to be particularly excellent in cold resistance.)

[0025]

By using the plasticizer for rubber of the present invention, it is possible to provide a rubber product having a well-balanced improvement in durability such as cold resistance, heat resistance and non-migration resistance. Further, the rubber composition containing this plasticizer for rubber has the characteristics of excellent cold resistance and durability, and is particularly suitable for treads of studless tires.

Claims (7)

[Claims] 1. A polyhydric alcohol having 3 to 9 carbon atoms and having 3 or more hydroxyl groups in one molecule, an aliphatic polycarboxylic acid having 2 to 12 carbon atoms, and an aliphatic monovalent carboxylic acid having 8 to 24 carbon atoms. A plasticizer for rubber, which comprises an ester having an acid and a molecular weight of 700 to 2500 and having substantially no hydroxyl group. 2. The polyhydric alcohol has 3 to 6 carbon atoms, and the aliphatic polyhydric carboxylic acid has 6 to 10 carbon atoms.
The plasticizer for rubber according to. 3. The aliphatic monocarboxylic acid having 14 to 14 carbon atoms.
22. The rubber plasticizer according to claim 1 or 2, which is 22. 4. The rubber plasticizer according to claim 1, wherein the polyhydric alcohol is glycerin and / or trimethylolpropane. 5. The rubber plasticizer according to claim 1, wherein the aliphatic polycarboxylic acid is adipic acid. 6. The rubber plasticizer according to claim 1, wherein the aliphatic monocarboxylic acid is oleic acid or linoleic acid. 7. A rubber composition comprising 30 to 100 parts by weight of carbon black and 5 to 150 parts by weight of the plasticizer for rubber according to claim 1 to 100 parts by weight of the rubber component. object.