JPH0625285B2 - Rubber composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rubber composition suitable for obtaining a rubber product such as a tire and a conveyor belt to which mechanical fatigue and thermal deterioration are applied.

(Prior Art) Conventionally, a technology of blending a melamine compound with a rubber composition is known, and for example, Japanese Patent Publications No. 40-16421, 45-27463, and
46-10295, 47-7640 and the like. However, these are for the purpose of improving the adhesiveness between the rubber and the fiber or the metal, and have not paid attention to the fatigue resistance and heat deterioration resistance of the rubber product obtained therefrom.

Generally, automobile tires and the like used under the condition of being subjected to repeated mechanical deformation are strongly required to have dynamic properties, particularly fatigue resistance and heat deterioration resistance due to self-heating of rubber.

In particular, belts and plies of automobile tires that are used in the form of a composite of rubber and materials with greatly different rigidity, such as fibers and metals, have a large difference in rigidity due to adhesion deterioration between fibers and metals and rubber. Due to the large deformation that occurs at the interface rubber part, fatigue progresses significantly locally.

In particular, recent automobile tires have become a market environment where the quality of products is improved and the service life is improved to improve the service life, and after the end of the first service life, only the tread is renewed for reuse. It is necessary to develop a rubber composition with excellent fatigue resistance to improve the life of the product.

Deterioration of rubber properties due to mechanical repetition of rubber products is governed by the size of deformation and heat / heat resistance. That is, it is governed by the dynamic characteristics of dynamic elastic modulus E'correlated with the magnitude of dynamic deformation and lost tangent tan δ correlated with dynamic self-heating.

Generally, rubber, polymer, carbon black,
There are white fillers, softening agents, resins, vulcanization aids, vulcanization accelerators, vulcanizing agents and the like. Therefore, the types and amounts of these compounding agents are changed to improve the fatigue resistance and heat deterioration resistance of the rubber composition, that is, the dynamic characteristics that the dynamic elastic modulus E ′ is high and the lost tangent tan δ is low. However, there are few compounding agent factors that significantly improve both of these two contradictory properties, which are generally contradictory, and factors such as increasing the amount of the vulcanization accelerator that are relatively in line with this purpose are different from those of fiber and metal. It was found that the adhesiveness of the product deteriorated and it did not serve its final purpose.

Therefore, as a result of extensive studies to improve the dynamic properties of rubber products, the amount of bound formalin in a specific range per molecule of resorcin or resorcin derivative and melamine,
By blending a natural or synthetic rubber with a melamine derivative having a number of methoxy groups and having a specific content of a certain monomer, the adhesion to a reinforcing material and the processability of an unvulcanized rubber compound are impaired. However, the inventors have found that the dynamic properties of vulcanized rubber are significantly improved, and completed the present invention.

(Problems to be Solved by the Invention) An object of the present invention is to provide a rubber composition suitable for obtaining a rubber product having excellent dynamic properties.

Another object of the present invention is to provide a rubber composition suitable for obtaining a rubber product excellent in adhesiveness between rubber and fiber or metal, other vulcanized rubber characteristics, and processing characteristics.

(Means for Solving Problems) The present invention provides a natural rubber or a synthetic rubber containing resorcin or a derivative containing a resin containing at least resorcin and formaldehyde as a component, and a reaction product of melamine and formalin. The number of bound formalins and the number of methoxy groups per molecule are in the range of 4 ≦ (the number of bound formalins) ≦ 6, 2 ≦ (the number of methoxy groups) <6, and the monomer content is
It relates to a rubber composition with improved dynamic properties, characterized in that it contains 60 to 90% of a melamine derivative.

Generally, there are two types of compounding systems such as a belt part and a ply part of an automobile tire, a system containing silica and a system not containing silica. In the system containing silica, adhesiveness between rubber and a reinforcing material such as metal or fiber is Although advantageous, the processability of unvulcanized rubber blends tends to be rather disadvantageous.

The present invention can be applied to both cases of the system containing silica and the system not containing such silica, but the number of bound formalin and the number of methoxy groups per molecule of melamine is the same as above for the system containing silica. It is particularly preferable that 4 ≦ (the number of bound formalin) ≦ 6 and 2 ≦ (the number of methoxy groups) <6.

In the melamine derivative of the present invention, as the content of the monomer is higher, the vulcanized rubber shows more excellent dynamic properties, and the unvulcanized rubber compound shows higher scorch stability. That is, when the content of the monomer is less than 60%, excellent dynamic characteristics and high scorch stability can be obtained even if the number of bound formalin and the number of methoxy groups per melamine molecule are within the range of the present invention. Absent. When the content of the monomer is more than 90%, it cannot be obtained by the usual production method and requires a special refining step, which significantly increases the production cost and lowers the industrial value. The content of the monomer is selected in the range of 60 to 90%.

Further, the larger the number of bound formalins per molecule of melamine, the more the dynamic properties of the vulcanized rubber tend to be excellent, and if the number of bound formalins is less than 4, a sufficient effect cannot be obtained.

Further, the ratio of methoxy groups to free methylol groups in the melamine derivative greatly affects the dynamic properties of the vulcanized rubber and the processability of the unvulcanized rubber. That is, even if the monomer content of the melamine derivative and the number of bound formalins per molecule of melamine are constant, the smaller the number of methoxy groups is, the larger the number of free methylol groups is, and the dynamic properties of the vulcanized rubber are slightly improved. However, there is a point that the workability of unvulcanized rubber is significantly lowered, and this tendency is remarkable in the system containing silica.

Therefore, the number of methoxy groups is 2 or more in the system containing no silica, and the number of methoxy groups is 4 in the system containing silica.
The above is practically preferable.

As described above, in the present invention, natural rubber or synthetic rubber has resorcin or resorcin derivative, and the number of bound formalin and the number of methoxy groups per molecule of melamine are within a specific range, and the content of the monomer is within a specific range. Only when the target vulcanized rubber has excellent dynamic properties,
In addition, since it does not impair the adhesiveness to fibers or metals and the scorch stability of unvulcanized rubber, it has a very high practical value in the social situation described above.

In the present invention, the resorcin or resorcin derivative is usually 0.1 to 100 parts by weight of rubber (weight part, hereinafter the same).
7 parts, preferably 0.3 to 5 parts are blended. Here, as the resorcin derivative, a derivative containing at least a resin containing resorcin and formaldehyde as components is used, and examples thereof include resorcin-formaldehyde resin, resorcin-formaldehyde resin and alkylphenol.
Examples thereof include a melt mixture with a formaldehyde resin.

The melamine derivative is usually 0.5 to 7 per 100 parts of rubber.
Parts, preferably 1 to 5 parts.

In the present invention, as the rubber component, one type or two or more types of natural rubber (NR) and synthetic rubber are used. Examples of synthetic rubber include polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene rubber (SB
R), isoprene / isobutylene rubber (IIR), ethylene / propylene / diene rubber (EPDM), modified products thereof, blended products thereof and the like can all be used.

The rubber composition of the present invention can be obtained by kneading the above components with a conventional processing device such as a roll, a Banbury mixer or a kneader. In addition to the above components, known vulcanizing agents, vulcanization accelerators, vulcanization accelerators, vulcanization retarders, organic peroxides, reinforcing agents, fillers, antioxidants, tackifiers, coloring agents, etc. Of course, it can be added.

(Example) Below, a reference example, an example, and a comparative example are given and demonstrated.
Incidentally, “% or part” simply means “% by weight” or “part by weight”.

Reference Example 1 (Synthesis of Melamine Derivative) 259.6 g (3.20%) of formalin (37%) was placed in a glass three-necked flask (1) equipped with a stirrer, a thermometer and a reflux condenser.
After adjusting the pH to 9.0 to 9.5 with a small amount of caustic soda, 50.5 g (0.40 mol) of melamine was charged, and the content liquid was heated to a reflux state (about 80 ° C.) and kept warm in an oil bath.
After 60 minutes from the start of reflux, the oil bath was removed, the mixture was cooled to room temperature, and 202.6 g (6.33 mol) of methanol was charged. Further, the pH was lowered to 2-3 by sulfuric acid, and the methoxylation reaction was carried out at about 30 ° C. for 120 minutes. The reaction solution thus synthesized was distilled off under reduced pressure to remove water and methanol, and then taken out in a heated state.

The monomer content of this melamine derivative is 81%, the number of bound formalin is 5.7 and the number of methoxy groups is 4.2 per molecule of melamine.
It was.

Various melamine derivatives were produced by the same method while changing the molar ratio of formalin or methanol and the reaction temperature and the like.

The melamine derivative monomer content, the number of bound formalins and the number of methoxy groups were measured by the following methods.

(Measurement method) Monomer content: Area percentage by GPC (gel permeation chromatography).

Amount of bound formalin: After addition of phosphoric acid, formalin was removed by distillation, and the obtained amount of formalin was calculated by iodine-sodium thiosulfate titration.

Number of methoxy groups: Calculated by potassium iodide-sodium thiosulfate titration after adding hydriodic acid to a solution of melamine derivative in phenol and propionic acid.

(In the examples, the number of free methylol groups is shown for reference in order to clarify the structure of the melamine derivative, but the number of free methylol groups was also calculated by titrating by the iodine-sodium thiosulfate method as in the other cases. The characteristics of the vulcanized rubbers obtained in the examples were measured by the following methods.

Dynamic viscoelastic characteristics: Initial strain 15 using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho
%, Amplitude 1%, frequency 50 Hz, room temperature 30 ° C. The values of the dynamic elastic modulus E ′ and the loss tangent tan δ were indexed and displayed. The higher the index of E ', the higher the index of tan δ.
The lower the better.

Mooney scorch property: The scorch time at 125 ° C was indexed and displayed. Inde
The higher the x, the longer the scorch time and the more stable the machining process.

Adhesiveness with steel cord: The pulling force measured by the H test method using a steel cord with 7 × 4 × 0.007 brass plating was indexed and displayed.
The heat-resistant adhesive strength was evaluated by a pulling force after heat aging at 120 ° C. for 48 hours, and the wet heat adhesive strength was evaluated by a pulling force after wet heat aging at 75 ° C. × 80 RH% × 48 hours. The higher the number, the better.

Hs is hardness, M ₁₀₀ is 100% tensile stress, T _B is tensile strength, and E _B is elongation.

Example 1 80 parts of natural rubber (RSS # 1), isoprene rubber (IR22
00) 20 parts, LS-HAF carbon 60 parts, zinc white 10 parts, cobalt naphthenate (Co content 10%) 3 parts, antioxidant (6
C) 1 part, resorcin 1 part, sulfur 6 parts, vulcanization accelerator (D
Z) 1 part was mixed with the melamine derivative shown in Table 1 or other additives and sufficiently kneaded for 4 minutes with a Banbury mixer to obtain a rubber composition. No. 10 did not contain resorcin.

The obtained rubber composition was mold-vulcanized at 150 ° C. for 30 minutes, and its characteristics were measured. The results are shown in Table 1.

From Table 1, the rubber compositions of Nos. 1 to 4 have an E '/ tan δ value of about 1.5 to 1.8, which is an index showing high E'and low tan δ property, and No. 5 to No.
7 is higher than about 1.2 to 1.3 of the rubber composition of 7 and shows an excellent common effect. Also, there is no significant difference between the two groups in the adhesiveness with the steel cord. The hexamethylenetetramine of No. 8 also has an excellent E '/ tan δ value of 1.5, but its wet heat adhesiveness is significantly inferior to about half that of the melamine rubber composition. In the table, the number of bound formalin, the number of methoxy groups, and the number of free methylol groups are melamine 1 respectively.
It is a value per molecule, and is the same in the following tables.

Example 2 Example 1 except that the melamine derivative described in Table 2 was used.
A rubber composition was obtained in the same manner as in. Vulcanization characteristics of the obtained rubber composition are also shown in Table 2.

From Table 2, from No. 1 to No. 5, as the number of methoxy groups increases, the scorch time increases, but tan δ increases, and E '
Also tends to be lower.

Example 3 80 parts of natural rubber (RSS # 1), isoprene rubber (IR22
00) 20 parts, LS-HAF carbon 52 parts, silica 10 parts, zinc white 7 parts, cobalt naphthenate (Co content 10%) 2 parts, antioxidant (6C) 1 part, resorcin 1 part, sulfur 4.2 parts,
0.7 part of the vulcanization accelerator (DZ) was mixed with the melamine derivative shown in Table 3 or other additives, and sufficiently kneaded for 4 minutes with a Banbury mixer to obtain a rubber composition. Incidentally, No. 6
1 part of resorcin-formalin condensate was blended in place of resorcin, and No. 12 was not blended with resorcin.

Vulcanization characteristics of the obtained rubber composition are also shown in Table 3.

From Table 3, the rubber compositions No. 1 to 6 have an E '/ tan δ value of about
Compared with 1.3 to 1.8 of the rubber compositions of 1.6 to 1.8 and No. 7 to No. 9, they show excellent common effects. Also, there is no significant difference between the two groups in the adhesiveness with the steel cord. The No. 10 rubber composition has a high E ′ / tan δ value of 1.81, which is excellent, but the scorch time Index is 60, which is extremely poor. The No. 11 rubber composition also has an excellent E '/ tan δ value of 1.62, but is excellent in the wet heat adhesive strength Index of 58.

Example 4 (tire drum test) As a steel belt topping rubber, a steel belt edge tape rubber, and a steel belt edge insertion rubber,
Tires of 1000R2014P were manufactured by using the rubber composition having the same composition as in Example 1 in which various melamine derivatives or hexamethylenetetramine were mixed, and tires of the United States Tire and Rim
Tread Ieaving carcass (TL
After running for a certain period of time under the condition C), the tires were disassembled, and the lengths of the separations from the second and third belt ends were measured at 20 points on the circumference, and the average length was displayed as Index. The smaller the index, the shorter and better the separation length. The results are shown in Tables 4-5. Table 4 shows the drum test result of the tire using the belt rubber containing no silica,
Table 5 shows the drum test results of the tire using the belt rubber containing silica having the same composition as in Example 3.

The tires using the rubber compositions of Nos. 1 to 3 in Table 4 and Nos. 1 and 2 in Table 5 have good Index of 60 to 70. However, other tires have a large index. The tire of the rubber composition using hexamethylenetetramine of No. 4 in Table 5 had a good Index of 72, but the wet heat resistance of the tire sample was as bad as the evaluation in the test room.

Claims (3)

[Claims] 1. A reaction product of resorcin or a resin containing at least resorcin and formaldehyde in natural rubber or synthetic rubber, and a reaction product of melamine and formalin, wherein one molecule of melamine comprises:
The number of bound formalins and the number of methoxy groups are in the range of 4 ≦ (number of bound formalins) ≦ 6, 2 ≦ (number of methoxy groups) <6, and the content of the monomer is
A rubber composition with improved dynamic properties, characterized in that it contains 60-90% of a melamine derivative. 2. The rubber composition according to claim 1, wherein the rubber does not contain silica. 3. The rubber composition according to claim 1, wherein the rubber contains silica, and the melamine derivative has a number of methoxy groups per melamine molecule of 4 ≦ (number of methoxy groups) <6.