JPH07107103B2 - Fiber reinforced rubber molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention has a polyvinyl alcohol-based synthetic fiber (hereinafter referred to as PV) having a flat cross section and a large ratio of length to width of crystal.
The present invention relates to a rubber molded product reinforced with A type fiber).

<Prior Art> Generally, rubber products such as tires, rubber tarpaulins, and rubber hoses are generally reinforced with fibers in order to improve strength, form stability, and pressure resistance.

Recently, the trend toward lighter, thinner, shorter, smaller, and higher-performance products has been steadily progressing, and the reinforcing fibers used in rubber moldings have become stronger and more elastic than conventional organic fibers, and have attracted attention. By using high-strength and high-elasticity fibers, the amount of fibers used can be reduced, and the amount of rubber used can also be reduced, resulting in a rubber molded product that is light and easy to handle.

In recent years, it has been found that aramid fiber is used as a high-strength / high-elasticity fiber in rubber moldings, but its adhesiveness with rubber, durability, etc. are not yet sufficient, and it is used so much because of its high price. The current situation is not.

In addition, PVA-based fibers have the highest strength and elasticity among general-purpose fibers and are excellent in adhesiveness with rubber, so they are strongly used for reinforcement for rubber materials. There is a demand for elasticity and high durability, and it is becoming difficult for the current PVA-based fibers to sufficiently meet this demand. Especially in rubber moldings, the adhesive strength between fibers and rubber is important to obtain high durability. If they are not sufficiently adhered and integrated, friction between fibers and rubber or between fibers will occur and heat will be generated. Therefore, the fiber life is shortened and the durability is deteriorated.

Against the above problems, as a result of intensive investigations by the present inventors, by using a PVA-based fiber satisfying specific conditions, it is possible to obtain higher strength, higher elasticity, higher durability, and lower cost than ever before. It has been found that a satisfactory rubber molding can be obtained.

<Problems to be Solved by the Invention> An object of the present invention is to provide a high-performance rubber molded product having a specific PVA-based fiber excellent in rubber-reinforcing property as a reinforcing material.

<Means for Solving Problems> The inventors of the present invention investigated the reinforcing effect of various PVA-based fibers in order to develop a rubber molded product having excellent performance. In addition to strength and high elasticity, it is not clear why, but the ratio of the length (L) to the width (W) of the fiber crystal (hereinafter abbreviated as L / W) is more closely related and has high durability. In order to obtain, it is essential that the L / W is 2.1 or more and the cross-sectional solidity described below is 65% or less, preferably the L / W is 2.3 or more, and the cross-sectional solidity is The present invention was found to be 65% or less.

The crystal length L of the fiber has little correlation with the mechanical properties and durability of the fiber, and a strong correlation appears for the first time as L / W. If the L / W is less than 2.1, the durability when subjected to bending fatigue is poor, which is not preferable in practice. If the cross-sectional solidity exceeds 65%, the surface area of the fiber will decrease,
It is not preferable because sufficient adhesive force cannot be obtained.

An effective method for producing a PVA-based fiber used in the present invention is a spinning stock solution of a PVA aqueous solution containing boric acid or borate,
This is a method in which wet spinning is performed in an alkaline coagulation bath at 55 to 95 ° C. containing a salt having a dehydrating ability, and the obtained spun raw yarn is drawn at a draw ratio of 17 times or more. Such a method is conventionally 20 ~ 50 ℃
This is carried out at 55-95, whereas it is carried out at the coagulation bath temperature of
It is characterized in that the temperature is raised to ℃. The obtained fiber has a flat cross section, and since the drawability is greatly improved, the L / W of the fiber is increased and the mechanical properties of the fiber are also significantly improved. I'm not sure why, but
It is considered that the solidification mechanism is completely different from that of the conventional spinning method.

Hereinafter, an example of the method for producing the PVA fiber used in the present invention will be described in detail.

The degree of polymerization of PVA used is 1500 or more, preferably 2000 or more,
More preferably, it is 3000 or more.

The spinning solution is an aqueous solution having a concentration of 5 to 30% by weight of the PVA,
The content of boric acid or borate is 0.5 to 5% by weight based on the PVA, and the concentration of PVA is preferably 6 to 25% by weight, more preferably 7 to 18% by weight, depending on the degree of polymerization of PVA. It is preferable to adjust it appropriately.

The spinning dope temperature is 85 to 125 ° C., preferably 95 to 120 ° C. If it is too low, the drawability is hindered, and if it is too high, the stock solution boils. In order to stabilize the spinning condition, an appropriate amount of organic acid such as acetic acid or inorganic acid such as nitric acid may be added to the stock solution for spinning.

The temperature of the coagulation bath is 55 to 95 ° C, preferably 60 to 80 ° C.
When the temperature is 55 ° C or lower, the cross section of the fiber is not so flat, and the drawability is low, so that the L / W does not increase. On the other hand, if the temperature is 95 ° C or higher, it is not preferable because boiling of the coagulating bath and sticking between the single fibers occur.

A caustic alkali such as sodium hydroxide or potassium hydroxide is used as the alkali component of the coagulation bath, and the concentration thereof is 2
~ 200 g / l, preferably 5-50 g / l. Further, as the salt component of the coagulation bath, a salt having a dehydrating ability such as sodium sulfate and sodium carbonate is used, and the concentration is 100 g / l to a saturated concentration, and it is preferable that the concentration is close to saturation.

As the spinning nozzle, an ordinary circular nozzle or a nozzle having a shape close to it is used.

The fiber after spinning may be subjected to alkali neutralization, wet heat drawing, washing with water, drying, drawing and heat treatment according to a conventional method, but it is necessary to draw at least 17 times or more, preferably 20 times or more. The larger the draw ratio, the larger the L / W.
If it is less than 7 times, the L / W will not reach 2.1.

The rubber used in the present invention is not particularly limited, and natural rubber (NR), synthetic rubber (styrene-butadiene rubber (SBR), chloroprene rubber (CR), nitrile rubber (NBR), ethylene-propylene diene rubber ( EPD
M), other synthetic rubbers) and the like can be used. It is also possible to use them in combination, and they may be used in the form of a latex.

In the present invention, such a PVA fiber is used in a woven or twisted state, but it may be used in a state of a non-woven fabric, a short fiber, a chopped strand or the like depending on the application.

The method for producing the rubber molded product may be the same as the conventional method, except that the known PVA-based fiber is simply changed to the above-mentioned fiber.

For example, after twisting and coding the PVA-based fiber, if necessary, adhesion treatment is performed, weaving, knitting and overlapping with rubber, or weaving PVA-based fiber, and adhering treatment as necessary after knitting. Then, a rubber molded product may be obtained by a general method such as the step of molding with a rubber.

<Effect of the Invention> The rubber molded product of the present invention has the following features.

1) Compared with the conventional PVA fiber, the fiber used in the present invention is L / W
Is large, has excellent mechanical performance, and has a
Since the cross section is flat and the surface area is large, such as 65% or less,
The obtained rubber molded product has good adhesion to rubber, good strength retention after bending fatigue, high strength, high elasticity and high durability.

2) Compared with conventional PVA-based fibers, it is possible to mold the same strength with a smaller amount of yarn, so that the weight of the molded product can be reduced and the surface smoothness is also improved.

By utilizing the above excellent performance, the molded product of the present invention can be applied to various tire members, tarpaulins, sheets, various hoses, diaphragms and the like.

Hereinafter, it will be described more specifically by way of examples. The cross-sectional solidity (degree of flatness of cross-section; smaller number means flatness), the ratio of crystal length to width (L / W), and mechanical properties specified in the present invention are measured by the following methods. It is something.

○ Cross-section perfection A cross-sectional photograph of the fiber is enlarged to about 100 mm ² and the cross-sectional area F is obtained.

Next, the widest width B in the cross section was obtained and calculated by the following formula.

In addition, this value is obtained for 20 single fibers arbitrarily taken out from one multifilament yarn, and the average value thereof is defined as the cross-sectional solidity of the fibers constituting the multifilament yarn.

○ Ratio of crystal length and width It was measured under the following conditions by a known wide-angle X-ray diffraction method.

Wide-angle X-ray (1) Rigaku Denki Co., Ltd. rotating anticathode X-ray diffractometer (Type RAD-rA) 40kV, 100mA CuK α (Graphite Monochromator) with scintillation counter (2) Goniometer slit system: DS1 / 2 °, SS1 / 2 °, RS0.15mm Scanning speed: 2θ = 1/2 ° / min (3) Fiber sample of sample (125 mg fibers arranged in parallel with length 2.5 cm and width 1.5 cm) The sample was attached to a table and the diffraction curves of surface indices (020) and (100) were measured by the transmission method to obtain the half-value width B (hkl) of each curve.

Ratio of crystal size (L / W) Calculate each crystal size from Scherrer's formula from the half-value width B (hkl) of the peaks of plane index (020) and (100) obtained by the above transmission method. did.

D (hkl) = Kλ / Bo (hkl) COSθ (hkl) However, K = 0.9 λ = 1.5418 (Å) Bo: Jones method of correcting the slit after the diffraction curve spread (radian) θ (hkl): Bragg angle (Deg.) L / W = D (020) / D (100).

○ Dry rupture strength / elongation, initial elastic modulus (1) Sample …… Multifilament yarn (2) Dry rupture strength / elongation, initial elastic modulus …… Complies with JIS-1017 in an atmosphere of temperature 20 ℃ and relative humidity 65% Then, it was measured with an Instron tester at a test length of 20 cm and a pulling speed of 10 cm / min, and the initial elastic modulus was obtained from its elongation-load curve.

(3) Number of measurements: 10 measurements were performed and the average value was calculated.

Examples 1 to 3 Comparative Examples 1 and 2 Completely saponified PVA having a degree of polymerization of 3500 was dissolved in water to a concentration of 9% by weight, and boric acid was added thereto at 3.5% by weight to prepare a spinning dope. This spinning dope is then heated to 105 ° C. and contains 15 g / l sodium hydroxide and 350 g / l sodium sulfate.
0 ° C (Example 1), 70 ° C (Example 2, Comparative Example 1), 90 ° C
(Example 3) A coagulation bath consisting of an aqueous solution at each temperature of 30 ° C (Comparative Example 2) was spun through a spinneret having a 1000-hole circular nozzle, and was spun at a speed of 6 m / min. Subsequently, roller drawing, neutralization, wet heat drawing, washing with water and drying were carried out according to a conventional method, and dry drawing was carried out at 230 ° C to produce a yarn. The total draw ratio is 22.5 (Example 1), 26.8 (Example 2), 25.4
(Example 3), 16.2 (Comparative Example 1) and 14.6 (Comparative Example 2).

Next, twist the lower and upper twists of the yarn to the yarn by 30T / 10cm and then 1800
A D / 1 × 2 cord was prepared, and RFL adhesion treatment was performed on the cord to form a dipped cord. The dipped cords were further arranged in a dull shape, and rubber was laminated and vulcanized to obtain a fiber-reinforced rubber sheet. After bending this with a bending fatigue tester, the cord was taken out and the residual strength was measured. The above results are shown in Table 1.

Comparative Example 3 A fully saponified PVA having a degree of polymerization of 3500 was dissolved in dimethylsulfoxide at a concentration of 10% by weight to prepare a spinning stock solution, which was dry-wet spun from a 50-hole nozzle into a methanol coagulation bath at 10 ° C. The spinning stock solution thus obtained was subjected to 6 times wet stretching while being desolvated and dried. Then, dry stretching was carried out at 240 ° C., and the total stretching ratio was 24 times.

Using this fiber, a fiber-reinforced rubber sheet was produced in the same manner as in the above-mentioned example. The results are shown in Table 1.

As is clear from Table 1, the rubber sheet using the PVA-based fiber of the present invention has a good adhesive property and a good strength remaining rate after bending fatigue.

Adhesive strength performance evaluation method …… Deep cords are placed at regular intervals and embedded in raw rubber, and after vulcanization, the force to peel off three cords simultaneously is measured. Flexural cord strength retention rate evaluation method …… After bending 250,000 times by the belt bending method The cord was taken out of the rubber, the strength was measured, and the strength was determined by the ratio with the strength of the cord before bending.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Shoichi Nishiyama 1-2-1, Kaigan-dori, Okayama-shi, Okayama Kuraray Co., Ltd. (72) Inventor Isao Sakuragi 1-12-39, Umeda, Kita-ku, Osaka-shi, Osaka Kuraray Co., Ltd. (56) References Japanese Patent Publication No. 40-40767 (JP, B1)

Claims (1)

[Claims] 1. A rubber molded product reinforced with a polyvinyl alcohol-based synthetic fiber having a cross-sectional solidity of 65% or less and a ratio of length to crystal width of 2.1 or more.