JPH0576495B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for improving the adhesion between aromatic polyamide fibers and rubber. Specifically, the surface of aromatic polyamide fibers is subjected to low-temperature plasma treatment, and the treated fibers are treated with a high molecular weight resorcinol-formaldehyde initial condensate. Rubber latex (hereinafter referred to as this mixture)
RFL) is treated with an improved adhesive composition, further heated and cured, and then vulcanized by contact with unvulcanized rubber, thereby firmly adhering to the rubber. . When aromatic polyamide fibers and rubber are bonded by the method of the present invention, the adhesive properties are significantly improved compared to those obtained by conventional bonding methods, and the physical properties of the fibers are not degraded, and the adhesive layer is flexible. Significant improvements in flexibility and fatigue resistance can be expected. Therefore, the method of the present invention can be applied to industrial products such as tires, conveyor belts, hoses, rubber crawlers, etc., and is particularly effectively employed in tires and belts that require high performance. Prior Art Aromatic polyamides represented by poly-m-phenylene isophthalamide or poly-p-phenylene terephthalamide have superior heat resistance and chemical resistance, as well as high modulus of elasticity and high strength, compared to aliphatic polyamides. It has good dimensional stability. Therefore, it is used in many fields as a structural material by combining it with materials such as thermoplastic resins, thermosetting resins, or rubber. In particular, it is suitable as a reinforcing member for tires because it has the same level of strength as steel cord, is lightweight, and is flexible. However, aromatic polyamide fibers having the above characteristics still have the following drawbacks.
In other words, it has heat resistance and high strength properties, so it can be used for things that require these properties.
It lacks flexibility, is susceptible to bending and fatigue, and lacks adhesion to other materials, especially rubber. For example, when used as a reinforcing material for tires, RFL adhesives that have been widely used in the past are 6-nylon, 6-nylon, 6-nylon, 6-nylon,
Compared to aliphatic polyamide fibers such as 6-nylon, aromatic polyamide fibers are inferior in adhesion to rubber and fatigue resistance. For this reason, two-bath bonding methods have been developed. For example, for adhesion between aromatic polyamide fibers and rubber, the following formulation is shown in the information from DuPont: Water 850g 10% NaOH aqueous solution 10g 5% dioctyl sodium sulfosuccinate aqueous solution 20g 2-pyrrolidone 100g Glycerol diglycidyl ether 20g The method used is to apply adhesive treatment with 1000g of adhesive treatment liquid (for undercoat), and then adhere with RFL adhesive (for topcoat). In addition, improvements in adhesion are mainly related to undercoat adhesives, and many are looking forward to adhesives with a high epoxy group content. However, as the epoxy group content increases, the adhesive layer naturally becomes harder and the treated fiber cord becomes more rigid.
Flexibility, fatigue resistance, etc. tend to decrease. Purpose of the Invention The purpose of the present invention is to eliminate the drawbacks in adhesion between aromatic polyamide fibers and rubber and the drawbacks in aliphatic polyamide fibers.
By subjecting the surface of aromatic polyamide fibers to low-temperature plasma treatment and treating the treated fibers with an adhesive composition with improved RFL, we have improved the adhesion to rubber and the fatigue resistance of the finished structure. It is something. Structure of the Invention The present invention relates to poly-p-phenylene terephthalamide, poly-m-phenylene terephthalamide, or poly-p-benzamide, which has an amide bond and an aromatic group in the molecule called aromatic polyamide. Typical aromatic polyamide fibers are passed through a vacuum zone of 10 ^-3 to 10 Torr in advance, and excited with audio waves, high frequencies, or microwaves in an atmosphere of non-polymerizable gas, polymerizable gas, or heated vaporized gas, either alone or in combination. After surface treatment with the generated low-temperature plasma, the adhesive (REL) is a mixture of a high molecular weight resorcinol-formaldehyde initial condensate and rubber latex, and a low molecular weight resorcinol-formaldehy initial condensate is further added to polyhydric phenol polysulfide. This method improves the adhesion to rubber by immersion treatment in an aqueous solution of an adhesive composition mixed with the following, and then heating and curing. More specifically, low-temperature plasma treatment of aromatic polyamide fibers imparts hydrophilic groups to the fiber surface, or the etching effect significantly improves the wettability of the aromatic polyamide fibers with the above adhesive composition, which is an aqueous adhesive. As a result, the adhesive composition not only adheres to the fiber surface but also quickly impregnates the inside of the fiber bundle and embeds between the filaments, thereby preventing bending failure. In addition, aromatic polyamide fibers treated with low-temperature plasma and adhesive treatment show no decrease in physical properties such as strength and elongation compared to those without this surface treatment, or compared to conventionally attempted ozone treatment, acid treatment, or ultraviolet treatment. Not only that, but even a trend of improvement can be observed. As a result of these effects, the rate of decline in physical properties of aromatic polyamide fibers after being integrated with rubber after bending fatigue is significantly improved. As the low-temperature plasma gas used in the low-temperature plasma treatment of twisted aromatic polyamide fiber cords, non-polymerizable gases, polymerizable gases, or heated vaporized gases can be used alone or in combination as described above, such as helium, hydrogen, etc. , argon, oxygen, nitrogen, air, chlorine, ammonia, carbon monoxide, carbon dioxide, sulfur dioxide, nitrogen monoxide, formaldehyde, hydrogen chloride, etc., and gases that vaporize under reduced pressure include carbon tetrachloride and halogen-deficient hydrocarbons. (triclene etc.), formaldehyde water, water,
Methylamine, ammonia water, water vapor, etc. are preferably introduced, and after adjusting the pressure reduction area to 10 ^-1 to 10 Torr, low-temperature plasma is generated with an output of 1 W to 10 kW using an audio wave, high frequency, or microwave generator. Under that atmosphere 1~10 ³
Apply surface treatment by irradiating for seconds. In order to perform plasma treatment continuously, it is necessary to use a closed-type device that incorporates a fiber cord unwinding and winding device in a vacuum container, or an external unwinding and winding device, and a pressure roller or a small diameter hole. A semi-hermetic device using so-called differential pumping is used, which gradually creates a reduced-pressure atmosphere using a sealing material having a pressure-reducing atmosphere. The adhesive composition used in the method of the present invention includes a solution in which polyphenol polysulfide is dissolved in a low molecular weight resorcinol-formaldehyde initial condensate obtained by reacting 0.05 to 0.8 mol of formaldehyde with 1 mol of resorcinol; An adhesive composition is used in which an equal amount of REL adhesive is mixed, and the adhesive strength is greatly improved by one-bath treatment with this adhesive composition. Furthermore, a so-called two-bath adhesive treatment in which an epoxy compound solution conventionally used as an adhesive for general aromatic polyamide fibers is used in the first bath, and then an adhesive composition according to the present invention is used in the second bath can also be applied. Although there is no problem, this method is complicated and uneconomical. REL adhesive is a mixture of rubber latex and a relatively high-molecular-weight initial condensate obtained by reacting resorcin and formaldehyde in the presence of a basic catalyst such as sodium hydroxide, ammonium hydroxide, or potassium hydroxide. In this case, the reaction molar ratio of resorcin and formaldehyde is 0.8 to 7.5 formaldehyde to 1 mole of resorcin.
Moles are preferred. On the other hand, as the rubber latex, natural rubber latex, styrene-butadiene copolymer rubber latex, acrylonitrile-styrene-butadiene copolymer rubber latex, chloroprene rubber latex, vinylpyridine-styrene-butadiene copolymer rubber latex, and corboxyl group-modified rubber latexes thereof may be used alone or in combination. The above may be used in combination, and these may be changed arbitrarily depending on the type of rubber to be adhered. In this case, polymeric resorcinol-
The mixing ratio of the formaldehyde initial condensate is preferably 5 to 30% by weight of the condensate and 95 to 70% by weight of the rubber latex based on the total solid content. The low molecular weight resorcin-formaldehyde initial condensate (1 mol of resorcin and 0.05 to 0.8 mol of formaldehyde) used in combination with the polyhydric phenol polysulfide in the above RFL adhesive is usually obtained without catalyst or with a trace amount of acidic catalyst. Polyvalent phenol polysulfide compounds are phenols having at least two or more hydroxyl groups per benzene nucleus, such as hydroquinone, resorcinol, orcinol, pyrogallol, chloroglucinol, pyrocatechin, etc., which have sulfur sulfur between the benzene nuclei. Sulfides, which are a group of compounds with a relatively complex structure having a chain of atoms, and which are effective in the present invention are polysulfides whose sulfur chain has one or more sulfur atoms, and have the general formula:

[Formula, x is 1 to 6, y is 2 to 3, n is 1 to 15
This is a compound represented by In such cases, the adhesive composition should be RFL2.5~
15.0% by weight, 5 to 50% by weight of a low molecular weight resorcinol-formaldehyde initial condensate, 1.0 to 10.0% by weight of polyphenol polysulfide, and 30 to 70% by weight of rubber latex. As detailed above, the method of the present invention involves subjecting an aromatic polyamide fiber cord to low-temperature plasma treatment, adhering the treated fibers with an RFL-based improved adhesive composition, curing with heat, and bonding this with unvulcanized rubber. This is a method of adhering fibers and rubber, in which a composite with excellent adhesive performance is obtained by vulcanizing a rubber composition by heating and pressurizing. The method of the present invention is used in industrial products such as tires, conveyor belts, hoses, and rubber crawlers, and is particularly effectively applied to tires and belts that require high performance. Example 1 A device capable of differential pumping, equipped with a microwave generator and a plasma processing chamber for treating plasma generated by the device, and capable of continuously moving fibers was equipped with poly-para Multifilament cord of phenylene terephthalamide (manufactured by Dubon; Kevlar 29) (1500-D/2, 30S
30Z) and continuously moving the pressure in the plasma processing area with each differential pump.
Below 0.1 Torr, air, helium,
Gases such as N ₂ , O ₂ , Ar, CO, CO ₂ , SO ₂ , NO, etc. are introduced through the inlet to reduce the pressure in the plasma processing area.
1Torr, and in that state generate each gas plasma with an output of 1KW using a microwave generator with a frequency of 2.45GHz, adjust the speed so that the fiber cord passes through the plasma generation area in 20 seconds and 120 seconds, and generate plasma. Processed. The fiber cord subjected to the plasma treatment as described above is immersed in RFL adhesive A or adhesive composition B according to the present invention shown in Tables 1 and 2 below using a Ritzler treatment machine as a fiber adhesion treatment device. , and then dried at a temperature of 140°C for 30 seconds, and further heat-treated at a temperature of 240°C for 60 seconds to obtain an adhesive-treated cord.

【table】

[Table] Each fiber cord that has been treated as described above has a length of 200 mm.
The unvulcanized rubber compound listed in Table 3 below, which is lined with reinforcing cloth, is bonded onto the mold after being stretched to a thickness of 2 mm, heated at 160°C for 20 minutes, and then pressurized. The cord was peeled from the vulcanized rubber at a tensile speed of 300 mm/min, and the peel adhesion between the rubber and the cord was measured. The results were as shown in Table 4.

[Table] For comparison, fiber cords that were not subjected to plasma treatment were subjected to the adhesive treatment described above using adhesives A or B in Tables 1 and 2 (comparative examples), and also fiber cords that were not plasma treated. was immersed in an epoxy compound adhesive having the composition listed in Table 5, then heat treated at 240°C for 60 seconds, and then further immersed in an RFL adhesive having the composition listed in Table 5, followed by a temperature of 240°C. The peel adhesion between the rubber and the cord was measured using the method described above for the sample that had been heat-treated for 60 seconds (comparative example), and the results are also shown in Table 4.

【table】

【table】

[Table] From the results in Table 4, it is clear that the peel adhesion strength of the aromatic polyamide fiber cord and rubber bonded by the method of the present invention is excellent. Example 2 The continuous processing equipment used in Example 1 was
Install a device that generates a high frequency of 13.56MHz,
Plasma treatment of the various gases used in Example 1 was performed as follows. Reduce the pressure in the plasma processing area to 0.1 Torr or less, and introduce various gases from the gas inlet to increase the pressure.
With the temperature adjusted to 1.0 Torr, a high frequency device generates plasma with an output of 100 W, and 20 Torr is applied to the fiber cord.
Plasma treatment was performed for 120 seconds and 120 seconds. Thereafter, adhesive and vulcanization were applied in the same manner as in Example 1 to obtain an adhesive-treated cord. Regarding the obtained adhesive treatment code, Example 1
The peel adhesion between the rubber and the cord was measured in the same manner as described above. The results were as shown in Table 6.

[Table] Example 3 In the continuous microwave generation device used in Example 1,
Ammonium hydroxide and formaldehyde aqueous solutions are heated and vaporized and introduced into the plasma generation area either alone or together with oxygen, and the pressure is 1 Torr and the output is
Plasma was generated at 1 KW, and the fiber cord was subjected to plasma treatment for 20 seconds, and then adhesive treatment and vulcanization treatment were performed in the same manner as in Example 1. Regarding the obtained adhesive-treated cord, the peel adhesive force between the rubber and the cord was measured in the same manner as in Example 1. The results were as shown in Table 7.

[Table] Example 4 The treated cords obtained in Examples 1 to 3 and subjected to plasma treatment for 20 seconds were subjected to a fatigue resistance test based on strength elongation measurement and belt bending test method. Fifty treated cords were placed in parallel in the length direction of a mold with a length of 50 cm, a width of 5 cm, and a depth of 1 cm, and were bonded with the unvulcanized rubber composition listed in Table 3 at a temperature of 160°C.
Vulcanization was performed by heating and pressurizing for 20 minutes. The test piece obtained by the above method was subjected to bending fatigue 500,000 times using a belt bending tester under conditions of a pulley diameter of 32φ and a load of 125 kg. The strength and elongation of the cord taken out from the test piece was measured using a fiber cord tensile testing device at a tensile speed of 300 mm/min, and compared with the strength and elongation before initial fatigue application. The results obtained were as shown in Table 8.

[Table] As shown in the above examples, when aromatic polyamide fiber cords are subjected to various plasma treatments and then treated with the adhesive composition of the present invention, adhesion to rubber is improved and fatigue resistance is further improved. It was done.

Claims (1)

[Claims] 1. The surface of aromatic polyamide fibers is treated in a low-temperature plasma gas atmosphere under reduced pressure, and then the treated fibers are treated with a high molecular weight resorcinol-formaldehyde initial condensate and rubber latex, and then with a low molecular weight resorcinol-formaldehyde initial condensate and a rubber latex. 1. A method for adhering aromatic polyamide fibers and rubber, the method comprising adhering with an adhesive composition containing a formaldehyde initial condensate and polyphenol polysulfide. 2. The method according to claim 1, wherein the high molecular weight resorcinol-formaldehyde initial condensate in the adhesive composition is reacted with formaldehyde at a ratio of 0.8 to 7.5 moles per mole of resorcinol. 3. The method according to claim 1, wherein the low molecular weight resorcinol-formaldehyde initial condensate is reacted at a ratio of 0.05 to 0.8 mol of formaldehyde per 1 mol of resorcin. 4 The polyvalent phenol polysulfide is represented by the general formula: The method according to claim 1. 5. The method according to claim 1, wherein the low-temperature plasma gas is a non-polymerizable gas, a polymerizable gas, and a heated vaporized gas, either alone or in combination. 6. The method according to claim 1, wherein the low temperature plasma is excited by an audio wave, high frequency or microwave generator.