JPH0124810B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for surface treatment of molded rubber materials. More particularly, it relates to a method for surface treatment of molded rubber materials with improved surface properties. [Prior Art] Various proposals have been made to improve the surface properties of molded rubber materials, such as reducing surface friction resistance, imparting solvent resistance, water repellency or ozone resistance, and reducing tackiness. For individual purposes such as removal, sulfur chloride solution (Japanese Patent Publication No. 26-134,
No. 35-4608), peracetic acid solution (No. 36-190), chlorine gas, bromine gas or sodium sulfonate solution (No. 37-3807), aqueous alkali solution (No. 45-34706), alkyl Hypohalide (Japanese Patent Publication No. 50-27503), bromine or iodine and peroxodisulfuric acid (Japanese Patent Publication No. 53-27751), antimony pentafluoride (Japanese Patent Publication No. 50-23483), polyamine (Japanese Patent Publication No. 51-55379) ), polyorganosiloxane (Publication No. 54-90375) or graphite (Publication No. 54-90375),
Various chemicals such as heat (Publication No. 51-30883) or ultraviolet rays (Publication No. 54-22482),
57576) and other methods have been proposed. However, in many of these methods treated with various chemicals, the rubber surface becomes hard deep down, so when this is used for sliding parts, fine cracks occur on the surface, making it difficult to adjust the treatment conditions. If the conditions are made too severe, there are various drawbacks such as loss of rubber elasticity and large cracks in the molding material. Furthermore, graphite treatment and ultraviolet treatment also have the disadvantage that they cannot withstand long-term use because the treatment depth is shallow. In the treatment method using antimony pentafluoride, antimony pentafluoride is used as a mixed air stream with an inert carrier gas, and after treatment, the treatment is sequentially washed with an aqueous alkali metal carbonate solution and water.
The surface condition of rubber materials treated in this way is improved, but in the case of chemically stable rubber such as fluorocarbon rubber, the surface treatment not only hardly progresses, but also contains toxic elements. The use of antimony compounds, which are known as antimony, poses undesirable problems such as problems in the preparation of the working environment and wastewater treatment. [Problems to be Solved by the Invention] When using a molded rubber material as a member that involves sliding or separation, such as an oil seal, an O-ring, or a valve, it is necessary to maintain good rubber elasticity while still maintaining its surface. It is required to have low frictional resistance and excellent chemical and oil resistance. Furthermore, it is also necessary that it does not cause problems such as environmental destruction. As a result of various studies on surface treatment methods for molded rubber materials that meet all of these requirements, the applicant has found that in the method using antimony pentafluoride, a more reactive fluorine gas can be used instead of antimony pentafluoride. It was discovered that these problems could be solved by using
126146). While chlorine gas only reacts with unsaturated bonds such as double bonds, fluorine gas reacts not only with addition reactions to unsaturated bonds but also with hydrogen due to its good reactivity. It can be done easily. For this reason, it also effectively acts on the surface treatment of rubbers that do not have unsaturated bonds in their rubber molecules. Moreover, the 1,2-difluoride produced by the addition reaction is thermally stable compared to 1,2-dichloride and the like. Other 1,2-dihalides are 1,2
-dichloride, 1,2-dibromide, 1,2
- It is known that the halogen molecules are easily desorbed in the order of diaiodide, and the desorbed halogen molecules corrode metals etc. that come into contact with them. On the other hand, fluorinated materials are stable and have low surface energy, resulting in a low coefficient of friction. By the way, various fillers are generally mixed into rubber materials, but in the case of the above-mentioned surface treatment method using fluorine gas, if the blended carbon black filler is fine, the surface treatment method is not necessarily suitable. It turned out that things were not going smoothly. This also varies depending on the type of rubber material being surface treated.
For example, this tendency is particularly seen in the case of acrylonitrile-butadiene copolymer rubber and fluorocarbon rubber. One possible countermeasure to this problem is to raise the temperature of the fluorine gas, but this surface treatment reaction is exothermic, making it difficult to control the reaction, resulting in an excessive fluorination reaction and cracks on the surface of the rubber material. This leads to a situation like this. [Means for solving the problem] Therefore, as a result of various studies on fluorination reactions for molding materials made of carbon black-containing acrylonitrile-butadiene copolymer rubber or fluorine rubber, we found that the relationship between the flow rate of fluorine gas and the reaction rate was It has been found that there is a correlation between the two, and by utilizing this relationship, it has become possible to make the surface treatment reaction proceed smoothly using factors other than reaction temperature and gas pressure. That is, in the present invention, acrylonitrile containing carbon black with a particle size of about 100 μm or less is used.
When surface-treating a molding material made of butadiene copolymer rubber or fluorine rubber by holding it in a fluorine gas stream, fluorine gas is applied at a treatment temperature of 10 to 150°C for 20 to 30 minutes.
Circulation is carried out at a flow rate of 400 cm/min. When fluorine gas is circulated under these conditions, the fluorination reaction can be carried out smoothly and sufficiently, even for compounded rubber materials containing this type of carbon black, which was difficult to proceed with in the past. proceed. Furthermore, no phenomena such as hardening, cracking, or uneven surface treatment of the rubber material surface due to the fluorination reaction were observed. The amount of fluorine gas being circulated is
If it is less than 20 cm/min, the desired fluorine reaction will not proceed sufficiently, and if it is more than 400 cm/min, hardening of the rubber material surface or excessive bonding reaction with fluorine will occur. The molded rubber material to be surface-treated includes acrylonitrile-butadiene copolymer rubber or fluorocarbon rubber, a vulcanizing agent and other compounding agents, such as fillers other than carbon black, reinforcing agents, softeners, plasticizers, anti-aging agents, It is a vulcanized molded product of a rubber compound mixed with processing aids etc. as necessary. Generally, in order to adjust the strength and hardness of rubber materials depending on the intended use, the type, particle size, amount, etc. of the filler added thereto are changed.
Regarding carbon black, from the smallest particle size, HAF (25 to 35 μm), FEF (31 to 58 μm),
SRF (59-86μm), FT (120-190μm), MT (250
~500 μm), and since fluorine gas has poor affinity with these carbon blacks, it is thought that diffusion becomes difficult to occur, especially as the particles become smaller or the amount blended increases. However, in the surface treatment method using fluorine gas according to the present invention, the particle size is smaller than that of SRF (approximately
Rubber materials containing carbon black (100 μm or less) as a filler are also characterized by effective surface treatment. Fluorine gas as a surface treatment agent can be used as an air stream alone or as a mixed air stream diluted to about 100 times with an inert carrier gas such as helium, argon, nitrogen, carbon tetrafluoride, or sulfur hexafluoride. It is used by circulating under normal pressure to increased pressure (~20 atmospheres) or reduced pressure (~1/100 atmospheres). The processing temperature is generally selected within the range of 10 to 150°C, preferably 20 to 100°C, depending on the type of molded rubber material and the processing temperature.
Additionally, the treatment time is generally shorter if the treatment temperature is higher, and longer if the treatment temperature is lower, but if workability is taken into account, the treatment time should be shorter at a higher temperature within a range that does not impede the effectiveness of flow rate control. This is desirable. Molded rubber materials that have been subjected to circulation treatment using a fluorine gas stream or a mixed stream of fluorine gas and an inert carrier gas are immediately immersed in an aqueous alkali metal carbonate solution to remove the fluorine gas adhering to the surface. Washed. Examples of aqueous alkali metal carbonate solutions include sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, etc.
It is used as an aqueous solution with a concentration of ~20%. The immersion treatment is performed at a temperature of about 10 to 100°C for about 5 to 30 minutes.
Preferably done for about 10-15 minutes, then washed with water for about 10 minutes
Wash for ~15 minutes and dry under warm air. [Effects of the Invention] According to the method of the present invention, the surface of a molding material made of acrylonitrile-butadiene copolymer rubber or fluorine rubber containing carbon black with a particle size of about 100 μm or less can be smoothly treated with fluorine gas. The molded rubber material whose surface has been treated in this way can provide members that require sliding or separation, such as oil seals, O-rings, and valves, with low surface frictional resistance while retaining rubber elasticity. . [Example] Next, the present invention will be explained with reference to an example. Example 1 Acrylonitrile-butadiene copolymer rubber (per 100 parts by weight of copolymer rubber) of acrylonitrile-butadiene copolymer rubber (per 100 parts by weight of copolymer rubber) was placed in a cylindrical stainless steel reaction vessel with an inner diameter of 80 mm and a length of 300 mm. Add 73 parts by weight) sheet and 10 g of sodium fluoride (a pellet-like material with a diameter of about 2 mm and a length of about 5 mm is filled on the fluorine gas outlet side to absorb hydrogen fluoride gas), and then heated with nitrogen gas. It is filled with 3 times diluted fluorine gas at a pressure of approximately 1/3 atmosphere. The gas in the reaction vessel is circulated at a flow rate of 120 cm/min using a bellows type pump (capacity of about 6 min at room temperature and pressure), and then the temperature is raised to 30°C. 30
After circulating the gas for 1.5 hours at a temperature of ~38 °C, the gas inside is discharged, and the rubber sheet is taken out and washed with a 10% aqueous sodium carbonate solution and running water for 10 minutes each, and dried. The rubber sheet treated in this manner has no cracks in appearance and exhibits a uniform surface condition, resulting in a clear reduction in frictional resistance as shown in Tables 1 and 2 below. When physical property values were measured, the following values were obtained. Note that the data listed inside the box are values for untreated rubber sheets. 100% modulus: 26Kg/cm ² (28Kg/cm ² ) Breaking strength: 174Kg/cm ² (178Kg/cm ² ) Elongation at break: 560% (569%) Reference example In Example 1, instead of SRF carbon black Using a copolymer rubber sheet containing 80 parts by weight of MT carbon black with a particle size of 250 to 300 μm,
Fluorine gas treatment was performed at a circulating gas flow rate of 15 cm/min. The coefficient of friction of the treated rubber sheet was 0.6 immediately after the start of the test, and 0.8 one hour after the start of the test. Example 2 In Example 1, instead of the acrylonitrile-butadiene copolymer rubber sheet, a fluorocarbon rubber sheet (25 parts by weight of FEF carbon black, 5 parts by weight of calcium hydroxide, 3 parts by weight of magnesium oxide, per 100 parts by weight of fluorocarbon rubber) was used. 2 parts by weight of bisphenol AF and 0.5 parts by weight of 1-benzylpyridinium chloride
Fluorine diluted three times with nitrogen gas was placed in a reaction vessel using a vulcanized sheet prepared by blending parts by weight and press vulcanizing at 180°C for 5 minutes and oven vulcanizing at 230°C for 22 hours. Gas was filled at 130° C. under a pressure of about 1/2 atmosphere, the gas was circulated at the same flow rate for 6 hours at that temperature, and the same treatment was performed after the gas was discharged. The rubber sheet treated in this way had no cracks on the surface, and as shown in Table 3 below, a clear reduction in frictional resistance was observed. When physical property values were measured, the following values were obtained. Note that the data listed inside the box are values for an untreated rubber sheet. Hardness: 85 (85) Breaking strength: 155Kg/cm ² (158Kg/cm ² ) Elongation at break: 232% (235%) Comparative example 1 In Example 1, diluted fluorine gas was used without gas circulation. The reaction vessel was allowed to stand at 40° C. for 4 hours, and after the gas was discharged, the same treatment was performed. The appearance of the rubber sheet treated in this manner is almost unchanged from that before treatment, and no decrease in frictional resistance is observed. Comparative Example 2 In Comparative Example 1, the pressure of the diluted fluorine gas filled in the reaction vessel was set to about 1 atmosphere. The rubber sheet treated in this manner showed hardening on its surface, and it was also observed that carbon-like powder was floating on the surface. When physical property values were measured, the following values were obtained. 100% modulus: 32 Kg/cm ² Strength at break: 168 Kg/cm ² Elongation at break: 474% Comparative example 3 In Example 1, fluorine gas diluted 9 times with nitrogen gas was heated at 40°C under a pressure of about 1 atm. After that, gas was circulated at the same temperature for 4 hours at a flow rate of 15 cm/min, and the same treatment was carried out thereafter. The rubber sheet treated in this manner shows almost no change in its surface, and as shown in Table 1 below, almost no decrease in frictional resistance is observed. Acrylonitrile of Example 1 and Comparative Example 3
Friction resistance tests were conducted on the butadiene copolymer rubber sheet and the fluorine rubber sheet of Example 2 using a Suzuki friction tester. The test conditions are as follows. Load: 2Kg Mating metal material: S45C Surface roughness: 1.5S Outer circumference: 71.6mm Contact area: 2cm ² rotations: 100rpm The friction coefficients of the untreated vulcanized sheet immediately after the start of the test and 1 hour later were measured. The values are shown in Table 1 below.

[Table] Comparative Example 4 In Example 2, the gas circulation was not increased and fluorine gas diluted three times with nitrogen gas was filled at 150°C with a pressure of about 1 atm, and kept at this temperature for 6 hours. The mixture was allowed to stand still in the reaction vessel, and after the gas was discharged, it was treated in the same manner. The rubber sheet treated in this manner shows almost no change in its surface. Examples 3 to 5 In Example 1, the flow rate of the circulating nitrogen gas diluted fluorine gas was changed as follows, and the friction coefficient of the treated rubber sheet was measured. The results obtained are shown in Table 2 below.

[Table] Examples 6 to 8 In Example 2, the flow rate of the circulating nitrogen gas diluted fluorine gas was changed as follows, and the friction coefficient of the treated rubber sheet was measured. The results obtained are shown in Table 3 below.

[Table] From the comparison of the above examples and comparative examples, the following can be said. First, acrylonitrile-
In the case of butadiene copolymer rubber, when the gas is circulated in the treatment reaction vessel, surface treatment hardly progresses even at higher temperatures when left standing at the same fluorine gas concentration; It can be seen that the surface treatment progresses only by
5-Comparative Example 1). However, even if the product is allowed to stand still, as soon as the gas pressure is increased, the surface treatment reaction progresses significantly, hardening and carbonization of the surface are observed, and physical property values also decrease (Comparative Example 2) . On the other hand, in the case of molded rubber materials containing carbon black with a particle size of approximately 100 μm or less, the fluorination treatment is carried out smoothly even with circulating gas treatment at a flow rate of 15 cm/min, reducing the coefficient of friction and reducing the friction coefficient. shows a behavior that is in contrast to the case where carbon black with a particle size of about 100 μm or less is used (Reference Example - Comparative Example 3). In addition, in the case of fluorine rubber, if the gas is allowed to stand still, the surface treatment reaction will not proceed even if the treatment temperature is further increased (Comparative Example 4), but if the fluorine gas is circulated, the surface treatment will proceed smoothly. It can be seen that this progresses (Examples 2 and 6 to 8).

Claims (1)

[Claims] 1. A molding material made of acrylonitrile-butadiene copolymer rubber or fluorocarbon rubber containing carbon black with a particle size of about 100 μm or less is circulated at a processing temperature of 10 to 150°C at a flow rate of 20 to 400 cm/min. A surface treatment method for a molded rubber material that involves sliding or spacing, characterized by holding the molded rubber material in an airflow of fluorine gas. 2. The method for surface treatment of a molded rubber material according to claim 1, wherein fluorine gas is used after being diluted with an inert gas.