JPH0554591B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention is applicable to disc brake caliper pistons, drum brake wheel cylinder pistons, clutch operation cylinder pistons, etc., which are made of a phenolic resin molded article with excellent heat resistance. This invention relates to a piston for a hydraulic cylinder. [Prior Art] Hereinafter, the caliper piston of a disc brake will be mainly described. In recent automobiles, the use of disc brakes has become common for the purpose of improving braking performance. This is due to the braking performance of disc brakes.
This is because it is easier to ensure instantaneous braking force and continuous braking force compared to other methods. FIG. 1 is a sectional view showing the structure of a disc brake. 1 is a caliper piston, 2 is a seal, 3 is a disc brake pad, 4 is a disc, and 5 is brake fluid. Conventionally, the caliper piston 1 is often made of chrome-plated steel. Disc brakes generate frictional heat when braking. Since kinetic energy is converted into thermal energy, the amount of heat generated increases as the vehicle speed at the start of braking increases and as the vehicle weight increases. This heat travels through the brake pads and caliper pistons, raising the temperature of the brake fluid.
It is well known that repeated sudden braking or continuous braking on long downhill slopes can cause the brake fluid to boil, a condition known as paper lock development, which can reduce the effectiveness of the brakes. Improving braking performance requires heat countermeasures, that is, heat radiation into the air and insulation of the brake fluid. The recent trend is that brake pads have been changing from molded bodies using asbestos as the main compound and a binder such as phenol resin, which has been used for a long time to improve friction characteristics.
Molded products that use steel wool as the main compounding material are rapidly changing. Furthermore, the use of sintered bodies made of various metal powders, mainly copper, called sintered pads, has begun to be seen in some car models. This tendency increases the amount of heat transferred to the brake fluid if the conventional design is used, making paper lock development more likely to occur. To solve this problem, making the caliper piston resin and insulating it is effective in preventing the brake fluid from rising in temperature.The caliper piston is manufactured from phenol resin and has been partially put into practical use. During braking, the caliper piston locally
Since it reaches temperatures of over 200℃, it is required to have strength when hot, a small coefficient of thermal expansion, and small dimensional changes over a wide temperature range, so dimensions and strength do not change significantly when coexisting with brake fluid. It is necessary. It is difficult for phenolic resin caliper pistons to meet the above requirements, especially heat resistance above 200°C and small dimensional change rate over a wide temperature range, and their application is limited to vehicles that generate a small amount of heat during braking. It can be said that it was limited to. However, with the exception of special heat-resistant resins such as polyimide,
Phenol resin is highly practical as a resin for caliper pistons due to its heat resistance, and since its application as a caliper piston will be expanded, it has been strongly desired to improve the heat resistance by some method. Improvements in heat resistance and dimensional stability have also been desired in wheel cylinder pistons for drum brakes and operation cylinder pistons for clutches. [Object of the Invention] Based on the above background, the present invention has found that heat resistance can be improved by mixing resol type phenolic resins with different structures in a resin system and using fillers such as reinforcing fibers. Based on this knowledge, various studies have been carried out and the present invention has been completed. The purpose is to provide a piston for a hydraulic cylinder such as a disc brake caliper piston made of a phenolic resin molded article with excellent heat resistance. [Structure of the Invention] The present invention provides a solid resol type phenol resin having a number average molecular weight (hereinafter referred to as M=) excluding free phenol of 800 to 1200 and a dimethyl ether group composition ratio of phenol core binding functional groups of 40 to 60 mol%. , number average molecular weight excluding free phenol (M=) is 600~
1000, 100 parts by weight of a phenolic resin having a mixing ratio (weight ratio) of 3:7 to 7:3 with a solid resol-type phenolic resin whose phenol core-binding functional group has a dimethylene ether group composition ratio of 0 to 20 mol%. The present invention relates to a piston for a hydraulic cylinder, characterized in that it is made of a molded body of a composition containing 100 to 250 parts by weight of a filler. Note that the ratio of functional groups was determined by NMR measurement after acetylating the resin. The piston for a hydraulic cylinder of the present invention can be obtained by injection molding using a screw type injection molding machine, or by plasticizing a molding material using a screw type extruder, and then heating and compression molding the plasticized product in a predetermined mold. Therefore, the composition of the present invention must have a structure that allows it to be plasticized using a screw. This is because a powder or a preformed powder is plasticized by high frequency, infrared rays, etc., and then heated and compression molded in a mold, resulting in poor heat resistance, especially thermal shock resistance. The present invention will be explained in detail below. All of the phenolic resins used in the present invention are solid resol type phenolic resins. If it is in liquid form, the process of making it into a molding material is complicated, which is industrially disadvantageous. In addition, novolac type phenolic resins that use hexamethylenetetramine or paraformaldehyde as a curing agent do not have high heat resistance because their reaction mechanism does not increase crosslinking density or generates gas from a small amount of residual curing agent. It has disadvantages such as not being able to absorb water easily, has inferior chemical resistance compared to the resol type, and is easily attacked by brake fluid, etc., and is not suitable for use in pistons for hydraulic cylinders. The composition of the solid resol type phenolic resin is M=
800 to 1200, a solid resol type phenol resin (hereinafter referred to as dimethylene ether type resol) in which the dimethylene ether group composition ratio of the phenol core binding functional group is 40 to 60 mol%, and M = 600 to 1000, a phenol core A solid resol-type phenolic resin (hereinafter referred to as methylol-type resol) whose binding functional group has a dimethylene ether group composition ratio of 0 to 20 mol%.
The ratio (weight ratio) is 3:7 to 7:3. Dimethylene ether type resols have a large activation energy of approximately 30 kcal/mol, and the reaction does not proceed easily at relatively low temperatures, whereas the reaction tends to proceed at high temperatures, making them suitable for injection molding, whereas methylol type resols are suitable for injection molding. has an activation energy of approximately
Since the reaction proceeds at a relatively low temperature with a small amount of 10 kcal/mol, the thermal stability of the preplasticized product in the screw during molding is poor. Cured products of dimethylene ether type resols have a considerable amount of remaining dimethylene ether groups due to their curing mechanism, and the distance between phenol nuclei is relatively long, so crosslinking density is less likely to increase than cured products of methylol type resols, and heat resistance is improved. is inferior. Therefore, in order to obtain a resin composition that has high heat resistance and excellent thermal stability of the preplastic in the screw, the blending ratio of dimethylene ether type resol and methylol type resol should be 3:7 to 7:3. do. If the ratio of dimethylene type resol is less than 3:7, preplasticization with a screw is difficult, and conversely, if the ratio of methylol type resol is less than 7:3, heat resistance will be insufficient. It is appropriate that the filler used in the present invention is mainly inorganic. Organic materials such as wood flour and pulp have poor heat resistance. In order to obtain heat resistance as a piston for a hydraulic cylinder, it is necessary to have strong strength against distortion during heating and a small coefficient of thermal expansion. Desirable fillers for this purpose are inorganic reinforcing fibers, such as glass fibers, carbon fibers, graphite fibers, etc., and it is optional to partially use glass powder, clay, mica, graphite powder, etc. in combination. The amount of the filler used in the present invention is in the range of 100 to 250 parts by weight per 100 parts by weight of the phenolic resin. If the amount exceeds 1 part by weight, problems such as poor fluidity during molding will occur. Generally, a curing aid, a mold release agent, a pigment, etc. are added to these compositions and mixed, and then heated and kneaded to obtain a molding material. The piston for a hydraulic cylinder of the present invention is produced by injection molding the molding material using a screw type injection molding machine, or by plasticizing the molding material using a screw type extruder, and then heating and compression molding the plasticized product in a predetermined mold. can be obtained. It is desirable to perform post-curing after molding in order to improve heat resistance and dimensional stability. [Effects of the Invention] The piston for hydraulic cylinders of the present invention improves the crosslinking density of the molded product due to its resin composition, so it has excellent heat resistance such as a small weight loss rate and a small decrease in strength under high temperature conditions. This is what I did. [Example] M=1000, the composition ratio of dimethylene ether group is
Table 1 shows a phenolic resin having a ratio of 1:1 between a dimethylene ether type resol having a concentration of 41 mol% and a methylol type resol having an M=800 and a composition ratio of dimethylene ether groups of 20 mol%. After mixing glass fiber and other ingredients with the following composition, the mixture was kneaded with hot rolls to obtain a molding material. Comparative Example 1 Using only dimethylene ether type resol as a resin component, glass fiber and others were mixed in the composition shown in Table 1, and then kneaded with hot rolls to obtain a molding material. Comparative Example 2 Using only methylol-type resol as a resin component,
After mixing glass fiber and others with the composition shown in Table 1, the mixture was kneaded with hot rolls to obtain a molding material. Comparative tests were conducted on the following physical properties of these molding materials. (1) Specific gravity, (2) Surface strength (Rockwell M scale), (3) Bending strength, (4) Flexural modulus, (5) Compressive strength, (6) Linear expansion coefficient, (7) Thermal shock resistance , (8) Dimensional stability For items (1) to (6), test pieces were obtained by injection molding,
Measured according to JIS K 6911. For items (7) and (8), the caliper piston model 6 shown in FIG. 2 was obtained by injection molding and evaluated using the following method. Thermal shock resistance: approximately 300 for caliper piston model
After heating to ℃, cool with water. This was repeated to evaluate thermal shock resistance. Dimensional stability: A caliper piston model was immersed in brake fluid, air, grease, etc. at 150°C for 400 hours to evaluate its dimensional stability. 【table】

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a disc brake. FIG. 2 is a partially sectional front view of the caliper piston model of the embodiment.

Claims (1)

[Claims] 1 Free phenol excluded number average molecular weight is 800~
1200, a solid resol type phenol resin with a dimethylene ether group composition ratio of the phenol core binding functional group of 40 to 60 mol%, and a number average molecular weight excluding free phenol of 600 to 1000, and a dimethylene ether group of the phenol core binding functional group A composition comprising 100 parts by weight of a phenolic resin having a mixing ratio (weight ratio) of 3:7 to 7:3 with a solid resol type phenolic resin having a composition ratio of 0 to 20 mol% and 100 to 250 parts by weight of a filler. A piston for a hydraulic cylinder, characterized by comprising a molded body.