JPS6179070A - Caliper piston - Google Patents

Abstract

PURPOSE:To achieve stable sliding performance even at a high temperature, by making a caliper piston of a phenol resin containing a resol-type phenol resin as the main constituent, 2-5wt% of a compound such as a hydroxy acid salt phosphorus and a filler containing an inorganic substance as the main constituent. CONSTITUTION:A caliper piston for an automobile disk brake is made of a molded composite material prepared by adding 2-5wt% of a compound such an a hydroxy acid salt of phosphorus and 200-350wt% of a filler containing an inorganic substance as the main constituent, to a phenol resin containing a resol-type phenol resin as the main constituent. When the composite material is thermally molded, the condensation polymerization of the thermosetting resin is promoted to reduce the amount of a portion remaining not subjected to the condensation polymerization after the molding. For that reason, the caliper piston is stabilized against oxidation or the like at a high temperature after the molding.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention relates to a caliper piston for disc brakes, and more specifically, it relates to a caliper piston for disc brakes, and more specifically, it relates to a caliper piston for disc brakes. This relates to a caliper piston for disc brakes, which is made of a molded body of a composition containing a filler mainly composed of a type of filler, and has good heat resistance and exhibits stable sliding characteristics with extremely little dimensional shrinkage even at high temperatures. be.

(Conventional technique @) Disc brakes are increasingly being used in recent automobiles for the purpose of improving braking performance.

Figure 1 shows a caliber piston for a disc brake and its surrounding parts. In Figure 1, 1 is a disk, 2
is a disc brake pad, 3 is IIi! A friction material, 4 a back metal, 5 a caliber piston, 6 a boot, 7 a seal, 8 a cylinder, 9 a brake fluid, and 10 a caliper. The friction material 3 of the disc brake pad 2 is manufactured by compression molding asbestos or steel wool, graphite, metal powder, barium sulfate, etc. using a phenol resin as a binder. The back metal 4 is generally made of metal such as stainless steel, and the caliber piston 5 is made of chrome-plated steel. When the disc brake operates, that is, when braking, disc 1 and Ili! Frictional heat is generated between the friction materials 3. The amount of heat increases as the vehicle speed at the start of braking increases; in other words, kinetic energy is converted into thermal energy. As a result, when strong braking is repeated, the surface of the friction material becomes high temperature, and this heat is transmitted from the friction material to the brake fluid 9 via the metal back metal 4 and the piston 5. As a result, the temperature of the brake 9 increases and there is no problem during normal driving, but if the brakes are used frequently, especially on steep and long downhill slopes, the so-called paper lock phenomenon occurs, where the brake fluid no longer functions properly. The brakes become less effective.

In order to solve these problems, consideration has been given to insulating the back metal or the caliber piston by making it resin to prevent the temperature of the shim or brake fluid from rising.

Conventionally, thermoplastic resins and thermosetting resins have been widely used as plastic molding materials, but one of the major drawbacks of these resin materials is that they have poor heat resistance compared to metal materials such as iron and aluminum. Therefore, its range of application was limited.

That is, the thermal deformation temperature of thermoplastic resins generally used as molding materials is 180° C. or lower, and deformation occurs when used at higher temperatures. Furthermore, even if the heat distortion temperature is 180°C or higher, the glass transition temperature is 1.
If the temperature is lower than 80°C, minute dimensional changes will occur if used for a long period of time under a temperature condition of 180°C or higher. Furthermore, although thermosetting resins such as phenolic resins and unsaturated polyester resins have heat distortion temperatures of 190°C to 200°C or higher, they have the problem of shrinking in size when placed under high temperature conditions after molding. has. This is caused by the above-mentioned thermosetting curing reaction and cannot be avoided. For this reason, these thermosetting resins are sufficiently after-cured (also referred to as post-cure or post-cure) after molding to stabilize their dimensions before use as a product. Here, the term "after cure" refers to a treatment method in which a thermosetting resin such as a phenolic resin is left under suitable temperature conditions for a relatively long period of time after molding to allow the curing reaction to proceed and stabilize it. In particular, for materials with strict dimensional accuracy, such as sliding materials, the dimensions are determined by machining after boss curing before use as a product.

However, even if after-curing is performed sufficiently, dimensional shrinkage is not completely eliminated, and some shrinkage occurs when exposed to high temperatures after after-curing.

This shrinkage becomes a big problem in materials such as 1-layer materials that have extremely tight dimensional tolerances. For example, U.S. Pat. No. 4,170.926 discloses that a caliper piston for automobile disc brakes is manufactured from a material mainly composed of novolac resin, and this has already been put into practical use in the United States.

(Problems to be Solved by the Invention) When manufacturing this caliper piston using phenolic resin, it is necessary to perform heat and pressure molding using a mold.
After-cure must be sufficiently performed at a temperature of 00 to 250°C. At this time, the molded article generally shrinks by about 0.1%. For this purpose, this caliper piston is first formed into a molded body slightly larger than the predetermined outer diameter, sufficiently after-cured and shrunk, and then dimensional adjusted by machining and polished. Used as a product. This is shown below.

Heat and pressure molding Bost cure 150℃ 300kg / cTl' 250℃ several hours
Lower than the specified machining dimensions → Stable dimensional shrinkage → (1;
7] Grinding and polishing) Dry and enlarge. In order to obtain the desired dimensions, cutting and polishing steps are required after the boss cure, which is a cause of increased product costs.

Here, it is possible to set the dimensions of the molded object by calculating the shrinkage rate in advance, but since the shrinkage rate differs in each part of the molded object, in reality, it is difficult to reproducibly obtain the required dimensions. It is difficult to achieve a good finish, and the current situation is that it is produced using the process described above. Therefore, during the 7-year period after molding, there was a desire for a material that would exhibit no or extremely small dimensional shrinkage when actually used as a product at high temperatures.

(Means for Solving the Problems) The present invention was made by focusing on the problems of the prior art, and involves adding a phosphorus oxy-acid salt compound to a phenolic resin, which is mainly a resol type. 2 to 5% by weight, and 200 to 350% by weight of inorganic fillers.
It was confirmed that the above-mentioned problems could be solved by adding it.

That is, when a molded article is made by thermoforming using such a composition, since the phenol resin is mainly resol-based, even if the amount of phosphorus oxy-acid-based compound added is small, the coexisting oxy-acid-based compound Mechanical properties such as elastic modulus and compounds promote the condensation polymerization reaction of the thermosetting resin during molding, reducing the amount of unreacted components remaining after molding, making it stable against oxidation reactions at high temperatures after molding. At the same time, the gasification of moisture and other volatile components is suppressed, and the combined use of a filler has the effect of improving mechanical properties such as strength and modulus of elasticity, and heat resistance. Although this effect is not as great as adding a phosphorus oxy-acid salt compound in an amount exceeding 5% to the phenol resin, it is sufficient for use as a caliper piston for a disc brake. This is thought to be due to the use of mainly resol-type phenolic resins; in the case of novolac-type phenolic resins that generate ammonia gas, 2 to 5% by weight of phosphorus oxyacid salts It is difficult to obtain a sufficient effect for use as a caliper piston for disc brakes by adding . In other words, in the case of resol-type phenolic ail fat, it is impossible to completely suppress the ignition support phenomenon by adding 2 to 5% by weight of phosphorus oxyacid, but it is effective for caliper pistons. It has been revealed through experiments by the present inventors that it can be used. Further, by adding 2 to 5% by weight of a phosphorus oxy-acid salt compound, dimensional stability of the molded article can be obtained. In other words, when after-curing after molding, and furthermore, when exposed to heat again before after-curing, those with no additives will shrink, those with 5% or more added will expand, but those with 2-5% by weight will change in size. There is no, or if there is, it is very small. The present invention was achieved as a result of extensive research into these two effects of thermal stability and dimensional stability.

That is, the caliper piston of the present invention uses a phenolic resin mainly composed of resol type and 2 to
5% by weight of a phosphorus oxyacid salt compound, and 200% by weight
The present invention relates to a caliper piston made of a filler mainly composed of ~350% by weight of an intact system.

This Somei caliper piston is obtained from the above composition by heat compression molding. Before putting the molding material into the mold, the molding material is preheated using an oven or high frequency, or preplasticized using a screw type injection molding machine or extruder to stabilize the quality and shorten the molding time. Measure the shortening of. After the molding, the molded body is sufficiently after-aged at a temperature of 210° C. to 270° C., and then subjected to some machining to become a piston. However, since the piston of this invention has excellent dimensional stability, the main purpose of machining is to cut parts that cannot be directly molded by compression molding, such as the 11 part.

The caliper piston of the present invention will be explained below based on its configuration. The phenolic resin used in this invention is mainly of the resol type, but solid resols are more preferably used than general liquid resols. This solid resol is obtained by dehydrating a liquid resol under reduced pressure and has a low free phenol content, so it provides good physical properties.

The phosphorus oxy-acid salt compounds used in this invention include silicon polyphosphate, alkali metal salts of silicon polyphosphate,
Various phosphates such as titanium phosphate, zirconium phosphate, aluminum phosphate, calcium phosphate, magnesium phosphate, zinc phosphate, barium phosphate, lead phosphate, and sodium phosphate are used singly or in combination of two or more. Ru. In these phosphates, the phosphoric acid content can be present in the form of orthophosphoric acid or in the form of metaphosphoric acid, birophosphoric acid, tripolyphosphoric acid or other condensed phosphoric acids, but usually this phosphoric acid content is highly concentrated. Preferably, it is present in condensed form. The above-mentioned phosphate may be an acidic phosphate or a basic phosphate, and the ratio of the phosphoric acid content (P2O3) to the metal content (MOII+/2) is expressed by the following formula: MOm /2 ・n P205 (In the formula, M represents a metal including silicon, m represents a valence of metal to 1, and n is 0.1 to 0.7, preferably 0.2
0.5) can be varied over a wide range.

Among the phosphorus oxy-acid salt compounds, silicon polyphosphate or a metal salt thereof is particularly preferred, followed by aluminum polyphosphate or boron polyphosphate or a metal salt thereof.

Phosphorus oxy-acid compounds are 2
If the amount is less than 5% by weight, the above-mentioned effects of addition, that is, the effect of improving mechanical properties and heat resistance, and the effect of preventing dimensional shrinkage, cannot be obtained sufficiently, and if it is added more than 5% by weight, the effect of adding This is not preferable because it may cause expansion.

Next, the filler used in this invention refers to a wide range of fillers including solid lubricants and reinforcing materials, and must be mainly inorganic. This is because organic materials generally have poor heat resistance themselves and often contain volatile components such as moisture. This is because not only can it have a bad influence, but also physical properties such as strength and elastic modulus, and dimensional stability are not good.

Inorganic fillers include clay, talc, silica, alumina, magnesia, titania, calcium silicate, diatomaceous earth, calcium carbonate, graphite, carbon black, mica, metals, etc., and are in the form of powder, flakes,
It is fibrous. It goes without saying that fibrous materials are suitable for increasing strength. In order to further improve the heat resistance of the caliper piston obtained by molding the composition in this invention, it is effective to increase the thermal conductivity and decrease the coefficient of linear expansion. This not only promotes heat dissipation from the molded body by increasing its thermal conductivity, but also reduces the width of the temperature distribution in each part of the molded body, and by reducing the coefficient of linear expansion, the molded body This is because dimensional stability can be achieved. For this purpose, carbon fibers or graphite m-fibers are most preferably used, followed by glass fibers, glass powder, graphite powder, carbon powder, etc. Judging comprehensively from the above-mentioned effects of adding inorganic fillers, costs, etc., short glass fibers are most commonly used as inorganic fillers.

The amount of inorganic filler added is preferably 200 to 350ffi m% based on the phenol resin, and 25
More preferably, it is 0 to 280% by weight. This is because if the amount of filler is less than 200% by weight, the elastic modulus of the molded product obtained using the composition, especially the compressive elastic modulus at high temperatures, will be insufficient, the rigidity will decrease, and the linear expansion coefficient will also increase. If the amount of the filler added exceeds 350% by weight, the fluidity of the composition during compression molding will deteriorate, resulting in not only poor moldability but also poor impact resistance of the resulting molded product.

In order to ensure the function of the caliper piston of this invention, it is necessary to use a reinforcing material as a filler with a ratio of 10% to phenolic resin.
It is desirable to contain the solid lubricant in an amount of 5 to 30% by weight based on the phenol resin as a solid lubricant. Glass fiber is the most commonly used reinforcing material.
Other materials such as carbon fibers, graphite fibers, and metal fibers are used. Graphite powder is most commonly used as the solid lubricant, and molybdenum disulfide, boron nitride, etc. are also used.

As already mentioned, an internal mold release agent is generally added to the composition used to form the caliper piston of the present invention in order to improve mold release during molding. It is appropriate to use 0.5 to 3% by weight based on the total amount of the composition.

As the internal release agent, all common mold release agents can be used, but zinc stearate and calcium stearate are preferably used.

Furthermore, the composition used for molding the caliper piston of the present invention contains calcium hydroxide, magnesium oxide, and an inorganic filler as an auxiliary agent to promote the curing reaction in the mold, and to improve the wetting of the inorganic filler with the phenolic resin. In order to achieve this, an appropriate amount of a coupling agent mainly composed of silane is added.

The composition used in this invention is made by blending a predetermined amount of a phosphorus oxy-acid heat stabilizer and a filler with the resol-type phenolic resin as a main component, and an internal mold release agent, etc. as required. Therefore, it is extremely important to sufficiently mix these components to achieve a good dispersion state. The composition thus obtained is generally a molding material in a form that is easily fed to a molding machine in order to efficiently perform molding processing when producing a molded object.

The general method for preparing such a molding material is to thoroughly mix it using a mixer ribbon blender, a pudding blender, etc., then knead it with a roll, co-kneader, etc., cool it to solidify, and then crush it. The mixture may be heated and granulated at the same time as the mixing.

The caliper piston of the present invention is obtained by heating and compression molding the above-mentioned molding material, and generally the molding material is preheated in an oven or by high frequency before being put into the molding die, thereby stabilizing the quality and improving productivity. Measure.

Furthermore, the above-mentioned molding material is kneaded using a screw set injection molding machine or a screw set extruder, and after being pre-plasticized to give it fluidity, the plasticized material is placed in a mold of a predetermined shape. A molded article can be obtained by heating and compression molding. This is shown in FIG.

Although this method has good productivity, it is necessary that the molding material has good fluidity. In either method, the molded article must be sufficiently after-aged.

Next, appropriate machining is performed on this to obtain a caliper piston. - An example is shown in FIG.

(Function) In the caliper piston of the present invention, which is made of a molded product obtained by heating and compression molding in this way, the phosphorus oxy-acid salt compound in the composition improves the thermal stability of the molded product. Because it works effectively, gas generation phenomena and changes in dimensions and physical properties are extremely small even under high temperature conditions exceeding 200℃ during after-aging and actual use.It has excellent heat resistance and can be used even under high temperature conditions. Stable[! I
It has J characteristics.

Although there is still no clear mechanism as to why the caliper piston of the present invention has the above-mentioned effect of improving heat resistance, it is estimated as follows.

1-------→Hydrolysis of oxyacid MOm/2+polyphosphoric acid The polyphosphoric acid generated in this way is attached to the next bond (~ part) which is the main cause of contraction of the phenolic resin. Although it is a strong dehydrating agent,
It is a mild test drug, does not cause carbonization of the compound during the reaction, and also reacts mildly with the hydroxyl moiety.

Furthermore, since reactions such as phosphorylation do not occur on aromatic moieties, the basic properties of the phenol resin do not change.

In other words, the effect of this invention is to start releasing the above-mentioned polyphosphoric acid during the molding process.If the phosphoric acid component is released before molding, that is, during the mixing and cross-wiring process, it will be released during the cross-wire by the rolls. It becomes difficult to control the curing reaction of the phenol resin.

(Examples) The present invention will be explained using the following examples, reference examples, and comparative examples.

In the Examples and Comparative Examples, a phosphorus oxy-acid salt compound produced by the method shown below was used.

(1) First, silicon polyphosphate was added to JP-A-56-5015.
It was produced by the method shown below in accordance with the method described in the specification of No. 9.

(a) Commercially available sodium silicate (JIS3@ product, Na
2 012.9g/100mA, S i 0
237. OfJ/100nl) directly using iti!
Sodium silicate is dropped one drop at a time into an aqueous sulfuric acid solution heated to 90°C at 10% acidity, and sodium ions and sulfate ions are washed off from the granular silica gel produced by reaction on the so-called acidic side. The silica hydrogel (water content: 92.5%) was washed until substantially no sodium ions were found therein and recovered. Commercially available phosphorus ImL for this silica hydrogel
IISI grade 85%, H3PO4 specific gravity 1.69) with respect to the silicon content raw material, the molar ratio of phosphoric acid content and silicic acid content is P2
Phosphoric acid and silica hydrogel are added and mixed at the maximum ratio such that the O5/SiO2 molar ratio is 0.33, and then the whole is concentrated and the dried product is ground until it passes through a 200 mesh sieve. After sufficiently drying at 200°C (10 hours), it was calcined at 950°C for 1 hour and further classified using a 200 mesh sieve to produce silicon polyphosphate (H8-1>).

(b) As another silicon polyphosphate, silicon polyphosphate (H3-1) has a molar ratio of phosphoric acid and silicic acid of P2O.
Polysilicon polyphosphate ()-18-2 was prepared using exactly the same method as ()Is-1) except that phosphoric acid and silica hydrogel were added and mixed in an amount such that the molar ratio of 5/SiO2 was 0.5. ) was created.

(Sodium polysilicon polyphosphate ('H-1') manufactured by Mizusawa Chemical Industry Co., Ltd. by the method described in JP-A No. 56-50159), Silicon oxide (H-2) and aluminum polyphosphate (H-3> are respectively phosphoric acid oxy-acid salt compounds 1-18-3.H8-4, and H3-
I gave it a 5.

Reference Example 1 An example of the effect of a phosphorus oxy-acid salt compound on improving heat resistance is shown in FIG. This is a solid resol resin (S-1 made by Asahi Yukizai ((2), equivalent to JP-A No. 59-6461616)) and silicon polyphosphate (H8-1) at 0.1.1.5.2. .5. After adding and mixing 5 parts by weight, 20 liters of each were heat compression molded under the conditions shown below.

The plate-shaped molded product thus obtained was heated at a temperature of 150°C, a pressure of 500 kg/cd, and a time of 5 minutes. After crushing, take out 100mg from each and heat ff1f! This is a measurement of changes (by hot bottle method).

The pattern of thermogravimetric change is 0. 1. As with the product added with 1.5 parts by weight, the weight started to increase from around 200℃, and 2
There is a pattern in which the temperature peaks at around 80°C and a rapid decrease in temperature (failure pattern), and a pattern in which there is almost no change in temperature up to around 350°C (passing pattern), such as when 2.5.5 parts by weight is added. being classified. Needless to say, those with acceptable patterns have excellent heat resistance.

Reference example 2 There are many functions required for a disc brake caliper piston, such as sliding properties (friction, wear), bending strength, elastic modulus, compressive strength, impact strength, and coefficient of linear expansion. Since the function of the caliper piston cannot be measured by the shape of the caliper piston, a cylindrical body with a diameter of 130 mm and 11 degrees and a thickness of 50 mm was made using a mold that was precisely machined and lapped so that the maximum surface roughness was 0.16 μm. , by heating compression molding), and test pieces used in each test were created from this cylindrical body and measurements were performed.

This will be explained below.

As the phenol resin, resol type phenol resin powder (manufactured by Asahi Yukozai Kogyo ■) S-1, 8-2 was selected. These properties are shown in Table 1 below.

Table 1 Silicon polyphosphate (H8-1) is selected as the phosphorus oxy-acid salt compound, and milled glass fiber (manufactured by Nittobo Co., Ltd., trade name PFA-101°), kaolin clay, calcium carbonate, and In particular, as a reinforcing material, milled glass fiber (manufactured by Unitika Hayashi, ES
25T (trade name, diameter 25μn, length 250μm)) and carbon fiber chop (Kureha Chemical Industry ■product, M-107T, tradename) In particular, as a solid lubricant, flaky graphite (ACP manufactured by Nippon Graphite ■, tradename) I chose. Calcium stearate (manufactured by Nippon Konica Co., Ltd., 5T-Ca) was selected as a mold release agent. Magnesium oxide Mu O was selected as a curing aid, and silane coupling agent (manufactured by Nippon Konica Co., Ltd.) was selected as a surface treatment agent. A-110
0, product name) was selected. These were thoroughly mixed at the hanging ratios shown in Table 2 using a Henschel mixer kept at room temperature to obtain compositions R-1 to R-3 and C-1 to C-3.

As is clear from Table 2, R-1 to R-3 are compositions within the scope of this invention, and C-1 to G-3 are compositions outside the scope of this invention. These compositions are kneaded using two rolls at a temperature of 80 to 90°C to form a sheet, which is then crushed to give molding materials R--1 to R=-3,C''-
1 to C'-3 were obtained.

This molding material, R'-1~R"-3,0--1~C'
-3 was heated and compression molded under the following conditions to a diameter of 130 mm.
A cylindrical body with a thickness of 50 mm and a density of 1.9 to 2.0 (+/cj) was obtained.

Preheating 100℃ 30 minutes (in oven) Mold temperature 150℃ Pressure 500kg/CD curing time 5
This cylindrical molded body was placed in an oven at 150°C for 3 hours.

After-aging treatment was performed continuously at 200°C for 3 hours and at 230°C for 5 hours, and this was used as the test material R”-1~
R''-3, C''-1 to G''-3, physical property test pieces were cut out from each sample and the following physical property tests were conducted.

(1) Gas generation phenomenon (2) Surface roughness (3), specific gravity (-) hardness (5) Impact resistance (6) Bending strength 1 Elastic modulus (7) Compressive strength 8) Coefficient of linear expansion (9) The test methods for dimensional change rate (10) thermal deterioration characteristics (11) thermogravimetric change will be explained below.

(1) Gas generation phenomenon A reflector-like sample was formed and the degree of blistering (large, medium, small, or none) was judged. Material R″-1 to R″-3,
0''-1 to G''-2 were used as substrates. In addition, as a base coat varnish, polyester (UE-8 manufactured by NOF ■) is used.
, isocyanate (Coronate manufactured by Takeda Pharmaceutical Co., Ltd.) was selected, and these were added and mixed so that the molar ratio of isocyanate groups and alcohol groups was 1, and NGOloH was spray-painted on the above material (thickness about 10
μm), baking was performed at 180° C. for about 1 hour. After applying aluminum to the base coated material using a vacuum deposition bag (manufactured by Tokuda Seisakusho Co., Ltd.) at a vacuum level of approximately 4 x 10-5 mmHQ, approximately 0.1 μm of aluminum was deposited.
A clear top coat (manufactured by Nippon Oil & Fats Corporation, AL-8) was spray-painted and baked at 80° C. for about 30 minutes to obtain a reflector.

After that, the reflector was left in an oven kept at 200°C for 2 hours, then cooled to room temperature (about 20°C), and checked for thermal deformation and blistering. The degree of gas generation was determined based on the first observation.

(2) Surface roughness Regarding the molding surface, before and after after-aging and R
"-1~R"-3,0" -1~CN-3 was further exposed to heat in an oven at 250°C for 8 hours, and the surface roughness was measured using a universal precision surface profile test material (beltmeter S6P type, Pelten). The roughness curve is shown as y-f(x), and the roughness curve is expressed as y-f(x), and the roughness curve is expressed as y-f(x), and the roughness curve is expressed as y-f(x). When you hit it, Ra
= 'I/J2f'1f (x) l.

(3) Specific gravity Measured by underwater displacement method.

(4) Hardness Rockwell hardness was measured in accordance with ASTM D 785. (5) Impact resistance was measured by the Charpy method in accordance with JIS K6911.

(6) Bending strength elastic modulus Measured in accordance with JIS K6911.

(7) Compressive strength Measured in accordance with JIS K6911.

(8) Linear expansion coefficient Measured in accordance with ASTM D616.

(9) Dimensional change rate Dimensional change rate and R''-1 before and after after-aging
~R"-3, C"-1 to C"-3 are further heated in an oven for 2
The dimensional change rate when exposed to heat at 50°C for 8 hours was determined. The measurement was performed by measuring the outer diameter of the cylinder at five locations each with an accuracy of 1/1000 mm and calculating the average value.

(10) Thermal deterioration characteristics After further heat-exposing the materials R"-1 to R"-3,0"-1 to C"-3 at 250°C for 8 hours, the flexural modulus, impact resistance, and compressive strength were determined as above. It was measured using the method.

(11) Thermogravimetric change Measured by the method shown in Reference Example 1, and classified according to pass pattern and fail pattern.

The results obtained in the above test are shown in Table 3.

Reference Example 3 All compositions were prepared in the same manner as Reference Example 2 except that the proportions (parts by weight) shown in Table 4 below were used.
~C-6 was produced. Note that 5T-Zn in Table M4 represents zinc stearate. Further, S-3 is a novolak type phenolic resin powder for molding, and is mixed with 14% hexamethylenetetramine in advance.

R-4 to R-6 are Ii of this invention! C-4
~G-6 is the W of this invention! It's out of bounds. These compositions were kneaded in the same manner as in Reference Example 2 to obtain molding materials R'-4 to R'.
-6,0'-4 to C'-6 were obtained, and further heat compression molding after-aging was performed under the same conditions as Reference Example 2,
Materials R"-4 to R"-6,0"-4 to C"-6 were obtained.

Various physical properties of these were also measured in the same manner as in Reference Example 2, and the obtained results are also listed in Table 3.

”Keiji LL- According to the above-mentioned reference examples, the molded articles of the compositions within the scope of the present invention have excellent physical properties, and as shown in Table 3, there is no gas generation phenomenon or even if there is, there is very little liquid gas generation. It is clear that the liquid does not leak even when pressure is applied, and there is little thermal deterioration, making it suitable as a piston. In particular, the major features of this invention are that the changes in dimensions and surface roughness are extremely small due to after-aging and exposure to high temperatures, and that the weight hardly changes up to 300°C.

Example 1 R--1~ described in Reference Examples 2 and 3 as molding materials
Using R'-4 and C'-1 to C'-4 for comparison, the diameter was about 54 mm and the length was about 5 mm under the conditions shown in Reference Example 2.
A 0 mm hollow cylindrical molded body was obtained.

However, for R-4, instead of preheating in the oven,
Preliminary plasticization was performed by high-frequency heating for 0 seconds. The molded bodies thus obtained were after-aged under the conditions shown in Reference Example 2, and then machined to obtain pistons RP1 to RP4 and CPR1 to CPR4 shown in FIG. 3.

As shown in FIG. 1, these pistons were evaluated as disc brake assemblies as follows.

Sliding test Normal temperature durability test High temperature durability test Thermal shock test Regarding the above evaluation tests, the pistons of this invention all showed good characteristics, and in particular had a great advantage over the comparative ones in opening characteristics after exposure to heat. showed that.

Example 2 R'-5°R'-6 shown in Reference Example 3 as a molding material
Using C'-5 and C'-6 for comparison, plasticization was performed using a screw using the molding apparatus shown in FIG. 2, and then heat compression molding was performed.

That is, each molding material is supplied to the hopper 11 of the molding machine shown in FIG. It was discharged and compressed by pressing punches 17 and 18 with a hydraulic cylinder. FIG. 2 shows the molded body 19 in a compressed state.

Pistons were manufactured and evaluated using the same method as shown in Example 1 for each of the molded bodies thus obtained, and the pistons of this invention showed good characteristics and had stable sliding performance compared to the comparative ones. It became clear that it was.

(Effects of the Invention) As described above, the disc brake caliper piston of the present invention has stable sliding performance, especially after being treated at high temperatures, and is found to be excellent as a resin piston. . This is because, as described in Reference Examples 1 to 3, the piston of the present invention has a small degree of gas generation from the surface and a good surface roughness, as well as dimensions and lf
This is a special feature obtained from the fact that the stability of f1 is extremely stable. Therefore, in the piston of the present invention, machining of the outer circumferential driving surface after after-aging is not necessary at all or only to a very small extent if the mold design and manufacturing are carried out with good viscosity.

On the other hand, pistons made outside of this invention generate gas even during post-curing, which not only deteriorates the surface roughness but also forms pores inside the molded product, so machining is not performed after post-curing. However, good surface roughness cannot be obtained. If the treatment is carried out at an even higher temperature, the surface will become even rougher due to the gas generation phenomenon, and the dimensional shrinkage will increase (which not only makes the opening function unstable, but also causes a large change in weight and a decrease in physical properties).

As described above, the piston of the present invention has excellent sliding properties, especially sliding properties at high temperatures, and also has properties that are well-suited to various physical properties at high temperatures, making it suitable as a caliber piston for automobile disc brakes. I understand.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a disc brake caliper piston and its peripheral parts, Fig. 2 is a cross-sectional view of the molding compensation used in the example, and Fig. 3 is a partially cutaway side view of the caliper piston of the example. , FIG. 4 is a diagram showing the thermogravimetric change depending on the amount of silicon polyphosphate added to the solid resol resin. 1... Disc 2... Disc brake pad 3... Friction material 4... Back metal 5... Caliber piston 6... Boot 7... Seal 8... Cylinder 9... Brake fluid 10... Caliper 11... Hopper 12... Cylinder
13...Screw 14...Nozzle 15
．． 16...Mold 17.18...Punch 19.
... Molded object box 4 Figure 1

Claims (1)

[Scope of Claims] 1. A phenolic resin mainly of the resol type, and a filler mainly consisting of 2 to 5% by weight of a phosphorus oxy-acid salt compound and 200 to 350% by weight of an inorganic type based on the phenolic resin. A caliper piston for a disc brake, comprising a molded body of a composition comprising: 2. The caliper piston for a disc brake according to claim 1, wherein the phosphorus oxy-acid salt compound is silicon polyphosphate.