High-strength phenolic moulding compound for automobile brake piston and preparation method of phenolic moulding compound

Abstract

The invention relates to a high-strength phenolic moulding compound for an automobile brake piston and a preparation method of the phenolic moulding compound. The phenolic moulding compound is prepared from the following raw materials: thermosetting phenolic resin, thermoplastic phenolic resin, glass fibers, wollastonite fiber powder, active whisker silicon, iron oxide pigment, a curing agent, a curing accelerator and a release agent. Wherein the thermosetting phenolic resin is obtained by feeding and reacting phenol and formaldehyde according to a molar ratio of 1: (1.90-1.95), the softening point of the thermosetting phenolic resin is 65-75 DEG C, the free phenol content is less than or equal to 5.5%, and the polymerization speed is 35-80S. The preparation method comprises the following steps: mixing the raw materials except for the glass fiber, and crushing the mixture at the temperature of less than 20 DEG C until the fineness is 100 meshes, so as to obtain a mixture; and uniformly mixing the mixture with the glass fiber, heating and mixing or extruding, and finally granulating and forming to obtain the glass fiber reinforced plastic. The high-aldehyde-ratio thermosetting phenolic resin is used as a main adhesive, so that the high-temperature performance is excellent, and the size can be stabilized; fiber fillers with three particle sizes are used, so that the strength, hardness and wear resistance of a workpiece are improved; the resin system is tightly combined, so that the product is water-resistant and solvent-resistant, and the application is expanded.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite materials, in particular to a high-strength phenolic molding plastic for automobile brake pistons and a preparation method thereof. BACKGROUND

[0002] Phenolic molding plastics have replaced traditional metal materials in the past few decades due to their small relative density, excellent forming and processing performance, good decoration, and good hand feeling. They have excellent heat resistance, thermal insulation, dimensional stability, and chemical corrosion resistance, and are widely used in the automotive industry. In automotive applications, 100 kg of plastic material can replace 200-300 kg of traditional metal materials, resulting in significant weight reduction, which is of great significance for energy saving and greenhouse gas emission reduction.

[0003] The application of phenolic molding plastics in automobile brake systems can be traced back to the 1970s. In 1975, DUREZ Company in the United States first developed phenolic molding plastics for automobile brake pistons. After decades of development, American brake system designers and experts confirmed that phenolic pistons are as safe and reliable as steel pistons, and even better in some performance aspects.

[0004] With the evolution of the market and technology, end users have higher requirements for the current mainstream phenolic piston materials, especially in terms of high temperature resistance and high strength. Chinese patent CN116751436A discloses a phenolic piston material, which contains 10-25% of phenolic resin (linear phenolic resin) and 2-5% of inorganic substrate (glass fiber). However, extensive tests have shown that the dimensional stability of the product made of linear phenolic resin as the base resin after high temperature aging test cannot meet the requirements, and it is difficult to achieve high strength standards.

[0005] Chinese patent CN202310782701 uses thermosetting phenolic resin as the base resin, and adds polyether-modified silicone oil and MBS particles. The polyether-modified silicone oil is a thermoplastic linear polymer and cannot crosslink with the phenolic resin. The MBS particles are elastomer particles. The addition of polyether-modified silicone oil and MBS particles significantly reduces the hardness of the phenolic piston, which cannot meet the requirement of high hardness (Rockwell hardness (HRE) 110±5) of the piston material. SUMMARY

[0006] To solve the above problems, the present application provides a high-strength phenolic molding plastic for automobile brake pistons and a preparation method thereof.

[0007] In a first aspect, the high-strength phenolic molding plastic for automobile brake pistons provided by the present application adopts the following technical solution: A kind of high-strength phenolic molding compound for automobile brake piston, the raw materials used for preparation include the following components according to weight percentage: Thermosetting phenolic resin 15-23%, thermoplastic phenolic resin 2-10%, glass fiber 25-45%, wollastonite fiber powder 20-40%, active whisker silicon 5-10%, iron oxide pigment 1-3%, curing agent 0.5-2%, curing accelerator 1-3%, release agent 1-2%; Wherein, the thermosetting phenolic resin is prepared by the following method: Phenol and formaldehyde (F) are loaded into a reaction kettle equipped with reflux condenser, stirrer, heating and cooling device and dehydration equipment according to a certain proportion, i.e. the molar ratio of phenol to formaldehyde is 1: (1.90-1.95), (the amount of raw materials should not be more than 40% of the volume of the reaction kettle, and the maximum used reaction kettle should not be more than 5m 3 ); 50% liquid alkali is added to the reaction mixture, the pH value of the reaction system is adjusted to 9.0, the temperature is slowly raised to 60℃, the system is naturally heated to 73-75℃ by reaction heat, and the reaction is refluxed for 1.5 hours. Since it is an exothermic reaction, it needs to be cooled intensively during the reaction, and vacuum reflux is necessary. Then cool to 50℃, add phosphoric acid slowly and carefully, and stir well (avoid acidic conditions), adjust the pH value to 7.0-7.1, then gradually increase the vacuum degree to more than -0.095Mpa, and dehydrate at a temperature gradually rising to 98℃ (the temperature during dehydration should not exceed 98℃), to remove phenol, until the desired softening point is reached, finally to obtain high formaldehyde phenol ratio thermosetting phenolic resin. The storage temperature of the resin should not exceed 20℃, the softening point is 65-75℃, the free phenol is ≤5.5%, and the polymerization rate is 35-80S.

[0008] Further, the thermoplastic phenolic resin is obtained by mixing and reacting phenol and formaldehyde according to a molar ratio of 1: (0.78-0.80), and has a softening point of 100-110℃, a free phenol of ≤2.5%, and a polymerization rate of 80-110S.

[0009] Further, the glass fiber is alkali-free glass fiber with a diameter of 9-13μm and a length of 1-2mm.

[0010] Further, the wollastonite fiber powder is active wollastonite fiber after surface treatment with silane coupling agent, with an aspect ratio of (10-15): 1 and a fineness of 200-600 mesh.

[0011] Further, the active whisker silicon is whisker silicon material after surface modification treatment with silane coupling agent, with a particle size of 1-5μm.

[0012] Further, the curing agent is urotropine.

[0013] Furthermore, the curing accelerator is magnesium oxide and / or calcium hydroxide.

[0014] Furthermore, the release agent is selected from at least one of calcium stearate, zinc stearate, stearic acid, stearamide, and ethylene bis-stearamide.

[0015] Secondly, the preparation method of a high-strength phenolic molding compound for automotive brake pistons provided in this application adopts the following technical solution: A method for preparing a high-strength phenolic molding compound for automotive brake pistons includes the following steps: Thermosetting phenolic resin, thermoplastic phenolic resin, wollastonite fiber powder, active whisker silicon, iron oxide pigment, curing agent, curing accelerator and release agent are mixed and then pulverized to a fineness of 100 mesh at <20℃ to obtain a mixture. The mixture is then mixed evenly with glass fiber, heated and kneaded or extruded, and finally granulated to obtain high-strength phenolic molding compound for automotive brake pistons.

[0016] In summary, this application has the following beneficial effects: 1. This application uses high formaldehyde-phenol ratio thermosetting phenolic resin as the main component and thermoplastic phenolic resin as an auxiliary component as a binder. The unique molecular structure of high formaldehyde-phenol ratio thermosetting phenolic resin enables it to maintain good mechanical strength in high-temperature environments. At the same time, during high-temperature aging, the hydroxymethyl functional groups in its molecules will undergo further cross-linking reactions. The resulting shrinkage can offset the expansion effect caused by high-temperature treatment, thereby effectively improving the dimensional stability of the material at high temperatures and meeting the requirements of high-strength automotive brake pistons under complex high-temperature conditions. 2. This application uses three types of reinforcing fibers and fibrous fillers with different particle sizes: glass fiber, activated wollastonite fiber powder, and activated whisker silicon. This combination makes the phenolic resin more effective at wetting the fillers, the filler system is more compact, forming a tight structure, and the fibrous filler system can increase the toughness of the material. Based on these characteristics, the mechanical strength and hardness of the molded phenolic molding compound are significantly improved, and the wear resistance is also better, which can better withstand the friction and stress generated by the brake piston of an automobile during operation. 3. The phenolic resin system selected in this application will further increase its crosslinking degree during high-temperature aging, and the bond between the phenolic resin and the active mineral filler system will be tighter. This tight bond avoids the generation of small molecules that are easily soluble in solvents and are free outside the phenolic resin crosslinking system. Therefore, the molded parts have better water and solvent resistance and can maintain stable performance in humid environments and when in contact with various solvents, further expanding the application range of this phenolic molding compound in the field of high-strength automotive brake pistons. Detailed Implementation

[0017] The present invention will be further illustrated below with reference to specific embodiments. The purpose of these embodiments is to provide a better understanding of the content and essential features of the present invention. Therefore, the examples given should not be considered as limitations on the scope of protection of the present invention. Any product identical or similar to the present invention, derived by any person based on the teachings of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0018] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0019] The manufacturing method of the molding material in this application can be the traditional two-roll plasticizer mixing method or the screw extrusion method.

[0020] Performance testing The test specimens were molded specimens with the following molding conditions: preheating temperature: 100-110℃, molding temperature: 170-175℃, and curing time: 1.0 min / mm.

[0021] Before testing, the test specimens need to undergo a post-treatment baking process, which generally requires baking in an air-circulating oven at 205±5℃ (other baking temperatures may be selected depending on the material characteristics and the requirements of the piston manufacturer, with the highest temperature possibly reaching 240℃) for 16 hours.

[0022] (a) Density: Required to be 2.10 ± 0.05 g / cm³ 3 ; (ii) Rockwell hardness (HRE): needs to be 110±5; (III) Air Aging Test: A piston test sample with a diameter of 50 mm and a thickness of 6.5 mm is placed at a temperature of 177℃±2℃ for 130 hours. The material should not show cracks or blistering, and the volume change should not exceed ±0.2%, and the hardness change should not be less than 0 or greater than +6; (iv) Oil aging test: When a piston test sample with a diameter of 50 mm and a thickness of 6.5 mm is placed in a brake oil bath and immersed in it at a temperature of 150℃±2℃ for 14 days, the weight change of the material shall not exceed -0.80%, the volume change shall not exceed ±0.20%, and the hardness change shall not be less than 0 or greater than +6.

[0023] Examples 1-3 A high-strength phenolic molding compound for automotive brake pistons, the raw materials used in its preparation are shown in the table below by weight percentage.

[0024] Raw materials Example 1 Example 2 Example 3 Thermosetting phenolic resin 22.0 20.0 18.0 Thermoplastic phenolic resin 3.0 4.7 6.4 Glass fiber 40.0 40.0 40.0 Wollastonite fiber powder 21.9 21.9 21.9 Active whisker silicon 8.0 8.0 8.0 Iron oxide black 2.0 2.0 2.0 Methenamine 0.6 0.9 1.2 Calcium hydroxide 1.0 1.0 1.0 Zinc stearate 1.5 1.5 1.5 and by the following preparation method: The thermosetting phenolic resin, thermoplastic phenolic resin, wollastonite fiber powder, active whisker silicon, iron oxide pigment, curing agent, curing accelerator and release agent are mixed and crushed at low temperature (below 20℃) to a fineness of 100 mesh, then the mixture is mixed with glass fiber, heated and mixed, and finally granulated and formed to obtain the high-strength phenolic molding plastic for automobile brake pistons.

[0025] The thermosetting phenolic resin is prepared by the following method: Phenol and formaldehyde are mixed in a molar ratio of 1:1.90 and loaded into a reaction kettle equipped with a reflux condenser, stirrer, heating and cooling device and dehydration equipment; 50% liquid caustic is added to the reaction mixture to adjust the pH value of the reaction system to 9.0, and the temperature is slowly raised to 60℃, the system is naturally heated to 73-75℃ by reaction heat, and refluxed for 1.5 hours, then cooled to 50℃, carefully and slowly add phosphoric acid, and fully stir, adjust the pH value to 7.0-7.1, then gradually increase the vacuum degree to more than -0.095 Mpa, and dehydrate, the temperature is gradually raised to 98℃ to remove phenol until the desired softening point is reached, finally the thermosetting phenolic resin with high formaldehyde to phenol ratio is obtained, the storage temperature of the resin should not exceed 20℃, the softening point is 65-75℃, the free phenol is ≤5.5%, and the polymerization rate is 35-80S.

[0026] The performance test results are shown in the following table.

[0027] Performance index Example 1 Example 2 Example 3 Density 2.10 2.10 2.09 Rockwell hardness (HRE) 111 112 110 Compressive strength (Mpa) 290 291 285 Heat distortion temperature (°C) 296 295 292 Volume change after air aging (%) 0.11 0.12 0.12 Hardness change after air aging (HRE) +1.2 +1.0 +0.9 Weight change after oil aging (%) -0.32 -0.35 -0.35 Volume change after oil aging (%) 0.11 0.13 0.13 Comparative Example 1 A molding plastic for automobile brake pistons, a common foreign brand on the market.

[0028] The performance of the molding plastic for automobile brake pistons in the above Comparative Example 1 was detected by referring to the aforementioned test methods, and the test results are shown in the following table.

[0029] Performance index Comparative example 1 Density 2.10 Rockwell hardness (HRE) 110 Compressive strength (Mpa) 260 Heat distortion temperature (°C) 285 Volume change after air aging (%) 0.12 Hardness change after air aging (HRE) +0.8 Weight change after oil aging (%) -0.34 Volume change after oil aging (%) 0.14 From the test results analysis can be known, in the embodiment 1-3 of the application, the raw material formula adopts the combination of high formaldehyde phenol ratio thermosetting phenolic resin as the main part, thermoplastic phenolic resin as the auxiliary, at the same time, glass fiber and wollastonite fiber are selected as reinforcing fibers, and active whisker silicon, curing agent, curing accelerator and release agent are matched. Such raw material combination can make the material parts after molding meet the requirements of piston parts on various performances. The specific data shows that the compressive strength of the material of the embodiment is in the range of 285-291 MPa, and the heat distortion temperature is in the range of 292-296 DEG C, compared with the data (compressive strength 260 MPa, heat distortion temperature 285 DEG C) of the comparative example 1 (commercial brand), the advantage is obvious.

[0030] Therefore, in the application, high formaldehyde phenol ratio thermosetting phenolic resin is compounded as the main part, thermoplastic phenolic resin is compounded as the auxiliary, and three kinds of reinforcing fibers and fibrous fillers with different particle sizes, i.e. glass fiber, active wollastonite fiber powder and active whisker silicon are introduced. This unique raw material matching method has a synergistic effect on the high temperature resistance, compressive strength and solvent aging resistance of the finally prepared phenolic molding compound.

[0031] Based on the above advantages, the phenolic molding compound provided by the application can fully meet the stringent requirements of high-strength automobile brake piston phenolic molding compound.

[0032] The possible reasons are analyzed as follows: The high aldehyde ratio thermosetting phenolic resin used in the application contains more hydroxymethyl functional groups in the molecular structure, which makes it have better heat resistance. On the one hand, it can improve the crosslinking density of the molding compound; on the other hand, during the high temperature aging process of the piston part, the hydroxymethyl functional groups will further crosslink, and the shrinkage caused by the crosslinking reaction can offset the expansion effect caused by high temperature treatment, thereby improving the dimensional stability of the part. From the thermogravimetric analysis (TGA) data of the thermosetting phenolic resin, the higher the molar ratio of formaldehyde to phenol, the higher the thermal decomposition temperature of the thermosetting phenolic resin; The relatively small amount of thermoplastic phenolic resin is added because the molecular weight of thermoplastic phenolic resin is relatively large, and the thermal rigidity after curing reaction is good. The thermal rigidity of thermosetting phenolic resin is insufficient when it is cured out of the mold, which can easily lead to deformation of the part. Therefore, the addition of a relatively small amount of thermoplastic phenolic resin can improve the thermal rigidity of the piston part when it is molded out of the mold; In addition, the application uses a large proportion (25-45 wt%) of glass fiber as reinforcing fiber, which can improve the mechanical strength of the piston part. Generally, the length of the glass fiber used is 3 mm or longer, but the resin proportion of the piston material is generally not more than 25%. Due to the difficulty of transportation and processing caused by high proportion of long glass fiber, the application uses relatively short glass fiber with a length of 1-2 mm, and the more accurate length is 1.7 mm. The active whisker silicon (5-10wt%) used in the present application is a whisker silicon material treated by silane coupling agent surface modification. The whisker silicon is a fibrous inorganic material with high-purity silicon dioxide as the main component, which has high hardness (Mohs hardness 7), high whiteness, chemical stability, and excellent dispersibility, etc. The particle size is 1-5µm. Silane modification can improve the compatibility of whisker silicon and phenolic resin system, making it easier for phenolic resin to infiltrate. Combined with the Mohs hardness and fibrous morphology of whisker silicon, it can improve the wear resistance, hardness, mechanical strength, and high temperature resistance of the piston parts; The three kinds of reinforcing fibers and filler systems used in the present application are glass fibers with a diameter of 7-13µm, wollastonite fiber powder with a particle size of 25-74µm, and whisker silicon with a particle size of 1-5µm. These three kinds of fibers and fillers with different diameters can form a better packing morphology, making the material system more compact. The large proportion of coarse particles and small proportion of fine particles make the low content of phenolic resin adhesive more fully infiltrate the fillers; The present application uses iron oxide pigments instead of carbon black or other organic pigments. The high hardness (Mohs hardness 5.5-6.5), high temperature resistance, and solvent resistance of iron oxide pigments reduce the defects caused by the poor high temperature resistance and solvent resistance of organic pigments; Because the low formaldehyde-phenol ratio of thermosetting phenolic resin has a low softening point (65-75℃), it is easy to soften at room temperature and not easy to crush. Therefore, after mixing thermosetting phenolic resin, thermoplastic phenolic resin, and other fillers (excluding glass fibers) at low temperature (below 20℃), on the one hand, the low melting point thermosetting phenolic resin can be separated by fillers and not stick together after crushing, which is convenient for powder delivery. On the other hand, it also makes the resin and filler system more evenly dispersed, thereby improving the mechanical strength and heat resistance of the phenolic molding compound.

[0033] The above are modifications or obvious technical solutions that can be made by those skilled in the art after reading the present specification without creative contribution, but as long as they are within the scope of the claims of the present application, they should be protected by the Patent Law.

Claims

1. A high-strength phenolic molding compound for automotive brake pistons, characterized in that, The raw materials used for preparation include the following components in percentage by weight: thermosetting phenolic resin 15-23%, thermoplastic phenolic resin 2-10%, glass fiber 25-45%, wollastonite fiber powder 20-40%, active whisker silicon 5-10%, iron oxide pigment 1-3%, curing agent 0.5-2%, curing accelerator 1-3%, release agent 1-2%; The thermosetting phenolic resin is prepared by the following method: phenol and formaldehyde are mixed according to a molar ratio of 1:(1.90-1.95), then 50% mass fraction liquid alkali is added, the pH of the reaction system is adjusted to 9.0, and the temperature is slowly raised to 60℃; the reaction is exothermic, the temperature is raised to 73-75℃, and the reaction is refluxed for 1.5h, then cooled to 50℃, slowly add phosphoric acid, and fully stir to adjust the pH to 7.0-7.1, then gradually increase the vacuum degree to above-0.095Mpa for dehydration, the temperature is simultaneously raised to 98℃ to remove phenol, and the softening point is reached, finally the thermosetting phenolic resin is obtained; The softening point of the thermosetting phenolic resin is 65-75℃, the free phenol is ≤5.5%, and the polymerization speed is 35-80S.

2. The high strength phenolic molding compound for automotive brake pistons according to claim 1, characterized in that, The thermoplastic phenolic resin is obtained by mixing phenol and formaldehyde according to a molar ratio of 1:(0.78-0.80), the softening point is 100-110℃, the free phenol is ≤2.5%, and the polymerization speed is 80-110S.

3. The high strength phenolic molding compound for automotive brake pistons according to claim 1, characterized in that, The glass fiber is alkali-free glass fiber with a diameter of 9-13μm and a length of 1-2mm.

4. The high strength phenolic molding compound for automotive brake pistons according to claim 1, characterized in that, The wollastonite fiber powder is active wollastonite fiber after surface treatment with silane coupling agent, the aspect ratio is (10-15):1, and the fineness is 200-600mesh.

5. The high strength phenolic molding compound for automotive brake pistons according to claim 1, characterized in that, The active whisker silicon is whisker silicon material after surface modification treatment with silane coupling agent, the particle size is 1-5μm.

6. The high strength phenolic molding compound for automotive brake pistons according to claim 1, characterized in that, The curing agent is urotropine.

7. The high strength phenolic molding compound for automotive brake pistons according to claim 1, characterized in that, The curing accelerator is magnesium oxide and / or calcium hydroxide.

8. The high strength phenolic molding compound for automotive brake pistons according to claim 1, characterized in that, The release agent is selected from at least one of calcium stearate, zinc stearate, stearic acid, stearic acid amide, and ethylene bis-stearamide.

9. The process for preparing a high-strength phenolic molding compound for automobile brake pistons according to any one of claims 1 to 8, characterized by, The following steps are included: The thermosetting phenolic resin, thermoplastic phenolic resin, wollastonite fiber powder, active whisker silicon, iron oxide pigment, curing agent, curing accelerator, and release agent are mixed, then crushed to a fineness of 100mesh at a temperature below 20℃, to obtain a mixture; then the mixture is mixed with glass fiber, heated and mixed or extruded, and finally granulated and formed, to obtain the high-strength phenolic molding compound for automobile brake piston.