Phenolic resin for low-free-phenol friction material and preparation method of phenolic resin

Abstract

The invention provides phenolic resin for a low-free-phenol friction material and a preparation method of the phenolic resin, and belongs to the technical field of preparation of high polymer materials. The adhesive is prepared from 4000-5000kg of phenol, 2800-3500kg of 37% formaldehyde, 60-75kg of oxalic acid and 256-320kg of a modifier, the curing time of the adhesive is less than or equal to 110 seconds, the fluidity of the adhesive is 20-30mm, the hexamine content of the adhesive is 12%-14%, and the molecular weight of the adhesive is 13000-15000Mw. The preparation method comprises the following steps: mixing phenol and a modifier, adding oxalic acid, and heating to a preset temperature; dropwise adding formaldehyde at a constant speed within a certain time, heating to 100 DEG C, and carrying out reflux reaction at normal pressure for 3 hours; after detecting that the free aldehyde is less than 1%, dehydrating under a vacuum condition until the viscosity is reached and the free phenol is qualified; and finally, cooling by a steel belt, crushing and sieving to obtain a phenolic resin product. The problem that the existing friction material phenolic resin is high in flexibility, heat resistance, hardenability and free phenol content is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material preparation, in particular to a phenolic resin for low-free phenol friction material and a preparation method thereof. Background Art

[0002] As the main binder of friction materials, phenolic resin is widely used in power transmission and suppression components such as automobile brake pads and clutches. Its performance directly affects the reliability and safety of friction products. Existing phenolic resins used in friction materials generally have the following defects:

[0003] (1) Insufficient overall performance: Traditional resin formulas lack efficient modified components and precise cross-linking structure control, resulting in poor flexibility and difficulty in adapting to the complex stress environment of friction parts; insufficient heat resistance, prone to resin decomposition or bonding failure at high temperatures; slow hardening speed, requiring long-term high-temperature curing, which not only increases energy consumption but also affects production efficiency. (2) Environmental defects: The existing process does not completely remove free phenol, and the free phenol content is high. During production and use, harmful substances are released, polluting the environment and endangering health, making it difficult to meet increasingly stringent environmental protection standards. (3) Poor process adaptability: The resin molecular weight distribution is uneven and the fluidity fluctuates greatly, resulting in poor dispersion when mixed with fillers, low product performance consistency, and failure to meet the stringent stability requirements of high-end friction materials.

[0004] To address these issues, existing technologies attempt to improve performance through single-component modification or simple process adjustments. However, due to a lack of coordinated optimization of formulation and process, they remain unable to simultaneously address the technical contradictions of flexibility, heat resistance, hardenability, and low free phenol content. Therefore, developing a phenolic resin for friction materials that combines excellent overall performance with environmentally friendly properties and a preparation method for the resin remain urgent challenges in this field. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the purpose of the present invention is to provide a phenolic resin for low-free phenol friction material and a preparation method thereof, which solves the problems of softness, heat resistance, hardenability and high free phenol content of the existing phenolic resin for friction material. The resin is low in free phenol and has excellent comprehensive performance. It is suitable for friction materials such as automotive brake pads and clutches, effectively reducing environmental pollution and meeting high performance requirements.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A phenolic resin for low-free phenol friction material comprises the following raw materials in the following weight ratios: 4000-5000 kg of phenol, 2800-3500 kg of 37% formaldehyde, 60-75 kg of oxalic acid, and 256-320 kg of a modifier.

[0008] Preferably, the phenolic resin has a curing time of ≤110 seconds, a fluidity of 20-30 mm, a hexamine content of 12%-14%, and a molecular weight of 13,000-15,000 Mw.

[0009] The present invention also provides a method for preparing the above-mentioned phenolic resin for low-free phenol friction material, comprising the following steps:

[0010] S1. Phenol is added to a reactor, and a modifier is simultaneously introduced into the reactor and stirring is started. Oxalic acid is then added and the temperature is raised to a preset temperature.

[0011] S2. uniformly adding formaldehyde dropwise to the reactor. After the addition is complete, heating the reactor to a first target temperature and performing a reflux reaction under normal pressure with stirring.

[0012] After S3 and stopping stirring, the upper layer water in the reactor was taken to detect the free aldehyde content to qualified, and then the reactor was heated up and dehydrated under vacuum until the viscosity and free phenol content were qualified;

[0013] S4. Finally, the material is introduced into a steel belt for cooling and forming into flake particles, which are then crushed and sieved to obtain a powdered phenolic resin product.

[0014] Preferably, in S1, phenol is added to a reactor, and a modifier is simultaneously pumped into the reactor and stirred at a stirring rate of 80 to 100 rpm, and the purity of the phenol is not less than 99.9%, and the purity of the oxalic acid is not less than 99%.

[0015] Preferably, in S1, the modifier is a composition of hexamethylenetetramine and a flexible polymer compound, and the mass ratio of the hexamethylenetetramine to the flexible polymer compound is 1:1 to 1.5.

[0016] Preferably, in S2, formaldehyde is added dropwise at a uniform rate within 1 hour, wherein the formaldehyde is a formaldehyde aqueous solution with a mass concentration of 37% and the dropwise addition rate is 2800-3500 kg / h; after the formaldehyde is added dropwise, the reactor is heated to 100° C. within 30 minutes and maintained at 100±1° C. under normal pressure for reflux reaction for 3 hours.

[0017] Preferably, in S3, the detection standard for the free aldehyde content is less than 1%.

[0018] Preferably, in S3, the reactor is heated to 140°C and dehydrated under a vacuum condition of -0.09 to -0.096 MPa until the viscosity is 20 to 35P at 150°C and the free phenol content is no more than 3%.

[0019] Preferably, in S4, the temperature of the steel strip during cooling and forming is 50-80°C, and the material introduction rate is 50-100 kg / min.

[0020] Preferably, in S4, the formed sheet-like resin is crushed by a grinder to a particle size of no more than 100 μm, and then sieved by a vibrating screen to obtain a uniform powdered phenolic resin product.

[0021] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0022] (1) The present invention introduces a modifier composed of hexamethylenetetramine and a flexible polymer compound into the raw material formula to synergistically optimize the molecular cross-linking structure of the phenolic resin, thereby effectively improving the softness, heat resistance and hardening properties of the phenolic resin. The flexible polymer compound imparts good flexibility to the phenolic resin, enabling it to adapt to the stress deformation of friction parts under complex working conditions; the hexamethylenetetramine promotes the cross-linking reaction, thereby improving the heat resistance stability and hardening speed of the phenolic resin, allowing the phenolic resin to maintain excellent bonding properties in high temperature environments, significantly shortening the molding and curing time, and meeting the needs of automotive brake pads, clutches, etc. for rapid hardening and long-lasting wear resistance.

[0023] (2) The present invention controls the reaction process and impurity removal efficiency. During the vacuum dehydration stage, the vacuum degree of -0.09 to -0.096 MPa and the temperature of 140°C synergistically remove the water generated by the reaction and the residual free phenol, thereby significantly reducing the free phenol content of the resin and fundamentally reducing the release of harmful substances during production and use. This meets strict environmental protection standards and has both industrial production feasibility and green manufacturing advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 The present invention is a flow chart of a method for preparing a phenolic resin for low-free phenol friction material. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] like Figure 1 As shown, the present invention provides a method for preparing a phenolic resin for a low-free phenol friction material, comprising the following steps:

[0029] S1. Phenol is added to a reactor, and a modifier is simultaneously introduced into the reactor and stirring is started. Oxalic acid is then added and the temperature is raised to a preset temperature.

[0030] S2. uniformly adding formaldehyde dropwise to the reactor. After the addition is complete, heating the reactor to a first target temperature and performing a reflux reaction under normal pressure with stirring.

[0031] After S3 and stopping stirring, the upper layer water in the reactor was taken to detect the free aldehyde content to qualified, and then the reactor was heated up and dehydrated under vacuum until the viscosity and free phenol content were qualified;

[0032] S4. Finally, the material is introduced into a steel belt for cooling and forming into flake particles, which are then crushed and sieved to obtain a powdered phenolic resin product.

[0033] In the above steps, phenol is added to the reactor, and a modifier is simultaneously introduced into the reactor and stirred at a stirring rate of 80 to 100 rpm. The purity of the phenol is not less than 99.9%, and the purity of the oxalic acid is not less than 99%. In S1, the modifier is a composition of hexamethylenetetramine and a flexible polymer compound, and the mass ratio of the hexamethylenetetramine to the flexible polymer compound is 1:1 to 1.5. In S2, formaldehyde is added dropwise at a uniform rate within 1 hour. The formaldehyde is a formaldehyde aqueous solution with a mass concentration of 37%, and the addition rate is 2800-3500 kg / h. After the formaldehyde is added, the reactor is heated to 100°C within 30 minutes and maintained at 100±1°C under normal pressure for reflux reaction for 3 hours.

[0034] In S3, the detection standard of the free aldehyde content is less than 1%. The reactor is heated to 140°C and dehydrated under a vacuum condition of -0.09 to -0.096 MPa until the viscosity at 150°C is 20 to 35P and the free phenol content is not more than 3%.

[0035] In S4, the steel strip is cooled and formed at a temperature of 50-80°C, and the material introduction rate is 50-100 kg / min. The formed flake resin is crushed by a crusher to a particle size of no more than 100 μm, and then sieved through a vibrating screen to obtain a uniform powdered phenolic resin product.

[0036] The phenolic resin for the low-free phenol friction material comprises the following raw materials in the following weight ratios: 4000-5000 kg of phenol, 2800-3500 kg of 37% formaldehyde, 60-75 kg of oxalic acid, and 256-320 kg of a modifier.

[0037] In addition, the phenolic resin has a curing time of ≤110 seconds, a fluidity of 20-30 mm, a hexamine content of 12%-14%, and a molecular weight of 13000-15000 Mw.

[0038] Example 1

[0039] In this embodiment, the raw material ratio is: 4000 kg of phenol, 2800 kg of 37% formaldehyde, 60 kg of oxalic acid, and 256 kg of modifier, wherein the modifier is a combination of hexamethylenetetramine and a flexible polymer compound, and the mass ratio of the two is 1:1.

[0040] The preparation method of this embodiment is:

[0041] First, phenol was added to the reactor according to the weight ratio, and the modifier was simultaneously pumped into the reactor and stirred at a rate of 80 rpm. Subsequently, oxalic acid was added and the temperature was raised to 90°C.

[0042] Secondly, formaldehyde was added dropwise to the reactor at a uniform rate of 2800 kg / h. After the addition was completed for 1 hour, the reactor was heated to 100°C and refluxed for 3 hours under normal pressure with stirring.

[0043] After stopping stirring again, the upper layer of water in the reactor was taken to detect the free aldehyde content of less than 1%, and then the reactor was heated to 150°C and dehydrated under a vacuum condition of -0.09 MPa until the viscosity at 150°C reached 20P and the free phenol content reached 2.8%;

[0044] Finally, the material is introduced into a steel belt at an introduction rate of 50 kg / min to be cooled and formed into flaky particles at a cooling temperature of 50° C. The powdered phenolic resin product is obtained after being crushed and sieved.

[0045] Example 2

[0046] In this embodiment, the raw material ratio is: 4500 kg of phenol, 3150 kg of 37% formaldehyde, 67.5 kg of oxalic acid, and 288 kg of modifier, wherein the modifier is a combination of hexamethylenetetramine and a flexible polymer compound, and the mass ratio of the two is 1:1.2.

[0047] The preparation method of this embodiment is:

[0048] First, phenol was added to the reactor according to the weight ratio, and the modifier was pumped into the reactor and stirred at a stirring rate of 90 rpm. Then, oxalic acid was added and the temperature was raised to 90°C.

[0049] Secondly, formaldehyde was uniformly added dropwise to the reactor at a rate of 3150 kg / h. After the addition was completed for 1 hour, the reactor was heated to 100°C and refluxed for 3 hours under normal pressure while stirring.

[0050] After stopping stirring again, the upper layer of water in the reactor was taken to detect the free aldehyde content of less than 1%, and then the reactor was heated to 150 ° C and dehydrated under a vacuum condition of -0.093 MPa until the viscosity at 150 ° C was 27.5P and the free phenol content was 2.5%;

[0051] Finally, the material is introduced into a steel belt at an introduction rate of 75 kg / min to be cooled and formed into flaky particles at a cooling temperature of 65° C. The powdered phenolic resin product is obtained after being crushed and sieved.

[0052] Example 3

[0053] In this embodiment, the raw material ratio is: 5000 kg of phenol, 3500 kg of 37% formaldehyde, 75 kg of oxalic acid, and 320 kg of modifier, wherein the modifier is a combination of hexamethylenetetramine and a flexible polymer compound, and the mass ratio of the two is 1:1.5.

[0054] The preparation method of this embodiment is:

[0055] First, phenol was added to the reactor according to the weight ratio, and the modifier was simultaneously pumped into the reactor and stirred at a stirring rate of 100 rpm. Subsequently, oxalic acid was added and the temperature was raised to 90°C.

[0056] Secondly, formaldehyde was added dropwise to the reactor at a constant rate of 3500 kg / h. After the addition was completed for 1 hour, the reactor was heated to 100°C and refluxed for 3 hours under normal pressure while stirring.

[0057] After stopping stirring again, the upper layer of water in the reactor was taken to detect the free aldehyde content of less than 1%, and then the reactor was heated to 150°C and dehydrated under a vacuum condition of -0.096 MPa until the viscosity at 150°C reached 35P and the free phenol content reached 2.2%;

[0058] Finally, the material is introduced into a steel belt at an introduction rate of 100 kg / min to be cooled and formed into flaky particles at a cooling temperature of 80° C. The powdered phenolic resin product is obtained after being crushed and sieved.

[0059] Comparative Example 1

[0060] The difference from Example 1 is that the raw material ratio is: 4500 kg of phenol, 3150 kg of 37% formaldehyde, and 67.5 kg of oxalic acid, and no modifier is added;

[0061] The preparation method of this comparative example is:

[0062] First, phenol was added to the reactor according to the weight ratio, and the reactor was stirred at 700 rpm. Then, oxalic acid was added and the temperature was raised to 85°C.

[0063] Secondly, formaldehyde was uniformly added dropwise to the reactor at a rate of 2500 kg / h. After 1 hour of addition, the reactor was heated to 95°C and refluxed for 2.5 hours under normal pressure with stirring.

[0064] After stopping stirring again, the upper layer of water in the reactor was taken to detect the free aldehyde content of less than 1%, and then the reactor was heated to 150 ° C and dehydrated under a vacuum condition of -0.08 MPa until the viscosity at 150 ° C was 40P and the free phenol content was 4.5%;

[0065] Finally, the material is introduced into a steel belt at an introduction rate of 120 kg / min to be cooled and formed into flaky particles at a cooling temperature of 90° C. The powdered phenolic resin product is obtained after being crushed and sieved.

[0066] The performance tests of Examples 1 to 3 and Comparative Example 1 provided above were performed, and the test results obtained are shown in Table 1.

[0067] Table 1 Performance test results

[0068]

[0069] As shown in Table 1, through the synergistic optimization of modifiers and processes, Examples 1-3 achieved a 23%-27% shorter curing time, a 22%-56% higher fluidity, and a 24%-49% higher flexural strength, significantly outperforming Comparative Example 1. Furthermore, the free phenol content of Examples 1-3 was reduced by 51%-58% compared to Comparative Example 1, meeting application requirements. Furthermore, the thermal decomposition temperature of Examples 1-3 was increased by 11%-15% compared to Comparative Example 1 to accommodate the high-temperature environment of high-speed braking systems. Finally, the friction coefficient fluctuation range of Examples 1-3 was reduced to one-fifth of that of Comparative Example 1, significantly improving braking reliability.

[0070] Therefore, the use of the above-mentioned phenolic resin for low-free phenol friction material and its preparation method solves the problems of softness, heat resistance, hardenability and high free phenol content of the existing phenolic resin for friction material, and the obtained resin has low free phenol and excellent comprehensive performance. It is suitable for friction materials such as automobile brake pads and clutches, effectively reducing environmental pollution and meeting high performance requirements.

[0071] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0072] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A phenolic resin for low-free phenol friction material, characterized in that: The method comprises the following raw materials in the following weight proportions: 4000-5000 kg of phenol, 2800-3500 kg of 37% formaldehyde, 60-75 kg of oxalic acid, and 256-320 kg of a modifier.

2. The phenolic resin for low-free phenol friction material according to claim 1, characterized in that: The phenolic resin has a curing time of ≤110 seconds, a fluidity of 20-30 mm, a hexamine content of 12%-14%, and a molecular weight of 13000-15000 Mw.

3. A method for preparing a phenolic resin for a low-free-phenol friction material according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1. Phenol is added to a reactor, and a modifier is simultaneously introduced into the reactor and stirring is started. Oxalic acid is then added and the temperature is raised to a preset temperature. S2. uniformly adding formaldehyde dropwise to the reactor. After the addition is complete, heating the reactor to a first target temperature and performing a reflux reaction under normal pressure with stirring. After S3 and stopping stirring, the upper layer water in the reactor was taken to detect the free aldehyde content to qualified, and then the reactor was heated up and dehydrated under vacuum until the viscosity and free phenol content were qualified; S4. Finally, the material is introduced into a steel belt for cooling and forming into flake particles, which are then crushed and sieved to obtain a powdered phenolic resin product.

4. The method for preparing a phenolic resin for low-free phenol friction material according to claim 3, characterized in that: In S1, phenol is added into a reactor, and a modifier is simultaneously introduced into the reactor and stirred at a stirring rate of 80-100 rpm. The purity of the phenol is not less than 99.9%, and the purity of the oxalic acid is not less than 99%.

5. The method for preparing a phenolic resin for low-free phenol friction material according to claim 3, characterized in that: In S1, the modifier is a composition of hexamethylenetetramine and a flexible polymer compound, and the mass ratio of the hexamethylenetetramine to the flexible polymer compound is 1:1 to 1.

5.

6. The method for preparing a phenolic resin for low-free phenol friction material according to claim 3, characterized in that: In S2, formaldehyde is added dropwise at a uniform rate within 1 hour. The formaldehyde is a 37% formaldehyde aqueous solution at a dropping rate of 2800-3500 kg / h. After the formaldehyde is added, the reactor is heated to 100° C. within 30 minutes and maintained at 100±1° C. under normal pressure for reflux reaction for 3 hours.

7. The method for preparing a phenolic resin for low-free phenol friction material according to claim 3, characterized in that: In S3, the detection standard of the free aldehyde content is less than 1%.

8. The method for preparing a phenolic resin for low-free phenol friction material according to claim 3, characterized in that: In S3, the reactor is heated to 140°C and dehydrated under a vacuum condition of -0.09 to -0.096 MPa until the viscosity is 20 to 35P at 150°C and the free phenol content is no more than 3%.

9. The method for preparing a phenolic resin for low-free phenol friction material according to claim 3, characterized in that: In S4, the temperature of the steel strip during cooling and forming is 50-80°C, and the material introduction rate is 50-100 kg / min.

10. The method for preparing a phenolic resin for low-free phenol friction material according to claim 3, characterized in that: In S4, the formed flake resin is crushed by a crusher to a particle size of no more than 100 μm, and then sieved by a vibrating screen to obtain a uniform powdered phenolic resin product.

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