High flame-retardant drum brake pad and preparation method thereof

Abstract

The application discloses a high-flame-retardant drum brake pad and a preparation method thereof, and relates to the technical field of brake pads. The high-flame-retardant drum brake pad is prepared by the following method: preparing a flame-retardant base, mixing the flame-retardant base and then performing banburying to obtain a banburying material; roll-kneading the banburying material to form a roll-kneaded product, crushing the roll-kneaded product to obtain heat-resistant flame-retardant particles; uniformly distributing the heat-resistant flame-retardant particles in a friction base material to obtain a mixed friction material; and hot-pressing the mixed friction material to form the high-flame-retardant drum brake pad. In the process of hot-pressing and heat curing, the wrapping layer of the heat-resistant flame-retardant particle material completely covers the economical flame-retardant material, preventing the direct precipitation of crystal water in the flame-retardant material into the friction base material; in addition, in the high-temperature braking section, the wrapping layer in the flame-retardant base directly decomposes, so that the crystal water in the flame-retardant material is rapidly precipitated, the ignition point is reduced, a large amount of heat is absorbed, and the occurrence of ignition during braking is suppressed.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of brake linings, in particular to a high-flame-retardant drum brake lining and a preparation method thereof. BACKGROUND

[0002] With the rapid development of domestic commercial vehicles, especially the rapid development of the logistics transportation industry, the fire accidents of commercial vehicles caused by high-temperature braking or braking lockup occur from time to time, which brings great safety hazards to the transportation industry. The fundamental reason for the brake fire is that long-time braking drag grinding leads to high-temperature braking (500-600 DEG C), and at the same time, the organic matter in the friction material decomposes into small molecular free radicals, and the temperature reaches the ignition point of the friction material, resulting in an open flame.

[0003] To solve the above problems and reduce the safety risk of transportation, a new type of high-flame-retardant drum brake lining has emerged in the market. In order to improve the heat resistance of this friction material, high-temperature resistant resins such as modified phenolic resin or polyimide resin, benzoxazine resin are generally used, or one or more of the above resins are mixed. However, it is found that during long-term vehicle road test, especially in the long downhill sections of Yunnan-Guizhou-Chongqing area in China, the highest brake temperature of the chassis brake system-air pressure drum brake of heavy-duty commercial vehicles is as high as 580-600 DEG C, which is much higher than the thermal decomposition temperature of the above-mentioned resins. In order to prevent the fire accident caused by high-temperature braking, it is necessary to add one or more flame-retardant materials. Due to the particularity of resin-based friction material ratio, processing technology and working condition, halogen flame retardant is not suitable for use, and molybdenum and antimony flame retardant materials have high cost. From the economic point of view, the number of flame-retardant materials needed for development is limited. Economical flame-retardant materials such as hydrated aluminum hydroxide, magnesium hydroxide and zinc borate have relatively low prices, but in the process of hot pressing and heat curing of friction materials, due to the high temperature (hot pressing temperature 180-200 DEG C, heat curing maximum temperature 200-220 DEG C), the above-mentioned economical flame-retardant materials will be decomposed by heat H2O molecules, resulting in high instantaneous water vapor content in the friction matrix material, which causes the hot-pressed product to appear delamination, blistering and even product scrap, greatly limiting the application of economical flame-retardant materials in the manufacture of drum brake linings.

[0004] Therefore, there is an urgent need for a production process for producing high-flame-retardant drum brake linings using economical flame-retardant materials. SUMMARY

[0005] Therefore, the present application aims to provide a high flame-retardant drum brake pad and a preparation method thereof.

[0006] To achieve or at least partially achieve the above-mentioned purposes, the present application provides the following technical solutions:

[0007] In a first aspect, the present application provides a preparation method of a high flame-retardant drum brake pad, comprising:

[0008] In a first step, a flame-retardant base is prepared, and the flame-retardant base is mixed and then subjected to banburying to obtain a banburying material;

[0009] In a second step, the banburying material is roll-molded, and the roll-molded product is crushed to obtain heat-resistant flame-retardant particles;

[0010] In a third step, the heat-resistant flame-retardant particles are uniformly distributed in a friction base material to obtain a mixed friction material;

[0011] In a fourth step, the mixed friction material is hot-pressed and then subjected to heat curing to obtain a high flame-retardant drum brake pad.

[0012] In a second aspect, the present application provides a high flame-retardant drum brake pad prepared by the above-mentioned preparation method.

[0013] Compared with the prior art, the technical solutions provided by the present application have at least the following beneficial effects:

[0014] 1. The present application uses phosphorus-modified epoxy resin as a binder, aluminum hydroxide and zinc borate as flame retardants, barium sulfate, light magnesium oxide, and mica as fillers to prepare heat-resistant flame-retardant particles. The mass fraction of the binder and the filler in the heat-resistant flame-retardant particles is relatively large, and the ductility is higher than that of the flame retardant. Through the processes of banburying and roll-molding, the flame retardant is coated (a flexible polymer and a part of the filler with good ductility are used to coat the rigid flame retardant to form a core-shell dispersed phase through the processes of banburying and roll-molding). The heat-resistant flame-retardant particles will not cause product delamination and bulging due to the release of H2O molecules during the processes of hot pressing and heat curing, resulting in product scrap. During high-temperature braking, the binder in the coating layer decomposes rapidly, losing the coating effect. At this time, the crystallization water in the flame retardant is rapidly released, reducing the ignition point of the friction material, and the crystallization water is released to the surface of the friction plate under the action of braking pressure, thereby blocking air and suppressing ignition.

[0015] 2. The high flame-retardant drum brake pad prepared by the application adds porous high-temperature-resistant partition agents including kaolin, calcium silicate and light magnesium oxide in the friction base material. In the process of high-temperature braking, the high-temperature-resistant partition agents can absorb the free radicals containing hydrogen and oxygen elements generated by the high-temperature decomposition of the friction base material, and at the same time form a protective film to wrap and block the oxygen needed for combustion, thereby preventing rapid ignition.

[0016] 3. In the high flame-retardant drum brake pad sample prepared by the application, the oxygen index (OL) is > 35, the UL94 test shows that the combustion time of a 10mm brake pad sample is < 5S, and both reach the V-0 superior standard. The high flame-retardant drum brake pad prepared by the application is applied to a heavy commercial vehicle, and no brake ignition event occurs in the continuous braking test on the Yunnan-Guizhou-Sichuan long downhill section. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the application more clear and understandable, the application will be further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the application and not to limit the application.

[0018] Those skilled in the art can understand that, unless specifically stated, "said" and "that" and "the foregoing" used in the text of the application can also include plural forms. It should be further understood that the phrase "comprising" used in the specification of the application means that the features, steps, operations exist, but does not exclude the existence or addition of one or more other features, integers, steps.

[0019] The performance evaluation method of the flame-retardant drum brake pad prepared by the embodiments of the application is as follows:

[0020] (1) Coefficient of friction: refer to GB / T34007-2017 Road vehicles-Brake pads-Friction material-Method of test for friction performance by towing;

[0021] (2) Wear loss: refer to GB / T34007-2017 Road vehicles-Brake pads-Friction material-Method of test for friction performance by towing;

[0022] (3) Oxygen index OL (10mm): Plastics-Determination of the burning behavior by oxygen index method-Part 2: Room temperature test;

[0023] (4) UL94 test (10mm): US UL94-Combustible performance test of plastic parts of equipment and appliances.

[0024] In the prior art, in the process of using economic flame-retardant materials such as aluminum hydroxide, magnesium hydroxide, zinc borate, etc. to prepare brake pads by hot-pressing with friction materials, the economic flame-retardant materials will be decomposed into water molecules due to the hot-pressing temperature of 180-200℃ and the highest heat curing temperature of 200-220℃, resulting in a high water molecule content in the friction material of the brake pad and a delamination and bubbling phenomenon, so that a qualified flame-retardant brake pad product cannot be prepared. To solve the above-mentioned processing bottleneck problem, the embodiment of the present application changes the one-step hot-pressing process into a new multi-step forming process. Before the hot-pressing step, a heat-resistant flame-retardant particle is prepared. The heat-resistant flame-retardant particle plays the following roles in the hot-pressing and brake high-temperature flame-retardant process: at the hot-pressing temperature of 180-200℃ and the highest heat curing temperature of 200-220℃, the wrapping layer completely covers the economic flame-retardant material to prevent the direct precipitation of crystal water in the economic flame-retardant material into the friction matrix material; in addition, at the brake high-temperature (500-600℃) section, the wrapping resin in the flame-retardant matrix material directly decomposes to lose the function of wrapping the economic flame-retardant material, the crystal water in the economic flame-retardant material quickly precipitates, reduces the temperature of the friction matrix material, and reduces the ignition point. This process will also absorb a large amount of heat, and under the action of the brake pressure, the crystal water precipitates to the surface of the friction pad to block air and suppress the occurrence of fire.

[0025] Based on this, the embodiment of the present application provides a preparation method of a high-flame-retardant drum brake pad, which comprises the following steps: (1) adding a flame-retardant matrix into a banbury mixer for banburying, wherein the banburying time is 10-15 min, the banburying temperature ranges from 15 to 80℃, the double-roller speed is 20-30 r / min, and a banburying product is obtained; (2) adding the banburying product prepared in step (1) into a roll mixer for roll mixing, wherein the double-roller gap of the roll mixer is less than 0.3 mm, the roll mixing temperature is 90-95℃, the roll mixing product is crushed to form a heat-resistant flame-retardant particle; (3) uniformly distributing the heat-resistant flame-retardant particle prepared in step (2) in a friction matrix material to obtain a mixed friction material; and (4) hot-pressing and subsequent heat curing the mixed friction material obtained in step (3) to obtain a final high-flame-retardant drum brake pad.

[0026] In some embodiments, in the first step, the components of the flame-retardant matrix include, by mass fraction, 10-15 parts of phosphorus-modified epoxy resin, 5-10 parts of aluminum hydroxide, 4-8 parts of zinc borate, 30-40 parts of barium sulfate, 20-30 parts of light magnesium oxide, and 5-10 parts of mica; wherein the phosphorus-modified epoxy resin is used as a binder component, the aluminum hydroxide and zinc borate are used as flame retardant components, and the barium sulfate, light magnesium oxide, and mica are used as fillers; the mass fraction of the flame retardant components in the flame-retardant matrix is 10-15 parts; the mass fraction of the binder and the fillers in the flame-retardant matrix is large; and the ductility of the binder and the fillers is higher than that of the flame retardant, so that the phosphorus-modified epoxy resin is coated in the process of internal mixing and roll mixing.

[0027] In some preferred embodiments, in the first step, the components of the flame-retardant matrix include, by mass fraction, 12 parts of phosphorus-modified epoxy resin, 8 parts of aluminum hydroxide, 7 parts of zinc borate, 30 parts of barium sulfate, 30 parts of light magnesium oxide, and 8 parts of mica.

[0028] In some embodiments, in the second step, the thickness of the roll-mixed product is 0.9-1.5 mm.

[0029] In some embodiments, in the second step, the particle size of the obtained heat-resistant flame-retardant particles is 1.5-3 mm.

[0030] In some embodiments, in the third step, the components of the friction base material include benzoxazine resin, glass fiber, mineral fiber, high-temperature-resistant partition agent, and friction performance modifier; the high-temperature-resistant partition agent includes kaolin, calcium silicate, and light magnesium oxide, which can absorb H2 and O2 generated by the decomposition of the friction base material at high temperature, form a protective film to wrap, block the oxygen required for combustion, and quickly suppress the fire; and the friction performance modifier includes flake graphite, synthetic graphite, aluminum oxide, and zirconium silicate components.

[0031] In some embodiments, in the third step, the components of the mixed friction material include, by mass fraction, 10%-15% of benzoxazine resin, 8%-10% of glass fiber, 20%-25% of heat-resistant flame-retardant particles, 10%-15% of mineral fiber, 10%-16% of kaolin, 7%-12% of calcium silicate, 7%-12% of light magnesium oxide, 4%-6% of flake graphite, 4%-6% of synthetic graphite, 2%-4% of aluminum oxide, and 2%-4% of zirconium silicate.

[0032] In some embodiments, in the fourth step, the hot-pressing temperature in the hot-pressing process is 180-200°C, and the maximum temperature of subsequent heat curing is 200-220°C.

[0033] Based on this, the embodiment of the application further provides a high flame-retardant drum brake pad prepared by the preparation method provided in the foregoing embodiment.

[0034] The technical solutions and the technical effects achieved by the application will be described in more detail through more specific embodiments.

[0035] Embodiment 1

[0036] The embodiment provides a preparation method of a high flame-retardant drum brake pad, and the specific steps are as follows:

[0037] (1) Prepare a flame-retardant base, and the components of the flame-retardant base include, by mass fraction, 12 parts of phosphorus-modified epoxy resin, 8 parts of aluminum hydroxide, 7 parts of zinc borate, 30 parts of barium sulfate, 30 parts of light magnesium oxide, and 8 parts of mica; the prepared flame-retardant base is added into a 100L plowshare mixer for mixing, the stirring speed is 50r / min, and the mixing time is 5min; the obtained mixture is added into a 60L internal mixer for internal mixing, the internal mixing time is 12min, the internal mixing temperature ranges from 15 to 80℃, the upper ram pressure is 0.6Mpa, and the double-roller speed is 20r / min, to obtain an internal mixed material;

[0038] (2) The internal mixed material obtained in (1) is added into a double-movement roll mill, the double-roller gap is adjusted to 0.2mm, and the roller temperature is 95℃; a 1-1.2mm-thick roll-milled product is obtained, the roll-milled product is crushed to obtain heat-resistant flame-retardant particles X1, and the particle size is controlled to be 2-3mm;

[0039] (3) The heat-resistant flame-retardant particles X1 obtained in (2) are mixed with a friction base material Y1 at a mass ratio of 24:76 to obtain a mixed friction material, and the mass fraction of the components of the mixed friction material is shown in Table 1;

[0040] Table 1

[0041]

[0042] (4) The mixed friction material in (3) is hot-pressed at a temperature of 180℃, and then hot-cured at a temperature of 200℃

[0043] to obtain a high flame-retardant drum brake pad Z1.

[0044] Embodiment 2

[0045] The embodiment provides a preparation method of a high flame-retardant drum brake pad, and the specific steps are as follows:

[0046] (1) Formulate a flame-retardant base, the components of which include, by mass fraction, phosphorus-modified epoxy resin 12 parts, aluminum hydroxide 8 parts, zinc borate 7 parts, barium sulfate 30 parts, light magnesium oxide 30 parts, and mica 8 parts; add the formulated flame-retardant base to a 100L plowshare mixer for mixing, with a stirring speed of 50r / min and a mixing time of 5min; add the obtained mixture to a 60L internal mixer for internal mixing, with an internal mixing time of 10min, an internal mixing temperature range of 15-80℃, an upper plunger pressure of 0.6Mpa, and a double-roller speed of 25r / min, to obtain an internal mixed material;

[0047] (2) Add the internal mixed material obtained in (1) to a double-movement roll mill, adjust the double-roller gap to 0.2mm, and the roller temperature to 90℃; obtain a 1-1.2mm-thick roll-milled product, crush the roll-milled product to obtain heat-resistant flame-retardant particles X2, with a particle size controlled to 2-3mm;

[0048] (3) Mix the heat-resistant flame-retardant particles X2 obtained in (2) with a friction base material Y2 at a mass ratio of 20:80 to obtain a mixed friction material, with the mass fractions of the components shown in Table 2 below;

[0049] Table 2

[0050]

[0051] (4) Hot-press the mixed friction material in (3) at a temperature of 190℃, and subsequently heat-cure it at 210℃, to obtain a high-flame-retardant drum brake pad Z2.

[0052] Example 3

[0053] The present embodiment provides a preparation method of a high-flame-retardant drum brake pad, with the specific steps as follows:

[0054] (1) Formulate a flame-retardant base, the components of which include, by mass fraction, phosphorus-modified epoxy resin 12 parts, aluminum hydroxide 8 parts, zinc borate 7 parts, barium sulfate 30 parts, light magnesium oxide 30 parts, and mica 8 parts; add the formulated flame-retardant base to a 100L plowshare mixer for mixing, with a stirring speed of 50r / min and a mixing time of 5min; add the obtained mixture to a 60L internal mixer for internal mixing, with an internal mixing time of 15min, an internal mixing temperature range of 15-80℃, an upper plunger pressure of 0.7Mpa, and a double-roller speed of 30r / min, to obtain an internal mixed material;

[0055] (2) Add the internal mixed material obtained in (1) to a double-movement roll mill, adjust the double-roller gap to 0.15mm, and the roller temperature to 92℃; obtain a 0.9-1mm-thick roll-milled product, crush the roll-milled product to obtain heat-resistant flame-retardant particles X3, with a particle size controlled to 1.5-2mm;

[0056] (3) The heat-resistant and flame-retardant particles X3 obtained in (2) are mixed with the friction base material Y3 at a mass ratio of 24:76 to obtain a mixed friction material, the mass fractions of the components of which are shown in Table 3 below;

[0057] Table 3

[0058]

[0059]

[0060] (4) The mixed friction material in (3) is hot-pressed at a temperature of 200°C, and then heat-cured at 220°C to obtain a high-flame-retardant drum brake pad Z3.

[0061] Comparative Example 1

[0062] The present comparative example provides a preparation method of a drum brake pad, the specific steps of which are as follows:

[0063] (1) A friction base material Y4 is prepared, the mass fractions of the components of which are as follows:

[0064] Table 4

[0065]

[0066] (2) The friction base material Y4 is hot-pressed at a temperature of 160°C to obtain a drum brake pad Z4.

[0067] The high-flame-retardant drum brake pads Z1, Z2 and Z3 prepared in Examples 1-3 and Z4 prepared in Comparative Example 1 are respectively subjected to flame-retardant performance tests, the test items of which include friction coefficient, wear amount, oxygen index OL (10 mm) and UL94 test (10 mm); wherein the friction coefficient is a main functional parameter of the brake pad, directly affects the size of the braking torque, and is an important parameter to ensure driving safety, the design value of the friction coefficient of a conventional drum friction plate is between 0.35-0.45, which not only ensures sufficient braking torque to ensure driving safety, but also does not produce braking noise due to a larger friction coefficient, affecting driving comfort; the wear amount test is an important indicator for investigating the service life of the friction plate, and the wear amount of the small sample test can be used to calculate the service life of the friction plate; the oxygen index OL refers to the lowest oxygen concentration required for the material to burn in the oxygen-nitrogen mixed gas flow under specified conditions, which is an important indicator of the flame-retardant performance of the material; the UL94 test refers to the time required for the material to self-extinguish after removing the fire source after heating and burning the test sample of a specific thickness under an air atmosphere, and the rating is: <10S for V-0, 10-20S for V-1, and 20-30S for V-2.

[0068] The flame-retardant performance test results are shown in Table 5 below:

[0069] Table 5

[0070]

[0071] From the results shown in Table 5, it can be seen that the friction coefficients of the high flame-retardant drum brake linings Z1, Z2 and Z3 prepared in the examples and the drum brake lining Z4 prepared in the comparative example are all in the range of 0.35-0.45, and the wear amounts of Z1, Z2 and Z3 are basically equivalent to that of Z4, which indicates that the high flame-retardant drum brake linings provided in the examples will not affect the friction performance due to the addition of flame-retardant materials.

[0072] From Table 5, it can be seen that the oxygen index OL(10mm) of the high flame-retardant drum brake linings prepared in Examples 1-3 is above 35, while the OL(10mm) of the drum brake lining prepared in the comparative example is only 31. In addition, comparing the UL94 test (10mm) results, the combustion time of the high flame-retardant drum brake linings prepared in the examples is below 4S, which is much lower than the combustion time (16S) of the drum brake lining prepared in the comparative example. The UL94 test (10mm) level of the high flame-retardant drum brake linings prepared in the examples all reaches the optimal V-0 level, which is better than the UL94 test (10mm) level (V-1 level) of the drum brake lining prepared in the comparative example. The above results show that the high flame-retardant drum brake linings prepared in the examples have excellent flame-retardant performance.

[0073] The above has described the present application in detail, and the principles and implementation modes of the present application have been described by applying specific examples. The above description of the examples is only for the purpose of helping to understand the present application and the core idea. It should be pointed out that, for ordinary skilled persons in the technical field, some improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A method of producing a high flame-retardant drum brake pad, characterized by, It comprises the following steps: In the first step, the components of the fire-retardant matrix, calculated by mass fraction, include 10-15 parts of phosphorus-modified epoxy resin, 5-10 parts of aluminum hydroxide, 4-8 parts of zinc borate, 30-40 parts of barium sulfate, 20-30 parts of light magnesium oxide, and 5-10 parts of mica. The components of the fire-retardant matrix, calculated by mass fraction, include 12 parts of phosphorus-modified epoxy resin, 8 parts of aluminum hydroxide, 7 parts of zinc borate, 30 parts of barium sulfate, 30 parts of light magnesium oxide, and 8 parts of mica. In the first step, the temperature of the mixing is 15-80 ℃, and the mixing time is 10-15 min; in the second step, the rolling temperature during the rolling process is 85-95 ℃. In the second step, the thickness of the rolling product is 0.9-1.5 mm. The particle size of the obtained heat-resistant fire-retardant particles is 1.5-3 mm.

2. The production method according to claim 1, characterized by, In the third step, the components of the friction matrix material include benzoxazine resin, glass fiber, mineral fiber, high-temperature-resistant partition agent, and friction performance regulator; the high-temperature-resistant partition agent includes kaolin, calcium silicate, and light magnesium oxide; the friction performance regulator includes flake graphite, synthetic graphite, aluminum oxide, and zirconium silicate components.

3. The preparation method according to claim 1, characterized in that, The components of the mixed friction material, calculated by mass fraction, include 10%-15% of benzoxazine resin, 8%-10% of glass fiber, 20%-25% of heat-resistant fire-retardant particles, 10%-15% of mineral fiber, 10%-16% of kaolin, 7%-12% of calcium silicate, 7%-12% of light magnesium oxide, 4%-6% of flake graphite, 4%-6% of synthetic graphite, 2%-4% of aluminum oxide, and 2%-4% of zirconium silicate.

4. The method of claim 1, wherein, The hot pressing temperature during the hot pressing process is 180-200 ℃, and the highest temperature of the subsequent heat curing is 200-220 ℃.

5. The preparation method according to claim 1, characterized in that, Obtained by the preparation method of any one of claims 1-8.

6. The method of claim 1, wherein, ​ 7. The production method according to claim 6, wherein ​ 8. The method of claim 1, wherein, ​ 9. A high flame retardant drum brake pad characterized by, ​

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