CN114197250A

CN114197250A - Wet paper-based friction material based on foam molding and preparation method thereof

Info

Publication number: CN114197250A
Application number: CN202111434408.6A
Authority: CN
Inventors: 张春辉; 林洺岑; 侯夫庆; 丁能鑫; 杨会康
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2021-11-29
Filing date: 2021-11-29
Publication date: 2022-03-18
Anticipated expiration: 2041-11-29
Also published as: CN114197250B

Abstract

The invention belongs to the field of friction materials, and particularly relates to a wet paper-based friction material based on foam molding and a preparation method thereof. The method comprises the following steps: firstly, adding natural fibers, synthetic fibers, a filler and a dispersing agent into water, mixing, pouring into a foaming barrel, and adding a surfactant for foaming to obtain foam slurry; then, carrying out vacuum dehydration on the foam slurry, and drying to obtain base paper of the paper-based friction material; then, dipping the base paper in a phenolic resin solution, taking out the base paper, and drying to obtain the dipped base paper; and finally, pre-curing, hot-pressing and curing the gum-dipped base paper to obtain the wet paper-based friction material formed by foam. The invention uses water-based bubbles to replace water as a dispersion medium and a carrier, and can obviously improve the bulk and porosity of the base paper, thereby realizing the regulation and control of the porosity and pore structure of the base paper, improving the permeability and gum dipping amount of the gum solution, and further improving the heat conductivity coefficient, compression resilience and durability of the material.

Description

Wet paper-based friction material based on foam molding and preparation method thereof

Technical Field

The invention belongs to the field of friction materials, and particularly relates to a wet paper-based friction material based on foam molding and a preparation method thereof.

Background

The paper-based friction material is a transmission material at the core of an automatic gearbox in a transmission system, has higher compression resilience and stable friction coefficient due to loose and porous internal structure, has good capability of permeating and exchanging heat for oil under a lubricating oil system, and is also a 'breathing' type material.

The existing wet paper-based friction plate preparation method comprises the following steps: defibering and dispersing fibers and fillers in water, pouring the fibers and the fillers into a former at one time, and filtering and forming by vacuum suction to obtain raw paper; drying, gumming, hot-pressing and curing the base paper to obtain a paper-based friction material; the friction material is prepared into the paper-based friction plate through the working procedures of cutting, bonding a core plate, milling a groove and the like.

However, the paper-based friction material has the problems of high water consumption, poor dispersibility of fiber and filler and the like in the preparation process at present; meanwhile, in order to improve the dehydration rate in the base paper forming process, high vacuum filtration is needed, so that the problems of low porosity of the base paper, poor and uneven permeability of glue solution and the like are caused, and the comprehensive performance of the paper base friction material is seriously influenced. Therefore, a new method for preparing a paper-based friction material needs to be developed.

Unlike wet forming with water as medium, foam forming is a material preparing technology that takes micron-sized water-based bubbles (water, surfactant and air) as dispersing medium, uniformly disperses fibers in a foam system, and then is formed through dehydration (defoaming) and drying.

Disclosure of Invention

In order to overcome the defects of the existing wet paper-based friction material body paper forming technology, the invention mainly aims to provide a preparation method of a wet paper-based friction material based on foam forming.

It is another object of the present invention to provide a wet paper-based friction material based on foam molding.

Firstly, a stable foam slurry system with uniform bubble size distribution and high-efficient fiber/filler dispersion is prepared by a mechanical stirring foaming method, and then the paper-based friction material base paper with controllable performances such as porosity, pore structure, fiber orientation and the like is obtained by changing a dehydration (defoaming) curve, so that the bottleneck problems of easy flocculation of fibers, poor base paper uniformity, poor and uneven glue solution permeability, poor compression resilience of friction materials and the like in the traditional method are solved. The wet paper-based friction material prepared by the invention has the advantages of obviously increased sizing amount, more uniform glue solution distribution, larger average pore diameter, increased heat conductivity coefficient and greatly reduced compression deformation rate, and provides a new method for preparing the wet paper-based friction material.

The invention is realized by the following technical scheme:

a preparation method of a wet paper-based friction material based on foam molding comprises the following steps:

(1) foaming: adding natural fibers, synthetic fibers, a filler and a dispersing agent into water, mixing, pouring into a foaming barrel, and adding a surfactant for foaming to obtain foam slurry;

(2) defoaming: performing vacuum dehydration on the foam slurry obtained in the step (1), and drying to obtain base paper of the paper-based friction material;

(3) gum dipping: dipping the base paper obtained in the step (2) in a phenolic resin solution, taking out, and drying to obtain dipped base paper;

(4) and (3) curing: and (4) pre-curing, hot-pressing and curing the gum dipping base paper obtained in the step (3) to obtain the wet paper-based friction material formed by foam.

Preferably, the natural fibers in the step (1) account for 20-30% by mass, the synthetic fibers account for 15-30% by mass, the filler accounts for 40-60% by mass, and the slurry concentration is 0.5-1% by mass.

Preferably, the natural fiber in the step (1) is one or more than two of sisal fiber, cotton fiber, bamboo fiber or cellulose fiber; the synthetic fiber is one or more than two of carbon fiber, aramid fiber, glass fiber and polyimide fiber.

Preferably, the dispersant in the step (1) is one or more than two of PEO, PVA and APAM;

the filler is one or more than two of graphite, alumina, diatomite, silicon dioxide, potassium titanate whisker and friction powder;

the surfactant is one or more than two of alkyl glycoside, sodium dodecyl sulfate, polyvinyl alcohol and tween-80.

Preferably, the foaming conditions in step (1) are: stirring speed is 1000-1500 rpm, and foaming time is 10-20 min; the side wall of the foaming barrel is provided with a baffle; the air content in the foam slurry is 50-80%, and the concentration of the surfactant in the slurry is 2.5-4 g/L.

Preferably, the vacuum dehydration conditions in step (2) are as follows: the vacuum degree is 0.01-0.06Mpa, the dehydration is 5-20s, the drying temperature is 40-60 ℃, and the drying time is 3-5 h; the thickness of the base paper is 0.5-5 mm.

Preferably, the dipping time in the step (3) is 5-10min, the drying temperature is 60-80 ℃, and the time is 20-40 min.

Preferably, the pre-curing temperature in the step (4) is 150-; the hot pressing temperature is 150-; the curing temperature is 150 ℃ and 180 ℃, and the time is 1-2 h.

Preferably, the addition amount of the dispersing agent in the step (1) is 1-3% of the total mass of the fiber.

A wet paper-based friction material formed by foam is prepared by the method.

The invention has the following advantages and beneficial effects:

(1) the invention provides a preparation method of a wet paper-based friction material based on foam molding, which is characterized in that the fibers, the filler, the friction performance regulator and the like are prepared into a stable foam slurry system by a mechanical stirring method, water-based bubbles are used as a dispersion medium and a carrier instead of water, the bulk and porosity of the base paper can be obviously improved, and a series of paper-based friction material base paper with controllable performances such as porosity, pore structure, fiber orientation and the like can be obtained by changing a dehydration (defoaming) curve.

(2) The invention obviously improves the gum dipping amount of the paper-based friction material, and has the advantages of 27.4-109.0% higher than the comparison ratio, more uniform glue solution distribution, higher heat conductivity coefficient, 7.1-14.3% higher than the comparison ratio, lower compression deformation rate and 16.3-34.9% lower than the comparison ratio.

(3) The average pore diameter of the light-load paper-based friction material is larger than that of the heavy-load paper-based friction material, and the heat conduction performance is better; while the paper-based friction material for heavy load has a smaller compression deformation ratio at 4.18MPa than that of the material for light load.

Drawings

FIG. 1 is a flow chart of a preparation process of a wet paper-based friction material based on foam molding.

Fig. 2 is a foaming apparatus including a stirrer 1, a baffle 2, and a foaming tub 3.

Fig. 3 shows a wet type paper sheet forming apparatus, which comprises a pulp barrel 1, a screw 2, a sealing washer 3, a forming net 4, a groove 5 and a water outlet 6.

FIG. 4 shows a view of a light load (300 g/m) vehicle²) Comparative example pore size distribution plot with foam-formed paper-based friction material of different thickness.

FIG. 5 shows a view of a heavy-duty vehicle (500 g/m)²) Comparative example pore size distribution plot with foam-formed paper-based friction material of different thickness.

FIG. 6 shows a view of a light load (300 g/m) vehicle²) Comparative example compression performance plots with foam-molded paper-based friction materials of different thicknesses.

FIG. 7 shows a view of a heavy-duty vehicle (500 g/m)²) Comparative example compression performance plots with foam-molded paper-based friction materials of different thicknesses.

FIG. 8 shows a view of a light load (300 g/m) vehicle²) Comparative example and scanning electron microscope cross-sectional views of base papers of foam-molded paper-based friction materials with different thicknesses, 8a, 8b and 8c are comparative example 1 and implementationExample 1 and example 2 friction materials scanning electron microscopy cross-sectional views.

FIG. 9 shows a view of a heavy-duty vehicle (500 g/m)²) Comparative example and different thicknesses of the foam formed paper based friction material base scanning electron microscope cross section, 9a, 9b and 9c are the comparative example 2, example 3 and example 4 friction material scanning electron microscope cross section respectively.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto, and may be carried out with reference to conventional techniques for process parameters not particularly noted.

Referring to fig. 1, a foaming apparatus includes a foaming tub 3 having a baffle 2 and a stirrer 1. The baffle can ensure that turbulent flow is formed in the stirring process, and the formation of water-based foam is promoted.

Referring to fig. 2, a wet type sheet forming apparatus, a pulp bucket 1 is connected with a certain mesh number of forming wires 4 by screws 2, and a sealing gasket 3 is added to ensure sealing. The forming net 4 is clamped in the designed groove 5, the lower part is connected with a suction bottle and a vacuum pump through an external connection way for vacuum dehydration defoaming and forming, and liquid is discharged from a water outlet 6.

Abrasive powder (available from caldela, usa), PEO (molecular weight 300 million, available from sumitomo group, japan).

The invention will now be further described with reference to the examples:

comparative example 1 aqueous forming:

step 1: according to the weight percentage, the basis weight of the paper-based friction material base paper for light load is 300g/m²26% of cotton fiber, 12% of aramid fiber, 12% of carbon fiber, 16% of diatomite, 15% of graphite, 3% of silicon dioxide, 2% of alumina, 6% of potassium titanate whisker and 8% of friction powder (solidified cardanol powder) are weighed.

Step 2: adding the raw materials and a PEO dispersant (the dosage is 1 percent of the total mass of the fibers) into water, wherein the concentration of slurry is 0.5 percent (mass percentage), defibering and mixing the raw materials in a defibering device for 10000 turns, then pouring the mixture into a sheet making device, dehydrating (defoaming) the mixture for 10s in a vacuum suction mode, wherein the vacuum degree is 0.04MPa, the thickness of base paper is controlled to be 0.8mm, and drying the dehydrated sample at 50 ℃ to obtain the base paper of the paper-based friction material.

And step 3: and (3) soaking the base paper obtained in the step (2) in 10% cashew nut shell oil modified phenolic resin solution for 5min, taking out, and drying in an oven at 60 ℃ to obtain the impregnated paper.

And 4, step 4: and (3) placing the gum dipping paper in a drying oven at 160 ℃ for pre-curing, then carrying out hot pressing to 0.7mm by a flat vulcanizing machine, and finally continuing curing for 2h in the drying oven to obtain the paper-based friction material.

Comparative example 2 aqueous forming:

according to the mass percentage, the basis weight of the paper-based friction material base paper for heavy load is 500g/m²Weighing raw materials, 26% of cotton fiber, 12% of aramid fiber, 12% of carbon fiber, 16% of diatomite, 15% of graphite, 3% of silicon dioxide, 2% of aluminum oxide, 6% of potassium titanate whisker and 8% of friction powder (solidified cardanol powder). The forming was carried out according to the method of comparative example 1, the thickness of the base paper was controlled to be 1.5mm, the thickness of the material after hot pressing was 1.1mm, and the other steps were kept the same as in comparative example 1.

Example 1

Step 1: according to the weight percentage, the basis weight of the base paper of the light-load paper-based friction material is 300g/m²26% of cotton fiber, 12% of aramid fiber, 12% of carbon fiber, 16% of diatomite, 15% of graphite, 3% of silicon dioxide, 2% of alumina, 6% of potassium titanate whisker and 8% of friction powder (solidified cardanol powder) are weighed.

Adding the raw materials and 1% of PEO dispersant (the dosage is 1% of the total mass of the fiber) into water, wherein the concentration of the slurry is 0.5% (mass percent), fluffing and mixing the mixture in a fluffer for 10000 turns, then pouring the mixture into a foaming device (shown as a figure 2), adding alkyl glycoside (APG), wherein the concentration of the alkyl glycoside in the slurry is 2.5g/L, and mechanically stirring and foaming the mixture at 1300rpm for 10min to obtain foam slurry with 65% of air content.

Step 2: the slurry was then poured into a sheet former (see FIG. 3) and dewatered (defoamed) by vacuum suction for 10 seconds at a vacuum of 0.04MPa and a base paper thickness of 1 mm. And drying the dehydrated sample at 50 ℃ for 3h to obtain the base paper of the paper-based friction material.

And step 3: and (3) soaking the base paper obtained in the step (2) in 10% cashew nut shell oil modified phenolic resin solution for 5min, taking out, and drying in an oven at 60 ℃ for 20min to obtain the impregnated paper.

And 4, step 4: the gum dipping paper is placed in an oven at 160 ℃ for pre-curing for 40min, then is hot-pressed to 0.73mm (the pressure is 5Mpa, the time is 2min) by a flat vulcanizing machine, so that the porosity of the gum dipping paper is similar to that of the comparative example 1, the quantitative difference materials can be theoretically controlled to reach the similar porosity by adjusting the hot-pressing thickness, and finally, the paper base friction material is continuously cured for 2h in the oven at 170 ℃ to obtain the paper base friction material.

Example 2

The thickness of the base paper is controlled to be 2mm in the foam forming process, the final hot pressing thickness is 1.1mm, the porosity of the material is controlled to be similar to that of the comparative example 1, and other steps are consistent with those of the example 1.

Example 3

According to the mass percentage, the basis weight of the paper-based friction material base paper for heavy load is 500g/m²Weighing raw materials with the same formula as that in the example 1 according to the mass fraction of the base paper, controlling the thickness of the base paper to be 1.7mm in the foam forming process, controlling the final hot pressing thickness to be 1.2mm, controlling the porosity of the materials to be similar to that in the comparative example 2, and keeping the other steps consistent with that in the example 1.

Example 4

The thickness of the base paper is controlled to be 3.5mm in the foam forming process, the final hot pressing thickness is 1.35mm, the porosity of the material is controlled to be similar to that of the comparative example 2, and other steps are consistent with those of the example 3.

Example 5

And (3) porosity determination: the measurement was carried out by referring to the method GB/T13826 & 2008 & ltWet (non-metallic) Friction Material & gt.

Measuring the gum dipping amount:

the sample gum dipping amount is calculated according to the following formula:

the gum dipping amount is (gum dipping paper mass-base paper mass)/gum dipping paper mass multiplied by 100 percent

Measuring thermal diffusivity, specific heat capacity and thermal conductivity: the thermal diffusivity of the sample is measured by an LFA-447 flash point method thermal conductivity instrument according to the standard of ASTME1461-2011 Standard test method for measuring thermal diffusivity by a flash method.

The specific heat capacity was measured by DSC-204 differential scanning calorimeter using a comparative method. And calculating the specific heat capacity of the sample by taking the sapphire as a standard sample and measuring the energy absorbed by the sample.

The thermal conductivity is then calculated by the following formula:

λ＝α×ρ×C_P

in the formula:

λ -thermal conductivity, in units of W/(m.K);

alpha-thermal diffusion coefficient in mm²/s；

Rho-sample density in g/cm³；

C_p-sample specific heat capacity, in units of J/(g · K);

the performance of the paper based friction material of example 1, example 2 and comparative example 1 were compared, and the performance of the paper based friction material of example 3, example 4 and comparative example 2 were compared.

Paper-based friction material base paper with different thicknesses is prepared by a foam forming method, and the properties of the paper-based friction material base paper are shown in table 1. As can be seen from Table 1, under the same suction vacuum degree, the foam forming can prepare base paper with larger thickness and higher porosity, the porosity of the base paper of the paper-based friction materials in examples 1 and 2 is 83.6% and 91.8% respectively, and is improved by 4.6% and 14.9% compared with that in comparative example 1; the gum dipping amount is 31.6 percent and 44.5 percent respectively, and is improved by 27 percent and 79 percent compared with the comparative example 1. The porosity of the base paper of the paper-based friction materials in the embodiment 3 and the embodiment 4 is 83.5 percent and 92.2 percent respectively, which are improved by 2.6 percent and 13.3 percent compared with the comparison ratio 2; the gum dipping amounts are respectively 31.8% and 46.6%, which are 42.6% and 109% higher than the comparative example 2, and the results show that the porosity of the base paper seriously affects the permeability and gum dipping amount of the glue solution under the conditions of the same glue concentration and the same gum dipping time.

TABLE 1

Fig. 4 and 5 are graphs of pore size distributions for light and heavy duty paper-based friction materials, respectively. As can be seen from FIG. 4, when the porosities are similar, the average pore diameter of comparative example 1 is 2.51. mu.m, the average pore diameter of example 1 is 11.17. mu.m, which is larger than that of comparative example 1, and the average pore diameter of example 2 is 8.49. mu.m, which is also larger than that of comparative example 1; as can be seen from FIG. 5, when the porosities are similar, the average pore diameter of comparative example 2 is 1.78 μm, the average pore diameter of example 3 is 8.49 μm, which is larger than that of comparative example 2, and the average pore diameter of example 4 is 6.56 μm, which is also larger than that of comparative example 2.

Therefore, the pore structures of examples 1-4 are more conducive to the penetration and diffusion of the dope, and the heat exchange performance of the material.

In addition, regardless of the molding method, the average pore diameter of the paper-based friction material for heavy loading is slightly smaller than that for light loading.

Table 2 shows thermal performance data (comparative and examples) for paper-based friction materials for light and heavy loads. As can be seen from Table 2, the specific heat capacities of examples 1-2 are higher than that of comparative example 1, and the specific heat capacities of examples 3-4 are higher than that of comparative example 2 because the content of the high specific heat capacity resin (cashew nut shell oil-modified phenolic resin) in the paper-based friction material of the examples is higher. The thermal diffusion coefficient has little change, and the change rule is basically consistent with the porosity. The change rule of the thermal conductivity coefficient is consistent with the gum dipping amount, the thermal conductivity coefficient of the paper-based friction material in the embodiment 1 is improved by 14.3% compared with that in the comparison 1, the thermal conductivity coefficient of the paper-based friction material in the embodiment 3 is improved by 7.1% compared with that in the comparison 2, the thermal conductivity coefficient is increased along with the increase of the gum dipping amount, but the thermal conductivity coefficient of the material is reduced due to the excessively high gum dipping amount (the embodiment 2 and the embodiment 4).

TABLE 2

Fig. 6 and 7 are graphs showing the variation tendency of compression resilience performance of paper-based friction materials for light and heavy loads, respectively (comparative example and example). As can be seen from fig. 6, after 500 compression cycles under a pressure of 4.18MPa, the deformation ratio of the paper-based friction material for light load of example 1 was 7.2%, the deformation ratio of the paper-based friction material for light load of example 2 was 5.6%, and the deformation ratio of the paper-based friction material for light load of comparative example 1 was 8.6%, which was a 16.3 to 34.9% reduction in deformation ratio.

As can be seen from fig. 7, after 500 compression cycles under a pressure of 4.18MPa, the deformation ratio of the paper-based friction material for heavy duty of example 3 was 5.0%, the deformation ratio of the paper-based friction material for heavy duty of example 4 was 3.7%, and the deformation ratio of the paper-based friction material for heavy duty of comparative example 2 was 5.4%, and the deformation ratio was reduced by 7.4 to 31.5%.

The wet paper-based friction materials prepared in examples 1-4 have smaller deformation rates than those of comparative examples 1 and 2, which shows that the wet paper-based friction materials prepared in examples 1-4 have better compression resilience performance and durability.

Fig. 8 and 9 are scanning electron microscope cross-sectional views (comparative example and example) of base paper of paper-based friction material for light and heavy loads, respectively. It can be seen visually that, compared with comparative examples 1-2, examples 1-4 have better internal pore structures and higher porosity, which indicates that the foam forming method has controllability for preparing base paper of paper-based friction materials with different pore structures.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A preparation method of a wet paper-based friction material based on foam molding is characterized by comprising the following steps:

2. The method according to claim 1, wherein the natural fibers in the step (1) are 20-30% by mass, the synthetic fibers are 15-30% by mass, the filler is 40-60% by mass, and the slurry concentration is 0.5-1% by mass.

3. The method according to claim 1, wherein the natural fiber in the step (1) is one or more of sisal fiber, cotton fiber, bamboo fiber or cellulose fiber; the synthetic fiber is one or more than two of carbon fiber, aramid fiber, glass fiber and polyimide fiber.

4. The method according to claim 1, wherein the dispersant in step (1) is one or more of PEO, PVA and APAM;

5. The method of claim 1 or 2 or 3 or 4, wherein the foaming conditions of step (1) are: stirring speed is 1000-1500 rpm, and foaming time is 10-20 min; a baffle is arranged on the side wall inside the foaming barrel; the air content in the foam slurry is 50-80%, and the concentration of the surfactant in the slurry is 2.5-4 g/L.

6. The method of claim 5, wherein the vacuum dehydration conditions of step (2) are: the vacuum degree is 0.01-0.06Mpa, the dehydration is 5-20s, the drying temperature is 40-60 ℃, and the drying time is 3-5 h; the thickness of the base paper is 0.5-5 mm.

7. The method as claimed in claim 6, wherein the dipping time in the step (3) is 5-10min, the drying temperature is 60-80 ℃, and the time is 20-40 min.

8. The method as claimed in claim 7, wherein the pre-curing temperature in step (4) is 150 ℃ to 180 ℃, and the pre-curing time is 30-60 min; the hot pressing temperature is 150-; the curing temperature is 150 ℃ and 180 ℃, and the time is 1-2 h.

9. The method of claim 1, wherein the dispersant is added in an amount of 1-3% by weight of the total fiber mass in step (1).

10. A foam-formed wet paper-based friction material characterized by being prepared by the method of any one of claims 1 to 9.