CN102167886B - Epoxy resin composition and a method for preparing the same - Google Patents

Abstract

The invention relates to an epoxy resin composition with excellent electronic packaging manufacturability and a preparation method thereof. The epoxy resin composition has at least the following components: (A) epoxy resin: 100 parts by weight, (B) novolak resin: 10-100 parts by weight, (C) curing accelerator: 0.01-15 parts by weight , (D) Microsilica powder: 400-1600 parts by weight, the curing accelerator includes two or more accelerators selected from imidazole compounds, tertiary amine compounds, organic phosphine compounds, and latent accelerators. The epoxy resin composition of the present invention is suitable for use in the microelectronics, electronics and optoelectronic industries as packaging materials for chips or devices, and has excellent packaging process performance.

Description

Epoxy resin composition and preparation method thereof

technical field

The invention relates to an epoxy resin composition and a preparation method thereof. The epoxy resin composition is a composite material used for packaging chips or devices in microelectronics, electronics and optoelectronics industries.

Background technique

In the electronics and microelectronics industry, the protection of electronic components or chips is usually encapsulated with a thermosetting epoxy resin composition. With the rapid development of the information industry, the miniaturization, light weight and multi-functionality of electronic devices are irreversible trends. Type QFN, CSP, BGA, etc. For this reason, the epoxy resin composition material encapsulated outside the chip is getting thinner and thinner, thus, the reliability requirements for the packaging material are getting higher and higher. At the same time, during the packaging process, the impact of shape defects on the performance of electronic components becomes more obvious.

As a thermosetting composite epoxy resin composition, there has always been a problem in large-scale production and use. Because its production and packaging can only be completed at one time, it is difficult to rework, so its production control is difficult. In addition, in When in use, defects in the package shape will cause a high rejection rate of electronic devices.

In the prior art, for example, in Patent Document 1 (CN1233626A) and Patent Document 2 (US6822341B1), the method of adopting a novel curing accelerator to improve packaging manufacturability has been reported respectively. However, the curing accelerator used in it is cured in the composition package When the speed is slow, it is easy to cause the problem that the molten rubber overflows from the mold gap during the packaging process. The latent accelerator introduced in Patent Document 3 (CN1600809A) improves the curing speed, but its rapid curing at high temperature leads to a rapid increase in the viscosity of the material, which easily causes defects such as pits and marks on the surface of the packaged electronic device. At the same time, the The stability of the accelerator is poor, and its quality is difficult to control when producing epoxy resin compositions. Patent Document 4 (Japanese Patent Laid-Open No. 5-239321) proposes a method for improving the fluidity of the filler, but it does not significantly improve the encapsulation manufacturability.

Contents of the invention

The present invention is made in view of the above problems. Through intensive research by the present inventors, a method for optimally controlling the reactivity according to the difference in catalytic activity of various curing accelerators has been proposed. Specifically, control the curing of the epoxy resin composition during the encapsulation process by using a combination of a variety of different types of curing accelerators, and/or using a combination of non-latent accelerators and latent accelerators The speed is to adjust the viscosity increase speed of the composition in the high-temperature molten state, so that the surface defects of the packaged electronic components or integrated circuit products are reduced, the yield is greatly improved, and the purpose of excellent packaging processability is achieved.

The invention provides an epoxy resin composition, characterized in that it has at least the following components:

(A) epoxy resin: 100 parts by weight,

(B) curing agent: 10 to 100 parts by weight,

(C) curing accelerator: 0.01 to 15 parts by weight,

(D) inorganic filler: 400～1600 parts by weight,

Wherein, the curing accelerator includes two or more accelerators selected from imidazole compounds, tertiary amine compounds, organic phosphine compounds, and latent accelerators.

Preferably, the curing accelerator contains at least one latent accelerator, and the content of the latent accelerator in the total curing accelerator is 5-99% by weight, more preferably 10-90% by weight.

The amount of the curing accelerator is preferably 0.1-10 parts by weight relative to 100 parts by weight of the epoxy resin.

Furthermore, the present invention provides a method for preparing an epoxy resin composition, which comprises the following steps: metering the composition raw materials having the above components into a high-speed mixer, and performing high-speed dispersion mixing; subsequently, extruding machine and/or double-roller plasticizer to heat and mix, and after discharging, it is rolled into flakes, and after cooling, it is pulverized into powder to make finished products.

According to the epoxy resin composition of the present invention, due to the combined use of two or more different types of curing accelerators and/or the combined use of non-latent accelerators and latent accelerators, the epoxy resin can be optimally controlled as desired. During the curing process of the resin composition, the reactivity of the curing accelerator to the active group can be suppressed, and at the same time, the reactivity of the curing accelerator to the active group during storage and transportation of the epoxy resin composition product can be suppressed, thereby reducing the risk of damage caused by packaging and using The defect of the electronic device is beneficial to improving the operability of the epoxy resin composition in use.

In addition, according to the manufacturing method of the epoxy resin composition of the present invention, since the above-mentioned raw material components are used, in the process of using the composition to encapsulate electronic devices, it has higher fluidity when flowing on a high-temperature mold, And when the specified reaction temperature is reached, the curing of the epoxy composition can be rapidly promoted, so that the yield of packaged electronic components or integrated circuits can be greatly improved.

Detailed ways

Epoxy resin composition of the present invention has following component at least:

(A) epoxy resin: 100 parts by weight,

(B) curing agent: 10 to 100 parts by weight,

(C) curing accelerator: 0.01 to 15 parts by weight,

(D) Inorganic filler: 400-1600 parts by weight.

Above-mentioned epoxy resin can use the epoxy resin commonly used in this field, preferably uses and is selected from o-cresol formaldehyde epoxy resin, biphenyl type epoxy resin, naphthalene type epoxy resin, dicyclopentadiene type epoxy resin, heterocyclic type At least one of epoxy resin, bisphenol F epoxy resin, and bisphenol A epoxy resin.

Above-mentioned curing agent can use the curing agent commonly used in this field, preferably use the phenolic novolac resin selected from phenol novolac resin, phenol novolac resin, monohydroxyl or dihydroxy naphthol aldehyde resin, p-xylene and phenol or naphthol polycondensation Resin, at least one of dicyclopentadiene type phenolic resin, aminophenolic resin, melamine type phenolic resin, phenylene type phenolic resin and biphenyl type phenolic resin.

The above-mentioned inorganic fillers can be inorganic fillers commonly used in the field, preferably at least one selected from crystalline silica powder, fused silica powder, spherical silica powder, and spherical alumina powder.

The curing accelerator of the present invention includes at least two accelerators selected from imidazole compounds, tertiary amine compounds, organic phosphine compounds, and latent accelerators, that is to say, the curing accelerator of the present invention is two A composite accelerator formed by combining the above different types of accelerators.

In the epoxy resin composition of the present invention, by adopting the combination of more than two different accelerators, the reactivity of the curing accelerator as a whole for the curing reaction of the composition resin can be optimally controlled, and then the epoxy resin composition can be controlled at The curing speed in the encapsulation process can adjust the viscosity increase rate of the composition in the high-temperature molten state, and improve the fluidity, thereby reducing the surface defects of the encapsulated electronic components or finished integrated circuits, and greatly increasing the yield.

The present inventor has studied the reaction characteristic of above-mentioned various accelerators, finds that according to the difference of the reaction initiation temperature of different kinds of accelerators and the reaction rate, can design the specific combination of more than two kinds of different accelerators, it has The present invention has been completed because of the effect that the reactivity is low up to a predetermined reaction temperature and the reactivity becomes high when the predetermined reaction temperature is reached.

The imidazole compound used as the curing accelerator of the present invention is not particularly limited, and can be a general imidazole compound commonly used in the art, preferably selected from 2-methylimidazole, 2,4-dimethylimidazole, 2-ethylimidazole At least one of base-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-heptadecylimidazole, more preferably 2-methylimidazole, 2,4 - Dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, particularly preferably 2-methylimidazole, 2,4-dimethylimidazole.

The tertiary amine compound as the curing accelerator of the present invention is not particularly limited, and can be a general tertiary amine compound commonly used in the art, preferably selected from triethylamine benzyl dimethylamine, α-methyl benzyl dimethicone Methylamine, 2-(dimethylaminomethyl)phenol, 2,4,6-tris(dimethylaminomethyl)phenol, 1,8-diazabicyclo(5.4.0)undecene- At least one of 7 (DBU). More preferably triethylamine benzyldimethylamine, 2-(dimethylaminomethyl) phenol, 1,8-diazabicyclo (5.4.0) undecene-7 (DBU), particularly preferably Triethylamine benzyldimethylamine, 1,8-diazabicyclo(5.4.0)undecene-7 (DBU).

The organic phosphine compound used as the curing accelerator of the present invention is not particularly limited, and may be a general organic phosphine compound commonly used in the art, preferably selected from triphenylphosphine, trimethylphosphine, triethylphosphine, triethylphosphine, and triphenylphosphine. At least one of butylphosphine, tri(p-methylphenyl)phosphine and tri(nonylphenyl)phosphine. More preferred are triphenylphosphine, tributylphosphine, and tri(p-methylphenyl)phosphine, and particularly preferred are triphenylphosphine and tributylphosphine.

The latent accelerator as the curing accelerator of the present invention is not particularly limited, and can be a general latent accelerator commonly used in the art, preferably selected from boron trifluoride monoethylamine, boron trifluoride ethylenediamine, Boron trifluoride aniline, boron trifluoride o-methylaniline, boron trifluoride dimethylaniline, boron trifluoride benzylamine, boron trifluoride ethylaniline, boron trifluoride pyridine, triphenylphosphine- At least one of benzoquinone adduct, tetraphenylphosphine-o-binaphthoborate, and tetraphenylphosphine-o-binaphthosilicate. More preferred are boron trifluoride monoethylamine, boron trifluoride aniline, boron trifluoride benzylamine, triphenylphosphine-benzoquinone adduct, tetraphenylphosphine-o-naphthyl borate, tetraphenyl Phosphine-o-naphthalene silicates are particularly preferably boron trifluoride monoethylamine, triphenylphosphine-benzoquinone adducts.

As the specific combination (composite accelerator) of the curing accelerator of the present invention, two or more can be arbitrarily selected from the above-mentioned accelerators, as long as the selected two or more accelerators have different reaction characteristics (such as Reaction initiation temperature, reaction rate, reaction characteristic curve under high and low temperature, etc.), just can carry out arbitrary combination as required, to adapt to the specific requirements of epoxy resin composition in different curing reactions. For example, when the curing reaction of the epoxy resin composition needs to be carried out slowly and stably at low temperature, but is completed quickly at high temperature, an accelerator with a stable reaction rate in a wide temperature range can be used and an accelerator that does not react at low temperature. Combination of accelerators with high reaction rates at high temperatures. In addition, according to the required viscosity and fluidity requirements of the epoxy resin composition, the type and combination of the accelerator can be properly selected.

Specifically, the two or more accelerators selected above may belong to the same type of compound, for example, they all belong to imidazole compounds, tertiary amine compounds, organic phosphine compounds or latent accelerators, or they may belong to different types of compounds , For example, two or more accelerators belong to imidazole compounds, tertiary amine compounds, organic phosphine compounds or latent accelerators. Specific examples of the combination of the curing accelerator of the present invention include, for example, a combination of 2-methylimidazole and triphenylphosphine, a combination of 2-methylimidazole and DBU, triphenylphosphine-benzoquinone addition Combination of compound and DBU, combination of triphenylphosphine-benzoquinone adduct and 2-methylimidazole, combination of triphenylphosphine-benzoquinone adduct and triphenylphosphine, 2-phenyl-4- Combination of methylimidazole and DBU, combination of 2-phenyl-4-methylimidazole and triphenylphosphine-benzoquinone adduct, combination of boron trifluoride monoethylamine and DBU, boron trifluoride monoethylamine The combination of amine and 2-methylimidazole, the combination of boron trifluoride monoethylamine and triphenylphosphine, etc.

The amount of the curing accelerator used (that is, the total amount of two or more accelerators) is 0.01 to 15 parts by weight relative to 100 parts by weight of the epoxy resin. If the amount of the curing accelerator is less than 0.01 parts by weight, there may be problems of insufficient curing or too long a curing reaction. If it is higher than 15 parts by weight, too fast curing may occur, and the number of defects in the packaged device may increase. For problems such as a high reject rate, it is preferably 0.1 to 10 parts by weight, more preferably 1 to 8 parts by weight, particularly preferably 1.5 to 5 parts by weight, based on 100 parts by weight of the epoxy resin.

Among them, it is preferable that at least one of the aforementioned latent accelerators is included in the curing accelerator. The content of the latent accelerator in all the curing accelerators is 0 to 99% by weight, preferably 5 to 99% by weight, more preferably 10 to 90% by weight. By including more than 10% by weight of the latent accelerator in all the curing accelerators, the characteristics of the latent accelerators to accelerate the curing reaction at a specified reaction temperature can be fully utilized to further effectively control the reactivity and the progress of the curing reaction. From the viewpoint of the balance of activity control, the content of the latent accelerator in all the curing accelerators is particularly preferably 40 to 80% by weight.

If two different latent accelerators are used in combination, the progress of the reaction can be controlled stepwise at different reaction temperatures according to the respective reaction initiation temperatures. However, when a non-latent accelerator is used in combination with a latent accelerator, compared with the case of using two or more latent accelerators alone, it is possible to effectively avoid the possible insufficient reactivity of the latent accelerator. The reaction rate is also low at the reaction temperature.

The non-latent accelerator described in the present invention may be any one selected from the above-mentioned imidazole compounds, tertiary amine compounds, and organic phosphine compounds.

In addition, the epoxy resin composition of the present invention may further contain a flame retardant, and the flame retardant is selected from the combination of brominated epoxy resin and antimony trioxide, aluminum hydroxide, magnesium hydroxide, 9,10 - At least one of dihydro-9-oxa-10-phosphaphenanthrene, 2-(6-oxo-6-hydro-phosphaphenanthrene) 1,4-hydroquinone, and zinc borate.

In the present invention, coupling agents well known in the industry can be added as needed, for example selected from γ-(2,3-epoxypropoxy)propyltrimethoxysilane, 2-(3,4 epoxycyclohexyl ) at least one selected from the group consisting of ethyltrimethoxysilane, anilinopropyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane.

In addition, in the present invention, a release agent known in the industry can be added as needed, such as at least one selected from carnauba wax, S wax, OP wax, 161P wax, polyethylene wax, stearic acid, and the like.

Furthermore, in the present invention, colorants known in the industry can be added as needed, for example, any one selected from carbon black, phthalocyanine, titanium dioxide, and the like.

According to the present invention, due to the combination of two or more different types of accelerators used as the curing accelerator and/or the combination of a non-latent accelerator and a latent accelerator, the epoxy resin can be optimally controlled as desired. The curing accelerator in the curing process of the composition is reactive to the active groups, so the restrictions on the amount, curing temperature and curing time of the curing accelerator in the epoxy resin composition are relaxed, which is beneficial to prolong the mixing time and/or Increase the mixing temperature to make the components more fully mixed, and reduce the defects of electronic devices caused by uneven product packaging and use. At the same time, it can suppress the reactivity of the curing accelerator to active groups during storage and transportation of the epoxy resin composition product, which is beneficial to improving the operability of the epoxy resin composition product in use.

The preparation method of the epoxy resin composition of the present invention can adopt the common method of this industry, comprises the following steps: the composition raw material that has above-mentioned composition of the present invention is metered in the high-speed mixer, carries out high-speed dispersion mixing; Subsequently, It is heated and mixed by a screw extruder and/or a twin-roll plasticizer, rolled into flakes after discharge, and crushed into powder after cooling to make a finished product. In addition, it can also be pressed into a cylindrical product by a forming cake maker as required.

In the production method of the present invention, the heating temperature in the screw extruder is preferably 90-135°C, and the heating temperature in the twin-roll plasticizer is preferably 80-98°C. Under the above-mentioned temperature conditions, the epoxy resin composition of the present invention has higher fluidity when flowing on a high-temperature mold in the process of being used for encapsulating electronic devices, and when reaching the reaction temperature, the composite curing of the present invention promotes The reaction speed of the agent is fast, which can effectively promote the curing of the epoxy composition, reduce the defects (such as flashes, pits, pores, etc.) of the packaged electronic components or finished integrated circuits, and greatly increase the yield.

[Example]

The following examples will be used to describe the present invention in detail. However, as long as the gist of the present invention is not exceeded, the present invention is not limited to the specific examples disclosed below.

In the following examples or comparative examples, as the raw material components of the epoxy resin composition, a biphenyl type epoxy resin (YX4000H, epoxy equivalent 193, softening point 102°C) as an epoxy resin, a curing agent Novolak resin (TD2131, hydroxyl equivalent 103, softening point 80°C), spherical silica powder (SS-0183R, median diameter 16.3μm) as inorganic filler, coupling agent (KH560), 2 -Methylimidazole (2-MZ), triphenylphosphine-benzoquinone adduct (TPP-BQ), 1,8-diazabicyclo (5.4.0) undecene-7 (DBU), three Phenylphosphine (TPP), flame retardant (aluminum hydroxide), release agent (carnauba wax), colorant (carbon black), etc. All of the above substances are commercially available reagents.

The preparation method of the epoxy resin composition sample of each embodiment and comparative example is as follows:

(Example 1)

Add 800 parts by weight of spherical silica powder (SS-0183R) into a high-speed mixer, spray 5 parts by weight of KH560 coupling agent, and then add 100 parts by weight of biphenyl epoxy resin (YX4000H), novolac resin ( TD2131) 100 parts by weight, 1 part by weight of triphenylphosphine-benzoquinone adduct (TPP-BQ), 0.8 parts by weight of DBU accelerator, 1 part by weight of carnauba wax, 20 parts by weight of aluminum hydroxide, 0.2 parts by weight of carbon black share. Then stir and mix in a high-speed mixer for 20 minutes, take out the powder and heat and knead for 5 minutes on a double-roller plastic mill preheated to 85-90°C, remove the kneaded material and cool it to room temperature, and pulverize it. A sample powder of the epoxy resin composition was obtained.

(Example 2)

As a curing accelerator, 0.4 parts by weight of 2-methylimidazole was used instead of 0.8 parts by weight of DBU accelerator. Other components were the same as in Example 1, and the preparation method was also the same as in Example 1.

(Example 3)

As a curing accelerator, 1.1 parts by weight of triphenylphosphine was used instead of 0.8 parts by weight of DBU accelerator. Other components were the same as in Example 1, and the preparation method was also the same as in Example 1.

(Example 4)

As a curing accelerator, 0.4 parts by weight of 2-methylimidazole and 0.8 parts by weight of a DBU accelerator were used. Other components were the same as in Example 1, and the preparation method was also the same as in Example 1.

(comparative example 1)

As a curing accelerator, triphenylphosphine-benzoquinone adduct (TPP-BQ) is not used, and the amount of DBU accelerator is changed to 1.3 parts by weight, except that, other components are the same as in Example 1, and prepared The method is also the same as in Example 1.

(comparative example 2)

As curing accelerator, do not use triphenylphosphine-benzoquinone adduct (TPP-BQ), and change the consumption of 2-methylimidazole into 0.8 weight part, except that, other components are identical with embodiment 1 , the preparation method is also the same as in Example 1.

The physical properties (gelation time, spiral flow length, water absorption rate, package reject rate, flame retardancy) of the epoxy resin compositions obtained in each of the Examples and Comparative Examples were measured. The specific detection method is as follows.

Gelation time: hot plate method, heat the electric heating plate to control the temperature at 175±1°C, take 0.3~0.5g powder sample and put it on the electric heating plate, the powder melts into a fluid and then solidifies, and records the change from fluid to solidified colloidal state the time required.

Spiral flow length: Measured on a transfer molding press using EMMI-1-66 spiral flow metal mold, mold temperature 175±1°C, transfer pressure 70±2kg/cm ² , powder sample 20±5g.

Water absorption: Measure the cured 125mm×13mm×3.2mm sample by high-pressure cooking (PCT) method, temperature 121±2°C, air pressure 2atm, 24hr, and measure the percentage of weight gain before and after cooking.

Packaging waste rate: package TO-3P transistors with cake samples, take out 100 pieces, check various surface defects, including traces, overflow glue, pits, voids, pores, cracks, etc., and calculate the waste rate.

Flame retardant performance: determined according to the national GB/T2408-1996 plastic combustion performance test method, using a horizontal and vertical combustion instrument.

Table 1 shows the measurement results of the above-mentioned physical properties. The content unit of each component in the table is parts by weight.

Table 1:

As can be seen from the above table, in Examples 1 to 4 in which two or more accelerators were used in combination as the curing accelerator of the present invention, Examples 1 to 3 containing a latent accelerator (TPP-BQ) were used. The effect of fluidity and water absorption is to a certain extent better than that of Example 4 without using a latent accelerator, but compared with Comparative Examples 1-2 using only one accelerator alone, the gelation time is approximately Under the same conditions, any of the examples has achieved excellent effects of greatly improving the fluidity, reducing the water absorption rate, and greatly reducing the packaging waste rate.

Claims (8)

1. An epoxy resin composition characterized by having at least the following components:

(A) epoxy resin: 100 parts by weight of,

(B) Curing agent: 10 to 100 parts by weight of,

(C) Curing accelerator: 0.01 to 15 parts by weight of,

(D) Inorganic filler: 400 to 1600 parts by weight of a stabilizer,

wherein,

the epoxy resin is at least one selected from o-cresol formaldehyde epoxy resin, biphenyl epoxy resin, naphthalene epoxy resin, dicyclopentadiene epoxy resin and heterocyclic epoxy resin;

the curing agent is at least one selected from phenol novolac resin, cresol novolac resin, monohydroxy or dihydroxy naphthalene novolac resin, phenol-formaldehyde resin obtained by condensation polymerization of p-xylene and phenol or naphthol, dicyclopentadiene type phenol-formaldehyde resin, amino phenol-formaldehyde resin, melamine phenol-formaldehyde resin, phenylene type phenol-formaldehyde resin and biphenyl type phenol-formaldehyde resin;

the inorganic filler is at least one selected from crystalline silica powder, fused silica powder, spherical silica powder and spherical alumina powder;

the cure accelerator is a combination of a non-latent accelerator and a latent accelerator,

the non-latent accelerator is any one selected from imidazole compounds, tertiary amine compounds and organic phosphine compounds;

the latent accelerator is at least one selected from the group consisting of triphenylphosphine-benzoquinone adduct, tetraphenylphosphine-o-dinaphthylborate, and tetraphenylphosphine-o-dinaphthylsilicate.

2. The epoxy resin composition according to claim 1, wherein the content of the latent accelerator in the entire curing accelerator is 40 to 80% by weight.

3. The epoxy resin composition according to claim 1 or 2, wherein the imidazole compound is at least one selected from the group consisting of 2-methylimidazole, 2, 4-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 2-heptadecylimidazole;

the tertiary amine compound is at least one selected from triethylamine benzyl dimethylamine, alpha-methyl benzyl dimethylamine, 2- (dimethylaminomethyl) phenol, 2, 4, 6-tri (dimethylaminomethyl) phenol and 1, 8-diazabicyclo (5.4.0) undecene-7;

the organic phosphine compound is at least one selected from triphenylphosphine, trimethylphosphine, triethylphosphine, tributylphosphine, tri (p-methylphenyl) phosphine and tri (nonylphenyl) phosphine.

4. The epoxy resin composition according to claim 1 or 2, wherein the curing accelerator is a combination of a triphenylphosphine-benzoquinone adduct and DBU, a combination of a triphenylphosphine-benzoquinone adduct and 2-methylimidazole, a combination of a triphenylphosphine-benzoquinone adduct and triphenylphosphine, or a combination of 2-phenyl-4-methylimidazole and a triphenylphosphine-benzoquinone adduct.

5. The epoxy resin composition according to claim 1 or 2, wherein the curing accelerator is used in an amount of 0.1 to 10 parts by weight relative to 100 parts by weight of the epoxy resin.

6. The epoxy resin composition according to claim 1 or 2, further comprising a flame retardant which is at least one selected from the group consisting of a combination of brominated epoxy resin and antimony trioxide, aluminum hydroxide, magnesium hydroxide, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene, 2- (6-oxo-6-hydro-phosphaphenanthrene) 1, 4-hydroquinone, and zinc borate.

7. The preparation method of the epoxy resin composition is characterized by comprising the following steps: metering a composition raw material with the components of any one of claims 1-6 into a high-speed mixer for high-speed dispersive mixing; and heating and mixing the mixture by a screw extruder and/or a double-roller plastic mixer, discharging, rolling the mixture into sheets, cooling and crushing the sheets into powder to obtain a finished product.

8. The method according to claim 7, wherein the heating temperature in the screw extruder is 90 to 135 ℃ and the heating temperature in the two-roll mill is 80 to 98 ℃.