CN106373792B

CN106373792B - Composite material of high polymer material and metal and preparation process thereof

Info

Publication number: CN106373792B
Application number: CN201610780383.8A
Authority: CN
Inventors: 韩辉升; 丁阳; 张红梅; 陆婷; 施捷; 孙强
Original assignee: Nantong Memtech Technologies Co ltd
Current assignee: Nantong Memtech Technologies Co ltd
Priority date: 2016-08-30
Filing date: 2016-08-30
Publication date: 2021-06-08
Anticipated expiration: 2036-08-30
Also published as: DE112017003833B4; CN106373792A; DE112017003833T5; WO2018041007A1

Abstract

The invention discloses a composite material of a high polymer material and porous metal and a preparation process thereof. The composite material with high molecular material shrinkage or collapse is prepared through compounding and forming high molecular material containing extractable matter and porous metal under certain condition to obtain sheet, and solvent extraction of the sheet to extract the extractable matter. The porous metal of the composite material prepared in the way protrudes out of the surface of the conductive composite material, so that the composite material is more suitable to be used as an electric contact material.

Description

Composite material of high polymer material and metal and preparation process thereof

Technical Field

The invention relates to the field of composite materials, in particular to a conductive material compounded by high polymer materials and metal, which can be used for manufacturing electric contacts in a conductive plate and a key.

Background

The various rubbers are inherently electrically insulating. To date, all conductive rubbers are not intrinsic. Although the conductive plastic is intrinsic, the intrinsic conductive plastic has high production cost, difficulty in production process, generally inferior conductivity and stability to the metal conductor, and has not been mass-produced and applied. At present, the widely used conductive polymer materials are generally composite polymer materials, and are compounded by polymer materials (such as rubber and plastics) and conductive fillers. The antistatic polymer material and the conductive polymer material can be prepared by adding conductive carbon black into the polymer base material. The conductive polymer material with better conductivity can be prepared by adding metal powder, particularly silver powder or silver-plated powder into the polymer base material. It has also been reported that a conductive polymer material is prepared by adding a conductive fiber to a polymer material. As the Conductive fibers, there are metallized glass fibers (as described in U.S. Pat. No. 4332853, "Conductive plastic with metallized glass fibers recycled in partial films"), carbon fibers or carbon nanotubes (as described in "Anisotropic Conductive rubber and its production method" of Chinese patent No. 201210011604.7), and the like. Since the conductive carbon black, the metal powder and the conductive fibers are dispersed in the conductive rubber, the volume resistivity and the surface resistivity of the conductive polymer material prepared from the fillers are still higher than those of common metal conductive materials, and the capability of conducting larger current is insufficient in some occasions.

The patent document "a conductive plastic and a processing method and a processing device thereof" of application No. 200510086201.9 discloses a conductive plastic comprising 0.1 to 45 v% of conductive fibers, 55 to 99 v% of a thermoplastic and 0 to 3 v% of a processing aid, wherein the conductive fibers are arranged in a three-dimensional network in the thermoplastic; the conductive plastic fibers are uniformly dispersed, the number of lap joints among the fibers is large, and the conductivity is high, so that the shielding efficiency is remarkably improved, the SE value can reach 40-99dB, and the antistatic and electromagnetic shielding effects are good. In order to further improve the conductivity of conductive polymer materials, the skilled person has prepared continuous composites of metal materials and polymer materials as substitutes for conventional conductive polymer materials. The patent document 'a high-efficiency conductive material' with application number 201110448918.9 discloses a high-efficiency conductive material which can be used as an antenna of satellite and ground radar, a directional antenna for broadcast communication, a cable, an electromagnetic interference shielding element of aviation and automobiles, and the structure of the high-efficiency conductive material at least comprises a metal fiber non-woven felt layer which can conduct electricity, heat and electromagnetism at high speed, and is preferably aluminum fiber non-woven felt; the matrix is made of various plastics, preferably glass fiber reinforced plastics. Patent document "composite conductive sheet" of application No. 201010592410.1 discloses a composite conductive sheet composed of a polymer matrix and a metal foil compounded therein. The metal foil is nickel foil, copper foil, aluminum foil, stainless steel foil, gold foil, silver foil or woven mesh containing holes, and the polymer matrix is silicone rubber, nitrile rubber, ethylene propylene rubber, natural rubber, rubber plastic material, thermoplastic plastic, thermosetting plastic or fiber reinforced plastic. Patent document "a conductive rubber and its use" of application No. 201010609386.8 discloses compounding rubber with a metal fiber sintered felt (or metal nonwoven fabric) having pores at least partially filled with rubber by molding or injection to obtain a conductive rubber. U.S. patent 6475933, "high density conductive elastomeric sheet," discloses a Highly conductive rubber sheet comprised of a conductive mesh and an elastomeric matrix filled with conductive particles, wherein the conductive particles are sub-micron sized carbonaceous materials. Chinese patent application No. 200680015484.0, "conductive contact and method of making the same" and U.S. patent No. 7964810, "Electrically conductive contact and method for production therof" disclose electrical contacts made of metal sponge that is at least partially infiltrated by an elastomeric material. U.S. patent application 20040242095, "Composites recovered by wire net or mesh for light, Strength and stiffness," discloses a polymer-based or metal-based composite material reinforced with one or more networks, meshes or mesh structures.

When a composite material made of continuous metal material and polymer material is used as an electrical contact, since the thermal expansion coefficient of polymer material is usually much larger than that of common metal material, sometimes even more than ten times (for example, the thermal expansion coefficient of silicone rubber is about 15 times that of pure nickel), when the temperature is raised, the polymer material in these composite materials will protrude out of the surface of the composite material due to the larger thermal expansion coefficient, so that the surface contact resistance of the electrical contact becomes large, and even the electrical contact may become non-conductive and completely fail. In fact, keys containing such electrical contacts, such as those used in automobiles, may create safety issues.

Therefore, a method for effectively solving the problem of failure of an electrical contact made of a composite material of a polymer material and a continuous metal material at high temperature is urgently needed by the production industry.

Disclosure of Invention

The purpose of the invention is as follows: a composite material of a polymer material and a porous metal having a projected metal material on at least one surface thereof, suitable for making an electrical contact which does not fail in its conductive function even under elevated temperature conditions, and a method for producing the same are provided.

Electrical contacts are a key component of a key that is typically used to mate with a contact switch of a Printed Circuit Board (PCB). It must have a low contact resistance. If the contact resistance is too large, the function of the key switch is invalid and misjudged.

The following is an example of a failure of the conduction function of the electrical contacts: when the composite material prepared from the rubber and the metal expanded metals is used as an electric contact on a rubber key, the phenomenon that the rubber expands and protrudes out of the surface of the electric contact occurs when the temperature is increased from room temperature to 80 ℃, so that the conduction is influenced, and the contact resistance is increased from 0.4 omega to more than 2 omega, and even the composite material is not conductive. As shown in fig. 1. The reason for the rubber bulge is due to the large coefficient of thermal expansion of the rubber. For example, the coefficient of thermal expansion of silicone rubber is about 15 times that of metallic nickel.

The technical scheme is as follows: the invention discloses a composite material and a preparation process thereof, wherein the composite material comprises the following steps: the polymer material containing the extractable substance and the porous metal are compounded in a thermosetting molding mode, a hot vulcanization molding mode, a radiation curing molding mode, a thermoplastic molding mode and the like to prepare the molded object containing the polymer material containing the extractable substance and the porous metal, in particular to prepare the molded object with the polymer material containing the extractable substance and the metal exposed on at least one surface. The holes in the porous metal in the forming object are partially or completely filled by the polymer material during composite forming, and then the extractables in the forming object are extracted by using a solvent, so that the volume of the polymer material in the forming object is shrunk, and the surface of the polymer material in the forming object is collapsed, thereby preparing the polymer material and porous metal composite material with the porous metal protruding from at least one surface. The composite material may be a sheet, a rod, a tube or a profile.

The porous metal in the present invention refers to a metal material or a metal material product having pores or holes, and includes a metal sheet, a metal mesh, a sintered metal mesh, a metal lath, a metal foam or a metal fiber sintered felt having a plurality of uniformly distributed or randomly distributed holes, or a multi-layer metal structure containing the same. The metal net and the sintered metal net can be single-layer or multi-layer, and the metal net and the metal lath are made into a porous metal through a specific vacuum sintering process. The holes in the porous metal are independent or communicated with each other, and at least part of the holes are exposed out of the surface of the porous metal, so that the high polymer material can permeate into the holes. The holes may be regular cylinders, e.g. all holes in the expanded metal are 0.25mm in diameter, or irregular. The diameter of the cross-sectional area of the holes may be in the range of 1 μm to 3.0 mm.

For example, the porous metal can be a metal lath with uniformly distributed pores, the pore diameter of 50 μm-1.0mm, the pore spacing of 25 μm-1.0mm, and the pore pattern of a circle, a regular polygon or other geometrical shapes.

The porous metal may be of various materials. The porous metal may be composed of aluminum, iron, cobalt, nickel, copper, zinc, tin, manganese, tungsten, silver, gold, or alloys thereof. The alloy comprises Hastelloy, Monel, Inconel and the like. Stainless steel, nickel or nickel alloys are preferred. This is because stainless steel, nickel or nickel alloy is chemically stable at room temperature and is inexpensive and readily available.

The porous metal is composed of homogeneous or heterogeneous metal materials; furthermore, the outer surface of the porous metal and the pores thereof can be provided with a metal coating, and the metal coating can completely or partially cover the surface of the porous metal and the inner surface of the pores of the porous metal. Preferably gold or silver plated. The gold and the silver have relatively good conductivity, and can be used as the plating layer of the outer layer of the metal material, so that the surface conductivity of the electric contact can be improved, the contact resistance of the electric contact can be reduced, the electric conductivity of the electric contact can be improved, and the service life of the electric contact can be prolonged. The porous metal is free of or contains a metal coating; the metal coating covers the surface of the porous metal and the inner surfaces of the pores of the porous metal, either completely or partially.

The outer surface of the porous metal or the inner surface of the pores may be coated with an adhesion promoter, a coupling agent or a primer having an average thickness of not more than 1 μm to increase the adhesive strength between the porous metal and the polymer material. The adhesion promoter, coupling agent or primer applied must not be too thick, the average thickness of the coating must not exceed 1 μm, or else the contact resistance of the porous metal is increased significantly, thereby affecting the electrical conductivity of the electrical contact.

The porous metal can be various, the material selection range of the high polymer material in the invention is also very wide, the composite material of the high polymer material and the metal and the preparation process thereof can be respectively characterized in that: the high polymer material is thermosetting rubber, thermoplastic plastic, thermosetting plastic, radiation curing material, adhesive, printing ink or paint. As the thermosetting rubber, liquid or solid diene rubber, olefin liquid rubber, polyurethane rubber, acrylate rubber, polysulfide rubber, silicone rubber, fluororubber, fluorosilicone rubber, etc. can be used for preparing the conductive composite material with the porous metal. The liquid rubber is selected because it has a lower viscosity than solid raw rubber, and is convenient for compounding rubber and porous metal together by various methods. This is not to say that solid raw rubber cannot be used. The solid green rubber and the porous metal can be similarly compounded by a method such as laminating the solid green rubber and the porous metal (e.g., expanded metal), placing the laminated product in a mold cavity, pressing the laminated product with a press vulcanizer to cause the solid green rubber to penetrate into pores of the porous metal, and vulcanizing and molding the solid green rubber and the porous metal at a high temperature.

The subsequent use of these composites should be considered when selecting the rubber type. If these composites are used to make electrical contacts on rubber keys, it will be appreciated which rubber is used to make the rubber keys so that there is good adhesion between the electrical contacts and the key substrate during hot vulcanization molding or radiation cure molding. For example, electrical contacts made from composites made from liquid or solid nitrile rubber and sintered nickel wire mesh are suitable for making nitrile rubber keys, electrical contacts made from composites made from liquid or solid silicone rubber and stainless steel sheet mesh are suitable for making silicone rubber keys, electrical contacts made from composites made from liquid or solid fluororubber and sintered nickel fiber felt are suitable for making fluororubber keys.

The formulation of the polymeric material may contain various adjuvants such as pigments, fillers or conductive fillers. The present invention is different from the common polymer material recipe in that extractables must be added into the polymer material recipe. The purpose of adding the extractable matter into the formula of the high polymer material is not to enable the extractable matter to be remained in the high polymer material to play a certain role after the high polymer material is formed, but to drive the extractable matter out of the high polymer material by an extraction method after the high polymer material is formed, so that a high polymer matrix in the composite material of the high polymer material and the porous metal is shrunk, and the high polymer matrix in the pores of the porous metal in the composite material is collapsed.

Before being compounded with the porous metal, the content of the extractable matter in the high polymer material is 1-95 w%. These extractables are low molecular weight compounds, oligomers or uncrosslinked polymers that are compatible or partially compatible with the high molecular weight materials.

The polymeric material and the extractables contained therein need to be compatible or partially compatible so that the volume of the polymeric material shrinks as the extractables are extracted from the polymeric material, rather than forming pores in the polymeric material so that no or substantially no shrinkage occurs.

When the composite material of the polymer material and the metal is prepared by using the liquid silicone rubber or the solid silicone rubber, various substances such as silicone oil, liquid paraffin, solid paraffin, chlorinated paraffin, naphthalene, tetrahydronaphthalene, decahydronaphthalene, tetramethylbenzene, hexamethylbenzene, or high-boiling-point solvent oil may be added as extractables to the liquid silicone rubber or the solid silicone rubber, and after the silicone rubber and the metal are compounded and molded, the extractables are partially or completely extracted.

The methods of making the composite materials of the present invention are also versatile. The polymer material containing the extractable material and the porous metal can be combined together by the modes of superposition, transfer printing, screen printing, brush coating, roller brush coating, blade coating, spray coating, dip coating, curtain coating and pump coating, and then the composite material containing the polymer material containing the extractable material and the porous metal is prepared by the curing molding of a thermoplastic molding process, a thermosetting molding process or a radiation curing process, and then the composite material is soaked in a volatile solvent and pumpedBy extraction with steam or solvent vapour, or by supercritical CO₂The extraction method extracts part or all of the extractables in the obtained composite material, so that the volume of the high polymer material in the composite material is shrunk, and the shape or volume of the porous metal in the composite material is basically kept unchanged, so that the porous metal protrudes out of the surface of the composite material. The molding process depends on the type of the polymer material. The composite material may be die cut into small disks or other geometric shapes having a diameter of 1.0 to 10.0 before or after extraction.

Has the advantages that: the composite material described in the invention is punched into a small wafer with the diameter of 1.0-10.0mm, has good conductivity, the contact resistance can be less than 1 omega, and the small wafer can be used as an electric contact in a rubber key. The surface of the electric contact prepared by using the composite material is contracted and collapsed after the high polymer material is extracted, and the material of the porous metal protrudes out of the surface of the composite material, so that the electric contact has good dust resistance and oil stain resistance, and has good electric conduction capability when the temperature is increased. Although the thermal expansion coefficient of the polymer material is generally larger than that of the metal material, the thermal expansion of the polymer material caused by the larger thermal expansion coefficient of the polymer material can be offset due to the shrinkage and collapse of the polymer material in the composite material, so that the influence of the protrusion of the polymer material on the surface of the composite material on the contact conductivity can be prevented.

Drawings

FIG. 1 is a schematic view of the surface of a composite material made of rubber and expanded metal in the present invention, as the temperature is increased; wherein, 1-rubber, 2-metal plate net;

FIG. 2 is a schematic view of the present invention showing the shrinkage of rubber in porous metal pores by extraction; wherein, 3-nickel plate net, 4-rubber;

FIG. 3 is a schematic view of the extraction of rubber in porous metal pores to shrink in the present invention; wherein, 5-nickel plate net, 6-rubber;

FIG. 4 is a schematic view showing that the rubber in the porous metal pores does not protrude from the surface of the porous metal at elevated temperature, and the dotted lines indicate the position of the rubber surface in the porous metal pores before the temperature is elevated; wherein, the material comprises 7-nickel plate net and 8-rubber.

Detailed Description

The present invention will be further described with reference to the following specific examples.

Example 1

The formula A is as follows: 100 parts by weight of a rubber mixture of methyl vinyl silicone rubber containing fumed silica (SE 4705U available from Dow Corning Co., Ltd.), 50 parts by weight of dimethyl silicone oil (XiameterPMX-200 available from Dow Corning Co., Ltd., 1000cs), 1 parts by weight of vinyl tri-t-butylperoxysilane (VTPS) and 0.5 parts by weight of dicumyl peroxide (DCP).

And the formula B is as follows: SE 4705U 100, VTPS 1, DCP 0.5.

And (3) overlapping the mixed rubber sheets of the formula A and the formula B with a nickel plate net (the purity of nickel is not less than 99.5%) with the thickness of 0.25mm, the aperture of 0.5mm and the hole spacing of 0.25mm respectively, putting the nickel plate net and the nickel plate net into a mold cavity with a Teflon coating, pressing for 10 minutes at the temperature of 175 ℃, and vulcanizing and molding to prepare a sheet with the thickness of 0.25 mm. The sheet was die-cut into small disks with a diameter of 3.0 mm. The small disks prepared from formulation a and formulation B were extracted with ethanol as solvent for 3 hours using a soxhlet extractor. Then dried at 60 ℃ to a substantially constant weight.

The small wafer obtained by the formula B is used as an electric contact, and under the condition of temperature rise, the contact resistance between the electric contact and a matched PCB electric contact is increased from not more than 0.5 omega to more than 2 omega, and even is not conducted. Compared with the small wafer obtained by using the formula B, the small wafer obtained by using the formula A has the advantages that the surface of the small wafer is extracted to cause the shrinkage and collapse of rubber in the metal hole (as shown in figure 2), the small wafer is used as an electric contact, has good dust resistance and oil stain resistance, can overcome the defect that the resistance is increased or is not conducted at high temperature due to the large thermal expansion coefficient of silicon rubber, and has a good temperature application range. When the temperature is raised, the contact resistance is still below 0.5.

Example 2

One side of the nickel screen in the first example was coated with a Polyimide (PI) self-adhesive film with a thickness of 0.025mm, and then the rubber compound of the formula A and the nickel screen were compounded to form a composite sheet with a thickness of 0.8 mm. Removing PI self-adhesive film, and die cutting into small discs with diameter of 2.0-5.0 mm. Soaking in solvent gasoline to extract silicone oil from the small piece of silicone rubber, and shrinking the rubber in the holes of the nickel screen (FIG. 3).

These small disks serve as electrical contacts and also have good electrical conductivity at elevated ambient temperatures. This is because when the temperature is increased, for example, from 25 ℃ to 80 ℃, the rubber in the pores of the porous metal does not protrude from the surface of the porous metal even though the rubber has a low expansion coefficient (as shown in fig. 4).

Example 3

And a formula C: 100 parts of PVC (P ═ 500), 45 parts of ethylene-vinyl acetate-carbon monoxide copolymer (Elvaloy 741 made by DuPont), 2 parts of dioctyltin dilaurate, 3.5 parts of epoxidized soybean oil, 0.3 part of polyethylene wax, 3 parts of glyceryl monostearate, 65 parts of trioctyl trimellitate and 5 parts of polyvinyl butyral (molecular weight 20000). The polyvinyl butyral is added to improve the adhesion of PVC to metal.

According to the formula C, putting the materials into a high-speed mixer for mixing and stirring, controlling the time to be about 15 minutes and the temperature to be 110-120 ℃, allowing the PVC powder to absorb the plasticizer without stickiness, and putting the PVC powder into a low-speed cooling stirrer for stirring and cooling; when the temperature is cooled to about 25 ℃, the materials are discharged. The material is applied on a multi-layer stainless steel sintering net which is made by 5 layers of 80-mesh AISI 304 stainless steel plain net through the processes of special lamination pressing, vacuum sintering and the like, or is plasticated into a sheet with the thickness of 1.5mm by a double-roller mill at 160 ℃, the sheet is placed on the multi-layer stainless steel sintering net and is placed into a mold cavity with a Teflon coating at 175 ℃, and the sheet with the thickness of 1.5mm is manufactured by hot-pressing composite molding on a flat vulcanizing machine. The sheet or a small round sheet which is punched by the sheet and has the diameter of 2.5-10mm is extracted by a 120 # solvent gasoline soaking method or a Soxhlet extractor for 5-120 minutes, so that the low molecular substances such as trioctyl trimellitate and epoxidized soybean oil in the sheet are partially or almost completely extracted. The extraction time and other parameters can be determined according to the collapse degree of the resin in the required multilayer stainless steel sintering net. The composite material of the polyvinyl chloride-stainless steel sintering net prepared by the method has the advantages that the polyvinyl chloride shrinks towards the inner part of the material, and the stainless steel protrudes on the surface. The composite material can be used as a conductive material, a shielding material or an electric contact with good high-temperature electric conduction performance.

The composite material of the polymer material and the porous metal is prepared by an extraction method, which is beneficial to environmental protection because the extracted plasticizer can be recycled and is not discharged into the environment.

Example 4:

this example prepares a composite of a polymer material and a porous metal as in example 1, wherein the polymer material is based on formulation a in example 1, and the porous material used is a gold plating having a purity greater than 99.0% with an average thickness of 0.05-0.75 μm on the surface and on the interior surfaces of the pores in example 3. Gold plating can reduce the surface contact resistance of the composite material, and the contact resistance is kept at 0.3 omega.

Example 5:

the preparation method is the same as that of the example 1, a small round piece with the diameter of 2-10mm is prepared, and after the small round piece is subjected to an extraction process, gold with the diameter of 0.1 μm is plated by an electroless plating method. In this example, the composite material or electrical contact made in this example consumed less gold than in example 4, and the surface contact resistance of the composite material or electrical contact was substantially the same as or similar to the surface contact resistance of the composite material or electrical contact made in example 1.

The present invention is not limited to the above-mentioned preferred embodiments, and any other products in various forms can be obtained by anyone in the light of the present invention, but any changes in the shape or structure thereof, which have the same or similar technical solutions as those of the present application, fall within the protection scope of the present invention.

Claims

1. A composite material of a high polymer material and a metal, characterized in that: the composite material is a sheet, a bar, a pipe or a profiled bar which is compounded by a high polymer material and porous metal; carrying out composite forming on a high polymer material containing an extractable substance and a porous metal in a thermosetting forming, hot vulcanization forming, radiation curing forming or thermoplastic forming mode to prepare a composite material containing the high polymer material containing the extractable substance and the porous metal, wherein the high polymer material and the metal are simultaneously exposed on at least one surface of the composite material, holes or pores in the porous metal are partially or completely filled with the high polymer material containing the extractable substance, and then extracting the extractable substance in a forming object by using a solvent to ensure that the volume of the high polymer material in the forming object is shrunk and the surface of the high polymer material in the forming object is collapsed, thereby preparing the composite material of the high polymer material and the porous metal with the porous metal protruding from at least one surface;

the porous metal is a metal sheet, a sintered metal mesh, a metal expanded metal, a metal foam or a metal fiber sintered felt with a plurality of uniformly or randomly distributed holes, or a layered composite of the metal sheet, the sintered metal mesh, the metal expanded metal, the metal foam and the metal fiber sintered felt; the holes are independent or mutually communicated; at least part of the holes are exposed out of the surface of the porous metal; the diameter of the hole is 1 mu m-3.0 mm;

the metal lath is a metal lath with uniformly distributed holes, the hole diameter of 50 mu m-1.0mm, the hole distance of 25 mu m-1.0mm and the hole pattern of a circle, a regular polygon or other geometrical shapes;

the porous metal is composed of aluminum, iron, cobalt, nickel, copper, zinc, tin, manganese, tungsten, silver, gold or alloy thereof; the porous metal is made of homogeneous or heterogeneous metal materials; the porous metal is free of or contains a metal coating; the metal coating is completely or partially covered on the outer surface of the porous metal and the inner surface of the porous metal hole;

the outer surface of the porous metal or the inner surface of the hole is coated with a layer of adhesion promoter, coupling agent or primer with the average thickness of not more than 1 mu m;

the high polymer material is thermosetting rubber, thermoplastic plastic, thermosetting plastic, radiation curing material, adhesive, printing ink or paint;

the extractable substance is a low molecular compound, oligomer or uncrosslinked polymer which is compatible or partially compatible with the high molecular material, or a mixture thereof; the content of the extractable substance in the high polymer material before being compounded with the porous metal is 1-95 percent;

the preparation method of the composite material comprises the following steps: combining the polymer material containing the extractable substance and the porous metal by one of the modes of superposition, transfer printing, silk-screen printing, brush coating, knife coating, spray coating, dip coating, curtain coating and pump coating, pressing, or curing and molding by a thermoplastic molding process, a thermosetting molding process or a radiation curing process to prepare the molded product containing the polymer material containing the extractable substance and the porous metal, and then carrying out dipping extraction by a volatile solvent, extraction by water vapor or solvent vapor, or supercritical CO extraction₂Extracting the extractable substances in the obtained molded product partially or completely by an extraction method, so that the volume of the high polymer material in the composite material is shrunk, and the porous metal protrudes out of the surface of the composite material; before or after extraction, the composite is die cut into small disks or other geometric shapes having a diameter of 1.0-10.0 mm.