CN115820177A - Graphite-based conductive adhesive, preparation method and application thereof - Google Patents

Abstract

The embodiment of the application discloses a graphite-based conductive adhesive, a preparation method and application thereof, wherein the graphite-based conductive adhesive comprises a resin adhesive, graphite, expanded graphite and a mixed conductive filler, wherein the expanded graphite and the graphite form the mixed conductive filler; the addition amount of the graphite accounts for not less than 12.5% of the mass fraction of the graphite-based conductive adhesive, and the addition amount of the expanded graphite accounts for 0.5-3.5% of the mass fraction of the mixed filler. According to the technical scheme, the conductivity of the graphite-based conductive adhesive can be greatly improved only by adding a very small amount of expanded graphite, and the manufacturing cost of each kilogram of the graphite-based conductive adhesive is only increased by about 2 yuan.

Description

Graphite-based conductive adhesive, preparation method and application thereof

Technical Field

The invention relates to the technical field of adhesives, in particular to a graphite-based conductive adhesive and a preparation method thereof; the invention also relates to the application of the graphite-based conductive adhesive, in particular to an electric heating plywood prepared by utilizing the conductive adhesive and a preparation method of the electric heating plywood.

Background

The wood-based electric heating functional material is a novel electric heating material which is prepared by compounding wood materials serving as a matrix with conductive substances such as carbon-based materials, metal materials and the like. The prior art is recorded that conductive plywood is prepared by coating conductive adhesive on the surface of a wood veneer, and conductive fiberboard or conductive shaving board is prepared by mixing wood fiber, wood shavings and conductive adhesive. In the technical scheme, the comprehensive properties of the conductive adhesive, such as manufacturing cost, dispersibility and adhesive layer resistivity, have a decisive influence on the properties of the prepared conductive artificial board.

In the prior art, there are many records about the formula and preparation method of the conductive adhesive, and the addition of the conductive metal powder is the most traditional technical scheme. For example, in chinese patent database, patent application publication No. CN103881609a entitled "method for preparing conductive adhesive and conductive adhesive obtained by the method" describes a technical solution for preparing conductive adhesive by adding conductive metal powder, such as silver powder, to epoxy resin adhesive and adding fumed silica as an adhesion matrix of the conductive metal powder to promote diffusion.

However, due to the reasons that the dispersion effect of the conductive metal powder in the adhesive is not good, the use cost of the conductive metal powder is relatively high, and the conductivity of the adhesive prepared by using the conductive metal powder as a heating base material is not good, the prior art further provides a product of the carbon-based heating adhesive and a preparation method thereof. For example, in the chinese patent database, the invention patent application with the publication number CN108753213A and the name of "a conductive adhesive and its preparation method and application method" and the invention patent application with the publication number CN114736631a and the name of "a preparation method of a conductive adhesive" are disclosed. The former describes a technical scheme of adding a single-walled carbon nanotube, a conductive filler and the like into an acrylate resin adhesive to prepare the conductive adhesive, wherein the conductive filler is one or more of nickel powder, silver nanowires, copper powder and aluminum powder. The latter describes a technical scheme of adding a multi-wall carbon nanotube solution and a graphene solution into an adhesive dissolved in an organic solvent to prepare a conductive adhesive layer.

In addition to single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, carbon fibers, and nickel-plated expanded graphite are also two of the more common carbon-based conductive materials. The invention patent application with the publication number of CN111621253A and the name of 'a graphite-based high-strength heat-conducting epoxy resin adhesive and a preparation method thereof' describes a technical scheme of adding modified graphite, composite glass fiber and the like into the epoxy resin adhesive to prepare the conductive adhesive, wherein the modified graphite is a graphene nanosheet of the graphite prepared by a stripping method. The invention patent application with the publication number of CN107312484A and the name of 'an epoxy resin type conductive adhesive and a preparation method thereof' describes a technical scheme for preparing the conductive adhesive by adding conductive particles and the like into aliphatic epoxy resin, wherein the conductive particles are modified carbon fiber materials, and specifically, the conductive adhesive is prepared by fully mixing carbon fibers and aniline monomers, adding a dodecyl benzene sulfonic acid solution into the mixed solution to obtain a mixed solution, dropwise adding a mixture of ammonium persulfate and dodecyl benzene sulfonic acid into the mixed solution, and finally filtering, washing, drying and crushing a product obtained by reaction. The invention patent application with the publication number of CN105694797A and the name of 'a preparation method of a composite conductive adhesive' describes a formula of 45 parts of an adhesive matrix, 15 parts of nickel-plated activated expanded graphite, 15 parts of a curing agent and 2 parts of auxiliary materials, and the prepared conductive adhesive can be used for bonding electrode plates and magnet crystals.

The carbon-based heating adhesive has better conductivity than a metal-based conductive adhesive, but single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, carbon fibers and expanded graphite have the defects of high price and poor dispersibility, the expanded graphite needs chemical nickel plating for pre-activation treatment, the mass fraction of the activated expanded graphite reaches 23%, and the use cost of the adhesive is greatly improved.

On the other hand, the artificial board is not a high value-added product, and the price of the adhesive in the main raw materials (wood materials and adhesives) determines the price of the finished artificial board. One or more of the single-walled carbon nanotubes, the multi-walled carbon nanotubes, the graphene and the carbon fibers are mixed to be used as the conductive adhesive of the conductive matrix, and due to poor dispersibility, a relatively large amount of matrix is often required to be used, so that the price of the conductive adhesive is increased, and further the price of the finished conductive artificial board greatly exceeds the expected price of the artificial board product in the market. Therefore, the conductive artificial board prepared by the method is not promoted all the time.

Based on the consideration of cost factors, the technical scheme of preparing the artificial board by using the adhesive added with the graphite particles to bond the wood material is more practical. For example, patent application publication No. CN1994696 entitled "method for manufacturing plywood with electromagnetic shielding function" describes a technical scheme of preparing conductive plywood by mixing graphite powder with urea-formaldehyde resin or phenolic resin adhesive to obtain conductive adhesive and bonding veneers with the conductive adhesive. However, the main technical purpose of the patent application is to provide the plywood with the electromagnetic wave shielding function, and if considering the conductivity, it is known that the graphite powder has low price, relatively low conductivity efficiency and relatively poor conductivity.

In summary, a conductive adhesive with relatively good conductivity and relatively low price is lacked in the prior art.

Disclosure of Invention

The invention aims to overcome the technical problems, and provides a graphite-based conductive adhesive, and a preparation method and application thereof.

In order to achieve the first technical object, a first embodiment of the present invention provides a graphite-based conductive adhesive, which comprises a resin adhesive, graphite, and expanded graphite, wherein the expanded graphite and the graphite form a mixed conductive filler; the addition amount of the graphite accounts for not less than 12.5% of the mass fraction of the graphite-based conductive adhesive, and the addition amount of the expanded graphite accounts for 0.5-3.5% of the mass fraction of the mixed filler.

Preferably, the addition amount of the graphite accounts for 13-15% of the mass fraction of the graphite-based conductive adhesive, and the addition amount of the expanded graphite accounts for 1-2% of the mass fraction of the mixed conductive filler.

Preferably, the graphite is in the form of particles having a particle size of 300 to 340 mesh.

Preferably, the expanded graphite is in the form of particles having a particle size of 75 to 85 mesh.

Preferably, the resin adhesive is a urea-formaldehyde resin adhesive or a phenol-formaldehyde resin adhesive.

In order to achieve the second technical object, a second embodiment of the present invention provides a method for preparing the above graphite-based conductive adhesive, wherein a mixture of the graphite and the expanded graphite is added to the resin adhesive under normal temperature conditions, and then mechanically stirred at a rotation speed of 350 to 450r/min for 8 to 12min.

In order to achieve the third technical object, a third embodiment of the present invention provides a conductive plywood using the graphite-based conductive adhesive, including multiple laminated veneers, where two veneers are bonded together by glue layers, at least one glue layer is a conductive glue layer, the conductive glue layer is formed by the graphite-based conductive adhesive, and conductive tapes are laid at two ends of the conductive glue layer.

Preferably, the application amount of the graphite-based conductive adhesive is 110-130 g per square meter.

Preferably, at least one of the glue layers is a conductive glue layer, and the rest glue layers are common glue layers; the common adhesive layer is formed by coating a non-conductive adhesive in a coating weight of 120-150 g/square meter.

In order to achieve the fourth technical object, a fourth embodiment of the present invention provides a method for manufacturing the above-mentioned conductive plywood, characterized in that,

firstly, sizing one side of at least one layer of first veneer, and coating the graphite-based conductive adhesive to form a conductive adhesive layer on the surface of the first veneer; then, laying the conductive adhesive tapes at two ends of the conductive adhesive layer;

secondly, gluing a single surface of a second single plate, coating a non-conductive adhesive to form a common adhesive layer on the surface of the second single plate, and then mutually laminating and assembling the first single plate and the second single plate to obtain the conductive assembly material;

and finally, carrying out hot pressing on the conductive assembly material to obtain the conductive plywood.

In summary, compared with the prior art, the invention has the beneficial effects that:

1. according to the technical scheme, the conductivity of the graphite-based conductive adhesive can be greatly improved only by adding a very small amount of expanded graphite, and the manufacturing cost of each kilogram of the graphite-based conductive adhesive is only increased by about 2 yuan.

2. Another beneficial effect of the technical scheme of the application is the reduction of the glue application amount. The existence of proper amount of graphite particles can fill the bonding interface of the veneer so as to reduce the roughness of the interface, and further, the amount of the graphite-based conductive adhesive for filling and leveling the bonding interface is correspondingly reduced, so that the gluing amount of the graphite-based conductive adhesive is reduced compared with that of the common plywood. Although the glue application amount of the graphite-based conductive adhesive is reduced, the bonding strength of the conductive plywood is not affected, and the overall rigidity of the conductive plywood is improved. And due to the reduction of the glue application amount, the use cost of the adhesive in the technical scheme can be further reduced.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without inventive exercise.

Fig. 1 is a schematic structural view of a three-layer conductive plywood in embodiment 1 of the present application.

Fig. 2a is a schematic view of the conductive network of the graphite single-component conductive adhesive layer.

Fig. 2b is a schematic view of the conductive network of the graphite-based conductive adhesive of example 1 of the present application.

Fig. 3 is a schematic structural view of a five-layer conductive plywood (single-layer conductive adhesive layer) according to example 1 of the present application.

Fig. 4 is a schematic structural view of a five-layer conductive plywood (double-layer conductive adhesive layer) in example 1 of the present application.

Fig. 5a is an SEM image of the conductive glue layer of the graphite single component conductive glue layer.

Fig. 5b is an SEM image of the conductive adhesive layer of example 5 of the present application.

Fig. 5c is an SEM image of the conductive adhesive layer of example 7 of the present application.

Fig. 5d is an SEM image of the conductive adhesive layer of example 9 of the present application.

Fig. 6a shows the plate surface temperature infrared distribution of the three-layer conductive plywood prepared by the graphite single-component conductive adhesive.

Fig. 6b is a panel temperature infrared profile of the three-layer conductive plywood of example 5 of the present application.

Fig. 6c is a panel temperature infrared profile of the three-layer conductive plywood of example 7 of the present application.

Fig. 6d is a panel temperature infrared profile of a three-layer conductive plywood of example 9 of the present application.

In the figure: 100. the structure comprises a first single plate, 200, a second single plate, a conductive adhesive layer, b and a common adhesive layer.

Detailed Description

In order to make those skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The application discloses a graphite-based conductive adhesive, which comprises a resin adhesive, graphite and expanded graphite, wherein the graphite accounts for not less than 12.5% of the mass fraction of the graphite-based conductive adhesive, and the addition amount of the expanded graphite accounts for 0.5-3.5% of the mass fraction of a mixed filler.

Graphite, expanded graphite, is a common choice for the conductive matrix of the conductive adhesive. Graphite is a traditional cheap carbon-based material and has wide sources, but the graphite has relatively low conductive efficiency and relatively poor conductive performance. The expanded graphite is obtained by intercalating, washing, drying and high-temperature expanding natural graphite flakes, is composed of a large number of nano graphite micro-sheets and has excellent electric (thermal) conductivity, and is expensive, so that the expanded graphite is commonly used for manufacturing molded products (such as the technical scheme disclosed in the invention patent with the publication number of CN 104245304B), heat-conducting pressure-sensitive adhesives (such as the technical scheme disclosed in the invention patent application with the publication number of CN 102741372A) and other heat-conducting products with relatively high added values. Those skilled in the art have also tried to add a mixed conductive filler of graphite and expanded graphite to some adhesives, and the expanded graphite is intended to replace a portion of the graphite to obtain a graphite-based conductive adhesive having relatively high conductivity and relatively low cost. The Chinese patent with publication number CN109148047B and name of 'a resistance value debugging method for coating carbon on the surface of polystyrene foam ball' describes a technical scheme shared by graphite and expanded graphite, and the coating of the technical scheme consists of 25-40% of acetylene carbon black, 3-7% of superconducting carbon black, 6-18% of expanded graphite and 6-18% of nano graphite, and the balance is other non-conductive additives. The use of expanded graphite and nano-graphite in the ratio of 1:1 is given.

In light of this technology, one first adds expanded graphite and graphite to the wood adhesive in a ratio of 1:1. The results show that (1) the adhesive loses fluidity after the mass fraction of the expanded graphite exceeds 3%; (2) Although the addition of 3% by mass of graphite and 3% by mass of expanded graphite to the wood adhesive can successfully complete coating and form an effective conductive adhesive layer, the plywood bonded by the adhesive hardly forms current after being electrified, and the plywood does not have the phenomenon of temperature rise.

Under the guidance of a general thinking mode, people increase the mass fraction of graphite to 15%, and reduce the addition amount of the expanded graphite to 2.5% in order to form a continuous glue line; meanwhile, the carpentry adhesive with only 15% graphite added is taken as a reference. The results show that the plywood bonded by the wood adhesive with only 15% graphite added can form current after 12V stable voltage is connected, and the surface temperature of the plywood can reach 25 ℃ after being electrified for 30 minutes. But the wood-bound plywood with 15% graphite and 2.5% expanded graphite added was able to develop current, but the plywood surface temperature reached only 22 ℃ after 30 minutes of energisation. The experimental result obviously shows that the technical scheme of replacing part of the nano-graphite by the original expanded graphite cannot achieve the effects of reducing the cost and improving the conductivity, and the addition of the original expanded graphite influences the conductivity of the nano-graphite.

The previous researches and experiments default that the combined action of the expanded graphite and the graphite is only reflected in the superposition of two different conduction modes, namely that the porous structure of the expanded graphite can be inserted into a two-dimensional conductive network formed by the graphite to form a three-dimensional communicated three-dimensional conductive network. It is clear that the results of the experiments were not developed according to the above premises. Finally, it is concluded that when the two-dimensional conductive network formed by graphite overlaps the three-dimensional conductive network formed by expanded graphite, there is some mutual interference between the two, so that the conductivity of the conductive adhesive added in the adhesive is lower than that of the conductive adhesive added with graphite alone, and the addition of expanded graphite in graphite not only increases the cost, but also reduces the conductivity.

In the technology against this application, the inventor overcomes the above technical prejudice and conventional thinking inertia, and creatively discovers that: when the two conditions that (1) the number of the graphite conductive particles reaches a threshold value and (2) the number of the expanded graphite conductive particles just can be communicated with a plane conductive network are met, the performance of the graphite or graphite-based conductive adhesive can be greatly improved by the addition of the extremely small expanded graphite.

Specifically, the number of the graphite conductive particles in the conductive adhesive reaches a threshold value, that is, the mass fraction of the graphite conductive particles in the conductive adhesive is 12.5% (although the number is slightly different according to the type of the adhesive, the number is approximately 12.5% or slightly higher), the graphite sheets are mutually connected, and a two-dimensional planar conductive network which is stably connected can be formed between carbon atoms in the graphite crystal. At this time, if the proper amount of expanded graphite conductive particles are also present in the conductive adhesive, that is, the amount of the expanded graphite conductive particles is just capable of communicating the planar conductive network formed by the graphite conductive particles in the vertical direction, the graphite micro-sheets of the expanded graphite continuously extend towards the space on the basis of the sheet layer of the graphite, and communicate two adjacent planar conductive networks formed by the graphite, so as to gradually form a three-dimensional conductive network. The inventors have creatively found that the "amount of graphite" is appropriate and the "amount of graphite" is an amount that can connect the planar conductive network in the vertical direction, which means that the amount of the expanded graphite added is 0.5 to 3.5% by mass of the mixed conductive filler, in other words, the ratio of the graphite to the expanded graphite added in the mixed conductive filler is (99.5. In this case, the main planar network structure of the three-dimensional conductive network is formed by carbon atoms in graphite crystals, the quantity of expanded graphite is very small and is not enough to independently form the three-dimensional conductive network, but the graphite micro-sheets therein serve as bridges to connect two adjacent planar conductive network structures formed by graphite, and finally form the three-dimensional conductive network which takes the planar conductive network structure formed by graphite as a plane and is connected by the expanded graphite. Compared with the prior art, the method is essentially different from the prior research, the technical scheme of the application is based on graphite, and the three-dimensional conductive network is formed by bridging the expanded graphite, but the three-dimensional conductive network formed by the expanded graphite is not added into the planar conductive network formed by the graphite. Compared with the graphite conductive adhesive, the addition of the expanded graphite accounting for 0.5-3.5% of the mass fraction of the mixed conductive filler (the mass fraction of the expanded graphite accounting for the graphite-based conductive adhesive is obtained by converting the actual addition amount of the graphite) hardly increases the manufacturing cost of the graphite-based conductive adhesive, but the conductive performance is improved in a leap manner. Obviously, the creativity of the embodiment is that on the premise that the original expanded graphite with the limited addition amount of 3% cannot play a role in electric conduction, the wood adhesive can be endowed with relatively good electric conduction performance after more than 12.5% of graphite is mixed with a very small amount of expanded graphite.

On the other hand, according to the creative discovery of the inventor, the failure reasons of past research and experiments can be understood reversely. (1) When the addition amount of the graphite is too low, the quantity of the graphite conductive particles is not enough to form a two-dimensional plane conductive network; (2) When the addition amount of the graphite exceeds a threshold value but the addition amount of the expanded graphite is too high, the graphite is used for communicating redundant expanded graphite outside the planar conductive network with the adhesive layer to form a new interface, the integrity of the adhesive layer is damaged, the bonding surface between two types of conductive particles is reduced, instead, an efficient three-dimensional conductive network passage cannot be constructed, and the heating power of a heating element (a graphite-based conductive adhesive layer) is reduced.

The technical solution of the present application is further illustrated by some examples with more detailed data.

Example 1

A graphite-base conductive adhesive is prepared from resin adhesive, graphite and expanded graphite. The resin adhesive is a commercially available urea-formaldehyde resin adhesive. The graphite is powdery, the particle size is 300-340 meshes, the graphite particles in the particle size range can be used without further screening, the adding amount of the graphite particles and the expanded graphite particles accounts for 13% of the mass fraction of the graphite-based conductive adhesive, the adding amount ratio of the graphite particles to the expanded graphite particles is 99.

Take 1000g of the graphite-based conductive adhesive of this example as an example. Firstly, weighing 128.7g of graphite particles and 1.3g of expanded graphite particles, mixing to form the graphite/expanded graphite conductive filler, and weighing 870.0g of the urea-formaldehyde resin adhesive according to the proportion. And then, adding the graphite/expanded graphite conductive filler into a urea-formaldehyde resin adhesive at normal temperature, and mechanically stirring at a rotating speed of 400r/min for 10min to obtain the graphite-based conductive adhesive of the embodiment. The stirring speed is in the range of 350-450 r/min, and the stirring time is in the range of 8-12 min, and those skilled in the art can know that the stirring time should be properly reduced when a higher stirring speed is selected, and the stirring time should be properly increased when the higher stirring speed is selected.

Take the preparation of three-layer conductive plywood as an example. Firstly, taking 3 poplar veneers with the specification of 300mm multiplied by 2mm, wherein 1 poplar veneer is marked as a first veneer 100, the other 2 poplar veneers are marked as second veneers 200, coating a graphite-based conductive adhesive on the surface of the first veneer 100, and forming a conductive adhesive layer a with the coating amount of 125g per square meter; the surface of 1 of the second veneers 200 is coated with the non-conductive adhesive, the coating weight is 145 g/square meter to form a common adhesive layer b, and the urea-formaldehyde resin adhesive which is the same as the basic adhesive of the graphite-based conductive adhesive is selected in the embodiment. And then, laying conductive adhesive tapes at two ends of the conductive adhesive layer a. And finally, sequentially laminating a second veneer 200,100,200, a first veneer and a second veneer from top to bottom, and carrying out hot pressing for 6min under the process conditions of 120 ℃ and 1.25MPa to obtain the three-layer conductive plywood of the embodiment. Referring to fig. 1, the three-layer conductive plywood of the embodiment includes three laminated veneers 200,100,200, the three veneers are bonded to each other through glue layers, one glue layer is a conductive glue layer a, the conductive glue layer a is formed by a graphite-based conductive adhesive, and conductive tapes are laid at two ends of the conductive glue layer a.

Referring to fig. 2a, in the conductive adhesive layer formed by the graphite-based conductive adhesive of this embodiment, the number of graphite conductive particles in the graphite-based conductive adhesive reaches a threshold value, the graphite sheets are mutually connected, a two-dimensional planar conductive network which is stably connected can be formed between carbon atoms in the graphite crystal, and gaps still exist between the adjacent graphite sheets. Referring to fig. 2b, after the expanded graphite conductive particles are added according to a mass ratio of 99.

According to the gluing theory, the strength of the glued interface of the plywood is related to the degree of wetting of the adhesive on the surface of the wood. Because the surface of the wood veneer is rough, after the glue is applied to the common glue layer, part of the adhesive permeates into the wood to fill uneven grooves, and then the glue is applied, so that the needed glue application amount is larger. And a large amount of micron-sized graphite particles exist in the conductive adhesive layer, and can fill the grooves with uneven surfaces of the veneers during hot pressing, so that further adhesive bonding is generated, and the adhesive applying amount can be saved. In the prior art, it is generally considered that the addition of graphite components influences the bonding strength of the adhesive. This is because, in the prior art, a relatively large amount of graphite particles should be added to achieve the required thermal conductivity, and the existence of a large amount of graphite particles affects the continuity of the adhesive layer, and in turn affects the adhesion performance of the conductive adhesive. In the embodiment, only a few graphite particles and expanded graphite particles are needed to achieve the required electrical conductivity, the graphite particles and the expanded graphite particles are enough to fill the grooves of the veneer gluing interface in advance, but the continuity and the film forming performance of the adhesive are not affected, and the electrical conductivity can be improved while the gluing performance required by the standard regulation and the use can be met with relatively small glue application amount. The adhesive cost, which is slightly increased by the addition of the expanded graphite, can be substantially offset due to the reduction in the amount of application.

Another unexpected technical effect is the increase in material rigidity of the electrically conductive plywood. The inventors believe that this is due to the increased overall rigidity of the conductive plywood as a result of the graphite filling effect. The data from the above experiment are shown in the modulus of elasticity in Table 1.

Take the preparation of five-layer conductive plywood as an example. Firstly, taking 5 poplar veneers with the specification of 300mm multiplied by 2mm, wherein 1 poplar veneer is marked as a first veneer 100, and the other 4 poplar veneers are marked as second veneers 200, coating a graphite-based conductive adhesive on the surface of the first veneer 100, wherein the coating amount is 125 g/square meter to form a conductive adhesive layer a; the surfaces of 3 second veneers 200 are coated with the non-conductive adhesive, and the coating weight is 145 g/square meter to form a common adhesive layer b. And then, laying conductive adhesive tapes at two ends of the conductive adhesive layer a. And finally, sequentially laminating the second veneers 200, the first veneers 100 and the 3 glued second veneers 200 from top to bottom, and carrying out hot pressing for 6min at the temperature of 120 ℃ and under the process condition of 1.30MPa to obtain the five-layer conductive plywood. Referring to fig. 3, the five-layer conductive plywood of the embodiment includes five-layer laminated single boards 200,100,200,200,200, the single boards are bonded to each other through glue layers, one glue layer is a conductive glue layer a, the conductive glue layer a is formed by a graphite-based conductive adhesive, and conductive tapes are laid at two ends of the conductive glue layer a.

Take the preparation of five-layer conductive plywood as an example. Firstly, taking five poplar veneers, wherein 2 poplar veneers are marked as first veneers 100, the other 3 poplar veneers are marked as second veneers 200, and coating graphite-based conductive adhesive on the surfaces of the 2 poplar veneers 100, wherein the coating weight is 125 g/square meter to form a conductive adhesive layer a; the surfaces of 2 second veneers 200 are coated with the non-conductive adhesive, and the coating weight is 145 g/square meter to form a common adhesive layer b. And then, laying conductive adhesive tapes at two ends of the conductive adhesive layer a. And finally, sequentially laminating the second veneer 200 without glue application, the first veneer 100, the second veneer 200 with glue application, the first veneer 100 and the second veneer 200 with glue application from top to bottom, and carrying out hot pressing for 6min under the process conditions of 120 ℃ and 1.30MPa to obtain the five-layer conductive plywood of the embodiment. Referring to fig. 4, the five-layer conductive plywood of the embodiment includes five stacked veneers 200,100,200,100,200, the veneers are bonded to each other through glue layers, two glue layers are conductive glue layers a, the conductive glue layers a are formed by graphite-based conductive adhesives, and conductive tapes are laid at two ends of the two conductive glue layers a.

Example 2

Example 2 differs from example 1 in that, among 1000g of the graphite-based conductive adhesive, 870.0g of urea resin adhesive, 127.4g of graphite particles, 2.6g of expanded graphite particles were included, in other words, the addition amount ratio of graphite particles to expanded graphite particles was 98.

The three-layer conductive adhesive is prepared according to the method of example 1, and the graphite-based conductive adhesive prepared according to the formula of this example is coated on the surface of the first single board 100, wherein the coating weight is 120 g/square meter.

Example 3

Example 3 differs from example 1 in that 870.0g of urea formaldehyde resin adhesive, 126.1g of graphite particles, 3.9g of expanded graphite particles were included in 1000g of graphite-based conductive adhesive, in other words, the addition amount ratio of graphite particles to expanded graphite particles was 97.

The three-layer conductive adhesive is prepared according to the method of example 1, and the graphite-based conductive adhesive prepared according to the formula of this example is coated on the surface of the first single board 100, wherein the coating weight is 120 g/square meter.

The material properties of each of the conductive plywood of examples 1 to 3 are shown in table 1. And testing the surface temperature change condition of each conductive plywood by using a TP720 temperature polling instrument, selecting 3 different conductive plywood, selecting 5 temperature measuring points on each conductive plywood, respectively arranging thermocouples, applying 12V voltage, electrifying for 30min, recording the surface temperature of the conductive plywood, and averaging the results. And (3) measuring the heat conductivity of the conductive adhesive layer by adopting a TC3000E heat conductivity tester, wherein the diameter of the sample is 50mm, the thickness of the sample is 5mm, sampling and measuring are carried out for three times, and the results are averaged. A BY302X2/2 universal experimental press is adopted to test the bonding strength, static bending strength and elastic modulus of the conductive plywood BY referring to GB/T17657-2013 physicochemical property test method for artificial boards and veneered artificial boards. The control group 1 was a normal three-layer plywood prepared using a urea formaldehyde resin adhesive having the same coating weight of 125 g/square meter as the base adhesive of the graphite-based conductive adhesive. The conductive adhesive of the control group 2 uses a conductive adhesive with a single graphite component, wherein the resin adhesive is a urea-formaldehyde resin adhesive, and the mass fraction of graphite is 15%.

TABLE 1 Material Properties of each of the electrically conductive plywood sheets of examples 1 to 3

Example 4

Example 4 differs from example 1 in that 850.0g of urea-formaldehyde resin binder, 149.25g of graphite particles, 0.75g of expanded graphite particles are included in 1000g of graphite-based conductive adhesive, in other words, the ratio of the addition amount of graphite particles to expanded graphite particles is 99.5.

The three-layer conductive adhesive is prepared according to the method of example 1, and the graphite-based conductive adhesive prepared according to the formula of this example is coated on the surface of the first single board 100, wherein the coating weight is 120 g/square meter.

Example 5

Example 5 differs from example 4 in that 850.0g of urea resin binder, 148.5g of graphite particles, and 1.5g of expanded graphite particles were included in 1000g of the graphite-based conductive adhesive, in other words, the addition amount ratio of the graphite particles to the expanded graphite particles was 99.

Referring to fig. 5a, the sheets of graphite in the conductive adhesive layer are overlapped, but there still exist pores which cannot form a continuous flat interface. Referring to fig. 5b, when about 1wt% (relative to the mass fraction of the mixed conductive filler) of the expanded graphite is added, the expanded graphite having a high aspect ratio allows more dense bridging between the conductive particles, and the surface of the adhesive layer tends to be flat. In fig. 5b, the expanded graphite particles cannot be observed due to the small content.

Referring to fig. 6a and 6b, it is apparent that the addition of the expanded graphite improves the surface temperature uniformity while improving the heat generation performance of the conductive plywood.

Example 6

Example 6 differs from example 4 in that the 1000g of graphite-based conductive adhesive comprises 850.0g of urea formaldehyde resin adhesive, 147.75g of graphite particles, and 2.25g of expanded graphite particles, in other words, the ratio of the addition amount of the graphite particles to the addition amount of the expanded graphite particles is 98.5.

Example 7

Example 7 is different from example 1 in that 850.0g of urea resin binder, 147.0g of graphite particles, and 3.0g of expanded graphite particles were included in 1000g of the graphite-based conductive adhesive, in other words, the ratio of the addition amount of the graphite particles to the expanded graphite particles was 98.

Taking the preparation of a three-layer conductive plywood as an example, the difference between the example 7 and the example 1 is that the coating quantity of the graphite-based conductive adhesive on the surface of the first veneer 100 is 120g per square meter, and the coating quantity of the non-conductive adhesive on the surface of the second veneer 200 is 140g per square meter.

Referring to fig. 5c, when the addition amount of the expanded graphite reaches 2wt% (relative to the mass fraction of the mixed conductive filler), the expanded graphite particles can be obviously observed, at this time, the graphite micro-sheets continuously extend towards the space, a three-dimensional conductive network is gradually formed, the conductive efficiency formed by the conductive network is rapidly improved, and the heating rate of the conductive plywood is obviously accelerated.

Comparing fig. 6c with fig. 6b and 6d, the heating effect is most remarkable and the temperature distribution is most uniform when the amount of the expanded graphite added is 2wt% (relative to the mass fraction of the mixed conductive filler).

Taking the preparation of five-layer conductive plywood as an example, the difference between the example 7 and the example 1 is that the coating weight of the graphite-based conductive adhesive on the surface of the first veneer 100 is 120g per square meter, and the coating weight of the non-conductive adhesive on the surface of the second veneer 200 is 140g per square meter.

Taking the preparation of five-layer conductive plywood as an example, the difference between the example 7 and the example 1 is that the coating quantity of the graphite-based conductive adhesive on the surface of 2 first veneers 100 is 110g per square meter, and the coating quantity of the non-conductive adhesive on the surface of a second veneer 200 is 140g per square meter.

Example 8

Example 8 differs from example 4 in that 850.0g of urea resin binder, 146.25g of graphite particles, and 3.75g of expanded graphite particles were included in 1000g of the graphite-based conductive adhesive, in other words, the addition amount ratio of the graphite particles to the expanded graphite particles was 97.5.

Example 9

Example 9 differs from example 4 in that 850.0g of the urea resin adhesive, 145.5g of the graphite particles, and 4.5g of the expanded graphite particles were included in 1000g of the graphite-based conductive adhesive, in other words, the addition amount ratio of the graphite particles to the expanded graphite particles was 97.

Referring to fig. 5d, when the expanded graphite is increased to 3wt% (relative to the mass fraction of the mixed conductive filler), a large number of expanded graphite micro-platelets can be observed. And the phenomenon that the integrity of the conductive adhesive layer is damaged by too many conductive particles can be observed, at the moment, the joint surface between two types of conductive particles is reduced, but a high-efficiency network channel cannot be constructed, and the heating power of the conductive adhesive layer is reduced. However, the conductivity of the conductive adhesive layer is still better than that of the conductive adhesive layer with single component of graphite when the addition amount of the expanded graphite is 3wt% (relative to the mass fraction of the mixed conductive filler).

Comparing fig. 6d with fig. 6b and 6c, the uniformity of the temperature distribution at the addition amount of 3wt% (relative to the mass fraction of the mixed conductive filler) of the expanded graphite is inferior to the case of 2wt% (relative to the mass fraction of the mixed conductive filler) of the addition amount, but still superior to the case of 1wt% (relative to the mass fraction of the mixed conductive filler) of the addition amount. This is due to the difference in thermal conductivity of the electrothermal layer in a direction parallel to the electrothermal layer.

Example 10

Example 10 differs from example 4 in that the 1000g of graphite-based conductive adhesive comprises 850.0g of urea formaldehyde resin adhesive, 144.75g of graphite particles, 5.25g of expanded graphite particles, in other words, the ratio of the addition amount of the graphite particles to the expanded graphite particles is 96.5.

The material properties of each of the conductive plywood of examples 4 to 10 are shown in table 2.

TABLE 2 Material Properties of each of the electrically conductive plywood of examples 4 to 10

Example 11

Example 11 differs from example 1 in that 830.0g of the urea resin adhesive, 168.3g of the graphite particles, and 1.7g of the expanded graphite particles were included in 1000g of the graphite-based conductive adhesive, in other words, the addition amount ratio of the graphite particles to the expanded graphite particles was 99.

The three-layer conductive adhesive is prepared according to the method of example 1, the graphite-based conductive adhesive prepared according to the formula of this example is coated on the surface of the first veneer 100, the coating weight is 115 g/square meter, and the coating weight of the non-conductive adhesive on the surface of the second veneer 200 is 135 g/square meter.

Example 12

Example 12 is different from example 11 in that 830.0g of the urea resin binder, 166.6g of the graphite particles, and 3.4g of the expanded graphite particles were included in 1000g of the graphite-based conductive adhesive, in other words, the ratio of the addition amount of the graphite particles to the expanded graphite particles was 98.

Example 13

Example 13 differs from example 11 in that 830.0g of the urea resin adhesive, 164.9g of the graphite particles, and 5.1g of the expanded graphite particles were included in 1000g of the graphite-based conductive adhesive, in other words, the addition amount ratio of the graphite particles to the expanded graphite particles was 97.

The material properties of the three-layer conductive plywood of examples 11 to 13 are shown in table 3.

TABLE 3 Material Properties of each of the electrically conductive plywood of examples 11 to 13

Example 14

Example 14 differs from example 1 in that the resin adhesive is a phenol resin adhesive, and that the 1000g of graphite-based conductive adhesive includes 860.0g of phenol resin adhesive, 138.6g of graphite particles, and 1.4g of expanded graphite particles, in other words, the addition amount ratio of graphite particles to expanded graphite particles is 99.

The three-layer conductive adhesive is prepared according to the method of example 1, the graphite-based conductive adhesive prepared according to the formula of this example is coated on the surface of the first veneer 100, the coating weight is 110 g/square meter, and the coating weight of the non-conductive adhesive on the surface of the second veneer 200 is 130 g/square meter.

Example 15

Example 15 differs from example 14 in that 860.0g of phenolic resin binder, 137.2g of graphite particles, 2.8g of expanded graphite particles were included in 1000g of graphite-based conductive adhesive, in other words, the ratio of the addition amount of graphite particles to expanded graphite particles was 98.

The three-layer conductive adhesive is prepared according to the method of example 1, the graphite-based conductive adhesive prepared according to the formula of this example is coated on the surface of the first veneer 100, the coating weight is 120 g/square meter, and the coating weight of the non-conductive adhesive on the surface of the second veneer 200 is 140 g/square meter.

Example 16

Example 16 differs from example 14 in that 860.0g of phenolic resin binder, 135.8g of graphite particles, 4.2g of expanded graphite particles were included in 1000g of graphite-based conductive adhesive, in other words, the ratio of the addition amount of graphite particles to expanded graphite particles was 97.

The three-layer conductive adhesive is prepared according to the method of example 1, the graphite-based conductive adhesive prepared according to the formula of this example is coated on the surface of the first veneer 100, the coating weight is 130 g/square meter, and the coating weight of the non-conductive adhesive on the surface of the second veneer 200 is 140 g/square meter.

The material properties of the three-layer conductive plywood of examples 14 to 16 are shown in table 4.

TABLE 4 Material Properties of each of the electrically conductive plywood of examples 14 to 16

Example 17

Example 17 differs from example 1 in that the resin adhesive is a phenol resin adhesive, and that 840.0g of the phenol resin adhesive, 158.4g of graphite particles, and 1.6g of expanded graphite particles are included in 1000g of the graphite-based conductive adhesive, in other words, the addition amount ratio of the graphite particles to the expanded graphite particles is 99.

The three-layer conductive adhesive is prepared according to the method of example 1, the graphite-based conductive adhesive prepared according to the formula of this example is coated on the surface of the first veneer 100, the coating weight is 110 g/square meter, and the coating weight of the non-conductive adhesive on the surface of the second veneer 200 is 130 g/square meter.

Example 18

Example 18 differs from example 1 in that the resin adhesive is a phenol resin adhesive, and that 840.0g of the phenol resin adhesive, 156.8g of graphite particles, and 3.2g of expanded graphite are included in 1000g of the graphite-based conductive adhesive, in other words, the addition amount ratio of the graphite particles to the expanded graphite particles is 98.

The three-layer conductive adhesive is prepared according to the method of example 1, the graphite-based conductive adhesive prepared according to the formula of this example is coated on the surface of the first veneer 100, the coating weight is 120 g/square meter, and the coating weight of the non-conductive adhesive on the surface of the second veneer 200 is 140 g/square meter.

Example 19

Example 19 differs from example 1 in that the resin binder is a phenolic resin binder, and that 1000g of the graphite-based conductive binder comprises 840.0g of the phenolic resin binder, 155.2g of graphite particles, and 4.8g of expanded graphite, in other words, the ratio of the addition amount of the graphite particles to the addition amount of the expanded graphite particles is 97.495%.

The three-layer conductive adhesive is prepared according to the method of example 1, the graphite-based conductive adhesive prepared according to the formula of this example is coated on the surface of the first veneer 100, the coating weight is 130 g/square meter, and the coating weight of the non-conductive adhesive on the surface of the second veneer 200 is 140 g/square meter.

The material properties of the three-layer conductive plywood of examples 17 to 19 are shown in table 5. In order to better show the gluing performance of the three-layer conductive plywood of the examples 17 to 19, the plywood made by gluing the phenolic resin adhesive is changed in the control groups 3 and 4 in the table 5.

Table 5 material properties of each of the conductive plywood of examples 17 to 19

The foregoing description is intended to be illustrative and not limiting. Many embodiments and many applications other than the examples provided will be apparent to those of skill in the art upon reading the above description. The scope of the present teachings should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are hereby incorporated by reference for all purposes. The omission in the foregoing claims of any aspect of subject matter that is disclosed herein is not a disclaimer of such subject matter, nor is it to be construed that the applicant does not consider such subject matter to be part of the disclosed subject matter.

Claims (10)

1. A graphite-based conductive adhesive comprises a resin adhesive and graphite, and is characterized in that the conductive adhesive also comprises expanded graphite, wherein the expanded graphite and the graphite form a mixed conductive filler; the addition amount of the graphite accounts for not less than 12.5% of the mass fraction of the graphite-based conductive adhesive, and the addition amount of the expanded graphite accounts for 0.5-3.5% of the mass fraction of the mixed filler.

2. The graphite-based conductive adhesive as claimed in claim 1, wherein the graphite is added in an amount of 13-15% by mass of the graphite-based conductive adhesive, and the expanded graphite is added in an amount of 1-2% by mass of the mixed conductive filler.

3. The graphite-based conductive adhesive as claimed in claim 1, wherein the graphite is in the form of particles with a particle size of 300-340 mesh.

4. The graphite-based conductive adhesive according to claim 1 or 3, wherein the expanded graphite is in the form of particles having a particle size of 75 to 85 mesh.

5. The graphite-based conductive adhesive according to claim 1, wherein the resin adhesive is a urea formaldehyde resin adhesive or a phenol formaldehyde resin adhesive.

6. A method for preparing the graphite-based conductive adhesive according to claim 1, wherein a mixture of the graphite and the expanded graphite is added to the resin adhesive at normal temperature, and then mechanically stirred at a rotation speed of 350 to 450r/min for 8 to 12min.

7. An electrically conductive plywood using the graphite-based electrically conductive adhesive according to claim 1, comprising a plurality of laminated veneers bonded to each other by adhesive layers, wherein at least one of the adhesive layers is an electrically conductive adhesive layer, the electrically conductive adhesive layer is formed by the graphite-based electrically conductive adhesive, and electrically conductive adhesive tapes are laid on both ends of the electrically conductive adhesive layer.

8. The electrically conductive plywood of claim 7 wherein the graphite-based electrically conductive adhesive has a sizing amount of from 110 to 130 grams per square meter.

9. The electrically conductive plywood of claim 8 wherein at least one of said adhesive layers is a conductive adhesive layer and the remaining adhesive layers are conventional adhesive layers, said conventional adhesive layers being formed by applying a non-conductive adhesive in a coating weight of 120 to 150 grams per square meter.

10. A method for producing an electrically conductive plywood as claimed in claim 7,

firstly, sizing one side of at least one layer of first veneer, and coating the graphite-based conductive adhesive to form a conductive adhesive layer on the surface of the first veneer; then, laying the conductive adhesive tapes at two ends of the conductive adhesive layer;

secondly, gluing a single surface of a second single plate, coating a non-conductive adhesive to form a common adhesive layer on the surface of the second single plate, and then mutually laminating and assembling the first single plate and the second single plate to obtain the conductive assembly material;

and finally, carrying out hot pressing on the conductive assembly material to obtain the conductive plywood.

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