Expandable composite paper and preparation method thereof

Abstract

The invention belongs to the technical field of functional composite materials, and particularly relates to expandable composite paper and a preparation method thereof.The expandable composite paper comprises a middle layer, expandable bonding layers arranged on the two sides of the middle layer, transition bonding layers connected with the expandable bonding layers and outer isolation layers; and the transition bonding layer is an adhesive and is positioned between the expandable bonding layer and the isolating layer on the outermost side. The composite paper is mainly used for filling a narrow gap of an electrical insulation space and fixing an element in the narrow space. According to the composite paper disclosed by the invention, the outermost isolating layer is subjected to surface pretreatment and is coated with a low-viscosity adhesive material, so that a smooth structure is formed on the surface of the composite side of the isolating layer, the problem that layers are easily layered after an existing expandable composite material is expanded is solved, and meanwhile, better stiffness and tensile strength can be kept.

Description

TECHNICAL FIELD

[0001] The present application relates to an inflatable composite paper and a preparation method thereof, and belongs to the technical field of functional composite materials. BACKGROUND

[0002] In recent years, inflatable composite paper materials have gradually become a research hotspot due to their heat-expandable function. Heat-expandable composite paper has many application scenarios, such as being used in the insulation and fixation of new energy automobile motor stator slot insulation, reducing the subsequent varnish process, reducing production costs, and ensuring slot fullness; being used in the gap sealing of the building and fire fighting fields; being used in the flexible circuit board preparation process to reduce stress concentration and effectively release thermal stress; and being used in semiconductor packaging materials to play a role in heat conduction buffering.

[0003] Currently, there are mainly two kinds of inflatable composite paper products on the market. One is to directly coat inflatable slurry on the outside of a plastic film. This product has high surface roughness and a large friction coefficient, and it is difficult to insert into narrow gaps, and the inflatable microspheres are exposed to the outside, which can easily fall off after heat expansion, affecting the filling effect. The other is to build a "sandwich" structure, coat an inflatable adhesive on the outside of a plastic film, and then bond an isolation layer on the outside of the adhesive.

[0004] Currently, the isolation layer of the inflatable composite paper used in semiconductor packaging materials is generally aramid paper or polyester non-woven fabric. This product has a smooth surface and good stiffness, which can make up for the difficulty of insertion caused by the rough surface of the inflatable slurry coated on the outside of the plastic film, and the isolation layer on the outside can protect the expanded inflatable microspheres from falling off due to external friction. However, since the external isolation layer is aramid paper or non-woven fabric structure material, which is composed of fibers with small pores, and the main component of the inflatable adhesive is epoxy resin, the adhesive property of the epoxy resin is poor after further curing by heat expansion, the effective bonding area with the external isolation layer is reduced, and delamination problem is likely to occur, causing safety hazards.

[0005] In summary, the existing technology has obvious deficiencies. For filling narrow gaps in electrical insulation space and fixing components in narrow space, it is necessary to develop an inflatable composite paper that can enhance the bonding force between the isolation layer and the inflatable bonding layer, prevent delamination, and maintain the original structure after heat expansion of the inflatable bonding layer. SUMMARY

[0006] The present application provides an inflatable composite paper and a preparation method thereof to solve the delamination problem between the isolation layer and the inflatable adhesive layer of the existing products in the application process.

[0007] The technical scheme for solving the above technical problems is as follows: an inflatable composite paper, the composite paper comprising a middle layer, inflatable adhesive layers arranged on both sides of the middle layer, a transition adhesive layer connected with the inflatable adhesive layers, and an outer isolation layer. The transition adhesive layer is an adhesive between the inflatable adhesive layers and the outer isolation layer. The middle layer is a plastic film. The inflatable adhesive layer is provided by an inflatable adhesive, and the inflatable adhesive comprises heat-expandable microspheres and a thermosetting resin. The outer isolation layer is a non-woven material.

[0008] Further, the mass content of the heat-expandable microspheres is 10-30% of the total mass of the inflatable adhesive; preferably, the content is 15-20%.

[0009] Further, the thickness of the plastic film is 50-125 μm; the thickness of the inflatable adhesive layer before expansion is 2-10 μm; the thickness of the transition adhesive layer is 1-5 μm; and the thickness of the isolation layer is 25-85 μm.

[0010] Further, the thickness of the plastic film is 75 μm; the thickness of the inflatable adhesive layer before expansion is 3-5 μm; the thickness of the transition adhesive layer is 2-3 μm; and the thickness of the isolation layer is 50 μm.

[0011] Further, the heat-expandable microspheres are high-molecular polymers with an expansion temperature range of 100-160℃, a diameter of 2-20 μm before expansion, and an expansion ratio of 30-50 times.

[0012] Further, the thermosetting resin comprises a modified epoxy resin, a curing agent, and a thermoplastic component.

[0013] Further, the modified epoxy resin is at least one of bisphenol epoxy resin, fatty acid skeleton epoxy resin, glycidyl ether epoxy resin, phenolic modified epoxy resin, and cyclic epoxy resin; and the thermoplastic component is phenoxy resin.

[0014] Further, the transition adhesive layer is at least one of epoxy adhesive, acrylate adhesive, and polyurethane adhesive.

[0015] Further, the plastic film is any one of polyethylene terephthalate (PET) film, polyethylene naphthalate (PEN) film, polyimide (PI) film, polyphenylene sulfide (PPS) film, and polyether ether ketone (PEEK) film.

[0016] Further, the isolation layer is at least one of aramid paper, kraft paper, barley paper, and polyester non-woven fabric.

[0017] The application further discloses a preparation method of the inflatable composite paper. S1, two isolation layers are unwound, a transition adhesive layer is coated on the isolation layers, the isolation layers are dried, and the isolation layers are wound for standby; S2, a plastic film of an intermediate layer is unwound, inflatable adhesive is coated on two surfaces of the plastic film to form an inflatable adhesive layer, the inflatable adhesive layer is combined with the isolation layers treated in the step S1 at room temperature, and the inflatable composite paper is obtained after the inflatable adhesive layer is cured by winding.

[0018] Further, in the step S2, after the inflatable adhesive is coated on two surfaces of the intermediate layer, the inflatable adhesive is passed through an oven duct at 65-85 DEG C, and the inflatable adhesive stays in the oven for 30-70 seconds.

[0019] Further, in the step S2, the inflatable adhesive layer is combined with the treated isolation layers at room temperature, and the interval time is not more than 5 min.

[0020] Further, in the step (2), the combined pressure is 1-4 MPa.

[0021] The application has the following beneficial effects: (1) The inflatable composite paper disclosed by the application performs surface pretreatment on the outermost isolation layer, coats a low-viscosity adhesive material to form a transition adhesive layer, forms a smooth structure on one side of the isolation layer, and makes the adhesive of the inflatable adhesive layer more compatible with the smooth transition adhesive layer, so that the adhesive layer is more firmly combined.

[0022] (2) The preparation method of the inflatable composite paper solves the delamination phenomenon of the inflatable composite paper prepared by the previous method due to insufficient adhesion and fiber falling off after the inflatable composite paper is heated and expanded, and increases the stiffness, tensile strength and elongation of the inflatable composite paper through the mutual interaction between the layers, so that the mechanical properties of the composite paper are more beneficial, and the safety and stability of the motor as a whole are improved.

[0023] The inflatable composite paper disclosed by the application can be better adhered to the outermost isolation layer and the inflatable adhesive layer after the outermost isolation layer is pretreated and the surface of the outermost isolation layer is coated with a low-viscosity adhesive material to form a transition bonding layer, and the pores and gaps between the fibers on the surface of the non-woven structure material are filled through the transition bonding layer to form a smooth structure on the surface, increase the effective bonding area, and further make the outermost isolation layer and the inflatable adhesive layer adhere more closely. The inflatable adhesive layer can better adhere to the inflatable adhesive layer and the outer isolation layer after being heated and expanded, preventing the delamination phenomenon of the inflatable composite paper after expansion.

[0024] (3) The inflatable composite paper disclosed by the application is mainly applied to filling narrow gaps in electrically insulated spaces and fixing components in narrow spaces. Taking the insulation of the stator slot of a flat wire motor in a new energy vehicle as an example, the inflatable composite paper disclosed by the application can be expanded by heating after being inserted into the slot of the flat wire motor stator copper wire, thereby playing a role in fixing the flat copper wire, effectively saving the process of paint dripping in the prior art, simplifying the motor production process, improving production efficiency, and reducing production cost. At the same time, compared with paint dripping, the inflatable composite paper can better fix the copper wire, prevent copper wire displacement and vibration, and improve the performance, safety and stability of the entire motor. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The figure is a structural schematic diagram of the inflatable composite paper disclosed by the application. DETAILED DESCRIPTION

[0026] The specific embodiments of the application will be described in detail below. The application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the application, so the application is not limited by the disclosed specific embodiments.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terms used are only for describing specific embodiments and are not intended to limit the application.

[0028] AsFigure 1 As shown in the figure, an inflatable composite paper, the composite paper includes an intermediate layer 1, an inflatable adhesive layer 2 arranged on both sides of the intermediate layer, a transition adhesive layer 3 connected with the inflatable adhesive layer and an outer side isolation layer 4; the transition adhesive layer 3 is an adhesive, between the inflatable adhesive layer 2 and the outermost isolation layer 4; the intermediate layer 1 is a plastic film; the inflatable adhesive layer 2 is provided by an inflatable adhesive, the inflatable adhesive includes heat-expandable microspheres and thermosetting resin; the outer side isolation layer 4 is a non-woven material.

[0029] The inflatable composite paper in the embodiment of the present application includes a seven-layer structure, but the present application technology is not limited to the seven-layer structure, and can be multi-layered according to needs.

[0030] Specifically, the mass content of the heat-expandable microspheres is 10-30% of the total mass of the inflatable adhesive; preferably, the content is 15-20%.

[0031] Specifically, the thickness of the plastic film is 50-125 μm; the thickness of the inflatable adhesive layer before expansion is 2-10 μm; the thickness of the transition adhesive layer is 1-5 μm; the thickness of the isolation layer is 25-85 μm.

[0032] More specifically, the thickness of the plastic film is 75 μm; the thickness of the inflatable adhesive layer before expansion is 3-5 μm; the thickness of the transition adhesive layer is 2-3 μm; the thickness of the isolation layer is 50 μm.

[0033] Specifically, the heat-expandable microspheres are high polymer with an expansion temperature range of 100-160°C, a diameter of 2-20 μm before expansion and an expansion ratio of 30-50 times.

[0034] Specifically, the thermosetting resin includes modified epoxy resin, curing agent, thermoplastic component and additive. In actual production and application process, other additives required can be added in the thermosetting resin according to the use needs Specifically, the modified epoxy resin is at least one of bisphenol epoxy resin, epoxy resin with fatty acid skeleton, glycidyl ether epoxy resin, phenolic modified epoxy resin and cyclic epoxy resin; the thermoplastic component is phenoxy resin, and the addition of phenoxy resin as the thermoplastic component can enhance the film forming property of the heat-expandable epoxy adhesive.

[0035] Specifically, the glue for the transition adhesive layer has good compatibility and adhesion between the inflatable adhesive layer and the outer side isolation layer, and the transition adhesive layer is at least one of epoxy adhesive, acrylate adhesive and polyurethane adhesive.

[0036] Specifically, the plastic film is any one of polyethylene terephthalate (PET) film, polyethylene naphthalate (PEN) film, polyimide (PI) film, polyphenylene sulfide (PPS) film and polyether ether ketone (PEEK) film.

[0037] Specifically, the outer isolation layer has a smooth outer surface, and has good tear resistance and bending resistance, and the isolation layer is at least one of aramid paper, kraft paper, barley paper and polyester non-woven fabric.

[0038] The preparation of the inflatable composite paper in the embodiment of the application comprises the following steps: S1, two rolls of isolation layer are unwound and coated with a transition adhesive layer, dried through a drying channel, and wound for standby; S2, the plastic film of the middle layer is unwound, double-sided coated with an inflatable adhesive, and passed through a 65-85℃ oven channel for 30-70 seconds to remove the solvent in the inflatable adhesive to form an inflatable adhesive layer, so that it is in a semi-cured state and is pressure-bonded with the isolation layer treated in step S1 at room temperature, the pressure-bonding pressure is 1-4MPa, and the inflatable composite paper is obtained after winding and curing.

[0039] More specifically, the interval time before the inflatable adhesive layer in step S2 is pressure-bonded with the isolation layer treated in step S1 at room temperature should not exceed 5 minutes. After 5 minutes, the inflatable adhesive layer is prone to solidification, resulting in non-stickiness of the adhesive surface and affecting the compounding effect.

[0040] The raw materials involved in the specific embodiments of the application are as follows: Aramid paper: Minshida YT564.

[0041] Acrylate glue: Jiaofeng 5020.

[0042] Polyurethane glue: 3M DP6310NS.

[0043] Epoxy glue: Hans MegaGlue.

[0044] Polyethylene terephthalate (PET) film: Xunfeili Hostaphan.

[0045] Polyethylene naphthalate (PEN) film: Xunfeili Teonex Q51.

[0046] Polyimide (PI) film: Xunfeili Kapton.

[0047] Polyphenylene sulfide (PPS) film: Toray Torelina.

[0048] Example 1 Preparation of an inflatable composite paper, specifically comprising the following steps: S1, two rolls of aramid paper with a thickness of 50 μm are unwound as isolation layers, and acrylic adhesive with a thickness of 2 μm is coated to form a transition bonding layer, and then dried through an oven, and wound up for standby.

[0049] S2, a PEN plastic film with a thickness of 75 μm is unwound, and inflatable adhesive with a thickness of 3 μm is coated on both sides, wherein the mass content of the inflatable microspheres in the inflatable adhesive is 20% of the total mass of the inflatable adhesive; the solvent in the inflatable adhesive is removed through a 70°C oven duct, and the time in the oven is 50 seconds, to form an inflatable bonding layer; the inflatable bonding layer is combined with the isolation layer treated in S1 at room temperature in a semi-cured state, and then wound up for curing to obtain the inflatable composite paper.

[0050] Example 2 Preparation of an inflatable composite paper, specifically comprising the following steps: S1, two rolls of aramid paper with a thickness of 50 μm are unwound as isolation layers, and polyurethane adhesive with a thickness of 3 μm is coated to form a transition bonding layer, and then dried through an oven, and wound up for standby.

[0051] S2, a PI plastic film with a thickness of 75 μm is unwound, and inflatable adhesive with a thickness of 5 μm is coated on both sides, wherein the mass content of the inflatable microspheres in the inflatable adhesive is 20% of the total mass of the inflatable adhesive; the solvent in the inflatable adhesive is removed through a 65°C oven duct, and the time in the oven is 60 seconds, to form an inflatable bonding layer; the inflatable bonding layer is combined with the isolation layer treated in S1 at room temperature in a semi-cured state, and then wound up for curing to obtain the inflatable composite paper.

[0052] Example 3 Preparation of an inflatable composite paper, specifically comprising the following steps: S1, two rolls of polyester non-woven fabric with a thickness of 50 μm are unwound as isolation layers, and polyurethane adhesive with a thickness of 2 μm is coated to form a transition bonding layer, and then dried through an oven, and wound up for standby.

[0053] S2, a PET plastic film with a thickness of 75 μm is unwound, and inflatable adhesive with a thickness of 3 μm is coated on both sides, wherein the mass content of the inflatable microspheres in the inflatable adhesive is 20% of the total mass of the inflatable adhesive; the solvent in the inflatable adhesive is removed through a 85°C oven duct, and the time in the oven is 30 seconds, to form an inflatable bonding layer; the inflatable bonding layer is combined with the isolation layer treated in S1 at room temperature in a semi-cured state, and then wound up for curing to obtain the inflatable composite paper.

[0054] Example 4 Preparation of an inflatable composite paper, specifically comprising the following steps: S1, two rolls of aramid paper with a thickness of 50 μm were unwound as isolation layers, and acrylic adhesive with a thickness of 3 μm was coated to form a transition adhesive layer, and then the transition adhesive layer was dried through an oven, and was wound for standby.

[0055] S2, a PEN plastic film with a thickness of 75 μm was unwound, and expandable adhesive with a thickness of 8 μm was coated on both sides, wherein the mass content of the expanded microspheres in the expandable adhesive was 30% of the total mass of the expandable adhesive; the solvent in the expandable adhesive was removed through a 65℃ oven duct, and the time in the oven was 70 seconds, to form an expandable adhesive layer; the expandable adhesive layer was hot-pressed and combined with the isolation layer treated in S1 when it was in a semi-cured state, and the expandable composite paper was obtained after winding and curing.

[0056] Example 5 A preparation method of an expandable composite paper, specifically comprising the following steps: S1, two rolls of aramid paper with a thickness of 25 μm were unwound as isolation layers, and acrylic adhesive with a thickness of 1 μm was coated to form a transition adhesive layer, and then the transition adhesive layer was dried through an oven, and was wound for standby.

[0057] S2, a PPS plastic film with a thickness of 50 μm was unwound, and expandable adhesive with a thickness of 2 μm was coated on both sides, wherein the mass content of the expanded microspheres in the expandable adhesive was 15% of the total mass of the expandable adhesive; the solvent in the expandable adhesive was removed through a 65℃ oven duct, and the time in the oven was 50 seconds, to form an expandable adhesive layer; the expandable adhesive layer was hot-pressed and combined with the isolation layer treated in S1 when it was in a semi-cured state, and the expandable composite paper was obtained after winding and curing.

[0058] Example 6 A preparation method of an expandable composite paper, specifically comprising the following steps: S1, two rolls of aramid paper with a thickness of 85 μm were unwound as isolation layers, and epoxy adhesive with a thickness of 5 μm was coated to form a transition adhesive layer, and then the transition adhesive layer was dried through an oven, and was wound for standby.

[0059] S2, a PEEK plastic film with a thickness of 125 μm was unwound, and expandable adhesive with a thickness of 10 μm was coated on both sides, wherein the mass content of the expanded microspheres in the expandable adhesive was 10% of the total mass of the expandable adhesive; the solvent in the expandable adhesive was removed through a 65℃ oven duct, and the time in the oven was 70 seconds, to form an expandable adhesive layer; the expandable adhesive layer was hot-pressed and combined with the isolation layer treated in S1 when it was in a semi-cured state, and the expandable composite paper was obtained after winding and curing.

[0060] Comparative Example 1 A preparation method of an expandable composite paper, the same as that of Example 1, except that the outermost isolation layer of aramid paper in Comparative Example 1 was not coated with acrylic adhesive to form a transition adhesive layer.

[0061] Specifically comprising the following steps: S1, the PEN plastic film of the thickness 75 μm intermediate layer is unwound, and the expandable adhesive with the thickness of 3 μm is coated on both sides, wherein the mass content of the expanded microspheres in the expandable adhesive is 20% of the total mass of the expandable adhesive; the solvent in the expandable adhesive is removed through the oven duct of 70°C for 50 seconds in the oven to form the expandable adhesive layer, so that the expandable adhesive layer is in the semi-cured state and is pressure-bonded with aramid paper at room temperature, and the expandable composite paper is obtained after winding and curing.

[0062] Comparative Example 2 An expandable composite paper is prepared in the same manner as in Example 1, except that in step S2, the epoxy resin adhesive without adding expanded microspheres is coated on both sides of the intermediate layer.

[0063] Specifically comprising the following steps: S1, two rolls of aramid paper with a thickness of 50 μm are unwound as the isolation layer, and the acrylate glue is coated to form a transition adhesive layer, and then dried through the oven duct, and wound for standby.

[0064] S2, the PEN plastic film of the thickness 75 μm intermediate layer is unwound, and the epoxy resin adhesive without adding expanded microspheres is coated on both sides, and the solvent in the expandable adhesive is removed through the oven duct of 70°C for 50 seconds in the oven to form the expandable adhesive layer, so that the expandable adhesive layer is in the semi-cured state and is pressure-bonded with the isolation layer treated in S1 at room temperature, and the expandable composite paper is obtained after winding and curing.

[0065] Comparative Example 3 An expandable composite paper is prepared in the same manner as in Example 4, except that in step S2, the mass content of the expanded microspheres in the expandable adhesive is 50%.

[0066] Specifically comprising the following steps: S1, two rolls of aramid paper with a thickness of 50 μm are unwound as the isolation layer, and the acrylate glue with the thickness of 3 μm is coated to form a transition adhesive layer, and then dried through the oven duct, and wound for standby.

[0067] S2, the PEN plastic film of the thickness 75 μm intermediate layer is unwound, and the expandable adhesive with the thickness of 8 μm is coated on both sides, wherein the mass content of the expanded microspheres in the expandable adhesive is 50% of the total mass of the expandable adhesive; the solvent in the expandable adhesive is removed through the oven duct of 65°C for 70 seconds in the oven to form the expandable adhesive layer, so that the expandable adhesive layer is in the semi-cured state and is hot-pressed and bonded with the isolation layer treated in S1, and the expandable composite paper is obtained after winding and curing.

[0068] Comparative Example 4 A preparation of an inflatable composite paper, specifically comprising the following steps: S1, two rolls of aramid paper with a thickness of 50 μm are unwound as isolation layers, and acrylic adhesive with a thickness of 2 μm is coated to form a transition bonding layer, and then dried through an oven, and wound up for standby.

[0069] S2, a PEN plastic film with a thickness of 75 μm is unwound as an intermediate layer, and inflatable adhesive with a thickness of 3 μm is coated on both sides, wherein the mass content of the inflatable microspheres is 5% of the total mass of the inflatable adhesive; the inflatable adhesive is removed through a 70°C oven duct for 30 seconds, to remove the solvent in the inflatable adhesive and form an inflatable bonding layer, which is then combined with the isolation layer treated in S1 at room temperature in a semi-cured state, and wound up for curing to obtain the inflatable composite paper.

[0070] Comparative Example 5 A preparation of an inflatable composite paper, which is prepared in the same manner as in Example 1, except that the acrylic adhesive coated in step S1 has a thickness of 10 μm, which is outside the range set by the present application.

[0071] Specifically comprising the following steps: S1, two rolls of aramid paper with a thickness of 50 μm are unwound as isolation layers, and acrylic adhesive with a thickness of 10 μm is coated to form a transition bonding layer, and then dried through an oven; Phenomenon: after drying, the substrate is wrinkled and curled, and cannot be further compounded.

[0072] Comparative Example 6 A preparation of an inflatable composite paper, which is prepared in the same manner as in Example 1, except that in step S2, the oven duct is 50°C, which is lower than in Example 1.

[0073] Specifically comprising the following steps: S1, two rolls of aramid paper with a thickness of 50 μm are unwound as isolation layers, and acrylic adhesive with a thickness of 1 μm is coated to form a transition bonding layer, and then dried through an oven, and wound up for standby.

[0074] S2, a PEN plastic film with a thickness of 75 μm is unwound as an intermediate layer, and inflatable adhesive with a thickness of 3 μm is coated on both sides, wherein the mass content of the inflatable microspheres is 20% of the total mass of the inflatable adhesive; the inflatable adhesive is removed through a 50°C oven duct for 50 seconds, to remove the solvent in the inflatable adhesive and form an inflatable bonding layer, which is then combined with the isolation layer treated in S1 at room temperature in a semi-cured state, and wound up for curing to obtain the inflatable composite paper.

[0075] Phenomenon: In step S2, when the temperature of the oven duct is lower than the temperature set in the present application, wrinkles will appear in step S3 when the transition adhesive layer is pressed at room temperature, affecting the flatness between the layers during the pressing process, and the expandable adhesive layer will overflow during the pressing process.

[0076] Comparative Example 7 An expandable composite paper was prepared in the same manner as in Example 1, except that in step S2, the time in the oven was 20 seconds, which was shorter than in Example 1.

[0077] Specifically, the following steps are included: S1, two rolls of aramid paper with a thickness of 50 μm were unwound as isolation layers and coated with an acrylic adhesive with a thickness of 1 μm to form a transition adhesive layer, then dried through an oven, and wound for standby.

[0078] S2, a PEN plastic film with a thickness of 75 μm was unwound, and both sides were coated with an expandable adhesive with a thickness of 3 μm, wherein the mass content of the expandable microspheres was 20% of the total mass of the expandable adhesive; the expandable adhesive was passed through a 70°C oven duct for 20 seconds to remove the solvent and form an expandable adhesive layer, which was then pressed at room temperature with the isolation layer treated in S1, and wound for curing to obtain an expandable composite paper.

[0079] Phenomenon: In step S2, when the temperature of the oven duct is lower than the temperature set in the present application, wrinkles will appear in step S3 when the transition adhesive layer is pressed at room temperature, affecting the flatness between the layers during the pressing process, and the expandable adhesive layer will overflow during the pressing process.

[0080] Comparative Example 8 An expandable composite paper was prepared in the same manner as in Example 1, except that in step S2, the oven duct was passed through a 95°C oven duct, and the temperature of the oven duct was higher than in Example 1.

[0081] Specifically, the following steps are included: S1, two rolls of aramid paper with a thickness of 50 μm were unwound as isolation layers and coated with an acrylic adhesive with a thickness of 1 μm to form a transition adhesive layer, then dried through an oven, and wound for standby.

[0082] S2, the thickness of 75 μm PEN plastic film is unwound, and the expandable adhesive with a thickness of 3 μm is coated on both sides, wherein the mass content of the expandable microspheres in the expandable adhesive is 20% of the total mass of the expandable adhesive; the expandable adhesive is removed through a 95℃ oven duct, the time in the oven is 50 seconds, and the solvent in the expandable adhesive is removed to form an expandable bonding layer; the expandable bonding layer is in a semi-cured state and is pressure-bonded with the isolation layer treated in S1 at room temperature; and the expandable composite paper is obtained after rolling and curing.

[0083] Phenomenon: In step S3, the expandable bonding layer and the transition bonding layer are not completely bonded and the bonding is not strong when pressure-bonding.

[0084] Comparative Example 9 An expandable composite paper is prepared in the same manner as in Example 1, except that in step S2, the time in the oven is 80 seconds, which is longer than that in Example 1.

[0085] Specifically, the following steps are included: S1, two rolls of aramid paper with a thickness of 50 μm are unwound as isolation layers, and the acrylate glue with a thickness of 1 μm is coated to form a transition bonding layer, which is dried through an oven duct and rolled for standby use.

[0086] S2, the thickness of 75 μm PEN plastic film is unwound, and the expandable adhesive with a thickness of 3 μm is coated on both sides, wherein the mass content of the expandable microspheres in the expandable adhesive is 20% of the total mass of the expandable adhesive; the expandable adhesive is removed through a 95℃ oven duct, the time in the oven is 50 seconds, and the solvent in the expandable adhesive is removed to form an expandable bonding layer; the expandable bonding layer is in a semi-cured state and is pressure-bonded with the isolation layer treated in S1 at room temperature; and the expandable composite paper is obtained after rolling and curing.

[0087] Phenomenon: In step S3, the expandable bonding layer and the transition bonding layer are not completely bonded and the bonding is not strong when pressure-bonding.

[0088] Comparative Example 10 An expandable composite paper is prepared, and in Comparative Example 10, the transition bonding layer is coated on the expandable bonding layer, and then pressure-bonded with the isolation layer at room temperature, and the amounts of the components are the same as in Example 1.

[0089] Specifically, the following steps are included: S1, the thickness of 75 μm PEN plastic film is unwound, and the expandable adhesive with a thickness of 3 μm is coated on both sides, wherein the mass content of the expandable microspheres in the expandable adhesive is 20% of the total mass of the expandable adhesive; the expandable adhesive is removed through a 95℃ oven duct, the time in the oven is 50 seconds, and the solvent in the expandable adhesive is removed to form an expandable bonding layer; the expandable bonding layer is in a semi-cured state and is pressure-bonded with the isolation layer treated in S1 at room temperature; and the expandable composite paper is obtained after rolling and curing.

[0090] S2, the surface of the expandable adhesive layer in step S1 is coated with an acrylate glue with a thickness of 1 μm to form a transition adhesive layer, and the solvent is dried through an oven channel, so that the transition adhesive layer is in a semi-cured state and is pressure-bonded with aramid paper with a thickness of 50 μm at room temperature, and the expandable composite paper is obtained after winding and curing.

[0091] Phenomenon: If in step S1, the expandable adhesive layer is coated with an acrylic glue in a semi-cured state, since the semi-cured glue layer is still in a flowing state, it is difficult to ensure uniformity of the coating glue, and uneven coating of the transition adhesive layer may occur, and there may be glue hanging and wire drawing. Therefore, in the comparative example 10, after the expandable adhesive is coated, the solvent in the expandable adhesive is removed in the oven channel, and the formed expandable adhesive layer is completely cured before the acrylic glue is coated.

[0092] The expandable composite paper prepared in the examples and comparative examples is subjected to performance testing, and the measurement method involved refers to GB / T5591.2-2017; the test method for the expansion ratio is as follows: the average thickness of five points of the sample before heat expansion is measured and recorded as h1, then the sample is placed in a 150℃ oven for 5 min, and the average thickness of the sample after heat treatment is measured in the same way as above and recorded as h2, and the calculation formula of the expansion ratio (Δ) is: Δ = h2 / h1; the test method for whether the sample after heat expansion is delaminated is as follows: the appearance of the sample after heat expansion is observed to determine whether there is delamination phenomenon such as edge lifting and cracking between layers. The performance test data of the expandable composite paper prepared in the examples and comparative examples are shown in Table 1.

[0093] Table 1 Performance test data of the expandable composite paper prepared in the examples and comparative examples

[0094] As can be seen from the data in Table 1, the expandable composite paper prepared by the preparation method of the present application in examples 1-6 has good stiffness and tensile strength, and does not delaminate after expansion in use. Especially in examples 1-6, the composite paper not only does not delaminate after expansion, but also has better expansion ratio, and can maintain better stiffness and tensile strength. The preparation method of the expandable composite paper of the present application performs surface pretreatment on the outermost isolation layer, fills the pores and gaps between the fibers on the surface of the non-woven structure material through the transition adhesive layer, forms a smooth structure on the surface, and then makes the outermost isolation layer and the expandable adhesive layer adhere more closely, so that the expandable adhesive layer can better adhere the expandable adhesive layer and the outermost isolation layer after heat expansion, and solves the delamination phenomenon between layers of the expandable composite paper after expansion. The presence of the transition adhesive layer makes the stiffness of the outermost aramid paper better, and the stronger adhesion between the aramid paper and the expandable adhesive layer, so that the stiffness, elongation strength and elongation rate of the whole material increase after the layers jointly act after curing.

[0095] The material of the non-woven fabric structure is composed of fibers, has micro pores, and the main component of the expandable adhesive is epoxy resin. After the epoxy resin is further cured by heat expansion, the adhesion is poor, the effective adhesion area with the external isolation layer is reduced, and the delamination problem is easy to occur, causing safety hazards.

[0096] According to the data in Table 1, it can be seen from the comparison of the experimental results of Comparative Example 1 and Example 1 that when the outermost isolation layer is not coated with acrylic adhesive to form a transition bonding layer, the elongation and stiffness of the obtained expandable composite paper are significantly reduced, and the expandable adhesive layer appears delamination during use. This is because the surface of aramid paper is chemically inert, and the adhesion between the expandable adhesive layer is poor; because aramid paper is composed of fibers, has micro pores and gaps, and the viscosity of the expandable adhesive layer is large, it cannot better penetrate into the pores and gaps of the aramid paper when it is in contact with the aramid paper. Therefore, during use, when the expandable adhesive layer expands, delamination occurs due to insufficient adhesion and fiber falling. In Example 1, the surface of the aramid paper is pretreated with acrylic adhesive to form a transition intermediate layer with strong adhesion on the surface of the outermost aramid paper, which is compatible and bonded with the expandable adhesive layer. The transition intermediate layer can be well bonded together, so that the material does not delaminate during use after expansion. Because the acrylic adhesive has good flowability when treating aramid paper, and has good compatibility with aramid paper, it can ensure that the pores and gaps on the surface of aramid paper are filled, and also has a certain penetration depth. The existence of the transition bonding layer makes the stiffness of the outermost aramid paper better, and the stronger bonding between the aramid paper and the expandable adhesive layer makes the stiffness and elongation of the entire material increase.

[0097] According to the data in Table 1, it can be seen from the comparison of the experimental results of Comparative Example 2 and Example 1 that in Comparative Example 2, the intermediate layer is coated with epoxy resin adhesive without adding expansion microspheres in step S2, and the final obtained composite paper does not have expandable performance. This is because the expansion performance of the composite paper is mainly realized by the expansion microspheres. If the expansion microspheres are not added, the composite paper will not have the expansion performance, and thus will not meet the use requirements.

[0098] According to the data in Table 1, from the comparison of the experimental results of Comparative Example 3 and Example 4, it can be seen that in step S2, when the mass content of the expandable microspheres in the coated expandable adhesive is 50%, the expansion ratio increases, and after expansion, delamination occurs in the expansion layer, but the elongation of the expandable composite material decreases. This is because the expansion performance is mainly provided by the expandable microspheres, and when the content of the expandable microspheres in the expandable adhesive layer is too high, the expansion ratio increases. Under the action of external force, each microsphere is a defect point on the overall structure of the composite paper, and cracks are easily generated and expanded at these relatively weak microsphere-fiber interfaces; the more the number of microspheres, the more the stress concentration points, and the tensile strength, burst strength and tear strength of the paper will decrease sharply.

[0099] According to the data in Table 1, from the comparison of the experimental results of Comparative Example 4 and Example 1, it can be seen that in step S2, when the mass content of the expandable microspheres in the coated expandable adhesive is 5%, the expansion ratio decreases. This is because the expansion performance is mainly provided by the expandable microspheres, and when the content of the expandable microspheres in the expandable adhesive layer is too low, the expansion ratio decreases.

[0100] According to the data in Table 1, from the comparison of the experimental results of Comparative Example 5 and Example 1, it can be seen that in step S1, when the coated acrylate glue is thicker than the thickness set by the present application, the time for the isolation layer to pass through the oven after gluing is prolonged to ensure complete drying of the glue layer during the preparation process, thereby reducing the vehicle speed and affecting the production efficiency; and the transition adhesive layer is cured during drying in the oven, and the shrinkage stress generated during the curing process is large, which exceeds the tear resistance of the isolation layer substrate, resulting in wrinkles and curling of the substrate, and the next step of compounding cannot be performed.

[0101] In the preparation process of Comparative Example 6 and Comparative Example 7, in step S3, wrinkles occur when the transition adhesive layer is pressed at room temperature, which affects the flatness between the layers during the pressing process, and the expandable adhesive layer also appears to overflow during the pressing process. According to the data in Table 1, by comparing the experimental results of Comparative Example 6, Comparative Example 7 and Example 1, it can be seen that in step S2, when the temperature of the oven duct or the residence time in the oven is lower than the range set by the present application, the solvent in the glue layer is not completely volatilized, and the glue layer has a large flowability, which is prone to cause wrinkles or overflow during the pressing process in the subsequent compounding process, affecting the appearance of the product. This is because in step S2, the temperature of the oven duct in Comparative Example 6 is lower than the temperature set by the present application, and the time in the oven in Comparative Example 7 is lower than the temperature set by the present application, resulting in incomplete volatilization of the solvent in the expandable adhesive layer, and the glue has flowability, so wrinkles and overflow of the expandable adhesive layer occur in step S3; and the composite paper is not flat and uniform, which affects the downstream application.

[0102] In the preparation of Comparative Example 8 and Comparative Example 9, in step S3, when the expandable adhesive layer was pressure-bonded with the transition adhesive layer at room temperature, the expandable adhesive layer and the transition adhesive layer were not completely bonded, and the bonding was not strong. This is because, in Comparative Example 8, the oven duct temperature was too high, and in Comparative Example 9, the residence time in the oven was too long, causing the expandable adhesive layer to solidify, and the adhesive layer bonding ability to decrease, so that the expandable adhesive layer and the transition adhesive layer were not completely bonded, and the bonding was not strong, affecting the compounding effect.

[0103] According to the data in Table 1, from the comparison of the experimental results of Comparative Example 10 and Example 1, it can be seen that in Comparative Example 10, the transition adhesive layer was coated on the expandable adhesive layer, and then directly pressure-bonded with the release layer at room temperature, and the final expandable composite paper was delaminated during use. This is because: the compounding process sequence of Comparative Example 10 is the same as that of conventional expandable composite paper, and after the transition adhesive layer is coated on the expandable adhesive layer and dried in the oven, the adhesive layer of the transition adhesive layer is in a semi-solidified state, and when it is compounded with the outermost release layer, it cannot achieve the effect of penetrating the adhesive into the inside of the release layer, and the adhesive layer of the transition adhesive layer only bonds with the fibers of the outermost layer of the release layer, greatly reducing the bonding area, and after expansion under heat, it will still delaminate due to the same problem as conventional expandable composite paper on the market. The transition adhesive layer in the conventional compounding process in Comparative Example 10 cannot achieve the effect mentioned in the present application.

[0104] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, all possible combinations of the technical features in the above-described embodiments are not exhaustively listed, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present disclosure.

[0105] For those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of the present application. The scope of protection of the present application is subject to the appended claims.

Claims

1. An expandable composite paper, characterized in that, The composite paper includes an intermediate layer, expandable adhesive layers disposed on both sides of the intermediate layer, a transition adhesive layer connected to the expandable adhesive layers, and an outer isolation layer. The transition adhesive layer is an adhesive and is located between the expandable adhesive layer and the outer isolation layer; The intermediate layer is a plastic film; The expandable adhesive layer is provided by an expandable adhesive comprising thermally expandable microspheres and a thermosetting resin; The outer isolation layer is made of non-woven material.

2. The expandable composite paper according to claim 1, characterized in that, The mass content of the thermally expandable microspheres is 10-30% of the total mass of the expandable adhesive.

3. The expandable composite paper according to claim 1, characterized in that, The thickness of the plastic film is 50~125μm; The thickness of the expandable adhesive layer before expansion is 2~10μm; The thickness of the transition bonding layer is 1~5μm; The thickness of the isolation layer is 25~85μm.

4. The expandable composite paper according to claim 3, characterized in that, The thickness of the plastic film is 75 μm; The thickness of the expandable adhesive layer before expansion is 3~5μm; The thickness of the transition bonding layer is 2~3μm; The thickness of the isolation layer is 50 μm.

5. The expandable composite paper according to claim 1, characterized in that, The thermally expandable microspheres are high molecular polymers with a diameter of 2-20 μm and an expansion ratio of 30-50 times before expansion in the expansion temperature range of 100-160℃. The thermosetting resin includes a modified epoxy resin, a curing agent, and a thermoplastic component.

6. The expandable composite paper according to claim 5, characterized in that, The modified epoxy resin is at least one of bisphenol epoxy resin, fatty acid backbone epoxy resin, glycidyl ether epoxy resin, phenolic modified epoxy resin, and cyclic epoxy resin. The thermoplastic component is phenoxy resin.

7. The expandable composite paper according to claim 1, characterized in that, The transition bonding layer is at least one of epoxy adhesives, acrylate adhesives, and polyurethane adhesives.

8. The expandable composite paper according to claim 1, characterized in that, The plastic film is any one of polyethylene terephthalate film, polyethylene naphthalate film, polyimide film, polyphenylene sulfide film, and polyetheretherketone film; The outer insulating layer is at least one of aramid paper, kraft paper, barley paper, and polyester nonwoven fabric.

9. A method for preparing an expandable composite paper according to any one of claims 1-8, characterized in that, The preparation method includes the following steps: S1. Unwind the two rolls of separator layer, coat them with the transition adhesive layer, dry them, and rewind them for later use. S2. Unwind the plastic film of the middle layer, coat both sides with expandable adhesive to form an expandable adhesive layer, press the expandable adhesive layer with the isolation layer prepared in step S1 at room temperature, and then roll it up and cure to obtain expandable composite paper.

10. The method for preparing an expandable composite paper according to claim 9, characterized in that, In step S2, after the expandable adhesive is coated on both sides of the intermediate layer, it is passed through the oven tunnel at 65~85℃ and the residence time in the oven is 30~70 seconds to form an expandable adhesive layer.

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