Preparation method of expansion insulating sheet

Abstract

The invention discloses an expansion insulating sheet which comprises a base material and expansion bonding layers arranged on the two sides of the base material. The expansion bonding layer comprises epoxy resin with the softening point being 40 DEG C or above, a temperature-sensitive foaming agent, a curing agent, an accelerant, thermoplastic resin and flaky filler. According to the expansion insulation sheet prepared by the invention, the surface adhesion of the expansion bonding layers at normal temperature (less than or equal to 40 DEG C) can be obviously reduced, and particularly, when multiple layers of expansion insulation sheets are stacked, the expansion bonding layers are not adhered; the bonding strength between the expansion bonding layer and the base material at high temperature can be improved; and the cost can be obviously reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of fine chemical industry, and in particular relates to a method for preparing an expansion insulating sheet. Background Art

[0002] Epoxy resin adhesives have excellent heat resistance and strong adhesion, so they are widely used for component bonding, structural bonding, etc. In related fields such as electrical and electronic equipment, automobiles, and civil engineering, adhesive sheets are often used to fix components. Sometimes it is necessary to achieve bonding in a small area of ​​an industrial component. For example, in the motors of electric vehicles and hybrid vehicles that have developed rapidly in recent years, the coils wound with enameled wire need to be fixed to the stator core with adhesives. Since the gap between the coil and the stator core is very narrow, it is necessary to use an adhesive sheet with heat expansion properties, which will expand to fill the gap and solidify when heated.

[0003] CN105940071B discloses an adhesive sheet that maintains sufficient foaming performance while also offering excellent workability. The solution involves applying a coating layer on top of the expandable adhesive layer. This coating, composed of a resin, is non-sticky at room temperature but softens and disappears upon heating, rendering the expandable insulating sheet non-sticky at room temperature. However, applying the coating layer on top of the expandable adhesive layer increases manufacturing complexity. Furthermore, since the coating layer contains a solvent, it can partially dissolve the previously applied expandable adhesive layer, reducing process stability.

[0004] CN112189041B proposes a heat-expandable adhesive sheet, which is a solution that adds a permeable non-woven fabric layer to the outside of the expansion adhesive layer. The surface is non-sticky at room temperature. When heated, the expansion adhesive layer penetrates the non-woven fabric layer for bonding. This solution increases the complexity of preparation. Summary of the Invention

[0005] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0006] In order to achieve these objects and other advantages according to the present invention, an expansion insulating sheet is provided, comprising a substrate and expansion adhesive layers arranged on both sides of the substrate; the expansion adhesive layers comprise an epoxy resin with a softening point above 40°C, a temperature-sensitive foaming agent, a curing agent, an accelerator, a thermoplastic resin, and a flaky filler.

[0007] Preferably, the substrate is one or a combination of at least two of a polyester film, a polyimide film, an aramid film, and polyethylene naphthalate, and the thickness of the substrate is in the range of 25-200 μm.

[0008] Preferably, the flaky filler is any one of mica powder and talc powder or a combination of at least two thereof, the aspect ratio of the flaky filler is greater than 10, D50 is less than 50 microns, and the mass fraction of the flaky filler is 10-50wt% of the expansion bonding layer.

[0009] Preferably, the epoxy resin with a softening point above 40° C. is any one of o-cresol epoxy resin, phenolic epoxy resin, and 1,1,1-tris(4-hydroxyphenyl)ethyl triglycidyl ether, or a combination of at least two thereof, and the mass fraction of the epoxy resin is 20-80wt% of the expansion adhesive layer.

[0010] Preferably, the temperature-sensitive foaming agent is a heat-expandable microsphere with a diameter of 5-40 μm, and the mass fraction of the temperature-sensitive foaming agent is 3-15 wt % of the expansion adhesive layer.

[0011] Preferably, the thermoplastic resin is one or a combination of at least two of polyester, polyurethane, polyolefin, phenoxy resin, and acrylic resin; and the mass fraction of the thermoplastic resin is 5-45wt% of the expansion adhesive layer.

[0012] Preferably, the curing agent is dicyandiamide, and the mass fraction of the curing agent is 1-5 wt % of the expansion bonding layer.

[0013] Preferably, the mass fraction of the accelerator is 0.5-2 wt % of the expansion bonding layer.

[0014] The present invention also provides a method for preparing an expandable insulating sheet, comprising the following steps: S1. dissolving an epoxy resin with a softening point above 40° C., a temperature-sensitive foaming agent, a curing agent, an accelerator, a thermoplastic resin, and a sheet filler in a ketone solvent to form a glue solution; S2. Apply the glue directly or successively to both sides of the substrate, and dry at 100°C to obtain an expandable insulating sheet; or apply the glue to release paper, dry at 100°C, and then transfer the expandable adhesive layer to both sides of the substrate by transfer printing to obtain an expandable insulating sheet.

[0015] Preferably, the ketone solvent is one or a combination of acetone and butanone, and the mass fraction of the ketone solvent accounts for 30-70wt% of the glue solution.

[0016] The present invention has at least the following beneficial effects: the present invention can significantly reduce the surface adhesion of the expansion adhesive layer at room temperature (≤40°C), which is specifically reflected in the fact that when multiple expansion insulating sheets are stacked, there is no adhesion between the expansion adhesive layers; the bonding strength between the expansion adhesive layer and the substrate at high temperature can be improved; and the cost can be significantly reduced.

[0017] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0018] The present invention is described in further detail below so that those skilled in the art can implement the invention with reference to the description.

[0019] The materials described in Table 1 and Table 2 were used in Examples 1-4 and Comparative Examples 1-4.

[0020] Table 1 Product Name Element source NPPN442 Trifunctional epoxy resin Nan Ya Plastics PKHB Phenoxy resin Huntsman Amicure CG-1200G Dicyandiamide Evonik PN-50 Accelerator Ajinomoto EMH302 Expandable microspheres Sekisui, Japan Table 2 name Specification F1 Talc, D50 7 microns, diameter-to-thickness ratio about 20 F2 Mica powder, D50 5 microns, diameter-to-thickness ratio about 80 S1 Silica powder, D50 6 microns The remaining materials are commonly sold.

[0021] The method for preparing an expandable insulating sheet described in Examples 1-4 and Comparative Examples 1-4 comprises the following steps and the proportions (in parts by weight) shown in Table 3: S1. Epoxy resin, temperature-sensitive foaming agent, curing agent, accelerator, thermoplastic resin, flake filler or silica powder with a temperature above 40°C are mixed in a ketone solvent (MEK) to form a glue solution; S2. Apply the adhesive directly or successively to both sides of the substrate (PEN), and dry at 100°C to obtain an expandable insulating sheet; or apply the adhesive to release paper, dry at 100°C, and then transfer the expandable adhesive layer to both sides of the substrate by transfer printing to obtain an expandable insulating sheet.

[0022] Table 3 Product Name Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 NPPN442 40 40 40 40 40 40 40 40 PKHB 45 45 45 45 45 45 45 45 EMH302 10 10 10 10 10 10 10 10 Amicure CG-1200G 4 4 4 4 4 4 4 4 PN-50 1 1 1 1 1 1 1 1 F1 15 35 100 10 150 F2 25 S1 25 MEK 100 100 100 100 100 100 100 100 The intumescent insulating sheets prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to performance tests.

[0023] Surface adhesion testing method: Cut the samples of the examples and comparative examples into 5cm x 5cm pieces and stack five layers of them between two 8cm x 8cm glass plates. Place a 10kg load on top and leave at 40°C for at least 8 hours. Then, open the glass plates and peel off the samples to confirm adhesion. If there is no adhesion between the samples and the surface is glossy, mark it as A. If there is slight adhesion between the samples, but the expansion layer is intact and has not separated from the substrate, mark it as B. If the expansion layer adheres to each other and separates from the substrate, mark it as unsatisfactory (C).

[0024] Bending resistance test method: Cut the example and comparative example samples into 5 cm x 50 cm pieces, bend them 180 degrees at any point, and visually inspect the condition of the expansion layer. If no cracking or lifting of the expansion layer is observed, mark the sample as passing. If cracking or lifting is observed, mark the sample as failing.

[0025] Shear strength test method: Sample size 12.5mm x 25mm, placed between two stainless steel test pieces with a 0.3mm gap, and placed in a 160°C oven for 30 minutes. Test at 200°C and a shear rate of 5mm / min.

[0026] The test results are shown in Table 3 below.

[0027] Table 3 Product Name Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 NPPN442 40 40 40 40 40 40 40 40 PKHB 45 45 45 45 45 45 45 45 EMH302 10 10 10 10 10 10 10 10 Amicure CG-1200G 4 4 4 4 4 4 4 4 PN-50 1 1 1 1 1 1 1 1 F1 15 35 100 10 150 F2 25 S1 25 Bending resistance qualified qualified qualified qualified qualified qualified Unqualified qualified Surface stickiness A A A A B A A B Shear strength, MPa 2.2 2.3 2.5 2.0 1.9 2.0 1.7 1.9 The test results of Examples 1-4 and Comparative Examples 1-4 demonstrate that the addition of flaky fillers to the intumescent adhesive layer can reduce the surface adhesion of the intumescent adhesive layer at room temperature, allowing for adhesion-free stacking of multiple intumescent insulating sheets. This is due to the parallel arrangement of the flaky fillers within the intumescent adhesive layer, forming a multilayer structure that prolongs the penetration path for foreign substances. Furthermore, the flaky fillers are highly compatible with the epoxy resin, resulting in uniform dispersion of the fillers and a continuous barrier that reduces the intermolecular forces between the intumescent adhesive layer and contaminants, thereby lowering surface adhesion. Furthermore, the flaky filler structure is thermally stable, with a thermal expansion coefficient at high temperatures much lower than that of the resin. Compared to other inorganic fillers, the addition of flaky fillers to the intumescent adhesive layer can inhibit thermal deformation of the intumescent adhesive layer and improve adhesive strength at high temperatures.

[0028] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. An expansion insulation sheet, characterized in that: The invention comprises a substrate and expansion bonding layers arranged on both sides of the substrate; the expansion bonding layers comprise epoxy resin with a softening point above 40°C, a temperature-sensitive foaming agent, a curing agent, an accelerator, a thermoplastic resin and a flaky filler.

2. The expandable insulating sheet according to claim 1, wherein The substrate is one of polyester film, polyimide film, aramid film, and polyethylene naphthalate, or a combination of at least two thereof, and the thickness of the substrate is in the range of 25-200 μm.

3. The expandable insulating sheet according to claim 1, wherein The flaky filler is any one of mica powder and talc powder or a combination of at least two of them. The diameter-to-thickness ratio of the flaky filler is greater than 10, D50 is less than 50 microns, and the mass fraction of the flaky filler is 10-50wt% of the expansion bonding layer.

4. The expandable insulating sheet according to claim 1, wherein The epoxy resin with a softening point above 40° C. is any one of o-cresol epoxy resin, phenolic epoxy resin, and 1,1,1-tris(4-hydroxyphenyl)ethyl triglycidyl ether, or a combination of at least two thereof. The mass fraction of the epoxy resin with a softening point above 40° C. is 20-80wt% of the expansion adhesive layer.

5. The expandable insulating sheet according to claim 1, wherein The temperature-sensitive foaming agent is a heat-expandable microsphere with a diameter of 5-40 μm. The mass fraction of the temperature-sensitive foaming agent is 3-15 wt % of the expansion bonding layer.

6. The expandable insulating sheet according to claim 1, wherein The thermoplastic resin is one or a combination of at least two of polyester, polyurethane, polyolefin, phenoxy resin, and acrylic resin; the mass fraction of the thermoplastic resin is 5-45wt% of the expansion bonding layer.

7. The expandable insulating sheet according to claim 1, wherein The curing agent is dicyandiamide, and the mass fraction of the curing agent is 1-5wt% of the expansion bonding layer.

8. The expandable insulating sheet according to claim 1, wherein The mass fraction of the accelerator is 0.5-2 wt % of the expansion bonding layer.

9. A method for preparing an expandable insulating sheet according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. dissolving an epoxy resin with a softening point above 40° C., a temperature-sensitive foaming agent, a curing agent, an accelerator, a thermoplastic resin, and a sheet filler in a ketone solvent to form a glue solution; S2. Apply the glue directly or successively to both sides of the substrate, and dry at 100°C to obtain an expandable insulating sheet; or apply the glue to release paper, dry at 100°C, and then transfer the expandable adhesive layer to both sides of the substrate by transfer printing to obtain an expandable insulating sheet.

10. The method for preparing an expandable insulating sheet according to claim 9, wherein: The ketone solvent is one of acetone and butanone or a combination of the two, and the mass fraction of the ketone solvent accounts for 30-70wt% of the glue solution.