Preparation method of expansion insulating sheet

Abstract

The invention discloses an expansion insulating sheet which comprises a base material and two expansion bonding layers arranged on the two sides of the base material respectively. 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, cellulose resin and thermoplastic resin. According to the prepared expansion insulating sheet, the bending resistance of the expansion bonding layer can be remarkably improved, and breakage caused by bending of the expansion bonding layer is avoided; in addition, the adhesiveness of the expansion bonding layers to the base material can be remarkably improved, floating of the bonding layers is avoided in the cutting process, and meanwhile stripping of the expansion bonding layers and the base material caused by mutual bonding of the expansion bonding layers in the storage process is avoided.

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, exhibits no stickiness at room temperature but softens and disappears upon heating, rendering the expandable insulating sheet non-sticky and non-tearable 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] CN115348998B discloses an expandable insulating sheet with an expandable adhesive layer having a peel force of at least 2N. The solution involves adding an intermediate layer between the expandable adhesive layer and the substrate. This increases the peel force of the expandable adhesive layer and prevents the expandable adhesive layer from floating or breaking during cutting. However, adding an intermediate layer between the expandable adhesive layer and the substrate undoubtedly increases the complexity of the production process. 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, there is provided an expansion insulating sheet comprising a substrate and expansion bonding layers provided on both sides of the substrate; the expansion bonding layers comprise an epoxy resin having a softening point above 40°C, a temperature-sensitive foaming agent, a curing agent, an accelerator, a cellulose resin, and a thermoplastic resin.

[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 cellulose resin is any one of methyl cellulose, ethyl cellulose, cellulose acetate, cellulose butyrate, cellulose acetate-propionate, cellulose acetate-butyrate, and cellulose acetate phthalate, or a combination of at least two thereof.

[0009] Preferably, the cellulose resin is ethyl cellulose, and the mass fraction of the cellulose resin is 5-30 wt % of the expansion bonding layer.

[0010] Preferably, the epoxy resin having 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 having a softening point above 40°C is 30-80wt% of the expansion adhesive layer.

[0011] 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 bonding layer.

[0012] 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 10-45wt% of the expansion adhesive layer.

[0013] Preferably, the fixing agent is dicyandiamide, and the mass fraction of the fixing agent is 1-5 wt % of the expansion bonding layer; 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 having a softening point above 40° C., a temperature-sensitive foaming agent, a curing agent, an accelerator, a cellulose resin, and a thermoplastic resin 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: it can significantly improve the bending resistance of the expansion adhesive layer and avoid the expansion adhesive layer from breaking due to bending; and the present invention can significantly improve the adhesion of the expansion adhesive layer to the substrate, avoid the floating of the adhesive layer during the cutting process, and avoid the peeling of the expansion adhesive layer and the substrate caused by the mutual adhesion between the expansion adhesive layers during storage.

[0017] Other advantages, objectives and features of the present invention will be reflected in part through the following description, and in part 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 were used in Examples 1-6 and Comparative Examples 1-5.

[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 STD10 Ethyl cellulose Dow CAB-381-0.5 Cellulose butyrate Eastman CAP-504-0.2 Cellulose acetate-propionate Eastman CA-398-3 Cellulose acetate Eastman Mowital B20H Polyvinyl butyral Eastman BR73 polyacrylic acid Mitsubishi 8663-55D Linear polyurethane Lubrizol The remaining materials are commonly sold.

[0021] The materials and proportions in Examples 1-6 and Comparative Examples 1-5 are as shown in Table 2 (parts by weight).

[0022] Table 2 Product Name Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 NPPN442 40 40 40 40 40 40 40 40 40 40 40 PKHB 40 35 15 35 35 35 42 10 35 35 35 STD10 5 10 30 3 35 CAB-381-0.5 10 CAP-504-0.2 10 CA-398-3 10 Mowital B20H 10 BR73 10 8663-55D 10 EMH302 10 10 10 10 10 10 10 10 10 10 10 Amicure CG-1200G 4 4 4 4 4 4 4 4 4 4 4 PN-50 1 1 1 1 1 1 1 1 1 1 1 MEK 100 100 100 100 100 100 100 100 100 100 100 Example 1 S1. Dissolve 40 parts NPPN442, 40 parts PKHB, and 5 parts STD10 in 100 parts MEK at room temperature, then add 10 parts EHM302, 4 parts Amicure CG-1200G, and 1 part PN-50 and disperse at high speed at room temperature for 1 hour to prepare expansion layer adhesive A. S2. Apply the expansion layer glue A onto the release paper and dry it at 100°C to form an expansion adhesive layer B attached to the release paper. Then, transfer the upper and lower expansion adhesive layers B to both sides of the substrate (PEN, 75μm) at a temperature higher than the softening point of the expansion adhesive layer B (100°C) to obtain an expansion insulating sheet.

[0023] Examples 2-5 refer to Example 1 Example 6 S1. Dissolve 40 parts NPPN442, 35 parts PKHB, and 10 parts CA-398-3 in 100 parts MEK at room temperature, then add 10 parts EHM302, 4 parts Amicure CG-1200G, and 1 part PN-50 and disperse at high speed at room temperature for 1 hour to prepare expansion layer adhesive A. S2. Apply the expansion layer glue A directly on both sides of the substrate (PEN, 75 μm) and dry it at 100°C to obtain the expansion insulation sheet.

[0024] Comparative Examples 1-5 refer to Example 1.

[0025] The intumescent insulating sheets prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to performance tests.

[0026] Bending resistance test method: Cut the samples of the examples and comparative examples into 5 cm x 50 cm pieces, bend them 180 degrees at any point, and visually inspect the condition of the expandable adhesive layer. If no cracking or lifting of the expandable adhesive layer is observed, the sample is marked as passing. If cracking or lifting of the expandable adhesive layer is observed, the sample is marked as failing.

[0027] Cutting test method: Use a utility knife to cut approximately 5-10 cm incisions on the samples of the examples and comparative examples. Observe whether the expandable adhesive layer at the cut surface lifts off the substrate. If no lift is observed, label it A; if lift is observed but the expandable adhesive layer remains intact, label it B; if lift is observed and the expandable adhesive layer also falls off, label it C.

[0028] 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 the samples apart to confirm adhesion. If the expandable adhesive layer remains intact after peeling, the sample is marked as acceptable. If the expandable adhesive layer adheres to itself or separates from the substrate, the sample is marked as unacceptable.

[0029] The test results are shown in Table 3 below.

[0030] Table 3 Product Name Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 NPPN442 40 40 40 40 40 40 40 40 40 40 40 PKHB 40 35 15 35 35 35 42 10 35 35 35 STD10 5 10 30 3 35 CAB-381-0.5 10 CAP-504-0.2 10 CA-398-3 10 Mowital B20H 10 BR73 10 8663-55D 10 EMH302 10 10 10 10 10 10 10 10 10 10 10 Amicure CG-1200G 4 4 4 4 4 4 4 4 4 4 4 PN-50 1 1 1 1 1 1 1 1 1 1 1 MEK 100 100 100 100 100 100 100 100 100 100 100 Bending resistance qualified qualified qualified qualified qualified qualified Unqualified qualified Unqualified Unqualified Unqualified Cutting experiment A A A A A A B B C C C Surface stickiness qualified qualified qualified qualified qualified qualified qualified qualified Unqualified qualified qualified It can be seen from the test results of Examples 1-6 and Comparative Examples 1-5 that the present invention adds cellulose resin to the expandable insulating sheet, and utilizes its rigid and regular linear structure composed of glucose units connected by β-1,4-glycosidic bonds to effectively improve the mechanical strength of the expandable adhesive layer. Compared with the addition of other synthetic polymer materials, the bending resistance of the expandable adhesive layer is significantly improved, and the rupture of the expandable adhesive layer caused by bending is avoided; and the addition of cellulose resin helps to stabilize the dispersion of the coating liquid and prevent flocculation, so that the main adhesive resin can be more effectively distributed around the particles and finally form a continuous film on the substrate, ensuring that the main adhesive resin has good contact with the substrate. The polar groups contained in the cellulose resin can also form hydrogen bonds or dipole interactions with the polar groups on the surface of the substrate, thereby improving the adhesion of the expandable adhesive layer to the substrate, avoiding the floating of the expandable adhesive layer during the cutting process, and avoiding the peeling of the expandable adhesive layer and the substrate caused by the mutual adhesion between the expandable adhesive layers during storage.

[0031] 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 specific details.

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 cellulose resin and a thermoplastic resin.

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 cellulose resin is any one of methyl cellulose, ethyl cellulose, cellulose acetate, cellulose butyrate, cellulose acetate-propionate, cellulose acetate-butyrate, and cellulose acetate phthalate, or a combination of at least two thereof.

4. The expandable insulating sheet according to claim 1, wherein The cellulose resin is ethyl cellulose, and the mass fraction of the cellulose resin is 5-30 wt % of the expansion bonding layer.

5. 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 30-80wt% of the expansion adhesive layer.

6. 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.

7. 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 10-45wt% of the expansion adhesive layer.

8. The expandable insulating sheet according to claim 1, wherein The fixing agent is dicyandiamide, and the mass fraction of the fixing agent is 1-5wt% of the expansion bonding layer; the mass fraction of the accelerator is 0.5-2wt% 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 having a softening point above 40° C., a temperature-sensitive foaming agent, a curing agent, an accelerator, a cellulose resin, and a thermoplastic resin 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.