Expansion bonding sheet and preparation method thereof

Abstract

The present invention relates to an expansion adhesive sheet comprising: a base material; two thermal expansion adhesive layers respectively disposed on both sides of the substrate; the expansion bonding sheet is characterized in that the expansion bonding sheet further comprises a release paper layer which is arranged on the surface of one thermal expansion bonding agent layer; and the release paper is double-sided release paper. The invention has the following beneficial effects: during winding, only one layer of release paper (the upper layer or the lower layer) is peeled off, so that the molding equipment is simplified, the winding can be carried out at a higher temperature without using measures for reducing the product performance, and the adhesion is avoided during winding; compared with a five-layer structure attached with non-woven fabric or sprayed with a release agent, the operation convenience is improved, and the requirements of instruments and equipment are simplified; according to the scheme, the degree of freedom of adhesive formula design can be improved at the same time, and the softening point of the expansion bonding layer can be reduced on the premise of ensuring that the expansion bonding layer is non-viscous at room temperature.

Description

Technical Field

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

[0002] Epoxy resin adhesives have excellent heat resistance and strong adhesion, so they are widely used in component bonding, structural bonding, etc. In related fields such as electrical and electronic, 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 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] The expansion adhesive sheet is a multi-layer structure, and its core structure is three layers, namely: expansion adhesive layer + substrate + expansion adhesive layer. After the expansion adhesive sheet is prepared, it needs to be rolled up, but there is residual heat generated during drying and transfer. At this time, the temperature of the expansion adhesive layer is higher than its softening point, and it is sticky. If it is rolled up immediately, it will cause adhesion. In addition, when storing or transporting the adhesive sheet, high temperature may occur. When the temperature rises, the adhesive sheet shows stickiness, adheres to each other or adheres to other objects, making it unusable. In order to prevent the adhesive sheet from sticking after rolling up, and not sticking when it is stored and transported at high temperatures, the prior art usually adopts a non-woven fabric (i.e., non-woven fabric) attached to the three-layer structure to form a five-layer structure, i.e., non-woven fabric + expansion adhesive layer + substrate + expansion adhesive layer + non-woven fabric, or spraying a release agent on the surface of the expansion adhesive layer outside the three-layer structure, but both methods will cause the product performance to deteriorate when the adhesive sheet is used. For example, CN112189041B discloses a heat-expandable adhesive sheet, which has a permeable layer of non-woven fabric outside the three-layer structure. The thickness and density of the layer will reduce the stickiness of the adhesive sheet surface, resulting in decreased adhesion when the product is used, and the expanded adhesive layer may penetrate at high temperatures, causing adhesion. CN105940071B discloses an adhesive sheet that maintains sufficient foaming performance while also having excellent operability. The adhesive layer has a coating, which will cause product performance to decline when used. Summary of the invention

[0004] 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.

[0005] In order to achieve these purposes and other advantages according to the present invention, an expansion adhesive sheet is provided, comprising a substrate and two heat expansion adhesive layers, each arranged on both sides of the substrate; the expansion adhesive sheet also includes a release paper layer, which is arranged on the surface of one of the heat expansion adhesive layers; the release paper is a double-sided release paper.

[0006] Preferably, the thermal expansion adhesive layer comprises a multifunctional epoxy resin, a curing agent, an accelerator, a temperature-sensitive foaming agent, and a thermoplastic resin.

[0007] Preferably, the thermoplastic resin is one or more of polyester, polyurethane, polyolefin, phenoxy resin, acrylic resin, and polyvinyl butyral (PVB).

[0008] Preferably, the multifunctional epoxy resin is one or more of o-cresol epoxy resin, phenol novolac epoxy resin, and 1,1,1-tris(4-hydroxyphenyl)ethyl triglycidyl ether.

[0009] Preferably, the curing agent is dicyandiamide, and the content of the curing agent is 1-15 parts by mass relative to 100 parts by mass of the epoxy resin.

[0010] Preferably, the accelerator is one or more of an imidazole accelerator containing 2-methylimidazole, 2-methyl-4-ethylimidazole or 2-phenylimidazole, a tertiary amine accelerator containing 1,8-diazabicyclo[5.4.0]undec-7-ene, triethylenediamine or benzyldimethylamine, and an organic phosphorus accelerator containing tributylphosphine or triphenylphosphine, and the content of the accelerator is 0.2-10 parts by mass relative to 100 parts by mass of the epoxy resin.

[0011] Preferably, the temperature-sensitive foaming agent is a heat-expandable microsphere with a diameter of 5-50 μm, and the content of the temperature-sensitive foaming agent is 1-20 parts by mass relative to 100 parts by mass of the epoxy resin.

[0012] Preferably, the substrate is one or more of a polyester film, a polyimide film, an aramid film, and polyethylene naphthalate, and the thickness of the substrate is in the range of 5-200 um.

[0013] The present invention also provides a method for preparing an expansion adhesive sheet, which is characterized by comprising the following steps:

[0014] S1, dissolving a multifunctional epoxy resin, a curing agent, an accelerator, a temperature-sensitive foaming agent, and a thermoplastic resin in a ketone solvent in proportion to prepare an adhesive solution A;

[0015] S2. Apply adhesive solution A directly or successively to both sides of the substrate, dry to obtain a heat-expandable adhesive layer, and then cover one of the heat-expandable adhesive layers with release paper, and roll it up to obtain an expandable adhesive sheet product; or apply adhesive solution A to release paper, dry to obtain a heat-expandable adhesive layer B, and transfer the heat-expandable adhesive layer B to both sides of the substrate successively or simultaneously at a temperature higher than the softening point of the heat-expandable adhesive layer B by transfer printing, and then peel off the release paper on one of the heat-expandable adhesive layers, and roll it up to obtain an expandable adhesive sheet product; or apply adhesive solution A to release paper, dry to obtain a heat-expandable adhesive layer B, and then apply another adhesive solution A to one side of the substrate, and then transfer the heat-expandable adhesive layer B to the other side of the substrate that is not coated at a temperature higher than the softening point of the heat-expandable adhesive layer B, and roll it up to obtain an expandable adhesive sheet product.

[0016] Preferably, the ketone solvent is one or a combination of acetone and butanone, and the content thereof is 100-300 parts by mass relative to 100 parts by mass of the epoxy resin.

[0017] The present invention includes at least the following beneficial effects: when rolling up, only one layer of release paper (upper layer or lower layer) is peeled off, and while simplifying the molding equipment, it can be rolled up at a higher temperature without using measures that reduce product performance, and there will be no adhesion during rolling up; compared with a five-layer structure with attached non-woven fabric or sprayed release agent, the performance of the product will not decrease, and the operational convenience is improved and the requirements for instruments and equipment are simplified; this solution can also increase the degree of freedom in the design of adhesive formulas.

[0018] Other advantages, objectives and features of the present invention will be embodied 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

[0019] The present invention is described in further detail below so that those skilled in the art can implement it according to the description.

[0020] Example 1

[0021] A method for preparing an adhesive sheet comprises the following steps:

[0022] S1, dissolving 100g of phenol novolac epoxy resin F44, 6g of dicyandiamide as a curing agent, 6g of heat-expandable microspheres (EMH302, particle size 15-25um, manufactured by Sekisui Chemical) as a temperature-sensitive foaming agent, 25g of PVB (Kuraray, Mowital B20H) as a thermoplastic resin, and 1g of 2-methylimidazole as a accelerator in 125g of butanone to prepare an adhesive solution A; applying the adhesive solution A onto a release paper, and drying to form an expanded adhesive layer B attached to the release paper;

[0023] S2. Then, the two expandable adhesive layers B are simultaneously transferred to both sides of a 100 μm thick polyimide film at a temperature (80° C.) higher than the softening point of the expandable adhesive layer B by transfer printing, and one layer of the release paper is peeled off and rolled up to obtain an expandable adhesive sheet product.

[0024] After the product was cured at 160°C for 30 minutes, the tensile shear strength at room temperature was tested to be 10.40 MPa (test area 25 mm×12.5 mm).

[0025] Example 2

[0026] A method for preparing an adhesive sheet comprises the following steps:

[0027] S1, 100g of phenol novolac epoxy resin F44, 6g of dicyandiamide as a curing agent, 6g of heat-expandable microspheres (SEKISUI CHEMICAL, EMH302, particle size 15-25um) as a temperature-sensitive foaming agent, 25g of PVB (Kuraray, Mowital B20H) as a thermoplastic resin, and 1g of 2-methylimidazole as a accelerator were dissolved in 125g of butanone to prepare an adhesive solution A;

[0028] S2. Apply adhesive solution A to both sides of a 100 um thick polyimide film, dry it to obtain a heat-expandable adhesive layer B, and then laminate a release paper on one of the heat-expandable adhesive layers B by hot pressing, and roll it up to obtain an expandable adhesive sheet product.

[0029] After the product was cured at 160°C for 30 minutes, the tensile shear strength at room temperature was tested to be 10.46 MPa (test area 25 mm×12.5 mm).

[0030] Example 3

[0031] A method for preparing an adhesive sheet comprises the following steps:

[0032] S1, 100g of phenol novolac epoxy resin F44, 6g of dicyandiamide as a curing agent, 6g of heat-expandable microspheres (SEKISUI CHEMICAL, EMH302, particle size 15-25um) as a temperature-sensitive foaming agent, 25g of PVB (Kuraray, Mowital B20H) as a thermoplastic resin, and 1g of 2-methylimidazole as a accelerator were dissolved in 125g of butanone to prepare an adhesive solution A;

[0033] S2. Apply adhesive solution A onto release paper and dry to obtain heat-expandable adhesive layer B, then apply adhesive solution A onto one side of a substrate, then transfer the heat-expandable adhesive layer B on the release paper to the other side of the substrate that is not coated at a temperature higher than the softening point of the heat-expandable adhesive layer B, and roll up to obtain an expandable adhesive sheet product.

[0034] After the product was cured at 160°C for 30 minutes, the tensile shear strength at room temperature was tested to be 10.42 MPa (test area 25 mm×12.5 mm).

[0035] Comparative Example 1

[0036] S1, same as in Example 1;

[0037] S2. Then, the upper and lower expandable adhesive layers B are simultaneously transferred to both sides of a 100 um thick polyimide film at a temperature (80°C) higher than the softening point of the expandable adhesive layer B by transfer printing, and the two layers of release paper are peeled off at the same time. Subsequently, two layers of non-woven fabrics are attached to the upper and lower surfaces by heat pressing, and the product is rolled up.

[0038] After the product was cured at 160°C for 30 minutes, the tensile shear strength at room temperature was tested to be 5.5 MPa (test area 25 mm×12.5 mm).

[0039] Comparative Example 2

[0040] S1, same as in Example 1;

[0041] S2. Then, the upper and lower expansion adhesive layers B are simultaneously transferred to both sides of a 100 μm thick polyimide film at a temperature (80° C.) higher than the softening point of the expansion adhesive layer B by transfer printing, and the two layers of release paper are peeled off at the same time. Then, a release agent is sprayed on the upper and lower surfaces by spraying, and the product is rolled up.

[0042] After the product was cured at 160°C for 30 minutes, the tensile shear strength at room temperature was tested to be 6.2 MPa (test area 25 mm×12.5 mm).

[0043] Comparative Example 3

[0044] S1, same as in Example 1;

[0045] S2. Apply adhesive solution A to both sides of a 100 um thick polyimide film, dry it to obtain a heat-expandable adhesive layer B, then attach two layers of non-woven fabrics to the two layers of heat-expandable adhesive layer B by hot pressing, and roll them up to obtain the product.

[0046] After the product was cured at 160°C for 30 minutes, the tensile shear strength at room temperature was tested to be 5.6 MPa (test area 25 mm×12.5 mm).

[0047] Comparative Example 4

[0048] S1, same as in Example 1;

[0049] S2. Apply the adhesive solution A onto both sides of a 100 um thick polyimide film, dry it to obtain a heat expansion adhesive layer B, then spray a release agent on the surfaces of the two layers of heat expansion adhesive layer B, and roll it up to obtain the product.

[0050] After the product was cured at 160°C for 30 minutes, the tensile shear strength at room temperature was tested to be 6.4 MPa (test area 25 mm×12.5 mm).

[0051] Comparative Example 5

[0052] S1, same as in Example 1;

[0053] S2. Apply adhesive solution A to both sides of a 100 um thick polyimide film, dry it to obtain a heat-expandable adhesive layer B, and then roll up the product. During the rolling process, the expanded adhesive sheet product will adhere.

[0054] It can be seen from the test results of Examples 1-3 and Comparative Examples 1-5 that the products prepared by the present invention can maintain relatively high tensile shear strength while ensuring that the products will not stick during rolling.

[0055] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and implementation modes, and can be fully applicable 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 the examples shown and described herein.

Claims

1. An expansion adhesive sheet, characterized in that: The expansion adhesive sheet comprises a substrate and two heat expansion adhesive layers respectively arranged on both sides of the substrate; the expansion adhesive sheet also comprises a release paper layer arranged on the surface of one of the heat expansion adhesive layers; the release paper is a double-sided release paper.

2. The expansion adhesive sheet according to claim 1, characterized in that: The thermal expansion adhesive layer comprises a multifunctional epoxy resin, a curing agent, an accelerator, a temperature-sensitive foaming agent and a thermoplastic resin.

3. The expansion adhesive sheet according to claim 2, characterized in that: The thermoplastic resin is one or more of polyester, polyurethane, polyolefin, phenoxy resin, acrylic resin, and polyvinyl butyral.

4. The expansion adhesive sheet according to claim 2, characterized in that: The multifunctional epoxy resin is one or more of o-cresol epoxy resin, phenol novolac epoxy resin, and 1,1,1-tris(4-hydroxyphenyl)ethyl triglycidyl ether.

5. The expandable adhesive sheet according to claim 2, characterized in that: The curing agent is dicyandiamide, and the content of the curing agent is 1-15 parts by mass relative to 100 parts by mass of the epoxy resin.

6. The expandable adhesive sheet according to claim 2, characterized in that: The accelerator is one or more of an imidazole accelerator containing 2-methylimidazole, 2-methyl-4-ethylimidazole or 2-phenylimidazole, a tertiary amine accelerator containing 1,8-diazabicyclo[5.4.0]undec-7-ene, triethylenediamine or benzyldimethylamine, and an organic phosphorus accelerator containing tributylphosphine or triphenylphosphine. The content of the accelerator is 0.2-10 parts by mass relative to 100 parts by mass of the epoxy resin.

7. The expandable adhesive sheet according to claim 2, characterized in that: The temperature-sensitive foaming agent is a heat-expandable microsphere with a diameter of 5-50 μm. The content of the temperature-sensitive foaming agent is 1-20 parts by mass relative to 100 parts by mass of the epoxy resin.

8. The expandable adhesive sheet according to claim 2, characterized in that: The substrate is one or more of polyester film, polyimide film, aramid film, polyethylene naphthalate, and the thickness of the substrate is in the range of 5-200 um.

9. A method for preparing an expandable adhesive sheet according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1, dissolving a multifunctional epoxy resin, a curing agent, an accelerator, a temperature-sensitive foaming agent, and a thermoplastic resin in a ketone solvent in proportion to prepare an adhesive solution A; S2. Apply adhesive solution A directly or successively to both sides of the substrate, dry to obtain a heat-expandable adhesive layer, and then cover one of the heat-expandable adhesive layers with release paper, and roll it up to obtain an expandable adhesive sheet product; or apply adhesive solution A to release paper, dry to obtain a heat-expandable adhesive layer B, and transfer the heat-expandable adhesive layer B to both sides of the substrate successively or simultaneously at a temperature higher than the softening point of the heat-expandable adhesive layer B by transfer printing, and then peel off the release paper on one of the heat-expandable adhesive layers, and roll it up to obtain an expandable adhesive sheet product; or apply adhesive solution A to release paper, dry to obtain a heat-expandable adhesive layer B, and then apply another adhesive solution A to one side of the substrate, and then transfer the heat-expandable adhesive layer B to the other side of the substrate that is not coated at a temperature higher than the softening point of the heat-expandable adhesive layer B, and roll it up to obtain an expandable adhesive sheet product.

10. The method for preparing an expandable adhesive sheet according to claim 9, characterized in that: The ketone solvent is one or a combination of acetone and butanone, and the content of the ketone solvent is 100-300 parts by mass relative to 100 parts by mass of the epoxy resin.