WO2008103008A1

WO2008103008A1 - Adhesive resin for expansion sheet using mutually reactive copolymers and expansion sheet using their adhesive

Info

Publication number: WO2008103008A1
Application number: PCT/KR2008/001054
Authority: WO
Inventors: Kwang Choon Chung; Myoung Seon Gong; Myoung Hee Joo; Hee Yong Ahn
Original assignee: Haeum Chemtec Co., Ltd.
Priority date: 2007-02-22
Filing date: 2008-02-22
Publication date: 2008-08-28
Also published as: CN101541907A; TWI374923B; JP5235904B2; KR100831081B1; CN101541907B; TW200904926A; JP2010519379A

Abstract

The present invention relates to an adhesive resin for expansion sheet using mutually reactive copolymers and an expansion sheet using the same. Particularly, the present invention provides an adhesive resin having excellent adhesive strength on a substrate before expansion and excellent upholding power for microsphere to inhibit expansion and a heat-peelable adhesive sheet that is easily separated from the substrate when adhesive strength is lost by heat treatment at high temperature. The adhesive resin prepared by mixing mutually reactive copolymers has advantages of long-term shelf-life since cross-linking does not occur at room temperature, maintaining upholding power of the expansion layer during the production of a heat-peelable adhesive sheet, and increasing expansion temperature of microsphere so that it facilitates easy separation from a substrate when the substrate is heated at high temperature owing to the reduced or lost adhesive strength thereafter.

Description

[DESCRIPTION]

[invention Title]

ADHESIVE RESIN FOR EXPANSION SHEET USING MUTUALLY REACTIVE COPOLYMERS AND EXPANSION SHEET USING THEIR ADHESIVE

[Technical Field]

The present invention relates to an adhesive resin for expansion sheet which has a long-term stability and no cross- linking reaction at room temperature, prepared by using mutually reactive copolymers and an expansion sheet (heat- peelable adhesive sheet) which is easily peeled from the substrate at high temperature and has excellent adhesive strength using the same.

[Background Art]

The conventional adhesive resin used for expansion sheet is a copolymer resin comprising acryl monomer and other monomer containing hydroxyl group as a cross-linking functional group and is generally prepared by using isocyanate cross-linking agent. The recent expansion sheet applied in electrical equipment needed to be expanded at least of 150"C . high temperature. However, microsphere for expansion sheet which is expanded at high temperature is limited in use at high temperature as it starts expansion from 150^°C . This limitation can be solved by inhibiting of the expansion of microsphere using the adhesive resin that has high cohesive force or bearing power or can be regulated by chemical construction of vinyl monomer forming adhesive resin, which is not easy though.

Thus, it is rather preferred to modify cross-linking method considering adhesion, cohesive force, heat-resistance, softness and elasticity. As for the conventional adhesive resin for expansion sheet It takes long time to produce completely mixed and dispersive microsphere. During this process, a cross- linking agent added thereto is reacting slowly to increase viscosity or induce gelation, resulting defects in coating. In particular, the increased degree of cross-linking for inhibiting the expansion of microsphere causes more serious problems.

The conventional adhesive resin for heat-peelable expansion sheet is an acryl-based resin containing a cross- linking functional group. So, after adding a cross-linking agent, cross- linking reaction proceeds slowly during the mixing, dispersing, and coating of microsphere a**≡t—coating to change viscosity, resulting in irregular coating. This phenomenon becomes more peculiar with the increase of the ratio of cross- linking functional group used to increase cross -linking degree. [Disclosure]

[Technical Problem]

The expansion sheet using the adhesive resin of the present invention designed to solve the above mentioned problem can be used for the field of electrode printing, fixation, cutting and heat-based sticking/peeling, etc. of parts in the manufacturing process of FPCB sticking/peeling, semiconductor wafer grinding, semiconductor chip, chip condenser, chip varistor and inductor, etc. in the process performed at high temperature or repeatedly at high temperature .

To overcome the above mentioned problem, the present inventors studied and confirmed that co-treatment of an adhesive resin containing microsphere with mutually reactive copolymers could extend working life long enough and caused no viscosity change even after leaving 2 - 3 days after mixing. Based on this finding, the inventors completed this invention.

Precisely, the present inventors found out that amide- ester chemical cross-linking and at the same time physical cross- linking such as hydrogen bond could be induced by the reaction of the two functional groups, namely carboxyl group and oxazoline group. The present inventors further confirmed that the increase of cross-linking degree resulted in the increase of cross-linking density and cohesive force, which could make microsphere to be expanded at higher temperature so as to facilitate high temperature expansion to foam or expand adhesive 1ayer .

So, this heat-peelable adhesive sheet has the advantage of reducing adhesive force to be separated from the substrate easily by expanding microsphere included in adhesive layer at higher temperature than the general expansion temperature of microsphere. Particularly, expansion at high temperature at least 150^°C or at repeated high temperature, which means when the procedure is repeated as heating at high temperature and cooling down and then heating at high temperature again, continuously reduces expansion temperature of the expansion sheet. Therefore, an expansion sheet which is able to be expanded at high temperature is required. It is an object of the present invention to provide the adhesive for that purpose.

The adhesive resin of the present invention produced by mixing mutually reactive copolymers having carboxyl group and oxazoline group as functional groups is highly stable at room temperature. The copolymers are reacted at 100^°C or higher to form ester-amide bond, resulting in cross-linking. So, when microsphere expands, cohesive force and elasticity of adhesive increase to raise expansion temperature of microsphere. Thus, the present invention provides a heat-peelable adhesive sheet which has excellent early adhesive strength and successfully maintained bearing power and might experience the decrease or lose of adhesive strength only when it is treated at high temperature by heating.

The adhesive of the present invention bringing the above effect is produced by mixing two mutually reactive copolymer solutions, the first is a copolymer containing carboxyl group and the second is a copolymer containing oxazoline group. At this time, cross-linking is not induced at room temperature, which means it is safe enough to be stored at room temperature for a long term, and as the cross-linking is induced at around 100^°C, it facilitates the production of the expansion sheet having high density adhesive layer.

The present invention also provides an expansion sheet expanded at high temperature of at least 150"C by using an adhesive produced by mixing two acryl copolymers respectively containing carboxyl group and oxazoline group, the mutually reactive groups, and the coating resin for expansion sheet produced by dispersing microsphere.

[Technical Solution]

The present invention relates to an adhesive resin for expansion sheet prepared by using mutually reactive copolymers and an expansion sheet using the same. Herein, the adhesive resin is characteristically prepared by mixing mutually reactive copolymers containing heat-expandable microsphere. The adhesive resin prepared thereby is coated to form an adhesive layer on one side or both sides of a substrate to prepare the expansion sheer (heat-peelable adhesive sheet) in which the adhesive layer is foamed or expanded by heat.

Hereinafter, the adhesive resin of the present invention and the expansion sheet using the same are described in detail.

The adhesive resin of the present invention characteristically comprises heat-expandable microsphere and mutually reactive copolymers.

The heat-expandable microsphere is a substance facilitating gasification and heat-expandable like isobutane, propane and pentane . The outer shell of the microsphere is composed of heat-soluble substances or heat-expandable substances, such copolymers as vinylidene chloride, acrylonitrile and methylmethacrylate . Various microspheres having different expansion temperature ranging from 100 to 170^°C, according to the components of the shell and thickness, are sold on market. However, the above temperature is the maximum expansion temperature and the expansion starting temperature is 20 - 50 °C lower than that.

The microsphere is preferably 10 - 25 μm in mean diameter for the dispersion in the adhesive resin and its adhesive layer is easily modified by heat with reducing adhesive strength. The dried expansion adhesive layer is preferably thicker than the maximum diameter of the heat-expandable microsphere in order to make the surface of the adhesive layer smooth and secure the adhesive strength stably before heat treatment.

To take advantage of the decrease of adhesive strength of the adhesive layer by heat treatment, the heat-expandable microsphere had better not to be broken after expansion with 10 times the volume expansion rate. The content of the heat- expandable microsphere is determined by considering expansion rate of the adhesive layer or the reduced margin of adhesive strength. In general, the preferable content of microsphere is 5 - 20 weight part for 100 weight part of the adhesive resin forming adhesive layer. On the other hand, The mutually reactive copolymers playing a role in dispersing the microsphere is the resin comprising the first copolymer prepared by copolymerization of vinyl monomer, comonomer and the monomer containing carboxyl group and the second copolymer prepared by copolymerization of vinyl monomer, comonomer and the monomer containing oxazoline group .

The vinyl monomer and the vinyl comonomer composing the first and the second copolymers are not limited, but preferably selected, for the purpose of enhancing adhesion, cohesive force, heat-resistance and softness of the expansion sheet, from the group consisting of vinyl monomer containing alkyl group such as methylacrylate, methylmethacrylate, ethylacrylate, ethylmethacrylate, propylacrylate, propylmethacrylate, butylacrylate, butylmethacrylate, hexylacrylate, hexylmethacrylate, octylacrylate and 2- ethylhexylacrylate ; vinyl monomer containing hydroxyl group such as hydroxyethylacrylate, hydroxyethylmethacrylate, hydroxypropylacrylate, hydroxypropylmethacrylate, hydroxybutylacrylate, hydroxybutylmethacrylate, hydroxyhexylacrylate and hydroxyhexylmethacrylate; N- substituted amide vinyl monomer such as N, N-dimethyl acrylamide and N, N-dimethyl methacrylamide; al koxyalkylacrylate vinyl monomer such as methoxyethylacrylate, methoxyethylmethacrylate, ethoxyethylacrylate and ethoxyethylmethacrylate; vinyl monomer such as vinylacetate, vinylpropionate, N- vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-vinylcarboxamide, stylene, α-methylstylene and N-vinylcaprolactam; cyanoacrylate vinyl monomer such as acrylonitrile and methacrylonitrile; acryl monomer containing epoxy group such as glycidylacrylate and glycidylmethacrylate; glycol acrylester monomer such as polyethyleneglycolacrylate, polyethyleneglycolmethacrylate, polypropyleneglycolaerylate, polypropyleneglycolmethacrylate, methoxyethyleneglycolacrylate, methoxypolyethyleneglycolmethacrylate, methoxypolypropyleneglycolacrylate and methoxypolypropyleneglycolmethacrylate; acrylic acid ester monomer such as tetrahydrofurfurylacrylate, tetrahydrofurfurylmethacrylate and 2-methoxyethyl acrylate; such monomers as isoprene, butadiene, isobutylene, vinylether; and a mixture of at least two of those.

The preferable content of the vinyl monomer and comonomer composing the first copolymer containing carboxyl group and the second copolymer containing oxazoline group is 80 - 95 weight% for the total weight of the adhesive resin. If the content of the vinyl monomer and comonomer is less than 80 weight%, the amount of cross-linking functional group will be increased to bring high cross-linking, resulting in the decrease or loss of adhesive power and obtaining brittleness. The copolymerization with such monomers having high polar functional group makes the control of polymerization speed or composition ratio of the copolymer difficult because of the differences of polarity and reaction rates. The vinyl comonomer can be a mixture of at least two of those or any conventional vinyl comonomer that can enhance the characteristics of the adhesive resin by regulating the content thereof .

The first copolymer containing carboxyl group is prepared by solution polymerization, particularly by copolymerization of at least two or three monomers selected from the group consisting of monomers containing carboxyl group such as acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid and crotonic acid; and acid anhydride monomers such as maleic anhydride and itaconic anhydride, for the purpose of enhancing the cross-linking degree.

As a cross-linking functional group forming the copolymer, the vinyl monomer containing carboxyl group is preferably included by 5 - 20 weight% for the total monomer of the copolymer, and 5 - 10 weight% is more preferred. If the content of the vinyl monomer containing carboxyl group is less than 5 weight%, the degree of cross-linking will not be sufficient, so that softness of membrane will be increased but cohesive force will be reduced, suggesting that it is impossible to control the expansion of microsphere.

The second copolymer containing oxazoline is prepared by solution polymerization, particularly by copolymerization of two or more compounds selected from the group consisting of 2- vinyl-2-oxazoline, 2-vinyl-4-vinyl-2-oxazoline, 2-vinyl-5- vinyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-

5-ethyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-

(vinylbenzyloxy-1-methylethyl) -2-oxazoline, 2- (2-hydroxy-l- methylethyl ) acrylate and 2- (2-hydroxy-l- methylethyl)methacrylate, for the purpose of enhancing the cross-linking degree.

The vinyl monomer containing oxazoline group composing the copolymer is preferably added by 5 - 20 weight% for the total monomer of the copolymer and 10 - 5 weight% is more preferred. If the content of the vinyl monomer containing oxazoline group is less than 5 weight%, the degree of cross- linking will not be sufficient, so that softness of membrane will be increased but cohesive force will be reduced, suggesting that it is impossible to control the expansion of microsphere .

The adhesive resin for expansion sheet of the present invention that is prepared by using mutually reactive copolymers is prepared by the following three steps. In step 1, the first copolymer containing carboxyl group is synthesized. In step 2, the second copolymer containing oxazoline group is synthesized. In step 3, microsphere is dispersed in the adhesive resin comprising the first and the second copolymers. The adhesive resin produced by the above steps is a very stable coating solution without time course change and allows the increase of expansion temperature by 20 - 30^°C or more.

To produce the expansion sheet of the present invention, the adhesive resin prepared above is coated on one side or both sides of a substrate to form an adhesive layer, which is coated with a release film. At this time, in order to increase adhesive power between the substrate and the adhesive layer, surface treatment process can be included. Fig. 1 is a cross- section illustrating an example of the expansion sheet of the present invention, which is composed of the substrate (1) , the surface treatment layer (2) , the expansion adhesive layer (3) prepared by the mixture of mutually reactive copolymers and the release film (4) .

[Advantageous Effect]

The adhesive solution using the mutually reactive copolymer mixture composed of the first copolymer having carboxyl group and the second copolymer containing oxazoline group according to the present invention facilitates the production of an adhesive resin for expansion sheet with excellent stability.

In the case of other resin solutions with high reactivity of a cross-linking agent, the solution is prepared as two liquids which are mixed right before being used as an adhesive resin. In that case, in addition to inconvenience, it has disadvantages of difficulty of even coating or coating itself on a substrate because of reaction of the functional group of the adhesive resin and the cross-linking agent or gelation. If coated, thickness varies, indicating severe deviations in the expansion sheet characteristics. However, the mutually reactive copolymer mixture each containing carboxyl group and oxazoline group does not induce any reaction at room temperature, suggesting that the adhesive resin comprising the copolymers is stable at room temperature with small deviations in the adhesive resin characteristics.

Besides, the use of a copolymer cross-linking agent induces formation of physical bond such as hydrogen bond and increases cross-linking density in between resins, resulting in the increase of cohesive force and bearing power to inhibit the expansion of microsphere, indicating that expansion temperature can be increased by 20 - 30^°C.

[Description of Drawings] The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which: Fig. 1 is a cross-section illustrating the expansion sheet of the present invention.

Fig. 2 is a diagram showing the formula representing cross-linking mechanism of the mutually reactive copolymers. * Mark description about main parts of drawing 1: substrate,

2: surface treatment layer, 3 : expansion adhesive layer 4 : release film

[Best Mode]

Practical and presently preferred embodiments of the present invention are illustrative as shown in the following Examples . However, it will be appreciated that those skilled in the art, on consideration of this disclosure, may make modifications and improvements within the spirit and scope of the present invention.

[Manufacturing Example 1] Step 1: preparation of the first copolymer

Ethylacrylate (45 g) as monomer, n-butylacrylate (45 g) as comonomer and acrylic acid (10 g) were added to a 2 L glass reactor equipped with stirrer, condenser, dropping funnel, thermometer and jacket and mixed. α, α ' -azobisisobutyronitrile (initiator, O.Olg) dissolved in ethylacetate (100 g) and toluene (20 g) was added thereto, followed by radical polymerization at 70^°C . About 30 minutes later, ethylacrylate

(135 g) , n-butylacrylate (comonomer, 135 g) and acrylic acid (30 g) were mixed, to which α, α ' -azobisisobutyronitrile

(initiator, 0.5 g) dissolved in ethylacetate (100 g) and toluene (40 g) was dropped for 90 minutes using dropping funnel. During the dropping, temperature was maintained. Upon completion of the reaction, a radical initiator (1 g) dissolved in ethylacetate (50 g) and ethanol (50 g) was dropped for 60 minutes to eliminate non-reacted monomers. The reaction was additionally induced for three more hours to give the first copolymer.

Step 2 : Preparation of the second copolymer Ethylacrylate (45 g) as monomer, n-butylacrylate (45 g) as comonomer and 2-isopropyl-2-oxazoline (10 g) were added to a 2 L glass reactor equipped with stirrer, condenser, dropping funnel, thermometer and jacket and mixed. α, α'- azobisisobutyronitrile (initiator, O.Olg) dissolved in ethylacetate (100 g) and toluene (20 g) was added thereto, followed by radical polymerization at 70^°C by the same manner as described in the above polymerization of the copolymer containing carboxyl group. About30 minutes later, ethylacrylate (135 g) , n-butylacrylate (comonomer, 135 g) and acrylic acid (30 g) were mixed, to which α,α'- azobisisobutyronitrile (initiator, 0.5 g) dissolved in ethylacetate (100 g) and toluene (40 g) was dropped for 90 minutes using dropping funnel. During the dropping, temperature was maintained. Upon completion of the reaction, radical initiator (1 g) dissolved in ethylacetate (50 g) and ethanol (50 g) was dropped for 60 minutes to eliminate non- reacted monomers. The reaction was additionally induced for three more hours to give the second copolymer. Step 3: Preparation of an adhesive resin

The two copolymer resins, the first and the second copolymers prepared in step 1 and in step 2, were mixed at the weight ratio of 1:1. Microsphere F-50D (Matsumoto, expansion starting temperature: 100 - 105°C) (10 g) was added to the resin mixture (100 g) , followed by dispersion to give an adhesive resin.

[Manufacturing Example 2]

The adhesive resin was prepared by the same manner as described in Example 1 except that the weight ratio of monomers used in step 1 of Manufacturing Example 1, ethylacrylate/n-butylacrylate/acrylic acid, was adjusted to

4.5/4.5/1.5.

[Manufacturing Example 3] The adhesive resin was prepared by the same manner as described in Manufacturing Example 1 except that the weight ratio of monomers used in step 1 of Manufacturing Example 1, ethylacrylate/n-butylacrylate/acrylic acid, was adjusted to 4.5/4.5/0.6. [Manufacturing Example 4]

The adhesive resin was prepared by the same manner as described in Manufacturing Example 1 except that microsphere F- 8OGSD (Matsumoto, expansion starting temperature: 110 115^°C) was used instead of microsphere F-50D used in step 3 of Manufacturing Example 1.

[Manufacturing Example 5]

The adhesive resin was prepared by the same manner as described in Manufacturing Example 1 except that microsphere F-80VSD (Matsumoto, expansion starting temperature: 150 160^°C) was used instead of microsphere F-50D used in step 3 of Manufacturing Example 1. [Example 1~5]

The adhesive resins prepared in Manufacturing Examples 1 - 5 were coated on PET film (50 //m) respectively to form a 37 μx\ thick expansion adhesive layer. A 36 //in releasing film was laminated thereto to produce an expansion sheet. Aging of the expansion sheet was performed for 7 days, followed by the final test.

[Comparative Manufacturing Example 1] Ethylacrylate (48.5 g) , n-butylacrylate (48.5 g) , acrylic acid (2 g) and hydroxypropylacrylate (1.0 g) were added to a 2 L glass reactor equipped with stirrer, condenser, dropping funnel, thermometer and jacket and mixed. α,α'- azobisisobutyronitrile (O.Olg) dissolved in ethylacetate (160 g) and toluene (270 g) was added thereto by using dropping funnel, followed by nitrogen substitution. During reflux, dropping continued at 80^°C, followed by radical polymerization for 8 hours. In the late stage of the reaction, excessive amount of radical initiator was added to eliminate non-reacted monomers. Then, microsphere F-50D (Matsumoto, expansion starting temperature: 100 - 105 ^"C) (10 g) was added and dispersed to give an adhesive resin.

[Comparative Manufacturing Example 2] The adhesive resin was prepared by the same manner as described in Comparative Manufacturing Example 1 except that the amount of hydroxypropylacrylate (2.0 g) having cross- linking functional group was increased, compared with that of Comparative Manufacturing Example 1. [Comparative Manufacturing Example 3]

The adhesive resin was prepared by the same manner as described in Comparative Manufacturing Example 1 except that microsphere F-8OGSD (Matsumoto, expansion starting temperature: 110 - 115^"C) was used. [Comparative Manufacturing Example 4]

The adhesive resin was prepared by the same manner as described in Comparative Manufacturing Example 1 except that microsphere F-80VSD (Matsumoto, expansion starting temperature: 150 - 160°C) was used. [Comparative Example 1~4]

AK-75 (Aekyung Chemical Co.), the isocyanate cross- linking agent, was added to each adhesive resin prepared in Comparative Manufacturing Examples 1 - 4 by double the amount of hydroxyl group (functional group) of the adhesive resin, followed by stirring to give an adhesive resin. The adhesive resin was coated on PET film (50 μm) to form a 37 μm thick expansion adhesive layer. A 36 p releasing film was laminated thereto to produce an expansion sheet. Aging of the expansion sheet was performed for 7 days, followed by the final test.

Manufacturing Examples 1 - 5 and Comparative Manufacturing Examples 1 - 4 are summarized in Table 1. Physical properties of the adhesive resins and expansion sheets prepared in Manufacturing Examples, Examples and Comparative Manufacturing Examples were tested as follows and the results are shown in Table 2 and Table 3. 1. Viscosity changes of adhesive resin

The prepared adhesive resin was put in a container with preventing evaporation of a solvent at a fixed temperature and viscosity was measured over the time by using Brookfield viscometer (DV-II+) .

2. Expansion temperature

Expansion temperature was measured by using Perkin-Elmer DSC 7 at the speed of 10^°C/min. Particularly, the adhesive resin comprising microsphere was coated on PET film, followed by aging. Upon completion of cross-linking, samples were taken from the film. 10 mm thick stainless plate was put on the hot plate with regulated temperature. After equalizing the temperature, the expansion sheet was put in between, followed by measuring the expansion temperature. The obtained temperature was compared with the temperature measured by thermometer.

3. Adhesive strength On the test plate (SUS 304) (2 mm in thickness, 50 mm in width, 200 mm in length) completely washed with isopropanol, the heat-peelable adhesive sheets of 20 mm in width and 150 mm in length, obtained in Examples and Comparative Examples, were adhered with facing the adhesive layer down by using 2 kg automatic pressure rubber roller at the speed of 30 cm/min, and rolling back and forth for one time, which was then left at room temperature for 30 minutes. Based on "KSA 1107 : 2004", adhesive strength was measured by the same manner as used for measuring 180 degree shell adhesive strength (peeling speed: 300 mm/min, 23^°C). Mean values of adhesive strength were obtained from three test samples .

[Table 3;

example 4

As explained hereinbefore, viscosity changes were hardly observed in the adhesive resin of the present invention. And the adhesive resin of the present invention facilitates the production of the expansion sheet which can be expanded at 20

30°C higher than the expansion temperature of the conventional expansion sheet using same microsphere.

[industrial Applicability] The present invention provides an adhesive resin containing microsphere capable of increasing the expansion temperature about 20 - 30^°C higher than usual, and a coating resin for expansion sheet having excellent coating properties, adhesive strength, bearing power and cohesive force as well as various functions. Therefore, the present invention is very useful for the production of the high temperature expansion sheet applicable in electronic, electric and material fields.

It is also possible to use the expansion sheet of the present invention for permanent adhesion of a substrate with proper materials. However, the preferable usage of the sheet is to adhere a substrate for a required time and peel off after achieving the purpose. That is, the present invention provides the expansion sheet that is able to be applied in assembling, cutting, and polishing of electronic, electric equipments composed of at least two materials for example polymer materials and metals, fibers or papers at high temperature; in carrier tape used for circuit process such as FPCB; in temporary fixative or surface protector to protect metal plate, plastic plate and glass plate from contamination or damage thereby; or in masking agent.

Claims

[CLAIMS]

[Claim l]

An adhesive resin for expansion sheet, characteristically prepared by mixing two or more mutually reactive copolymers and heat-expandable microsphere.

[Claim 2]

The adhesive resin for expansion sheet according to claim 1, wherein the mutually reactive copolymers are the vinyl copolymer containing carboxyl group and the vinyl copolymer having oxazoline group.

[Claim 3]

The adhesive resin for expansion sheet according to claim 2, wherein the vinyl copolymer containing carboxyl group is selected from the group consisting of monomers having one or more carboxyl groups prepared from carboxyl group containing monomers such as acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid and crotonic acid; acid anhydride monomers and a mixture comprising at least two of those.

[Claim 4l

The adhesive resin for expansion sheet according to claim 3, wherein the monomer is included by 5 - 20 weight% for the total monomer composing the vinyl copolymer containing carboxyl group .

[Claim 5]

The adhesive resin for expansion sheet according to claim 2, wherein the vinyl copolymer containing oxazoline group is selected from the group consisting of monomers prepared from such monomers as 2-vinyl-2-oxazoline, 2-vinyl-4-vinyl-2- oxazoline, 2-vinyl-5-vinyl-2-oxazoline, 2-isopropenyl-2- oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2-isopropenyl- 5-methyl-2-oxazoline, 2- (vinylbenzyloxy-1-methylethyl) -2- oxazoline, 2- (2-hydroxy-l-methylethyl ) acrylate and 2- (2- hydroxy-1-methylethyl) methacrylate and a mixture comprising at least two of those.

[Claim β]

The adhesive resin for expansion sheet according to claim 5, wherein the monomer is included by 5 - 20 weight% for the total monomer composing the vinyl copolymer containing oxazoline group.

[Claim 7]

The adhesive resin for expansion sheet according to claim 2, wherein the vinyl copolymer is selected from the group consisting of vinyl monomer containing alkyl group, vinyl monomer containing hydroxyl group, N-substituted amide vinyl monomer, alkoxyalkylacrylate, cyanoacrylate, acryl monomer containing epoxy group, glycol acrylester, acrylic acid ester, vinylacetate, vinylpropionate, N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N- vinylcarboxamide, stylene, α-methylstylene, N- vinylcaprolactam, isoprene, butadiene, isobutylene, vinylether and a mixture of at least two of those.

[Claim 8] The adhesive resin for expansion sheet according to claim 7, wherein the vinyl monomer containing alkyl group is methylacrylate, methylmethacrylate, ethylacrylate, ethylmethacrylate, propylacrylate, propylmethacrylate, butylacrylate, butylmethacrylate, hexylacrylate, hexylmethacrylate, octylacrylate or 2-ethylhexylacrylate; the vinyl monomer containing hydroxyl group is hydroxyethylaerylate, hydroxyethylmethacrylate, hydroxypropylaerylate, hydroxypropylmethacrylate, hydroxybutylacrylate, hydroxybutylmethacrylate, hydroxyhexylacrylate or hydroxyhexylmethacrylate; the N- substituted amide vinyl monomer is N, N-dimethyl acrylamide or N, N-dimethyl methacrylamide; the alkoxyalkylacrylate vinyl monomer is methoxyethylacrylate, methoxyethylmethacrylate, ethoxyethylacrylate or ethoxyethylmethacrylate; the cyanoacrylate is acrylonitrile or methacrylonitrile; the acryl monomer containing epoxy group is glycidylacrylate or glycidylmethacrylate; the glycol acrylester monomer is polyethyleneglycolacrylate, polyethyleneglycolmethacrylate, polypropyleneglycolacrylate, polypropyleneglycolmethacrylate, methoxyethyleneglycolacrylate, methoxypolyethyleneglycolmethacrylate, methoxypolypropyleneglycolacrylate or methoxypolypropyleneglycolmethacrylate; and the acrylic acid ester monomer is tetrahydrofurfurylacrylate, tetrahydrofurfurylmethacrylate or 2-methoxyethyl acrylate.

[Claim 9]

The adhesive resin for expansion sheet according to claim 1, wherein mean diameter of the heat-expandable microsphere is 10 - 25 μm.

[Claim lθ]

An expansion sheet, which is prepared by coating one side or both sides of a substrate with one of the adhesive resins of claim 1 - claim 9 to form an adhesive layer and then laminating a releasing film thereon.

[Claim 11]

The expansion sheet according to claim 10, wherein the substrate is surface-treated before being coated with the adhesive resin.