JP5074715B2 - Adhesive sheet - Google Patents

Description

  The present invention relates to a pressure-sensitive adhesive sheet used for temporarily fixing components and the like.

  Conventionally, adhesive sheets for temporarily fixing parts used in the fields of electronic parts, semiconductor wafers, liquid crystals and the like have a high adhesive force when fixing the parts, and are adhesive when peeling from the parts. It is required that the power is reduced and can be easily removed. Examples of these pressure-sensitive adhesive sheets include foamed pressure-sensitive adhesive sheets and pressure-sensitive adhesive sheets using side chain crystalline polymers.

The foamed pressure-sensitive adhesive sheet contains a foaming agent in a predetermined pressure-sensitive adhesive, and the adhesive strength is reduced by expansion or foaming of the foaming agent by heat treatment (see, for example, Patent Documents 1 and 2).
However, the decrease in the adhesive strength due to the foaming agent is not sufficient, and the adhesive strength cannot be increased too much. When the adhesive strength is increased, there is a problem that it is difficult to remove.

  On the other hand, for example, a pressure-sensitive adhesive sheet using a side chain crystalline polymer as described in Patent Document 3 contains a side chain crystalline polymer in a predetermined pressure-sensitive adhesive, and has a melting point of the side chain crystalline polymer. When the heat treatment is performed up to the above temperature, the side chain crystalline polymer exhibits fluidity, whereby the adhesive strength of the adhesive layer is sufficiently reduced. For example, Patent Document 3 describes that the adhesive strength to a stainless steel plate when heated to 35 ° C. or higher is 10% or less of the adhesive strength to a stainless steel plate at 23 ° C. Therefore, when the side chain crystalline polymer is used, the adhesive strength of the adhesive layer can be designed to be high.

  However, even if the adhesive strength is lowered due to the side chain crystalline polymer, the adhesive strength is not completely lost. Therefore, there is a problem that some force must be applied when removing from the component.

JP 63-33487 A JP-A-5-43851 JP 2000-355684 A

  An object of the present invention is to provide an adhesive sheet that has a high adhesive force when fixing a component and can be easily removed when the component is peeled off.

  As a result of intensive studies to solve the above problems, the present inventors have found that the pressure-sensitive adhesive layer contains a pressure-sensitive adhesive and a temperature-sensitive pressure-sensitive adhesive containing a side chain crystalline polymer, and a foaming agent. Even if the adhesive force when fixing the component is sufficiently high, when peeling from the component, the adhesive sheet itself is heated to a predetermined temperature to reduce the adhesive force of the adhesive layer itself and foam In combination with a decrease in the adhesive strength due to the agent, the adhesive strength can be greatly reduced, so the new fact that it can be easily removed has been found and the present invention has been completed.

That is, the pressure-sensitive adhesive sheet of the present invention has the following configuration.
(1) A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer provided on one or both sides of a base film, wherein the pressure-sensitive adhesive layer comprises a pressure-sensitive adhesive and a side-chain crystalline polymer, and a foaming agent. And a pressure-sensitive adhesive sheet that exhibits a decrease in adhesive strength at a temperature equal to or higher than the melting point of the side-chain crystalline polymer.
(2) The pressure-sensitive adhesive sheet according to (1), wherein the side-chain crystalline polymer has a melting point of 50 ° C. or higher, crystallizes at a temperature lower than the melting point, and exhibits fluidity at a temperature higher than the melting point.
(3) The adhesive sheet according to (1) or (2), wherein the adhesive force of the adhesive layer is 5 to 20 N / 25 mm at 23 ° C.
(4) The pressure-sensitive adhesive sheet according to any one of (1) to (3), wherein the side chain crystalline polymer has a weight average molecular weight of 3,000 to 30,000.
(5) The pressure-sensitive adhesive sheet according to any one of (1) to (4), wherein the side chain crystalline polymer is contained in a proportion of 1 to 20 parts by weight with respect to 100 parts by weight of the pressure-sensitive adhesive.
(6) The pressure-sensitive adhesive sheet according to any one of (1) to (5), wherein the foaming agent is contained in an amount of 1 to 60 parts by weight with respect to 100 parts by weight of the pressure-sensitive adhesive.
(7) The adhesive sheet in any one of said (1)-(6) whose thickness of the said adhesive layer is 30-60 micrometers.

  According to the present invention, since the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet contains a side-chain crystalline polymer, the side-chain crystalline polymer is obtained by heating the pressure-sensitive adhesive layer to a temperature equal to or higher than the melting point of the side-chain crystalline polymer. It exhibits fluidity and the adhesive strength of the adhesive layer itself is reduced. And since this adhesive layer contains a foaming agent, in addition to the fall of the adhesive force of adhesive layer itself, the fall of the adhesive force by a foaming agent is also added. Accordingly, the adhesive force of the pressure-sensitive adhesive layer can be increased to securely fix the components and the like, and the adhesive force can be sufficiently reduced during removal, and as a result, the components can be easily removed.

The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer provided on one side or both sides of a base film.
<Adhesive layer>
The pressure-sensitive adhesive layer in the present invention contains a temperature-sensitive pressure-sensitive adhesive and a foaming agent. The said temperature sensitive adhesive means the adhesive from which adhesive force changes according to a temperature change. The temperature-sensitive pressure-sensitive adhesive in the present invention contains a pressure-sensitive adhesive and a side-chain crystalline polymer, and the adhesive strength decreases at a temperature equal to or higher than the melting point of the side-chain crystalline polymer.

(Pressure sensitive adhesive)
The pressure-sensitive adhesive is not particularly limited as long as it is a polymer having a tackiness. For example, natural rubber adhesive; synthetic rubber adhesive; styrene / butadiene latex-based adhesive; block copolymer type heat Examples thereof include plastic rubber; butyl rubber; polyisobutylene; acrylic adhesive; vinyl ether copolymer. In particular, in the present invention, an acrylic adhesive is preferable, and it is preferably a copolymer having a main component of an acrylic ester and / or methacrylic ester [hereinafter referred to as (meth) acrylate] having 1 to 12 carbon atoms, For example, it is preferable to polymerize one or more of ethylhexyl (meth) acrylate, hydroxyethyl (meth) acrylate, methyl (meth) acrylate and the like.

(Side-chain crystalline polymer)
The side chain crystalline polymer is preferably crystallized at a temperature below the melting point and exhibits fluidity at a temperature above the melting point. That is, the polymer is preferably a polymer that reversibly causes a crystalline state and a fluid state in response to a temperature change. Thereby, at a temperature below the melting point, the side chain crystalline polymer is in a crystalline state, whereby the temperature-sensitive adhesive can ensure high adhesive strength, and at a temperature above the melting point, the side chain crystalline polymer is By becoming a fluid state, the adhesive force of the temperature-sensitive adhesive can be reduced. Therefore, the pressure-sensitive adhesive layer of the present invention exhibits a decrease in adhesive strength at a temperature equal to or higher than the melting point of the side chain crystalline polymer.

  In the present invention, the melting point means a temperature at which a specific portion of the polymer originally aligned in an ordered arrangement becomes disordered by an equilibrium process, and is 10 ° C./min by a differential thermal scanning calorimeter (DSC). It is a value obtained by measuring under the measurement conditions. In the present invention, the side chain crystalline polymer has a melting point of 50 ° C. or higher, preferably 50 to 70 ° C. Thereby, since the side chain crystalline polymer is crystallized at room temperature, workability | operativity improves.

  The composition of the side chain crystalline polymer is, for example, 30 to 99 parts by weight of a (meth) acrylate having a linear alkyl group having 16 or more carbon atoms, preferably 16 to 22 carbon atoms, and an alkyl group having 1 to 6 carbon atoms. Examples include polymers obtained by polymerizing 0 to 70 parts by weight of acrylic acid ester or methacrylic acid ester having 1 to 10 parts by weight of polar monomers.

  Examples of the (meth) acrylate having a linear alkyl group having 16 or more carbon atoms as a side chain include cetyl (meth) acrylate, stearyl (meth) acrylate, eicosyl (meth) acrylate, and behenyl (meth) acrylate. Examples include (meth) acrylates having 16 to 22 linear alkyl groups. Examples of the (meth) acrylate having an alkyl group having 1 to 6 carbon atoms include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, and the like. Examples of polar monomers include carboxyl group-containing ethylenically unsaturated monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meta And ethylenically unsaturated monomers having a hydroxyl group such as acrylate and 2-hydroxyhexyl (meth) acrylate.

  The polymer, that is, the side chain crystalline polymer has a weight average molecular weight of 3,000 to 30,000, preferably 5,000 to 25,000. When the weight average molecular weight is within this range, the adhesive strength of the pressure-sensitive adhesive layer is sufficiently lowered when the side-chain crystalline polymer exhibits fluidity at a temperature equal to or higher than the melting point. On the other hand, when the weight average molecular weight is less than 3,000, when the pressure-sensitive adhesive sheet is removed from the part, the adhesive layer may remain on the part, so-called adhesive residue may increase. Moreover, when a weight average molecular weight exceeds 30,000, there exists a possibility that adhesive force may become difficult to fall. The weight average molecular weight is a value obtained by measuring a side chain crystalline polymer by gel permeation chromatography (GPC) and converting the obtained measurement value to polystyrene.

  The side chain crystalline polymer is contained in an amount of 1 to 20 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the pressure-sensitive adhesive. Thereby, when the side chain crystalline polymer exhibits fluidity at a temperature equal to or higher than the melting point, the adhesive strength of the adhesive layer is sufficiently reduced. On the other hand, when the content of the side chain crystalline polymer is less than 1 part by weight, the adhesive force is hardly lowered even when the pressure-sensitive adhesive layer is heated to a temperature equal to or higher than the melting point of the side chain crystalline polymer. Moreover, when it exceeds 20 weight part, there exists a possibility that adhesive residue may increase.

  The side chain crystalline polymer is preferably incompatible with the pressure sensitive adhesive. As a result, the side chain crystalline polymer is dispersed in an incompatible state (island with no continuity) with respect to the pressure-sensitive adhesive (sea) as a base material, forming a so-called sea-island structure. The shape following property and adhesion of the temperature-sensitive adhesive are improved, and when the side chain crystalline polymer exhibits fluidity, the adhesive force of the temperature-sensitive adhesive tends to decrease.

(Foaming agent)
The foaming agent is not particularly limited, and any ordinary chemical foaming agent and physical foaming agent can be employed. Chemical foaming agents include pyrolytic and reactive organic foaming agents and inorganic foaming agents.

  Examples of the pyrolytic organic foaming agent include various azo compounds (such as azodicarbonamide), nitroso compounds (such as N, N′-dinitrosopentamethylenetetramine), and hydrazine derivatives [4,4′-oxybis (benzene). Sulfonyl hydrazide) and the like], semicarbazide compounds (hydrazodicarbonamide and the like), azide compounds, tetrazole compounds and the like. Examples of the reactive organic foaming agent include isocyanate compounds.

  Examples of the thermal decomposition type inorganic foaming agent include bicarbonate / carbonate (sodium bicarbonate, etc.), nitrite / hydride, etc. Examples of the reaction type inorganic foaming agent include sodium bicarbonate and the like. The combination with an acid, the combination of hydrogen peroxide and yeast, the combination of zinc powder and an acid, etc. are mentioned.

  Examples of the physical foaming agent include organic physical foaming agents such as aliphatic hydrocarbons such as butane, pentane and hexane, chlorohydrocarbons such as dichloroethane and dichloromethane, and fluorochlorohydrocarbons such as chlorofluorocarbons; air, carbonic acid Examples thereof include inorganic physical foaming agents such as gas and nitrogen gas.

  As other foaming agents, microencapsulated thermally expandable fine particles (so-called microballoon foaming agents) can be employed. The microballoon foaming agent is obtained by encapsulating a heat-expandable substance made of a solid, liquid, or gas inside a polymer shell made of a thermoplastic or thermosetting resin. The microballoon foaming agent expands in volume by 40 times or more by heating, and a foam in the form of closed cells is obtained. Therefore, the microballoon foaming agent has a characteristic that the expansion ratio is considerably larger than that of a normal foaming agent.

  The foaming agent is contained in an amount of 1 to 60 parts by weight, preferably 1 to 50 parts by weight, based on 100 parts by weight of the pressure-sensitive adhesive. This reduces the adhesive strength of the pressure-sensitive adhesive layer itself due to the fluidity of the side chain crystalline polymer, and also reduces the adhesive strength even when the foaming agent expands or foams by heat treatment. The power can be reduced sufficiently. On the other hand, if the content of the foaming agent is less than 1 part by weight, the adhesive strength is difficult to decrease. If the content is more than 60 parts by weight, the surface of the adhesive layer is uneven, such as unevenness derived from the foaming agent. Since the surface property of the agent layer may be lowered, it is not preferable.

  The temperature at which the foaming agent expands or foams is not particularly limited, but is usually 180 ° C. or lower, and is a temperature of 80 ° C. or higher in order to suppress foaming during coating drying. Is preferred. Although the average particle diameter of a foaming agent is not specifically limited, Usually, it is about 5-50 micrometers. The average particle diameter is a value obtained by measuring with a particle size distribution measuring apparatus.

<Base film>
Examples of the base film include sheets of synthetic resin films such as polyethylene, polypropylene, polyester, polyamide, polyimide, polycarbonate, ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, ethylene polypropylene copolymer, and polyvinyl chloride. Can be mentioned. Moreover, this film may consist of a single layer body or these multilayer bodies, and thickness is about 5-500 micrometers normally. In order to improve the adhesion to the pressure-sensitive adhesive layer, the surface of the base film may be subjected to surface treatment such as corona discharge treatment, plasma treatment, blast treatment, chemical etching treatment, and primer treatment.

  The pressure-sensitive adhesive layer described above is provided on one side or both sides of the base film. In general, a knife coater, a roll coater, a calendar coater, a comma coater or the like is often used to provide the adhesive layer on the base film. Depending on the coating thickness and material viscosity, a gravure coater, a rod coater or the like can be used. The thickness of the pressure-sensitive adhesive layer is 30 to 60 μm, preferably 30 to 50 μm. When the thickness is within this range, the pressure-sensitive adhesive layer can exhibit high adhesive strength.

  The pressure-sensitive adhesive layer provided on one or both sides of the base film as described above is combined with a decrease in the adhesive strength of the pressure-sensitive adhesive layer itself and a decrease in the adhesive strength due to the foaming agent by heating to a predetermined temperature. Since the adhesive strength can be greatly reduced, the adhesive strength can be increased. Specifically, at 23 ° C., the adhesive strength of the adhesive layer is 5 to 20 N / 25 mm, preferably 9 to 20 N / 25 mm. Thereby, since this adhesive layer can show high adhesive force at room temperature, workability | operativity improves and components can be fixed reliably at room temperature.

  On the other hand, if the adhesive force is less than 5 N / 25 mm, the component may not be fixed, and if it exceeds 20 N / 25 mm, the adhesive force cannot be sufficiently reduced and the component may not be removed. . The adhesive strength is a value obtained by measurement according to JIS Z0237. In order to set the melting point and adhesive strength to predetermined values, the structure of the side chain crystalline polymer, the formulation of the pressure-sensitive adhesive layer (for example, the composition of the pressure-sensitive adhesive, the thickness and the composition of the pressure-sensitive adhesive layer), etc. are changed. Can be done arbitrarily.

  Moreover, in order to raise the cohesion force of an adhesive layer, you may add a crosslinking agent. Examples of the crosslinking agent include isocyanate compounds, aziridine compounds, epoxy compounds, metal chelate compounds, and the like. Arbitrary components such as a plasticizer, a tackifier, and a filler can be added to the pressure-sensitive adhesive layer as necessary. Examples of the tackifier include special rosin ester, terpene phenol, petroleum resin, high hydroxyl value rosin ester, and hydrogenated rosin ester.

  Next, an example using the pressure-sensitive adhesive sheet of the present invention will be described based on the drawings. FIG. 1 is a schematic explanatory view showing a method of dicing an electronic component using the pressure-sensitive adhesive sheet of the present invention. First, as shown to Fig.1 (a), the electronic component 3 is fixed on the base 1 through the adhesive sheet 2 of this invention. At this time, since the pressure-sensitive adhesive sheet 2 is provided with the pressure-sensitive adhesive layer on both sides of the base film, the pressure-sensitive adhesive layer provided on one side is the electronic component 3 and the pressure-sensitive adhesive layer provided on the other side is the base 1. The electronic component 3 is fixed on the pedestal 1 via the adhesive sheet 2 with a high fixing force.

  After fixing, the electronic component 3 is cut. The cutting is cutting with the rotary blade 4 as shown in FIG. Here, at the time of cutting, the electronic component 3 is pushed by the rotary blade, and the jump of the electronic component 3 due to movement or vibration in the lateral direction can be suppressed by the adhesive sheet 2. In this way, a plurality of cut pieces 5 are formed.

  Next, the adhesive sheet 2 is heat-treated. The heating is performed so that the temperature is equal to or higher than the melting point of the side chain crystalline polymer in the pressure-sensitive adhesive layer and the foaming agent expands or foams. As a result, the side chain crystalline polymer exhibits fluidity at a temperature equal to or higher than the melting point, and the foaming agent expands or foams, so that the adhesive strength of the adhesive layer is sufficiently reduced. In this state, as shown in FIG. 1C, the cut piece 5 is taken out from the adhesive sheet 2, so that the cut piece 5 can be easily detached from the adhesive sheet 2.

  In the above description, the case where it is used for dicing an electronic component has been described. However, the present invention is not limited to this. For example, a multilayer ceramic inductor, resistor, ferrite, sensor element, thermistor, varistor, piezoelectric ceramic, etc. The present invention can be similarly applied to the production of ceramic electronic parts, semiconductor wafers, liquid crystals, and the like.

  Hereinafter, the pressure-sensitive adhesive sheet of the present invention will be described in detail with reference to synthesis examples and examples, but the present invention is not limited only to the following synthesis examples and examples. In the following description, “part” means part by weight.

(Synthesis Example 1: Pressure-sensitive adhesive)
52 parts of ethylhexyl acrylate (manufactured by Nippon Shokubai Co., Ltd.), 40 parts of methyl acrylate (manufactured by Nippon Shokubai Co., Ltd.), 8 parts of hydroxyethyl acrylate (manufactured by Nippon Shokubai Co., Ltd.) and 0. These monomers were polymerized in a proportion of 5 parts each into 230 parts of ethyl acetate / n-heptane (7 to 3) and stirred at 60 ° C. for 5 hours. The weight average molecular weight of the obtained copolymer was 470,000.

(Synthesis Example 2: Side chain crystalline polymer)
40 parts of behenyl acrylate (manufactured by NOF Corporation), 35 parts of stearyl acrylate (manufactured by NOF Corporation), 20 parts of methyl acrylate (manufactured by Nippon Shokubai Co., Ltd.), 5 parts of acrylic acid (manufactured by NOF Corporation), dodecyl mercaptan 6 parts (manufactured by NOF Corporation) and 1 part of perhexyl PV (manufactured by NOF Corporation) are mixed in 100 parts of toluene and stirred at 80 ° C. for 5 hours to polymerize these monomers. It was. The resulting copolymer had a weight average molecular weight of 7,900 and a melting point of 51 ° C.

  The copolymers of Synthesis Examples 1 and 2 are shown in Table 1. The weight average molecular weight is a value obtained by measuring the copolymer by gel permeation chromatography (GPC) and converting the obtained measurement value to polystyrene. The melting point of the copolymer of Synthesis Example 2 was measured with a differential thermal scanning calorimeter (DSC) under measurement conditions of 10 ° C./min.

[Examples 1-8 and Comparative Examples 1-3]
<Creation of adhesive sheet>
First, a copolymer solution was prepared using the pressure-sensitive adhesive and side chain crystalline polymer obtained above in the combinations shown in Table 2. Next, a foaming agent was added to the copolymer solution in the combinations shown in Table 2. As the foaming agent, microencapsulated thermally expandable fine particles (“009DU80” manufactured by EXPANCEL) were used. In Table 2, the amount of the side chain crystalline polymer added is a value relative to 100 parts by weight of the pressure sensitive adhesive, and the amount of the foaming agent added is a value relative to 100 parts by weight of the pressure sensitive adhesive.

  This copolymer solution was applied to one side of a base film (polyethylene terephthalate film) and dried to form a pressure-sensitive adhesive layer having the thickness shown in Table 2 to obtain each pressure-sensitive adhesive sheet (Examples in Table 2). 1-8 and Comparative Examples 1-3).

<Evaluation>
About each adhesive sheet obtained above, peeling strength and peelability were evaluated. Each evaluation method is shown below, and the results are also shown in Table 2. In addition, as a result of visually observing the adhesive layer surface of each obtained adhesive sheet, all were smooth and the unevenness | corrugation derived from a foaming agent was not observed.

(Peel strength)
The peel strength (adhesive strength) to a stainless steel plate (SUS) at 23 ° C. was measured according to JIS Z0237.

(Peelability)
After the pressure-sensitive adhesive sheet is attached to a stainless steel plate (SUS) at 23 ° C., the pressure-sensitive adhesive sheet is heated to 150 ° C. (temperature equal to or higher than the melting point of the side chain crystalline polymer and the foaming agent expands). It was visually observed whether or not it was peeled from SUS only by its own weight. The following criteria were used.
○: Peeled only by the weight of the tape ×: Not peeled

  As is clear from Table 2, the pressure-sensitive adhesive sheets of Examples 1 to 8 are excellent in releasability by containing a side chain crystalline polymer and a foaming agent even if the pressure-sensitive adhesive strength at 23 ° C. is increased. I understand. On the other hand, since the pressure-sensitive adhesive sheets of Comparative Examples 1 and 2 did not contain a side chain crystalline polymer, the results showed inferior peelability when the adhesive force was almost the same as in Examples. Moreover, since the adhesive sheet of the comparative example 3 did not contain a foaming agent, the result inferior to peelability was shown in the adhesive force substantially equivalent to an Example.

It is a schematic explanatory drawing which shows the method of dicing an electronic component using the adhesive sheet of this invention.

Explanation of symbols

1 Pedestal 2 Adhesive Sheet 3 Laminated Body 4 Cutting Blade 5 Cut Piece

Claims (4)

An adhesive sheet provided with an adhesive layer on one or both sides of a base film,
The pressure-sensitive adhesive layer contains a pressure-sensitive adhesive and a temperature-sensitive pressure-sensitive adhesive containing a side chain crystalline polymer, and a foaming agent, and exhibits a decrease in adhesive strength at a temperature equal to or higher than the melting point of the side chain crystalline polymer. And the thickness is 30-60 μm and the adhesive strength at 23 ° C. is 5-20 N / 25 mm,
The side-chain crystalline polymer has a weight average molecular weight of 3,000 to 30,000 .   The pressure-sensitive adhesive sheet according to claim 1, wherein the side-chain crystalline polymer has a melting point of 50 ° C or higher, crystallizes at a temperature lower than the melting point, and exhibits fluidity at a temperature higher than the melting point. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the side chain crystalline polymer is contained in an amount of 1 to 20 parts by weight with respect to 100 parts by weight of the pressure-sensitive adhesive. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3 , wherein the foaming agent is contained in a ratio of 1 to 60 parts by weight with respect to 100 parts by weight of the pressure-sensitive adhesive.