Adhesive composition

Abstract

To provide an adhesive sheet that has sufficient adhesive strength, prevents adhesive leftover where an adhesive layer is transferred onto the adherend from which the adhesive sheet has been removed, and effectively absorbs surface irregularities.SOLUTION: An adhesive sheet includes a sheet-form base material and an adhesive layer formed on one surface of the base material. The adhesive layer comprises a cured product of an adhesive composition. The gel fraction is 50-65 mass%. The adhesive composition includes a polyurethane (A), a (meth)acrylic monomer (B) that comprises a compound having a (meth)acryloyloxy group, a chain transfer agent (C), and a photopolymerization initiator (D). The polyurethane (A) includes a polyurethane (a1) with a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, featuring (meth)acryloyl groups at two or more ends.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an adhesive sheet and an adhesive composition. This application claims priority based on Japanese Patent Application No. 2019-138812 filed in Japan on July 29, 2019, the content of which is incorporated herein by reference.

Background Art

[0002] With the demand for thinning of semiconductor devices, a back grinding process of a semiconductor wafer is performed in the manufacturing process of semiconductor devices. In the back grinding process of a semiconductor wafer, the surface of the semiconductor wafer is protected with an adhesive sheet, and then the back surface is ground to thin the semiconductor wafer.

[0003] Conventionally, various adhesive sheets have been proposed for protecting the surface of a semiconductor wafer. In recent years, as an adhesive sheet, there has been a demand for a sheet having sufficient unevenness absorbability even for a semiconductor wafer having uneven portions on its surface, such as a semiconductor wafer having bumps (electrodes) made of solder or the like formed on its surface.

[0004] For example, Patent Document 1 discloses a back grinding sheet having an unevenness absorbing layer on a substrate, wherein the unevenness absorbing layer is formed from a film-forming composition containing (A) urethane (meth) acrylate and (B) a polymerizable monomer other than the component (A), and is a layer satisfying a loss tangent, a relaxation rate, and a storage elastic modulus within a specific range.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When performing a back grinding process on a semiconductor wafer having bumps on its surface, an adhesive sheet used for protecting the surface is required to have sufficient adhesive force. However, when an adhesive sheet with high adhesive force is attached to a semiconductor wafer having bumps on its surface and the back grinding process is performed, after the back grinding process, glue residue occurs where the adhesive layer of the adhesive sheet is transferred around the bumps of the semiconductor wafer from which the adhesive sheet has been peeled off.

[0007] Also, when performing a back grinding process on a semiconductor wafer having bumps on its surface, if the unevenness absorbency of the adhesive sheet for protecting the surface with respect to the semiconductor wafer is insufficient, voids are generated around the bumps. If water used in the back grinding process enters this void, the semiconductor wafer may be contaminated.

[0008] As described above, an adhesive sheet that is attached to an adherend having uneven portions on its surface and then peeled off is required to have sufficient adhesive force, be less likely to cause glue residue, and have excellent unevenness absorbency. However, conventional adhesive sheets do not have sufficient adhesive force, are less likely to cause glue residue, and are not excellent in unevenness absorbency. For this reason, when using a conventional adhesive sheet, it is necessary to provide an unevenness absorption layer separately from the adhesive layer of the adhesive sheet or to heat and soften the adhesive layer in order to obtain sufficient adhesive force and unevenness absorbency with respect to the semiconductor wafer.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide an adhesive sheet that has sufficient adhesive force, is less likely to cause glue residue where the adhesive layer is transferred to the adherend after peeling off the adhesive sheet, and has excellent unevenness absorbency. Another object of the present invention is to provide an adhesive composition that has sufficient adhesive force, is less likely to cause glue residue, and can obtain a cured product having excellent unevenness absorbency and is suitable as a material for the adhesive layer of the adhesive sheet.

Means for Solving the Problems

[0010] The first aspect of the present invention is the following pressure-sensitive adhesive sheet. [1] A pressure-sensitive adhesive sheet having at least a sheet-like base material and a pressure-sensitive adhesive layer formed on one side of the base material, wherein the pressure-sensitive adhesive layer is composed of a cured product of a pressure-sensitive adhesive composition and has a gel fraction of 50 to 65% by mass, the pressure-sensitive adhesive composition includes a polyurethane (A), a (meth)acrylic monomer (B) composed of a compound having a (meth)acryloyloxy group, a chain transfer agent (C), and a photopolymerization initiator (D), the polyurethane (A) has a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and includes a polyurethane (a1) having a (meth)acryloyl group at two or more terminals, and is characterized by a pressure-sensitive adhesive sheet.

[0011] The pressure-sensitive adhesive sheet of the first aspect of the present invention preferably includes the following features [2] to [3]. The following features may be combined with each other in two or more. [2] The pressure-sensitive adhesive layer has a storage elastic modulus at 25 °C measured at a frequency of 1 Hz of 1.0×10 4 ~1.0×10 5 and a loss tangent at 25 °C measured at a frequency of 1 Hz of 0.25 to 0.55, the pressure-sensitive adhesive sheet according to [1]. [3] The thickness of the pressure-sensitive adhesive layer is 50 to 500 μm, the pressure-sensitive adhesive sheet according to [1] or [2].

[0012] The second aspect of the present invention is the following pressure-sensitive adhesive composition. [4] A pressure-sensitive adhesive composition including a polyurethane (A), a (meth)acrylic monomer (B) composed of a compound having a (meth)acryloyloxy group, a chain transfer agent (C), and a photopolymerization initiator (D), the polyurethane (A) has a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and includes a polyurethane (a1) having a (meth)acryloyl group at two or more terminals, irradiation dose 1000 mJ / cm 2 ​An adhesive composition characterized in that the gel fraction of the cured product photocured is 50 to 65% by mass.

[0013] The pressure-sensitive adhesive composition of the second aspect of the present invention preferably includes the following features [5] to

[10] . The following features may be combined with each other in two or more. [5] The cured product has a storage elastic modulus at 25 ° C measured at a frequency of 1 Hz of 1.0×10 4 ~1.0×10 5 and the loss tangent at 25 ° C measured at a frequency of 1 Hz is 0.25 to 0.55, the adhesive composition according to [4].

[0014] [6] The (meth)acrylic monomer (B) contains a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate, the adhesive composition according to [4] or [5]. [7] When the total of the (meth)acrylic monomer (B) is 100 mol%, the monofunctional (meth)acrylate is contained in an amount of 85 to 99 mol% and the polyfunctional (meth)acrylate is contained in an amount of 1 to 15 mol%, the adhesive composition according to [6].

[0015] [8] The chain transfer agent (C) is a polyfunctional thiol, the adhesive composition according to any one of [4] to [7]. [9] The polyurethane (A) is 20 to 50% by mass, the (meth)acrylic monomer (B) is 49 to 79% by mass, the chain transfer agent (C) is 0.5 to 5% by mass, the adhesive composition according to any one of [4] to [8], containing 0.01 to 5% by mass of the photopolymerization initiator (D).

[10] Further containing a fatty acid ester (E), the adhesive composition according to any one of [4] to [9].

Advantages of the Invention

[0016] The pressure-sensitive adhesive sheet of the present invention has, on one side of a sheet-like base material, a pressure-sensitive adhesive layer composed of a cured product of a specific pressure-sensitive adhesive composition and having a gel fraction of 50 to 65% by mass. Therefore, the pressure-sensitive adhesive sheet of the present invention has sufficient adhesive force, and it is difficult for adhesive residue to occur in which the pressure-sensitive adhesive layer is transferred to the adherend after the pressure-sensitive adhesive sheet is peeled off, and it is excellent in unevenness absorbability. Therefore, when the pressure-sensitive adhesive sheet of the present invention is used for applications where it is attached to an adherend having uneven portions on its surface and then peeled off, it is not necessary to provide an unevenness absorption layer separately from the pressure-sensitive adhesive layer or to heat and soften the pressure-sensitive adhesive layer as in the case of using a conventional pressure-sensitive adhesive sheet. Therefore, the pressure-sensitive adhesive sheet of the present invention is suitable for applications where it is attached to an adherend having uneven portions on its surface and then peeled off.

[0017] The pressure-sensitive adhesive composition of the present invention has a specific composition and gel fraction. Therefore, by curing the pressure-sensitive adhesive composition of the present invention, a cured product having sufficient adhesive force, being less likely to cause adhesive residue, and being excellent in unevenness absorbability can be obtained. Therefore, the pressure-sensitive adhesive composition of the present invention is suitable as a material for the pressure-sensitive adhesive layer in a pressure-sensitive adhesive sheet that is attached to an adherend having uneven portions on its surface and then peeled off.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, the pressure-sensitive adhesive sheet and the pressure-sensitive adhesive composition of the present invention will be described in detail. Note that the present invention is not limited only to the embodiments shown below. Within the scope of the present invention, it is also possible to omit, change, exchange, and / or add the type, amount, composition, ratio, number, numerical value, position, size, etc. as necessary. <Pressure-Sensitive Adhesive Sheet> The pressure-sensitive adhesive sheet of the present embodiment has a sheet-like base material and a pressure-sensitive adhesive layer formed on one side of the base material. The pressure-sensitive adhesive layer is composed of a cured product of a pressure-sensitive adhesive composition described later.

[0019] The material of the base material can be appropriately selected, and examples include resin materials. Examples of resin materials include polyolefins such as polyethylene (PE) and polypropylene (PP); polyester sheets such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate; polyvinyl chloride (PVC); polyimide (PI); polyphenylene sulfide (PPS); ethylene vinyl acetate (EVA); polytetrafluoroethylene (PTFE), etc. Among these resin materials, it is preferable to use PE, PP, or PET because a sheet with appropriate flexibility can be obtained. The resin material may be used alone as one type, or two or more types may be mixed and used.

[0020] When using a resin sheet made of a resin material as the base material, the resin sheet may be single-layer or may have a multi-layer structure of two or more layers (for example, a three-layer structure). In a resin sheet having a multi-layer structure, the resin material constituting each layer may be a resin material containing only one type alone, or a resin material containing two or more types.

[0021] As the base material, one that has been subjected to an antistatic treatment may be used. The antistatic treatment applied to the base material is not particularly limited, and methods such as providing an antistatic layer on at least one side of the base material and kneading an antistatic agent into the base material can be used. Furthermore, on the surface where the adhesive layer of the base material is formed, if necessary, an adhesion-promoting treatment such as acid treatment, alkali treatment, primer treatment, corona treatment, plasma treatment, ultraviolet treatment, ozone treatment, etc. may be performed.

[0022] The thickness of the base material can be appropriately selected according to the material of the base material and the like. When the adhesive sheet is used for protecting a semiconductor wafer having uneven portions on its surface in the processing step of the semiconductor wafer, and a resin sheet is used as the base material, the thickness of the base material is preferably, for example, 10 to 1000 μm, and preferably 50 to 300 μm. When the thickness of the base material is 10 μm or more, the rigidity (stiffness) of the adhesive sheet increases. Therefore, when the adhesive sheet is attached to or peeled from the semiconductor wafer as the adherend, wrinkles and lifting are less likely to occur in the adhesive sheet. Further, when the thickness of the base material is 1000 μm or less, the adhesive sheet attached to the semiconductor wafer can be easily peeled from the semiconductor wafer, and the workability (handleability, handling) becomes good.

[0023] The thickness of the adhesive layer is preferably 50 to 500 μm, more preferably 60 to 400 μm, and even more preferably 70 to 300 μm. When the thickness of the adhesive layer is 50 μm or more, the uneven absorption property of the adhesive sheet becomes even better. Further, when the thickness of the adhesive layer is 500 μm or less, the film thickness control of the adhesive layer becomes easy.

[0024] When the adhesive sheet of the present embodiment is an adhesive sheet to be attached to an adherend having uneven portions on its surface, the thickness of the adhesive layer greatly depends on the height of the uneven portions on the surface. The thickness of the adhesive layer is preferably equal to or greater than the height of the uneven portions on the surface so that sufficient uneven absorption property can be obtained. Therefore, for example, when the unevenness on the surface is a bump formed on a semiconductor wafer, the thickness of the adhesive layer is preferably 2 times or more the height dimension of the bump. The height of the bump is usually 30 to 200 μm. For example, when the height of the bump is 100 μm, the thickness of the adhesive layer is preferably 200 μm or more, and when the height of the bump is 200 μm, the thickness of the adhesive layer is preferably 400 μm or more.

[0025] The adhesive layer of the pressure-sensitive adhesive sheet of the present embodiment has a gel fraction in the range of 50 to 65% by mass. Therefore, the pressure-sensitive adhesive sheet of the present embodiment has sufficient adhesive strength, is less likely to leave glue residue, and is excellent in unevenness absorption. The gel fraction of the adhesive layer is preferably 52% by mass or more. Also, the gel fraction of the adhesive layer is preferably 63% by mass or less. On the other hand, when the gel fraction is less than 50% by mass, glue residue is likely to occur when the pressure-sensitive adhesive sheet is peeled off after being attached to the adherend. Further, when the gel fraction exceeds 65% by mass, the fluidity tends to be insufficient when used as the adhesive layer of the pressure-sensitive adhesive sheet. Therefore, when the pressure-sensitive adhesive sheet is sent to an adherend having uneven portions on the surface, a gap is likely to occur between the uneven portions of the adherend.

[0026] (Measurement of gel fraction of adhesive layer) The gel fraction of the adhesive layer can be measured, for example, by the method shown below. A square sheet measuring 8 cm in length and 8 cm in width is cut out from the pressure-sensitive adhesive sheet, and the base material is peeled off from the adhesive layer of the obtained square sheet. Then, the adhesive layer peeled off from the square sheet is used as a measurement sample. The obtained measurement sample can be measured using the same method as the method for measuring the gel fraction of the measurement sample composed of the cured product of the adhesive composition described later.

[0027] The adhesive layer of the pressure-sensitive adhesive sheet of the present embodiment has a storage elastic modulus at 25°C measured at a frequency of 1 Hz of 1.0×10 4 ~1.0×10 5 and preferably has a loss tangent at 25°C measured at a frequency of 1 Hz of 0.25 to 0.55. An adhesive layer having a storage elastic modulus and a loss tangent within the above ranges has good flexibility and fluidity. Therefore, when the pressure-sensitive adhesive sheet is attached to a workpiece (adherend) such as a semiconductor wafer having uneven portions such as bumps, it is possible to prevent a gap from occurring between the uneven portions and the pressure-sensitive adhesive sheet.

[0028] The storage elastic modulus of the adhesive layer is more preferably 2.0×10 4 or more, and 3.0×10 4It is more preferable that it is as described above. Further, the above storage elastic modulus is 9.0×10 4 It is more preferably below, and 8.0×10 4 It is even more preferably below. The adhesive layer with the above storage elastic modulus of 1.0×10 4 or more is not too soft. Therefore, an adhesive sheet having an adhesive layer with a storage elastic modulus of 1.0×10 4 or more is more preferable because even if it is peeled off after being attached to an adherend, less adhesive residue is likely to occur. Further, the adhesive layer with the above storage elastic modulus of 1.0×10 5 or less has good flexibility. Therefore, when an adhesive sheet having an adhesive layer with a storage elastic modulus of 1.0×10 5 or less is attached to an adherend having uneven portions on its surface, it is more preferable because a gap is less likely to occur between the uneven portions of the adherend.

[0029] It is more preferable that the above loss tangent of the adhesive layer is 0.30 or more. Also, it is more preferable that the above loss tangent is 0.50 or less. The adhesive layer with the above loss tangent of 0.25 or more has good fluidity. Therefore, when an adhesive sheet having an adhesive layer with a loss tangent of 0.25 or more is attached to an adherend having uneven portions on its surface, a gap is less likely to occur between the uneven portions of the adherend, which is preferable. Also, the adhesive layer with the above loss tangent of 0.55 or less does not have too high fluidity. Therefore, an adhesive sheet having an adhesive layer with a loss tangent of 0.55 or less is more preferable because less adhesive residue is likely to occur even if it is peeled off after being attached to an adherend.

[0030] (Measurement of Storage Elastic Modulus and Loss Tangent of Adhesive Layer) The storage elastic modulus and loss tangent of the adhesive layer can be measured, for example, by the method shown below. First, peel the substrate from the adhesive sheet. Then, laminate the adhesive layer from which the substrate has been peeled to form a laminated sheet having a thickness in the range of 1 to 2 mm. Cut out a square sheet measuring 8 mm in length and 8 mm in width from the obtained laminated sheet to obtain a measurement sample. The obtained measurement sample can be measured using the same method as the method for measuring the storage elastic modulus and loss tangent of the measurement sample composed of the cured product of the adhesive composition described below.

[0031] For the adhesive sheet, a transparent separator may be provided on the surface of the adhesive layer opposite to the substrate for the purpose of protecting the adhesive layer. The separator is preferably laminated on the surface of the adhesive layer. As the material of the separator, for example, paper, plastic film, etc. can be used, and it is preferable to use a plastic film from the viewpoint of excellent surface smoothness. The plastic film used as the separator is not particularly limited as long as it can protect the above-described adhesive layer, and examples thereof include polyethylene, polypropylene, polyethylene terephthalate, polybutene, etc.

[0032] <Adhesive Composition> The adhesive layer of the adhesive sheet of the present embodiment is composed of a cured product of an adhesive composition. Hereinafter, the adhesive composition used as the material of the adhesive layer of the adhesive sheet of the present embodiment will be described in detail. The adhesive composition of the present embodiment contains polyurethane (A), (meth)acrylic monomer (B), chain transfer agent (C), and photopolymerization initiator (D).

[0033] (Polyurethane (A)) Polyurethane (A) contains polyurethane (a1). Polyurethane (A) may contain polyurethane (a2) described below for the purpose of adjusting the cohesive force in the cured product of the adhesive composition, in addition to polyurethane (a1). It is preferable that polyurethane (A) does not contain components other than polyurethane (a1) and, if necessary, polyurethane (a2).

[0034] [Polyurethane (a1)] Polyurethane (a1) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate. Further, polyurethane (a1) has two or more, that is, a plurality of (meth)acryloyl groups at its terminals. The (meth)acryloyl group at the terminal of polyurethane (a1) is preferably part of a (meth)acryloyloxy group.

[0035] In the present invention, the "plurality of terminals" of polyurethane means two terminals when the polyurethane is a linear polymer, and two or more terminals out of the same number of terminals as the number of each branched chain when the polyurethane is a branched polymer. Also, in the present invention, the (meth)acryloyl group means one or more selected from the functional group represented by the chemical formula CH 2 =CH-CO-, and the functional group represented by the chemical formula CH 2 =C(CH 3 )-CO-.

[0036] [Polyurethane (a2)] Polyurethane (a2) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, similar to polyurethane (a1). Different from polyurethane (a1), polyurethane (a2) has a (meth)acryloyl group at only one terminal. The (meth)acryloyl group at the terminal of polyurethane (a2) is preferably part of a (meth)acryloyloxy group. The terminal of polyurethane (a2) having no (meth)acryloyl group preferably has any one selected from an isocyanato group, a structure derived from an alkyl alcohol, and a structure derived from an alkyl isocyanate, and more preferably has a structure derived from an alkyl alcohol.

[0037] "Structure derived from a polyoxyalkylene polyol" As the polyoxyalkylene polyol that forms the structure derived from the polyoxyalkylene polyol contained in the skeletons of polyurethane (a1) and polyurethane (a2), those having an alkylene chain with 2 to 4 carbon atoms are preferred. Specific examples include polyoxyethylene polyol, polyoxypropylene polyol, polyoxybutylene polyol, and the like.

[0038] The polyoxyalkylene polyol that forms the structure derived from the polyoxyalkylene polyol may contain one type of alkylene chain or may contain two or more types of alkylene chains. The polyoxyalkylene polyol that forms the structure derived from the polyoxyalkylene polyol preferably has two or three hydroxyl groups at the terminals (diol-type or triol-type polyoxyalkylene polyol), more preferably is a polyoxyalkylene glycol (diol-type), and particularly preferably is a polypropylene glycol having an alkylene chain with 3 carbon atoms.

[0039] For example, when the polyoxyalkylene polyol is polypropylene glycol, the hydroxyl value is preferably 20 to 120 mgKOH / g, more preferably 30 to 100 mgKOH / g, and even more preferably 40 to 80 mgKOH / g. Specific examples of polypropylene glycol include, for example, polypropylene glycol having a hydroxyl group (hydroxy group) with a hydroxyl value of 56 mgKOH / g at the terminals (Actocol D-2000; manufactured by Mitsui Chemicals, number average molecular weight 2000, diol-type), and the like.

[0040] Here, the hydroxyl value of the polyoxyalkylene polyol is the hydroxyl value of the polyoxyalkylene polyol measured in accordance with JIS K0070. That is, it means the number of milligrams of potassium hydroxide required to neutralize the free acetic acid when 1 g of the polyoxyalkylene polyol is acetylated. Specifically, it can be determined by acetylating the hydroxyl groups in the sample (polyoxyalkylene polyol) using acetic anhydride and titrating the free acetic acid generated therein with a potassium hydroxide solution.

[0041] The number average molecular weight of the polyoxyalkylene polyol is preferably from 500 to 5,000, more preferably from 800 to 4,000, and even more preferably from 1,000 to 3,000. When the number average molecular weight of the polyoxyalkylene polyol is 500 or more, the pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer composed of a cured product of the pressure-sensitive adhesive composition containing the polyurethane (A) synthesized using the same has a high peel strength. Further, when the number average molecular weight of the polyoxyalkylene polyol is 5,000 or less, the polyurethane (A) synthesized using the same contains a sufficient amount of urethane bonds. Therefore, the cured product obtained by curing the pressure-sensitive adhesive composition containing the polyurethane (A) has good cohesive strength.

[0042] The structure derived from the polyoxyalkylene polyol contained in the skeletons of the polyurethane (a1) and the polyurethane (a2) may be only one type or a structure containing two or more types. The polyurethane (a1) and the polyurethane (a2) may have a structure in which structures derived from two or more different polyoxyalkylene polyols are bonded with a structure derived from a polyisocyanate interposed therebetween. The structure derived from the polyoxyalkylene polyol contained in the skeleton of the polyurethane (a1) and the structure derived from the polyoxyalkylene polyol contained in the skeleton of the polyurethane (a2) may be the same or different.

[0043] "Structure derived from polyisocyanate" As the polyisocyanate that forms the structure derived from polyisocyanate contained in the skeletons of polyurethane (a1) and polyurethane (a2), a compound having a plurality of isocyanato groups is used, and it is preferable to use a diisocyanate. Examples of the diisocyanate include tolylene diisocyanate and its hydrogenated product, xylylene diisocyanate and its hydrogenated product, diphenylmethane diisocyanate and its hydrogenated product, 1,5-naphthylene diisocyanate and its hydrogenated product, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, norbornane diisocyanate, and the like.

[0044] Among these polyisocyanates, from the viewpoints of the light resistance of the polyurethane (A) synthesized using it and the control of the reactivity with the polyoxyalkylene polyol, it is preferable to use isophorone diisocyanate or a hydrogenated product of diphenylmethane diisocyanate. From the viewpoint of the reactivity with the polyoxyalkylene polyol, it is more preferable to use a hydrogenated product of diphenylmethane diisocyanate.

[0045] Specific examples of the polyisocyanate that forms the structure derived from polyisocyanate include a hydrogenated product of diphenylmethane diisocyanate (Desmodur W, manufactured by Sumika Covestro Polyurethane), isophorone diisocyanate (Desmodur I, manufactured by Sumika Covestro Polyurethane), and the like.

[0046] The structure derived from polyisocyanate contained in the skeletons of polyurethane (a1) and polyurethane (a2) may be only one type, or may be a structure containing two or more types. Also, the structure derived from polyisocyanate contained in the skeleton of polyurethane (a1) and the structure derived from polyisocyanate contained in the skeleton of polyurethane (a2) may be the same or different.

[0047] When the structures derived from polyisocyanate and the structures derived from polyoxyalkylene polyol contained in the skeletons of polyurethane (a1) and polyurethane (a2) are the same, polyurethane (a1) and polyurethane (a2) can be synthesized simultaneously, and it is preferable that polyurethane (A) can be efficiently produced.

[0048] The proportion of polyurethane (a1) contained in polyurethane (A) is preferably 80 to 100% of polyurethane (A) on a molecular number basis, more preferably 90 to 100%, and even more preferably 100%. The proportion of polyurethane (a2) contained in polyurethane (A) is preferably 0 to 20% of polyurethane (A) on a molecular number basis, more preferably 0 to 10%, and even more preferably 0%. When the proportion of polyurethane (a1) contained in polyurethane (A) is 80% or more, the cured product of the pressure-sensitive adhesive composition containing polyurethane (A) will have sufficiently high cohesive strength, which is preferable.

[0049] Among all the terminal numbers contained in polyurethane (A) (the total number of the terminal numbers of polyurethane (a1) and the terminal numbers of polyurethane (a2) contained as necessary), it is preferable that 90 to 100% of the molecular number basis has (meth)acryloyl groups introduced, more preferably 95 to 100%, and even more preferably 100%. When the introduction amount of (meth)acryloyl groups among all the terminal numbers contained in polyurethane (A) is 90% or more on a molecular number basis, the cohesive strength of the cured product obtained by curing the pressure-sensitive adhesive composition containing polyurethane (A) will be sufficiently high.

[0050] Among all the terminal numbers contained in polyurethane (A), the proportion of the terminal numbers with (meth)acryloyl groups introduced on a molecular number basis can be calculated using the results of analyzing polyurethane (A) using methods such as infrared absorption spectrum (IR) method and nuclear magnetic resonance spectrum (NMR) method.

[0051] The ratio of the contents of polyurethane (a1) and polyurethane (a2) contained in polyurethane (A), that is, the ratio of the number of terminals into which (meth)acryloyl groups are introduced on a molecular number basis among all the terminal numbers contained in polyurethane (A) can be adjusted by the method for producing polyurethane (A) described below.

[0052] The mass average molecular weight of polyurethane (A) is preferably from 30,000 to 200,000, more preferably from 50,000 to 150,000, and even more preferably from 60,000 to 100,000. When the mass average molecular weight of polyurethane (A) is 30,000 or more, the cured product obtained by curing the pressure-sensitive adhesive composition containing polyurethane (A) has good flexibility. Further, when the mass average molecular weight of polyurethane (A) is 200,000 or less, the pressure-sensitive adhesive composition containing polyurethane (A) is easy to handle and has good workability.

[0053] (Method for measuring the mass average molecular weight of polyurethane (A)) The mass average molecular weight of polyurethane (A) is a value in terms of polystyrene measured by gel permeation chromatography (GPC-101; Shodex (registered trademark) manufactured by Showa Denko K.K.) (hereinafter referred to as GPC). The measurement conditions of GPC are as follows. Column: LF-804 (manufactured by Showa Denko K.K.) Column temperature: 40 °C Sample: 0.2 mass% tetrahydrofuran solution of polyurethane (A) Flow rate: 1 ml / min Eluent: Tetrahydrofuran Detector: RI detector (differential refractive index detector)

[0054] In the pressure-sensitive adhesive composition of this embodiment, the content of polyurethane (A) is preferably 20 to 50% by mass, more preferably 25 to 45% by mass, and even more preferably 30 to 40% by mass. When the content of polyurethane (A) is 20% by mass or more, the cured product obtained by curing the pressure-sensitive adhesive composition has sufficient cohesive force and excellent adhesive force can be obtained. In addition, for the pressure-sensitive adhesive sheet using this cured product as the pressure-sensitive adhesive layer, the softness of the pressure-sensitive adhesive layer is within an appropriate range, and it is difficult for air bubbles to be trapped between the pressure-sensitive adhesive layer and the adherend. Further, when the content of polyurethane (A) is 50% by mass or less, the cured product obtained by curing the pressure-sensitive adhesive composition has sufficient flexibility. Therefore, for the pressure-sensitive adhesive sheet using this cured product as the pressure-sensitive adhesive layer, the wettability with respect to the adherend is good.

[0055] ((meth)acrylic monomer (B)) (Meth)acrylic monomer (B) may be any compound having a (meth)acryloyloxy group and is not particularly limited. As (meth)acrylic monomer (B), only one kind of compound having a (meth)acryloyloxy group may be used alone, or two or more kinds may be mixed and used. As (meth)acrylic monomer (B), monofunctional (meth)acrylate may be used, polyfunctional (meth)acrylate may be used, or both monofunctional (meth)acrylate and polyfunctional (meth)acrylate may be used.

[0056] In the present invention, "monofunctional" in monofunctional (meth)acrylate means a (meth)acrylate in which the number of (meth)acryloyloxy groups is only one. Also, in the present invention, "polyfunctional" in polyfunctional (meth)acrylate means a (meth)acrylate in which the number of (meth)acryloyloxy groups is two or more.

[0057] As the (meth)acrylic monomer (B), from the viewpoints of the cohesive force of the cured product obtained by curing the pressure-sensitive adhesive composition and the curability of the pressure-sensitive adhesive composition, it is preferable to use a combination of a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate, more preferably to contain a monofunctional (meth)acrylate and a (meth)acrylate having three or more functional groups, and particularly most preferably to contain a monofunctional (meth)acrylate and a trifunctional (meth)acrylate having three (meth)acryloyloxy groups.

[0058] Examples of the monofunctional (meth)acrylate include alkyl (meth)acrylate, cyclic alkyl (meth)acrylate such as isobornyl (meth)acrylate, alkoxyalkyl (meth)acrylate, alkoxy(poly)alkylene glycol (meth)acrylate, hydroxy group-containing (meth)acrylate, carboxy group-containing (meth)acrylate, fluorinated alkyl (meth)acrylate, dialkylaminoalkyl (meth)acrylate, (meth)acrylamide, epoxy group-containing (meth)acrylate, (meth)acryloylmorpholine, and the like.

[0059] Among these monofunctional (meth)acrylates, since the adhesive strength (peeling force) of the cured product obtained by curing the pressure-sensitive adhesive composition, the storage elastic modulus, loss tangent, and gel fraction described below are more likely to be in a more appropriate range when the cured product is used as the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet, it is preferable to contain an alkyl (meth)acrylate. As the alkyl (meth)acrylate, it is more preferable to use an alkyl (meth)acrylate having an alkyl group with 4 to 10 carbon atoms. Specifically, examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and the like. Among these, it is particularly preferable to use 2-ethylhexyl (meth)acrylate and / or n-butyl (meth)acrylate.

[0060] The polyfunctional (meth)acrylate is a compound other than the polyurethane (A) and having a plurality of (meth)acryloyloxy groups. As the polyfunctional (meth)acrylate, it is preferable to use the poly(meth)acrylate of a polyol compound. Specific examples of the polyfunctional (meth)acrylate include polyethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, hydroxypivalic acid ester neopentyl glycol di(meth)acrylate, 1,3-bis(hydroxyethyl)-5,5-dimethylhydantoin di(meth)acrylate, α,ω-di(meth)acrylbisdiethylene glycol phthalate, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, diacryloxyethyl phosphate, pentaerythritol tetra(meth)acrylate and the like. Among these, from the viewpoint of the curability of the pressure-sensitive adhesive composition, it is preferable to use trimethylolpropane tri(meth)acrylate as the polyfunctional (meth)acrylate.

[0061] When the (meth)acrylic monomer (B) contains both a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate, when the total of the (meth)acrylic monomer (B) is 100 mol%, it preferably contains 85 to 99 mol% of the monofunctional (meth)acrylate and 1 to 15 mol% of the polyfunctional (meth)acrylate. In this case, the content of the monofunctional (meth)acrylate is more preferably 90 to 99 mol%, and even more preferably 95 to 98 mol%. Also, the content of the polyfunctional (meth)acrylate is more preferably 1 to 10 mol%, and even more preferably 2 to 5 mol%.

[0062] When containing a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate, if the content of the monofunctional (meth)acrylate is 85 mol% or more, the fluidity of the cured product obtained by curing the pressure-sensitive adhesive composition falls within a preferable range when the cured product is used as the pressure-sensitive adhesive layer of a pressure-sensitive adhesive sheet. Therefore, a pressure-sensitive adhesive sheet using this cured product as the pressure-sensitive adhesive layer can obtain sufficient unevenness absorbency, and when it is adhered to an adherend having uneven portions on the surface, it is preferable because voids are less likely to occur between the uneven portions of the adherend. Also, if the content of the monofunctional (meth)acrylate is 99 mol% or less, when the pressure-sensitive adhesive sheet using the cured product of the pressure-sensitive adhesive composition as the pressure-sensitive adhesive layer is peeled from the adherend, it is less likely to leave glue, which is preferable.

[0063] When containing a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate, if the content of the polyfunctional (meth)acrylate is 1 mol% or more, the fluidity of the cured product obtained by curing the pressure-sensitive adhesive composition does not become too large, which is preferable. Also, if the content of the polyfunctional (meth)acrylate is 15 mol% or less, the fluidity of the cured product obtained by curing the pressure-sensitive adhesive composition falls within a preferable range when the cured product is used as the pressure-sensitive adhesive layer of a pressure-sensitive adhesive sheet. Therefore, the pressure-sensitive adhesive sheet using the cured product as the pressure-sensitive adhesive layer has sufficient unevenness absorbency, and when it is adhered to an adherend having uneven portions on the surface, it is preferable because voids are less likely to occur between the uneven portions of the adherend.

[0064] The content of the (meth)acrylic monomer (B) in the pressure-sensitive adhesive composition of the present embodiment is preferably 49 to 79% by mass, more preferably 53 to 73% by mass, and even more preferably 56 to 66% by mass. If the content of the (meth)acrylic monomer (B) is 49% by mass or more, the viscosity of the pressure-sensitive adhesive composition does not become too high, which is preferable because of excellent coatability. Also, if the content of the (meth)acrylic monomer (B) is 79% by mass or less, the viscosity of the pressure-sensitive adhesive composition does not become too low, and it is easy to control the thickness of the coating film composed of the pressure-sensitive adhesive composition, which is preferable.

[0065] (Chain transfer agent (C)) The chain transfer agent (C) is incorporated into the pressure-sensitive adhesive composition for the purpose of controlling the storage elastic modulus, loss tangent, and gel fraction of the cured product obtained by curing the pressure-sensitive adhesive composition. As the chain transfer agent (C), for example, polyfunctional thiols can be preferably used. Polyfunctional thiols are compounds having two or more mercapto groups in the molecule.

[0066] The polyfunctional thiols are not particularly limited, and examples thereof include 1,2-ethanedithiol, 1,4-bis(3-mercaptobutyryloxy)butane, tetraethylene glycol bis(3-mercaptopropionate), trimethylolethane tris(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptobutyrate), pentaerythritol tetrakis(3-mercaptopropionate), 1,3,5-tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, tris-[(3-mercaptopropionyloxy)-ethyl]-isocyanurate, dipentaerythritol hexakis(3-mercaptopropionate), and the like. Among the above, as the chain transfer agent (C), from the viewpoint of the reactivity of the pressure-sensitive adhesive composition, it is preferable to use pentaerythritol tetrakis(3-mercaptobutyrate).

[0067] The content of the chain transfer agent (C) in the pressure-sensitive adhesive composition of the present embodiment is preferably 0.5 to 5% by mass, more preferably 1 to 5% by mass, and even more preferably 3 to 4.5% by mass. When the content of the chain transfer agent (C) is 0.5% by mass or more, the fluidity of the cured product obtained by curing the pressure-sensitive adhesive composition falls within a preferable range when the cured product is used as the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet. Therefore, the pressure-sensitive adhesive sheet using the cured product as the pressure-sensitive adhesive layer has sufficient unevenness absorbency, and it is difficult for voids to occur between the uneven portions of the adherend, which is preferable. When the content is 5% by mass or less, it is preferable that there is little glue residue when the pressure-sensitive adhesive sheet using the cured product of the pressure-sensitive adhesive composition as the pressure-sensitive adhesive layer is peeled from the adherend.

[0068] (Photoinitiator (D)) The photoinitiator (D) is not particularly limited, but a photo radical polymerization initiator is preferable. As the photoinitiator (D), for example, a carbonyl-based photoinitiator, a sulfide-based photoinitiator, an acylphosphine oxide-based photoinitiator, a quinone-based photoinitiator, a sulfochloride-based photoinitiator, a thioxanthone-based photoinitiator, etc. can be used. Among these photoinitiators (D), from the viewpoint of the transparency of the cured product obtained by photocuring the pressure-sensitive adhesive composition, it is preferable to use an acylphosphine oxide-based photoinitiator. Specifically, it is preferable to use 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[0069] The content of the photoinitiator (D) in the pressure-sensitive adhesive composition of the present embodiment is preferably 0.01 to 5% by mass, more preferably 0.05 to 3% by mass, and even more preferably 0.1 to 2% by mass. When the content of the photoinitiator (D) is 0.01% by mass or more, the photocuring of the pressure-sensitive adhesive composition proceeds sufficiently. Further, when the content of the photoinitiator (D) is 5% by mass or less, there is no excessive increase in low molecular weight components during the photocuring of the pressure-sensitive adhesive composition. For this reason, it is preferable that there is little glue residue when the pressure-sensitive adhesive sheet using the cured product of the pressure-sensitive adhesive composition as the pressure-sensitive adhesive layer is peeled from the adherend.

[0070] (Fatty acid ester (E)) The pressure-sensitive adhesive composition of this embodiment contains polyurethane (A), (meth)acrylic monomer (B), chain transfer agent (C), and photopolymerization initiator (D), and may further contain fatty acid ester (E) as needed. The fatty acid ester (E) is contained for the purpose of controlling the adhesive force in a pressure-sensitive adhesive sheet using the cured product of the pressure-sensitive adhesive composition as a pressure-sensitive adhesive layer, and improving the laminating property (wettability) and air-bleeding property (ease of escape of air trapped when the pressure-sensitive adhesive sheet is bonded to an adherend) of the pressure-sensitive adhesive layer.

[0071] As the fatty acid ester (E), an ester of a fatty acid and an alkyl alcohol can be used. From the perspective of compatibility with other components, an ester of a fatty acid having 8 to 18 carbon atoms and a monofunctional alcohol having a branched hydrocarbon group having 3 to 18 carbon atoms, and an ester of an unsaturated fatty acid having 14 to 18 carbon atoms and a 2- to 4-functional alcohol are preferably used.

[0072] Examples of the ester of a fatty acid having 8 to 18 carbon atoms and a monofunctional alcohol having a branched hydrocarbon group having 3 to 18 carbon atoms include isostearyl laurate, isopropyl myristate, isocetyl myristate, octyldodecyl myristate, isopropyl palmitate, isostearyl palmitate, isocetyl stearate, 2-ethylhexyl stearate, octyldodecyl oleate, diisostearyl adipate, diisocetyl sebacate, trioleyl trimellitate, and triisocetyl trimellitate. Among these, isopropyl myristate, isopropyl palmitate, and 2-ethylhexyl stearate are preferably used, and isopropyl myristate and / or 2-ethylhexyl stearate are particularly preferably used.

[0073] Examples of esters of unsaturated fatty acids having 14 to 18 carbon atoms and polyhydric alcohols having 2 to 4 functional groups include esters of unsaturated fatty acids such as myristoleic acid, oleic acid, linoleic acid, linolenic acid, isopalmitic acid, and isostearic acid, and alcohols such as ethylene glycol, propylene glycol, glycerin, trimethylolpropane, pentaerythritol, and sorbitan.

[0074] The content of the fatty acid ester (E) in the pressure-sensitive adhesive composition of the present embodiment is preferably 3 to 18% by mass, more preferably 5 to 15% by mass. When the content of the fatty acid ester (E) is 3% by mass or more, the adhesive strength in the pressure-sensitive adhesive sheet using the cured product of the pressure-sensitive adhesive composition as the pressure-sensitive adhesive layer is within a preferable range as a pressure-sensitive adhesive sheet, and the laminating property and degassing property of the pressure-sensitive adhesive layer are good. When the content of the fatty acid ester (E) is 18% by mass or less, it is preferable because paste residue containing the fatty acid ester (E) hardly occurs when the pressure-sensitive adhesive sheet using the cured product of the pressure-sensitive adhesive composition as the pressure-sensitive adhesive layer is peeled from the adherend.

[0075] (Solvent) The pressure-sensitive adhesive composition of the present embodiment may contain a solvent, but is more preferably a solvent-free one that substantially does not contain a solvent. When the pressure-sensitive adhesive composition of the present embodiment contains a solvent, for example, the solvent can be used as a leveling agent and / or a softening agent.

[0076] When the pressure-sensitive adhesive composition of the present embodiment is solvent-free, when forming the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet using this, the step of heating and drying the solvent can be omitted, so excellent productivity can be obtained. In particular, when manufacturing a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a thickness exceeding 50 μm using the pressure-sensitive adhesive composition of the present embodiment, the effect of improving productivity by omitting the step of heating and drying the solvent becomes remarkable, so it is preferably solvent-free.

[0077] In the present invention, the meaning that the pressure-sensitive adhesive composition "substantially does not contain a solvent" means that the content of the solvent in the pressure-sensitive adhesive composition is 0 to 1% by mass, preferably 0 to 0.5% by mass, and more preferably 0 to 0.1% by mass.

[0078] (Others) The pressure-sensitive adhesive composition of the present embodiment may contain other additives as necessary, as long as the effects of the present invention are not impaired. Examples of the additives include plasticizers, surface lubricants, antioxidants, anti-aging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, light stabilizers such as benzotriazole-based ones, phosphate ester-based and other flame retardants, antistatic agents such as surfactants, dyes, and the like.

[0079] (Gel fraction) The pressure-sensitive adhesive composition of the present embodiment is photocurable, and the gel fraction of the cured product cured at an irradiation dose of 1000 mJ / cm 2 is in the range of 50 to 65% by mass so that the thickness after curing becomes 150 μm. The gel fraction of the cured product cured at an irradiation dose of 1000 mJ / cm 2 can be adjusted by controlling the content of the chain transfer agent (C) and / or the photopolymerization initiator (D) in the pressure-sensitive adhesive composition of the present embodiment containing the polyurethane (A), the (meth)acrylic monomer (B), the chain transfer agent (C), and the photopolymerization initiator (D). More specifically, increasing the content of the chain transfer agent (C) and / or the photopolymerization initiator (D) decreases the gel fraction, and decreasing the content of the chain transfer agent (C) and / or the photopolymerization initiator (D) increases the gel fraction.

[0080] The cured product having a gel fraction of 50 to 65% by mass obtained by curing the pressure-sensitive adhesive composition of the present embodiment at an irradiation dose of 1000 mJ / cm 2 has sufficient adhesive strength, hardly causes adhesive residue, and is excellent in unevenness absorption. Therefore, the pressure-sensitive adhesive composition of the present embodiment is suitable as a material for the pressure-sensitive adhesive layer in a pressure-sensitive adhesive sheet used for applications where it is attached to an adherend having uneven portions on the surface and then peeled off. The pressure-sensitive adhesive composition of the present embodiment is irradiated with an irradiation dose of 1000 mJ / cm 2The gel fraction of the cured product obtained by curing is preferably 52% by mass or more. Further, the gel fraction of the cured product is preferably 63% by mass or less.

[0081] On the other hand, an adhesive sheet using a cured product having a gel fraction of less than 50% by mass as an adhesive layer is likely to have adhesive residue when peeled off after being attached to an adherend. Further, a cured product having a gel fraction exceeding 65% by mass has insufficient fluidity when used as an adhesive layer of an adhesive sheet. For this reason, when an adhesive sheet using a cured product having a gel fraction exceeding 65% by mass as an adhesive layer is attached to an adherend having uneven portions on the surface, voids are likely to occur between the uneven portions of the adherend.

[0082] (Measurement of gel fraction) In the present invention, the gel fraction of the cured product obtained by curing the adhesive composition with an irradiation dose of 1000 mJ / cm 2 is measured as follows. First, the adhesive composition is applied onto a release PET film having a thickness of 75 μm (manufactured by Toyama Film Co., Ltd., trade name: Clean Sepa (trademark) HY-S10-2) using an applicator so that the thickness after curing becomes 150 μm. Next, the coated surface of the adhesive composition is covered with a silicone-based ultra-light release PET film having a thickness of 75 μm (manufactured by Toyobo Co., Ltd., product name: E7006).

[0083] Subsequently, using an ultraviolet irradiation device (manufactured by Eye Graphics Co., Ltd., UV irradiation device 3 kW, high-pressure mercury lamp), ultraviolet rays are irradiated through the ultra-light release PET film under the conditions of an irradiation distance of 25 cm, a lamp moving speed of 1.0 m / min, and an irradiation dose of 1000 mJ / cm 2 to cure the adhesive composition to obtain a cured product (adhesive layer).

[0084] Next, a square sheet with a length of 8 cm and a width of 8 cm is cut out from the sheet having the cured product (adhesive layer), and the PET film and the ultra-light release PET film are peeled off from the adhesive layer of the obtained square sheet. Then, the adhesive layer peeled off from the square sheet is used as a measurement sample, and its mass is measured. Subsequently, the measurement sample is immersed in 50 ml of toluene and left standing at room temperature for 72 hours. Thereafter, the measurement sample is taken out from the toluene, dried at 80 °C for 5 hours, and the mass is measured again. Then, the gel fraction is measured based on the following formula. Gel fraction (%) = [A / B] × 100 A: Mass of the measurement sample after immersion in toluene (excluding the mass of toluene) B: Mass of the measurement sample before immersion in toluene

[0085] (Storage elastic modulus and loss tangent) The cured product obtained by curing the adhesive composition of the present embodiment with an irradiation amount of 1000 mJ / cm 2 has a storage elastic modulus at 25 °C measured at a frequency of 1 Hz of 1.0×10 4 ~1.0×10 5 and preferably has a loss tangent of 0.25 to 0.55. The storage elastic modulus and loss tangent at 25 °C measured at a frequency of 1 Hz of the cured product cured with an irradiation amount of 1000 mJ / cm 2 can be adjusted by controlling the content of the chain transfer agent (C) and / or the photoinitiator (D) contained in the adhesive composition. More specifically, when the content of the chain transfer agent (C) and / or the photoinitiator (D) is increased, the storage elastic modulus decreases and the loss tangent increases. Also, when the content of the chain transfer agent (C) and / or the photoinitiator (D) is decreased, the storage elastic modulus increases and the loss tangent decreases.

[0086] The adhesive composition of the present embodiment is cured with an irradiation amount of 1000 mJ / cm 2 to obtain the above storage elastic modulus of 1.0×10 4 ~1.0×10 5The cured product having a loss tangent of 0.25 to 0.55 has good flexibility and fluidity. Therefore, when an adhesive sheet using this cured product as an adhesive layer is attached to a workpiece (adherend) such as a semiconductor wafer having uneven portions such as bumps, it is possible to prevent the generation of voids between the uneven portions and the adhesive sheet.

[0087] The storage modulus at 25°C measured at a frequency of 1 Hz of the cured product obtained by curing the adhesive composition of the present embodiment with an irradiation dose of 1000 mJ / cm 2 is more preferably 2.0×10 4 or more, and even more preferably 3.0×10 4 or more. Further, the storage modulus is more preferably 9.0×10 4 or less, and even more preferably 8.0×10 4 or less.

[0088] The cured product having a storage modulus of 1.0×10 4 or more is not too soft when used as the adhesive layer of the adhesive sheet. Therefore, an adhesive sheet using a cured product having a storage modulus of 1.0×10 4 or more as the adhesive layer is preferable because it is less likely to leave glue even when peeled off after being attached to the adherend. Further, the cured product having a storage modulus of 1.0×10 5 or less has good flexibility when used as the adhesive layer of the adhesive sheet. Therefore, when an adhesive sheet using a cured product having a storage modulus of 1.0×10 5 or less as the adhesive layer is attached to an adherend having uneven portions on its surface, it is less likely to generate voids between the uneven portions of the adherend, which is preferable.

[0089] The loss tangent at 25°C measured at a frequency of 1 Hz of the cured product obtained by curing the adhesive composition of the present embodiment with an irradiation dose of 1000 mJ / cm 2 is more preferably 0.30 or more. Further, the loss tangent is more preferably 0.50 or less.

[0090] When the cured product has a loss tangent of 0.25 or more, it has good fluidity when used as the adhesive layer of the adhesive sheet. Therefore, when an adhesive sheet using a cured product with a loss tangent of 0.25 or more as the adhesive layer is attached to an adherend having uneven portions on the surface, voids are less likely to occur between the uneven portions of the adherend, which is preferable. Further, when the cured product has a loss tangent of 0.55 or less, the fluidity is not too large when used as the adhesive layer of the adhesive sheet. Therefore, an adhesive sheet using a cured product with a loss tangent of 0.55 or less as the adhesive layer is less likely to have adhesive residue even when peeled off after being attached to the adherend, which is preferable.

[0091] (Measurement of storage elastic modulus and loss tangent) In the present invention, the storage elastic modulus and loss tangent at 25°C measured at a frequency of 1 Hz of a cured product obtained by curing the adhesive composition with an irradiation amount of 1000 mJ / cm 2 are measured by the following method. First, in the same manner as the method for measuring the gel fraction described above, the adhesive composition is cured to produce a sheet having a cured product (adhesive layer) with a thickness of 150 μm. The PET film and the ultra-light release PET film are peeled off from the adhesive layer of the sheet having the cured product (adhesive layer). Then, 10 peeled adhesive layers with a thickness of 150 μm are laminated to form a laminated sheet with a thickness of 1.5 mm. A square sheet with a length of 8 mm and a width of 8 mm is cut out from the obtained laminated sheet and used as a measurement sample.

[0092] Thereafter, for the obtained measurement sample, using a rotational viscoelasticity measuring device (rheometer) (manufactured by TA Instruments, product name "AR2000"), the storage elastic modulus and loss elastic modulus at -20 to 120°C at a frequency of 1 Hz (6.28 rad / sec) are measured in a shear mode, and the storage elastic modulus and loss tangent at 25°C are calculated.

[0093] <Method for manufacturing adhesive composition> Next, the method for manufacturing the adhesive composition of the present embodiment will be described in detail with examples. Hereinafter, among the components included in the pressure-sensitive adhesive composition of the present embodiment, for the polyurethane (A), a preferred synthesis method will be described with examples. Among the components included in the pressure-sensitive adhesive composition of the present embodiment, for each component other than the polyurethane (A), such as the (meth)acrylic monomer (B), the chain transfer agent (C), the photopolymerization initiator (D), and the fatty acid ester (E), commercially available products can be easily purchased, and since the synthesis methods vary depending on the types of compounds used as each component, the description of the synthesis methods will be omitted.

[0094] <Synthesis Method of Polyurethane (A)> Hereinafter, an example of a preferred synthesis method of the polyurethane (A) included in the pressure-sensitive adhesive composition of the present embodiment will be described. Note that the synthesis method of the polyurethane (A) is not limited to the synthesis method shown below, and can be appropriately changed depending on conditions such as the raw materials and equipment used in the synthesis.

[0095] In the synthesis method of the polyurethane (A) shown below, the reaction between the hydroxy group and the isocyanato group is carried out in the presence of an organic solvent inert to the isocyanato group in any step using a urethanization catalyst such as dibutyltin dilaurate, dibutyltin diethylhexoate, or dioctyltin dilaurate. Also, the reaction between the hydroxy group and the isocyanato group is preferably carried out continuously at 30 to 100 °C for 1 to 5 hours in any step. The amount of the urethanization catalyst used is preferably 50 to 500 mass ppm with respect to the total mass of the reactants (raw materials).

[0096] To synthesize the polyurethane (A), first, a polyoxyalkylene polyol and a polyisocyanate are charged in a ratio such that the amount of isocyanato groups (on a molecular number basis, the same hereinafter) is more than the amount of hydroxy groups (on a molecular number basis, the same hereinafter). Then, the polyoxyalkylene polyol and the polyisocyanate are reacted to synthesize a polyurethane having an isocyanato group at the terminal as a precursor of the polyurethane (A). Specific examples of the polyoxyalkylene polyol and the polyisocyanate used as raw materials are as exemplified in the section of the polyurethane (A).

[0097] At this time, by adjusting the ratio of the amount of isocyanato groups to the amount of hydroxy groups contained in the raw materials, the molecular weight (degree of polymerization) of the polyurethane having isocyanato groups at its terminals can be adjusted. Specifically, the smaller the excess amount of isocyanato groups relative to the amount of hydroxy groups, the larger the molecular weight of the polyurethane having isocyanato groups at its terminals. Also, the larger the excess amount of isocyanato groups relative to the amount of hydroxy groups, the smaller the molecular weight of the polyurethane having isocyanato groups at its terminals. In the present embodiment, the mass average molecular weight of the target polyurethane (A) is adjusted by adjusting the molecular weight of the polyurethane having isocyanato groups at its terminals.

[0098] Next, a polyurethane having isocyanato groups at its terminals is reacted with a compound having hydroxy groups and (meth)acryloyl groups to produce a polyurethane (A) containing a polyurethane (a1) having a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate and having (meth)acryloyl groups at a plurality of terminals. The (meth)acryloyl groups at the terminals of the produced polyurethane (A) are preferably a part of the (meth)acryloyloxy groups.

[0099] The compounds having a hydroxy group and a (meth)acryloyl group are not particularly limited, and examples thereof include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and monoalcohols having a (meth)acryloyl group derived from various polyols such as 1,3-butanediol mono(meth)acrylate, 1,4-butanediol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, and 3-methylpentanediol mono(meth)acrylate. These compounds having a hydroxy group and a (meth)acryloyl group may be used alone or in combination of two or more. Among these compounds having a hydroxy group and a (meth)acryloyl group, 2-hydroxyethyl (meth)acrylate is preferably used from the viewpoints of reactivity with the isocyanato group of the polyurethane having an isocyanato group at the terminal and photocurability of the adhesive composition.

[0100] Further, the polyurethane (A) may be produced by reacting a polyurethane having an isocyanato group at the terminal with an alkyl alcohol having no (meth)acryloyl group and having one hydroxy group, together with a compound having a hydroxy group and a (meth)acryloyl group. The alkyl alcohol may be any one that has no (meth)acryloyl group and has one hydroxy group, and linear, branched, or alicyclic alkyl alcohols and the like can be used, and it is not particularly limited. The above alkyl alcohol may be used alone or in combination of two or more.

[0101] By reacting a compound having a hydroxy group and a (meth)acryloyl group, an alkyl alcohol having no (meth)acryloyl group and having one hydroxy group, and a polyurethane having an isocyanato group at the terminal to produce the polyurethane (A), the introduction amount of the (meth)acryloyl group with respect to the polyurethane having an isocyanato group at the terminal can be adjusted.

[0102] More specifically, according to the above reaction, as the polyurethane (A), a product containing a plurality of types of polyurethanes with different amounts of introduced terminal (meth)acryloyl groups is produced. Among the plurality of types of polyurethanes, a polyurethane (a1) having (meth)acryloyl groups at a plurality of terminals is included. Further, among the plurality of types of polyurethanes, not only the polyurethane (a1) but also a polyurethane in which at least a part of the plurality of terminals has a structure derived from the above alkyl alcohol is included. Therefore, among the plurality of types of polyurethanes produced, a polyurethane in which at least a part of the plurality of terminals does not have a (meth)acryloyl group is included. Further, among the plurality of types of polyurethanes produced, a polyurethane (a2) having a (meth)acryloyl group at only one terminal may also be included.

[0103] <Another example of the synthesis method of polyurethane (A)> Next, another example of a preferred synthesis method of polyurethane (A) will be described. In the synthesis method of polyurethane (A) shown below, similar to the example of the above synthesis method, the reaction between the hydroxy group and the isocyanato group is carried out using a urethanization catalyst such as dibutyltin dilaurate, dibutyltin diethylhexoate, dioctyltin dilaurate, etc. in the presence of an organic solvent inert to the isocyanato group in any step. Also, the reaction between the hydroxy group and the isocyanato group is preferably carried out continuously at 30 to 100 °C for 1 to 5 hours in any step. The usage amount of the urethanization catalyst is preferably 50 to 500 mass ppm with respect to the total mass of the reactants (raw materials).

[0104] When synthesizing polyurethane (A) using this synthesis method, different from the example of the above synthesis method, a polyurethane having a hydroxy group at the terminal is synthesized as a precursor of polyurethane (A). Specifically, first, polyoxyalkylene polyol and polyisocyanate are charged in a ratio such that the amount of hydroxy groups (on a molecular number basis, the same applies hereinafter) is greater than the amount of isocyanato groups (on a molecular number basis, the same applies hereinafter). Then, polyoxyalkylene polyol and polyisocyanate are reacted to synthesize a polyurethane having a hydroxy group at the terminal as a precursor of polyurethane (A).

[0105] At this time, by adjusting the ratio of the amount of hydroxy groups to the amount of isocyanato groups contained in the raw materials, the molecular weight (degree of polymerization) of the polyurethane having a hydroxy group at the terminal can be adjusted. Specifically, the smaller the excess amount of the hydroxy group amount relative to the isocyanato group amount, the larger the molecular weight of the polyurethane having a hydroxy group at the terminal. Also, the larger the excess amount of the hydroxy group amount relative to the isocyanato group amount, the smaller the molecular weight of the polyurethane having a hydroxy group at the terminal. In this embodiment, the mass average molecular weight of the target polyurethane (A) is adjusted by adjusting the molecular weight of the polyurethane having a hydroxy group at the terminal.

[0106] Next, the polyurethane having a hydroxy group at the terminal is reacted with a compound having an isocyanato group and a (meth)acryloyl group to produce a polyurethane (A) containing a polyurethane (a1) having a skeleton containing a structure derived from polyoxyalkylene polyol and a structure derived from polyisocyanate and having (meth)acryloyl groups at a plurality of terminals. The (meth)acryloyl groups at the terminals of the produced polyurethane (A) are preferably part of the (meth)acryloyloxy groups.

[0107] The compounds having an isocyanato group and a (meth)acryloyl group are not particularly limited, and examples thereof include 2-(meth)acryloyloxyethyl isocyanate, 2-(meth)acryloyloxypropyl isocyanate, 1,1-bis(acryloyloxymethyl)ethyl isocyanate, and the like. Commercially available products of the compounds having an isocyanato group and a (meth)acryloyl group include, for example, Karenz MOI (registered trademark) and Karenz AOI (registered trademark) manufactured by Showa Denko K.K. These compounds having an isocyanato group and a (meth)acryloyl group may be used alone or in combination of two or more. Among these compounds having an isocyanato group and a (meth)acryloyl group, 2-(meth)acryloyloxyethyl isocyanate is preferably used from the viewpoints of reactivity with the hydroxy group of the polyurethane having a hydroxy group at the terminal and photocurability of the adhesive composition.

[0108] Further, the polyurethane (A) may be produced by reacting a compound having an isocyanato group and a (meth)acryloyl group together with an alkyl isocyanate having no (meth)acryloyl group and having one isocyanato group with a polyurethane having a hydroxy group at the terminal. The alkyl isocyanate may be any one that has no (meth)acryloyl group and has one isocyanato group, and linear, branched, or alicyclic alkyl isocyanates and the like can be used, and it is not particularly limited. The above alkyl isocyanate may be used alone or in combination of two or more.

[0109] By reacting a compound having an isocyanato group and a (meth)acryloyl group, an alkyl isocyanate having no (meth)acryloyl group and having one isocyanato group, and a polyurethane having a hydroxy group at the terminal to produce the polyurethane (A), the introduction amount of the (meth)acryloyl group into the polyurethane having a hydroxy group at the terminal can be adjusted.

[0110] More specifically, according to the above reaction, as the polyurethane (A), a product containing a plurality of types of polyurethanes with different amounts of introduced terminal (meth)acryloyl groups is produced. Among the plurality of types of polyurethanes, a polyurethane (a1) having (meth)acryloyl groups at a plurality of terminals is included. Further, among the plurality of types of polyurethanes, not only the polyurethane (a1) but also polyurethanes in which at least a part of the plurality of terminals have a structure derived from the above alkyl isocyanate are included. Therefore, among the plurality of types of polyurethanes produced, polyurethanes in which at least a part of the plurality of terminals do not have (meth)acryloyl groups are included. Further, among the plurality of types of polyurethanes produced, a polyurethane (a2) having a (meth)acryloyl group at only one terminal may also be included.

[0111] <Method for mixing each component contained in the pressure-sensitive adhesive composition> The pressure-sensitive adhesive composition of the present embodiment can be produced by a method of mixing the polyurethane (A) obtained by the above synthesis method, the (meth)acrylic monomer (B), the chain transfer agent (C), the photopolymerization initiator (D), and the fatty acid ester (E) and other additives added as necessary. The method for mixing each component contained in the pressure-sensitive adhesive composition of the present embodiment is not particularly limited, and for example, it can be carried out using a stirring device equipped with a stirring blade such as a homodisper or a paddle blade.

[0112] The pressure-sensitive adhesive composition of the present embodiment contains a polyurethane (A), a (meth)acrylic monomer (B), a chain transfer agent (C), and a photopolymerization initiator (D). The polyurethane (A) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and contains a polyurethane (a1) having (meth)acryloyl groups at a plurality of terminals. The irradiation dose is 1000 mJ / cm 2The gel fraction of the cured product photocured is 50 to 65% by mass. Therefore, by curing the pressure-sensitive adhesive composition of the present embodiment, a cured product having sufficient adhesive strength, hardly causing adhesive residue, and excellent in unevenness absorbability can be obtained. Therefore, the pressure-sensitive adhesive composition of the present embodiment is suitable as a material for a pressure-sensitive adhesive layer in a pressure-sensitive adhesive sheet used for an application where it is attached to an adherend having uneven portions on the surface and then peeled off.

[0113] <Method for manufacturing a pressure-sensitive adhesive sheet> Next, the method for manufacturing the pressure-sensitive adhesive sheet of the present embodiment will be described. The method for manufacturing the pressure-sensitive adhesive sheet of the present embodiment is not particularly limited and can be manufactured using a known method. For example, a pressure-sensitive adhesive composition is applied onto a sheet-like base material, and a separator is laminated to form a laminate. Then, ultraviolet rays are irradiated onto the pressure-sensitive adhesive composition through the separator to photocure the pressure-sensitive adhesive composition. As a result, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed of a cured product of the pressure-sensitive adhesive composition is obtained on the base material.

[0114] The method for applying the pressure-sensitive adhesive composition to the base material is not particularly limited and can be appropriately selected. For example, as a method for applying the pressure-sensitive adhesive composition to the base material, methods using various coaters such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, a spray coater, a comma coater, and a direct coater, and a screen printing method can be mentioned.

[0115] Examples of the light source when photocuring the pressure-sensitive adhesive composition include a black light, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, and a xenon lamp. The light irradiation intensity may be any condition as long as the pressure-sensitive adhesive composition can be sufficiently cured and the gel fraction of the cured product is within the range of 50 to 65% by mass. For example, 50 to 3000 mW / cm 2It is preferably so. If the irradiation intensity of light is weak, it takes time for curing and the productivity decreases. Further, it is more preferable to adjust the irradiation intensity of light so that the values of the storage elastic modulus and the loss tangent of the cured product at 25°C measured at a frequency of 1 Hz are within a desired range.

[0116] In this embodiment, the adhesive composition is irradiated with ultraviolet rays through a transparent separator. However, when the base material and the separator are transparent, ultraviolet rays may be irradiated from either the separator side or the base material side.

[0117] <Applications and Required Performance of the Adhesive Sheet> The adhesive sheet of this embodiment can be used for applications where it is attached to an adherend having uneven portions on the surface and then peeled off. Specifically, it can be suitably used as an adhesive sheet that is attached to the surface of a semiconductor wafer on which bumps are formed, protects the surface of the semiconductor wafer, and is peeled off after a predetermined processing step.

[0118] When the adhesive sheet of this embodiment is used for the purpose of protecting the bump formation surface of a semiconductor wafer, the peel strength (adhesive force) of the adhesive sheet needs to be such that the semiconductor wafer is firmly fixed to the adhesive sheet, for example, in a back grinding process in the semiconductor device processing step. On the other hand, when peeling the adhesive sheet from the semiconductor wafer after a predetermined processing step, it needs to be of a strength that does not damage the components of the semiconductor device. From these viewpoints, the peel strength of the adhesive sheet used for the above applications is preferably 10 to 300 gf / 25 mm, more preferably 15 to 200 gf / 25 mm, and even more preferably 20 to 150 gf / 25 mm when the peel rate is 0.3 m / min. and the thickness of the adhesive layer is 50 to 200 μm. A specific method for measuring the peel strength of the adhesive sheet will be described later in the examples.

[0119] The pressure-sensitive adhesive sheet of the present embodiment has a pressure-sensitive adhesive layer made of a cured product of the pressure-sensitive adhesive composition of the present embodiment on one side of a sheet-like base material. Therefore, the pressure-sensitive adhesive sheet of the present embodiment has sufficient adhesive strength, and it is difficult for adhesive residue to occur in which the pressure-sensitive adhesive layer is transferred to the adherend after the pressure-sensitive adhesive sheet is peeled off, and it is excellent in unevenness absorption. Therefore, the pressure-sensitive adhesive sheet of the present embodiment is suitable for applications where it is attached to an adherend having uneven portions on the surface and then peeled off.

[0120] The pressure-sensitive adhesive sheet of the present embodiment can be preferably used, for example, as a pressure-sensitive adhesive sheet that is attached when performing a back grinding process of a semiconductor wafer having uneven portions formed by bumps on the surface and peeled off after the back grinding process. In this case, the semiconductor wafer is fixed with sufficient adhesive strength by the pressure-sensitive adhesive sheet of the present embodiment, and it is difficult for a gap to occur between the pressure-sensitive adhesive sheet attached to the semiconductor wafer and the periphery of the bumps. Therefore, it is possible to prevent water used in the back grinding process from entering the gap between the pressure-sensitive adhesive sheet and the periphery of the bumps and contaminating the semiconductor wafer. Further, it is preferable that adhesive residue hardly occurs around the bumps of the semiconductor wafer after the back grinding process when the pressure-sensitive adhesive sheet is peeled off.

Examples

[0121] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. Note that the present invention is not limited only to the following Examples.

[0122] <Synthesis of Polyurethane (A-1)> Into a reactor equipped with a thermometer, a stirrer, a dropping funnel, and a condenser with a drying tube, 0.55 kg (2.1 mol) of a hydrogenated product of diphenylmethane diisocyanate (Desmodur W, manufactured by Sumika Covestro Polyurethanes), and 4.01 kg (2.0 mol) of polypropylene glycol having a hydroxy group with a hydroxyl value of 56 mgKOH / g at the terminal (Actocol D-2000; manufactured by Mitsui Chemicals, number average molecular weight 2000), and 0.8 g of dioctyltin (Neostan U-810, manufactured by Nitto Kasei Co., Ltd.), which is a urethanization catalyst, were charged.

[0123] Subsequently, the temperature of the reactor was raised to 60 °C and reacted for 4 hours to obtain a polyurethane having isocyanato groups at both ends as a precursor of polyurethane (A). Subsequently, 23.22 g (0.2 mol) of 2-hydroxyethyl acrylate was added to the reactor, the temperature was raised to 70 °C and reacted for 2 hours to obtain 4.58 kg of polyurethane (A-1) with a mass average molecular weight of 67,000.

[0124] The obtained polyurethane (A-1) was analyzed by the infrared absorption spectrum (IR) method. As a result, no peak derived from isocyanato group was observed. Therefore, it was confirmed that polyurethane (A-1) is a polyurethane (a1) in which acryloyloxy groups are introduced at all terminals.

[0125] <Synthesis of Polyurethane (A-2)> A polyurethane (A-2) with a mass average molecular weight of 66,000 was obtained in the same manner as the synthesis method of polyurethane (A-1), except that 2.1 mol of isophorone diisocyanate (Desmodur I, manufactured by Sumitomo Covestro Polyurethane) was used instead of the hydrogenated product of diphenylmethane diisocyanate.

[0126] The obtained polyurethane (A-2) was analyzed by the infrared absorption spectrum (IR) method. As a result, no peak derived from isocyanato group was observed. Therefore, it was confirmed that polyurethane (A-2) is a polyurethane (a1) in which acryloyloxy groups are introduced at all terminals.

[0127] <Preparation of Adhesive Composition> The polyurethane (A-1) or (A-2) thus obtained, the (meth)acrylic monomer (B) shown in Table 1 or 2, the chain transfer agent (C), the photopolymerization initiator (D), and the fatty acid ester (E) were blended at the ratios described in Table 1 or 2, and mixed at 25 °C using a disperser to obtain the adhesive compositions of Examples 1 to 5 and Comparative Examples 1 to 5.

[0128]

Table 1

[0129]

Table 2

[0130] The following symbols described in Table 1 or 2 are the compounds shown below. 2EHA: 2-Ethylhexyl acrylate (manufactured by Toagosei Co., Ltd.) BUA: n-Butyl acrylate (manufactured by Toagosei Co., Ltd.) ACMO: Acryloylmorpholine (manufactured by Shin-Nakamura Chemical Co., Ltd.) IBOA: Isobornyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.) TMPTA: Trimethylolpropane triacrylate (manufactured by Toagosei Co., Ltd.)

[0131] PE1: Pentaerythritol tetrakis(3-mercaptobutyrate) (manufactured by Showa Denko K.K.) NR1: 1,3,5-Tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (manufactured by Showa Denko K.K.) TPO (Omnirad TPO H): 2,4,6-Trimethylbenzoyldiphenylphosphine oxide (manufactured by IGM Resins B.V.) Exceparl IPM: Isopropyl myristate (manufactured by Kao Corporation) Exceparl EH-S: 2-Ethylhexyl stearate (manufactured by Kao Corporation)

[0132] <Measurement of gel fraction> Using the adhesive compositions of Examples 1 to 5 and Comparative Examples 1 to 5, measurement samples were prepared by the above method, and the gel fraction of the cured product photocured at an irradiation dose of 1000 mJ / cm 2 was measured. The results are shown in Table 1 or 2.

[0133] <Measurement of storage elastic modulus and loss tangent> Using the above method, measurement samples were prepared using the pressure-sensitive adhesive compositions of Examples 1 to 5 and Comparative Examples 1 to 5, and the storage elastic modulus and loss tangent at 25°C measured at a frequency of 1 Hz of the cured product photocured at an irradiation dose of 1000 mJ / cm 2 were measured. The results are shown in Table 1 or 2.

[0134] <Preparation of Adhesive Sheet> As a sheet-like substrate, a 50-μm-thick PET film (manufactured by Toyobo Co., Ltd., product name: Ester (trademark) Film E5100) was prepared. Then, on the corona-treated surface of the substrate, the pressure-sensitive adhesive composition of Example 1 was applied using an applicator so that the thickness after curing would be 150 μm.

[0135] Next, as a separator, a 75-μm-thick silicone-based ultra-light release PET film (manufactured by Toyobo Co., Ltd., product name: E7006) was laminated on the coated surface of the pressure-sensitive adhesive composition using a rubber roller. Thereafter, through the separator, the pressure-sensitive adhesive composition was irradiated with ultraviolet rays using an ultraviolet irradiation device (manufactured by Aigraphics Co., Ltd., UV irradiation device 3 kW, high-pressure mercury lamp) under the conditions of an irradiation distance of 25 cm, a lamp moving speed of 1.0 m / min, and an irradiation dose of 1000 mJ / cm 2 to photocure the pressure-sensitive adhesive composition. As a result, an adhesive sheet of Example 1 in which an adhesive layer, which is a cured product of the pressure-sensitive adhesive composition, and a separator were laminated on the substrate was obtained.

[0136] Next, instead of the pressure-sensitive adhesive composition of Example 1, adhesive sheets were prepared in the same manner as the adhesive sheet of Example 1 using the pressure-sensitive adhesive compositions of Examples 2 to 5 and Comparative Examples 1 to 5, respectively. As a result, adhesive sheets of Examples 2 to 5 and Comparative Examples 2 to 4 were obtained. However, for the pressure-sensitive adhesive compositions of Comparative Examples 1 and 5, due to poor curing, an adhesive layer composed of a cured product of the pressure-sensitive adhesive composition could not be formed.

[0137] Next, the adhesive sheets of Examples 1 to 5 and Comparative Examples 2 to 4 were evaluated for the following items. <Peeling force (peeling strength)> The pressure-sensitive adhesive sheet was cut into a size of 25 mm in length and 150 mm in width, the separator was peeled off to expose the adhesive layer. Then, the entire exposed adhesive layer was laminated on a glass plate, and a rubber roller (diameter: 85 mm, width: 50 mm) with a mass of 2 kg (load: 19.6 N) was reciprocated once to obtain a measurement sample. The obtained measurement sample was left in an environment of 23 °C and 50% RH for 30 minutes. Then, according to JIS K 6854-2, a tensile test in the 180° direction was carried out at a peeling speed of 0.3 m / min. to measure the peeling strength (gf / 25 mm) with respect to the glass plate. The results are shown in Table 1 or 2.

[0138] <Uneven absorption> The pressure-sensitive adhesive sheet was cut into a size of 25 mm in length and 50 mm in width, the separator was peeled off to expose the adhesive layer. Then, the surface of the exposed adhesive layer was placed opposite to the bumps of a wafer with bumps (manufactured by WALTS, WALTS-TEG FC150SCJY LF(PI), bump height: 75 μm, bump size: diameter 90 μm). And a rubber roller (diameter: 85 mm, width: 50 mm) with a mass of 2 kg (load: 19.6 N) was reciprocated 3 times at a speed of 10 mm / sec on the base material of the pressure-sensitive adhesive sheet to bond the pressure-sensitive adhesive sheet and the wafer with bumps.

[0139] The wafer with bumps bonded to the pressure-sensitive adhesive sheet was observed from the base material side of the pressure-sensitive adhesive sheet with a digital optical microscope (manufactured by KOHYOLEX CORPORATION, RH-2000), and the uneven absorption to the bumps was evaluated according to the following criteria. The results are shown in Table 1 or 2. 「Criteria」 ○ (Acceptable): There is no gap between the adhesive layer of the pressure-sensitive adhesive sheet and the periphery of the bumps of the wafer with bumps. × (Unacceptable): There is a gap between the adhesive layer of the pressure-sensitive adhesive sheet and the periphery of the bumps of the wafer with bumps.

[0140] <Adhesive residue> The pressure-sensitive adhesive sheet was cut into a size of 25 mm in length and 50 mm in width, and the separator was peeled off to expose the adhesive layer. Then, it was placed facing the bumps of the wafer with bumps (manufactured by WALTS, WALTS-TEG FC150SCJY LF(PI), bump height: 75 μm, bump size: diameter 90 μm). And a rubber roller (diameter: 85 mm, width: 50 mm) with a mass of 2 kg (load 19.6 N) was reciprocated 3 times at a speed of 10 mm / sec on the base material of the pressure-sensitive adhesive sheet to bond the pressure-sensitive adhesive sheet and the wafer with bumps.

[0141] The wafer with bumps bonded to the pressure-sensitive adhesive sheet was left at 23 °C for 24 hours, and then the pressure-sensitive adhesive sheet was peeled off by hand at a speed of approximately 2 m / min. Then, the surface of the wafer with bumps was observed with a digital optical microscope (manufactured by Hylocks Corporation, RH-2000), and the presence or absence of glue residue was evaluated according to the following criteria. The results are shown in Table 1 or 2. "Criteria" ○(Acceptable): There is no glue residue around the bumps. ×(Unacceptable): There is glue residue around the bumps.

[0142] As shown in Table 1 or 2, the pressure-sensitive adhesive sheets of Examples 1 to 5 with a gel fraction of 50 to 65 mass% all had a peel strength of 10 gf / 25 mm or more and had sufficient adhesiveness. Also, for the pressure-sensitive adhesive sheets of Examples 1 to 5, the evaluations of unevenness absorption and glue residue were both "○(Acceptable)".

[0143] On the other hand, the pressure-sensitive adhesive sheets of Comparative Example 2 and Comparative Example 4 with a gel fraction of less than 50 mass% both had an evaluation of unevenness absorption of "○(Acceptable)", but an evaluation of glue residue of "×(Unacceptable)". Also, the pressure-sensitive adhesive sheet of Comparative Example 3 with a gel fraction exceeding 65 mass% had an evaluation of glue residue of "○(Good)", but an evaluation of unevenness absorption of "×(Unacceptable)".

Industrial Applicability

[0144] The present invention can provide an adhesive sheet that has sufficient adhesiveness, hardly causes adhesive residue in which the adhesive layer is transferred to the adherend after peeling the adhesive sheet, and is excellent in unevenness absorbency.

Claims

1. The composition comprises 20 to 50% by mass of a polyurethane (A), a (meth)acrylic monomer (B) composed of a compound having a (meth)acryloyloxy group, 0.5 to 5% by mass of a chain transfer agent (C), and 0.01 to 5% by mass of a photopolymerization initiator (D), the polyurethane (A) includes a polyurethane (a1) having a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate and having (meth)acryloyl groups at two or more ends; The irradiation dose was 1000 mJ / cm so that the thickness after curing was 150 μm. ２ The gel fraction of the cured product photocured by the above procedure is 50 to 65% by mass. The (meth)acrylic monomer (B) contains a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate, A pressure-sensitive adhesive composition comprising 85 to 99 mol % of the monofunctional (meth)acrylate and 1 to 15 mol % of the polyfunctional (meth)acrylate when the total amount of the (meth)acrylic monomers (B) is 100 mol %.

2. The cured product had a storage modulus of 1.0×10 at 25° C., measured at a frequency of 1 Hz. ４ ~1.0 x 10 ５ and The pressure-sensitive adhesive composition according to claim 1, which has a loss tangent of 0.25 to 0.55 at 25° C. measured at a frequency of 1 Hz.

3. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the chain transfer agent (C) is a polyfunctional thiol.

4. The pressure-sensitive adhesive composition according to claim 1 or 2, comprising 49 to 79 mass % of the (meth)acrylic monomer (B).

5. The pressure-sensitive adhesive composition according to claim 1 or 2, further comprising a fatty acid ester (E).

6. The pressure-sensitive adhesive composition according to claim 1, comprising 45 to 79 mass % of the (meth)acrylic monomer (B).

7. The pressure-sensitive adhesive composition according to claim 1, comprising 53 to 73 mass % of the (meth)acrylic monomer (B).

8. The pressure-sensitive adhesive composition according to claim 1, comprising 25 to 45 mass % of the polyurethane (A).

9. The pressure-sensitive adhesive composition according to claim 1, comprising 30 to 40 mass % of the polyurethane (A).

10. The pressure-sensitive adhesive composition according to claim 1 , which is used as a material for a pressure-sensitive adhesive layer in a pressure-sensitive adhesive sheet.

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