JP2013185148A - Self-adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self-adhesive sheet in which the variation in adhesive power during storing the self-adhesive sheet is suppressed and a protective layer has excellent peelability.SOLUTION: A self-adhesive sheet 100 including a substrate layer 10, a self-adhesive layer 20, and a protective layer 30 in this order, wherein the self-adhesive layer includes a first resin component and a second resin component; and the surface free energies of the first resin component, the second resin component, and the protective layer satisfy the relation of first resin component<second resin component≤protective layer. The self-adhesive sheet, in which the surface free energy of the protective layer is 32 to 50 mJ/m, is provided.

Description

  The present invention relates to an adhesive sheet.

  A workpiece (for example, a semiconductor wafer) that is an assembly of electronic components is manufactured in a large diameter state, and after forming a pattern on the surface, the back surface is usually ground so that the thickness of the wafer is about 100 μm to 600 μm ( Back-grinded), and then cut and separated (diced) into element pieces, and further transferred to a mounting process. In this back grinding process and dicing process, an adhesive sheet is used to fix the wafer. In such an adhesive sheet for wafer processing, it is important to fix the wafer in each step and adjust the adhesive force to such an extent that it can be peeled off from the wafer or chip after back grinding or dicing.

  As a means for adjusting the adhesive strength of the adhesive layer, mixing a plurality of resin components having different effects of exerting adhesive strength is performed (for example, Patent Document 1). However, in the pressure-sensitive adhesive layer containing a plurality of resin components, the individual resin components may move within the pressure-sensitive adhesive layer during storage of the pressure-sensitive adhesive sheet. As a result, the ratio of the resin component on the surface of the pressure-sensitive adhesive layer changes, and the pressure-sensitive adhesive force of the pressure-sensitive adhesive layer may change from a desired value. For example, when a resin component having an effect of increasing the adhesive force segregates on the surface of the adhesive layer, the adhesive force of the adhesive layer becomes larger than designed. Therefore, after the back grinding or dicing, there may be a problem in peeling of the adhesive sheet.

  Usually, the pressure-sensitive adhesive sheet protects the pressure-sensitive adhesive layer with a separator until it is used. This separator is typically subjected to a surface treatment using a silicone-based release agent or the like in order to ensure releasability. However, the component that imparts peelability to the separator and the resin that forms the pressure-sensitive adhesive layer react during storage of the pressure-sensitive adhesive sheet, which may adversely affect the pressure-sensitive adhesiveness of the pressure-sensitive adhesive sheet.

JP 2009-275209 A

  The present invention has been made in order to solve the above-described conventional problems, and an object of the present invention is to provide a pressure-sensitive adhesive having excellent releasability in which a change in adhesive force during storage of the pressure-sensitive adhesive sheet is suppressed. To provide a sheet.

As a result of repeated studies by the inventors, the pressure-sensitive adhesive layer contains the first resin component and the second resin component, and the surface energy of these resin component and protective layer is the first resin component <the second resin component. It has been found that the above-mentioned problems can be solved by using a pressure-sensitive adhesive sheet satisfying the relationship of resin component ≦ protective layer.
That is, the pressure-sensitive adhesive sheet of the present invention includes a base material layer, a pressure-sensitive adhesive layer, and a protective layer in this order. The pressure-sensitive adhesive layer includes a first resin component and a second resin component, and the surface free energy of the first resin component, the second resin component, and the protective layer is the first resin component <second. Satisfy the relationship of resin component ≦ protective layer.
In a preferred embodiment, the surface free energy of the protective layer is ^{32mJ / m 2 ~50mJ / m 2} .
In a preferred embodiment, the first surface free energy of the resin component and the second resin component is ^{20mJ / m 2 ~40mJ / m 2} .
In a preferred embodiment, the difference between the surface free energy of the first resin component and the surface free energy of the protective layer is 0.1 mJ / m ^{2 to} 18 mJ / m ² .
In a preferred embodiment, the pressure-sensitive adhesive layer contains an amorphous resin as the first resin component and a crystalline resin as the second resin component.
In a preferred embodiment, the amorphous resin is an amorphous polypropylene resin, and the crystalline resin is a crystalline polypropylene resin.
In a preferred embodiment, the pressure-sensitive adhesive sheet of the present invention is for semiconductor processing.

  According to the present invention, the pressure-sensitive adhesive layer contains at least two types of resin components having different surface free energies, and the surface free energies of these resin components and the protective layer are the first resin component <second resin component ≦ protection. By satisfy | filling the relationship of a layer, the change of the adhesive force of the adhesive layer during an adhesive sheet preservation | save can be suppressed. Furthermore, in this invention, instead of a separator, the normal film which does not give surface treatment can be used as a protective layer. Therefore, the pressure-sensitive adhesive sheet of the present invention can maintain a desired pressure-sensitive adhesive force even after storage. Moreover, the separator with high peelability (namely, surface free energy is small) is normally used for the adhesive sheet. The protective layer of the pressure-sensitive adhesive layer of the present invention has a surface free energy larger than that of the conventional separator, but has good peelability of the protective layer.

It is a schematic sectional drawing of the adhesive sheet by preferable embodiment of this invention.

A. Overall configuration diagram 1 of the adhesive sheet is a schematic sectional view of a pressure-sensitive adhesive sheet according to a preferred embodiment of the present invention. The pressure-sensitive adhesive sheet 100 of the present invention includes a base material layer 10, a pressure-sensitive adhesive layer 20, and a protective layer 30 in this order. The pressure-sensitive adhesive layer 20 includes a first resin component and a second resin component. The surface free energy of the first resin component, the second resin component, and the protective layer 30 satisfies the relationship of first resin component <second resin component ≦ protective layer. Of the resin components contained in the pressure-sensitive adhesive layer 20, the first resin component having a small surface free energy mainly exerts an effect of improving the pressure-sensitive adhesive strength of the pressure-sensitive adhesive. On the other hand, the second resin component having a large surface free energy exerts the effect of mainly suppressing the adhesive force of the adhesive and controlling the peelability. When a separator having a small surface free energy subjected to surface treatment is used for the pressure sensitive adhesive sheet having a pressure sensitive adhesive layer containing a resin having a different effect to be imparted to the pressure sensitive adhesive, the surface free energy is reduced during storage of the pressure sensitive adhesive sheet. It is considered that the small first resin component segregates at the interface between the pressure-sensitive adhesive layer and the separator, and the adhesive force becomes higher than the design. In the present invention, the surface free energy of the pressure-sensitive adhesive layer and the protective layer is designed so as to satisfy the relationship of the first resin component <the second resin component ≦ the protective layer, thereby changing the adhesive force during storage of the pressure-sensitive adhesive sheet. Can be suppressed. In this invention, it replaces with a general separator and can use the normal film which does not surface-treat as a protective layer. Therefore, it is possible to prevent an adverse effect on the pressure-sensitive adhesive layer due to the release agent used for the surface treatment. Moreover, when using a protective layer with large surface free energy as a protective layer of an adhesive layer, there exists a subject that peeling of a protective layer becomes difficult at the time of use. However, the protective layer of the pressure-sensitive adhesive sheet of the present invention has excellent peelability as in the case of using a separator whose surface free energy is reduced by surface treatment of the protective layer.

Here, in this specification, “surface free energy” means that the contact angle is measured with water and methylene iodide on the target solid surface, respectively, and the measured value and the surface free energy value of the contact angle measurement liquid. (Known from the literature) is substituted into the following equation (1) derived from the Young equation and the extended Fowkes equation, and the obtained two equations are solved as simultaneous linear equations to obtain the surface free energy value of the solid. Means. In addition, the surface free energy of the 1st resin component and 2nd resin component which are contained in an adhesive layer is a surface free energy value measured about this test piece, producing a test piece using each resin component independently. is there. The surface free energy γ _S of a solid is the sum of γ _S ^d and γ _S ^v .
(1 + cos θ) γ _L = 2√ (γ _S ^d γ _L ^d ) + 2√ (γ _S ^v γ _L ^v ) (1)
However, each symbol in the formula is as follows.
θ: contact angle γL: surface free energy γ _L ^{d of} contact angle measurement liquid: dispersion force component γ _L ^{v at} rL: polar force component γ _S ^{d at} rL: dispersion force component γ _S ^{v at} solid surface free energy Polar force component in surface free energy of water

  The thickness of the adhesive sheet 100 can be set to any appropriate value. The thickness of the said adhesive sheet is 115 micrometers-535 micrometers, for example. Further, the thickness of the pressure-sensitive adhesive sheet in use (that is, the thickness of the pressure-sensitive adhesive sheet after peeling off the protective layer) is preferably 90 μm to 285 μm, more preferably 105 μm to 225 μm, and still more preferably 120 μm to 205 μm.

  The thickness of the base material layer 10 is preferably 30 μm to 185 μm, more preferably 55 μm to 175 μm.

  The thickness of the pressure-sensitive adhesive layer 20 is preferably 3 μm to 100 μm, more preferably 5 μm to 65 μm.

  The thickness of the protective layer is set to any appropriate value. The thickness of the protective layer is preferably 25 μm to 250 μm.

  The pressure-sensitive adhesive sheet of the present invention may further include any appropriate other layer. Examples of the other layer include a surface layer (heat-resistant layer) that is provided on the side opposite to the adhesive of the base material layer and can impart heat resistance to the pressure-sensitive adhesive sheet.

B. Pressure-sensitive adhesive layer The pressure-sensitive adhesive layer contains a first resin component and a second resin component having different surface free energies. The 1st resin component with small surface free energy is a resin component which mainly provides adhesive force to an adhesive layer. On the other hand, the second resin component having a large surface free energy is a resin component that mainly suppresses the adhesive force of the pressure-sensitive adhesive layer and controls the peelability. By combining these resin components at a predetermined ratio, the adhesive strength of the pressure-sensitive adhesive layer can be adjusted to a desired value. By using these resin components in combination, a pressure-sensitive adhesive layer having a desired pressure-sensitive adhesive force can be formed, and changes in the pressure-sensitive adhesive force during storage of the pressure-sensitive adhesive sheet can be suppressed.

The first surface free energy of the resin component and the second resin component is preferably ^{20mJ / m 2 ~40mJ / m 2} , more preferably ^{25mJ / m 2 ~35mJ / m 2} . The first resin component and the second resin component preferably have the surface free energy of each resin component within the above range and satisfy the relationship of the first resin component <the second resin component. If the surface free energy of the first resin component and the second resin component is within the above range, a desired adhesive force can be imparted to the adhesive layer, and the adhesive strength during storage of the adhesive sheet can be increased. Changes can be suppressed.

The difference between the surface free energy of the first resin component and the surface free energy of the second resin component is preferably 0.1 mJ / m ^{2 to 5} mJ / m ² , more preferably 0.5 mJ / m ^2. it is a ~4mJ / ^{m 2.} When the difference in surface free energy between the first resin component and the second resin component is less than 0.1 mJ / m ² , the difference in surface free energy is small, and the change in adhesive force during storage of the adhesive sheet is sufficiently suppressed. There are cases where it is not possible. When the difference between the first resin component and the second resin component exceeds 5 mJ / m ² , the pressure-sensitive adhesive layer may cause a large phase separation, and the function of the pressure-sensitive adhesive layer may deteriorate.

  Any appropriate resin can be used for the first resin component and the second resin component as long as the surface free energy satisfies the first resin component <the second resin component. Examples of the combination of the first resin component and the second resin component include a combination of a crystalline resin and an amorphous resin. In the combination, the amorphous resin corresponds to the first resin component, and the crystalline resin corresponds to the second resin component. A combination of a crystalline resin and an amorphous resin is preferable in that the adhesive strength of the adhesive layer can be designed in a wide range.

  The content ratio between the first resin component and the second resin component is set to any appropriate value according to the desired adhesive strength. The content ratio of the first resin component and the second resin component (first resin component / second resin component, weight ratio) is, for example, 95/5 to 20/80.

B-1. 1st resin component The said 1st resin component is a component which mainly provides a desired adhesive force to an adhesive. The first resin component is preferably an amorphous resin. Any appropriate non-crystalline resin can be used as the non-crystalline resin. The non-crystalline resin is preferably a non-crystalline polypropylene resin. If it is a pressure-sensitive adhesive layer containing an amorphous polypropylene resin, it is possible to produce a pressure-sensitive adhesive sheet by co-extrusion molding with the material forming the base material layer, using a small number of steps and using an organic solvent An adhesive sheet can be obtained without doing. The non-crystalline polypropylene resin is preferably an amorphous propylene- (1-butene) copolymer. In the present specification, “non-crystalline” and “amorphous” refer to properties that do not have a clear melting point, such as crystalline.

  The amorphous propylene- (1-butene) copolymer is preferably obtained by polymerizing propylene and 1-butene using a metallocene catalyst. More specifically, the amorphous propylene- (1-butene) copolymer performs, for example, a polymerization step in which propylene and 1-butene are polymerized using a metallocene catalyst, and the catalyst residue is removed after the polymerization step. It can be obtained by performing post-processing steps such as a step and a foreign matter removing step. The amorphous propylene- (1-butene) copolymer is obtained in such a form as a powder or a pellet through such steps. Examples of the metallocene catalyst include a metallocene homogeneous mixed catalyst containing a metallocene compound and an aluminoxane, a metallocene supported catalyst in which a metallocene compound is supported on a particulate carrier, and the like.

The pressure-sensitive adhesive layer using an amorphous propylene- (1-butene) copolymer obtained by solution polymerization using a metallocene catalyst as described above is F ⁻ , Cl ⁻ , Br ⁻ , NO ₂ ^−. , NO ₃ ⁻ , SO ₄ ²⁻ , Li ⁺ , Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ and NH ₄ ⁺ are substantially not contained. Therefore, it is possible to prevent the adherend from being contaminated with the ions. Moreover, when an adhesive sheet provided with such an adhesive layer is used, for example, for semiconductor wafer processing, it is possible to prevent circuit disconnection or short circuit. In solution polymerization using the metallocene catalyst, the amorphous propylene- (1-butene) copolymer is purified by repeating precipitation isolation (reprecipitation method) using a poor solvent different from the polymerization solvent. Therefore, a pressure-sensitive adhesive layer that does not contain the ions can be obtained. In this specification, “F ⁻ , Cl ⁻ , Br ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ , Li ⁺ , Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , NH ₄ ⁺ are substantially "Not included" means that it is below the detection limit in standard ion chromatographic analysis (for example, ion chromatographic analysis using trade names "DX-320" and "DX-500" manufactured by Dionex). Say. Specifically, F ⁻ , Cl ⁻ , Br ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ and K ⁺ are 0.49 μg or less, and Li ⁺ and Na ⁺ are each 1 g of the adhesive layer. Each case is 0.20 μg or less, Mg ²⁺ and Ca ²⁺ are each 0.97 μg or less, and NH ₄ ⁺ is 0.5 μg or less.

  The amorphous propylene- (1-butene) copolymer polymerized using the metallocene catalyst as described above exhibits a narrow molecular weight distribution. The molecular weight distribution (Mw / Mn) of the amorphous propylene- (1-butene) copolymer is preferably 3 or less, more preferably 2 or less, and even more preferably 1.1 to 2, particularly Preferably it is 1.2-1.9. Since the amorphous propylene- (1-butene) copolymer having a narrow molecular weight distribution has few low molecular weight components, if such an amorphous propylene- (1-butene) copolymer is used, bleeding of the low molecular weight component can be achieved. It is possible to obtain a pressure-sensitive adhesive sheet that can prevent the adherend from being contaminated by the above.

  The content ratio of the structural unit derived from propylene in the amorphous propylene- (1-butene) copolymer is preferably 80 mol% to 99 mol%, more preferably 85 mol% to 99 mol%, Preferably it is 90 mol%-99 mol%.

  The content ratio of the structural unit derived from 1-butene in the above-mentioned amorphous propylene- (1-butene) copolymer is preferably 1 mol% to 15 mol%, more preferably 1 mol% to 10 mol%. . If it is such a range, the adhesive sheet excellent in the balance of toughness and a softness | flexibility can be obtained.

  The amorphous propylene- (1-butene) copolymer may be a block copolymer or a random copolymer.

  The weight average molecular weight (Mw) of the amorphous propylene- (1-butene) copolymer is preferably 200,000 or more, more preferably 200,000 to 500,000, and still more preferably 200,000. ~ 300,000. If the weight average molecular weight (Mw) of the amorphous propylene- (1-butene) copolymer is within such a range, a general styrene-based thermoplastic resin, acrylic-based thermoplastic resin (Mw is 100,000 or less) ), A pressure-sensitive adhesive sheet that has less low molecular weight components and can prevent contamination of the adherend can be obtained. Further, during coextrusion molding, the pressure-sensitive adhesive layer can be formed without processing defects, and an appropriate pressure-sensitive adhesive force can be obtained.

  The melt flow rate of the amorphous propylene- (1-butene) copolymer at 230 ° C. and 2.16 kgf is preferably 1 g / 10 min to 50 g / 10 min, more preferably 5 g / 10 min to 30 g / 10 min. Yes, and more preferably 5 g / 10 min to 20 g / 10 min. When the melt flow rate of the amorphous propylene- (1-butene) copolymer is in such a range, a pressure-sensitive adhesive layer having a uniform thickness can be formed by coextrusion molding without processing defects. The melt flow rate can be measured by a method according to JISK7210.

  The amorphous propylene- (1-butene) copolymer may further contain other monomer-derived structural units as long as the effects of the present invention are not impaired. Examples of other monomers include α-olefins such as ethylene, 1-pentene, 1-hexene, 1-octene, 1-decene, 4-methyl-1-pentene, and 3-methyl-1-pentene. .

B-2. Second resin component The second resin component is a resin component that mainly suppresses the adhesive force of the adhesive and controls the peelability. The second resin component is preferably a crystalline resin. Any appropriate crystalline resin can be used as the crystalline resin. The crystalline resin is preferably a crystalline polypropylene resin.

  The crystalline polypropylene resin may be homopolypropylene or a copolymer obtained from propylene and a monomer copolymerizable with propylene. Examples of monomers copolymerizable with propylene include α-olefins such as ethylene, 1-pentene, 1-hexene, 1-octene, 1-decene, 4-methyl-1-pentene, and 3-methyl-1-pentene. Etc.

  The crystalline polypropylene resin is preferably obtained by polymerization using a metallocene catalyst in the same manner as the amorphous propylene- (1-butene) copolymer. By using the crystalline polypropylene resin thus obtained, it is possible to prevent contamination of the adherend due to bleeding of low molecular weight components.

  The crystallinity of the crystalline polypropylene resin is preferably 10% or more, more preferably 20% or more. The crystallinity is typically determined by differential scanning calorimetry (DSC) or X-ray diffraction.

B-3. Other Components The pressure-sensitive adhesive layer may contain other resin components other than the first resin component and the second resin component as necessary. As said other resin component, as long as the effect of this invention is acquired, arbitrary appropriate resin can be used. Only one type of the other resin components may be used, or two or more types may be used in combination. By adjusting the type, addition amount, etc. of other resin components, characteristics such as charge amount can be adjusted within a desired range. In this case, the surface free energy of the other resin component is preferably lower than that of the first resin component.

  The pressure-sensitive adhesive layer may further contain other components as long as the effects of the present invention are not impaired. Examples of the other components include an antioxidant, an ultraviolet absorber, a light stabilizer, a heat resistance stabilizer, and an antistatic agent. The kind and usage-amount of another component can be suitably selected according to the objective.

C. Base material layer The base material layer is formed of any appropriate resin. Preferably, it is a thermoplastic resin that can be coextruded as described later. Examples of the thermoplastic resin include a polyethylene resin. Specific examples of the polyethylene resin include ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer (EEA), ethylene-methacrylic acid copolymer (EMA), styrene-ethylene-butylene-styrene block polymer ( SEBS), high molecular weight polyethylene (HDPE), low molecular weight polyethylene (LDPE), linear low molecular weight polyethylene (LLDPE), and the like. The base material layer preferably contains an ethylene-vinyl acetate copolymer.

  The ethylene-vinyl acetate copolymer preferably has a weight average molecular weight (Mw) of 10,000 to 200,000, more preferably 30,000 to 190,000. When the weight average molecular weight (Mw) of the ethylene-vinyl acetate copolymer is in the above range, the substrate layer can be formed without processing defects during coextrusion molding.

  The melt flow rate at 190 ° C. and 2.16 kgf of the ethylene-vinyl acetate copolymer is preferably 2 g / 10 min to 20 g / 10 min, more preferably 5 g / 10 min to 15 g / 10 min, and even more preferably 7 g. / 10 min to 12 g / 10 min. When the melt flow rate of the ethylene-vinyl acetate copolymer is in such a range, the base material layer can be formed without co-extrusion molding without processing defects.

  The base material layer may further contain other components as long as the effects of the present invention are not impaired. As the other components, for example, resin components other than the above-exemplified resins and / or other components similar to other components that can be included in the pressure-sensitive adhesive layer described in the section B can be used.

D. Protective layer The protective layer has a surface free energy satisfying the relationship of first resin component <second resin component ≦ protective layer. When the surface free energy of a protective layer satisfy | fills said relationship, the change of the adhesive force during adhesive sheet preservation | save can be suppressed. In the pressure-sensitive adhesive sheet being stored, as a protective layer for the pressure-sensitive adhesive layer, a separator that has been subjected to surface treatment and has reduced surface free energy is used. On the other hand, the protective layer of the present invention is excellent in the peelability of the protective layer, although the surface free energy is larger than that of a general separator.

The surface free energy of the protective layer only needs to satisfy the relationship of first resin component <second resin component ≦ protective layer, and can be set to any appropriate value. The surface free energy of the protective layer is preferably 32 mJ / m ^{2 to} 50 mJ / m ² , more preferably 32 mJ / m ^{2 to} 45 mJ / m ² . If the surface free energy of a protective layer is in said range, the change of the adhesive force during storage of an adhesive sheet can be suppressed.

The difference in surface free energy between the protective layer and the first resin component is preferably 0.1 mJ / m ^{2 to} 18 mJ / m ² , more preferably 0.1 mJ / m ^{2 to} 13 mJ / m ² . is there. If the difference between the surface free energy of the protective layer and the first resin component is within the above range, a change in adhesive force during storage of the adhesive sheet can be suppressed.

The difference in surface free energy between the protective layer and the second resin component is preferably 0 mJ / m ^{2 to} 13 mJ / m ² , more preferably 0 mJ / m ^{2 to} 10 mJ / m ² . If the difference in surface free energy between the protective layer and the second resin component is within the above range, a change in adhesive force during storage of the adhesive sheet can be suppressed.

  The protective layer is formed of any appropriate resin component. For example, polyethylene, ethylene-vinyl acetate copolymer, polyethylene terephthalate, polyethylene naphthalate, polyimide, ethylene-ethyl acrylate copolymer (EEA), ethylene-methacrylic acid copolymer (EMA), styrene-ethylene-butylene-styrene A block polymer (SEBS) etc. are mentioned. Polyethylene and polyethylene terephthalate are preferred because they are easily available and have excellent workability.

E. Surface layer capable of imparting heat resistance The pressure-sensitive adhesive sheet of the present invention may further include a surface layer capable of imparting heat resistance. The surface layer may be provided on the side of the base material layer opposite to the pressure-sensitive adhesive layer. By providing the surface layer, the base material layer and the pressure-sensitive adhesive layer can be protected from heat received during wafer processing. The surface layer preferably contains a polypropylene resin.

  The polypropylene resin is preferably obtained by polymerization using a metallocene catalyst. More specifically, for example, the polypropylene-based resin performs a polymerization step of polymerizing a monomer composition containing propylene using a metallocene catalyst, and after the polymerization step, a post-treatment step such as a catalyst residue removal step and a foreign matter removal step. Can be obtained. The polypropylene resin is obtained through such a process, for example, in a powder form, a pellet form, or the like. Examples of the metallocene catalyst include the metallocene catalysts exemplified above.

  The melting point of the polypropylene resin is preferably 110 ° C to 200 ° C, more preferably 120 ° C to 170 ° C, and further preferably 125 ° C to 160 ° C. If it is such a range, the adhesive sheet excellent in heat resistance can be obtained. Such an adhesive sheet is particularly useful when heated by contact. For example, when the pressure-sensitive adhesive sheet is used as a pressure-sensitive adhesive sheet for processing a semiconductor wafer, the surface of the pressure-sensitive adhesive sheet is hardly fused to the heating stage of the semiconductor manufacturing apparatus, and processing defects can be prevented. Furthermore, in addition to being excellent in heat resistance, the pressure-sensitive adhesive sheet of this embodiment is also excellent in flexibility. Thus, the adhesive sheet excellent in balance between heat resistance and flexibility is useful, for example, as an adhesive sheet for processing semiconductor wafers. More specifically, it is useful as an adhesive sheet for processing semiconductor wafers used in a production method (so-called 2-in-1 production method) in which the processes from the back grinding process to the completion of the dicing process are performed in-line. In such a manufacturing system, the pressure-sensitive adhesive sheet is continuously subjected to a back grinding process and a dicing process. If the pressure-sensitive adhesive sheet of the present invention is used as a pressure-sensitive adhesive sheet for semiconductor wafer processing in a 2-in-1 manufacturing method, when the dicing film (or dicing die attach film) is attached to the back surface of the semiconductor wafer with the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive sheet is heated by a heating table (for example, 100 ° C.), the adhesive sheet surface can be prevented from being fused to the heating table, and the semiconductor wafer can be prevented from being damaged due to the contact of the adhesive sheet.

  The said polypropylene resin may contain the structural unit derived from another monomer in the range which does not impair the effect of this invention. Examples of the other monomer include α-olefins such as ethylene, 1-pentene, 1-hexene, 1-octene, 1-decene, 4-methyl-1-pentene, and 3-methyl-1-pentene. When it contains the structural unit derived from another monomer, a block copolymer may be sufficient and a random copolymer may be sufficient.

  A commercially available product may be used as the polypropylene resin. Specific examples of commercially available polypropylene resins include trade names “WINTEC” and “WELNEX” series manufactured by Nippon Polypro Co., Ltd.

  The surface layer may further contain other components as long as the effects of the present invention are not impaired. As said other component, the component similar to the other component which can be contained in the adhesive layer demonstrated by the said B term can be used, for example.

F. Production method of pressure-sensitive adhesive sheet The pressure-sensitive adhesive sheet of the present invention can be produced by any appropriate method. For example, the pressure-sensitive adhesive sheet of the present invention is obtained by co-extrusion forming the pressure-sensitive adhesive layer and the base material layer forming material, and the pressure-sensitive adhesive layer of the laminate of the co-extruded pressure-sensitive adhesive layer forming material and the base material layer forming material. It is manufactured by bringing the forming material and the protective layer into contact with each other. By coextrusion molding, a pressure-sensitive adhesive sheet having good interlayer adhesion can be produced with a small number of steps and without using an organic solvent.

  In the co-extrusion molding, as the material for forming the pressure-sensitive adhesive layer and the base material layer, a material obtained by mixing the components of the respective layers by any appropriate method can be used.

  As a specific method of the co-extrusion molding, for example, among at least two extruders connected to a die, an adhesive layer forming material is supplied to one and a base material layer forming material is supplied to another. Then, after melting, extruding, and taking up by a touch roll forming method, a method of forming a laminate can be mentioned. It is preferable that the portion where the forming materials are joined at the time of extrusion is closer to the die outlet (die slip). This is because it is difficult for the formation materials to merge together in the die. Accordingly, a multi-manifold die is preferably used as the die. The screw type of the extruder used for melting each forming material may be uniaxial or biaxial. There may be three or more extruders. When there are three or more extruders, other layer forming materials can be supplied.

  The molding temperature in the coextrusion molding is preferably 160 ° C to 220 ° C, more preferably 170 ° C to 200 ° C. Within such a range, the molding stability is excellent.

  The protective layer can be formed by any appropriate method. For example, the method of forming a protective layer by extruding the material which forms a protective layer separately from a base material layer forming material and an adhesive layer forming material, etc. are mentioned. Moreover, the protective layer forming material may be coextruded and molded together with the base material layer forming material and the pressure sensitive adhesive layer forming material to produce a protective layer for the pressure sensitive adhesive sheet. A commercially available film may be used as the protective layer.

  The laminate of the co-extruded pressure-sensitive adhesive layer and the base material layer and the protective layer can be bonded together by bringing them into contact with each other by any appropriate method. Examples of the contact means include a touch roll.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples at all. Moreover, a part means a weight part.

[Example 1]
As a base material layer forming material, an ethylene-vinyl acetate copolymer (manufactured by Mitsui DuPont, trade name “Evaflex P-1007”; melting point 94 ° C., softening point 71 ° C.) was used.
As a surface layer forming material imparting heat resistance, a polypropylene resin polymerized by a metallocene catalyst (trade name “WINTEC: WSX02” manufactured by Nippon Polypro Co., Ltd.) was used.
As an adhesive layer forming material, an amorphous propylene- (1-butene) copolymer polymerized by a metallocene catalyst as the first resin component (manufactured by Sumitomo Chemical Co., Ltd., trade name “Tufselen H5002”: propylene-derived structural unit 90 mol% / 1-butene-derived structural unit 10 mol%, Mw = 230,000, Mw / Mn = 1.8) 60 parts, and a crystalline polypropylene resin polymerized by a metallocene catalyst as the second resin component (Nippon Polypro Co., Ltd., trade name “WINTEC: WFX4”, melting point 125 ° C., softening point 115 ° C., Mw = 363,000, Mw / Mn = 2.8) was used as a mixture with 40 parts.
Polyethylene (manufactured by Nippon Polyethylene Co., Ltd., trade name “NOVATEC LD: 440C”) was T-die melt extruded to prepare a protective layer having a thickness of 50 μm.
100 parts of the surface layer forming material, 100 parts of the base material layer forming material, and 100 parts of the pressure sensitive adhesive forming material were put into each extruder and co-extruded with a T die (extrusion temperature 180 ° C.). The adhesive layer and protective layer of the laminate of surface layer / base material layer / adhesive layer coextruded from the T-die are laminated, and the surface layer (thickness 30 μm) / base material layer (thickness 55 μm) / adhesive layer A pressure-sensitive adhesive sheet having a four-layer structure of (thickness 45 μm) / protective layer (thickness 50 μm) was obtained. The thickness of each layer was controlled by the shape of the T-die outlet.

[Example 2]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that an ethylene-vinyl acetate copolymer (manufactured by Mitsui DuPont, trade name “Evaflex P-1007”) was used as a material for forming the protective layer.

[Example 3]
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that polyethylene terephthalate (trade name “Tetron Film: G2” manufactured by Teijin Limited) was used as a material for forming the protective layer.

[Example 4]
Example 3 was used except that a crystalline polypropylene resin polymerized by a metallocene catalyst (trade name “WELNEX: RFG4VA”, polymerized by Nippon Polypro Co., Ltd.) was used as the second resin component of the pressure-sensitive adhesive layer forming material. Thus, an adhesive sheet was obtained.

(Comparative Example 1)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that a silicone-coated PET separator (manufactured by Mitsubishi Chemical Corporation, trade name “Diafoil”, thickness 38 μm) was used as the protective layer.

(Comparative Example 2)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that a PET separator coated with a long-chain alkyl release agent (Asioresin: RA-95H) was used as the protective layer.

(Comparative Example 3)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that a copolymer of 2-ethylhexyl acrylate / 2-hydroxyethyl acrylate (80/20) was used as a material for forming the protective layer.

(Comparative Example 4)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that polypropylene (manufactured by Nippon Polypropylene, trade name “WINTEC: WSX02”) was used as a material for forming the protective layer.

(Comparative Example 5)
Comparative Example 1 was used except that a crystalline polypropylene resin polymerized with a metallocene catalyst (trade name “WELNEX: RFG4VA”) polymerized with a metallocene catalyst was used as the second resin component of the pressure-sensitive adhesive layer forming material. Thus, an adhesive sheet was obtained.

[Evaluation]
The surface free energy of the material forming each layer used in Examples and Comparative Examples was measured by the following method. The results are shown in Table 1.
A test film was produced using the base material layer forming material, the first resin component, the second resin component, and the protective layer forming material. Water and methylene iodide are dropped onto each of the produced test films and the separators used in Comparative Examples 1 and 2, and the contact angle is measured using a contact angle meter (trade name: CA-X, manufactured by Kyowa Interface Science Co., Ltd.). It was measured. This measured value and the surface free energy value (known from the literature) of the contact angle measuring liquid are substituted into the following formula (1) derived from the Young formula and the extended Fowkes formula, and the two obtained formulas are simultaneous linear equations. And the surface free energy value was calculated. The surface free energy γ _S of a solid is the sum of γ _S ^d and γ _S ^v .
(1 + cos θ) γ _L = 2√ (γ _S ^d γ _L ^d ) + 2√ (γ _S ^v γ _L ^v ) (1)
Each symbol in the formula is as follows.
θ: contact angle γL: surface free energy γ _L ^{d of} contact angle measurement liquid: dispersion force component γ _L ^{v at} rL: polar force component γ _S ^{d at} rL: dispersion force component γ _S ^{v at} solid surface free energy Polar force component in surface free energy of water

Using the pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples, the amount of change in adhesive strength was evaluated as follows. The results are shown in Table 1.
The obtained pressure-sensitive adhesive sheet was affixed to a mirror surface (made of silicon) of a 4-inch semiconductor wafer, and a method according to JIS Z 0237 (2000) (bonding conditions: 2 kg roller 1 reciprocation, peeling speed: 300 mm / min, peeling) (Angle: 180 °). The initial adhesive strength was 0.125 N / 20 mm for all the adhesive sheets.
After another adhesive sheet was stored at 50 ° C. for 4 days, the adhesive strength of each adhesive sheet was measured in the same manner. The difference between the initial adhesive strength and the adhesive strength after storage for 4 days was calculated and used as the amount of change in adhesive strength. If the amount of change in adhesive force is less than 0.2 N / 20 mm, the change in adhesive force is small and the product is good.

  As is clear from the examples, according to the present invention, a pressure-sensitive adhesive sheet having a small amount of change in adhesive force even after storage of the pressure-sensitive adhesive sheet was obtained. Therefore, the pressure-sensitive adhesive sheet of the present invention can exhibit a desired pressure-sensitive adhesive strength even after storage. Moreover, the protective layer of the adhesive sheet preserve | saved for 4 days was able to peel easily.

  On the other hand, the adhesive sheets of Comparative Examples 1 to 5 in which the surface free energy was not in the order of first resin component <second resin component ≦ protective layer had a large amount of change in adhesive force.

  The pressure-sensitive adhesive sheet of the present invention can be suitably used, for example, for protecting a workpiece (semiconductor wafer or the like) when manufacturing a semiconductor device.

DESCRIPTION OF SYMBOLS 10 Adhesive layer 20 Base material layer 30 Protective layer 100 Adhesive sheet

Claims (7)

A pressure-sensitive adhesive sheet comprising a base material layer, a pressure-sensitive adhesive layer, and a protective layer in this order,
The pressure-sensitive adhesive layer contains a first resin component and a second resin component,
The pressure-sensitive adhesive sheet, wherein the surface free energy of the first resin component, the second resin component, and the protective layer satisfies a relationship of first resin component <second resin component ≦ protective layer. Surface free energy of the protective layer is ^{32mJ / m 2 ~50mJ / m 2} , the pressure-sensitive adhesive sheet according to claim 1. The first resin component and a second surface free energy of the resin component is ^{20mJ / m 2 ~40mJ / m 2} , the pressure-sensitive adhesive sheet according to claim 1 or 2. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein a difference between a surface free energy of the first resin component and a surface free energy of the protective layer is 0.1 mJ / m ^{2 to} 18 mJ / m ² .   The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer contains an amorphous resin as the first resin component and a crystalline resin as the second resin component.   The pressure-sensitive adhesive sheet according to claim 5, wherein the non-crystalline resin is a non-crystalline polypropylene resin, and the crystalline resin is a crystalline polypropylene resin.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, which is used for semiconductor processing.

Images