Adhesive sheet and method for manufacturing electronic component using the same

Abstract

To provide an adhesive sheet and a method for manufacturing an electronic component using the same, the adhesive sheet being capable of being easily peeled from an adherend even when, in an electronic component manufacturing process, it is applied to the adherend and subjected to a prolonged heating step at a relatively high temperature, then left to stand at room temperature, and subsequently reheated at a specific temperature.SOLUTION: An adhesive sheet has an adhesive layer formed from a crosslinked product of an adhesive composition containing (A) an acrylic resin having a specific mass-average molecular mass, (B) an acrylic resin having a specific mass-average molecular mass, (C) a crosslinking agent, and (D) thermally expandable microspheres having a specific expansion starting temperature, where component (B) is contained in an amount of 2-45 mass% relative to the total resin components. When the adhesive layer is applied to a stainless steel plate and subjected to a specific heating condition (a prolonged heating step at a relatively high temperature, followed by standing at room temperature, and then reheating at a specific temperature), the arithmetic mean height Sa of the surface of the adhesive layer attached to the stainless steel plate after peeling the adhesive sheet from the stainless steel plate is 11 μm or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer in which heat-expandable microspheres expand upon heating, thereby reducing the adhesive strength. [Background technology]

[0002] Conventionally, there have been known pressure-sensitive adhesive sheets that, after being attached to an adherend and having served their purpose and are no longer needed, can be easily peeled off from the adherend because the adhesive strength is reduced by heating due to the expansion of heat-expandable microspheres. Examples of such PSA sheets include those that can be easily peeled off when attached to an adherend, subjected to a heating step at a temperature lower than the expansion temperature of heat-expandable microspheres (for example, around 60°C), and then heated again at a temperature higher than the expansion temperature of heat-expandable microspheres (Patent Document 1, paragraph 0008). Another example of a pressure-sensitive adhesive sheet is one that can maintain sufficient adhesion to an adherend when the sheet is applied to the adherend and the adherend is heated at 50 to 90°C for a short period of time, and can then be easily peeled off from the adherend by heating to a temperature at which the heat-expandable microspheres expand without leaving any adhesive residue or other contamination on the adherend (Patent Document 2, paragraphs 0001, 0003, and 0019). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-059124 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-160765 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, such pressure-sensitive adhesive sheets have been used in the production of, for example, multilayer ceramic capacitors, multilayer varistors, and SAW filters. In these production processes, the pressure-sensitive adhesive sheet is first attached to an adherend and subjected to a long-term heating step at a temperature approximately 10°C lower than the expansion initiation temperature of the heat-expandable microspheres (e.g., heating at 80 to 140°C for 30 minutes to 1 hour). Hereinafter, the "long-term heating step at a temperature approximately 10°C lower than the expansion initiation temperature of the heat-expandable microspheres" will be referred to as the "long-term heating step at a higher temperature." Before the next processing step, the adherend with the pressure-sensitive adhesive sheet subjected to the long-term heating step at a higher temperature may be temporarily left in a room temperature environment (e.g., stored in a warehouse for several minutes to several days) or transported by truck or ship to a location where the next processing will be performed, resulting in a period of several minutes to several weeks in a room temperature environment. In this specification, room temperature refers to a temperature of 15 to 30°C. After such storage and transportation, the PSA sheet undergoes the next processing step, where it is heated at the expansion temperature of the heat-expandable microspheres (for example, a temperature about 20 to 40°C higher than the expansion initiation temperature of the heat-expandable microspheres) to peel and remove the unnecessary sheet from the adherend.

[0005] However, the PSA sheets described in Patent Documents 1 and 2, when attached to an adherend and then heated at a high temperature for a long period of time, and then left at room temperature for several minutes to several weeks, exhibit insufficient peelability from the adherend when heated again at the expansion temperature of the heat-expandable microspheres, making it difficult to easily peel the PSA sheet from the adherend. This is thought to be because the heat-expandable microspheres aggregate during the heating process at a high temperature for a long period of time, and the heat-expandable microspheres become fixed in this aggregated state within the PSA layer, resulting in increased cohesive strength, when left at room temperature for several minutes to several weeks after the heating process at a high temperature for a long period of time. [Means for solving the problem]

[0006] The present inventors have discovered that, by satisfying certain conditions, a pressure-sensitive adhesive sheet attached to an adherend can be easily peeled from the adherend without agglomeration when heated again at the expansion temperature of the heat-expandable microspheres, even after a prolonged heating step at a high temperature and subsequent lapse of several minutes to several weeks at room temperature, thereby developing the present invention. Specifically, the present invention provides the following heat-peelable pressure-sensitive adhesive sheet, and a laminate and method for producing an electronic component using the same.

[0007] The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer whose adhesive strength decreases due to the expansion of heat-expandable microspheres upon heating, and is characterized by satisfying the following three requirements. First, the pressure-sensitive adhesive layer is formed from a crosslinked product of a pressure-sensitive adhesive composition, and the pressure-sensitive adhesive composition has (A) a mass-average molecular weight of 1.0 × 10 5 ~1.0×10 6 (B) an acrylic resin having a mass average molecular weight of 1.0 × 10 3 ~1.0×10 4 (C) a crosslinking agent; and (D) heat-expandable microspheres having an expansion starting temperature of 90 to 150°C. Second, the (B) is contained in an amount of 2 to 45 mass % of the total resin components of the pressure-sensitive adhesive composition. Third, when the pressure-sensitive adhesive layer is bonded to a stainless steel plate (hereinafter sometimes referred to as a SUS plate) and the following conditions A, B, C, and D are applied in this order, the arithmetic mean height Sa of the pressure-sensitive adhesive layer surface on the side bonded to the stainless steel plate, as measured by ISO 25178, is 11 μm or more. Condition A: Heat for 1 hour at a temperature 10°C lower than the expansion starting temperature of (D) above. Condition B: Leave at 23°C for 30 minutes. Condition C: Heating for 10 minutes at a temperature 20 to 40° C. higher than the expansion starting temperature of (D). Condition D: The adhesive sheet was peeled off from the stainless steel plate.

[0008] In the pressure-sensitive adhesive sheet of the present invention, the (C) is preferably an epoxy-based crosslinking agent. More preferably, the epoxy equivalent of the epoxy-based crosslinking agent is 50 to 150 g / eq.

[0009] The pressure-sensitive adhesive sheet of the present invention may have the pressure-sensitive adhesive layer on a substrate. Furthermore, the pressure-sensitive adhesive sheet of the present invention may have the pressure-sensitive adhesive layer and release sheet in this order on a substrate.

[0010] The pressure-sensitive adhesive sheet of the present invention may comprise a first release sheet, the pressure-sensitive adhesive layer, and a second release sheet in this order. [Effects of the Invention]

[0011] The pressure-sensitive adhesive sheet of the present invention exhibits the advantage that even when the pressure-sensitive adhesive sheet is attached to an adherend and then subjected to a prolonged heating step at a high temperature and then left at room temperature for several minutes to several weeks, the unnecessary pressure-sensitive adhesive sheet can be easily peeled and removed from the adherend by reheating at the expansion temperature of the heat-expandable microspheres (for example, a temperature about 20 to 40°C higher than the expansion initiation temperature of the heat-expandable microspheres). DETAILED DESCRIPTION OF THE INVENTION

[0012] The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiments. Appropriate modifications and improvements to the following embodiments based on the common knowledge of a person skilled in the art are also within the scope of the present invention, provided they do not deviate from the spirit of the present invention. In this specification, the symbol "to" indicating a numerical range indicates a range that includes the numerical values ​​stated as the upper and lower limits. Furthermore, when a unit is stated only for the upper limit of a numerical range, this means that the lower limit is expressed in the same unit as the upper limit.

[0013] The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer in which the adhesive strength is reduced by the expansion of heat-expandable microspheres upon heating, and the pressure-sensitive adhesive layer is formed from a crosslinked pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition has (A) a mass-average molecular weight of 1.0 × 10 5 ~1.0×106 (B) an acrylic resin having a mass average molecular weight of 1.0 × 10 3 ~1.0×10 4 (B) is an acrylic resin having a crosslinking agent, (C) a crosslinking agent, and (D) heat-expandable microspheres having an expansion initiation temperature of 90 to 150°C, and (B) accounts for 2 to 45 mass% of the total resin components of the pressure-sensitive adhesive composition. Furthermore, the pressure-sensitive adhesive sheet of the present invention is prepared by laminating the pressure-sensitive adhesive layer to a stainless steel plate as an adherend, heating for 1 hour at a temperature 10°C lower than the expansion initiation temperature of (D) (condition A), allowing to stand for 30 minutes at 23°C (condition B), and then, after allowing to stand, heating for 10 minutes at a temperature 20 to 40°C higher than the expansion initiation temperature of (D) (condition C), and peeling the pressure-sensitive adhesive sheet from the stainless steel plate (condition D). When the pressure-sensitive adhesive layer surface on the side laminated to the stainless steel plate has an arithmetic mean height Sa according to ISO 25178 of 11 μm or more.

[0014] The pressure-sensitive adhesive sheet of the present invention comprises a pressure-sensitive adhesive composition as described above, a pressure-sensitive adhesive layer formed from a crosslinked product of the pressure-sensitive adhesive composition, and further comprises a pressure-sensitive adhesive layer having an arithmetic mean surface height Sa of 11 μm or more on the side bonded to the stainless steel plate when the pressure-sensitive adhesive sheet is subjected to the above conditions A, B, C, and D in this order. This pressure-sensitive adhesive sheet can be easily peeled and removed from the adherend when no longer needed by heating it again at the expansion temperature of the heat-expandable microspheres, even when the pressure-sensitive adhesive sheet is left at room temperature for several minutes to several weeks after being subjected to a prolonged heating process at a high temperature while attached to the adherend.

[0015] <Adhesive composition> The pressure-sensitive adhesive composition used in the present invention comprises (A) a polymer having a mass average molecular weight of 1.0×10 5 ~1.0×10 6 (B) an acrylic resin having a mass average molecular weight of 1.0 × 10 3 ~1.0×10 4 The essential components are (C) an acrylic resin, (D) a crosslinking agent, and (E) heat-expandable microspheres having an expansion starting temperature of 90 to 150° C. Each component will be described in detail below.

[0016] -(A)- The (A) used to form the pressure-sensitive adhesive composition is a copolymer having a mass average molecular weight of 1.0 × 10 5 ~1.0×10 6 The acrylic resin is not particularly limited as long as it has a functional group capable of reacting with (C) described below. By including (A), when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is prepared, crosslinking can be performed using (C), and the pressure-sensitive adhesive layer can form a coating film. By blending (B) described below in a predetermined content and adjusting the mass average molecular weight of (A) to 1.0 x 10 5 By making the mass average molecular weight equal to or greater than 1.0×10, when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is prepared, the sheet is attached to an adherend for use, and when it has completed its purpose and is no longer needed, it is possible to make it difficult for adhesive residue to remain on the adherend when it is peeled off and removed from the adherend. 6 By setting the thickness as below, it is possible to ensure sufficient tackiness of the adhesive body required when bonding the adhesive sheet to an adherend.

[0017] The acid value of (A) is preferably 1 mgKOH / g or more, more preferably 10 mgKOH / g or more, and even more preferably 30 mgKOH / g or more. By setting the acid value of (A) to 1 mgKOH / g or more, the crosslinking density can be increased when crosslinking is performed using (C) described below. Therefore, when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is produced, deterioration of the pressure-sensitive adhesive layer due to the expansion of (D) when heated at the expansion temperature of (D) described below is suppressed. Furthermore, when the pressure-sensitive adhesive sheet is subsequently peeled and removed from the adherend, the pressure-sensitive adhesive layer is less likely to leave adhesive residue on the adherend and releasability can be further improved. In this specification, the term "acid value" refers to the amount (mg) of potassium hydroxide required to neutralize the free fatty acids and resin acids contained in 1 g of a sample (pressure-sensitive adhesive composition). It is measured in accordance with JIS K0070 and can be calculated by the neutralization titration method using the following formula (1):

[0018] Acid value A = B×F×5.611 / S…(1)

[0019] [B: Amount (ml) of 0.1 mol / l potassium hydroxide ethanol solution used in the measurement, F: Factor of 0.1 mol / l potassium hydroxide ethanol solution, S: mass of sample (g), 5.611: formula weight of potassium hydroxide (56.11 x 1 / 10)

[0020] Furthermore, (A) is capable of reacting with (C), which will be described later. Such (A) includes copolymers of alkyl acrylate and / or alkyl methacrylate with a monomer having a functional group capable of reacting with (C). Hereinafter, "alkyl acrylate and / or alkyl methacrylate" will be referred to as "(a)," and "monomer having a functional group capable of reacting with (C)" will be referred to as "(b)." Examples of the "alkyl ester" constituting (a) include methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, isobutyl ester, s-butyl ester, t-butyl ester, pentyl ester, hexyl ester, heptyl ester, octyl ester, isooctyl ester, 2-ethylhexyl ester, isodecyl ester, dodecyl ester, tridecyl ester, pentadecyl ester, octadecyl ester, nonadecyl ester, eicosyl ester, etc. Among these, it is preferable to contain butyl ester and / or 2-ethylhexyl ester from the viewpoint of improving the initial adhesive strength when the pressure-sensitive adhesive sheet is attached to an adherend and / or the adhesive strength in a room temperature environment after a heating step at a high temperature for a long period of time, and it is preferable to contain methyl ester and / or ethyl ester from the viewpoint of improving the cohesive strength of the pressure-sensitive adhesive layer during a heating step at a high temperature for a long period of time. Examples of the functional group (b) include a carboxy group, a hydroxy group, a glycidyl group, an acrylamide group, etc., and from the viewpoint of heat resistance, a carboxy group is preferred.

[0021] Examples of monomers in which the functional group of (b) is a carboxy group include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc. Examples of monomers in which the functional group of (b) is a hydroxy group include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, hydroxyhexyl acrylate, hydroxyhexyl methacrylate, hydroxyoctyl acrylate, hydroxyoctyl methacrylate, hydroxydecyl acrylate, hydroxydecyl methacrylate, hydroxylauryl acrylate, hydroxylauryl methacrylate, etc.

[0022] (a) may be used alone or in combination of two or more. (b) may also be used alone or in combination of two or more. The ratio of (a) to (b) is preferably in the range of 79:21 to 98:2 by mass. If the blending ratio of (b) is lower than this range, when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is formed, upon heating at the expansion temperature of (D) described below and (D) expanding, the releasability from the adherend tends to be impaired. On the other hand, if the blending ratio of (b) is higher than this range, the adhesive strength to the adherend tends to be poor. From the viewpoint of improving the adhesiveness to the adherend and the releasability from the adherend, the ratio of (a) to (b) is more preferably 85:15 to 98:2 by mass, and even more preferably 88:12 to 97:3.

[0023] If desired, other monomers besides (a) and (b) can be used in combination, such as styrene, vinyl acetate, acrylonitrile, acrylamide, polyethylene glycol acrylate, polyethylene glycol methacrylate, N-vinylpyrrolidone, tetrafurfuryl acrylate, and tetrafurfuryl methacrylate.

[0024] (A) can be obtained by radical copolymerization of the above (a) and (b), and, if necessary, other monomer components other than (a) and (b). The copolymerization method can be a conventionally known polymerization method, such as emulsion polymerization, solution polymerization, bulk polymerization, suspension polymerization, and photopolymerization.

[0025] The glass transition temperature of (A) is preferably -70°C or higher and 20°C or lower, and more preferably -70°C or higher and 0°C or lower. By setting the glass transition temperature to -70°C or higher, when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is made, it is possible to make it less likely that adhesive residue will remain on the adherend when the pressure-sensitive adhesive sheet is attached to an adherend and used, and is then peeled off and removed from the adherend after having served its purpose and is no longer needed, and it is also possible to further improve releasability. Furthermore, by setting the glass transition temperature to 20°C or lower, it is possible to easily adjust the initial adhesive strength when the pressure-sensitive adhesive sheet is attached to an adherend, i.e., the adhesive strength to the adherend before heating, to a sufficient level.

[0026] The content of (A) is not particularly limited as long as it is adjusted so that the content of (B), which will be described later, falls within a predetermined range. However, from the viewpoints of improving the coating strength of the adhesive layer when made into an adhesive sheet having the adhesive layer, and suppressing tackiness of the adhesive sheet when it is attached to an adherend in use and then peeled off and removed from the adherend, the content of (A) is preferably 35 to 72 mass %, and more preferably 50 to 72 mass %, of the total resin components of the adhesive composition.

[0027] The above-mentioned (A) may be used alone or in combination of two or more kinds.

[0028] -(B)- The (B) used to form the pressure-sensitive adhesive composition is a copolymer having a mass average molecular weight of 1.0 × 10 3 ~1.0×10 4 The acrylic resin is not particularly limited as long as it has a functional group capable of reacting with (C) described below. (A) is blended so that the content of (B) is adjusted to a predetermined value, and the mass average molecular weight of (B) is adjusted to 1.0×10 3By doing so, when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is prepared, it is possible to make it difficult for adhesive residue to remain on the adherend when the sheet is attached to an adherend and, after serving its purpose and becoming unnecessary, is peeled off and removed from the adherend. Also, releasability can be improved.

[0029] In addition, the mass average molecular weight is 1.0 × 10 4 By satisfying the following conditions, when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is prepared, it is possible to prevent aggregation of (D), which will be described later, within the pressure-sensitive adhesive layer during a long-term heating step at a high temperature while the pressure-sensitive adhesive layer is adhered to an adherend. It is also possible to prevent (D) from being fixed in an aggregated state within the pressure-sensitive adhesive layer when the pressure-sensitive adhesive layer is left to stand in a room temperature environment after the heating step. This makes it possible to adjust the surface roughness of the pressure-sensitive adhesive layer surface, for example, the arithmetic mean height Sa according to ISO 25178, of the surface adhered to the adherend when the pressure-sensitive adhesive sheet is peeled off and removed after being left in a room temperature environment for several minutes to several weeks following the long-term heating step at a high temperature, and then heated again at the expansion temperature of (D). Thus, in the present invention, when the pressure-sensitive adhesive layer is laminated to a stainless steel plate and conditions A, B, C, and D are performed in this order, the arithmetic mean height Sa of the pressure-sensitive adhesive layer surface on the side laminated to the stainless steel plate is adjusted to 11 μm or more according to ISO 25178. By adjusting the arithmetic mean height Sa to 11 μm or more, the contact area between the pressure-sensitive adhesive sheet and the adherend after heating at the expansion temperature (D) can be reduced, allowing the pressure-sensitive adhesive sheet to be easily peeled from the adherend.

[0030] The acid value of (B) is preferably 1 mgKOH / g or more, more preferably 10 mgKOH / g or more, and even more preferably 30 mgKOH / g or more. By making the acid value of (B) 1 mgKOH / g or more, the crosslinking density can be increased when crosslinking is performed using (C) described below. Therefore, when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is produced, deterioration of the pressure-sensitive adhesive layer due to expansion of (D) when heated at the expansion temperature of (D) described below is suppressed. Furthermore, when the pressure-sensitive adhesive sheet is subsequently peeled and removed from the adherend, it is possible to make it less likely for adhesive residue of the pressure-sensitive adhesive layer to remain on the adherend and to further improve releasability.

[0031] Furthermore, (B) is capable of reacting with (C), which will be described later. Such (B) includes copolymers of (a) and (b). The "alkyl ester" constituting (a) can be the same component as described for (A). The functional group of (b) can be the same functional group as described for (A), and from the viewpoint of heat resistance, a carboxy group is preferable. The same component as described for (A) can be used for (b). (a) can be used alone or in combination of two or more types, and (b) can also be used alone or in combination of two or more types. The mass ratio of (a) to (b) is preferably within the same range as described for (A), and when it is within the same range, the same effects as described for (A) can be obtained. Furthermore, (B) can be used in combination with other monomers other than (a) and (b) if desired, and the other monomers can be the same components as those described above for (A).

[0032] (B) can be obtained by radical copolymerization of the above (a) and (b), and, if necessary, other monomer components other than (a) and (b). The copolymerization method can be a conventionally known polymerization method, for example, the same polymerization method as that for the above-mentioned (A).

[0033] The glass transition temperature of (B) is preferably -70°C or higher and 20°C or lower, and more preferably -60°C or higher and 0°C or lower. By setting the glass transition temperature to -70°C or higher, when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is made, it is less likely to leave adhesive residue on the adherend when the pressure-sensitive adhesive sheet is attached to an adherend and used, and is then peeled off and removed from the adherend after serving its purpose and becoming unnecessary, and releasability can be further improved by preventing deterioration due to a decrease in the elastic modulus of the pressure-sensitive adhesive layer. Furthermore, by setting the glass transition temperature to 20°C or lower, it is possible to easily adjust the initial adhesive strength when the pressure-sensitive adhesive sheet is attached to an adherend, i.e., the adhesive strength to the adherend before heating, to a sufficient level.

[0034] The content of (B) is determined taking into consideration the mass average molecular weight, glass transition temperature, number of functional groups, etc. of (A) and (B), but must be in the range of 2 to 45 mass% of the total resin components of the pressure-sensitive adhesive composition. By ensuring that the content of (B) is 2% by mass or more of the total resin components, when a PSA sheet having a PSA layer is produced, it is possible to prevent aggregation of (D), described below, within the PSA layer during a prolonged heating step at a high temperature while the PSA layer is adhered to an adherend. Furthermore, it is possible to prevent (D) from being fixed in an aggregated state within the PSA layer when the PSA layer is left to stand at room temperature after the heating step. This makes it possible to adjust the surface roughness of the PSA layer surface, for example, the arithmetic mean height Sa according to ISO 25178, of the surface adhered to the adherend when the PSA sheet is peeled off and removed after being left to stand at room temperature for several minutes to several weeks following the prolonged heating step at a high temperature. Thus, in the present invention, when the pressure-sensitive adhesive layer is laminated to a stainless steel plate and conditions A, B, C, and D are performed in this order, the arithmetic mean height Sa of the pressure-sensitive adhesive layer surface on the side laminated to the stainless steel plate is adjusted to 11 μm or more according to ISO 25178. By adjusting the arithmetic mean height Sa to 11 μm or more, the contact area between the pressure-sensitive adhesive sheet and the adherend after heating at the expansion temperature (D) can be reduced, allowing the pressure-sensitive adhesive sheet to be easily peeled from the adherend. While there are no particular limitations on the upper limit of the arithmetic mean height Sa, from the viewpoint of improving adhesion to the adherend and / or suppressing curling of the pressure-sensitive adhesive sheet after heating at the expansion temperature (D), it is preferably 50 μm or less, and more preferably 40 μm or less. Furthermore, by making the content of (B) 45 mass % or less of the total resin components, adhesive residue on the adherend is less likely to occur when the pressure-sensitive adhesive sheet is peeled from the adherend.

[0035] The above-mentioned (B) may be used alone or in combination of two or more kinds.

[0036] From the viewpoint of compatibility, it is preferable that the alkyl chains in the monomers constituting (A) and (B) are the same.

[0037] The ratio of (A) to (B) is preferably 98:2 to 50:50 by mass. By ensuring that the blending ratio of (B) is at least the lower limit of this range, (D) does not aggregate when heated at the expansion temperature of (D), ensuring heat-peelability. Furthermore, by ensuring that the blending ratio of (B) is at most the upper limit of this range, sufficient coating strength can be achieved for the production of the pressure-sensitive adhesive layer and the use process of the pressure-sensitive adhesive sheet. From the viewpoint of suppressing tackiness of the pressure-sensitive adhesive sheet when it is attached to an adherend and used as a pressure-sensitive adhesive sheet, and then peeled and removed from the adherend, the ratio of (A) to (B) is more preferably 98:2 to 70:30 by mass, and even more preferably 98:2 to 83:17.

[0038] -(C)- (C) acts as a component that crosslinks (A) and (B). The crosslinking reaction between (C) and (A) and (B) improves the cohesive strength of the pressure-sensitive adhesive layer, thereby ensuring sufficient initial adhesive strength when the pressure-sensitive adhesive sheet is attached to an adherend, i.e., adhesive strength to the adherend before heating.

[0039] The (C) used to form the pressure-sensitive adhesive composition is not particularly limited, and may be appropriately selected from those having functional groups capable of reacting with the above-mentioned (A) and (B). Specific examples of (C) include metal chelate crosslinking agents, epoxy-based crosslinking agents, etc. Among these, it is preferable to use an epoxy-based crosslinking agent. By using an epoxy-based crosslinking agent, when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is produced, the adhesive strength to the adherend can be maintained even during a long heating process at a high temperature. Furthermore, when the pressure-sensitive adhesive sheet is subsequently peeled off and removed from the adherend, it is possible to make it less likely that adhesive will remain on the adherend and to further improve releasability.

[0040] Examples of epoxy crosslinking agents include bisphenol epoxy resins (e.g., bisphenol A type, bisphenol F type, bisphenol AD ​​type), phenol novolac type epoxy resins, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diglycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane. The epoxy crosslinking agent preferably has an epoxy equivalent within the range of 50 to 150 g / eq. An epoxy equivalent within the range of 50 to 150 g / eq is preferred in that it allows for easy adjustment of the peel strength. Furthermore, it is even more preferred that the epoxy equivalent of the epoxy crosslinking agent is within the above range and that (A) and / or (B) have a carboxy group as the functional group of (b). By having a carboxy group, when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is prepared, it is possible to prevent adhesive residue from being left on the adherend when the pressure-sensitive adhesive sheet is peeled from the adherend after being attached to an adherend and no longer needed after having served its purpose, and also to improve the peel strength.

[0041] (C) may be used alone or in combination of two or more. The blending ratio of (C) may be appropriately adjusted taking into consideration the reaction ratio with the functional groups of (A) and (B) described above.

[0042] -(D)- The (D) used to form the pressure-sensitive adhesive composition is a microsphere having a structure in which a substance that gasifies upon heating is encapsulated inside an elastic outer shell, and which exhibits thermal expandability (the property of expanding as a whole upon heating). A suitable microsphere may be selected from those with an expansion initiation temperature of 90 to 150°C, taking into consideration the temperature of the process in which the pressure-sensitive adhesive sheet is used. Specifically, it is preferable to use a microsphere whose expansion initiation temperature is 25°C or more higher than the processing temperature of the cutting process, fragmentation process, etc. of the adherend to which the pressure-sensitive adhesive sheet is attached when the pressure-sensitive adhesive sheet is formed into a pressure-sensitive adhesive sheet. The expansion initiation temperature of (D) refers to the thermal expansion initiation temperature measured by TMA (thermomechanical analysis), and does not mean the temperature at which the volume of (D) expands to its maximum. Furthermore, in this specification, the expansion temperature of (D) generally refers to the temperature at which the volume of (D) expands to an extent that, when formed into a pressure-sensitive adhesive sheet, the pressure-sensitive adhesive sheet can be peeled from the adherend, and refers to a temperature approximately 20 to 40°C higher than the expansion initiation temperature of (D). Suitable examples of the elastic shell include those formed from a heat-fusible substance or a substance that breaks down due to thermal expansion, such as vinylidene chloride-acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, polysulfone, etc. The interior of the elastic shell can be made from a substance that easily gasifies and expands when heated, such as hydrocarbons such as isobutane, propane, and pentane. Commercially available products include, for example, the "Matsumoto Microsphere" series (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.), the "Advancell EM" series (manufactured by Sekisui Chemical Co., Ltd.), and "Expancel" (manufactured by Nippon Phillite Co., Ltd.).

[0043] The size of (D) may be appropriately selected depending on the application of the pressure-sensitive adhesive sheet, and specifically, the volume average particle size before heating is preferably 5 to 50 μm. By using (D) within this size range, it becomes easier to adjust the initial adhesive strength when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is formed, and it also becomes easier to control the surface shape of the pressure-sensitive adhesive layer after heat peeling. In the present invention, the volume average particle size was measured using a laser diffraction / scattering particle size distribution analyzer.

[0044] The expansion ratio of (D) is preferably 5 times or more, and more preferably 7 times or more. On the other hand, it is preferably 15 times or less, and more preferably 12 times or less. If it is in the range of 5 times or more and 15 times or less, when a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is formed, the adhesive strength of the pressure-sensitive adhesive layer can be efficiently reduced by heat treatment at the temperature at which (D) expands. It is preferable that the outer shell of (D) has an appropriate strength so that it will not rupture even when (D) expands to the predetermined expansion ratio.

[0045] (D) may be used alone or in combination of two or more. The blending ratio of (D) may be appropriately selected so that sufficient unevenness can be formed on the surface of the pressure-sensitive adhesive layer when the pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer is heated at the expansion temperature of (D). It is typically in the range of 3 to 30 parts by mass relative to the total resin components of the pressure-sensitive adhesive composition. If the blending ratio of (D) is less than 3 parts by mass, the number of convex portions on the surface of the pressure-sensitive adhesive layer after heat treatment tends to be reduced, making peeling difficult. Furthermore, if the blending ratio exceeds 30 parts by mass, more unevenness than necessary may be formed on the surface of the pressure-sensitive adhesive layer before heat treatment. In such cases, the adhesion between the pressure-sensitive adhesive layer and the adherend before heat treatment tends to decrease, which is undesirable. From the viewpoints of adhesion to the adherend before heat treatment and peelability from the adherend after heat treatment, the blending ratio is preferably 5 to 25 parts by mass, more preferably 8 to 20 parts by mass.

[0046] The pressure-sensitive adhesive composition of the pressure-sensitive adhesive sheet of the present invention may contain optional components other than the above (A), (B), (C), and (D), as long as the effects of the present invention are not impaired. Examples of optional components include thermoplastic resins or thermosetting resins other than (A) and (B), and components known as additives for pressure-sensitive adhesive layers. Examples of additives include polymerization inhibitors, crosslinking accelerators, antioxidants, stabilizers, viscosity modifiers, tackifying resins, and organic or inorganic fillers. In particular, the addition of a tackifier resin further enhances the cohesive strength of the adhesive, thereby improving the initial adhesive strength to the adherend before heating when the PSA sheet is attached to the adherend. Examples of tackifier resins include terpene-based resins, xylene-based resins, and phenol-based resins.

[0047] The blending amount of the tackifier resin is preferably 5 to 50 parts by mass per 100 parts by mass of the combined blending amount of (A) and (B), and from the viewpoint of lamination of the pressure-sensitive adhesive sheet to the adherend and adhesion to the substrate, the blending amount is more preferably 10 to 40 parts by mass.

[0048] <Adhesive layer> The pressure-sensitive adhesive layer in the present invention is formed from a crosslinked pressure-sensitive adhesive composition obtained by mixing the essential components ((A), (B), (C), and (D)) of the pressure-sensitive adhesive composition described above, and optional components as needed. The order in which the components are mixed is not particularly limited, as long as these components are mixed evenly.

[0049] The pressure-sensitive adhesive composition may contain a solvent. In this case, the solvent is used to improve the coatability of the pressure-sensitive adhesive composition. Examples of the solvent include hydrocarbons such as toluene, halogenated hydrocarbons, alcohols, ethers, ketones such as methyl isobutyl ketone, esters, polyols such as ethylene glycol monomethyl ether, and derivatives thereof. When the pressure-sensitive adhesive composition contains a solvent, the solvent is removed by heating the pressure-sensitive adhesive composition.

[0050] <Adhesive sheet> Next, the pressure-sensitive adhesive sheet of the present invention will be described. The pressure-sensitive adhesive sheet according to one embodiment of the present invention has a pressure-sensitive adhesive layer on a substrate.

[0051] The constituent material of the substrate is not particularly limited and can be appropriately selected from materials conventionally used as substrates for pressure-sensitive adhesive sheets depending on the intended use of the pressure-sensitive adhesive sheet. Specifically, the material can be selected from synthetic resins such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyethylene, polypropylene, polycarbonate, triacetyl cellulose, cellophane, polyimide, polyamide, polyphenylene sulfide, polyetherimide, polyethersulfone, aromatic polyamide, or polysulfone, glass, metal, or ceramic. The substrate may be transparent or colored. Coloring can be achieved by blending various pigments or dyes into the constituent materials of the substrate. The surface of the substrate is not limited to being smooth, and may be matte.

[0052] The substrate may contain conventionally known additives, specifically heat stabilizers, oxidation stabilizers, weather stabilizers, UV absorbers, antistatic agents, etc., among its constituent materials. Furthermore, it is preferable to use a substrate that has been subjected to a surface treatment in order to improve adhesion to the pressure-sensitive adhesive layer. Examples of surface treatments include discharge treatments such as corona discharge treatment and glow discharge treatment, plasma treatment, flame treatment, ozone treatment, ionizing ray treatments such as UV treatment, electron beam treatment, and radiation treatment, surface roughening treatments such as sand matte treatment, anchor treatment, hairline treatment, and embossing, chemical treatment, and coating of an easy-adhesion layer.

[0053] From the viewpoint of ease of handling, the pressure-sensitive adhesive sheet may have a pressure-sensitive adhesive layer on a substrate, and may further have a release sheet on the pressure-sensitive adhesive layer. The constituent material of the release sheet is not particularly limited, and can be appropriately selected from materials that have conventionally been used as release sheets for pressure-sensitive adhesive sheets. Specifically, polyethylene-laminated paper, plastic films such as polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, triacetyl cellulose, polyvinyl chloride, acrylic, polystyrene, polyamide, polyimide, vinylidene chloride-vinyl chloride copolymer, and the like, and plastic films with one side subjected to a release treatment can be used.

[0054] The method for producing a pressure-sensitive adhesive sheet is as follows: First, a pressure-sensitive adhesive composition is applied to one surface of a substrate or a release sheet to form a pressure-sensitive adhesive layer from the pressure-sensitive adhesive composition. A known method can be used for the application, such as a roll coater method, a comma coater method, a die coater method, a reverse coater method, a silk screen method, or a gravure coater method. Next, the pressure-sensitive adhesive is heated and dried, laminated with a release sheet or substrate, and crosslinked at room temperature or by heating to form a pressure-sensitive adhesive layer formed from the crosslinked pressure-sensitive adhesive composition. Heat-drying conditions may be adjusted appropriately depending on the thickness of the pressure-sensitive adhesive layer and the heat resistance of the substrate (substrate or release sheet). An example of drying conditions is 100°C to 200°C for 0.5 to 10 minutes, preferably 120°C to 180°C for 1 to 5 minutes. In one embodiment, the crosslinked product of the pressure-sensitive adhesive composition obtained after heat drying and crosslinking may be stored (left to stand) for a predetermined period of time. That is, the production of the pressure-sensitive adhesive layer may include a curing step in addition to the heating step. By performing curing after heat drying, the crosslinking reaction can be completed even if uncrosslinked portions of (A), (B), and (C) remain, which can contribute to stabilizing the performance of the pressure-sensitive adhesive layer. The curing conditions are, for example, 20°C to 60°C for 3 days to 2 weeks.

[0055] Another embodiment of the pressure-sensitive adhesive sheet of the present invention comprises a first release sheet, a pressure-sensitive adhesive layer, and a second release sheet, in that order. For example, a method for producing such a pressure-sensitive adhesive sheet involves applying a pressure-sensitive adhesive composition to one surface of the first or second release sheet using a method similar to the known coating method described above to form a pressure-sensitive adhesive layer from the pressure-sensitive adhesive composition. The pressure-sensitive adhesive layer is then dried by heating, laminated with the second or first release sheet, and crosslinked at room temperature or by heating to form a pressure-sensitive adhesive layer formed from the crosslinked product of the pressure-sensitive adhesive composition. Heat-drying conditions can be adjusted as appropriate depending on the thickness of the pressure-sensitive adhesive layer and the heat resistance of the substrate (the first or second release sheet).

[0056] The adhesive sheet can be used by first peeling off the first release sheet and attaching the exposed first adhesive layer surface to a first adherend, and then peeling off the second release sheet and attaching the exposed second adhesive layer surface to a second adherend.

[0057] The first and second release sheets can be the same as the release sheets described above. However, it is preferable that the first release sheet has a lighter peel force when peeled from the pressure-sensitive adhesive layer than the second release sheet. From the viewpoint of making the release force of the first release sheet lighter than that of the second release sheet, it is preferable that the thickness of the first release sheet is thinner than that of the second release sheet. It is also preferable that the surface of the first release sheet onto which the pressure-sensitive adhesive composition is applied is subjected to a release treatment. Examples of release treatments include silicone treatment and application of a release agent such as a long-chain alkyl resin or a fluorine-based resin.

[0058] The thickness of the pressure-sensitive adhesive layer before heating can be adjusted depending on the selected size of (D). For example, when (D) having a volume average particle size of 20 μm to 30 μm is used, the thickness of the pressure-sensitive adhesive layer is preferably set to a lower limit of 30 μm or more, more preferably 35 μm or more, and to an upper limit of 65 μm or less, even more preferably 55 μm or less, and even more preferably 50 μm or less. By setting the thickness of the pressure-sensitive adhesive layer to 65 μm or less, cohesive failure is less likely to occur when the pressure-sensitive adhesive layer is attached to an adherend after use, heat-treated, and peeled from the adherend, making it easier to achieve better releasability. Furthermore, the energy required to sufficiently expand (D) during heat-treatment is more easily distributed throughout the pressure-sensitive adhesive layer, making it easier to peel the pressure-sensitive adhesive layer from the adherend after heat-treatment without leaving any adhesive residue.

[0059] <Electronic component manufacturing method> Next, a method for manufacturing an electronic component will be described in detail. One method for manufacturing electronic components includes a step of temporarily fixing a workpiece, which is a precursor of the electronic component, to an adhesive sheet, and then subjecting the workpiece in the temporarily fixed state to processing including a heating step at a high temperature for a long period of time, and then peeling off the adhesive sheet to obtain the processed body.The adhesive sheet used in this step can be the adhesive sheet of the present invention.

[0060] The method for manufacturing electronic components of the present invention is characterized in that the adhesive sheet of the present invention is used as the adhesive sheet.The adhesive sheet of the present invention is attached to a workpiece, which is a precursor of the electronic component, and after a long heating process at a high temperature, it is left in a room temperature environment and then heated again, whereby it can be easily peeled off from the workpiece without leaving any adhesive residue, thereby making it possible to easily obtain electronic components without performing complicated manufacturing processes. For example, when manufacturing a multilayer ceramic capacitor, the process is usually carried out in the following steps: (1) forming a green sheet, (2) forming conductor layers for internal electrodes, (3) laminating, (4) pressing, (5) cutting, (6) firing, and (7) forming conductor layers for external electrodes.

[0061] (1) In the green sheet forming process, a slurry containing ceramic powder, a dispersion medium, a binder, etc. is thinned using a doctor blade method, a calendar method, etc. to obtain a green sheet.

[0062] (2) In the step of forming the conductor layer for the internal electrode, a metal electrode (internal electrode) is printed on the surface of the green sheet obtained in the step (1) using a conductive paste or the like.

[0063] (3) In the lamination process, the green sheets on which the internal electrodes are printed are stacked without misalignment.

[0064] (4) In the pressing step, the stacked green sheets are pressed together under a pressure of preferably 5 to 200 MPa to form an integrated body. Pressures below 5 MPa are undesirable because delamination may occur, while pressures above 200 MPa are undesirable because the green sheets may crack during stacking. From the viewpoint of preventing delamination and cracking, a pressure range of 20 to 100 MPa is more preferable. This results in a green sheet laminate (hereinafter simply referred to as "laminate"), which is the precursor of a multilayer ceramic capacitor and has metal electrodes (internal electrodes) arranged between the layers.

[0065] In the (5) cutting step, the laminate obtained in the (4) step is bonded to and fixed on the pressure-sensitive adhesive sheet of the present invention, and a dicing step is carried out in which the temporarily fixed laminate is cut into small pieces into a dice pattern using a cutting device such as a guillotine blade at a temperature (e.g., 80 to 140°C) about 10°C lower than the expansion onset temperature of the above-mentioned (D) contained in the pressure-sensitive adhesive sheet. Thereafter, the laminate is left in a room temperature environment, and then heated again at a temperature (e.g., 110 to 190°C) about 20 to 40°C higher than the expansion onset temperature of the above-mentioned (D) contained in the pressure-sensitive adhesive sheet, thereby peeling and removing the pressure-sensitive adhesive sheet to obtain chip-like electronic components.

[0066] In the firing step (6), the cut pieces obtained in the step (5) are fired in an atmosphere at 1000 to 1300° C. to obtain sintered chip-type electronic components.

[0067] (7) In the step of forming conductor layers for external electrodes, the sintered chip electronic component obtained in step (6) is bonded to and fixed on the pressure-sensitive adhesive sheet of the present invention, external electrodes are applied to both end faces of the sintered chip electronic component, and a drying step is performed at a temperature about 10°C lower than the expansion start temperature of the above-mentioned (D) contained in the pressure-sensitive adhesive sheet (e.g., 80 to 140°C). Thereafter, the resultant product is left in a room temperature environment, and is heated again at a temperature about 20 to 40°C higher than the expansion start temperature of the above-mentioned (D) contained in the pressure-sensitive adhesive sheet (e.g., 110 to 190°C) to peel and remove the pressure-sensitive adhesive sheet, followed by baking at a temperature of 750°C to 850°C (around 800°C) to obtain a chip electronic component with external electrodes.

[0068] As described above, the electronic component manufacturing method of the present invention can be suitably used, first, when the workpiece is a green sheet laminate and the processing is a dicing process in which the workpiece is cut into small pieces into a dice pattern. Second, the electronic component manufacturing method of the present invention can be suitably used when the workpiece is a diced semiconductor chip and the processing is a process of forming external electrode conductor layers by applying external electrodes to the workpiece and drying them. However, the electronic component manufacturing method of the present invention can be applied not only to the manufacture of multilayer ceramic capacitors but also to the manufacture of general electronic components in which processing is performed while the workpiece is temporarily fixed. Specifically, in addition to multilayer ceramic capacitors, the electronic component manufacturing method can be suitably used to manufacture various electronic components such as multilayer ceramic inductors, resistors, ferrites, sensor elements, thermistors, varistors, piezoelectric ceramics, and silicon wafers. [Example]

[0069] The present invention will be specifically described below based on experimental examples (including examples and comparative examples), but the present invention is not limited to these experimental examples. In the following description, "parts" means "parts by mass" and "%" means "% by mass".

[0070] The components in Tables 1 and 2 are as follows: (A) Mass average molecular weight is 1.0 × 10 5 ~1.0×10 6 Acrylic resin A1 ((a) alkyl ester: butyl ester, (b) acrylic acid, (a) to (b) ratio: 94:6, mass average molecular weight: 5.1 × 10 5 , glass transition temperature: -31℃, acid value: 46mgKOH / g) A2 ((a) alkyl ester: butyl ester, (b) acrylic acid, (a) to (b) ratio: 92:8, mass average molecular weight: 4.5 × 10 5 , glass transition temperature: -24℃, acid value: 60mgKOH / g) A3 ((a) alkyl ester: butyl ester, (b) acrylic acid, (a) to (b) ratio: 96:4, mass average molecular weight: 5.0 × 10 5, glass transition temperature: -38℃, acid value: 30mgKOH / g) A4 ((a) alkyl esters: butyl ester, 2-ethylhexyl ester, methyl ester; (b) acrylic acid; (a) to (b) ratio: 98:2; mass average molecular weight: 5.3 × 10 5 , glass transition temperature: -27℃, acid value: 14.5mgKOH / g) A5 ((a) alkyl esters: butyl ester, 2-ethylhexyl ester, ethyl ester; (b) acrylic acid; (a) to (b) ratio: 79.5:20.5; mass average molecular weight: 1.0 × 10 6 , glass transition temperature: -49℃, acid value: 88mgKOH / g) (A') Mass average molecular weight is 1.0 × 10 5 ~1.0×10 6 Not acrylic resin A'6 ((a) alkyl esters: butyl ester, 2-ethylhexyl ester; (b) acrylic acid; (a) to (b) ratio: 79.5:20.5; mass average molecular weight: 1.2 × 10 6 , glass transition temperature: -49℃, acid value: 88mgKOH / g)

[0071] (B) Mass average molecular weight is 1.0 × 10 3 ~1.0×10 4 Acrylic resin B1 ((a) alkyl ester: butyl ester, (b) acrylic acid, (a) to (b) ratio: 95:5, mass average molecular weight: 2.0 × 10 3 , glass transition temperature: -50℃, acid value: 70mgKOH / g) B2 ((a) alkyl ester: butyl ester, (b) acrylic acid, (a) to (b) ratio: 93.5:6.5, mass average molecular weight: 2.0 × 10 3 , glass transition temperature: -49℃, acid value: 90mgKOH / g) (B') Mass average molecular weight is 1.0 × 10 3 ~1.0×10 4 Not acrylic resin B'3 ((a) alkyl ester: butyl ester, (b) acrylic acid, mass average molecular weight: 8.0 × 10 2 , (a) to (b) ratio: 96:4, glass transition temperature: -51°C, acid value: 31 mg KOH / g)

[0072] (C) The following crosslinking agents were prepared: C1 (epoxy crosslinker (N,N,N',N'-tetraglycidyl-m-xylylenediamine), epoxy equivalent: 103g / eq)

[0073] (D) The following heat-expandable microspheres with an expansion starting temperature of 90 to 150°C were prepared. D1 (Expansion start temperature: 130-140°C, volume average particle size: 22-28 μm, product name: Advancell EHM-301, manufactured by Sekisui Chemical Co., Ltd.)

[0074] The following optional ingredients were prepared: Tackifying resin (product name: YS Polyster G150, manufactured by Yasuhara Chemical Co., Ltd.) Toluene (product name: Toluol (toluene), manufactured by Maruzen Petrochemical Co., Ltd.)

[0075] <Adhesive sheet> (Experimental Examples 1-18) The above components were uniformly mixed and dissolved at the solid content ratios (by mass) shown in Tables 1 and 2 to prepare a pressure-sensitive adhesive composition (coating liquid) with a solid content concentration of 40%. Next, this coating liquid was applied to one side of a 100 μm-thick transparent PET film using a Baker-type applicator. The thickness of the pressure-sensitive adhesive layer after drying was adjusted to the thickness shown in Tables 1 and 2. After drying at 120°C for 3 minutes to form a pressure-sensitive adhesive layer, a 38 μm-thick PET film (release sheet) with one surface treated with silicone release was placed on the surface of this pressure-sensitive adhesive layer, thereby preparing the pressure-sensitive adhesive sheet of each example.

[0076] (Experimental Example 19) A pressure-sensitive adhesive composition (coating liquid) was prepared in the same manner as in Experimental Example 6 using the same components as in Experimental Example 6 so that the solids concentration was 40%. Next, this coating liquid was applied using a Baker-type applicator to one side of a 38 μm-thick PET film (first release sheet) one surface of which had been treated with a silicone release agent. The thickness of the pressure-sensitive adhesive layer after drying was adjusted to 47 μm. A pressure-sensitive adhesive layer was formed by drying at 120°C for 3 minutes, and then a 50 μm-thick PET film (second release sheet) one surface of which had been treated with a silicone release agent was placed on the surface of this pressure-sensitive adhesive layer to prepare the pressure-sensitive adhesive sheet of Experimental Example 19.

[0077] The produced pressure-sensitive adhesive sheets were evaluated as follows. The evaluation results obtained for Experimental Examples 1 to 18 are shown in Tables 1 and 2. The evaluation items were evaluated by the following methods.

[0078] (1) Initial adhesive strength (JIS Z0237:2022) The pressure-sensitive adhesive sheets obtained in Experimental Examples 1 to 19 were cut to a size of (25 mm wide x 100 mm long). The release sheet was peeled off from the resulting sheet piece in Experimental Examples 1 to 18, and the first release sheet was peeled off in Experimental Example 19 to obtain test specimens (substrate or second release sheet / adhesive layer). A stainless steel plate (SUS plate) was attached to the entire surface of the adhesive layer of the test specimen (temperature 23°C, humidity 65%, 1 round trip with a 2 kg roller). The evaluation samples obtained in this manner were subjected to a tensile test. The evaluation samples were placed in a tensile tester and left for 20 minutes in an environment of 23°C and 65% humidity before the tensile test began. The tensile test conditions were a peel angle of 180° and a peel speed (pulling rate): 300 mm / min. The load when peeling the stainless steel plate (SUS plate) from the pressure-sensitive adhesive sheet was measured, and the maximum load at this time was recorded as the initial adhesive strength of the pressure-sensitive adhesive sheet.

[0079] (2) Peelability The evaluation sample obtained using the same process as in the initial adhesive strength evaluation was heated in an oven at 120°C for 1 hour, and then left to stand for 30 minutes in an environment at 23°C and 65% humidity. The evaluation sample was then heated again, and once the temperature reached 150°C, it was heated for 10 minutes. After cooling, the adhesive layer of the adhesive sheet was visually evaluated at room temperature (23°C) to determine whether it had peeled from the stainless steel plate (SUS plate). The evaluation was given as "○" if peeling had occurred, and "×" if no peeling had occurred.

[0080] (3) Arithmetic mean height For the pressure-sensitive adhesive sheets obtained by the same process as in the peelability evaluation above, the arithmetic mean height Sa of the pressure-sensitive adhesive layer surface on the side that was attached to the stainless steel plate was measured in accordance with ISO 25178.

[0081] [Table 1]

[0082] [Table 2]

[0083] As shown in Tables 1 and 2, in Experimental Examples 3 to 9, 12 to 15, and 17, the mass average molecular weight of (A) in the liquid formulation was 1.0 × 10 5 ~1.0×10 6 (B) an acrylic resin having a mass average molecular weight of 1.0 × 10 3 ~1.0×10 4 (B) a crosslinking agent; and (D) heat-expandable microspheres having an expansion starting temperature of 90 to 150°C, wherein (B) accounts for 2 to 45 mass% of the total resin components. The pressure-sensitive adhesive sheets have a pressure-sensitive adhesive layer formed on a substrate. The pressure-sensitive adhesive sheets also had an arithmetic mean height Sa of 11 μm or greater. All pressure-sensitive adhesive sheets were heated at 120°C for 1 hour, allowed to stand at room temperature for 30 minutes, and then heated again at 150°C for 10 minutes. When the pressure-sensitive adhesive sheets were peeled from the adherends, they were easily peeled without leaving any adhesive residue on the adherends.

[0084] Next, the pressure-sensitive adhesive sheet of Experimental Example 1 contained (A), (C), and (D) in the liquid formulation but did not contain (B), and had an arithmetic mean height Sa of 10.5 μm, which was lower than the lower limit. As a result, when the pressure-sensitive adhesive sheet was peeled from the adherend, adhesive residue remained on the adherend, and the peelability was not satisfactory. The pressure-sensitive adhesive sheet of Experimental Example 2 contained (A), (B), (C), and (D) in the liquid formulation, but the content of (B) in the total resin components was 0.7 mass%, which was lower than the lower limit, and the arithmetic mean height Sa was 10.0 μm, which was also lower than the lower limit. As a result, the pressure-sensitive adhesive sheet could not be easily peeled from the adherend. Next, the adhesive sheet of Experimental Example 10 had a content of (B) in the total resin components of 49.3 mass%, which was higher than the upper limit, and when the adhesive sheet was peeled from the adherend, adhesive residue remained on the adherend, making it impossible to achieve satisfactory peelability. Furthermore, the adhesive sheet of Experimental Example 11 contains (B), (C), and (D) in the liquid formulation, but does not contain (A), so the adhesive layer of the adhesive sheet does not become a coating film, and the adhesive sheet of the present invention was not produced. On the other hand, the PSA sheets of Experimental Examples 3 to 9 contained (A), (B), (C), and (D) in a liquid formulation, with the content of (B) adjusted to within the range of 2 to 45 mass% of the total resin components, and had an arithmetic mean height Sa of 11 μm or more. As a result, all of the PSA sheets were heated at 120°C for 1 hour, left to stand at room temperature for 30 minutes, and then heated again at 150°C for 10 minutes to peel the PSA sheet from the adherend, and were easily peeled without leaving any adhesive residue on the adherend. The results of Experimental Examples 1 to 11 demonstrate that the effects of the present invention can be achieved by incorporating 2 to 45 mass% of (B) in the total resin components of the PSA composition as one of the characteristics.

[0085] Next, the PSA sheet of Experimental Example 16 contains (B), (C), and (D) in a liquid formulation, the content of (B) being within the range of 2 to 45 mass% of the total resin components, but does not contain (A), and (A') has a mass average molecular weight of 1.0 × 10 5 ~1.0×10 6The adhesive layer contained more than 100g of acrylic resin, and the adhesive layer lacked tack, making it impossible to bond the adhesive layer to a stainless steel plate. On the other hand, the pressure-sensitive adhesive sheets of Experimental Examples 6 and 12 to 15 contained (A), (B), (C), and (D) in the liquid formulation, with the content of (B) being within the range of 2 to 45 mass% of the total resin components, and had an arithmetic mean height Sa of 11 μm or more. As a result, all of the pressure-sensitive adhesive sheets were heated at 120°C for 1 hour, then left to stand at room temperature for 30 minutes, and then heated again at 150°C for 10 minutes, and when peeled from the adherend, they could be easily peeled without leaving any adhesive residue on the adherend. From the results of Experimental Examples 6 and 12 to 16, it was found that (A) had a mass-average molecular weight of 1.0 × 10 5 ~1.0×10 6 It can be seen that the effects of the present invention can be obtained by incorporating an acrylic resin having the above formula (I) as one of the features.

[0086] Next, the pressure-sensitive adhesive sheet of Experimental Example 18 contains (A), (C), and (D) in the liquid formulation, but does not contain (B), and (B') has a mass average molecular weight of 1.0 × 10 3 ~1.0×10 4 When the pressure-sensitive adhesive sheet was peeled from the adherend, adhesive residue was left on the adherend, and the peelability was not satisfactory. On the other hand, the pressure-sensitive adhesive sheets of Experimental Examples 6 and 17 contained (A), (B), (C), and (D) in the liquid formulation, the content of (B) was within the range of 2 to 45 mass% of the total resin components, and the arithmetic mean height Sa was 11 μm or more. In addition, the mass average molecular weight of (B) was 1.0 × 10 3 ~1.0×10 4 The acid value was adjusted within the range of 1.0 × 10. As a result, all of the pressure-sensitive adhesive sheets were heated at 120°C for 1 hour, left to stand at room temperature for 30 minutes, and then heated again at 150°C for 10 minutes to peel the pressure-sensitive adhesive sheet from the adherend, and the sheet could be easily peeled off without leaving any adhesive residue on the adherend. From the results of Experimental Examples 6, 17, and 18, it was found that (B) the mass-average molecular weight was 1.0 × 10 3 ~1.0×10 4It can be seen that the effects of the present invention can be obtained by incorporating an acrylic resin having the above formula (I) as one of the features.

[0087] Although the PSA sheet of Experimental Example 19 is not specified in Tables 1 and 2, as described above, it was prepared by preparing a PSA composition (coating liquid) in the same manner as Experimental Example 6 using the same components as in Experimental Example 6. Therefore, the PSA sheet contained (A), (B), (C), and (D), with a PSA layer made of a PSA composition containing 2 to 45 mass% of (B) based on the total resin components, and had a first release sheet, a PSA layer, and a second release sheet, in that order. The PSA sheet also had an arithmetic mean height Sa of 11 μm or greater. As a result, the PSA sheet could be easily peeled from the adherend without leaving any adhesive residue on the adherend.

[0088] <Electronic component manufacturing> A multilayer ceramic capacitor was manufactured as an electronic component using the adhesive sheet obtained in Experimental Example 6. A multilayer ceramic capacitor is manufactured through the following steps: (1) green sheet formation, (2) internal electrode conductor layer formation, (3) lamination, (4) pressing, (5) cutting, (6) firing, and (7) external electrode conductor layer formation. The adhesive sheet of Experimental Example 6 was used in the (5) cutting and (7) external electrode conductor layer formation steps.

[0089] (5) Regarding the cutting process, green sheets with printed electrodes were stacked and pressed to obtain a laminate, which was then attached and fixed to the adhesive sheet obtained in Experimental Example 6. The laminate was then cut into dice shapes at a temperature of 120°C, allowed to stand at room temperature, and then heated again at a temperature of 150 to 180°C, whereby the adhesive sheet, which was no longer needed, was peeled off and removed, thereby obtaining chip-type electronic components.

[0090] (7) In the process of forming the conductor layer for the external electrodes, green sheets on which electrodes have been printed are stacked and pressed, and the resulting laminate is cut into a dice pattern to obtain a chip-type electronic component. The chip-type electronic component is then sintered at a temperature of 1000 to 1300°C to obtain a sintered chip-type electronic component, which is then bonded to and fixed on the adhesive sheet obtained in Experimental Example 6. External electrodes are then applied to both end surfaces of the sintered chip-type electronic component, which is then dried at 110°C and left to stand in a room temperature environment. After this, the product is heated again at a temperature of 150 to 180°C, and the adhesive sheet, which is no longer needed, is peeled off and removed. The product is then baked at a temperature of around 800°C to obtain a chip-type electronic component with external electrodes.

Claims

1. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer in which heat-expandable microspheres expand upon heating, thereby reducing adhesive strength, the pressure-sensitive adhesive layer is formed from a crosslinked product of a pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition contains at least (A), (B), (C), and (D), and (B) accounts for 2 to 45 mass% of the total resin components of the pressure-sensitive adhesive composition; The pressure-sensitive adhesive sheet is characterized in that, when the pressure-sensitive adhesive layer is attached to a stainless steel plate and conditions A, B, C, and D are performed in this order, the arithmetic mean height Sa of the pressure-sensitive adhesive layer surface on the side attached to the stainless steel plate, as measured in ISO 25178, is 11 μm or more. (A) Mass average molecular weight is 1.0 × 10 5 ~1.0 x 10 6 Acrylic resin (B) Mass average molecular weight is 1.0 × 10 3 ~1.0 x 10 4 Acrylic resin (C) Crosslinking agent (D) Heat-expandable microspheres with an expansion starting temperature of 90 to 150°C Condition A: Heat for 1 hour at a temperature 10°C lower than the expansion starting temperature of (D). Condition B: Leave to stand at 23°C for 30 minutes. Condition C: Heat for 10 minutes at a temperature 20 to 40° C. higher than the expansion starting temperature of (D). Condition D: The pressure-sensitive adhesive sheet was peeled off from the stainless steel plate.

2. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein said (C) is an epoxy-based crosslinking agent.

3. 3. The pressure-sensitive adhesive sheet according to claim 2, wherein the epoxy equivalent of the epoxy-based crosslinking agent is 50 to 150 g / eq.

4. 4. The pressure-sensitive adhesive sheet according to claim 1, comprising the pressure-sensitive adhesive layer on a substrate.

5. 4. The pressure-sensitive adhesive sheet according to claim 1, comprising a first release sheet, the pressure-sensitive adhesive layer, and a second release sheet in this order.

6. A method for producing an electronic component, comprising laminating and pressing green sheets on which electrodes are printed, to obtain a laminate, bonding and fixing the laminate to the adhesive sheet according to any one of claims 1 to 3, and then performing a dicing step in which the laminate is cut into small pieces in a dice pattern at a temperature 10°C lower than the expansion start temperature of (D) contained in the adhesive sheet, followed by leaving the laminate in a room temperature environment and heating it again at a temperature 20 to 40°C higher than the expansion start temperature of (D) contained in the adhesive sheet, thereby peeling and removing the adhesive sheet that is no longer needed, thereby obtaining a chip-like electronic component.

7. A method for producing an electronic component, comprising stacking and pressing green sheets on which electrodes have been printed, cutting the resulting laminate into a dice shape to obtain a chip-type electronic component, sintering the chip-type electronic component at a temperature of 1000 to 1300°C to obtain a sintered chip-type electronic component, bonding and fixing the sintered chip-type electronic component to the adhesive sheet according to any one of claims 1 to 3, applying external electrodes to both end surfaces of the sintered chip-type electronic component, and performing a drying step at a temperature 10°C lower than the expansion start temperature of (D) contained in the adhesive sheet. Thereafter, the resulting product is left in a room temperature environment, and is heated again at a temperature 20 to 40°C higher than the expansion start temperature of (D) contained in the adhesive sheet, thereby peeling and removing the adhesive sheet that is no longer needed, and baking is performed at a temperature of 750 to 850°C to obtain a chip-type electronic component having external electrodes.

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