JP7396837B2 - adhesive sheet - Google Patents

Description

The present invention relates to an adhesive sheet.

In general, adhesives (also referred to as pressure-sensitive adhesives, hereinafter the same) exhibit a soft solid state (viscoelastic body) in a temperature range around room temperature, and have the property of easily adhering to an adherend under pressure. Taking advantage of these properties, adhesives are widely used in various fields in the form of adhesive sheets with a base material that have an adhesive layer on the base material, or in the form of base material-less adhesive sheets that do not have a base material. It's being used.

Adhesives are required to have various properties depending on their use. Some of these characteristics are difficult to achieve at a high level, such as when trying to improve one characteristic, the other tends to deteriorate. An example of such characteristics that are difficult to coexist is adhesion to an adherend and reworkability. The above-mentioned rework is, for example, when an adhesive sheet fails to adhere to an adherend (misalignment, generation of wrinkles or air bubbles, foreign matter gets caught, etc.), or when an adhesive sheet is attached to an adherend after it has been applied. This refers to peeling off the adhesive sheet from the adherend and reapplying it if a defect is found. In response to such a demand, Patent Document 1 proposes a pressure-sensitive adhesive sheet that exhibits low adhesive strength at the initial stage of attachment to an adherend, and that can greatly increase the adhesive strength thereafter.

Patent No. 6355874

According to the adhesive sheet described in Patent Document 1, by performing processes such as positioning and inspection before increasing the adhesive strength, good repositionability (reworkability) is exhibited in the process, and the member can be reused. Moreover, after increasing the adhesive strength by heating etc., strong adhesiveness can be exhibited. On the other hand, Patent Document 1 does not consider facilitating re-peeling of a pressure-sensitive adhesive sheet whose adhesive strength has once increased. Improving the peelability of the adhesive sheet is beneficial in situations such as repair, recovery, and disposal of members to which the adhesive sheet is attached.

Therefore, the present invention aims to provide a pressure-sensitive adhesive sheet that exhibits low tackiness at the initial stage of attachment to an adherend, can greatly increase its tackiness by heating, and has the function of facilitating re-peeling. purpose.

This specification provides a pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer. The adhesive layer includes Polymer A as a base polymer and thermally expandable microspheres having an expansion start temperature T1. The adhesive sheet is bonded to a stainless steel (SUS) plate and heated for 5 minutes at a temperature 20°C lower than the expansion start temperature T1, and then the adhesive strength N2 (hereinafter also referred to as "adhesive strength after heating") is measured at 23°C. ) is 3.0 times or more the adhesive strength N1 (hereinafter also referred to as "initial adhesive strength") measured after being bonded to a SUS plate and held at 23° C. for 30 minutes.

Since the pressure-sensitive adhesive sheet with such a structure has a large ratio of the pressure-sensitive adhesive force (N2) after heating to the initial pressure-sensitive adhesive force (N1) (hereinafter also referred to as "adhesive strength increase ratio"), the thermal expansion property blended in the pressure-sensitive adhesive layer is large. Adhesive strength can be greatly increased without expanding the microspheres. Moreover, by heating to a temperature equal to or higher than the expansion start temperature T1, the thermally expandable microspheres are expanded, the adhesive force is reduced, and the releasability of the adhesive sheet from the adherend can be improved.

The polymer A has a storage modulus G' (hereinafter also referred to as "storage modulus G'(T1)") at the expansion start temperature T1 in a range of approximately 1×10 ⁴ Pa to 1×10 ⁶ Pa. It is preferable that there be. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing such polymer A as a base polymer has good adhesion to an adherend when the heat-expandable microspheres are not expanded, and has good peelability when the heat-expandable microspheres are expanded. Easily expressed.

The polymer A preferably has a glass transition temperature _TgA calculated from the Fox equation based on the composition of the monomer components constituting the polymer A of -65°C or more and less than 0°C. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer using such polymer A as a base polymer has good adhesion to the adherend surface when the heat-expandable microspheres are not expanded, and has good removability by expanding the heat-expandable microspheres. is likely to occur.

The content of the thermally expandable microspheres in the adhesive layer can be, for example, in the range of 10 parts by weight or more and 200 parts by weight or less, based on 100 parts by weight of the polymer A. According to a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having such a composition, it is possible to suitably achieve both strong adhesiveness after increasing adhesive strength and peelability due to expansion of thermally expandable microspheres.

In some embodiments of the adhesive sheet disclosed herein, the adhesive layer may further include a polymer B that is a copolymer of a monomer having a polyorganosiloxane skeleton and a (meth)acrylic monomer. By using Polymer B, a pressure-sensitive adhesive sheet having an adhesive force increase ratio of 3.0 or more can be suitably realized.

The polymer B has a glass transition temperature _TgB (hereinafter sometimes simply referred to as " _TgB ") calculated from the Fox formula based on the composition of the (meth)acrylic monomer of 30°C or higher and 120°C. It is preferable that it is below ℃. The pressure-sensitive adhesive sheet disclosed herein can be preferably implemented using polymer B having Tg _B within the above range.

In some embodiments, as the polymer B, a polymer whose glass transition temperature _TgB is 20° C. or more lower than the expansion start temperature T1 can be preferably used. According to the polymer _{B having such Tg B} , it is possible to suitably realize a pressure-sensitive adhesive sheet that has high adhesive strength after heating and has good releasability due to expansion of the thermally expandable microspheres.

In some embodiments, the content of the polymer B in the pressure-sensitive adhesive layer can be in the range of, for example, 0.5 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the polymer A. According to the content within the above range, it is possible to preferably achieve both low tackiness at the initial stage and strong tackiness after increasing the tackiness.

The adhesive sheet disclosed herein includes a support base material having a first surface and a second surface, and the adhesive layer is laminated on at least the first surface side of the support base material, that is, the base material It can be implemented in the form of a sticky adhesive sheet. Such a pressure-sensitive adhesive sheet with a base material can be easily handled and processed.

The adhesive layer may be directly laminated on the first surface side of the support base material, or may be laminated via another layer (intermediate layer). In one preferred embodiment, an elastic intermediate layer is disposed between the adhesive layer and the first surface of the support base material. As a result, the adhesive force reduction effect due to the expansion of the thermally expandable microspheres contained in the adhesive layer can be effectively exerted on the adherend, and the adhesive layer can be attached to the supporting base via the elastic intermediate layer. The laminated form can be suitably maintained.

Note that an appropriate combination of each of the above-mentioned elements may also be included within the scope of the invention for which protection by patent is sought by the present patent application.

FIG. 1 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to an embodiment. FIG. 3 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to another embodiment. FIG. 3 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to another embodiment.

Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention are based on the teachings for carrying out the invention described in this specification and the common general knowledge at the time of filing. Can be understood by vendors. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the field.
In addition, in the following drawings, the same reference numerals may be attached and explained to members and parts that have the same function, and overlapping explanations may be omitted or simplified. Further, the embodiments shown in the drawings are schematic for clearly explaining the present invention, and do not necessarily accurately represent the size or scale of the actually provided products.

In addition, in this specification, "acrylic polymer" refers to a polymer containing monomer units derived from (meth)acrylic monomers in the polymer structure, typically monomer units derived from (meth)acrylic monomers. It refers to a polymer containing units in a proportion exceeding 50% by weight. Moreover, the (meth)acrylic monomer refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, the term "(meth)acryloyl group" is meant to comprehensively refer to acryloyl groups and methacryloyl groups. Therefore, the concept of a (meth)acrylic monomer here may include both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer). Similarly, in this specification, "(meth)acrylic acid" comprehensively refers to acrylic acid and methacrylic acid, and "(meth)acrylate" comprehensively refers to acrylate and methacrylate, respectively.

<Structure example of adhesive sheet>
The adhesive sheet disclosed herein includes an adhesive layer. The adhesive sheet disclosed herein may be in the form of a base-attached adhesive sheet in which the adhesive layer is laminated on one or both sides of a supporting base material, or may be in the form of a base-less adhesive sheet having no supporting base material. It may be a form. Hereinafter, the supporting base material may be simply referred to as "base material".

The structure of a pressure-sensitive adhesive sheet according to one embodiment is schematically shown in FIG. This adhesive sheet 1 is a single-sided adhesive sheet with a base material, which includes a sheet-like support base material 10 having a first surface 10A and a second surface 10B, and an adhesive layer 21 provided on the first surface 10A side. It is configured. In the configuration shown in FIG. 1, an elastic intermediate layer 50 is disposed between the first surface 10A of the support base material 10 and the adhesive layer 21. That is, the adhesive layer 21 is laminated on the first surface 10A of the support base material 10 via the elastic intermediate layer 50, and is preferably fixed. This elastic intermediate layer 50 is an optional component and may be omitted. For example, the adhesive layer 21 may be directly laminated on the first surface 10A side of the support base material 10, and preferably fixed.
The adhesive sheet 1 is used by attaching the adhesive layer 21 to an adherend. As shown in FIG. 1, the adhesive sheet 1 before use (that is, before being attached to an adherend) has a surface (adhesive surface) 21A of the adhesive layer 21 that is releasable at least on the side facing the adhesive layer 21. It may be a component of the adhesive sheet 100 with a release liner that is in contact with the release liner 31 serving as the surface (release surface). As the release liner 31, for example, a sheet-like base material (liner base material) that is configured by providing a release layer made of a release treatment agent on one side so that one side becomes a release surface can be preferably used. Alternatively, the release liner 31 may be omitted, the second surface 10B may be the release surface, and the adhesive surface 21A may be attached to the second surface 10B of the support substrate 10 by winding the adhesive sheet 1. It may also be in a contact form (roll form). When attaching the adhesive sheet 1 to an adherend, the release liner 31 or the second surface 10B of the support base material 10 is peeled off from the adhesive surface 21A, and the exposed adhesive surface 21A is pressure-bonded to the adherend.

FIG. 2 schematically shows the structure of a pressure-sensitive adhesive sheet according to another embodiment. This adhesive sheet 2 includes a sheet-like support base material 10 having a first surface 10A and a second surface 10B, an adhesive layer 21 provided on the first surface 10A side, and an adhesive layer 21 provided on the second surface 10B side. The adhesive layer 22 is configured as a double-sided adhesive sheet with a base material. In the configuration shown in FIG. 2, the adhesive layer (first adhesive layer) 21 is on the first surface 10A of the support base material 10, and the adhesive layer (second adhesive layer) 22 is on the second surface of the support base material 10. 10B, each directly laminated and preferably fixed. Alternatively, in the configuration shown in FIG. 2, between one or both of the first surface 10A of the support base material 10 and the adhesive layer 21 and the second surface 10B of the support base material 10 and the adhesive layer 22, An elastic intermediate layer may also be provided as in FIG.
The adhesive sheet 2 is used by attaching adhesive layers 21 and 22 to different locations on an adherend. The locations on which the adhesive layers 21 and 22 are attached may be on different members, or may be on different locations within a single member. In the adhesive sheet 2 before use, as shown in FIG. It may be a component of the pressure-sensitive adhesive sheet 200 with a release liner that is in contact with release liners 31 and 32 whose sides opposite to 22 are release surfaces, respectively. As the release liners 31 and 32, it is preferable to use, for example, a sheet-like base material (liner base material) that is constructed by providing a release layer made of a release treatment agent on one side so that one side becomes a release surface. obtain. Alternatively, the release liner 32 may be omitted and a release liner 31 having release surfaces on both sides may be used, and this and the adhesive sheet 2 may be overlapped and spirally wound so that the second adhesive surface 22A is attached to the release liner 31. An adhesive sheet with a release liner may be configured in a form (roll form) in contact with the back surface of the adhesive sheet.

FIG. 3 schematically shows the structure of a pressure-sensitive adhesive sheet according to yet another embodiment. This adhesive sheet 3 is configured as a base material-less double-sided adhesive sheet consisting of an adhesive layer 21. The adhesive sheet 3 has a first adhesive surface 21A constituted by one surface (first surface) of the adhesive layer 21 and a second adhesive surface constituted by the other surface (second surface) of the adhesive layer 21. 21B are attached to different parts of the adherend. As shown in FIG. 3, the adhesive sheet 3 before use includes release liners 31 and 32 in which the first adhesive surface 21A and the second adhesive surface 21B are release surfaces, respectively, at least on the side facing the adhesive layer 21. It may be a component of the adhesive sheet 300 with a release liner that is in contact with the release liner. Alternatively, the release liner 32 may be omitted, and a release liner 31 having release surfaces on both sides may be used, and this and the adhesive sheet 3 may be overlapped and spirally wound so that the second adhesive surface 21B is on the release liner 31. An adhesive sheet with a release liner may be configured in a form (roll form) in contact with the back surface of the adhesive sheet.

The adhesive sheet disclosed herein may optionally contain an intermediate layer other than the elastic intermediate layer, such as an undercoat layer, an adhesive layer, or an antistatic layer, between the support base material and the adhesive layer. Good too. In the case of an adhesive sheet having an elastic intermediate layer between the support base material and the adhesive layer, such an intermediate layer may be disposed between the support base material and the elastic intermediate layer, and the elastic intermediate layer may be disposed between the support base material and the elastic intermediate layer. It may be arranged between the layer and the adhesive layer.

Note that the concept of adhesive sheet here may include what is called an adhesive tape, an adhesive film, an adhesive label, and the like. The pressure-sensitive adhesive sheet may be in the form of a roll or sheet, or may be cut or punched into an appropriate shape depending on the purpose and manner of use. The adhesive layer in the technology disclosed herein is typically formed continuously, but is not limited to this, and may be formed in a regular or random pattern such as dots or stripes. good.

<Characteristics of adhesive sheet>
(Adhesive strength increase ratio)
The adhesive sheet disclosed herein has an adhesive strength increase ratio defined as the ratio of the adhesive strength after heating (N2) [N/20mm] to the initial adhesive strength (N1) [N/20mm] (i.e., N2/N1). is preferably 3.0 or more. Adhesive sheets with a large adhesive force increase ratio can be heated for a relatively short period of time at a temperature sufficiently lower than the expansion start temperature T1 of the expandable microspheres (for example, 20°C lower than the expansion start temperature T1). Adhesive strength can be greatly increased. Therefore, with a pressure-sensitive adhesive sheet having a high adhesive force increase ratio, it is possible to suitably achieve both low initial adhesiveness and strong adhesiveness during use. Furthermore, since the adhesive sheet after the adhesive strength has been increased contains unexpanded thermally expandable microspheres, by expanding these at an arbitrary timing, the peelability of the adhesive sheet whose adhesive strength has been increased can be improved.

In some embodiments, the adhesive strength increase ratio is preferably 4.0 or more, and 5.0 or more, from the viewpoint of achieving both low initial tackiness and strong tackiness during use at a higher level. More preferably, it is 6.0 or more, 7.5 or more, 10 or more, 15 or more, or 18 or more. The upper limit of the adhesive force increase ratio is not particularly limited, but from the viewpoint of facilitating the development of peelability due to expansion of the thermally expandable microspheres, it may be, for example, 150 or less, 100 or less, 80 or less, It may be 50 or less, 40 or less, or 30 or less. The adhesive sheet disclosed herein may also be suitably implemented in an embodiment in which the adhesive strength increase ratio is 20 or less, 14 or less, or 9 or less.

(Initial adhesive strength)
The initial adhesive strength of the adhesive sheet disclosed herein is not particularly limited. The initial adhesive strength can be set so as to exhibit desired reworkability depending on the purpose and manner of use of the adhesive sheet. In some embodiments, the initial adhesion may be, for example, less than 2.5 N/20 mm, suitably less than 2.3 N/20 mm, and may be less than 2.0 N/20 mm, 1. It may be less than 5N/20mm, or less than 1.0N/20mm. The lower limit of the initial adhesive force is not particularly limited, and may be, for example, 0.001 N/20 mm or more. From the viewpoint of workability of pasting to the adherend and prevention of positional shift before the adhesive strength increases, it is usually appropriate for the initial adhesive strength to be 0.01 N/20 mm or more, and the strength after the adhesive strength increases. From the viewpoint of easily achieving both adhesion, it may be, for example, 0.1 N/20 mm or more. In some embodiments, the initial adhesive strength may be, for example, 0.3 N/20 mm or more, 0.5 N/20 mm or more, 0.8 N/20 mm or more, or 1.2 N/20 mm or more.

(Adhesive strength after heating)
In the adhesive sheet disclosed herein, the adhesive strength after heating is not particularly limited, and can be set depending on the purpose and manner of use of the adhesive sheet. From the viewpoint of bonding reliability, in some embodiments, the adhesive force after heating may be, for example, 2.5 N/20 mm or more, usually preferably 3.0 N/20 mm or more, and 4.0 N/20 mm. More preferably, it is 5.0 N/20 mm or more, 7.0 N/20 mm or more, 10 N/20 mm or more, or 12 N/20 mm or more. The upper limit of the adhesive strength after heating is not particularly limited, but from the viewpoint of ease of manufacturing the adhesive sheet and economic efficiency, it may be, for example, 50 N/20 mm or less, 40 N/20 mm or less, 30 N/20 mm or less, or 25 N/20 mm or less. /20mm or less may be sufficient. In some embodiments, from the viewpoint of increasing the peelability due to expansion of the thermally expandable microspheres, the adhesive force N2 after heating may be, for example, 20 N/20 mm or less, 17 N/20 mm or less, or 13 N/20 mm or less. It is also possible to implement an embodiment in which the force is 9N/20mm or less.

Here, the initial adhesion strength [N/20mm] is measured after pressure-bonding to a stainless steel (SUS) plate as an adherend and leaving it for 30 minutes in an environment of 23°C and 50% RH. degree Celsius), by measuring the adhesive strength at 180° peeling under the conditions of a peeling angle of 180° and a pulling speed of 300 mm/min.
Adhesive strength after heating [N/20 mm] is 20°C from the expansion start temperature T1 [°C] of thermally expandable microspheres contained in the adhesive layer of the adhesive sheet to be evaluated, which is pressure-bonded to the SUS plate as the adherend. After heating at a low temperature (hereinafter also referred to as "heat treatment temperature T2") for 5 minutes, and then leaving it in an environment of 23 ° C. and 50% RH for 30 minutes, in the same environment, a peeling angle of 180 degrees and a tensile speed of 300 mm/ This can be determined by measuring the adhesive strength after 180° peeling under conditions of 10 minutes.
As the adherend, a SUS304BA plate is used in all measurements of the initial adhesive strength, the adhesive strength after heating, and the peel strength after expansion treatment N3 described below. In the measurement, if necessary, the adhesive sheet to be measured can be reinforced with a suitable backing material (for example, a PET film with a thickness of about 25 μm). More specifically, these adhesive forces can be measured according to the method described in the Examples below.

Note that the adhesive strength after heating of the adhesive sheet disclosed herein represents one characteristic of the adhesive sheet, and does not limit the manner in which the adhesive sheet is used. In other words, the mode of use of the adhesive sheet disclosed herein is not limited to the mode in which the adhesive strength is increased by heating at a heat treatment temperature T2 for 5 minutes after being attached to an adherend, but, for example, in the room temperature range (usually It can also be used in an embodiment in which no particular heating treatment is performed above 20° C. to 30° C., typically 23° C. to 25° C.). Even in such a usage mode, the adhesive strength increases over a long period of time, and a strong bond can be realized. Moreover, the adhesive sheet disclosed herein can promote an increase in adhesive strength by performing heat treatment at a temperature higher than 30° C. and lower than the expansion start temperature T1 at an arbitrary timing after pasting. The heating temperature T3 in this heat treatment is not particularly limited, and can be set in consideration of workability, economic efficiency, heat resistance of the base material of the pressure-sensitive adhesive sheet, the adherend, and the like. The heating temperature T3 is not particularly limited as long as it is lower than the expansion start temperature T1, and may be, for example, less than 170°C, 150°C or less, 120°C or less, or 100°C or less. Often, the heating temperature T3 may be 80°C or lower, or 70°C or lower, and the heating temperature T3 may be, for example, 40°C or higher, 50°C or higher, 60°C or higher, or 70°C. The temperature may be higher than that, 80°C or higher, or 100°C or higher. The heating time is not particularly limited, and may be, for example, 1 hour or less, 30 minutes or less, 10 minutes or less, or 5 minutes or less. Further, the heating time may be, for example, 1 minute or more, 3 minutes or more, 7 minutes or more, or 15 minutes or more. Alternatively, heat treatment may be performed for a longer period of time as long as the pressure-sensitive adhesive sheet or adherend does not undergo significant thermal deterioration. Note that the heat treatment may be performed at once or may be performed in multiple steps.

In some embodiments, the heating temperature T3 [°C] is preferably 5°C or more lower than the expansion start temperature T1 [°C], more preferably 10°C or more lower, 15°C or more, or The temperature may be lower than 20°C. By increasing the temperature difference (T1-T3), it is possible to better suppress the unintentional expansion of thermally expandable microspheres due to non-uniform temperature during heat treatment to increase adhesive strength. I can do it. The upper limit of the temperature difference (T1-T3) is not particularly limited, and can be set to, for example, 150°C or lower, and may be set to 125°C or lower from the viewpoint of heat treatment efficiency, may be set to 100°C or lower, or may be set to 80°C or lower. The temperature may preferably be 50°C or lower.

(expansion process)
The adhesive layer of the adhesive sheet disclosed herein can be removed from the adherend by performing a treatment (expansion treatment) to expand the thermally expandable microspheres contained in the adhesive layer after being attached to the adherend. The removability of the film can be improved. For example, when the heat-expandable microspheres expand, the adhesive layer containing the heat-expandable microspheres expands and deforms, resulting in a decrease in adhesion to an adherend and a decrease in adhesive force. The heating temperature in the expansion treatment is usually about the same level as or higher than the expansion start temperature T1 of the thermally expandable microspheres (e.g., 5°C or more, 10°C or more, or 15°C or more higher than the expansion start temperature T1). It is appropriate to The upper limit of the heating temperature in the above-mentioned expansion treatment is not particularly limited, but from the viewpoint of heat resistance of the adherend or adhesive sheet, energy cost, etc., it is usually appropriate to set it at 250°C, and 200°C or less is preferable. Preferably, the temperature may be 180°C or lower. The heating means used in the expansion treatment is not particularly limited, and one or more known heating means may be applied simultaneously or in stages. Non-limiting examples of such heating means may include hot plates, hot air dryers, infrared lamps, hot water supplies, and the like. The heating time in the thermal expansion treatment can be set so that the expansion of the thermally expandable microspheres progresses appropriately. In some embodiments, from the viewpoint of ease of process control and productivity, the heating time can be selected from a range of, for example, about 1 second to 30 minutes, preferably about 10 seconds to 15 minutes.

In some embodiments of the adhesive sheet disclosed herein, the adhesive sheet has an adhesive force N3 of less than 1.0 N/20 mm after expansion treatment measured by the following steps (1) to (5). It is preferably less than 0.5 N/20 mm, and more preferably less than 0.5 N/20 mm. Here, the adhesive force after expansion treatment N3 [N/20 mm] is the value of the 180° peeling adhesive force measured in the following procedure (5) per 20 mm width of the measurement sample, for example, the following procedure (4) ), even if part of the area of the measurement sample peels off from the adherend and floats up, it is not converted into a value per 20 mm width of the portion where the measurement sample is in close contact with the adherend. In addition, in step (5) below, if the measurement sample peels off from the adherend very easily and the tensile test cannot be performed properly (for example, the expansion treatment in (4) above causes most of the area of the measurement sample to is peeled off from the adherend and floats), it can be evaluated that the releasability at the expansion start temperature T1 is good.
[Measurement procedure of peel strength N3 after expansion treatment]
(1) A measurement sample is prepared by pressing the adhesive sheet to be evaluated onto a SUS plate as an adherend.
(2) The measurement sample is heated for 5 minutes at a temperature 20° C. lower (heat treatment temperature T2) than the expansion start temperature T1 [° C.] of the thermally expandable microspheres contained in the adhesive layer of the adhesive sheet.
(3) The above measurement sample is left in an environment of 23° C. and 50% RH for 30 minutes.
(4) Next, the measurement sample is heated at an expansion start temperature T1 [° C.] for 5 minutes.
(5) After leaving the above measurement sample in an environment of 23°C and 50% RH for 30 minutes, it was peeled off at 180° in the same environment (i.e., at 23°C) at a peeling angle of 180° and a pulling speed of 300 mm/min. Measure adhesion.

<Adhesive layer>
The adhesive layer in the technology disclosed herein contains Polymer A as a base polymer and thermally expandable microspheres. Polymer A is a polymer of monomer raw material A. The adhesive layer may be formed from an adhesive composition containing a complete polymer or a partial polymer of monomer raw material A and thermally expandable microspheres. The form of the adhesive composition is not particularly limited, and may be in various forms such as a solvent type, a water dispersion type, a hot melt type, and an active energy ray-curable type (for example, a photocurable type).

(Thermally expandable microspheres)
The thermally expandable microspheres are not particularly limited and can be appropriately selected from known thermally expandable microspheres (such as various inorganic thermally expandable microspheres and organic thermally expandable microspheres). As the thermally expandable microspheres, a microencapsulated blowing agent can be suitably used from the viewpoint of easy mixing operation. Examples of such thermally expandable microspheres include microspheres in which a substance that easily gasifies and expands upon heating, such as isobutane, propane, and pentane, is enclosed in an elastic shell. The shell is often formed of a heat-fusible material or a material that breaks due to thermal expansion. Examples of the substance forming the shell include vinylidene chloride-acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, and polysulfone.

Thermally expandable microspheres can be produced by a conventional method, such as a coacervation method or an interfacial polymerization method. Thermally expandable microspheres include, for example, the Matsumoto Microsphere series manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. (for example, the Matsumoto Microsphere F-30, Matsumoto Microsphere F-30), 301D", "Matsumoto Microsphere F-50D", "Matsumoto Microsphere F-501D", "Matsumoto Microsphere F-80SD", "Matsumoto Microsphere F-80VSD", etc.) , product name "051DU", "053DU", "551DU", "551-20DU", "551-80DU" manufactured by Expancel, product name "Advancel" manufactured by Sekisui Chemical Co., Ltd. Commercially available products such as can be used.

The average particle diameter D of the thermally expandable microspheres can be appropriately selected depending on the thickness Ta of the adhesive layer containing the thermally expandable microspheres. In some embodiments, heat-expandable microspheres are used in order to maintain the smoothness of the adhesive layer surface (adhesive surface) to be attached to the adherend and to avoid cohesive failure of the adhesive layer due to expansion of the heat-expandable microspheres. The average particle size of may be, for example, 100 μm or less, 80 μm or less, 50 μm or less, 30 μm or less, 20 μm or less, 15 μm or less, or 13 μm or less. Further, from the viewpoint of handling properties of the thermally expandable microspheres and peeling effect due to expansion, in some embodiments, the average particle diameter of the thermally expandable microspheres may be, for example, 1 μm or more, 3 μm or more, or 5 μm or more. The thickness may be greater than 8 μm. The average particle diameter herein refers to the particle diameter at 50% of the integrated value in the volume-based particle size distribution obtained by a measuring device based on a laser diffraction scattering method (50% volume average particle diameter). Adjustment of the particle size of the thermally expandable microspheres may be performed during the process of generating the thermally expandable microspheres, or may be performed by means such as classification after generation. In some embodiments, the thermally expandable microspheres may have a uniform particle size by means such as classification.

The expansion start temperature T1 of the thermally expandable microspheres is not particularly limited, but is usually 60° C. from the viewpoint of preventing the thermally expandable microspheres from expanding inadvertently at a timing when the adhesive sheet is not intended to be peeled off. The temperature is preferably 70°C or higher, 80°C or higher, 90°C or higher, 100°C or higher, 120°C or higher, 140°C or higher, or 160°C or higher. . In addition, from the viewpoint of heat resistance of the adherend and energy cost, the expansion start temperature T1 of the thermally expandable microspheres is usually appropriate to be 230°C, preferably 210°C or less, and 200°C. It is more preferably below, and may be 180°C or below, 150°C or below, 130°C or below, or 100°C or below.

In this specification, the expansion start temperature T1 of the thermally expandable microspheres refers to the temperature at which the volume of the microcapsules starts to increase when measured using a thermomechanical analyzer at a heating rate of 10°C/min. It refers to the temperature at which

From the viewpoint of efficiently and stably reducing the adhesion force to the adherend by the expansion of the thermally expandable microspheres, the volumetric expansion coefficient should be at least 5 times, especially at least 7 times, and especially at least 10 times, so as not to burst. Thermally expandable microspheres having high strength are preferred.

The amount of heat-expandable microspheres in the adhesive layer is not particularly limited, and can be set so that the effect of improving peelability (reducing adhesive strength) by expanding the heat-expandable microspheres is appropriately exhibited. . In some embodiments, the content of thermally expandable microspheres relative to 100 parts by weight of the base polymer (i.e., polymer A) of the adhesive layer can be, for example, 1 part by weight or more, and usually 10 parts by weight or more. The amount may be 25 parts by weight or more, 35 parts by weight or more, 50 parts by weight or more, 70 parts by weight or more, or 85 parts by weight or more. In addition, from the viewpoint of adhesion of the adhesive layer to the adherend before expanding the thermally expandable microspheres, the content of the thermally expandable microspheres is usually 200 parts by weight based on 100 parts by weight of the base polymer of the adhesive layer. It is appropriate that the amount is not more than 150 parts by weight, more preferably not more than 120 parts by weight.

(foaming agent)
The adhesive layer of the adhesive sheet disclosed herein may further contain a known foaming agent (this is a concept that does not include heat-expandable microspheres) in addition to the heat-expandable microspheres. As the blowing agent, various blowing agents such as various inorganic blowing agents and organic blowing agents can be appropriately selected and used. The blowing agents can be used alone or in combination of two or more. Typical examples of inorganic blowing agents include ammonium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium boron hydroxide, and various azides. Typical examples of organic blowing agents include, for example, water; salt fluorinated alkane compounds such as trichloromonofluoromethane and dichloromonofluoromethane; azobisisobutyronitrile, azodicarbonamide, and barium azodicarboxylate. Azo compounds such as paratoluenesulfonylhydrazide, diphenylsulfone-3,3'-disulfonylhydrazide, 4,4'-oxybis(benzenesulfonylhydrazide), allylbis(sulfonylhydrazide) and other hydrazine compounds; p-toluylene Semicarbazide compounds such as sulfonyl semicarbazide and 4,4′-oxybis(benzenesulfonyl semicarbazide); Triazole compounds such as 5-morpholyl-1,2,3,4-thiatriazole; N,N′-dinitrosopentamethylene telo Examples include -nitroso compounds such as lamin, N,N'-dimethyl-N,N'-dinitrosoterephthalamide, and the like.

When using such a foaming agent, the amount used can be, for example, in the range of 0.01 parts by weight to 25 parts by weight, based on 100 parts by weight of the base polymer of the adhesive layer (i.e., polymer A). . From the viewpoint of ease of controlling the timing of increasing or decreasing the adhesive strength, the amount of the blowing agent used per 100 parts by weight of the base polymer is usually preferably 20 parts by weight or less, and preferably 10 parts by weight or less. More preferably, the amount may be 5 parts by weight or less, or 1 part by weight or less. Preferably, no blowing agents are used.

(Polymer A)
Polymer A is the base polymer of the adhesive layer containing the thermally expandable microspheres. Here, in this specification, the base polymer of the adhesive layer is typically a main component of the polymer components contained in the adhesive constituting the adhesive layer, that is, a component that accounts for more than 50% by weight, for example. It may be a component that accounts for 75% by weight or more of the above polymer components. In some embodiments, the polymer A is a component that accounts for more than 50% by weight of the entire pressure-sensitive adhesive layer, and may be a component that accounts for 70% by weight or more.
In the adhesive sheet disclosed herein, the polymer A includes acrylic polymers, rubber polymers, polyester polymers, urethane polymers, polyether polymers, silicone polymers, and polyamide polymers known in the adhesive field. One or more of various polymers exhibiting rubber elasticity at room temperature, such as , fluorine-based polymers, etc., can be used.

The glass transition temperature _TgA of the polymer A is not particularly limited, and can be selected so as to obtain preferable characteristics in the pressure-sensitive adhesive sheet disclosed herein. In some embodiments, polymer A having a Tg _A of less than 0° C. may be preferably employed. Since the adhesive containing such polymer A exhibits appropriate fluidity (for example, the mobility of the polymer chains contained in the adhesive), it can efficiently increase the adhesive force without expanding the thermally expandable microspheres. Suitable for realizing an adhesive sheet that can be lifted up. The adhesive sheet disclosed herein can be preferably implemented using a polymer A having a Tg _A of less than -10°C, less than -20°C, less than -30°C, or less than -35°C. In some embodiments, Tg _A may be less than -40°C, and may be less than -45°C. The lower limit of _TgA is not particularly limited. From the viewpoint of easy availability of materials and improvement of the cohesive force of the adhesive layer, polymer A having a Tg _A of -80°C or higher, -70°C or higher, or -65°C or higher can usually be preferably employed. In some embodiments, Tg _A can be, for example, -63°C or higher, -55°C or higher, -50°C or higher, or -45°C or higher.

Here, in this specification, the glass transition temperature (Tg) of a polymer is a nominal value described in literature, catalogs, etc., or is calculated by Fox's formula based on the composition of monomer raw materials used for the preparation of the polymer. This refers to the required Tg. The Fox equation, as shown below, is a relational equation between Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer.
1/Tg=Σ(Wi/Tgi)
In the above Fox equation, Tg is the glass transition temperature of the copolymer (unit: K), Wi is the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi is the homopolymer of monomer i. represents the glass transition temperature (unit: K) of When the target polymer whose Tg is specified is a homopolymer, the Tg of the homopolymer and the Tg of the target polymer match.

As the glass transition temperature of the homopolymer used to calculate Tg, the value described in a known document shall be used. Specifically, numerical values are listed in the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989). For monomers for which multiple values are listed in the Polymer Handbook, the highest value is used.

As the glass transition temperature of a homopolymer of a monomer not described in the above Polymer Handbook, a value obtained by the following measurement method shall be used.
Specifically, 100 parts by weight of monomer, 0.2 parts by weight of 2,2'-azobisisobutyronitrile, and acetic acid as a polymerization solvent were placed in a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser. Add 200 parts by weight of ethyl and stir for 1 hour while passing nitrogen gas. After removing oxygen in the polymerization system in this manner, the temperature was raised to 63° C. and the reaction was allowed to proceed for 10 hours. Next, it is cooled to room temperature to obtain a homopolymer solution with a solid content concentration of 33% by weight. Next, this homopolymer solution is cast onto a release liner and dried to produce a test sample (sheet-like homopolymer) with a thickness of about 2 mm. This test sample was punched into a disk shape with a diameter of 7.9 mm, sandwiched between parallel plates, and subjected to shear strain at a frequency of 1 Hz using a viscoelasticity testing machine (manufactured by TA Instruments Japan, model name "ARES"). The viscoelasticity is measured in the shear mode at a temperature range of -70° C. to 150° C. and a heating rate of 5° C./min while giving the same temperature, and the temperature corresponding to the peak top temperature of tan δ is taken as the Tg of the homopolymer.

Although not particularly limited, it is appropriate that the weight average molecular weight (Mw) of Polymer A is usually about 20×10 ⁴ or more. With polymer A having such a Mw, it is easy to obtain an adhesive exhibiting good cohesion. The Mw of polymer A may be, for example, 30×10 ⁴ or more, 40×10 ⁴ or more, or 50×10 ⁴ or more. From the viewpoint of obtaining higher cohesive force, in some embodiments, the Mw of polymer A may be 60×10 ⁴ or more, or 80×10 ⁴ or more. Further, it is appropriate that the Mw of the polymer A is usually about 500×10 ⁴ or less. Polymer A with such a Mw easily forms an adhesive that exhibits appropriate fluidity (movement of polymer chains), so it is suitable for adhesive sheets that have low adhesive strength at the initial stage of application and high adhesive strength after the adhesive strength increases. suitable for implementation. In some embodiments, the Mw of Polymer A may be, for example, 250×10 ⁴ or less, 200×10 ⁴ or less, or 150×10 ⁴ or less.

In this specification, the Mw of Polymer A and Polymer B described below can be determined in terms of polystyrene by gel permeation chromatography (GPC). More specifically, Mw can be measured according to the method and conditions described in the Examples below.

The storage elastic modulus G' (storage elastic modulus G'(T1)) of polymer A at the expansion start temperature T1 of thermally expandable microspheres is not particularly limited, and is, for example, about 1×10 ³ Pa to 1×10 ⁶ Pa. It can be. Since the storage modulus G' at the expansion start temperature T1 is not too low, the function of deforming the adhesive layer by expansion of the thermally expandable microspheres to improve peelability (reduce adhesive force) can be preferably expressed. . From this viewpoint, the storage modulus G' (T1) is preferably 10 kPa (10 x 10 ³ Pa) or more, more preferably 15 kPa or more, 20 kPa or more, 40 kPa or more, 60 kPa or more. But that's fine. In addition, from the viewpoint of adhesion to the adherend before expanding the thermally expandable microspheres, the storage modulus G' (T1) is usually suitably 500 kPa or less, and 300 kPa or less. is preferable, more preferably 150 kPa or less, may be 100 kPa or less, may be 80 kPa or less, or may be 50 kPa or less.

As the polymer A in the pressure-sensitive adhesive sheet disclosed herein, an acrylic polymer can be preferably employed. In particular, in an embodiment in which the adhesive layer contains polymer B, which will be described later, in addition to polymer A, when an acrylic polymer is used as polymer A, good compatibility with polymer B tends to be easily obtained. Good compatibility between polymer A and polymer B is preferable because it can contribute to reducing the initial adhesive force and improving the adhesive force after heating through improving the mobility of polymer B within the adhesive layer.

The acrylic polymer is, for example, a polymer containing 50% by weight or more of monomer units derived from (meth)acrylic acid alkyl ester, that is, 50% of the total amount of monomer components (monomer raw material A) for preparing the acrylic polymer. It may be a polymer in which a weight percent or more is (meth)acrylic acid alkyl ester. As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having a linear or branched alkyl group having 1 to 20 carbon atoms (ie, C _1-20 ) can be preferably used. Since it is easy to balance the properties, the proportion of (meth)acrylic acid C _1-20 alkyl ester in the monomer raw material A may be, for example, 50% by weight or more, 60% by weight or more, or 70% by weight or more. But that's fine. For the same reason, the proportion of (meth)acrylic acid C _1-20 alkyl ester in monomer raw material A may be, for example, 99.9% by weight or less, 98% by weight or less, or 95% by weight or less. . In some embodiments, the proportion of (meth)acrylic acid C _1-20 alkyl ester in the monomer raw material A may be, for example, 90% by weight or less, 85% by weight or less, or 80% by weight or less.

Non-limiting specific examples of (meth)acrylic acid C _1-20 alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, ( n-butyl meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, (meth) Hexyl acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, (meth)acrylate ) Decyl acrylate, Isodecyl (meth)acrylate, Undecyl (meth)acrylate, Dodecyl (meth)acrylate, Tridecyl (meth)acrylate, Tetradecyl (meth)acrylate, Pentadecyl (meth)acrylate, (Meth) Examples include hexadecyl acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

Among these, it is preferable to use at least C _1-18 alkyl (meth)acrylic acid ester, and more preferably to use at least C _1-14 alkyl (meth)acrylic acid ester. In some embodiments, the acrylic polymer is at least one selected from (meth)acrylic acid C _4-12 alkyl esters (preferably acrylic acid C _4-10 alkyl esters, such as acrylic acid C _6-10 alkyl esters). may be contained as a monomer unit. For example, an acrylic polymer containing one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) is preferred, and an acrylic polymer containing at least 2EHA is particularly preferred. Examples of other (meth)acrylic acid C _1-18 alkyl esters that may be preferably used include methyl acrylate, methyl methacrylate (MMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA). , isostearyl acrylate (ISTA), and the like.

Monomer raw material A may contain other monomers (copolymerizable monomers) that can be copolymerized with the (meth)acrylic acid alkyl ester, if necessary, along with the (meth)acrylic acid alkyl ester as the main component. . As the copolymerizable monomer, a monomer having a polar group (for example, a carboxy group, a hydroxyl group, a nitrogen atom-containing ring, etc.) can be suitably used. A monomer having a polar group can be useful for introducing crosslinking points into the acrylic polymer or increasing the cohesive strength of the acrylic polymer. The copolymerizable monomers can be used alone or in combination of two or more.

Specific non-limiting examples of copolymerizable monomers include the following.
Hydroxyl group-containing monomer: For example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, (meth)acrylate 4-hydroxybutyl acid, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, (4-hydroxy) Hydroxyalkyl (meth)acrylates such as methylcyclohexyl)methyl (meth)acrylate, etc.
Monomers having a nitrogen atom-containing ring: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N- Vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3 -Morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinyl Thiazole, N-vinylisothiazole, N-vinylpyridazine, etc.;
For example, a monomer having a succinimide skeleton, such as N-(meth)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxyhexamethylene succinimide, N-(meth)acryloyl-8-oxyhexamethylene succinimide;
For example, maleimides such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide; and
For example, N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, N-laurylitaconimide, etc. , itaconimides.
Carboxy group-containing monomers: for example, acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc.
Acid anhydride group-containing monomers: for example, maleic anhydride, itaconic anhydride.
Epoxy group-containing monomers: For example, epoxy group-containing acrylates such as glycidyl (meth)acrylate and 2-ethyl glycidyl (meth)acrylate, allyl glycidyl ether, glycidyl (meth)acrylate, and the like.
Cyano group-containing monomers: for example, acrylonitrile, methacrylonitrile, etc.
Isocyanate group-containing monomer: for example, 2-isocyanatoethyl (meth)acrylate.
Amide group-containing monomer: For example, (meth)acrylamide; N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth) N,N-dialkyl (meth)acrylamide, such as acrylamide, N,N-di(n-butyl)(meth)acrylamide, N,N-di(t-butyl)(meth)acrylamide; N-ethyl(meth) N-alkyl (meth)acrylamides such as acrylamide, N-isopropyl (meth)acrylamide, N-butyl (meth)acrylamide, N-n-butyl (meth)acrylamide; N-vinylcarboxylic acid amides such as N-vinylacetamide; Monomers having a hydroxyl group and an amide group, such as N-(2-hydroxyethyl)(meth)acrylamide, N-(2-hydroxypropyl)(meth)acrylamide, N-(1-hydroxypropyl)(meth) Acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, N-(4-hydroxybutyl)( N-hydroxyalkyl (meth)acrylamide such as meth)acrylamide; monomers having an alkoxy group and an amide group, such as N-methoxymethyl (meth)acrylamide, N-methoxyethyl (meth)acrylamide, N-butoxymethyl ( N-alkoxyalkyl (meth)acrylamide such as meth)acrylamide; others such as N,N-dimethylaminopropyl (meth)acrylamide and N-(meth)acryloylmorpholine.
Aminoalkyl (meth)acrylates: For example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, (meth)acrylic acid t -Butylaminoethyl.
Alkoxy group-containing monomers: For example, 2-methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, (meth)acrylic acid Alkoxyalkyl (meth)acrylates such as butoxyethyl and ethoxypropyl (meth)acrylate; Alkoxyalkylene glycol (meth)acrylates such as methoxyethylene glycol (meth)acrylate and methoxypolypropylene glycol (meth)acrylate kind.
Monomers containing sulfonic or phosphoric acid groups: for example, styrene sulfonic acid, allyl sulfonic acid, sodium vinyl sulfonate, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfonate Propyl (meth)acrylate, (meth)acryloyloxynaphthalene sulfonic acid, 2-hydroxyethyl acryloyl phosphate, etc.
(Meth)acrylic acid esters having an alicyclic hydrocarbon group: for example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, etc.
(Meth)acrylic acid ester having an aromatic hydrocarbon group: For example, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, etc.
Vinyl ethers: For example, vinyl alkyl ethers such as methyl vinyl ether and ethyl vinyl ether.
Vinyl esters: for example, vinyl acetate, vinyl propionate, etc.
Aromatic vinyl compounds: For example, styrene, α-methylstyrene, vinyltoluene, etc.
Olefins: For example, ethylene, butadiene, isoprene, isobutylene, etc.
In addition, heterocycle-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, halogen atom-containing (meth)acrylates such as vinyl chloride and fluorine atom-containing (meth)acrylates, and silicon atom-containing such as silicone (meth)acrylates. (Meth)acrylate, (meth)acrylic acid ester obtained from terpene compound derivative alcohol, etc.

When such a copolymerizable monomer is used, the amount used is not particularly limited, but it is usually appropriate to use 0.01% by weight or more of the monomer raw material A. From the viewpoint of better exhibiting the effect of using the copolymerizable monomer, the amount of the copolymerizable monomer used may be 0.1% by weight or more of the monomer raw material A, or may be 1% by weight or more. Further, the amount of the copolymerizable monomer used can be 50% by weight or less of the monomer raw material A, and preferably 45% by weight or less. This prevents the cohesive force of the adhesive from becoming too high and improves the tackiness at room temperature (25° C.). In some embodiments, the amount of the copolymerizable monomer used may be 40% by weight or less, or 35% by weight or less of the monomer raw material A.

In some embodiments, monomer feedstock A may include a monomer having a nitrogen atom-containing ring. By using a monomer having a nitrogen atom-containing ring, the cohesive force and polarity of the adhesive can be adjusted, and the adhesive strength after heating can be suitably improved. By including a monomer having a nitrogen atom-containing ring in the monomer raw material A, the compatibility between the polymer A formed from the monomer raw material A and the polymer B tends to be improved. This makes it easier to obtain a pressure-sensitive adhesive sheet that can greatly increase adhesive strength at a temperature lower than the expansion start temperature T1.

The monomer having a nitrogen atom-containing ring can be appropriately selected from, for example, the above examples and used alone or in combination of two or more. In some embodiments, the monomer raw material A may contain at least one monomer selected from the group consisting of N-vinyl cyclic amides represented by the following general formula (M1) as a monomer having a nitrogen atom-containing ring. preferable. Monomer raw material A may contain only one or more N-vinyl cyclic amides as a monomer having a nitrogen atom-containing ring.

ここで、上記一般式（Ｍ１）中のＲ^１は、２価の有機基である。

Here, R ¹ in the above general formula (M1) is a divalent organic group.

Specific examples of N-vinyl cyclic amide include N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3 -oxazin-2-one, N-vinyl-3,5-morpholinedione and the like. Particularly preferred are N-vinyl-2-pyrrolidone and N-vinyl-2-caprolactam.

The amount of the monomer having a nitrogen atom-containing ring is not particularly limited, and is usually 0.01% by weight or more (preferably 0.1% by weight or more, for example, 0.5% by weight or more) of the monomer raw material A. is appropriate. In some embodiments, the amount of the monomer having a nitrogen atom-containing ring used may be 1% by weight or more of the monomer raw material A, 5% by weight or more, 10% by weight or more, 12% by weight or more. You can also use it as In addition, from the viewpoint of improving tackiness at room temperature (25°C) and improving flexibility at low temperatures, it is appropriate that the amount of the monomer having a nitrogen atom-containing ring used is usually 40% by weight or less of the monomer raw material A. Yes, the content may be 30% by weight or less, 20% by weight or less, or 18% by weight or less.

In some preferred embodiments, monomer raw material A contains a hydroxyl group-containing monomer. By using a hydroxyl group-containing monomer, the cohesive force and polarity of the adhesive can be adjusted, and the adhesive strength after heating can be suitably improved. In addition, the hydroxyl group-containing monomer provides a reaction site with a crosslinking agent (for example, an isocyanate crosslinking agent), which will be described later, and can increase the cohesive force of the adhesive through the crosslinking reaction.

Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and N-(2-hydroxyethyl)(meth)acrylamide. It can be used suitably. Among these, preferred examples include 2-hydroxyethyl acrylate (HEA), 4-hydroxybutyl acrylate (4HBA), and N-(2-hydroxyethyl)acrylamide (HEAA).

The amount of the hydroxyl group-containing monomer to be used is not particularly limited, and it is usually appropriate to use 0.01% by weight or more (preferably 0.1% by weight or more, for example 0.5% by weight or more) of the monomer raw material A. . In some embodiments, the amount of the hydroxyl group-containing monomer used may be 1% by weight or more, 5% by weight or more, or 10% by weight or more of the monomer raw material A. In addition, from the viewpoint of mobility of Polymer B within the adhesive layer, improvement of tackiness at room temperature (25°C), and improvement of flexibility at low temperatures, the amount of the hydroxyl group-containing monomer used is usually 40% of the monomer raw material A. It is appropriate to set the content to 30% by weight or less, 20% by weight or less, 10% by weight or less, or 5% by weight or less.

In some embodiments, a monomer having a nitrogen atom-containing ring (for example, N-vinyl cyclic amide) and a hydroxyl group-containing monomer can be used together as the copolymerizable monomer. In this case, the total amount of the monomer having a nitrogen atom-containing ring and the hydroxyl group-containing monomer may be, for example, 0.1% by weight or more of the monomer raw material A, may be 1% by weight or more, and may be 5% by weight or more. The content may be 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more. Further, the total amount of the monomer having a nitrogen atom-containing ring and the hydroxyl group-containing monomer can be, for example, 50% by weight or less of the monomer raw material A, and preferably 40% by weight or less.

In an embodiment in which the monomer raw material A contains a combination of a monomer having a nitrogen atom-containing ring and a hydroxyl group-containing monomer, the content (W _{N ) of the monomer having a nitrogen atom-containing ring and the content (W N} ) of the hydroxyl group-containing monomer in the monomer raw material A The relationship (weight basis) with W _OH ) is not particularly limited. W _N /W _OH may be, for example, 0.01 or more, usually 0.05 or more is appropriate, 0.1 or more, 0.2 or more, 0.5 or more, 0. It may be .7 or more. Further, W _N /W _OH may be, for example, 100 or less, usually 20 or less is appropriate, 10 or less, 5 or less, 2 or less, or 1.5 or less.

In some embodiments, the monomer raw material A does not contain a monomer (monomer S1) having a polyorganosiloxane skeleton that is preferably used as a component of the monomer raw material B described below, or the content of the monomer is lower than that of the monomer raw material A. It is preferably less than 10% by weight (more preferably less than 5% by weight, for example less than 2% by weight). According to the monomer raw material A having such a composition, a pressure-sensitive adhesive sheet that satisfactorily balances initial reworkability and strong adhesiveness after increasing the adhesive strength can be suitably realized. For similar reasons, in some other embodiments, monomer raw material A does not contain monomer S1, or if it contains monomer S1, its content (on a weight basis) is lower than the content of monomer S1 in monomer raw material B. Preferably it is low.

The method for obtaining polymer A is not particularly limited, and various polymerization methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization can be appropriately employed. In some embodiments, solution polymerization methods may be preferably employed. The polymerization temperature when performing solution polymerization can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and is, for example, about 20°C to 170°C (typically 40°C to 140°C). ℃).

The initiator used for polymerization can be appropriately selected from conventionally known thermal polymerization initiators, photopolymerization initiators, etc., depending on the polymerization method. The polymerization initiators can be used alone or in combination of two or more.

Examples of thermal polymerization initiators include azo polymerization initiators (for example, 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis( Dimethyl 2-methylpropionate), 4,4'-azobis-4-cyanovalerianic acid, azobisisovaleronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2 -(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(N,N'-dimethylene) isobutyramidine) dihydrochloride, etc.); persulfates such as potassium persulfate; peroxide-based polymerization initiators (e.g., dibenzoyl peroxide, t-butyl permaleate, lauroyl peroxide, etc.); redox-based polymerization initiators, etc. can be mentioned. The amount of the thermal polymerization initiator used is not particularly limited, but for example, 0.01 parts by weight to 5 parts by weight, preferably 0. Amounts can range from .05 parts to 3 parts by weight.

The photopolymerization initiator is not particularly limited, but includes, for example, a benzoin ether photopolymerization initiator, an acetophenone photopolymerization initiator, an α-ketol photopolymerization initiator, an aromatic sulfonyl chloride photopolymerization initiator, and a photoactive initiator. Oxime photoinitiator, benzoin photoinitiator, benzyl photoinitiator, benzophenone photoinitiator, ketal photoinitiator, thioxanthone photoinitiator, acylphosphine oxide photoinitiator Agents etc. can be used. The amount of the photopolymerization initiator used is not particularly limited, but for example, an amount within the range of 0.01 parts by weight to 5 parts by weight, preferably 0.05 parts by weight to 3 parts by weight, based on 100 parts by weight of monomer raw material A. It can be done.

In some embodiments, the polymer A is a partial polymer (polymer syrup) obtained by irradiating ultraviolet (UV) light to a mixture of monomer raw materials A and a polymerization initiator as described above to polymerize a portion of the monomer components. ) may be included in the adhesive composition for forming the adhesive layer. An adhesive composition containing such a polymer syrup can be applied to a predetermined object and irradiated with ultraviolet rays to complete polymerization. That is, the polymer syrup can be understood as a precursor of polymer A. The adhesive layer disclosed herein can be formed using an adhesive composition containing the above polymer syrup and polymer B, for example.

(Polymer B)
The pressure-sensitive adhesive sheet disclosed herein includes a polymer A (for example, an acrylic polymer) as described above, and a polymer B, which is a copolymer of a monomer having a polyorganosiloxane skeleton and a (meth)acrylic monomer. This can be preferably realized using a pressure-sensitive adhesive layer that includes a pressure-sensitive adhesive layer. Such an adhesive layer may be formed from an adhesive composition containing polymer A in the form of a complete polymer or partial polymer of monomer raw material A and polymer B. The form of the adhesive composition is not particularly limited, and may be in various forms such as a solvent type, a water dispersion type, a hot melt type, and an active energy ray-curable type (for example, a photocurable type).

Polymer B in the technology disclosed herein is a copolymer of a monomer having a polyorganosiloxane skeleton (hereinafter also referred to as "monomer S1") and a (meth)acrylic monomer. Polymer B has an adhesive force that suppresses the initial adhesive force to the adherend due to the low polarity and mobility of the polyorganosiloxane structure derived from the monomer S1, and increases the adhesive force to the adherend by heating. May function as a rise retardant. The monomer S1 is not particularly limited, and any monomer containing a polyorganosiloxane skeleton can be used. Due to its low polarity derived from its structure, monomer S1 promotes the uneven distribution of polymer B on the surface of the adhesive layer in the adhesive sheet before use (before attachment to the adherend), resulting in light peeling at the initial stage of lamination. (low adhesiveness). As the monomer S1, a monomer having a structure having a polymerizable reactive group at one end can be preferably used. By such copolymerization of the monomer S1 and the (meth)acrylic monomer, a polymer B having a polyorganosiloxane skeleton in the side chain is formed. Polymer B having such a structure tends to have low initial adhesive strength and high adhesive strength after heating due to the mobility and ease of movement of the side chains.

ここで、上記一般式（１），（２）中のＲ^３は水素またはメチルであり、Ｒ^４はメチル基または１価の有機基であり、ｍおよびｎは０以上の整数である。 As the monomer S1, for example, a compound represented by the following general formula (1) or (2) can be used. More specifically, single-end reactive silicone oils manufactured by Shin-Etsu Chemical Co., Ltd. include X-22-174ASX, X-22-2426, X-22-2475, KF-2012, and the like. Monomer S1 can be used alone or in combination of two or more.

Here, R ³ in the above general formulas (1) and (2) is hydrogen or methyl, R ⁴ is a methyl group or a monovalent organic group, and m and n are integers of 0 or more.

The functional group equivalent of the monomer S1 can be set to any appropriate value within a range where the desired effect can be achieved using the monomer S1, and is not limited to a specific range. From the viewpoint of sufficiently suppressing the initial adhesive strength, the functional group equivalent may be, for example, 140 g/mol or more, 200 g/mol or more, and usually 300 g/mol or more (for example, 500 g/mol or more). is appropriate, preferably 700 g/mol or more, may be 800 g/mol or more, may be 850 g/mol or more, may be 1000 g/mol or more, or may be 1500 g/mol or more. In some embodiments, the functional group equivalent may be 2500 g/mol or more, 3000 g/mol or more, or 4500 g/mol, from the viewpoint of achieving both low tackiness at the initial stage of pasting and increased adhesive strength over time. It may be more than 6000 g/mol, it may be more than 9000 g/mol, it may be more than 12000 g/mol, it may be more than 15000 g/mol (for example, more than 16000 g/mol). The functional group equivalent weight of monomer S1 can be, for example, 50000 g/mol or less. From the viewpoint of increasing adhesive strength over time, the functional group equivalent is preferably, for example, 30,000 g/mol or less, more preferably 20,000 g/mol or less. In some embodiments, the functional group equivalent weight of monomer S1 may be less than 18000 g/mol, may be less than 15000 g/mol, may be less than 10000 g/mol, may be less than 6000 g/mol, may be less than 5000 g/mol. . When the functional group equivalent of the monomer S1 is within the above range, it is easy to adjust the compatibility (for example, compatibility with the base polymer) and mobility within the adhesive layer to an appropriate range, and the adhesive has a high adhesive strength increase ratio. It becomes easier to realize the agent layer.

Non-limiting examples of suitable ranges of the functional group equivalent of monomer S1 include 700 g/mol or more and 50,000 g/mol or less, 700 g/mol or more and 30,000 g/mol or less, 700 g/mol or more and 20,000 g/mol or less, and 700 g/mol or more and 18,000 g/mol or less. /mol, 700g/mol or more and less than 15000g/mol, 800g/mol or more and less than 10000g/mol, 850g/mol or more and less than 6000g/mol, and 1500g/mol or more and less than 5000g/mol. In some embodiments, the preferred range of the functional group equivalent of the monomer S1 is 3000 g/mol or more and 50000 g/mol or less, 6000 g/mol or more and 50000 g/mol or less, 12000 g/mol or more and 50000 g/mol or less, and 15000 g/mol or more and 50000 g/mol or less. It can be less than mol.

Here, "functional group equivalent" means the weight of the main skeleton (for example, polydimethylsiloxane) bonded to one functional group. Regarding the title unit g/mol, it is converted to 1 mol of functional group. The functional group equivalent of the monomer S1 can be calculated, for example, from the spectral intensity of ¹ H-NMR (proton NMR) based on nuclear magnetic resonance (NMR). Calculation of the functional group equivalent (g/mol) of the monomer S1 based on the spectral intensity of ¹ H-NMR is based on a general structural analysis method related to ¹ H-NMR spectrum analysis, and if necessary, the method described in Japanese Patent No. 5951153. This can be done by referring to the description in the official gazette.

Note that when two or more types of monomers having different functional group equivalents are used as the monomer S1, an arithmetic mean value can be used as the functional group equivalent of the monomer S1. That is, the functional group equivalent of the monomer S1, which is composed of n types of monomers (monomer S1 ₁ , monomer S1 ₂ . . . monomer S1 _n ) having different functional group equivalents, can be calculated using the following formula.
Functional group equivalent of monomer S1 (g/mol) = (functional group equivalent of monomer S1 ₁ x blending amount of monomer S1 ₁ + functional group equivalent of monomer S1 ₂ x blending amount of monomer S1 ₂ + ... + monomer S1 _n functional group equivalent x amount of monomer S1 _n )/(amount of monomer S1 ₁ + amount of monomer S1 ₂ +...+ amount of monomer S1 _n )

The content of monomer S1 may be, for example, 5% by weight or more of the total amount of monomer components (monomer raw material B) for preparing polymer B, from the viewpoint of better exhibiting the effect as an adhesive strength increase retarder. The content is preferably 10% by weight or more, may be 15% by weight or more, or may be 20% by weight or more. Further, from the viewpoint of polymerization reactivity and compatibility, the content of monomer S1 in monomer raw material B is suitably 60% by weight or less, may be 50% by weight or less, and may be 40% by weight or less. , 30% by weight or less. If the content of monomer S1 is less than 5% by weight, the initial adhesive strength may not be sufficiently suppressed. If the content of monomer S1 is more than 60% by weight, the increase in adhesive strength may become insufficient.

Monomer raw material B contains, in addition to monomer S1, a (meth)acrylic monomer copolymerizable with monomer S1. By copolymerizing one or more types of (meth)acrylic monomers and monomer S1, the mobility of polymer B within the adhesive layer can be suitably adjusted. Copolymerizing monomer S1 and a (meth)acrylic monomer may also help improve the compatibility between polymer B and polymer A (eg, an acrylic polymer).

Examples of (meth)acrylic monomers that can be used as monomer raw material B include (meth)acrylic acid alkyl esters. For example, one or more of the monomers exemplified above as the (meth)acrylic acid alkyl ester that can be used when the polymer A is an acrylic polymer can be used as a constituent component of the monomer raw material B. In some embodiments, monomer feedstock B is a (meth)acrylic acid C _4-12 alkyl ester (preferably a (meth)acrylic acid C _4-10 alkyl ester, such as a (meth)acrylic acid C _6-10 alkyl ester) It may contain at least one of the following. In some other embodiments, monomer feedstock B may contain at least one type of methacrylic acid C _1-18 alkyl ester (preferably methacrylic acid C _1-14 alkyl ester, such as methacrylic acid C _1-10 alkyl ester). . Monomer raw material B may contain, for example, one or more selected from MMA, BMA, and 2EHMA as (meth)acrylic monomers.

Other examples of the (meth)acrylic monomer include (meth)acrylic acid esters having an alicyclic hydrocarbon group. For example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, etc. can be used. In some embodiments, monomer raw material B may contain at least one selected from dicyclopentanyl methacrylate, isobornyl methacrylate, and cyclohexyl methacrylate as a (meth)acrylic monomer.

The content of the (meth)acrylic acid alkyl ester and the (meth)acrylic ester having an alicyclic hydrocarbon group in the monomer raw material B may be, for example, 10% by weight or more and 95% by weight or less, and 20% by weight. It may be more than 95% by weight, it may be more than 30% by weight and less than 90% by weight, it may be more than 40% by weight and less than 90% by weight, and it can be more than 50% by weight and less than 85% by weight. Good too. From the viewpoint of ease of controlling the behavior of increase in adhesive strength, it may be advantageous to use an alkyl (meth)acrylate ester. In some embodiments, the content of the (meth)acrylic ester having an alicyclic hydrocarbon group may be less than 50% by weight of monomer raw material B, may be less than 30% by weight, and may be less than 15% by weight. Often less than 10% by weight, even less than 5% by weight. It is not necessary to use a (meth)acrylic acid ester having an alicyclic hydrocarbon group.

In some preferred embodiments, the (meth)acrylic monomer that is a component of the monomer raw material B may include a monomer M2 whose homopolymer Tg is 50° C. or higher. In Polymer B, by copolymerizing Monomer S1 and Monomer M2, the mobility and mobility of the polyorganosiloxane structural part due to temperature rise can be suitably controlled, making it easy to obtain a pressure-sensitive adhesive sheet with a high adhesive force increase ratio. Become. In some embodiments, the Tg of the homopolymer of monomer M2 may be 60°C or higher, 70°C or higher, 80°C or higher, or 90°C or higher. Further, the upper limit of Tg of the homopolymer of monomer M2 is not particularly limited, but from the viewpoint of ease of synthesizing polymer B, etc., it is usually suitable that it is 200° C. or less. In some embodiments, the Tg of the homopolymer of monomer M2 may be, for example, 180°C or less, 150°C or less, or 120°C or less.

As the monomer M2, for example, from among the (meth)acrylic monomers exemplified above, those whose homopolymer Tg satisfies the conditions can be used. For example, one or more monomers selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid esters having an alicyclic hydrocarbon group can be used. As the (meth)acrylic acid alkyl ester, a methacrylic acid alkyl ester in which the number of carbon atoms in the alkyl group is in the range of 1 to 4 can be preferably employed.

In an embodiment in which monomer raw material B contains monomer M2, the content of monomer M2 may be, for example, 5% by weight or more of monomer raw material B, 10% by weight or more, 15% by weight or more, 20% by weight or more. It may be 25% by weight or more, or 30% by weight or more. In some embodiments, the content of the monomer M2 may be 35% by weight or more, 40% by weight or more, 45% by weight or more, 50% by weight or more, 55% by weight or more of the monomer raw material B. But that's fine. Further, the content of the monomer M2 may be, for example, 90% by weight or less, and is usually suitably 80% by weight or less. In polymer B, by restricting the copolymerization ratio of monomer M2 having a Tg of 50° C. or higher to a predetermined value or less, it becomes easy to exhibit good adhesion strength increasing property at a temperature lower than the expansion start temperature T1. In some embodiments, the content of monomer M2 is preferably 75% by weight or less, may be 70% by weight or less, may be 65% by weight or less, may be 60% by weight or less, may be 50% by weight or less, and may be 45% by weight or less. It may be less than %.

The content of the monomer M2 is such that, for example, the monomer M2 is one or more monomers selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid esters having an alicyclic hydrocarbon group. It can be preferably applied in an embodiment in which the monomer M2 consists of one or more monomers selected from (meth)acrylic acid alkyl esters (for example, methacrylic acid alkyl esters). A preferred example of such an embodiment is an embodiment in which the monomer M2 is MMA.

In some embodiments, the (meth)acrylic monomer may include a monomer M3 whose homopolymer Tg is less than 50°C (typically -20°C or more and less than 50°C). By using monomer M3, it becomes easier to obtain a pressure-sensitive adhesive sheet that has both adhesive force and cohesive force in a well-balanced manner after increasing the adhesive force. From the viewpoint of making it easier to exhibit such effects, it is preferable to use monomer M3 in combination with monomer M2.

As the monomer M3, for example, from among the (meth)acrylic monomers exemplified above, those whose homopolymer Tg satisfies the conditions can be used. For example, one or more monomers selected from the group consisting of (meth)acrylic acid alkyl esters can be used.

In an embodiment in which monomer raw material B contains monomer M3, the content of monomer M3 may be, for example, 5% by weight or more of monomer raw material B, 10% by weight or more, 15% by weight or more, or 20% by weight or more. It may be 25% by weight or more, 30% by weight or more, or 35% by weight or more. Further, the content of the monomer M3 is usually suitably 70% by weight or less of the monomer raw material B, and may be 60% by weight or less, or may be 50% by weight or less. The above content of monomer M3 can be preferably applied, for example, in an embodiment in which monomer M3 consists of one or more monomers selected from alkyl (meth)acrylates (for example, alkyl methacrylates).

In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, it is preferable that the monomer raw material B has a content of a monomer whose homopolymer Tg is higher than 170° C. at 30% by weight or less. Here, in this specification, the term "the content of the monomer is X% by weight or less" includes an embodiment in which the content of the monomer is 0% by weight, that is, an embodiment that does not substantially contain the monomer, unless otherwise specified. It is a concept. Further, "substantially free" means that the above monomer is not used, at least intentionally. By restricting the copolymerization ratio of monomers whose homopolymer Tg is higher than 170° C., it becomes easier to exhibit a good adhesive strength increase property at a temperature lower than the expansion start temperature T1. In some embodiments, the content of monomers whose homopolymer has a Tg higher than 170° C. may be 20% by weight or less, 10% by weight or less, 5% by weight or less, or 2% by weight or less.

In some embodiments, the monomer raw material B preferably contains at least MMA as the (meth)acrylic monomer. According to Polymer B in which MMA is copolymerized, a pressure-sensitive adhesive sheet with a large _N50 can be easily obtained. The proportion of MMA in the total amount of (meth)acrylic monomers contained in monomer raw material B may be, for example, 5% by weight or more, 10% by weight or more, 20% by weight or more, 30% by weight or more. It may be 40% by weight or more. In some embodiments, the proportion of MMA in the total amount of the (meth)acrylic monomers may be, for example, more than 50% by weight, more than 55% by weight, more than 60% by weight, 65% by weight. It may be more than 70% by weight. Further, the proportion of MMA in the total amount of the (meth)acrylic monomers is usually suitably 95% by weight or less, may be 90% by weight or less, or may be 85% by weight or less. In some preferred embodiments, the proportion of MMA in the total amount of the (meth)acrylic monomers may be 75% by weight or less, from the viewpoint of increasing adhesive strength at a temperature lower than the expansion start temperature T1, and may be 65% by weight or less. % or less, 60% by weight or less, or 55% by weight or less (for example, 50% by weight or less).

Other examples of monomers that can be included together with monomer S1 as monomer units constituting polymer B include the carboxyl group-containing monomers and acid anhydride group-containing monomers exemplified above as monomers that can be used when polymer A is an acrylic polymer. Monomer, hydroxyl group-containing monomer, epoxy group-containing monomer, cyano group-containing monomer, isocyanate group-containing monomer, amide group-containing monomer, monomer having a nitrogen atom-containing ring (N-vinyl cyclic amide, monomer having a succinimide skeleton, maleimides, itaconimide) etc.), aminoalkyl (meth)acrylates, vinyl esters, vinyl ethers, olefins, (meth)acrylic esters having aromatic hydrocarbon groups, (meth)acrylates containing heterocycles, halogen atom-containing (meth)acrylates, etc. ) acrylate, (meth)acrylic acid ester obtained from terpene compound derivative alcohol, and the like.

Still other examples of monomers that may be included together with monomer S1 as monomer units constituting polymer B include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di( Oxyalkylene di(meth)acrylates such as meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, and tripropylene glycol di(meth)acrylate; monomers having a polyoxyalkylene skeleton, such as polyethylene glycol A polyoxyalkylene chain such as polyoxyalkylene or polypropylene glycol has a polymerizable functional group such as a (meth)acryloyl group, vinyl group, or allyl group at one end, and an ether structure (alkyl ether, aryl ether, arylalkyl group) at the other end. (ether, etc.); methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxy (meth)acrylate Alkoxyalkyl (meth)acrylates such as propyl; salts such as alkali metal salts of (meth)acrylates; polyhydric (meth)acrylates such as trimethylolpropane tri(meth)acrylates; vinylidene chloride, (meth)acrylic acid -Halogenated vinyl compounds such as 2-chloroethyl; Oxazoline group-containing monomers such as 2-vinyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, and 2-isopropenyl-2-oxazoline; (meth)acryloyl Aziridine group-containing monomers such as aziridine, 2-aziridinylethyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, lactones and (meth)acrylate Hydroxyl group-containing vinyl monomers such as adducts with 2-hydroxyethyl acid; fluorine-containing vinyl monomers such as fluorine-substituted (meth)acrylic acid alkyl esters; reactive halogen-containing vinyl monomers such as 2-chloroethyl vinyl ether and monochlorovinyl acetate. Organosilicon-containing vinyl monomers such as vinyltrimethoxysilane, γ-(meth)acryloxypropyltrimethoxysilane, allyltrimethoxysilane, trimethoxysilylpropylallylamine, and 2-methoxyethoxytrimethoxysilane; Examples include macromonomers having a radically polymerizable vinyl group at the end of the polymerized monomer. These can be copolymerized with monomer S1 alone or in combination of two or more.

In some embodiments of the adhesive sheet disclosed herein, the composition of the (meth)acrylic monomer contained in the monomer raw material B has a glass transition temperature Tg _B [°C] based on the composition of the (meth)acrylic monomer. It is preferable to set the temperature to be lower than the expansion start temperature T1 [° C.]. That is, it is preferable that T1-Tg _B is 0°C or higher. According to such polymer B, the adhesive force can be greatly increased without expanding the thermally expandable microspheres through the mobility of polymer B in a temperature range lower than the expansion start temperature T1.

The glass transition temperature _TgB is usually preferably 30°C or higher, more preferably 40°C or higher, 45°C or higher, or 50°C or higher. Polymer _B , which has a high TgB, allows the adhesive sheet attached to the adherend to absorb heat generated by the operation of equipment used in the manufacturing process, exhaust heat from nearby equipment, etc. during the period when reworkability is required for the adhesive sheet attached to the adherend. Accordingly, reworkability can be appropriately maintained even when a temperature higher than room temperature is applied to the pressure-sensitive adhesive sheet. This is because, by appropriately increasing the Tg _B of Polymer B, the mobility and mobility of the polyorganosiloxane structural portion as the temperature rises can be improved by increasing the monomer units derived from the (meth)acrylic monomer contained in Polymer B. It is thought that this is because the low tackiness caused by the presence of the polyorganosiloxane structure can be better maintained. In some embodiments, Tg _B may be 55°C or higher, 60°C or higher, 65°C or higher, or 70°C or higher. In addition, from the viewpoint of heat resistance of the adherend or adhesive sheet, energy cost for heat treatment, etc., Tg _B is usually suitably 150°C or less, preferably 120°C or less, The temperature is more preferably 100°C or lower, 90°C or lower, 85°C or lower, 80°C or lower, 70°C or lower, 60°C or lower, or 50°C or lower.

From the viewpoint of efficiently increasing the adhesive strength without expanding the thermally expandable microspheres, the composition of the monomer raw material B is usually such that Tg _B [°C] is 5°C or more lower than the expansion start temperature T1 [°C]. It is appropriate to adjust the temperature so that T1-Tg _B is 5°C or higher. In some embodiments, T1-Tg _B may be 10°C or higher, 15°C or higher, preferably 20°C or higher, more preferably 30°C or higher, 40°C or higher, and 60°C or higher. The temperature may be higher than 70°C, or higher than 70°C. Further, T1-Tg _B is normally suitably 250°C or less, may be 200°C or less, may be 150°C or less, may be 100°C or less, or may be 80°C or less.

Here, the glass transition temperature Tg _B based on the composition of the (meth)acrylic monomer mentioned above is based on the composition of only the (meth)acrylic monomer among the monomer components used for the preparation of polymer B, and is calculated according to the Fox equation. This refers to the required Tg. Tg _B is determined by applying the above-mentioned Fox equation to only the (meth)acrylic monomer among the monomer components used in the preparation of Polymer B, and calculating the glass transition temperature of the homopolymer of each (meth)acrylic monomer and , and the weight fraction of each (meth)acrylic monomer in the total amount of the (meth)acrylic monomer. From the viewpoint of facilitating the effect of appropriately setting Tg _B , the total amount of monomer S1 and (meth)acrylic monomer in all monomer components for preparing polymer B is, for example, 50% by weight or more. The content may be 70% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more, or substantially 100% by weight.

From the viewpoint of easily controlling the mobility of polymer B within the adhesive layer, in some embodiments, the composition of monomer raw material B is such that TTg _B is higher than Tg _A in relation to the glass transition temperature Tg _A of polymer A. It can be set so that the temperature is 20°C or more higher, that is, Tg _B −Tg _A is 20°C or more. In some embodiments, Tg _B - Tg _A can be, for example, 50°C or higher, 60°C or higher, 70°C or higher, or 80°C or higher. Also, in some embodiments, Tg _B -Tg _A may be, for example, 150°C or less, 140°C or less, 130°C or less, or 120°C or less.

When heat treatment is performed to promote an increase in adhesive strength, the heating temperature T3 [°C] in the heat treatment is equal to or higher than the glass transition temperature Tg _B [°C] from the viewpoint of the mobility of polymer B within the adhesive layer. The temperature is preferably set to , and more preferably the temperature is higher than the glass transition temperature Tg _B [°C] (ie, (T3-Tg _B )>0). From the viewpoint of enhancing the effect of promoting an increase in adhesive strength, in some embodiments, the temperature difference (T3 - Tg _B ) between the heating temperature T3 [°C] and the glass transition temperature Tg _B [°C] is, for example, 5° C. or more. The temperature may be 10°C or higher, 20°C or higher, 40°C or higher, or 60°C or higher. The upper limit of the temperature difference (T3-Tg _B ) is not particularly limited and may be, for example, 150° C. or less. In some embodiments, the temperature difference (T3-Tg _B ) may be, for example, 100°C or less, taking into consideration workability, economic efficiency, heat resistance of the adhesive sheet base material and adherend, etc. The temperature may be lower than or equal to 50°C, or lower than 35°C.

The glass transition temperature of the polymer B (that is, the glass transition temperature Tg _Ball based on the composition of the monomer raw material B) is not particularly limited, and can be selected so as to obtain preferable characteristics in the pressure-sensitive adhesive sheet disclosed herein. The Tg _Ball may be, for example, less than 50°C, less than 30°C, less than 20°C, less than 15°C, and less than 10°C. When the Tg _Ball of the polymer B is lowered, the mobility of the polymer B is improved, and the adhesive strength tends to be increased by heating in a temperature range lower than the expansion start temperature T1. Further, in some embodiments, the Tg _Ball may be, for example, -40°C or higher, -30°C or higher, -20°C or higher, or -10°C or higher. As the Tg _Ball increases, reworkability tends to be maintained more easily even if temperatures above room temperature are applied after the adhesive sheet is attached.

In some embodiments, as the polymer B, a polymer that does not have a functional group that causes a crosslinking reaction with the polymer A can be preferably employed. In other words, it is preferable that the polymer B is contained in the adhesive layer in a form that is not chemically bonded to the polymer A. The adhesive layer containing the polymer B in such a form has good mobility of the polymer B during heating, and is suitable for improving the adhesive force increase ratio. The functional group that causes a crosslinking reaction with the polymer A may vary depending on the type of functional group that the polymer A has, and may be, for example, an epoxy group, an isocyanate group, a carboxy group, an alkoxysilyl group, an amino group, or the like.

The Mw of polymer B is not particularly limited. The Mw of the polymer B may be, for example, 1000 or more, or 5000 or more. The Mw of the polymer B may be, for example, 10,000 or more, 12,000 or more, 15,000 or more, 20, It may be 000 or more. In some embodiments, the Mw of Polymer B may be greater than or equal to 50,000, greater than or equal to 80,000, greater than or equal to 100,000, or greater than or equal to 120,000 (eg, greater than or equal to 150,000). The upper limit of Mw of polymer B is, for example, 500,000 or less, may be 350,000 or less, may be 350,000 or less, or may be less than 100,000. From the viewpoint of adjusting the compatibility and mobility within the adhesive layer to an appropriate range and increasing the adhesive strength at a temperature lower than the expansion start temperature T1, the Mw of the polymer B may be less than 80,000, and may be 70,000. It may be less than 50,000, it may be less than 40,000, it may be less than 20,000, and it may be less than 10,000.

In some preferred embodiments, the Mw of Polymer B is preferably lower than the Mw of Polymer A. This makes it easy to realize a pressure-sensitive adhesive sheet that has both good reworkability at the initial stage of pasting and the ability to increase adhesive strength at a temperature lower than the expansion start temperature T1. The Mw of polymer B may be, for example, 0.8 times or less, 0.75 times or less, 0.5 times or less, 0.3 times or less, or 0.1 times or less than the Mw of polymer A. It may be less than twice, 0.05 times or less, or 0.03 times or less (for example, 0.02 times or less).

Polymer B can be produced, for example, by polymerizing the above-mentioned monomers by a known method such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, a photopolymerization method, or the like.

In order to adjust the molecular weight of polymer B, a chain transfer agent can be used as necessary. Examples of chain transfer agents to be used include compounds having a mercapto group such as octylmercaptan, laurylmercaptan, t-nonylmercaptan, t-dodecylmercaptan, mercaptoethanol, and α-thioglycerol; thioglycolic acid, methyl thioglycolate, Ethyl thioglycolate, propyl thioglycolate, butyl thioglycolate, t-butyl thioglycolate, 2-ethylhexyl thioglycolate, octyl thioglycolate, isooctyl thioglycolate, decyl thioglycolate, dodecyl thioglycolate, ethylene Examples include thioglycolic acid esters such as thioglycolic acid ester of glycol, thioglycolic acid ester of neopentyl glycol, and thioglycolic acid ester of pentaerythritol; α-methylstyrene dimer; and the like.

The amount of the chain transfer agent to be used is not particularly limited, but is usually 0.05 to 20 parts by weight, preferably 0.1 to 15 parts by weight, per 100 parts by weight of the monomer. , more preferably 0.2 parts by weight to 10 parts by weight. By adjusting the amount of chain transfer agent added in this manner, polymer B having a suitable molecular weight can be obtained. Chain transfer agents can be used alone or in combination of two or more.

As means for adjusting the molecular weight of Polymer B, various conventionally known means including the use of the chain transfer agent described above can be used alone or in appropriate combinations. The same applies to the molecular weight of polymer A. Non-limiting examples of such means include selection of polymerization method, selection of type and amount of polymerization initiator used, selection of polymerization temperature, selection of type and amount of polymerization solvent used in solution polymerization methods, photopolymerization. This includes legal selection of light irradiation intensity, etc. Those skilled in the art can understand how to obtain a polymer having a desired molecular weight based on the description of this specification including specific examples described below and the common general knowledge at the time of filing of this application.

In the pressure-sensitive adhesive sheet disclosed herein, the amount of polymer B used per 100 parts by weight of polymer A can be, for example, 0.1 part by weight or more, and from the viewpoint of obtaining a higher effect, 0.5 parts by weight. It may be more than 1 part by weight, it may be 1 part by weight or more, or it may be 2 parts by weight or more. In some embodiments, from the viewpoint of improving reworkability, the amount of the polymer B used can be, for example, 3 parts by weight or more, 4 parts by weight or more, or 5 parts by weight or more. Further, the amount of polymer B used relative to 100 parts by weight of polymer A may be, for example, 75 parts by weight or less, 60 parts by weight or less, or 50 parts by weight or less. From the viewpoint of avoiding excessive reduction in the cohesive force of the adhesive layer, in some embodiments, the amount of polymer B used relative to 100 parts by weight of polymer A can be, for example, 40 parts by weight or less, and 35 parts by weight or less. , 30 parts by weight or less, or 25 parts by weight or less. From the viewpoint of obtaining higher adhesive strength after heating, in some embodiments, the amount of the polymer B used may be 20 parts by weight or less, 17 parts by weight or less, 15 parts by weight or less, 12 parts by weight or less. It may be less than 10 parts by weight, it may be less than 8 parts by weight, it may be less than 6 parts by weight, and it may be less than 4 parts by weight (for example, less than 3 parts by weight).

The adhesive layer may contain a polymer (any polymer) other than Polymer A and Polymer B, as necessary, within a range that does not significantly impair the performance of the adhesive sheet disclosed herein. The amount of such optional polymer used is usually suitably 20% by weight or less of the total polymer components contained in the adhesive layer, and may be 15% by weight or less, or 10% by weight or less. In some embodiments, the amount of the optional polymer used may be 5% by weight or less, 3% by weight or less, or 1% by weight or less of the total polymer components. The adhesive layer may be substantially free of polymers other than Polymer A and Polymer B.

(Crosslinking agent)
A crosslinking agent may be used in the adhesive layer as necessary for purposes such as adjusting cohesive force. As the crosslinking agent, crosslinking agents known in the field of adhesives can be used, such as epoxy crosslinking agents, isocyanate crosslinking agents, silicone crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, and silane crosslinking agents. Examples include crosslinking agents, alkyl etherified melamine crosslinking agents, metal chelate crosslinking agents, and the like. In particular, isocyanate crosslinking agents, epoxy crosslinking agents, and metal chelate crosslinking agents can be suitably used. The crosslinking agents can be used alone or in combination of two or more.

Specifically, examples of isocyanate-based crosslinking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, and naphthalene. Examples include diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenylisocyanate, and adducts of these with polyols such as trimethylolpropane. Alternatively, a compound having at least one isocyanate group and one or more unsaturated bond in one molecule, specifically, 2-isocyanatoethyl (meth)acrylate, etc. can also be used as an isocyanate-based crosslinking agent. I can do it. These can be used alone or in combination of two or more.

Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin-type epoxy resin, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, and trimethylolpropane triglycidyl ether. Glycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, etc. I can do it. These can be used alone or in combination of two or more.

Examples of the metal chelate compound include metal components such as aluminum, iron, tin, titanium, and nickel, and chelate components such as acetylene, methyl acetoacetate, and ethyl lactate. These can be used alone or in combination of two or more.

The amount of the crosslinking agent used is not particularly limited, and may be, for example, more than 0 parts by weight based on 100 parts by weight of the polymer A. Further, the amount of the crosslinking agent used can be, for example, 0.01 parts by weight or more, and preferably 0.05 parts by weight or more, based on 100 parts by weight of the polymer A. Increasing the amount of crosslinking agent used tends to suppress the adhesive force at the initial stage of pasting and improve reworkability. From the viewpoint of suppressing cohesive failure of the adhesive layer due to expansion of the thermally expandable microspheres, in some embodiments, the amount of the crosslinking agent used relative to 100 parts by weight of the polymer A may be 0.1 part by weight or more, The amount may be 0.5 parts by weight or more, 0.8 parts by weight or more, 1 part by weight or more, or 2 parts by weight or more. On the other hand, from the viewpoint of increasing the adhesive force increase ratio by allowing the mobility of Polymer B to be appropriate, it is appropriate that the amount of crosslinking agent used per 100 parts by weight of Polymer A is usually 15 parts by weight or less, and 10 parts by weight. The amount may be less than 5 parts by weight, or less than 5 parts by weight.

The technology disclosed herein can be preferably implemented in an embodiment using at least an isocyanate-based crosslinking agent as a crosslinking agent. From the viewpoint of achieving both good reworkability at the initial stage of pasting and an increase in adhesive strength at a temperature lower than the expansion start temperature T1, in some embodiments, the amount of the isocyanate crosslinking agent used relative to 100 parts by weight of the polymer A is, for example, 0. 01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, 0.5 parts by weight or more. Alternatively, the amount may be 0.8 parts by weight or more, 1 part by weight or more, or 2 parts by weight or more. Further, the amount of the isocyanate crosslinking agent to be used per 100 parts by weight of the polymer A is usually 15 parts by weight or less, preferably 10 parts by weight or less, 7 parts by weight or less, and 5 parts by weight or less. The amount may be less than 3 parts by weight, or less than 3 parts by weight.

Although not particularly limited, when an isocyanate-based crosslinking agent is used in a structure in which the adhesive layer contains a hydroxyl group-containing monomer as a monomer unit, the usage amount W _OH of the hydroxyl group-containing monomer relative to the usage amount W _NCO of the isocyanate-based crosslinking agent is: The amount can be such that W _OH /W _NCO is 2 or more on a weight basis. By increasing the amount of hydroxyl group-containing monomer used in the isocyanate-based crosslinking agent in this way, a crosslinked structure suitable for significantly increasing the adhesive strength at a temperature lower than the expansion start temperature T1 is formed compared to the adhesive strength at the initial stage of application. can be done. In some embodiments, W _OH /W _NCO may be 3 or more, 5 or more, 10 or more, 20 or more, 30 or more. It may be 50 or more. The upper limit of W _OH /W _NCO is not particularly limited, and from the viewpoint of achieving a degree of crosslinking that allows appropriate movement of polymer B by heating at a temperature lower than the expansion start temperature T1, W _OH /W _NCO is, for example, 500 or less. It may be 200 or less, 100 or less, or 50 or less.

A crosslinking catalyst may be used to more effectively advance any of the crosslinking reactions described above. As the crosslinking catalyst, for example, a tin-based catalyst (especially dioctyltin dilaurate) can be preferably used. The amount of the crosslinking catalyst used is not particularly limited, but may be, for example, approximately 0.0001 part by weight to 1 part by weight per 100 parts by weight of polymer A.

A polyfunctional monomer may be used in the adhesive layer, if necessary. Polyfunctional monomers can be used in place of or in combination with the above-mentioned crosslinking agents, and can be useful for purposes such as adjusting cohesive force. For example, a polyfunctional monomer can be preferably used in an adhesive layer formed from a photocurable adhesive composition.
Examples of polyfunctional monomers include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, Pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecane Diol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate, butyl Examples include diol (meth)acrylate, hexyldiol di(meth)acrylate, and the like. Among them, trimethylolpropane tri(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and dipentaerythritol hexa(meth)acrylate can be preferably used. The polyfunctional monomers can be used alone or in combination of two or more.

The amount of the polyfunctional monomer used varies depending on its molecular weight, number of functional groups, etc., but it is usually appropriate to range from 0.01 parts by weight to 3.0 parts by weight based on 100 parts by weight of polymer A. . In some embodiments, the amount of the polyfunctional monomer used may be, for example, 0.02 parts by weight or more, or 0.03 parts by weight or more, based on 100 parts by weight of the polymer A. Increasing the amount of polyfunctional monomer used tends to suppress the adhesive force at the initial stage of pasting and improve reworkability. On the other hand, from the viewpoint of ensuring the mobility of polymer B and controlling its movement with a crosslinked network to adjust the increase in adhesive strength after heating at a temperature lower than the expansion start temperature T1, the amount of polyfunctional monomer used is The amount may be 2.0 parts by weight or less, 1.0 parts by weight or less, or 0.5 parts by weight or less based on 100 parts by weight of the polymer A.

(tackifying resin)
The adhesive layer can contain a tackifier resin as necessary. The tackifier resin is not particularly limited, but includes, for example, a rosin-based tackifier resin, a terpene-based tackifier resin, a phenol-based tackifier resin, a hydrocarbon-based tackifier resin, a ketone-based tackifier resin, a polyamide-based tackifier resin, Examples include epoxy tackifying resins and elastomer tackifying resins. The tackifying resin can be used alone or in combination of two or more.

Examples of rosin-based tackifier resins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin, and modified rosins (raw rosins) that are modified by polymerizing, disproportionating, and hydrogenating these unmodified rosins. Examples include polymerized rosin, stabilized rosin, disproportionated rosin, fully hydrogenated rosin, partially hydrogenated rosin, and other chemically modified rosins) as well as various rosin derivatives.
Examples of the above-mentioned rosin derivatives include:
Rosin phenolic resin obtained by adding phenol to rosin (unmodified rosin, modified rosin, various rosin derivatives, etc.) with an acid catalyst and thermally polymerizing it;
Rosin ester compounds (unmodified rosin esters) obtained by esterifying unmodified rosin with alcohols, modified rosins such as polymerized rosin, stabilized rosin, disproportionated rosin, fully hydrogenated rosin, and partially hydrogenated rosin with alcohols. Rosin ester resins such as modified rosin ester compounds (polymerized rosin esters, stabilized rosin esters, disproportionated rosin esters, fully hydrogenated rosin esters, partially hydrogenated rosin esters, etc.);
Unsaturated fatty acid-modified rosin resin, which is obtained by modifying unmodified rosin or modified rosin (polymerized rosin, stabilized rosin, disproportionated rosin, fully hydrogenated rosin, partially hydrogenated rosin, etc.) with unsaturated fatty acids;
Unsaturated fatty acid modified rosin ester resin obtained by modifying rosin ester resin with unsaturated fatty acid;
Carboxyl groups in unmodified rosin, modified rosin (polymerized rosin, stabilized rosin, disproportionated rosin, fully hydrogenated rosin, partially hydrogenated rosin, etc.), unsaturated fatty acid modified rosin resin, and unsaturated fatty acid modified rosin ester resin Rosin alcohol-based resin subjected to reduction treatment;
Examples include unmodified rosin, modified rosin, and metal salts of rosin resins (especially rosin ester resins) such as various rosin derivatives.

Terpene-based tackifier resins include, for example, terpene-based resins such as α-pinene polymer, β-pinene polymer, dipentene polymer, and modified terpene-based resins (phenol modification, aromatic modification, hydrogenation modification, etc.). Examples include modified terpene resins (eg, terpene phenol resins, styrene-modified terpene resins, aromatic-modified terpene resins, hydrogenated terpene resins, etc.).

Examples of phenolic tackifying resins include condensates of various phenols (e.g., phenol, m-cresol, 3,5-xylenol, p-alkylphenol, resorcinol, etc.) and formaldehyde (e.g., alkylphenol resins, xylene formaldehyde, etc.). resols obtained by addition-reacting the above-mentioned phenols and formaldehyde using an alkali catalyst, and novolaks obtained by conducting a condensation reaction between the above-mentioned phenols and formaldehyde using an acid catalyst.

Examples of hydrocarbon tackifying resins include aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic/aromatic petroleum resins (styrene-olefin copolymers, etc.) ), aliphatic/alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumaron-based resins, coumaron-indene-based resins, and various other hydrocarbon-based resins.

Commercially available polymerized rosin esters that can be preferably used include the product names "Pensel D-125", "Pensel D-135", "Pensel D-160", "Pensel KK", and "Pensel D-135", manufactured by Arakawa Chemical Industry Co., Ltd. Examples include, but are not limited to, "C".

Commercially available terpene phenol resins that can be preferably used include Yasuhara Chemical Co., Ltd.'s product names "YS Polyster S-145," "YS Polyster G-125," "YS Polyster N125," and "YS Polyster U-115." Examples include, but are not limited to, "Tamanol 803L" and "Tamanol 901" manufactured by Arakawa Chemical Co., Ltd., and "Sumilite Resin PR-12603" manufactured by Sumitomo Bakelite Co., Ltd.

The content of the tackifier resin is not particularly limited, and can be set so that appropriate adhesive performance is exhibited depending on the purpose and use. The content of the tackifier resin (if two or more types of tackifier resins are included, the total amount thereof) based on 100 parts by weight of the polymer A can be, for example, about 5 to 500 parts by weight.

As the tackifier resin, one having a softening point (softening temperature) of approximately 80° C. or higher (preferably approximately 100° C. or higher, for example approximately 120° C. or higher) can be preferably used. According to the tackifier resin having a softening point equal to or higher than the above-mentioned lower limit, a pressure-sensitive adhesive sheet having high adhesive strength after heating can be easily obtained. The upper limit of the softening point is not particularly limited, and may be, for example, approximately 200°C or lower (typically 180°C or lower). The softening point of the tackifier resin can be measured based on the softening point test method (ring and ball method) specified in JIS K2207.

In addition, the adhesive layer in the technology disclosed herein may contain a leveling agent, a plasticizer, a softener, a coloring agent (dye, pigment, etc.), a filler, an antistatic agent, as long as the effects of the present invention are not significantly impaired. If necessary, the adhesive may contain known additives that can be used in adhesives, such as anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, and preservatives.

The adhesive layer constituting the adhesive sheet disclosed herein may be a cured layer of an adhesive composition. That is, the adhesive layer is formed by applying (e.g., coating) a water-dispersed, solvent-based, photocurable, hot-melt, or other adhesive composition to an appropriate surface, and then appropriately performing a curing treatment. obtain. When performing two or more types of curing treatments (drying, crosslinking, polymerization, cooling, etc.), these can be performed simultaneously or in multiple stages. In pressure-sensitive adhesive compositions using partial polymers (polymer syrup) of monomer raw materials, a final copolymerization reaction is typically performed as the curing treatment. That is, the partially polymerized product is further subjected to a copolymerization reaction to form a complete polymerized product. For example, in the case of a photocurable adhesive composition, light irradiation is performed. Curing treatments such as crosslinking and drying may be performed as necessary. For example, if the photocurable adhesive composition needs to be dried, photocuring may be performed after drying. In an adhesive composition using a complete polymer, typically, as the curing treatment, treatments such as drying (heat drying) and crosslinking are performed as necessary.

The adhesive composition can be applied using a conventional coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, and a spray coater.

The thickness of the adhesive layer is not particularly limited, and can be, for example, 3 μm or more. From the viewpoint of suppressing a decrease in the smoothness of the adhesive surface due to the inclusion of thermally expandable microspheres, the thickness of the adhesive layer is usually suitably 7 μm or more, preferably more than 10 μm, It may be more than 15 μm, more than 25 μm, or more than 35 μm. The upper limit of the thickness of the adhesive layer is not particularly limited, but it is usually suitably 300 μm or less, and may be 200 μm or less, 150 μm or less, 100 μm or less, or 70 μm or less. It may be advantageous that the thickness of the adhesive layer is not too large from the viewpoint of avoiding cohesive failure of the adhesive layer due to expansion of the thermally expandable microspheres. In some embodiments, the thickness of the adhesive layer may be 60 μm or less, 50 μm or less, or 45 μm or less.

The thickness Ta of the adhesive layer is preferably larger than the average particle diameter D of the thermally expandable microspheres. That is, it is preferable that Ta/D is larger than 1.0. From the viewpoint of the smoothness of the adhesive surface, in some embodiments Ta/D is preferably 2.0 or more, may be 3.0 or more, or may be 4.0 or more. In addition, from the viewpoint of facilitating the exfoliation effect due to expansion of the thermally expandable microspheres, Ta/D is usually suitably 50 or less, preferably 20 or less, and may be 15 or less, It may be 10 or less.

In addition, in the case of a pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on the first and second surfaces of the base material, the thickness of the pressure-sensitive adhesive layer described above is at least the thickness of the first pressure-sensitive adhesive layer. can be applied to The thickness of the second adhesive layer may also be selected from a similar range. Further, in the case of a base material-less adhesive sheet, the thickness of the adhesive sheet matches the thickness of the adhesive layer.
In addition, in the adhesive sheet disclosed herein, an adhesive layer containing heat-expandable microspheres (an adhesive having first and second adhesive layers containing heat-expandable microspheres on the first and second surfaces of the base material) In the sheet, each adhesive layer) may have a single layer structure or a multilayer structure of two or more layers. In some embodiments, the adhesive layer preferably has a single-layer structure from the viewpoint of controllability of the adhesive force before expansion of the thermally expandable microspheres.

<Support base material>
The pressure-sensitive adhesive sheet according to some embodiments may be in the form of a pressure-sensitive adhesive sheet with a base material, which includes a pressure-sensitive adhesive layer on one or both sides of a supporting base material. The material of the support base material is not particularly limited, and can be appropriately selected depending on the purpose and manner of use of the pressure-sensitive adhesive sheet. Non-limiting examples of base materials that can be used include polyolefin films mainly composed of polyolefins such as polypropylene and ethylene-propylene copolymers; polyester films mainly composed of polyesters such as polyethylene terephthalate and polybutylene terephthalate; Plastic films such as polyvinyl chloride film whose main component is polyvinyl chloride; Foam sheets made of foams such as polyurethane foam, polyethylene foam, and polychloroprene foam; Various fibrous materials (natural fibers such as hemp and cotton, Woven fabrics and non-woven fabrics, such as synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc., alone or in blends; Papers such as Japanese paper, high-quality paper, kraft paper, and crepe paper; Aluminum foil; Examples include metal foil such as copper foil. A base material having a composite structure of these materials may also be used. Examples of such composite base materials include base materials having a structure in which metal foil and the above-mentioned plastic film are laminated, and plastic base materials reinforced with inorganic fibers such as glass cloth.

Various film base materials can be preferably used as the base material for the pressure-sensitive adhesive sheet disclosed herein. The film base material may be a porous base material such as a foam film or a non-woven fabric sheet, or a non-porous base material, and may have a porous layer and a non-porous layer. The base material may have a laminated structure. In some embodiments, as the above-mentioned film base material, a base film that includes a (self-supporting or independent) resin film that can maintain its shape independently can be preferably used. Here, the term "resin film" refers to a resin film that has a non-porous structure and typically is substantially void-free. Therefore, the resin film is a concept that is distinguished from foam films and nonwoven fabrics. As the resin film, one that can maintain its shape independently (self-supporting or independent) can be preferably used. The resin film may have a single layer structure or a multilayer structure of two or more layers (for example, a three layer structure).

Examples of resin materials constituting the resin film include polyester, polyolefin, nylon 6, nylon 66, polyamide (PA) such as partially aromatic polyamide, polyimide (PI), polyamideimide (PAI), and polyether ether ketone (PEEK). ), fluororesins such as polyethersulfone (PES), polyphenylene sulfide (PPS), polycarbonate (PC), polyurethane (PU), ethylene-vinyl acetate copolymer (EVA), polytetrafluoroethylene (PTFE), acrylic resin , polyacrylate, polystyrene, polyvinyl chloride, polyvinylidene chloride, and other resins can be used. The resin film may be formed using a resin material containing only one type of such resin, or may be formed using a resin material that is a blend of two or more types. good. The resin film may be unstretched or may be stretched (for example, uniaxially or biaxially stretched).

Suitable examples of resin materials constituting the resin film include polyester resins, PPS resins, and polyolefin resins. Here, the polyester resin refers to a resin containing polyester in a proportion exceeding 50% by weight. Similarly, PPS resin refers to a resin containing PPS in a proportion exceeding 50% by weight, and polyolefin resin refers to a resin containing polyolefin in a proportion exceeding 50% by weight.

As the polyester resin, a polyester resin containing as a main component a polyester obtained by polycondensing a dicarboxylic acid and a diol is typically used. Specific examples of polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate, and the like.

As the polyolefin resin, one type of polyolefin can be used alone or two or more types of polyolefin can be used in combination. The polyolefin may be, for example, a homopolymer of α-olefins, a copolymer of two or more α-olefins, a copolymer of one or more α-olefins and another vinyl monomer, or the like. Specific examples include ethylene-propylene copolymers such as polyethylene (PE), polypropylene (PP), poly-1-butene, poly-4-methyl-1-pentene, and ethylene propylene rubber (EPR); Examples include butene copolymers, ethylene-butene copolymers, ethylene-vinyl alcohol copolymers, ethylene-ethyl acrylate copolymers, and the like. Both low density (LD) and high density (HD) polyolefins can be used. Examples of polyolefin resin films include unoriented polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low density polyethylene (LDPE) film, linear low density polyethylene (LLDPE) film, and medium density polyethylene (MDPE). films, high-density polyethylene (HDPE) films, polyethylene (PE) films that are a blend of two or more types of polyethylene (PE), and PP/PE blend films that are a blend of polypropylene (PP) and polyethylene (PE).

Specific examples of resin films that can be preferably used as the base film of the adhesive sheet disclosed herein include PET film, PEN film, PPS film, PEEK film, CPP film, and OPP film. Examples of base films preferable from the viewpoint of strength and dimensional stability include PET film, PEN film, PPS film, and PEEK film. PET film and PPS film are particularly preferred from the viewpoint of availability of the base material, and PET film is particularly preferred.

The resin film may contain known substances such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, anti-blocking agents, etc., to the extent that the effects of the present invention are not significantly impaired. Additives may be added as necessary. The blending amount of the additive is not particularly limited, and can be appropriately set depending on the use of the pressure-sensitive adhesive sheet.

The method for producing the resin film is not particularly limited. For example, conventionally known general resin film forming methods such as extrusion molding, inflation molding, T-die casting molding, and calender roll molding can be appropriately employed.

The substrate may consist essentially of such a base film. Alternatively, the base material may include an auxiliary layer in addition to the base film. Examples of the above-mentioned auxiliary layers include optical property adjustment layers (e.g., colored layers, antireflection layers), printing layers and laminating layers for imparting a desired appearance to the substrate, antistatic layers, undercoat layers, and release layers. Examples include surface treatment layers such as.

The thickness of the base material is not particularly limited, and can be selected depending on the purpose and manner of use of the pressure-sensitive adhesive sheet. The thickness of the substrate can be, for example, 1000 μm or less. In some embodiments, from the viewpoint of handleability and processability of the adhesive sheet, the thickness of the base material may be, for example, 500 μm or less, 300 μm or less, 250 μm or less, or 200 μm or less. It may be the following. In some embodiments, the thickness of the base material may be, for example, 160 μm or less, 130 μm or less, or 100 μm or less, from the viewpoint of reducing the size and weight of products to which the adhesive sheet is applied. It may be 90 μm or less, 80 μm or less, 60 μm or less, 50 μm or less, 25 μm or less, 10 μm or less, or 5 μm or less. As the thickness of the base material decreases, the flexibility of the adhesive sheet and the ability to follow the surface shape of the adherend tend to improve. Further, from the viewpoint of handleability, processability, etc., the thickness of the base material may be, for example, 2 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, 25 μm or more, or more than 25 μm. In some embodiments, the thickness of the substrate may be, for example, 30 μm or more, 35 μm or more, 55 μm or more, 70 μm or more, 75 μm or more, 90 μm or more, 120 μm or more. . For example, in a pressure-sensitive adhesive sheet that can be used for the purpose of reinforcing, supporting, impact mitigation, etc. of an adherend, a base material having a thickness of 30 μm or more can be preferably employed.

The first surface of the base material may be subjected to conventionally known surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and formation of an undercoat layer by applying an undercoat (primer), as necessary. It may be processed. Such surface treatment improves the anchoring ability of the adhesive layer to the base material (the direct anchoring ability of the adhesive layer laminated directly to the base material, and the ability of other layers such as an elastic intermediate layer to This treatment includes the indirect anchoring ability of the adhesive layer laminated on the substrate via the adhesive layer (the same shall apply hereinafter). For example, in a pressure-sensitive adhesive sheet having a base material containing a resin film as a base film, a base material subjected to such an anchoring property improvement treatment can be preferably employed. The above surface treatments can be applied alone or in combination. The composition of the primer used to form the undercoat layer is not particularly limited, and can be appropriately selected from known primers. The thickness of the undercoat layer is not particularly limited, but it is usually approximately 0.01 μm to 1 μm, preferably approximately 0.1 μm to 1 μm. Other treatments that may be applied to the first surface of the base material as needed include antistatic layer formation treatment, colored layer formation treatment, printing treatment, and the like.

When the adhesive sheet disclosed herein is in the form of a single-sided adhesive sheet having an adhesive layer only on the first side of the base material, the second side of the base material may be subjected to release treatment or antistatic treatment as necessary. A conventionally known surface treatment such as a treatment may be applied. For example, by surface-treating the back side of the base material with a release agent (typically by providing a release layer with a release agent), the unwinding force of the adhesive sheet wound into a roll can be reduced. It can be made lighter. As the release agent, silicone release agent, long chain alkyl release agent, olefin release agent, fluorine release agent, fatty acid amide release agent, molybdenum sulfide, silica powder, etc. can be used. . In addition, treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, and alkali treatment are applied to the second side of the base material for the purpose of improving printability, reducing light reflection, and improving stackability. may have been done. In addition, in the case of a double-sided adhesive sheet, the second side of the base material may be subjected to a surface treatment similar to that exemplified above as a surface treatment that can be applied to the first side of the base material, if necessary. Good too. Note that the surface treatment applied to the first surface of the base material and the surface treatment applied to the second surface may be the same or different.

<Elastic intermediate layer>
The adhesive sheet disclosed herein may include an elastic intermediate layer disposed between the base material and the adhesive layer. This elastic intermediate layer is a layer provided as needed, and does not necessarily need to be provided. By interposing an elastic intermediate layer between the base material and the adhesive layer, the ability of the adhesive layer to anchor to the base material can be improved. For example, when the heat-expandable microspheres in the adhesive layer are expanded by heating to increase the releasability of the adhesive sheet from the adherend, the adhesive force reduction effect due to the expansion is effectively applied to the adherend. It is possible to suitably maintain the form in which the pressure-sensitive adhesive layer is bonded to the support base material via the elastic intermediate layer while exhibiting its effectiveness. Providing the elastic intermediate layer on the back side of the adhesive layer (the side opposite to the side to be attached to the adherend) can also contribute to improving releasability by heating and expanding the thermally expandable microspheres. For example, when the adhesive layer expands with the expansion of the thermally expandable microspheres, the shape of the adhesive layer changes three-dimensionally by reducing the restraint on expansion in the plane direction of the adhesive sheet. It can promote the formation of a structure (for example, the generation of warpage) and promote the peeling (lifting) of the pressure-sensitive adhesive sheet from the adherend. Further, when the pressure-sensitive adhesive sheet is attached to an adherend, the deformability of the elastic intermediate layer can improve the adhesion of the surface of the pressure-sensitive adhesive layer to the surface of the adherend.

In some embodiments, the hardness of the elastic intermediate layer is preferably, for example, 50 or less, more preferably 40 or less, as measured by Type D durometer (Shore D) based on ASTM D-2240.

In some embodiments, an adhesive can be preferably used as the constituent material of the elastic intermediate layer. The adhesive constituting the elastic intermediate layer is not particularly limited, and includes, for example, an acrylic adhesive using an acrylic polymer as a base polymer, a rubber adhesive using a rubber such as natural rubber or synthetic rubber as a base polymer, and vinyl alkyl ether. Known adhesives such as silicone-based adhesives, silicone-based adhesives, polyester-based adhesives, polyamide-based adhesives, urethane-based adhesives, styrene-diene block copolymer-based adhesives, creep property-improved adhesives, radiation-curable adhesives, etc. The adhesive can be appropriately selected from among various adhesives. Furthermore, the adhesive component that can be used in the adhesive layer described above can be preferably employed as a constituent material of the elastic intermediate layer.

When the base polymer of the adhesive used in the elastic intermediate layer (hereinafter also referred to as "Polymer I") is an acrylic polymer, the acrylic polymer may contain, for example, a methyl group, an ethyl group, a propyl group, a butyl group, Alkyl having 20 or less carbon atoms such as 2-ethylhexyl group, isooctyl group, isononyl group, isodecyl group, dodecyl group, lauryl group, tridecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, eicosyl group It may be a polymer of a monomer raw material containing a (meth)acrylic acid alkyl ester having a group as a main monomer (component accounting for 50% by weight or more of the monomer raw material for preparing the above-mentioned acrylic polymer). Monomer raw materials used in the preparation of Polymer I include acrylic acid, methacrylic acid, itaconic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, N-methylolacrylamide, It may further contain one or more submonomers selected from acrylonitrile, methacrylonitrile, glycidyl acrylate, glycidyl methacrylate, vinyl acetate, styrene, isoprene, butadiene, isobutylene, vinyl ether, and the like.

When the base polymer (polymer A) of the adhesive layer containing thermally expandable microspheres is an acrylic polymer, from the viewpoint of affinity between the adhesive layer and the elastic intermediate layer, the base polymer (polymer I) of the elastic intermediate layer An acrylic polymer can be preferably used as the material. Polymer I can be selected from the same acrylic polymers that can be used as polymer A.

The elastic intermediate layer is not limited to one constructed using an adhesive as described above. For example, natural rubber; synthetic rubber such as nitrile, diene, and acrylic resin; thermoplastic elastomer such as polyolefin and polyester; rubber such as ethylene-vinyl acetate copolymer, polyurethane, polybutadiene, and soft polyvinyl chloride. The elastic intermediate layer may be constructed using one or more elastic materials selected from elastic synthetic resins and the like.

The adhesive or the elastic material constituting the elastic intermediate layer includes a crosslinking agent, a tackifier resin, a leveling agent, a plasticizer, a softener, a coloring agent (dye, pigment, etc.), a filler, an antistatic agent, and an antiaging agent. , ultraviolet absorbers, antioxidants, light stabilizers, preservatives, and other known additives may be included as necessary. The crosslinking agent may be appropriately selected from the crosslinking agents exemplified above and used as an optional component of the adhesive layer, for example. The amount of the crosslinking agent used in the elastic intermediate layer can be selected from the range exemplified above as the amount of the crosslinking agent used in the adhesive layer. The above-mentioned tackifying resin can be used, for example, by appropriately selecting from the tackifying resins exemplified above as an optional component of the adhesive layer. The amount of the tackifier resin used in the elastic intermediate layer can be selected from the ranges exemplified above as the amount of the tackifier resin used in the adhesive layer.

In some embodiments, the elastic intermediate layer can be of a composition that does not include or has a limited content of thermally expandable microspheres. In such an embodiment, the weight proportion of the thermally expandable microspheres in the entire elastic intermediate layer is usually suitably less than 5% by weight, preferably less than 1% by weight, and preferably less than 0.5% by weight. It is more preferable that For example, an elastic intermediate layer that does not contain thermally expandable microspheres may be preferably employed.

The method of forming the elastic intermediate layer is not particularly limited, and examples include a method of applying a coating liquid containing an elastic intermediate layer forming material to a base material (coating method), a method of adhering a film made of an elastic intermediate layer forming material to a base material, or a method of applying a coating liquid containing an elastic intermediate layer forming material to a base material. , or a method in which a laminated film in which a layer made of an elastic intermediate layer-forming material is formed on the back surface of the adhesive layer (the surface opposite to the surface to be affixed to the adherend) is adhered to the base material (dry lamination method); An appropriate method may be employed, such as a method of coextruding the base material forming material and the elastic intermediate layer forming material (coextrusion method).

The elastic intermediate layer may be composed of a foamed film (eg, polyethylene foam, polyurethane foam, etc.). Foaming can be carried out by conventional methods, such as mechanical stirring, using reaction product gas, using a blowing agent, removing soluble substances, spraying, forming syntactic foam, This can be done by a sintering method, etc.

The thickness of the elastic intermediate layer is not particularly limited, and can be set so that the desired effect can be achieved by providing the elastic intermediate layer. The thickness of the elastic intermediate layer can be, for example, 0.1 μm or more, 1 μm or more, or 5 μm or more. From the viewpoint of better demonstrating the effect of providing the elastic intermediate layer, it is appropriate that the thickness of the elastic intermediate layer is usually 10 μm or more, and from the viewpoint of reducing the restriction of expansion in the plane direction of the pressure-sensitive adhesive sheet. Advantageously, it is greater than or equal to 25 μm, for example greater than or equal to 50 μm, greater than or equal to 75 μm, greater than or equal to 100 μm, greater than or equal to 100 μm, greater than or equal to 125 μm, or greater than or equal to 150 μm. In addition, from the viewpoint of handling and processability of the adhesive sheet, the thickness of the elastic intermediate layer is usually suitably 1000 μm or less, preferably 500 μm or less, 300 μm or less, and even 200 μm or less. good.

The elastic intermediate layer may have a single layer structure or a multilayer structure including two or more sublayers. The thickness of each sublayer may be, for example, 0.1 μm or more, usually suitably 5 μm or more, 10 μm or more, 25 μm or more, 40 μm or more, or 60 μm or more. Further, the thickness of each sublayer may be, for example, 300 μm or less, preferably 200 μm or less, and more preferably 100 μm or less from the viewpoint of suppressing cohesive failure of the elastic intermediate layer.

The elastic intermediate layer of the multilayer structure may have support sheets between adjacent sublayers. The support sheet can be useful for suppressing cohesive failure of the elastic intermediate layer, improving workability of the pressure-sensitive adhesive sheet, and the like. For example, if the elastic intermediate layer is relatively thick (e.g. 50 μm or more, 100 μm or more or 125 μm or more thick), a multilayer elastic intermediate layer comprising at least one support sheet between the sub-layers is preferably employed. obtain. Similar to the support base material described above, the support sheet can be appropriately selected from various plastic films, foam sheets, woven fabrics, non-woven fabrics, papers, metal foils, sheets with a composite structure of these, etc. . Examples of support sheets that can be preferably employed include nonwoven fabrics and plastic films. The thickness of the nonwoven fabric may be, for example, 10 μm or more, 20 μm or more, 50 μm or more, and usually suitably 120 μm or less, 100 μm or less, or 80 μm or less. The thickness of the above plastic film is usually suitably 20 μm or less, preferably 15 μm or less from the viewpoint of flexibility of the elastic intermediate layer, 10 μm or less, 5 μm or less, and usually is suitably 2 μm or more.

<Adhesive sheet with base material>
When the adhesive sheet disclosed herein is in the form of an adhesive sheet with a base material, the thickness of the adhesive sheet may be, for example, 1000 μm or less, 600 μm or less, 350 μm or less, or 300 μm or less. The thickness may be 250 μm or less. In some embodiments, the thickness of the adhesive sheet may be, for example, 200 μm or less, or 175 μm or less, from the viewpoint of reducing the size, weight, and thickness of products to which the adhesive sheet is applied. The thickness may be 140 μm or less, 120 μm or less, or 100 μm or less (for example, less than 100 μm). In addition, from the viewpoint of handleability, the thickness of the adhesive sheet may be, for example, 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, or 30 μm or more. In some embodiments, the thickness of the adhesive sheet may be, for example, 50 μm or more, 60 μm or more, 80 μm or more, 100 μm or more, 120 μm or more, 150 μm or more, or 200 μm or more. . The upper limit of the thickness of the adhesive sheet is not particularly limited.
Note that the thickness of the adhesive sheet refers to the thickness of the portion to be attached to the adherend. For example, in the adhesive sheet 1 having the configuration shown in FIG. 1, the thickness refers to the thickness from the adhesive surface 21A of the adhesive sheet 1 to the second surface 10B of the base material 10, and does not include the thickness of the release liner 31.

The pressure-sensitive adhesive sheet disclosed herein can be suitably implemented, for example, in an embodiment in which the thickness Ts of the supporting base material is greater than the thickness Ta of the adhesive layer, that is, in an embodiment in which Ts/Ta is greater than 1. Although not particularly limited, Ts/Ta may be, for example, 1.1 or more, 1.2 or more, 1.5 or more, or 1.7 or more. Good too. For example, in a pressure-sensitive adhesive sheet that can be used for the purpose of reinforcing, supporting, impact mitigation, etc. of an adherend, an increase in Ts/Ta tends to make the pressure-sensitive adhesive sheet more effective even if it is made thinner. In some embodiments, Ts/Ta may be 2 or more (eg, greater than 2), 2.5 or more, or 2.8 or more. Further, Ts/Ta may be, for example, 50 or less, or 20 or less. From the viewpoint of easily exhibiting high adhesive strength after heating even if the pressure-sensitive adhesive sheet is made thinner, Ts/Ta may be, for example, 10 or less, 8 or less, or 5 or less.

It is preferable that the adhesive layer is adhered to the supporting base material directly or via an elastic intermediate layer. Here, adhesion refers to an adhesive sheet whose adhesive strength has increased after being applied to an adherend, and the adhesive layer is fixed to such an extent that the adhesive layer does not separate from the supporting substrate when the adhesive sheet is peeled from the adherend. This refers to exhibiting sufficient anchoring ability (anchoring ability may be achieved through an elastic intermediate layer) with respect to the supporting base material. According to the adhesive sheet with a base material in which the adhesive layer is adhered to the support base material, the adherend and the support base material can be firmly integrated. A suitable example of a pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer is adhered to a base material is an adhesive that does not cause peeling (anchor failure) between the pressure-sensitive adhesive layer and the supporting base material during the above-mentioned measurement of adhesive strength after heating. Examples include sheets. An adhesive sheet having an adhesive force of 10 N/20 mm or more after heating and which does not cause anchoring failure when measuring the adhesive force after heating is a suitable example of an adhesive sheet whose adhesive layer is adhered to a base material. It is.

A pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer is directly adhered to a supporting substrate can be obtained by, for example, contacting a liquid pressure-sensitive adhesive composition with the first surface of the substrate, and applying the pressure-sensitive adhesive composition on the first surface. It can be preferably manufactured by a method including, in this order, curing to form an adhesive layer. Curing of the pressure-sensitive adhesive composition may involve one or more of drying, crosslinking, polymerization, cooling, etc. of the pressure-sensitive adhesive composition. According to this method of forming an adhesive layer by curing a liquid adhesive composition on the first surface of a substrate, the adhesive layer after curing is bonded to the first surface of the substrate. Compared to the method of arranging the adhesive layer on the first surface, the anchoring ability of the adhesive layer to the base material can be improved. Utilizing this fact, it is possible to suitably produce a pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer is fixed to a base material.

In some embodiments, as a method of bringing the liquid adhesive composition into contact with the first surface of the substrate, a method of directly applying the above-mentioned adhesive composition onto the first surface of the substrate can be adopted. By bringing the first surface (adhesive surface) of the adhesive layer cured on the first surface of the substrate into contact with the release surface, the second surface of the adhesive layer is fixed to the first surface of the substrate. A pressure-sensitive adhesive sheet can be obtained in which the first surface of the pressure-sensitive adhesive layer is in contact with the release surface. As the release surface, the surface of a release liner, the back surface of a release-treated base material, etc. can be used.

In addition, for example, in the case of a photocurable adhesive composition using a partial polymer of a monomer raw material (polymer syrup), for example, after applying the adhesive composition to a release surface, the applied adhesive composition may be The uncured adhesive composition is brought into contact with the first surface of the substrate by covering the object with the first surface of the substrate, and in that state, the object is sandwiched between the first surface of the substrate and the release surface. The adhesive layer may be formed by curing the adhesive composition by irradiating it with light.

Note that the method exemplified above does not limit the method for manufacturing the pressure-sensitive adhesive sheet disclosed herein. In producing the pressure-sensitive adhesive sheet disclosed herein, any suitable method capable of adhering the pressure-sensitive adhesive layer to the first surface of the base material can be used alone or in combination of two or more. Examples of such methods include forming an adhesive layer by curing a liquid adhesive composition on the first surface of the substrate, as described above, and forming an adhesive layer on the first surface of the substrate. Examples include a method of performing a surface treatment to improve the anchoring property of the base material, a method of providing an undercoat layer on the first surface of the base material, a method of interposing an elastic intermediate layer between the first surface of the base material and the adhesive layer, etc. For example, there are methods for attaching a cured adhesive layer to the first surface of a base material that has been surface-treated to improve anchoring properties, and methods for attaching a cured adhesive layer to an elastic intermediate layer provided on the first surface of the base material. The pressure-sensitive adhesive sheet may be manufactured by a method such as bonding adhesive layers together. Furthermore, the anchoring ability of the adhesive layer to the base material can be improved by selecting the material of the base material and the composition of the adhesive. Further, by applying a temperature higher than room temperature to a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on the first surface of the base material, anchoring ability of the pressure-sensitive adhesive layer to the base material can be enhanced. The temperature applied to improve the anchoring property is selected from a temperature lower than the expansion start temperature T1 of the thermally expandable microspheres (preferably 5°C or more, more preferably 10°C or more lower), for example, 35°C to 80°C. The temperature may be about 40°C to 70°C, or about 45°C to 60°C.

The adhesive sheet disclosed herein has a first adhesive layer provided on the first surface side of a base material and a second adhesive layer provided on the second surface side of the base material (i.e. , a double-sided adhesive adhesive sheet with a base material), the first adhesive layer and the second adhesive layer may have the same configuration or may have different configurations. When the configurations of the first adhesive layer and the second adhesive layer are different, the difference may be, for example, a difference in composition or a difference in structure (thickness, surface roughness, formation range, formation pattern, etc.). For example, the second adhesive layer may be a layer that does not have a function of facilitating re-peeling, for example, it may be an adhesive layer that does not contain thermally expandable microspheres. Further, the surface of the second adhesive layer (second adhesive surface) may be a surface that is not intended to achieve both low initial adhesiveness and strong adhesiveness during use.

<Adhesive sheet with release liner>
The adhesive sheet disclosed herein can take the form of an adhesive product in which the surface (adhesive surface) of an adhesive layer is brought into contact with the release surface of a release liner. Therefore, this specification provides a pressure-sensitive adhesive sheet with a release liner (adhesive product) that includes any pressure-sensitive adhesive sheet disclosed herein and a release liner having a release surface that comes into contact with the pressure-sensitive adhesive surface of the pressure-sensitive adhesive sheet. obtain.

The thickness of the release liner is not particularly limited, but is usually approximately 5 μm to 200 μm. It is preferable that the thickness of the release liner is within the above range because it provides excellent lamination workability to the adhesive layer and excellent peeling workability from the adhesive layer. In some embodiments, the thickness of the release liner can be, for example, 10 μm or more, 20 μm or more, 30 μm or more, 40 μm or more. Further, the thickness of the release liner may be, for example, 100 μm or less, or 80 μm or less, from the viewpoint of facilitating peeling from the adhesive layer. The release liner may be subjected to a known antistatic treatment, such as a coating type, kneading type, vapor deposition type, etc., as necessary.

The release liner is not particularly limited, and includes, for example, a release liner having a release layer on the surface of a liner base material such as a resin film or paper (paper laminated with a resin such as polyethylene), or a fluorine-based polymer. A release liner made of a resin film made of a low adhesive material such as (polytetrafluoroethylene, etc.) or polyolefin resin (polyethylene, polypropylene, etc.) can be used. Since they have excellent surface smoothness, a release liner having a release layer on the surface of a resin film as a liner base material or a release liner made of a resin film made of a low adhesive material can be preferably employed. The resin film is not particularly limited as long as it can protect the adhesive layer, and examples include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, and vinyl chloride copolymer. Film, polyester film (PET film, PBT film, etc.), polyurethane film, ethylene-vinyl acetate copolymer film, and the like. For forming the above-mentioned release layer, for example, a silicone-based release agent, a long-chain alkyl-based release agent, an olefin-based release agent, a fluorine-based release agent, a fatty acid amide-based release agent, molybdenum sulfide, silica powder, etc. , a known release agent can be used. Particularly preferred is the use of silicone release agents.

The thickness of the release layer is not particularly limited, but it is usually about 0.01 μm to 1 μm, preferably about 0.1 μm to 1 μm. The method for forming the release layer is not particularly limited, and any known method can be appropriately employed depending on the type of release treatment agent used.

<Application>
The adhesive sheet provided in this specification can exhibit good reworkability, for example, in the initial stage of bonding to an adherend, thereby suppressing yield loss and improving the quality of products containing the adhesive sheet. can contribute to The adhesive strength of the adhesive sheet can be greatly increased by aging (which may include heating at a temperature lower than the expansion start temperature T1, aging, a combination thereof, etc.). For example, by heating at a desired timing, the adhesive sheet can be firmly adhered to an adherend. Furthermore, by heating the adhesive sheet to a temperature equal to or higher than the expansion start temperature T1, the thermally expandable microspheres are expanded to improve releasability from the adherend, and the adhesive sheet can be easily peeled from the adherend. can. Taking advantage of these characteristics, the adhesive sheet disclosed herein can be used in various fields for the purpose of fixing, joining, molding, decorating, protecting, reinforcing, supporting, impact mitigation, etc. of components included in various products. It is preferable as an adhesive sheet that can be easily re-peeled from the above-mentioned member by heating it to a temperature equal to or higher than the expansion start temperature T1 if desired (for example, when repairing the member or recovering the member when disposing of the product). can be used. Therefore, the adhesive sheet disclosed herein can be useful for improving convenience in repairing products, etc., and improving recyclability of members included in products. Further, the adhesive sheet disclosed herein can have initial reworkability, strong adhesiveness after increasing adhesive strength, and removability when heated to a temperature equal to or higher than the expansion start temperature T1. Therefore, it is also useful as a highly reliable temporary fixing means.

The adhesive sheet disclosed herein is, for example, in the form of a base-attached adhesive sheet in which an adhesive layer is provided on at least the first side of a film-like base material having a first surface and a second surface. It can be preferably used as a reinforcing film that is attached to an adherend to reinforce the adherend. In such a reinforcing film, as the film base material, one containing a resin film as a base film can be preferably used. Moreover, from the viewpoint of improving reinforcing performance, it is preferable that the adhesive layer is fixed to the first surface of the film-like base material.
For example, optical components used in optical products and electronic components used in electronic products are becoming highly integrated, smaller, lighter, and thinner. Electronic components may be stacked. By attaching the reinforcing film as described above to such a member, appropriate rigidity can be imparted to the optical member/electronic member. Thereby, in the manufacturing process and/or the manufactured product, it is possible to suppress curls and curvatures caused by stress that may occur between the plurality of members having different linear expansion coefficients and thicknesses.
In addition, in the manufacturing process of optical products/electronic products, when shape processing such as cutting is performed on thin optical/electronic components as described above, it is possible to process the thin optical/electronic components by attaching a reinforcing film to the components. It is possible to alleviate the local stress concentration on the optical member/electronic member accompanying this, and reduce the risk of cracks, cracks, peeling of the laminated member, etc. Attaching reinforcing members to optical/electronic components when handling them helps alleviate local stress concentration during transportation, stacking, rotation, etc. of the components, and suppresses bending or bending due to the component's own weight. It can be helpful.
Furthermore, devices such as optical products and electronic products that contain the above-mentioned reinforcing film may be dropped, placed under a heavy object, or collided with flying objects while being used by consumers in the market. Even when unintentional stress is applied, such as in cases where the device is unintentionally applied, the stress applied to the device can be alleviated by including the reinforcing film in the device. Therefore, by including a reinforcing film in the device, the durability of the device can be improved.

In addition, the pressure-sensitive adhesive sheet disclosed herein can be preferably used, for example, in a manner in which it is attached to members constituting various types of mobile devices (portable devices). Here, "portable" does not mean that it is sufficient to simply be able to carry it, but it also means that it has a level of portability that allows an individual (standard adult) to carry it relatively easily. do. Examples of mobile devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices, digital cameras, digital video cameras, audio devices (portable music players, IC recorders, etc.), and calculators ( Calculators, etc.), portable game devices, electronic dictionaries, electronic notebooks, electronic books, in-vehicle information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, and other portable electronic devices, as well as mechanical watches and pocket pockets. May include watches, flashlights, hand mirrors, etc. Examples of the members constituting the portable electronic device may include optical films and display panels used in image display devices such as thin-layer displays such as liquid crystal displays and film-type displays. The adhesive sheet disclosed herein can also be preferably used in a mode where it is attached to various members in automobiles, home appliances, etc.

Hereinafter, some examples related to the present invention will be described, but the present invention is not intended to be limited to what is shown in these specific examples. Note that "parts" and "%" in the following description are based on weight unless otherwise specified.

<Preparation of Polymer A>
(Polymer A1)
In a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, and condenser, 100 parts of n-butyl acrylate (BA), 5 parts of vinyl acetate (VAc), 3 parts of acrylic acid (AA), and 2-hydroxyethyl acrylate. (HEA) 0.1 part, 2,2'-azobisisobutyronitrile (AIBN) 0.3 part as a polymerization initiator, and toluene as a polymerization solvent were charged, and the reaction was carried out at 60°C for 6 hours to form a polymer. A solution of A1 was obtained. The weight average molecular weight (Mw) of Polymer A1 was 55×10 ⁴ .

(Polymer A2)
In a reaction vessel equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a cooler, 60 parts of 2-ethylhexyl acrylate (2EHA), 15 parts of N-vinyl-2-pyrrolidone (NVP), and 10 parts of methyl methacrylate (MMA) were added. , 15 parts of HEA, 0.2 parts of AIBN, and 200 parts of ethyl acetate as a polymerization solvent were charged, and the reaction was carried out at 60° C. for 6 hours to obtain a solution of polymer A2. The Mw of Polymer A2 was 110×10 ⁴ .

(Polymer A3)
100 parts of 2EHA, 2 parts of AA, 0.2 parts of AIBN, and 200 parts by mass of ethyl acetate as a polymerization solvent were charged into a reaction vessel equipped with a stirring blade, a thermometer, a nitrogen gas introduction tube, and a cooler, and the reaction was carried out at 60°C for 6 hours. A solution of polymer A3 was obtained. Mw of polymer A3 was 110×10 ⁴ .

<Preparation of Polymer B>
(Polymer B1)
In a reaction vessel equipped with a stirring blade, a thermometer, a nitrogen gas introduction pipe, and a condenser, 60 parts of MMA, 10 parts of n-butyl methacrylate (BMA), 10 parts of 2-ethylhexyl methacrylate (2EHMA), and a functional group equivalent of 900 g/mol. 8.7 parts of a polyorganosiloxane skeleton-containing methacrylate monomer (trade name: X-22-174ASX, manufactured by Shin-Etsu Chemical Co., Ltd.), a polyorganosiloxane skeleton-containing methacrylate monomer (trade name: KF -2012, manufactured by Shin-Etsu Chemical Co., Ltd.), 100 parts of ethyl acetate, and 0.8 parts of α-thioglycerol as a chain transfer agent, and stirred at 70°C for 1 hour under a nitrogen atmosphere. , 0.2 part of AIBN was added, and the reaction was carried out at 70°C for 2 hours. Then, 0.1 part by weight of AIBN was added, and then the reaction was carried out at 80°C for 5 hours. In this way, a solution of polymer B1 was obtained. Mw of polymer B1 was 2.0×10 ⁴ .

(Polymer B2)
The composition of the monomer components was 40 parts of MMA, 20 parts of BMA, 20 parts of 2EHMA, 8.7 parts of a polyorganosiloxane skeleton-containing methacrylate monomer (X-22-174ASX) with a functional group equivalent of 900 g/mol, and Polymer B2 was prepared in the same manner as in the preparation of Polymer B1, except that 11.3 parts of an organosiloxane skeleton-containing methacrylate monomer (KF-2012) was used. The Mw of polymer B2 was 2.2×10 ⁴ .

The weight average molecular weight of each of the above-mentioned polymers was measured using a GPC device (manufactured by Tosoh Corporation, HLC-8220GPC) under the following conditions, and was determined in terms of polystyrene.
[GPC conditions]
・Sample concentration: 0.2wt% (tetrahydrofuran (THF) solution)
・Sample injection volume: 10μL
・Eluent: THF ・Flow rate: 0.6mL/min
・Measurement temperature: 40℃
·column:
Sample column; TSKguardcolumn SuperHZ-H (1 column) + TSKgel SuperHZM-H (2 columns)
Reference column; TSKgel SuperH-RC (1 column)
・Detector: Differential refractometer (RI)

<Preparation of elastic intermediate layer>
(Elastic intermediate layer F1)
In a solution of polymer A1, 40 parts of tackifier resin and isocyanate crosslinking agent X1 (manufactured by Tosoh Corporation, trade name "Coronate L", trimethylolpropane/tolylene diisocyanate) are added to 100 parts of acrylic polymer contained in the solution. 2 parts of a 75% ethyl acetate solution of the trimer adduct were added and mixed with stirring to prepare an adhesive composition f1 for forming an elastic intermediate layer. The above-mentioned tackifier resin includes 10 parts of polymerized rosin ester with a softening point of about 125°C (product name "Haritac PCJ", manufactured by Harima Kasei Co., Ltd.), stabilized rosin ester with a softening point of about 80°C (product name "Haritac SE10", Harima Chemicals Co., Ltd.) 10 parts, hydrogenated rosin methyl ester (trade name "M-HDR", Guangxi Wuzhou Nisei Forest Products Co., Ltd., liquid), 5 parts, and terpene phenol resin with a softening point of about 133°C (product 15 parts of Sumilite Resin PR-12603 (manufactured by Sumitomo Bakelite Co., Ltd.) were used.

Two polyester release films were prepared, one side of which was treated with a silicone release agent. The pressure-sensitive adhesive composition f1 was applied to the release surfaces of these release films and dried to form pressure-sensitive adhesive layers of the same thickness on each release film. These adhesive layers were pasted on the first and second sides of a 75 μm thick nonwoven fabric (nonwoven fabric made of 99% Manila hemp mixed with 1% vinylon, density 0.30g/cm ³ ), and the A double-sided pressure-sensitive adhesive sheet with a base material having a total thickness of 160 μm and having pressure-sensitive adhesive layers on both sides was produced. This double-sided adhesive sheet was used as the elastic intermediate layer F1.

(Elastic intermediate layer F2)
To a solution of polymer A2, 2.5 parts of isocyanate crosslinking agent X2 (manufactured by Mitsui Chemicals, trade name: Takenate D110N, trimethylolpropane xylylene diisocyanate) is added to 100 parts of acrylic polymer contained in the solution, By stirring and mixing, an adhesive composition f2 for forming an elastic intermediate layer was prepared.
The pressure-sensitive adhesive composition f2 was applied to the release surface of a polyester release film, one side of which was treated with a silicone release treatment agent, and dried to produce a substrate-less double-sided pressure-sensitive adhesive sheet with a thickness of 30 μm. This base material-less double-sided adhesive sheet was used as the elastic intermediate layer F2.

<Preparation of adhesive sheet>
(Example 1)
In a solution of polymer A1, per 100 parts of polymer A1 contained in the solution, 5 parts of polymer B1, 5 parts of isocyanate crosslinking agent X1 (Coronate L) on a solid basis, thermally expandable microspheres C1 (Matsumoto 100 parts of Matsumoto Microsphere F-501D (trade name, manufactured by Yakuhin Co., Ltd., expansion start temperature 120° C., average particle diameter 10 μm) were added and mixed uniformly to prepare adhesive composition D1.
The above adhesive composition D1 was applied to the release surface of release liner R1 (manufactured by Mitsubishi Chemical Corporation, MRQ25T100, thickness 25 μm), in which one side of the polyester film was a release surface treated with a silicone release treatment agent, and the pressure-sensitive adhesive composition D1 was applied at 70°C for 50 minutes. It was dried for a minute to form a thermally expandable adhesive layer E1 having a thickness of 40 μm.
One adhesive surface of the elastic intermediate layer F1 was bonded to the first surface of a 50 μm thick polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc., trade name "Lumirror") as a supporting base material. Next, a thermally expandable adhesive layer E1 was bonded to the other adhesive surface of the elastic intermediate layer F1. In this way, the pressure-sensitive adhesive sheet according to Example 1 was obtained in the form of a pressure-sensitive adhesive sheet with a release liner in which the release surface of the release liner R1 was in contact with the pressure-sensitive adhesive surface.

(Example 2)
In a solution of polymer A1, per 100 parts of polymer A1 contained in the solution, 5 parts of polymer B2, 5 parts of isocyanate crosslinking agent X1 (Coronate L) on a solid basis, thermally expandable microspheres C2 (Matsumoto 100 parts of Matsumoto Microsphere F-100VSD (trade name, manufactured by Yakuhin Co., Ltd., expansion start temperature 170° C., average particle diameter 10 μm) were added and mixed uniformly to prepare adhesive composition D2.
A pressure-sensitive adhesive sheet according to Example 2 was produced in the same manner as in Example 1 except that pressure-sensitive adhesive composition D2 was used instead of pressure-sensitive adhesive composition D1.

(Example 3)
In a solution of polymer A2, per 100 parts of polymer A2 contained in the solution, 2.5 parts of polymer B2, 2.5 parts of isocyanate crosslinking agent X2 (Takenate D110N) on a solid content basis, and thermally expandable microspheres. 50 parts of C1 (Matsumoto Microspheres F-501D) were added and mixed uniformly to prepare adhesive composition D3.
A pressure-sensitive adhesive sheet according to Example 3 was produced in the same manner as in Example 1 except that pressure-sensitive adhesive composition D3 was used instead of pressure-sensitive adhesive composition D1.

(Example 4)
In a solution of polymer A3, per 100 parts of polymer A3 contained in the solution, 2.5 parts of polymer B1, 2 parts of isocyanate crosslinking agent X1 (Coronate L) on a solid basis, and thermally expandable microspheres C3 ( 30 parts of Matsumoto Microsphere F-301SD (trade name, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., expansion start temperature 90°C, average particle diameter 15 μm) were added and mixed uniformly to prepare adhesive composition D4.
A pressure-sensitive adhesive sheet according to Example 4 was produced in the same manner as in Example 1, except that pressure-sensitive adhesive composition D4 was used instead of pressure-sensitive adhesive composition D1, and elastic intermediate layer F2 was used instead of elastic middle layer F1. did.

<Measurement and evaluation>
(Storage modulus G'(T1))
The storage modulus G' (T1) of the polymer A1 contained in the adhesive layer of the adhesive sheet according to Example 1 was determined by dynamic viscoelasticity measurement. Specifically, an adhesive layer was formed under basically the same conditions as in Example 1 except that the adhesive composition was applied to the release surface of a release liner instead of a PET film, and the thickness was increased by stacking multiple adhesive layers. An adhesive layer having a thickness of about 2 mm was formed. A measurement sample prepared by punching out this adhesive layer into a disk shape with a diameter of 7.9 mm was sandwiched and fixed between parallel plates, and then tested using a viscoelasticity tester (ARES, manufactured by TA Instruments) under the following conditions. Dynamic viscoelasticity measurement was performed to determine the storage modulus G' at the expansion start temperature T1 (ie, 120° C.) of the thermally expandable microspheres C1.
・Measurement mode: Shear mode ・Temperature range: -50℃~200℃
・Heating rate: 5℃/min
・Measurement frequency: 1Hz

Similarly, the storage elastic modulus G' at the expansion start temperature T1 of the thermally expandable microspheres contained in the adhesive layer was determined for Polymer A contained in the adhesive layer according to Examples 2 to 4.

(Measurement of adhesive force N1)
A test piece was prepared by cutting the pressure-sensitive adhesive sheet according to each example into a width of 20 mm together with the release liner.
Under a standard environment of 23°C and 50% RH, the release liner covering the adhesive surface of the test piece was peeled off, and the exposed adhesive surface was attached to a stainless steel plate (SUS304BA plate) as an adherend by moving a 2 kg roller back and forth once. I crimped it. After leaving this in the above standard environment for 30 minutes, using a universal tension compression testing machine (device name: "Tension Compression Testing Machine, TCM-1kNB" manufactured by Minebea), the peeling angle was 180 degrees according to JIS Z0237. The 180° peeling adhesive strength (resistance to the above-mentioned tension) was measured at a tension speed of 300 mm/min. The measurement was performed three times, and the average value thereof is shown in Table 1 as the initial adhesive strength (N1) [N/20 mm].

(Measurement of adhesive force N2)
A test piece pressure-bonded to an adherend in the same manner as in the measurement of the adhesive force N1 above was heated at a temperature 20°C lower than the expansion start temperature T1 of the thermally expandable microspheres contained in the adhesive layer of the test piece (heat treatment temperature T2). ) for 5 minutes, and then left in the above standard environment for 30 minutes, and then 180° peeling and adhesive strength was measured in the same manner. The measurement was performed three times, and the average value thereof is shown in Table 1 as the adhesive strength after heating (N2) [N/20 mm].

(Evaluation of peelability at expansion start temperature T1)
A test piece crimped onto an adherend in the same manner as in the measurement of adhesive strength N1 above was heated at a heat treatment temperature T2 for 5 minutes, left in the above standard environment for 30 minutes, and then heated at an expansion start temperature T1 for 5 minutes. After leaving it for 30 minutes under the above standard environment, the adhesive strength was measured in the same manner when peeled off at 180°. The measurement was performed three times, and the average value thereof was taken as the adhesive force after expansion treatment (N3). Based on the obtained results, the releasability was evaluated in the following three stages. The results are shown in Table 1. In addition, when the pressure-sensitive adhesive sheets of Examples 1 to 3 are heated for 5 minutes at the expansion start temperature T1, the majority of the test piece from both sides in the width direction to the vicinity of the width center peels off from the adherend and lifts up. was extremely easily peeled off from the adherend.
E: Adhesive force after expansion treatment is less than 0.5 N/20 mm (excellent releasability)
G: Adhesive force after expansion treatment is 0.5 N/20 mm or more and less than 1.0 N/20 mm (good releasability)
P: Adhesive force after expansion treatment is 1.0 N/20 mm or more (poor releasability)

As shown in Table 1, the adhesive sheets according to Examples 1 to 3 all have an adhesive force increase ratio (N2/N1) of 3.0 or more, and have a temperature sufficiently lower than the expansion start temperature T1 (heat treatment temperature T2 ) The initial adhesive strength was significantly increased by heating for 5 minutes. Further, the adhesive sheets of Examples 1 to 3 were able to be easily peeled off from the adherend by heating at the expansion start temperature T1 after increasing the adhesive strength by heating at the heat treatment temperature T2.

Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The techniques described in the claims include various modifications and changes to the specific examples illustrated above.

1, 2, 3 Adhesive sheet 10 Support base material 10A First surface 10B Second surface 21 Adhesive layer (first adhesive layer)
21A Adhesive surface (first adhesive surface)
21B Adhesive surface (second adhesive surface)
22 Adhesive layer (second adhesive layer)
22A Adhesive surface (second adhesive surface)
31, 32 Release liner 50 Elastic intermediate layer 100, 200, 300 Adhesive sheet with release liner (adhesive product)

Claims (8)

An adhesive sheet including an adhesive layer,
The adhesive layer includes polymer A as a base polymer and thermally expandable microspheres having an expansion start temperature T1,
The polymer A is an acrylic polymer,
The glass transition temperature _TgA calculated by the Fox formula based on the composition of the monomer components constituting the polymer A is -65°C or more and less than 0°C,
The adhesive layer further includes polymer B,
The polymer B is a copolymer of a monomer having a polyorganosiloxane skeleton and a (meth)acrylic monomer,
The adhesive force N2 is measured at 23°C after being attached to a stainless steel plate and heated at a temperature 20°C lower than the expansion start temperature T1 for 5 minutes, and the adhesive force N2 is measured after being attached to a stainless steel plate and held at 23°C for 30 minutes. An adhesive sheet having an adhesive force of 3.0 times or more as adhesive force N1. The pressure-sensitive adhesive sheet according to claim 1, wherein the polymer A has a storage modulus G' of 1×10 ⁴ Pa to 1×10 ⁶ Pa at the expansion start temperature T1. The adhesive sheet according to claim 1 or 2, wherein the adhesive layer contains 10 parts by weight or more and 200 parts by weight or less of the thermally expandable microspheres based on 100 parts by weight of the polymer A. The polymer B according to any one of claims 1 to 3 , wherein the glass transition temperature _TgB calculated by the Fox formula based on the composition of the (meth)acrylic monomer is 30°C or more and 120°C or less. Adhesive sheet as described. The adhesive sheet according to claim 4 , wherein the glass transition temperature _TgB is 20°C or more lower than the expansion start temperature T1. The pressure-sensitive adhesive sheet according to any one of claims 1 to 5 , wherein the content of the polymer B in the pressure-sensitive adhesive layer is from 0.5 parts by weight to 40 parts by weight based on 100 parts by weight of the polymer A. The adhesive layer according to any one of claims 1 to 6 , comprising a support base material having a first surface and a second surface, and the adhesive layer is laminated on at least the first surface side of the support base material. adhesive sheet. The pressure-sensitive adhesive sheet according to claim 7 , wherein an elastic intermediate layer is disposed between the pressure-sensitive adhesive layer and the first surface of the support base material.

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