JP2015120877A - Double-sided adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double-sided adhesive sheet excellent in workability.SOLUTION: The double-sided adhesive sheet is provided which includes a foam substrate, a first adhesive layer provided on a first surface of the foam substrate, and a second adhesive layer provided on a second surface of the foam substrate. The foam substrate has an expansion ratio of 2.0 cm/g or less. An adhesive constituting at least one of the first adhesive layer and the second adhesive layer has a peak top temperature of loss tangent tanδ of -30°C or higher.

Description

  The present invention relates to a double-sided pressure-sensitive adhesive sheet provided with a foam substrate.

  In general, a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive; the same shall apply hereinafter) is in the form of a soft solid (viscoelastic body) in a temperature range near room temperature and has a property of easily adhering to an adherend by pressure. Taking advantage of such properties, the pressure-sensitive adhesive is, for example, in the form of a double-sided pressure-sensitive adhesive sheet with a base material provided with a pressure-sensitive adhesive layer on both surfaces of the base material, and is widely used for the purpose of bonding and fixing in various fields. .

  Generally as a base material in the said double-sided adhesive sheet with a base material, the foam etc. which have a bubble structure other than a plastic film, a nonwoven fabric, paper, etc. can be used. The double-sided pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet with a foam base material) using the above-mentioned foam has points such as impact absorbability and unevenness followability as compared with a double-sided pressure-sensitive adhesive sheet based on a plastic film having no cell structure. Can be advantageous. Moreover, compared with the double-sided adhesive sheet which uses a nonwoven fabric as a base material, it can become advantageous at points, such as waterproofness and a sealing performance. For this reason, for example, the present invention can be preferably applied to joining and fixing of components in portable electronic devices such as mobile phones, smartphones, tablet computers, and notebook computers. Patent documents 1-3 are mentioned as technical literature about a double-sided adhesive sheet with a foam substrate.

JP 2010-155969 A International Publication No. 2013/099755 International Publication No. 2013/141167

  By the way, the double-sided pressure-sensitive adhesive sheet with a foam base material is appropriately sized by being cut along the thickness direction of the double-sided pressure-sensitive adhesive sheet, typically using an appropriate cutting means (for example, Thomson blade). Or it may be processed into a shape. At this time, in the double-sided pressure-sensitive adhesive sheet that has been subjected to the cutting process, the other part of the pressure-sensitive adhesive sheet from which the pressure-sensitive adhesive in the cutting region (for example, the cut end face) has been separated by cutting (typically, the other part formed by cutting). There may be a phenomenon (re-adhesion of the adhesive) that adheres again by contact with the cut end face. The re-adhesion of the pressure-sensitive adhesive can cause an increase in resistance and occurrence of defects in a process of picking up a part of the double-sided pressure-sensitive adhesive sheet after the cutting process, and can cause a decrease in workability.

  In recent years, from the viewpoint of miniaturization and weight reduction of products, it has been required to reduce the width of a double-sided pressure-sensitive adhesive sheet used for joining parts, etc., and high accuracy is required for cutting the double-sided pressure-sensitive adhesive sheet. . This invention is made | formed in view of this situation, and it aims at providing the double-sided adhesive sheet excellent in workability.

The double-sided pressure-sensitive adhesive sheet disclosed herein includes a foam base material, a first pressure-sensitive adhesive layer provided on the first surface of the foam base material, and a second surface provided on the second surface of the foam base material. And two adhesive layers. The foam base has an expansion ratio of 2.0 cm ³ / g or less. Since the double-sided pressure-sensitive adhesive sheet containing such a foam substrate is difficult to be deformed during the cutting process, the adhesive in the cutting region can be prevented from adhering to other parts of the pressure-sensitive adhesive sheet than expected. For this reason, generation | occurrence | production of the disadvantage resulting from reattachment of an adhesive can be prevented or suppressed suitably.

  In the double-sided pressure-sensitive adhesive sheet disclosed herein, the pressure-sensitive adhesive constituting at least one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer has a peak top temperature of loss tangent tan δ of −30 ° C. or higher. According to the double-sided pressure-sensitive adhesive sheet containing such a pressure-sensitive adhesive, the occurrence of a phenomenon (hereinafter also referred to as pressure-sensitive adhesive blocking) in which the pressure-sensitive adhesive in the cutting region separated by the cutting process comes into contact again and is integrated is preferably suppressed. Can be done. For this reason, according to such a double-sided pressure-sensitive adhesive sheet, the occurrence of inconvenience due to the reattachment of the pressure-sensitive adhesive can be suitably prevented or suppressed.

In a preferred embodiment of the double-sided pressure-sensitive adhesive sheet disclosed herein, the pressure-sensitive adhesive constituting at least one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer has a storage elastic modulus G ′ at 20 ° C. of 8 × 10 ⁴ Pa. That's it. In the double-sided pressure-sensitive adhesive sheet containing such a pressure-sensitive adhesive, reattachment of the pressure-sensitive adhesive after processing can be suitably suppressed. For this reason, the workability of such a double-sided PSA sheet tends to improve.

  In a preferred embodiment of the double-sided PSA sheet disclosed herein, the foam base material has a 25% compressive strength of 200 kPa or more. The double-sided pressure-sensitive adhesive sheet containing such a foam substrate is not easily deformed during the cutting process. Therefore, the double-sided pressure-sensitive adhesive sheet including such a foam base material has good processing accuracy and can be prevented from causing inconvenience due to re-adhesion of the pressure-sensitive adhesive.

  In a preferred embodiment of the double-sided pressure-sensitive adhesive sheet disclosed herein, the foam base material has a tensile strength in the flow direction (also referred to as MD, the same applies hereinafter) of 15 MPa or more. The double-sided pressure-sensitive adhesive sheet containing such a foam base material can exhibit good handleability.

  In a preferable embodiment of the double-sided PSA sheet disclosed herein, as the foam base material, for example, a material having a tensile elongation of 400% or more in the flow direction (also referred to as MD, hereinafter the same) is preferably used. Can do. The double-sided pressure-sensitive adhesive sheet containing such a foam substrate is preferable from the viewpoint of the handleability of the double-sided pressure-sensitive adhesive sheet. From this viewpoint, the tensile elongation in the width direction (also referred to as TD, hereinafter the same) of the foam base material is preferably 200% or more.

  In a preferable embodiment of the double-sided pressure-sensitive adhesive sheet disclosed herein, the foam base material has a base material cohesive force of 40 N / 20 mm or more. The double-sided pressure-sensitive adhesive sheet containing such a foam substrate is not easily deformed during the cutting process. Therefore, the double-sided pressure-sensitive adhesive sheet including such a foam base material has good processing accuracy and can be prevented from causing inconvenience due to re-adhesion of the pressure-sensitive adhesive.

  In a preferred embodiment of the double-sided PSA sheet disclosed herein, the PSA may contain a tackifier resin. The tackifying resin preferably has a softening point of 120 ° C. or higher. Since the double-sided pressure-sensitive adhesive sheet containing such a pressure-sensitive adhesive is easy to suppress re-adhesion of the pressure-sensitive adhesive after cutting, the processability can be improved.

  Since the double-sided PSA sheet disclosed herein is excellent in processability, it can also be suitably used as a double-sided PSA sheet that is processed into a small size or a complicated shape. Moreover, since the double-sided pressure-sensitive adhesive sheet disclosed herein is excellent in impact resistance and level difference followability, it is suitable as a double-sided pressure-sensitive adhesive sheet used, for example, for joining parts of portable electronic devices.

It is typical sectional drawing which shows the structure of the double-sided adhesive sheet which concerns on one Embodiment. It is explanatory drawing which shows the sample for evaluation used when measuring press adhesive force. It is explanatory drawing which shows the measuring method of press adhesive force. It is explanatory drawing which shows the sample for evaluation used when evaluating impact resistance. It is explanatory drawing which shows the measuring method of the thickness direction deformation | transformation amount at the time of an impact. It is explanatory drawing which shows the measuring method of base-material cohesion force. It is explanatory drawing which shows the method of workability evaluation.

Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.
In the following drawings, members / parts having the same action may be described with the same reference numerals, and redundant descriptions may be omitted or simplified. In addition, the embodiment described in the drawings is schematically illustrated for clearly explaining the present invention, and does not accurately represent the size and scale of the pressure-sensitive adhesive sheet of the present invention actually provided as a product.

In this specification, the “pressure-sensitive adhesive” refers to a material that exhibits a soft solid (viscoelastic body) state in a temperature range near room temperature and has a property of easily adhering to an adherend by pressure as described above. . A pressure-sensitive adhesive referred to here, "CA Dahlquist," Adhesion: Fundamental and Practice ", McLaren & Sons, (1966) P. 143 ," as defined in the, generally, the complex tensile modulus E ^{* (1Hz)} <10 < ⁷ > dyne / cm < ² > material (typically a material having the above properties at 25 [deg.] C.). The “base polymer” of the pressure-sensitive adhesive is the main component (that is, 50% by weight of the rubber-like polymer) of the rubber-like polymer (polymer exhibiting rubber elasticity in the temperature range near room temperature) contained in the pressure-sensitive adhesive. Component which occupies the above).

  In this specification, “blocking of the pressure-sensitive adhesive” typically means the pressure-sensitive adhesive of one pressure-sensitive adhesive sheet when the end faces of the pressure-sensitive adhesive separated by the cutting process are in contact with each other thereafter or by the cutting process. Is in a state where a part thereof is integrated (or adhered) again when it comes into contact with the end face of the other adhesive sheet. In this specification, “pickup” refers to an operation of removing a double-sided PSA sheet (which may be a part of the double-sided PSA sheet) supported on a release liner from the release liner. For example, among the double-sided pressure-sensitive adhesive sheet separated into a plurality of parts by a cutting process (half-cut process) performed so as to penetrate the double-sided pressure-sensitive adhesive sheet and not to penetrate the release liner, a part of the release liner is used as the part. This is an operation to take up and remove.

<Configuration of double-sided PSA sheet>
The double-sided pressure-sensitive adhesive sheet disclosed herein (which may be in a long form such as a tape shape) is provided on a foam base material and first and second surfaces of the foam base material, respectively. It is comprised including the one adhesive layer and the 2nd adhesive layer. For example, it may be a double-sided pressure-sensitive adhesive sheet having a cross-sectional structure shown in FIG. The double-sided pressure-sensitive adhesive sheet 1 includes a sheet-like foam base material 15, and a first pressure-sensitive adhesive layer 11 and a second pressure-sensitive adhesive layer 12 that are respectively supported on both surfaces of the base material 15. More specifically, the first pressure-sensitive adhesive layer 11 and the second pressure-sensitive adhesive layer 12 are provided on the first surface 15A and the second surface 15B (both non-peelable) of the base material 15, respectively. As shown in FIG. 1, the double-sided pressure-sensitive adhesive sheet 1 before use (before being attached to an adherend) is wound in a spiral shape with the front surface 17A and the back surface 17B overlapped with a release liner 17 that is a release surface. It can be in the form of In the double-sided pressure-sensitive adhesive sheet 1 in this form, the surface of the second pressure-sensitive adhesive layer 12 (second pressure-sensitive adhesive surface 12A) is protected by the front surface 17A of the release liner 17, and the surface of the first pressure-sensitive adhesive layer 11 (first pressure-sensitive adhesive surface 11A). ) Is protected by the back surface 17B of the release liner 17. Alternatively, the first adhesive surface 11A and the second adhesive surface 12A may be protected by two independent release liners.

  The total thickness of the double-sided PSA sheet disclosed herein is not particularly limited, but is, for example, 50 μm to 1000 μm, preferably 70 μm to 500 μm, more preferably 100 μm to 350 μm, and even more preferably 150 μm to 320 μm, for example 190 μm or more. It can be 300 μm or less. By making the total thickness of the double-sided PSA sheet equal to or less than the above-described upper limit value, it can be advantageous in terms of reducing the thickness of the product, reducing the size, reducing the weight, and saving resources. Moreover, by making the total thickness of the double-sided pressure-sensitive adhesive sheet equal to or more than the lower limit value described above, excellent impact resistance and waterproofness can be exhibited.

  Here, the total thickness of the double-sided pressure-sensitive adhesive sheet refers to the thickness from one pressure-sensitive adhesive surface to the other pressure-sensitive adhesive surface, and in the example shown in FIG. 1, the thickness t from the first pressure-sensitive adhesive surface 11A to the second pressure-sensitive adhesive surface 12A. Say. Therefore, for example, even if it is a double-sided pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive surface is protected by a release liner before being attached to an adherend, the thickness of the release liner is included in the thickness of the double-sided pressure-sensitive adhesive sheet here. Make it not exist.

<Foam substrate>
In the technology disclosed herein, the foam base material is a base material having a portion having a bubble (bubble structure), and typically, at least one thin layered foam (foam layer) ). The foam base material may be a base material substantially constituted only by the foam layer. Although it does not specifically limit, The foam base material which consists of a single layer (one layer) foam layer as a suitable example of the foam base material in the technique disclosed here is mentioned.

  The thickness of the foam substrate is not particularly limited, and can be appropriately set according to the strength, flexibility, purpose of use, etc. of the double-sided pressure-sensitive adhesive sheet. From the viewpoint of easily ensuring the thickness of the pressure-sensitive adhesive layer capable of exhibiting desired adhesive properties, it is usually appropriate to set the thickness of the foam substrate to 700 μm or less, and from the viewpoint of repulsion resistance, 400 μm or less is appropriate. Preferably, it is 300 μm or less, for example, 200 μm or less. A foam substrate having a thickness of 180 μm or less may be used. The repulsion resistance as used herein means that when the double-sided pressure-sensitive adhesive sheet is elastically deformed along the surface shape of the adherend (which may be a curved surface, a stepped surface, etc.), It refers to the performance of holding the double-sided pressure-sensitive adhesive sheet in the elastically deformed shape against the repulsive force to return to the shape (that is, the ability to withstand the repulsive force of the double-sided pressure-sensitive adhesive sheet). From the viewpoint of impact resistance of the double-sided pressure-sensitive adhesive sheet, it is appropriate that the thickness of the foam substrate is 30 μm or more, preferably 50 μm or more, more preferably 60 μm or more (for example, 80 μm or more). .

  The material of the foam base material is not particularly limited. Usually, a foam base material including a foam layer formed of a foam of plastic material (plastic foam) is preferable. The plastic material for forming the plastic foam (meaning including a rubber material) is not particularly limited, and can be appropriately selected from known plastic materials. One plastic material can be used alone, or two or more plastic materials can be used in appropriate combination.

  Specific examples of plastic foams include polyolefin resin foams such as polyethylene foams and polypropylene foams; polyesters such as polyethylene terephthalate foams, polyethylene naphthalate foams, and polybutylene terephthalate foams. Foam made of resin; Foam made of polyvinyl chloride resin such as foam made of polyvinyl chloride; Foam made of vinyl acetate resin; Foam made of polyphenylene sulfide resin; Foam made of fatty acid polyamide (nylon) resin, wholly aromatic Amide resin foams such as polyamide (aramid) resin foams; Polyimide resin foams; Polyetheretherketone (PEEK) foams; Polystyrene ether foams such as polystyrene foams; Polyurethane resins Examples include foams made of urethane resin such as foams; . Moreover, you may use rubber-type resin-made foams, such as a polychloroprene rubber foam, as a plastic foam.

  Examples of preferred foams include polyolefin resin foams (hereinafter also referred to as “polyolefin foams”). As the plastic material (that is, polyolefin resin) constituting the polyolefin foam, various known or commonly used polyolefin resins can be used without particular limitation. Examples thereof include polyethylene such as low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and high density polyethylene (HDPE), polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, and the like. Examples of LLDPE include Ziegler-Natta catalyst linear low density polyethylene, metallocene catalyst linear low density polyethylene, and the like. Such polyolefin resin can be used individually by 1 type or in combination of 2 or more types as appropriate.

  As a suitable example of the foam base material in the technology disclosed herein, from the viewpoint of impact resistance, water resistance, etc., a polyethylene foam base material substantially composed of a foam of a polyethylene resin, a polypropylene base Examples thereof include a polypropylene-based foam base material substantially composed of a resin foam. Here, the polyethylene-based resin refers to a resin having ethylene as a main monomer (that is, a main component of the monomer), and other than HDPE, LDPE, LLDPE, etc., the ethylene copolymerization ratio exceeds 50% by weight. -A propylene copolymer, an ethylene- vinyl acetate copolymer, etc. may be included. Similarly, a polypropylene resin refers to a resin having propylene as a main monomer. As the foam substrate in the technology disclosed herein, a polyethylene-based foam substrate can be preferably employed.

It does not specifically limit as a manufacturing method of the said plastic foam (typically polyolefin-type foam), It can manufacture by a well-known method. For example, it can be produced by a method including a molding step, a crosslinking step and a foaming step of the plastic material or the plastic foam. Moreover, an extending | stretching process may be included as needed.
Examples of the method of crosslinking the plastic foam include a chemical crosslinking method using an organic peroxide or the like, or an ionizing radiation crosslinking method of irradiating ionizing radiation. These methods can be used in combination. Examples of the ionizing radiation include electron beams, α rays, β rays, and γ rays. The dose of ionizing radiation is not particularly limited, and can be set to an appropriate irradiation dose in consideration of the target physical properties (for example, the degree of crosslinking) of the foam substrate.

Although the average diameter (average cell diameter (XY)) of the bubbles occupying the XY plane of the foam base material (for example, polyolefin-based foam base material) is not particularly limited, it is usually 500 μm or less from the viewpoint of waterproofness. It is preferably 300 μm or less, more preferably 250 μm or less, for example 200 μm or less. On the other hand, from the viewpoint of impact resistance, the average cell diameter (XY) of the foam substrate is preferably 5 μm or more, more preferably 10 μm or more.
In addition, the average diameter (average bubble diameter (XY)) of the bubble which occupies XY plane of a foam base material here is X when the flow direction of this base material is made into X direction, and the width direction is set to Y direction. This refers to the average bubble diameter of bubbles that can be observed in a cross section cut along a plane parallel to the direction and the Y direction (XY cross section). The average bubble diameter (XY) can be measured by, for example, an optical microscope. Specifically, an XY cross section of the foam substrate is observed with an optical microscope, and a predetermined number (for example, five) of bubbles appearing in the cross section has a diameter of a circle having the same area as the projected area of each bubble image. Is calculated. By calculating the average value, the average bubble diameter (XY) can be obtained.

In a preferred aspect of the technology disclosed herein, as the foam base material, for example, a foam base having an expansion ratio of 2.15 cm ³ / g or less can be used. From the viewpoint of suppressing re-deposition of cutting during deformed by suppressing the adhesive, expansion ratio of the foam substrate is preferably at 2.0 cm 3 / ^g or less, more preferably 1.95 cm ³ / g or less, more preferably 1.9 cm ³ / g or less. Expansion ratio 1.7 cm ³ / g or less, and further may be used 1.55 cm ³ / g or less of the foam substrate. The lower limit of the expansion ratio is not particularly limited. From the viewpoint of impact resistance, expansion ratio of the foam substrate is typically a suitably 1.1 cm ³ / g or more, preferably 1.2 cm ³ / g or more, more preferably 1.25cm ³ / g or more, more preferably 1.3 m ³ / g or more. By increasing the expansion ratio, the flexibility is improved, and the step following property and the repulsion resistance tend to be improved. When the double-sided pressure-sensitive adhesive sheet has good step followability, generally, even when bonded to an adherend having a step, a gap is hardly formed between the adherend surface and the waterproof property is improved. In addition, in this specification, the expansion ratio of a foam base material is defined as the reciprocal number of the apparent density (g / cm < ³ >) measured based on JISK6767.

  The tensile elongation of the foam base material (for example, a polyolefin-based foam base material) is not particularly limited. For example, the tensile elongation in the flow direction (MD) is 200% or more and 800% or less (more preferably 300% or more and 700% or less, more preferably 400% or more and 600% or less, for example, 450 or more and 550% or less). preferable. Further, the tensile elongation in the width direction (TD) is 50% or more and 800% or less (more preferably 100% or more and 600% or less, more preferably 200% or more and 500% or less, for example, 250% or more and 400% or less). Is preferred. By setting the elongation equal to or higher than the above-described lower limit, impact resistance and step following ability can be improved. Moreover, the intensity | strength of a foam base material improves by setting it as the elongation below the upper limit mentioned above, and handleability can improve. The elongation of the foam substrate is measured according to JIS K 6767. The elongation of the foam base material can be controlled by, for example, the degree of crosslinking and the expansion ratio.

  The tensile strength (tensile strength) of the foam base material (for example, polyolefin-based foam base material) is not particularly limited. For example, the tensile strength in the flow direction (MD) is 5 MPa or more and 35 MPa or less (more preferably 10 MPa or more and 30 MPa or less, more preferably 12 MPa or more and 28 MPa or less, typically 15 MPa or more and 25 MPa or less, for example, 16 MPa or more and 23 MPa or less). It is preferable. Further, the tensile strength in the width direction (TD) is 1 MPa or more and 25 MPa or less (more preferably 5 MPa or more and 20 MPa or less, more preferably 7 MPa or more and 18 MPa or less, typically 8 MPa or more and 15 MPa or less, for example, 9 MPa or more and 13 MPa or less). It is preferable. By setting the tensile strength to be equal to or higher than the lower limit value described above, for example, when the double-sided PSA sheet that has failed to be peeled off is peeled off, the substrate (and thus the double-sided PSA sheet) can be easily peeled off without being broken. (Reworkability) can be shown. Moreover, the ease of peeling off the double-sided pressure-sensitive adhesive sheet in this manner is advantageous when disassembling the product and recycling the parts, or when replacing defective parts. On the other hand, by setting the tensile strength to be equal to or less than the above-described upper limit value, impact resistance and level difference followability can be improved. The tensile strength (tensile strength in the flow direction, tensile strength in the width direction) of the foam substrate is measured in accordance with JIS K 6767. The tensile strength of the foam base material can be controlled by, for example, the degree of crosslinking and the expansion ratio.

  The 25% compressive strength of the foam base material (for example, polyolefin-based foam base material) is not particularly limited, but is usually suitably 100 kPa or more, preferably 200 kPa or more, more preferably 400 kPa or more, Preferably it is 500 kPa or more (typically 550 kPa or more, for example, 750 kPa or more). From the viewpoint of impact resistance of the double-sided PSA sheet, the 25% compressive strength of the foam base material is preferably 1200 kPa or less, more preferably 1100 kPa or less, and even more preferably 1000 kPa or less (for example, 900 kPa or less). Here, the 25% compressive strength of the foam base material means that the foam base material is stacked so as to have a thickness of about 25 mm and sandwiched between flat plates, and the thickness is equivalent to 25% of the original thickness. The load when only compressed. That is, the 25% compressive strength of the foam base material refers to a load when the stacked foam base materials are compressed to a thickness corresponding to 75% of the original thickness. When the 25% compressive strength is increased, the foam base material and the double-sided pressure-sensitive adhesive sheet including the foam base material are less likely to be deformed during the cutting process. Thereby, since reattachment of an adhesive can be suppressed, generation | occurrence | production of the malfunction at the time of pick-up is suppressed suitably. Furthermore, the increase in the 25% compressive strength can contribute to the suppression of the deformation amount in the thickness direction when the double-sided pressure-sensitive adhesive sheet is subjected to an impact such as dropping (hereinafter also referred to as the deformation amount in the thickness direction upon impact). An increase in the 25% compressive strength can contribute to an improvement in processing accuracy (dimensional accuracy, shape accuracy, etc.) in the cutting process of the double-sided pressure-sensitive adhesive sheet. On the other hand, by setting the 25% compressive strength to 1200 kPa or less, the repulsion resistance and the step following ability can be improved. The 25% compressive strength of the foam substrate is measured in accordance with JIS K 6767. The 25% compressive strength of the foam base material can be controlled by, for example, the degree of crosslinking and the expansion ratio.

Generally, the 25% compressive strength of the foam base material tends to improve as the foaming ratio of the foam base material decreases. Although it does not specifically limit, the value (henceforth (25% compressive strength) / (foaming ratio)) which divided the value of 25% compressive strength of the said foam base material by the value of foaming ratio is. It is preferably 100 g · kPa / cm ³ or more, more preferably 180 g · kPa / cm ³ or more, still more preferably 200 g · kPa / cm ³ or more, for example 250 g · kPa / cm ³ or more, typically 300 g · It is preferably kPa / cm ³ or more. When the above (25% compressive strength) / (foaming ratio) is equal to or higher than the lower limit value described above, the amount of deformation in the thickness direction upon impact of the double-sided PSA sheet tends to be better suppressed. In a preferred embodiment, a foam base material having (25% compressive strength) / (foaming ratio) of 400 g · kPa / cm ³ or more, further 450 g · kPa / cm ³ or more, for example, 500 g · kPa / cm ³ or more is used. May be. The upper limit of the above (25% compressive strength) / (foaming ratio) is not particularly limited, but is preferably 1100 g · kPa / cm ³ or less, more preferably 800 g · kPa, from the viewpoint of repulsion resistance and step following ability. / Cm ³ or less, more preferably 700 g · kPa / cm ³ or less, for example, 600 g · kPa / cm ³ or less.

The density of the foam substrate (apparent density) can be not particularly limited, largely 0.9 g / cm ³ or less than, for example 0.46 g / cm ^3. In one embodiment of the foam base material disclosed herein, the density of the foam base material is preferably 0.5 g / cm ³ or more and 0.85 g / cm ³ or less, more preferably 0.51 g / cm ^{3. 3} to 0.8 g / cm ³ or less, more preferably 0.53 g / cm ³ greater than 0.75 g / cm ³ or less (typically 0.55 g / cm ³ or more 0.73 g / cm ³ or less, for example 0 .6g / cm ³ or more 0.7g / cm ³ or less). By increasing the density, there is a tendency to suppress deformation during processing, improve processing accuracy, or improve the strength of the foam base material (and thus the strength of the double-sided pressure-sensitive adhesive sheet). On the other hand, when the density is 0.9 g / cm ³ or less, the step following property, repulsion resistance, and waterproof property tend to be improved. In addition, the density (apparent density) of a foam base material can be measured by the method based on JISK6767, for example.

  The cohesive force (also referred to as base cohesive force, unit: N / 20 mm) measured by the measurement method described later of the foam base material is not particularly limited, but is preferably 30 N / 20 mm or more. The base material cohesive force is more preferably 40 N / 20 mm or more, still more preferably 50 N / 20 mm or more (typically 55 N / 20 mm or more, for example, 75 N / 20 mm or more). Further, the upper limit value of the base material cohesive force is not particularly limited. For example, a foam base material having a base cohesive force of 200 N / 20 mm or less, more preferably 150 N / 20 mm or less, for example, 100 N / 20 mm or less is preferably used. Can be. The foam base material in which the base material cohesive force is equal to or higher than the lower limit value described above tends to suppress deformation during processing, and the double-sided pressure-sensitive adhesive sheet provided with such a base material is adhesive during cutting processing. Reattachment of the agent is difficult to occur. In addition, such a double-sided PSA sheet is better prevented from damage to the foam base material due to impact, and therefore has good bonding reliability and can exhibit better impact resistance. When the base material cohesive force of the foam base material is not more than the above-described upper limit value, the impact absorbability is good and there is a tendency to exhibit good impact resistance.

  For the foam base material, if necessary, a filler (inorganic filler, organic filler, etc.), an anti-aging agent, an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a plasticizer, a flame retardant, Various additives such as a surfactant may be blended.

  The foam base material in the technology disclosed herein is colored in order to develop desired design properties and optical characteristics (for example, light shielding property, light reflectivity, etc.) in the double-sided pressure-sensitive adhesive sheet including the foam base material. It may be. For this coloring, a known organic or inorganic coloring agent can be used singly or in appropriate combination of two or more.

  For example, when the double-sided pressure-sensitive adhesive sheet disclosed herein is used for light shielding, the visible light transmittance of the foam substrate is not particularly limited, but is 0% or more, similar to the visible light transmittance of the double-sided pressure-sensitive adhesive sheet described below. It is preferably 15% or less, more preferably 0% or more and 10% or less. Moreover, when using the double-sided pressure-sensitive adhesive sheet disclosed herein for light reflection applications, the visible light reflectance of the foam substrate is preferably 20% or more and 100% or less, similar to the visible light reflectance of the double-sided pressure-sensitive adhesive sheet, More preferably, it is 25% or more and 100% or less.

  The visible light transmittance of the foam base material is measured using one of the foam base materials at a wavelength of 550 nm using a spectrophotometer (for example, spectrophotometer manufactured by Hitachi High-Technologies Corporation, model “U-4100”). It can be determined by measuring the intensity of light irradiated from the surface side and transmitted to the other surface side. The visible light reflectance of the foam base material can be determined by measuring the intensity of light reflected and irradiated on one surface of the foam base material at a wavelength of 550 nm using the spectrophotometer. The visible light transmittance and visible light reflectance of the double-sided PSA sheet can also be determined by the same method.

  When the double-sided pressure-sensitive adhesive sheet disclosed herein is used for light shielding purposes, the foam base material is preferably colored black. As black, L * (lightness) defined by the L * a * b * color system is preferably 35 or less (for example, 0 to 35), more preferably 30 or less (for example, 0 to 30). . Note that a * and b * defined in the L * a * b * color system can be appropriately selected according to the value of L *. Although it does not specifically limit as a * and b *, It is preferable that both are the range of -10-10 (more preferably -5-5, still more preferably -2.5-2.5). For example, it is preferable that both a * and b * are 0 or substantially 0.

  In this specification, L *, a *, and b * defined in the L * a * b * color system are color difference meters (for example, color difference meters manufactured by Minolta, trade name “CR-200”). It is calculated | required by measuring using "). The L * a * b * color system is a color space recommended by the International Commission on Illumination (CIE) in 1976, and is a color space called the CIE 1976 (L * a * b *) color system. It means that. The L * a * b * color system is defined in JIS Z 8729 in the Japanese Industrial Standard.

  Examples of the black colorant used for coloring the foam base material black include carbon black (furnace black, channel black, acetylene black, thermal black, lamp black, etc.), graphite, copper oxide, manganese dioxide, aniline. Black, perylene black, titanium black, cyanine black, activated carbon, ferrite (nonmagnetic ferrite, magnetic ferrite, etc.), magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complex, complex oxide black pigment, anthraquinone organic black A pigment | dye etc. can be used. Carbon black is exemplified as a preferable black colorant from the viewpoint of cost and availability. The amount of the black colorant used is not particularly limited, and can be an amount adjusted appropriately so as to impart desired optical characteristics.

  When the double-sided pressure-sensitive adhesive sheet disclosed herein is used for light reflection, the foam base material is preferably colored white. As white, L * (brightness) defined by the L * a * b * color system is preferably 87 or more (for example, 87 to 100), more preferably 90 or more (for example, 90 to 100). . Each of a * and b * defined by the L * a * b * color system can be appropriately selected according to the value of L *. For example, both a * and b * are preferably in the range of −10 to 10 (more preferably −5 to 5, more preferably −2.5 to 2.5). For example, it is preferable that both a * and b * are 0 or substantially 0.

  Examples of the white colorant used for coloring the foam base material white include titanium oxide (titanium dioxide such as rutile titanium dioxide and anatase titanium dioxide), zinc oxide, aluminum oxide, silicon oxide, and zirconium oxide. , Magnesium oxide, calcium oxide, tin oxide, barium oxide, cesium oxide, yttrium oxide, magnesium carbonate, calcium carbonate (light calcium carbonate, heavy calcium carbonate, etc.), barium carbonate, zinc carbonate, aluminum hydroxide, calcium hydroxide, Magnesium hydroxide, zinc hydroxide, aluminum silicate, magnesium silicate, calcium silicate, barium sulfate, calcium sulfate, barium stearate, zinc white, zinc sulfide, talc, silica, alumina, clay, kaolin, titanium phosphate, mica, gypsum, white -Inorganic white colorants such as bon, diatomaceous earth, bentonite, lithopone, zeolite, sericite, hydrous halloysite, acrylic resin particles, polystyrene resin particles, polyurethane resin particles, amide resin particles, polycarbonate resin particles, silicone Organic white colorants such as resin-based resin particles, urea-formalin-based resin particles, and melamine-based resin particles. The amount of the white colorant used is not particularly limited, and can be an amount appropriately adjusted so that desired optical properties can be imparted.

  The surface of the foam substrate may be subjected to an appropriate surface treatment as necessary. This surface treatment can be, for example, a chemical or physical treatment for enhancing adhesion to an adjacent material (for example, an adhesive layer). Examples of such surface treatment include corona discharge treatment, chromic acid treatment, ozone exposure, flame exposure, ultraviolet irradiation treatment, plasma treatment, and application of a primer (primer).

<Adhesive>
In the technology disclosed herein, the type of the pressure-sensitive adhesive contained in each of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer is not particularly limited. The pressure-sensitive adhesive preferably has a loss tangent tan δ peak top temperature of −30 ° C. or higher, more preferably −20 ° C. or higher, still more preferably −10 ° C. or higher (typically −9 ° C. or higher, eg −7 ° C. or higher). Although the upper limit of the peak top temperature of the loss tangent tan δ of the pressure-sensitive adhesive is not particularly limited, it is usually suitably 15 ° C. or less, preferably 5 ° C. or less, more preferably 0 ° C. or less. When the peak top temperature of the loss tangent tan δ of the adhesive is −30 ° C. or higher, the re-adhesion of the adhesive after the cutting process can be suppressed. Can be suppressed. When the peak top temperature of the loss tangent tan δ of the pressure-sensitive adhesive is 15 ° C. or lower, an appropriate adhesive force tends to be obtained with respect to the adherend.

  Here, the peak top temperature of the loss tangent tan δ of the adhesive is measured by the following method. First, a 1 mm thick sheet-shaped adhesive is punched into a disk shape with a diameter of 7.9 mm and sandwiched between parallel plates. A viscoelasticity tester (manufactured by TI Instruments Japan Co., Ltd., model name “ARES”) ), The storage elastic modulus G ′ and the loss elastic modulus G ″ are measured by the shear mode at a temperature increase rate of −70 ° C. to 150 ° C. and 5 ° C./min while giving a shear strain of a frequency of 1 Hz. Then, the loss tangent tan δ is calculated by the following formula: tan δ = G ″ / G ′; and the temperature dependence is plotted to obtain the temperature corresponding to the peak top (the temperature at which the tan δ curve becomes maximum). Can do.

In the technology disclosed herein, the storage elastic modulus G ′ of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not particularly limited as long as the peak top temperature of the loss tangent tan δ is within the above-described preferable range. From the viewpoint of suppressing the re-adhesion of the pressure-sensitive adhesive, the storage elastic modulus G ′ (hereinafter also referred to as G ′ (20 ° C.)) at 20 ° C. of the pressure-sensitive adhesive is 8 × 10 ⁴ Pa or more. Preferably, it is 10 × 10 ⁴ Pa or more, more preferably 12 × 10 ⁴ Pa or more (for example, 15 × 10 ⁴ Pa or more, typically 20 × 10 ⁴ Pa or more). The upper limit of G ′ (20 ° C.) of the pressure-sensitive adhesive is not particularly limited, but is usually 100 × 10 ⁴ Pa or less, preferably 80 × 10 ⁴ Pa or less, more preferably 50 × 10 ⁴ Pa or less, and Preferably, it is 30 × 10 ⁴ Pa or less.

  The pressure-sensitive adhesive disclosed herein is, for example, one selected from various polymers (adhesive polymers) such as acrylic, polyester, urethane, polyether, rubber, silicone, polyamide, and fluorine. The pressure-sensitive adhesive may contain two or more types as a base polymer. In a preferred embodiment, the main component of the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive. The technology disclosed herein can be preferably implemented in the form of a double-sided pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer consisting essentially of an acrylic pressure-sensitive adhesive.

  Here, the “acrylic pressure-sensitive adhesive” refers to a pressure-sensitive adhesive having an acrylic polymer as a base polymer (a main component of the polymer component, that is, a component occupying 50% by weight or more). “Acrylic polymer” means a monomer having at least one (meth) acryloyl group in one molecule (hereinafter sometimes referred to as “acrylic monomer”) as a main constituent monomer component (main monomer component). Component, that is, a polymer that constitutes 50% by weight or more of the total amount of monomers constituting the acrylic polymer). In the present specification, the term “(meth) acryloyl group” means an acryloyl group and a methacryloyl group comprehensively. Similarly, “(meth) acrylate” is a generic term for acrylate and methacrylate.

The acrylic polymer is typically a polymer containing alkyl (meth) acrylate as a main constituent monomer component. As said alkyl (meth) acrylate, the compound represented by following formula (1) can be used suitably, for example.
CH ₂ = C (R ¹ ) COOR ² (1)
Here, R ¹ in the above formula (1) is a hydrogen atom or a methyl group. R ² is an alkyl group having 1 to 20 carbon atoms. Since an adhesive having excellent adhesive properties is easily obtained, R ² is an alkyl group having 2 to 14 carbon atoms (hereinafter, the range of such carbon atoms may be represented as C _2-14 ). Certain alkyl (meth) acrylates are preferred. Specific examples of the C _2-14 alkyl group include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, s-butyl group, t-butyl group, n-pentyl group and isoamyl group. , Neopentyl group, n-hexyl group, n-heptyl group, n-octyl group, isooctyl group, 2-ethylhexyl group, n-nonyl group, isononyl group, n-decyl group, isodecyl group, n-undecyl group, n- A dodecyl group, n-tridecyl group, n-tetradecyl group, etc. are mentioned.

In a preferred embodiment, the total amount of monomers used for the synthesis of the acrylic polymer is about 50% by weight or more (typically 50% by weight or more and 99.9% by weight or less), more preferably 70% by weight or more (typically 70 wt% or more and 99.9 wt% or less), for example, about 85 wt% or more (typically 85 wt% or more and 99.9 wt% or less). In the above formula (1), R ² is C ₂ One or more selected from _-14 alkyl (meth) acrylates (more preferably C _4-10 alkyl (meth) acrylates, particularly preferably one or both of butyl acrylate and 2-ethylhexyl acrylate) Occupied. An acrylic polymer obtained from such a monomer composition is preferable because a pressure-sensitive adhesive exhibiting good adhesive properties is easily formed.

  Although it does not specifically limit, As an acrylic polymer in the technique disclosed here, what copolymerized the acrylic monomer which has a hydroxyl group (-OH) can be used preferably. Specific examples of the acrylic monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4- Hydroxybutyl (meth) acrylate, 2-hydroxyhexyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl ( (Meth) acrylate, (4-hydroxymethylcyclohexyl) methyl acrylate, polypropylene glycol mono (meth) acrylate, N-hydroxyethyl (meth) acrylamide, N-hydroxypropyl (meta) Acrylamide, and the like. Such hydroxyl group-containing acrylic monomers may be used alone or in combination of two or more.

  An acrylic polymer in which such a hydroxyl group-containing acrylic monomer is copolymerized is preferable because an adhesive having an excellent balance between adhesive force and cohesive force and excellent removability can be easily obtained. Particularly preferred hydroxyl group-containing acrylic monomers include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl ( And hydroxyalkyl (meth) acrylates such as (meth) acrylate. For example, a hydroxyalkyl (meth) acrylate in which the alkyl group in the hydroxyalkyl group is a straight chain having 2 to 4 carbon atoms can be preferably used.

  Such a hydroxyl group-containing acrylic monomer is preferably used in a range of about 0.001 wt% to 10 wt% of the total amount of monomers used for the synthesis of the acrylic polymer. By this, the double-sided adhesive sheet which balanced the said adhesive force and cohesion force at a higher level can be implement | achieved. By using the hydroxyl group-containing acrylic monomer in an amount of about 0.01 wt% to 5 wt% (for example, 0.05 wt% to 2 wt%), even better results can be achieved. Alternatively, the acrylic polymer in the technology disclosed herein may be one in which a hydroxyl group-containing acrylic monomer is not copolymerized.

  Monomers (other monomers) other than those described above may be copolymerized in the acrylic polymer in the technology disclosed herein within a range that does not significantly impair the effects of the present invention. Such a monomer can be used, for example, for the purpose of adjusting the glass transition temperature of the acrylic polymer, adjusting the adhesive performance (for example, peelability), and the like. Examples of monomers that can improve the cohesive strength and heat resistance of the pressure-sensitive adhesive include sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, cyano group-containing monomers, vinyl esters, and aromatic vinyl compounds. In addition, as a monomer that can introduce a functional group that can serve as a crosslinking base point into an acrylic polymer or contribute to an improvement in adhesion, a carboxyl group-containing monomer, an acid anhydride group-containing monomer, an amide group-containing monomer, an amino group-containing monomer, Examples include imide group-containing monomers, epoxy group-containing monomers, (meth) acryloylmorpholine, and vinyl ethers. For example, an acrylic polymer obtained by copolymerizing a carboxyl group-containing monomer as the other monomer is preferable.

Examples of the sulfonic acid group-containing monomer include styrene sulfonic acid, allyl sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, (meth) acrylamide propane sulfonic acid, sulfopropyl (meth) acrylate, and (meth) acryloyloxy. Examples thereof include naphthalene sulfonic acid and sodium vinyl sulfonate.
Examples of the phosphoric acid group-containing monomer include 2-hydroxyethyl acryloyl phosphate.
Examples of the cyano group-containing monomer include acrylonitrile and methacrylonitrile.
Examples of vinyl esters include vinyl acetate, vinyl propionate, vinyl laurate, and the like.
Examples of the aromatic vinyl compound include styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, and other substituted styrene.

Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.
Examples of the acid anhydride group-containing monomer include maleic anhydride, itaconic anhydride, and acid anhydride bodies of the above carboxyl group-containing monomers.
Examples of amide group-containing monomers include acrylamide, methacrylamide, diethylacrylamide, N-vinylpyrrolidone, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, N, N-diethylacrylamide, N, N-diethylmethacrylamide, Examples thereof include N, N′-methylenebisacrylamide, N, N-dimethylaminopropyl acrylamide, N, N-dimethylaminopropyl methacrylamide, diacetone acrylamide and the like.
Examples of the amino group-containing monomer include aminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate and the like.
Examples of the imide group-containing monomer include cyclohexylmaleimide, isopropylmaleimide, N-cyclohexylmaleimide, and itaconimide.
Examples of the epoxy group-containing monomer include glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, and allyl glycidyl ether.
Examples of vinyl ethers include methyl vinyl ether, ethyl vinyl ether, isobutyl vinyl ether and the like.

  Such “other monomers” may be used singly or in combination of two or more, but the total content is determined based on the monomer used for the synthesis of the acrylic polymer. The total amount is preferably about 40% by weight or less (typically 0.001% to 40% by weight), and is preferably about 30% by weight or less (typically 0.01% to 30% by weight). In the following, for example, it is more preferably 0.1 wt% or more and 10 wt% or less. When a carboxyl group-containing monomer is used as the other monomer, the content thereof can be, for example, 0.1 wt% or more and 10 wt% or less of the total monomer amount, and usually 0.2 wt% or more and 8 wt% or less. In the following, for example, it is appropriate that the content is 0.5% by weight or more and 5% by weight or less. Moreover, when using vinyl esters (for example, vinyl acetate) as the other monomer, the content can be, for example, 0.1% by weight or more and 20% by weight or less of the total amount of the monomers, and usually 0.5%. It is appropriate that the content is not less than 10% by weight.

  The copolymer composition of the acrylic polymer is suitably designed so that the glass transition temperature (Tg) of the polymer is −70 ° C. or higher. From the viewpoint of preventing blocking of the pressure-sensitive adhesive, the Tg of the acrylic polymer is preferably −60 ° C. or higher, and preferably −55 ° C. or higher (eg, −53 ° C. or higher). Further, from the viewpoint of exerting an appropriate adhesive force to the adherend, the Tg of the acrylic polymer is usually preferably −15 ° C. or lower, and is −25 ° C. or lower from the viewpoint of low temperature characteristics and the like. It is preferably −35 ° C. or lower (for example, −40 ° C. or lower).

  The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (that is, the type and amount ratio of monomers used for the synthesis of the polymer). Here, the Tg of the acrylic polymer refers to a fox based on the Tg of the homopolymer (homopolymer) of each monomer constituting the polymer and the weight fraction (copolymerization ratio based on weight) of the monomer. The value obtained from the formula. As the Tg of the homopolymer, the value described in known materials is adopted.

In the technique disclosed here, the following values are specifically used as the Tg of the homopolymer.
2-Ethylhexyl acrylate -70 ° C
Butyl acrylate -55 ° C
Ethyl acrylate -22 ° C
Methyl acrylate 8 ℃
Methyl methacrylate 105 ° C
2-hydroxyethyl acrylate -15 ° C
4-hydroxybutyl acrylate -40 ° C
Vinyl acetate 32 ° C
Styrene 100 ° C
Acrylic acid 106 ℃
Methacrylic acid 228 ° C

  For the Tg of homopolymers other than those exemplified above, the values described in “Polymer Handbook” (3rd edition, John Wiley & Sons, Inc, 1989) are used. If not described in “Polymer Handbook” (3rd edition, John Wiley & Sons, Inc., 1989), a homopolymer synthesized by solution polymerization is formed into a sheet shape, and a frequency of 1 Hz is measured using a viscoelasticity tester. While applying shear strain, measure the viscoelasticity in a shear mode at a temperature increase rate of −70 ° C. to 150 ° C. and 5 ° C./min, and the temperature corresponding to the peak top temperature of the loss elastic modulus G ″ (G ″ curve) Can be the Tg of the homopolymer.

  The method for obtaining such an acrylic polymer is not particularly limited, and various polymerization methods known as synthetic methods for acrylic polymers, such as solution polymerization method, emulsion polymerization method, bulk polymerization method, suspension polymerization method, etc. are appropriately employed. can do. For example, a solution polymerization method can be preferably used. As a monomer supply method when performing solution polymerization, a batch charging method, a continuous supply (dropping) method, a divided supply (dropping) method, or the like that supplies all monomer raw materials at once can be appropriately employed. The polymerization temperature can be appropriately selected according to the type of monomer and solvent to be used, the type of polymerization initiator, and the like, for example, about 20 ° C. to 170 ° C. (typically 40 ° C. to 140 ° C.). it can.

  The solvent (polymerization solvent) used in the solution polymerization can be appropriately selected from known or common organic solvents. For example, aromatic compounds (typically aromatic hydrocarbons) such as toluene and xylene; aliphatic or alicyclic hydrocarbons such as ethyl acetate, hexane, cyclohexane, methylcyclohexane; 1,2-dichloroethane, etc. Halogenated alkanes: lower alcohols such as isopropyl alcohol, 1-butanol, sec-butanol, tert-butanol (for example, monohydric alcohols having 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether Any one solvent selected from ketones such as methyl ethyl ketone and acetylacetone, and the like, or a mixed solvent of two or more may be used. For example, a polymerization solvent (which may be a mixed solvent) having a boiling point of 20 ° C. or higher and 200 ° C. or lower (typically 50 ° C. or higher and 150 ° C. or lower) at a total pressure of 1 atm can be used. In a preferred embodiment, a polymerization solvent having a boiling point in the range of 60 ° C. or higher and 150 ° C. or lower (eg, 80 ° C. or higher and 130 ° C. or lower) can be employed.

  The initiator used for the polymerization can be appropriately selected from known or commonly used polymerization initiators according to the type of polymerization method. For example, an azo polymerization initiator can be preferably used. Specific examples of the azo polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylpropionamidine) disulfate, 2,2′-azobis (2-amidino). Propane) dihydrochloride, 2,2′-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis (N, N′-dimethyleneisobutylamidine), 2,2′-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] hydrate, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2′- Azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2-methylbutyronitrile), 1,1'-azobis (cyclohexane-1-carbonit Le), 2,2'-azobis (2,4,4-trimethylpentane), dimethyl-2,2'-azobis (2-methyl propionate), and the like.

  Other examples of the polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate; benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl Peroxides such as peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclododecane, hydrogen peroxide Initiators; substituted ethane-based initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and the like. Still another example of the polymerization initiator includes a redox initiator based on a combination of a peroxide and a reducing agent. Examples of such redox initiators include a combination of peroxide and ascorbic acid (such as a combination of hydrogen peroxide solution and ascorbic acid), a combination of peroxide and iron (II) salt (hydrogen peroxide solution). And a combination of a persulfate and sodium hydrogen sulfite, and the like.

  Such a polymerization initiator can be used individually by 1 type or in combination of 2 or more types. The polymerization initiator may be used in an ordinary amount, for example, 0.005 to 1 part by weight (typically 0.01 to 1 part by weight with respect to 100 parts by weight of all monomer components). It can be selected from a range of about part by weight or less.

  According to such solution polymerization, a polymerization reaction solution in which an acrylic polymer is dissolved in an organic solvent is obtained. As the acrylic polymer in the technology disclosed herein, the polymerization reaction solution or a solution obtained by subjecting the reaction solution to an appropriate post-treatment can be preferably used. Typically, the acrylic polymer-containing solution after the post-treatment is used after adjusting to an appropriate viscosity (concentration). Alternatively, an acrylic polymer is synthesized using a polymerization method other than the solution polymerization method (for example, emulsion polymerization, photopolymerization, bulk polymerization, etc.), and the polymer is dissolved in an organic solvent to prepare a solution. It may be used.

The weight average molecular weight (Mw) of the acrylic polymer in the technology disclosed herein is not particularly limited, and may be, for example, in the range of 10 × 10 ⁴ or more and 500 × 10 ⁴ or less. From the viewpoint of balancing the suppression of the blocking of the adhesive and the adhesive performance at a high level, the Mw of the acrylic polymer is preferably in the range of 10 × 10 ⁴ or more and 150 × 10 ⁴ or less, and 15 × 10 ⁴ or more and 100 A range of × 10 ⁴ or less is more preferable, and a range of 15 × 10 ⁴ or more and 75 × 10 ⁴ or less is more preferable. In a preferred embodiment, the Mw of the acrylic polymer can be 20 × 10 ⁴ or more and less than 75 × 10 ⁴ . In a more preferred embodiment, the Mw of the acrylic polymer is 20 × 10 ⁴ or more and less than 70 × 10 ⁴ (for example, 32 × 10 ⁴ or more and 67 × 10 ⁴ or less, typically 35 × 10 ⁴ or more and 65 × 10 ⁴ or less). It is good. Here, Mw refers to a standard polystyrene equivalent value obtained by GPC (gel permeation chromatography).

  The pressure-sensitive adhesive composition in the technology disclosed herein may be a composition containing a tackifying resin. Although it does not restrict | limit especially as tackifying resin, For example, various rosin type, terpene type, hydrocarbon type, epoxy type, polyamide type, an elastomer type, a phenol type, a ketone type, etc. can be used. Such tackifying resins can be used alone or in combination of two or more.

  Specific examples of rosin-based tackifying resins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, tall oil rosin; modified rosins modified by hydrogenation, disproportionation, polymerization, etc. Hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosins, etc.); various other rosin derivatives; Examples of the rosin derivatives include those obtained by esterifying unmodified rosin with alcohols (ie, rosin esterified products) and modified rosins (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.) with alcohols. Rosin esters such as modified rosin esterified products (ie, unmodified rosins and modified rosins (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.) modified with unsaturated fatty acids. Unsaturated fatty acid-modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids; Unmodified rosin, modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.), unsaturated fatty acid-modified rosin or unsaturated fatty acid Rosin alcohols obtained by reducing carboxyl groups in modified rosin esters; unmodified rosin, modified rosin Metal salts of rosins (particularly rosin esters) such as various rosin derivatives; rosin phenol obtained by adding phenol to an rosin (unmodified rosin, modified rosin, various rosin derivatives, etc.) with an acid catalyst and thermal polymerization Resin; and the like.

  Examples of terpene-based tackifier resins include terpene resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers; modification of these terpene resins (phenol modification, aromatic modification, hydrogenation modification, hydrocarbons) Modified terpene resin) and the like. Examples of the modified terpene resin include terpene phenol resin, styrene modified terpene resin, aromatic modified terpene resin, hydrogenated terpene resin and the like.

  Examples of hydrocarbon tackifying resins include aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic / aromatic petroleum resins (styrene-olefin copolymers, etc. ), Various hydrocarbon resins such as aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, coumarone indene resins, and the like. Examples of the aliphatic hydrocarbon resin include polymers of one or more aliphatic hydrocarbons selected from olefins and dienes having about 4 to 5 carbon atoms. Examples of the olefin include 1-butene, isobutylene, 1-pentene and the like. Examples of the diene include butadiene, 1,3-pentadiene, isoprene and the like. Examples of aromatic hydrocarbon resins include polymers of vinyl group-containing aromatic hydrocarbons having about 8 to 10 carbon atoms (styrene, vinyl toluene, α-methylstyrene, indene, methylindene, etc.). It is done. Examples of the aliphatic cyclic hydrocarbon resin include an alicyclic hydrocarbon resin obtained by cyclizing and dimerizing a so-called “C4 petroleum fraction” or “C5 petroleum fraction”; a cyclic diene compound ( Cyclopentadiene, dicyclopentadiene, ethylidene norbornene, dipentene, etc.) polymer or hydrogenated product thereof; aromatic hydrocarbon resin or alicyclic hydrocarbon system in which aromatic ring of aliphatic / aromatic petroleum resin is hydrogenated Resin; and the like.

  In the technique disclosed herein, a resin having a softening point (softening temperature) of about 100 ° C. or higher (preferably 110 ° C. or higher, more preferably 120 ° C. or higher) can be preferably used as the tackifier resin. According to the pressure-sensitive adhesive containing the tackifying resin having the softening point equal to or higher than the lower limit value described above, a double-sided pressure-sensitive adhesive sheet in which blocking of the pressure-sensitive adhesive is effectively suppressed can be realized. Of the tackifying resins exemplified above, a terpene tackifying resin having such a softening point (for example, a terpene phenol resin), a rosin tackifying resin (for example, an esterified product of polymerized rosin), or the like can be preferably used. . According to the pressure-sensitive adhesive containing a tackifying resin having a softening point of 140 ° C. or higher, particularly excellent repulsion resistance can be realized. For example, a terpene phenol resin having a softening point of 140 ° C. or higher can be preferably used. In the technique disclosed herein, the proportion of the tackifying resin having a softening point of 140 ° C. or higher in the total tackifying resin contained in the pressure-sensitive adhesive is more than 50% by weight, more preferably 70% by weight or more, and still more preferably 85% by weight. % Or more (for example, 95 wt% or more and 100 wt% or less). The upper limit of the softening point of the tackifying resin is not particularly limited, and can be, for example, about 200 ° C. or lower (typically about 180 ° C. or lower). In addition, the softening point of the tackifier resin here is defined as a value measured by a softening point test method (ring and ball method) defined in either JIS K 5902 or JIS K 2207.

  The amount of the tackifying resin used is not particularly limited, and can be appropriately set according to the target tack performance (adhesive strength, etc.). For example, on the basis of solid content, the tackifier resin is about 10 parts by weight or more and 100 parts by weight or less (more preferably 15 parts by weight or more and 80 parts by weight or less, more preferably 20 parts by weight or more) with respect to 100 parts by weight of the acrylic polymer. 60 parts by weight or less) is preferably used.

  A crosslinking agent may be used in the pressure-sensitive adhesive composition as necessary. The type of the crosslinking agent is not particularly limited, and is a known or conventional crosslinking agent (for example, an isocyanate crosslinking agent, an epoxy crosslinking agent, an oxazoline crosslinking agent, an aziridine crosslinking agent, a melamine crosslinking agent, a peroxide crosslinking agent). , Urea crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, carbodiimide crosslinking agents, amine crosslinking agents, etc.). A crosslinking agent can be used individually by 1 type or in combination of 2 or more types. The amount of the crosslinking agent used is not particularly limited, and is, for example, about 10 parts by weight or less (for example, about 0.005 parts by weight to 10 parts by weight, preferably about 0.01 parts by weight or more with respect to 100 parts by weight of the acrylic polymer. It can be selected from a range of about 5 parts by weight or less.

  The above-mentioned pressure-sensitive adhesive composition comprises a leveling agent, a crosslinking aid, a plasticizer, a softening agent, a filler, a colorant (pigment, dye, etc.), an antistatic agent, an anti-aging agent, an ultraviolet absorber, and an oxidation, as necessary. It may contain various additives that are common in the field of pressure-sensitive adhesive compositions, such as inhibitors and light stabilizers. About such various additives, conventionally well-known things can be used by a conventional method, and since it does not characterize this invention in particular, detailed description is abbreviate | omitted.

  As the release liner, those known or commonly used in the field of double-sided pressure-sensitive adhesive sheets can be appropriately selected and used. For example, a release liner having a configuration in which a release treatment is performed on the surface of the liner substrate can be suitably used. As a liner base material (exfoliation processing object) constituting this type of release liner, various resin films, papers, cloths, rubber sheets, foam sheets, metal foils, and composites thereof (for example, A sheet having a laminated structure in which an olefin resin is laminated on both surfaces of paper) can be appropriately selected and used. The release treatment can be performed by a conventional method using a known or commonly used release treatment agent (for example, a silicone-based, fluorine-based, or long-chain alkyl-based release treatment agent). In addition, a low-adhesive liner base material such as olefin resin (eg, polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene / polypropylene mixture), fluorine polymer (eg, polytetrafluoroethylene, polyvinylidene fluoride) is used. The surface of the liner substrate may be used as a release liner without being subjected to a release treatment. Or you may use what performed the peeling process to this low adhesive liner base material.

  In the technique disclosed herein, a method for adjusting the peak top temperature of the loss tangent tan δ of the pressure-sensitive adhesive to the above-described preferable range is not particularly limited. For example, as the Tg of the base polymer increases, the tan δ peak top temperature of the pressure-sensitive adhesive tends to increase. Further, as the Mw of the base polymer increases, the tan δ peak top temperature tends to increase. The peak top temperature of tan δ can also be increased by blending a filler in the pressure-sensitive adhesive layer as necessary. Further, the peak top temperature of tan δ of the pressure-sensitive adhesive can be adjusted by whether or not a tackifier resin is blended in the pressure-sensitive adhesive, and the blending amount and type (for example, softening point) when blended. Usually, when the compounding amount of the tackifying resin with respect to the base polymer increases, the peak top temperature of tan δ tends to increase. Further, by using a tackifier resin having a higher softening temperature, the peak top temperature of tan δ tends to increase. These methods can be employed singly or in combination of two or more.

  As a suitable example of the pressure-sensitive adhesive in the technology disclosed herein, a tackifying resin having a softening temperature of 120 ° C. or higher (preferably 130 ° C. or higher, more preferably 140 ° C. or higher) is 15 weights with respect to 100 parts by weight of the base polymer. The pressure-sensitive adhesive has a composition containing not less than 60 parts by weight and not more than 60 parts by weight, preferably not less than 20 parts by weight and not more than 55 parts by weight, more preferably not less than 25 parts by weight and not more than 50 parts by weight (eg, not less than 35 parts by weight and not more than 45 parts by weight) An adhesive having such a composition is preferable because the peak top temperature of tan δ tends to be −30 ° C. or higher. Moreover, as a suitable example of the said base polymer, Tg is -60 degreeC or more and -15 degrees C or less, More preferably, it is -55 degreeC or more and -25 degrees C or less, for example, -55 degreeC or more -35 degrees C or less acrylic polymer is mentioned. According to the pressure-sensitive adhesive comprising the acrylic polymer having such Tg and the above-mentioned tackifying resin having the softening temperature and the content, and having a peak top temperature of tan δ of −30 ° C. or higher, processability and other pressure-sensitive adhesive performance (For example, repulsion resistance) can be highly compatible.

  In the technology disclosed herein, the peeling force (liner peeling strength) between the double-sided PSA sheet and the release liner is not particularly limited. From the viewpoint of workability, the peeling force is preferably 0.1 N / 50 mm or more, more preferably 0.2 N / 50 mm or more, still more preferably 0.23 N / 50 mm or more (for example, 0.24 N / 50 mm or more). ). From the viewpoint of handleability, the peeling force is usually suitably 1 N / 50 mm or less, preferably 0.5 N / 50 mm or less, more preferably 0.4 N / 50 mm or less, and still more preferably 0.35 N. / 50 mm or less (for example, 0.33 N / 50 mm or less). The liner peel strength can be measured by the procedure described in the examples described later.

  Application of the pressure-sensitive adhesive composition can be performed using a known or 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, or a spray coater. . Although not particularly limited, the amount of the pressure-sensitive adhesive composition applied is such that a pressure-sensitive adhesive layer having a thickness of about 5 μm to 150 μm (thickness per side) is formed after drying (that is, based on the solid content). The amount can be as much as possible. From the viewpoint of balancing the double-sided pressure-sensitive adhesive sheet in weight and / or thickness and pressure-sensitive adhesive performance at a high level, the thickness of the pressure-sensitive adhesive layer per side is suitably about 10 μm to 110 μm, and about 15 μm. The thickness is preferably 100 μm or less, typically 20 μm or more and 80 μm or less. From the viewpoint of reducing the thickness of the double-sided PSA sheet, the thickness of the PSA layer may be 50 μm or less, and may be 35 μm or less. From the viewpoint of promoting the crosslinking reaction and improving the production efficiency, the pressure-sensitive adhesive composition is preferably dried under heating. Usually, for example, a drying temperature of about 40 ° C. to 120 ° C. can be preferably used.

  As a method for forming the pressure-sensitive adhesive layer on the foam substrate, various conventionally known methods can be applied. For example, a method of directly applying the pressure-sensitive adhesive composition to a foam substrate (direct method), applying the pressure-sensitive adhesive composition on a suitable release surface, and forming a pressure-sensitive adhesive layer on the release surface And a method of transferring the pressure-sensitive adhesive layer on a foam substrate (transfer method). You may use combining these methods. Moreover, you may employ | adopt a different method with a 1st adhesive layer and a 2nd adhesive layer. In the case of using a pressure-sensitive adhesive composition containing a solvent, it is preferable to dry the pressure-sensitive adhesive composition under heating from the viewpoints of promoting a crosslinking reaction and improving production efficiency.

The total thickness of the pressure-sensitive adhesive layer (total thickness of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer) is not particularly limited, but can be, for example, 10 μm or more and 600 μm or less. From the viewpoint of adhesive performance, it is usually appropriate that the total thickness of the adhesive layer is 20 μm or more, preferably 30 μm or more, more preferably 40 μm or more. Further, from the viewpoint of easily ensuring the thickness of the foam base material capable of exhibiting desired characteristics, it is usually appropriate that the total thickness of the pressure-sensitive adhesive layer is 200 μm or less, preferably 160 μm or less, more preferably Is 150 μm or less, more preferably 100 μm or less, for example 70 μm or less.
The thickness of the first pressure-sensitive adhesive layer and the thickness of the second pressure-sensitive adhesive layer may be the same or different. Usually, a configuration in which the thicknesses of both pressure-sensitive adhesive layers are approximately the same can be preferably employed. Each pressure-sensitive adhesive layer may have either a single layer or multiple layers.

  The gel fraction of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not particularly limited, and may be, for example, 10% by weight or more and 70% by weight or less. From the viewpoint of balancing handling properties such as reworkability and removability and impact resistance at a high level, the gel fraction of the pressure-sensitive adhesive is usually in the range of 15 wt% to 50 wt%. The range of 18% to 45% by weight is preferable, and the range of 20% to 40% by weight (for example, 20% to 35% by weight) is particularly preferable. The gel fraction can be adjusted by the monomer composition and molecular weight of the base polymer, the crosslinking agent and other additives. The gel fraction of the pressure-sensitive adhesive can be determined by the following method.

  After the pressure-sensitive adhesive composition is dried at 130 ° C. for 2 hours, about 0.1 g of the dried product (sample) is wrapped with a porous sheet made of polytetrafluoroethylene (PTFE) resin, and the mouth is tied with a kite string. The package is placed in a 50 mL screw tube, filled with ethyl acetate and allowed to stand at room temperature (typically 23 ° C.) for 7 days. The package is then removed and dried at 130 ° C. for 2 hours. The gel fraction is calculated by the following formula: rate (%) = (sample weight after immersion / drying) / (sample weight before immersion) × 100; As the PTFE resin porous sheet, a trade name “Nitoflon (registered trademark) NTF1122” manufactured by Nitto Denko Corporation or its equivalent can be used.

  The double-sided pressure-sensitive adhesive sheet disclosed herein is a layer other than the foam base material and the pressure-sensitive adhesive layer (intermediate layer, undercoat layer, etc .; hereinafter also referred to as “other layers”) as long as the effects of the present invention are not significantly impaired. May further be included. For example, the said other layer may be provided between the foam base material and either one or both adhesive layers. In the double-sided pressure-sensitive adhesive sheet having such a configuration, the thickness of the other layer is included in the total thickness of the double-sided pressure-sensitive adhesive sheet (that is, the thickness from one pressure-sensitive adhesive surface to the other pressure-sensitive adhesive surface).

  According to a preferred aspect of the technology disclosed herein, a double-sided pressure-sensitive adhesive sheet having a pressure adhesive force of 40 N or more (more preferably 100 N or more, more preferably 200 N or more, such as 300 N or more, typically 330 N or more). Can be provided. Thus, the double-sided pressure-sensitive adhesive sheet having a high pressure-adhesive force is preferable since peeling due to internal stress hardly occurs when the members are bonded using the double-sided pressure-sensitive adhesive sheet, and the adhesive reliability is excellent.

  The pressing adhesive force is a 59 mm width, 113 mm length, 1 mm wide double-sided pressure-sensitive adhesive sheet (also referred to as “frame shape”), and a stainless steel (SUS) plate and a glass plate are subjected to a 5 kg load for 10 seconds. A sample for evaluation is prepared by pressing and bonding together, and the glass plate is pressed in the thickness direction of the glass plate from the inside toward the outside at a load speed of 10 mm / min in the sample for evaluation. Is defined as the maximum stress observed before the stainless steel plate separates. The said press adhesive force can be measured by the procedure as described in the Example mentioned later, for example.

  According to a preferable embodiment of the double-sided pressure-sensitive adhesive sheet disclosed herein, the tackiness of the pressure-sensitive adhesive surface of the pressure-sensitive adhesive layer is in the following range. That is, the ball diameter in the ball tack test is 0.3 mm to 15 mm (more preferably 0.5 mm to 10 mm, more preferably 0.6 mm to 9.5 mm, for example 0.7 mm to 5 mm, typically It is preferable that the tack is 0.8 mm or more and 2 mm or less. The double-sided pressure-sensitive adhesive sheet showing the above-described tack can realize performance that achieves both workability and handleability. The ball tack test is performed by the method described in the examples described later.

  According to another preferable aspect of the technology disclosed herein, in the impact resistance evaluation performed by the method described in the examples described later, after dropping 60 times, joining such as peeling and cracking of the foam base material A double-sided pressure-sensitive adhesive sheet exhibiting a level of impact resistance that does not cause any defects can be realized.

  The double-sided PSA sheet disclosed herein may have desired optical properties (transmittance, reflectance, etc.). For example, the double-sided pressure-sensitive adhesive sheet used for light shielding applications preferably has a visible light transmittance of 0% to 15% (more preferably 0% to 10%). Moreover, it is preferable that the double-sided pressure-sensitive adhesive sheet used for light reflection has a visible light reflectance of 20% to 100% (more preferably 25% to 100%). The optical characteristics of the double-sided pressure-sensitive adhesive sheet can be adjusted, for example, by coloring the foam substrate as described above.

  The double-sided PSA sheet disclosed herein is preferably halogen-free from the viewpoint of preventing corrosion of the metal. The fact that the double-sided pressure-sensitive adhesive sheet is halogen-free can be an advantageous feature, for example, when this double-sided pressure-sensitive adhesive sheet can be used for fixing electric / electronic components. Moreover, since generation | occurrence | production of the halogen containing gas at the time of combustion can be suppressed, it is preferable also from a viewpoint of environmental load reduction. Halogen-free double-sided pressure-sensitive adhesive sheets are used when a halogen compound is not intentionally used as a foam base material or a raw material for a pressure-sensitive adhesive, when a foam base material not intentionally blended with a halogen compound is used, or when an additive is used. It can be obtained by employing means such as not using an additive derived from a halogen compound alone or in combination as appropriate.

  The double-sided pressure-sensitive adhesive sheet disclosed herein is not particularly limited. For example, metal materials such as stainless steel (SUS) and aluminum; inorganic materials such as glass and ceramics; polycarbonate (PC), polymethyl methacrylate (PMMA), and polypropylene It can be used for adherends made of resin materials such as polyethylene terephthalate (PET); rubber materials such as natural rubber and butyl rubber; and composite materials thereof.

The double-sided pressure-sensitive adhesive sheet disclosed herein can be prevented from reattaching the pressure-sensitive adhesive at the time of cutting and has excellent processing accuracy. For this reason, it can be suitable as a double-sided pressure-sensitive adhesive sheet used for the purpose of joining components having a small size or a complicated shape. Moreover, the double-sided pressure-sensitive adhesive sheet disclosed herein can be excellent in step followability, repulsion resistance, and waterproofness. Therefore, taking advantage of such features, for electronic device applications, for example, for fixing a protective panel (lens) that protects the display part of a portable electronic device (for example, a mobile phone, a smartphone, a tablet computer, a laptop computer, etc.) It can be preferably applied to applications such as fixing a key module member of a cellular phone, fixing a decoration panel of a television, fixing a battery pack of a personal computer, and waterproofing a lens of a digital video camera. A particularly preferred application is a portable electronic device. In particular, it can be preferably used for a portable electronic device incorporating a liquid crystal display device. For example, in such a portable electronic device, it is suitable for applications such as joining a protective panel (lens) that protects the display unit and a housing.
In addition, the “lens” in the present specification is a concept including both a transparent body showing a light refraction action and a transparent body having no light refraction action. In other words, the “lens” in the present specification includes a protective panel that has no refractive action and simply protects a display portion of a portable electronic device.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples. In the following description, “parts” and “%” are based on weight unless otherwise specified.

The double-sided pressure-sensitive adhesive sheets according to Examples 1 to 17 were produced as follows.
(Example 1)
[Preparation of acrylic polymer a]
In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser and a dropping funnel, 100 parts of n-butyl acrylate, 5 parts of acrylic acid, and 2,2′-azobisisobutyrate as a polymerization initiator 0.2 part of nitrile and toluene as a polymerization solvent were charged, nitrogen gas was introduced while gently stirring, and the polymerization temperature was kept at around 60 ° C. for about 6 hours to carry out the polymerization reaction, A toluene solution of acrylic polymer a was obtained. Mw of this acrylic polymer a was 55 × 10 ⁴ .
Here, Mw of the acrylic polymer a was determined as follows. That is, after the toluene solution was dried at room temperature, the solid content was dissolved in tetrahydrofuran (THF) to prepare a THF solution containing the acrylic polymer a at a concentration of about 0.1 g / liter. The filtrate obtained by filtering this THF solution with a membrane filter having an average pore size of 0.45 μm was subjected to GPC to obtain Mw (converted to standard polystyrene) of the acrylic polymer a. As a GPC device, a product of Tosoh Corporation, model name “HLC-8320GPC” (column: TSKgel GMH-H (S)) was used.

[Preparation of pressure-sensitive adhesive composition A]
30 parts of product name “Tamanol 803L” (terpene phenol resin: manufactured by Arakawa Chemical Industries, softening point 145 ° C. to 160 ° C.) and product name as tackifier resin with respect to 100 parts of acrylic polymer a contained in the toluene solution 10 parts of “YS Polystar S145” (terpene phenol resin: Yashara Chemical Co., Ltd., softening point: 140 ° C. to 150 ° C.) is added, and an isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Industry, product name “Coronate L”) as a crosslinking agent. Acrylic pressure-sensitive adhesive composition A was prepared by adding 1 part and 0.03 part of an epoxy-based crosslinking agent (trade name “Tetrad C” manufactured by Mitsubishi Gas Chemical Co., Ltd.).

Two commercially available release liners (trade name “SLB-80W3D”, manufactured by Sumika Kogyo Co., Ltd.) were prepared. The pressure-sensitive adhesive composition A was applied to one surface (release surface) of each of these release liners so that the thickness after drying was 25 μm, and dried at 100 ° C. for 2 minutes. In this way, an adhesive layer was formed on each of the release surfaces of the two release liners.
A foam base material (hereinafter referred to as “base material No. 1”) made of a polyethylene foam sheet having a corona discharge treatment on one surface and the other surface was prepared. The base material No. The thickness of No. 1 was 150 μm, the tensile strength in the flow direction (tensile strength (MD)) was 19.2 MPa, and the tensile strength in the width direction (tensile strength (TD)) was 11.8 MPa.
This substrate No. The pressure-sensitive adhesive layers formed on the two release liners were bonded to one surface and the other surface of 1, respectively. The release liner was left on the pressure-sensitive adhesive layer as it was and used for protecting the surface (pressure-sensitive surface) of the pressure-sensitive adhesive layer. The obtained structure was passed once through a laminator (0.3 MPa, speed 0.5 m / min) at 80 ° C., and then cured in an oven at 50 ° C. for 1 day. Thus, the double-sided adhesive sheet (example) which has a 1st adhesive layer and a 2nd adhesive layer in the 1st surface and the 2nd surface of a foam base material (No. 1), respectively, and total thickness is 200 micrometers. 1) was obtained.

(Example 2, Example 3)
The base material No. The double-sided pressure-sensitive adhesive layer was prepared in the same manner as the double-sided pressure-sensitive adhesive sheet of Example 1 except that the thickness of the pressure-sensitive adhesive layer formed on each side of 1 was 50 μm (Example 2) or 75 μm (Example 3) after drying. Sheets (Example 2, Example 3) were obtained.

(Examples 4 to 6)
The foam substrate No. In place of the base No. 1 2 and the substrate No. The double-sided pressure-sensitive adhesive sheet of Example 1 was used except that the thickness of the pressure-sensitive adhesive layer formed on both sides of 2 was changed to 25 μm (Example 4), 50 μm (Example 5), and 75 μm (Example 6). In the same manner as the production method, double-sided PSA sheets (Examples 4 to 6) were obtained.
Here, the base material No. Reference numeral 2 denotes a foam base material made of a polyethylene foam sheet having one surface and the other surface subjected to corona discharge treatment, the thickness thereof is 150 μm, and the tensile strength (tensile strength (MD (MD )) Was 16.3 MPa, and the tensile strength in the width direction (tensile strength (TD)) was 9.5 MPa.

(Examples 7 to 9)
[Preparation of acrylic polymer b]
In a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel, 100 parts of n-butyl acrylate, 2 parts of acrylic acid, 5 parts of vinyl acetate, 2-hydroxyethyl acrylate,. 1 part, 2,2′-azobisisobutyronitrile 0.2 part as a polymerization initiator, and toluene as a polymerization solvent were charged, and solution polymerization was performed at 60 ° C. for 6 hours to obtain a toluene solution of acrylic polymer b Got. Mw of the acrylic polymer b measured by the same method as that for the acrylic polymer a described above was 50 × 10 ⁴ .

[Preparation of pressure-sensitive adhesive composition B]
To 100 parts of the acrylic polymer b contained in the toluene solution, as a tackifier resin, 30 parts of a polymerized rosin ester resin (Arakawa Chemical Industries, product name “Pencel D-125”, softening point 125 ° C.) is added, An acrylic pressure-sensitive adhesive composition B was prepared by adding 2 parts of an isocyanate-based cross-linking agent (manufactured by Nippon Polyurethane Industry Co., Ltd., product name “Coronate L”) as a cross-linking agent.

  Use of the pressure-sensitive adhesive composition B instead of the pressure-sensitive adhesive composition A, and the foam substrate No. Of the double-sided pressure-sensitive adhesive sheet of Example 4 except that the thickness of the pressure-sensitive adhesive layer formed on both sides of 2 is changed to 25 μm (Example 7), 50 μm (Example 8), and 75 μm (Example 9). In the same manner as the production method, double-sided PSA sheets (Examples 7 to 9) were obtained.

(Example 10 to Example 12)
[Preparation of acrylic polymer c]
In a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel, 70 parts of n-butyl acrylate, 30 parts of 2-ethylhexyl acrylate, 3 parts of acrylic acid, 4-hydroxy Acrylic polymer prepared by solution polymerization at 60 ° C. for 6 hours with 0.1 part of butyl acrylate, 0.1 part of 2,2′-azobisisobutyronitrile as a polymerization initiator and toluene as a polymerization solvent. A toluene solution of c was obtained. Mw of the acrylic polymer c measured by the same method as that for the acrylic polymer a described above was 44 × 10 ⁴ .

[Preparation of pressure-sensitive adhesive composition C]
An acrylic pressure-sensitive adhesive composition C was prepared by adding 1 part of an isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Industry Co., Ltd., product name “Coronate L”) as a crosslinking agent to 100 parts of the acrylic polymer c contained in the toluene solution. .

  In place of the pressure-sensitive adhesive composition A, the pressure-sensitive adhesive composition C is used, and the foam base material No. Of the double-sided pressure-sensitive adhesive sheet of Example 4 except that the thickness of the pressure-sensitive adhesive layer formed on both sides of 2 is changed to 25 μm (Example 10), 50 μm (Example 11), and 75 μm (Example 12). In the same manner as the production method, double-sided PSA sheets (Examples 10 to 12) were obtained.

(Example 13, Example 14)
The adhesive composition B is used in place of the adhesive composition A, and the substrate No. In place of the base No. 1 3 and the substrate No. Except that the thickness after drying of the pressure-sensitive adhesive layer formed on both surfaces of 3 (Example 13) and 75 μm (Example 14), respectively, is the same as the method for producing the double-sided pressure-sensitive adhesive sheet of Example 1, Double-sided PSA sheets (Example 13, Example 14) were obtained.
Here, the base material No. Reference numeral 3 denotes a foam base material made of a polyethylene foam sheet having one surface and the other surface subjected to corona discharge treatment, the thickness thereof is 150 μm, and the tensile strength in the flow direction (tensile strength (MD )) Was 12.3 MPa, and the tensile strength in the width direction (tensile strength (TD)) was 7.5 MPa.

(Example 15, Example 16)
The adhesive composition B is used in place of the adhesive composition A, and the substrate No. In place of the base No. 1 4 and the base material No. Except that the thickness after drying of the pressure-sensitive adhesive layer formed on both sides of 4 is 50 μm (Example 15) and 100 μm (Example 16), respectively, in the same manner as the method for producing the double-sided pressure-sensitive adhesive sheet of Example 1, Double-sided PSA sheets (Example 15, Example 16) were obtained.
Here, the base material No. Reference numeral 4 denotes a foam base material made of a polyethylene foam sheet having one surface and the other surface subjected to corona discharge treatment, the thickness thereof is 100 μm, and the tensile strength (tensile strength (MD (MD )) Was 9.5 MPa, and the tensile strength in the width direction (tensile strength (TD)) was 8.2 MPa.

(Example 17)
The adhesive composition B is used in place of the adhesive composition A, and the substrate No. In place of the base No. 1 5 and the substrate No. A double-sided PSA sheet (Example 17) was obtained in the same manner as the double-sided PSA sheet preparation method of Example 1 except that the thickness of the PSA layer formed on both sides of No. 5 was 50 μm after drying.
Here, the base material No. Reference numeral 5 denotes a foam base material made of a polyethylene foam sheet having one surface and the other surface subjected to corona discharge treatment, the thickness thereof is 300 μm, and the tensile strength in the flow direction (tensile strength (MD )) Was 10.3 MPa, and the tensile strength in the width direction (tensile strength (TD)) was 8.5 MPa.

  The base material No. used for preparation of the double-sided pressure-sensitive adhesive sheets of Examples 1 to 17 above. 1-No. The foaming ratio, 25% compressive strength, tensile strength and tensile elongation of 5 are summarized in Table 1.

  Table 2 summarizes the gel fraction, the tan δ peak top temperature, and the storage elastic modulus G ′ (20 ° C.) at 20 ° C. used in the preparation of the double-sided PSA sheets of Examples 1 to 17.

<Evaluation test>
[180 degree peel strength]
The release liner covering one adhesive surface of the double-sided pressure-sensitive adhesive sheet was peeled off, and a polyethylene terephthalate (PET) film having a thickness of 25 μm was bonded to the one adhesive surface. This was cut into a size of 20 mm in width and 100 mm in length to produce a measurement sample.
In an environment of 23 ° C. and 50% RH, the other adhesive surface of the measurement sample was exposed, and the other adhesive surface was pressed against the surface of a stainless steel plate (SUS304BA plate) by reciprocating a 2 kg roller once. . After leaving this in the same environment for 30 minutes, using a universal tensile and compression tester (device name “Tensile and compression tester, TG-1kN” manufactured by Minebea Co., Ltd.), the tensile speed was determined according to JIS Z 0237. The peel strength (N / 20 mm width) was measured under the conditions of 300 mm / min and a peel angle of 180 degrees.

[Press adhesive strength]
The double-sided PSA sheet was cut into a window frame shape (frame shape) having a width of 59 mm, a length of 113 mm and a width of 1 mm as shown in FIG. Using this window frame-shaped double-sided pressure-sensitive adhesive sheet, a stainless steel plate having a horizontal plate of 59 mm, a vertical length of 113 mm, and a thickness of 1 mm (Corning Gorilla glass was used. A steel plate (SUS plate) (width 70 mm, length 130 mm, thickness 2 mm) was bonded to each other by pressing a 5 kg load over 10 seconds to obtain a sample for evaluation.
2A and 2B are schematic views of the evaluation sample, wherein FIG. 2A is a top view and FIG. 2B is a cross-sectional view taken along line AA ′. In FIG. 2, reference numeral 21 denotes a SUS plate, reference numeral 2 denotes a window frame-like double-sided pressure-sensitive adhesive sheet, reference numeral 22 denotes a glass plate, and reference numeral 21 </ b> A denotes a through hole provided in the SUS plate 21.
These samples for evaluation were set in the universal tension / compression tester. Then, a round bar was passed through the through hole of the SUS plate, and the round bar was lowered at a speed of 10 mm / min, thereby pressing the glass plate away from the SUS plate. And the maximum stress observed until a glass plate and a SUS board isolate | separated was measured as press adhesive force. The measurement was performed in an environment of 23 ° C. and 50% RH.
FIG. 3 is a schematic cross-sectional view showing a method for measuring the pressure adhesive force, where reference numeral 21 is a SUS plate, reference numeral 2 is a window frame-shaped double-sided adhesive sheet, reference numeral 22 is a glass plate, reference numeral 23 is a round bar, reference numeral 24 is A support stand is shown. The evaluation sample is fixed to the support 24 of the tensile and compression tester as shown in FIG. 3, and the glass plate 22 of the evaluation sample is pressed by the round bar 23 that has passed through the through hole 21 </ b> A of the SUS plate 21. In the measurement of the pressing adhesive force, the SUS plate 21 was not bent or damaged by a load applied when the glass plate 22 was pressed by the round bar 23.

[Shock resistance]
The double-sided PSA sheet was cut into a window frame shape (frame shape) having a width of 59 mm, a length of 113 mm, and a width of 1 mm as shown in FIG. A load of 5 kg is applied to the first PC board (width 70 mm, length 130 mm, thickness 2 mm) and the second PC board (width 59 mm, length 113 mm, thickness 0.55 mm) using this window frame-shaped double-sided adhesive sheet. Were bonded together by pressure bonding for 10 seconds to obtain a sample for evaluation (see FIGS. 4A and 4B).
4A and 4B are schematic views of the sample for evaluation, wherein FIG. 4A is a top view and FIG. 4B is a BB ′ cross-sectional view thereof. In FIG. 4, the code | symbol 31 has shown the 1st PC board, the code | symbol 3 has shown the window frame-shaped double-sided adhesive sheet, and the code | symbol 32 has shown the 2nd PC board.
A 160-g weight was attached to the back surface (surface opposite to the surface bonded to the second PC plate) of the first PC plate of these evaluation samples. About the sample for evaluation with the said weight, the drop test which makes it fall freely to a concrete board 60 times from the height of 1.2 m in normal temperature (about 23 degreeC) was done. At this time, the direction of the fall was adjusted so that the six surfaces of the sample for evaluation became sequentially lower. That is, 10 cycles of one drop pattern were performed for each of the six surfaces.
Then, each time it is dropped, it is visually confirmed whether or not the bonding between the first PC board and the second PC board is maintained, and the first PC board and the second PC board are peeled off ( The number of drops until separation) was evaluated as impact resistance against dropping at room temperature. When peeling was not observed after dropping 60 times, “60 times or more” or “> 60” was displayed.

[Repulsion resistance]
A double-sided PSA sheet is cut to a size of 10 mm in width and 100 mm in length, the release liner covering one of the adhesive surfaces is peeled off, and this is bonded to an aluminum plate having a thickness of 0.5 mm, a width of 10 mm, and a length of 100 mm. A piece was made. The test piece was bent in an arc along the cylinder with a radius of 15 mm (with the aluminum plate side inside), and then the release liner covering the other adhesive layer of the test piece was peeled off, and a laminator was used. The specimen was pressure-bonded to a PC plate having a thickness of 2 mm while returning the bent shape of the test piece. This was allowed to stand in an environment of 23 ° C. for 24 hours, and then heated at 70 ° C. for 2 hours, and then the height (mm) of both ends of the test piece that floated from the PC plate surface was measured. The measurement was performed using three test pieces (that is, n = 3), and an average value of these six measurement values was calculated.

[Thickness direction deformation during impact]
The double-sided PSA sheet was cut into a window frame shape (frame shape) having a width of 59 mm, a length of 113 mm, and a width of 1 mm to obtain a window frame-like double-sided PSA sheet. In addition, a stainless steel plate (SUS plate) (70 mm wide, 130 mm long, 2 mm thick) having a rectangular through-hole of 50 mm wide and 90 mm long in the center, and a glass plate (59 mm wide, 113 mm long, 1.5 mm thick) Corning Gorilla glass) was prepared. The window frame-shaped double-sided pressure-sensitive adhesive sheet was bonded so as to be sandwiched between the SUS plate and the glass plate, and a 5 kg load was applied for 10 seconds to obtain a test piece. In the test piece, the SUS plate was set in an impact test apparatus so that the glass plate side faced downward and the adhesive surface between the SUS plate and the double-sided PSA sheet was horizontal. Prepare a steel ball (diameter 11 mm, weight 28 g), and when this steel ball is dropped vertically, the steel ball passes through the inside of the through hole in the SUS plate and touches the SUS plate or double-sided adhesive sheet at all. It was arranged at a position that directly collided with the surface of the glass plate. At this time, the fall height of the steel ball (the distance (vertical distance) between the lowermost part of the steel ball before dropping and the glass plate) was adjusted to 1 m.
FIG. 5 is an explanatory diagram showing a method of measuring the deformation amount in the thickness direction at the time of impact. In FIG. 5, the code | symbol 41 shows a stainless steel plate (SUS board), the code | symbol 4 has a window frame-shaped double-sided adhesive sheet, the code | symbol 42 has shown the glass plate, and the code | symbol 43 has shown the steel ball.
As shown in FIG. 5, the steel ball 43 was freely dropped from above in an environment of about 23 ° C. and 50% RH. By photographing the behavior of the double-sided pressure-sensitive adhesive sheet 4 when the steel ball 43 collides with the glass plate 42 with a high-speed camera (Photolon Co., Ltd., photographing speed: 50000 FPS (frame per second)), image analysis of the result is performed. The deformation amount (elongation amount) in the thickness direction of the double-sided pressure-sensitive adhesive sheet 4 was measured. Specifically, the thickness (initial thickness) of the double-sided pressure-sensitive adhesive sheet 4 before dropping the steel ball 43 and the double-sided pressure-sensitive adhesive sheet 4 applied with force downward in the vertical direction due to the collision of the steel ball 43 are maximized in the thickness direction. From the thickness when displaced (maximum thickness), the amount of deformation in the thickness direction upon impact was calculated by the following equation (2).
(Amount of deformation in the thickness direction upon impact) = (maximum thickness)-(initial thickness) (2)

[Base material cohesion]
Cut the double-sided PSA sheet to a size of 20mm wide and 200mm long, and paste stainless steel foil of 30mm width, 300mm length, and 0.3mm thickness on the double-sided adhesive side respectively and press at a pressure of 1.0MPa for 20 seconds Was crimped. The bonding was performed by aligning the center of the double-sided pressure-sensitive adhesive sheet with the center of the stainless steel foil. A sample for evaluation was aged for 24 hours in an atmosphere of 50 ° C. and 50% RH.
About this sample for evaluation, the base material cohesion force was measured using an all-purpose tensile compression tester (device name “tensile compression tester, TG-1kN” manufactured by Minebea Co., Ltd.) in an atmosphere of 23 ° C. and 50% RH. . Specifically, as shown in FIG. 6, the first stainless steel foil 56 and the second stainless steel foil 57 bonded to the first adhesive layer 51 and the second adhesive layer 52 of the double-sided adhesive sheet 5, respectively. Stainless steel bonded with the double-sided adhesive sheet 5 by gripping one end in the longitudinal direction with chucks 58 and 59 of the above-mentioned testing machine and pulling the chuck 58 upward and chuck 59 downward at a speed of 150 mm / min. The foils 56 and 57 were peeled off into a T shape. The force required for the T-type peeling was measured with the above tester, and this was defined as the base material cohesive force (N / 20 mm width). In addition, the sample for evaluation after T-shaped peeling was observed visually, and peeling was not peeling at the adhesive interface between the pressure-sensitive adhesive layers 51 and 52 and the stainless steel foils 56 and 57 in the double-sided pressure-sensitive adhesive sheet, but foaming as shown in FIG. It was confirmed that this occurred due to breakage within the thickness of the body substrate 55.

[Processability evaluation]
The release liner covering one adhesive surface of the double-sided pressure-sensitive adhesive sheet according to each example is peeled off, and a resin (PET) release liner (thickness: 25 μm, release force against the adhesive surface: 0.10 N) on the exposed adhesive surface / 50 mm or more and 0.15 N / 50 mm or less) was attached so that the peeled surface was in contact with the adhesive surface. The operation of cutting the double-sided pressure-sensitive adhesive sheet from the resin release liner side to the double-sided pressure-sensitive adhesive sheet in the thickness direction of the pressure-sensitive adhesive sheet is performed using a known cutting machine, and a window having a width of 59 mm, a length of 113 mm, and a width of 1 mm. A frame-like (frame-like) double-sided PSA sheet was obtained. At this time, in the cutting machine, the cutter of the cutting machine passes through the resin release liner and the double-sided pressure-sensitive adhesive sheet, but does not pass through the release liner (peelable support) that covers the other pressure-sensitive adhesive surface. Operated.

In this workability evaluation, an operation procedure when the double-sided pressure-sensitive adhesive sheet is cut into a window frame will be described with reference to the drawings. FIGS. 7A to 7D schematically show cross-sectional views of the double-sided pressure-sensitive adhesive sheet and the cutting machine in the cutting operation or the pick-up operation. The double-sided pressure-sensitive adhesive sheet 6 is typically composed of a foam base material 65, a first pressure-sensitive adhesive layer 61, and a second pressure-sensitive adhesive layer 62.
As shown in FIG. 7 (a), as the first cutting operation, the double-sided pressure-sensitive adhesive sheet 6 is cut in the thickness direction by moving the cutter 72 of the cutting machine 70 downward from above the resin release liner 66. did. The cutter 72 was operated so as to penetrate the double-sided pressure-sensitive adhesive sheet 6 but not the release liner 67. Thus, the part which comprises the outer periphery of a window frame shape among the double-sided adhesive sheets 6 was isolate | separated.
Next, as shown in FIG. 7B, the outer edge of the double-sided pressure-sensitive adhesive sheet 6 is formed while leaving the double-sided pressure-sensitive adhesive sheet 6 constituting the inner portion of the window frame-shaped outer edge on the release liner 67. The part was removed from the release liner 67 by picking up by hand.
Subsequently, a second cutting operation was performed as shown in FIG. In the second cutting operation, similarly to the first cutting operation, the cutter 72 of the cutting machine 70 was moved downward from above the resin release liner 66 to cut the double-sided pressure-sensitive adhesive sheet 6 in the thickness direction. The cutter 72 was operated so as to penetrate the double-sided pressure-sensitive adhesive sheet 6 but not the release liner 67. Thereby, the part which comprises the inside of the said window frame shape among the double-sided adhesive sheets 6 was isolate | separated from the window frame shape part.
Finally, as shown in FIG. 7 (d), while leaving the window frame-shaped double-sided pressure-sensitive adhesive sheet 6 on the release liner 67, the part of the double-sided pressure-sensitive adhesive sheet 6 separated inside the window frame shape is hand-held. It was removed from above the release liner 67 by picking up with.
A window frame-like double-sided PSA sheet was obtained by such a series of processes.

  The obtained window frame-shaped double-sided PSA sheet was visually observed to confirm whether or not the PSA sheet was formed satisfactorily. Specifically, when the window frame-like double-sided pressure-sensitive adhesive sheet remained on the release liner while maintaining the shape of the window frame without lifting up from the release liner below the entire window frame, the workability was “good”. Moreover, when the double-sided pressure-sensitive adhesive sheet could not maintain the shape of the window frame by the series of cutting operations described above, the workability was judged as “bad”. Each of the double-sided pressure-sensitive adhesive sheets in each example was subjected to the processability evaluation test 20 times, and the number of times that the processability was “good” was counted and recorded.

[Liner peel strength]
The double-sided pressure-sensitive adhesive sheet according to each example was cut into a width of 50 mm to prepare a test piece. The test piece was set in a tensile tester, and the release liner was peeled off under the conditions of a measurement temperature of 25 ° C., a tensile speed of 300 mm / min, and a peeling angle of 180 degrees, and the peel strength at that time was measured. The test was performed 3 times and the average value was calculated.

[Ball tack evaluation]
With respect to the double-sided PSA sheet according to each example, an inclined ball tack (inclination angle of 30 degrees) was measured according to JIS Z 0237: 2009. The diameter of the largest ball that was stopped in the measuring section for 5 seconds or more was recorded as a ball tack.

  Tables 3 and 4 show the configurations of the double-sided PSA sheets according to Examples 1 to 17 and the results of the evaluation tests described above.

  As is clear from the results shown in Tables 3 and 4 above, No. 1 was used as the base material. 1 or No. 2 and the double-sided PSA sheets according to Examples 1 to 9 using the PSA composition A or B were confirmed to have excellent results in workability evaluation. Specifically, the double-sided PSA sheets according to Examples 1 to 9 showed good workability results with the number of times exceeding 10 times (frequency exceeding 50%) out of 20 times of the above-described workability evaluation test. Moreover, as a base material, it is No. 1 or No. 2 and the double-sided PSA sheet according to Examples 1 to 6 using the PSA composition A was found to have better processability.

  In addition, the liner peel strengths of the double-sided PSA sheets according to Examples 1 to 9 were all in the range of 0.23 N / 50 mm or more and 0.35 N / 50 mm or less. Moreover, all the double-sided adhesive sheets which concern on Examples 1-9 had the ball tack in the range of 0.8 mm or more and 9.5 mm or less. The double-sided pressure-sensitive adhesive sheets of Examples 1 to 6 having a ball tack of 5 mm or less showed better workability.

  No. as a base material. 1 or No. 2 and the double-sided pressure-sensitive adhesive sheet according to Examples 1 to 9 using the pressure-sensitive adhesive composition A or B showed a press adhesive force of approximately 200 N or more and was found to have good adhesive performance. Moreover, as a base material, it is No. 1 or No. 2 and the double-sided PSA sheet according to Examples 1 to 6 using the PSA composition A has a thickness direction deformation amount of 0.23 mm or less at the time of impact, and the deformation of the PSA sheet upon receiving an impact It became clear that the amount was small. The double-sided PSA sheets according to Examples 1 to 6 showed excellent performance in terms of repulsion resistance and 180 degree peel strength. Furthermore, No. 1 or No. The double-sided PSA sheets according to Examples 1 to 9 using 2 exhibited excellent impact resistance and high base material cohesion.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Double-sided adhesive sheet 11 1st adhesive layer 11A 1st adhesive surface 12 2nd adhesive layer 12A 2nd adhesive surface 15 Foam base material 15A 1st surface 15B 2nd surface 17 Release liner 17A Release liner front surface 17B Release liner Back side 2 Double-sided adhesive sheet 21 Stainless steel plate 21A Through hole 22 Glass plate 23 Round bar 24 Support base 3 Double-sided adhesive sheet 31, 32 Polycarbonate plate 4 Double-sided adhesive sheet,
41 Stainless steel plate 42 Glass plate 43 Steel ball 5 Double-sided adhesive sheet 51 First adhesive layer 52 Second adhesive layer 55 Foam substrate 56 First stainless steel foil 57 Second stainless steel foils 58 and 59 Chuck 6 Both sides Adhesive sheet 61 First adhesive layer 62 Second adhesive layer 65 Foam substrate 66 Resin release liner 67 Release liner 70 Cutting machine 72 Cutter

Claims (8)

A foam substrate;
A first pressure-sensitive adhesive layer provided on the first surface of the foam substrate;
A second pressure-sensitive adhesive layer provided on the second surface of the foam substrate,
The foam base material has an expansion ratio of 2.0 cm ³ / g or less,
The pressure-sensitive adhesive constituting at least one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer is a double-sided pressure-sensitive adhesive sheet having a peak top temperature of loss tangent tan δ of −30 ° C. or higher. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive has a storage elastic modulus G ′ at 20 ° C. of 8 × 10 ⁴ Pa or more.   The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the foam substrate has a 25% compressive strength of 200 kPa or more.   The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the foam substrate has a tensile strength in the flow direction of 15 MPa or more.   The double-sided pressure-sensitive adhesive according to any one of claims 1 to 4, wherein the foam base material has a tensile elongation in the flow direction of 400% or more and a tensile elongation in the width direction of 200% or more. Sheet.   The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein the foam base material has a base material cohesive force of 40 N / 20 mm or more. The pressure-sensitive adhesive includes a tackifier resin,
The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 6, wherein the tackifying resin has a softening point of 120 ° C or higher.   The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 7, which is used for joining parts of a portable electronic device.

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