JP6683765B2 - Double-sided adhesive sheet - Google Patents

Description

  The present invention relates to a double-sided PSA sheet having a foam base material.

  Generally, a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive; the same applies below) exhibits a soft solid state (viscoelastic body) in a temperature range around room temperature and has a property of easily adhering to an adherend by pressure. Taking advantage of these properties, the pressure-sensitive adhesive is widely used in various fields for the purpose of bonding or fixing, for example, in the form of a double-sided pressure-sensitive adhesive sheet with a substrate in which pressure-sensitive adhesive layers are provided on both sides of the substrate. .

  As the base material in the double-sided pressure-sensitive adhesive sheet with a base material, generally, in addition to plastic film, non-woven fabric, paper and the like, foam having a cell structure can be used. The double-sided pressure-sensitive adhesive sheet using the foam (double-sided pressure-sensitive adhesive sheet with a foam substrate) has impact absorption and uneven conformability as compared with a double-sided pressure-sensitive adhesive sheet having a plastic film as a base material. Can be advantageous. Further, it can be advantageous in terms of waterproofness, sealing property, etc., as compared with a double-sided pressure-sensitive adhesive sheet using a nonwoven fabric as a base material. Therefore, it 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 to 3 are cited as technical documents relating to the double-sided PSA sheet with a foam substrate.

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

  In recent years, from the viewpoint of downsizing and weight reduction of products, it has been required to reduce the width of double-sided pressure-sensitive adhesive sheets used for joining parts. For example, a double-sided adhesive sheet used for fixing a display panel (glass lens, etc.) of a portable electronic device has a double-sided adhesive sheet from the viewpoints of a large screen of the information display part, improvement in designability, and improvement in design flexibility. It is meaningful to narrow the sheet.

By the way, a double-sided pressure-sensitive adhesive sheet used for joining components or the like in a portable electronic device or the like is required to have the ability to withstand an impact such as a drop and maintain the joining (hereinafter, also referred to as impact resistance).
On the other hand, due to the narrowing of the double-sided pressure-sensitive adhesive sheet, a phenomenon such as a display panel in a portable electronic device or the like, which is not originally designed to be subjected to a shock, may be damaged by a shock such as a drop. It has become possible to be. Therefore, the double-sided pressure-sensitive adhesive sheet is required to have a property (hereinafter, also referred to as impact protection property) of suppressing the product from being damaged when it receives an impact such as a drop.
Therefore, it is an object of the present invention to provide a double-sided pressure-sensitive adhesive sheet which is excellent in impact protection in addition to impact resistance.

  As a result of detailed investigation of the behavior of the double-sided pressure-sensitive adhesive sheet with respect to impact, the present inventor has found that the phenomenon in which the pressure-sensitive adhesive sheet is instantaneously deformed in the thickness direction due to impact is one of the causes of impairing impact protection. Then, the present invention has been completed by finding a double-sided PSA sheet suitable for both impact resistance and impact protection.

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 first adhesive layer provided on the second surface of the foam base material. Two adhesive layers. The expansion ratio of the foam base material is 2.0 cm ³ / g or less. The 25% compressive strength of the foam substrate is 200 kPa or more. The double-sided pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet with a foam base material) having such a configuration can have excellent impact resistance. In addition, the amount of deformation in the thickness direction when receiving an impact (also referred to as the amount of deformation in the thickness direction at the time of impact; the same applies hereinafter) is small, and good impact protection can be exhibited.

  In a preferred aspect of the double-sided PSA sheet disclosed herein, the 25% compressive strength of the foam substrate is 500 kPa or more. A double-sided pressure-sensitive adhesive sheet containing such a foam substrate has a small amount of deformation in the thickness direction upon impact, and can exhibit better impact protection.

  In a preferred embodiment of the double-sided PSA sheet disclosed herein, the foam substrate has a substrate cohesive force of 40 N / 20 mm or more. A double-sided pressure-sensitive adhesive sheet containing such a foam substrate can exhibit better impact resistance.

  In a preferred embodiment of the double-sided PSA sheet disclosed herein, as the foam substrate, for example, one having a tensile elongation of 400% or more in its flow direction (also referred to as MD; hereinafter the same) is preferably used. You can A double-sided PSA sheet containing such a foam substrate is preferable from the viewpoint of handleability of the double-sided PSA sheet. From this point of view, the tensile elongation in the width direction of the foam substrate (also referred to as TD, the same applies hereinafter) is preferably 200% or more.

  In a preferred embodiment of the double-sided PSA sheet disclosed herein, the foam base material has a tensile strength of 15 MPa or more in the machine direction (MD). A double-sided PSA sheet containing such a foam base material can exhibit better handleability.

  In a preferable embodiment of the double-sided PSA sheet disclosed herein, the foam base material is a polyolefin-based foam base material. A double-sided pressure-sensitive adhesive sheet containing such a foam base material can be excellent in impact protection and exhibit good impact resistance.

  In a preferred embodiment of the double-sided PSA sheet disclosed herein, the PSA forming at least one of the first PSA layer and the second PSA layer contains a tackifying resin having a softening point of 135 ° C. or higher. According to this mode, a double-sided pressure-sensitive adhesive sheet having more excellent repulsion resistance can be realized.

  The double-sided pressure-sensitive adhesive sheet disclosed herein is suitable as, for example, a double-sided pressure-sensitive adhesive sheet used for joining components of a portable electronic device because it has excellent impact resistance and impact protection.

It is a typical sectional view showing composition of a double-sided PSA sheet concerning one embodiment. It is explanatory drawing which shows the sample for evaluation used when measuring a 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 amount at the time of impact. It is explanatory drawing which shows the measuring method of base material cohesive force.

Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters particularly referred to in the present specification and matters necessary for carrying out the present invention can be understood as design matters for those skilled in the art based on conventional techniques in the field. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the field.
In the following drawings, members and parts having the same operation may be described with the same reference numerals, and redundant description may be omitted or simplified. In addition, the embodiments described in the drawings are schematically illustrated for clearly explaining the present invention, and do 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 term "adhesive" refers to a material that is in the state of a soft solid (viscoelastic body) in the temperature range near room temperature and has the property of easily adhering to an adherend by pressure, as described above. . The adhesive used herein generally has a complex tensile modulus E ^* (1 Hz) as defined in “CA Dahlquist,“ Adhesion: Fundamental and Practice ”, McLaren & Sons, (1966) P. 143”. A material having a property of satisfying <10 ⁷ dyne / cm ² (typically, a material having the above property at 25 ° 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. Ingredients occupying the above).

  The double-sided pressure-sensitive adhesive sheet disclosed herein (which may be in the form of a tape or the like) has a foam base material and a first surface and a second surface respectively provided on the foam base material. It is configured to include one adhesive layer and a second adhesive layer. For example, it may be a double-sided PSA sheet having a cross-sectional structure shown in FIG. The double-sided pressure-sensitive adhesive sheet 1 includes a sheet-shaped foam base material 15, and a first pressure-sensitive adhesive layer 11 and a second pressure-sensitive adhesive layer 12 supported on both surfaces of the base material 15, respectively. 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 of which are non-peeling) 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 superposed with a release liner 17 whose front surface 17A and back surface 17B are both release surfaces and is wound in a spiral shape. It may be in the formed form. In the double-sided pressure-sensitive adhesive sheet 1 having such a 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.

  As the release liner, a commonly used release paper or the like can be used and is not particularly limited. For example, a release liner having a release treatment layer on the surface of a liner substrate such as a plastic film or paper; from a low-adhesion material such as a fluoropolymer (polytetrafluoroethylene, etc.) or a polyolefin resin (polyethylene, polypropylene, etc.) And the like. The release treatment layer may be formed by subjecting the liner substrate to a surface treatment with a release treatment agent such as silicone-based, long-chain alkyl-based, fluorine-based or molybdenum sulfide.

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

  Here, the total thickness of the double-sided pressure-sensitive adhesive sheet means 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 in the case of 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 provided with a portion having cells (cell structure), and is typically at least one thin layered foam (foam layer). ) Is included. The foam base material may be a base material substantially constituted by only the foam layer. Although not particularly limited, a preferable example of the foam substrate in the technology disclosed herein is a foam substrate including a single layer (one layer) of foam layer.

  The thickness of the foam base material is not particularly limited, and can be appropriately set depending on the strength and flexibility of the double-sided pressure-sensitive adhesive sheet, the purpose of use, and the like. From the viewpoint of easily securing the thickness of the pressure-sensitive adhesive layer that can exhibit desired pressure-sensitive adhesive properties, it is usually appropriate to set the thickness of the foam substrate to 700 μm or less, preferably 400 μm or less, and more preferably It is 300 μm or less, for example 200 μm or less. A foam base material having a thickness of 180 μm or less may be used. Further, from the viewpoint of the repulsion resistance and impact resistance of the double-sided PSA 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). And above). The repulsion resistance as used herein means that when the double-sided pressure-sensitive adhesive sheet is elastically deformed along the surface shape (curved surface, stepped surface, etc.) of the adherend, the double-sided pressure-sensitive adhesive sheet has the original shape. It refers to the ability to hold 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).

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

  Specific examples of the plastic foam include polyolefin-based resin foams such as polyethylene foam and polypropylene foam; polyester-based foams such as polyethylene terephthalate foam, polyethylene naphthalate foam, and polybutylene terephthalate foam. Resin foam; polyvinyl chloride resin foam such as polyvinyl chloride foam; vinyl acetate resin foam; polyphenylene sulfide resin foam; aliphatic polyamide (nylon) resin foam, wholly aromatic Polyamide (aramid) resin foam or other amide resin foam; Polyimide resin foam; Polyether ether ketone (PEEK) foam; Polystyrene foam or other styrene resin foam; Polyurethane Urethane-based resin foams such as resin foams; . Further, as the plastic foam, a rubber-based resin foam such as a polychloroprene rubber foam may be used.

  As a preferable foam, a polyolefin resin foam (hereinafter, also referred to as “polyolefin foam”) is exemplified. As the plastic material (that is, the polyolefin-based resin) forming the polyolefin-based foam, various known or commonly used polyolefin-based 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-based linear low-density polyethylene and metallocene catalyst-based linear low-density polyethylene. Such polyolefin resins can be used alone or in combination of two or more kinds.

  A preferable example of the foam base material in the technology disclosed herein is a polyethylene foam base substantially composed of a polyethylene resin foam from the viewpoint of impact resistance, impact protection, waterproofness, and the like. And a polypropylene-based foam base material that is substantially composed of a polypropylene-based resin foam. Here, the polyethylene-based resin refers to a resin having ethylene as a main monomer (that is, a main component among the monomers), and in addition to HDPE, LDPE, LLDPE, etc., ethylene having an ethylene copolymerization ratio of more than 50% by weight. -Propylene copolymer, ethylene-vinyl acetate copolymer and the like may be included. Similarly, the polypropylene resin refers to a resin containing propylene as a main monomer. As the foam base material in the technology disclosed herein, a polyethylene-based foam base material can be preferably adopted.

The method for producing the plastic foam (typically a polyolefin-based foam) is not particularly limited, and it can be produced by a known method. For example, the plastic material or the plastic foam can be produced by a method including a molding step, a crosslinking step and a foaming step. In addition, a stretching step may be included if necessary.
Examples of the method for cross-linking the plastic foam include a chemical cross-linking method using an organic peroxide and the like, an ionizing radiation cross-linking method in which ionizing radiation is applied, and these methods can be used in combination. Examples of the ionizing radiation include electron beams, α rays, β rays, γ rays and the like. 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, degree of crosslinking) of the foam base material.

  The average cell diameter of the foam base material (for example, a polyolefin-based foam base material) is not particularly limited, but is usually preferably 500 μm or less, more preferably 300 μm or less, and further preferably from the viewpoint of waterproofness. It is 100 μm or less, for example, 75 μm or less. On the other hand, from the viewpoint of impact resistance, the average cell diameter of the foam base material is preferably 5 μm or more, and more preferably 10 μm or more. The average bubble diameter can be measured, for example, by an optical microscope.

  It is suitable that the average cell diameter is usually 50% or less, and preferably 30% or less (for example, 10% or less) of the thickness of the foam base material which is the cell-containing layer. When the average cell diameter is 50% or less of the thickness of the foam substrate, the waterproof property tends to be further improved.

In a preferred embodiment of the technique disclosed herein, as the foam substrate, for example, a foaming ratio of 2.15 cm ³ / g or less can be used. The foaming ratio of the foam base material is preferably 2.0 cm ³ / g or less, and more preferably 1.95 cm ³ / g or less, from the viewpoint of better suppressing the deformation in the thickness direction at the time of impact and improving the impact protection property. And more preferably 1.9 cm ³ / g or less. In a preferred embodiment, the expansion ratio of the foam substrate, for example 1.85 cm ³ / g may be less, may be less further 1.8 cm ³ / g. 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, 1.5 cm ³ / g More preferably (for example, 1.6 cm ³ / g or more). Increasing the expansion ratio tends to improve flexibility, improve step followability and repulsion resistance. When the double-sided pressure-sensitive adhesive sheet has a good step-following property, generally, even when the double-sided pressure-sensitive adhesive sheet is attached to an adherend having a step, a gap is less likely to form between the surface of the adherend and the waterproof property is improved. In this specification, the expansion ratio of the foam substrate is defined as the reciprocal of the apparent density (g / cm ³ ) measured according to JIS K6767.

In another preferable aspect of the technique disclosed herein, the foaming ratio of the foam substrate is preferably 1.8 cm ³ / g or less, and 1.7 cm ³ / g or less (typically 1 cm ³ / g or less). It is more preferably 0.6 cm ³ / g or less, for example 1.55 cm ³ / g or less). At this time, the lower limit of the expansion ratio is not particularly limited, but for example, 1.1 cm ³ / g or more is suitable, 1.2 cm ³ / g or more is preferable, and 1.25 cm ³ / g or more. Is more preferable. A double-sided pressure-sensitive adhesive sheet using a foam having a foaming ratio in the above range is preferable because it can exhibit a high pressure-sensitive adhesive force even if it has a narrow width (for example, less than 1 mm).

  The tensile elongation of the foam base material (for example, the polyolefin foam base material) is not particularly limited. For example, the tensile elongation in the machine direction (MD) is 200% or more and 800% or less (more preferably 300% or more and 700% or less, further preferably 400% or more and 600% or less, for example 450 or more and 500% or less). preferable. 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, further preferably 200% or more and 500% or less, for example, 250% or more and 400% or less). Is preferred. By setting the elongation to the above lower limit or more, impact resistance and step followability can be improved. Moreover, when the elongation is equal to or less than the above-mentioned upper limit value, the strength of the foam substrate can be improved, and the handleability and the impact protection property can be improved. The elongation of the foam substrate is measured according to JIS K6767. The elongation of the foam base material can be controlled by, for example, the degree of cross-linking or the expansion ratio.

  The tensile strength (tensile strength) of the foam base material (for example, the polyolefin-based foam base material) is not particularly limited. For example, the tensile strength in the machine direction (MD) is 5 MPa or more and 35 MPa or less (more preferably 10 MPa or more and 30 MPa or less, further 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 20 MPa or less). It is preferable. 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, further preferably 7 MPa or more and 15 MPa or less, typically 8 MPa or more and 12 MPa or less, for example, 9 MPa or more and 11 MPa or less). It is preferable. By setting the tensile strength to the above lower limit or more, for example, when peeling off a double-sided pressure-sensitive adhesive sheet that has been stuck, the base material (and by extension, the double-sided pressure-sensitive adhesive sheet) can be easily peeled off without tearing and has excellent handleability. (Reworkability). In addition, the fact that the double-sided pressure-sensitive adhesive sheet is easily peeled off as described above is also advantageous when the product is disassembled and the parts are recycled, or when the defective part is replaced. On the other hand, when the tensile strength is equal to or less than the above-mentioned upper limit value, impact resistance and step followability can be improved. The tensile strength of the foam base material (tensile strength in the flow direction, tensile strength in the width direction) is measured according to JIS K6767. The tensile strength of the foam base material can be controlled by, for example, the degree of cross-linking or the expansion ratio.

  The 25% compressive strength of the foam base material (for example, the polyolefin-based foam base material) is not particularly limited and may be, for example, 100 kPa or more and 1200 kPa or less. From the viewpoint of impact protection, the 25% compressive strength of the foam base material is preferably 200 kPa or more and 1100 kPa or less, more preferably 400 kPa or more and 1000 kPa or less, further preferably 500 kPa or more and 900 kPa or less, for example, 550 kPa or more and 850 kPa or less. Preferably there is. Here, the 25% compressive strength of the foam base material means that the foam base materials are stacked so as to have a thickness of about 25 mm and sandwiched by flat plates, and the thickness is equivalent to 25% of the initial thickness. It is the load when compressed. That is, it refers to the load when the stacked foam base materials are compressed to a thickness corresponding to 75% of the initial thickness. By increasing the 25% compressive strength, the amount of deformation of the double-sided PSA sheet in the thickness direction upon impact tends to be suppressed, and good impact protection may tend to be exhibited, and the dimensional stability during processing may be improved. On the other hand, when the 25% compression strength is 1200 kPa or less, the repulsion resistance and the step followability can be improved. The 25% compressive strength of the foam substrate is measured according to JIS K 6767. The 25% compressive strength of the foam base material can be controlled by, for example, the degree of crosslinking or the expansion ratio.

Generally, the 25% compressive strength of the foam substrate tends to improve as the expansion ratio of the foam substrate decreases. Although not particularly limited, the value obtained by dividing the value of 25% compressive strength of the foam substrate by the value of expansion ratio (hereinafter, also referred to as (25% compression strength) / (expansion ratio)) is It is preferably 100 g · kPa / cm ³ or more, more preferably 180 g · kPa / cm ³ or more, further 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 (25% compressive strength) / (foaming ratio) is equal to or more than the above lower limit, the deformation amount in the thickness direction of the double-sided PSA sheet at the time of impact is better suppressed, and the impact protection property tends to be improved. In a preferred embodiment, a foam substrate having a (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 (25% compressive strength) / (foaming ratio) is not particularly limited, but from the viewpoint of repulsion resistance and step followability, it is preferably 1100 g · kPa / cm ³ or less, more preferably 800 g · kPa. / 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. From the viewpoint of impact protection, the density of the foam substrate is preferably 0.5 g / cm ³ or more and 0.8 g / cm ³ or less, and more preferably 0.51 g / cm ³ or more and 0.75 g / cm. ³ or less, and in another preferable embodiment, a foam substrate having a density of 0.55 g / cm ³ or more and 0.72 g / cm ³ or less (for example, 0.6 g / cm ³ or more and 0.7 g / cm ³ or less). Materials can be used. By increasing the density, there is a tendency that the amount of deformation in the thickness direction upon impact is suppressed, the strength of the foam substrate (and thus the strength of the double-sided PSA sheet) is improved, and the impact resistance and handleability are improved. On the other hand, when the density is 0.9 g / cm ³ or less, the step followability, the repulsion resistance and the waterproof property tend to be improved. The density (apparent density) of the foam substrate can be measured, for example, by a method according to JIS K6767.

  The cohesive force (also referred to as base material cohesive force, unit: N / 20 mm) of the foam base material measured by the measurement method described later 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, further preferably 50 N / 20 mm or more, for example 55 N / 20 mm or more. The upper limit of the cohesive strength of the base material is not particularly limited, but for example, a foam base material having a cohesive strength of the base material 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 done. When the cohesive strength of the base material of the foam base material is equal to or more than the above lower limit, damage to the foam base material due to impact is better prevented, so that bonding reliability is good and better impact resistance can be exhibited. When the cohesive strength of the base material of the foam base material is not more than the above-mentioned upper limit value, the shock absorbing property tends to be good, and good impact resistance tends to be exhibited.

  In the foam substrate, if necessary, a filler (inorganic filler, organic filler, etc.), antioxidant, antioxidant, ultraviolet absorber, antistatic agent, lubricant, plasticizer, flame retardant, Various additives such as a surfactant may be blended.

  The foam substrate in the technology disclosed herein is colored in order to exhibit desired design properties and optical characteristics (for example, light shielding property, light reflectivity, etc.) in a double-sided pressure-sensitive adhesive sheet including the foam substrate. May be. For this coloring, known organic or inorganic coloring agents can be used alone or in combination of two or more kinds.

  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 it is 0% or more like 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. When the double-sided PSA sheet disclosed herein is used for light reflection, the visible light reflectance of the foam substrate is preferably 20% or more and 100% or less, like the visible light reflectance of the double-sided PSA sheet, It is more preferably 25% or more and 100% or less.

  The visible light transmittance of the foam substrate is measured by using a spectrophotometer (for example, a spectrophotometer manufactured by Hitachi High-Technologies Corporation, model “U-4100”) at a wavelength of 550 nm. It can be determined by measuring the intensity of light that is 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 by irradiating one surface of the foam base material at a wavelength of 550 nm using the spectrophotometer. The visible light transmittance and the visible light reflectance of the double-sided pressure-sensitive adhesive sheet can be determined by the same method.

  When the double-sided PSA sheet disclosed herein is used for light shielding, the foam base material is preferably colored black. Black is L * (brightness) defined by the L * a * b * color system, and is preferably 35 or less (for example, 0 to 35), more preferably 30 or less (for example, 0 to 30). . It should be noted that a * and b * defined by the L * a * b * color system can be appropriately selected according to the value of L *. The a * and b * are not particularly limited, but both 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 almost 0.

  In the present specification, L *, a *, and b * defined by the L * a * b * color system are colorimeters (for example, a colorimeter manufactured by Minolta Co., Ltd., trade name “CR-200”. )) Is used for measurement. 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. Further, the L * a * b * color system is defined in JIS Z 8729 in the Japanese Industrial Standards.

  Examples of the black colorant used for coloring the foam substrate in 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 (non-magnetic ferrite, magnetic ferrite, etc.), magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complex, complex oxide black pigment, anthraquinone organic black A dye or the like 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 may be an amount appropriately adjusted so as to impart desired optical characteristics.

  When the double-sided PSA sheet disclosed herein is used for light reflection, the foam base material is preferably colored white. The white color is L * (lightness) defined by the L * a * b * color system, and 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 *. Both a * and b * are preferably in the range of, for example, -10 to 10 (more preferably -5 to 5 and further preferably -2.5 to 2.5). For example, it is preferable that both a * and b * are 0 or almost 0.

  Examples of the white colorant used for coloring the foam base material in white include titanium oxide (titanium dioxide such as rutile titanium dioxide and anatase titanium dioxide), zinc oxide, aluminum oxide, silicon oxide, 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 carbon, diatomaceous earth, bentonite, lithopone, zeolite, sericite, hydrohaloysite, acrylic resin particles, polystyrene resin particles, polyurethane resin particles, amide resin particles, polycarbonate resin particles, silicone Examples include organic white colorants such as resin particles, urea-formalin resin particles, and melamine resin particles. The amount of white colorant used is not particularly limited, and may be an amount appropriately adjusted so as to impart desired optical characteristics.

  The surface of the foam substrate may be subjected to an appropriate surface treatment, if necessary. This surface treatment can be, for example, a chemical or physical treatment for enhancing the 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).

  In the technology disclosed herein, the type of adhesive contained in each of the first adhesive layer and the second adhesive layer is not particularly limited. Examples of the adhesive include one or more selected from various polymers (adhesive polymers) such as acrylic, polyester, urethane, polyether, rubber, silicone, polyamide, and fluorine. Can be used as a base polymer. In a preferred aspect, the main component of the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive. The technology disclosed herein can be preferably carried out 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 among polymer components, that is, a component accounting for 50% by weight or more). "Acrylic polymer" means a monomer having at least one (meth) acryloyl group in one molecule (hereinafter, this may be referred to as "acrylic monomer") as a main constituent monomer component (mainly monomer). Component, that is, a polymer that constitutes 50% by weight or more of the total amount of monomers constituting the acrylic polymer). In addition, in the present specification, the term “(meth) acryloyl group” means a generic term for an acryloyl group and a methacryloyl group. Similarly, "(meth) acrylate" is meant to refer to acrylates and methacrylates comprehensively.

The acrylic polymer is typically a polymer containing an alkyl (meth) acrylate as a main constituent monomer component. As the alkyl (meth) acrylate, for example, a compound represented by the following formula (1) can be preferably used.
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. R ² is an alkyl group having 2 to 14 carbon atoms (hereinafter, such a range of the number of carbon atoms may be referred to as C _2-14 ) because an adhesive having excellent adhesive properties can be easily obtained. Certain alkyl (meth) acrylates are preferred. Specific examples of the C _2-14 alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a s-butyl group, a t-butyl group, an n-pentyl group and an 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- Dodecyl group, n-tridecyl group, n-tetradecyl group and the like can be mentioned.

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

  Although not particularly limited, as the acrylic polymer in the technique disclosed herein, a copolymer of an acrylic monomer having a hydroxyl group (—OH) can be preferably used. 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, and 4-hydroxypropyl (meth) acrylate. 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 (meth Acrylamide, and the like. These 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 it is easy to obtain a pressure-sensitive adhesive having an excellent balance between adhesive strength and cohesive strength and excellent removability. Particularly preferred hydroxyl group-containing acrylic monomers are 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and 4-hydroxybutyl ( Hydroxyalkyl (meth) acrylates such as (meth) acrylates. For example, a hydroxyalkyl (meth) acrylate in which the alkyl group in the hydroxyalkyl group is a linear chain having 2 to 4 carbon atoms can be preferably used.

  Such a hydroxyl group-containing acrylic monomer is preferably used in the range of approximately 0.001% by weight or more and 10% by weight or less based on the total amount of the monomers used for the synthesis of the acrylic polymer. As a result, a double-sided pressure-sensitive adhesive sheet can be realized in which the pressure-sensitive adhesive force and the cohesive force are balanced at a higher level. By using the hydroxyl group-containing acrylic monomer in an amount of about 0.01% by weight or more and 5% by weight or less (for example, 0.05% by weight or more and 2% by weight or less), better results can be achieved. Alternatively, the acrylic polymer in the technology disclosed herein may not be copolymerized with a hydroxyl group-containing acrylic monomer.

  The acrylic polymer in the technique disclosed herein may be copolymerized with a monomer (other monomer) other than the above, within a range that does not significantly impair the effects of the present invention. Such a monomer can be used for the purpose of, for example, adjusting the glass transition temperature of the acrylic polymer, adjusting the adhesive performance (for example, releasability), and the like. Examples of the monomer capable of improving the cohesive force 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, aromatic vinyl compounds and the like. Further, as a monomer that can introduce a functional group that can serve as a cross-linking group point into an acrylic polymer or contribute to the improvement of adhesive strength, a carboxyl group-containing monomer, an acid anhydride group-containing monomer, an amide group-containing monomer, an amino group-containing monomer, Examples thereof include imide group-containing monomers, epoxy group-containing monomers, (meth) acryloylmorpholine, and vinyl ethers. For example, an acrylic polymer in which a carboxyl group-containing monomer is copolymerized as the above-mentioned other monomer is preferable.

Examples of the sulfonic acid group-containing monomer include styrenesulfonic acid, allylsulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, (meth) acrylamidopropanesulfonic acid, sulfopropyl (meth) acrylate, (meth) acryloyloxy. Examples thereof include naphthalene sulfonic acid and sodium vinyl sulfonate.
2-hydroxyethyl acryloyl phosphate is illustrated as a phosphoric acid group containing monomer.
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 aromatic vinyl compounds include styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, and other substituted styrenes.

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 substances of the carboxyl group-containing monomer.
Examples of the amide group-containing monomer include acrylamide, methacrylamide, diethylacrylamide, N-vinylpyrrolidone, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, N, N-diethylacrylamide, N, N-diethylmethacrylamide. Examples 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 and N, N-dimethylaminopropyl (meth) acrylate.
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, methylglycidyl (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 alone or in combination of two or more, but the total content is the amount of the monomers used for the synthesis of the acrylic polymer. The total amount is preferably about 40% by weight or less (typically 0.001% by weight to 40% by weight), and about 30% by weight or less (typically 0.01% by weight to 30% by weight). Below, for example, 0.1 wt% or more and 10 wt% or less) is more preferable. When a carboxyl group-containing monomer is used as the other monomer, the content thereof can be, for example, 0.1% by weight or more and 10% by weight or less, and usually 0.2% by weight or more and 8% by weight or less, based on the total amount of the above monomers. Below, for example, 0.5 wt% or more and 5 wt% or less is appropriate. When vinyl esters (for example, vinyl acetate) are used as the above-mentioned other monomers, the content thereof can be, for example, 0.1% by weight or more and 20% by weight or less of the total amount of the above monomers, and is usually 0.5% by weight or less. It is appropriate to set the content in the range of 10% to 10% by weight.

  It is appropriate that the copolymer composition of the acrylic polymer is designed so that the glass transition temperature (Tg) of the polymer is −15 ° C. or lower (typically −70 ° C. or higher and −15 ° C. or lower). It is preferably -25 ° C or lower (for example, -60 ° C or higher and -25 ° C or lower), more preferably -40 ° C or lower (for example, -60 ° C or higher and -40 ° C or lower). It is preferable that the Tg of the acrylic polymer is not more than the above-mentioned upper limit value from the viewpoint of impact resistance of the double-sided PSA sheet.

  The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (that is, the kind and the amount ratio of the monomers used for the synthesis of the polymer). Here, the Tg of the acrylic polymer means the Fox based on the Tg of the homopolymer (homopolymer) of each monomer constituting the polymer and the weight fraction of the monomers (copolymerization ratio on a weight basis). The value obtained from the formula. As the Tg of the homopolymer, the value described in publicly known data shall be adopted.

In the technology disclosed herein, the following values are specifically used as Tg of the homopolymer.
2-ethylhexyl acrylate -70 ° C
Butyl acrylate -55 ° C
Ethyl acrylate-22 ° C
Methyl acrylate 8 ℃
Methyl methacrylate 105 ° C
Cyclohexyl methacrylate 66 ° C
Vinyl acetate 32 ° C
Styrene 100 ℃
Acrylic acid 106 ℃
Methacrylic acid 228 ° C

  Regarding the Tg of homopolymers other than those exemplified above, the values described in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc, 1989) shall be used.

Unless described in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc, 1989), the value obtained by the following measuring method shall be used.
Specifically, in a reactor equipped with a thermometer, a stirrer, a nitrogen introducing tube and a reflux cooling tube, 100 parts by weight of the monomer, 0.2 parts by weight of azobisisobutyronitrile and 200 parts by weight of ethyl acetate as a polymerization solvent were added. It is charged and stirred for 1 hour while circulating nitrogen gas. After removing oxygen in the polymerization system in this way, the temperature is raised to 63 ° C. and the reaction is carried out for 10 hours. Then, it is cooled to room temperature to obtain a homopolymer solution having a solid content concentration of 33% by weight. Then, this homopolymer solution is cast-coated on a release liner and dried to prepare a test sample (sheet-like homopolymer) having a thickness of about 2 mm. This test sample was punched into a disk shape with a diameter of 7.9 mm, sandwiched by parallel plates, and a shear strain with a frequency of 1 Hz was measured using a viscoelasticity tester (TA Instruments Japan, Inc., model name "ARES"). The viscoelasticity was measured in a shear mode at a temperature range of −70 ° C. to 150 ° C. and a temperature increase rate of 5 ° C./min., And a temperature (G ”curve corresponding to the peak top temperature of the shear loss elastic modulus G ″ was measured. The maximum temperature) is taken as the Tg of the homopolymer.

  The pressure-sensitive adhesive in the technology disclosed herein is designed such that the shear loss modulus G ″ of the pressure-sensitive adhesive has a peak top temperature of −10 ° C. or lower (typically −40 ° C. or higher and −10 ° C. or lower). For example, the pressure-sensitive adhesive is preferably designed so that the peak top temperature is −35 ° C. or higher and −15 ° C. or lower. The shear loss elastic modulus G ″ has a peak top temperature of a sheet having a thickness of 1 mm. -Shaped adhesive is punched into a disk shape with a diameter of 7.9 mm, sandwiched between parallel plates, and a frequency of 1 Hz is obtained using the above-mentioned viscoelasticity testing machine (TA Instruments Japan, model name "ARES"). The temperature dependence of the loss elastic modulus G ″ was measured by the shear mode at a temperature increasing rate of −70 ° C. to 150 ° C. and a temperature increase rate of 5 ° C./min while applying the shear strain. Temperature can be grasped by obtaining the (G "curve temperature at which the maximum).

  The peak top temperature of the shear loss modulus G ″ of the acrylic polymer is adjusted by appropriately changing the monomer composition of the acrylic polymer (that is, the kind and the amount ratio of the monomers used for the synthesis of the polymer). The peak top temperature of the shear loss elastic modulus G ″ of the pressure-sensitive adhesive is determined by the monomer composition of the acrylic polymer (that is, the kind and the ratio of the amounts of the monomers used for the synthesis of the polymer) and the tackifier described later. It can be adjusted by appropriately changing the presence or absence of the use of, the type of use, the amount used, and the like.

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

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

  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-based polymerization initiator can be preferably used. Specific examples of the azo-based polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylpropionamidine) disulfate, and 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-carbonite) 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 is a redox type initiator obtained by combining a peroxide and a reducing agent. Examples of such redox initiators include a combination of peroxide and ascorbic acid (a combination of hydrogen peroxide solution and ascorbic acid), a combination of a peroxide and an iron (II) salt (hydrogen peroxide solution). And iron (II) salt), a combination of persulfate and sodium bisulfite, and the like.

  Such polymerization initiators may be used alone or in combination of two or more. The amount of the polymerization initiator used may be a usual amount, and for example, 0.005 parts by weight or more and 1 part by weight or less (typically 0.01 parts by weight or more It can be selected from the range of about 1 part by weight or less).

  According to such solution polymerization, a polymerization reaction liquid in which an acrylic polymer is dissolved in an organic solvent is obtained. As the acrylic polymer in the technique disclosed herein, the above-mentioned polymerization reaction liquid or the one obtained by subjecting the reaction liquid to an appropriate post-treatment can be preferably used. Typically, the acrylic polymer-containing solution after the post-treatment is adjusted to an appropriate viscosity (concentration) before use. Alternatively, one prepared by synthesizing an acrylic polymer using a polymerization method other than the solution polymerization method (for example, emulsion polymerization, photopolymerization, bulk polymerization, etc.) and dissolving the polymer in an organic solvent to prepare a solution You may use.

The weight average molecular weight (Mw) of the acrylic polymer in the technique 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 achieving a high level of balance between handling properties such as reworkability and removability, and adhesive properties such as 180 ° peel strength, the Mw of the acrylic polymer is in the range of 10 × 10 ⁴ or more and 150 × 10 ⁴ or less. It is preferable that the range is 15 × 10 ⁴ or more and 100 × 10 ⁴ or less, more preferably 15 × 10 ⁴ or more and 75 × 10 ⁴ or less. In a preferable embodiment, the Mw of the acrylic polymer can be 20 × 10 ⁴ or more and less than 75 × 10 ⁴ . In a more preferable 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). May be Here, Mw refers to a standard polystyrene conversion 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. The tackifying resin is not particularly limited, but various tackifying resins such as rosin-based, terpene-based, hydrocarbon-based, epoxy-based, polyamide-based, elastomer-based, phenol-based, and ketone-based resins can be used. Such tackifier resins can be used alone or in combination of two or more kinds.

  Specific examples of the rosin-based tackifying resin include unmodified rosins such as gum rosin, wood rosin and tall oil rosin (raw rosin); modified rosins obtained by modifying these unmodified rosins by hydrogenation, disproportionation, polymerization or the like ( Hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosins); various other rosin derivatives; and the like. Examples of the rosin derivative include esterification of unmodified rosin with alcohols (that is, esterified product of rosin) and modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.) with alcohols. (I.e., modified rosin esterification products); unmodified rosins obtained by modifying unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.) with unsaturated fatty acids Unsaturated fatty acid modified rosin ester obtained by modifying rosin ester with unsaturated fatty acid; 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 the carboxyl group of modified rosin esters; unmodified rosin and modified rosin Metal salts of rosins (especially rosin esters) such as various rosin derivatives; rosin phenol obtained by thermally polymerizing rosins (unmodified rosin, modified rosin, various rosin derivatives, etc.) with an acid catalyst Resin; etc. are mentioned.

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

  Examples of hydrocarbon tackifying resins include aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic / aromatic petroleum resins (styrene-olefin copolymers, etc. ), Aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone-based resins, coumarone-indene-based resins, and various other hydrocarbon-based resins. 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, vinyltoluene, α-methylstyrene, indene, methylindene, etc.). To be Examples of the aliphatic cyclic hydrocarbon resin include an alicyclic hydrocarbon resin obtained by polymerizing so-called "C4 petroleum fraction" or "C5 petroleum fraction" after cyclization dimerization; cyclic diene compound ( Polymers of cyclopentadiene, dicyclopentadiene, ethylidene norbornene, dipentene, etc. or hydrogenated products thereof; alicyclic hydrocarbons obtained by hydrogenating an aromatic ring of an aromatic hydrocarbon resin or an aliphatic / aromatic petroleum resin Resin; etc. are mentioned.

  In the technology disclosed herein, the tackifying resin having a softening point (softening temperature) of about 100 ° C. or higher (preferably about 120 ° C. or higher, more preferably about 135 ° C. or higher) can be preferably used. By using 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 having more excellent repulsion resistance can be realized. Among the tackifying resins exemplified above, a terpene-based tackifying resin having such a softening point (for example, a terpene phenol resin), a rosin-based tackifying resin (for example, an esterified product of polymerized rosin) and the like can be preferably used. . The tackifying resin can be preferably used in a mode including a terpene phenol resin having a softening point of 135 ° C. or higher, for example. Moreover, particularly excellent repulsion resistance can be realized by using a pressure-sensitive adhesive containing a tackifying resin having a softening point of 140 ° C. or higher. For example, a terpene phenol resin having a softening point of 140 ° C. or higher can be preferably used. The technology disclosed herein is such that the ratio of the tackifying resin having a softening point of 140 ° C. or higher in the total tackifying resins contained in the pressure-sensitive adhesive is more than 50% by weight, more preferably 70% by weight or more, and further preferably 85% by weight. % Or more (for example, 95% by weight or more and 100% by weight or less). The upper limit of the softening point of the tackifying resin is not particularly limited and may be, for example, about 200 ° C. or lower (typically about 180 ° C. or lower). The softening point of the tackifying resin here is defined as a value measured by the softening point test method (ring and ball method) defined in either JIS K5902 or JIS K2207.

  The amount of the tackifying resin used is not particularly limited and can be appropriately set according to the desired tacking performance (adhesive strength, etc.). For example, based on the solid content, the tackifying resin is approximately 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, further preferably 20 parts by weight or more, based on 100 parts by weight of the acrylic polymer. It is preferable to use it in a ratio of 60 parts by weight or less).

  A crosslinking agent may be used in the pressure-sensitive adhesive composition, if necessary. The type of the cross-linking agent is not particularly limited, and a known or common cross-linking agent (for example, an isocyanate cross-linking agent, an epoxy cross-linking agent, an oxazoline cross-linking agent, an aziridine cross-linking agent, a melamine cross-linking agent, a peroxide cross-linking agent). , Urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, amine-based crosslinking agents, and the like). The cross-linking agents may be used alone or in combination of two or more. The amount of the cross-linking 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 or more and 10 parts by weight or less, preferably about 0.01 parts by weight or more, relative to 100 parts by weight of the acrylic polymer. It can be selected from the range of about 5 parts by weight or less).

  The pressure-sensitive adhesive composition, if necessary, a leveling agent, a crosslinking aid, a plasticizer, a softening agent, a filler, a colorant (a pigment, a dye, etc.), an antistatic agent, an antiaging agent, an ultraviolet absorber, an oxidation agent. It may contain various additives generally used in the field of pressure-sensitive adhesive compositions, such as inhibitors and light stabilizers. As such various additives, conventionally known ones can be used by a conventional method, and since they do not particularly characterize the present invention, detailed description thereof will be omitted.

  As the release liner, one 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 structure in which the surface of a liner base material is subjected to a release treatment can be preferably used. Examples of the liner base material (release target) that constitutes this type of release liner include 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) or the like can be appropriately selected and used. The peeling treatment can be carried out by a conventional method using a known or commonly used peeling treatment agent (for example, a silicone-based, fluorine-based or long-chain alkyl-based peeling treatment agent). In addition, a low-adhesive liner base material such as olefin resin (eg, polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene / polypropylene mixture), fluoropolymer (eg, polytetrafluoroethylene, polyvinylidene fluoride), etc. Alternatively, it may be used as a release liner without subjecting the surface of the liner substrate to a release treatment. Alternatively, such a low-adhesive liner base material that has been subjected to a release treatment may be used.

  Application of the pressure-sensitive adhesive composition can be performed using a known or commonly used coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, and a spray coater. . Although not particularly limited, the coating amount of the pressure-sensitive adhesive composition is such that after drying (that is, on the basis of solid content), a pressure-sensitive adhesive layer having a thickness of about 5 μm or more and 150 μm or less (thickness per one surface) is formed. The amount can be as small as From the viewpoint of balancing the weight reduction and / or thinning of the double-sided pressure-sensitive adhesive sheet and the pressure-sensitive adhesive performance at a high level, it is appropriate that the thickness of the pressure-sensitive adhesive layer per one side is approximately 10 μm or more and 110 μm or less, approximately 15 μm. It is preferably 100 μm or more and typically 20 μm or more and 80 μm or less. From the viewpoint of thinning the double-sided pressure-sensitive adhesive sheet, the thickness of the pressure-sensitive adhesive layer may be 50 μm or less, and may be 35 μm or less. From the viewpoint of accelerating the crosslinking reaction, improving the production efficiency, etc., it is preferable to dry the pressure-sensitive adhesive composition under heating. Usually, for example, a drying temperature of about 40 ° C. to 120 ° C. can be preferably adopted.

  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 above-mentioned pressure-sensitive adhesive composition to a foam substrate (direct method), applying the above-mentioned pressure-sensitive adhesive composition onto an appropriate release surface to form a pressure-sensitive adhesive layer on the release surface. And a method of transferring by laminating the pressure-sensitive adhesive layer on a foam substrate (transfer method). You may use combining these methods. Further, different methods may be adopted for the first adhesive layer and the second adhesive layer. When a pressure-sensitive adhesive composition containing a solvent is used, it is preferable to dry the pressure-sensitive adhesive composition under heating from the viewpoint of accelerating the crosslinking reaction and improving the 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 securing the thickness of the foam base material capable of exhibiting desired characteristics, it is usually appropriate to set the total thickness of the pressure-sensitive adhesive layer to 200 μm or less, preferably 160 μm or less, and 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 thickness of both pressure-sensitive adhesive layers is approximately the same can be preferably adopted. Further, each pressure-sensitive adhesive layer may have either a single-layer form or a multi-layer form.

  The gel fraction of the pressure-sensitive adhesive forming 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 the handling property such as reworkability and removability with impact resistance at a high level, it is usually appropriate that the gel fraction of the pressure-sensitive adhesive is in the range of 15% by weight or more and 50% by weight or less. The range of 18 wt% or more and 45 wt% or less is preferable, and the range of 20 wt% or more and 40 wt% or less (for example, 20 wt% or more and 35 wt% or less, typically 20 wt% or more and less than 30 wt%) is particularly preferable. 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.

[Gel fraction]
After drying the pressure-sensitive adhesive composition at 130 ° C. for 2 hours, about 0.1 g of the dried product (sample) is wrapped with a polytetrafluoroethylene (PTFE) resin porous sheet, and the mouth is bound with a kite string. The package was placed in a screw tube having a volume of 50 mL, and the mixture was filled with ethyl acetate and allowed to stand at room temperature (typically 23 ° C.) for 7 days. Then, the package was taken out and dried at 130 ° C. for 2 hours. The gel fraction is calculated by the following formula: ratio (%) = (sample weight after immersion / drying) / (sample weight before immersion) × 100. As the PTFE resin porous sheet, a product 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 substrate and the pressure-sensitive adhesive layer (intermediate layer, undercoat layer, etc .; hereinafter also referred to as "other layer"), as long as the effects of the present invention are not significantly impaired. May be further included. For example, the above-mentioned other layer may be provided between the foam substrate and either or both of the pressure-sensitive 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 embodiment of the technology disclosed herein, a double-sided pressure-sensitive adhesive sheet showing a performance of a pressure-sensitive adhesive force of 40 N or more (more preferably 100 N or more, further preferably 180 N or more, typically 200 N or more, for example 240 N or more). Can be provided. Such a double-sided pressure-sensitive adhesive sheet having a high pressure-sensitive adhesive strength is preferable because when the members are bonded together using the double-sided pressure-sensitive adhesive sheet, peeling due to internal stress is unlikely to occur and the adhesion reliability is excellent.

  According to another preferred aspect of the technology disclosed herein, a double-sided PSA sheet having the pressure-sensitive adhesive force of 250 N or more (more preferably 300 N or more, still more preferably 330 N or more) can be provided. The double-sided pressure-sensitive adhesive sheet having a pressing adhesive force of 250 N or more can exhibit higher adhesion reliability.

  The pressure-sensitive adhesive force is applied to a stainless steel (SUS) plate and a glass plate with a load of 5 kg for 10 seconds using a double-sided adhesive sheet having a window frame shape (also referred to as "frame shape") having a width of 59 cm, a length of 113 cm, and a width of 1 mm. An evaluation sample was prepared by laminating the glass plate under pressure bonding conditions, and in this evaluation sample, the glass plate was pressed from the inside to the outside in the thickness direction of the glass plate at a load speed of 10 mm / min, so that the glass plate and the stainless steel plate were pressed together. It is defined as the maximum stress observed during the separation from the plate. The pressing adhesive force can be measured, for example, by the procedure described in Examples described later.

  In the following description, the pressure-sensitive adhesive force measured using the window frame-shaped double-sided pressure-sensitive adhesive sheet having a width of 59 mm, a length of 113 mm, and a width of 1 mm as described above may be referred to as “pressure-bonding force (1 mm width)”. . Similarly, the pressure-sensitive adhesive force measured using a window frame-shaped double-sided pressure-sensitive adhesive sheet having a width of 59 mm, a length of 113 mm, and a width of Amm may be expressed as “pressure-bonding force (Amm width)”. Among them, the pressure-sensitive adhesive force measured using the window frame-shaped double-sided pressure-sensitive adhesive sheet with A <1 may be referred to as “narrow-width pressure-sensitive adhesive force”. The narrow width pressure-sensitive adhesive force can be measured in the same manner as the pressure-pressure adhesive force (1 mm width), except that a window frame-shaped double-sided pressure-sensitive adhesive sheet having a width of 59 mm, a length of 113 mm and a width of A mm (where A <1) is used. it can.

According to a preferred aspect of the technology disclosed herein, the pressure-sensitive adhesive force (0.7 mm width) is 28 N or more (more preferably 100 N or more, further preferably 140 N or more, typically 160 N or more, for example 250 N or more). Some double-sided PSA sheets can be realized.
According to a preferred embodiment of the technology disclosed herein, the pressing adhesive force (0.5 mm width) is 20 N or more (more preferably 50 N or more, further preferably 80 N or more, typically 110 N or more, for example 160 N or more). Some double-sided PSA sheets can be realized.
According to a preferred embodiment of the technology disclosed herein, the pressure-sensitive adhesive force (0.3 mm width) is 12 N or more (more preferably 30 N or more, further preferably 40 N or more, typically 60 N or more, for example 100 N or more). Some double-sided PSA sheets can be realized.

  According to another preferred aspect of the technology disclosed herein, in impact resistance evaluation performed by the method described in Examples described later, joining such as peeling or cracking of the foam base material even after dropping 60 times. It is possible to realize a double-sided pressure-sensitive adhesive sheet that exhibits a level of impact resistance that is free from defects.

  The double-sided PSA sheet disclosed herein may have desired optical characteristics (transmittance, reflectance, etc.). For example, the double-sided pressure-sensitive adhesive sheet used for shading preferably has a visible light transmittance of 0% or more and 15% or less (more preferably 0% or more and 10% or less). The double-sided pressure-sensitive adhesive sheet used for light reflection is preferably 20% or more and 100% or less (more preferably 25% or more and 100% or less) in visible light reflectance. The optical characteristics of the double-sided pressure-sensitive adhesive sheet can be adjusted, for example, by coloring the foam base material as described above.

  The double-sided pressure-sensitive adhesive sheet disclosed herein is preferably halogen-free from the viewpoint of preventing metal corrosion. The halogen-free double-sided pressure-sensitive adhesive sheet can be an advantageous feature, for example, when the double-sided pressure-sensitive adhesive sheet can be used for fixing electric / electronic components. Further, since the generation of halogen-containing gas during combustion can be suppressed, it is preferable from the viewpoint of reducing the environmental load. Halogen-free double-sided PSA sheet is used when a halogen compound is not intentionally used as a foam base material or a raw material for an adhesive, a foam base material not intentionally blended with a halogen compound is used, and an additive is used. It can be obtained by adopting 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, but examples thereof include metallic materials such as stainless steel (SUS) and aluminum; inorganic materials such as glass and ceramics; polycarbonate (PC), polymethylmethacrylate (PMMA), polypropylene. , A resin material such as polyethylene terephthalate (PET); a rubber material such as natural rubber or butyl rubber; and an adherend made of a composite material of these materials.

The double-sided PSA sheet disclosed herein can be excellent in impact protection and high in impact resistance because the amount of deformation in the thickness direction upon impact is suppressed. Therefore, it can be suitable as a double-sided pressure-sensitive adhesive sheet used for the purpose of joining, fixing, shock absorption, etc. in a mobile device that is easily affected by a drop or the like. In addition, the double-sided pressure-sensitive adhesive sheet disclosed herein can be excellent in step-following property, repulsion resistance, and waterproof property since it contains a foam base material. Therefore, by utilizing such a feature, for protection of a display panel of an electronic device application, for example, a portable electronic device (for example, a mobile phone, a smartphone, a tablet computer, a notebook computer, etc.), a protective panel (lens) is fixed, It can be preferably applied to applications such as fixing a key module member of a mobile 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. Particularly preferred applications include portable electronic device applications. In particular, it can be preferably used in 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) for protecting the display unit to a housing.
The “lens” in the present specification is a concept that includes both a transparent body that exhibits a light refracting action and a transparent body that does not have a light refracting action. That is, the “lens” in the present specification includes a protective panel that does not have a refracting action and simply protects the display unit of the portable electronic device.

  Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to the examples. In the following description, "part" and "%" are based on weight unless otherwise specified.

<Experimental example 1>
The samples of the double-sided pressure-sensitive adhesive sheets (Examples 1 to 10) were prepared as follows.
(Example 1)
[Preparation of acrylic polymer (A)]
In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas introduction tube, a reflux condenser and a dropping funnel, 100 parts of n-butyl acrylate, 5 parts of acrylic acid, and 2,2'-azobisisobutyi as a polymerization initiator. 0.2 parts of ronitrile and toluene as a polymerization solvent were charged, nitrogen gas was introduced with gentle stirring, the liquid temperature in the reaction vessel was kept at around 60 ° C., and a polymerization reaction was carried out for about 6 hours, A toluene solution of acrylic polymer (A) was obtained. The Mw of this acrylic polymer (A) was 55 × 10 ⁴ .
Here, the Mw of the acrylic polymer (A) was determined as follows. That is, after drying the toluene solution 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 THF solution was filtered through a membrane filter having an average pore size of 0.45 μm, and the filtrate was subjected to GPC to determine the Mw (converted to standard polystyrene) of the acrylic polymer (A). As a GPC device, a model name “HLC-8320GPC” (column: TSKgel GMH-H (S)) manufactured by Tosoh Corporation was used.

[Preparation of adhesive composition (B)]
30 parts of a product name "Tamanor 803L" (terpene phenol resin: manufactured by Arakawa Chemical Industry Co., Ltd., softening point 145 ° C to 160 ° C) as a tackifying resin for 100 parts of the acrylic polymer (A) contained in the toluene solution. And 10 parts of the product name "YS Polystar S145" (terpene phenol resin: manufactured by Yasuhara Chemical Co., Ltd., softening point: 140 ° C to 150 ° C) are added, and an isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Industry Co., Ltd., product name: Coronate L ”) and 1 part of an epoxy-based crosslinking agent (trade name“ Tetrad C ”manufactured by Mitsubishi Gas Chemical Co., Inc.) were added to prepare an acrylic pressure-sensitive adhesive composition (B).

Two sheets of commercially available release liners (trade name "SLB-80W3D", manufactured by Sumika Paper Co., Ltd.) were prepared. The pressure-sensitive adhesive composition (B) was applied on 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, pressure-sensitive adhesive layers were formed on 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 one surface and the other surface subjected to corona discharge treatment 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 16.3 MPa, and the tensile strength in the width direction (tensile strength (TD)) was 9.5 MPa.
This base material No. The pressure-sensitive adhesive layers formed on the above two release liners were adhered to one surface and the other surface of No. 1, respectively. The release liner was left as it was on the pressure-sensitive adhesive layer and used for protecting the surface (pressure-sensitive surface) of the pressure-sensitive adhesive layer. The obtained structure was passed through a laminator (0.3 MPa, speed 0.5 m / min) at 80 ° C. once, and then cured in an oven at 50 ° C. for 1 day. In this way, a double-sided pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on the first surface and the second surface of the foam substrate (No. 1), respectively, and having a total thickness of 200 μm (example 1) was obtained.

(Examples 2 and 3)
The base material No. Double-sided pressure-sensitive adhesive was prepared in the same manner as in the double-sided pressure-sensitive adhesive sheet of Example 1 except that the thickness of the pressure-sensitive adhesive layer to be formed on both sides of 1 was 50 μm each (Example 2) or 75 μm each (Example 3). Sheets (Examples 2 and 3) were obtained.

(Example 4)
[Preparation of acrylic polymer (C)]
In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas introduction tube, a reflux condenser, and a dropping funnel, 100 parts of n-butyl acrylate, 2 parts of acrylic acid, 5 parts of vinyl acetate, and 0. 1 part, 2,2′-azobisisobutyronitrile 0.2 part as a polymerization initiator, and toluene as a polymerization solvent were charged and solution polymerized at 60 ° C. for 6 hours to prepare an acrylic polymer (C). A toluene solution was obtained. The Mw of the acrylic polymer (C) measured in the same manner as the acrylic polymer (A) was 50 × 10 ⁴ .

[Preparation of adhesive composition (D)]
To 100 parts of the acrylic polymer (C) contained in the above toluene solution, 30 parts of a polymerized rosin ester resin (manufactured by Arakawa Chemical Industry Co., Ltd., product name “Pencel D-125”, softening point 125 ° C.) was used as a tackifying resin. Then, 2 parts of an isocyanate cross-linking agent (manufactured by Nippon Polyurethane Industry Co., Ltd., product name "Coronate L") was added as a cross-linking agent to prepare an acrylic pressure-sensitive adhesive composition (D).

  A double-sided pressure-sensitive adhesive sheet (Example 4) was obtained in the same manner as the double-sided pressure-sensitive adhesive sheet of Example 1 except that the pressure-sensitive adhesive composition (D) was used instead of the pressure-sensitive adhesive composition (B).

(Examples 5 to 7)
The foam base material No. Substrate No. 1 instead of No. 1 2 is used and the 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 each of the two surfaces after drying is 25 μm each (Example 5), 50 μm each (Example 6), and 75 μm each (Example 7). Double-sided PSA sheets (Examples 5 to 7) were obtained in the same manner as in the production.
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 in the flow direction (tensile strength (MD )) Was 12.3 MPa, and the tensile strength (tensile strength (TD)) in the width direction was 7.5 MPa.

(Example 8)
The foam base material No. Substrate No. 2 instead of No. 2 3 and the base material No. A double-sided pressure-sensitive adhesive sheet (Example 8) was obtained in the same manner as in the method for producing the double-sided pressure-sensitive adhesive sheet of Example 4, except that the thickness of the pressure-sensitive adhesive layer formed on each of both surfaces of No. 3 was 50 μm after drying.
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 100 μm, and the tensile strength in the flow direction (tensile strength (MD )) Was 9.5 MPa, and the tensile strength (tensile strength (TD)) in the width direction was 8.2 MPa.

(Example 9)
The foam base material No. Substrate No. 2 instead of No. 2 A double-sided pressure-sensitive adhesive sheet (Example 9) was obtained in the same manner as in the method for producing the double-sided pressure-sensitive adhesive sheet of Example 4 except that 4 was used.
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 200 μm, and the tensile strength in the flow direction (tensile strength (MD )) Was 5.1 MPa, and the tensile strength (tensile strength (TD)) in the width direction was 4.6 MPa.

(Example 10)
The foam base material No. Substrate No. 2 instead of No. 2 5 and the base material No. A double-sided pressure-sensitive adhesive sheet (Example 10) was obtained in the same manner as in the method for producing the double-sided pressure-sensitive adhesive sheet of Example 4 except that the thickness of the pressure-sensitive adhesive layer formed on each side of No. 5 was 20 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 60 μm, and the tensile strength in the flow direction (tensile strength (MD )) Was 4.8 MPa, and the tensile strength (tensile strength (TD)) in the width direction was 4.3 MPa.

  The base material No. used for producing the double-sided pressure-sensitive adhesive sheets of Examples 1 to 10 above. 1-No. The foaming ratio, the 25% compressive strength, the tensile strength and the tensile elongation of No. 5 are summarized in Table 1.

<Evaluation test>
(1) 180 ° Peel Strength A release liner covering one adhesive surface of a double-sided pressure-sensitive adhesive sheet was peeled off, and a polyethylene terephthalate (PET) film having a thickness of 25 μm was attached to the one adhesive surface. This was cut into a size having a width of 20 mm and a length of 100 mm to prepare a measurement sample.
Under the 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 the stainless steel plate (SUS304BA plate) by reciprocating a 2 kg roller once. . After leaving this for 30 minutes in the same environment, using a universal tensile compression tester (device name "tensile compression tester, TG-1kN" manufactured by Minebea Co., Ltd.), according to JIS Z 0237, the pulling speed The peel strength (N / 20 mm width) was measured under the conditions of 300 mm / min and peel angle of 180 degrees.

(2) Pressing Adhesion Strength The double-sided pressure-sensitive adhesive 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. 2 to obtain a window frame-shaped double-sided pressure-sensitive adhesive sheet. Using this double-sided window frame adhesive sheet, a glass plate having a width of 59 mm, a length of 113 mm, and a thickness of 1 mm (Gorilla glass manufactured by Corning Co., Ltd. was used. The same applies hereinafter) and stainless steel having a through hole with a diameter of 15 mm in the central portion. A steel plate (SUS plate) (width 70 mm, length 130 mm, thickness 2 mm) was bonded by pressure bonding with a load of 5 kg for 10 seconds to obtain a sample for evaluation.
2A and 2B are schematic views of the evaluation sample, in which FIG. 2A is a top view and FIG. 2B is a sectional view taken along line AA ′. In FIG. 2, reference numeral 21 is an SUS plate, reference numeral 2 is a window frame double-sided adhesive sheet, reference numeral 22 is a glass plate, and reference numeral 21A is a through hole provided in the SUS plate 21.
These evaluation samples were set in the universal tensile 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 to press the glass plate in a direction away from the SUS plate. Then, the maximum stress observed until the glass plate and the SUS plate were separated was measured as the pressing 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-sensitive adhesive force. 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, and reference numeral 24 is The support base is shown. The evaluation sample is fixed to the support base 24 of the tensile compression tester as shown in FIG. 3, and the glass plate 22 of the evaluation sample is pressed by the round bar 23 passing through the through hole 21A of the SUS plate 21. In the above-mentioned measurement of the pressure-sensitive adhesive force, the SUS plate 21 was not bent or damaged by the load applied by the glass plate 22 being pressed by the round bar 23.

(3) Impact resistance The double-sided pressure-sensitive adhesive 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. 4 to obtain a window frame-shaped double-sided pressure-sensitive adhesive sheet. Using this window frame double-sided pressure-sensitive adhesive sheet, a first PC board (width 70 mm, height 130 mm, thickness 2 mm) and a second PC board (width 59 mm, length 113 mm, thickness 0.55 mm) were loaded under a load of 5 kg. Was adhered by pressure bonding under the condition of applying for 10 seconds to obtain an evaluation sample (see FIGS. 4A and 4B).
4A and 4B are schematic views of the evaluation sample, where FIG. 4A is a top view and FIG. 4B is a BB ′ cross-sectional view thereof. In FIG. 4, reference numeral 31 is a first PC board, reference numeral 3 is a window frame-shaped double-sided adhesive sheet, and reference numeral 32 is a second PC board.
A 160 g weight was attached to the back surface of the first PC board (the surface opposite to the surface bonded to the second PC board) of these evaluation samples. With respect to the evaluation sample with the weight, at room temperature (about 23 ° C.), a drop test was performed in which the sample was allowed to freely drop 60 times from a height of 1.2 m on a concrete plate. At this time, the direction of the drop was adjusted so that the six faces of the evaluation sample were sequentially downward. That is, the falling pattern was performed once for each of the six surfaces for 10 cycles.
Then, every 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 separated ( The number of drops before separation) was evaluated as impact resistance against drops at room temperature. When no peeling was observed after dropping 60 times, it was displayed as "60 times or more" or ">60".

(4) Repulsion resistance A double-sided pressure-sensitive adhesive sheet is cut into a size having a width of 10 mm and a length of 100 mm, a release liner covering one of the pressure-sensitive adhesive surfaces is peeled off, and this is 0.5 mm thick, 10 mm wide, and 100 mm long aluminum. A test piece was prepared by laminating it on a plate. The test piece was bent in an arc shape along the cylinder having a radius of 15 mm (aluminum plate side is the inner side), then the release liner covering the other adhesive layer of the test piece was peeled off, and a laminator was used. A PC plate having a thickness of 2 mm was crimped while restoring the bent shape of the test piece. After this was left in an environment of 23 ° C. for 24 hours and then heated at 70 ° C. for 2 hours, the heights (mm) of both ends of the test piece floating from the PC plate surface were measured. The measurement was performed using three test pieces (that is, n = 3), and the average value of those six measurement values was calculated.

(5) Deformation in thickness direction at impact The double-sided pressure-sensitive adhesive 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-shaped double-sided pressure-sensitive adhesive sheet. Further, a stainless steel plate (SUS plate) (width 70 mm, length 130 mm, thickness 2 mm) having a rectangular through hole of width 50 mm and length 90 mm in the central portion, and a glass plate of width 59 mm, length 113 mm, thickness 1.5 mm ( Corning Gorilla glass) was prepared. The window frame-shaped double-sided pressure-sensitive adhesive sheet was stuck so as to be sandwiched between the SUS plate and the glass plate, and a load of 5 kg was applied for 10 seconds for pressure bonding to obtain a test piece. The SUS plate was set in the impact test device so that the glass plate side of the test piece faced downward and the adhesive surface between the SUS plate and the double-sided pressure-sensitive adhesive 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 and double-sided adhesive sheet at all. Instead, it was placed at such a position as to directly collide with the surface of the glass plate. At this time, the falling height of the steel ball (the distance (vertical distance) between the lowermost part of the steel ball and the glass plate before falling) was adjusted to be 1 m.
FIG. 5 is an explanatory diagram showing a method for measuring the amount of deformation in the thickness direction at the time of impact. In FIG. 5, reference numeral 41 indicates a stainless steel plate (SUS plate), reference numeral 4 indicates a window frame-shaped double-sided adhesive sheet, reference numeral 42 indicates a glass plate, and reference numeral 43 indicates a 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. The behavior of the double-sided pressure-sensitive adhesive sheet 4 when the steel ball 43 collides with the glass plate 42 is photographed by a high-speed camera (Photoron Co., shooting speed: 50000 FPS (frame per second)), and the result is analyzed by an image. The deformation amount (elongation amount) in the thickness direction of the double-sided adhesive sheet 4 was measured. Specifically, the thickness (initial thickness) of the double-sided pressure-sensitive adhesive sheet 4 before the steel balls 43 are dropped, and the double-sided pressure-sensitive adhesive sheet 4 to which a force is applied downward in the vertical direction due to the collision of the steel balls 43 is maximized in the thickness direction. From the thickness when displaced (maximum thickness), the amount of deformation in the thickness direction at impact was calculated by the following equation (2).
(Amount of deformation in thickness direction at impact) = (maximum thickness)-(initial thickness) (2)

(6) Base material cohesive strength A double-sided pressure-sensitive adhesive sheet is cut into a size with a width of 20 mm and a length of 200 mm, and a stainless steel foil having a width of 30 mm, a length of 300 mm, and a thickness of 0.3 mm is attached to each of the pressure-sensitive adhesive surfaces on both sides, and the pressure is applied. It was pressure-bonded by pressing at 1.0 MPa for 20 seconds. The above-mentioned bonding was performed by aligning the width center of the double-sided pressure-sensitive adhesive sheet with the width center of the stainless steel foil. This was aged for 24 hours in an atmosphere of 50 ° C. and 50% RH to obtain a sample for evaluation.
For this evaluation sample, the cohesive strength of the base material was measured in a 23 ° C., 50% RH atmosphere using a universal tensile compression tester (device name “tensile compression tester, TG-1kN” manufactured by Minebea Co., Ltd.). . Specifically, as shown in FIG. 6, a first stainless steel foil 56 and a second stainless steel foil 57, which are attached to the first adhesive layer 51 and the second adhesive layer 52 of the double-sided adhesive sheet 5, respectively. One end in the longitudinal direction of each of the chucks 58 and 59 of the testing machine is respectively gripped, and the chuck 58 is pulled upward and the chuck 59 is pulled downward at a speed of 150 mm / min. The foils 56 and 57 were peeled off into a T shape. The force required for this T-type peeling was measured by the above tester, and this was taken as the substrate cohesive force (N / 20 mm width). It should be noted that the evaluation sample after the T-shaped peeling was visually observed, and the peeling did not occur 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 foamed as shown in FIG. It was confirmed that the breakage occurred within the thickness of the body substrate 55.

(7) Holding power The release liner covering one side of the double-sided pressure-sensitive adhesive sheet was peeled off, and a 25 μm-thick PET film was attached to back it up. This was cut into a size of 50 mm in length and 25 mm in width to prepare a test piece. The release liner covering the other surface of these sample pieces (that is, the side opposite to the surface lined with the PET film in the test piece) was peeled off and adhered to a phenol resin plate as an adherend with a width of 25 mm and a length of 25 mm. Pasted by area. After this was left in an environment of 23 ° C. for 30 minutes, a phenol resin plate was hung down and a load of 2 kg was applied to the free end of the sample piece. According to JIS Z 0237 (2004), the sample was left for 12 hours in an environment of 23 ° C. and 50% RH with the load applied. When the sample piece had fallen after 12 hours, it was determined that the holding time was less than 12 hours (shown as "falling" in Table 2). In other cases, the deviation distance (mm) of the test piece from the first attachment position was measured.

  Table 2 shows the results of the measurement or evaluation of the double-sided pressure-sensitive adhesive sheets of Examples 1 to 10 by the method described above. This Table 2 also shows the schematic constitution of the double-sided PSA sheet according to each example and the gel fraction value obtained by the method described above for the PSA constituting the PSA layer of the double-sided PSA sheet. .

As shown in Table 2 above, the base material No. The double-sided pressure-sensitive adhesive sheet examples 1 to 4 using No. 1 are base material Nos. 2 to No. As compared with the double-sided PSA sheet examples 5 to 10 in which No. 5 was used, the amount of deformation in the thickness direction at impact was suppressed. Moreover, the double-sided pressure-sensitive adhesive sheets of Examples 1 to 4 showed excellent impact resistance and high base material cohesive force as compared with the double-sided pressure-sensitive adhesive sheets of Examples 5 to 10. In addition, the double-sided pressure-sensitive adhesive sheets of Examples 1 to 4 had high pressure-adhesive strength and excellent holding power. The double-sided pressure-sensitive adhesive sheets of Examples 1 to 3 exhibited even better performance than the double-sided pressure-sensitive adhesive sheet of Example 4 in terms of repulsion resistance and 180 degree peel strength.
In addition, regarding the double-sided pressure-sensitive adhesive sheets of Examples 5 to 10, when the separation mode of the first polycarbonate plate and the second polycarbonate plate in the impact resistance test was observed, the base material No. 3 to No. In the double-sided pressure-sensitive adhesive sheets of Examples 8 to 10 using No. 5, the foam base material was torn within the thickness over the entire circumference of the window frame-shaped double-sided pressure-sensitive adhesive sheet. In addition, the base material No. The double-sided pressure-sensitive adhesive sheets of Examples 5 to 7 using No. 2 are the double-sided pressure-sensitive adhesive sheets in which the foam base material is torn within the thickness in a part of the entire circumference of the window frame-shaped double-sided pressure-sensitive adhesive sheet and in other parts. Was peeled off at the interface with the first or second polycarbonate plate.

<Experimental example 2>
Samples of the double-sided pressure-sensitive adhesive sheets according to Examples 11 to 13 were produced as follows.
(Examples 11 to 13)
The foam base material No. Substrate No. 1 instead of No. 1 6 and using the base material No. 6 except that the thickness after drying of the pressure-sensitive adhesive layer to be formed on both sides of 6 is 25 μm (Example 11), 50 μm (Example 12), and 75 μm (Example 13). Double-sided PSA sheets (Examples 11 to 13) were obtained in the same manner as in the production method.
Here, the base material No. No. 6 is 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 direction of flow (tensile strength (MD )) Was 19.2 MPa, and the tensile strength (tensile strength (TD)) in the width direction was 11.8 MPa.

  Substrate No. used in the production of the double-sided pressure-sensitive adhesive sheets of Examples 11 to 13 above. The foaming ratio, the 25% compressive strength, the tensile strength and the tensile elongation of No. 6 are summarized in Table 3.

  Table 4 shows the results obtained by measuring or evaluating the double-sided PSA sheets according to Examples 11 to 13 by the same method as in Experimental Example 1. In Table 4, a schematic configuration of the double-sided PSA sheet according to each of Examples 11 to 13 and a gel fraction value obtained by the above-described method for the PSA constituting the PSA layer of the double-sided PSA sheet are shown. Are also shown.

  As shown in Tables 4 and 2 above, the base material No. The double-sided pressure-sensitive adhesive sheets according to Examples 11 to 13 using No. 2 to No. As compared with the double-sided PSA sheet using No. 5 (Examples 5 to 10), the amount of deformation in the thickness direction at the time of impact was suppressed. In addition, the double-sided pressure-sensitive adhesive sheets according to Examples 11 to 13 have base material Nos. Even when compared with the double-sided pressure-sensitive adhesive sheets using No. 1 (Examples 1 to 4), it was revealed that the amount of deformation in the thickness direction at the time of impact was further suppressed. Moreover, the double-sided pressure-sensitive adhesive sheets according to Examples 11 to 13 exhibited excellent impact resistance and higher base material cohesive force. Furthermore, the double-sided pressure-sensitive adhesive sheets according to Examples 11 to 13 had a higher pressure-sensitive adhesive force (1 mm width) and a higher holding force. In addition, the double-sided pressure-sensitive adhesive sheets according to Examples 11 to 13 exhibited high 180-degree peel strength and excellent repulsion resistance.

<Experimental example 3>
With respect to the double-sided pressure-sensitive adhesive sheets according to Examples 1 to 13, the pressure-sensitive adhesive force (narrow width pressure-sensitive adhesive force) when the width of the window frame-shaped double-sided pressure-sensitive adhesive sheet was smaller than 1 mm was measured by the following method.
That is, a double-sided PSA sheet cut into a window frame shape (frame shape) having a width of 59 mm, a length of 113 mm and a width of 0.3 mm, and a window frame shape having a width of 59 mm, a length of 113 mm and a width of 0.5 mm (frame shape). And the one cut into a window frame shape (frame shape) having a width of 59 mm, a length of 113 mm, and a width of 0.3 mm were prepared. Other than using the window frame-shaped double-sided pressure-sensitive adhesive sheet having the width of 0.3 mm, the width of 0.5 mm, or the width of 0.7 mm, the same as the above-described pressure-sensitive adhesive force measurement using the window-frame-shaped double-sided pressure-sensitive adhesive sheet of 1 mm in width. Then, the narrow width pressing adhesive force was measured. The results obtained are shown in Table 5.

  As shown in Table 5 above, in the double-sided pressure-sensitive adhesive sheets according to each example, the smaller the width, the smaller the pressure-sensitive adhesive force. However, according to the double-sided pressure-sensitive adhesive sheets according to Examples 1 to 4 and Examples 11 to 13, a high pressure-adhesive force of 160 N or more was obtained even with a width of 0.7 mm. Moreover, according to the double-sided pressure-sensitive adhesive sheets according to Examples 1 to 4 and Examples 11 to 13, a high pressure-adhesive force of 110 N or more was obtained even with a width of 0.5 mm. Furthermore, according to the double-sided pressure-sensitive adhesive sheets according to Examples 1 to 4 and Examples 11 to 13, a high pressure-adhesive force of 60 N or more was obtained even with a width of 0.3 mm. In particular, the double-sided pressure-sensitive adhesive sheets according to Examples 11 to 13 exhibited higher pressure-sensitive adhesive strength.

  Specific examples of the present invention have been described above in detail, 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.

1 Double-sided Adhesive Sheet 11 First Adhesive Layer 11A First Adhesive Side 12 Second Adhesive Layer 12A Second Adhesive Side 15 Foam Substrate 15A First Side 15B Second Side 17 Release Liner 17A Release Liner Front 17B Release Liner Back surface 2 Double-sided adhesive sheet 21 Stainless steel plate 21A Through hole 22 Glass plate 23 Round bar 24 Support stand 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 Foil 58, 59 Chuck

Claims (8)

A foam substrate,
A first pressure-sensitive adhesive layer provided on the first surface of the foam substrate,
Including a second adhesive layer provided on the second surface of the foam substrate,
The foam substrate has an expansion ratio of 1.95 cm ³ / g or less,
The foam substrate has a 25% compressive strength of 100 kPa or more,
The foam substrate is a tensile elongation in the flow direction over 400% state, and are tensile elongation in the width direction more than 200%,
The foam substrate is a double-sided pressure-sensitive adhesive sheet , wherein a value obtained by dividing the value of the 25% compressive strength by the value of the expansion ratio is 250 g · kPa / cm ³ or more .   The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the foam substrate has a 25% compressive strength of 500 kPa or more.   The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the foam substrate has a substrate cohesive force of 40 N / 20 mm or more.   The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the foam substrate has a tensile strength in the flow direction of 15 MPa or more.   The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the foam base material is a polyolefin-based foam base material.   The pressure-sensitive adhesive forming at least one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer contains a tackifying resin having a softening point of 135 ° C. or higher, and the double-sided pressure-sensitive adhesive according to claim 1. Sheet. The total thickness of the double-sided pressure-sensitive adhesive sheet is 70μm or more 500μm or less double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 6. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 7 , which is used for joining components of a portable electronic device.

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