JP2020094224A - Double-sided adhesive sheet - Google Patents

Abstract

To provide a double-sided adhesive sheet excellent in adhesion reliability.SOLUTION: A double-sided adhesive sheet includes: a foam substrate; a first adhesive layer formed on a first face of the foam substrate; and a second adhesive layer formed on a second face. The foam substrate is 1000 μm thick or less, an aspect ratio (CD/VD) is 3 or less, the aspect ratio (CD/VD) expressed by a ratio of an average cell diameter in a crosswise direction (CD) to an average cell diameter in a thickness direction (VD), and an aspect ratio (MD/CD) is larger than 1, the aspect ratio (MD/CD) expressed by a ratio of an average cell diameter in a flow direction (MD) to the average cell diameter in the crosswise direction (CD).SELECTED DRAWING: Figure 1

Description

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

Generally, a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive; the same applies hereinafter) exhibits a soft solid (viscoelastic body) state in a temperature range near room temperature and has a property of easily adhering to an adherend by pressure. Taking advantage of such 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 a substrate. ..

As the base material in the double-sided pressure-sensitive adhesive sheet with a base material, generally, in addition to plastic films, non-woven fabrics, papers and the like, foams having a cell structure can be used. The double-sided pressure-sensitive adhesive sheet using the above-mentioned foam (double-sided pressure-sensitive adhesive sheet with a foam base material) has shock absorption and unevenness as compared with a double-sided pressure-sensitive adhesive sheet having a base material such as a plastic film having no cell structure or a nonwoven fabric. It can be advantageous in terms of conformability, waterproofness, sealability, and the like. 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 and 2 can be cited as technical documents relating to the double-sided PSA sheet with a foam substrate.

JP, 2010-155969, A International Publication No. 2005/007731

By the way, the double-sided pressure-sensitive adhesive sheet is required to have excellent adhesiveness to an adherend. On the other hand, 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 and the like. When the double-sided pressure-sensitive adhesive sheet is used for fixing a display panel in a portable electronic device, etc., narrowing of the double-sided pressure-sensitive adhesive sheet is particularly significant from the viewpoint of increasing the screen size of the display panel and improving the design flexibility. .. However, the narrowed double-sided pressure-sensitive adhesive sheet may be easily peeled off from the adherend due to a decrease in the adhesion area with the adherend. Therefore, further improvement in performance of the double-sided PSA sheet is required in order to obtain sufficient member fixing performance even with a narrow width.
Therefore, an object of the present invention is to provide a double-sided PSA sheet having more excellent adhesion reliability.

The double-sided PSA sheet disclosed herein includes a foam base material, a first 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. And two adhesive layers. The foam substrate has a thickness of 1000 μm or less. The foam base material has an aspect ratio (CD) represented by the ratio of the average cell diameter in the width direction (CD) of the foam base material to the average cell diameter in the thickness direction (VD) of the foam base material. /VD) is 3 or less, and the aspect ratio (MD) is represented by the ratio of the average cell diameter in the flow direction (MD) of the foam substrate to the average cell diameter in the width direction (CD) of the foam substrate. /CD) is greater than 1. The double-sided pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet with a foam base material) having such a constitution can exhibit excellent pressure-sensitive adhesive strength. The improvement of the pressing adhesive force can contribute to the improvement of the adhesion reliability.

In a preferred embodiment of the double-sided PSA sheet disclosed herein, the double-sided PSA sheet has a thickness of 100 μm or more and 500 μm or less. Such a double-sided PSA sheet can exhibit excellent impact resistance in addition to excellent pressure-sensitive adhesive strength.

In a preferred embodiment of the double-sided PSA sheet disclosed herein, the foam base material is a polyolefin-based foam base material. A double-sided PSA sheet containing such a foam substrate can exhibit good impact resistance and waterproofness.

In a preferable embodiment of the double-sided PSA sheet disclosed herein, as the foam substrate, for example, one having a 25% compressive strength of 50 kPa or more can be preferably used. A double-sided pressure-sensitive adhesive sheet containing such a foam base material can exhibit better impact resistance.

The double-sided pressure-sensitive adhesive sheet disclosed herein exhibits excellent pressure-sensitive adhesive strength, and is also excellent in waterproofness and impact resistance, and thus is suitable as, for example, a double-sided pressure-sensitive adhesive sheet used for joining components of portable electronic devices.

It is a typical sectional view showing composition of a double-sided adhesive sheet concerning one embodiment. 3 is a photograph of a cross section of the substrate A used in Example 1 taken along a plane parallel to CD and VD, when observed with a scanning electron microscope (SEM). 6 is a photograph of a cross section of the substrate C used in Example 3 taken along a plane parallel to CD and VD, when observed with a scanning electron microscope (SEM). 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.

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 a person skilled in the art based on conventional technology 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 drawings below, members and parts having the same action 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 or 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 exhibits a soft solid (viscoelastic) state 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 is generally 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 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 (which may be in the form of a tape or the like) disclosed herein includes a foam base material and a first surface provided on the first surface and a second surface of 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 pressure-sensitive adhesive sheet having a form having the 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 wound in a spiral shape by being superposed on a release liner 17 whose front surface 17A and back surface 17B are both release surfaces. It may be in the form of a composite. 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 adhesive 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.

Generally, the double-sided PSA sheet disclosed herein can be preferably carried out in a mode in which the total thickness is 1500 μm or less. The total thickness of the double-sided PSA sheet is typically 50 μm or more and 800 μm or less, preferably 100 μm or more and 500 μm or less, more preferably 110 μm or more and 400 μm or less, still more preferably 120 μm or more and 300 μm or less, for example, 130 μm or more and 280 μm or less. it can. By setting the total thickness of the double-sided pressure-sensitive adhesive sheet to be equal to or less than the above-mentioned upper limit value, it can be advantageous in terms of product thinning, downsizing, weight saving, resource saving, and the like. Further, by setting the total thickness of the double-sided pressure-sensitive adhesive sheet to be equal to or more 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 typically, a thin layered foam (foam layer) is a constituent element. As a base material. The foam base material may be a base material substantially composed of only one layer or two or more foam layers. Although not particularly limited, a single layer (one layer) can be preferably used as the foam substrate in the technique disclosed herein.

The thickness of the foam base material 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 capable of exhibiting desired pressure-sensitive adhesive properties, it is usually appropriate to set the thickness of the foam substrate to 1000 μm or less, preferably 500 μm or less, and more preferably It is 300 μm or less, for example 250 μm or less, typically 200 μm or less. A foam substrate having a thickness of 180 μm or less may be used. From the viewpoint of impact resistance and repulsion resistance of the double-sided pressure-sensitive adhesive sheet, it is appropriate that the foam substrate has a thickness of 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 means 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 performance to withstand the repulsive force of the double-sided pressure-sensitive adhesive sheet).

The material of the foam base material is not particularly limited. Generally, 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 foam such as polyethylene foam and polypropylene foam; polyester resin foam such as polyethylene terephthalate foam, polyethylene naphthalate foam and polybutylene terephthalate foam; polychlorination. Polyvinyl chloride resin foam such as vinyl foam; Vinyl acetate resin foam; Polyphenylene sulfide resin foam; Polyamide (nylon) resin foam, amide resin foam such as wholly aromatic polyamide (aramid) resin foam And the like; polyimide resin foams; polyether ether ketone (PEEK) foams; styrene resin foams such as polystyrene foams; urethane resin foams such as polyurethane resin foams; Further, a rubber-based resin foam such as polychloroprene rubber foam may be used as the plastic foam.

Examples of preferable foams include polyolefin resin foams (hereinafter, also referred to as polyolefin foams). 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. For example, polyethylene such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), metallocene catalyst-based linear low-density polyethylene, polypropylene, ethylene-propylene copolymer, ethylene- Examples thereof include vinyl acetate copolymer. Such polyolefin resins can be used alone or in combination of two or more kinds as appropriate.

Suitable examples of the foam base material in the technology disclosed herein include, from the viewpoint of impact resistance, waterproofness, etc., a polyethylene foam base material substantially composed of a foam of polyethylene resin, a polypropylene base material. Examples thereof include a polypropylene-based foam base material substantially composed of a resin foam. Here, the polyethylene-based resin refers to a resin containing 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. A polyethylene-based foam substrate can be preferably used as the foam substrate in the technique disclosed herein.

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 the ionizing radiation can be appropriately adjusted to obtain the desired physical properties of the plastic foam, such as the desired degree of crosslinking and flexibility.

The average cell diameter (converted to a true sphere) of the foam substrate (for example, a polyolefin-based foam substrate) is not particularly limited, but is usually preferably 10 μm or more and 500 μm or less, more preferably 15 μm or more and 300 μm or less. It is more preferably 20 μm or more and 200 μm or less, for example 25 μm or more and 100 μm or less. By setting the average cell diameter (converted to a true sphere) of the foam substrate to 10 μm or more, impact resistance tends to be improved. On the other hand, when the average cell diameter (converted to a true sphere) of the foam base material is 500 μm or less, the waterproof property tends to be improved.

Here, in the present specification, the average cell diameter (converted to a true sphere) of the foam substrate is a value measured as described below. That is, after observing an arbitrary cut surface of the foam base material with a scanning electron microscope (SEM), the image is binarized with image processing software to obtain a bubble portion and other portions (for example, a plastic resin portion). ) And separate, and measure the area of each bubble in the bubble portion. Next, the average value of the individual diameters when this cell area is converted into a true circle area is calculated, and this is set as the average cell diameter of the foam substrate (true cell conversion). As the SEM, the device name "S-4800" manufactured by Hitachi High-Technologies Corporation or its equivalent can be used. As the image processing software, the product name “IMAGE J” manufactured by National Institute of Health, USA or its equivalent can be used.

The average cell diameter (converted to a true sphere) of the foam substrate is usually appropriate to be 50% or less of the thickness of the foam substrate, and 30% or less (for example, 10% or less). Is preferred. By setting the average cell diameter (converted to a true sphere) of the foam base material to 50% or less of the thickness of the foam base material, the waterproof property tends to be further improved.

In the present specification, the flow direction of the foam base material (also referred to as MD; hereinafter the same) refers to the extrusion direction in the foam base material manufacturing process. Although not particularly limited, when the foam base material has a long shape such as a tape shape, the MD of the foam base material is usually aligned with the lengthwise direction. Further, the width direction of the foam substrate (also referred to as CD, hereinafter the same) means a direction orthogonal to the MD and along the surface of the foam substrate. Further, the thickness direction of the foam base material (also referred to as VD, hereinafter the same) is a direction orthogonal to the surface of the foam base material, that is, a direction orthogonal to each of the MD and the CD. It means that.

In the present specification, as an index showing the shape of the bubbles contained in the foam substrate, as shown by the following formula (1), the average cell diameter in the thickness direction (VD) of the foam substrate is The "aspect ratio (CD/VD)" represented by the ratio of the average cell diameter in the width direction (CD) of the foam base material, and the width of the foam base material as shown by the following formula (2). The "aspect ratio (MD/CD)" represented by the ratio of the average cell diameter in the flow direction (MD) of the foam substrate to the average cell diameter in the direction (CD) is used.
Aspect ratio (CD/VD)=CD average bubble diameter/VD average bubble diameter (1)
Aspect ratio (MD/CD) = MD average bubble diameter/CD average bubble diameter (2)

Here, in the present specification, the “average bubble diameter of MD” is defined as being measured as follows.
That is, the foam base material is cut along a plane parallel to MD and VD (that is, a plane in which the direction of the perpendicular line corresponds to CD) at approximately the center of the CD, and the center of the cut surface is cut. The image is taken with the scanning electron microscope (SEM).
Next, the photographed image is printed on A4 size paper, and one straight line having a length of 60 mm parallel to the MD is drawn on the image. At this time, the magnification of the electron microscope is adjusted so that 10 to 20 bubbles are present on a straight line of 60 mm.
The number of cells existing on the straight line is visually counted, and the average cell diameter of MD in the foam substrate is calculated based on the following formula (3).
MD average bubble diameter (μm)=60 (mm)×10 ³ /(number of bubbles (number)×magnification ratio) (3)

Further, the "average bubble diameter of CD" is defined as being measured as follows.
That is, the foam base material is cut along a plane parallel to CD and VD (that is, a plane in which the direction of the perpendicular line corresponds to MD), and the central portion of the cut surface is photographed by the scanning electron microscope. To do.
Next, the photographed image is printed on A4 size paper, and one straight line having a length of 60 mm parallel to the CD is drawn on the image. At this time, the magnification of the electron microscope is adjusted so that about 10 to 20 bubbles are present on the straight line of 60 mm.
The number of cells existing on the straight line is visually counted, and the average cell diameter of CD in the foam substrate is calculated based on the following formula (4).
CD average bubble diameter (μm)=60 (mm)×10 ³ /(number of bubbles (number)×magnification ratio) (4)

Further, the "average cell diameter of VD" is defined as being measured as follows.
That is, in the same manner as when calculating the average cell diameter of the CD, the foam substrate is cut along a plane parallel to CD and VD, and the cut surface is photographed by the scanning electron microscope. , Print the obtained image. Next, three straight lines parallel to VD and divided into four equal parts to CD are drawn on the image from one surface of the double-sided pressure-sensitive adhesive sheet to the other surface. The length of each straight line is measured and the total value of these is calculated. In addition, the number of cells existing on the straight line is visually counted, and the average cell diameter of VD in the foam substrate is calculated based on the following formula (5).
VD average bubble diameter (μm)=total length of three straight lines on the image (mm)×10 ³ /(number of bubbles (pieces)×magnification ratio) (5)

When drawing a straight line, the straight line should penetrate the bubble as much as possible without making point contact. When some bubbles come into point contact with a straight line, the bubbles are counted as one. Furthermore, when both ends of the straight line are located inside the bubble without penetrating the bubble, the number of bubbles is counted as 0.5.

The above-mentioned average cell diameter in each direction of MD, CD, and VD is, for example, the conditions of the manufacturing process (foaming process, stretching process, etc.) of the foam substrate, the composition of the foam substrate (the amount of the foaming agent used). Etc.) can be controlled. Although not particularly limited, in the case where the foam base material is formed into a long shape by stretching a plastic molded body with an extruder, normally, the foam base material The direction showing the longest average cell diameter tends to coincide with the longitudinal direction (that is, MD) of the foam substrate.

The foam substrate preferably has an aspect ratio (CD/VD) of 3 or less. The aspect ratio (CD/VD) is more preferably 2.8 or less, further preferably 2.5 or less, for example 2.3 or less. Further, the aspect ratio (CD/VD) is preferably larger than 1, more preferably 1.3 or more, typically 1.5 or more, for example 1.7 or more. By setting the aspect ratio (CD/VD) to be equal to or less than the above upper limit value, the double-sided pressure-sensitive adhesive sheet provided with the foam base material can exhibit high pressure-sensitive adhesive force. As one of the factors for improving the pressure-sensitive adhesive force, the thickness of the double-sided pressure-sensitive adhesive sheet is controlled by controlling the bubble shape of the foam base material so as to be in the range of the aspect ratio (CD/VD) described above. It is considered that the stress when extruding in the direction can be more dispersed in the foam substrate. Further, by making the aspect ratio (CD/VD) larger than the above lower limit value, the flexibility of the double-sided PSA sheet using the foam base material tends to increase, and the unevenness followability and impact resistance are improved. You can

The foam substrate preferably has an aspect ratio (MD/CD) of more than 1. The aspect ratio (MD/CD) is more preferably 1.4 or more, further preferably 1.6 or more, typically 2 or more, for example, 2.3 or more. The aspect ratio (MD/CD) is preferably 5 or less, more preferably 4 or less, further preferably 3.5 or less, for example 3 or less. By making the aspect ratio (MD/CD) larger than the lower limit value described above, the handleability of the double-sided PSA sheet using the foam base material can be improved. Further, by setting the aspect ratio (MD/CD) to be equal to or less than the upper limit value described above, the waterproof property of the double-sided PSA sheet using the foam base material can be improved.

The density (apparent density) of the foam substrate is not particularly limited, but is preferably 0.2 g/cm ³ or more and 0.6 g/cm ³ or less, for example. The density of the foam substrate is more preferably 0.25 g/cm ³ or more and 0.55 g/cm ³ or less, further preferably more than 0.3 g/cm ³ and 0.5 g/cm ³ or less (for example, 0 .35g / cm ³ or more 0.5 g / cm ³ or less). By setting the density to 0.2 g/cm ³ or more, the strength of the foam substrate (and thus the strength of the double-sided pressure-sensitive adhesive sheet) and the impact resistance and handleability tend to be achieved. On the other hand, when the density is 0.6 g/cm ³ or less, the unevenness 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 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 preferably 1 MPa or more and 30 MPa or less (more preferably 2 MPa or more and 20 MPa or less, further preferably 2.5 MPa or more and 10 MPa or less, typically 3 MPa or more and 7 MPa or less). The tensile strength in the width direction (CD) is preferably 1 MPa or more and 30 MPa or less (more preferably 3 MPa or more and 20 MPa or less, further preferably 4 MPa or more and 15 MPa or less, typically 4.5 MPa or more and 10 MPa or less). By setting the tensile strength to the above lower limit or more, the base material (and thus the double-sided pressure-sensitive adhesive sheet) can be easily peeled without tearing when the double-sided pressure-sensitive adhesive sheet is peeled off for the purpose of recovering parts. (Reworkability) can be exhibited. On the other hand, when the tensile strength is not more than the above-mentioned upper limit value, impact resistance and unevenness followability can be improved. The tensile strength of the foam substrate (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 density.

The 25% compressive strength of the foam base material (for example, the polyolefin foam base material) is not particularly limited, but is preferably 50 kPa or more and 1000 kPa or less, for example. The 25% compressive strength of the foam base material is more preferably more than 60 kPa and 1000 kPa or less, 75 kPa or more and 1000 kPa or less, 75 kPa or more and 500 kPa or less, further preferably 80 kPa or more and 500 kPa or less, typically 90 kPa or more and 300 kPa or less, for example 100 kPa. It is preferably 250 kPa or less. 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. The load when compressed only, that is, the load when compressed until the thickness of the substrate becomes 75% of the initial thickness. By setting the 25% compressive strength to 50 kPa or more, the impact resistance of the double-sided pressure-sensitive adhesive sheet tends to be improved, and the dimensional stability during processing can be improved. On the other hand, when the 25% compression strength is 1000 kPa or less, the repulsion resistance and the unevenness 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 density.

The MD dimensional change rate at 90° C. (90° C. dimensional change rate (MD)) of the foam substrate (for example, a polyolefin-based foam substrate) is not particularly limited, but is, for example, −10% or more and 10%. The following is preferable. The 90°C heating dimensional change rate (MD) of the foam base material is more preferably -5% or more and 5% or less, still more preferably -4% or more and 4% or less. By setting the 90°C heating dimensional change rate (MD) within the above range, expansion/contraction of the double-sided PSA sheet provided with the foam base material is suppressed even in a high temperature environment (for example, 40°C to 90°C). , Can exhibit excellent adhesion reliability.
The heating dimensional change rate of CD (90° C. heating dimensional change rate (CD)) at 90° C. of the foam base material (for example, a polyolefin-based foam base material) is not particularly limited, but is, for example, −10% or more and 10%. The following is preferable. The 90° C. heating dimensional change rate (CD) of the foam base material is more preferably −5% or more and 5% or less, still more preferably −4% or more and 4% or less. By setting the 90°C heating dimensional change rate (CD) within the above range, expansion/contraction of the double-sided PSA sheet provided with the foam base material is suppressed even in a high temperature environment (for example, 40°C to 90°C). , Can exhibit excellent adhesion reliability.
The dimensional change rate of 90° C. heating of MD and CD of the foam substrate is measured according to JIS K 6767, except that the heating temperature is 90° C.

The degree of crosslinking of the foam substrate (for example, a polyolefin-based foam substrate) is not particularly limited, but is preferably 10% or more and 50% or less, for example. The degree of crosslinking of the foam base material is more preferably 20% or more and 45% or less, and further preferably 30% or more and 40% or less (for example, 32% or more and 40% or less).
Here, the degree of crosslinking in the present specification means a value obtained by measurement as follows. That is, about 100 mg of a test piece is collected from the foam base material to be measured, and the weight A (mg) of the test piece is precisely weighed. Next, this test piece is immersed in xylene 30 cm ³ at 120° C., left for 24 hours, and then filtered through a 200-mesh wire net. The insoluble matter on the wire net is collected and vacuum dried, and the weight B (mg) of the insoluble matter is precisely weighed. From the obtained value, the degree of crosslinking is calculated by the following formula (6).
Crosslinking degree (%)=(B/A)×100 (6)

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 designability and optical properties (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 may be used alone or in appropriate 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 base material is measured by using a spectrophotometer (for example, 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 emitted 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 pressure-sensitive adhesive sheet disclosed herein is used for light shielding, the foam base material is preferably colored black. The black color is L* (lightness) 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 in 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 color difference meters (for example, a color difference meter manufactured by Minolta Co., Ltd. under the 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 CIE1976 (L*a*b*) color system. It means that. 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 −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 carbon, diatomaceous earth, bentonite, lithopone, zeolite, sericite, inorganic white colorants such as hydrohaloysite, acrylic resin particles, polystyrene resin particles, polyurethane resin particles, amide resin particles, polycarbonate resin particles, Examples include organic white colorants such as silicone resin particles, urea-formalin resin particles, and melamine resin particles. The amount of the 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 base material may be subjected to an appropriate surface treatment, if necessary. This surface treatment can be, for example, a chemical or physical treatment for increasing 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 types of pressure-sensitive adhesives contained in the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer provided on the first surface and the second surface of the foam substrate are 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. It can be an adhesive containing 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 PSA sheet provided with a PSA layer consisting essentially of an acrylic PSA.

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 accounts for more than 50% by weight 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 acrylate and methacrylate inclusively.

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 (7) can be preferably used.
CH ₂ =C(R ¹ )COOR ² (7)
Here, R ¹ in the above formula (7) is a hydrogen atom or a methyl group. R ² is an alkyl group having 1 to 20 carbon atoms. Since it is easy to obtain an adhesive having excellent adhesive properties, R ² is an alkyl group having 2 to 14 carbon atoms (hereinafter, such a range of the number of carbon atoms may be represented as C _2-14 ). Certain alkyl (meth)acrylates are preferred. Specific examples of the C _2-14 alkyl group include 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 about 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 (7) is C _{2 -14} alkyl (meth)acrylate (more preferably C _4-10 alkyl (meth)acrylate, and particularly preferably one or both of butyl acrylate and 2-ethylhexyl acrylate). Be done. An acrylic polymer obtained from such a monomer composition is preferable because a pressure-sensitive adhesive exhibiting good pressure-sensitive adhesive properties is easily formed.

Although not particularly limited, as the acrylic polymer in the technique disclosed herein, a polymer obtained by copolymerizing 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-hydroxybutyl (meth)acrylate. Hydroxybutyl (meth)acrylate, 2-hydroxyhexyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl ( Examples thereof include (meth)acrylate, (4-hydroxymethylcyclohexyl)methyl acrylate, polypropylene glycol mono(meth)acrylate, N-hydroxyethyl (meth)acrylamide, and N-hydroxypropyl (meth)acrylamide. 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 force and cohesive force and excellent removability. As particularly preferred hydroxyl group-containing acrylic monomer, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl( Examples include hydroxyalkyl (meth)acrylates such as (meth)acrylate. 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 be one in which the hydroxyl group-containing acrylic monomer is not copolymerized.

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 example, for the purpose of 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 crosslinking group point into the 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 include naphthalene sulfonic acid and sodium vinyl sulfonate.
Examples of the phosphoric acid group-containing monomer include 2-hydroxyethyl acryloyl phosphate.
Examples of the cyano group-containing monomer include acrylonitrile and methacrylonitrile.
Examples of vinyl esters include vinyl acetate, vinyl propionate, vinyl laurate and the like.
Examples of 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, isocrotonic acid and the like.
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, N,N-dimethylaminopropyl (meth)acrylate and the like.
Examples of the imide group-containing monomer include cyclohexylmaleimide, isopropylmaleimide, N-cyclohexylmaleimide, and itaconimide.
Examples of the epoxy group-containing monomer include glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, and allylglycidyl 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 total amount of monomers used for the synthesis of the acrylic polymer. It is preferable to set the content to about 40% by weight or less (typically 0.001% by weight or more and 40% by weight or less), and about 30% by weight or less (typically 0.01% by weight or more and 30% by weight or less). More preferably, for example, 0.1% by weight or more and 10% by weight or less). 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, it is suitable that the content is 0.5% by weight or more and 5% by weight or less. When vinyl esters (for example, vinyl acetate) are used as the other monomer, 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. It is appropriate to set the content in the range of 10% by weight to 10% by weight.

It is suitable 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). Yes, it is preferably -25°C or lower (for example, -60°C or higher and -25°C or lower), and more preferably -40°C or lower (for example, -60°C or higher and -40°C or lower). When the Tg of the acrylic polymer is too high, the pressure-sensitive adhesive force of the pressure-sensitive adhesive containing the acrylic polymer as a base polymer (for example, the pressure-sensitive adhesive force in a low temperature environment, the pressure-sensitive adhesive force to a rough surface, etc.) may be easily lowered. .. If the Tg of the acrylic polymer is too low, the curved surface adhesiveness of the pressure-sensitive adhesive may be reduced, or the removability may be reduced (for example, adhesive residue may be generated).

The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (that is, the type of monomer used in the synthesis of the polymer and the ratio of the amounts used). 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 the Tg of the homopolymer.
2-ethylhexyl acrylate -70°C
Butyl acrylate -55°C
Ethyl acrylate-22°C
Methyl acrylate 8℃
Methyl methacrylate 105°C
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 otherwise 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 a monomer, 0.2 parts by weight of azobisisobutyronitrile and 200 parts by weight of ethyl acetate as a polymerization solvent were added. Charge and stir for 1 hour while circulating nitrogen gas. After removing the 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. Next, 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, model name "ARES"). The viscoelasticity was measured in a shear mode at a temperature rising rate of -70°C to 150°C, 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, it is preferable that the pressure-sensitive adhesive is 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 1 mm in thickness. -Shaped pressure-sensitive 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 viscoelasticity tester (TA Instruments Japan, Inc., model name "ARES"). The temperature dependence of the loss elastic modulus G″ is measured by the shear mode at a temperature rising rate of −70° C. to 150° C., 5° C./min while the shear strain of G is given, and the temperature corresponding to the peak top (G It can be understood by finding the "temperature at which the curve reaches its 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 the 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 depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and is, for example, about 20° C. to 170° C. (typically 40° C. to 140° C.). it can.

The 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; lower alcohols such as isopropyl alcohol, 1-butanol, sec-butanol, and tert-butanol (for example, monohydric alcohols having 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether 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. It is preferable to use an organic solvent (which may be a mixed solvent) having a boiling point in the range of 20° C. to 200° C. (more preferably 25° C. to 150° C.) at a total pressure of 1 atm.

The initiator used for the polymerization can be appropriately selected from known or commonly used polymerization initiators depending on the type of the 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-carbonitrile), 2,2′-azobis(2,2 4,4-trimethylpentane), dimethyl-2,2′-azobis(2-methylpropionate) 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 a redox initiator include a combination of peroxide and ascorbic acid (a combination of hydrogen peroxide solution and ascorbic acid, etc.), 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 solution in which an acrylic polymer is dissolved in an organic solvent is obtained. As the acrylic polymer in the technology disclosed herein, the above-mentioned polymerization reaction liquid or the reaction liquid 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.

If the weight average molecular weight (Mw) of the acrylic polymer in the technology disclosed herein is too small, the cohesive force of the pressure-sensitive adhesive is insufficient, and adhesive residue is likely to occur on the surface of the adherend, or curved adhesiveness Can easily decrease. On the other hand, if the Mw is too large, the adhesive force to the adherend may be easily reduced. An acrylic polymer having an Mw in the range of 10×10 ⁴ or more and 500×10 ⁴ or less is preferable in order to balance the adhesive performance and the removability at a high level. Better results can be achieved with an acrylic polymer having an Mw of 20×10 ⁴ or more and 400×10 ⁴ or less (for example, 30×10 ⁴ or more and 300×10 ⁴ or less). 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 may be used alone or in combination of two or more.

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, other chemically modified rosin, etc.); other various rosin derivatives; and the like. Examples of the above 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. (Ie, esterified products of modified rosin), etc.; unsaturated fatty acid modified 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 in modified rosin esters; metal salts of rosins (particularly rosin esters) such as unmodified rosin, modified rosin and various rosin derivatives; rosins (unmodified rosin, modified rosin, Rosin phenol resin obtained by adding phenol to various rosin derivatives and the like with an acid catalyst and conducting thermal polymerization; and the like.

Examples of terpene-based tackifying resins include terpene-based resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers; modified terpene-based resins (phenol modified, aromatic modified, hydrogenated modified, Hydrocarbon-modified etc.) modified terpene-based resin; and the like. Examples of the modified terpene resin include terpene-phenolic resin, styrene modified terpene resin, aromatic modified terpene resin, hydrogenated terpene resin and the like.

Examples of the hydrocarbon-based tackifying resin 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 8 to 10 carbon atoms (styrene, vinyltoluene, α-methylstyrene, indene, methylindene, etc.). Be done. Examples of the aliphatic cyclic hydrocarbon resin include an alicyclic hydrocarbon resin obtained by polymerizing a 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, for example 140° C. or higher) is used. It can be preferably used. Further, a terpene phenol resin having a softening point equal to or higher than the above lower limit value can be preferably used. Such a tackifying resin can realize a double-sided pressure-sensitive adhesive sheet having more excellent repulsion resistance. The upper limit of the softening point of the tackifying resin is not particularly limited and can be, for example, about 200° C. or lower (typically about 180° C. or lower). 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, about 10 parts by weight or more and 100 parts by weight or less of tackifying resin (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, based on the solid content. It is preferably used in a proportion of 60 parts by weight or less).

A crosslinking agent may be used in the pressure-sensitive adhesive composition, if necessary. The type of cross-linking agent is not particularly limited, and a known or common cross-linking agent (for example, isocyanate cross-linking agent, epoxy cross-linking agent, oxazoline cross-linking agent, aziridine cross-linking agent, melamine cross-linking agent, peroxide cross-linking agent) is used. , Urea-based crosslinkers, metal alkoxide-based crosslinkers, metal chelate-based crosslinkers, metal salt-based crosslinkers, carbodiimide-based crosslinkers, amine-based crosslinkers 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 PSA sheet can be appropriately selected and used. For example, a release liner having a structure in which the surface of a liner substrate 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 of these (for example, A sheet having a laminated structure in which an olefin resin is laminated on both sides of paper) or the like can be appropriately selected and used. The release treatment can be carried out by a conventional method using a known or commonly used release treatment agent (for example, a silicone-based, fluorine-based or long-chain alkyl-based release treatment agent). In addition, a low-adhesive liner base material such as an olefin resin (eg, polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene/polypropylene mixture), a 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 less (more preferably 20 μm or more and 75 μm or less, for example 20 μm or more and 50 μm or less, typically 20 μm or more and 35 μm or less). From the viewpoint of accelerating the crosslinking reaction and improving the production efficiency, 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 on a suitable release surface to form a pressure-sensitive adhesive layer on the release surface. , A method of transferring the adhesive layer by bonding it to a foam substrate (transfer method) and the like. You may use combining these methods. Also, 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, improving production efficiency, and the like.

The total thickness of the pressure-sensitive adhesive layer (the total value of the thickness of the first pressure-sensitive adhesive layer and the thickness of the second pressure-sensitive adhesive layer) is not particularly limited, but can be, for example, 10 μm or more and 300 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, and more preferably 40 μm or more. Further, from the viewpoint of easily securing the thickness of the foam base material that can exhibit desired characteristics, it is usually appropriate that the total thickness of the pressure-sensitive adhesive layer is 250 μm or less, preferably 200 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 from each other. Usually, it is possible to preferably adopt a configuration in which the thicknesses of both adhesive layers are substantially the same. Further, each pressure-sensitive adhesive layer may have either a single-layer form or a multi-layer form.

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 effect of the present invention is not significantly impaired. May be further included. For example, the above-mentioned other layer may be provided between the foam substrate and either one 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, the pressure-sensitive adhesive force is 45 N/cm ² or more (more preferably 60 N/cm ² or more, typically 75 N/cm ² or more, for example 80 N/cm ² or more). A double-sided PSA sheet exhibiting performance can be provided. Thus, the double-sided pressure-sensitive adhesive sheet having a high pressure-sensitive adhesive strength is excellent in adhesion reliability even if the double-sided pressure-sensitive adhesive sheet having a reduced width and the adherend are bonded together, unlikely to peel off due to internal stress. Therefore, it is preferable.
The pressure-sensitive adhesive force is such that a double-sided pressure-sensitive adhesive sheet having a width of 59 cm, a length of 113 cm, and a width of 1 mm and having a window frame shape (also referred to as "frame shape") makes a 5 kg roller reciprocate between a stainless steel plate (SUS plate) and a glass plate. 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, and the glass plate and SUS were pressed together. It is defined as the maximum stress observed during the separation from the plate. More specifically, the pressing adhesive force can be measured by the procedure described in Examples described later.

According to another preferred aspect of the technology disclosed herein, in the impact resistance evaluation performed by the method described in Examples described later, the sample is dropped 18 times at room temperature (23° C.) and then at a low temperature (−5° C.). It is possible to realize a double-sided pressure-sensitive adhesive sheet having a level of impact resistance in which peeling is not observed even after dropping 60 times.

According to another preferred aspect of the technique disclosed herein, in a 180° peel test for stainless steel (SUS304BA) performed by the method described in Examples described later, the peel strength (peeling strength) is 15 N/20 mm or more ( A double-sided pressure-sensitive adhesive sheet having a performance of more preferably 16 N/20 mm or more, further preferably 17 N/20 mm or more) can be provided. As described above, the double-sided PSA sheet having a high peel strength against SUS304BA is preferable because it shows a good adhesion performance with the adherend.

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. In addition, 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 sheets are 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 that does not intentionally contain a halogen compound is used, and an additive is used. It can be obtained by adopting such means as not using an additive derived from a halogen compound alone or in combination.

The double-sided pressure-sensitive adhesive sheet disclosed herein is not particularly limited, but examples thereof include metallic materials such as SUS and aluminum; inorganic materials such as glass and ceramics; polycarbonate (PC), polymethylmethacrylate (PMMA), polypropylene, polyethylene terephthalate ( It can be used for an adherend made of a resin material such as PET); a rubber material such as natural rubber or butyl rubber; and a composite material thereof.

The double-sided pressure-sensitive adhesive sheet disclosed herein exhibits excellent pressure-sensitive adhesive strength and can have high adhesive reliability. In addition, the double-sided pressure-sensitive adhesive sheet disclosed herein can be excellent in waterproofness, unevenness followability, sealability, and repulsion resistance because 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 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. As a particularly preferable application, it can be preferably used for a portable electronic device. For example, in such a portable electronic device, it is suitable for applications such as joining a protective panel (lens) that protects the display unit to a housing.
The “lens” in the present specification is a concept including both a transparent body exhibiting a refracting action of light and a transparent body having no refracting action of light. 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.

In the following description, the weight average molecular weight (Mw) was measured as follows.
After drying the pressure-sensitive adhesive composition at 130° C. for 2 hours, it is immersed in tetrahydrofuran (THF) for 12 hours to elute the THF-soluble component, and a THF solution containing the THF-soluble component at a concentration of 0.1 g/liter. Was prepared. 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 weight-average molecular weight of the THF-soluble component (standard polystyrene conversion). As a GPC device, a model name “HLC-8320GPC” (column: TSKgel GMH-H(S)) manufactured by Tosoh Corporation was used.

The samples of the double-sided pressure-sensitive adhesive sheets (Examples 1 to 4) were prepared as follows.
(Example 1)
[Preparation of acrylic polymer]
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 0.2 part of benzoyl peroxide as a polymerization initiator. Was dissolved using toluene as a solvent. Then, nitrogen gas was introduced while gently stirring, the liquid temperature in the reaction vessel was maintained at about 60° C., and a polymerization reaction was performed for about 6 hours to obtain an acrylic polymer. The acrylic polymer in the obtained solution had a weight average molecular weight Mw of 55×10 ⁴ .
[Preparation of adhesive composition]
Next, with respect to 100 parts of the acrylic polymer solution (nonvolatile content), 30 parts of a terpene phenol resin (manufactured by Arakawa Chemical Industry Co., Ltd., product name "Tamanor 803L") as a tackifying resin and a terpene phenol resin (Yasuhara Chemical Co., Ltd.) Manufactured by YS Polystar S145), and 10 parts of an isocyanate-based cross-linking agent (manufactured by Nippon Polyurethane Industry Co., Ltd., product name "Coronate L") and an epoxy-based cross-linking agent (Mitsubishi Gas Co., Ltd.). A chemical adhesive composition was prepared by adding 0.03 part of a product name "Tetrad C" manufactured by Kagaku Co., Ltd.

A polyethylene resin foam sheet (hereinafter referred to as "base material A") was prepared as a foam base material. The thickness of the base material A is 150 μm, the 25% compressive strength is 108 kPa, the tensile strength in the flow direction (tensile strength (MD)) is 3.18 MPa, and the tensile strength in the width direction (tensile strength (tensile strength CD)) was 5.50 MPa. The average bubble diameters in the flow direction (MD), the width direction (CD), and the thickness direction (VD) of the bubbles contained in the base material A, and the aspect ratios (CD/VD) and aspect ratios (MD) that are the ratios thereof. /CD) was measured and calculated by the above-mentioned measurement method, the aspect ratio (CD/VD) of the substrate A was 2.3 and the aspect ratio (MD/CD) was 2.6. FIG. 2 is a photograph of a cross section of the substrate A cut along a plane parallel to CD and VD (that is, a plane in which the direction of a perpendicular line corresponds to MD) when observed by a scanning electron microscope (SEM). Indicates.

The adhesive composition was applied to one surface of a commercially available release liner (product name "SLB-80W3D" manufactured by Sumika Kogyo Co., Ltd.) so that the thickness after drying was 25 μm, and 100 It dried at 2 degreeC for 2 minutes, and formed the adhesive layer. Next, the pressure-sensitive adhesive layer was attached to one surface of the base material A to obtain a single-sided pressure-sensitive adhesive sheet.
Next, the pressure-sensitive adhesive composition was applied to one surface of the same release liner as described above so that the thickness after drying was 25 μm, and dried at 100° C. for 2 minutes to form a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer was attached to the other surface of the foam substrate in the single-sided pressure-sensitive adhesive sheet. Then, the obtained structure was passed once through a laminator at 80° C. (0.3 MPa, speed 0.5 m/min) and then cured in an oven at 50° C. for 1 day. Thus, a double-sided PSA sheet (Example 1) having a total thickness of 200 μm was obtained.

(Example 2)
A double-sided pressure-sensitive adhesive sheet (Example 2) having a total thickness of 150 μm was obtained in the same manner as in the production of the double-sided pressure-sensitive adhesive sheet of Example 1 above, except that the substrate B was used instead of the substrate A.
Here, the base material B has a thickness of 100 μm, a 25% compressive strength of 149 kPa, a tensile strength in the flow direction (tensile strength (MD)) of 4.62 MPa, and a tensile strength in the width direction ( The tensile strength (CD) was 7.51 MPa. The base material B had an aspect ratio (CD/VD) of 1.9 and an aspect ratio (MD/CD) of 2.8.

(Example 3)
A double-sided pressure-sensitive adhesive sheet (Example 3) having a total thickness of 200 μm was obtained in the same manner as in the production of the double-sided pressure-sensitive adhesive sheet of Example 1 above, except that the substrate C was used instead of the substrate A.
Here, the substrate C has a thickness of 150 μm, a 25% compressive strength of 150 kPa, a tensile strength (tensile strength (MD)) in the flow direction of 9.50 MPa, and a tensile strength in the width direction ( The tensile strength (CD) was 8.20 MPa. The base material C had an aspect ratio (CD/VD) of 9.0 and an aspect ratio (MD/CD) of 0.7. FIG. 3 is a photograph of a cross section of the base material C cut along a plane parallel to CD and VD (that is, a plane in which the direction of a perpendicular line corresponds to MD) when observed by a scanning electron microscope (SEM). Indicates.
(Example 4)
A double-sided pressure-sensitive adhesive sheet (Example 4) having a total thickness of 150 μm was obtained in the same manner as in the production of the double-sided pressure-sensitive adhesive sheet of Example 1 above, except that the substrate D was used instead of the substrate A.
Here, the substrate D has a thickness of 100 μm, a 25% compressive strength of 75 kPa, a tensile strength (tensile strength (MD)) in the flow direction of 1.99 MPa, and a tensile strength in the width direction ( The tensile strength (CD) was 2.97 MPa. The substrate D had an aspect ratio (CD/VD) of 4.3 and an aspect ratio (MD/CD) of 0.9.

Thickness, type, apparent density, degree of cross-linking, average cell diameter aspect ratio (CD/VD, and MD/CD) of the substrate used to prepare the double-sided pressure-sensitive adhesive sheets of Examples 1 to 4 above, 25% compression Table 1 summarizes the strength, tensile strength (MD and CD), and 90°C heating dimensional change rate (MD and CD). Table 1 shows the thicknesses of the pressure-sensitive adhesive layers formed on both surfaces of the base material and the total thickness of the double-sided pressure-sensitive adhesive sheet.

<Evaluation test>

(1) Pressing Adhesive 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. 4 to obtain a window frame-shaped double-sided pressure-sensitive adhesive sheet. Using this double-sided window frame pressure-sensitive 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. 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) (horizontal 70 mm, vertical 130 mm, thickness 2 mm) was bonded by pressing the roller of 5 kg back and forth once to make a sample for evaluation.
4A and 4B are schematic views of the evaluation sample, in which FIG. 4A is a top view and FIG. 4B is a sectional view taken along line AA′. In FIG. 4, reference numeral 21 is a 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 a universal tensile compression tester (device name "tensile compression tester, TG-1kN" manufactured by Minebea Co., Ltd.). 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 a pressure bonding force (unit: N/cm ² ). The measurement was performed in an environment of 23° C. and 50% RH.
FIG. 5 is a schematic cross-sectional view showing a method for measuring the pressure-sensitive adhesive force, where reference numeral 21 is a SUS plate, reference numeral 2 is a window frame-shaped double-sided adhesive sheet, reference numeral 22 is a glass plate, reference numeral 23 is a round bar, 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. 5, 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 addition, in the above-mentioned measurement of the pressure-sensitive adhesive strength, 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.

(2) Peel strength test (against SUS304BA)
A 25 μm thick polyethylene terephthalate (PET) film was attached to one adhesive surface of the double-sided adhesive sheet, and this was cut into a size of 20 mm in width and 100 mm in length 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 pressure-bonded to 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 the above-mentioned universal tensile compression tester, according to JIS Z 0237, peeling was performed under the conditions of a pulling speed of 300 mm/min and a peeling angle of 180 degrees. The peel strength (also referred to as “peel strength”; unit: N/20 mm width) was determined by measuring the load.

(3) Impact resistance (room temperature and low temperature)
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. 6 to obtain a window frame-shaped double-sided pressure-sensitive adhesive sheet. Using this window frame double-sided adhesive sheet, a first PC plate (polycarbonate plate; width 70 mm, length 130 mm, thickness 2 mm) and a second PC plate (width 59 mm, length 113 mm, thickness 0.55 mm) A 5 kg roller was attached under pressure by reciprocating once to obtain a sample for evaluation (see FIGS. 6A and 6B).
6A and 6B are schematic views of the evaluation sample, where FIG. 6A is a top view and FIG. 6B is a sectional view taken along line BB′. In FIG. 6, 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, a drop test was carried out at room temperature (23° C.) by freely dropping 18 times from a height of 1.2 m onto a concrete plate. At this time, the direction of the drop was adjusted so that the six surfaces of the evaluation sample were sequentially downward. That is, the dropping pattern was performed once for each of the six surfaces for 3 cycles.
Then, each time it is dropped, it is visually confirmed whether or not peeling occurs between the first PC plate and the second PC plate, and the number of drops until peeling occurs at room temperature (23°C) Was evaluated as impact resistance. When no peeling was observed after dropping 18 times, it was displayed as "18 times or more" or ">18".
In the above-mentioned impact resistance test at room temperature, the samples in which no peeling was observed even after dropping 18 times were subsequently subjected to the impact resistance test at low temperature (-5°C). That is, the evaluation sample after the impact resistance test at room temperature is subjected to a drop test in which the concrete sample is allowed to freely drop from a height of 1.2 m under an environment of -5°C. It was visually confirmed whether or not peeling occurred between the first PC plate and the second PC plate, and the number of drops until peeling occurred was evaluated as impact resistance at low temperature (-5°C). .. At this time, one drop pattern was performed once for each of the six sides of the evaluation sample for 10 cycles, and when no peeling was observed after dropping 60 times, "60 times or more" or ">60" is displayed. did.

The results of the above-mentioned evaluations of the double-sided PSA sheets of Examples 1 to 4 are shown in Table 1 above.

As shown in Table 1 above, Example 1 of a double-sided pressure-sensitive adhesive sheet including a foam substrate having an aspect ratio (CD/VD) of 3 or less and an aspect ratio (MD/CD) of greater than 1 as the foam substrate. It was revealed that Example 2 and Example 2 exhibited higher pressure-sensitive adhesive strength than Example 3 and Example 4 of the double-sided PSA sheet. The double-sided pressure-sensitive adhesive sheets of Examples 1 and 2 also showed excellent peel strength. In addition, the double-sided pressure-sensitive adhesive sheets of Example 1 and Example 2 exhibited high impact resistance at room temperature (23°C) and low temperature (-5°C).

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.

DESCRIPTION OF SYMBOLS 1 Double-sided adhesive sheet 11 1st adhesive layer 11A 1st adhesive surface 12 2nd adhesive layer 12A 2nd adhesive surface 15 Foam base material 15A 1st surface 15B 2nd surface 17 Release liner 17A Release liner front surface 17B Release liner Back surface 2 Double-sided adhesive sheet 21 Stainless steel (SUS) plate 21A Through hole 22 Glass plate 23 Round bar 24 Support stand 3 Double-sided adhesive sheet 31, 32 Polycarbonate plate

Claims (5)

A foam substrate,
A first 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 a thickness of 1000 μm or less,
The foam base material has an aspect ratio (CD/CD) represented by a ratio of the average cell diameter in the width direction (CD) of the foam base material to the average cell diameter in the thickness direction (VD) of the foam base material. VD) is 3 or less,
The foam substrate has an aspect ratio (MD/CD) represented by the ratio of the average cell diameter in the flow direction (MD) of the foam substrate to the average cell diameter in the width direction (CD) of the foam substrate. ) Is greater than 1, a double-sided PSA sheet. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the double-sided pressure-sensitive adhesive sheet has a thickness of 100 μm or more and 500 μm or less. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the foam base material is a polyolefin-based foam base material. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the foam substrate has a 25% compressive strength of 50 kPa or more. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 4, which is used for joining components of a portable electronic device.