CN104774570B

CN104774570B - Double-sided adhesive sheet

Info

Publication number: CN104774570B
Application number: CN201510019667.0A
Authority: CN
Inventors: 渡边茂树; 中山直树; 广西正人
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2014-01-15
Filing date: 2015-01-15
Publication date: 2020-03-06
Anticipated expiration: 2035-01-15
Also published as: CN104774570A; JP2020094224A; JP2015155528A; JP6945025B2

Abstract

The present invention relates to a double-sided adhesive sheet. The invention provides a double-sided adhesive sheet with excellent adhesion reliability. According to the present invention, there is provided a double-sided adhesive sheet comprising a foam base, a first adhesive layer provided on a first surface of the foam base, and a second adhesive layer provided on a second surface of the foam base. The foam base material has a thickness of 1000 [ mu ] m or less, an aspect ratio (CD/VD) represented by the ratio of the average cell diameter in the width direction (CD) to the average cell diameter in the thickness direction (VD) of 3 or less, and an aspect ratio (MD/CD) represented by the ratio of the average cell diameter in the Machine Direction (MD) to the average cell diameter in the width direction (CD) of more than 1.

Description

Double-sided adhesive sheet

Technical Field

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

Background

In general, an adhesive (also referred to as a pressure-sensitive adhesive, the same applies hereinafter) is in a soft solid (viscoelastic body) state in a temperature range around room temperature, and has a property of being easily adhered to an adherend by pressure. By utilizing such properties, adhesives are widely used in various fields for the purpose of bonding, fixing, and the like, for example, in the form of a double-sided adhesive sheet with a substrate, in which an adhesive layer is provided on both surfaces of the substrate.

As the substrate in the double-sided pressure-sensitive adhesive sheet with a substrate, in general, a foam having a cell structure or the like can be used in addition to a plastic film, a nonwoven fabric, paper or the like. The double-sided pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet with foam substrate) using the foam is more advantageous in terms of impact absorbability, irregularity following property, water resistance, sealing property, and the like, than a double-sided pressure-sensitive adhesive sheet using a plastic film or nonwoven fabric or the like as a substrate having no cell structure. Therefore, the present invention can be preferably applied to joining, fixing, and the like of components in portable electronic devices such as mobile phones, smart phones, tablet computers, and notebook computers.

Patent documents

1 and 2 are cited as technical documents relating to a double-sided pressure-sensitive adhesive sheet with a foam substrate.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2010-155969

Patent document 2: international publication No. 2005/007731

Disclosure of Invention

Problems to be solved by the invention

Incidentally, the double-sided adhesive sheet requires excellent adhesion property to an adherend. On the other hand, in recent years, from the viewpoint of downsizing, weight reduction, and the like of products, a double-sided adhesive sheet used for joining of parts and the like is required to have a narrow width. When the double-sided adhesive sheet is used for fixing a display panel in a portable electronic device, the width of the double-sided adhesive sheet is particularly significant from the viewpoint of increasing the screen size of the display panel and improving the degree of freedom in design. However, a double-sided pressure-sensitive adhesive sheet having a narrow width may be easily peeled from an adherend due to, for example, a reduction in the adhesive area to the adherend. Therefore, in order to obtain sufficient member fixing performance even if the width is narrow, further improvement in performance of the double-sided adhesive sheet is required.

Accordingly, an object of the present invention is to provide a double-sided adhesive sheet having more excellent adhesion reliability.

Means for solving the problems

The double-sided adhesive sheet disclosed herein comprises a foam base, a first adhesive layer provided on a first surface of the foam base, and a second adhesive layer provided on a second surface of the foam base. The thickness of the foam base material is 1000 [ mu ] m or less. The foam base material has an aspect ratio (CD/VD) of 3 or less, which is 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, and an aspect ratio (MD/CD), which is represented by the ratio of the average cell diameter in the Machine Direction (MD) of the foam base material to the average cell diameter in the width direction (CD) of the foam base material, is greater than 1. The double-sided adhesive sheet (double-sided adhesive sheet with foam substrate) having the above-described structure can be a double-sided adhesive sheet exhibiting excellent pressure-sensitive adhesive strength. The improvement of the press adhesion force can contribute to the improvement of the adhesion reliability.

In a preferred embodiment of the double-sided adhesive sheet disclosed herein, the thickness of the double-sided adhesive sheet is 100 μm or more and 500 μm or less. The double-sided adhesive sheet can be a double-sided adhesive sheet which exhibits excellent impact resistance in addition to excellent pressure-sensitive adhesive strength.

In a preferred embodiment of the double-sided adhesive sheet disclosed herein, the foam base is a polyolefin foam base. The double-sided adhesive sheet containing the foam base material can be a double-sided adhesive sheet exhibiting excellent impact resistance and water resistance.

In a preferred embodiment of the double-sided adhesive sheet disclosed herein, a foam substrate having a 25% compressive strength of 50kPa or more, for example, can be preferably used as the foam substrate. The double-sided adhesive sheet containing the foam base material can be a double-sided adhesive sheet exhibiting more excellent impact resistance.

The double-sided adhesive sheet disclosed herein exhibits excellent pressure-sensitive adhesive strength and is excellent in water resistance and impact resistance, and therefore is suitable as a double-sided adhesive sheet for joining parts of portable electronic devices, for example.

Drawings

Fig. 1 is a schematic cross-sectional view showing a structure of a double-sided adhesive sheet according to an embodiment.

Fig. 2 is a photograph of a cross section of the substrate a used in example 1 cut along a plane parallel to CD and VD, observed with a Scanning Electron Microscope (SEM).

Fig. 3 is a photograph of a cross section of the base material C used in example 3 cut along a plane parallel to CD and VD, observed with a Scanning Electron Microscope (SEM).

Fig. 4 is an explanatory view showing an evaluation sample used in measuring the pressing adhesive force.

Fig. 5 is an explanatory diagram illustrating a method of measuring the pressing adhesion force.

FIG. 6 is an explanatory view showing an evaluation sample used for evaluating impact resistance.

Reference numerals

1 double-sided adhesive sheet

11 first adhesive layer

11A first adhesive surface

12 second adhesive layer

12A second adhesive surface

15 foam base material

15A first side

15B second side

17 Release liner

Front side of 17A Release liner

Back side of 17B release liner

2 double-sided pressure-sensitive adhesive sheet

21 stainless steel (SUS) plate

21A through hole

22 glass plate

23 round bar

24 support table

3 double-sided pressure-sensitive adhesive sheet

31. 32 polycarbonate plate

Detailed Description

Preferred embodiments of the present invention will be described below. Further, matters other than those specifically mentioned in the present specification which are required for carrying out the present invention may be understood as matters of design by those skilled in the art based on the prior art in the field. The present invention can be implemented based on the contents disclosed in the present specification and the common general knowledge in the art.

In the following drawings, members and portions that achieve the same functions are given the same reference numerals to describe the same, and redundant description may be omitted or simplified. The embodiments shown in the drawings are schematic for the purpose of clearly illustrating the present invention, and do not accurately show the size or scale of the pressure-sensitive adhesive sheet of the present invention actually provided as a product.

In the present specification, the "pressure-sensitive adhesive" refers to a material that is in a soft solid (viscoelastic body) state in a temperature range around room temperature and has a property of being easily adhered to an adherend by pressure, as described above. As used herein, the term "adhesive" includes, for example, "C.A. Dahlquist," adhesive "and" primer ", McLaren&Sons, (1966), P.143 ", generally speaking, has a modulus of elasticity satisfying complex tensile E (1Hz)<10⁷Dyne/cm²A material having the properties of (typically, at 25 ℃ C. having the above properties)A material of a substance). The "base polymer" of the pressure-sensitive adhesive is a main component (i.e., a component accounting for 50% by weight or more of the rubbery polymer) in the rubbery polymer (a polymer exhibiting rubber elasticity in a temperature range around room temperature) contained in the pressure-sensitive adhesive.

The double-sided adhesive sheet disclosed herein (which may be in the form of a tape or the like having a long dimension) is configured to include a foam base and a first adhesive layer and a second adhesive layer provided on a first surface and a second surface of the foam base, respectively. For example, the double-sided pressure-sensitive adhesive sheet may have a cross-sectional structure as shown in fig. 1. The double-sided adhesive sheet 1 has a foam base material 15 in a sheet form, and a first adhesive layer 11 and a second adhesive layer 12 supported on both sides of the base material 15. More specifically, the first and

second faces

15A and 15B (both non-releasable) of the substrate 15 are provided with the first and second

adhesive layers

11 and 12, respectively. Before use (before attachment to an adherend), the double-sided adhesive sheet 1 may be wound spirally on a release liner 17 having both a front surface 17A and a back surface 17B as shown in fig. 1. In the double-sided adhesive sheet 1 of the above embodiment, the surface (second adhesive surface 12A) of the second adhesive layer 12 is protected by the front surface 17A of the release liner 17, and the surface (first adhesive surface 11A) of the first adhesive layer 11 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 separate release liners.

The release liner is not particularly limited, and conventional release paper or the like can be used. For example, it is possible to use: release liners having a release treatment layer on the surface of a liner base material such as a plastic film or paper, and release liners comprising a low-tackiness material such as a fluoropolymer (polytetrafluoroethylene or the like) or a polyolefin resin (polyethylene, polypropylene or the like). The release-treated layer can be formed by surface-treating the liner base with a release-treating agent such as silicone, long-chain alkyl, fluorine-containing, or molybdenum sulfide.

The double-sided adhesive sheet disclosed herein can be preferably used so that the total thickness thereof is generally 1500 μm or less. The total thickness of the double-sided adhesive 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, further preferably 120 μm or more and 300 μm or less, and may be 130 μm or more and 280 μm or less, for example. By setting the total thickness of the double-sided adhesive sheet to the upper limit value or less, it is possible to be advantageous from the viewpoint of reduction in thickness, size, weight, resource saving, and the like of products. Further, by setting the total thickness of the double-sided adhesive sheet to be equal to or greater than the above-described lower limit value, a double-sided adhesive sheet exhibiting excellent impact resistance and water resistance can be obtained.

Here, the total thickness of the double-sided adhesive sheet is a thickness from one adhesive surface to the other adhesive surface, and in the example shown in fig. 1, is a thickness t from the first adhesive surface 11A to the second adhesive surface 12A. Therefore, 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, for example, the thickness of the release liner is not included in the thickness of the double-sided pressure-sensitive adhesive sheet described herein.

< foam base >

In the technology disclosed herein, the foam base material refers to a base material having a portion having cells (cell structure), and typically refers to a base material containing a thin layered foam (foam layer) as a constituent element. The foam base may be a base substantially composed of only one or two or more foam layers. Without particular limitation, as the foam base in the technology disclosed herein, a single-layer (one-layer) foam base may be preferably employed.

The thickness of the foam base material can be appropriately set according to the strength, flexibility, purpose of use, and the like of the double-sided pressure-sensitive adhesive sheet. From the viewpoint of easily ensuring the thickness of the pressure-sensitive adhesive layer that can exhibit the desired adhesive properties, it is generally appropriate to set the thickness of the foam base to 1000 μm or less, preferably 500 μm or less, more preferably 300 μm or less, for example, 250 μm or less, and typically 200 μm or less. A foam base material having a thickness of 180 μm or less can be used. In addition, from the viewpoint of impact resistance, repulsion resistance, and the like of the double-sided adhesive sheet, it is preferable to set the thickness of the foam base material to 30 μm or more, preferably 50 μm or more, and more preferably 60 μm or more (for example, 80 μm or more). The repulsion resistance as used herein refers to a property of holding the double-sided pressure-sensitive adhesive sheet in the shape after the elastic deformation against the repulsive force of the double-sided pressure-sensitive adhesive sheet to return to the original shape when the double-sided pressure-sensitive adhesive sheet is elastically deformed along the surface shape (which may be a curved surface, a surface having a level difference, or the like) of the adherend (that is, a property of resisting the repulsive force of the double-sided pressure-sensitive adhesive sheet).

The material of the foam base is not particularly limited. In general, a foam base material containing a foam layer formed of a foam of a plastic material (plastic foam) is preferable. The plastic material (meaning including rubber material) for forming the plastic foam is not particularly limited and may be appropriately selected from known plastic materials. The plastic material may be used singly or in combination of two or more kinds as appropriate.

Specific examples of the plastic foam include: polyolefin resin foams such as polyethylene foams and polypropylene foams; polyester resin foams such as polyethylene terephthalate foam, polyethylene naphthalate foam, and polybutylene terephthalate foam; polyvinyl chloride resin foams such as polyvinyl chloride foams; a vinyl acetate resin foam; a polyphenylene sulfide resin foam; amide resin foams such as polyamide (nylon) resin foam and wholly aromatic polyamide (Aramid) resin foam; a polyimide resin foam; polyether ether ketone (PEEK) foam; styrene resin foams such as polystyrene foam; urethane resin foams such as polyurethane resin foams; and the like. As the plastic foam, a rubber resin foam such as a polychloroprene foam may be used.

As a preferable foam, a polyolefin resin foam can be exemplified. As the plastic material (i.e., the polyolefin resin) constituting the above-mentioned polyolefin foam, various known or conventional polyolefin resins can be used without particular limitation. Examples thereof include: polyethylene such as Low Density Polyethylene (LDPE), Linear Low Density Polyethylene (LLDPE), High Density Polyethylene (HDPE), metallocene catalyst type linear low density polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, and the like. These polyolefin-based resins may be used singly or in combination of two or more kinds as appropriate.

Preferred examples of the foam base in the technology disclosed herein include a polyethylene-based foam base substantially composed of a foam of a polyethylene-based resin, a polypropylene-based foam base substantially composed of a foam of a polypropylene-based resin, and the like, from the viewpoints of impact resistance, water repellency, and the like. The polyethylene resin is a resin containing ethylene as a main monomer (i.e., a main component in the monomer), and may include an ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer, and the like, in which the copolymerization ratio of ethylene exceeds 50% by weight, in addition to HDPE, LDPE, LLDPE, and the like. Similarly, the polypropylene-based resin refers to a resin containing propylene as a main monomer. As the foam base material in the technology disclosed herein, a polyethylene-based foam base material can be preferably used.

The method for producing the plastic foam (typically, polyolefin foam) is not particularly limited, and can be produced by a known method. For example, the thermoplastic resin composition can be produced by a method including a molding step, a crosslinking step and a foaming step of the plastic material or the plastic foam. Further, a stretching step may be included as necessary.

Examples of the method of crosslinking the plastic foam include a chemical crosslinking method using an organic peroxide or the like, and an ionizing radiation crosslinking method by irradiation with ionizing radiation, which may be used in combination.

The average cell diameter (in terms of true spheres) of the foam base (e.g., polyolefin foam base) is not particularly limited, but is preferably 10 to 500 μm, more preferably 15 to 300 μm, still more preferably 20 to 200 μm, and for example preferably 25 to 100 μm. The foam base material tends to have improved impact resistance by adjusting the average cell diameter (in terms of true spheres) of 10 μm or more. On the other hand, the average cell diameter (in terms of true spheres) of the foam base material is adjusted to 500 μm or less, and thus the water repellency tends to be improved.

Here, the average cell diameter (in terms of true spheres) of the foam base material in the present specification is a value measured in the following manner. That is, an arbitrary cut surface of the foam base material is observed with a Scanning Electron Microscope (SEM), and then the image is subjected to binarization processing by image processing software to be separated into a cell portion and a portion other than the cell portion (for example, a plastic resin portion), and the area of each cell is measured with respect to the cell portion. Then, the average value of the diameters when the area of the cells was converted to the area of a true circle was calculated and used as the average cell diameter (converted to a true sphere) of the foam base material. As the SEM, the device name "S-4800" manufactured by Hitachi Kogyo or a product corresponding thereto may be used. As the IMAGE processing software, product name "IMAGE J" manufactured by national research on health in the united states or a product equivalent thereto can be used.

The average cell diameter (in terms of true spheres) of the foam base is preferably 50% or less, and preferably 30% or less (for example, 10% or less), of the thickness of the foam base. By adjusting the average cell diameter (in terms of true spheres) of the foam base material to 50% or less of the thickness of the foam base material, the water repellency tends to be further improved.

In the present specification, the longitudinal direction of the foam base (also referred to as MD; the same applies hereinafter) refers to the extrusion direction in the production process of the foam base. The foam base is not particularly limited, and when the foam base is in the form of a strip or the like having a long dimension, the MD of the foam base is generally aligned with the longitudinal direction thereof. The width direction of the foam base (also referred to as "CD"; the same applies hereinafter) is a direction perpendicular to the MD and along the surface of the foam base. The thickness direction of the foam base (also referred to as VD; the same applies hereinafter) is a direction perpendicular to the surface of the foam base, that is, a direction perpendicular to each of the MD and the CD.

In the present specification, as the index indicating the shape of the cells contained in the foam base material, "aspect ratio (CD/VD)" represented by the following formula (1) and represented by the following formula (2) is used, which is 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, and "aspect ratio (MD/CD)" represented by the ratio of the average cell diameter in the longitudinal direction (MD) of the foam base material to the average cell diameter in the width direction (CD) of the foam base material.

Aspect ratio (CD/VD) ═ average bubble diameter of CD/average bubble diameter of VD (1)

Aspect ratio (MD/CD) mean cell diameter of MD/mean cell diameter of CD (2)

Herein, in the present specification, "average cell diameter in MD" is defined as an average cell diameter measured as follows.

That is, the foam base material was cut at the approximate center of the CD along a plane parallel to MD and VD (i.e., a plane in which the direction of the perpendicular line coincides with the CD), and the center of the cut surface was photographed by the Scanning Electron Microscope (SEM).

Then, the photographed image was printed on a paper of a4 size, and a straight line of 60mm in length parallel to the MD was drawn on the image. At this time, the magnification of the electron microscope is adjusted so that about 10 to about 20 bubbles are present on a 60mm straight line.

The number of cells present on the straight line was visually counted, and the average cell diameter in the MD of the foam base material was determined based on the following formula (3).

Average cell diameter (μm) of MD 60(mm) × 10³/(number of bubbles (number) × magnification) (3)

In addition, "the average cell diameter of CD" is defined as the average cell diameter measured as follows.

That is, the foam base material was cut along a plane parallel to CD and VD (i.e., a plane in which the direction of the perpendicular line coincides with MD), and the central portion of the cut surface was photographed by the Scanning Electron Microscope (SEM).

Then, the photographed image was printed on a paper of a4 size, and a straight line of 60mm in length parallel to the CD was drawn on the image. At this time, the magnification of the electron microscope is adjusted so that about 10 to about 20 bubbles are present on a 60mm straight line.

The number of cells present on the straight line was visually counted, and the average cell diameter of the CD of the foam base was determined based on the following formula (4).

Average bubble diameter (μm) of CD 60(mm) × 10³/(number of air bubbles(s) × magnification) (4)

In addition, "the average bubble diameter of VD" is defined as an average bubble diameter measured as follows.

That is, the foam base material was cut along a plane parallel to the CD and VD in the same manner as when the average cell diameter of the CD was calculated, and the cut plane was photographed with a scanning electron microscope, and the obtained image was printed. Then, three straight lines parallel to the VD and quartered on the CD are drawn on the image from one surface to the other surface of the double-sided adhesive sheet, respectively. The length of each line is measured, and the total value of the measured lengths is calculated. The number of cells present on the straight line was visually counted, and the average cell diameter of VD of the foam base material was obtained based on the following formula (5).

The average bubble diameter (μm) of VD is the sum of the lengths of three straight lines on the image (mm) × 10³/(number of bubbles (number) × magnification) (5)

In addition, when drawing a straight line, the straight line is made to penetrate the bubble as much as possible without making point contact with the bubble. When a part of the bubbles was in point contact with the straight line, the number of the bubbles was counted as 1. In a state where both ends of the straight line were located in the bubbles without penetrating the bubbles, the number of the bubbles was counted as 0.5.

The average cell diameter in each direction of MD, CD, and VD can be controlled by adjusting, for example, the conditions of the production process (foaming process, stretching process, etc.) of the foam base material, and the composition of the foam base material (the amount of the foaming agent used, etc.). The foam base is not particularly limited, and when the plastic molded article is stretched by an extruder to be formed into a long shape, the direction of the longest average cell diameter of the cells contained in the foam base tends to be aligned with the longitudinal direction (that is, MD) of the foam base.

The aspect ratio (CD/VD) of the foam base is preferably 3 or less. The aspect ratio (CD/VD) is more preferably 2.8 or less, still more preferably 2.5 or less, and for example, preferably 2.3 or less. The aspect ratio (CD/VD) is preferably greater than 1, more preferably 1.3 or more, typically 1.5 or more, and for example, preferably 1.7 or more. By adjusting the aspect ratio (CD/VD) to the upper limit or less, the double-sided adhesive sheet having the foam base material can exhibit a high pressure-sensitive adhesive strength. One reason why the pressure-sensitive adhesive strength is improved in this manner is considered to be that by controlling the cell shape of the foam base material so as to obtain the above-mentioned range of the aspect ratio (CD/VD), the stress at the time of extruding the double-sided adhesive sheet in the thickness direction can be dispersed more in the foam base material. Further, by adjusting the aspect ratio (CD/VD) to be larger than the lower limit, the flexibility of the double-sided adhesive sheet using the foam base tends to be increased, and the unevenness follow-up property and impact resistance can be improved.

The aspect ratio (MD/CD) of the foam base material is preferably more than 1. The aspect ratio (MD/CD) is more preferably 1.4 or more, still more preferably 1.6 or more, typically 2 or more, for example, preferably 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, and for example, preferably 3 or less. By adjusting the aspect ratio (MD/CD) to be larger than the lower limit value, the workability of a double-sided adhesive sheet using the foam base material can be improved. Further, by adjusting the aspect ratio (MD/CD) to be not more than the upper limit value, the water repellency of the double-sided adhesive sheet using the foam base material can be improved.

The density (apparent density) of the foam base is not particularly limited, and is preferably 0.2g/cm³Above and 0.6g/cm³The following. The density of the foam base material is more preferably 0.25g/cm³Above and 0.55g/cm³Below, more preferably more than 0.3g/cm³And 0.5g/cm³Below, for example, 0.35g/cm³Above and 0.5g/cm³The following. By adjusting the density to 0.2g/cm³As described above, the foam base material tends to have improved strength (and hence strength of the double-sided adhesive sheet), and impact resistance and handling properties tend to be improved. On the other hand, by adjusting the density to 0.6g/cm³Hereinafter, the unevenness follow-up property, the rebound resistance, and the water repellency tend to be improved. The density (apparent density) of the foam base material can be measured, for example, by a method based on JIS K6767.

The tensile strength (tensile strength) of the foam base (for example, polyolefin foam base) is not particularly limited. For example, the tensile strength in the Machine Direction (MD) is preferably 1MPa or more and 30MPa or less (more preferably 2MPa or more and 20MPa or less, further preferably 2.5MPa or more and 10MPa or less, and typically 3MPa or more and 7MPa or less). The tensile strength in the width direction (CD) is preferably 1MPa or more and 30MPa or less (more preferably 3MPa or more and 20MPa or less, further preferably 4MPa or more and 15MPa or less, and typically 4.5MPa or more and 10MPa or less). By adjusting the tensile strength to be not less than the lower limit, excellent workability (reworkability) can be exhibited, such that the substrate (and hence the double-sided adhesive sheet) can be easily peeled without being torn when the double-sided adhesive sheet is peeled for recovering the member. On the other hand, by adjusting the tensile strength to the above-mentioned upper limit or less, the impact resistance and the level difference following property can be improved. The tensile strength (longitudinal tensile strength, width tensile strength) of the foam base material was measured in accordance with JIS K6767. The tensile strength of the foam base material can be controlled by, for example, the degree of crosslinking, the density, and the like.

The 25% compressive strength of the foam base (for example, polyolefin foam base) is not particularly limited, and is preferably 50kPa or more and 1000kPa or less, for example. The 25% compressive strength of the foam base material is more preferably more than 60kPa and 1000kPa or less, 75kPa and 500kPa or less, further preferably 80kPa and 500kPa or less, typically 90kPa and 300kPa or less, and for example, preferably 100kPa and 250kPa or less. Here, the 25% compressive strength of the foam base material means a load when the foam base materials are stacked to have a thickness of about 25mm and sandwiched by flat plates, and compressed by a thickness amount corresponding to 25% of the original thickness, that is, a load when the base materials are compressed to a thickness of 75% of the original thickness. By adjusting the 25% compressive strength to 50kPa or more, the impact resistance of the double-sided adhesive sheet tends to be improved, and the dimensional stability at the time of processing can be improved. On the other hand, by adjusting the 25% compressive strength to 1000kPa or less, the rebound resistance and the level difference following property can be improved. The 25% compressive strength of the foam base material was measured according to JIS K6767. The 25% compressive strength of the foam base material can be controlled by, for example, the degree of crosslinking, the density, and the like.

The heating dimensional change rate in MD at 90 ℃ (90 ℃ heating dimensional change rate (MD)) of the foam base (for example, polyolefin foam base) is not particularly limited, and is, for example, preferably from-10% to 10%. The dimensional change (MD) of the foam base material upon heating at 90 ℃ is more preferably-5% or more and 5% or less, and still more preferably-4% or more and 4% or less. By adjusting the 90 ℃ heating dimensional change (MD) within the above range, expansion and contraction of the double-sided adhesive sheet having the foam substrate can be suppressed even in a high-temperature environment (for example, 40 ℃ to 90 ℃), and excellent adhesion reliability can be exhibited.

The heating dimensional change rate of the CD at 90 ℃ (90 ℃ heating dimensional change rate (CD)) of the foam base (for example, polyolefin foam base) is not particularly limited, and is, for example, preferably from-10% to 10%. The dimensional Change (CD) of the foam base material upon heating at 90 ℃ is more preferably from-5% to 5%, still more preferably from-4% to 4%. By adjusting the 90 ℃ heating dimensional change rate (CD) within the above range, expansion and contraction of the double-sided adhesive sheet having the foam base can be suppressed even in a high-temperature environment (for example, 40 ℃ to 90 ℃), and excellent adhesion reliability can be exhibited.

The 90 ℃ heating dimensional change rate of MD and CD of the foam base material was measured according to JIS K6767 except that the heating temperature was set to 90 ℃.

The degree of crosslinking of the foam base (for example, polyolefin foam base) is not particularly limited, and 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 still more preferably 30% or more and 40% or less (for example, 32% or more and 40% or less).

Here, the crosslinking degree in the present specification means a value determined by the following measurement. That is, a test piece of about 100mg was taken out from the foam base material to be measured, and the weight A (mg) of the test piece was precisely measured. Then, the test piece was immersed in 30cm at 120 ℃³After being left in xylene for 24 hours, the mixture was filtered through a 200-mesh wire gauze. The insoluble component on the metal net was taken and dried in vacuum, and the weight B (mg) of the insoluble component was precisely weighed. From the obtained value, the crosslinking degree was calculated by the following formula (6).

Crosslinking agent (%) (B/a) × 100 (6)

The foam base material may contain various additives such as a filler (inorganic filler, organic filler, etc.), an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a plasticizer, a flame retardant, and a surfactant, if necessary.

The foam base in the art disclosed herein may be colored in order to allow a double-sided adhesive sheet having the foam base to exhibit desired design properties or optical properties (e.g., light-shielding properties, light-reflecting properties, etc.). The coloring may be carried out by using one kind of known organic or inorganic coloring agent alone or in an appropriate combination of two or more kinds.

For example, when the double-sided adhesive sheet disclosed herein is used for light-shielding applications, the visible light transmittance of the foam base is not particularly limited, and is preferably 0% or more and 15% or less, and more preferably 0% or more and 10% or less, as in the case of the visible light transmittance of the double-sided adhesive sheet described later. When the double-sided adhesive sheet disclosed herein is used for light reflection applications, the visible light reflectance of the foam base is preferably 20% or more and 100% or less, and more preferably 25% or more and 100% or less, as in the case of the double-sided adhesive sheet.

The visible light transmittance of the foam base can be determined by measuring the intensity of light irradiated from one surface side of the foam base to transmit to the other surface side at a wavelength of 550nm using a spectrophotometer (for example, a spectrophotometer manufactured by hitachi high-tech, ltd., model "U-4100"). The visible light reflectance of the foam base can be determined by measuring the intensity of light irradiated from one surface side of the foam base and reflected at a wavelength of 550nm using the above spectrophotometer. The visible light transmittance and visible light reflectance of the double-sided adhesive sheet can be determined by the same method.

When the double-sided adhesive sheet disclosed herein is used for light-shielding applications, the foam base is preferably colored black. The color of black is preferably 35 or less (e.g., 0 to 35), and more preferably 30 or less (e.g., 0 to 30). In addition, a and b defined by the color system of L × a × b may be appropriately selected according to the value of L × b. The a and b are not particularly limited, but both of them are preferably in the range of-10 to 10 (more preferably-5 to 5, and still more preferably-2.5 to 2.5). For example, it is preferred that both a and b are 0 or approximately 0.

In the present specification, L, a, b defined by the color system of la, b can be obtained by measurement using a color difference meter (for example, a color difference meter manufactured by medendar, trade name "CR-200"). The L × a × b color system is a color space recommended by the international commission on illumination (CIE) in 1976, and refers to a color space called CIE1976(L × a × b) color system. Note that L × a × b color system is defined by JIS Z8729 in japanese industrial standards.

Examples of the black coloring agent used for coloring the foam base material black include: carbon black (furnace black, channel black, acetylene black, thermal black, lamp black, etc.), graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, cyanine black, activated carbon, ferrite (nonmagnetic ferrite, magnetic ferrite, etc.), magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complex, composite oxide-based black pigment, anthraquinone-based organic black pigment, and the like. As a black colorant preferable from the viewpoint of cost, availability, and the like, carbon black can be exemplified. The amount of the black colorant to be used is not particularly limited, and may be appropriately adjusted to an amount capable of imparting desired optical characteristics.

When the double-sided adhesive sheet disclosed herein is used for light reflection applications, the foam base is preferably colored white. The color of white is preferably 87 or more (e.g., 87 to 100), and more preferably 90 or more (e.g., 90 to 100) in L (lightness) defined by L a b color system. In addition, a and b defined by the color system of L × a × b may be appropriately selected according to the value of L × b. The a and b are preferably both in the range of-10 to 10 (more preferably-5 to 5, and still more preferably-2.5 to 2.5), for example. For example, it is preferred that both a and b are 0 or approximately 0.

Examples of the white colorant used when coloring the foam base material to white include: titanium oxide (titanium dioxide such as rutile type titanium dioxide and anatase type 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, aluminum oxide, clay, kaolin, titanium phosphate, mica, gypsum, white carbon black, diatomaceous earth, bentonite, lithopone, zeolite, sericite, halloysite, and other inorganic white colorants, acrylic resin particles, polystyrene resin particles, polyurethane resin particles, amide resin particles, polycarbonate resin particles, etc, And organic white colorants such as silicone resin particles, urea resin particles, and melamine resin particles. The amount of the white colorant to be used is not particularly limited, and may be appropriately adjusted to an amount capable of imparting desired optical characteristics.

The surface of the foam base material may be appropriately surface-treated as necessary. The surface treatment may be a chemical or physical treatment for improving adhesion to an adjoining material (e.g., an adhesive layer). Examples of the surface treatment include corona discharge treatment, chromic acid treatment, exposure to ozone, exposure to flame, ultraviolet irradiation treatment, plasma treatment, and coating with a primer (primer).

In the technique disclosed herein, the kind of the adhesive contained in the first adhesive layer and the second adhesive layer provided on the first side and the second side of the foam base material is not particularly limited. The pressure-sensitive adhesive may be one containing, as a base polymer, one or more kinds selected from various polymers (pressure-sensitive adhesive polymers) such as acrylic polymers, polyester polymers, polyurethane polymers, polyether polymers, rubber polymers, silicone polymers, polyamide polymers, fluorine-containing polymers, and the like. In one preferred embodiment, the main component of the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive. The technique disclosed herein can be preferably implemented in the form of a double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer substantially composed of an acrylic pressure-sensitive adhesive.

Here, the "acrylic pressure-sensitive adhesive" refers to a pressure-sensitive adhesive containing an acrylic polymer as a base polymer (a main component in the polymer component, that is, a component accounting for 50% by weight or more). The "acrylic polymer" refers to a polymer having 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 (monomer main component, i.e., a component accounting for more than 50% by weight of the total amount of monomers constituting the acrylic polymer). In the present specification, "(meth) acryloyl group" means an acryloyl group and a methacryloyl group in a general manner. Likewise, "(meth) acrylate" is used in a generic sense to refer to both acrylates and methacrylates.

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.

CH₂＝C(R¹)COOR²(7)

Here, R in the above formula (7)¹Is a hydrogen atom or a methyl group. R²Is an alkyl group having 1 to 20 carbon atoms. Readily available adhesives with excellent adhesive propertiesFrom the viewpoint of the above, R is preferably²Has 2 to 14 carbon atoms (hereinafter, such a range of carbon atoms may be referred to as C)_2-14) Alkyl (meth) acrylates of alkyl groups of (a). As C_2-14Specific examples of the alkyl group include: ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, isooctyl, 2-ethylhexyl, n-nonyl, isononyl, n-decyl, isodecyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, and the like.

In a preferred embodiment, about 50% by weight or more (typically about 50% by weight or more and about 99.9% by weight or less), more preferably about 70% by weight or more (typically about 70% by weight or more and about 99.9% by weight or less), for example about 85% by weight or more (typically about 85% by weight or more and about 99.9% by weight or less) of the total amount of monomers used in the synthesis of the acrylic polymer is represented by R selected from the group consisting of the above formula (7)²Is C_2-14Alkyl (meth) acrylate alkyl ester of alkyl (more preferably C (meth) acrylate)_4-10One or two or more of alkyl esters, particularly preferably butyl acrylate and 2-ethylhexyl acrylate). An acrylic polymer obtained from such a monomer composition is preferable because an adhesive agent exhibiting good adhesive properties can be easily formed.

Without particular limitation, as the acrylic polymer in the technique disclosed herein, an acrylic polymer copolymerized with an acrylic monomer having a hydroxyl group (-OH) may 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, 4-hydroxybutyl (meth) acrylate, 2-hydroxyhexyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, (4-hydroxymethylcyclohexyl) methyl (meth) acrylate, polypropylene glycol mono (meth) acrylate, N-hydroxyethyl (meth) acrylamide, N-hydroxypropyl (meth) acrylamide, and the like. The hydroxyl group-containing acrylic monomer may be used alone or in combination of two or more.

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

Such hydroxyl group-containing acrylic monomer is preferably used in a range of about 0.001 wt% or more and about 10 wt% or less of the total amount of monomers used for synthesizing the acrylic polymer. Thereby, a double-sided adhesive sheet in which the above adhesive force and cohesive force are balanced at a higher level can be realized. By setting the amount of the hydroxyl group-containing acrylic monomer to about 0.01 wt% or more and about 5 wt% or less (for example, about 0.05 wt% or more and about 2 wt% or less), more favorable results can be achieved. Alternatively, the acrylic polymer in the technology disclosed herein may be an acrylic polymer not copolymerized with a hydroxyl group-containing acrylic monomer.

Monomers (other monomers) other than the above may be copolymerized in the acrylic polymer in the technique disclosed herein within a range not significantly impairing the effects of the present invention. The monomer can be used for the purpose of, for example, adjusting the glass transition temperature of the acrylic polymer, adjusting the adhesive properties (e.g., releasability), and the like. Examples of the monomer capable of improving the cohesive force and heat resistance of the adhesive include a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, a cyano group-containing monomer, vinyl esters, and aromatic vinyl compounds. Examples of the monomer that can introduce a functional group capable of serving as a crosslinking base point into the acrylic polymer or contribute to improvement of the adhesive strength include a carboxyl group-containing monomer, an acid anhydride group-containing monomer, an amide group-containing monomer, an amino group-containing monomer, an imide group-containing monomer, an epoxy group-containing monomer, (meth) acryloylmorpholine, vinyl ethers, and the like. For example, an acrylic polymer copolymerized with a carboxyl group-containing monomer as the 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, (meth) sulfopropyl acrylate, (meth) acryloyloxynaphthalenesulfonic acid, sodium vinylsulfonate, and the like.

Examples of the phosphoric acid group-containing monomer include: acryloyl 2-hydroxyethyl phosphate.

Examples of the cyano group-containing monomer include: acrylonitrile, methacrylonitrile, and the like.

Examples of the vinyl esters include: vinyl acetate, vinyl propionate, vinyl laurate, and the like.

Examples of the aromatic vinyl compound include styrene, chlorostyrene, chloromethylstyrene, α -methylstyrene and other substituted 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, anhydrides of the above carboxyl group-containing monomers, and the like.

Examples of the amide group-containing monomer include: acrylamide, methacrylamide, diethylacrylamide, N-vinylpyrrolidone, N-dimethylacrylamide, N-dimethylmethacrylamide, N-diethylacrylamide, N-diethylmethacrylamide, N' -methylenebisacrylamide, N-dimethylaminopropylacrylamide, N-dimethylaminopropylmethacrylamide, diacetoneacrylamide and the like.

Examples of the amino group-containing monomer include: aminoethyl (meth) acrylate, N-dimethylaminoethyl (meth) acrylate, N-dimethylaminopropyl (meth) acrylate, and the like.

Examples of the imide group-containing monomer include: cyclohexylmaleimide, isopropylmaleimide, N-cyclohexylmaleimide, itaconimide, and the like.

Examples of the epoxy group-containing monomer include: glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, allyl glycidyl ether, and the like.

Examples of the vinyl ethers include: methyl vinyl ether, ethyl vinyl ether, isobutyl vinyl ether, and the like.

Such "other monomer" may be used singly or in combination of two or more, and the content of the whole is preferably set to about 40% by weight or less (typically about 0.001% by weight or more and about 40% by weight or less), and more preferably set to about 30% by weight or less (typically about 0.01% by weight or more and about 30% by weight or less, for example about 0.1% by weight or more and about 10% by weight or less) of the total amount of monomers used for synthesizing the acrylic polymer. When a carboxyl group-containing monomer is used as the other monomer, the content thereof may be set to, for example, 0.1% by weight or more and 10% by weight or less, usually 0.2% by weight or more and 8% by weight or less, and for example, 0.5% by weight or more and 5% by weight or less, based on the total amount of the monomers. When a vinyl ester (e.g., vinyl acetate) is used as the other monomer, the content thereof may be set to, for example, 0.1% by weight or more and 20% by weight or less, and is preferably set to, usually, 0.5% by weight or more and 10% by weight or less, based on the total amount of the monomers.

The copolymerization composition of the acrylic polymer is suitably designed so that the glass transition temperature (Tg) of the polymer is-15 ℃ or lower (typically-70 ℃ or higher and-15 ℃ or lower), preferably-25 ℃ or lower (for example, -60 ℃ or higher and-25 ℃ or lower), and more preferably-40 ℃ or lower (for example, -60 ℃ or higher and-40 ℃ or lower). When the Tg of the acrylic polymer is too high, the adhesive strength (for example, adhesive strength in a low-temperature environment, adhesive strength to a rough surface, and the like) of an adhesive containing the acrylic polymer as a base polymer may be easily lowered. When the Tg of the acrylic polymer is too low, the curved surface adhesiveness of the pressure-sensitive adhesive may be easily reduced or the removability may be easily reduced (for example, a residual adhesive may be generated).

The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (i.e., the kind of monomer used in the synthesis of the polymer, the amount ratio used). Here, the Tg of the acrylic polymer is a value obtained from the Fox formula based on the Tg of a homopolymer (homopolymer) of each monomer constituting the polymer and the weight fraction (copolymerization ratio on a weight basis) of the monomer. The Tg of the homopolymer can be determined by the values described in the known art.

In the technique disclosed herein, the Tg of the homopolymer is specifically set to the following value.

For the Tg of the homopolymer other than those exemplified above, the values described in Polymer Handbook (Handbook of polymers) (3 rd edition, Wiley & Sons, Inc, 1989) can be used.

When no description is given in Polymer Handbook (3 rd edition, Wiley & Sons, Inc, 1989), the values obtained by the following measurement methods were used.

Specifically, 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 charged into a reactor having a thermometer, a stirrer, a nitrogen introduction tube and a reflux condenser, and stirred for 1 hour while introducing nitrogen. After the oxygen in the polymerization system was removed in this manner, the temperature was raised to 63 ℃ and the reaction was carried out for 10 hours. Then, the mixture was cooled to room temperature to obtain a homopolymer solution having a solid content of 33% by weight. Then, the homopolymer solution was cast on a release liner and dried to prepare a sample (homopolymer in a sheet form) having a thickness of about 2 mm. This sample was punched out into a disk shape having a diameter of 7.9mm, sandwiched between parallel plates, and viscoelasticity was measured by a shear mode in a temperature range of-70 to 150 ℃ at a temperature rise rate of 5 ℃/min while applying a shear strain having a frequency of 1Hz using a viscoelasticity tester (model "ARES"), and the temperature corresponding to the peak top temperature of the shear loss modulus G "(the temperature at which the G" curve is maximum) was taken as Tg of the homopolymer.

The adhesive in the technology disclosed herein is preferably designed in such a manner that the peak top temperature of the shear loss modulus G ″ of the adhesive is-10 ℃ or lower (typically-40 ℃ or higher and-10 ℃ or lower). For example, the adhesive is preferably designed so that the peak top temperature is-35 ℃ or higher and-15 ℃ or lower. The peak temperature of the shear loss modulus G ' can be grasped by punching a sheet-like adhesive having a thickness of 1mm into a disk shape having a diameter of 7.9mm, sandwiching the disk with parallel plates, measuring the temperature dependence of the loss modulus G ' in a shear mode at a temperature range of-70 ℃ to 150 ℃ at a temperature rise rate of 5 ℃/min while applying a shear strain having a frequency of 1Hz by using the above viscoelasticity tester (model "ARES", manufactured by TA Instrument Japan Co., Ltd.), and determining the temperature corresponding to the peak (the temperature at which the G ' curve is extremely large).

In addition, the peak top temperature of the shear loss modulus G ″ of the acrylic polymer can be adjusted by appropriately changing the monomer composition of the acrylic polymer (i.e., the kind of the monomer used in the synthesis of the polymer, the amount ratio used). The peak top temperature of the shear loss modulus G ″ of the adhesive can be adjusted by appropriately changing the monomer composition of the acrylic polymer (i.e., the kind and the amount ratio of the monomers used in synthesis of the polymer), the presence or absence of the tackifier to be described later, the kind and the amount of the tackifier to be used, and the like.

The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as a method for synthesizing an acrylic polymer, such as solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization, can be suitably used. For example, the solution polymerization method can be preferably employed. As a method of supplying the monomer in the solution polymerization, a batch feeding method, a continuous supply (dropwise) method, a stepwise supply (dropwise) method, or the like, in which all the monomer raw materials are supplied at once, can be suitably employed. The polymerization temperature may be appropriately selected depending on the kind of the monomer and the solvent to be used, the kind of the polymerization initiator, and the like, and may be set to, for example, about 20 ℃ to about 170 ℃ (typically about 40 ℃ to about 140 ℃).

The solvent used in the solution polymerization may be appropriately selected from known or conventional organic solvents. For example, it is possible to use: one solvent or a mixed solvent of two or more selected from aromatic compounds (typically aromatic hydrocarbons) such as toluene and xylene, aliphatic or alicyclic hydrocarbons such as ethyl acetate, hexane, cyclohexane and methylcyclohexane, halogenated alkanes such as 1, 2-dichloroethane, lower alcohols (e.g., monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol, 1-butanol, sec-butanol and tert-butanol, ethers such as tert-butyl methyl ether, ketones such as methyl ethyl ketone and acetylacetone, and the like. It is preferable to use an organic solvent (which may be a mixed solvent) having a boiling point in the range of 20 ℃ or higher and 200 ℃ or lower (more preferably 25 ℃ or higher and 150 ℃ or lower) under a total pressure of 1 atmosphere.

The initiator used in the polymerization may be appropriately selected from known or conventional polymerization initiators depending on the kind of the polymerization method. It may be preferable to use, for example: azo polymerization initiators. Specific examples of the azo polymerization initiator include: 2,2 ' -azobisisobutyronitrile, 2 ' -azobis (2-methylpropionamidine) disulfate, 2 ' -azobis (2-amidinopropane) dihydrochloride, 2 ' -azobis [2- (5-methyl-2-imidazolin-2-yl) propane ] dihydrochloride, 2 ' -azobis (N, N ' -dimethyleneisobutylamidine), 2 ' -azobis [ N- (2-carboxyethyl) -2-methylpropionamidine ] hydrate, 2 ' -azobis (4-methoxy-2, 4-dimethylvaleronitrile), 2 ' -azobis (2-methylbutyronitrile), 1,1 ' -azobis (cyclohexane-1-carbonitrile), 2 ' -azobis (2,4, 4-trimethylpentane), 2 ' -azobis (2-methylpropionic acid) dimethyl ester, and the like.

As other examples of the polymerization initiator, there may be mentioned: persulfates such as potassium persulfate and ammonium persulfate; peroxide initiators such as benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1-bis (t-butylperoxy) -3,3, 5-trimethylcyclohexane, 1-bis (t-butylperoxy) cyclododecane, and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; an aromatic carbonyl compound; and the like. As still other examples of the polymerization initiator, there may be mentioned: a redox initiator comprising a combination of a peroxide and a reducing agent. Examples of the redox initiator include: a combination of a peroxide and ascorbic acid (a combination of an aqueous hydrogen peroxide and ascorbic acid, or the like), a combination of a peroxide and an iron (II) salt (a combination of an aqueous hydrogen peroxide and an iron (II) salt, or the like), a combination of a persulfate and sodium bisulfite, or the like.

Such polymerization initiators may be used singly or in combination of two or more. The amount of the polymerization initiator to be used may be any amount that is generally used, and may be selected from the range of about 0.005 parts by weight or more and about 1 part by weight or less (typically about 0.01 parts by weight or more and about 1 part by weight or less) with respect to 100 parts by weight of the total monomer components, for example.

The solution polymerization can provide a polymerization reaction solution in which the acrylic polymer is dissolved in an organic solvent. As the acrylic polymer in the technique disclosed herein, the above-mentioned polymerization reaction liquid or a 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) and used. Alternatively, an acrylic polymer may be synthesized by a polymerization method other than the solution polymerization method (for example, emulsion polymerization, photopolymerization, bulk polymerization, or the like), and the polymer may be dissolved in an organic solvent to prepare a solution and used.

When the weight average molecular weight (Mw) of the acrylic polymer in the technique disclosed herein is too small, the cohesive force of the pressure-sensitive adhesive is insufficient, and adhesive residue tends to occur on the surface of the adherend or the curved surface adhesiveness tends to decrease in some cases. On the other hand, when Mw is too large, the adhesive force to an adherend may be easily lowered. In order to balance the adhesive property and the removability at a high level, it is preferable that Mw is 10X 10⁴Above and 500X 10⁴Acrylic polymers in the following ranges. By Mw of 20X 10⁴Above and 400 × 10⁴The following (e.g., 30X 10)⁴Above and 300 × 10⁴The following) can achieve more favorable results. Here, Mw is a value in terms of standard polystyrene obtained by GPC (gel permeation chromatography).

The adhesive composition in the art disclosed herein may be a composition containing a tackifying resin. The tackifier resin is not particularly limited, and various tackifier resins such as rosins, terpenes, hydrocarbons, epoxies, polyamides, elastomers, phenols, and ketones can be used. These tackifying resins may be used singly or in combination of two or more.

Specific examples of the rosin-based tackifier resin include: unmodified rosins (raw rosins) such as gum rosin, wood rosin, tall oil rosin and the like; modified rosins (hydrogenated rosins, disproportionated rosins, polymerized rosins, other chemically modified rosins, etc.) obtained by modifying these unmodified rosins by hydrogenation, disproportionation, polymerization, etc.; other various rosin derivatives; and the like. Examples of the rosin derivatives include: rosin esters such as those obtained by esterifying unmodified rosin with an alcohol (i.e., esterified products of rosin), and those obtained by esterifying modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.) with an alcohol (i.e., esterified products of modified rosin); unsaturated fatty acid-modified rosins obtained by modifying unmodified rosins or modified rosins (hydrogenated rosins, disproportionated rosins, polymerized rosins, etc.) with unsaturated fatty acids; unsaturated fatty acid-modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids; rosin alcohols obtained by reducing carboxyl groups in unmodified rosin, modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.), unsaturated fatty acid-modified rosin, or unsaturated fatty acid-modified rosin ester; metal salts of rosins (particularly, rosin esters) such as unmodified rosins, modified rosins, and various rosin derivatives; rosin phenol resins obtained by the addition polymerization of rosins (unmodified rosin, modified rosin, various rosin derivatives, and the like) and phenols in the presence of an acid catalyst; and the like.

Examples of the terpene-based tackifier resin include terpene-based resins such as α -pinene polymer, β -pinene polymer, and terpineol (ジペンテン) polymer, modified terpene-based resins obtained by modifying these terpene-based resins (for example, phenol modification, aromatic modification, hydrogenation modification, and hydrocarbon modification), and examples of the modified terpene-based resins include terpene-based resins, styrene-modified terpene-based resins, aromatic-modified terpene-based resins, and hydrogenated terpene-based resins.

Examples of the hydrocarbon tackifier resin include various hydrocarbon resins such as an aliphatic hydrocarbon resin, an aromatic hydrocarbon resin, an aliphatic cyclic hydrocarbon resin, an aliphatic/aromatic petroleum resin (e.g., a styrene-olefin copolymer), an aliphatic/alicyclic petroleum resin, a hydrogenated hydrocarbon resin, a coumarone resin, and a coumarone-indene resin, examples of the aliphatic hydrocarbon resin include one or more aliphatic hydrocarbon polymers selected from olefins having about 4 to about 5 carbon atoms and dienes, examples of the olefins include 1-butene, isobutylene, and 1-pentene, examples of the dienes include butadiene, 1, 3-pentadiene, and isoprene, examples of the aromatic hydrocarbon resins include vinyl aromatic hydrocarbon (e.g., styrene, vinyltoluene, α -methylstyrene, indene, and methylindene) polymers having about 8 to about 10 carbon atoms, examples of the aliphatic cyclic hydrocarbon resins include aromatic hydrocarbon resins obtained by polymerizing a so-called "C4 petroleum" or "C5 petroleum" to obtain a cyclic hydrocarbon fraction, alicyclic/aromatic hydrocarbon resins, and hydrogenated cyclopentadiene resin, and alicyclic/hydrocarbon resins obtained by polymerizing an alicyclic/aromatic hydrocarbon polymer, an alicyclic hydrocarbon resin, a hydrogenated cyclopentadiene resin, or a hydrogenated hydrocarbon compound obtained by polymerizing a so-derived from an alicyclic hydrocarbon resin.

In the technique disclosed herein, a tackifier resin having a softening point (softening temperature) of about 100 ℃ or higher (preferably about 120 ℃ or higher, more preferably about 135 ℃ or higher, for example, 140 ℃ or higher) can be preferably used as the tackifier resin. In addition, terpene-phenol resins having a softening point of the above-described lower limit or more can be preferably used. The tackifier resin can realize a double-sided adhesive sheet having more excellent rebound resilience. The upper limit of the softening point of the tackifier resin is not particularly limited, and may be, for example, about 200 ℃ or less (typically about 180 ℃ or less). The softening point of the tackifier resin as referred to herein is defined as a value measured by a softening point test method (ring and ball method) specified in any one of JIS K5902 and JIS K2207.

The amount of the tackifier resin to be used is not particularly limited, and may be appropriately set in accordance with the target adhesive performance (e.g., adhesive strength). For example, the tackifier resin is preferably used in a proportion of about 10 parts by weight or more and about 100 parts by weight or less (more preferably about 15 parts by weight or more and about 80 parts by weight or less, and further preferably about 20 parts by weight or more and about 60 parts by weight or less) with respect to 100 parts by weight of the acrylic polymer based on the solid content.

The adhesive composition may contain a crosslinking agent as needed. The kind of the crosslinking agent is not particularly limited, and may be selected from known or conventional crosslinking agents (e.g., isocyanate-based crosslinking agents, epoxy-based crosslinking agents,

oxazoline crosslinking agents, aziridine crosslinking agents, melamine crosslinking agents, peroxide crosslinking agents, urea crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, carbodiimide crosslinking agents, amine crosslinking agents, etc.) are appropriately selected and used. The crosslinking agent may be used singly or in combination of two or more. The amount of the crosslinking agent to be used is not particularly limited, and may be selected from the range of about 10 parts by weight or less (for example, about 0.005 parts by weight or more and about 10 parts by weight or less, preferably about 0.01 parts by weight or more and about 5 parts by weight or less) with respect to 100 parts by weight of the acrylic polymer, for example.

The pressure-sensitive adhesive composition may contain, as required, various additives generally used in the field of pressure-sensitive adhesive compositions such as leveling agents, crosslinking aids, plasticizers, softening agents, fillers, colorants (pigments, dyes, etc.), antistatic agents, antiaging agents, ultraviolet absorbers, antioxidants, light stabilizers, etc. The various additives can be conventionally used, and the features of the present invention are not particularly given, and therefore, detailed descriptions thereof are omitted.

As the release liner, one known or commonly used in the field of double-sided adhesive sheets can be appropriately selected and used. For example, a release liner having a structure in which a release treatment is applied to the surface of a liner base material can be preferably used. As a liner base material (object to be subjected to a release treatment) constituting such a release liner, various resin films, papers, cloths, rubber sheets, foam sheets, metal foils, composites thereof (for example, sheets having a laminated structure in which an olefin resin is laminated on both sides of paper), and the like can be appropriately selected and used. The above-mentioned release treatment can be carried out by a conventional method using a known or conventional release treatment agent (for example, a release treatment agent such as silicone, fluorine-containing type, long chain alkyl group, etc.). In addition, a liner base material having low adhesiveness such as an olefin resin (e.g., polyethylene, polypropylene, an ethylene-propylene copolymer, a polyethylene/polypropylene mixture), a fluorine-containing polymer (e.g., polytetrafluoroethylene, polyvinylidene fluoride) and the like can be used as a release liner without applying a release treatment to the surface of the liner base material. Alternatively, a release liner obtained by subjecting the liner base material having low adhesiveness to a release treatment may be used.

The application of the adhesive composition can be performed using a known or conventional coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, or a spray coater. The amount of the adhesive composition to be applied is not particularly limited, and may be set to an amount sufficient to form an adhesive layer having a thickness (thickness per one surface) of, for example, about 5 μm or more and about 150 μm or less after drying (i.e., based on the solid content). From the viewpoint of balancing the weight reduction and/or thinning of the double-sided adhesive sheet and the adhesive performance at a high level, it is appropriate to set the thickness of the adhesive layer per one side to about 10 μm or more and about 110 μm or less, preferably about 15 μm or more and about 100 μm or less (more preferably about 20 μm or more and about 75 μm or less, for example, about 20 μm or more and about 50 μm or less, typically about 20 μm or more and about 35 μm or less). From the viewpoint of accelerating the crosslinking reaction, improving the production efficiency, and the like, the drying of the adhesive composition is preferably performed under heating. Generally, drying temperatures of, for example, from about 40 ℃ to about 120 ℃ may be preferably employed.

As a method for forming the pressure-sensitive adhesive layer on the foam base material, various conventionally known methods can be applied. Examples thereof include: a method in which the pressure-sensitive adhesive composition is directly applied to a foam base material (direct method), a method in which a pressure-sensitive adhesive layer is formed on an appropriate release surface by applying the pressure-sensitive adhesive composition to the release surface, and the pressure-sensitive adhesive layer is bonded to the foam base material and transferred (transfer method), and the like. These methods may be used in combination. In addition, the first adhesive layer and the second adhesive layer may adopt different methods. When a binder composition containing a solvent is used, it is preferable to dry the binder composition under heating from the viewpoint of promoting the crosslinking reaction, improving the production efficiency, and the like.

The total thickness of the pressure-sensitive adhesive layers (the total of the thickness of the first pressure-sensitive adhesive layer and the thickness of the second pressure-sensitive adhesive layer) is not particularly limited, and may be set to, for example, 10 μm or more and 300 μm or less. From the viewpoint of adhesive performance, it is generally preferable to set the total thickness of the adhesive layer to 20 μm or more, preferably 30 μm or more, and more preferably 40 μm or more. In addition, from the viewpoint of easily ensuring the thickness of the foam base material capable of exhibiting desired characteristics, it is generally appropriate to set the total thickness of the pressure-sensitive adhesive layer to 250 μm or less, preferably 200 μm or less, more preferably 150 μm or less, further preferably 100 μm or less, for example 70 μm or less.

The thickness of the first adhesive layer and the thickness of the second adhesive layer may be the same thickness or different thicknesses. In general, it is preferable to adopt a structure in which the thicknesses of both adhesive layers are substantially the same. Each adhesive layer may have any form of a single layer or a plurality of layers.

The double-sided adhesive sheet disclosed herein may further contain a layer (intermediate layer, primer layer, etc.) other than the foam base material and the adhesive layer, within a range not significantly impairing the effects of the present invention. For example, the other layer described above may be provided between the foam base material and either one or both of the adhesive layers. With the double-sided adhesive sheet of such a configuration, the thickness of the above-mentioned other layer is included in the total thickness of the double-sided adhesive sheet (i.e., the thickness from one adhesive face to the other adhesive face).

According to a preferred mode of the technology disclosed herein, it is possible to provide a display showing a pressing adhesive force of 45N/cm²Above (more preferably 60N/cm)²Above, typically 75N/cm²Above, e.g. 80N/cm²The above) properties. A double-sided pressure-sensitive adhesive sheet having such a high pressure-sensitive adhesive strength is preferable because peeling due to internal stress is less likely to occur even when the double-sided pressure-sensitive adhesive sheet having a narrow width is bonded to an adherend, and the pressure-sensitive adhesive sheet has excellent adhesion reliability.

The above-mentioned press adhesion force is defined as follows: a stainless steel plate (SUS plate) and a glass plate were bonded to each other under pressure-bonding conditions in which a 5kg roller was reciprocated once, using a sash-shaped (also referred to as "frame-shaped") double-sided adhesive sheet having a width of 1mm, a width of 59mm in a transverse direction, 113mm in a longitudinal direction, to prepare an evaluation sample, the glass plate was pressed in a thickness direction of the glass plate from the inside to the outside at a load rate of 10 mm/min, and a maximum stress observed until the glass plate and the SUS plate were separated was defined as a pressing adhesive force. More specifically, the pressing adhesion force can be measured by the procedure described in the examples described later.

According to another preferred embodiment of the technology disclosed herein, a double-sided adhesive sheet can be realized which exhibits impact resistance at a level at which peeling is not observed even after dropping 18 times at room temperature (23 ℃) and then 60 times at low temperature (-5 ℃) in impact resistance evaluation by the method described in examples described later.

According to another preferred embodiment of the technology disclosed herein, a double-sided adhesive sheet can be provided which exhibits a performance of 15N/20mm or more (more preferably 16N/20mm or more, and still more preferably 17N/20mm or more) in a 180 ° peel test of stainless steel (SUS304BA) by a method described in examples described later. A double-sided pressure-sensitive adhesive sheet having such a high peel strength to SUS304BA is preferable because it exhibits good adhesive properties to an adherend.

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

The double-sided adhesive sheet disclosed herein preferably does not contain halogen from the viewpoint of preventing metal corrosion and the like. The double-sided adhesive sheet does not contain halogen, and can have favorable characteristics when the double-sided adhesive sheet is used for fixing electric and electronic components, for example. Further, since the generation of a halogen-containing gas during combustion can be suppressed, it is also preferable from the viewpoint of reducing the environmental load. The halogen-free double-sided adhesive sheet can be obtained by using the following means alone or in an appropriate combination: the foam base material and the binder are not intentionally made of a halogen compound, the foam base material is intentionally not mixed with a halogen compound, and when the additive is used, the additive derived from a halogen compound is not used.

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

The double-sided adhesive sheet disclosed herein exhibits excellent pressure-sensitive adhesive strength, and can be a double-sided adhesive sheet with high adhesion reliability. Further, the double-sided adhesive sheet disclosed herein contains a foam base material, and therefore can be a double-sided adhesive sheet excellent in water repellency, irregularity following properties, sealing properties, and repulsion resistance. Therefore, by utilizing such characteristics, it is possible to be preferably applied to electronic device uses such as: examples of applications include fixing a protective panel (lens) for protecting a display portion of a portable electronic device (e.g., a mobile phone, a smart phone, a tablet computer, a notebook computer, etc.), fixing a key module member of a mobile phone, fixing a decorative panel of a television, fixing a battery pack of a personal computer, and waterproofing a lens of a digital video camera. As a particularly preferred use, it can be preferably used for portable electronic devices. For example, the present invention is suitable for use in such a portable electronic device in which a protective panel (lens) for protecting a display portion is joined to a housing.

In addition, "lens" in the present specification is a concept including both a transparent body exhibiting a light refraction action and a transparent body having no light refraction action. That is, the "lens" in the present specification also includes a protective panel that has no refraction action and protects only the display portion of the portable electronic device.

Some examples related to the present invention will be described below, but the present invention is not intended to be limited to the examples shown. In the following description, "part" and "%" are not particularly specified on a weight basis.

In the following description, the weight average molecular weight (Mw) is measured as follows.

The adhesive composition was dried at 130 ℃ for 2 hours, and then immersed in Tetrahydrofuran (THF) for 12 hours to dissolve a THF-soluble component, thereby preparing a THF solution containing the THF-soluble component at a concentration of 0.1 g/L. The weight average molecular weight of the THF-soluble fraction (in terms of standard polystyrene) was determined by GPC on the filtrate obtained by filtering the THF solution through a membrane filter having an average pore size of 0.45. mu.m. As the GPC apparatus, the model "HLC-8320 GPC" (column: TSKgelGMH-H (S)) manufactured by Tosoh corporation was used.

Samples of double-sided adhesive sheets (examples 1 to 4) were produced as follows.

(example 1)

[ production of acrylic Polymer ]

In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen 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 were dissolved in toluene as a solvent. Then, the user can use the device to perform the operation,while stirring slowly, nitrogen gas was introduced, and polymerization was carried out for about 6 hours while maintaining the liquid temperature in the reaction vessel at about 60 ℃. The weight average molecular weight Mw of the acrylic polymer in the resulting solution was 55X 10⁴。

[ preparation of adhesive composition ]

Next, 30 parts of a terpene-phenol resin (product name "タマノル 803L" manufactured by mitsubishi chemical corporation) and 10 parts of a terpene-phenol resin (product name "YS ポリスター S145" manufactured by anjinghua chemical corporation) were added as tackifier resins to 100 parts of the acrylic polymer solution (nonvolatile matter), and 1 part of an isocyanate-based crosslinking agent (product name "コロネート L" manufactured by japan polyurethane chemical corporation) and 0.03 part of an epoxy-based crosslinking agent (product name "テトラッド C" manufactured by mitsubishi gas chemical corporation) were added as crosslinking agents, thereby producing an acrylic adhesive composition.

A foam sheet made of a polyethylene resin (hereinafter referred to as "substrate a") was prepared as a foam substrate. The thickness of the substrate A was 150 μm, the 25% compressive strength was 108kPa, the machine direction tensile strength (MD)) was 3.18MPa, and the width direction tensile strength (CD)) was 5.50 MPa. As a result of measuring and calculating the average cell diameters in the longitudinal direction (MD), the width direction (CD), and the thickness direction (VD) of the cells contained in the substrate a, and the aspect ratio (CD/VD) and the aspect ratio (MD/CD) as the ratio thereof, the aspect ratio (CD/VD) of the substrate a was 2.3, and the aspect ratio (MD/CD) was 2.6. Fig. 2 shows a photograph of a cross section obtained by cutting the substrate a along a plane parallel to the CD and VD (i.e., a plane in which the direction of the perpendicular line coincides with the MD) with a Scanning Electron Microscope (SEM).

The adhesive composition was applied to one surface of a commercially available release liner (manufactured by TOCHEMICAL PAPER CO., LTD., product name "SLB-80W 3D") to a thickness of 25 μm after drying, and dried at 100 ℃ for 2 minutes to form an adhesive layer. Then, the pressure-sensitive adhesive layer was bonded to one surface of the substrate a, thereby obtaining a single-sided pressure-sensitive adhesive sheet.

Then, the adhesive composition was applied to one side of the same release liner as described above so that the thickness after drying was 25 μm, and dried at 100 ℃ for 2 minutes, thereby forming an adhesive layer. The pressure-sensitive adhesive layer was bonded to the other surface of the foam base material of the single-sided pressure-sensitive adhesive sheet. Then, the resulting structure was passed once through a 80 ℃ laminator (0.3MPa, speed 0.5 m/min), and then cured in an oven at 50 ℃ for one day. Thus, a double-sided pressure-sensitive adhesive sheet (example 1) having a total thickness of 200 μm was obtained.

(example 2)

A double-sided adhesive sheet having a total thickness of 150 μm was obtained in the same manner as in the preparation of the double-sided adhesive sheet of example 1 except that the substrate B was used instead of the substrate a (example 2).

Here, the thickness of the substrate B was 100. mu.m, the 25% compressive strength was 149kPa, the machine direction tensile strength (MD)) was 4.62MPa, and the width direction tensile strength (CD)) was 7.51 MPa. The substrate B had an aspect ratio (CD/VD) of 1.9 and an aspect ratio (MD/CD) of 2.8.

(example 3)

A double-sided adhesive sheet having a total thickness of 200 μm was obtained in the same manner as in the preparation of the double-sided adhesive sheet of example 1 except that the substrate C was used instead of the substrate a (example 3).

Here, the thickness of the substrate C was 150 μm, the 25% compressive strength was 150kPa, the machine direction tensile strength (MD)) was 9.50MPa, and the width direction tensile strength (CD)) was 8.20 MPa. The substrate C had an aspect ratio (CD/VD) of 9.0 and an aspect ratio (MD/CD) of 0.7. Fig. 3 shows a photograph of a cross section of the substrate C when cut along a plane parallel to the CD and VD (i.e., a plane in which the direction of the perpendicular line coincides with the MD) by a Scanning Electron Microscope (SEM).

(example 4)

A double-sided adhesive sheet having a total thickness of 150 μm was obtained in the same manner as in the preparation of the double-sided adhesive sheet of example 1 except that the substrate D was used instead of the substrate a (example 4).

Here, the thickness of the substrate D was 100 μm, the 25% compressive strength was 75kPa, the machine direction tensile strength (MD)) was 1.99MPa, and the width direction 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.

The thickness, type, apparent density, degree of crosslinking, average bubble diameter aspect ratio (CD/VD and MD/CD), 25% compressive strength, tensile strength (MD and CD), and 90 ℃ heating dimensional change rate (MD and CD) of the substrates used to make the double-sided adhesive sheets of examples 1 to 4 are summarized in table 1. The thickness of the pressure-sensitive adhesive layer formed on both sides of the substrate and the total thickness of the double-sided pressure-sensitive adhesive sheet are also summarized in table 1.

TABLE 1

< evaluation test >

(1) Pressing adhesive force

The double-sided adhesive sheet was cut into a window frame shape (frame shape) of 59mm in the lateral direction, 113mm in the longitudinal direction, and 1mm in width as shown in fig. 4, to obtain a window frame-shaped double-sided adhesive sheet. Using this window frame-shaped double-sided adhesive sheet, a glass plate (Gorilla glass manufactured by Corning Corp., the same applies hereinafter) having a width of 59mm, a length of 113mm and a thickness of 1mm was bonded to a stainless steel plate (SUS plate) (70 mm, 130mm and 2mm in the width, length and thickness) having a through hole of 15mm in the center by reciprocating a 5kg roller at a time, thereby obtaining a sample for evaluation.

FIG. 4 is a schematic view of the above-mentioned evaluation sample, wherein (a) is a plan view and (b) is a sectional view taken along line A-A'. In fig. 4, reference numeral 21 denotes an SUS plate, reference numeral 2 denotes a window frame-shaped double-sided adhesive sheet, reference numeral 22 denotes a glass plate, and reference numeral 21A denotes a through hole provided in the SUS plate 21.

These samples for evaluation were set in a universal tensile compression tester (apparatus name "tensile compression tester TG-1 kNB", manufactured by ミネベア Co., Ltd.). Then, the round bar was passed through the through hole of the SUS plate, and the round bar was lowered at a speed of 10 mm/min, thereby pressing the glass plate in a direction away from the SUS plate. Then, the maximum stress observed until the glass plate was separated from the SUS plate was measured as the press adhesion force. The measurement was carried out at 23 ℃ and 50% RH.

Fig. 5 is a schematic cross-sectional view showing a method of measuring the pressing adhesion force, wherein reference numeral 21 denotes an SUS plate, reference numeral 2 denotes a sash-shaped double-sided adhesive sheet, reference numeral 22 denotes a glass plate, reference numeral 23 denotes a round bar, and reference numeral 24 denotes a support base. The sample for evaluation was fixed to a support stand 24 of a tensile compression tester as shown in fig. 5, and the glass plate 22 of the sample for evaluation was pressed by a round bar 23 passing through the through hole 21A of the SUS plate 21. In the above-described press adhesion measurement, the SUS plate 21 was not bent or broken by the load applied when the glass plate 22 was pressed by the round bar 23.

(2) Peel Strength test (for SUS304BA)

A polyethylene terephthalate (PET) film having a thickness of 25 μm was bonded to one of the adhesive surfaces of the double-sided adhesive sheet, and the film was cut into a size of 20mm in width and 100mm in length to prepare a measurement sample.

The other adhesive surface of the measurement sample was exposed in an atmosphere of 23 ℃ and 50% RH, and the other adhesive surface was pressure-bonded to the surface of a stainless steel plate (SUS304BA plate) by reciprocating a 2kg roller once. After leaving the sheet in the same environment for 30 minutes, the sheet was peeled off at a tensile speed of 300 mm/minute and a peeling angle of 180 ℃ in accordance with JIS Z0237 by using the above-mentioned universal tensile compression tester, and the average load at this time was measured to determine the peel strength (also referred to as "peel strength". unit: N/20mm width).

(3) Impact resistance (Normal and Low temperature)

The double-sided adhesive sheet was cut into a window frame shape (frame shape) of 59mm in the lateral direction, 113mm in the longitudinal direction, and 1mm in width as shown in fig. 6, to obtain a window frame-shaped double-sided adhesive sheet. Using this window-frame-shaped double-sided adhesive sheet, a first PC plate (polycarbonate plate, 70mm in the lateral direction, 130mm in the vertical direction, and 2mm in thickness) and a second PC plate (59 mm in the lateral direction, 113mm in the vertical direction, and 0.55mm in thickness) were laminated by reciprocating a 5kg roller at one time, thereby obtaining a sample for evaluation (see fig. 6(a) (b)).

FIG. 6 is a schematic view of the above-mentioned evaluation sample, wherein (a) is a plan view and (B) is a sectional view thereof taken along line B-B'. In fig. 6, reference numeral 31 denotes a first PC board, reference numeral 3 denotes a window frame-shaped double-sided adhesive sheet, and reference numeral 32 denotes a second PC board.

A weight of 160g was attached to the back surface (the surface opposite to the surface bonded to the second PC plate) of the first PC plate of these evaluation samples. The above-mentioned evaluation sample with a weight was subjected to a drop test in which the sample was allowed to freely fall 18 times from a height of 1.2m toward a concrete slab at room temperature (about 23 ℃). At this time, the dropping direction was adjusted so that 6 faces of the above-mentioned sample for evaluation were directed downward in this order. That is, the dropping pattern was repeated 3 times for each of the 6 surfaces.

Then, whether or not peeling occurred between the first PC board and the second PC board was visually confirmed for each falling, and the number of falling times until peeling occurred was evaluated as the impact resistance at room temperature (23 ℃). When no peeling was observed even after 18 drops, the number of drops was "18 or more" or "> 18".

For the sample in which no peeling was observed even after dropping 18 times in the above-mentioned impact resistance test at room temperature, an impact resistance test at a low temperature (-5 ℃ C.) was subsequently conducted. That is, the evaluation sample after the test of the impact resistance test at room temperature was subjected to a drop test of freely dropping from a height of 1.2m toward the concrete slab under an environment of-5 ℃, and whether or not peeling occurred between the first PC board and the second PC board was visually confirmed every drop, and the number of drops until peeling occurred was evaluated as the impact resistance at low temperature (-5 ℃). In this case, the evaluation sample was repeatedly applied 10 times so that 6 surfaces of the sample were once dropped, and when no peeling was observed even after 60 drops, the results were expressed as "60 times or more" or "> 60".

The evaluation results of the double-sided adhesive sheets of examples 1 to 4 are shown in table 1 above.

As shown in table 1, it is apparent that the double-sided pressure-sensitive adhesive sheets of examples 1 and 2 having a foam substrate with an aspect ratio (CD/VD) of 3 or less and an aspect ratio (MD/CD) of more than 1 exhibited higher pressure-sensitive adhesive strength than the double-sided pressure-sensitive adhesive sheets of examples 3 and 4. In addition, the double-sided adhesive sheets of examples 1 and 2 showed excellent peel strength. In addition, the double-sided adhesive sheets of examples 1 and 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 examples are merely illustrative and do not limit the claims. The techniques described in the claims include those obtained by variously changing or modifying the specific examples illustrated above.

Claims

1. A double-sided adhesive sheet comprising a foam base, a first adhesive layer provided on a first side of the foam base, and a second adhesive layer provided on a second side of the foam base;

the thickness of the foam base material is 1000 [ mu ] m or less;

an aspect ratio (CD/VD) of the foam base material, which is represented by a ratio of an average cell diameter in a width direction (CD) of the foam base material to an average cell diameter in a thickness direction (VD) of the foam base material, is 3 or less;

an aspect ratio (MD/CD) of the foam substrate, expressed as a ratio of an average cell diameter in a Machine Direction (MD) of the foam substrate to an average cell diameter in a width direction (CD) of the foam substrate, is greater than 1; and is

The pressure-sensitive adhesive sheet had a pressure-sensitive adhesive force of 45N/cm²In the above-mentioned manner,

the press adhesive force is defined as follows: a stainless steel plate and a glass plate were bonded to each other under pressure-bonding conditions in which a 5kg roller was reciprocated once by a sash-shaped double-sided adhesive sheet having a width of 1mm, a width of 113mm and a width of 59mm in the transverse direction, to prepare a sample for evaluation, and the glass plate was pressed from the inside to the outside in the thickness direction of the glass plate at a load rate of 10 mm/min, and the maximum stress observed until the glass plate and the stainless steel plate were separated was defined as the pressing adhesive force.

2. A double-sided adhesive sheet according to claim 1,

the thickness of the double-sided adhesive sheet is 100 [ mu ] m to 500 [ mu ] m.

3. The double-sided adhesive sheet according to claim 1 or 2,

the foam base material is a polyolefin foam base material.

4. The double-sided adhesive sheet according to claim 1 or 2,

the foam base material has a 25% compressive strength of 50kPa or more.

5. The double-sided adhesive sheet according to claim 1 or 2,

the foam base material has a longitudinal tensile strength of 1MPa or more and 30MPa or less.

6. The double-sided adhesive sheet according to claim 1 or 2,

the density of the foam base material is 0.2g/cm³Above and 0.6g/cm³The following.

7. The double-sided adhesive sheet according to claim 1 or 2,

the foam base material has a heating dimension change rate of-10% to 10% in the longitudinal direction at 90 ℃, and a heating dimension change rate of-10% to 10% in the width direction at 90 ℃.

8. The double-sided adhesive sheet according to claim 1 or 2,

at least either one of the first adhesive layer and the second adhesive layer contains an acrylic adhesive.

9. A double-sided adhesive sheet according to claim 8,

the acrylic polymer as the base polymer of the acrylic adhesive is an acrylic polymer obtained from a monomer composition containing 50% by weight or more of an alkyl (meth) acrylate represented by the following formula (7),

CH₂＝C(R¹)COOR²(7)

herein, R in said formula (7)¹Is a hydrogen atom or a methyl group, R in the formula (7)²Is an alkyl group having 2 to 14 carbon atoms.

10. A double-sided adhesive sheet according to claim 8,

an acrylic monomer having a hydroxyl group is copolymerized in an acrylic polymer as a base polymer of the acrylic adhesive.

11. A double-sided adhesive sheet according to claim 8,

the acrylic polymer as a base polymer of the acrylic adhesive is copolymerized with a carboxyl group-containing monomer.

12. A double-sided adhesive sheet according to claim 8,

the acrylic adhesive contains a tackifier resin having a softening point of 100 ℃ or higher.

13. The double-sided adhesive sheet as claimed in claim 1 or 2, which is used for joining parts of portable electronic devices.

14. The double-sided adhesive sheet according to claim 1 or 2,

the foam base material has an average cell diameter of 10 to 500 [ mu ] m in terms of true spheres.

15. The double-sided adhesive sheet according to claim 1 or 2,

the foam base material has an average cell diameter in terms of true spheres of 50% or less of the thickness of the foam base material.

16. The double-sided adhesive sheet according to claim 1 or 2,

the degree of crosslinking of the foam base material is 10% or more and 50% or less.

17. The adhesive sheet according to claim 1 or 2,

the sum of the thickness of the first adhesive layer and the thickness of the second adhesive layer is 10 to 300 [ mu ] m.