CN112143396A

CN112143396A - Double-sided adhesive sheet

Info

Publication number: CN112143396A
Application number: CN202010848202.7A
Authority: CN
Inventors: 中山直树; 渡边茂树; 广西正人
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2013-11-22
Filing date: 2014-11-21
Publication date: 2020-12-29
Also published as: CN104650757A

Abstract

The present invention relates to a double-sided adhesive sheet. The invention provides a double-sided adhesive sheet with excellent impact protection and impact resistance. The invention provides a double-sided adhesive sheet, which comprises a foam substrate, a first adhesive layer arranged on the first surface of the foam substrate, and a second adhesive layer arranged on the foam substrateA second adhesive layer on the second side of the substrate. The foaming ratio of the foaming base material is 2.0cm³(ii) a 25% compressive strength of 200kPa or higher.

Description

Double-sided adhesive sheet

The application is a divisional application of a Chinese patent application with an application date of 2014, namely 21 months and 21 days and an application number of 201410673912.5.

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 material) 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, an adhesive is widely used for the purpose of joining, fixing, and the like in various fields in the form of, for example, a double-sided adhesive sheet with a substrate having adhesive layers provided on both surfaces of the substrate.

As the substrate in the double-sided pressure-sensitive adhesive sheet with a substrate, a plastic film, a nonwoven fabric, paper, or the like, or a foam having a cell structure, or the like, can be generally used. A double-sided pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet with a foam substrate) using the foam is more advantageous in terms of impact absorbability, unevenness follow-up property, and the like than a double-sided pressure-sensitive adhesive sheet with a plastic film having no bubble structure as a substrate. Further, the double-sided pressure-sensitive adhesive sheet is more advantageous in terms of water resistance, sealing properties, and the like than a double-sided pressure-sensitive adhesive sheet having a nonwoven fabric as a base material. 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 to 3 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. 2013/099755

Patent document 3: international publication No. 2013/141167

Disclosure of Invention

Problems to be solved by the invention

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. For example, in a double-sided adhesive sheet used for fixing a display panel (such as a glass lens) of a portable electronic device, it is significant to narrow the width of the double-sided adhesive sheet from the viewpoints of increasing the screen size of an information display unit, improving design properties, improving the degree of freedom in design, and the like.

Incidentally, a double-sided adhesive sheet used for joining of parts in portable electronic devices and the like is required to have a property of withstanding impact such as dropping and maintaining the joining (hereinafter also referred to as impact resistance).

On the other hand, as the width of the double-sided adhesive sheet is narrowed, the following phenomenon is observed: due to an impact such as dropping, a component which is not originally designed as a part receiving the impact, for example, a display panel in a portable electronic apparatus or the like is damaged. Therefore, the double-sided pressure-sensitive adhesive sheet is required to have a property of suppressing breakage of the product when an impact such as dropping is applied (hereinafter, also referred to as impact protection).

Accordingly, an object of the present invention is to provide a double-sided adhesive sheet having not only impact resistance but also impact protection.

Means for solving the problems

The present inventors studied the behavior of a double-sided adhesive sheet against impact in detail, and as a result, found that a phenomenon in which the adhesive sheet is instantaneously deformed in the thickness direction by the impact is one of the factors that impair the impact protection. Further, the present inventors have found a double-sided pressure-sensitive adhesive sheet which is suitable for both impact resistance and impact protection, and have completed the present invention.

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 foaming ratio of the foaming base material is 2.0cm³The ratio of the carbon atoms to the carbon atoms is less than g. The foam base material has a 25% compressive strength of 200kPa or more. The double-sided adhesive sheet (double-sided adhesive sheet with foam substrate) having the above-mentioned structure can have impact resistanceAn excellent double-sided adhesive sheet. Further, the double-sided pressure-sensitive adhesive sheet can exhibit a small amount of deformation in the thickness direction upon impact (also referred to as an amount of deformation in the thickness direction upon impact, the same applies hereinafter) and excellent impact protection.

In a preferred embodiment of the double-sided adhesive sheet disclosed herein, the foam base has a 25% compressive strength of 500kPa or more. The double-sided adhesive sheet containing the foam base material can be a double-sided adhesive sheet which has a small amount of deformation in the thickness direction upon impact and exhibits more excellent impact protection.

In a preferred embodiment of the double-sided adhesive sheet disclosed herein, the foam base has a base cohesive force of 40N/20mm or more. The double-sided adhesive sheet containing the foam base material can be a double-sided adhesive sheet exhibiting more excellent impact resistance.

In a preferred embodiment of the double-sided adhesive sheet disclosed herein, a foam substrate having a tensile elongation of 400% or more in the machine direction (also referred to as MD.) can be preferably used as the foam substrate. A double-sided adhesive sheet containing the foam base is preferable in view of workability of the double-sided adhesive sheet. From such a viewpoint, the foam base preferably has a tensile elongation in the width direction (also referred to as TD.) of 200% or more.

In a preferred embodiment of the double-sided adhesive sheet disclosed herein, the foam base has a tensile strength in the Machine Direction (MD) of 15MPa or more. The double-sided adhesive sheet containing the foam base material can be a double-sided adhesive sheet showing more excellent workability.

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 having excellent impact protection properties and exhibiting good impact resistance.

In a preferred embodiment of the double-sided adhesive sheet disclosed herein, the adhesive constituting at least one of the first adhesive layer and the second adhesive layer contains a tackifier resin having a softening point of 135 ℃ or higher. According to this aspect, a double-sided adhesive sheet having more excellent repulsion resistance can be realized.

In a preferred embodiment of the double-sided adhesive sheet disclosed herein, a value obtained by dividing the value of the 25% compressive strength of the foam base material by the value of the foaming magnification is 250g kPa/cm³The above. The double-sided adhesive sheet containing the foam base material can be a double-sided adhesive sheet exhibiting more excellent impact protection.

In a preferred embodiment of the double-sided adhesive sheet disclosed herein, the total thickness of the double-sided adhesive sheet is 70 μm or more and 500 μm or less. The double-sided adhesive sheet can contribute to miniaturization of products and the like, and is excellent in impact resistance and water resistance.

The double-sided adhesive sheet disclosed herein is excellent in impact resistance and impact protection, 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 an explanatory view showing an evaluation sample used in measuring the pressing adhesive force.

Fig. 3 is an explanatory diagram illustrating a method of measuring the pressing adhesion force.

FIG. 4 is an explanatory view showing an evaluation sample used for evaluating impact resistance.

Fig. 5 is an explanatory diagram illustrating a method of measuring the amount of deformation in the thickness direction upon impact.

FIG. 6 is an explanatory view showing a method of measuring the cohesive force of the base material.

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 plate

21A through hole

22 glass plate

23 round bar

24 support table

3 double-sided pressure-sensitive adhesive sheet

31. 32 polycarbonate plate

4 double-sided pressure-sensitive adhesive sheet

41 stainless steel plate

42 glass plate

43 Steel ball

5 double-sided adhesive sheet

51 first adhesive layer

52 second adhesive layer

55 foam base material

56 first stainless steel foil

57 second stainless steel foil

58. 59 clamping head

Detailed Description

Preferred embodiments of the present invention will be described below. In addition, matters required for the implementation of the present invention other than those specifically mentioned in the present specification may be understood as design matters based on those skilled in the art in the prior art. 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 drawings, members and portions that achieve the same functions may be 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 dimensions or scale of the double-sided adhesive sheet of the present invention actually provided as a product.

In this specification, "stickyAs described above, the adhesive agent is a material that is in a soft solid state (viscoelastic body) in a temperature range around room temperature and has a property of easily adhering to an adherend by pressure. 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 above properties (typically, a material having the above properties at 25 ℃). 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 base material such as a plastic film or paper, and release liners comprising a low-adhesive 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 backing material with a release-treating agent such as silicone, long-chain alkyl, fluorine-containing, or molybdenum sulfide.

The total thickness of the double-sided adhesive sheet disclosed herein is not particularly limited, and may be set to, for example, 50 μm or more and 1000 μm or less, preferably 70 μm or more and 500 μm or less, more preferably 100 μm or more and 350 μm or less, further preferably 150 μm or more and 320 μm or less, for example 190 μm or more and 300 μm or less. 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 the product. 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 at least one thin layer of a foam (foam layer). The foam base may be a base substantially composed only of the foam layer. There are no particular restrictions on the foam base material, and a preferred example of the foam base material in the technology disclosed herein is a foam base material composed of a single-layer (one-layer) foam layer.

The thickness of the foam base is not particularly limited, and may be appropriately set according to the strength, flexibility, purpose of use, and the like of the double-sided adhesive sheet. From the viewpoint of easily ensuring the thickness of the pressure-sensitive adhesive layer that can exhibit desired adhesive properties, it is generally appropriate to set the thickness of the foam base to 700 μm or less, and from the viewpoint of rebound resistance, it is preferably 400 μm or less, more preferably 300 μm or less, and for example, 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 of the double-sided adhesive sheet, it is preferable to set the thickness of the foam base 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 (i.e., a property of resisting the repulsion of the double-sided pressure-sensitive adhesive sheet) against the repulsion of the double-sided pressure-sensitive adhesive sheet to return to its original shape when the double-sided pressure-sensitive adhesive sheet is elastically deformed along the surface shape of an adherend (which may be a curved surface, a surface having a level difference, or the like).

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; foamed products made of polyvinyl chloride resin such as foamed products made of polyvinyl chloride; a vinyl acetate resin foam; a polyphenylene sulfide resin foam; amide resin foams such as foams made of fatty acid polyamide (nylon) resin and foams made of wholly aromatic polyamide (Aramid) resin; a polyimide resin foam; a polyether ether ketone (PEEK) foam; a styrene resin foam such as a polystyrene foam; urethane resin foams such as polyurethane resin foams, and the like. As the plastic foam, a rubber resin foam such as a neoprene foam may be used.

As a preferred foam, a polyolefin resin foam (hereinafter also referred to as "polyolefin foam") can be exemplified. As the plastic material (i.e., 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), and High Density Polyethylene (HDPE), polypropylene, ethylene-propylene copolymer, and ethylene-vinyl acetate copolymer. Examples of LLDPE include Ziegler-Natta catalyst type linear low density polyethylene and metallocene catalyst type linear low density polyethylene. 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 foam base substantially composed of a polyethylene resin foam, a polypropylene foam base substantially composed of a polypropylene resin foam, and the like from the viewpoints of impact resistance, impact protection, 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 HDPE, LDPE, LLDPE, and the like, and an ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer, and the like, in which the copolymerization ratio of ethylene exceeds 50% by weight. 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 for crosslinking the plastic foam include a chemical crosslinking method using an organic peroxide or the like, and an ionizing radiation crosslinking method by irradiating an ionizing radiation. These methods may be used in combination. Examples of the ionizing radiation include electron beams, α rays, β rays, and γ rays. The irradiation amount of the ionizing radiation is not particularly limited, and may be set to an appropriate irradiation amount in consideration of the target physical properties (e.g., the degree of crosslinking) of the foam base material.

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

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

In a preferred embodiment of the technology disclosed herein, the foam base material may be, for example, a material having an expansion ratio of 2.15cm³A foam base material of not more than g. From the viewpoint of more suppressing the amount of deformation in the thickness direction upon impact and improving the impact protection, the expansion ratio of the foam base material is preferably 2.0cm³A value of 1.95cm or less per gram³A value of 1.9cm or less, preferably³The ratio of the carbon atoms to the carbon atoms is less than g. In a preferred embodiment, the expansion ratio of the foam base material may be, for example, 1.85cm³A concentration of 1.8cm or less³The ratio of the carbon atoms to the carbon atoms is less than g. The lower limit of the expansion ratio is not particularly limited. The expansion ratio of the foam base material is usually 1.1cm from the viewpoint of impact resistance and the like³Suitably,/g or more, preferably 1.2cm³A value of at least g, more preferably 1.5cm³More than g (e.g., 1.6 cm)³More than g). By increasing the foaming ratio, the flexibility is improved, the step following property and the recovery resistance are providedThe elasticity tends to be improved. When the double-sided pressure-sensitive adhesive sheet has good step following properties, generally, even when the sheet is bonded to an adherend having a step, voids are not easily generated between the sheet and the surface of the adherend, and water resistance is improved. In the present specification, the expansion ratio of the foam base material is defined as the apparent density (g/cm) measured according to JIS K6767³) The reciprocal of (c).

In another preferred embodiment of the technology disclosed herein, the foam base has an expansion ratio of 1.8cm³A value of 1.7cm or less, more preferably³(typically 1.6 cm) or less³Less than g, e.g. 1.55cm³(less than/g). In this case, the lower limit of the expansion ratio is not particularly limited. The foaming ratio of the foam base material is, for example, 1.1cm³Suitably,/g or more, preferably 1.2cm³A concentration of 1.25cm or more³More than g. A double-sided adhesive sheet using a foam base material having an expansion ratio within the above range is preferable because it can exhibit a high pressure-sensitive adhesive strength even with a narrow width (for example, less than 1 mm).

The tensile elongation of the foam base (for example, a polyolefin foam base) is not particularly limited, and for example, the tensile elongation in the (MD) machine direction is preferably 200% or more and 800% or less (more preferably 300% or more and 700% or less, further preferably 400% or more and 600% or less, for example, 450% or more and 500% or less). The tensile elongation in the width direction (TD) is preferably 50% or more and 800% or less (more preferably 100% or more and 600% or less, further preferably 200% or more and 500% or less, for example, 250% or more and 400% or less). By setting the tensile elongation to the above lower limit or more, impact resistance and level difference following property can be improved. On the other hand, by setting the tensile elongation to the above upper limit or less, the strength of the foam base material can be improved, and the handling property and the impact protection property can be improved. The tensile elongation of the foam base material was measured according to JIS K6767. The tensile elongation of the foam base material can be controlled by, for example, the degree of crosslinking, the expansion ratio, and the like.

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 5MPa or more and 35MPa or less (more preferably 10MPa or more and 30MPa or less, further preferably 12MPa or more and 28MPa or less, typically 15MPa or more and 25MPa or less, for example 16MPa or more and 20MPa or less). The tensile strength in the width direction (TD) is preferably 1MPa or more and 25MPa or less (more preferably 5MPa or more and 20MPa or less, further preferably 7MPa or more and 15MPa or less, typically 8MPa or more and 12MPa or less, for example 9MPa or more and 11MPa or less). Alternatively, in another embodiment of the foam base disclosed herein, the TD tensile strength is preferably 11MPa or more and 13MPa or less. By setting the tensile strength to the lower limit or more, for example, when a misapplied double-sided adhesive sheet is peeled off, excellent workability (reworkability) such as easy peeling without tearing the substrate (and thus the double-sided adhesive sheet) can be exhibited. Further, such easy peeling of the double-sided pressure-sensitive adhesive sheet is also advantageous when disassembling the product and recovering the component, when replacing a defective component, or the like. On the other hand, by setting the tensile strength to the above upper limit or less, impact resistance and level difference following property can be improved. The tensile strength (longitudinal tensile strength, width-direction tensile strength) of the foam base material was measured according to JIS K6767. The tensile strength of the foam base material can be controlled by, for example, the degree of crosslinking and the expansion ratio.

The 25% compressive strength of the foam base (for example, polyolefin foam base) is not particularly limited, and may be, for example, 100kPa or more and 1200kPa or less. From the viewpoint of impact protection, the 25% compressive strength of the foam base material is preferably 200kPa or more and 1100kPa or less, more preferably 400kPa or more and 1000kPa or more, still more preferably 500kPa or more and 900kPa or less, and is, for example, 550kPa or more and 850kPa or less. Here, the 25% compressive strength of the foam base material refers to a load when the foam base materials are overlapped to have a thickness of about 25mm and sandwiched by flat plates, and are compressed by a thickness amount corresponding to 25% of the original thickness. That is, the 25% compressive strength of the foam base material refers to a load when the foam base material after the overlapping is compressed to a thickness corresponding to 75% of the original thickness. By increasing the 25% compressive strength, the amount of deformation in the thickness direction of the double-sided adhesive sheet upon impact tends to be suppressed, and good impact protection properties tend to be exhibited. In addition, the dimensional stability during processing can be improved. On the other hand, by setting the 25% compressive strength to 1200kPa or less, the rebound resistance and the step 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 expansion ratio, and the like.

In general, the 25% compressive strength of the foam base material tends to be larger as the expansion ratio of the foam base material is smaller. The value obtained by dividing the 25% compressive strength of the foam base material by the expansion ratio (hereinafter also referred to as (25% compressive strength)/(expansion ratio)) is preferably 100g · kPa/cm, though not particularly limited³Above, more preferably 180 g.kPa/cm³More preferably 200 g.kPa/cm³Above, for example, 250 g.kPa/cm³Above, it is typically preferably 300 g.kPa/cm³The above. When the (25% compression strength)/(expansion ratio) is set to the lower limit or more, the amount of deformation in the thickness direction of the double-sided adhesive sheet upon impact tends to be more suppressed, and the impact protection tends to be improved. In a preferred embodiment, (25% compressive strength)/(expansion ratio) of 400 g.kPa/cm can be used³Above, further 450 g.kPa/cm³Above, for example, 500 g.kPa/cm³The foam base material described above. The upper limit of the above (25% compressive strength)/(expansion ratio) is not particularly limited. From the viewpoint of rebound resistance and step following property, (25% compression strength)/(expansion ratio) is preferably 1100g · kPa/cm³Hereinafter, more preferably 800 g.kPa/cm³Hereinafter, more preferably 700 g.kPa/cm³Hereinafter, for example, 600 g.kPa/cm is preferable³The following.

The density (apparent density) of the foam base is not particularly limited, and may be, for example, more than 0.46g/cm³And 0.9g/cm³The following. The density of the foam base is preferably 0.5g/cm from the viewpoint of impact protection³Above and 0.8g/cm³Hereinafter, more preferably 0.51g/cm³Above and 0.75g/cm³The following. In another preferred mode, a density of 0.55g/cm can be used³Above and 0.72g/cm³The following (e.g., 0.6 g/cm)³Above and 0.7g/cm³Below). By increasing the density of the foam base, the amount of deformation in the thickness direction at the time of impact is suppressed, the strength of the foam base (and further the strength of the double-sided adhesive sheet) is improved, and the impact resistance and handling properties tend to be improved. On the other hand, the density of the foam base material was set to 0.9g/cm³Hereinafter, the following properties tend to provide poor conformability, rebound resistance, and water repellency. The density (apparent density) of the foam base material can be measured, for example, by a method according to JIS K6767.

The cohesive force (also referred to as a base cohesive force, unit: N/20mm) of the foam base measured by a measurement method described later is not particularly limited, but is preferably 30N/20mm or more. The cohesive force of the base material is more preferably 40N/20mm or more, still more preferably 50N/20mm or more, for example, 55N/20mm or more. The upper limit of the cohesive force of the base material is not particularly limited. For example, the foam base material having a base cohesive force of 200N/20mm or less, more preferably 150N/20mm or less, for example 100N/20mm or less can be preferably used. When the base cohesive force of the foam base is adjusted to the lower limit or more, damage to the foam base due to impact can be more effectively prevented, and therefore, the bonding reliability is good and more excellent impact resistance can be exhibited. When the base cohesive force of the foam base is set to the upper limit or less, the impact absorption property tends to be good and the impact resistance tends to be good.

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 spectrophotometer described above. 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). Each of a and b defined by the color system of L × a × b may be appropriately selected according to the value of L × b. The values 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 ミノルタ, trade name "CR-200"). The L × a × b color system refers to a color space called CIE1976(L × a × b) color system recommended by the international commission on illumination (CIE) in 1976. Note that L × a × b color system is defined by JIS Z8729 in japanese industrial standards.

As the black coloring agent used for coloring the foam base material black, for example: 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. Each of a and b defined by the color system of L × a × b may be appropriately selected according to the value of L × b. The ranges of a and b are preferably both-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, Organic white coloring agents such as silicone resin particles, urea resin particles, melamine resin particles, and the like. The amount of the white colorant 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, for example, a chemical or physical treatment for improving adhesion to an adjacent 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 of a primer (primer).

In the technique disclosed herein, the kind of the adhesive contained in each of the first adhesive layer and the second adhesive layer is not particularly limited. The pressure-sensitive adhesive may be one containing, for example, one or more kinds of various polymers (pressure-sensitive adhesive polymers) selected from acrylic polymers, polyester polymers, polyurethane polymers, polyether polymers, rubber polymers, silicone polymers, polyamide polymers, fluorine-containing polymers, and the like as a base polymer. 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 (a monomer main component, i.e., a component accounting for 50% by weight or more 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 (1) can be preferably used.

CH₂＝C(R¹)COOR² (1)

Here, R in the above formula (1)¹Is a hydrogen atom or a methyl group. R²Is an alkyl group having 1 to 20 carbon atoms. From the viewpoint of easily obtaining an adhesive excellent in adhesive properties, R is preferred²Has 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 selected from R in the above formula (1)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 it can easily form an adhesive agent exhibiting good adhesive properties.

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 in the synthesis of 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 art disclosed herein may be a 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 that can serve 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, for example, 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 above-mentioned 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), more preferably-40 ℃ or lower (for example-60 ℃ or higher and-40 ℃ or lower). It is preferable to adjust the Tg of the acrylic polymer to the upper limit or less from the viewpoint of impact resistance of the double-sided adhesive sheet.

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 (3 rd edition, John Wiley & Sons, Inc, 1989) can be used.

When not described in Polymer Handbook (3 rd edition, John Wiley & Sons, Inc, 1989), the values obtained by the following measurement methods were used.

Specifically, 100 parts by weight of a monomer, 0.2 part 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 ℃ to react 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 defined as the Tg of the homopolymer.

The adhesive in the art disclosed herein is preferably designed such that the peak top temperature of the shear loss modulus G "of the adhesive is-10 ℃ or less (typically-40 ℃ or more and-10 ℃ or less). For example, the peak top temperature is preferably set to-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 ″ 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" manufactured by TA instruments Japan), and determining the temperature corresponding to the peak thereof (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 the synthesis of the polymer), whether or not a tackifier to be described later is used, the kind and the amount of the tackifier to be used when the tackifier is 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 (polymerization solvent) used in the solution polymerization may be appropriately selected from known or conventional organic solvents. For example, it is possible to use: one or more solvents 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. For example, a polymerization solvent (which may be a mixed solvent) having a boiling point in the range of 20 ℃ or higher and 200 ℃ or lower (typically 50 ℃ or higher and 150 ℃ or lower) under a total pressure of 1 atmosphere may be used. In a preferred embodiment, the polymerization solvent having the boiling point in the range of 60 ℃ or higher and 150 ℃ or lower (for example, 80 ℃ or higher and 130 ℃ or lower) can be used.

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.

The weight average molecular weight (Mw) of the acrylic polymer in the technique disclosed herein is not particularly limited, and may be, for example, 10 × 10⁴Above and 500X 10⁴The following ranges. From the viewpoint of balancing workability such as reworkability and removability and adhesive properties such as 180 degree peel strength at a high level, the Mw of the acrylic polymer is preferably 10X 10⁴Above and 150 × 10⁴More preferably in the range of 15X 10⁴Above and 100 × 10⁴More preferably, it is within the range of 15X 10⁴Above and 75 × 10⁴Within the following ranges. In a preferred embodiment, the Mw of the acrylic polymer can be adjusted to 20X 10⁴Above and below 75X 10⁴. In a more preferred embodiment, the Mw of the acrylic polymer can be adjusted to 20X 10⁴Above and below 70X 10⁴(e.g., 32X 10)⁴Above and 67X 10⁴Hereinafter, typically 35 × 10⁴Above and 65X 10⁴Below). Herein, Mw means a standard polystyrene conversion value 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. Such tackifying resins may be used alone 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 thermal polymerization of rosins (unmodified rosin, modified rosin, various rosin derivatives, and the like) and phenols using an acid catalyst; and the like.

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

Examples of hydrocarbon tackifying resins include: various hydrocarbon resins such as aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic/aromatic petroleum resins (styrene-olefin copolymers and the like), aliphatic/alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone-indene resins and the like. Examples of the aliphatic hydrocarbon resin include polymers of one or more aliphatic hydrocarbons selected from olefins having from about 4 to about 5 carbon atoms and dienes. Examples of the above olefins include: 1-butene, isobutene, 1-pentene, and the like. Examples of the above-mentioned dienes include: butadiene, 1, 3-pentadiene, isoprene, and the like. Examples of the aromatic hydrocarbon resin include: polymers containing vinyl aromatic hydrocarbons having about 8 to about 10 carbon atoms (e.g., styrene, vinyltoluene, α -methylstyrene, indene, methylindene, etc.). Examples of the aliphatic cyclic hydrocarbon resin include: alicyclic hydrocarbon resins obtained by polymerizing a so-called "C4 petroleum fraction" or "C5 petroleum fraction" after cyclodimerization; polymers of cyclic diene compounds (cyclopentadiene, dicyclopentadiene, ethylidene norbornene, terpineol, etc.) or hydrides thereof; an alicyclic hydrocarbon resin obtained by hydrogenating an aromatic ring of an aromatic hydrocarbon resin or an aliphatic/aromatic petroleum resin; and the like.

In the technique disclosed herein, a tackifier resin having a softening point (softening temperature) of about 100 ℃ or higher (preferably about 120 ℃ or higher, and more preferably about 135 ℃ or higher) can be preferably used as the tackifier resin. By using a pressure-sensitive adhesive containing a tackifier resin having a softening point of not less than the above-mentioned lower limit, a double-sided pressure-sensitive adhesive sheet having more excellent repulsion resistance can be realized. Among the above-exemplified tackifying resins, terpene-based tackifying resins (e.g., terpene phenol resins) having such a softening point, rosin-based tackifying resins (e.g., esterified products of polymerized rosin), and the like can be preferably used. The above-mentioned tackifier resin can be preferably used in a form containing, for example, a terpene-phenol resin having a softening point of 135 ℃ or higher. Further, a particularly excellent repulsion resistance can be achieved by the adhesive containing a tackifier resin having a softening point of 140 ℃ or higher. For example, terpene-phenol resins having a softening point of 140 ℃ or higher can be preferably used. The technique disclosed herein can be preferably performed so that the proportion of the tackifier resin having a softening point of 140 ℃ or higher in the entire tackifier resin contained in the adhesive is more than 50% by weight, more preferably 70% by weight or higher, and still more preferably 85% by weight or higher (for example, 95% by weight or higher and 100% by weight or lower). The upper limit of the softening point of the tackifier resin is not particularly limited, and may be set to, for example, about 200 ℃ or lower (typically about 180 ℃ or lower). 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) defined 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 low-adhesiveness liner base material 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 low-tackiness liner base material 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, and typically about 20 μm or more and about 80 μm or less. The thickness of the pressure-sensitive adhesive layer may be set to 50 μm or less, and may be set to 35 μm or less, from the viewpoint of thinning of the double-sided pressure-sensitive adhesive sheet and the like. 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 thickness of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer) is not particularly limited, and may be set to, for example, 10 μm or more and 600 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 thickness of the pressure-sensitive adhesive layer to 200 μm or less, preferably 160 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 gel fraction of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not particularly limited, and may be, for example, 10 wt% or more and 70 wt% or less. From the viewpoint of balancing workability such as reworkability and removability and impact resistance at a high level, the gel fraction of the pressure-sensitive adhesive is usually suitably in the range of 15 wt% to 50 wt%, preferably 18 wt% to 45 wt%, and particularly preferably 20 wt% to 40 wt% (for example, 20 wt% to 35 wt%, and typically 20 wt% to less than 30 wt%). The gel fraction can be adjusted by the monomer composition or molecular weight of the base polymer, other additives such as crosslinking agents, and the like. The gel fraction of the adhesive can be determined by the following method.

[ gel fraction ]

After drying the adhesive composition at 130 ℃ for 2 hours, about 0.1g of the dried product (sample) was wrapped with a porous sheet made of Polytetrafluoroethylene (PTFE) resin, and the mouth was tied with kite string. The package was placed in a threaded tube with a capacity of 50mL, filled with ethyl acetate and left at room temperature (typically 23 ℃) for 7 days, after which the package was removed and dried at 130 ℃ for 2 hours, according to the following formula: gel fraction (%) — (sample weight after impregnation/drying)/(sample weight before impregnation) × 100 was calculated as a gel fraction. As the porous sheet made of PTFE resin, a product having a trade name "ニトフロン (registered trademark) NTF 1122" manufactured by ritonan electric corporation or a product corresponding thereto can be used.

The double-sided adhesive sheet disclosed herein may further contain a foam base and layers other than the adhesive layer (an intermediate layer, an undercoat layer, and the like; hereinafter also referred to as "other layers") within a range not to significantly impair 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 embodiment of the technology disclosed herein, a double-sided adhesive sheet exhibiting a performance of a press adhesion of 40N or more (more preferably 100N or more, further preferably 180N or more, typically 200N or more, for example 240N or more) can be provided. A double-sided adhesive sheet having such a high pressure-sensitive adhesive strength is preferable because peeling due to internal stress is less likely to occur when the double-sided adhesive sheet is used to bond a member, and adhesion reliability is excellent.

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

The above-mentioned press adhesion is defined as: a stainless steel (SUS) plate was bonded to a glass plate under pressure-bonding conditions in which a load of 5kg was applied for 10 seconds by using a sash-shaped (also referred to as "frame-shaped") double-sided adhesive sheet having a width of 1mm, a width of 59mm in the transverse direction, 113mm in the longitudinal direction, thereby producing an evaluation sample, 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 until the glass plate and the stainless steel plate were separated from each other. The pressing adhesion force can be measured, for example, by the procedure described in the examples described later.

In the following description, the pressure-sensitive adhesive force measured using the sash-shaped double-sided adhesive sheet having a width of 59mm in the transverse direction, 113mm in the longitudinal direction and 1mm in the width direction as described above may be referred to as "pressure-sensitive adhesive force (1mm width)". Similarly, the pressure-sensitive adhesive force measured using a sash-shaped double-sided adhesive sheet having a transverse direction of 59mm, a longitudinal direction of 113mm, and a width of Amm is sometimes referred to as "pressure-sensitive adhesive force (Amm width)". Among them, the pressing adhesion measured using the sash-shaped double-sided adhesive sheet having a <1 may be particularly referred to as "narrow-width pressing adhesion". The narrow width pressing adhesive force was measured in the same manner as the pressing adhesive force (width of 1mm) except that a window frame-shaped double-sided adhesive sheet having a width of 59mm in the transverse direction, 113mm in the longitudinal direction and a width of Amm (where a <1) was used.

According to a preferred embodiment of the technology disclosed herein, a double-sided adhesive sheet having a pressure-sensitive adhesive force (0.7mm width) of 28N or more (more preferably 100N or more, still more preferably 140N or more, typically 160N or more, for example 250N or more) can be realized.

According to a preferred embodiment of the technology disclosed herein, a double-sided pressure-sensitive adhesive sheet having a pressing adhesion (0.5mm width) of 20N or more (more preferably 50N or more, still more preferably 80N or more, typically 110N or more, for example 160N or more) can be realized.

According to a preferred embodiment of the technology disclosed herein, a double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive force (0.3mm width) of 12N or more (more preferably 30N or more, still more preferably 40N or more, and typically 60N or more, for example 100N or more) can be realized.

According to another preferred embodiment of the technology disclosed herein, a double-sided pressure-sensitive adhesive sheet can be realized which exhibits impact resistance at a level at which bonding failure such as peeling or cracking of the foam base is not observed even after 60 drops in the impact resistance evaluation by the method described in the examples described below.

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 properties when the double-sided adhesive sheet is used for fixing an electric or electronic component, 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 or the binder is not intentionally made of a halogen compound, the foam base material is intentionally made without a halogen compound, and the additive derived from a halogen compound is not used when the additive is 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 stainless steel (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 has excellent impact protection properties and high impact resistance by suppressing the amount of deformation in the thickness direction upon impact. Therefore, the double-sided pressure-sensitive adhesive sheet can be suitably used for the purpose of bonding, fixing, shock absorbing, and the like in a portable device which is susceptible to a shock caused by dropping or the like. Further, the double-sided adhesive sheet disclosed herein contains a foam base material, and therefore can be a double-sided adhesive sheet excellent in level following property, repulsion resistance, and water resistance. Therefore, by utilizing such characteristics, it can be preferably applied to electronic device applications 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 computer, and waterproofing a lens of a digital camera. Particularly preferred uses include portable electronic device uses. In particular, it can be preferably used for a portable electronic device having a liquid crystal display device built therein. 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 which exhibits a light refraction action and a transparent body which does not exhibit a light refraction action. That is, the "lens" in this specification includes a protective panel having no refraction action and protecting only the display portion of the portable electronic device.

Hereinafter, some examples related to the present invention will be described, but it is not intended to limit the present invention to the examples. In the following description, "part" and "%" are not particularly specified on a weight basis.

< Experimental example 1>

Samples of double-sided adhesive sheets (examples 1 to 10) were produced as follows.

(example 1)

[ production of acrylic Polymer (A) ]

100 parts of n-butyl acrylate, 5 parts of acrylic acid, 0.2 part of 2, 2' -azobisisobutyronitrile as a polymerization initiator, and toluene as a polymerization solvent were put into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen introduction tube, a reflux condenser, and a dropping funnel, nitrogen was introduced while slowly stirring, and the liquid temperature in the reaction vessel was maintained at about 60 ℃ for about 6 hoursThe polymerization reaction was repeated to obtain a toluene solution of the acrylic polymer (A). The Mw of the acrylic polymer (A) was 55X 10⁴。

Here, the Mw of the acrylic polymer (a) is determined as follows. That is, the toluene solution was dried at room temperature, and then the solid content thereof was dissolved in Tetrahydrofuran (THF) to prepare a THF solution containing the acrylic polymer (a) at a concentration of about 0.1 g/L. The THF solution was filtered through a membrane filter having an average pore diameter of 0.45 μm, and the obtained filtrate was subjected to GPC to determine the Mw (in terms of standard polystyrene) of the acrylic polymer (A). As the GPC apparatus, the model "HLC-8320 GPC" manufactured by Tosoh corporation was used (column: TSKgel GMH-H (S)).

[ production of adhesive composition (B) ]

An acrylic adhesive composition (B) was prepared by adding 30 parts of a product name "タマノル 803L" (terpene-phenol resin, manufactured by Mitsubishi chemical industries, Ltd., softening point 145 to 160 ℃ C.) and 10 parts of a product name "YS ポリスター S145" (terpene-phenol resin, manufactured by ヤスハラケミカル Ltd., softening point 140 to 150 ℃ C.) as tackifying resins to 100 parts of the acrylic polymer (A) contained in the toluene solution, and adding 1 part of an isocyanate-based crosslinking agent (manufactured by Nippon polyurethane industries, Ltd., product name "コロネート L") and 0.03 part of an epoxy-based crosslinking agent (manufactured by Mitsubishi chemical corporation, product name "テトラッド C") as crosslinking agents.

Two commercially available release liners (trade name "SLB-80W 3D", manufactured by TOXIC-TOYOBO CO., LTD.) were prepared. The above adhesive composition (B) was applied to one surface (release surface) of each of these release liners so that the thickness after drying was 25 μm, and dried at 100 ℃ for 2 minutes. Thereby, adhesive layers were formed on the release surfaces of the two release liners, respectively.

A foam base material (hereinafter, also referred to as "base material No. 1") composed of a polyethylene-based foam sheet having one surface and the other surface subjected to corona discharge treatment was prepared. The substrate No.1 had a thickness of 150 μm, a longitudinal tensile strength (MD)) of 16.3MPa, and a widthwise tensile strength (TD)) of 9.5 MPa.

The pressure-sensitive adhesive layers formed on the two release liners were attached to one surface and the other surface of the base material No.1, respectively. The release liner remains on the pressure-sensitive adhesive layer as it is, and serves to protect the surface (pressure-sensitive adhesive surface) of the pressure-sensitive adhesive layer. The resulting structure was passed through a 80 ℃ laminator (0.3MPa, speed 0.5 m/min) once, and then cured in a 50 ℃ oven for one day. Thus, a double-sided adhesive sheet (example 1) having a first adhesive layer and a second adhesive layer on the first surface and the second surface of the foam base (No.1), respectively, and having a total thickness of 200 μm was obtained.

(examples 2 and 3)

Double-sided adhesive sheets (examples 2 and 3) were obtained in the same manner as in the production of the double-sided adhesive sheet of example 1, except that the dried thicknesses of the adhesive layers formed on both sides of the substrate No.1 were 50 μm each (example 2) and 75 μm each (example 3).

(example 4)

[ production of acrylic Polymer (C) ]

100 parts of n-butyl acrylate, 2 parts of acrylic acid, 5 parts of vinyl acetate, 0.1 part of 2-hydroxyethyl acrylate, 0.2 part of 2, 2' -azobisisobutyronitrile as a polymerization initiator, and toluene as a polymerization solvent were charged into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen introduction tube, a reflux condenser, and a dropping funnel, and solution polymerization was carried out at 60 ℃ for 6 hours to obtain a toluene solution of the acrylic polymer (C). The Mw of the acrylic polymer (C) measured in the same manner as for the acrylic polymer (A) was 50X 10⁴。

[ production of adhesive composition (D) ]

An acrylic pressure-sensitive adhesive composition (D) was prepared by adding 30 parts of a polymerized rosin ester resin (product name "ペンセル D-125" manufactured by Mitsukawa chemical industries, Ltd., softening point 125 ℃) as a tackifier resin and 2 parts of an isocyanate-based crosslinking agent (product name "コロネート L" manufactured by Nippon polyurethane industries, Ltd.) as a crosslinking agent to 100 parts of the acrylic polymer (C) contained in the toluene solution.

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

(examples 5 to 7)

A double-sided adhesive sheet (examples 5 to 7) was obtained in the same manner as in the production of the double-sided adhesive sheet of example 4, except that the base material No.2 was used in place of the foam base material No.1, and the dried thicknesses of the adhesive layers formed on both sides of the base material No.2 were 25 μm each (example 5), 50 μm each (example 6), and 75 μm each (example 7).

Here, substrate No.2 was a foam substrate composed of a polyethylene-based foam sheet having one surface and the other surface subjected to corona discharge treatment, and had a thickness of 150 μm, a longitudinal tensile strength (MD)) of 12.3MPa, and a width-directional tensile strength (TD)) of 7.5 MPa.

(example 8)

A double-sided adhesive sheet was obtained in the same manner as the method for producing the double-sided adhesive sheet of example 4 except that the substrate No.3 was used in place of the foam substrate No.2, and the dried thicknesses of the adhesive layers formed on both sides of the substrate No.3 were 50 μm, respectively (example 8).

Here, substrate No.3 was a foam substrate composed of a polyethylene-based foam sheet having one surface and the other surface subjected to corona discharge treatment, and had a thickness of 100 μm, a longitudinal tensile strength (MD)) of 9.5MPa, and a width-directional tensile strength (TD)) of 8.2 MPa.

(example 9)

A double-sided adhesive sheet was obtained in the same manner as the method for producing the double-sided adhesive sheet of example 4 except that the base material No.4 was used instead of the foam base material No.2 (example 9).

Here, substrate No.4 was a foam substrate composed of a polyethylene-based foam sheet having one surface and the other surface subjected to corona discharge treatment, and had a thickness of 200 μm, a longitudinal tensile strength (MD)) of 5.1MPa, and a width-directional tensile strength (TD)) of 4.6 MPa.

(example 10)

A double-sided adhesive sheet was obtained in the same manner as the method for producing the double-sided adhesive sheet of example 4 except that the substrate No.5 was used in place of the foam substrate No.2, and the dried thicknesses of the adhesive layers formed on both sides of the substrate No.5 were 20 μm, respectively (example 10).

Here, substrate No.5 was a foam substrate composed of a polyethylene-based foam sheet having one surface and the other surface subjected to corona discharge treatment, and had a thickness of 60 μm, a longitudinal tensile strength (MD)) of 4.8MPa, and a width-directional tensile strength (TD)) of 4.3 MPa.

The expansion ratios, 25% compressive strength, tensile strength and tensile elongation of the substrates nos. 1 to 5 used for producing the double-sided adhesive sheets of examples 1 to 10 are summarized in table 1.

TABLE 1

< evaluation test >

(1)180 degree peel strength

The release liner covering one adhesive surface of the double-sided adhesive sheet was peeled off, and a polyethylene terephthalate (PET) film having a thickness of 25 μm was laminated on the one adhesive surface, and 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. The sheet was left to stand under the same atmosphere for 30 minutes, and then the peel strength (N/20mm width) was measured under the conditions of a tensile speed of 300 mm/minute and a peel angle of 180 ℃ in accordance with JIS Z0237 using a universal tensile compression tester (apparatus name "tensile compression tester, TG-1 kN", manufactured by ミネベア Co., Ltd.).

(2) 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. 2, to obtain a window frame-shaped double-sided adhesive sheet. Using this window frame-shaped double-sided pressure-sensitive adhesive sheet, a glass plate (Gorilla glass manufactured by Corning Corp., hereinafter, the same shall apply) having a width of 59mm, a length of 113mm and a thickness of 1mm was pressure-bonded to a stainless steel plate (SUS plate) (70 mm, 130mm and 2mm in the width, length and thickness) having a through hole with a diameter of 15mm at the center by applying a load of 5kg for 10 seconds, and a sample for evaluation was obtained.

FIG. 2 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. 2, 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 evaluation samples were set on the above-mentioned universal tensile compression testing machine. 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 of separation 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. 3 is a schematic diagram 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. 3, 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.

(3) Impact resistance

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 first PC board (70 mm in the horizontal direction, 130mm in the vertical direction, and 2mm in thickness) and a second PC board (59 mm in the horizontal direction, 113mm in the vertical direction, and 0.55mm in thickness) were bonded by pressure bonding under a load of 5kg for 10 seconds, thereby obtaining a sample for evaluation (see fig. 4(a) (b)).

FIG. 4 is a schematic view of the above-mentioned evaluation sample, wherein (a) is a plan view and (B) is a cross-sectional view thereof taken along line B-B'. In fig. 4, 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 from a height of 1.2m to a concrete slab 60 times at normal 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 10 times for each of the 6 surfaces.

Then, whether or not the bonding of the first PC board and the second PC board was maintained was visually confirmed for each dropping, and the number of times of dropping until the first PC board and the second PC board were peeled (separated) was evaluated as impact resistance against dropping at normal temperature. When no peeling was observed even after 60 drops, the number of drops was represented as "60 or more" or "> 60".

(4) Resilience resistance

A double-sided pressure-sensitive adhesive sheet was cut into a size of 10mm in width and 100mm in length, a release liner covering one pressure-sensitive adhesive surface thereof was peeled off, and the peeled sheet was bonded to an aluminum plate 0.5mm in thickness, 10mm in width and 100mm in length to prepare a test piece. After bending the test piece in an arc shape along a column having a radius of 15mm (with the aluminum plate side as the inside) in the longitudinal direction, the release liner covering the other adhesive layer of the test piece was peeled off, and the test piece was pressure-bonded to a PC board having a thickness of 2mm while the bent shape of the test piece was restored by using a laminator. The test piece was left to stand at 23 ℃ for 24 hours and then heated at 70 ℃ for 2 hours, and then the heights (mm) of both ends of the test piece lifted from the surface of the PC board were measured. The measurement was performed using three test pieces (i.e., n is 3), and the average of the 6 measurement values was calculated.

(5) Amount of deformation in the thickness direction upon impact

The double-sided adhesive sheet was cut into a window frame shape (frame shape) of 59mm in the transverse direction, 113mm in the longitudinal direction, and 1mm in width, to obtain a window frame-shaped double-sided adhesive sheet. Further, a stainless steel plate (SUS plate) having a rectangular through hole of 50mm in the lateral direction and 90mm in the longitudinal direction in the central portion (70 mm in the lateral direction, 130mm in the longitudinal direction, and 2mm in thickness) and a glass plate (Gorila glass manufactured by Corning Corp.) of 59mm in the lateral direction, 113mm in the longitudinal direction, and 1.5mm in thickness were prepared. The SUS plate and the glass plate were bonded to each other with the window-frame-like double-sided adhesive sheet sandwiched therebetween, and pressure-bonded by applying a load of 5kg for 10 seconds, thereby obtaining a test piece. The SUS plate was placed on an impact tester so that the glass plate side of the test piece was downward and the adhesion surface of the SUS plate and the double-sided adhesive sheet was horizontal. A steel ball (diameter 11mm, weight 28g) was prepared and placed in a position where the steel ball passed through the inside of the through hole of the SUS plate when the steel ball was dropped vertically and directly struck against the surface of the glass plate and was completely out of contact with the SUS plate or double-sided adhesive sheet. At this time, the falling height of the steel ball (the distance (vertical distance) between the lowermost portion of the steel ball before falling and the glass plate) was adjusted to 1 m.

Fig. 5 is an explanatory view showing a method of measuring the amount of deformation in the thickness direction upon impact. In fig. 5, reference numeral 41 denotes a stainless steel plate (SUS plate), reference numeral 4 denotes a window frame-shaped double-sided adhesive sheet, reference numeral 42 denotes a glass plate, and reference numeral 43 denotes a steel ball.

As shown in FIG. 5, the steel ball 43 was allowed to freely fall from above in an atmosphere of about 23 ℃ and 50% RH. The behavior of the double-sided adhesive sheet 4 at the time of collision of the steel ball 43 with the glass plate 42 was photographed using a high-speed camera (manufactured by フォトロン, photographing speed: 50000FPS (frames per second)), and the result was subjected to image analysis, whereby the amount of deformation (elongation) in the thickness direction of the double-sided adhesive sheet 4 was measured. Specifically, the thickness-direction deformation amount at the time of impact is calculated by the following formula (2) from the thickness (initial thickness) of the double-sided adhesive sheet 4 before dropping the steel ball 43 and the thickness (maximum thickness) at which the displacement of the double-sided adhesive sheet 4, to which a force is applied in the vertically downward direction by the impact of the steel plate 43, is maximum in the thickness direction.

(deflection in thickness direction upon impact) (maximum thickness) - (initial thickness) (2)

(6) Cohesion of base material

The double-sided pressure-sensitive adhesive sheet was cut into a size of 20mm in width and 200mm in length, and stainless steel foils 30mm in width, 300mm in length and 0.3mm in thickness were bonded to the pressure-sensitive adhesive surfaces of both sides, and pressed under a pressure of 1.0MPa for 20 seconds to be pressure-bonded. The above bonding is performed by positioning so that the width center of the double-sided adhesive sheet coincides with the width center of the stainless steel foil. The sample was aged at 50 ℃ and 50% RH for 24 hours to obtain a sample for evaluation.

The sample for evaluation was subjected to a tensile compression testing machine (apparatus name "tensile compression testing machine, TG-1 kN", manufactured by ミネベア Co., Ltd.) at 23 ℃ under an atmosphere of 50% RH to measure the cohesion of the substrate. Specifically, as shown in fig. 6, one end in the longitudinal direction of the first stainless foil 56 and the second stainless foil 57 bonded to the first adhesive layer 51 and the second adhesive layer 52 of the double-sided adhesive sheet 5, respectively, was held by the

chucks

58 and 59 of the above-described testing machine, and the

stainless foils

56 and 57 bonded to the double-sided adhesive sheet 5 were T-peeled by pulling the chuck 58 upward and the chuck 59 downward at a speed of 150 mm/min, respectively. The force required for the T-shaped peeling was measured by the above-mentioned tester and used as the substrate cohesive force (N/20mm width). Further, the evaluation sample after T-type peeling was visually observed, and it was confirmed that peeling was caused by breakage within the thickness of the foam base 55 as shown in fig. 6, and was not peeling at the adhesive interface between the pressure-sensitive adhesive layers 51 and 52 and the stainless steel foils 56 and 57 in the double-sided pressure-sensitive adhesive sheet.

(7) Retention force

The release liner covering one side of the double-sided adhesive sheet was peeled off, and a PET film having a thickness of 25 μm was attached to the liner. The test piece was cut into a size of 50mm in length and 25mm in width to prepare a test piece. The release liner covering the other surface of the test piece (i.e., the surface of the test piece opposite to the surface lined with the PET film) was peeled off, and the peeled surface was adhered to a phenol resin plate as an adherend with an adhesive area of 25mm in width and 25mm in length. After the sheet was left to stand at 23 ℃ for 30 minutes, the phenolic resin sheet was allowed to sag, and a load of 2kg was applied to the free end of the test piece. According to JIS Z0237 (2004), the plate was left for 12 hours in an environment of 23 ℃ and 50% RH under the condition that the load was applied. When the test piece fell after the lapse of 12 hours, the holding time was judged to be less than 12 hours (indicated as "fell" in table 2). Otherwise, the offset distance (mm) of the test piece from the first adhesion position was measured.

The results of measurement or evaluation by the above-described method of the double-sided adhesive sheets of examples 1 to 10 are shown in table 2. Table 2 shows the general structure of the double-sided adhesive sheet of each example and the gel fraction value obtained by the above method for the adhesive constituting the adhesive layer of the double-sided adhesive sheet.

TABLE 2

As shown in table 2 above, the double-sided pressure-sensitive adhesive sheets of examples 1 to 4 using the substrate No.1 suppressed the amount of deformation in the thickness direction upon impact, as compared with the double-sided pressure-sensitive adhesive sheets of examples 5 to 10 using the substrates nos. 2 to 5. The double-sided pressure-sensitive adhesive sheets of examples 1 to 4 exhibited more excellent impact resistance and higher substrate cohesion than the double-sided pressure-sensitive adhesive sheets of examples 5 to 10. In addition, the double-sided pressure-sensitive adhesive sheets of examples 1 to 4 had high pressure-sensitive adhesive strength and excellent holding power. The double-sided pressure-sensitive adhesive sheets of examples 1 to 3 exhibited more excellent performance in the rebound resistance and 180 degree peel strength than the double-sided pressure-sensitive adhesive sheet of example 4.

Further, with respect to the double-sided adhesive sheets of examples 5 to 10, the separation state of the first polycarbonate sheet and the second polycarbonate sheet in the impact resistance test was observed, and as a result, the double-sided adhesive sheets of examples 8 to 10 using substrates nos. 3 to 5, the entire periphery of the sash-like double-sided adhesive sheet, the foam substrate, was torn within the thickness. In addition, using the double-sided adhesive sheets of examples 5 to 7 of substrate No.2, a part of the length of the entire periphery of the sash-like double-sided adhesive sheet was torn within the thickness of the foam substrate, and the other part of the double-sided adhesive sheet was peeled off at the interface with the first or second polycarbonate sheet.

< Experimental example 2>

Samples of the double-sided adhesive sheets of examples 11 to 13 were produced by the following procedure.

(examples 11 to 13)

A double-sided adhesive sheet (examples 11 to 13) was obtained in the same manner as the method for producing the double-sided adhesive sheet of example 1, except that the substrate No.6 was used in place of the foam substrate No.1, and the dried thicknesses of the adhesive layers formed on both sides of the substrate No.6 were 25 μm each (example 11), 50 μm each (example 12), and 75 μm each (example 13).

Here, substrate No.6 was a foam substrate composed of a polyethylene-based foam sheet having one surface and the other surface subjected to corona discharge treatment, and had a thickness of 150 μm, a longitudinal tensile strength (MD)) of 19.2MPa, and a width-directional tensile strength (TD)) of 11.8 MPa.

The expansion ratio, 25% compressive strength, tensile strength and tensile elongation of the base material No.6 used for producing the double-sided adhesive sheets of examples 11 to 13 are summarized in table 3.

TABLE 3

	Base Material No.6
		Species of	Polyethylene foam
Expansion ratio [ cm ]³/g]	1.49
		25% compressive strength [ kPa ]]	800
MD tensile Strength [ MPa ]]	19.2
		TD tensile Strength [ MPa ]]	11.8
MD tensile elongation [% ]]	500
		TD tensile elongation [% ]]	290

The results of measurement or evaluation of the double-sided pressure-sensitive adhesive sheets of examples 11 to 13 by the same method as in experimental example 1 are shown in table 4. Table 4 shows the general structure of the double-sided adhesive sheet of each of examples 11 to 13 and the gel fraction value obtained by the above method for the adhesive constituting the adhesive layer of the double-sided adhesive sheet.

TABLE 4

As shown in tables 4 and 2, the double-sided adhesive sheets of examples 11 to 13 using the substrate No.6 suppressed the amount of deformation in the thickness direction upon impact, as compared with the double-sided adhesive sheets (examples 5 to 10) using the substrates nos. 2 to 5. It is also apparent that the double-sided pressure-sensitive adhesive sheets of examples 11 to 13 are more suppressed in the amount of deformation in the thickness direction upon impact than the double-sided pressure-sensitive adhesive sheets using the substrate No.1 (examples 1 to 4). In addition, the double-sided adhesive sheets of examples 11 to 13 showed excellent impact resistance and higher cohesion of the substrate. The pressure-sensitive adhesive sheets of examples 11 to 13 had higher pressure-sensitive adhesive strength (1mm width) and more excellent holding power. In addition, the double-sided adhesive sheets of examples 11 to 13 exhibited high 180 degree peel strength and excellent repulsion resistance.

< Experimental example 3>

With respect to the double-sided adhesive sheets of examples 1 to 13, the pressure-sensitive adhesive force (narrow-width pressure-sensitive adhesive force) when the width of the sash-shaped double-sided adhesive sheet was less than 1mm was measured by the following method.

That is, a sample obtained by cutting the double-sided adhesive sheet into a window frame shape (frame shape) of 59mm in the lateral direction, 113mm in the longitudinal direction, and 0.3mm in width, a sample obtained by cutting the double-sided adhesive sheet into a window frame shape (frame shape) of 59mm in the lateral direction, 113mm in the longitudinal direction, and 0.5mm in width, and a sample obtained by cutting the double-sided adhesive sheet into a window frame shape (frame shape) of 59mm in the lateral direction, 113mm in the longitudinal direction, and 0.7mm in width were prepared. The narrow width pressure-sensitive adhesive force was measured in the same manner as the measurement of the pressure-sensitive adhesive force described above using the sash-shaped double-sided adhesive sheet having a width of 1mm, except that these sash-shaped double-sided adhesive sheets having a width of 0.3mm, a width of 0.5mm and a width of 0.7mm were used. The results obtained are shown in table 5.

TABLE 5

As shown in table 5, the smaller the width of the double-sided adhesive sheets of the examples, the smaller the pressing adhesion force tends to be. However, according to the double-sided pressure-sensitive adhesive sheets of examples 1 to 4 and examples 11 to 13, a high pressure-sensitive adhesive strength of 160N or more was obtained even with a width of 0.7 mm. Further, according to the double-sided adhesive sheets of examples 1 to 4 and examples 11 to 13, a high pressure-sensitive adhesive strength of 110N or more was obtained even with a width of 0.5 mm. Further, according to the double-sided adhesive sheets of examples 1 to 4 and examples 11 to 13, a high pressure-sensitive adhesive strength of 60N or more was obtained even with a width of 0.3 mm. In particular, the double-sided pressure-sensitive adhesive sheets of examples 11 to 13 exhibited higher pressure-sensitive adhesive strength.

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 recited in the claims include various modifications and changes to the specific examples described above.

Claims

1. 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 foaming ratio of the foaming base material is 2.0cm³(ii) a ratio of the total of the components in terms of the ratio of the total of the components to the total of the components in the total,

the foam base material has a 25% compressive strength of 200kPa or more.

2. The double-sided adhesive sheet according to claim 1, wherein the foam base has a 25% compressive strength of 500kPa or more.

3. The double-sided adhesive sheet according to claim 1 or 2, wherein the foam base has a base cohesive force of 40N/20mm or more.

4. A double-sided adhesive sheet as defined in any one of claims 1 to 3, wherein the foam base has a longitudinal tensile elongation of 400% or more and a width tensile elongation of 200% or more.

5. A double-sided adhesive sheet as defined in any one of claims 1 to 4, wherein the foam base has a longitudinal tensile strength of 15MPa or more.

6. A double-sided adhesive sheet as defined in any one of claims 1 to 5, wherein the foam base material is a polyolefin foam base material.

7. A double-sided adhesive sheet according to any one of claims 1 to 6,

the adhesive constituting at least one of the first adhesive layer and the second adhesive layer contains a tackifying resin having a softening point of 135 ℃ or higher.

8. A double-sided adhesive sheet according to any one of claims 1 to 7,

the value obtained by dividing the value of the 25% compressive strength of the foam base material by the value of the foaming ratio is 250 g-kPa/cm³The above.

9. A double-sided adhesive sheet according to any one of claims 1 to 8,

the total thickness of the double-sided adhesive sheet is 70 [ mu ] m to 500 [ mu ] m.

10. A double-sided adhesive sheet according to any one of claims 1 to 9, which is used for joining parts of portable electronic equipment.