CN115612409A

CN115612409A - Adhesive sheet and release liner-attached adhesive sheet

Info

Publication number: CN115612409A
Application number: CN202210782866.7A
Authority: CN
Inventors: 吉良佳子; 铃木立也; 粟根谅
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2021-07-12
Filing date: 2022-07-05
Publication date: 2023-01-17
Also published as: JP2023011339A

Abstract

The present invention relates to an adhesive sheet and a release liner-attached adhesive sheet. The invention provides a pressure-sensitive adhesive sheet which is not easy to visually recognize the surface shape of an adherend even when the pressure-sensitive adhesive sheet is adhered to the surface of the adherend having irregularities. The invention provides an adhesive sheet, which comprises an adhesive layer and a substrate for supporting the adhesive layer. The adhesive sheet has an adhesive surface formed of the adhesive layer, and a back surface opposite to the adhesive surface. Further, the back surface of the adhesive sheet has a gloss of 80GU or less, and the adhesive sheet has a total light transmittance of 75% or less.

Description

Adhesive sheet and release liner-attached adhesive sheet

Technical Field

The present invention relates to an adhesive sheet and a release liner-attached adhesive sheet.

Background

In general, an adhesive (also referred to as a pressure-sensitive adhesive; the same applies hereinafter) exhibits a soft solid (viscoelastic body) state in a temperature range around room temperature, and has a property of simply adhering to an adherend by pressure. By utilizing such properties, an adhesive is widely used for the purpose of bonding, fixing, protecting, sealing, and the like in various applications such as electronic devices, for example, in the form of a base material-attached adhesive sheet having an adhesive layer on a support base material. For example, patent document 1 is cited as a technical document relating to an adhesive sheet for hermetically sealing the internal space of a magnetic disk device.

Documents of the prior art

Patent literature

Patent document 1: japanese patent No. 6453799

Disclosure of Invention

Problems to be solved by the invention

The pressure-sensitive adhesive sheet described in patent document 1 has a gas-impermeable substrate having an aluminum layer and is excellent in gas barrier properties. Further, since the pressure-sensitive adhesive sheet has an aluminum layer, it does not rebound even when it is bent in accordance with the shape of an adherend, satisfactorily follows the shape of the adherend, and easily maintains an excellent adhesion state to the adherend. Therefore, for example, by bending and sticking the cover to the upper surface and the side surface of the case of the magnetic disk device, the inner space for accommodating the magnetic disk such as a Hard Disk (HD) can be hermetically sealed, and the cover can be satisfactorily used for this purpose.

However, in the case where the adhesive sheet having the above-described configuration is attached to a welded portion of a magnetic disk device or a surface having a bump such as a dent generated during production of the magnetic disk device, the aluminum layer of the adhesive sheet follows the unevenness of the welded portion or the depression of the bump, and therefore the unevenness may appear on the back surface of the adhesive sheet. Further, the surface gloss of the aluminum layer may make the unevenness of the back surface of the adhesive sheet conspicuous by reflection of light, which may impair the appearance of the product to which the adhesive sheet is attached. In particular, an end portion of an adherend (for example, a corner portion of a case of a magnetic disk device) is likely to generate a dent due to contact with a hard material such as another member or the like at the time of device assembly, and in this case, a pressure-sensitive adhesive sheet attached so as to cover the end portion of the adherend is excellent in followability such as bendability, and therefore also tends to follow the dent of the adherend, and tends to have a shape such as a dent on the surface of the adherend on the back surface. It is useful if a pressure-sensitive adhesive sheet can be provided which does not impair the properties required for the intended use, such as airtightness in the use for sealing the cover of a magnetic disk device, and which, even when the pressure-sensitive adhesive sheet is attached to an adherend having irregularities, is less likely to have a surface shape of the adherend recognized on the back surface of the pressure-sensitive adhesive sheet, and which can provide a good appearance.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a pressure-sensitive adhesive sheet which, even when the pressure-sensitive adhesive sheet is attached to a surface of an adherend having irregularities, is less likely to visually recognize the surface shape of the adherend. Another object of the present invention is to provide a release liner-attached pressure-sensitive adhesive sheet having the pressure-sensitive adhesive sheet.

Means for solving the problems

According to the present specification, there is provided an adhesive sheet having an adhesive layer and a substrate supporting the adhesive layer. The adhesive sheet has an adhesive surface formed of the adhesive layer, and a back surface opposite to the adhesive surface. Further, the back surface of the adhesive sheet has a gloss of 80GU or less, and the adhesive sheet has a total light transmittance of 75% or less. According to this configuration, even when the pressure-sensitive adhesive sheet is stuck on the surface having irregularities and the irregularities appear on the back surface of the pressure-sensitive adhesive sheet due to the conformability of the pressure-sensitive adhesive sheet, the gloss of the back surface of the pressure-sensitive adhesive sheet is 80GU or less, so that light reflection on the back surface of the pressure-sensitive adhesive sheet is suppressed and the irregularities caused by the adherend on the back surface of the pressure-sensitive adhesive sheet are less likely to become conspicuous. Further, since the total light transmittance of the psa sheet is 75% or less, the psa sheet has masking properties, and the uneven pattern of an adherend is not easily visually recognized through the psa sheet, regardless of whether the psa sheet attached to the uneven surface follows the surface shape of the adherend. In short, according to the pressure-sensitive adhesive sheet having a back surface gloss of 80GU or less and a total light transmittance of 75% or less, even when the pressure-sensitive adhesive sheet is attached to the surface of an adherend having irregularities, the attachment of the adherend with the surface shape thereof being difficult to recognize by visual observation can be realized. According to this pressure-sensitive adhesive sheet, the unevenness on the surface of the adherend is not readily visually recognized, and even when the unevenness based on the shape of the adherend appears on the back surface of the pressure-sensitive adhesive sheet, the unevenness is not conspicuous and is of such an extent that it cannot be visually recognized.

In some preferred embodiments, the arithmetic average roughness of the back surface of the adhesive sheet is in the range of 50nm or more and 3000nm or less. When the arithmetic average roughness is 50nm or more, reflection of light at the back surface is easily suppressed, and unevenness of the back surface is less likely to be conspicuous. In addition, the back surface has a good surface condition by the arithmetic average roughness of 3000nm or less. For example, in the case of printing on the back surface of the pressure-sensitive adhesive sheet, the printing tends to be excellent in printability and to be easily visually recognized.

In some preferred embodiments, the haze of the back surface of the adhesive sheet is 70% or more. When the haze of the back surface of the pressure-sensitive adhesive sheet is 70% or more, the masking property of the surface shape of the adherend tends to be improved.

In some preferred forms, the adhesive sheet has a gas generation amount of 1.0. Mu.g/cm as measured by gas chromatography/mass spectrometry (GC-MS method) at 130 ℃ for 30 minutes ² The following. The amount of gas generated during heating was 1.0. Mu.g/cm as described above ² The following adhesive sheet can be satisfactorily used in applications where gas generation is undesirable, such as precision equipment. For example, an adhesive sheet satisfying the above characteristics is suitable for applications of sealing an internal space of a magnetic disk device in which a volatile gas such as siloxane gas may cause a failure or malfunction.

In some preferred forms, the adhesive sheet has a siloxane gas generation amount of 0.1. Mu.g/cm as measured by gas chromatography/mass spectrometry (GC-MS method) at 130 ℃ for 30 minutes ² The following. The amount of siloxane gas generated was 0.1. Mu.g/cm as described above ² The following adhesive sheet can be satisfactorily used for applications where the presence of siloxane gas is undesirable. For example, an adhesive sheet satisfying the above characteristics is suitable for a silicone gas which may cause troubles or mishandlingThe inner space of the magnetic disk device is sealed.

In some embodiments, the substrate is composed of a single resin layer. According to the technology disclosed herein, in a form in which the substrate has a single resin layer structure, the gloss of the back surface of the pressure-sensitive adhesive sheet can be adjusted to 80GU or less, and the total light transmittance of the pressure-sensitive adhesive sheet can be adjusted to 75% or less, so that a desired effect can be achieved.

In an embodiment in which the substrate is formed of a single resin layer, the total light transmittance of the substrate is preferably 20% or less. When the total light transmittance of the substrate is 20% or less, the total light transmittance of the entire psa sheet is reduced, and unevenness on the surface of an adherend can be masked.

In an embodiment in which the substrate is formed of a single resin layer, the total light transmittance of the pressure-sensitive adhesive layer is preferably 20% or less. When the total light transmittance of the pressure-sensitive adhesive layer is 20% or less, the total light transmittance of the pressure-sensitive adhesive sheet as a whole is reduced, and unevenness on the surface of an adherend can be masked.

The thickness of the base material may be 20 μm or more and 200 μm or less. When the thickness of the substrate is 20 μm or more, the adhesive sheet can cover the adherend surface having irregularities while maintaining a flat back surface by the rigidity of the substrate, and the irregularities on the adherend surface can be suppressed from appearing on the back surface of the adhesive sheet. In addition, in a configuration in which the total light transmittance of the base material is limited, good light-shielding properties are easily obtained by utilizing the low light transmittance of the base material. Further, since the thickness of the substrate is 200 μm or less, the pressure-sensitive adhesive sheet having the substrate can satisfactorily follow the shape of the adherend, and, for example, even in a case where the pressure-sensitive adhesive sheet is folded and attached so as to extend over both surfaces of the adherend, the pressure-sensitive adhesive sheet is less likely to be lifted or peeled off. In the embodiment in which the substrate is formed of a single resin layer, the thickness of the substrate can be preferably used.

In other embodiments, the substrate has a metal layer and one or more resin layers. According to the technology disclosed herein, in a form in which the substrate has the resin layer and the metal layer, the glossiness of the back surface of the adhesive sheet can be adjusted to 80GU or less, and the total light transmittance of the adhesive sheet can be adjusted to 75% or less, so that the desired effects can be achieved. According to the structure having the metal layer, excellent gas barrier properties are easily obtained, and even in a system of bending and attaching the metal layer in accordance with the shape of the adherend, the adhesion state to the adherend is easily maintained. In the present specification, the gas barrier property means a property of blocking passage of various gas components and moisture (moisture) in the air, and includes moisture resistance.

The thickness of the metal layer is preferably 2 μm or more and 30 μm or less. When the thickness of the metal layer is within the above range, the adherend can be shielded. In addition, in the pressure-sensitive adhesive sheet having the metal layer with the above thickness, since the metal layer has a predetermined thickness, it is possible to appropriately suppress the following to the uneven surface of the adherend and to suppress the occurrence of the unevenness on the surface of the adherend on the back surface of the pressure-sensitive adhesive sheet.

The thickness of the resin layer is preferably 20 μm or more and 200 μm or less. By setting the thickness of the resin layer to 20 μm or more, the adhesive sheet can cover the uneven surface of the adherend while maintaining a flat back surface by the rigidity of the resin layer, and the occurrence of unevenness on the surface of the adherend on the back surface of the adhesive sheet can be suppressed. Further, since the thickness of the resin layer is 200 μm or less, the pressure-sensitive adhesive sheet having the resin layer can satisfactorily follow the shape of the adherend, and, for example, even in a case where the pressure-sensitive adhesive sheet is folded and attached so as to extend over both surfaces of the adherend, the pressure-sensitive adhesive sheet is less likely to be lifted or peeled off. When the resin layer has two or more layers, the thickness of the resin layer refers to the total thickness of the two or more resin layers.

The substrate has, as the resin layer, a resin layer A and a resin layer B disposed so as to sandwich the metal layer, wherein the resin layer A is disposed on the back side of the adhesive sheet. The technique disclosed herein is preferably implemented to include a substrate having a resin layer a, a metal layer, and a resin layer B in this order. According to this structure, by the presence of the metal layer, excellent gas barrier properties are provided, and by the presence of the resin layer sandwiching the metal layer, for example, even if the thickness of the metal layer (e.g., aluminum layer) is thin, the metal layer can be effectively protected from bending, wrinkling, breaking, and the like.

Further, according to the present specification, a release liner-equipped adhesive sheet is provided. The release liner-equipped adhesive sheet comprises any one of the adhesive sheets disclosed herein and a polyolefin-based release liner for protecting the adhesive surface of the adhesive sheet. The adhesive sheet is stored in a state that the adhesive surface is protected by the polyolefin release liner before use, and can be smoothly released from the polyolefin release liner for use.

According to the pressure-sensitive adhesive sheet disclosed herein, even when the pressure-sensitive adhesive sheet is attached to a surface of an adherend having irregularities, the attachment can be achieved in which the shape of the surface of the adherend is not easily recognized by visual observation, and a good appearance can be imparted to a product to which the pressure-sensitive adhesive sheet is attached. By attaching the adhesive sheet to at least one of the outer surfaces of the casing of a magnetic disk device such as a Hard Disk Drive (HDD), even when there are irregularities such as welding marks or impact marks on the surface of the magnetic disk device, the irregularities can be shielded so as not to be recognized, and a good appearance can be provided to the magnetic disk device.

The size of the adhesive sheet (sheet size) may be 20% or more and 150% or less of the area of at least one surface (surface to be bonded) of the outer surface of the case of the magnetic disk device. The pressure-sensitive adhesive sheet having such a size can shield only a part of the surface to be adhered, and can shield the entire surface to be adhered. The adhesive sheet may cover not only one surface of the surface to be bonded but also the adjacent surface thereof. Even when a recess is formed in a corner portion of the outer surface of the case, the adhesive sheet attached in this manner can be attached so as to extend over both surfaces including the corner portion, and therefore, masking in which the recess in the corner portion is not visually recognized can be achieved. The pressure-sensitive adhesive sheet to be attached so as to span at least two surfaces may have a size larger than one surface of the surface to be attached, may have a size smaller than the one surface, or may be used by being attached to an outer peripheral portion of a top cover of a magnetic disk device such as a hard disk drive. The pressure-sensitive adhesive sheet used in this manner can cover an end portion of an adherend (e.g., a corner portion of a case of a magnetic disk device) on which a dent is likely to be generated, thereby masking a surface shape of the adherend having the dent of the dent, and can impart a good appearance.

Drawings

Fig. 1 is a cross-sectional view schematically showing one configuration example of a pressure-sensitive adhesive sheet.

Fig. 2 is a cross-sectional view schematically showing another configuration example of the adhesive sheet.

Fig. 3 is a cross-sectional view schematically showing one configuration example of the magnetic disk device.

Fig. 4 is a plan view schematically showing the shape of the adhesive sheet before being attached to the magnetic disk device shown in fig. 3.

Fig. 5 is a schematic cross-sectional view showing a part of another configuration example of the magnetic disk device in cross section.

Fig. 6 is a schematic cross-sectional view showing a part of still another configuration example of the magnetic disk device in cross section.

Description of the reference symbols

1.2, 101, 201, 301: adhesive sheet

1A, 2A: adhesive surface

1B, 2B: back side of the panel

10: base material

12: resin layer A

14: inorganic layer

16: resin layer B

20: adhesive layer

30: release liner

51. 52: release liner-attached pressure-sensitive adhesive sheet

100. 200 and 300: magnetic disk device

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described. It is to be noted that matters necessary for the practice of the present invention other than the matters specifically mentioned in the present specification can be understood by those skilled in the art based on the teaching about the practice of the invention described in the present specification and the technical common knowledge at the time of application. The present invention can be implemented based on the contents disclosed in the present specification and the technical common knowledge in the art. In the following drawings, members and portions that perform the same function are sometimes described with the same reference numerals, and redundant description may be omitted or simplified. The embodiments shown in the drawings are illustrated for clarity of the present invention, and do not necessarily accurately show the size or scale of the product to be actually provided.

In the present specification, the "pressure-sensitive adhesive" refers to a material that exhibits a soft solid (viscoelastic body) state in a temperature range around room temperature and has a property of easily adhering to an adherend by pressure, as described above. The adhesives described herein are as described in "C.A. Dahlquist," Adhesion: fundamentals and Practice, "McLaren&Sons, (1966), page 143 ", can be generally defined as having a modulus E satisfying a complex tensile elasticity ^* (1Hz)<10 ⁷ Dyne/cm ² A material having the above properties (typically a material having the above properties at 25 ℃).

In addition, the concept of the adhesive sheet in the present specification may include articles called an adhesive tape, an adhesive label, an adhesive film, and the like. The pressure-sensitive adhesive sheet disclosed herein may be in a roll shape or a paper shape. Alternatively, the pressure-sensitive adhesive sheet may be processed into various shapes.

< construction of pressure-sensitive adhesive sheet >

The pressure-sensitive adhesive sheet disclosed herein may be, for example, in the form of a one-sided pressure-sensitive adhesive sheet having a cross-sectional structure shown in fig. 1. The adhesive sheet 1 has a substrate 10 and an adhesive layer 20 supported by one surface of the substrate 10. The adhesive layer 20 constitutes the adhesive surface 1A of the adhesive sheet 1. The substrate 10 is a laminate (laminated film) obtained by sequentially laminating a resin layer a12, an inorganic layer 14, and a resin layer B16. The resin layer a12 disposed on one surface side of the inorganic layer 14 constitutes the back surface 1B (opposite surface to the pressure-sensitive adhesive surface 1A) of the pressure-sensitive adhesive sheet 1, and the resin layer B16 is disposed on the other surface side of the inorganic layer 14 and on the pressure-sensitive adhesive layer 20 side. In other words, in the substrate 10, the resin layer a12 and the resin layer B16 are disposed so as to sandwich the inorganic layer 14. In this embodiment, the inorganic layer 14 is a metal layer. The psa sheet 1 before use (before being affixed to an adherend) may be in the form of a release liner-equipped psa sheet 51 protected by a release liner 30 having a release surface on at least the psa layer 20 side.

The pressure-sensitive adhesive sheet may have a cross-sectional structure shown in fig. 2. The psa sheet 2 shown in fig. 2 has the same structure as that of fig. 1 in that it includes a substrate 10 and a psa layer 20 supported on one surface of the substrate 10, but differs from the structure of fig. 1 in that the substrate 10 is composed of a resin layer 12. The adhesive layer 20 constitutes the adhesive surface 2A of the adhesive sheet 2, and the resin layer 12 constitutes the back surface 2B of the adhesive sheet 2. The psa sheet 2 before use (before being affixed to an adherend) may be in the form of a release liner-equipped psa sheet 52 protected by a release liner 30 having a release surface on at least the psa layer 20 side.

The adhesive sheet shown in fig. 1 has a substrate including a resin layer a, an inorganic layer, and a resin layer B, but is not limited thereto. The number of resin layers may be one as in the structure shown in fig. 2, or may be two or three or more. For example, the substrate may be a laminate of a single resin layer and an inorganic layer. In this laminate, the resin layer is preferably disposed on the back side of the adhesive sheet.

Further, an additional layer may be provided on the back surface of the substrate, for example, on the back surface side of the resin layer. Such an additional layer is a layer constituting the back surface of the adhesive sheet, and may be, for example, a layer called a top coat layer or a printed layer. An adhesive layer for bonding the layers and an undercoat layer (also referred to as a primer layer) for improving the adhesion of the layers may be provided between the layers constituting the substrate. Further, an undercoat layer for improving adhesion between the substrate and the adhesive layer may be provided between the substrate and the adhesive layer.

< characteristics of pressure-sensitive adhesive sheet >

One feature of the adhesive sheet disclosed herein is that the gloss of the back surface (60 ° gloss) is 80GU or less. According to the adhesive sheet satisfying this characteristic, even in the case where the adhesive sheet is adhered to a surface having irregularities, and the irregularities appear on the back surface of the adhesive sheet due to the conformability of the adhesive sheet, light reflection on the back surface of the adhesive sheet is suppressed, so that the irregularities caused by the adherend on the back surface of the adhesive sheet are less likely to become conspicuous. Further, by limiting the glossiness of the back surface of the adhesive sheet to a predetermined value or less, for example, when printing is performed on the back surface of the adhesive sheet, the printing property tends to be good and the printing tends to be easily visually recognized. In some preferred embodiments, the gloss of the back surface of the pressure-sensitive adhesive sheet is 60GU or less, may be 50GU or less, may be 40GU or less, may be 30GU or less, may be 20GU or less, and may be 15GU or less. The lower limit value of the gloss of the back surface of the pressure-sensitive adhesive sheet is 0GU, and the gloss of the back surface of the pressure-sensitive adhesive sheet may be 1GU or more, 5GU or more, 12GU or more, 25GU or more, 35GU or more, or 45GU or more, for example, from the viewpoint of harmony with the appearance of the pressure-sensitive adhesive sheet to be applied. The gloss of the back surface of the adhesive sheet can be determined by the selection of the substrate material; a method of molding a substrate (typically, a resin layer); the configuration of the back layer (e.g., a matting layer containing organic or inorganic particles); the back surface of the adhesive sheet is subjected to surface treatment (also referred to as matte treatment) such as embossing or sandblasting. The gloss (60 ° gloss) of the back surface of the pressure-sensitive adhesive sheet was measured by the method described in the examples described later.

Another feature of the adhesive sheet disclosed herein is that the total light transmittance is 75% or less. A pressure-sensitive adhesive sheet satisfying such characteristics has a masking property, and the uneven pattern of an adherend is not easily visually recognized through the pressure-sensitive adhesive sheet regardless of whether the pressure-sensitive adhesive sheet attached to the surface having unevenness follows the surface shape of the adherend. The total light transmittance of the psa sheet is preferably 60% or less, more preferably 40% or less, and even more preferably 20% or less. In some preferred embodiments, the total light transmittance of the pressure-sensitive adhesive sheet is 10% or less, and from the viewpoint of improving the masking property of an adherend, the total light transmittance of the pressure-sensitive adhesive sheet may be 3% or less, may be less than 1%, and may be less than 0.1%. The lower limit of the total light transmittance of the psa sheet is not particularly limited, and may be substantially 0%, i.e., not more than the detection limit, or not less than 0.01%, for example, not less than 0.1%, or not less than 1.0%. In some embodiments, the total light transmittance of the pressure-sensitive adhesive sheet may be 5% or more, may be 9% or more, and may be 12% or more (for example, 15% or more). The total light transmittance of the adhesive sheet can be adjusted by selecting a substrate material, laminating a component (e.g., a colorant) contained in the adhesive layer, a coloring layer, and the like. The total light transmittance of the pressure-sensitive adhesive sheet was measured by the method described in the examples described later.

The haze of the pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and may be, for example, 1% or more, 10% or more, 30% or more, or 50% or more. The higher the haze of the pressure-sensitive adhesive sheet is, the more the masking property of the adherend tends to be improved. The haze of the adhesive sheet is measured on the back surface of the adhesive sheet, and may be referred to as the haze on the back surface of the adhesive sheet instead. In some preferred embodiments, the haze of the psa sheet is 70% or more, more preferably 80% or more, still more preferably 90% or more, and may be 95% or more, or may be 99% or more. The upper limit of the haze is 100%, and in some embodiments, the haze may be 99% or less, or 90% or less, or 85% or less. The haze of the adhesive sheet can be adjusted by selecting a substrate material, selecting a component contained in the adhesive layer, surface treatment, and the like.

The "haze" refers to a ratio of diffuse transmitted light to total transmitted light when visible light is irradiated to a measurement object. Haze is also referred to as haze value. The haze may be represented by the following formula.

Th＝Td/Tt×100

In the above formula, th is haze [% ], td is diffuse light transmittance [% ], and Tt is total light transmittance [% ]. The haze of the adhesive sheet can be measured by the method described in the examples described later.

The arithmetic average roughness of the back surface of the pressure-sensitive adhesive sheet is not particularly limited, and may be 10000nm or less, for example. In some preferred embodiments, the arithmetic average roughness of the back surface of the pressure-sensitive adhesive sheet is 3000nm or less, more preferably 1500nm or less, still more preferably 1000nm or less, particularly preferably 800nm or less, and may be 500nm or less, or 300nm or less. The smaller the above arithmetic mean roughness is, the better the surface state of the back surface of the adhesive sheet is. For example, in the case of printing on the back surface of the pressure-sensitive adhesive sheet, the printing property is good and the printing tends to be easily visually recognized. The arithmetic average roughness of the back surface of the pressure-sensitive adhesive sheet is, for example, 10nm or more. In some preferred embodiments, the arithmetic average roughness of the back surface of the adhesive sheet is 50nm or more, more preferably 100nm or more, still more preferably 150nm or more, and particularly preferably 200nm or more (for example, 250nm or more). As the arithmetic mean roughness is higher, light reflection on the back surface of the pressure-sensitive adhesive sheet is more easily suppressed, and unevenness on the back surface due to the surface shape of the adherend tends to be less noticeable. In some other embodiments, the arithmetic average roughness of the back surface of the pressure-sensitive adhesive sheet may be 350nm or more, 450nm or more, or 550nm or more. The arithmetic mean roughness of the back surface of the adhesive sheet can be adjusted by selection of a substrate material, a molding method of a substrate (typically, a resin layer), and surface treatment (treatment such as embossing roller processing or sandblast processing) of the back surface of the adhesive sheet. The arithmetic mean roughness of the back surface of the pressure-sensitive adhesive sheet can be measured by the method described in examples described later.

Although not particularly limited, the gas generation amount of the adhesive sheet measured by GC-MS method at 130 ℃ for 30 minutes was 10. Mu.g/cm in some embodiments ² The following. The adhesive sheet in which the amount of generation of the heated gas is highly limited as such can be satisfactorily used for applications (typically, magnetic disk devices) in which the presence of volatile gas is undesirable. In some preferred forms, the above-mentioned gas generation amount of the adhesive sheet is 1.0. Mu.g/cm ² Hereinafter, more preferably 0.5. Mu.g/cm ² Below, it is more preferably less than 0.3. Mu.g/cm ² . When the pressure-sensitive adhesive sheet satisfying the above characteristics is used as a sealing material for sealing the internal space of a magnetic disk device in which a volatile gas such as a silicone gas may cause a failure or malfunction, it is possible to highly suppress the incorporation of the silicone gas or other gases that adversely affect the device into the system. The lower limit of the amount of gas generated is not particularly limited, and may be substantially 0. Mu.g/cm ² I.e., may be below the detection limit. The amount of gas generated can be measured by the method described in the examples described below.

Although not particularly limited, the silicone gas generation amount of the adhesive sheet measured by GC-MS method at 130 ℃ for 30 minutes is 1. Mu.g/cm in some embodiments ² The following. The adhesive sheet satisfying the above characteristics can be satisfactorily used for applications where the presence of siloxane gas is undesirable. For example, the sealing material is particularly suitable as a sealing material for sealing the internal space of a magnetic disk device in which silicone gas may cause malfunction or malfunction. In some preferred embodiments, the above-mentioned amount of silicone gas generation of the adhesive sheet is 0.1. Mu.g/cm ² Hereinafter, more preferably 10ng/cm ² Hereinafter, more preferably 1ng/cm ² Below, particularly preferably less than 0.4ng/cm ² . The lower limit of the amount of the siloxane gas generated is not particularly limited, and may be substantially 0. Mu.g/cm ² That is, the detection limit may be set to be lower than the detection limit. The amount of the generated siloxane gas can be measured by the method described in examples described later.

Although not particularly limited, in some embodiments, the moisture permeability of the adhesive sheet measured by the following method is preferably 1 g/(m) ² 24 hours) or less, more preferably 0.1 g/(m) ² 24 hours) or less, and more preferably less than 0.01 g/(m) ² 24 hours). The moisture permeability of the pressure-sensitive adhesive sheet was measured in accordance with JIS K7129B using a water vapor permeability measuring apparatus "PERMATRAN-W3/34G" manufactured by MOCON. Specifically, the water vapor transmission rate [ g/(m) was measured by isolating a low humidity chamber at 40 ℃ and 0% RH from a high humidity chamber at 40 ℃ and 90% RH using an adhesive sheet, and detecting a change in relative humidity in the low humidity chamber caused by water vapor transmitted through the adhesive sheet using an infrared sensor ² 24 hours)]. In the examples described later, the measurement was also performed by the same method. The adhesive sheet having a moisture permeability defined as described above can be satisfactorily used as a sealing material in applications where the presence of moisture is not desired or applications where moisture resistance is required, for example.

Although not particularly limited, in some aspects, the adhesive sheet preferably has no lift in a bend adhesion test measured by the method described below, that is, a lift height of 0mm. The above bending adhesion test was carried out as follows: an adhesive sheet cut to a size of 10mm × 40mm was adhered to the convex side surface of an L-shaped adherend made of a stainless steel plate (specifically, SUS304 plate) by bending so that the longitudinal direction of the adhesive sheet was orthogonal to the bent portion (bending line) of the L-shaped adherend, and pressure-bonded by reciprocating a 2kg roller once, and after storing the sheet in an oven at 60 ℃ for 72 hours, the lift height of both ends of the adhesive sheet was evaluated. In the examples described later, the measurement was also performed by the same method. The pressure-sensitive adhesive sheet that does not cause lifting in the above bending and adhesion test is likely to maintain a good adhesion state in which lifting or peeling is unlikely to occur even when the pressure-sensitive adhesive sheet is used in a form in which the pressure-sensitive adhesive sheet is bent and adhered in accordance with the shape of an adherend.

The total thickness of the pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and is preferably set to about 6 μm or more, and from the viewpoint of the masking property of an adherend, it is preferably 25 μm or more, more preferably 40 μm or more, further preferably 60 μm or more, and particularly preferably 80 μm or more. The larger the total thickness of the pressure-sensitive adhesive sheet is, the more excellent the masking property of the adherend tends to be. The total thickness is preferably about 1.2mm or less, and from the viewpoint of adherend conformability, reduction in thickness, and weight reduction, it is preferably 200 μm or less, more preferably 150 μm or less, and still more preferably 120 μm or less. The pressure-sensitive adhesive sheet having the above-described total thickness tends to have excellent followability to an adherend. The total thickness of the pressure-sensitive adhesive sheet is the total thickness of the substrate and the pressure-sensitive adhesive layer, and does not include the thickness of a release liner described later.

< substrate >

The material constituting the substrate of the adhesive sheet is not particularly limited. As the substrate, for example, various resin films (plastic films) can be appropriately selected and used depending on the use of the adhesive sheet; foam sheets including foams such as polyurethane foam, polyethylene foam, and polychloroprene foam; woven and nonwoven fabrics (meaning including papers such as japanese paper and fine paper) obtained by blending or blending various fibrous materials (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate fibers, etc.); metal foils such as aluminum foil and copper foil; a complex thereof; and the like.

(resin layer)

The substrate preferably comprises a resin layer. The glossiness and total light transmittance of the back surface of the resin layer can be easily adjusted by a molding method, addition of a colorant, surface treatment, lamination of colored layers, and the like, and a pressure-sensitive adhesive sheet having a predetermined glossiness and total light transmittance can be easily obtained depending on a substrate having the resin layer. Further, by disposing the resin layer, the adhesive sheet can cover the adherend surface having irregularities while maintaining a flat back surface by the rigidity of the resin layer, and the irregularities on the adherend surface tend to be easily suppressed from appearing on the back surface of the adhesive sheet. In some aspects, the substrate may be composed of a resin layer. As the substrate, for example, a substrate composed of a resin layer having a single-layer structure can be used. In other embodiments, the substrate may be a laminate having a resin layer and an inorganic layer (preferably a metal layer). With this configuration, the resin layer can function as a protective layer for preventing the inorganic layer from being damaged by bending deformation or friction of the adhesive sheet. In this embodiment, the resin layer is disposed on the back side of the adhesive sheet with respect to the inorganic layer. The substrate is preferably a substrate containing a resin layer in addition to the inorganic layer from the viewpoint of durability and reliability of substrate characteristics such as gas barrier properties, and is preferably a substrate or an adhesive sheet from the viewpoint of handleability. Further, by disposing the resin layer on the surface of the substrate on the pressure-sensitive adhesive layer side, the anchoring property of the pressure-sensitive adhesive layer can be improved. In the case where the inorganic layer is formed by a vapor deposition method, a sputtering method, or the like, the resin layer can be used as a base for forming the inorganic layer.

The structure of the resin layer is not particularly limited. For example, the resin layer may be a resin layer containing voids such as a fiber aggregate such as a woven fabric or a nonwoven fabric, or a foam such as a polyethylene foam, or may be a resin layer (resin film) containing substantially no voids. From the viewpoint of thinning the pressure-sensitive adhesive sheet, a resin layer substantially free of voids can be preferably used. As a preferable example of the resin layer, a resin film (may be a plastic film) can be preferably used. Here, the resin film typically refers to a non-porous resin sheet, and is a concept different from, for example, a nonwoven fabric and a woven fabric (in other words, a concept other than a nonwoven fabric and a woven fabric). The resin film may be any of an unstretched film, a uniaxially stretched film, and a biaxially stretched film.

Examples of the resin material constituting the resin layer include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyolefin resins such as Polyethylene (PE) and polypropylene (PP); polyimide (PI); polyetheretherketone (PEEK); chlorine-containing polymers such as polyvinyl chloride (PVC) and polyvinylidene chloride; polyamide resins such as nylon and aramid; a polyurethane resin; a polystyrene-based resin; an acrylic resin; a fluorine-containing resin; a cellulose-based resin; a polycarbonate-series resin; and the like. These resins may be used singly or in combination of two or more. When two or more resins are used in combination, these resins may be used after blending or may be used separately. Both thermoplastic resins and thermosetting resins may be used. From the viewpoint of film formability and the like, a thermoplastic resin is more preferably used.

In some embodiments, the resin layer is preferably a resin layer formed using a resin material containing a polyester resin such as PET or a polyolefin resin such as PE or PP as a main component. The resin layer (resin film layer) formed of the resin material has appropriate stiffness and is suppressed in followability to irregularities on the surface of an adherend, and thus tends to have excellent covering properties with respect to the shape of the adherend. In addition, the resin layer may be non-moisture-permeable or low-moisture-permeable, and thus is suitable for applications where moisture is not desired to pass (sealing applications). In some preferred modes, a PET film may be preferably used as the resin layer. In other modes, a BOPP (biaxially oriented polypropylene) film obtained by forming a resin material containing PP as a main component into a film shape and then biaxially stretching the film may be used as the resin layer.

The resin layer may be transparent or translucent, or may be colored. The form of coloring of the resin layer is not particularly limited, and coloring (specifically, whitening) may be performed by forming voids such as bubbles in the layer, or coloring may be performed by using a coloring agent. In some embodiments, the resin layer comprises a colorant. In the embodiment where the substrate has the resin layer a and the resin layer B, it is preferable that at least the resin layer a disposed on the back side of the adhesive sheet contains a colorant. By including a colorant in the resin layer, the total light transmittance of the adhesive sheet can be reduced, and by selecting an appropriate colorant, both low transmittance and low gloss can be satisfactorily achieved. As the colorant, conventionally known pigments and dyes can be used. Examples of the pigment include inorganic pigments and organic pigments. The colorant is not particularly limited, and may be, for example, black, gray, white, red, blue, yellow, green, yellow-green, orange, violet, gold, silver, pearlescent, or the like. The coloring agent may be used singly or in combination of two or more.

A white colorant is a preferred example of the colorant. By using a white colorant, the total light transmittance can be reduced and the haze can be increased. Specific examples of the white colorant include: metal oxides such as titanium oxide (titanium dioxide such as rutile titanium dioxide and anatase titanium dioxide), zinc oxide, cerium oxide, aluminum oxide, silicon oxide, zirconium oxide, magnesium oxide, calcium oxide, tin oxide, barium oxide, cesium oxide, and yttrium oxide; carbonic acid compounds such as magnesium carbonate, calcium carbonate (light calcium carbonate, heavy calcium carbonate, etc.), barium carbonate, and zinc carbonate; hydroxides such as aluminum hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide; silicic acid compounds such as aluminum silicate, magnesium silicate, and calcium silicate; barium sulfate, calcium sulfate, barium stearate, zinc white, zinc sulfide, talc, clay, kaolin, titanium phosphate, mica, gypsum, white carbon, diatomaceous earth, bentonite, lithopone, zeolite, sericite, halloysite, and the like; and inorganic materials; or organic materials such as acrylic resins, polystyrene resins, polyurethane resins, amide resins, polycarbonate resins, polysiloxane resins, urea resins, melamine resins, and the like. The white colorant may be used singly or in combination of two or more.

As another preferred example of the colorant, a black colorant can be cited. By using the black colorant, the total light transmittance of the adhesive sheet can be effectively reduced while suppressing the glossiness of the back surface of the adhesive sheet low. Specific examples of the black coloring agent include: carbon black, graphite, aniline black, perylene black, cyanine black, titanium black, an inorganic pigment hematite, activated carbon, molybdenum disulfide, a chromium complex, an anthraquinone colorant, and the like. Among them, carbon black is particularly preferable. As the carbon black, what is generally called carbon black (furnace black, channel black, acetylene black, thermal black, lamp black, pine smoke, etc.) can be used without particular limitation. The black coloring agent may be used singly or in combination of two or more as appropriate. As the carbon black, surface-modified carbon black particles having a functional group such as a carboxyl group, an amino group, a sulfonic acid group, or a silicon-containing group (for example, an alkoxysilyl group or an alkylsilyl group) can be used. Such surface-modified carbon black particles are also called self-dispersible carbon black, and it is not necessary to add a dispersant or the amount of the dispersant added can be reduced. The carbon black particles may be used singly or in combination of two or more.

As the colorant, a particulate colorant (pigment) can be preferably used. In some preferred embodiments, a colorant (for example, a particulate black colorant such as carbon black) having an average particle diameter of about 1nm or more (for example, about 10nm or more) may be used. The average particle diameter is, for example, about 50nm or more, may be about 100nm or more, and may be about 300nm or more. The upper limit of the average particle diameter of the colorant is not particularly limited, and is, for example, about 5000nm or less, and may be about 3000nm or less. The average particle diameter of the colorant is preferably about 1000nm or less, and more preferably about 500nm or less, from the viewpoint of reducing the total light transmittance.

The average particle diameter of the colorant in the present specification means a volume average particle diameter, specifically, a particle diameter at 50% in a cumulative value in a particle size distribution measured by a particle size distribution measuring apparatus based on a laser light scattering/diffraction method (50% volume average particle diameter; hereinafter, may be abbreviated as "D" simply in some cases) ₅₀ ). As the measuring apparatus, for example, a product name "Microtrac M" manufactured by MicrotracBEL Co., ltdT3000II "or an equivalent thereof.

The content of the colorant is not particularly limited, and may be set to a known range. For example, the content of the colorant in the resin layer may be set to 0.1% by weight or more, and from the viewpoint of more effectively exerting the effect of adding the colorant, the content of the colorant is preferably 1% by weight or more, and preferably 5% by weight or more. The content of the colorant in the resin layer is, for example, about 30 wt% or less, 25 wt% or less, 20 wt% or less, or 15 wt% or less (for example, 10 wt% or less).

Various additives such as a filler (inorganic filler, organic filler, etc.), an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, and a plasticizer may be blended in the resin layer as necessary. The compounding ratio of each additive is less than about 30 wt% (e.g., less than about 20 wt%, typically less than about 10 wt%).

The number of resin layers contained in the substrate is not particularly limited, and may be one layer or two or more layers (for example, about 2 to about 5 layers). From the viewpoint of productivity and availability, the number of resin layers contained in the base material is preferably set to 1 to 3, and more preferably set to 1 or 2. When the substrate includes a plurality of resin layers, the materials and structures (thickness, presence or absence of voids, and the like) of these resin layers may be the same or different from each other.

The method of forming the resin layer is not particularly limited. The resin layer can be formed by a conventionally known general resin film forming method such as an extrusion molding method, an inflation molding method, a T-die casting method, a calender roll molding method, a wet casting method, or the like. The resin layer may be unstretched or subjected to stretching treatment such as uniaxial stretching or biaxial stretching.

The thickness of the resin layer is not particularly limited, and from the viewpoint of film formability, the thickness of the resin layer is preferably set to 1 μm or more, more preferably 5 μm or more, and may be 10 μm or more. In some preferred embodiments, the substrate has a resin layer having a thickness of 20 μm or more, more preferably 25 μm or more, and still more preferably 30 μm or more. By increasing the thickness of the resin layer, the adhesive sheet can cover the adherend surface having irregularities while maintaining a flat back surface by the rigidity of the resin layer, and the occurrence of irregularities on the adherend surface on the back surface of the adhesive sheet can be suppressed. In addition, in the configuration in which the total light transmittance of the resin layer is limited, good shielding properties are easily obtained by utilizing the low light transmittance of the resin layer. In some embodiments, the substrate may have a resin layer with a thickness of 40 μm or more (e.g., 50 μm or more). In the case of a substrate comprising a single resin layer or a substrate comprising a single resin layer and an inorganic layer, the resin layer having the above thickness can be preferably used. In the case where the substrate includes a plurality of resin layers, the thickness of each of the plurality of resin layers may be within the above range, but it is preferable to set the thickness of one of the plurality of resin layers within the above range.

The upper limit of the thickness of the resin layer is not particularly limited, and may be set to, for example, 300 μm or less, and is preferably set to 200 μm or less, and more preferably 100 μm or less, from the viewpoint of making the pressure-sensitive adhesive sheet thinner and lighter in weight. By appropriately limiting the thickness of the resin layer, the pressure-sensitive adhesive sheet having the resin layer can satisfactorily follow the shape of an adherend, and is less likely to be lifted or peeled off even in a system in which the pressure-sensitive adhesive sheet is folded and attached so as to span both surfaces of the adherend, for example. This is significant in view of the fact that, when a dent is formed at an end portion (typically, a corner portion) of an adherend, a pressure-sensitive adhesive sheet is attached so as to extend over both surfaces including the end portion, and thus masking is achieved in which the dent of the corner portion is not recognized. The thickness of the resin layer may be 80 μm or less, or 70 μm or less, or 55 μm or less, or 45 μm or less. When the substrate includes a plurality of resin layers, the thickness of at least one of the plurality of resin layers may be set within the above range, or the total thickness of the plurality of resin layers may be set within the above range. The upper limit of the thickness is preferably the total thickness of the plurality of resin layers.

The resin layer may be subjected to a conventional surface treatment such as a chemical treatment or a physical treatment such as a matting treatment, a corona discharge treatment, a crosslinking treatment, a chromic acid treatment, exposure to ozone, exposure to flame, exposure to a high-voltage electric shock, and an ionizing radiation treatment.

(inorganic layer)

In some preferred forms, the substrate comprises an inorganic layer. Since the base material has the inorganic layer, the total light transmittance of the pressure-sensitive adhesive sheet is reduced, and the adherend can be masked. The material and structure of the inorganic layer are not particularly limited, and may be selected according to the purpose and mode of use. In applications where gas barrier properties are required, it is advantageous that the inorganic layer is substantially non-porous. The inorganic layer is preferably an inorganic layer substantially composed of an inorganic material. For example, an inorganic layer in which 95% by weight or more (more preferably 98% by weight or more, and further preferably 99% by weight or more) is composed of an inorganic material is preferable. The number of inorganic layers contained in the substrate is not particularly limited, and may be 1 layer or 2 or more (for example, about 2 to about 5 layers). From the viewpoint of productivity and availability, the number of inorganic layers contained in the base material is preferably set to about 1 to about 3, and more preferably to 1 or 2. When the substrate includes a plurality of inorganic layers, the materials and structures (thickness, etc.) of these inorganic layers may be the same or different from each other.

As the inorganic material constituting the inorganic layer, for example, there can be used: metal materials such as simple substances of metals such as aluminum, copper, silver, iron, tin, nickel, cobalt, and chromium, and alloys thereof; inorganic compounds such as oxides, nitrides and fluorides of metals or semimetals such as silicon, aluminum, titanium, zirconium, tin and magnesium; and so on. Specific examples of the inorganic compound include: silicon oxide (SiO) _x Typically SiO ₂ ) Alumina (Al) ₂ O ₃ ) Silicon nitride (Si) ₃ N ₄ ) Silicon oxynitride (SiO) _x N _y ) Titanium dioxide (TiO) ₂ ) Indium tin oxide (ITO; indium Tin Oxide), and the like.

The metal material may be used as the inorganic layer in the form of a metal foil (e.g., aluminum foil) formed by a known method such as rolling with a rolling mill. Alternatively, for example, a metal material formed into a layer by a known film formation method such as a vacuum deposition method, a sputtering method, or a plating method may be used as the inorganic layer.

The inorganic compound can be typically used as the inorganic layer in the form of a thin film formed by a known method. As a method for forming the thin film of the inorganic compound, various vapor deposition methods can be used, and for example, a physical vapor deposition method (PVD) such as a vacuum vapor deposition method, a sputtering method, and an ion plating method, a chemical vapor deposition method (CVD), or the like can be used. The substrate may further include a resin layer on the vapor deposition layer. The resin layer may be a top coat layer provided for the purpose of protecting the vapor deposition layer or the like.

From the viewpoint of productivity, availability, and the like, it is preferable to use a metal layer substantially made of a metal material as the inorganic layer. The metal layer is also excellent in gas barrier properties, and even if it is bent in accordance with the shape of an adherend, for example, the bent state is easily maintained, and excellent in followability to the shape of the adherend. As the inorganic layer made of a metal material, for example, an inorganic layer made of aluminum or an aluminum alloy can be preferably used.

The upper limit of the thickness of the inorganic layer is not particularly limited. From the viewpoint of obtaining the following property to the shape of the adherend, it is advantageous to set the thickness of the inorganic layer to 50 μm or less (preferably 30 μm or less). From the viewpoint of making the pressure-sensitive adhesive sheet thinner and lighter in weight, the thickness of the inorganic layer is, for example, 20 μm or less, and the thickness of the inorganic layer is suitably 15 μm or less, preferably 13 μm or less, more preferably 11 μm or less, and still more preferably 9 μm or less. When the substrate includes a plurality of inorganic layers, the total thickness of the inorganic layers is preferably set within the above range. The thickness of the inorganic layer (e.g., a metal layer such as an aluminum foil) is suitably 1 μm or more, preferably 2 μm or more, and more preferably 5 μm or more, from the viewpoint of gas barrier properties, productivity, availability, and the like. In the form of forming the inorganic layer by vapor deposition of an inorganic compound, the thickness of the inorganic layer is suitably in the range of 1nm to 1000nm, preferably 2nm to 300nm, and may be in the range of 5nm or more and less than 100 nm.

In some preferred embodiments, a laminate of an inorganic layer and one or more resin layers is preferably used as the substrate. By having the inorganic layer, the total light transmittance of the pressure-sensitive adhesive sheet is reduced, and the adherend can be well masked. In addition, the presence of the inorganic layer makes it easy to follow the shape of the adherend, while in the case where the adherend surface has irregularities such as weld marks, impact marks, etc., the adhesive sheet acquires irregularities of the adherend, and thus the irregularities may appear on the back surface of the adhesive sheet, and as a result, the inability to mask the shape of the adherend surface may occur, and in this case, by using the laminate of the resin layer and the inorganic layer as a substrate, the adhesive sheet can cover the adherend surface having irregularities while maintaining a flat back surface, and the irregularities of the adherend surface can be suppressed from appearing on the back surface of the adhesive sheet, while enjoying the advantages of the inorganic layer, by virtue of the rigidity of the resin layer. In addition, by disposing the resin layer, a back surface having low glossiness can be easily obtained.

In the substrate having the resin layer and the inorganic layer, the resin layer and the inorganic layer are preferably joined. The bonding method is not particularly limited, and a method known in the art can be suitably employed. For example, there may be employed: a method (extrusion lamination method) in which a resin material for forming a resin layer is extruded in a molten state together with an inorganic layer (typically, a metal foil) obtained by molding in advance; a method of applying a solution or dispersion of a resin material for forming a resin layer on an inorganic layer obtained by molding in advance and drying the solution or dispersion; and so on. In addition, a method of vapor-depositing an inorganic layer on a resin layer obtained by molding in advance; and a method of joining the resin layer and the inorganic layer obtained by independent molding. The bonding may be performed by, for example, hot pressing. The resin layer and the inorganic layer may be joined by an adhesive layer or a pressure-sensitive adhesive layer.

The adhesive layer for bonding the resin layer and the inorganic layer may be a primer layer formed by applying a primer such as a primer to the resin layer. As the primer, for example, known primers in the art such as a urethane primer, an ester primer, an acrylic primer, and an isocyanate primer can be used. From the viewpoint of thinning and weight reduction of the pressure-sensitive adhesive sheet, the thickness of the primer layer is preferably 7 μm or less, and more preferably 5 μm or less. The lower limit of the thickness of the undercoat layer is not particularly limited, and may be set to, for example, 0.01 μm or more (typically 0.1 μm or more).

Preferred examples of the substrate used in the pressure-sensitive adhesive sheet disclosed herein include: a substrate comprising a laminate comprising an inorganic layer, a resin layer A and a resin layer B disposed so as to sandwich the inorganic layer. According to this structure, by the presence of the inorganic layer, there is excellent gas barrier property, and by the presence of the resin layer sandwiching the inorganic layer, for example, even if the thickness of the inorganic layer (e.g., aluminum layer) is thin, the inorganic layer can be effectively protected from bending, wrinkling, breaking, and the like. Thus, even when the pressure-sensitive adhesive sheet is exposed to various loads in a production process or the like or exposed to a severe environment for a long period of time during use, the properties such as gas barrier properties can be maintained for a long period of time. The resin layer a and the resin layer B constituting the substrate may be in direct contact with the inorganic layer, or an undercoat layer as described above may be present between the respective layers in order to obtain interlayer adhesion. The resin layer a is a resin layer disposed on the back surface (surface of the substrate) side of the adhesive sheet when viewed from the inorganic layer, and the resin layer B is a resin layer disposed on the adhesive layer side.

The inorganic layer may be a metal layer made of the metal material, and for example, an aluminum layer is preferable. The resin layer a and the resin layer B may be layers formed of the same material, and for example, the thermoplastic resins exemplified above may be used. These materials may be used singly or in combination of two or more. The resin layer a and the resin layer B may each have a laminated structure of two or more layers, but are preferably a single layer. Among them, the material forming the resin layer a and the resin layer B is preferably PET, PP, polystyrene, or the like, more preferably PET and PP, and still more preferably PET.

Thickness T of resin layer A _A Thickness T of resin layer B _B Ratio of (T) _A /T _B ) The above ratio (T) is not particularly limited _A /T _B ) It is preferable to set the value to 0.5 or more, preferably 1 or more, more preferably 1.5 or more, and still more preferably 2The content is equal to or more than 0, may be equal to or more than 3.0, may be equal to or more than 4.0, and may be equal to or more than 5.0. Ratio (T) above _A /T _B ) The larger the size, the more excellent effect of shielding an adherend is easily obtained. In addition, the ratio (T) is set _A /T _B ) The content is preferably about 10 or less, and may be 8.0 or less, 7.0 or less, or 5.0 or less. By combining the above ratio (T) _A /T _B ) Within the above range, both the adherend following property and the adherend shielding property can be satisfactorily achieved. Thickness T of resin layer A _A It is preferably about 10 μm or more, more preferably 20 μm or more, further preferably 25 μm or more, further preferably 30 μm or more (for example, 35 μm or more), and may be 40 μm or more (for example, 45 μm or more). T above _A It is preferably about 100 μm or less, more preferably 70 μm or less, further preferably 60 μm or less, and may be 50 μm or less, and may be 45 μm or less. Thickness T of resin layer B _B It is preferably about 1 μm or more, more preferably 3 μm or more, further preferably 5 μm or more, and further preferably 7 μm or more. T above _B It is preferably about 25 μm or less, more preferably 20 μm or less, further preferably 15 μm or less, and further preferably 12 μm or less (for example, 10 μm or less).

Thickness T of resin layer A _A Thickness T of resin layer B _B Of (total thickness T) _R ) Thickness T relative to the inorganic layer _I Ratio of (T) _R /T _I ) The ratio (T) is not particularly limited, and is determined from the viewpoint of the masking property of the adherend and the like _R /T _I ) It is preferable to set the value to 1 or more, and 3 or more, 4 or more, and 5 or more (for example, 7 or more) are possible. The ratio (T) is set in consideration of the following property to an adherend when the adhesive is folded and attached in accordance with the shape of the adherend _R /T _I ) It is preferable to set the value to 15 or less, preferably 10 or less, and may be 8 or less, or less than 5. The thickness T of the resin layer A _A Thickness T of resin layer B _B Sum (T) _R ) It is preferably set to 15 μm or more, more preferably 25 μm or more, further preferably 35 μm or more, further preferably 40 μm or more, and may be 45 μm or more, or may be 55 μm or more. Mixing the aboveT _R It is preferably set to about 100 μm or less, more preferably 80 μm or less, further preferably 70 μm or less, and may be 60 μm or less (for example, 50 μm or less). According to the base material having the above configuration, the followability to the shape of the adherend based on the presence of the inorganic layer and the adherend-shielding property by the rigidity and glossiness of the resin can be satisfactorily satisfied.

As a method of forming a laminate having an inorganic layer, a resin layer a and a resin layer B, as described above, a method of forming each layer into a film by a known method and dry-laminating the layers by forming the undercoat layer; a method of forming an inorganic layer in an adhered state on the resin layer a and dry laminating or extrusion laminating the resin layer B thereon, and the like.

(colored layer)

At least a part of the surface of the base material may be colored with a coloring layer (may be a printing layer such as printing). The adhesive sheet having such a colored layer is preferably used as an adhesive label such as a print label. The colored layer may be disposed on at least one surface of the base material.

The colored layer can be typically formed by coating a composition for forming a colored layer containing a coloring agent and a binder on a base film. As the colorant, a conventionally known pigment or dye can be used as well as the colorant that can be contained in the resin layer. As the binder, a material known in the field of coating or printing can be used without particular limitation. For example, there may be exemplified: polyurethane, phenolic resin, epoxy resin, urea melamine resin, polymethyl methacrylate, and the like. The composition for forming a colored layer may be, for example, a solvent type, an ultraviolet curing type, a thermosetting type, or the like. The colored layer can be formed by any means conventionally used for forming colored layers without any particular limitation. For example, a method of forming a colored layer (printed layer) by printing such as gravure printing, flexographic printing, and offset printing can be preferably employed.

The colored layer may have a single-layer structure composed of one layer as a whole, or may have a multi-layer structure including 2 or 3 or more sub-colored layers. The colored layer having a multilayer structure including 2 or more sub-colored layers can be formed by, for example, repeating application (e.g., printing) of the composition for forming a colored layer. The coloring agent contained in each of the sub-coloring layers may be the same in color or different in blending amount. In the colored layer for providing a masking property, it is particularly significant to form a multilayer structure from the viewpoint of preventing the occurrence of pinholes.

The thickness of the entire colored layer is preferably about 1 μm to about 10 μm, more preferably about 1 μm to about 7 μm, and may be set to about 1 μm to about 5 μm, for example. In the colored layer including 2 or more sub-colored layers, the thickness of each sub-colored layer is preferably about 1 μm to about 2 μm.

The number of layers constituting the substrate is not particularly limited, and may be, for example, a single layer structure of a resin layer, or a laminated structure of 2 or 3 or more layers like a laminated body of a resin layer and an inorganic layer, or may further include a surface layer called a top coat layer or a printing layer, or an adhesive layer or a primer layer for improving adhesiveness of each layer.

(characteristics of the substrate)

As the substrate, a substrate having a gloss (60 ° gloss) of 80GU or less on one surface (for example, the surface of the resin layer) can be preferably used. By using the above-described substrate having a surface with a limited glossiness, the adherend surface shape is less likely to become conspicuous. Further, when printing is performed on the surface of the base material, the printing property is good, and the printed matter tends to be easily visually recognized. In some preferred embodiments, the substrate surface has a gloss of 60GU or less, or may have a gloss of 50GU or less, or may have a gloss of 40GU or less, or may have a gloss of 30GU or less, or may have a gloss of 20GU or less, or may have a gloss of 15GU or less. The lower limit value of the gloss of the substrate surface is 0GU, and from the viewpoint of, for example, harmonization with the appearance of the psa sheet to be applied, the gloss of the substrate surface may be 1GU or more, may be 5GU or more, may be 12GU or more, may be 25GU or more, may be 35GU or more, and may be 45GU or more. Substrates with low gloss can be obtained, for example, by: selecting a material of the resin layer (resin film) serving as the substrate; a commercially available product using a base material (e.g., a resin film) having low glossiness; disposing a matte layer (for example, a matte layer containing organic particles or inorganic particles) on a surface of a substrate; the surface of the base material (for example, the surface of the resin layer) is subjected to surface treatment (also referred to as matting) such as embossing or sandblasting. The gloss (60 ° gloss) of the surface of the substrate was measured by the method described in the examples described later.

In some embodiments, the total light transmittance of the substrate is preferably 75% or less. By using a substrate satisfying the above characteristics, the pressure-sensitive adhesive sheet has a masking property, and unevenness of an adherend is not easily visually recognized through the pressure-sensitive adhesive sheet. The total light transmittance of the substrate is preferably 60% or less, more preferably 40% or less, and still more preferably 20% or less, and in some preferred embodiments, the total light transmittance of the substrate is 10% or less, and may be 3% or less, or less than 1%, or less than 0.1% from the viewpoint of improving the shielding property of an adherend. The lower limit of the total light transmittance of the substrate is not particularly limited, and may be substantially 0%, that is, not more than the detection limit, or not less than 0.01%, for example, not less than 0.1%, or not less than 1.0%. In some embodiments, the total light transmittance of the substrate may be 5% or more, may be 9% or more, and may be 12% or more (for example, 15% or more). By providing an inorganic layer, containing a colorant in the resin layer, forming voids, and the like, the total light transmittance of the base material can be reduced. In other embodiments, the total light transmittance of the substrate can be greater than 75%, for example, can be greater than 90%. For example, where the adhesive layer has a low total light transmittance, the substrate may have a relatively high total light transmittance as described above. The total light transmittance of the substrate was measured by the method described in the examples described below.

In some preferred embodiments, the haze of the substrate is 70% or more, more preferably 80% or more, further preferably 90% or more, and may be 95% or more, or may be 99% or more. The higher the haze of the substrate, the more the masking property of the adherend tends to be improved. The haze of the substrate refers to the haze measured on one surface of the substrate (specifically, the surface on the back side of the adhesive sheet). The upper limit of the haze is 100%, and in some embodiments, the haze may be 99% or less, or 90% or less, or 85% or less. In other embodiments, the haze of the substrate may be, for example, 1% or more, 10% or more, 30% or more, or 50% or more. Substrates with high haze can be obtained, for example, by: selecting a material of the resin layer (resin film) serving as the substrate; a commercially available product using a base material (e.g., resin film) having high haze; disposing a surface layer (e.g., a layer containing organic particles or inorganic particles) on a surface of a substrate; the surface of the substrate (for example, the surface of the resin layer) is subjected to surface treatment such as embossing or sandblasting. The haze of the base material was measured by the method described in the examples described later.

The arithmetic average roughness of the substrate surface is not particularly limited, and may be 10000nm or less, for example. In some preferred embodiments, the arithmetic mean roughness of the surface of the base material is 3000nm or less, more preferably 1500nm or less, still more preferably 1000nm or less, particularly preferably 800nm or less, and may be 500nm or less, or 300nm or less. The smaller the above arithmetic average roughness, the better the surface state of the substrate surface. For example, in the case of printing on the surface of a substrate, the printing property is good, and the printing tends to be easily visually recognized. The arithmetic average roughness of the surface of the base material is, for example, 10nm or more. In some preferred embodiments, the arithmetic average roughness of the surface of the base material is 50nm or more, more preferably 100nm or more, still more preferably 150nm or more, and particularly preferably 200nm or more (for example, 250nm or more). By disposing the surface having the arithmetic mean roughness on the back surface side of the pressure-sensitive adhesive sheet, reflection of light on the back surface of the pressure-sensitive adhesive sheet is easily suppressed, and unevenness on the back surface due to the surface shape of the adherend tends not to be easily conspicuous. In some other embodiments, the arithmetic average roughness of the surface of the base material may be 350nm or more, 450nm or more, and 550nm or more. The arithmetic mean roughness of the substrate surface can be adjusted as follows: selecting a substrate material; a method of molding a substrate (typically, a resin layer); a commercially available product using a base material (e.g., a resin film) having a predetermined arithmetic mean roughness; surface treatment such as embossing or sandblasting is performed on the surface of the base material (for example, the surface of the resin layer); and so on. The arithmetic mean roughness of the surface of the base material can be measured by the method described in the examples described later.

(thickness of base)

The thickness of the base material is not particularly limited. From the viewpoint of productivity and handleability of the adhesive sheet, a thickness of the substrate is preferably about 3 μm or more, and a thickness of the substrate is preferably about 5 μm or more (for example, 10 μm or more). The thickness of the substrate is preferably 20 μm or more, more preferably 40 μm or more, further preferably 60 μm or more, and particularly preferably 70 μm or more. The larger the thickness of the base material is, the more excellent the shielding property and the gas barrier property of the surface shape of the adherend tend to be. The upper limit of the thickness of the substrate is, for example, about 1mm or less, and may be about 300 μm or less, and the thickness of the substrate is preferably about 200 μm or less (for example, 150 μm or less). The thickness of the substrate is preferably 100 μm or less, more preferably 80 μm or less, and may be 70 μm or less, for example, from the viewpoint of adherend-following ability of the pressure-sensitive adhesive sheet, reduction in thickness, and weight reduction.

The surface of the substrate on the adhesive layer side may be subjected to a conventional surface treatment such as a chemical treatment or a physical treatment such as a matting treatment, a corona discharge treatment, a crosslinking treatment, a chromic acid treatment, exposure to ozone, exposure to a flame, exposure to a high-voltage electric shock, an ionizing radiation treatment, or the like. Further, a primer layer formed by applying a primer such as a primer to the resin layer may be disposed on the surface of the substrate on the pressure-sensitive adhesive layer side. As the primer, for example, known primers in the art such as urethane, ester, acrylic, and isocyanate can be used. From the viewpoint of thinning and weight reduction of the pressure-sensitive adhesive sheet, the thickness of the primer layer is preferably 7 μm or less, more preferably 5 μm or less, and still more preferably 3 μm or less.

< adhesive layer >

(base Polymer)

In the technique disclosed herein, the kind of the adhesive constituting the adhesive layer is not particularly limited. The pressure-sensitive adhesive may contain, as a base polymer, one or more of various rubbery polymers known in the pressure-sensitive adhesive field, such as rubber-based polymers, acrylic polymers, polyester-based polymers, urethane-based polymers, polyether-based polymers, silicone-based polymers, polyamide-based polymers, and fluorine-containing polymers. From the viewpoint of gas barrier properties and reduction in gas generation amount, a rubber-based adhesive containing a rubber-based polymer as a base polymer or an adhesive containing an acrylic polymer as a base polymer can be preferably used. As another example, an adhesive containing a rubber-based polymer and an acrylic polymer as a base polymer can be cited. When the pressure-sensitive adhesive sheet disclosed herein is used in a magnetic disk device, it is preferable that the pressure-sensitive adhesive sheet does not substantially contain a silicone polymer that may generate a siloxane gas.

Hereinafter, a pressure-sensitive adhesive sheet having an acrylic pressure-sensitive adhesive layer and a pressure-sensitive adhesive sheet having a rubber pressure-sensitive adhesive layer will be mainly described, but the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet disclosed herein is not intended to be limited to a pressure-sensitive adhesive layer composed of an acrylic pressure-sensitive adhesive or a pressure-sensitive adhesive layer composed of a rubber pressure-sensitive adhesive.

The "base polymer" of the pressure-sensitive adhesive is a main component (i.e., a component accounting for more than 50% by weight of the rubbery polymer) of the rubbery polymer (a polymer exhibiting rubber elasticity in a temperature range around room temperature) contained in the pressure-sensitive adhesive.

(acrylic Polymer)

In some aspects of the technology disclosed herein, the adhesive layer may be an acrylic adhesive layer comprising an acrylic polymer as a base polymer. The acrylic polymer is preferably a polymer of a monomer raw material containing an alkyl (meth) acrylate as a main monomer and may further contain a secondary monomer copolymerizable with the main monomer. Here, the main monomer means a component contained in an amount of more than 50% by weight in the above monomer raw materials.

In the present specification, "(meth) acryloyl group" means an acryloyl group and a methacryloyl group in a general manner. Likewise, "(meth) acrylate" is a meaning that generically represents acrylate and methacrylate, and "(meth) acrylic acid" is a meaning that generically represents acrylic acid and methacrylic acid.

As the alkyl (meth) acrylate, for example, a compound represented by the following formula (1) can be suitably used.

CH ₂ ＝C(R ¹ )COOR ² (1)

Here, R in the above formula (1) ¹ Is a hydrogen atom or a methyl group. In addition, R ² Is a chain alkyl group having 1 to 20 carbon atoms (hereinafter, such a range of carbon atoms may be referred to as "C _1-20 "). From the viewpoint of storage modulus, adhesive properties, etc. of the adhesive, R is preferred ² Is C _1-18 The alkyl (meth) acrylate of (meth) acrylic acid chain alkyl group of (1), more preferably R ² Is C _2-14 The alkyl (meth) acrylate of (meth) acrylic acid chain alkyl group of (1), R is more preferable ² Is C _4-12 An alkyl (meth) acrylate having a chain alkyl group of (1). Among them, alkyl acrylate is preferably used as a main monomer. The chain (also referred to as acyclic) alkyl group includes a linear alkyl group and a branched alkyl group.

As R ² Is C _1-20 Examples of the alkyl (meth) acrylate of the chain alkyl group include: methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, nonadecyl (meth) acrylate, dodecyl (meth) acrylateEicosyl esters of acids, and the like. These alkyl (meth) acrylates may be used singly or in combination of two or more.

From the viewpoint of increasing the polymerization rate during the synthesis of the acrylic polymer and thereby facilitating the reduction in the amount of generated heating gas, it is preferable to use, as a main monomer for forming the acrylic polymer, an alkyl acrylate in which the chain alkyl group has 9 or less carbon atoms. For example, at least one of 2-ethylhexyl acrylate (2 EHA) and n-Butyl Acrylate (BA) is preferably used. The acrylic polymer may be a polymer obtained by using BA alone as a main monomer, may be a polymer obtained by using 2EHA alone as a main monomer, or may be a polymer obtained by using BA and 2EHA alone as main monomers. As a preferable example, an acrylic polymer obtained by using BA alone as a main monomer is cited. In some embodiments, the content of BA in all monomer components forming the acrylic polymer may be, for example, 50 wt% or more, or 70 wt% or more, or 85 wt% or more, or 90 wt% or more.

The content ratio of the alkyl (meth) acrylate as a main monomer in all monomer components forming the acrylic polymer is preferably 60% by weight or more, more preferably 70% by weight or more, further preferably 75% by weight or more, and may be 85% by weight or more, for example. The upper limit of the proportion of the alkyl (meth) acrylate is not particularly limited. From the viewpoint of improving cohesion, repulsion resistance, and the like, the proportion of the alkyl (meth) acrylate is preferably set to less than 98% by weight, and more preferably less than 96% by weight.

Examples of the secondary monomer that can introduce a functional group capable of serving as a crosslinking base point into the acrylic polymer or can contribute to improvement of the adhesive strength include: carboxyl group-containing monomers, hydroxyl group-containing monomers, acid anhydride group-containing monomers, amide group-containing monomers, amino group-containing monomers, imide group-containing monomers, epoxy group-containing monomers, (meth) acryloyl morpholine, vinyl ethers, and the like. Among them, hydroxyl group-containing monomers and carboxyl group-containing monomers are preferable.

As a preferable example of the acrylic polymer in the technology disclosed herein, there is an acrylic polymer obtained by copolymerizing the carboxyl group-containing monomer as the secondary monomer. Examples of the carboxyl group-containing monomer include: acrylic Acid (AA), methacrylic acid (MAA), carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, and the like. Among them, AA and MAA are preferable.

The content of the carboxyl group-containing monomer in the entire monomer components may be, for example, more than about 1% by weight, more than 3% by weight, more than 5% by weight, or more than 6% by weight. The content of the carboxyl group-containing monomer in the whole monomer components is usually suitably less than 15% by weight, and may be less than 12% by weight, less than 10% by weight, or less than 8% by weight.

The acrylic polymer in the art disclosed herein may be copolymerized with a hydroxyl group-containing monomer as the above-mentioned secondary monomer. Examples of hydroxyl group-containing 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; polypropylene glycol mono (meth) acrylate; n-hydroxyethyl (meth) acrylamide, and the like. Among these, preferable hydroxyl group-containing monomers include hydroxyalkyl (meth) acrylates in which the alkyl group is a linear alkyl group having 2 to 4 carbon atoms. For example, 2-hydroxyethyl acrylate (HEA), 4-hydroxybutyl acrylate (4 HBA), and the like can be preferably used.

The content of the hydroxyl group-containing monomer in the entire monomer components may be, for example, about 0.01 wt% or more, may be 0.03 wt% or more, and may be 0.05 wt% or more. The content of the hydroxyl group-containing monomer in the entire monomer components may be, for example, 10 wt% or less, or 5 wt% or less, or 1 wt% or less, or 0.5 wt% or less, or 0.2 wt% or less.

The above-mentioned secondary monomers may be used singly or in combination of two or more. From the viewpoint of cohesive force and the like, the proportion of the secondary monomer in the total monomer components is preferably set to be usually more than 1% by weight, preferably more than 2% by weight, more preferably more than 5% by weight, and may be more than 6% by weight. The upper limit of the proportion of the secondary monomer in the total monomer components is preferably set to about 30% by weight or less (for example, about 25% by weight or less), and may be 15% by weight or less, or may be 10% by weight or less.

As a preferable example of the acrylic polymer in the technology disclosed herein, there is an acrylic polymer obtained by using a hydroxyl group-containing monomer and a carboxyl group-containing monomer as the secondary monomers in combination. In the case of using the hydroxyl group-containing monomer and the carboxyl group-containing monomer in combination, the ratio of the amount of the carboxyl group-containing monomer to the amount of the hydroxyl group-containing monomer may be, for example, more than 3 times, more than 10 times, more than 30 times, and more than 50 times on a weight basis. By using a small amount of the hydroxyl group-containing monomer in combination with the carboxyl group-containing monomer in this manner, a pressure-sensitive adhesive sheet having both adhesive force and cohesive force can be suitably realized. The pressure-sensitive adhesive sheet can exhibit excellent repulsion resistance in a manner of being folded and adhered in accordance with the shape of an adherend. Although not particularly limited, the ratio of the amount of the carboxyl group-containing monomer to the amount of the hydroxyl group-containing monomer may be, for example, 1000 times or less, 500 times or less, 300 times or less, or 100 times or less.

As the monomer component constituting the acrylic polymer, other copolymerization components than the above-mentioned secondary monomers may be used for the purpose of improving the cohesive force of the acrylic polymer, adjusting Tg of the acrylic polymer, and the like. Examples of the copolymerization component include: vinyl ester monomers such as vinyl acetate; aromatic vinyl compounds such as styrene; cycloalkyl (meth) acrylates such as cyclohexyl (meth) acrylate; aromatic ring-containing (meth) acrylates such as aryl (meth) acrylates; olefin monomers such as ethylene, propylene, isoprene, butadiene, and isobutylene; polyfunctional monomers having two or more (e.g., three or more) polymerizable functional groups (e.g., (meth) acryloyl groups) in one molecule, such as 1, 6-hexanediol di (meth) acrylate; and so on. The amount of the other copolymerizable component may be appropriately selected depending on the purpose and use, and is not particularly limited. In general, the amount of the other copolymerizable component is preferably set to 10% by weight or less (for example, 1% by weight or less) of the total monomer components.

It is appropriate to design the composition of the monomer components constituting the acrylic polymer so that the glass transition temperature (Tg) of the acrylic polymer is about-5 ℃ or lower (for example, about-75 ℃ or higher and about-5 ℃ or lower). Here, the Tg of the acrylic polymer is the Tg obtained by the Fox equation based on the composition of the monomer component. The Fox formula is a relational expression between Tg of a copolymer and glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of monomers constituting the copolymer, as shown below.

1/Tg＝Σ(Wi/Tgi)

In the above Fox formula, tg represents the glass transition temperature (unit: K) of the copolymer, wi represents the weight fraction of the monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi represents the glass transition temperature (unit: K) of a homopolymer of the monomer i.

As the glass transition temperature of the homopolymer used for the calculation of Tg, the value described in the publicly known data is used. For example, for the monomers listed below, the following values are used as the glass transition temperatures of the homopolymers of the monomers.

For the glass transition temperature of a homopolymer of a monomer other than the above exemplified monomers, the values described in "handbook of polymers" (3 rd edition, john Wiley & Sons, inc., 1989) were used. The highest value is used for the monomers described in this document as having various values.

Although not particularly limited, the Tg of the acrylic polymer is favorably about-10 ℃ or lower, preferably about-15 ℃ or lower, more preferably-20 ℃ or lower, and still more preferably-35 ℃ or lower from the viewpoint of tackiness. From the viewpoint of cohesive force of the pressure-sensitive adhesive layer, the acrylic polymer advantageously has a Tg of about-75 ℃ or higher, preferably about-70 ℃ or higher, more preferably about-55 ℃ or higher, and may be higher than-50 ℃. 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).

The Mw of the acrylic polymer is not particularly limited, and may be, for example, about 10X 10 ⁴ Above and about 500X 10 ⁴ The following. The Mw is about 30X 10 from the viewpoint of cohesive force and reduction in gas generation amount ⁴ The above is advantageous, preferably about 50X 10 ⁴ Above (e.g., about 70X 10) ⁴ Above). In some preferred forms, the acrylic polymer has a Mw of about 90X 10 ⁴ Above, more preferably about 120X 10 ⁴ Above, more preferably about 140 × 10 ⁴ The above. According to the pressure-sensitive adhesive having Mw as described above, a favorable repulsion resistance can be exhibited in the form of folding and attaching the pressure-sensitive adhesive sheet in accordance with the shape of the adherend. Further, the Mw is usually about 300X 10 from the viewpoint of adhesiveness ⁴ The following are suitable, and about 200X 10 is preferable ⁴ Hereinafter, more preferably about 170 × 10 ⁴ The following.

The Mw is determined from a value obtained by Gel Permeation Chromatography (GPC) in terms of standard polystyrene. As the GPC apparatus, for example, the model name "HLC-8320GPC" (column: TSKgel GMH-H (S), manufactured by Tosoh corporation) can be used.

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 a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, and a photopolymerization method, can be suitably used. For example, the solution polymerization method can be preferably employed. As a method of supplying the monomer in the case of performing the solution polymerization, a one-shot method of supplying all the monomer raw materials at once, a continuous supply (dropwise) method, a stepwise supply (dropwise) method, and the like can be suitably employed. From the viewpoint of facilitating formation of a pressure-sensitive adhesive layer with a small amount of generated heating gas, it is preferable to set the polymerization conditions (polymerization time, polymerization temperature, etc.) so as to obtain a polymerization reaction liquid with a small amount of unreacted monomer.

The polymerization temperature may be appropriately selected depending on the kind of the monomer and the polymerization solvent used, the kind of the polymerization initiator, and the like, and may be set to, for example, about 20 ℃ to about 170 ℃ (more specifically, about 40 ℃ to about 140 ℃). In some embodiments, the polymerization temperature can be set to about 75 ℃ or less (more preferably about 65 ℃ or less, e.g., from about 45 ℃ to about 65 ℃). The polymerization may be carried out at this polymerization temperature and then the system may be held at a higher temperature (e.g., a temperature from about 5 ℃ to about 35 ℃ higher or from about 10 ℃ to about 20 ℃ higher) for, for example, from about 15 minutes to about 6 hours, preferably from about 30 minutes to about 3 hours, to reduce unreacted monomer.

The solvent (polymerization solvent) used for the solution polymerization can be appropriately selected from conventionally known organic solvents. For example, aromatic compounds (for example, aromatic hydrocarbons) selected from toluene, xylene, and the like; acetic acid esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; lower alcohols such as methanol, ethanol and isopropanol; one or a mixture of two or more solvents selected from ketones such as methyl ethyl ketone. From the viewpoint of easily obtaining a pressure-sensitive adhesive sheet with a small amount of generated heating gas, it is preferable to use a polymerization solvent which is easily volatilized and removed. For example, a single solvent (ethyl acetate, etc.) having a boiling point of less than 100 ℃, less than 90 ℃ or less than 80 ℃ or a mixed solvent having a composition that achieves the above boiling point may be preferably used.

The initiator used for the polymerization may be appropriately selected from conventionally known polymerization initiators according to the polymerization method. Examples thereof include: azo polymerization initiators such as 2,2' -azobisisobutyronitrile, 2' -azobis (2-methylbutyronitrile), dimethyl 2,2' -azobis (2-methylpropionate), 4' -azobis (4-cyanovaleric acid), azobisisovaleronitrile, 2' -azobis (2-amidinopropane) dihydrochloride, 2' -azobis [2- (5-methyl-2-imidazolin-2-yl) propane ] dihydrochloride, 2' -azobis (2-methylpropionamidine) disulfide, and 2,2' -azobis (N, N ' -dimethyleneisobutylamidine) dihydrochloride; persulfates such as potassium persulfate; peroxide polymerization initiators such as dibenzoyl peroxide; substituted ethane initiators such as phenyl-substituted ethane; an aromatic carbonyl compound; a redox initiator obtained by combining a peroxide and a reducing agent; and so on. The polymerization initiator may be used singly or in combination of two or more. The amount of the polymerization initiator to be used may be a usual amount, and may be selected from the range of about 0.005 to about 1 part by weight (usually about 0.01 to about 1 part by weight) relative to 100 parts by weight of the monomer component, for example.

In the technique disclosed herein, an azo-based polymerization initiator can be preferably used as the polymerization initiator. In the case of radical polymerization using an azo polymerization initiator, there is an advantage that the decomposition product of the polymerization initiator is less likely to remain in the pressure-sensitive adhesive composition as a gas component generated by heating and the generation of gas is more likely to be suppressed, as compared with the case of polymerization using an organic peroxide or another radical polymerization initiator. As a polymerization initiator, it is particularly desirable to avoid the use of organic peroxides. The acrylic polymer in the technique disclosed herein is preferably synthesized using, for example, only one or two or more azo initiators as a polymerization initiator.

(rubber Polymer)

In some embodiments, the adhesive layer may be a rubber-based adhesive layer formed of an adhesive composition having a rubber-based polymer as a base polymer. Examples of the base polymer include: natural rubber; styrene-butadiene rubber (SBR); a polyisoprene; butene polymers containing butene (i.e., 1-butene, cis-2-butene or trans-2-butene) and/or 2-methylpropene (isobutylene) as main monomers; examples of the ase:Sub>A-B-ase:Sub>A type block copolymer rubber and the hydrogenated product thereof include various rubber-based polymers such as styrene-butadiene-styrene block copolymer rubber (SBS), styrene-isoprene-styrene block copolymer rubber (SIS), styrene-isobutylene-styrene block copolymer rubber (SIBS), styrene-vinyl/isoprene-styrene block copolymer rubber (SVIS), styrene-ethylene-butylene-styrene block copolymer rubber (SEBS) which is ase:Sub>A hydrogenated product of SBS, styrene-ethylene-propylene-styrene block copolymer rubber (SEPS) which is ase:Sub>A hydrogenated product of SIS, and styrene-isoprene-propylene-styrene block copolymer rubber (SIPS). These rubber-like polymers may be used singly or in combination of two or more.

Preferable examples of the butene-based polymer include isobutylene-based polymers. Isobutylene polymers have a low mobility of the main chain in their molecular structure. Therefore, the pressure-sensitive adhesive layer (isobutylene-based pressure-sensitive adhesive layer) containing the isobutylene-based polymer as a base polymer can be a pressure-sensitive adhesive layer having a small gas diffusion property. This can be advantageous from the following point of view: inhibiting moisture (water vapor) from penetrating into the interior of the electronic device through the adhesive layer; suppressing leakage of a gas in an electronic device in which the gas is enclosed (for example, a magnetic disk device in which helium gas is enclosed in a casing); and the like. In addition, the pressure-sensitive adhesive layer has a good elastic modulus and tends to have excellent removability. Specific examples of the isobutylene polymer include polyisobutylene, a copolymer of isobutylene and isoprene (butyl rubber), and the like.

The monomer component for polymerization to give the rubber-like polymer disclosed herein comprises one or more monomers selected from the group consisting of butene, isobutylene, isoprene, butadiene, styrene, ethylene and propylene. The rubber-based polymer is obtained by polymerizing one or two or more of the above-exemplified monomers. The monomer component for polymerizing to obtain the rubber-based polymer disclosed herein typically contains one or two or more of the above-mentioned monomers in a proportion of 50% by weight or more (for example, 50% by weight to 100% by weight), preferably 75% by weight or more, more preferably 85% by weight or more, and further preferably 90% by weight or more (for example, 95% by weight or more). The content of the monomer in the total monomer components may be 99% by weight or more. Some preferred modes of the rubber-like polymer are polymers obtained by polymerizing one or two or more monomers selected from the group consisting of isobutylene, isoprene and butylene. The content of styrene in the monomer component is preferably less than 10% by weight, more preferably less than 1% by weight, from the viewpoint of reducing the amount of gas generated (particularly, suppressing the generation of gas that can reduce the durability, reliability, or operating accuracy of electronic equipment such as a magnetic disk device). The technique disclosed herein can be preferably carried out in such a manner that the monomer component substantially does not contain styrene.

In some preferred embodiments, more than 50% by weight (for example, 70% by weight or more, and further 85% by weight or more) of the polymer components contained in the adhesive is an isobutylene polymer. The adhesive may contain substantially no polymer component other than the isobutylene polymer. In the adhesive, for example, the proportion of the polymer other than the isobutylene-based polymer in the polymer component may be 1% by weight or less or the detection limit or less.

In the present specification, the term "isobutylene polymer" is a term including not only isobutylene homopolymer (homopolyisobutylene) but also a copolymer having isobutylene as a main monomer. The copolymer includes a copolymer in which isobutylene is a component in the largest proportion among monomers constituting the isobutylene-based polymer. Typically, the copolymer may contain isobutylene in an amount of more than 50% by weight, and more preferably 70% by weight or more of the components in the monomer. The copolymer may be, for example, a copolymer of isobutylene and butene (n-butene), a copolymer of isobutylene and isoprene (butyl rubber), a vulcanized product thereof, a modified product thereof, or the like. Examples of the copolymer include: butyl rubbers such as ordinary butyl rubber, chlorinated butyl rubber, brominated butyl rubber, and partially crosslinked butyl rubber. Examples of the vulcanized product and modified product include those modified with a functional group such as a hydroxyl group, a carboxyl group, an amino group, or an epoxy group. From the viewpoint of gas barrier properties, reduction in gas generation amount, adhesion, and the like, examples of isobutylene polymers that can be preferably used include: polyisobutylene, copolymers of isobutylene and isoprene (butyl rubber), and the like. The copolymer may be, for example, a copolymer (for example, an isobutylene/isoprene copolymer) in which a copolymerization ratio of monomers (isoprene and the like) other than isobutylene is less than 30 mol%.

In the present specification, "polyisobutylene" means polyisobutylene having a copolymerization ratio of monomers other than isobutylene of 10 wt% or less (preferably 5 wt% or less). Among them, homopolyisobutylene is preferable.

The molecular weight of the isobutylene polymer is not particularly limited, and for example, a weight average molecular weight (Mw) of about 5X 10 can be appropriately selected and used ⁴ Above (preferably about 15X 10) ⁴ Above, e.g. about 30X 10 ⁴ The above) isobutylene-based polymers. The upper limit of the Mw is not particularly limited, and may be about 150X 10 ⁴ The following (preferably about 100X 10) ⁴ Below, for example, about 80X 10 ⁴ Below). A plurality of isobutylene polymers having different Mw may be used in combination. When Mw is within the above range, the elastic modulus of the adhesive can be easily adjusted to a preferable range, and a good cohesive force can be easily exerted.

Although not particularly limited, as the polyisobutylene, polyisobutylene having a dispersity (Mw/Mn) expressed by the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in the range of 3 to 7 (more preferably 3 to 6, for example, 3.5 to 5.5) can be preferably used. It is also possible to use a plurality of polyisobutenes having different Mw/Mn values in combination.

Here, mw and Mn of the isobutylene polymer are values in terms of polystyrene determined by Gel Permeation Chromatography (GPC) measurement. As the GPC measurement device, for example, the model "HLC-8120GPC" manufactured by Tosoh (TOSOH) corporation can be used.

In the case of using butyl rubber, the molecular weight thereof is not particularly limited. For example, mw of 5X 10 can be appropriately selected and used ⁴ ～100×10 ⁴ Butyl rubber within the range of (a). In view of the balance between the formability of the pressure-sensitive adhesive layer and the adhesiveness to an adherend (adhesive force), the Mw of the butyl rubber is preferably 10 × 10 ⁴ Above, more preferably 15 × 10 ⁴ Above, in addition, excelIs selected as 100 × 10 ⁴ Hereinafter, more preferably 80 × 10 ⁴ The following. It is also possible to use a plurality of butyl rubbers having different Mw from each other in combination.

Although not particularly limited, the butyl rubber is preferably one having a dispersity (Mw/Mn) in the range of 3 to 8, and more preferably one having a dispersity (Mw/Mn) in the range of 4 to 7. It is also possible to use a plurality of butyl rubbers having different Mw/Mn from each other in combination. The Mw and Mn of the butyl rubber can be determined by GPC measurement similar to polyisobutylene.

The mooney viscosity of the butyl rubber is not particularly limited. For example, mooney viscosity ML can be used ₁₊₈ A butyl rubber having a temperature of 10 to 100 ℃ at 125 ℃. In view of the balance of the formability of the pressure-sensitive adhesive layer and the adhesiveness to an adherend (adhesive force), the mooney viscosity ML is preferably ₁₊₈ A butyl rubber having a temperature (125 ℃) of 15 to 80, more preferably a Mooney viscosity ML ₁₊₈ A butyl rubber having a temperature (125 ℃) of 30 to 70 (for example, 40 to 60).

Some preferred embodiments of the rubber-based adhesive layer include a rubber-based polymer a and a rubber-based polymer B as base polymers. Preferably, both the rubber-based polymer a and the rubber-based polymer B are isobutylene-based polymers. More preferably, the rubber-based polymer a is an isobutylene-based polymer obtained by polymerizing isobutylene in a proportion of 50% by weight or more (for example, 70% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more), and is typically polyisobutylene. The rubber-based polymer B is an isobutylene-based polymer (isobutylene-based copolymer) obtained by copolymerizing isobutylene and isoprene, and typically is a copolymer of isobutylene and isoprene. In this copolymer, the total amount of isobutylene and isoprene as monomer components is typically 50% by weight or more (for example, 70% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more) of the total monomer components. By using the rubber-based polymer a and the rubber-based polymer B, the elastic modulus of the pressure-sensitive adhesive layer tends to be in a preferable range, and more excellent gas barrier properties tend to be obtained.

When the rubber-based polymer A and the rubber-based polymer B are used, they may beTo set their mix ratios appropriately so that the desired performance is achieved. Rubber Polymer A (P) _A ) Relative to the rubber-like polymer B (P) _B ) Weight ratio (P) _A /P _B ) For example, it is set to 95/5 to 5/95, preferably 90/10 to 10/90, more preferably 80/20 to 20/80, further preferably 70/30 to 30/70, and particularly preferably 60/40 to 40/60.

In some preferred embodiments, the dispersity (Mw/Mn) of the entire base polymer is 3 or more, and more preferably 4 or more. The adhesive containing the base polymer can easily achieve both of adhesion and offset resistance. The elastic modulus of the pressure-sensitive adhesive layer is also in an appropriate range, and good gas barrier properties tend to be easily obtained. By adjusting the Mw/Mn to a predetermined value or more, a binder having a low solution viscosity can be produced although the Mw is high. The dispersity of the entire base polymer may be 5 or more, 6 or more, and further 7 or more. The upper limit of the degree of dispersion of the base polymer as a whole is not particularly limited, but is preferably 10 or less (for example, 8 or less).

The technique disclosed herein can be preferably implemented in a mode of having an adhesive layer (for example, a rubber-based adhesive layer) containing an adhesive (uncrosslinked adhesive) in which the base polymer is an uncrosslinked base polymer. Here, the "pressure-sensitive adhesive layer containing an uncrosslinked pressure-sensitive adhesive" refers to a pressure-sensitive adhesive layer in which no intentional treatment (i.e., crosslinking treatment, for example, addition of a crosslinking agent) for forming a chemical bond between base polymers is performed in forming the pressure-sensitive adhesive layer.

The rubber-based adhesive layer in the technique disclosed herein contains any one of the rubber-based polymers a described above as a base polymer, and may further contain a polymer C having a molecular weight smaller than that of the polymer a. As molecular weight for comparison with polymer a, mw may be used. The Mn of the polymer C is preferably 1000 or more. This can suppress gas generation and can enjoy the effects of the polymer C. In addition, the cohesive force can be maintained at a level that is practically used. The Mn of the polymer C is preferably 2000 or more, and more preferably 2500 or more. In addition, as for the upper limit of the molecular weight of the polymer C, as long as the molecular weight thereof is lower than that of the polymer A,without particular limitation, typically, the Mw of the polymer C is less than 5X 10 ⁴ . The Mw of polymer C may be less than about 1X 10 ⁴ And may be about 5000 or less. Some versions of polymer C are liquid or fluid that exhibits a viscous consistency at room temperature (e.g., 25 ℃).

The Mn of the polymer C was measured by a Vapor Pressure Osmometry (Vapor Pressure osmometer). The Mw of the polymer C is a value in terms of polystyrene determined by GPC measurement. As the GPC measurement device, for example, the model "HLC-8120GPC" manufactured by Tosoh (TOSOH) corporation can be used.

The kind of the polymer C is not particularly limited, and an appropriate kind can be selected depending on the kind of the polymer a and the like. As the polymer C, for example, one or two or more kinds of a rubber-based polymer (typically a diene-based polymer), an olefin-based polymer, an acrylic polymer, a polyester-based polymer, a urethane-based polymer, a polyether-based polymer, a silicone-based polymer, a polyamide-based polymer, a fluorine-containing polymer, and the like can be used. In the adhesive sheet for magnetic disks, it is desired to avoid the use of silicone polymers.

Some preferred modes of the polymer C are selected from olefin-based polymers and diene-based polymers. It is believed that these polymers are generally low in polarity and short in side chains, and therefore readily block the passage of water molecules. In addition, good compatibility or dispersion is facilitated in the adhesive layer containing the polymer a. Among them, olefin polymers excellent in thermal stability and weather resistance are more preferable. Examples of the monomer component to be polymerized to obtain the polymer C include one or two or more monomers selected from ethylene, propylene, butene, isobutylene, isoprene and butadiene. Butene as used herein is intended to include 1-butene as well as cis-2-butene or trans-2-butene. The polymer C is preferably a polymer containing a monomer component of one or two or more monomers exemplified above in a proportion of 50% by weight or more. Specific examples include: ethylene-butene copolymers, ethylene-propylene-butene copolymers, ethylene-butene-nonconjugated diene copolymers, ethylene-propylene-butene-nonconjugated diene copolymers, and the like. Examples of the polymer include polymers called ethylene-propylene rubbers.

The polymer C is preferably a polymer containing a monomer component of at least one monomer selected from the group consisting of butene, isobutylene, and isoprene at a ratio of 50% by weight or more. Since the polymer obtained from the monomer is hydrophobic and nonpolar, it has excellent barrier properties against polar components such as moisture in the air, and thus can easily realize excellent gas barrier properties. The monomer component used for the polymerization to obtain the polymer C contains one or two or more of the above monomers in a proportion of more than 75% by weight, more preferably 85% by weight or more, and particularly preferably 90% by weight or more (for example, 95% by weight or more). The content of the monomer in the total monomer components may be 99% by weight or more. One or two or more of other monomers copolymerizable with the above-exemplified monomers (e.g., butadiene, styrene, ethylene, propylene) may be copolymerized in the polymer C.

The polymer C is particularly preferably a polymer containing a monomer component selected from the group consisting of butene (i.e., 1-butene, cis-2-butene, trans-2-butene) and isobutylene (isobutylene), i.e., polybutene, in a proportion of 50% by weight or more. The polymerization ratio of butene and isobutylene in the polybutene as the polymer C is preferably about 75% by weight or more, more preferably about 85% by weight or more, and still more preferably about 90% by weight or more (for example, about 95% by weight or more). The content ratio of butene and isobutylene in the whole monomer components may be 99% by weight or more.

The above polybutene is typically a polymer having isobutylene as a main component and optionally containing a monomer component of a prescribed amount of n-butene (1-butene, cis-2-butene or trans-2-butene). Unlike diene rubbers, polybutene has no double bonds in the molecular chain, and therefore is excellent in thermal stability and weather resistance. Further, the mobility of the main chain in the molecular structure is low, and the gas barrier property tends to be excellent. The copolymerization ratio of isobutylene in the polybutene is preferably about 50% by weight or more, more preferably about 70% by weight or more, and may be about 80% by weight or more (for example, about 90% by weight or more).

The polymer C can be obtained by appropriately selecting various known polymerization methods. Or a commercially available product corresponding to the polymer C can be obtained and used. For example, polybutene can be obtained by polymerizing monomer components including butene and isobutylene using a lewis acid catalyst (e.g., aluminum chloride and boron trifluoride). Alternatively, a polymer corresponding to polymer C was selected from commercially available products such as "sunstone polybutene" series manufactured by JXTG energy company and "solar oil polybutene" series manufactured by solar oil company, and used.

In the adhesive layer disclosed herein, the content of the polymer C (C) _C ) Content relative to Polymer A (C) _A ) Ratio of (C) _C /C _A ) It is preferable to set the value to about 0.1 or more. Ratio (C) from the viewpoint of gas barrier property _C /C _A ) Preferably at least about 0.3, more preferably at least about 0.5, and even more preferably at least about 0.7 (e.g., at least about 0.9). Further, the above ratio (C) _C /C _A ) It is appropriate to set about 2 or less. Ratio (C) from the viewpoint of suppressing decrease in holding force _C /C _A ) Preferably about 1.5 or less, more preferably about 1.2 or less (e.g., about 1.1 or less).

The content of the polymer C in the adhesive layer may be appropriately set in consideration of the effect of the polymer C. The content of the polymer C in the pressure-sensitive adhesive layer may be, for example, about 1 wt% or more, or 5 wt% or more, 15 wt% or more, 25 wt% or more, or 35 wt% or more, from the viewpoint of gas barrier properties. From the viewpoint of suppressing the amount of generated heating gas and the cohesive force, the content of the polymer C in the pressure-sensitive adhesive layer is preferably about 70% by weight or less, and preferably about 60% by weight or less (for example, about 55% by weight or less). In some embodiments, the content of the polymer C in the adhesive layer may be, for example, 50 wt% or less, and may be less than 30 wt%, less than 20 wt%, or less than 10 wt%.

(blending of acrylic Polymer and rubber Polymer)

In some embodiments, the adhesive layer is a rubber-acrylic blended adhesive layer comprising a rubber-based polymer and an acrylic polymer as base polymers. As the rubber-based polymer, one or two or more of the above rubber-based polymers may be used, and as the acrylic polymer, one or two or more of the above acrylic polymers may be used. By appropriately mixing the rubber-based polymer and the acrylic polymer, the advantages of the rubber-based polymer (gas barrier property, etc.) and the advantages of the acrylic polymer (low gas generation amount, adhesion property, etc.) can be satisfactorily achieved at the same time. When the rubber-based polymer and the acrylic polymer are used in combination, the weight ratio (R/A) of the rubber-based polymer (R) to the acrylic polymer (A) may be, for example, 95/5 to 20/80, preferably 90/10 to 30/70, more preferably 80/20 to 40/60, and still more preferably 70/30 to 50/50.

In some preferred modes, the above adhesive layer may be a composition in which the total amount of the base polymer is more than 50% by weight of the total weight of the adhesive layer (i.e., the weight of the adhesive layer composed of the adhesive). For example, the total amount of the base polymer is preferably about 75% by weight or more, more preferably about 85% by weight or more, and still more preferably about 90% by weight or more (for example, 95% by weight or more) of the total weight of the pressure-sensitive adhesive layer.

(crosslinking agent)

The adhesive composition (preferably, solvent-based adhesive composition) used for the formation of the adhesive layer preferably contains a crosslinking agent as an optional ingredient. The pressure-sensitive adhesive layer (for example, an acrylic pressure-sensitive adhesive layer) in the technique disclosed herein may contain the above-mentioned crosslinking agent in a form after the crosslinking reaction, a form before the crosslinking reaction, a form after the partial crosslinking reaction, an intermediate form or a composite form thereof, or the like. The crosslinking agent is usually contained mainly in the pressure-sensitive adhesive layer in a form after the crosslinking reaction.

The kind of the crosslinking agent is not particularly limited, and can be appropriately selected from conventionally known crosslinking agents. Examples of such a crosslinking agent include: isocyanate crosslinking agent, epoxy crosslinking agent,

Oxazoline crosslinking agents, aziridine crosslinking agents, melamine crosslinking agents, carbodiimide crosslinking agents, hydrazine crosslinking agents, amine crosslinking agents, peroxide crosslinking agents, metal chelate crosslinking agents, metal alkoxide crosslinking agents, metal salt crosslinking agents and the like. The crosslinking agent may be used singly or in combination of two or more. From the viewpoint of suppressing gas generation, the crosslinking agent is preferably selected from substances other than peroxides. Examples of the crosslinking agent that can be preferably used in the technique disclosed herein include isocyanate-based crosslinking agents and epoxy-based crosslinking agents. Among these, isocyanate crosslinking agents are more preferable.

As the isocyanate-based crosslinking agent, polyfunctional isocyanates (which mean compounds having an average of two or more isocyanate groups per molecule, including compounds having an isocyanurate structure) can be preferably used. The isocyanate crosslinking agent may be used singly or in combination of two or more. Examples of the preferable polyfunctional isocyanate include polyfunctional isocyanates having an average of three or more isocyanate groups per molecule. The trifunctional or higher isocyanate may be a polymer (e.g., dimer or trimer) of a difunctional or trifunctional or higher isocyanate, a derivative (e.g., addition reaction product of a polyol and two or more molecules of a polyfunctional isocyanate), a polymer, or the like. Examples thereof include: polyfunctional isocyanates such as dimers or trimers of diphenylmethane diisocyanate, isocyanurate forms of hexamethylene diisocyanate (trimer adducts of isocyanurate structure), reaction products of trimethylolpropane and tolylene diisocyanate, reaction products of trimethylolpropane and hexamethylene diisocyanate, polymethylene polyphenyl isocyanates, polyether polyisocyanates, polyester polyisocyanates, and the like.

As the epoxy-based crosslinking agent, a compound having two or more epoxy groups in one molecule can be used without particular limitation. An epoxy-based crosslinking agent having 3 to 5 epoxy groups in one molecule is preferable. The epoxy crosslinking agent may be used singly or in combination of two or more. Although not particularly limited, specific examples of the epoxy crosslinking agent include: n, N, N ', N' -tetraglycidyl m-xylylenediamine, 1, 3-bis (N, N-diglycidylaminomethyl) cyclohexane, 1, 6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, and the like.

The content of the crosslinking agent in the adhesive composition disclosed herein is not particularly limited. From the viewpoint of the cohesiveness, the content of the crosslinking agent is preferably about 0.001 parts by weight or more, preferably about 0.002 parts by weight or more, more preferably about 0.005 parts by weight or more, and still more preferably about 0.01 parts by weight or more, based on 100 parts by weight of the base polymer (for example, acrylic polymer). From the viewpoint of the adhesive strength and the elastic modulus, the content of the crosslinking agent in the adhesive composition is suitably about 20 parts by weight or less, preferably about 15 parts by weight or less, and more preferably about 10 parts by weight or less (e.g., about 5 parts by weight or less), relative to 100 parts by weight of the base polymer (e.g., the acrylic polymer). By appropriately setting the amount of the crosslinking agent, the adhesive can exert a good cohesive force.

In the embodiment using the isocyanate-based crosslinking agent, the amount of the isocyanate-based crosslinking agent used is not particularly limited. The amount of the isocyanate-based crosslinking agent used may be set to, for example, about 0.5 parts by weight or more and about 10 parts by weight or less with respect to 100 parts by weight of the base polymer (for example, acrylic polymer). From the viewpoint of the cohesiveness, the amount of the isocyanate-based crosslinking agent to be used is suitably about 1 part by weight or more, preferably about 1.5 parts by weight or more, based on 100 parts by weight of the base polymer (for example, acrylic polymer). The amount of the isocyanate-based crosslinking agent used is suitably about 8 parts by weight or less, preferably about 5 parts by weight or less (for example, less than about 4 parts by weight) relative to 100 parts by weight of the base polymer (for example, an acrylic polymer). By appropriately setting the amount of the isocyanate-based crosslinking agent used, the cohesive force can be increased and favorable repulsion resistance can be obtained.

(coloring agent)

The pressure-sensitive adhesive layer may be a transparent pressure-sensitive adhesive layer or a colored pressure-sensitive adhesive layer. According to the colored pressure-sensitive adhesive layer, even if the substrate is transparent or translucent, the pressure-sensitive adhesive sheet can be provided with an adherend-shielding property as a whole. The form of the coloring of the pressure-sensitive adhesive layer is not particularly limited, and the coloring (specifically, whitening) may be performed by forming voids such as bubbles in the layer, or the coloring may be performed by using a coloring agent. In some approaches, the adhesive layer may contain a colorant. The coloring agent may be used singly or in combination of two or more.

As the colorant, a conventionally known pigment or dye can be used, as well as a colorant that can be used in the base material. The colorant is not particularly limited, and may be, for example, black, gray, white, red, blue, yellow, green, yellow-green, orange, violet, gold, silver, pearl, or the like. In some embodiments, the adhesive layer contains a black colorant. As the black colorant, one or two or more of the black colorants exemplified as the black colorant used in the base material can be used without limitation. As a preferable example of the black colorant, carbon black can be used. In other aspects, the adhesive layer may contain a white colorant. As the white colorant, one or two or more of the white colorants exemplified as the white colorant used in the base material can be used without limitation.

In the embodiment in which the pressure-sensitive adhesive layer contains the colorant, the content (total amount, total content) of the colorant in the pressure-sensitive adhesive layer is appropriately set in consideration of the target light transmittance, the required adhesive properties, and the like. The content of the colorant in the pressure-sensitive adhesive layer is preferably 0.1% by weight or more, and from the viewpoint of reducing the total light transmittance, it is preferably 0.5% by weight or more, more preferably 1% by weight or more, and still more preferably 2% by weight or more. The content of the colorant in the pressure-sensitive adhesive layer may be set to 30% by weight or less, and preferably 20% by weight or less, and preferably 10% by weight or less, and may be 5% by weight or less, from the viewpoint of maintaining the pressure-sensitive adhesive properties such as light transmittance, dispersibility in the pressure-sensitive adhesive, adhesive strength, and impact resistance. The techniques disclosed herein can also preferably be practiced in such a way that the adhesive layer contains substantially no colorant.

(other additives)

The pressure-sensitive adhesive composition may contain, in addition to the above-mentioned components, various additives that are generally used in the field of pressure-sensitive adhesives, such as a tackifier (tackifier resin), a leveling agent, a defoaming agent, a crosslinking assistant, a plasticizer, a filler, a softening agent, an antistatic agent, an antiaging agent, an ultraviolet absorber, an antioxidant, and a light stabilizer, as required. For such various additives, conventionally known additives can be used by a conventional method. In an adhesive sheet for use in applications where silicone gas is avoided (e.g., an adhesive sheet applied to the inside of a magnetic disk device or a portion in contact with the inside), it is desirable to avoid the use of silicone additives (e.g., a silicone leveling agent, a silicone defoaming agent).

From the viewpoint of limiting the amount of gas generated from the pressure-sensitive adhesive sheet, it is desirable to avoid the use of low-molecular-weight components that cause gas generation. From such a viewpoint, the content of other additives (e.g., tackifier resin, age resistor, ultraviolet absorber, antioxidant, light stabilizer) in the adhesive layer is preferably limited to less than about 30 wt% (preferably less than 10 wt%, typically less than 3 wt%, for example less than 1 wt%). The technique disclosed herein can be preferably implemented in such a manner that the adhesive layer contains substantially no tackifying resin. The technique disclosed herein can be preferably implemented in such a manner that the pressure-sensitive adhesive layer does not substantially contain an ultraviolet absorber such as a hindered amine-based light stabilizer or a hindered phenol-based antioxidant, an antioxidant, or a light stabilizer.

(formation of adhesive layer)

The adhesive layer can be formed according to a known method for forming an adhesive layer in an adhesive sheet. For example, the following method can be preferably employed: a method (direct method) in which an adhesive layer is formed by directly applying (typically coating) an adhesive composition obtained by dissolving or dispersing the above-described adhesive layer-forming material in an appropriate solvent onto a substrate and drying it. In addition, the following method may be adopted: by applying the above adhesive composition toA method (transfer method) in which a pressure-sensitive adhesive layer is formed on a surface having good releasability (for example, the surface of a release liner, the back surface of a substrate subjected to a release treatment) by drying the surface and the pressure-sensitive adhesive layer is transferred onto the substrate. The release surface may be a surface of a release liner or a back surface of a base material having good releasability. From the viewpoint of reducing the amount of silicone on the pressure-sensitive adhesive surface, the release surface preferably has a silicone amount of a predetermined value or less (for example, 20 ng/cm) as in the release liner constituting the release liner-equipped pressure-sensitive adhesive sheet described later ² Below).

The form of the adhesive composition is not particularly limited, and may be, for example: various forms such as an adhesive composition in which the above-described adhesive layer forming material is contained in an organic solvent (solvent type), an adhesive composition in which an adhesive is dispersed in an aqueous solvent (water dispersion type, typically aqueous emulsion type), an active energy ray (e.g., ultraviolet ray) -curable adhesive composition, and a hot melt adhesive composition. From the viewpoint of coatability and adhesive properties, a solvent-based adhesive composition can be preferably used. As the solvent, for example, aromatic compounds (typically aromatic hydrocarbons) selected from toluene, xylene, and the like; acetates such as ethyl acetate and butyl acetate; one or a mixture of two or more of aliphatic hydrocarbons such as hexane, cyclohexane, heptane and methylcyclohexane, alicyclic hydrocarbons and the like. Although not particularly limited, the solvent-based adhesive composition is preferably adjusted to a nonvolatile content (NV) of 5 to 45 wt%. When NV is too low, production cost tends to increase, and when NV is too high, workability such as coatability may decrease. From the viewpoint of facilitating the removal of volatile components possibly contained in addition to the solvent by evaporation together with the solvent at the time of drying the composition, and reducing the amount of generated heating gas in the adhesive layer, it may be advantageous to adjust NV of the solvent-based adhesive composition to a predetermined value or less (preferably 35 wt% or less, more preferably 30 wt% or less, for example, 28 wt% or less).

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 contact roll coater, a dip roll coater, a bar coater, a knife coater, or a spray coater. The pressure-sensitive adhesive layer disclosed herein is typically formed continuously, but is not limited to this form, and may be formed in a regular or irregular pattern such as dots or stripes, for example.

From the viewpoints of accelerating the crosslinking reaction, improving the production efficiency, and the like, the drying of the binder composition is preferably performed under heating. The drying temperature may be set, for example, to about 40 ℃ to about 150 ℃, preferably to about 60 ℃ to about 130 ℃. After drying the pressure-sensitive adhesive composition, aging may be further performed for the purpose of adjusting migration of components in the pressure-sensitive adhesive layer, proceeding of a crosslinking reaction, relaxation of strain that may be present in the pressure-sensitive adhesive layer, and the like.

(characteristics of adhesive layer)

The total light transmittance of the adhesive layer is not particularly limited. In some embodiments, the total light transmittance of the adhesive layer is preferably 75% or less. For example, when the substrate is transparent or translucent, the total light transmittance of the adhesive layer is reduced, whereby the total light transmittance of the entire adhesive sheet is reduced, and the entire adhesive sheet can be provided with an adherend-shielding property. The total light transmittance of the pressure-sensitive adhesive layer is preferably 60% or less, more preferably 40% or less, and further preferably 20% or less. In some embodiments, the total light transmittance of the adhesive layer may be 10% or less, may be 3% or less, and may be less than 1%. The lower limit of the total light transmittance of the pressure-sensitive adhesive layer is not particularly limited, and may be substantially 0%, that is, not more than the detection limit, or not less than 0.01%, for example, not less than 0.1%, or not less than 1.0%. In some embodiments, the total light transmittance of the adhesive layer may be 5% or more, may be 9% or more, and may be 12% or more (for example, 15% or more). The total light transmittance of the adhesive layer can be reduced by using an adhesive-containing component such as a colorant, and the like. In other aspects, the adhesive layer may have a total light transmittance of greater than 75%, for example, 90% or greater. For example, where the substrate has a low total light transmittance, the adhesive layer may have a relatively high total light transmittance as described above. The use of an adhesive layer having a high total light transmittance is advantageous from the viewpoint of maintaining adhesive properties such as adhesive force, cohesive force, and repulsion resistance. The total light transmittance of the pressure-sensitive adhesive layer was measured by the method described in the examples described below.

(thickness of adhesive layer)

In the technique disclosed herein, the thickness of the adhesive layer constituting the adhesive surface is not particularly limited. The thickness of the pressure-sensitive adhesive layer is preferably set to usually 3 μm or more, preferably 10 μm or more, and more preferably 20 μm or more. By increasing the thickness of the pressure-sensitive adhesive layer, the adhesive force to an adherend tends to be increased. The pressure-sensitive adhesive layer having a thickness of a predetermined value or more absorbs roughness of the surface of the adherend and adheres thereto. The pressure-sensitive adhesive layer having a thickness of 10 μm or more can achieve, for example, good adhesion to an adherend having a surface with an arithmetic average roughness Ra of about 1 μm to about 5 μm (for example, about 3 μm). The thickness of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive surface may be set to, for example, 150 μm or less, and the thickness of the pressure-sensitive adhesive layer is preferably 100 μm or less, and more preferably 70 μm or less. By reducing the thickness of the adhesive layer, the amount of gas generated from the adhesive layer can be reduced. From the viewpoint of making the pressure-sensitive adhesive sheet thinner and lighter in weight, it is also advantageous to reduce the thickness of the pressure-sensitive adhesive layer. In some embodiments, the thickness of the adhesive layer may be, for example, 50 μm or less, 35 μm or less, or 30 μm or less.

< Release liner >

In the technique disclosed herein, a release liner may be used when forming the pressure-sensitive adhesive layer, producing the pressure-sensitive adhesive sheet, storing, distributing, and processing the shape of the pressure-sensitive adhesive sheet before use, or the like. The release liner is not particularly limited, and for example, a release liner having a release treatment layer on the surface of a liner base material such as a resin film or paper; and release liners comprising low-adhesion materials such as fluoropolymers (e.g., polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymers, chlorofluoroethylene-vinylidene fluoride copolymers, etc.) and polyolefin resins (e.g., PE and PP). The release-treated layer may be formed by surface-treating the liner base with a release-treating agent such as silicone, long-chain alkyl, fluorine-containing, or molybdenum sulfide. When the adhesive sheet disclosed herein is applied to a magnetic disk device (for example, when used in the interior or a portion facing the interior of a magnetic disk device), it is particularly preferable to use a non-silicone release liner that does not contain a silicone release treating agent capable of generating a siloxane gas. Among them, a preferable release liner includes a single layer or a multilayer release liner (polyolefin-based release liner) having two or more layers of polyolefin-based resin, the layer forming the surface in contact with the pressure-sensitive adhesive layer. Particularly preferred is a release liner (polyethylene-based release liner) comprising polyethylene, which is a layer forming the surface in contact with the adhesive layer. The polyolefin-based release liner may be a laminate film of a polyolefin-based resin and a resin other than polyolefin-based resin, for example, as long as at least the layer forming the side in contact with the adhesive surface is made of the polyolefin-based resin.

The thickness of the release liner is not particularly limited, and may be, for example, 20 μm or more, 40 μm or more, or 60 μm or more. In some embodiments, the thickness of the release liner may be, for example, 180 μm or less, may be 150 μm or less, may be 120 μm or less, and may be 100 μm or less. From the viewpoint of reducing the total thickness of the release-liner-attached pressure-sensitive adhesive sheet, it is preferable that the release liner is not excessively thick.

< use >

The pressure-sensitive adhesive sheet disclosed herein is excellent in masking property of the surface shape of an adherend, and therefore is suitable for various applications requiring a good appearance or requiring an excellent appearance. For example, by adhering the film to a surface of an uneven portion such as a dent which may form an uneven portion such as a welding mark or a bump, it is possible to realize a shield in which the existence of the uneven portion is not visually recognized. The adhesive sheet disclosed herein is preferably used in various electronic devices, for example. More specifically, a sealing material (for example, a sealing material for sealing an internal space) used in the above-described electronic apparatus is preferable. In some preferred embodiments, the adhesive sheet is preferably used for sealing an internal space of a magnetic disk device such as an HDD. In this application, for example, a mixed gas such as a siloxane gas may cause a failure of the apparatus, and therefore it is important to prevent such a gas from being mixed. In addition, since the pressure-sensitive adhesive sheet of some preferred embodiments has excellent gas barrier properties, this feature can also be an advantageous feature in the above-mentioned applications. Specifically, for example, in a Magnetic disk device using HAMR (Heat Assist Magnetic Recording), it is important to prevent the mixing of water that adversely affects the write life. It should be noted that HAMR is, in short, a technique for improving the areal recording density by using a laser beam. By using the adhesive sheet disclosed herein in such applications, i.e., in the application of a sealing material (also referred to as cap sealing) for a HAMR type magnetic disk device, a higher density magnetic storage device can be realized. Other suitable applications include a print label attached to the outer surface of a product such as the magnetic disk device. By using the adhesive sheet disclosed herein as a print label, it is possible to provide product information and the like by the print label, and to shield irregularities such as weld marks and impact marks existing on the outer surface of a product to which the print label is attached.

Fig. 3 shows an example of a configuration of a magnetic disk device as a preferred example of an application target of the technology disclosed herein. Fig. 3 is a sectional view schematically showing a magnetic disk device. The magnetic disk device 100 includes a magnetic disk 110 for storing data, a spindle motor 112 for rotating the magnetic disk 110, a magnetic head 114 for reading and writing data from and to the magnetic disk 110, and an actuator 116 as a power source for the magnetic head 114. The actuator 116 incorporates a linear motor, not shown. In this configuration example, 2 magnetic disks 110 are incorporated, but the present invention is not limited thereto, and 3 or more magnetic disks may be incorporated.

These components of the magnetic disk apparatus 100 are disposed in a casing (also referred to as a housing) 120 that should be referred to as a cartridge of the magnetic disk apparatus 100. Specifically, the constituent components of the magnetic disk apparatus 100 are housed in a box-shaped case main body (support structure body) 122 having an opening on the upper surface, and a rigid cover member (also referred to as a top cover) 124 is covered on the opening on the upper surface of the case main body 122. More specifically, a step 126 is provided on the inner peripheral side of the opening on the upper surface of the housing main body 122, and the outer peripheral edge of the lid member 124 is placed on the bottom of the step 126, whereby the lid member 124 covers the opening. The adhesive sheet 101 is attached from the upper surface of the cover member 124 so as to cover the cover member 124 and the upper surface (the outer periphery of the opening) of the housing main body 122, that is, the entire upper surface of the housing 120. This seals a gap 140 existing between the case main body 122 and the cover member 124 or other holes or gaps penetrating the inside and outside of the magnetic disk apparatus 100, and keeps the inside of the apparatus airtight. Such a sealing structure using the adhesive sheet 101 as a sealing material (cap seal) can be reduced in thickness as compared with a conventional sealing structure in which airtightness is ensured using a cap member and a gasket. In addition, since a liquid gasket is not required, gas generation from the gasket can be eliminated.

Further, as shown in the figure, the adhesive sheet 101 is attached as follows: not only covers the upper surface of the housing 120 but also extends further therefrom, is bent at an end (corner) thereof, and covers a part of the side surface as an adjacent surface thereof. Thus, even when a recess is formed in a corner portion of the outer surface of the housing 120, the housing can be attached so as to straddle both faces including the corner portion, thereby realizing shielding in which the recess in the corner portion is not recognized. In this configuration example, the adhesive sheet 101 is at least partially stuck to the upper surface and the side surface of the housing 120 in a shape of "1246767. More specifically, the adhesive sheet 101 covers the cover member 124 and the upper surface (the outer periphery of the opening) of the case main body 122 together (covered with the main body portion 101a of the adhesive sheet 101), and has a portion (also referred to as an extension portion 101 b) extending from here further to the side surface of the case 120. Specifically, the extending portion 101b is bent from the upper surface of the case main body 122 along the corner portion of the end portion of the upper surface of the case main body 122 and reaches the side surface of the case main body 122. Such an extension 101b may be provided on the entire side of each side constituting the outer periphery of the upper surface of the housing 120, or may be provided partially on the side.

In the above embodiment, the cover members 124 and 224 are one member that covers the magnetic disks 110 and 210 or the actuators 116 and 216 at a time, but the present invention is not limited thereto, and the cover members may cover the magnetic disks 110 and 210, the actuators 116 and 216, and other members, respectively, or may cover the magnetic disks 110 and 210 without covering the actuators 116 and 216. Even with such a configuration, airtightness inside the apparatus can be obtained by attaching the adhesive sheet to the cover member. In the magnetic disk device having such a configuration, the thickness of the sealing structure is reduced because airtightness can be obtained by using the adhesive sheet having a small thickness. This improves the storage capacity of the magnetic disk, and makes it possible to increase the density and capacity of the magnetic disk device.

Fig. 4 is a plan view schematically showing the shape of the adhesive sheet 101 before being attached to the magnetic disk device 100. The adhesive sheet 101 has a rectangular main body portion 101a to be adhered to the upper surface of the disk device, and four extension portions 101b which are respectively provided extending on respective sides (four sides) of the main body portion 101a and are to be adhered to the side surfaces of the disk device. Each of the extending portions 101b has a rectangular shape having the same width as the length of each side of the main body portion 101a, but is not limited thereto, and may have a trapezoidal shape such as being tapered in the direction extending from the main body portion 101a, or may have various shapes such as an R shape obtained by chamfering a corner portion.

Fig. 5 and 6 show other examples of configurations of a magnetic disk device to which the technology disclosed herein can be applied. Fig. 5 and 6 are sectional views corresponding to fig. 3, but in these figures, the housing 120 of the

magnetic disk apparatus

200, 300 is simplified, and only the

adhesive sheets

201, 301 are schematically shown in section. In the magnetic disk apparatus 200 shown in fig. 5, an adhesive sheet 201 is attached to a part of the upper surface of the housing 120 of the magnetic disk apparatus 200. Such an adhesive sheet 201 can be used as a sealing material (cap seal) for the magnetic disk device 200, and can also be used as a print label. In the magnetic disk device 300 shown in fig. 6, an adhesive sheet 301 is annularly attached to the outer peripheral portion of the upper surface (top cover 124) of the housing 120 of the magnetic disk device. More specifically, the adhesive sheet 301 covers a corner portion located at an end portion of the upper surface of the housing 120, and is attached along the outer periphery of the upper surface of the housing 120 in a state of being bent so as to straddle the upper surface and the side surfaces of the housing 120. Other aspects of the configuration shown in fig. 5 and 6 are substantially the same as those shown in fig. 3, and therefore, a repetitive description is omitted.

Although not particularly limited, the size of the adhesive sheet may be 20% or more and 150% or less of the area of at least one surface (a surface to be bonded, typically the upper surface of the housing of the magnetic disk device) of the outer surface of the housing of the magnetic disk device. The pressure-sensitive adhesive sheet having such a size can cover only a part of the surface to be adhered or can cover the entire surface to be adhered. Further, the pressure-sensitive adhesive sheet can cover not only one surface of the surface to be adhered but also the adjacent surface thereof. Even when a dent such as a bump is formed in a corner portion of the outer surface of the housing of the magnetic disk device, the adhesive sheet attached in this manner can be shielded from the dent of the corner portion by being attached so as to straddle both faces including the corner portion. The pressure-sensitive adhesive sheet attached so as to span at least two surfaces may have a size larger than one surface of the surface to be attached, may have a size smaller than the one surface, and may be used by being attached to, for example, a top cover outer peripheral portion of a magnetic disk device such as an HDD.

In some preferred embodiments, the size of the pressure-sensitive adhesive sheet is greater than 100% of the surface to be bonded on the outer surface of the housing of the magnetic disk device (typically, the upper surface of the housing of the magnetic disk device), may be 110% or more and 120% or more, and the upper limit thereof may be 150% or less, 140% or less and 125% or less, for example. The adhesive sheet having such a size is preferably used as a cover seal that spans the upper surface and the side surfaces of the magnetic disk device and covers the corners thereof. In another embodiment, the size of the pressure-sensitive adhesive sheet may be 100% or less, 80% or less, or 60% or less of the surface to be bonded on the outer surface of the housing of the magnetic disk device (typically, the upper surface of the housing of the magnetic disk device), and the lower limit thereof may be 30% or more, or 50% or more, for example. The pressure-sensitive adhesive sheet having such a size is preferably used as a cover seal for a magnetic disk device or as a print label. For example, by attaching only a part of the surface of the adherend on which the impact mark or the like is formed, the shape of the adherend can be shielded. Such attachment may span both faces constituting the outer surface of the adherend and cover a part of each of the both faces.

Matters disclosed by the present specification include the following.

[1] A magnetic disk apparatus, said magnetic disk apparatus having:

one or more magnetic disks storing data;

a motor for rotating the magnetic disk;

a magnetic head for performing at least one of reading and writing of data to the magnetic disk;

an actuator for operating the magnetic head; and

a housing accommodating the magnetic disk, the motor, the magnetic head, and the actuator, wherein,

a cover seal is provided on the housing,

the lid seal is an adhesive sheet having an adhesive layer and a substrate supporting the adhesive layer,

the adhesive sheet has an adhesive surface formed of the adhesive layer and a back surface opposite to the adhesive surface,

the glossiness of the back surface of the adhesive sheet is 80GU or less, and the total light transmittance of the adhesive sheet is 75% or less.

[2] The magnetic disk apparatus according to the above [1], wherein the housing has a box-shaped housing main body whose upper surface is opened and a cover member covering the opening.

[3] The magnetic disk device according to the above [2], wherein a step is provided on an inner peripheral side of the opening on the upper surface of the housing main body, and an outer peripheral edge of the cover member is placed on a bottom portion of the step.

[4] The magnetic disk device according to any of the above [1] to [3], wherein a hole is formed in the cover member.

[5] The magnetic disk device according to any of the above [1] to [4], wherein the adhesive sheet seals an internal space of the magnetic disk device.

[6] The magnetic disk device according to any one of the above [1] to [5], wherein the adhesive sheet covers and seals an upper surface of a case main body of the magnetic disk device.

[7] The magnetic disk device according to any of the above [1] to [6], wherein the magnetic disk device is capable of thermally-assisted magnetic recording.

[8] The magnetic disk device according to any one of the above [1] to [7], wherein an arithmetic average roughness of the back surface of the adhesive sheet is in a range of 50nm or more and 3000nm or less.

[9] The magnetic disk device according to any of the above [1] to [8], wherein the adhesive sheet is adhered to at least one of outer surfaces of a housing of the magnetic disk device (for example, a hard disk drive), and

the adhesive sheet has a size of 20% to 150% of the area of the one surface.

[10] The magnetic disk device according to any one of the above [1] to [9], wherein the adhesive sheet is attached to an outer peripheral portion of a top cover of the magnetic disk device (for example, a hard disk drive).

[11] An adhesive sheet having an adhesive layer and a substrate supporting the adhesive layer, wherein,

[12] The adhesive sheet according to [11], wherein the arithmetic average roughness of the back surface of the adhesive sheet is in a range of 50nm or more and 3000nm or less.

[13] The adhesive sheet according to [11] or [12], wherein the haze of the back surface of the adhesive sheet is 70% or more.

[14]As described above [11]～[13]The adhesive sheet according to any one of claims, wherein the adhesive sheet has a gas generation amount of 1.0 μ g/cm as measured by gas chromatography/mass spectrometry at 130 ℃ for 30 minutes ² The following.

[15]As described above [11]～[14]The adhesive sheet according to any one of claims, wherein the adhesive sheet is prepared by gas chromatography/mass spectrometry at 130 ℃ for 30 minutesUnder the conditions of (1), the silicone gas generation amount of the adhesive sheet was 0.1. Mu.g/cm ² The following.

[16] The adhesive sheet according to any one of the above [11] to [15], wherein the substrate is composed of a single resin layer.

[17] The adhesive sheet according to [16], wherein the total light transmittance of the substrate is 20% or less.

[18] The adhesive sheet according to [16] or [17], wherein the total light transmittance of the adhesive layer is 20% or less.

[19] The adhesive sheet according to any one of the above [11] to [18], wherein the thickness of the substrate is 20 μm or more and 200 μm or less.

[20] The adhesive sheet according to any one of the above [11] to [15], wherein the substrate has a metal layer and one or more resin layers.

[21] The adhesive sheet according to [20], wherein the metal layer has a thickness of 2 μm or more and 30 μm or less.

[22] The adhesive sheet according to [20] or [21], wherein the thickness of the resin layer is 20 μm or more and 200 μm or less.

[23] The adhesive sheet according to any one of the above [20] to [22], wherein the substrate has, as the resin layer, a resin layer a and a resin layer B disposed so as to sandwich the metal layer, wherein the resin layer a is disposed on a back surface side of the adhesive sheet.

[24] A release-liner-equipped adhesive sheet comprising the adhesive sheet according to any one of [11] to [23] above and a polyolefin-based release liner for protecting the adhesive surface of the adhesive sheet.

[25] The adhesive sheet according to any one of the above [11] to [23], which is used by being adhered to at least one surface of an outer surface of a case of a hard disk drive, and has a size of 20% or more and 150% or less of an area of the one surface.

[26] The adhesive sheet according to any one of the above [11] to [23], which is used by being stuck to an outer peripheral portion of a top cover of a hard disk drive.

[27] A magnetic disk device having the adhesive sheet according to any one of [11] to [23 ].

[28] The magnetic disk device according to the above [27], wherein the adhesive sheet seals an inner space of the magnetic disk device.

[29] The magnetic disk device according to the above [27] or [28], wherein the adhesive sheet is a cover seal that covers and seals an upper surface of a case main body of the magnetic disk device.

[30] The magnetic disk device according to any one of the above [27] to [29], wherein the adhesive sheet is stuck on at least one surface of an outer surface of a case of the magnetic disk device (for example, a hard disk drive), and the adhesive sheet has a size of 20% or more and 150% or less of an area of the one surface.

[31] The magnetic disk device according to any one of the above [27] to [30], wherein the adhesive sheet is attached to an outer peripheral portion of a top cover of the magnetic disk device (for example, a hard disk drive).

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

< evaluation method >

[ 60 ℃ gloss on the back surface ]

The 60 ° gloss [ GU ] of the back surface of the pressure-sensitive adhesive sheet was measured under the condition of a measurement angle of 60 ° using a commercially available gloss meter (for example, a product name "cat. No.4563 micro-tri-gloss meter (micro-tri-gloss)" manufactured by BYK corporation), and the 60 ° gloss [ GU ] of the surface of the substrate was also measured by the same method as described above.

[ Total light transmittance and haze ]

The total light transmittance [% ] and haze [% ] of the adhesive sheet are the total light transmittance and haze, respectively, in the thickness direction of the adhesive sheet peeled from the release liner, measured according to JIS K7136 using a commercially available haze meter. The haze of the adhesive sheet is the haze of the back surface of the adhesive sheet, and may be the haze of the substrate itself after the adhesive layer is removed from the adhesive sheet. As the haze meter, a product name "HAZEMETER HZ-V3" manufactured by Happy testing machine or an equivalent thereof can be used. The total light transmittance [% ] of the substrate was also measured by the same method as described above. The total light transmittance of the adhesive layer was measured by the same method as described above, except that a value obtained by measuring a measurement sample obtained by laminating a single adhesive layer on a PET film (product name "lumiror #38-U48" manufactured by dongli corporation) having a high total light transmittance (specifically, a total light transmittance of 93%) was used as the total light transmittance of the adhesive layer. For example, the total light transmittance of the pressure-sensitive adhesive layer can be measured using, as a measurement sample, a sample obtained by peeling a release liner on the light release side from a single-layer pressure-sensitive adhesive (double-sided pressure-sensitive adhesive sheet) protected on both sides by release liners and bonding the release liner to the PET film.

[ arithmetic average roughness Ra of the backside ]

The arithmetic mean roughness Ra [ nm ] of the back surface of the pressure-sensitive adhesive sheet was measured using a general surface roughness measuring apparatus (for example, a non-contact three-dimensional surface shape measuring apparatus manufactured by Veeco, model "Wyko NT-3300"). The arithmetic mean roughness [ nm ] of the substrate surface was also measured by the same method as described above.

[ gas Generation amount and siloxane gas Generation amount ]

The gas generation amount of the pressure-sensitive adhesive sheet was measured by a dynamic headspace method. Specifically, the pressure-sensitive adhesive sheet to be measured was cut into 7cm ² And this was used as a measurement sample. The measurement sample was sealed in a 50mL vial, and heated at 130 ℃ for 30 minutes using a headspace autosampler. As the headspace automatic sampler, commercially available products can be used without particular limitation. For example, the product name "EQ-12031HSA" manufactured by JEOL corporation or its equivalent may be used. The total gas production amount (total amount of gas) and the production amount of siloxane gas (cyclic siloxane: trimer, tetramer, pentamer, and hexamer) generated from the measurement sample were measured using a gas chromatography/mass spectrometer (GC-MS). As GC-MS, commercially available products can be used. The above-mentioned gases areThe volume generation amount is the amount of gas generated per unit area of the adhesive sheet (unit: μ g/cm) ² Or ng/cm ² )。

[ evaluation of surface shape masking Property of adherend ]

The adherend surface shape masking property of the pressure-sensitive adhesive sheet was evaluated using a surface shape evaluation apparatus (product name "Optimap PSD") manufactured by Rhopoint Instruments. By using this surface shape evaluation device, the masking property evaluation by visual observation can be performed using an objective numerical value. Specifically, the degree of masking (visual masking) of the adherend surface shape of the pressure-sensitive adhesive sheet can be quantified (curvature [ m ] or the like) not only in the detection of unevenness but also in the image (uneven pattern or the like) of the adherend surface through the pressure-sensitive adhesive sheet ^-1 ]). The specific evaluation method is as follows. That is, a plate obtained by bonding an aluminum perforated plate (punched with a diameter of 5mm, thickness of 0.3 mm) formed with a plurality of punched holes to a stainless steel plate was used as an evaluation plate. An adhesive sheet to be evaluated was attached to the evaluation plate, and the X-Y data of a wavelength of 0.3mm to 1.0mm with respect to the back surface of the adhesive sheet was analyzed using the surface shape evaluation apparatus, whereby the curvature (corresponding to visual observation at a distance of 40 cm) was obtained. The smaller the curvature, the less likely the unevenness of the perforated plate is visually recognized through the adhesive sheet, and the curvature is 15m ^-1 The following is a determination that the surface shape of the adherend can be shielded.

< example 1>

(preparation of adhesive composition)

93 parts of butyl acrylate, 7 parts of acrylic acid and 0.1 part of 4-hydroxybutyl acrylate were solution-polymerized by a conventional method using ethyl acetate as a solvent and 0.1 part of azobisisobutyronitrile as an initiator, to thereby obtain a solution of an acrylic polymer having a weight average molecular weight of 150 ten thousand (solid content concentration of 25%). An acrylic pressure-sensitive adhesive composition solution was obtained by adding 2 parts (in terms of solid content) of an isocyanate-based crosslinking agent (trade name "Coronate L", manufactured by tokyo corporation, tolylene diisocyanate adduct of trimethylolpropane, solid content concentration: 75%) to 100 parts of the acrylic polymer.

(preparation of base Material)

A white PET film (product name "Lumiror E20" manufactured by Toray corporation) having a thickness of 38 μm as the resin layer A, an aluminum foil having a thickness of 7 μm as the metal layer, and a PET film having a thickness of 9 μm as the resin layer B were laminated in this order by dry lamination and adhesion, thereby obtaining a substrate of this example. An adhesive layer having a thickness of 4 μm was laminated between each resin layer and the metal layer.

(preparation of adhesive sheet)

The acrylic pressure-sensitive adhesive composition was applied to one surface (the surface on the resin layer B side) of the substrate so that the thickness after drying was 30 μm, and dried at 120 ℃ for 3 minutes, thereby forming a pressure-sensitive adhesive layer on the substrate. In this way, the adhesive sheet of this example was obtained. A polyolefin-based release liner (product name "SFL-70T4" manufactured by Sun a. Kaken, inc., 70 μm thick) subjected to a release treatment and an embossing treatment was bonded to the surface (adhesive surface) of the adhesive layer, thereby obtaining a release liner-equipped adhesive sheet of the present example.

< examples 2 to 3>

Adhesive sheets and release-liner-attached adhesive sheets of each example were obtained in the same manner as in example 1, except that the resin layer a, the metal layer, and the resin layer B were made of materials having thicknesses shown in table 1.

< example 4>

(preparation of adhesive composition)

50 parts of BUTYL rubber (IIR; trade name "JSR BUTYL 268", manufactured by JSR corporation, mw of about 54 ten thousand, mw/Mn of about 4.5) and 50 parts of polybutene (trade name "Rinshi polybutene HV-1900", manufactured by JXTG energy Co., ltd., mn of 2900) as base polymers were dissolved in toluene, thereby preparing an adhesive composition having a nonvolatile content (NV) of 25%.

(preparation of base Material)

The base material of the present example was obtained by laminating a PET film (product name "E-150" manufactured by Mitsubishi chemical corporation) having a thickness of 50 μm as the resin layer A, an aluminum foil having a thickness of 7 μm as the metal layer, and a PET film having a thickness of 9 μm as the resin layer B in this order by dry lamination. An adhesive layer having a thickness of 4 μm was laminated between each resin layer and the metal layer.

(preparation of adhesive sheet)

A pressure-sensitive adhesive sheet of this example was obtained in the same manner as in example 1, except that the pressure-sensitive adhesive composition and the substrate obtained above were used. Further, a release-treated silicone-based release liner (product name "HP-S0" manufactured by Fujiko corporation, thickness 50 μm) was bonded to the surface (pressure-sensitive adhesive surface) of the pressure-sensitive adhesive layer, thereby obtaining a release-liner-attached pressure-sensitive adhesive sheet of the present example.

< example 5>

The substrate (laminate of resin layer a/metal layer/resin layer B) of the present example was obtained in the same manner as in example 2, except that a PET film (product name "lumiror X42G", manufactured by dongli corporation) having a thickness of 50 μm was used as the resin layer a. A pressure-sensitive adhesive sheet and a release liner-attached pressure-sensitive adhesive sheet of this example were obtained in the same manner as in example 2, except that the substrate was used.

< example 6>

A film in which sand blasting was performed (124693189, 12512489, 124124124124124124831. A substrate (a laminate of resin layer a/metal layer/resin layer B) of this example was obtained in the same manner as in example 2, except that this film was used as resin layer a. A pressure-sensitive adhesive sheet and a release liner-attached pressure-sensitive adhesive sheet of this example were obtained in the same manner as in example 2, except that the substrate was used. In the adhesive sheet of this example, the matte-treated surface of the resin layer a was located on the back surface of the adhesive sheet.

< example 7>

A white PET film (product name "Lumiror E20" manufactured by Toray corporation) having a thickness of 75 μm as a resin layer and an aluminum foil having a thickness of 7 μm as a metal layer were laminated by dry lamination and adhesion, thereby obtaining a substrate of this example. An adhesive layer having a thickness of 4 μm was laminated between the resin layer and the metal layer. A psa sheet and a release liner-equipped psa sheet of this example were obtained in the same manner as in example 1, except that the substrate obtained in this way was used.

< example 8>

A white PET film (product name "Crisper #50", manufactured by Toyo Co., ltd.) having a thickness of 50 μm was used as a base material (base material composed of only a resin layer). Except for this, the pressure-sensitive adhesive sheet and the release liner-attached pressure-sensitive adhesive sheet of this example were obtained in the same manner as in example 1.

< example 9>

A film obtained by sandblasting one surface of a white PET film having a thickness of 50 μm ("Lumiror E20", manufactured by Toray corporation) was obtained. A psa sheet and a release liner-attached psa sheet of this example were obtained in the same manner as in example 1, except that the film was used as a substrate (substrate composed only of a resin layer). In the pressure-sensitive adhesive sheet of this example, the matte-treated surface of the substrate was located on the back surface of the pressure-sensitive adhesive sheet.

< example 10>

In the preparation of the acrylic pressure-sensitive adhesive composition of example 1,3 parts of a black pigment (product name "ATDN101 black" manufactured by daikon chemical industries) was added in addition to 2 parts of the isocyanate-based crosslinking agent to 100 parts of the acrylic polymer, thereby obtaining an acrylic pressure-sensitive adhesive composition solution of the present example.

The acrylic pressure-sensitive adhesive composition obtained above was applied to one surface of a PET film (product name "lumiror X42G", manufactured by toray corporation) having a thickness of 50 μm as a substrate so that the thickness after drying was 35 μm, and dried at 120 ℃ for 3 minutes, thereby forming a pressure-sensitive adhesive layer on the substrate. The adhesive sheet of this example was obtained in this manner. A polyolefin-based release liner (product name "SFL-70T4" manufactured by Sun a. Kaken, inc., 70 μm thick) subjected to a release treatment and an embossing treatment was bonded to the surface (adhesive surface) of the adhesive layer, thereby obtaining a release liner-equipped adhesive sheet of the present example. The total light transmittance of the adhesive layer alone in this example is 20% or less.

< comparative example 1>

A substrate (laminate of resin layer a/metal layer/resin layer B) of the present example was obtained in the same manner as in example 1, except that a transparent PET film (product name "lumiror S10", manufactured by dongli corporation) having a thickness of 25 μm was used as the resin layer a. A psa sheet and a release liner-equipped psa sheet of this example were obtained in the same manner as in example 1, except that the substrate was used.

< comparative examples 2 to 3>

The pressure-sensitive adhesive sheets and the pressure-sensitive adhesive sheets with release liners of the respective examples were obtained in the same manner as in example 1 except that a PET film (product name "E-150", manufactured by Mitsubishi chemical corporation) (comparative example 2) having a thickness of 50 μm or a PET film (product name "Lumiror EA3S", manufactured by Mitsubishi chemical corporation) (comparative example 3) having a thickness of 38 μm was used as a base material (base material composed of only a resin layer).

The outline and evaluation results of the adhesive sheets of the respective examples are shown in table 1.

As shown in Table 1, in the evaluation of the masking property of the surface shape of the adherend of the pressure-sensitive adhesive sheets of examples 1 to 10 in which the gloss of the back surface of the pressure-sensitive adhesive sheet was 80GU or less and the total light transmittance was 75% or less, the curvature of the back surface of the pressure-sensitive adhesive sheet was 15m ^-1 In contrast, the pressure-sensitive adhesive sheets of comparative examples 1 to 3, in which the gloss of the back surface of the pressure-sensitive adhesive sheet was more than 80GU or the total light transmittance was more than 75%, had a curvature of more than 15m in the evaluation of the masking property of the surface shape of the adherend ^-1 . From the above results, it is found that a pressure-sensitive adhesive sheet having a gloss of 80GU or less on the back surface thereof and a total light transmittance of 75% or less is difficult to visually recognize the surface shape of an adherend even when the pressure-sensitive adhesive sheet is stuck on the surface of the adherend having irregularities.

Note that, although not shown in the table, the adhesive sheets of all examples did not lift in the bending adhesion test. In addition, the adhesive sheets of examples 1 to 7 had a moisture permeability of less than 0.01 g/(m) ² 24 hours).

Specific examples of the present invention have been described above in detail, but these are merely examples and do not limit the claims. The techniques described in the claims include those obtained by making various changes and modifications to the specific examples illustrated above.

Claims

1. An adhesive sheet having an adhesive layer and a substrate supporting the adhesive layer, wherein,

2. The adhesive sheet according to claim 1, wherein the arithmetic average roughness of the back surface of the adhesive sheet is in the range of 50nm or more and 3000nm or less.

3. The adhesive sheet according to claim 1 or 2, wherein the haze of the back surface of the adhesive sheet is 70% or more.

4. The adhesive sheet according to any one of claims 1 to 3, wherein the adhesive sheet has a gas generation amount of 1.0 μ g/cm as measured by gas chromatography/mass spectrometry at 130 ℃ for 30 minutes ² The following.

5. The adhesive sheet according to any one of claims 1 to 4, wherein the adhesive sheet has a siloxane gas generation amount of 0.1 μ g/cm as measured by gas chromatography/mass spectrometry at 130 ℃ for 30 minutes ² The following.

6. The adhesive sheet according to any one of claims 1 to 5, wherein the substrate is composed of a single resin layer.

7. The adhesive sheet according to claim 6, wherein the substrate has a total light transmittance of 20% or less.

8. The adhesive sheet according to claim 6 or 7, wherein the total light transmittance of the adhesive layer is 20% or less.

9. The adhesive sheet according to any one of claims 1 to 8, wherein the thickness of the substrate is 20 μm or more and 200 μm or less.

10. The adhesive sheet according to any one of claims 1 to 5, wherein the substrate has a metal layer and one or more resin layers.

11. The adhesive sheet according to claim 10, wherein the metal layer has a thickness of 2 μm or more and 30 μm or less.

12. The adhesive sheet according to claim 10 or 11, wherein the thickness of the resin layer is 20 μm or more and 200 μm or less.

13. The adhesive sheet according to any one of claims 10 to 12, wherein the substrate has, as the resin layers, a resin layer a and a resin layer B disposed so as to sandwich the metal layer, wherein the resin layer a is disposed on the back side of the adhesive sheet.

14. A release-lined adhesive sheet comprising the adhesive sheet according to any one of claims 1 to 13 and a polyolefin-based release liner for protecting the adhesive surface of the adhesive sheet.

15. The adhesive sheet according to any one of claims 1 to 13, wherein the adhesive sheet is used by being stuck to at least one surface of an outer surface of a case of a hard disk drive, and the adhesive sheet has a size of 20% or more and 150% or less of an area of the one surface.

16. The adhesive sheet according to any one of claims 1 to 13, wherein the adhesive sheet is used by being attached to an outer peripheral portion of a top cover of a hard disk drive.