WO2023171069A1 - Adhesive sheet - Google Patents

Abstract

This adhesive sheet has a laminate in which a first adhesive layer and a second adhesive layer are laminated, wherein: when a surface on the first adhesive layer side among surfaces of the laminate is defined as the A surface, and a surface on the second adhesive layer side among the surfaces of the laminate is defined as the B surface, the A surface adhesive strength is greater than the B surface adhesive strength; and when a push-in depth at a point in time at which a push-in load becomes 5 N after continuously pushing in the A surface at a push-in speed of 0.01 mm/second is defined as the A surface push-in depth, and a push-in depth at a point in time at which a push-in load becomes 5 N after continuously pushing in the B surface at a push-in speed of 0.01 mm/second is defined as the B surface push-in depth, the A surface push-in ratio which is the A surface push-in depth relative to the thickness of the laminate, and the B surface push-in ratio which is the B surface push-in depth relative to the thickness of the laminate, are at least 35%.　Even when affixing a member having a step or a member having a curved surface shape, the adhesive sheet sufficiently follows the step and curved surface of the member and has good reworkability

Description

adhesive sheet

The present invention relates to an adhesive sheet.

Display bodies (displays) having liquid crystal elements, light emitting diode (LED) elements, organic electroluminescent (organic EL) elements, etc., and optical products having lenses are laminates in which members constituting the display body or optical product are laminated together. have.

A laminate of such members is generally formed by bonding one member and the other member using an adhesive layer of an adhesive sheet.

In addition, retrofitted members such as cases and films may be pasted or attached to mobile electronic devices such as smartphones for the purpose of giving them a design, protecting the mobile electronic device, etc.

When such members are bonded together, poor bonding may occur due to positional misalignment during bonding, which may lead to lower product yields, poor appearance, etc. Therefore, in particular, if a bonding defect occurs when bonding an expensive component and a cheap component, or if a bonding defect occurs during bonding/installation of a retrofitted component, the cheap component or the retrofitted component Sometimes it is peeled off and reused (reworked).

Therefore, pressure-sensitive adhesive sheets used for laminating such members are required not only to have adhesion to exhibit good lamination, but also to have the property of being able to be peeled off and reused after lamination (reworkability).

Patent Document 1 discloses imparting adhesiveness to resin and removability to glass to a double-sided adhesive tape used for attaching a film on which a resin layer is formed to sensor glass.

Japanese Patent Application Publication No. 2015-131924

However, when a member constituting a display body or an optical product, a retrofitted member, etc. is provided with a step for the purpose of imparting design or realizing predetermined optical characteristics, the member may have a curved shape. There are cases where there are.

When bonding a member with a step or a curved surface, the adhesive layer of the adhesive sheet needs to follow the step and curved surface of the member. If the adhesive layer cannot sufficiently follow steps and curved surfaces, there will be spaces (lifting, peeling, etc.) where the adhesive is not in contact with the component near the steps or on the curved surface, resulting in deterioration of optical properties, poor appearance, etc. There was a problem.

The present invention has been made in view of the above circumstances, and even when laminating members with steps or curved surfaces, the present invention can sufficiently follow the steps and curved surfaces of the members and has good reworkability. An object of the present invention is to provide a pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer having the following properties.

Aspects of the present invention are as follows.
[1] A pressure-sensitive adhesive sheet having a laminate in which a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer are stacked,
Among the surfaces of the laminate, when the surface on the first adhesive layer side is defined as side A, and the surface on the second adhesive layer side is defined as side B, the adhesive force of side A is greater than the adhesive force of side B. ,
Continuing to push side A at a pushing speed of 0.01 mm/sec, the pushing depth when the pushing load reaches 5N is the pushing depth of side A, continue pushing side B at a pushing speed of 0.01 mm/sec, When the indentation depth when the indentation load reaches 5N is the B-side indentation depth, the A-side indentation rate, which is the A-side indentation depth relative to the thickness of the laminate, and the B-side indentation relative to the thickness of the laminate. The pressure-sensitive adhesive sheet has a B-side indentation rate, which is a depth, of 35% or more.

[2] The adhesive sheet according to [1], wherein the first adhesive layer and the second adhesive layer are in contact with each other in the laminate.

[3] The adhesive sheet according to [1] or [2], wherein the B-side indentation rate is larger than the A-side indentation rate.

[4] The adhesive sheet according to any one of [1] to [3], wherein the ratio of the adhesive strength of the A side to the adhesive strength of the B side is within the range of 2 or more and 10,000 or less.

[5] The adhesive sheet according to any one of [1] to [4], wherein the first adhesive layer has a thickness of 30 μm or more and 800 μm or less.

[6] The adhesive sheet according to any one of [1] to [5], wherein the second adhesive layer has a thickness of 10 μm or more and 300 μm or less.

[7] The adhesive sheet according to any one of [1] to [6], wherein the first adhesive layer is composed of an acrylic adhesive and the second adhesive layer is composed of a urethane adhesive.

[8] The pressure-sensitive adhesive sheet according to any one of [1] to [7], wherein the pressure-sensitive adhesive sheet has a release sheet disposed on the A side and a release sheet disposed on the B side.

According to the present invention, even when bonding a member having a step or a curved surface, the adhesive layer includes an adhesive layer that sufficiently follows the step and curved surface of the member and has good reworkability. Adhesive sheets can be provided.

FIG. 1 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to an embodiment of the present invention. FIG. 2 is a schematic diagram for explaining the push-in rate.

Hereinafter, the present invention will be described in detail based on specific embodiments.

(1. Adhesive sheet)
As shown in FIG. 1, the adhesive sheet 1 according to this embodiment has a laminate 10 in which a first adhesive layer 11 and a second adhesive layer 12 are laminated. Moreover, the adhesive sheet 1 may have components other than the laminate 10 as long as the effects of the present invention can be obtained. In this embodiment, for example, as shown in FIG. 1, two release sheets 21 are placed on the surface of the laminate 10 to sandwich the laminate 10 in order to protect the laminate 10 until the adhesive sheet is used. , 22 are arranged.

The pressure-sensitive adhesive sheet according to this embodiment is suitably used for bonding members having steps and/or curved surfaces. One member to be bonded may have a step and/or a curved surface, or both members to be bonded may have a step and/or a curved surface.

Examples of adhesive sheets with good reworkability include adhesive sheets having a structure in which an adhesive layer exhibiting strong adhesive strength and an adhesive layer exhibiting weak adhesive strength are laminated, as disclosed in Patent Document 1. There is.

According to such a pressure-sensitive adhesive sheet, in two members bonded together via the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive layer exhibiting weak adhesive strength is replaced by the bonding member exhibiting strong adhesive strength. The member to which the agent layer is pasted can be easily peeled off together with the adhesive sheet.

However, when the member has a step and/or a curved surface, the entire adhesive layer needs to be significantly deformed to follow the step and/or curved surface during bonding. In this case, there was a problem that simply combining an adhesive layer with high adhesive strength and an adhesive layer with low adhesive strength could not sufficiently follow steps and/or curved surfaces, or could not provide good reworkability.

In order to deal with the above problem, in the adhesive sheet according to the present embodiment, the physical properties of the laminate composed of at least two adhesive layers are controlled. Below, the constituent elements of the adhesive sheet according to this embodiment will be explained in detail.

(1.1. Laminate)
The laminate according to this embodiment has a first adhesive layer and a second adhesive layer. In the laminate, the members are bonded together by the adhesive force exerted by the first adhesive layer and the second adhesive layer. The laminate according to this embodiment may have layers other than the first adhesive layer and the second adhesive layer, but in the laminate, the first adhesive layer and the second adhesive layer are the most Located in the outer layer. That is, it is preferable that the surfaces facing each other in the thickness direction of the laminate coincide with the exposed main surface of the first adhesive layer and the exposed main surface of the second adhesive layer.

The thickness of the laminate according to this embodiment is preferably 30 to 1000 μm, more preferably 60 to 700 μm, even more preferably 100 to 500 μm, particularly preferably 120 to 300 μm, Among these, it is preferably 140 to 200 μm. This makes it easier to satisfy the physical properties, adhesive strength, etc. related to the indentation rate, which will be described later, and also improves handling properties.

The thickness of the first adhesive layer constituting the laminate according to this embodiment is preferably 30 μm or more and 800 μm or less. This makes it easier to satisfy the physical properties, adhesive strength, etc. related to the indentation rate, which will be described later, and also improves handling properties. From this point of view, the thickness is preferably 40 to 500 μm, more preferably 50 to 300 μm, even more preferably 55 to 200 μm, and particularly preferably 60 to 130 μm.

The thickness of the second adhesive layer constituting the laminate according to this embodiment is preferably 10 μm or more and 300 μm or less. This makes it easier to satisfy the physical properties, adhesive strength, etc. related to the indentation rate, which will be described later, and also improves handling properties. From this point of view, the thickness is preferably 20 to 200 μm, more preferably 30 to 160 μm, even more preferably 40 to 120 μm, and particularly preferably 50 to 90 μm.

In the laminate according to the present embodiment, the ratio of the thickness of the first adhesive layer to the thickness of the second adhesive layer is preferably 0.01 to 1.4, more preferably 0.05 to 1. It is more preferably 3, even more preferably 0.1 to 1.2, even more preferably 0.3 to 1.1, and most preferably 0.5 to 1. When the ratio is within the above range, it becomes easier to satisfy the physical properties, adhesive strength, etc. related to the indentation rate, which will be described later, and the handleability tends to be good.

The laminate according to the present embodiment may not include any layer other than the first adhesive layer and the second adhesive layer (that is, the layer located between the first adhesive layer and the second adhesive layer). Although preferred, layers other than the first adhesive layer and the second adhesive layer may be provided within a range that does not impede the effects of the present invention. In this case, the thickness of the layer is preferably 1 to 200 μm, more preferably 20 to 100 μm. This improves the handling of the laminate.

Specific measurement conditions for the above-mentioned thickness will be described later in Examples.

In this embodiment, by controlling the following physical properties in the laminate, when laminating members having steps and/or curved surfaces, the adhesive layer conforms to the steps and/or curved shapes of the members. Good tracking and re-peeling (rework) of the member after lamination is achieved.

(1.2. Physical properties of laminate)
The laminate according to this embodiment has the following physical properties. Hereinafter, among the surfaces of the laminate, the surface on the first adhesive layer side will be referred to as side A, and the surface on the second adhesive layer side will be referred to as side B. In FIG. 1, the surface 10a of the laminate 10 (the surface 11a of the first adhesive layer 11) is the A side, and the surface 10b of the laminate 10 (the surface 12b of the second adhesive layer 12) is the B side.

(1.2.1. Indentation rate)
In this embodiment, the indentation rates of the A side and the B side are controlled. The indentation rate is calculated as the ratio of the indentation depth to the thickness of the laminate. As shown in FIG. 2, the indentation depth is determined by continuing to push the surface of the laminate 10 (A side 10a, 11a in FIG. 1) at a pushing speed of 0.01 mm/sec, and when the pushing load reaches 5N. is the indentation depth h.

Here, when A side is continuously pushed in at a pushing speed of 0.01 mm/sec and the indentation depth when the indentation load reaches 5N is defined as the A side indentation depth, the A side indentation depth is relative to the thickness of the laminate. Let this be the A-side indentation rate (%). For example, when the thickness of the laminate is 200 μm and the A-plane indentation depth is 50 μm, the A-plane indentation rate is 25%.

Similarly, if surface B is continued to be pushed in at a pushing speed of 0.01 mm/sec and the pushing depth when the pushing load reaches 5N is defined as the pushing depth of surface B, then the pushing depth of surface B is relative to the thickness of the laminate. Let this be the indentation rate (%) of the B side.

In this embodiment, both the A side indentation rate and the B side indentation rate are 35% or more. The indentation rate reflects the degree of resistance of the laminate to stress that causes deformation, and the higher the indentation rate, the lower the resistance of the laminate to deformation. As a result, even if the adhesive layer is deformed to follow a step, curved surface, etc., the laminate can easily maintain the following state.

Therefore, by setting the A side indentation rate and the B side indentation rate within the above range, the laminate having the first adhesive layer and the second adhesive layer can be bonded to a member having a step and/or a curved surface. Also, it is possible to sufficiently follow steps and/or curved surfaces.

From the above-mentioned viewpoint, the A-side indentation rate is preferably 35% or more, more preferably 38% or more, and even more preferably 40% or more. Further, the B-side indentation ratio is preferably 35% or more, more preferably 38% or more, even more preferably 40% or more, and particularly preferably 42% or more. On the other hand, the upper limits of the A-side indentation rate and the B-side indentation rate are not particularly limited, but in this embodiment, from the viewpoint of maintaining the shape of the adhesive sheet, the upper limit of the A-side indentation rate and the B-side indentation rate is 80%.

Furthermore, it is preferable that the B-side indentation rate is larger than the A-side indentation rate. The indentation rate does not reflect the properties of the first adhesive layer or the second adhesive layer alone, but rather the properties of the entire laminate. When measuring the indentation depth, for example, when an indentation load is applied to the first adhesive layer, since the second adhesive layer is located directly below the first adhesive layer, the first adhesive layer Although the deformation of the second adhesive layer is alleviated, since there is a hard table directly under the second adhesive layer, the deformation of the second adhesive layer is not alleviated so much. Therefore, if the adhesive layer constituting the surface opposite to the surface to which the indentation load is applied is easily deformed, the indentation rate will increase.

That is, the fact that the B-side indentation rate is larger than the A-side indentation rate means that the first adhesive layer is more easily deformed than the second adhesive layer. From this point of view, the first adhesive layer can more easily follow steps and/or curved surfaces. In addition, when the B side indentation rate is larger than the A side indentation rate, more specifically, it means that the value obtained by subtracting the value of the A side indentation rate from the value of the B side indentation rate is more than 0 points. do. The value is preferably more than 0 points, more preferably 1 point or more, and even more preferably 1.4 points or more.

The indentation rate can be determined by changing, for example, the composition of the adhesive, the molecular weight of the main polymer that makes up the adhesive, the structure of the adhesive, the viscoelasticity of the adhesive, the layer structure of the laminate, the thickness of each layer that makes up the laminate, etc. It can be adjusted by

The indentation rate is measured by a method that can evaluate the deformation of the entire adhesive layer by applying a load to the adhesive layer corresponding to the amount of deformation that the adhesive layer receives when following a step and/or a curved surface. I can do it. Since the adhesive layer is subject to large deformation in order to follow steps and/or curved surfaces, a method that can apply a relatively large load and measure the deformation of the entire adhesive layer is preferred. A measuring method for calculating the above-mentioned indentation rate will be explained in Examples.

In the laminate according to this embodiment, the A-side indentation depth is preferably 10 μm or more, more preferably 30 μm or more, and 50 μm or more, from the viewpoint of adjusting the indentation rate described above to a desired range. More preferably, it is 60 μm or more, and particularly preferably 66 μm or more. On the other hand, the upper limit of the A-side indentation depth is less than or equal to the upper limit of the thickness of the laminate, thereby making it possible to maintain the shape of the pressure-sensitive adhesive sheet and exhibiting desired performance. From the viewpoint of being able to adjust the above-mentioned indentation rate within a desired range, the A-side indentation depth is preferably 150 μm or less, more preferably 120 μm or less, even more preferably 90 μm or less, and 78 μm or less. The thickness is preferably 72 μm or less, particularly preferably 72 μm or less.

In the laminate according to the present embodiment, the B-side indentation depth is preferably 10 μm or more, more preferably 35 μm or more, and 55 μm or more, from the viewpoint of adjusting the above-mentioned indentation rate to a desired range. More preferably, it is 65 μm or more, and particularly preferably 70 μm or more. On the other hand, the upper limit of the B-side indentation depth is less than or equal to the upper limit of the thickness of the laminate, thereby making it possible to maintain the shape of the pressure-sensitive adhesive sheet and exhibiting desired performance. From the viewpoint of being able to adjust the above-mentioned indentation rate within a desired range, the indentation depth of surface B is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 110 μm or less, and 90 μm or less. The thickness is preferably 80 μm or less, especially 80 μm or less.

(1.2.2. Adhesive strength)
In the laminate according to this embodiment, the adhesive strength of the A side of the laminate to soda lime glass (A side adhesive force) and the adhesive strength of the B side of the laminate to soda lime glass (B side adhesive force) are different. It is preferable that the adhesive strength of the A side is larger than the adhesive strength of the B side. By providing a difference in adhesive strength in this way, the second adhesive layer can easily exhibit removability (reworkability).

In this embodiment, it is preferable that the adhesive force of the A side of the laminate to the soda lime glass (A side adhesive force) is 5 N/25 mm or more. That is, the adhesive force of the first adhesive layer to soda lime glass is preferably 5 N/25 mm or more. When the A-side adhesive strength is within the above range, it is easy to maintain the state in which the laminate follows steps and/or curved surfaces.

From the above viewpoint, the A-side adhesive strength is more preferably 15 to 100 N/25 mm, even more preferably 30 to 80 N/25 mm, particularly preferably 40 to 70 N/25 mm, and especially 45 to 80 N/25 mm. Preferably it is 60N/25mm.

Furthermore, in this embodiment, the adhesive force of the B side of the laminate to soda lime glass (B side adhesive force) is preferably 3 N/25 mm or less. That is, the adhesive force of the second adhesive layer to soda lime glass is preferably 3 N/25 mm or less. When the B-side adhesive strength is within the above range, the bonded state between the first member and the second member can be easily released (excellent reworkability).

From the above point of view, the B side adhesive strength is more preferably 0.01 to 2N/25mm, even more preferably 0.02 to 1N/25mm, and even more preferably 0.05 to 0.6N/25mm. It is particularly preferable, and particularly preferably 0.08 to 0.2 N/25 mm.

Furthermore, in the present embodiment, the ratio of the A-side adhesive strength to the B-side adhesive strength (A-side adhesive strength/B-side adhesive strength) is preferably within the range of 2 or more and 10,000 or less. When the ratio is within the above range, it is possible to achieve both step followability and/or curved surface followability and reworkability at a high level.

The ratio of the A side adhesive strength to the B side adhesive strength is more preferably 10 to 5000, even more preferably 100 to 1200, particularly preferably 200 to 800, and especially 400 to 600. is preferred.

Specific measurement conditions for the A-side adhesive strength and the B-side adhesive strength will be described later in Examples.

The total light transmittance of the laminate in this embodiment is preferably 70% or more, more preferably 85% or more, particularly preferably 95% or more, and even more preferably 99% or more. As a result, since the laminate has excellent transparency, the member in which the laminate is used exhibits an excellent appearance even when following steps or curved surfaces. The upper limit of the total light transmittance is usually 100% or less. Note that the total light transmittance in this specification is a value measured in accordance with JIS K7361-1:1997, and specific measurement conditions will be described later in Examples.

The haze value of the laminate in this embodiment is preferably 5% or less, more preferably 3% or less, particularly preferably 1% or less, even more preferably 0.6% or less, and especially preferably 0.4% or less. As a result, since the laminate has excellent transparency, the member in which the laminate is used exhibits an excellent appearance even when following steps or curved surfaces. The lower limit of the haze value is usually 0% or more. Note that the haze value in this specification is a value measured according to JIS K7136:2000, and specific measurement conditions will be described later in Examples.

(1.3. Composition of adhesive)
The composition of the adhesive constituting the first adhesive layer and the second adhesive layer is not particularly limited as long as the laminate according to the present embodiment has the above-mentioned physical properties. Examples include acrylic adhesives, urethane adhesives, polyester adhesives, rubber adhesives, and silicone adhesives. Further, the adhesive may be of an emulsion type, a solvent type, or a solvent-free type. Furthermore, the adhesive may or may not have a crosslinked structure.

In this embodiment, from the viewpoint of ease of realizing the above-mentioned physical properties, adhesive properties, optical properties, etc., the first adhesive constituting the first adhesive layer is preferably an acrylic adhesive; As the second adhesive constituting the second adhesive layer, a urethane adhesive is preferable. Below, a case where the first adhesive is an acrylic adhesive and the second adhesive is a urethane adhesive will be described.

(1.3.1. First adhesive)
In this embodiment, the first adhesive is an acrylic adhesive, and an acrylic adhesive having a crosslinked structure is more preferable. Specifically, the adhesive is an adhesive composition (hereinafter sometimes referred to as "adhesive composition P1") containing a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B). ) is preferably obtained by crosslinking. With such an adhesive, it is easy to satisfy the above-mentioned physical properties, and it is easy to obtain good adhesive strength. In addition, in this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. Furthermore, the concept of "copolymer" is also included in "polymer".

(1.3.1.1. (meth)acrylic acid ester polymer (A))
In this embodiment, the (meth)acrylic acid ester polymer (A) includes a reactive group-containing monomer having a reactive group that reacts with the crosslinking agent (B) in the molecule as a monomer unit constituting the polymer. It is preferable to include. The reactive group derived from this reactive group-containing monomer reacts with the crosslinking agent (B) to form a crosslinked structure (three-dimensional network structure), and an adhesive having the desired cohesive force is obtained.

The above-mentioned reactive group-containing monomers include monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomer), monomers having a carboxyl group in the molecule (carboxy group-containing monomer), and monomers having an amino group in the molecule (amino group-containing monomer). ) etc. are preferably mentioned. Among these, hydroxyl group-containing monomers or carboxy group-containing monomers that have excellent reactivity with the crosslinking agent (B) are preferred, and hydroxyl group-containing monomers are particularly preferred.

Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and ) 3-hydroxybutyl acrylate, 4-hydroxybutyl (meth)acrylate, and other hydroxyalkyl (meth)acrylates.

Among these, from the viewpoint of the reactivity of the hydroxyl group in the obtained (meth)acrylic acid ester polymer (A) with the crosslinking agent (B) and the copolymerizability with other monomers, those having 1 to 4 carbon atoms are preferred. A (meth)acrylic acid hydroxyalkyl ester having a hydroxyalkyl group is preferred. Specifically, preferred examples include 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate, with 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate being particularly preferred. These may be used alone or in combination of two or more.

Examples of the carboxy group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid is preferred from the viewpoint of the reactivity of the carboxy group in the resulting (meth)acrylic acid ester polymer (A) with the crosslinking agent (B) and the copolymerizability with other monomers. These may be used alone or in combination of two or more.

Examples of the amino group-containing monomer include aminoethyl (meth)acrylate, n-butylaminoethyl (meth)acrylate, and the like. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) preferably contains 1 to 50% by mass, and preferably 5 to 40% by mass, of a reactive group-containing monomer as a monomer unit constituting the polymer. More preferably, the content is 8 to 30% by mass, even more preferably 10 to 25% by mass, and especially preferably 12 to 18% by mass. As a result, a good crosslinked structure is formed in the resulting pressure-sensitive adhesive, and a desired cohesive force is obtained. As a result, it becomes easier to satisfy the physical properties such as the indentation rate and adhesive strength described above, and the step followability and curved surface followability become better.

It is also preferable that the (meth)acrylic acid ester polymer (A) does not contain a carboxy group-containing monomer as a monomer unit constituting the polymer. Since the carboxyl group is an acid component, by not containing a monomer containing a carboxyl group, the adhesive can be applied to materials that may cause problems due to acids, such as transparent conductive films such as tin-doped indium oxide (ITO) or metal films. Even if it exists, those problems (corrosion, resistance value change, etc.) caused by acid can be suppressed.

However, it is permissible to contain a predetermined amount of a carboxy group-containing monomer to the extent that the above-mentioned problems do not occur. Specifically, the (meth)acrylic acid ester polymer (A) contains a carboxy group-containing monomer as a monomer unit of 0.1% by mass or less, preferably 0.01% by mass or less, and more preferably 0.001% by mass or less. It is permissible to contain it in an amount of % by mass or less.

The (meth)acrylic acid ester polymer (A) preferably contains an alkyl (meth)acrylic ester as a monomer unit constituting the polymer. Thereby, good flexibility and adhesiveness can be exhibited. Alkyl groups may be linear or branched.

As the (meth)acrylic acid alkyl ester, from the viewpoint of adhesiveness, (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 20 carbon atoms are preferable. Examples of (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and n-(meth)acrylate. Butyl, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, (meth)acrylic acid Examples include n-dodecyl, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.

Among these, from the viewpoint of further improving adhesiveness, (meth)acrylic acid esters in which the alkyl group has 1 to 8 carbon atoms are preferred, and methyl (meth)acrylate, n-butyl (meth)acrylate, or (meth)acrylate is preferable. ) 2-ethylhexyl acrylate is particularly preferred, and n-butyl acrylate or 2-ethylhexyl acrylate is even more preferred. Note that these may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) preferably contains 40 to 99% by mass or more, and preferably 50 to 90% by mass or more of (meth)acrylic acid alkyl ester as monomer units constituting the polymer. More preferably, the content is 60 to 80% by mass or more. As a result, the (meth)acrylic acid ester polymer (A) can exhibit suitable flexibility and adhesiveness, which in turn makes it easier to satisfy the physical properties such as the indentation rate and adhesive strength described above, and improves step followability. and curved surface followability is improved. Further, a suitable amount of other monomer components such as a reactive functional group-containing monomer can be introduced into the (meth)acrylic acid ester polymer (A).

It is also preferable that the (meth)acrylic acid ester polymer (A) contains a monomer having an alicyclic structure in the molecule (monomer containing an alicyclic structure) as a monomer unit constituting the polymer. Since alicyclic structure-containing monomers are bulky, their presence in the polymer is thought to increase the distance between the polymers, making it possible to make the resulting adhesive highly flexible. . This makes it easier to satisfy the physical properties such as the indentation rate and adhesive strength described above, and improves the step followability and curved surface followability.

The carbon ring of the alicyclic structure in the alicyclic structure-containing monomer may have a saturated structure or may have an unsaturated bond in part. Further, the alicyclic structure may be a monocyclic alicyclic structure or a polycyclic alicyclic structure such as a bicyclic or tricyclic ring. From the viewpoint of optimizing the distance between the obtained (meth)acrylic acid ester polymers (A) and imparting higher stress relaxation properties to the adhesive, the above alicyclic structure is a polycyclic alicyclic structure ( A polycyclic structure) is preferable. Furthermore, in consideration of the compatibility between the (meth)acrylic acid ester polymer (A) and other components, it is particularly preferable that the polycyclic structure has two to four rings. In addition, from the viewpoint of imparting stress relaxation properties as mentioned above, the number of carbon atoms in the alicyclic structure (referring to the total number of carbon atoms in the part forming the ring, and when multiple rings exist independently, , the total number of carbon atoms) is usually preferably 5 or more, more preferably 7 or more. On the other hand, the upper limit of the number of carbon atoms in the alicyclic structure is not particularly limited, but from the viewpoint of compatibility as described above, it is preferably 15 or less, and particularly preferably 10 or less.

Specifically, the alicyclic structure-containing monomers include cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, adamantyl (meth)acrylate, isobornyl (meth)acrylate, and (meth)acrylic acid. Examples include dicyclopentenyl and dicyclopentenyloxyethyl (meth)acrylate.

Among these, dicyclopentanyl (meth)acrylate (number of carbon atoms in alicyclic structure: 10) and adamantyl (meth)acrylate (number of carbon atoms in alicyclic structure: 10) exhibit better adhesiveness. ) or isobornyl (meth)acrylate (number of carbon atoms in alicyclic structure: 7) is preferred, isobornyl (meth)acrylate is particularly preferred, and isobornyl acrylate is more preferred. These may be used alone or in combination of two or more.

When the (meth)acrylic acid ester polymer (A) contains an alicyclic structure-containing monomer as a monomer unit constituting the polymer, it must contain 1 to 30% by mass or more of the alicyclic structure-containing monomer. The content is preferably 3 to 25% by mass, more preferably 5 to 20% by mass, and particularly preferably 8 to 15% by mass. This makes it easier to satisfy the physical properties such as the indentation rate and adhesive strength described above, and improves the step followability and curved surface followability.

It is also preferable that the (meth)acrylic acid ester polymer (A) contains a nitrogen atom-containing monomer as a monomer unit constituting the polymer. By including a nitrogen atom-containing monomer as a structural unit in the polymer, it is possible to impart a predetermined polarity to the adhesive and make it highly compatible with adherends that have a certain degree of polarity. can. As the nitrogen atom-containing monomer, a monomer having a nitrogen-containing heterocycle is preferable from the viewpoint of imparting appropriate rigidity to the (meth)acrylic acid ester polymer (A). In addition, from the viewpoint of increasing the degree of freedom of the portion derived from the nitrogen atom-containing monomer in the higher-order structure of the adhesive, the nitrogen atom-containing monomer is used to form the (meth)acrylic acid ester polymer (A). It is preferred not to contain any reactive unsaturated double bond groups other than the one polymerizable group used in the polymerization of.

Examples of monomers having a nitrogen-containing heterocycle include N-(meth)acryloylmorpholine, N-vinyl-2-pyrrolidone, N-(meth)acryloylpyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloyl Pyrrolidine, N-(meth)acryloylaziridine, aziridinylethyl (meth)acrylate, 2-vinylpyridine, 4-vinylpyridine, 2-vinylpyrazine, 1-vinylimidazole, N-vinylcarbazole, N-vinylphthalimide, etc. Illustrated.

Among these, N-(meth)acryloylmorpholine, which exhibits superior adhesive strength, is preferred, and N-acryloylmorpholine is particularly preferred. These may be used alone or in combination of two or more.

When the (meth)acrylic acid ester polymer (A) contains a nitrogen atom-containing monomer as a monomer unit constituting the polymer, it preferably contains 1 to 30% by mass of the nitrogen atom-containing monomer, and preferably 2 to 30% by mass of the nitrogen atom-containing monomer. It is more preferable to contain 20% by mass, even more preferably to contain 3 to 10% by mass, and particularly preferably to contain 4 to 8% by mass. This makes it easier to satisfy the physical properties such as the indentation rate and adhesive strength described above, and improves the step followability and curved surface followability.

The (meth)acrylic acid ester polymer (A) may contain other monomers as monomer units constituting the polymer, if desired. As the other monomers, monomers containing no reactive functional groups are preferred in order not to inhibit the above-described effects of the monomers containing reactive functional groups. Examples of such monomers include alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) is preferably a linear polymer. Since it is a linear polymer, entanglement of molecular chains is likely to occur, which can be expected to improve cohesive force, making it easier to meet the physical properties such as indentation rate and adhesive strength, and improves step tracking and curved surface tracking. Improves sex.

Furthermore, the (meth)acrylic acid ester polymer (A) is preferably a solution polymer obtained by a solution polymerization method. By being a solution polymer, it is easier to obtain a polymer with a high molecular weight, and it is expected that the cohesive force will be improved, so it will be easier to meet the physical properties such as the indentation rate and adhesive strength, which will improve the ability to follow steps and curved surfaces. becomes better.

The polymerization mode of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

The weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably from 200,000 to 2,000,000, more preferably from 300,000 to 1,600,000, and even more preferably from 400,000 to 1,200,000. It is preferably 450,000 to 900,000, particularly preferably 500,000 to 700,000. This makes it easier to satisfy the physical properties such as the indentation rate and adhesive strength described above, and improves the step followability and curved surface followability. Note that the weight average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

In the adhesive composition P1, the (meth)acrylic acid ester polymer (A) may be used alone or in combination of two or more.

(1.3.1.2. Crosslinking agent (B))
The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) by heating the adhesive composition P1, making it possible to form a three-dimensional network structure favorably. This improves the cohesive force of the resulting adhesive, making it easier to satisfy the physical properties such as the indentation rate and adhesive strength described above, and resulting in better step followability and curved surface followability.

The crosslinking agent (B) may be one that reacts with the reactive group possessed by the (meth)acrylic acid ester polymer (A), such as an isocyanate crosslinking agent, an epoxy crosslinking agent, an amine crosslinking agent, Melamine crosslinking agents, aziridine crosslinking agents, hydrazine crosslinking agents, aldehyde crosslinking agents, oxazoline crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, ammonium salt crosslinking agents, etc. Illustrated.

Among these, it is preferable to use an isocyanate-based crosslinking agent that has excellent reactivity with the reactive group possessed by the (meth)acrylic acid ester polymer (A). Note that the crosslinking agent (B) can be used alone or in combination of two or more.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, and alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate. and their biuret forms, isocyanurate forms, and adduct forms which are reactants with low-molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. .

Examples of the epoxy crosslinking agent include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and ethylene glycol diglycidyl ether. , 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylaniline, diglycidylamine, and the like. Among these, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane is preferred from the viewpoint of reactivity with carboxy groups.

The content of the crosslinking agent (B) in the adhesive composition P1 is preferably 0.01 to 10 parts by mass, and 0.01 to 10 parts by mass, based on 100 parts by mass of the (meth)acrylic acid ester polymer (A). The amount is more preferably 0.5 to 5 parts by weight, even more preferably 0.1 to 2 parts by weight, and particularly preferably 0.2 to 1 part by weight. As a result, the obtained adhesive exhibits good cohesive force, easily satisfies the above-mentioned physical properties such as indentation rate and adhesive strength, and has good step followability and curved surface followability.

(1.3.1.3. Other additives)
Adhesive composition P1 may contain other additives as necessary. Such additives include silane coupling agents, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, rust preventives, infrared absorbers, colorants, softeners, fillers, Examples include refractive index adjusting agents. Note that the polymerization solvent and dilution solvent described below are not included in the additives constituting the adhesive composition P1.

It is preferable that the adhesive composition P1 contains a silane coupling agent among the above. This improves the adhesion to the adherend.

As the silane coupling agent, an organosilicon compound having at least one alkoxysilyl group in the molecule, which has good compatibility with the (meth)acrylic acid ester polymer (A) and has light transparency is used. preferable.

Examples of such silane coupling agents include silicon compounds containing polymerizable unsaturated groups such as vinyltrimethoxysilane, vinyltriethoxysilane, methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 2-( Silicon compounds having an epoxy structure such as 3,4-epoxycyclohexyl)ethyltrimethoxysilane, mercapto group-containing silicon compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxymethylsilane , 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and other amino group-containing silicon compounds; 3-chloropropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, or at least one of these, and an alkyl group-containing silicon compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, or ethyltrimethoxysilane. Examples include condensates of These may be used alone or in combination of two or more.

The content of the silane coupling agent in the adhesive composition P1 is preferably 0.05 to 2 parts by mass, and 0.10 parts by mass based on 100 parts by mass of the (meth)acrylic acid ester polymer (A). It is more preferably 1 part by mass, and even more preferably 0.20 to 0.5 part by mass. This improves the adhesion to the adherend, making it easier to satisfy the physical properties such as the adhesive strength described above, and improving the step followability and curved surface followability.

(1.3.2. Second adhesive)
In this embodiment, the second adhesive is a urethane adhesive, and a urethane adhesive having a crosslinked structure is more preferable. Specifically, the adhesive is an adhesive obtained by crosslinking an adhesive composition (hereinafter sometimes referred to as "adhesive composition P2") containing a polyurethane polyol and a polyisocyanate crosslinker. is preferred. With such an adhesive, the physical properties such as the indentation rate and adhesive force described above can be easily satisfied, and particularly the reworkability can be made good.

A polyurethane polyol is obtained by reacting a polyol and a polyisocyanate such that the equivalent ratio of isocyanate groups to hydroxyl groups is less than 1. As the polyol, polyester polyol, polyether polyol, etc. are preferable. Preferred examples of the polyether polyol include polypropylene glycol, polyethylene glycol, and polytetramethylene glycol.

The average number of functional groups per molecule of the polyether polyol is preferably 2.2 or more and 3.4 or less, more preferably 2.3 or more and 3.3 or less, and 2.4 or more and 3.2 or less. It is more preferable that Further, the number average molecular weight (Mn) of the polyether polyol is preferably 300 or more and 7,000 or less, more preferably 350 or more and 6,000 or less.

Examples of the polyisocyanate constituting the polyurethane polyol include aromatic polyisocyanate, aliphatic polyisocyanate, araliphatic polyisocyanate, alicyclic polyisocyanate, and the like. Further examples include trimethylolpropane adducts, biuret forms, nurate forms, and the like. Examples of the aromatic polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, and 4,4'-diphenylmethane diisocyanate.

The polymerization reaction between the polyol and polyisocyanate described above is generally carried out using a catalyst. Examples of the catalyst include tin-based organometallic compounds such as dioctyltin dilaurate.

On the other hand, examples of the polyisocyanate crosslinking agent include trimethylolpropane adducts, biuret forms, nurate forms, and the like of the above-mentioned polyisocyanates. The amount of the polyisocyanate crosslinking agent added to the polyurethane polyol is preferably such that the equivalent ratio of isocyanate groups to hydroxyl groups is 0.5 or more and 1.5 or less.

The adhesive composition P2 may contain other additives as necessary. As such an additive, the same additive as the first adhesive can be used.

(1.4. Release sheet)
The release sheets 21 and 22 protect the laminate 10 until the adhesive sheet 1 is used, and are peeled off when the adhesive sheet 1 (laminate 10) is used. In the adhesive sheet 1 according to this embodiment, one or both of the release sheets 21 and 22 are not necessarily required.

Examples of release sheets include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, Polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene/(meth)acrylic acid copolymer film, ethylene/(meth)acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film, fluororesin film, etc. is used. Moreover, these crosslinked films are also used. Furthermore, a laminated film of these may be used.

It is preferable that the release surface of the release sheet (particularly the surface in contact with the first adhesive layer and the second adhesive layer) is subjected to a release treatment. Examples of the release agent used in the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents. Note that among the release sheets, it is preferable that one of the release sheets be a heavy release type release sheet with a high peel force, and the other release sheet be a light release type release sheet with a low peel force.

There is no particular limit to the thickness of the release sheet, but it is usually about 20 to 150 μm.

(1.5. Manufacture of adhesive composition)
Adhesive composition P1 for preparing the first adhesive can be prepared, for example, by first manufacturing a (meth)acrylic ester polymer (A), and then combining the obtained (meth)acrylic ester polymer (A) with , and a crosslinking agent (B). Additives may be added if necessary.

The (meth)acrylic acid ester polymer (A) can be produced, for example, by polymerizing a mixture of monomers constituting the polymer using a normal radical polymerization method. The (meth)acrylic acid ester polymer (A) can be polymerized by a solution polymerization method using a polymerization initiator if necessary. By polymerizing the (meth)acrylic acid ester polymer (A) using a solution polymerization method, it becomes easy to increase the molecular weight of the obtained polymer and adjust the molecular weight distribution, and further reduces the production of low molecular weight substances. It becomes possible to do so.

Examples of the polymerization solvent used in the solution polymerization method include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone. One type of polymerization solvent may be used, or two or more types may be used in combination.

Examples of the polymerization initiator include azo compounds, organic peroxides, etc., and two or more types may be used in combination. Examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2-methylbutyronitrile), '-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate), 4 ,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), 2,2'-azobis[2-(2-imidazolin-2-yl)propane] etc. are exemplified.

Examples of organic peroxides include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, and di(2-ethoxyethyl)peroxydicarbonate. , t-butyl peroxyneodecanoate, t-butyl peroxy bivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide and the like.

Note that in the above polymerization step, the weight average molecular weight of the resulting polymer can be adjusted by incorporating a chain transfer agent such as 2-mercaptoethanol.

Subsequently, a crosslinking agent (B) and a diluent solvent were added to the obtained solution of the (meth)acrylic acid ester polymer (A) and mixed sufficiently to obtain an adhesive composition P1 diluted with the solvent. (Coating solution) is obtained. Additives may be added as necessary.

In addition, if any of the above components is a solid component, or if it is a component that will cause precipitation when mixed with other components in an undiluted state, that component can be prepared separately in advance. It may be dissolved or diluted in a diluting solvent and then mixed with other components.

Examples of diluent solvents include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane, aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methylene chloride and ethylene chloride, methanol, ethanol, propanol, butanol, and 1-methoxy. Examples include alcohols such as -2-propanol, ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone, esters such as ethyl acetate and butyl acetate, and cellosolve solvents such as ethyl cellosolve.

The concentration and viscosity of the prepared coating solution may be within a range that allows coating, and can be appropriately selected depending on the situation. For example, the adhesive composition P1 is diluted to a concentration of 10 to 60% by mass. In addition, when obtaining a coating solution, addition of a dilution solvent etc. is not a necessary condition, and if adhesive composition P1 has a viscosity etc. which can be coated, it is not necessary to add a dilution solvent. In this case, the adhesive composition P1 becomes a coating solution using the polymerization solvent of the (meth)acrylic acid ester polymer (A) as a diluting solvent.

Adhesive composition P2 for preparing the second adhesive can be produced in the same manner as adhesive composition P1. For example, first, a polyol and a polyisocyanate are reacted to produce a polyurethane polyol. By thoroughly mixing the obtained polyurethane polyol, polyisocyanate crosslinking agent, and diluting solvent, a solution-diluted adhesive composition P2 (coating solution) can be produced. Additives may be added if necessary.

(1.6. Manufacture of adhesive)
The adhesive constituting the adhesive layer is preferably obtained by crosslinking the above-described adhesive composition P1 and adhesive composition P2, respectively. Crosslinking of adhesive composition P1 and adhesive composition P2 can usually be performed by heat treatment. Note that this heat treatment can also serve as a drying treatment for volatilizing the diluting solvent and the like from the coating films of the adhesive compositions P1 and P2 applied to the desired object.

In the case of adhesive composition P1, the heating temperature of the heat treatment is preferably 50 to 150°C, more preferably 70 to 120°C. In the case of adhesive composition P2, the temperature is preferably 50 to 150°C, more preferably 70 to 120°C. Further, in the case of adhesive composition P1, the heating time is preferably 10 seconds to 10 minutes, more preferably 50 seconds to 2 minutes. In the case of adhesive composition P2, the time is preferably 10 seconds to 10 minutes, more preferably 50 seconds to 2 minutes.

After the heat treatment, a curing period of about 1 to 2 weeks may be provided at room temperature (for example, 23° C., 50% RH), if necessary. If curing is required, adhesives (first adhesive and second adhesive) having a crosslinked structure are obtained after the curing period has elapsed. When curing is not necessary, adhesives (first adhesive and second adhesive) having a crosslinked structure are obtained after the heat treatment is completed.

(1.7. Manufacture of adhesive sheet)
The method for manufacturing the adhesive sheet 1 is not particularly limited, and any known method may be used. For example, a coating solution of the adhesive composition P1 described above is applied to the release surface of one release sheet, heat treatment is performed to crosslink the adhesive composition, a coating layer is formed, and a release layer with the coating layer is released. Get a sheet. Further, the coating liquid of the adhesive composition P2 described above is applied to the release surface of the other release sheet, heat treatment is performed to crosslink the adhesive composition, a coating layer is formed, and the release layer with the coating layer is released. Get a sheet. Then, the release sheet 21 with the coating layer and the release sheet 22 with the coating layer are pasted together so that both coating layers are in contact with each other. If curing is required, the coating layer becomes an adhesive layer after a predetermined curing period. In addition, if curing is not necessary, the coating layer becomes the adhesive layer as it is. Thereby, the adhesive sheet 1 having the laminate 10 in which the first adhesive layer 11 and the second adhesive layer 12 are laminated is obtained.

Examples of methods for applying the coating liquids of adhesive compositions P1 and P2 include bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

In addition, in this specification, when "X to Y" (X, Y are arbitrary numbers) is written, unless otherwise specified, it means "more than or equal to X and less than or equal to Y", and also means "preferably larger than X" or "preferably is less than Y." In addition, when it is written as "more than or equal to X" (X is any number), unless otherwise specified, it includes the meaning of "preferably larger than X", and when it is written as "less than or equal to Y" (where Y is any number) , unless otherwise specified, also includes the meaning of "preferably smaller than Y".

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and may be modified in various ways within the scope of the present invention.

Hereinafter, the invention will be explained in more detail using examples, but the invention is not limited to these examples.

(Example 1)
1. Preparation of (meth)acrylic acid ester polymer (A) 65 parts by mass of 2-ethylhexyl acrylate, 10 parts by mass of 4-acryloylmorpholine, 10 parts by mass of isobornyl acrylate, and 15 parts by mass of 2-hydroxyethyl acrylate were dissolved in a solution. A (meth)acrylic acid ester polymer (A) was prepared by legal copolymerization. When the molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described below, it was found to have a weight average molecular weight (Mw) of 500,000.

The weight average molecular weight (Mw) is a polystyrene equivalent weight average molecular weight measured using gel permeation chromatography (GPC) under the following conditions (GPC measurement).
(Measurement condition)
・GPC measurement device: Tosoh Corporation, HLC-8020
・GPC column (passed in the following order): TSK guard column HXL-H manufactured by Tosoh Corporation
TSK gel GMHXL (x2)
TSK gel G2000HXL
・Measurement solvent: Tetrahydrofuran ・Measurement temperature: 40℃

2. Preparation of Adhesive Composition P1 100 parts by mass of the (meth)acrylic acid ester polymer (A) obtained above (solid content equivalent; the same applies hereinafter) and an isocyanate-based crosslinking agent (Mitsui Mix 0.20 parts by mass of Kagaku Co., Ltd., product name "Takenate D110N") and 0.20 parts by mass of 3-glycidyloxypropyltrimethoxysilane (manufactured by Shin-Etsu Silicone Co., Ltd., KBM403) as the silane coupling agent (C). The mixture was sufficiently stirred and diluted with methyl ethyl ketone to obtain a coating solution of acrylic adhesive composition P1 having a solid content concentration of 45% by mass.

3. Preparation of urethane polymer 100 parts by mass of trifunctional polypropylene glycol (number average molecular weight 1000), 7 parts by mass of trimethylolpropane adduct of tolylene diisocyanate, 0.01 part by mass of dioctyltin dilaurate, and 43 parts by mass of toluene were charged. The reaction was carried out at ℃ for 3 hours. Then, when the presence of isocyanate groups could no longer be confirmed by an infrared spectrophotometer, the solution was cooled to obtain a polyurethane polyol solution.

4. Preparation of Adhesive Composition P2 100 parts by mass of the obtained polyurethane polyol and 15 parts by mass of trimethylolpropane adduct of tolylene diisocyanate were mixed, sufficiently stirred, and diluted with ethyl acetate to form urethane. A coating solution of adhesive composition P2 was obtained.

5. Manufacture of adhesive sheet A coating solution of the obtained adhesive composition P1 was applied to the release-treated surface of a release sheet (manufactured by Lintec Corporation, product name "SP-PET752150") with a knife so that the thickness after drying was 100 μm. It was applied with a coater. After coating, heat treatment is performed at 90° C. for 1 minute to advance the crosslinking reaction to form a coating layer consisting of an adhesive having a crosslinked structure composed of a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B). was formed.

Subsequently, the coating layer on the release sheet obtained above was bonded to the release-treated surface of another release sheet (manufactured by Lintec, product name "SP-PET381130") so that they were in contact with each other. Thereafter, by curing for 7 days under conditions of 23° C. and 50% RH, a first adhesive layer having a first adhesive layer made of an acrylic adhesive (first adhesive) sandwiched between two release sheets is cured. A laminate was obtained.

Next, a coating solution of the obtained adhesive composition P2 was applied to the release-treated surface of a release sheet (manufactured by Lintec Corporation, product name "SP-PET752150") using a knife coater so that the thickness after drying was 50 μm. It was coated with. After coating, the diluting solvent was sufficiently removed by heating at 90° C. for 1 minute to form a second adhesive layer made of a urethane adhesive (second adhesive). The second adhesive layer on the release sheet obtained above and the release-treated surface of another release sheet (manufactured by Lintec, product name "SP-PET381130") were bonded together so that they were in contact with each other. A second laminate sandwiched between release sheets was obtained.

One release sheet (SP-PET381130) was peeled off from the first laminate having the first adhesive layer to expose the first adhesive layer. Subsequently, one release sheet (SP-PET381130) was peeled off from the second laminate having the second adhesive layer to expose the second adhesive layer.

The exposed main surface of the first adhesive layer and the exposed main surface of the second adhesive layer are bonded together and sandwiched between two release sheets, so that the first adhesive layer and the second adhesive layer are bonded together. A core-less pressure-sensitive adhesive sheet having laminates laminated in contact with each other was obtained.

Note that the thickness of the adhesive layer is a value measured using a constant pressure thickness measuring device (PG-02 manufactured by Techlock Co., Ltd.) in accordance with JIS K7130.

(Example 2)
A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that the thickness of the second pressure-sensitive adhesive layer was changed to 75 μm.

(Example 3)
A pressure-sensitive adhesive sheet was produced in the same manner as in Example 2, except that the thickness of the first pressure-sensitive adhesive layer was changed to 75 μm.

(Comparative example 1)
A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that the thickness of the first pressure-sensitive adhesive layer was changed to 150 μm and the second pressure-sensitive adhesive layer was not formed. That is, the adhesive layer of the adhesive sheet according to Comparative Example 1 was a single layer of the first adhesive.

(Comparative example 2)
After drying, a coating solution of adhesive composition P1 was applied onto one main surface of a 50 μm thick polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name “Cosmoshine TA063 (50 μm)”) as a core material. A first adhesive layer made of an acrylic adhesive (first adhesive) is formed by coating the adhesive composition P2 to a thickness of 50 μm, and then a coating solution of adhesive composition P2 is applied to the other side of the PET film. Adhesive was applied in the same manner as in Example 1, except that a second adhesive layer consisting of a urethane adhesive (second adhesive) was formed by coating the main surface to a thickness of 75 μm after drying. The sheet was manufactured. That is, the adhesive sheet according to Comparative Example 2 had a configuration in which a PET film as a core material was disposed between the first adhesive layer and the second adhesive layer.

(Comparative example 3)
A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that the thickness of the second pressure-sensitive adhesive layer was changed to 150 μm and the first pressure-sensitive adhesive layer was not formed. That is, the adhesive layer of the adhesive sheet according to Comparative Example 3 was a single layer of the second adhesive.

The physical properties of the obtained pressure-sensitive adhesive sheet were measured as follows.

(A side adhesive strength)
The adhesive strength (A-side adhesive strength) of the first adhesive layer was measured as follows. For Examples 1 to 3 and Comparative Example 2, the release sheet on the second adhesive layer side was peeled off, and a well-adhesive PET with a thickness of 100 μm (manufactured by Toyobo Co., Ltd., PET100A- A sample for measurement was prepared by attaching the well-adhesive surface of 4100) by thermal lamination (70° C., 1 m/min). In addition, for Comparative Examples 1 and 3, one release sheet (manufactured by Lintec Corporation, product name "SP-PET381130") was peeled off, and a well-adhesive PET (100 μm thick) was applied to the surface of the exposed adhesive layer. A sample for measurement was prepared by attaching the well-adhesive surface of PET100A-4100 (manufactured by Toyobo Co., Ltd.) by thermal lamination (70° C., 1 m/min). The measurement sample obtained above was cut into 25 mm width and 100 mm length. The release sheet was peeled off from the measurement sample in an environment of 23° C. and 50% RH, and the exposed first adhesive layer was attached to soda lime glass (manufactured by Nippon Sheet Glass Co., Ltd.). At this time, the first adhesive layer was applied by pressing it back and forth once with a 2 kg roller. After pasting, it was left for 24 hours at 23° C. and 50% RH. After standing, the adhesive force (N/25 mm) of the first adhesive layer was measured using a tensile tester (Tensilon, manufactured by Orientech Co., Ltd.) at a peeling speed of 300 m/min and a peeling angle of 180°. Note that the measurements were conducted under conditions other than those described here in accordance with JIS Z0237:2009. The results are shown in Table 1.

(B side adhesive strength)
The adhesive strength of the second adhesive layer (B-side adhesive strength) was measured as follows. The adhesive sheets of Examples and Comparative Examples were cut into 25 mm width and 100 mm length to prepare measurement samples. For Examples 1 to 3 and Comparative Example 2, the release sheet on the second adhesive layer side was peeled off from the measurement sample obtained above in an environment of 23°C and 50% RH, and the exposed second adhesive layer was peeled off from the measurement sample obtained above. The adhesive layer was attached to soda lime glass (manufactured by Nippon Sheet Glass Co., Ltd.). In addition, for Comparative Examples 1 and 3, the release sheet (SP-PET381130) was peeled off from the measurement sample obtained above in an environment of 23°C and 50% RH, and the exposed second adhesive layer was removed. It was attached to soda lime glass (manufactured by Nippon Sheet Glass Co., Ltd.). At this time, the second adhesive layer was applied by pressing it back and forth once with a 2 kg roller. After pasting, it was left for 24 hours at 23° C. and 50% RH. After standing, the adhesive force (N/25 mm) of the second adhesive layer was measured using a tensile tester (Tensilon, manufactured by Orientech Co., Ltd.) at a peeling speed of 300 m/min and a peeling angle of 180°. Note that the measurements were conducted under conditions other than those described here in accordance with JIS Z0237:2009. The results are shown in Table 1.

(indentation depth and indentation rate)
The release sheet on the second adhesive layer side was peeled off from the adhesive sheets produced in Examples and Comparative Examples, and the exposed second adhesive layer was attached to soda lime glass (manufactured by Nippon Sheet Glass Co., Ltd.). Next, the release sheet placed on the main surface of the first adhesive layer was peeled off to expose the first adhesive layer, and the configuration of the glass plate/second adhesive layer/first adhesive layer was revealed. A laminate A having the following properties was produced. Similarly, a laminate B having a structure of glass plate with exposed second adhesive layer/first adhesive layer/second adhesive layer was produced. Using a texture analyzer (TA. Continuing, the indentation depth at the time when the load reached 5N was measured and was defined as the A-side indentation depth. Similarly, the indentation depth of the main surface (B surface) of the second adhesive layer in the laminate B was measured, and was defined as the B surface indentation depth. In Comparative Example 1, since the adhesive sheet did not have a second adhesive layer, only the A-side indentation depth was measured. In Comparative Example 3, since the adhesive sheet did not have the first adhesive layer, only the B-side indentation depth was measured. The results are shown in Table 1.

Furthermore, from the obtained indentation depth, the ratio (indentation rate) (%) of the indentation depth to the total thickness of the laminate was calculated. In Examples 1 to 3 and Comparative Examples 1 and 3, the total thickness of the laminate was the total thickness of the first adhesive layer and the second adhesive layer. In Comparative Example 2, the total thickness of the laminate was the total thickness of the first adhesive layer, the second adhesive layer, and the core material. The results are shown in Table 1.

(Total light transmittance)
The adhesive layers of the adhesive sheets obtained in Examples and Comparative Examples were bonded to glass, and this was used as a sample for measurement. After background measurement was performed on the glass, total light transmission was measured using a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., product name "NDH-5000") in accordance with JISK7361-1:1997 for the above measurement sample. The rate (%) was measured. The results are shown in Table 1.

(Haze)
The haze of the adhesive sheets obtained in Examples and Comparative Examples was measured using a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., NDH-5000) in accordance with JISK7136:2000. The results obtained are shown in Table 1.

The following evaluations were performed on the pressure-sensitive adhesive sheets manufactured in Examples and Comparative Examples.

(Step followability)
On the surface of a glass plate (manufactured by NSG Precision, product name: Corning Glass Eagle A glass plate with a step was produced having a printing step of 90 mm long x 50 mm wide, 5 mm wide, and 5 μm high.

For Examples 1 to 3 and Comparative Example 2, the release sheet on the second adhesive layer side was peeled off, and the exposed second adhesive layer was placed on a glass plate (manufactured by NSG Precision, product name "Corning Glass Eagle XG", A laminate of 90 mm in length x 50 mm in width x 0.5 mm in thickness was laminated to produce a laminate for evaluation of step followability. In addition, for Comparative Examples 1 and 3, one release sheet (manufactured by Lintec Corporation, product name "SP-PET381130") was peeled off, and the exposed adhesive layer was removed from the glass plate (manufactured by NSG Precision Corporation, product name "SP-PET381130"). Corning Glass Eagle Next, the release sheet of the laminate for evaluation of step followability was peeled off to expose the adhesive layer. Then, using a laminator (manufactured by Fujipla Corporation, product name "LPD3214"), the exposed surface of the adhesive layer and the stepped surface of the stepped glass plate were bonded together so that the adhesive layer covered the entire frame-shaped printed surface. This was used as a sample for evaluation.

After autoclaving the obtained evaluation sample for 20 minutes at 50°C and 0.5 MPa, the adhesive layer pasted near the step was visually confirmed, and the initial step tracking was determined according to the following criteria. The gender was evaluated. Further, even after being allowed to stand for 12 hours in an environment of 23° C. and 50% RH, the adhesive layer bonded near the step was visually confirmed, and the followability of the step was evaluated according to the following criteria. The results are shown in Table 1.
A: All steps are followed, and no bubbles or peeling are observed.
F: Bubbles and peeling were observed at the stepped portion.

(Curved surface followability)
The release sheet on the first adhesive layer side was peeled off from the adhesive sheets obtained in Examples and Comparative Examples, and the exposed first adhesive layer was bonded to the inside of a plastic molded plate having a curved surface of 10 mmφ. . The adhesive layer after lamination was visually confirmed, and curved surface followability was evaluated according to the following criteria. The results are shown in Table 1.
A: It follows the curved surface, and no bubbles or peeling are observed.
E: At the beginning of lamination, it followed the curved surface, but after 1 minute, bubbles and peeling were observed on the curved surface.
F: Bubbles and peeling were observed, and the film did not conform to curved surfaces.

(Reworkability)
Reworkability was evaluated as follows. The release sheet on the second adhesive layer side was peeled off from the adhesive sheets obtained in Examples and Comparative Examples, and the exposed second adhesive layer was removed from a glass plate (manufactured by NSG Precision, product name "Corning Glass Eagle XG", It was pasted onto a surface measuring 90 mm long x 50 mm wide x 0.5 mm thick. After standing for 10 minutes in an environment of 23° C. and 50% RH, an attempt was made to peel off the second adhesive layer from the glass plate, and the reworkability was evaluated based on the following criteria. The results are shown in Table 1.
A: It could be easily peeled off from the glass plate, and there was no adhesive residue on the glass plate.
E: It was easily peeled off from the glass plate, but adhesive residue was left on the glass plate.
F: It adhered closely to the glass plate and could not be peeled off.

From Table 1, it was confirmed that the pressure-sensitive adhesive sheets of Examples 1 to 3 exhibited good step followability and curved surface followability, and good reworkability.

The pressure-sensitive adhesive sheet of the present invention has good reworkability and can be suitably used, for example, to bond members having steps and/or curved surfaces.

1... Adhesive sheet 10... Laminate 11... First adhesive layer 12... Second adhesive layer 21, 22... Release sheet

Claims (8)

1. An adhesive sheet having a laminate in which a first adhesive layer and a second adhesive layer are laminated,
   Among the surfaces of the laminate, when the surface on the first adhesive layer side is defined as side A, and the surface on the second adhesive layer side is defined as side B, the adhesive strength of the above A side is equal to that of the B side. greater than the adhesive strength,
   Continue to push in the A side at a pushing speed of 0.01 mm/sec, the pushing depth when the pushing load reaches 5N is the A side pushing depth, and continue pushing the B side at a pushing speed of 0.01 mm/sec. When the indentation depth at the time when the indentation load becomes 5N is the B-side indentation depth, the A-side indentation rate, which is the A-side indentation depth with respect to the thickness of the laminate, and the thickness of the laminate. A pressure-sensitive adhesive sheet having a B-side indentation ratio, which is the B-side indentation depth relative to the B-side indentation depth, of 35% or more.
2. The adhesive sheet according to claim 1, wherein in the laminate, the first adhesive layer and the second adhesive layer are in contact with each other.
3. The adhesive sheet according to claim 1 or 2, wherein the B-side indentation rate is greater than the A-side indentation rate.
4. The adhesive sheet according to any one of claims 1 to 3, wherein the ratio of the adhesive strength of the A side to the adhesive strength of the B side is within a range of 2 or more and 10,000 or less.
5. The adhesive sheet according to any one of claims 1 to 4, wherein the first adhesive layer has a thickness of 30 μm or more and 800 μm or less.
6. The adhesive sheet according to any one of claims 1 to 5, wherein the second adhesive layer has a thickness of 10 μm or more and 300 μm or less.
7. The adhesive sheet according to any one of claims 1 to 6, wherein the first adhesive layer is made of an acrylic adhesive, and the second adhesive layer is made of a urethane adhesive.
8. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, wherein the pressure-sensitive adhesive sheet includes a release sheet disposed on the A side and a release sheet disposed on the B side.

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