JP7574696B2 - Manufacturing method of laminate - Google Patents

Description

The present invention relates to a method for manufacturing a laminate.

Traditionally, input devices used in combination with display devices such as liquid crystal displays (LCDs) or display devices such as touch panels have been widely used. In the manufacture of these display devices and input devices, a transparent adhesive sheet is used when bonding optical members. A transparent adhesive sheet is also used when bonding the display device and the input device together, thereby forming the desired laminate.

After optical components are bonded together with an adhesive sheet, there is a demand to re-attach the adhesive sheet, i.e., to rework (re-peel off) the adhesive sheet in order to adjust the position of the optical components or to remove foreign matter such as air bubbles between the components. For this reason, development of adhesive sheets with improved reworkability is also underway. For example, Patent Documents 1 to 3 disclose technologies that can impart reworkability to adhesive sheets by incorporating particles into the adhesive layer.

International Publication No. 2019/239616 JP 2015-3943 A JP 2015-3944 A

However, while the techniques disclosed in Patent Documents 1 to 3 can impart reworkability to pressure-sensitive adhesive sheets, the inclusion of particles increases haze and impairs transparency, limiting their use in optical applications and making it difficult to obtain desired laminates. As such, there is a trade-off between reworkability and transparency, making it difficult to achieve both reworkability during the manufacturing process and the transparency of the resulting laminate.

The present invention has been made in view of the above, and aims to provide a manufacturing method that is suitable for obtaining a laminate that has excellent reworkability during the manufacturing process and requires transparency.

As a result of extensive research into achieving the above objective, the inventors discovered that the above objective could be achieved by using an adhesive sheet composed of specific components, leading to the completion of the present invention.

That is, the present invention includes, for example, the subject matter described in the following sections.
Item 1
A method for producing a laminate, comprising the steps of:
A step of bonding the pressure-sensitive adhesive sheet and the adherend together for temporary adhesion;
and a step of carrying out a heat treatment or a heat and pressure treatment to actually bond the pressure-sensitive adhesive sheet and the adherend,
The pressure-sensitive adhesive sheet is formed of a cured product of a pressure-sensitive adhesive composition,
The pressure-sensitive adhesive composition contains a crosslinkable (meth)acrylic copolymer (A), a methyl methacrylate polymer (B), (meth)acrylic resin particles (C), and a crosslinking agent (D),
The crosslinkable (meth)acrylic copolymer (A) is a polymer containing (meth)acrylic ester units (a) having an alkyl group having 4 to 10 carbon atoms and monomer units (b) having a carboxy group and/or a hydroxyl group,
The crosslinkable (meth)acrylic copolymer (A) contains 50 to 95% by mass of the (meth)acrylic ester unit (a) and 1 to 50% by mass of the monomer unit (b),
The weight average molecular weight of the methyl methacrylate polymer (B) is 1,000 to 10,000;
The methyl methacrylate polymer (B) is contained in an amount of 1 to 15 parts by mass per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A),
The (meth)acrylic resin particles (C) have an average particle size of 0.1 to 5 μm,
The crosslinking agent (D) is contained in an amount of 0.01 to 5 parts by mass per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A),
In an elastic modulus image taken of the surface in Peak Force Tapping mode using an atomic force microscope, there are 3 to 20 spherical or island-like areas having a higher elastic modulus than the surrounding areas within any 10 μm square range,
A method for producing a laminate, which is a pressure-sensitive adhesive sheet that satisfies the following physical properties (1) and (2):
Physical properties (1): The adhesive strength to glass 30 minutes after application, measured according to the adhesive strength measuring method described in JIS Z 0237, is 0.01 to 5 N/25 mm.
Physical property (2): The adhesive sheet is applied to a glass plate and heat-treated at 100° C. and 0.5 MPa for 30 minutes. The adhesive strength to glass measured according to the adhesive strength measuring method described in JIS Z 0237 is 10 N/25 mm or more.
Item 2
Item 2. The method for producing a laminate according to item 1, wherein the main bonding is performed by heat treatment at 50 to 120° C. for 1 to 120 minutes.
Item 3
Item 3. The method for producing a laminate according to item 1 or 2 , wherein a refractive index difference between the crosslinkable (meth)acrylic copolymer (A) and the (meth)acrylic resin particles (C) is 0 to 0.05.
Item 4
4. The method for producing a laminate according to any one of items 1 to 3 , wherein the crosslinking agent (D) comprises one selected from the group consisting of an isocyanate compound, an epoxy compound, and a metal chelate.
Item 5
Item 5. The method for producing a laminate according to any one of items 1 to 4 , wherein the laminate is for an optical device or an image display device.

The method for producing a laminate of the present invention has excellent reworkability during the production process and is suitable as a method for obtaining a laminate that requires transparency.

FIG. 2 is a schematic diagram illustrating an example of a laminate. 1 is a schematic diagram showing an example of a pressure-sensitive adhesive sheet with a release sheet used in the manufacturing method of the present invention. 1 is an example of an elastic modulus image of the surface of a pressure-sensitive adhesive sheet taken in Peak Force Tapping mode using an atomic force microscope.

The embodiments of the present invention will be described in detail below. In this specification, the expressions "contain" and "include" include the concepts of "contain", "include", "consist essentially of" and "consist only of". In addition, in this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower and upper limits.

1. Manufacturing method of laminate The manufacturing method of the laminate of the present invention comprises a step of laminating an adhesive sheet and an adherend to temporarily bond them, and a step of performing a heat treatment or a heat and pressure treatment to bond the adhesive sheet and the adherend. In this manufacturing method, an adhesive sheet that is composed of specific components and has predetermined physical properties is used, so that the manufacturing method has excellent reworkability during the manufacturing process. In addition, the adhesive sheet used in the manufacturing method of the present invention has excellent transparency, so it is suitable as a method for obtaining a laminate that requires transparency.

Hereinafter, the process of laminating the adhesive sheet and the adherend to form a temporary bond will be referred to as "Process 1," and the process of permanently bonding the adhesive sheet and the adherend by a heat treatment or a heat and pressure treatment will be referred to as "Process 2."

In step 1, there is no particular limitation on the method for contacting the adhesive sheet with the adherend. For example, pressure can be applied appropriately while the adhesive sheet and the adherend are in contact with each other. This pressure can be applied using a known pressure device such as a hand roller or a laminator. Temporary adhesion can also be achieved by simply contacting the adhesive sheet with the adherend without applying pressure.

When the adhesive sheet is a double-sided adhesive sheet, the adherend can be brought into contact with both sides of the adhesive sheet to perform temporary adhesion. Step 1 results in a laminate (temporarily bonded laminate) in which the adherend is temporarily bonded with the adhesive sheet.

Step 2 is a step for subjecting the temporarily bonded laminate obtained in step 1 to a heat treatment or heat and pressure treatment. This results in a stronger bond between the adhesive sheet and the adherend, forming a fully bonded laminate.

The temperature in the heating treatment or heating and pressurizing treatment in step 2 is preferably 50°C or higher, more preferably 80°C or higher, and preferably 120°C or lower, and more preferably 110°C or lower. The time in the heating treatment or heating and pressurizing treatment can be adjusted appropriately depending on the heating temperature, and is, for example, preferably 1 minute or higher, more preferably 5 minutes or higher, and even more preferably 10 minutes or higher, and preferably 120 minutes or lower, more preferably 100 minutes or lower, and even more preferably 90 minutes or lower. When the heating and pressurizing treatment is performed on the temporary adhesive laminate in step 2, the pressure conditions can be, for example, a pressure of 0.2 to 0.9 MPa.

The number of times the heat treatment or heat-pressure treatment is performed in step 2 is not particularly limited, and may be, for example, only once, or may be multiple times. In addition, when the adhesive sheet is a double-sided adhesive sheet, the adhesive sheet may be attached to one of the adherends and subjected to the heat treatment or heat-pressure treatment, and then the adherend may be attached to the other side of the adhesive sheet and subjected to the heat treatment or heat-pressure treatment.

According to the manufacturing method of the present invention, a laminate is obtained using an adhesive sheet with excellent reworkability, as described below. Therefore, in the temporary adhesion of step 1, when position adjustment between the adhesive sheet and the adherend, quality inspection, re-attachment, etc. become necessary, the adhesive sheet can be easily peeled off from the adherend. In addition, even when the adhesive sheet is peeled off from the adherend, the occurrence of adhesive residue from the adhesive sheet is suppressed.

Furthermore, after the main adhesion is performed by the heat treatment or heat and pressure treatment in step 2, the adhesive sheet and the adherend are firmly adhered to each other, and a laminate in which each layer is firmly adhered to each other can be obtained.

The laminate obtained by the manufacturing method of the present invention has low haze (i.e., high transparency), so the transparency of the obtained laminate is not easily impaired. Therefore, the manufacturing method of the present invention is suitable for manufacturing laminates that require high transparency.

2. Laminate The laminate obtained by the manufacturing method of the present invention comprises a pressure-sensitive adhesive sheet and an adherend. When a double-sided pressure-sensitive adhesive sheet is used as the pressure-sensitive adhesive sheet, the adherend is preferably provided directly on both sides of the pressure-sensitive adhesive sheet. In this case, the laminate has a structure in which the adherend/pressure-sensitive adhesive sheet/adherend are laminated in this order.

The type of adherend is not particularly limited, and it can be used, for example, to bond optical components used in optical devices, etc.

Examples of optical components include components in optical products such as touch panels or image display devices. Examples of components in touch panels include an ITO film in which an ITO film is provided on a transparent resin film, ITO glass in which an ITO film is provided on the surface of a glass plate, a transparent conductive film in which a transparent resin film is coated with a conductive polymer, a hard coat film, and a fingerprint-resistant film.

Constituent members of image display devices include, for example, anti-reflection films, alignment films, polarizing films, retardation films, and brightness enhancement films used in liquid crystal display devices. In the method for manufacturing the laminate of the present invention, modules such as a liquid crystal module and a touch panel module may be bonded together.

Specific examples of materials that may be used to form the adherend include glass, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, polyethylene naphthalate, cycloolefin polymer, triacetyl cellulose, polyimide, and cellulose acylate.

Figure 1 shows an example of a laminate obtained by the manufacturing method of the present invention. As shown in this Figure 1, the laminate 100 is preferably formed by laminating adherend 50 / pressure-sensitive adhesive layer 11 / adherend 50 in this order.

The laminate obtained by the manufacturing method of the present invention can be used in various applications, and can be suitably used in, for example, optical devices, image display devices, etc. In particular, since the laminate is formed by bonding with a highly transparent adhesive sheet, the design and visibility of the image can be further improved when applied to optical devices, image display devices, etc.

The adhesive sheet used in the manufacturing method of the present invention (hereinafter simply referred to as "adhesive sheet") is formed from a cured product of an adhesive composition. In other words, the adhesive sheet is obtained by curing the adhesive composition.

The pressure-sensitive adhesive composition contains a crosslinkable (meth)acrylic copolymer (A), a methyl methacrylate polymer (B), (meth)acrylic resin particles (C), and a crosslinking agent (D). In addition, the pressure-sensitive adhesive sheet has 3 to 20 spherical or island-like areas with a higher elastic modulus than the surrounding area within any 10 μm square range in an elastic modulus image taken of the surface using an atomic force microscope (hereinafter also referred to as "AFM") in Peak Force Tapping mode, and also has the physical properties (1) and (2) described below.

The adhesive sheet has excellent reworkability (i.e., position adjustment ability) and is also highly transparent. In addition to having an initial adhesive strength suitable for reworkability, the adhesive sheet has the property that the adhesive strength can be increased by heating after bonding the adherends together (so-called heat adhesion). This makes it possible for the adhesive sheet to firmly bond the adherends together.

<Crosslinkable (meth)acrylic copolymer (A)>
The crosslinkable (meth)acrylic copolymer (A) is a polymer containing (meth)acrylic ester units (a) having an alkyl group with 4 to 10 carbon atoms and monomer units (b) having a carboxy group and/or a hydroxyl group. The terms "unit" and "monomer unit" in the (meth)acrylic ester units (a) refer to repeating units constituting a polymer. Hereinafter, the (meth)acrylic ester units (a) having an alkyl group with 4 to 10 carbon atoms will be referred to simply as "(meth)acrylic ester units (a)" and the monomer units (b) having a carboxy group and/or a hydroxyl group will be referred to simply as "monomer units (b)."

In addition, in this specification, "(meth)acrylic" means "acrylic" or "methacrylic", "(meth)acrylate" means "acrylate" or "methacrylate", and "(meth)allyl" means "allyl" or "methallyl".

The (meth)acrylic ester unit (a) is a repeating unit derived from a (meth)acrylic ester compound having an alkyl group having 4 to 10 carbon atoms. Examples of the (meth)acrylic ester compound having an alkyl group having 4 to 10 carbon atoms include a wide variety of known (meth)acrylic ester compounds, specifically, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, and the like. It is preferable that the (meth)acrylic ester compound having an alkyl group having 4 to 10 carbon atoms does not have a hydroxyl group or a carboxy group.

In the (meth)acrylic ester unit (a), the alkyl group preferably has 4 to 8 carbon atoms, and more preferably has 4 to 6 carbon atoms.

The (meth)acrylic ester unit (a) contained in the crosslinkable (meth)acrylic copolymer (A) may be of only one type, or may contain two or more types.

In the crosslinkable (meth)acrylic copolymer (A), the content of the (meth)acrylic ester unit (a) is 50% by mass or more and 95% by mass or less. In this case, the adhesive sheet can have the desired reworkability and transparency and satisfies the physical properties (1) and (2). If the content of the (meth)acrylic ester unit (a) is less than 50% by mass, the initial adhesive performance (adhesive performance before heat treatment) of the adhesive sheet may deteriorate. In terms of the reworkability and transparency of the adhesive sheet being more easily improved, the content of the (meth)acrylic ester unit (a) in the crosslinkable (meth)acrylic copolymer (A) is preferably 55% by mass or more, more preferably 60% by mass or more, even more preferably 65% by mass or more, and particularly preferably 70% by mass or more. In addition, in order to more easily improve the reworkability and transparency of the pressure-sensitive adhesive sheet, the content of (meth)acrylic ester units (a) in the crosslinkable (meth)acrylic copolymer (A) is preferably 94% by mass or less, more preferably 93% by mass or less, even more preferably 92% by mass or less, and particularly preferably 90% by mass or less.

In the present invention, the content of each constituent unit in the crosslinkable (meth)acrylic copolymer (A) can be considered to be equal to the amount of polymerizable monomer derived from the corresponding constituent unit used when producing the crosslinkable (meth)acrylic copolymer (A).

Monomer unit (b) is a repeating unit derived from a monomer having a carboxy group and/or a hydroxyl group.

The monomer having a carboxy group can be, for example, a wide variety of known polymerizable monomers containing a carboxy group, specifically acrylic acid, methacrylic acid, etc.

Examples of monomers having a hydroxyl group include a wide variety of known hydroxyl group-containing polymerizable monomers, specifically 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, polyalkylene glycol mono(meth)acrylate, etc.

The crosslinkable (meth)acrylic copolymer (A) may contain, as the monomer unit (b), both a monomer unit having a carboxy group and a monomer unit having a hydroxyl group, or may contain only one of them. When the monomer unit (b) contains both a monomer unit having a carboxy group and a monomer unit having a hydroxyl group, the content ratio of these is not particularly limited, and the desired adhesive sheet can be obtained at any content ratio.

In the crosslinkable (meth)acrylic copolymer (A), the content of the monomer unit (b) is 1% by mass or more and 50% by mass or less. If the content of the monomer unit (b) is less than 1% by mass, the initial adhesive performance (adhesive performance before heat treatment) of the adhesive sheet deteriorates, and if it exceeds 50% by mass, the initial adhesive strength of the adhesive sheet becomes too large and the desired reworkability cannot be obtained. In this case, the adhesive sheet can have the desired reworkability and transparency and satisfies the physical properties (1) and (2). In terms of the adhesive sheet being likely to have excellent reworkability and transparency, the content of the monomer unit (b) in the crosslinkable (meth)acrylic copolymer (A) is preferably 1.5% by mass or more, more preferably 2% by mass or more, and even more preferably 2.5% by mass or more. In addition, in order to ensure that the pressure-sensitive adhesive sheet has excellent reworkability and transparency, the content of the monomer unit (b) in the crosslinkable (meth)acrylic copolymer (A) is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, and particularly preferably 20% by mass or less.

The crosslinkable (meth)acrylic copolymer (A) may contain other structural units in addition to the (meth)acrylic ester unit (a) and the monomer unit (b) as long as the effect of the present invention is not impaired. Examples of other structural units include a wide range of structural units derived from compounds that are copolymerizable with the (meth)acrylic ester compound. Specific examples of such compounds include (meth)acrylic ester compounds having 3 or less carbon atoms (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, etc.), (meth)acrylonitrile, vinyl acetate, styrene, vinyl chloride, vinylpyrrolidone, vinylpyridine, etc., and also include amino group-containing (meth)acrylic esters, glycidyl group-containing (meth)acrylic esters, alkoxyalkyl group-containing (meth)acrylic esters, etc.

When the crosslinkable (meth)acrylic copolymer (A) contains the other structural units, the content is 15% by mass or less, preferably 10% by mass or less, and more preferably 5% by mass or less, based on the total mass of the crosslinkable (meth)acrylic copolymer (A). The crosslinkable (meth)acrylic copolymer (A) may be composed of only (meth)acrylic ester units (a) and monomer units (b) (i.e., the content of the other structural units in the crosslinkable (meth)acrylic copolymer (A) may be 0% by mass).

In the crosslinkable (meth)acrylic copolymer (A), the order of arrangement of each constituent unit is not particularly limited, and it is possible to form, for example, a random copolymer, a block copolymer, a graft copolymer, etc., and a random copolymer is preferable in terms of ease of production.

The weight average molecular weight of the crosslinkable (meth)acrylic copolymer (A) is not particularly limited. For example, the weight average molecular weight of the crosslinkable (meth)acrylic copolymer (A) is preferably 100,000 to 2,000,000, and more preferably 200,000 to 1,500,000, in order to keep the initial adhesive strength of the adhesive sheet low while making it easy to increase the adhesive strength after heating. The weight average molecular weight of the crosslinkable (meth)acrylic copolymer means the value before crosslinking with a crosslinking agent described later. The weight average molecular weight of the crosslinkable (meth)acrylic copolymer (A) is measured by gel permeation chromatography (GPC) and is a value calculated based on polystyrene standards.

The pressure-sensitive adhesive composition may contain only one type of crosslinkable (meth)acrylic copolymer (A), or may contain two or more types.

The method for producing the crosslinkable (meth)acrylic copolymer (A) is not particularly limited, and the crosslinkable (meth)acrylic copolymer (A) can be obtained, for example, by a production method using a known polymerization method. The crosslinkable (meth)acrylic copolymer (A) can also be obtained from commercial products, etc.

The refractive index of the crosslinkable (meth)acrylic copolymer (A) is not particularly limited. From the viewpoint of increasing the transparency of the pressure-sensitive adhesive sheet, the refractive index of the crosslinkable (meth)acrylic copolymer (A) is preferably 1.45 to 1.50, and more preferably 1.46 to 1.49.

The refractive index of the crosslinkable (meth)acrylic copolymer (A) referred to here is the value measured by Method A described in JIS K 7142 (2014) "Plastics - Determination of refractive index."

<Methyl methacrylate polymer (B)>
The methyl methacrylate polymer (B) is a polymer obtained by polymerizing a polymerizable monomer M mainly composed of methyl methacrylate (MMA). The polymerizable monomer M preferably contains 50% by mass or more of MMA, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. When the polymerizable monomer M contains a polymerizable monomer other than MMA, the type is not particularly limited. The polymerizable monomer M may be only MMA. In this case, the inclusion of a monomer inevitably contained in MMA is permitted.

The weight average molecular weight of the methyl methacrylate polymer (B) is not particularly limited. For example, the weight average molecular weight of the methyl methacrylate polymer (B) is preferably 1,000 to 10,000, in that it is easy to improve the reworkability of the pressure-sensitive adhesive sheet and the haze can be further reduced. The weight average molecular weight of the methyl methacrylate polymer (B) is a value measured by gel permeation chromatography (GPC) and calculated based on polystyrene standards.

The methyl methacrylate polymer (B) may have either a non-crosslinked structure or a crosslinked structure.

The adhesive composition may contain only one type of methyl methacrylate polymer (B), or may contain two or more types.

The method for producing the methyl methacrylate polymer (B) is not particularly limited, and for example, the methyl methacrylate polymer (B) can be obtained by a production method using a known polymerization method. The methyl methacrylate polymer (B) can also be obtained from commercial products, etc.

<(Meth)acrylic resin particles (C)>
The (meth)acrylic resin particles (C) are a fine particle material containing a (meth)acrylic resin as a main component.

In the (meth)acrylic resin particles (C), the type of (meth)acrylic resin is not particularly limited, and a wide variety of known (meth)acrylic resins can be exemplified. Examples of (meth)acrylic resins include polymers of (meth)acrylic acid esters. Specific examples of such (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, and propyl (meth)acrylate, as well as the above-mentioned (meth)acrylic ester compounds having an alkyl group with 4 to 10 carbon atoms, hydroxyalkyl (meth)acrylate (having an alkyl carbon number of, for example, 2 to 10), and glycidyl (meth)acrylate. Among these, the (meth)acrylic resin is preferably a methyl (meth)acrylate polymer, in that it is easy to impart reworkability to the pressure-sensitive adhesive sheet and to reduce haze.

The (meth)acrylic resin in the (meth)acrylic resin particles (C) may be a homopolymer or a copolymer. When the (meth)acrylic resin is a copolymer, examples include polymers containing two or more of the above-mentioned (meth)acrylic ester units, and the (meth)acrylic resin may also be a copolymer of a (meth)acrylic ester and a polymerizable monomer other than the (meth)acrylic ester. Examples of polymerizable monomers other than the (meth)acrylic ester include styrene, α-methylstyrene, maleic anhydride, (meth)acrylonitrile, vinyl acetate, vinyl chloride, vinylpyrrolidone, and vinylpyridine.

The (meth)acrylic resin in the (meth)acrylic resin particles (C) is preferably a homopolymer of a (meth)acrylic acid ester, a copolymer of a (meth)acrylic acid ester, or a copolymer of a (meth)acrylic ester and a polymerizable monomer other than the (meth)acrylic ester, and more preferably a homopolymer of a (meth)acrylic acid ester or a copolymer of a (meth)acrylic acid ester. Among these, it is particularly preferable that the (meth)acrylic resin particles (C) are crosslinked or non-crosslinked polymethyl methacrylate particles, in that the refractive index and haze can be easily adjusted.

The (meth)acrylic resin in the (meth)acrylic resin particles (C) can have a crosslinked structure or a non-crosslinked structure. When the (meth)acrylic resin has a crosslinked structure, the crosslinked structure can be formed by a known crosslinking agent such as a polyfunctional polymerizable monomer.

The average particle size of the (meth)acrylic resin particles (C) is not particularly limited. In terms of improving the reworkability of the adhesive sheet and reducing haze, the average particle size of the (meth)acrylic resin particles (C) is preferably 0.1 to 5 μm, and more preferably 0.2 to 3 μm.

In this specification, the average particle size of the (meth)acrylic resin particles (C) means a value measured using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). Specifically, one fine particle observed in a TEM image or SEM image of the pressure-sensitive adhesive sheet is randomly selected, and its maximum length (Dmax) and maximum perpendicular length (DV-max) are measured to calculate the geometric mean value of the fine particle (i.e., the value of (Dmax x DV-max) ^1/2 ). The geometric mean value of each of a total of 100 fine particles is calculated in the same manner, and the average value is determined as the average particle size of the (meth)acrylic resin particles (C) contained in the pressure-sensitive adhesive sheet. That is, the average particle size of the (meth)acrylic resin particles (C) means the number-average particle size. The maximum length (Dmax) is the maximum length at two points on the contour of the particle image, and the maximum perpendicular length (DV-max) is the shortest length between two straight lines parallel to the maximum length when the particle image is sandwiched between these two straight lines.

The refractive index of the (meth)acrylic resin particles (C) is not particularly limited. From the viewpoint of increasing the transparency of the adhesive sheet, the refractive index of the (meth)acrylic resin particles (C) is preferably 1.45 to 1.51, and more preferably 1.46 to 1.50.

More specifically, with regard to the refractive index of the (meth)acrylic resin particles (C), it is further preferable that the difference (absolute value) in the refractive index between the crosslinkable (meth)acrylic copolymer (A) and the (meth)acrylic resin particles (C) contained in the pressure-sensitive adhesive composition is 0 to 0.05. In this case, the pressure-sensitive adhesive sheet can have better transparency.

The refractive index of the (meth)acrylic resin particles (C) referred to here is the value measured by method B described in JIS K 7142 (2014) "Plastics - Determination of refractive index."

The adhesive composition may contain only one type of (meth)acrylic resin particles (C), or may contain two or more types.

The method for producing the (meth)acrylic resin particles (C) is not particularly limited, and the (meth)acrylic resin particles (C) can be produced, for example, by a method similar to a known method. The (meth)acrylic resin particles (C) can also be obtained from commercial products.

<Crosslinking Agent (D)>
The crosslinking agent (D) may be a wide variety of components capable of promoting the crosslinking reaction of the crosslinkable (meth)acrylic copolymer (A). In particular, the crosslinking agent may be a wide variety of components capable of reacting with a carboxy group or a hydroxyl group.

Such a crosslinking agent (D) can be selected from known crosslinking agents such as isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, metal chelate compounds, and butylated melamine compounds.

Among them, it is preferable that the crosslinking agent (D) contains one selected from the group consisting of an isocyanate compound, an epoxy compound, and a metal chelate. In this case, the resulting pressure-sensitive adhesive sheet can exhibit excellent reworkability and tends to have high transparency. When the crosslinking agent (D) contains a metal chelate, it is preferable to use a crosslinking retarder described below in combination.

Examples of isocyanate compounds include polyisocyanates such as tolylene diisocyanate, isophorone diisocyanate, chlorophenylene diisocyanate, diphenylmethane diisocyanate, butylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and xylylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate and cyclohexylene diisocyanate; and aromatic isocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, and 4,4'-diphenylmethane diisocyanate. The isocyanate compounds can be used alone or in combination of two or more different types. Examples of commercially available products include a tolylene diisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) and a xylylene diisocyanate compound (Takenate D-110N, manufactured by Mitsui Chemicals, Inc.).

Examples of epoxy compounds include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexanone, trimethylolpropane polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and sorbitol polyglycidyl ether. Commercially available epoxy compounds include, for example, TETRAD-C (manufactured by Mitsubishi Gas Chemical Co., Ltd.) and TETRAD-X (manufactured by Mitsubishi Gas Chemical Co., Ltd.).

Examples of metal chelate compounds include known metal chelate compounds used in crosslinking reactions, and examples of commercially available products include Aluminum Chelate A (manufactured by Kawaken Fine Chemicals Co., Ltd.).

<Adhesive composition>
As described above, the pressure-sensitive adhesive composition contains the crosslinkable (meth)acrylic copolymer (A), the methyl methacrylate polymer (B), the (meth)acrylic resin particles (C), and the crosslinking agent (D).

In the adhesive composition, the methyl methacrylate polymer (B) is contained in an amount of 1 to 15 parts by mass per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A). If the content of the methyl methacrylate polymer (B) per 100 parts by mass of the (meth)acrylic copolymer (A) is less than 1 part by mass, the initial adhesive strength of the adhesive sheet becomes too large and the desired reworkability cannot be obtained, and if the content exceeds 15 parts by mass, the haze increases and the transparency of the adhesive sheet deteriorates. The methyl methacrylate polymer (B) is preferably contained in an amount of 2 parts by mass or more per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A), more preferably 2.5 parts by mass or more, and even more preferably 3 parts by mass or more. In addition, the methyl methacrylate polymer (B) is preferably contained in an amount of 14 parts by mass or less per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A), more preferably 13 parts by mass or less, and even more preferably 12 parts by mass or less.

In the pressure-sensitive adhesive composition, the content of the (meth)acrylic resin particles (C) is not particularly limited, and can be, for example, 0.3 to 5 parts by mass, and preferably 0.5 to 3 parts by mass, per 100 parts by mass of the total mass of the crosslinkable (meth)acrylic copolymer (A). In this case, the obtained pressure-sensitive adhesive sheet can have a small haze value while maintaining excellent reworkability.

In the pressure-sensitive adhesive composition, the content of the crosslinking agent (D) is not particularly limited, and can be, for example, 0.01 to 5 parts by mass per 100 parts by mass of the total mass of the crosslinkable (meth)acrylic copolymer (A). In this case, the processability of the resulting pressure-sensitive adhesive sheet is likely to be improved. The content of the crosslinking agent (D) can be 0.05 to 3 parts by mass per 100 parts by mass of the total mass of the crosslinkable (meth)acrylic copolymer (A).

As described above, the adhesive composition contains the crosslinkable (meth)acrylic copolymer (A), the methyl methacrylate polymer (B), the (meth)acrylic resin particles (C), and the crosslinking agent (D), and may also contain a solvent as necessary. When the adhesive composition contains a solvent, the coatability of the adhesive composition is improved, making it easier to form an adhesive sheet.

Examples of solvents include hydrocarbons such as hexane, heptane, octane, toluene, xylene, ethylbenzene, cyclohexane, and methylcyclohexane; halogenated hydrocarbons such as dichloromethane, trichloroethane, trichloroethylene, tetrachloroethylene, and dichloropropane; alcohols such as methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutyl alcohol, and diacetone alcohol; ethers such as diethyl ether, diisopropyl ether, dioxane, and tetrahydrofuran; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, isophorone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, amyl acetate, and ethyl butyrate; and polyols and derivatives thereof such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monomethyl ether acetate.

The content of the solvent in the adhesive composition is not particularly limited, and is preferably 25 to 500 parts by mass, and more preferably 30 to 400 parts by mass, per 100 parts by mass of the crosslinkable (meth)acrylic copolymer. In addition, the content of the solvent relative to the total mass of the adhesive composition is preferably 10 to 90% by mass, and more preferably 20 to 80% by mass.

The adhesive composition may contain one solvent or two or more solvents.

The adhesive composition may contain other components in addition to those described above, provided that the effects of the present invention are not impaired. Examples of other components include known components used as additives to adhesive compositions. Other components may be selected as necessary from, for example, crosslinking retarders, plasticizers, antioxidants, metal corrosion inhibitors, tackifiers, silane coupling agents, ultraviolet absorbers, and light stabilizers such as hindered amine compounds. Dyes and pigments may also be added for coloring purposes.

Examples of crosslinking retarders include acetylacetone. In particular, when the crosslinking agent (D) contains a metal chelate, it is preferable to use a crosslinking retarder in combination. Examples of plasticizers include non-functional acrylic polymers. Examples of non-functional acrylic polymers include polymers consisting of only acrylic monomer units that have no functional groups other than acrylate groups, and polymers consisting of acrylic monomer units that have no functional groups other than acrylate groups and non-acrylic monomer units that have no functional groups. Since non-functional acrylic polymers do not crosslink, they can improve step-following ability without affecting adhesion.

Examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, lactone-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants. These antioxidants may be used alone or in combination of two or more. As a metal corrosion inhibitor, benzoriazole-based resins are preferred because of their compatibility with the adhesive and their high effectiveness. Examples of the tackifier include rosin-based resins, terpene-based resins, terpene-phenol-based resins, coumarone-indene-based resins, styrene-based resins, xylene-based resins, phenol-based resins, and petroleum resins. Examples of the silane coupling agent include mercaptoalkoxysilane compounds (e.g., mercapto-substituted alkoxy oligomers, etc.). Examples of the ultraviolet absorbing agent include benzotriazole-based compounds, benzophenone-based compounds, and triazine-based compounds.

When the pressure-sensitive adhesive composition contains other components, the content ratio thereof is not particularly limited, and can be, for example, 15 parts by mass or less, preferably 10 parts by mass or less, per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A).

The method for preparing the adhesive composition is not particularly limited, and for example, any of the known methods for preparing adhesive compositions can be widely used.

<Constitution and properties of pressure-sensitive adhesive sheet>
The adhesive sheet is made of a cured product of the adhesive composition. That is, the adhesive sheet can be obtained by curing the adhesive composition. The cured product of the adhesive composition can function as an adhesive layer in the adhesive sheet. The adhesive sheet can be composed of, for example, only an adhesive layer. That is, the adhesive sheet can also be formed of only a cured product of the adhesive composition. The adhesive layer can have a single-layer structure, or can have a multi-layer structure in which a plurality of single-layer adhesive layers are laminated. The adhesive sheet may be either a single-sided adhesive sheet or a double-sided adhesive sheet, and is preferably a double-sided adhesive sheet.

In an elastic modulus image of the adhesive sheet taken of the surface in Peak Force Tapping mode using an AFM, there are 3 to 20 spherical or island-shaped areas with a higher elastic modulus than the surrounding area within any 10 μm square range. Figure 3 shows an example of an elastic modulus image taken of the surface of an adhesive sheet in Peak Force Tapping mode using an AFM with an autoscale tool with a measurement range of 1 GPa to 100 GPa. In Figure 3, spherical or island-shaped areas with a higher elastic modulus than the surrounding area are shown in white, and areas with a relatively lower elastic modulus than the surrounding area are shown in black. Note that the relatively small white images such as dots and lines in Figure 3 are considered to be images due to noise, and are not counted as spherical or island-shaped areas with a higher elastic modulus than the surrounding area.

The number of spherical or island-shaped areas having a higher elastic modulus than the surrounding area is preferably 4 or more, more preferably 5 or more, and even more preferably 6 or more, in terms of particularly improving reworkability. Also, the number is preferably 16 or less, more preferably 13 or less, and even more preferably 10 or less, in terms of particularly improving transparency.

The number of spherical or island-shaped areas with a higher elastic modulus than the surrounding area can be measured using the following method.

First, an elastic modulus image is taken of the surface of the pressure-sensitive adhesive sheet in Peak Force Tapping mode using an AFM by the following method.
Equipment used: MultiMode8 (manufactured by Bruker Nano)
<Peak Force Tapping Mode>
Cantilever: ScanAsyst-Air
Scan Size: 10μm square Gain: Auto
Setpoint: 10μm square_4.0nN
Sync Distance: about 75.0 Using the above method, 10 different fields of view are observed to prepare 10 elasticity images. In each elasticity image, the number of spheres or islands with a higher elasticity than the surroundings is measured by visually counting the number of white spheres or islands. The average value of the 10 elasticity images is calculated as the measured value of the number of spheres or islands with a higher elasticity than the surroundings.

The elastic modulus of the spherical or island-shaped areas having a higher elastic modulus than the surrounding area is relatively higher than the surrounding area, and the elastic modulus is preferably 1 GPa or more, and more preferably 5 GPa or more. The upper limit of the elastic modulus is not particularly limited, and may be about 60 GPa. The elastic modulus of the surrounding areas having a relatively lower elastic modulus other than the spherical or island-shaped areas having a higher elastic modulus than the surrounding area is preferably less than 1 GPa, more preferably 0.5 GPa or less, even more preferably 0.1 GPa or less, and particularly preferably 0.05 GPa or less. The lower limit of the elastic modulus is not particularly limited, and may be less than -0.01 GPa.

The elastic modulus of a spherical or island-shaped area having a higher elastic modulus than the surrounding area is preferably at least 10 times the elastic modulus of the surrounding area having a relatively lower elastic modulus other than the spherical or island-shaped area having a higher elastic modulus than the surrounding area.

The above elastic modulus can be measured by analyzing the elastic modulus image taken of the surface in Peak Force Tapping mode using the AFM described above, using software provided with the device.

<Physical properties of adhesive sheet>
(Physical Properties 1)
The pressure-sensitive adhesive sheet satisfies the following physical property (1).
Physical properties (1): The adhesive strength to glass 30 minutes after application, measured according to the adhesive strength measuring method described in JIS Z 0237, is 0.01 to 5 N/25 mm.

In the physical property (1), when measuring the adhesive strength of the adhesive sheet to glass, the adhesive strength to glass is measured 1 minute after application to glass in accordance with the adhesive strength measurement method described in JIS Z 0237. More specifically, 100 μm PET (manufactured by Toyobo Co., Ltd./product number: Cosmoshine A4300) is applied to one side of the adhesive sheet, and then this is treated in an autoclave for 30 minutes at 100 ° C and 0.5 MPa (meaning gauge pressure). The adhesive sheet having a PET substrate on one side thus treated is applied to soda glass (Hiraoka Special Glass Manufacturing Co., Ltd., the pressure-bonded surface is the opposite side to the tin float). At this time, a measurement sample is prepared in accordance with the 180 ° peel adhesive strength measurement method described in JIS Z 0237, except that soda glass is used as the test plate. Then, the adhesive strength is measured 1 minute after application at a peel speed of 300 mm / min. This adhesive strength is the adhesive strength to glass in physical property (1).

In physical property (1), the adhesive strength to glass is preferably 0.05 N/25 mm or more, since this particularly improves reworkability. In addition, the adhesive strength to glass in physical property (1) is preferably 4.8 N/25 mm or less, more preferably 4.6 N/25 mm or less, and even more preferably 4.5 N/25 mm or less.

The adhesive strength to glass in property (1) can be adjusted by adjusting the type and ratio of the constituent units of the crosslinkable (meth)acrylic copolymer, the amount of methyl methacrylate polymer (B), the average particle size and amount of (meth)acrylic resin particles (C), and the amount of crosslinking agent (D).

(Physical Properties 2)
The pressure-sensitive adhesive sheet satisfies the following physical property (2).
Physical property (2): The adhesive sheet is attached to a glass plate and heat-treated for 30 minutes under conditions of 100°C and 0.5 MPa (gauge pressure), and then the adhesive strength to glass measured according to the adhesive strength measuring method described in JIS Z 0237 is 10 N/25 mm or more.

In physical property (2), when measuring the adhesive strength of the adhesive sheet to glass, a measurement sample is prepared in the same manner as in physical property (1). This measurement sample is then treated in an autoclave at 100°C and 0.5 MPa for 30 minutes, and then allowed to stand in an environment of 23°C and 50% relative humidity for 2 hours. The adhesive strength is then measured at a peel speed of 300 mm/min in the same manner as in physical property (1). This adhesive strength is regarded as the adhesive strength to glass in physical property (2).

In physical property (2), the adhesive strength to glass is preferably 10 N/25 mm or more, more preferably 15 N/25 mm or more, even more preferably 20 N/25 mm or more, and particularly preferably 25 N/25 mm or more, in order that the adhesive strength to the adherend after heat treatment is likely to increase. In addition, the adhesive strength to glass in physical property (2) is not particularly limited, and is preferably 50 N/25 mm or less, in order that, for example, displays and the like can be easily disposed of or disassembled.

The adhesive strength to glass in property (2) can be adjusted by adjusting the type and ratio of the constituent units of the crosslinkable (meth)acrylic copolymer, the amount of methyl methacrylate polymer (B), the average particle size and amount of (meth)acrylic resin particles (C), and the amount of crosslinking agent (D).

The adhesive sheet preferably has a haze measured in accordance with JIS K 7136 of 0 to 2%, more preferably 1.9% or less, and even more preferably 1.8% or less, in order to increase the transparency of the adhesive sheet. The haze value may be 0%.

When measuring the haze of the adhesive sheet, it is measured in accordance with JIS K 7136. Specifically, a pair of transparent glass plates (S9112, manufactured by Matsunami Glass Industry Co., Ltd.) with a thickness of 1.2 mm is laminated with an adhesive sheet to prepare a laminated sample, and the haze is measured using the laminated sample in accordance with JIS K7136 (2000). A haze meter NDH7000 manufactured by Nippon Denshoku Industries Co., Ltd. can be used for this measurement. The laminated sample is prepared, for example, as follows. The release sheet on the light release side of the adhesive sheet with release sheet is peeled off and the sheet is laminated to one transparent glass plate, and then the other transparent glass plate is laminated to the surface from which the release sheet on the heavy release side (heavy release separator) has been peeled off, so as to prevent air from being mixed in. This is then treated in an autoclave at 100°C and 0.5 MPa (gauge pressure) for 30 minutes, and then left to stand for 2 hours in an environment of 23°C and 50% relative humidity to obtain a laminated sample.

The haze value can be adjusted by adjusting the type and ratio of the constituent units of the crosslinkable (meth)acrylic copolymer, the amount of the methyl methacrylate polymer (B), and the refractive index, average particle size, and amount of the (meth)acrylic resin particles (C).

Since the adhesive sheet has the above physical property (1), the initial adhesive strength is not too strong, and as a result, the adhesive sheet has excellent position adjustment ability (reworkability). Therefore, when the adhesive sheet is used to bond components together, for example, for bonding optical components, the adhesive sheet can be easily peeled off from the optical component, making it easy to re-bond the components, and also reducing the risk of adhesive residue remaining from the adhesive sheet.

Since the adhesive sheet has the above physical property (2), the adhesive strength can be increased by bonding the adherends together and then heating. This makes it possible to bond the adherends firmly together. In this way, the adhesive sheet has low initial adhesive strength while being able to increase adhesive strength after heating, and thus combines two opposing adhesive properties.

Furthermore, the adhesive sheet has 3 to 20 spherical or island-shaped areas with a higher elastic modulus than the surrounding area in an elastic modulus image measured under specific conditions using an AFM, making it possible to simultaneously achieve high reworkability, strong adhesion after heating, and high transparency. Therefore, the adhesive sheet is also suitable for use in optical applications that require high transparency and reworkability.

As described above, the adhesive sheet has the physical properties (1) and (2), and the number of spherical or island-shaped parts with a higher elastic modulus than the surrounding area in an elastic modulus image measured under specific conditions using an AFM is 3 to 20, so that the adhesive sheet can be endowed with reworkability and high transparency, and the adhesive sheet can achieve both transparency and reworkability, which were previously in a trade-off relationship. Furthermore, the adhesive sheet does not peel off even after the passage of time after lamination, and has excellent stability over time. Therefore, the adhesive sheet is suitable for use in the laminate manufacturing method of the present invention.

<Other properties of the adhesive sheet>
The thickness of the pressure-sensitive adhesive sheet is not particularly limited as it can be appropriately set depending on the application, and is, for example, preferably 5 to 300 μm, more preferably 8 to 200 μm, and particularly preferably 10 to 150 μm.

The gel fraction of the adhesive sheet is not particularly limited and can be set appropriately depending on the components and types contained in the adhesive sheet. For example, the gel fraction of the adhesive sheet is 35 to 100%, preferably 40 to 95%, and more preferably 45 to 90%. Note that the above gel fraction is the gel fraction before the adhesive sheet is heated, but since the change in gel fraction before and after heating is small in the adhesive sheet, it is preferable that the gel fraction of the adhesive sheet after heat treatment for 30 minutes under conditions of 100°C and 0.5 MPa is also within the above range.

The gel fraction of the adhesive layer is a value measured by the following method. First, about 0.1 g of the adhesive sheet (adhesive layer) is collected in a sample bottle, 30 ml of ethyl acetate is added, and the mixture is shaken for 24 hours. The contents of the sample bottle are then filtered through a 150 mesh stainless steel wire mesh, and the residue on the wire mesh is dried at 100° C. for 1 hour to measure the dry mass (g). The gel fraction is calculated from the obtained dry mass using the following formula 1.
Gel fraction (mass%)=(dry mass/collected mass of pressure-sensitive adhesive sheet)×100 Equation 1

<Adhesive sheet with release sheet>
As shown in Fig. 2, the pressure-sensitive adhesive sheet used in the manufacturing method of the present invention can be provided with a release sheet to form a pressure-sensitive adhesive sheet with a release sheet. The pressure-sensitive adhesive sheet with a release sheet 10 can have release sheets 12a and 12b on both surfaces of the pressure-sensitive adhesive layer 11 (pressure-sensitive adhesive sheet).

As the release sheet, for example, a wide variety of known release sheets can be used, including a release laminate sheet in which a release agent layer is formed on one side of a release sheet substrate, and other low-polarity substrates made of polyolefin films such as polyethylene films and polypropylene films. For example, paper and polymer films can be used as the release sheet substrate.

As the release agent constituting the release agent layer, for example, a general-purpose addition type or condensation type silicone-based release agent or a compound containing a long chain alkyl group is used. In particular, an addition type silicone-based release agent having high reactivity is preferably used. Specific examples of the silicone-based release agent include BY24-4527 and SD-7220 manufactured by Toray Dow Corning Silicone Co., Ltd., and KS-3600, KS-774, and X62-2600 manufactured by Shin-Etsu Chemical Co., Ltd. In addition, it is also preferable that the silicone-based release agent contains a silicone resin, which is an organosilicon compound having SiO ₂ units and (CH ₃ ) ₃ SiO _1/2 units or CH ₂ ═CH(CH ₃ )SiO _1/2 units in the silicone-based release agent. Specific examples of silicone resins include BY24-843, SD-7292, SHR-1404, etc. manufactured by Toray Dow Corning Silicone Co., Ltd., and KS-3800, X92-183, etc. manufactured by Shin-Etsu Chemical Co., Ltd.

The peelable laminate sheet can be obtained commercially, for example, a heavy separator film made by Teijin DuPont Films Co., Ltd., which is a release-treated polyethylene terephthalate film, or a light separator film made by Teijin DuPont Films Co., Ltd., which is a release-treated polyethylene terephthalate film.

The adhesive sheet with release sheet preferably has a pair of release sheets with different release strengths on both surfaces of the adhesive sheet. That is, to facilitate peeling, it is preferable that the release sheets 12a and 12b have different releasability. If the releasability from one side is different from the releasability from the other, it becomes easier to peel off only the release sheet with the higher releasability (light release side) before the heavy release side.

(Method of manufacturing pressure-sensitive adhesive sheet)
The method for producing the pressure sensitive adhesive sheet is not particularly limited, and known methods can be widely adopted.Among them, it is preferable to form the pressure sensitive adhesive sheet by a production method including a step of forming a coating film by applying the above-mentioned pressure sensitive adhesive composition on a release sheet, and a step of heating this coating film.In such a production method, when the pressure sensitive adhesive composition contains a solvent, the solvent is removed in the heating step, and at the same time, the reaction of the crosslinkable (meth)acrylic copolymer and the crosslinking agent proceeds to form a cured product (pressure sensitive adhesive layer).

The adhesive composition can be applied using a known coating device. Examples of the coating device include an applicator, a blade coater, an air knife coater, a roll coater, a bar coater, a gravure coater, a microgravure coater, a rod blade coater, a lip coater, a die coater, and a curtain coater.

The substrate used for applying the adhesive composition is not particularly limited. For example, the adhesive composition can be applied to various substrates such as a resin substrate or a glass substrate. For example, when obtaining an adhesive sheet with a release sheet, a release sheet can be selected as the substrate. The adhesive composition can also be applied directly onto the member to be adhered.

The thickness of the adhesive composition after application is not particularly limited and can be set appropriately depending on the desired thickness of the adhesive layer.

In the step of heating the coating film, the heating temperature is not particularly limited, and is preferably, for example, 50 to 150°C. The heating time can be appropriately adjusted depending on the heating temperature, the thickness of the coating film, and the content of the solvent in the adhesive composition, and can be, for example, 1 to 60 minutes. A known heating device such as a heating furnace or an infrared lamp can be used to heat the coating film. After heating, it is preferable to carry out an aging treatment in which the adhesive sheet is left to stand at a constant temperature for a certain period of time. The aging treatment can be carried out, for example, by leaving it to stand at 23°C for 7 days.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[Synthesis of Crosslinkable (Meth)acrylic Copolymer A-1]
Monomers prepared by mixing butyl acrylate (BA), acrylic acid (AA) and methyl acrylate (MA) in a mass ratio of 87:3:10 were polymerized in ethyl acetate, a polymerization solvent, in the presence of AIBN (azobisisobutyronitrile) by heating to 60° C. This resulted in a solution of a crosslinkable (meth)acrylic copolymer (A-1) (represented as “A-1” in Table 1) having a solid content concentration of 30% by mass and a weight average molecular weight of 740,000.

[Synthesis of Crosslinkable (Meth)acrylic Copolymer A-2]
A monomer mixture of BA, 2-hydroxyethyl acrylate (2HEA) and MA in a mass ratio of 70:20:10 was polymerized in ethyl acetate, a polymerization solvent, in the presence of AIBN (azobisisobutyronitrile) by heating to 60° C. This resulted in a solution of a crosslinkable (meth)acrylic copolymer (A-2) (represented as “A-2” in Table 1) having a solid content of 35% by mass and a weight average molecular weight of 600,000.

[Synthesis of methyl methacrylate polymer B-1]
A solution of methyl methacrylate (MMA) and a polymerization initiator AIBN dissolved in ethyl acetate was heated to 80° C. to polymerize, thereby obtaining a methyl methacrylate polymer (B-1) (represented as “B-1” in Table 1) having a weight average molecular weight of 5,000.

[Synthesis of methyl methacrylate polymer B-2]
A solution of methyl methacrylate (MMA) and a polymerization initiator AIBN dissolved in ethyl acetate was heated to 80° C. to polymerize, thereby obtaining a methyl methacrylate polymer (B-2) (represented as “B-2” in Table 1) having a weight average molecular weight of 9,000.

Example 1
[Preparation of Pressure-Sensitive Adhesive Composition]
The raw materials containing 3 parts by mass of methyl methacrylate polymer (B-1), 1 part by mass of MX-80H3WT (average particle size 0.8 μm, manufactured by Soken Chemical Industries, Ltd.) as (meth)acrylic resin particles (C), 0.1 parts by mass and 0.5 parts by mass of an epoxy compound (Tetrad X, manufactured by Mitsubishi Gas Chemical Co., Ltd.) and a metal chelate compound (Aluminum Chelate A, manufactured by Kawaken Fine Chemicals Co., Ltd.) as crosslinking agents, 5 parts by mass of acetylacetone (manufactured by Tokyo Chemical Industry Co., Ltd.) as a crosslinking retarder, and 0.5 parts by mass of a silane coupling agent (KBM403, manufactured by Shin-Etsu Chemical Co., Ltd.) were added to ethyl acetate so that the concentration of the raw materials was 25% by mass, and stirred to prepare a pressure-sensitive adhesive composition a-1.

[Preparation of adhesive sheet]
The pressure-sensitive adhesive composition a-1 prepared as described above was uniformly applied with an applicator to the surface of a 50 μm-thick polyethylene terephthalate film (first release sheet, Oji F-Tex Co., Ltd., 50RL-07(2)) equipped with a release agent layer treated with a silicone-based release agent, so as to form a coating film with a coating thickness of 25 μm after drying. The coating film was dried at 100° C. for 3 minutes in an air-circulating constant temperature oven, thereby forming a pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) on the surface of the first release sheet.

Next, a 38 μm-thick second release sheet (Oji F-Tex Co., Ltd., 38RL-07(L)) with a release strength different from that of the first release sheet was attached to the surface of the adhesive layer, and the sheet was left to cure for 14 days under conditions of 23°C and 50% relative humidity. This resulted in an adhesive sheet with release sheet having a first release sheet/adhesive sheet/second release sheet configuration in which the adhesive layer (adhesive sheet) is sandwiched between a pair of release sheets with different release strengths.

The obtained adhesive sheet with release sheet was temporarily attached to an optical member, and the position adjustment ability (reworkability) described below was evaluated. In addition, a laminate (laminate sample) was formed using the obtained adhesive sheet with release sheet by the method described in the image design and visibility described below.

Example 2
A pressure-sensitive adhesive sheet with a release sheet was obtained in the same manner as in Example 1, except that the (meth)acrylic resin particles (C) were changed to MX-300 (average particle size 3 μm, manufactured by Soken Chemical & Engineering Co., Ltd.), and a laminate (laminate sample) was formed.

Example 3
Raw materials containing 10 parts by mass of methyl methacrylate polymer (B-2), 1.5 parts by mass of XX-5910 (average particle size 0.3 μm, manufactured by Sekisui Chemical Co., Ltd.) as (meth)acrylic resin particles (C), 0.1 part by mass of an isocyanate compound (Coronate L-55, manufactured by Tosoh Corporation) as a crosslinking agent, and 0.5 parts by mass of a silane coupling agent (KBM403, manufactured by Shin-Etsu Chemical Co., Ltd.) per 100 parts by mass of acrylic copolymer (A-2), were added to ethyl acetate so that the concentration of the raw materials was 27% by mass, and stirred to prepare a pressure-sensitive adhesive composition a-2.

Next, an adhesive sheet with a release sheet was obtained and a laminate (laminate sample) was formed in the same manner as in Example 1, except that adhesive composition a-1 was changed to adhesive composition a-2.

Example 4
A pressure-sensitive adhesive sheet with a release sheet was obtained and a laminate (laminate sample) was formed in the same manner as in Example 3, except that the (meth)acrylic resin particles (C) were changed to BMSA-18GN (average particle size 0.8 μm, manufactured by Sekisui Chemical Co., Ltd.) and the amount used was changed to 2 parts by mass.

Example 5
A pressure-sensitive adhesive sheet with a release sheet was obtained in the same manner as in Example 4, except that the amount of the (meth)acrylic resin particles (C) used was changed to 0.5 parts by mass, to form a laminate (laminate sample).

(Comparative Example 1)
A pressure-sensitive adhesive sheet with a release sheet was obtained in the same manner as in Example 1, except that a pressure-sensitive adhesive composition was prepared without using the (meth)acrylic resin particles (C), and a laminate (laminate sample) was formed.

(Comparative Example 2)
An adhesive sheet with a release sheet was obtained and a laminate (laminate sample) was formed in the same manner as in Example 3, except that the (meth)acrylic resin particles (C) were replaced with melamine resin particles Eposter M30 (average particle size 3 μm, manufactured by Nippon Shokubai Co., Ltd.).

(Comparative Example 3)
A pressure-sensitive adhesive sheet with a release sheet was obtained and a laminate (laminate sample) was formed in the same manner as in Example 3, except that the (meth)acrylic resin particles (C) were changed to MBX-20 (average particle size 20 μm, manufactured by Sekisui Chemical Co., Ltd.) and the amount used was changed to 1 part by mass.

[Physical Property 1: Adhesion to Glass]
The adhesive strength was measured according to the method for measuring the adhesive strength described in JIS Z 0237. First, the release sheet on the light release side of the adhesive sheet with a release sheet was peeled off and laminated with 100 μm PET (manufactured by Toyobo Co., Ltd./product number: Cosmoshine A4300), and then treated in an autoclave for 30 minutes under conditions of 100 ° C. and 0.5 MP (gauge pressure) a to obtain an adhesive sheet having a PET substrate on one side. The release sheet on the heavy release side of this adhesive sheet having a PET substrate on one side was peeled off and laminated to soda glass (Hiraoka Special Glass Manufacturing Co., Ltd., the pressure-bonded surface was the opposite side to the tin float). At this time, a measurement sample was prepared according to the method for measuring the 180 ° peel adhesive strength described in JIS Z 0237, except that soda glass was used as the test plate. Then, the adhesive strength was measured at a peel speed of 300 mm / min 1 minute after pressure bonding, and this adhesive strength was taken as the adhesive strength to glass in physical property (1).

[Physical Property 2: Adhesion to Glass]
A measurement sample was prepared in the same manner as in the physical property 1, up to the step of bonding to the test plate. After that, the measurement sample was treated for 30 minutes under conditions of 100°C and 0.5 MPa (gauge pressure) using an autoclave, and then left to stand for 2 hours in an environment of 23°C and 50% relative humidity. Then, the adhesive strength was measured at a peeling speed of 300 mm/min in the same manner as in the physical property (1), and this adhesive strength was defined as the adhesive strength to glass in the physical property (2).

[Measurement of the number of spherical or island-like portions by AFM]
First, an elastic modulus image was taken of the surface of the pressure-sensitive adhesive sheet in Peak Force Tapping mode using an AFM by the following method.
Equipment used: MultiMode8 (manufactured by Bruker Nano)
<Peak Force Tapping Mode>
Cantilever: ScanAsyst-Air
Scan Size: 10μm square Gain: Auto
Setpoint: 10μm square_4.0nN
Sync Distance: about 75.0 Using the above method, 10 different fields of view were observed to prepare 10 elasticity images. In each elasticity image, the number of spheres or islands with a higher elasticity than the surroundings was measured by visually counting the number of white spheres or islands. The average value of the 10 elasticity images was calculated as the measured value of the number of spheres or islands with a higher elasticity than the surroundings.

[Weight average molecular weight]
The weight average molecular weights of the crosslinkable (meth)acrylic copolymer (A) and the methyl methacrylate polymer (B) were measured by gel permeation chromatography (GPC) under the following conditions.
Solvent: Tetrahydrofuran Column: Shodex KF801, KF803L, KF800L, KF800D (four columns manufactured by Showa Denko K.K. were used in combination)
Column temperature: 40°C
Sample concentration: 0.5% by mass
Detector: RI-2031plus (JASCO)
Pump: RI-2080plus (JASCO)
・Flow rate (flow rate): 0.8ml/min
Injection volume: 10 μl
Calibration curve: Standard polystyrene Shodex standard polystyrene (manufactured by Showa Denko KK) A calibration curve using 10 samples with Mw=1,320 to 2,500,000 was used.

[Measurement of refractive index]
The refractive index of the crosslinkable (meth)acrylic copolymer (A) was measured in accordance with Method A described in JIS K 7142 (2014) "Plastics - Determination of refractive index". The refractive index of the (meth)acrylic resin particles (C) was measured in accordance with Method B described in JIS K 7142 (2014) "Plastics - Determination of refractive index".

(Evaluation of Adhesive Sheets)
The pressure-sensitive adhesive sheets obtained in each of the Examples and Comparative Examples were evaluated according to the following procedures.

[Position adjustment ability (reworkability)]
A test piece was obtained by cutting a pressure-sensitive adhesive sheet having a PET substrate on one side, obtained in the process of preparing a sample for measuring physical property (1), into a size of 50 mm x 60 mm. A laminate was prepared by pressing the pressure-sensitive adhesive sheet onto a float glass sheet (manufactured by Nippon Sheet Glass Co., Ltd.) measuring 30 mm x 40 mm (thickness 10 mm) so that the center of the float glass sheet and the center of the adhesive sheet overlapped each other. In an environment of 23°C and 50% relative humidity, the adhesive sheet was placed on a horizontal table so that the adhesive sheet side faced the table and pressure-bonded. Within one minute of bonding, the adhesive sheet protruding from the glass plate was removed. While lightly holding the glass plate with one hand, the glass plate was picked up with the other hand and peeled upward from the adhesive sheet. The peelability at this time was evaluated according to the following criteria.
◯: Easy to peel off and excellent reworkability.
×: Not peelable or difficult to peelable (for example, it can only be peeled off by placing the adhesive sheet side up and pulling up the adhesive sheet from the edge), and poor reworkability.

[Whether or not peeling occurs over time]
The laminate prepared in the process of evaluating the position adjustability (reworkability) was treated for 240 hours using a thermohygrostat at 65° C. (relative humidity 95%), and then left to stand for 60 minutes in an environment of 23° C. and 50% relative humidity. Thereafter, it was visually evaluated according to the following criteria.
○: No peeling or lifting occurs ×: Peeling or lifting occurs at the edges, etc.

[Image design and visibility]
The release sheet on the light release side of the adhesive sheet with release sheet was peeled off, and the adhesive sheet was laminated with 100 μm PET (manufactured by Toyobo Co., Ltd./product number: Cosmoshine A4300), and the adhesive sheet was cut into a size of 150 mm x 70 mm to obtain a test piece. Next, the release sheet on the heavy release side of this test piece was peeled off, and the entire surface of the exposed surface and the surface opposite to the black printed surface of a 150 mm x 70 mm (thickness 6 mm) float plate glass (manufactured by Nippon Sheet Glass Co., Ltd.) having a black printed surface were laminated using a hand roller to obtain a laminated sample. The obtained laminate was treated in an autoclave under conditions of 100 ° C. and 0.5 MPa (gauge pressure) for 30 minutes, and then left to stand for 2 hours in an environment of 23 ° C. and relative humidity 50% to prepare an evaluation sample. Apart from this evaluation sample, a float plate glass similar to the float plate glass used to prepare the evaluation sample was prepared as a blank. The PET surface of the evaluation sample was visually compared with the glass surface opposite the black printed surface of the blank product, and the design and visibility of the image were evaluated based on the following criteria.
◯: Blackness and glossiness similar to that of the blank product.
△: Slightly less black and glossy than the blank product.
×: Inferior blackness and glossiness compared to the blank product.

[Haze]
The haze of the adhesive sheet was measured in accordance with JIS K 7136. Specifically, a pair of transparent glass plates (S9112, manufactured by Matsunami Glass Industry Co., Ltd.) having a thickness of 1.2 mm was laminated with an adhesive sheet to prepare a laminated sample, and the laminated sample was used to measure the haze in accordance with JIS K7136 (2000). A haze meter NDH7000 manufactured by Nippon Denshoku Industries Co., Ltd. was used for the measurement. The laminated sample was prepared as follows. First, the release sheet on the light release side of the adhesive sheet with a release sheet was peeled off and laminated to one transparent glass plate, and then the other transparent glass plate was laminated to the surface from which the release sheet (heavy release separator) on the heavy release side was peeled off so as not to allow air to be mixed in. This was treated in an autoclave under conditions of 100°C and 0.5 MPa (gauge pressure) for 30 minutes, and then left to stand for 2 hours in an environment of 23°C and relative humidity of 50% to obtain a laminated sample.

Table 1 shows the conditions for producing the adhesive sheets of each of the above-mentioned Examples and Comparative Examples, as well as the physical properties and evaluation results of each adhesive sheet. In Table 1, "(A)-(C) refractive index difference" refers to the refractive index difference (absolute value) between the crosslinkable (meth)acrylic copolymer (A) and the (meth)acrylic resin particles (C).

From Table 1, it can be seen that the adhesive sheets obtained in the examples have excellent reworkability and low haze, i.e., excellent transparency. Moreover, the adhesive sheets obtained in the examples did not peel off even after time had passed after lamination, and had excellent stability over time. Furthermore, the laminates produced using the adhesive sheets obtained in the examples were found to have excellent image design and visibility, making them suitable for use in image display devices, etc.

REFERENCE SIGNS LIST 10 Pressure-sensitive adhesive sheet with release sheet 11 Pressure-sensitive adhesive layer 12a Release sheet 12b Release sheet 50 Adherend 100 Laminate

Claims (5)

A method for producing a laminate, comprising the steps of:
A step of bonding the pressure-sensitive adhesive sheet and the adherend together for temporary adhesion;
and a step of carrying out a heat treatment or a heat and pressure treatment to actually bond the pressure-sensitive adhesive sheet and the adherend,
The pressure-sensitive adhesive sheet is formed of a cured product of a pressure-sensitive adhesive composition,
The pressure-sensitive adhesive composition contains a crosslinkable (meth)acrylic copolymer (A), a methyl methacrylate polymer (B), (meth)acrylic resin particles (C), and a crosslinking agent (D),
The crosslinkable (meth)acrylic copolymer (A) is a polymer containing (meth)acrylic ester units (a) having an alkyl group having 4 to 10 carbon atoms and monomer units (b) having a carboxy group and/or a hydroxyl group,
The crosslinkable (meth)acrylic copolymer (A) contains 50 to 95% by mass of the (meth)acrylic ester unit (a) and 1 to 50% by mass of the monomer unit (b),
The weight average molecular weight of the methyl methacrylate polymer (B) is 1,000 to 10,000;
The methyl methacrylate polymer (B) is contained in an amount of 1 to 15 parts by mass per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A),
The (meth)acrylic resin particles (C) have an average particle size of 0.1 to 5 μm,
The crosslinking agent (D) is contained in an amount of 0.01 to 5 parts by mass per 100 parts by mass of the crosslinkable (meth)acrylic copolymer (A),
In an elastic modulus image taken of the surface in Peak Force Tapping mode using an atomic force microscope, there are 3 to 20 spherical or island-like areas having a higher elastic modulus than the surrounding areas within any 10 μm square range,
A method for producing a laminate, which is a pressure-sensitive adhesive sheet that satisfies the following physical properties (1) and (2):
Physical properties (1): The adhesive strength to glass 30 minutes after application, measured according to the adhesive strength measuring method described in JIS Z 0237, is 0.01 to 5 N/25 mm.
Physical property (2): The adhesive sheet is applied to a glass plate and heat-treated at 100° C. and 0.5 MPa for 30 minutes. The adhesive strength to glass measured according to the adhesive strength measuring method described in JIS Z 0237 is 10 N/25 mm or more. The method for manufacturing a laminate according to claim 1, wherein the main adhesion is performed by heat treatment at 50 to 120°C for 1 to 120 minutes. 3. The method for producing a laminate according to claim 1 , wherein a refractive index difference between the crosslinkable (meth)acrylic copolymer (A) and the (meth)acrylic resin particles (C) is 0 to 0.05. The method for producing a laminate according to any one of claims 1 to 3 , wherein the crosslinking agent (D) comprises one selected from the group consisting of an isocyanate compound, an epoxy compound, and a metal chelate. The method for producing a laminate according to any one of claims 1 to 4 , wherein the laminate is for an optical device or an image display device.

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