JP7338318B2 - Adhesive sheet, adhesive sheet with release sheet and laminate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive sheet with a release sheet, and a laminate.

2. Description of the Related Art Conventionally, a display device such as a liquid crystal display (LCD) and an input device used in combination with a display device such as a touch panel have been widely used. In the manufacture of these display devices and input devices, transparent adhesive sheets are used for bonding optical members, and transparent adhesive sheets are also used for bonding display devices and input devices. .

In various display devices, pressure-sensitive adhesive sheets are used for bonding optical members, but optical members are often more expensive than pressure-sensitive adhesive sheets. There is also a demand to rework (re-peel) the adhesive sheet when such as is required. For example, Patent Document 1 discloses a pressure-sensitive adhesive sheet including a support and a pressure-sensitive adhesive layer laminated on at least one side of the support, and the elastic modulus of the pressure-sensitive adhesive sheet and the adhesive strength to a stainless steel plate. is within a predetermined range to produce a PSA sheet that satisfactorily achieves both initial low tackiness and strong tackiness during use.

Further, Patent Document 2 discloses a monomer component containing 61 to 93% by mass of alkoxyalkyl (meth)acrylate, 6 to 19% by mass of tertiary nitrogen-containing monomer, and 1 to 20% by mass of crosslinkable functional group-containing monomer. A pressure-sensitive adhesive composition containing a polymer (meth)acrylic copolymer (A) and a cross-linking agent (B) is disclosed.

Japanese Patent No. 6355874 JP 2018-159018

However, since the pressure-sensitive adhesive sheet of Patent Document 1 has a support, it may be unsuitable for lamination of optical members that have become thinner in recent years. In addition, in the adhesive sheets in the conventional literature, the difference between the initial adhesive strength and the adhesive strength after heating is not sufficiently large, and there are cases where the contradictory properties of good reworkability and high adhesive strength after heating cannot be exhibited. .

Therefore, in order to solve such problems of the conventional technology, the present inventors have found that while the initial adhesive strength is weak and the position adjustment ability (reworkability) is excellent, the adhesive strength is excellent after heating. The study proceeded with the aim of providing an adhesive sheet.

As a result of intensive studies to solve the above problems, the present inventors have found that a pressure-sensitive adhesive sheet obtained by curing a pressure-sensitive adhesive composition containing a crosslinkable (meth)acrylic copolymer and a cross-linking agent, A crosslinkable (meth)acrylic copolymer, units derived from an alkoxyalkyl group-containing (meth)acrylate, units derived from a crosslinkable functional group-containing (meth)acrylate, units derived from a nitrogen-containing monomer and methyl methacrylate It has been found that a pressure-sensitive adhesive sheet having weak initial adhesive strength and excellent position adjustment ability (reworkability) while exhibiting excellent adhesive strength after heating can be obtained by constituting from units derived from.
Specifically, the present invention has the following configurations.

[1] A pressure-sensitive adhesive sheet obtained by curing a pressure-sensitive adhesive composition containing a crosslinkable (meth)acrylic copolymer and a crosslinking agent,
The crosslinkable (meth)acrylic copolymer includes units derived from an alkoxyalkyl group-containing (meth)acrylate, units derived from a crosslinkable functional group-containing (meth)acrylate, units derived from a nitrogen-containing monomer, and methyl methacrylate. contains units derived from
The content of units derived from the alkoxyalkyl group-containing (meth) acrylate is 40 to 90% by mass with respect to the total mass of the crosslinkable (meth) acrylic copolymer, and is derived from the crosslinkable functional group-containing (meth) acrylate. The content of units is 4 to 20% by mass, the content of units derived from a nitrogen-containing monomer is 3 to 20% by mass, and the content of units derived from methyl methacrylate is 3 to 20% by mass. can be,
An adhesive sheet that satisfies the following physical properties (1) and (2);
Physical properties (1): Adhesive strength to glass after 1 minute of lamination, measured according to the adhesive strength measurement method described in JIS Z 0237, is 0.05 to 3 N/25 mm;
Physical properties (2): The pressure-sensitive adhesive sheet was laminated to a glass plate, heat-treated at 100°C and 0.5 MPa for 30 minutes, and then measured according to the method for measuring adhesive strength described in JIS Z 0237. Adhesion to glass is 10N/25mm or more.
[2] The pressure-sensitive adhesive sheet according to [1], wherein the adhesive strength to glass in physical properties (2) is 100 times or more the adhesive strength to glass in physical properties (1).
[3] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the crosslinkable functional group of the (meth)acrylate containing a crosslinkable functional group is a hydroxyl group or a carboxy group.
[4] The pressure-sensitive adhesive sheet according to any one of [1] to [3], wherein the crosslinkable (meth)acrylic copolymer has a block-like branched chain in which 3 or more units derived from methyl methacrylate are continuous. .
[5] The pressure-sensitive adhesive sheet according to any one of [1] to [4], wherein the cross-linking agent contains at least one selected from isocyanate compounds, epoxy compounds and metal chelate compounds.
[6] A pressure-sensitive adhesive sheet with a release sheet, comprising a pair of release sheets having different release forces on both surfaces of the pressure-sensitive adhesive sheet according to any one of [1] to [5].
[7] A laminate comprising the adhesive sheet according to any one of [1] to [5] and an optical member.
[8] The laminate according to [7], wherein the pressure-sensitive adhesive sheet is a heat-curable sheet.

According to the present invention, it is possible to obtain a pressure-sensitive adhesive sheet exhibiting excellent adhesive strength after heating while having weak initial adhesive strength and excellent position adjustment ability (reworkability).

FIG. 1 is a schematic diagram showing a cross section of a pressure-sensitive adhesive sheet having a release sheet or substrate.

The present invention will be described in detail below. Although the constituent elements described below may be described based on representative embodiments and specific examples, the present invention is not limited to such embodiments. In the present specification, a numerical range represented by "-" means a range including the numerical values described before and after "-" as lower and upper limits.

In this specification, "(meth)acryl" represents both or either of acryl and methacryl. Moreover, in the present specification, "monomer" and "monomer" have the same meaning, and "polymer" and "polymer" have the same meaning.

<Adhesive sheet>
The present invention relates to a pressure-sensitive adhesive sheet obtained by curing a pressure-sensitive adhesive composition containing a cross-linkable (meth)acrylic copolymer and a cross-linking agent. Here, the crosslinkable (meth)acrylic copolymer is a unit derived from an alkoxyalkyl group-containing (meth)acrylate, a unit derived from a crosslinkable functional group-containing (meth)acrylate, a unit derived from a nitrogen-containing monomer And containing units derived from methyl methacrylate, the content of units derived from alkoxyalkyl group-containing (meth) acrylate is 40 to 90% by mass with respect to the total mass of the crosslinkable (meth) acrylic copolymer, and crosslinked The content of units derived from a functional group-containing (meth)acrylate is 4 to 20% by mass, the content of units derived from a nitrogen-containing monomer is 3 to 20% by mass, and is derived from methyl methacrylate. The unit content is 3 to 20% by mass. Moreover, the pressure-sensitive adhesive sheet of the present invention satisfies the following physical properties (1) and (2).
Physical properties (1): Adhesive strength to glass after 1 minute of lamination, measured according to the method for measuring adhesive strength described in JIS Z 0237, is 0.05 to 3 N/25 mm.
Physical properties (2): The pressure-sensitive adhesive sheet was laminated to a glass plate, heat-treated at 100°C and 0.5 MPa for 30 minutes, and then measured according to the method for measuring adhesive strength described in JIS Z 0237. Adhesion to glass is 10N/25mm or more.

When measuring the adhesive strength to glass in physical property (1), the adhesive strength to glass is measured 1 minute after bonding to glass according to the method for measuring adhesive strength described in JIS Z 0237. More specifically, 100 μm PET (manufactured by Toyobo Co., Ltd./product number: Cosmoshine A4300) is attached to one surface of the adhesive sheet, and treated using an autoclave at 100° C. and 0.5 MPa for 30 minutes. Then, the single-sided PET-based pressure-sensitive adhesive sheet obtained in this manner is adhered to soda glass (manufactured by Hiraoka Special Glass Co., Ltd., the pressure-bonded surface is the opposite surface of the tin float). At this time, a sample for measurement is prepared according to the method for measuring 180° peeling adhesive strength described in JIS Z 0237, except that soda glass is used for the test plate. Then, after one minute of pressure bonding, the adhesive force is measured at a peeling speed of 300 mm/min. Let this adhesive force be the adhesive force with respect to glass in physical property (1).
The adhesion to glass in physical property (1) may be 0.05 N/25 mm or more, preferably 0.10 N/25 mm or more, and more preferably 0.15 N/25 mm or more. Further, the adhesive strength to glass in the physical property (1) may be 3 N/25 mm or less, preferably 2 N/25 mm or less, more preferably 1.5 N/25 mm or less, and 1 N/25 mm or less. It is even more preferable to have

When measuring the adhesion to glass in physical property (2), a sample for measurement is prepared in the same manner as in physical property (1). Thereafter, this measurement sample is treated in an autoclave under conditions of 100° C. and 0.5 MPa for 30 minutes, and then allowed to stand in an environment of 23° C. and a relative humidity of 50% for 2 hours. Then, the adhesive force is measured at a peeling speed of 300 mm/min in the same manner as in physical properties (1). Let this adhesive force be the adhesive force to glass in physical property (2).
The adhesive strength to glass in physical property (2) may be 10 N/25 mm or more, preferably 15 N/25 mm or more, more preferably 20 N/25 mm or more, and more preferably 30 N/25 mm or more. preferable. Further, the adhesion to glass in the physical properties (2) is preferably 50 N/25 mm or less.

Since the pressure-sensitive adhesive sheet of the present invention has the above structure, the initial pressure-sensitive adhesive strength is weak and the position adjustability (reworkability) is excellent. Therefore, when the pressure-sensitive adhesive sheet of the present invention is used for bonding optical members, for example, and re-sticking becomes necessary, the pressure-sensitive adhesive sheet can be easily peeled off from the optical member. Specifically, the adhesive sheet can be easily peeled off from the optical member, and the occurrence of adhesive residue due to the adhesive sheet is suppressed. Furthermore, the pressure-sensitive adhesive sheet of the present invention can exhibit excellent adhesive strength after heating. For this reason, the pressure-sensitive adhesive sheet of the present invention can exhibit excellent adhesive strength by heating after bonding the pressure-sensitive adhesive sheet to an optical member. This makes it possible to firmly bond the adherends together. As described above, the pressure-sensitive adhesive sheet of the present invention has succeeded in increasing the pressure-sensitive adhesive strength after heating while suppressing the initial pressure-sensitive adhesive strength, and has two conflicting pressure-sensitive adhesive properties.

In the adhesive sheet of the present invention, the adhesive strength to glass in physical property (2) is preferably 100 times or more, more preferably 120 times or more, and 130 times the adhesive strength to glass in physical property (1). It is more preferably 150 times or more, and particularly preferably 150 times or more. Thus, in the pressure-sensitive adhesive sheet of the present invention, it is preferable that the adhesive strength to glass in the physical property (2) and the adhesive strength to glass in the physical property (1) are largely different. As a result, the position adjustability (reworkability) can be more effectively improved, and the post-heating adhesive strength can be made stronger.

<Structure of Adhesive Sheet>
The adhesive sheet of the present invention has an adhesive layer. The pressure-sensitive adhesive sheet is preferably a pressure-sensitive adhesive sheet composed only of a pressure-sensitive adhesive layer, and more preferably a double-sided pressure-sensitive adhesive sheet. In this case, the pressure-sensitive adhesive sheet may be a single-layer pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer, or may be a multi-layer pressure-sensitive adhesive sheet obtained by laminating a plurality of pressure-sensitive adhesive layers.

The present invention may also relate to a pressure-sensitive adhesive sheet with a release sheet provided with release sheets on both surfaces of the pressure-sensitive adhesive sheet. When the pressure-sensitive adhesive sheet of the present invention is provided with release sheets on both surfaces, the pressure-sensitive adhesive sheet 10 with release sheets may have release sheets 12a and 12b on both surfaces of the pressure-sensitive adhesive layer 11 as shown in FIG. preferable.

As the release sheet, a release laminated sheet having a release sheet base material and a release agent layer provided on one side of the release sheet base material, or a polyolefin film such as a polyethylene film or a polypropylene film as a low-polarity base material. is mentioned.
Papers and polymer films are used as the base material for the release sheet in the release laminated sheet. 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 silicone release agents 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. is mentioned. In addition, the silicone release agent may contain a silicone resin which is an organic silicon compound having _SiO2 units and ( _CH3 ) _{3SiO1/ 2} units or _CH2 =CH( _CH3 )SiO1 _/2 units. preferable. Specific examples of silicone resins include BY24-843, SD-7292, SHR-1404, etc. manufactured by Dow Corning Toray Silicone Co., Ltd., and KS-3800, X92-183, etc. manufactured by Shin-Etsu Chemical Co., Ltd.
A commercially available product may be used as the peelable laminate sheet. Examples include a heavy separator film that is a release-treated polyethylene terephthalate film manufactured by Teijin DuPont Films Limited, and a light separator film that is a release-treated polyethylene terephthalate film manufactured by Teijin DuPont Films Limited. can.

The pressure-sensitive adhesive sheet with a release sheet preferably has a pair of release sheets having different peel strengths on both surfaces of the pressure-sensitive adhesive sheet. That is, it is preferable that the release sheet 12a and the release sheet 12b have different releasability so that they can be easily separated. When the releasability from one side and the releasability from the other are different, it becomes easy to peel off only the release sheet with higher releasability first. In that case, the releasability of the release sheets 12a and 12b may be adjusted according to the bonding method and the bonding order.

<Adhesive layer>
The pressure-sensitive adhesive sheet of the present invention is obtained by curing a pressure-sensitive adhesive composition containing a cross-linkable (meth)acrylic copolymer and a cross-linking agent. In addition, it is preferable that an adhesive sheet consists of an adhesive layer.

The gel fraction of the pressure-sensitive adhesive layer is preferably 40% by mass or more, more preferably 45% by mass or more, and even more preferably 50% by mass or more. In addition, the gel fraction of the pressure-sensitive adhesive layer is preferably 100% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less. The above gel fraction is the gel fraction before heating the adhesive sheet, but in the adhesive sheet of the present invention, since the change in gel fraction before and after heating is small, the conditions of 100 ° C. and 0.5 MPa are It is preferable that the gel fraction of the pressure-sensitive adhesive sheet after heat treatment for 30 minutes is also within the above range.

The gel fraction of the pressure-sensitive 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 shaken for 24 hours. Thereafter, the contents of the sample bottle are filtered through a 150-mesh stainless 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 by the following formula 1.
Gel fraction (% by mass) = (dry mass/collected mass of adhesive sheet) x 100 Equation 1

The thickness of the pressure-sensitive adhesive layer can be appropriately set according to the application and is not particularly limited, but is preferably 5 to 300 μm, more preferably 8 to 200 μm, and particularly preferably 10 to 150 μm. By setting the thickness of the pressure-sensitive adhesive layer within the above range, it is possible to suppress the protrusion and stickiness of the pressure-sensitive adhesive, so that workability can be improved. Furthermore, by setting the thickness of the pressure-sensitive adhesive layer within the above range, the production of the double-sided pressure-sensitive adhesive sheet is facilitated.

<Adhesive composition>
The adhesive composition contains a crosslinkable (meth)acrylic copolymer and a crosslinker.

<Crosslinkable (meth)acrylic copolymer>
The crosslinkable (meth)acrylic copolymer includes units derived from an alkoxyalkyl group-containing (meth)acrylate, units derived from a crosslinkable functional group-containing (meth)acrylate, units derived from a nitrogen-containing monomer, and methyl methacrylate. contains units derived from In the present specification and claims, "units" are repeating units (monomer units) constituting a polymer.

A crosslinkable (meth)acrylic copolymer contains units derived from an alkoxyalkyl group-containing (meth)acrylate. Alkoxyalkyl group-containing (meth)acrylates are alkoxyalkyl (meth)acrylates. As the alkoxyalkyl (meth)acrylate, for example, an alkoxyalkyl (meth)acrylate in which the alkoxy group has 1 to 12 carbon atoms and the alkylene group bonded to the alkoxy group has 1 to 18 carbon atoms is preferable. The alkoxy group preferably has 1 to 8 carbon atoms, more preferably 1 to 4 carbon atoms, and particularly preferably 1 or 2 carbon atoms. The number of carbon atoms in the alkylene group bonded to the alkoxy group is preferably 1 to 12, more preferably 1 to 8, even more preferably 1 to 4, particularly 1 to 3. preferable.

Examples of such alkoxyalkyl (meth)acrylates include 2-methoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxymethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate and the like. Among these, 2-methoxyethyl (meth)acrylate is particularly preferred.

The content of units derived from an alkoxyalkyl group-containing (meth)acrylate is preferably 40% by mass or more, more preferably 45% by mass or more, relative to the total mass of the crosslinkable (meth)acrylic copolymer. It is preferably 50% by mass or more, more preferably 55% by mass or more, and particularly preferably 60% by mass or more. Moreover, the content of units derived from the alkoxyalkyl group-containing (meth)acrylate is preferably 90% by mass or less with respect to the total mass of the crosslinkable (meth)acrylic copolymer. By setting the content of the unit derived from the alkoxyalkyl group-containing (meth)acrylate within the above range, the initial adhesive strength of the PSA sheet can be kept low while the adhesive strength after heating can be easily increased.

A crosslinkable (meth)acrylic copolymer contains units derived from a crosslinkable functional group-containing (meth)acrylate. Units derived from crosslinkable functional group-containing (meth)acrylates include units derived from carboxy group-containing (meth)acrylates, units derived from hydroxy group-containing (meth)acrylates, and units derived from amino group-containing (meth)acrylates. , a unit derived from a glycidyl group-containing (meth)acrylate. Among them, the crosslinkable functional group is particularly preferably a hydroxyl group or a carboxy group. That is, it is particularly preferable that the unit derived from a crosslinkable functional group-containing (meth)acrylate is a unit derived from a carboxy group-containing (meth)acrylate or a unit derived from a hydroxy group-containing (meth)acrylate.

Units derived from carboxy group-containing (meth)acrylates include acrylic acid and methacrylic acid.
Units derived from hydroxy group-containing (meth)acrylates include, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 3-chloro-2-hydroxy Propyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, polyalkylene glycol mono(meth)acrylate and the like.
Examples of units derived from amino group-containing (meth)acrylates include (meth)acrylamide and allylamine.
Units derived from a glycidyl group-containing (meth)acrylate include glycidyl (meth)acrylate and the like.

The content of units derived from the crosslinkable functional group-containing (meth)acrylate is preferably 4% by mass or more, and is 4.5% by mass or more, relative to the total mass of the crosslinkable (meth)acrylic copolymer. is more preferable, and 5% by mass or more is even more preferable. In addition, the content of units derived from the crosslinkable functional group-containing (meth)acrylate is preferably 20% by mass or less, and is 15% by mass or less, relative to the total mass of the crosslinkable (meth)acrylic copolymer. is more preferable. By setting the content of the unit derived from the crosslinkable functional group-containing (meth)acrylate within the above range, the initial adhesive strength of the PSA sheet can be kept low while the adhesive strength after heating can be easily increased.

Crosslinkable (meth)acrylic copolymers contain units derived from nitrogen-containing monomers. A nitrogen-containing monomer is a monomer containing a nitrogen element in one molecule. Nitrogen-containing monomers include, for example, dimethylacrylamide, diethylacrylamide, acryloylmorpholine, hydroxyethylacrylamide, methylolacrylamide, methoxymethylacrylamide, ethoxymethylacrylamide, dimethylaminoethylacrylamide, N-vinylcaprolactam, N-vinyl-2- Pyrrolidone, dimethylaminoethyl (meth)acrylate, N-vinylformamide and the like can be mentioned. Among them, the nitrogen-containing monomer is preferably at least one selected from acrylamide derivatives, amino group-containing monomers and nitrogen-containing heterocyclic ring-containing monomers, and more preferably acrylamide derivatives. The acrylamide derivative is more preferably at least one selected from dimethylacrylamide, diethylacrylamide and acryloylmorpholine, and particularly preferably dimethylacrylamide. When the crosslinkable (meth)acrylic copolymer contains units derived from a nitrogen-containing monomer as described above, the initial adhesive strength of the adhesive sheet can be kept low, while the adhesive strength after heating can be increased. easier.

The content of the units derived from the nitrogen-containing monomer is preferably 3.0% by mass or more, more preferably 3.5% by mass or more, relative to the total mass of the crosslinkable (meth)acrylic copolymer. More preferably, it is 4.0% by mass or more. In addition, the content of units derived from the nitrogen-containing monomer is preferably 20% by mass or less, more preferably 15% by mass or less, relative to the total mass of the crosslinkable (meth)acrylic copolymer. . By setting the content of the unit derived from the nitrogen-containing monomer within the above range, the initial adhesive strength of the PSA sheet can be kept low while the adhesive strength after heating can be easily increased.

Crosslinkable (meth)acrylic copolymers contain units derived from methyl methacrylate. The content of units derived from methyl methacrylate is preferably 3% by mass or more, more preferably 3.5% by mass or more, and 4% by mass or more, relative to the total mass of the crosslinkable acrylic polymer. is more preferably 4.5% by mass or more, and particularly preferably 5% by mass or more. The content of units derived from methyl methacrylate is preferably 20% by mass or less, more preferably 15% by mass or less, relative to the total mass of the crosslinkable acrylic polymer. By setting the content of the units derived from methyl methacrylate within the above range, the initial adhesive strength of the adhesive sheet can be kept low while the adhesive strength after heating can be easily increased.

The crosslinkable (meth)acrylic copolymer preferably has a block-like branched chain in which 3 or more units derived from methyl methacrylate are continuous. The crosslinkable (meth)acrylic copolymer preferably has a block polymerization portion in which three or more units derived from methyl methacrylate are continuous, and the block polymerization portion is a branch of the crosslinkable (meth)acrylic copolymer. It preferably constitutes a chain. By having a block-like branched chain in which the crosslinkable (meth)acrylic copolymer has 3 or more consecutive units derived from methyl methacrylate, the initial adhesive strength of the adhesive sheet is more effectively suppressed, while heating It becomes easy to increase the post-adhesive strength.

When a block-like branched chain in which three or more units derived from methyl methacrylate are continuously introduced into a crosslinkable (meth)acrylic copolymer, when synthesizing the crosslinkable (meth)acrylic copolymer, methyl methacrylate It is preferable to blend a macromonomer of The macromonomer is an oligomer or polymer having a polymerizable reactive group at its terminal. At this time, the macromonomer is preferably polymerized from 3 to 500 methyl methacrylates. Moreover, a polymerizable functional group is introduced at the end of the macromonomer, and it is preferable that a polymerizable group such as an acryloyl group or a methacryloyl group is introduced as the polymerizable functional group. Among them, a macromonomer in which a methacryloyl group is bonded to the end of a polymer chain in which 3 to 500 methyl methacrylates are polymerized is preferably used. A commercial product such as AA-6 manufactured by Toagosei Co., Ltd. can also be used as such a macromonomer.

The crosslinkable (meth)acrylic copolymer may have a repeating unit derived from a (meth)acrylic acid alkyl ester in addition to the monomer units described above. Examples of (meth)acrylic acid alkyl esters include ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, ( meth) isobutyl acrylate, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, ( meth) n-nonyl acrylate, isononyl (meth) acrylate, n-decyl (meth) acrylate, isodecyl (meth) acrylate, n-undecyl (meth) acrylate, n-dodecyl (meth) acrylate, ( meth)stearyl acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate and the like. Among the above (meth)acrylic acid alkyl esters, at least one selected from n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate is preferable because of its high adhesiveness.

Moreover, the crosslinkable (meth)acrylic copolymer may have other monomer units as necessary. Other monomers may be those copolymerizable with the acrylic monomers described above, and examples include (meth)acrylonitrile, vinyl acetate, styrene, vinyl chloride, vinylpyrrolidone, vinylpyridine and the like.

<Weight average molecular weight of crosslinkable (meth)acrylic copolymer>
The weight average molecular weight of the crosslinkable (meth)acrylic copolymer is preferably 100,000 to 2,000,000, more preferably 200,000 to 1,500,000. When the weight-average molecular weight is within the above range, it becomes easy to keep the initial adhesive strength of the adhesive sheet low and increase the adhesive strength after heating. The weight-average molecular weight of the crosslinkable (meth)acrylic copolymer is the value before cross-linking with a cross-linking agent, which will be described later. The weight average molecular weight is a value measured by size exclusion chromatography (SEC) and determined based on polystyrene standards. As the crosslinkable (meth)acrylic copolymer, a commercially available one may be used, or one synthesized by a known method may be used.

<Crosslinking agent>
The adhesive composition contains a cross-linking agent. The cross-linking agent can be appropriately selected in consideration of the reactivity with the cross-linkable functional group of the cross-linkable (meth)acrylic copolymer. For example, it can be selected from known cross-linking agents such as isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, metal chelate compounds and butylated melamine compounds. Among them, the cross-linking agent preferably contains at least one selected from isocyanate compounds, epoxy compounds and metal chelate compounds.

Examples of isocyanate compounds include tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and the like. Examples of commercially available products include a tolylene diisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.), a xylylene diisocyanate compound (Takenate D-110N, manufactured by Mitsui Chemicals, Inc.), and the like. Examples of epoxy compounds include TETRAD-C (manufactured by Mitsubishi Gas Chemical Company) and TETRAD-X (manufactured by Mitsubishi Gas Chemical Company). Examples of metal chelate compounds include aluminum chelate A (manufactured by Kawaken Fine Chemicals).

The content of the cross-linking agent in the pressure-sensitive adhesive composition is appropriately selected depending on the desired adhesiveness, etc., and is 0.01 to 5 parts by mass with respect to 100 parts by mass of the cross-linkable (meth)acrylic copolymer. is preferred, and 0.1 to 3 parts by mass is more preferred. By setting the content of the cross-linking agent within the above range, processability can be further enhanced. As the cross-linking agent, one type may be used alone or two or more types may be used in combination. When two or more types are used in combination, the total mass is preferably within the above range.

<Solvent>
The adhesive composition may contain a solvent. In this case, the solvent is used to improve the coatability of the pressure-sensitive adhesive composition. Examples of solvents include hydrocarbons such as hexane, heptane, octane, toluene, xylene, ethylbenzene, cyclohexane, and methylcyclohexane; halogenated hydrocarbons such as dichloromethane, trichloroethane, trichlorethylene, tetrachloroethylene, and dichloropropane; methanol, ethanol, Alcohols such as 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; Methyl acetate , Esters such as ethyl acetate, butyl acetate, isobutyl acetate, amyl acetate, and ethyl butyrate; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene Polyols such as glycol monomethyl ether acetate and derivatives thereof are included.

The content of the solvent in the adhesive composition is not particularly limited, but is preferably 25 to 500 parts by mass, more preferably 30 to 400 parts by mass, relative to 100 parts by mass of the crosslinkable (meth)acrylic copolymer.
Also, the content of the solvent is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, relative to the total mass of the pressure-sensitive adhesive composition. One type of solvent may be used alone, or two or more types may be used in combination. When two or more types are used in combination, the total mass is preferably within the above range.

<Other ingredients>
The pressure-sensitive adhesive composition may contain components other than the above as long as the effects of the present invention are not impaired. Other components include components known as additives for pressure-sensitive adhesives. For example, it can be selected from plasticizers, antioxidants, metal corrosion inhibitors, tackifiers, silane coupling agents, UV absorbers, light stabilizers such as hindered amine compounds, and the like, as required. Dyes and pigments may also be added for the purpose of coloring.

As a plasticizer, for example, a non-functional acrylic polymer may be used. Examples of the non-functional acrylic polymer include a polymer consisting only of acrylic monomer units having no functional groups other than acrylate groups, and acrylic monomer units having no functional groups other than acrylate groups and no functional groups. Polymers composed of non-acrylic monomeric units may be mentioned. Since the non-functional acrylic polymer does not crosslink, it is possible to improve the step followability without affecting the adhesiveness.
Examples of antioxidants include phenol antioxidants, amine antioxidants, lactone antioxidants, phosphorus antioxidants, sulfur antioxidants, and the like. One type of these antioxidants may be used alone, or two or more types may be used in combination.
As the metal corrosion inhibitor, a benzoriazole-based resin can be mentioned as a preferable example because of its compatibility with the adhesive and its high effect.
Examples of tackifiers 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.
Silane coupling agents include, for example, mercaptoalkoxysilane compounds (eg, mercapto group-substituted alkoxy oligomers, etc.).
Examples of ultraviolet absorbers include benzotriazole-based compounds, benzophenone-based compounds, and triazine-based compounds.

<Method for manufacturing adhesive sheet>
The method for producing the pressure-sensitive adhesive sheet of the present invention preferably includes the steps of applying the pressure-sensitive adhesive composition described above onto a release sheet to form a coating film, and heating the coating film. When the adhesive composition contains a solvent, the solvent is removed in this heating step, and at the same time, the reaction between the crosslinkable (meth)acrylic copolymer and the crosslinking agent proceeds by heating the coating film to form a cured product (adhesive layer) is formed.

In the step of heating the coating film, the heating temperature is preferably 50 to 150° C., and the heating time varies depending on the thickness of the coating film and the content of the solvent in the pressure-sensitive adhesive composition, but may be 1 to 60 minutes. preferable. A known heating device such as a heating furnace or an infrared lamp can be used to heat the coating film. Moreover, after heating, it is preferable to perform an aging treatment in which the pressure-sensitive adhesive sheet is allowed to stand at a constant temperature for a certain period of time. The aging treatment can be performed by standing at 23° C. for 7 days, for example.

Coating of the pressure-sensitive adhesive composition can be carried out using a known coating device. Coating devices include, for example, blade coaters, air knife coaters, roll coaters, bar coaters, gravure coaters, micro gravure coaters, rod blade coaters, lip coaters, die coaters and curtain coaters.

<How to use the adhesive sheet>
When using the pressure-sensitive adhesive sheet of the present invention, it is preferable to include a step of contacting the pressure-sensitive adhesive sheet with the surface of the adherend, and a step of heating the pressure-sensitive adhesive sheet after the pressure-sensitive adhesive layer is brought into contact with the surface of the adherend. Since the pressure-sensitive adhesive sheet of the present invention has a low initial adhesive strength, it can be easily peeled immediately after being attached to an adherend, and has excellent reworkability. By doing so, the adhesiveness of the adhesive sheet to the adherend increases. In the method of using the adhesive sheet, when heating the adhesive sheet after bonding to the adherend, the heating temperature is preferably 50 to 120° C., and the heating time is preferably 1 to 120 minutes. . Moreover, pressurization may be applied during the heat treatment, and it is preferable to apply a pressure of 0.2 to 0.9 MPa, for example. By performing such a heat treatment, the adhesive strength of the adhesive sheet is remarkably increased, and the adhesive sheet adheres more firmly to the adherend.

<Application of adhesive sheet>
The pressure-sensitive adhesive sheet of the present invention is preferably used for laminating optical members. Examples of optical members include constituent members in optical products such as touch panels and image display devices. Examples of constituent members of the touch panel include an ITO film in which an ITO film is provided on a transparent resin film, an 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, Examples include hard coat films and anti-fingerprint films. Examples of constituent members of the image display device include antireflection films, oriented films, polarizing films, retardation films, brightness enhancement films and the like used in liquid crystal display devices. Moreover, the pressure-sensitive adhesive sheet of the present invention may be used for bonding modules such as a liquid crystal module and a touch panel module.
Materials used for these members include glass, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, polyethylene naphthalate, cycloolefin polymer, triacetyl cellulose, polyimide, cellulose acylate, and the like.

<Laminate>
The present invention also relates to a laminate comprising the pressure-sensitive adhesive sheet described above and an adherend. The adherends are preferably provided on both sides of the pressure-sensitive adhesive sheet. That is, the laminate of the present invention is preferably a laminate of adherend/adhesive sheet/adherend in this order. The adherend is preferably an optical member, and examples of the optical member include the members described above.

The pressure-sensitive adhesive sheet in the present invention is preferably a heat-curable sheet that is further subjected to heat treatment after being attached to the adherend. More specifically, the pressure-sensitive adhesive sheet of the present invention is preferably bonded to an adherend while being primarily heated, and may be subjected to secondary heating after being bonded to the adherend. preferable. By subjecting the adherend to heat treatment after lamination, the adhesiveness between the pressure-sensitive adhesive sheet and the adherend is remarkably improved. For example, when the pressure-sensitive adhesive sheet is attached to an adherend, the adhesive strength before heat treatment is P, and the adhesive strength after heat treatment is Q, the value of Q/P is 100 or more. is preferably 120 or more, more preferably 130 or more, and particularly preferably 150 or more.

EXAMPLES The characteristics of the present invention will be described more specifically below with reference to examples and comparative examples. The materials, amounts used, proportions, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed to be limited by the specific examples shown below.

(Example 1)
(Synthesis of crosslinkable (meth)acrylic copolymer A-1)
Methyl methacrylate (MMA), 2-methoxyethyl acrylate monomer (MEA), dimethylacrylamide (DMAA), and 2-hydroxyethyl acrylate monomer (2HEA) were blended in a weight ratio of 10:75:5:10 to form radicals. AIBN (azobisisobutyronitrile) was dissolved in the solution as a polymerization initiator. The solution was heated to 60° C. for random copolymerization to obtain an acrylic copolymer solution (A-1) having a solid concentration of 40% by mass.

<Production of adhesive sheet>
To 100 parts by mass of the solid content of the crosslinkable (meth)acrylic copolymer A-1, 0.8 parts by mass of an isocyanate-based cross-linking agent (Mitsui Chemicals, Takenate D-110N) was added, and the solid content was adjusted with ethyl acetate. A pressure-sensitive adhesive composition was prepared by diluting and stirring so as to obtain a solution having a concentration of 34% by mass. The pressure-sensitive adhesive composition prepared as described above was applied to a polyethylene terephthalate film (first release sheet) having a thickness of 38 μm (first release sheet) (38RL-07, manufactured by Oji F-Tex Co., Ltd.) and having a release layer treated with a silicone release agent. On the surface of (2)), uniformly coat with an applicator so that the coating thickness after drying is 25 μm, dry in an air circulation constant temperature oven at 100 ° C. for 3 minutes, and apply to the surface of the first release sheet. An adhesive layer was formed. Next, a second release sheet (38RL-07(L), manufactured by Oji F-Tex Co., Ltd.) having a thickness of 38 μm was attached to the surface of the pressure-sensitive adhesive layer. In this way, a double-sided pressure-sensitive adhesive sheet with a release sheet having a configuration of first release sheet/adhesive layer/second release sheet in which the pressure-sensitive adhesive layer is sandwiched between a pair of release sheets having different peeling strengths is obtained. Ta. The double-sided pressure-sensitive adhesive sheet was aged for 7 days under the conditions of 23° C. and 50% relative humidity.

(Example 2)
(Synthesis of crosslinkable (meth)acrylic copolymer A-2)
Methyl methacrylate (MMA) macromonomer (manufactured by Toagosei Co., Ltd., AA-6), n-butyl acrylate (BA), 2-methoxyethyl acrylate (MEA), dimethylacrylamide (DMAA), 2-hydroxyethyl acrylate monomer (2HEA ) in a mass ratio of 10:5:70:5:10 in the same manner as in the synthesis of the crosslinkable (meth)acrylic copolymer A-1, acrylic with a solid content concentration of 40% by mass A copolymer solution (A-2) was obtained. The methyl methacrylate (MMA)-based macromonomer has a methacryloyl group at the end of a methyl methacrylate (MMA) oligomer. The degree of polymerization of the oligomer of methyl methacrylate (MMA) is about 60.

<Production of adhesive sheet>
Double-sided adhesive with a release sheet in the same manner as in Example 1 except that A-2 was used instead of the crosslinkable (meth)acrylic copolymer A-1 and the amount of the crosslinking agent was changed to 0.5 parts by mass. got a sheet.

(Example 3)
(Synthesis of crosslinkable (meth)acrylic copolymer A-3)
Crosslinkable (meth) except that methyl methacrylate (MMA), 2-methoxyethyl acrylate (MEA), dimethylacrylamide (DMAA), and acrylic acid (AA) were blended in a mass ratio of 10:75:10:5 An acrylic copolymer solution (A-3) having a solid concentration of 40% by mass was obtained in the same manner as in the synthesis of the acrylic copolymer A-1.

<Production of adhesive sheet>
A-3 was used instead of the crosslinkable (meth)acrylic copolymer A-1, and 0.3 parts by mass of an epoxy-based cross-linking agent (Mitsubishi Gas Chemical Co., Ltd., TETRAD X) was added instead of the isocyanate-based cross-linking agent. A double-sided pressure-sensitive adhesive sheet with a release sheet was obtained in the same manner as in Example 1 except for the above.

(Example 4)
(Synthesis of crosslinkable (meth) acrylic copolymer A-4)
Methyl methacrylate (MMA) macromonomer (manufactured by Toagosei Co., Ltd., AA-6), n-butyl acrylate (BA), 2-methoxyethyl acrylate (MEA), dimethylacrylamide (DMAA), acrylic acid (AA) in mass ratio An acrylic copolymer solution with a solid content concentration of 40% by mass in the same manner as in the synthesis of the crosslinkable (meth)acrylic copolymer A-1 except that it was blended so that the ratio was 10:5:7:10:5. (A-4) was obtained.

<Production of adhesive sheet>
Except for using A-4 instead of the crosslinkable (meth)acrylic copolymer A-1 and adding 0.8 parts by mass of a metal chelate cross-linking agent (Kawaken Fine Chemicals Aluminum Chelate A) instead of the isocyanate cross-linking agent. A double-sided pressure-sensitive adhesive sheet with a release sheet was obtained in the same manner as in Example 1.

(Comparative example 1)
(Synthesis of crosslinkable (meth)acrylic copolymer B-1)
Crosslinkable (meth)acrylic copolymer A except that n-butyl acrylate (BA), dimethylacrylamide (DMAA), and 2-hydroxyethyl acrylate monomer (2HEA) were blended at a mass ratio of 80:10:10 An acrylic copolymer solution (B-1) having a solid content concentration of 40% by mass was obtained in the same manner as in the synthesis of -1.

<Production of adhesive sheet>
A double-sided pressure-sensitive adhesive sheet with a release sheet was obtained in the same manner as in Example 1 except that B-1 was used instead of the crosslinkable (meth)acrylic copolymer A-1.

(Comparative example 2)
(Synthesis of crosslinkable (meth) acrylic copolymer B-2)
The solid content concentration was determined in the same manner as in the synthesis of the crosslinkable (meth)acrylic copolymer A-1, except that 2-ethylhexyl acrylate (2EHA) and acrylic acid (AA) were blended at a mass ratio of 95:5. An acrylic copolymer solution (B-2) having a content of 40% by mass was obtained.

<Production of adhesive sheet>
Example 1 except that B-2 was used instead of the crosslinkable (meth)acrylic copolymer A-1, and 1.2 parts by mass of the isocyanate cross-linking agent was changed to Coronate L-55 manufactured by Tosoh Corporation. A double-sided pressure-sensitive adhesive sheet with a release sheet was obtained in the same manner as above.

(Comparative Example 3)
2-Methoxyethyl acrylate monomer (MEA), dimethylacrylamide (DMAA), and 2-hydroxyethyl acrylate monomer (2HEA) were blended at a mass ratio of 85:10:5, and AIBN (Azobis isobutyronitrile) was dissolved into the solution. The solution was heated to 60° C. for random copolymerization to obtain an acrylic copolymer solution (B-3) having a solid concentration of 40% by mass.

<Production of adhesive sheet>
Example 1 except that B-3 was used instead of the crosslinkable (meth)acrylic copolymer A-1, and the isocyanate cross-linking agent was changed to Y-75 manufactured by Soken Kagaku Co., Ltd. and added 0.6 parts by mass. A double-sided pressure-sensitive adhesive sheet with a release sheet was obtained in the same manner as above.

(measurement)
<Adhesive strength to glass>
Physical properties (1)
After peeling off the release sheet on the light release side of the double-sided pressure-sensitive adhesive sheets with release sheets of Examples and Comparative Examples and laminating with 100 μm PET (manufactured by Toyobo Co., Ltd./product number: Cosmoshine A4300), 0.5 MPa at 100 ° C. using an autoclave. A pressure-sensitive adhesive sheet having a PET substrate on one side was obtained by treating for 30 minutes under the conditions of The release sheet on the heavy release side of the single-sided PET base pressure-sensitive adhesive sheet thus obtained was peeled off, and the adhesive sheet was laminated to soda glass (manufactured by Hiraoka Special Glass Co., Ltd., the pressure-bonded surface being the opposite surface of the tin float). At this time, a sample for measurement was prepared according to the method for measuring 180° peeling adhesive strength described in JIS Z 0237, except that soda glass was used for the test plate. After 1 minute from pressure bonding, the adhesive strength was measured at a peeling speed of 300 mm/min. This adhesive force was defined as physical property (1).

Physical properties (2)
A sample for measurement was prepared in the same manner as in the method of physical properties (1) up to pressure bonding to a test plate. Thereafter, this measurement sample was treated in an autoclave under conditions of 100° C. and 0.5 MPa for 30 minutes, and then allowed to stand in an environment of 23° C. and a relative humidity of 50% for 2 hours. Then, the adhesive strength was measured at a peeling speed of 300 mm/min in the same manner as in physical property (1). This adhesive force was defined as physical property (2).

(evaluation)
<Position adjustability (reworkability)>
A single-sided PET base adhesive sheet prepared by the method of physical properties (1) was cut into a size of 50 mm × 60 mm, and a 30 mm × 40 mm (thickness: 10 mm) float plate glass (manufactured by Nippon Sheet Glass Co., Ltd.) was attached to the adhesive sheet using a hand roller. and press-bonded so that their center points overlapped to produce a laminate. The laminate thus produced was placed on a horizontal stand in an environment of 23° C. and a relative humidity of 50% with the adhesive sheet side facing down. Within 1 minute after pressure bonding, the glass plate was peeled upward from the adhesive sheet by pinching the glass plate with the other hand while lightly holding the adhesive sheet protruding from the glass plate with one hand. The peelability at this time was evaluated according to the following criteria.
○: Easy to peel ×: Cannot be peeled off, or cannot be peeled off unless the adhesive sheet is turned up and the adhesive sheet is pulled up from the edge

<Adhesiveness after heating>
A laminate prepared in the same manner as in the evaluation method for position adjustability (reworkability) was treated in an oven at 80 ° C. (less than 10% relative humidity) for 30 minutes, and then subjected to an environment of 23 ° C. and 50% relative humidity for 60 minutes. Let stand for a minute. Thereafter, the releasability of the glass plate was evaluated according to the following criteria in the same manner as the evaluation method for position adjustability (reworkability).
○: Can not be peeled off, or cannot be peeled off unless the adhesive sheet is pulled up from the edge with the adhesive sheet side up ×: Easy to peel off

The adhesive sheets of Examples exhibited weak initial adhesive strength and excellent position adjustment ability (reworkability), while exhibiting excellent adhesive strength after heating.

10 Adhesive sheet with release sheet 11 Adhesive layer 12a Release sheet 12b Release sheet

Claims (7)

A pressure-sensitive adhesive sheet obtained by curing a pressure-sensitive adhesive composition containing a crosslinkable (meth)acrylic copolymer and a cross-linking agent,
The crosslinkable (meth)acrylic copolymer includes units derived from an alkoxyalkyl group-containing (meth)acrylate, units derived from a hydroxy group- containing (meth)acrylate, units derived from a nitrogen-containing monomer, and methyl methacrylate. contains the units from which
The content of units derived from the alkoxyalkyl group-containing (meth)acrylate is 40 to 75 % by mass with respect to the total mass of the crosslinkable (meth)acrylic copolymer, and the units derived from the hydroxy group- containing (meth)acrylate is 10 to 20% by mass, the content of units derived from a nitrogen-containing monomer is 3 to 20% by mass, and the content of units derived from methyl methacrylate is 3 to 20% by mass. ,
An adhesive sheet that satisfies the following physical properties (1) and (2);
Physical properties (1): Adhesive strength to glass after 1 minute of lamination, measured according to the adhesive strength measurement method described in JIS Z 0237, is 0.05 to 3 N/25 mm;
Physical property (2): The pressure-sensitive adhesive sheet was attached to a glass plate, heat-treated at 100°C and 0.5 MPa for 30 minutes, and then measured according to the adhesive strength measurement method described in JIS Z 0237. , the adhesion to glass is 10N/25mm or more. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the adhesive strength to glass in physical property (2) is 100 times or more the adhesive strength to glass in physical property (1). The adhesive sheet according to claim 1 or 2 , wherein the crosslinkable (meth)acrylic copolymer has a block-like branched chain in which 3 or more units derived from the methyl methacrylate are continuous. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3 , wherein the cross-linking agent contains at least one selected from isocyanate compounds, epoxy compounds and metal chelate compounds. A pressure-sensitive adhesive sheet with a release sheet, comprising a pair of release sheets having different release forces on both surfaces of the pressure-sensitive adhesive sheet according to any one of claims 1 to 4 . A laminate comprising the adhesive sheet according to any one of claims 1 to 4 and an optical member. The laminate according to claim 6 , wherein the adhesive sheet is a heat-curable sheet.