JP2024094208A - Adhesive sheet rolls and adhesive sheets - Google Patents

Abstract

To provide an adhesive sheet roll for a flexible display with excellent quality.SOLUTION: An adhesive sheet roll 10 is obtained by winding a long adhesive sheet 3 around a core. The adhesive sheet 3 has an adhesive layer 7 with a thickness of 5-150 μm sandwiched between a light release sheet 8 and a heavy release sheet 6. In the adhesive sheet 3 unwound from the adhesive sheet roll 10, a peeling force Pl in peeling the light release sheet 8 from the adhesive layer 7 is 0.02-0.30 N/25 mm; and, when a 50-μm PET film is attached to the exposed adhesive layer 7, a peeling force Ph in further peeling the heavy release sheet 6 from the adhesive layer 7 is 0.10-0.80 N/25 mm; where Ph/Pl is 2 to 6. A thickness Tl of the light release sheet and a thickness Th of the heavy release sheet are within specific ranges. The light release sheet is on the outer side of the roll.SELECTED DRAWING: Figure 1

Description

This disclosure relates to an adhesive sheet roll and an adhesive sheet having a substrate-less double-sided adhesive layer.

Substrate-less double-sided pressure-sensitive adhesive sheets are known. Such double-sided pressure-sensitive adhesive sheets are used to bond adherends together, and typically have an adhesive layer sandwiched between release sheets. Such pressure-sensitive adhesive sheets are produced in sheet form, or may be manufactured as pressure-sensitive adhesive sheet rolls wound around a core to increase productivity.

Patent Documents 1 and 2 disclose a rolled adhesive sheet with a specific range of roll hardness, which is made by winding a laminated sheet of a first release sheet/adhesive layer having a specific range of shear storage modulus at 120°C/second release sheet into a roll, with the objective of providing an adhesive sheet roll in which the occurrence of glue overflow and tunnel-shaped lifting is suppressed.

In recent years, there has been active development of technology that allows displays to be made larger while maintaining the size of the device. Examples include foldable displays and rollable displays. The former are foldable displays that can be opened and closed freely, while the latter are displays with panels that can be rolled up. The adhesive layers for such flexible displays are required to have flexibility and recovery properties in addition to the properties that have traditionally been required for adhesive layers.

JP 2021-1272 A JP 2021-1273 A

From the viewpoint of productivity, there is a demand in the market for substrate-less double-sided adhesive sheets in the form of adhesive sheet rolls. However, when in roll form, tension is applied to the adhesive sheet, which can cause problems such as deformation of the adhesive layer due to the inclusion of foreign matter such as dust and dirt, or the formation of minute irregularities (dents) in the adhesive layer. In addition, the tension of the adhesive sheet in roll form, or when unrolling from the roll, can cause a tunneling phenomenon in which peeling or floating (air bubbles) occurs between the release sheet and the adhesive layer, leaving traces of peeling on the adhesive layer.

The occurrence of deformation, dents, or tunneling in the adhesive layer may result in a decrease in adhesion between the adhesive layer and the adherend. Furthermore, when the adhesive layer is used to attach display components, image quality may decrease. Such problems are particularly serious in adhesive layers designed with flexibility and resilience in mind for application to flexible devices.

This disclosure has been made in consideration of the above problems, and aims to provide a high-quality adhesive sheet roll and adhesive sheet for flexible displays.

The present disclosure provides the following pressure-sensitive adhesive sheet roll and pressure-sensitive adhesive sheet.
[1]: An adhesive sheet roll in which a long adhesive sheet is wound around a core,
The pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer having a thickness of 5 to 150 μm and sandwiched between a light release sheet and a heavy release sheet,
the adhesive sheet unwound from the adhesive sheet roll has a peel force Pl of 0.02 to 0.30 N/25 mm when the light release sheet is peeled from the adhesive layer in an environment of 23° C. and 50% relative humidity at a peel angle of 180° and a peel speed of 300 mm/min;
after the light release sheet is peeled off from the adhesive layer, a 50 μm PET film is attached to the exposed adhesive layer, and the heavy release sheet is further peeled off from the adhesive layer in an environment of 23° C. and 50% relative humidity at a peel angle of 180° and a peel speed of 300 mm/min, the peel force Ph is 0.10 to 0.80 N/25 mm,
Ph/Pl is 2 to 6;
The thickness Tl of the light release sheet is 25 to 100 μm,
The thickness Th of the heavy release sheet is 50 to 188 μm,
And, Tl<Th,
A pressure-sensitive adhesive sheet roll for flexible displays, comprising the light release sheet on the outside of the roll.
[2]: The pressure-sensitive adhesive sheet roll according to [1], wherein the standard deviation σ of the thickness of the pressure-sensitive adhesive sheet is 10% or less with respect to the layer thickness.
[3]: The adhesive layer is
The gel fraction is 50 to 90% and the storage modulus at −30° C. is 10 MPa or less,
The adhesive layer contains an adhesive resin having a weight average molecular weight of 500,000 or more,
The pressure-sensitive adhesive resin contains a (meth)acrylic copolymer (a),
The pressure-sensitive adhesive sheet roll according to [1] or [2], wherein the (meth)acrylic copolymer (a) is a copolymer having a structural unit derived from an alicyclic (meth)acrylate monomer and/or a structural unit derived from a linear or branched alkyl (meth)acrylate monomer having an alkyl group with a carbon number of 8 to 20.
[4]: An adhesive sheet for flexible displays, which is unwound from the adhesive sheet roll according to any one of [1] to [3] and punched.

The present disclosure has the excellent effect of providing high-quality adhesive sheet rolls and adhesive sheets for flexible displays.

FIG. 2 is a schematic perspective view showing an example of a pressure-sensitive adhesive sheet roll according to an embodiment. FIG. 2 is a cross-sectional view taken along line II-II of FIG.

The present disclosure will be described in detail below. Needless to say, other embodiments are also included in the scope of the present disclosure as long as they are consistent with the spirit of the present disclosure. In addition, in this specification, a numerical range specified using "~" includes the numerical values written before and after "~" as the range of the lower and upper limits. In this specification, "film", "sheet" and "tape" are synonymous and are not distinguished by thickness or shape. (Meth)acrylic means acrylic or methacrylic. In addition, various components appearing in this specification may be used independently alone or in combination of two or more types, unless otherwise noted. The numerical values specified in this specification refer to values obtained by the method described in the examples.

1. Adhesive Sheet Roll The adhesive sheet roll of the present disclosure (hereinafter also referred to as the present adhesive sheet roll) is a roll sheet in which a long adhesive sheet (hereinafter also referred to as the present adhesive sheet) is wound around a core. The present adhesive sheet is a substrate-less double-sided adhesive laminate in which a light release sheet/adhesive layer/heavy release sheet are laminated in this order. The present adhesive sheet roll is suitable for flexible display applications. However, this does not exclude applications other than the above.

For this adhesive sheet roll, the adhesive sheet is unwound and cut and punched as necessary. After the light release sheet is peeled off and removed, the exposed adhesive layer is affixed to an adherend, and then the heavy release sheet is peeled off and removed, and the adhesive layer thus exposed is affixed to another adherend. Through these steps, the adherends are joined together.

The present pressure-sensitive adhesive sheet roll has a pressure-sensitive adhesive sheet that satisfies the following (i) to (v).
(i) The thickness of the adhesive layer is set to 5 to 150 μm.
(ii) In the adhesive sheet unwound from the adhesive sheet roll, the peel force Pl when the light release sheet is peeled from the adhesive layer at a peel angle of 180° and a peel speed of 300 mm/min in an environment of 23° C. and a relative humidity of 50% is 0.02 to 0.30 N/25 mm.
(iii) After the light release sheet is peeled off from the adhesive layer, a 50 μm PET film is attached to the exposed adhesive layer, and a heavy release sheet is further peeled off from the adhesive layer in an environment of 23° C. and relative humidity 50%, at a peel angle of 180° and a peel speed of 300 mm/min., and the peel force Ph is 0.10 to 0.80 N/25 mm.
(iv) The ratio of the peeling force Ph to the peeling force Pl, Ph/Pl, is 2 to 6.
(v) The light release sheet has a thickness Tl of 25 to 100 μm, the heavy release sheet has a thickness Th of 50 to 188 μm, and Tl<Th, and the light release sheet is provided on the outside of the roll.

The release force Pl of the light release sheet and the release force Ph of the heavy release sheet can be adjusted by the release treatment of the surface of each release sheet attached to the adhesive layer. For example, the release force can be adjusted by the type of sheet and the type of release agent applied to the substrate surface. The release force can also be adjusted by the amount of release agent applied. Furthermore, it may be adjusted by the surface roughness of the release layer. It may also be adjusted by the adhesive composition forming the adhesive layer. If you want to reduce the value of the release force, it is effective to increase the surface roughness or increase the amount of release agent applied, and if you want to increase the value of the release force, you can adjust it in the opposite way.
The release force Pl of the light release sheet and the release force Ph of the heavy release sheet in this disclosure were measured by the method described in the examples below. As shown in the examples below, the measured value of the release force of the light release sheet/adhesive layer/PET film 50 μm (G2L, manufactured by Toyobo Co., Ltd.) and the measured value of the light release sheet measured with the light release sheet/adhesive layer/heavy release sheet (50 μm or more) are substantially the same release force.

When the adhesive sheet roll is wound up, tension is applied to the adhesive layer. This can cause minute irregularities and deformation in the adhesive layer. In addition, foreign matter such as dust and dirt adhering to the adhesive sheet can cause deformation of the adhesive layer through the heavy or light release sheet. Furthermore, during the manufacture, storage, and transportation of the adhesive sheet roll, floating (air bubbles) and tunneling phenomena such as partial peeling can occur between the adhesive layer and the release sheet.

Deformation of the adhesive layer, dents, or tunneling phenomena can be confirmed, for example, by shining a light on the adhesive sheet and projecting it onto a screen. In displays in which functional layers such as polarizing plates and antistatic films are attached via adhesive layers, such dents affect visibility and hinder the development of high definition displays.

As a result of extensive research by the present inventors, it was found that an adhesive sheet that satisfies the above (i) to (v) can maintain the lamination balance of the light release sheet/adhesive layer/heavy release sheet even when made into a roll, effectively suppressing lifting and partial peeling of the adhesive layer and release sheet, and suppressing deformation and minute irregularities in the adhesive layer. It was also found that air bubbles can be effectively suppressed even when repeatedly folded. With this adhesive sheet, a high-quality adhesive sheet roll can be obtained even when used for flexible displays.

The adhesive layer Ta has a thickness of 5 to 150 μm, a peel strength Pl of 0.02 to 0.30 N/25 mm, a peel strength Ph of 0.10 to 0.80 N/25 mm, and Ph/Pl of 2 to 6. Furthermore, the thickness Tl of the light release sheet is 25 to 100 μm, and the thickness Th of the heavy release sheet is 50 to 188 μm. By providing the light release sheet on the outside of the roll, tunneling can be effectively prevented and peel marks can be suppressed. In addition, by making the adhesive layer within the above specific range, it is possible to maintain good light transparency and flexibility while exerting adhesive strength.

By setting the thickness Tl of the light release sheet in the range of 25 to 100 μm and the thickness Th of the heavy release sheet in the range of 50 to 188 μm, with the relationship Tl<Th, and providing the light release sheet on the outside of the roll in this adhesive sheet, cushioning properties are imparted to the heavy release sheet, and the occurrence of dents due to foreign matter or shaking during transportation can be suppressed. In addition, by providing the light release sheet, which is thinner than the heavy release sheet, on the outside of the roll, it is possible to effectively prevent the light release sheet and the adhesive layer from floating, while at the same time increasing the conformability to the adhesive layer, and effectively increasing the conformability of the adhesive layer to surface irregularities of the adhesive layer or microprotrusions of the adhesive layer resulting from foreign matter outside the adhesive sheet. In addition, by combining the heavy release sheet and the light release sheet, deformation of the adhesive layer can be suppressed.

Furthermore, by setting the peel force Pl to 0.02 to 0.30 N/25 mm, tunneling phenomena such as floating and partial peeling of the light release sheet and adhesive layer can be effectively suppressed. In addition, by setting Ph to 0.10 to 0.80 N/25 mm in a range where Ph/Pl is in the range of 2 to 6 in terms of the relationship between the peel force Ph and the peel force Pl, the phenomenon of the adhesive layer and the heavy release sheet coming apart can be effectively suppressed. Note that in cases where a foam layer or other member described below is included, this outer diameter is the outer diameter including the foam layer, etc.

Figure 1 shows an example of a schematic diagram of the adhesive sheet roll. The adhesive sheet roll 10 has a long adhesive sheet 3 wound around a core 1. The core 1 can be cylindrical or columnar. The outer diameter (diameter) of the core 1 is, for example, about 100 to 1000 mm. The width of the adhesive sheet roll is, for example, about 100 to 3000 mm, and the wound length of the adhesive sheet is, for example, about 10 to 3000 m.

Figure 2 is a cross-sectional view of the II-II section of Figure 1. The adhesive sheet 3 unwound from the adhesive sheet roll 10 has an adhesive layer 7 sandwiched between a light release sheet 8 and a heavy release sheet 6, as shown in Figure 2. This adhesive sheet 3 is a substrate-less laminate, with the release surface of the light release sheet 8 facing the adhesive layer 7 and the release surface of the heavy release sheet 6 facing the adhesive layer 7. As shown in Figure 2, it is preferable that the light release sheet 8 and the heavy release sheet 6 have an adhesive layer non-forming region at both ends in the width direction. Spacers may be placed between the release sheets in the adhesive layer non-forming region. The spacers can be placed in any shape, such as a line shape or a dot shape, along the longitudinal direction of the end. By providing a spacer, it is possible to maintain the opposing distance and suppress the adhesive layer from protruding. The non-opposing region Wa can be, for example, more than 20 mm and less than 30 mm.

The core 1 preferably has a foam layer 2 on its outer circumferential surface. The foam layer 2 preferably has a 25% compression load of 10 to 1000 kPa measured in accordance with JIS K 6254. By setting the load within this range, the yield of the adhesive sheet roll can be increased, and the productivity can be improved. Furthermore, deformation of the adhesive layer can be more effectively suppressed. A more preferred range is 30 to 300 kPa, and an even more preferred range is 50 to 200 kPa.

Aging a double-sided PSA sheet in a rolled state can increase productivity. However, aging in a rolled state can cause a problem of large variation in thickness of the PSA sheet. One of the reasons for this is that unevenness occurs in the release sheet due to thermal shrinkage during the aging process.
As a result of intensive research by the present inventor, it was found that the occurrence of dents can be significantly suppressed by making the standard deviation σ of the thickness Tt of the present adhesive sheet 10% or less of the layer thickness of the adhesive sheet. When the standard deviation σ of the thickness Tt of the present adhesive sheet is 10% or less of the layer thickness of the adhesive sheet, the thickness variation of the adhesive layer is small, so the adhesion area between the adhesive layer and the release sheet is large. It is considered that the adhesive layer closely adheres to the unevenness caused by the thermal shrinkage of the release sheet in the aging process, and prevents dents in the adhesive sheet. On the other hand, when it is more than 10%, the adhesion between the adhesive layer and the release sheet is reduced, so that when the adhesive layer follows the unevenness of the release sheet, minute peeling occurs, which is considered to lead to the occurrence of dents. It is more preferable that the standard deviation σ is 8% or less, and even more preferable that it is 5% or less.

One method for making the standard deviation σ of the adhesive sheet thickness Tt 10% or less is to place the light release sheet on the outside of the roll of adhesive sheet that combines the thicknesses and release forces of the light release sheet and heavy release sheet specified in the adhesive sheet. Other methods include adjusting the thickness of the adhesive layer specified in the adhesive sheet, and adjusting the thickness of the light release sheet and heavy release sheet specified in the adhesive sheet.

2. Adhesive layer The adhesive layer is a double-sided adhesive layer with a thickness of 5 to 150 μm, and serves to bond adherends together. The adhesive layer is sandwiched between a light release sheet and a heavy release sheet at the stage of the adhesive sheet roll. The thickness Ta of the adhesive layer is more preferably in the range of 8 to 100 μm, and even more preferably in the range of 25 to 75 μm. The thickness Ta of the adhesive layer can be determined by the method of the examples described later.

From the viewpoint of enduring repeated bending and exhibiting excellent restoring force when returning from a bent state to the original state, and from the viewpoint of more effectively preventing deformation of the adhesive layer in the state of a pressure-sensitive adhesive sheet roll, the storage modulus of the adhesive layer at 23° C. and a frequency of 1 Hz is preferably 1×10 ⁴ to 100×10 ⁴ Pa. In addition, by using an adhesive layer in the above range, the balance of the release force with the light release sheet and the heavy release sheet can be easily designed. By having a storage modulus of 1×10 ⁴ or more, the adhesive layer has adhesive force to the adherend, and the release forces (ii) and (iii) above can be easily adjusted. In addition, the adhesive layer can have excellent flexibility. The storage modulus can be measured, for example, by DHR-2 manufactured by TA Instruments. The storage modulus can be adjusted by the monomer composition, the molecular weight of the resin, the blending amount of the curing agent, the drying conditions, and the like. By setting it in the above range, the flexibility is improved.

The adhesive strength of the adhesive layer is preferably 10 to 40 N/25 mm against the polyimide substrate under 25°C conditions. By setting the adhesive strength in this range, it is easy to adjust the release strength between the light release sheet and the heavy release sheet to the above range. In addition, flexibility can be effectively exhibited. A more preferable range is 15 to 35 N/25 mm, and an even more preferable range is 20 to 30 N/25 mm. The adhesive strength of the adhesive layer can be controlled by the composition of the adhesive resin constituting the adhesive composition described below, the Tg of the adhesive resin, the amount of the curing agent in the adhesive composition, and the like. When an acrylic copolymer is used as the adhesive resin, the adhesive strength can be increased by including a highly polar acrylic monomer derived from a carboxyl group-containing monomer such as acrylic acid. In addition, the adhesive strength tends to be higher as the Tg of the adhesive resin is lower. Furthermore, the adhesive strength tends to be higher as the amount of the curing agent in the adhesive composition is smaller.

The adhesive layer 7 is a layer formed from an adhesive composition. The adhesive composition is a crosslinked adhesive or a non-crosslinked adhesive, and may be an emulsion type, a solvent type, or a solventless type.

The adhesive composition contains an adhesive resin as the main component. The main component here refers to the component with the largest content (mass) among the non-volatile components. Examples of the adhesive resin include acrylic copolymers, rubber-based resins, silicone-based resins, urethane-based resins, polyamide resins, polyimide resins, polyester resins, and fluororesins. These resins may be used alone or in combination of two or more. Acrylic copolymers are preferred from the viewpoint of excellent transparency in addition to adhesion.

The adhesive composition may contain a curing agent as necessary. Examples of the curing agent include isocyanate compounds, epoxy compounds, aziridine compounds, carbodiimide compounds, metal chelates, etc. The curing agent may be a low molecular weight compound or a high molecular weight compound. Among these, isocyanate compounds are preferred from the viewpoint of achieving both high cohesive strength and adhesion.

A suitable adhesive layer is one which has a gel fraction of 50 to 90% and a storage modulus of 10 MPa or less at −30° C. and is formed by crosslinking an adhesive composition containing a (meth)acrylic copolymer. A suitable example of the (meth)acrylic copolymer is (a) having a structural unit derived from an alicyclic (meth)acrylate monomer and/or a structural unit derived from a linear or branched alkyl (meth)acrylate monomer having an alkyl group with a carbon number of 8 to 20.
Further, a suitable example of the (meth)acrylic copolymer (a) is a (meth)acrylic copolymer (a) having a structural unit derived from an alicyclic (meth)acrylate monomer and/or a structural unit derived from a linear alkyl (meth)acrylate monomer having an alkyl group with 10 to 20 carbon atoms, and a structural unit derived from a branched alkyl (meth)acrylate monomer having 8 to 20 carbon atoms.
The inclusion of a structural unit derived from an alicyclic (meth)acrylate monomer and/or a structural unit derived from a linear alkyl (meth)acrylate monomer having an alkyl group with a carbon number of 10 to 20 can reduce the stress applied when the adhesive layer is repeatedly bent, and can prevent the adhesive layer from slipping. In addition, the inclusion of a structural unit derived from a branched alkyl (meth)acrylate monomer having a carbon number of 8 to 20 can increase the cohesive force of the adhesive layer, prevent whitening of the bent portion, and provide a good evaluation of air bubbles as described in the examples.

The gel fraction is more preferably in the range of 55 to 85%, and even more preferably in the range of 60 to 80%. The storage modulus of the adhesive layer at −30° C. is more preferably in the range of 8 MPa or less, and even more preferably in the range of 5 MPa or less. By setting the gel fraction in the above range, air bubbles at the bent portion are improved.
The gel fraction of the adhesive layer can be adjusted by adjusting the aging time, aging temperature, and amount of curing agent. In the (meth)acrylic copolymer (a), the gel fraction can be controlled within the above range by adjusting the ratio of the hydroxyl group-containing monomer. By increasing the ratio of the hydroxyl group-containing monomer, the gel fraction tends to be higher. The lower limit of the storage modulus of the adhesive layer at -30°C is preferably 0.5 MPa from the viewpoint of air bubbles at the bending portion. The storage modulus can be adjusted by using a structural unit derived from a linear and/or branched alkyl (meth)acrylate monomer having an alkyl group with 8 to 20 carbon atoms in the (meth)acrylic copolymer (a). The larger the number of carbon atoms in the alkyl group of the alkyl (meth)acrylate monomer is, or the more branched portions there are, the more the bulky alkyl group becomes entangled in the adhesive layer, so the storage modulus tends to be lower.

2-1. Pressure-sensitive adhesive resin The weight-average molecular weight (Mw) of the pressure-sensitive adhesive resin is 500,000 or more from the viewpoint of achieving both strength and punching processability, preferably 800,000 to 1,800,000, more preferably 900,000 to 1,700,000, and even more preferably 1,000,000 to 1,500,000. In addition, the Tg of the pressure-sensitive adhesive resin is preferably -30°C or less, more preferably -32°C or less, and even more preferably -35°C or less, as obtained by subjecting the pressure-sensitive adhesive layer to differential scanning calorimetry (DSC), from the viewpoint of providing excellent flexibility to the pressure-sensitive adhesive layer. The lower limit of the Tg of the pressure-sensitive adhesive resin is not particularly limited, but from the viewpoint of heat resistance, it is preferably -50°C or more.

The (meth)acrylic copolymer can be obtained, for example, by copolymerizing a functional group-containing monomer with a (meth)acrylic acid ester. A suitable example of the (meth)acrylic acid ester is an alkyl (meth)acrylic acid ester.

The alkyl group of the (meth)acrylic acid alkyl ester may be any of a linear, branched, or cyclic alkyl group, and is preferably an alkyl group having 1 to 20 carbon atoms.
From the viewpoint of enhancing flexibility, a (meth)acrylic copolymer (a) obtained by copolymerizing a monomer containing at least a cyclic alkyl group (alicyclic) and/or a linear or branched alkyl (meth)acrylate monomer having an alkyl group carbon number of 8 to 20 is preferred. Specific examples of the monomer include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, (meth)acrylic acid, Examples of the acrylates include decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, 4-n-butylcyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. Among these, in terms of flexibility and adhesive strength, methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, hexyl (meth)acrylate, dodecyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate are preferred, and 2-ethylhexyl acrylate, dodecyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate are particularly preferred.

The (meth)acrylic acid alkyl ester preferably has a homopolymer Tg of −80 to 110° C. In addition, it is preferable to use a (meth)acrylic acid alkyl ester having a linear alkyl group and a (meth)acrylic acid alkyl ester having an alicyclic alkyl group in combination.
The Tg of the homopolymer can be calculated from the Tgn of a polymer obtained by polymerizing an alkyl (meth)acrylate alone according to the following Fox equation.
Fox formula: 100/Tg=Σ(Wn/Tgn)
Tg: Calculated Tg of the polymer (K)
Wn: mass fraction of monomer n (%)
Tgn: glass transition temperature (K) of homopolymer of monomer n
The Tg value (Tgn) of the homopolymer of monomer n is described in, for example, technical documents of monomer manufacturers such as Nippon Shokubai Co., Ltd., Mitsubishi Chemical Corporation, and Toa Gosei Co., Ltd., Polymer Data Handbook (published by Baifukan, edited by the Society of Polymer Science (Basics), first edition January 1986), and Polymer Handbook 4th edition (J. Brandrup, E. H. Immergut, E. A. Grulke, published in 1999, Wiley-Interscience). For example, the homopolymer Tg of each monomer is methyl methacrylate (105°C), dodecyl acrylate (-10°C), 2-ethylhexyl acrylate (-70°C), butyl acrylate (-54°C), isobornyl acrylate (94°C), cyclohexyl acrylate (19°C), and 4-hydroxybutyl acrylate (-40°C).

Among the (meth)acrylic copolymers, the above-mentioned (meth)acrylic copolymer (a) is particularly preferred. The structural unit derived from a linear or branched (meth)acrylic acid alkyl ester having an alkyl group of 8 to 20 carbon atoms is preferably 10 to 100 mass%, more preferably 20 to 90 mass%, and even more preferably 30 to 85 mass%, based on 100 mass% of the (meth)acrylic copolymer (a).
Furthermore, the content of the structural unit derived from an alicyclic (meth)acrylate monomer and/or the structural unit derived from a linear alkyl (meth)acrylate monomer having an alkyl group of 10 to 20 carbon atoms is preferably 10 to 90 mass%, more preferably 10 to 75 mass%, and even more preferably 15 to 50 mass%, relative to 100 mass% of the (meth)acrylic copolymer (a).
Furthermore, the content of the structural unit derived from a branched alkyl (meth)acrylate monomer having 8 to 20 carbon atoms is preferably 10 to 90 mass%, more preferably 20 to 85 mass%, and even more preferably 40 to 85 mass%, relative to 100 mass% of the (meth)acrylic copolymer (a).

The (meth)acrylic copolymer (a) may contain a functional group monomer. Examples of functional group-containing monomers include carboxy group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, and amino group-containing monomers. By including a functional group-containing monomer, the cohesive strength of the adhesive is improved, and a tough adhesive layer is obtained.

Examples of carboxy group-containing monomers include (meth)acrylic acid, β-carboxyethyl acrylate, p-carboxybenzyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, citraconic acid, and isocrotonic acid. Among these, (meth)acrylic acid is particularly preferred from the viewpoint of cohesive strength and adhesive strength.

Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. Among these, from the viewpoint of cohesive strength and adhesive strength, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate are more preferred.

Examples of epoxy group-containing monomers include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, and 6-methyl-3,4-epoxycyclohexylmethyl (meth)acrylate.

Examples of amino group-containing monomers include monoalkylamino (meth)acrylates such as monomethylaminoethyl (meth)acrylate, monoethylaminoethyl (meth)acrylate, monomethylaminopropyl (meth)acrylate, and monoethylaminopropyl (meth)acrylate.

The total amount of the structural units derived from the functional group-containing monomer is preferably 1 to 20% by mass relative to 100% by mass of the (meth)acrylic copolymer (a). By setting the amount within this range, the cohesive strength can be adjusted by the reaction with the curing agent, and the flexibility and restoring force can be improved.
The content of the structural unit derived from the carboxyl group-containing monomer is preferably 1 to 10% by mass relative to 100% by mass of the (meth)acrylic copolymer (a). This range allows the adhesive layer to have both cohesive strength and relaxation properties. In addition, the content of the structural unit derived from the hydroxyl group-containing monomer is preferably 1 to 10% by mass relative to 100% by mass of the (meth)acrylic copolymer (a). This range allows the adhesive layer to have both cohesive strength and relaxation properties.

The (meth)acrylic copolymer (a) may contain structural units derived from other monomers that are copolymerizable with the above-mentioned monomers. Examples include monomers having an alkyleneoxy group and other vinyl monomers. Examples include methoxyethyl acrylate, methoxydiethylene glycol acrylate, vinyl acetate, vinyl crotonate, styrene, and acrylonitrile. The structural units derived from the other monomers preferably account for 0.1 to 20% by mass of 100% by mass of the (meth)acrylic copolymer (a).

The (meth)acrylic copolymer (a) is obtained by polymerizing the monomer mixture. During polymerization, a polymerization initiator can be used as necessary. The content of the polymerization initiator is, for example, 0.01 to 10 parts by mass per 100 parts by mass of the monomer mixture. The polymerization method is not limited. Examples include solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization. Examples of the solvent used in solution polymerization include acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, and cyclohexanone. The polymerization temperature is, for example, 60 to 120°C, and the polymerization time is about 5 to 12 hours.

The polymerization initiator is preferably a radical polymerization initiator. Peroxides and azo compounds are suitable as radical polymerization initiators. Examples of azo compounds include 2,2'-azobisbutyronitrile such as 2,2'-azobisisobutyronitrile (ABN) and 2,2'-azobis(2-methylbutyronitrile); 2,2'-azobisvaleronitrile such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile); 2,2'-azobispropionitrile such as 2,2'-azobis(2-hydroxymethylpropionitrile); and 1,1'-azobis-1-alkanenitrile such as 1,1'-azobis(cyclohexane-1-carbonitrile). Examples of the peroxide include dialkyl peroxides such as di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, and 2,5-di(t-butylperoxy)hexyne-3; peroxy esters such as t-butylperoxybenzoate, t-butylperoxyacetate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 1 peroxyketals such as 1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and n-butyl-4,4-bis(t-butylperoxy)valerate; hydroperoxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, and 2,5-dimethylcyclohexane-2,5-dihydroperoxide; diacyl peroxides such as benzoyl peroxide, decanoyl peroxide, lauroyl peroxide, and 2,4-dichlorobenzoyl peroxide; and peroxydicarbonates such as bis(t-butylcyclohexyl)peroxydicarbonate.

2-2. Curing agent The adhesive composition may contain a curing agent as necessary. By having a crosslinked structure, an adhesive layer having excellent adhesive strength and cohesive strength can be provided. Suitable examples of the curing agent can be designed according to the functional group of the adhesive resin. Suitable curing agents include isocyanate compounds, epoxy compounds, aziridine compounds, carbodiimide compounds, metal chelates, and the like. When the functional group is a hydroxy group or a carboxy group, isocyanate compounds and epoxy compounds are preferred, and among these, isocyanate compounds are preferred from the viewpoint of achieving both high cohesive strength and adhesion. Suitable examples include an adhesive composition in which the (meth)acrylic copolymer (a) is used as the adhesive resin and an isocyanate compound is used as the curing agent.

The isocyanate compound is an isocyanate having two or more isocyanate groups. The isocyanate compound is preferably, for example, an isocyanate monomer such as an aromatic polyisocyanate, an aliphatic polyisocyanate, an araliphatic polyisocyanate, or an alicyclic polyisocyanate, as well as a biuret, a nurate, or an adduct thereof.

Examples of aromatic polyisocyanates include 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, and 4,4',4"-triphenylmethane triisocyanate.

Examples of aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (also known as HMDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

Examples of aromatic aliphatic polyisocyanates include ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate.

Examples of alicyclic polyisocyanates include 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI, isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanatomethyl)cyclohexane.

The biuret form is a self-condensation product having a biuret bond formed by self-condensation of an isocyanate monomer. An example of the biuret form is the biuret form of hexamethylene diisocyanate.

The nurate is a trimer of an isocyanate monomer. Examples include a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, and a trimer of tolylene diisocyanate.

The adduct is a bifunctional or higher isocyanate compound obtained by reacting an isocyanate monomer with a bifunctional or higher low-molecular-weight active hydrogen-containing compound. Examples of the adduct include a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with tolylene diisocyanate, a compound obtained by reacting trimethylolpropane with xylylene diisocyanate, a compound obtained by reacting trimethylolpropane with isophorone diisocyanate, and a compound obtained by reacting 1,6-hexanediol with hexamethylene diisocyanate.

From the viewpoint of forming a sufficient crosslinked structure, the isocyanate compound is preferably a trifunctional isocyanate compound. The isocyanate compound is more preferably an adduct or nurate, which is a reaction product between an isocyanate monomer and a trifunctional low-molecular-weight active hydrogen-containing compound. The isocyanate compound is preferably a trimethylolpropane adduct of hexamethylene diisocyanate, a nurate of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, a nurate of tolylene diisocyanate, a trimethylolpropane adduct of isophorone diisocyanate, or a nurate of isophorone diisocyanate, and more preferably a trimethylolpropane adduct of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, or a trimethylolpropane adduct of isophorone diisocyanate.

Examples of epoxy compounds include glycerin diglycidyl ether, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidylaminophenylmethane.

Examples of aziridine compounds include N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxite), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, and 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane.

The carbodiimide compound is preferably a high molecular weight polycarbodiimide produced by a decarboxylation condensation reaction of a diisocyanate compound in the presence of a carbodiimide catalyst. The commercially available high molecular weight polycarbodiimide is preferably the Carbodilite series from Nisshinbo Industries. Among these, Carbodilite V-03, 07, and 09 are preferred because of their excellent compatibility with organic solvents.

Preferred metal chelates are coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium with acetylacetone or ethyl acetoacetate. Examples of metal chelates include aluminum ethyl acetoacetate diisopropylate, aluminum trisacetylacetonate, aluminum bisethyl acetoacetate monoacetylacetonate, and aluminum alkyl acetoacetate diisopropylate.

The curing agent is preferably contained in an amount of 0.001 to 1 part by mass, and more preferably 0.01 to 0.1 part by mass, per 100 parts by mass of the adhesive resin. A content of 0.01 part by mass or more improves the cohesive strength, while a content of 1 part by mass or less is preferable because it is easier to achieve both cohesive strength and flexibility.

2-3. Other Additives The present pressure-sensitive adhesive composition may further contain a solvent, a tackifier, a silane coupling agent, a filler, a tackifier resin, a colorant, an antioxidant, an antistatic agent, an ultraviolet absorber, etc., as necessary.

Examples of solvents include esters such as ethyl acetate, propyl acetate, and butyl acetate, and ketones such as acetone, methyl ethyl ketone, and cyclohexanone. Other examples include aromatic hydrocarbons such as toluene, xylene, benzene, and solvent naphtha, and aliphatic hydrocarbons such as cyclopentane, cyclohexane, methylcyclohexane, dimethylcyclohexane, trimethylcyclohexane, ethylcyclohexane, diethylcyclohexane, decahydronaphthalene, bicycloheptane, tricyclodecane, hexahydroindenecyclohexane, cyclooctane, α-pinene, terpinolene, and limonene. Solvents may be used alone or in combination.

Examples of the silane coupling agent include alkoxysilane compounds having a (meth)acryloxy group, such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropyltripropoxysilane, 3-(meth)acryloxypropyltributoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane;
Alkoxysilane compounds having a vinyl group, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinylmethyldimethoxysilane, and vinylmethyldiethoxysilane;
alkoxysilane compounds having an amino group, such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltripropoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane;
alkoxysilane compounds having a mercapto group, such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltripropoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylmethyldiethoxysilane;
alkoxysilane compounds having an epoxy group, such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyltripropoxysilane, 3-glycidoxypropyltributoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane;
tetraalkoxysilane compounds such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane;
Examples of the silane include 3-chloropropyltrimethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, styryltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate, 3-isocyanatepropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, hexamethyldisilazane, and silicone resins having an alkoxysilyl group in the molecule.

It is preferable to use 0.01 to 10 parts by mass of the silane coupling agent per 100 parts by mass of the adhesive resin, and more preferably 0.05 to 5 parts by mass.

The optical and mechanical properties can be adjusted by adding fillers. Examples of fillers include inorganic white pigments such as silica, calcium carbonate, aluminum hydroxide, magnesium hydroxide, clay, talc, and titanium dioxide.

Examples of tackifier resins include rosin resins, polymerized rosin resins, rosin ester resins, polymerized rosin ester resins, terpene resins, terpene phenol resins, coumarone resins, coumarone indene resins, xylene resins, phenol resins, and petroleum resins. When an acrylic copolymer is used as the adhesive resin, rosin resins, polymerized rosin resins, rosin ester resins, and polymerized rosin ester resins are preferred, and rosin ester resins and polymerized rosin ester resins are more preferred, in terms of good compatibility and improved adhesive performance. The tackifier resin is preferably used in an amount of 0.01 to 10 parts by mass, and more preferably 0.5 to 7 parts by mass, per 100 parts by mass of (meth)acrylic copolymer (a). High adhesive strength can be obtained by using 0.01 to 10 parts by mass of the tackifier resin.

3. Light Release Sheet and Heavy Release Sheet The light release sheet and the heavy release sheet serve to protect the adhesive layer. The light release sheet and the heavy release sheet satisfy the above (ii) to (v). A more preferred range for Tl is 25 to 75 μm, and an even more preferred range is 25 to 50 μm. A more preferred range for Th is 50 to 150 μm, and an even more preferred range is 75 to 125 μm. From the viewpoint of increasing productivity, the light release sheet and the heavy release sheet may be made of the same material but with different thicknesses.

The thickness difference (Th-Tl) is preferably 15 μm or more, and more preferably 25 μm or more. The upper limit is preferably 140 μm or less, and more preferably 95 μm or less. By making the thickness difference 15 μm or more, the stress applied to the adhesive when the light release sheet is peeled off is distributed to the heavy release sheet, preventing cohesive failure of the adhesive when peeled off. By making the thickness difference 140 μm or less, the stress applied to the adhesive when the light release sheet is peeled off is distributed to the heavy release sheet, making it easier to peel off the light release sheet smoothly and preventing zipping.

The more preferred range for Ph/Pl is 2.5 to 5. The more preferred range for Pl is 0.02 to 0.2 N/25 mm, and even more preferred is 0.02 to 0.1 N/25 mm. The more preferred range for Ph is 0.15 to 0.6 N/25 mm, and even more preferred is 0.2 to 0.5 N/25 mm.

Examples of light release sheets and heavy release sheets (hereinafter collectively referred to as "release sheets") include polyethylene sheets, polypropylene sheets, polybutene sheets, polybutadiene sheets, polymethylpentene sheets, polyvinyl chloride sheets, vinyl chloride copolymer sheets, polyethylene terephthalate sheets, polyethylene naphthalate sheets, polybutylene terephthalate sheets, polyurethane sheets, ethylene vinyl acetate sheets, ionomer resin sheets, ethylene-(meth)acrylic acid copolymer sheets, ethylene-(meth)acrylic acid ester copolymer sheets, polystyrene sheets, polycarbonate sheets, polyimide sheets, and fluororesin sheets. The release sheets may be single layer or laminated.

In addition to using a release sheet that has releasability in itself, a release sheet in which a release agent is applied to a substrate may be used. Releasability can be imparted by applying a release agent to the bonding surface with the adhesive layer. The release sheet may have other functional layers in addition to the substrate/release layer. Examples of release layers having other functional layers include antistatic layer/substrate/release layer and substrate/antistatic layer/release layer.

Specific examples of release agents include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based agents. The above (ii) to (iv) can be adjusted depending on the type of release agent. Another method for adjusting (ii) to (iv) is to adjust the thickness of the light release sheet and the heavy release sheet, as described below.

From the viewpoint of ease of designing the peel strength, it is preferable to use a silicone-based release agent. A suitable example is a release agent that contains linear silicone as the main component and also contains branched silicone.

Silicone-based release agents include silicones with siloxane bonds in the main chain. For example, silicones include those with three organic substituents bonded to silicon and one oxygen atom (M units), those with two organic substituents bonded to silicon and two oxygen atoms (D units), those with one organic substituent bonded to silicon and three oxygen atoms (T units), and those with no organic substituents bonded to silicon and four oxygen atoms (Q units). By combining these types of silicones, various silicones with different peeling properties can be obtained, and the peel strength can be controlled by the ratio of these types. In many cases, linear silicones composed of M units or D units can be used to make the peeling easier, while branched silicones that include T units or Q units in the linear silicone structure can be used to make the peeling heavier.

As the linear silicone, a composition that has D units as the main component and M units appropriately to adjust the molecular weight is preferred. The organic substituent represents a hydrogen atom, a hydroxyl group, or an alkyl group, and from the viewpoint of ease of solubility in organic solvents, an alkyl group, specifically a methyl group or a phenyl group, is preferred.

Linear silicone can have a crosslinked structure to impart various resistances. Linear silicone preferably has two or more vinyl groups at its ends and/or side chains as crosslinking points. Curing agents include hydrogen-modified silicone, which must have two or more SiH groups in one molecule. It is preferable to include 0.1 to 20 parts by mass of hydrogen-modified silicone per 100 parts by mass of linear silicone.

The branched silicone preferably contains T units and/or Q units, and preferably contains 70% by mass or more of T units and/or Q units in 100% by mass of the branched silicone. The branched silicone may contain M units and D units in addition to T units and/or Q units.

The release layer is formed from a release agent. The release agent according to the present invention contains linear silicone and branched silicone in a ratio of linear silicone:branched silicone = 100:0 to 99:1 (mass ratio). By containing branched silicone in an amount of 1 mass% or less based on the total mass of the release agent (linear silicone, hydrogen-modified silicone, and branched silicone), dust resistance and resistance to winding slippage are improved. The ratio of branched silicone is more preferably 0.5 mass% or less, and even more preferably 0.2 mass% or less.

The total content of linear silicone, hydrogen-modified silicone, and branched silicone is preferably 50 to 100% by mass, more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass, out of a total mass of 100% by mass of the release agent.

Silicone-based release agents can be synthesized by addition reaction, peroxide condensation reaction, or UV crosslinking reaction, but it is preferable to form them by addition reaction. The addition reaction is the crosslinking of vinyl groups contained in linear silicone and SiH groups contained in hydrogen-modified silicone.

When the release agent is synthesized by an addition reaction, a catalyst is included. The catalyst is not particularly limited, but is preferably a platinum-based catalyst, and more preferably chloroplatinic acid such as chloroplatinic acid or chloroplatinic acid, alcohol compounds of chloroplatinic acid, aldehyde compounds, or complexes of chloroplatinic acid and various olefins. The amount of catalyst added is preferably 0.01 to 10 mass%, more preferably 0.2 to 2 mass%, based on the total mass of the release agent (100 mass%).

The release agent may contain any other appropriate components as long as the effects of the present disclosure are not impaired. Examples include reaction inhibitors, inorganic fillers, organic fillers, colorants (dyes, pigments, etc.), plasticizers, UV absorbers, antioxidants, etc.

The release layer is preferably formed by applying a release agent composition onto the release substrate. The release agent may contain a solvent when applied. The type of solvent is not limited, but examples include organic solvents such as hydrocarbon solvents such as normal hexane, cyclohexane, and normal heptane; aromatic solvents such as toluene and xylene; ester solvents such as ethyl acetate and methyl acetate; ketone solvents such as acetone and methyl ethyl ketone; and alcohol solvents such as methanol, ethanol, and butanol.

The release agent can be applied onto the substrate by a microgravure coater, a gravure coater, etc. The release agent can be applied so that the solid content mass is, for example, about 0.1 to 2.0 g/m ² , preferably about 0.5 to 1.2 g/m ² , and then cured to provide a release layer.

The release agent coating film is preferably cured by heat curing. Heat curing can efficiently promote the addition reaction. There are no limitations on the curing temperature, but 80 to 130°C is preferable. By setting the temperature at 80°C or higher, the curing reaction can be carried out efficiently, and productivity can be increased. Furthermore, by setting the temperature at 130°C or lower, deterioration of the substrate (such as the occurrence of wrinkles due to heat) can be reduced and the options for substrates can be increased. There are no limitations on the thickness of the release layer, but it is, for example, about 0.1 to 2 μm.

4. Manufacturing of the adhesive sheet roll The manufacturing method of the adhesive sheet roll of the present disclosure can be manufactured by a known method. For example, a step of forming an adhesive layer by applying an adhesive composition to a heavy release sheet and curing the applied film, and a step of attaching a light release sheet to one exposed surface of the adhesive layer to obtain an adhesive sheet. Then, the adhesive sheet obtained is wound into a roll.

Coating can be performed, for example, with a microgravure coater, gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, rod blade coater, knife coater, spray coater, die coater, or curtain coater. If the adhesive composition contains a solvent, the solvent is removed by a drying process after coating. Curing can be achieved, for example, by aging. In the case of a photocurable adhesive composition, curing can be achieved by irradiating it with UV light or the like.

After the adhesive sheet is produced, or while the adhesive sheet is being produced, the adhesive sheet is wound around a core into a roll to obtain an adhesive sheet roll. The winding length can be designed depending on the application. Also, it can be designed appropriately depending on the length of the adhesive sheet, but from the viewpoint of increasing productivity, it is preferably 50 m or more, and more preferably 100 m or more. From the viewpoint of production yield, it is preferable that the winding length is 2500 m or less.

Alternatively, the adhesive layer may be applied to the release surfaces of a light release sheet and a heavy release sheet so that the thickness after drying is a predetermined thickness, forming two adhesive layers, and then the adhesive layers may be attached to each other.

5. Flexible display The flexible display comprises an optical element such as a liquid crystal element or an organic EL element, and an adhesive layer formed from the adhesive sheet unwound from the adhesive sheet roll. The flexible display is a bendable display, and is preferably a display that can be repeatedly bent, including folded. For example, an organic electroluminescence (organic EL) display, an electrophoretic display (electronic paper), a liquid crystal display using a plastic substrate (film) as a substrate, and a foldable display can be exemplified.

The adhesive layer formed from this adhesive sheet is suitable for bonding bendable components together. For example, it is suitable for bonding any combination of components including liquid crystal polymer sheets, light-emitting polymer sheets, sheet-like liquid crystal modules, organic EL modules (organic EL sheets), electronic paper modules, transparent conductive sheets, metal mesh sheets, sheet sensors, cover sheets, barrier films, polarizing films, polarizers, retardation films, viewing angle compensation films, brightness enhancement films, contrast enhancement films, diffusion films, semi-transmissive reflective films, and electrode films.

The present disclosure will be explained in more detail below based on examples. However, the present disclosure is not limited to these. Unless otherwise specified, "parts" in the examples indicate "parts by mass" and "%" indicates "% by mass." Blank spaces in the tables indicate that no compound was added.

(a) Measurement Method The values obtained in the present examples were obtained by the following methods: Each measurement point (film thickness, peel force, etc.) on the pressure-sensitive adhesive sheet roll was performed at a position that was 50% of the wound length of the pressure-sensitive adhesive sheet roll.

a-1. Glass transition temperature The glass transition temperature (Tg) of the (meth)acrylic copolymer (a) and the adhesive layer was measured by a robot DSC (differential scanning calorimeter, Seiko Instruments Inc. "RDC220"). Approximately 2 mg of the sample was placed in an aluminum pan, weighed, and set in the differential scanning calorimeter, and an aluminum pan of the same type without the sample was used as a reference. After being held at a temperature of 100°C for 5 minutes, it was rapidly cooled to -120°C using liquid nitrogen, and then heated at a heating rate of 5°C/min, and Tg (°C) was determined from the obtained DSC chart.

a-2. Mw of resin
The Mw was determined by conversion using a GPC "LC-GPC system" manufactured by Shimadzu Corporation, with polystyrene of known molecular weight used as a standard substance.
Device name: Shimadzu Corporation, LC-GPC system "Prominence"
Column: Four GMHXL columns manufactured by Tosoh Corporation and one HXL-H column manufactured by Tosoh Corporation were connected together.
Mobile phase solvent: tetrahydrofuran Flow rate: 1.0 mL/min Column temperature: 40° C.

a-3. Film thickness Ten equally spaced locations were determined from one end to the other end in the width direction of the adhesive sheet roll, the thicknesses of the ten locations were measured, and the average value was taken as the thickness Tt of the adhesive sheet. The end here refers to the end where the light release sheet/adhesive layer/heavy release sheet are laminated. Next, the light release sheet was peeled off from the adhesive sheet roll, and the thicknesses of the peeled light release sheet were measured at 10 locations corresponding to the same positions as described above. The average value was taken as the thickness Tl of the light release sheet. Thereafter, the heavy release sheet was further peeled off from the adhesive layer, and the thicknesses of the peeled heavy release sheet were measured at 10 locations corresponding to the same positions as described above. The average value was taken as the thickness Th of the heavy release sheet. The thickness Ta of the adhesive layer was calculated by Tt-Tl-Th.

Standard deviation of thickness of adhesive sheet The standard deviation σ of the in-plane thickness of the thickness Tt of the adhesive sheet was determined from "a-3" above. That is, the standard deviation σ was determined from the film thickness at 10 equally spaced locations from one end to the other end in the width direction of the adhesive sheet roll.

a-5. Storage modulus G' of adhesive layer (storage modulus at -30°C)
Two sets of adhesive sheets were prepared by peeling off the light release sheet from the adhesive sheet roll, and the adhesive layers were bonded together with a laminator to prepare a laminate of heavy release sheet/adhesive layer/heavy release sheet. The heavy release sheet on one side of the laminate was peeled off, and the adhesive sheets from which the light release sheet had been peeled off were repeatedly bonded together to form a laminate of adhesive layers with a thickness of 1 mm. The storage modulus G' of this laminate was measured using a rheometer (manufactured by TA Instruments, DHR-2) with a φ8 mm measurement probe under conditions of strain 0.1%, frequency 1 Hz, and heating rate 10°C/min from -70°C to 200°C, and the storage modulus G' at -30°C was obtained.

a-6. Peel strength Pl of light release sheet against adhesive layer
After the adhesive sheet was produced by the method described below, it was left in an environment of 23°C and 50% relative humidity for 24 hours, and then the light release sheet was peeled off in the same environment at a peel angle of 180° and a peel speed of 300 mm/min, and the peel force Pl of the light release sheet to the adhesive layer was determined.

a-7. Peel strength Ph of the heavy release sheet against the adhesive layer
For the sample for which the peel strength Pl of the light release sheet was determined in a-6 above, a 50 μm PET film (G2L, manufactured by Toyobo Co., Ltd.) was laminated to the exposed surface of the adhesive layer, and the heavy release sheet was then peeled off at a peel angle of 180° and a peel speed of 300 mm/min, and the peel strength Ph of the heavy release sheet to the adhesive layer was determined.

a-8. Gel fraction of adhesive layer The adhesive sheet was cut to a size of 30 mm x 100 mm, and the adhesive layer exposed by peeling off the light release sheet was attached to a weighed 300 mesh stainless steel wire mesh (mass W0). Next, the heavy release sheet was peeled off to obtain a sample of stainless steel wire mesh/adhesive layer. The weight of the sample was W1, and the sample was left to stand in ethyl acetate for 24 hours, then removed, dried at 100 ° C. for 1 hour, and weighed to obtain a mass W2, and the gel fraction was calculated using the following formula.
Gel fraction (%)={(W2−W0)/(W1−W0)}×100

(b) Production Example of Adhesive Resin b-1. Adhesive Resin R1
A reaction vessel (hereinafter simply referred to as "reaction vessel") equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen inlet tube was charged with 100 parts of ethyl acetate, 83 parts of 2-ethylhexyl acrylate (2EHA), 15 parts of isobornyl acrylate (IBXA), 2 parts of 4-hydroxybutyl (meth)acrylate (4HAB), and 0.1 parts of 2,2'-azobisisobutyronitrile (hereinafter simply referred to as "AIBN") as an initiator, and the atmosphere in the reaction vessel was replaced with nitrogen gas. Thereafter, the reaction solution was heated to 65°C while stirring under a nitrogen atmosphere, and reacted at 65°C for 4 hours. After the reaction was completed, the reaction vessel was cooled and diluted with ethyl acetate to obtain a pressure-sensitive adhesive resin ((meth)acrylic copolymer (a)) R1 solution (Mw: 1.2 million, Tg: -48°C) with a non-volatile content of 30%.

b-2. Adhesive resins R2 and R3
Adhesive resins ((meth)acrylic copolymer (a)) R2 and R3 were obtained in the same manner as for adhesive resin R1, except that the monomers and blending amounts were changed to those shown in Table 1. Mw and Tg are shown in Table 1.
The symbols in Table 1 are as follows.
MA: Methyl acrylate (linear alkyl group with 1 carbon atom)
BA: butyl acrylate (linear alkyl group with 4 carbon atoms)
2EHA: 2-ethylhexyl acrylate (branched alkyl group with 8 carbon atoms)
DOA: dodecyl acrylate (linear alkyl group with 12 carbon atoms)
IBXA: isobornyl acrylate (alicyclic alkyl group)
CHA: cyclohexyl acrylate (alicyclic alkyl group)
4HBA: 4-hydroxybutyl (meth)acrylate AA: acrylic acid

(c) Preparation of adhesive composition c-1. Manufacture of adhesive composition C1 0.5 parts of aromatic isocyanate D-110N as a curing agent was mixed with 100 parts of the nonvolatile content of the adhesive resin R1, and ethyl acetate was further added so that the nonvolatile content was 20%, and the mixture was stirred to obtain an adhesive composition C1 (see Table 2).

c-2. Production of Pressure-Sensitive Adhesive Compositions C2 and C3 Pressure-Sensitive Adhesive Compositions C2 and C3 were obtained in the same manner as in the production of Pressure-Sensitive Adhesive Composition C1, except that the pressure-sensitive adhesive resin R1 was changed to R2 or R3 (see Table 2).

(d) Production of release sheet d-1. Release sheet RS1
100 parts of silicone A, 1 part of platinum catalyst, and 200 parts of toluene were mixed and stirred thoroughly to prepare a release agent. The obtained release agent was coated on a polyethylene terephthalate (PET) film having a thickness of 49 μm by a gravure coater so that the film thickness after drying was 1 μm, and dried at 120 ° C for 2 minutes to obtain a release sheet RS1 having a release layer of 50 μm. The adhesive composition C1 was coated on the release layer of the release sheet RS1 so that the thickness Ta after drying was 50 μm. After coating, the adhesive layer was formed by drying at 100 ° C for 3 minutes. Next, a PET film of 50 μm (G2L, manufactured by Toyobo Co., Ltd.) was attached to the exposed surface of the adhesive layer to obtain a test piece having a configuration of release sheet RS1 / adhesive layer L1 / PET film. The release sheet RS1 was then peeled from the adhesive layer at a peel angle of 180° and a peel speed of 300 mm/min in an environment of 23° C. and 50% relative humidity, and the peel strength was determined.

d-2. Release sheets RS2 to RS24
Release sheets RS2 to RS24 were obtained in the same manner as for release sheet RS1, except that the components of the release agent, the thickness of the release agent on the substrate after drying, and the type and thickness of the substrate were changed as shown in Table 3. The peel strength of each release sheet from the adhesive layer L1 was measured in the same manner as for release sheet RS1, and is also shown in Table 3.
The symbols in Table 3 are as follows.
Silicone A: KS-847 (manufactured by Shin-Etsu Silicone Co., Ltd.)
Silicone B: DOWSIL (registered trademark) LTC755 Coating (manufactured by Dow Toray Industries, Inc.)
Silicone C: KS-841 (manufactured by Shin-Etsu Silicone Co., Ltd.)
Silicone D: KS-830E (manufactured by Shin-Etsu Silicone Co., Ltd.)
Silicone E: DOWSIL LTC 759 Coating (manufactured by Dow Toray)
Platinum catalyst: platinum (0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex solution (Sigma-Aldrich)

(e) Production Example of Pressure-Sensitive Adhesive Sheet Roll e-1. Example 1
A coating machine equipped with a heavy release sheet supplying section, a die coater head, a drying furnace, a light release sheet and a laminating machine was used to manufacture the adhesive sheet roll. First, a heavy release sheet roll (release sheet RS3, size width 1100 mm x 100 m) was set in the heavy release sheet supplying section, and the adhesive composition C1 was coated on the release layer of this heavy release sheet so that the thickness Ta after drying was 25 μm. After coating, the adhesive layer was formed by drying at 100 ° C. for 3 minutes. The coating layer had a 25 mm adhesive layer non-forming portion at both ends in the width direction of the heavy release sheet.

Next, a light release sheet roll (release sheet RS11, size: width 1100 mm x length 100 m) was set in the light release sheet supply section, and the release layer surface of this light release sheet was attached to the exposed surface of the adhesive layer described above to obtain adhesive sheet S1 having a "heavy release sheet/adhesive layer/light release sheet" configuration. The adhesive sheet S1 was then wound around a core having a diameter of 3 inches and a length of 120 cm, and aged for one week under conditions of a temperature of 25°C and a relative humidity of 50%, to obtain an adhesive sheet roll having an adhesive layer 1.1 m in width and 100 m in length. Measurements of film thickness, release force, etc. were performed at a position that is 50% of the length of the adhesive sheet roll (a position where 50 m has been unwound).

e-2. Examples 2 to 26 and Comparative Examples 1 to 8
Adhesive sheet rolls of each Example and Comparative Example were obtained in the same manner as in Example 1, except that the types of adhesive composition, light release sheet, and heavy release sheet were changed as shown in Tables 4 to 6.

(g) Evaluation of adhesive sheet roll g-1. Observation of dents The adhesive sheet roll of each Example and Comparative Example was unwound, and a light source (230VILS, manufactured by Ushio Inc.) was irradiated onto the adhesive sheet from a distance of 100 cm in front, and the adhesive sheet was projected at 1:1 magnification onto a screen located 100 cm behind. The screen was then visually observed, and the dents of the adhesive sheet were evaluated according to the following criteria. The dents were those that could be visually counted, and those with a major axis of 0.5 mm or more were counted as one.
5: There are less than 50 dents per ^square meter.
4: The number of dents is 50 or more and less than ¹⁰⁰ per ^square meter.
3: The number of dents is 100 or more and less than ^{300 per square} meter.
2: The number of dents is 300 or more and less than ^{500 per} square meter.
1: The number of dents is 500 or more and less than ^1,000 per ^square meter.

g-2. Air bubbles generated during folding The pressure-sensitive adhesive sheet roll of each Example and Comparative Example was unwound, the light release sheet was peeled off, and the exposed pressure-sensitive adhesive layer was laminated onto a polyimide film.
The heavy release sheet was then peeled off from the adhesive layer, and the exposed adhesive layer was laminated onto an easy-adhesion PET film. The laminate was placed in an autoclave and held at 50° C. for 20 minutes. The laminate was then removed and left at 25° C. and 50% RH for 30 minutes, and then cut into a size of 70 mm wide and 100 mm long to obtain a test laminate consisting of an easy-adhesion PET film/adhesive layer/polyimide.
Next, the test laminate was subjected to 200,000 cycles of twisting in a planar body no-load twisting tester (manufactured by Yuasa System Co., Ltd.) at 25°C and 50% RH, with one cycle being the time it took for the laminate to return to its original state before twisting. The number of sample tests was N=5, and the appearance after the test was visually evaluated. The evaluation criteria were as follows. Air bubbles were visually determined, and voids with a diameter of 100 μm or more were counted.
5: No air bubbles were observed in all 5 samples.
Air bubbles were visible in the 4:1 sample.
3: Air bubbles were observed in the 2 samples.
2: Air bubbles were observed in the 3 sample.
Air bubbles were observed in the 1:4 sample or in all samples.

g-3. Punching yield The sheet was punched using a die (Thomson blade). The punched shape and size was A4. The processing yield is the frequency at which no cracks occurred when punching was performed 20 times.
5: The number of times the anger occurred was less than once.
4: The number of times that the cry occurred was more than two and less than three.
3: The number of times that the tantrum occurred was 4 or more and 5 or less.
2: The number of times that the anger occurred was more than 6 but less than 7.
1: The number of times that the anger occurred is 8 or more times.

g-4. Deformation of the adhesive layer after lamination The light release sheet was peeled off from the adhesive sheet, and a 50 μm PET film (G2L, manufactured by Toyobo Co., Ltd.) was laminated as an adherend to prepare a test piece with a width of 1000 mm and a length of 1000 mm. A light source (230VILS, manufactured by Ushio Inc.) was irradiated onto the test piece from a distance of 100 cm in front, and the test piece was directly observed visually from a distance of 20 cm or less, and the lifting of the adhesive layer was evaluated according to the following criteria. The lifting refers to a lifting of 0.5 mm or more. If a large lifting of 10 mm or more exists, the evaluation was rated as 1.
5: Less than 10 pieces/ ^m2 of floats less than 1 mm, and less than 10 pieces/ ^m2 of floats 1 mm or more but less than 10 mm.
4: Less than 30 pieces/ ^m2 of floats less than 1 mm, and less than 10 pieces/ ^m2 of floats 1 mm or more but less than 10 mm.
3: Less than 30 pieces/ ^m2 of floats less than 1 mm, and 10 or more pieces/ ^m2 of floats 1 mm or more but less than 10 mm.
2: There are 30 or more floats less than ¹ mm per square meter, and less than 10 floats 1 mm or more but less than 10 mm per ^square meter.
1: None of the above ratings 2 to 5 applies, or there is 1 or more floating pieces of 10 mm or more per ^square meter.

As shown in Comparative Example 1, adhesive sheet rolls with a heavy release sheet wound outside were confirmed to have problems with air bubbles and deformation of the adhesive layer after lamination. Also, adhesive sheet rolls formed with release sheets whose release force Pl is outside the range of 0.02 to 0.30 N/25 mm or whose release force Ph is outside the range of 0.10 to 0.80 N/25 mm, even if the release force ratio Ph/Pl is 2 to 6, were confirmed to have problems with air bubbles as shown in Comparative Examples 2 and 3. Similarly, adhesive sheet rolls combined with release sheets whose release force ratio Ph/Pl does not satisfy the ratio of release force Ph/Pl of 2 to 6 were confirmed to have problems with air bubbles as shown in Comparative Examples 4, 5, and 7. As shown in Comparative Example 6, adhesive sheet rolls having an adhesive layer with a thickness of more than 150 μm were confirmed to have dents. Also, adhesive sheet rolls combined with release sheets whose light release sheet and heavy release sheet are the same thickness or whose Tl>Th had problems with dents as shown in Comparative Examples 7 and 8. On the other hand, this embodiment has been confirmed to provide a high-quality adhesive sheet roll that suppresses the occurrence of dents and bubbles, has excellent punching yields, and can suppress deformation of the adhesive layer after lamination.

1: Roll core 2: Foam layer 3: Adhesive sheet 6: Heavy release sheet 7: Adhesive layer 8: Light release sheet 10: Adhesive sheet roll

Claims (4)

An adhesive sheet roll in which a long adhesive sheet is wound around a core,
The pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer having a thickness of 5 to 150 μm and sandwiched between a light release sheet and a heavy release sheet,
the adhesive sheet unwound from the adhesive sheet roll has a peel force Pl of 0.02 to 0.30 N/25 mm when the light release sheet is peeled from the adhesive layer in an environment of 23° C. and 50% relative humidity at a peel angle of 180° and a peel speed of 300 mm/min;
after the light release sheet is peeled off from the adhesive layer, a 50 μm PET film is attached to the exposed adhesive layer, and the heavy release sheet is further peeled off from the adhesive layer in an environment of 23° C. and 50% relative humidity at a peel angle of 180° and a peel speed of 300 mm/min, the peel force Ph is 0.10 to 0.80 N/25 mm,
Ph/Pl is 2 to 6;
The thickness Tl of the light release sheet is 25 to 100 μm,
The thickness Th of the heavy release sheet is 50 to 188 μm,
And, Tl<Th,
A pressure-sensitive adhesive sheet roll for flexible displays, comprising the light release sheet on the outside of the roll. The adhesive sheet roll according to claim 1, characterized in that the standard deviation σ of the thickness of the adhesive sheet is 10% or less of the layer thickness. The adhesive layer is
The gel fraction is 50 to 90% and the storage modulus at −30° C. is 10 MPa or less,
The adhesive layer contains an adhesive resin having a weight average molecular weight of 500,000 or more,
The pressure-sensitive adhesive resin contains a (meth)acrylic copolymer (a),
The pressure-sensitive adhesive sheet roll according to claim 1, wherein the (meth)acrylic copolymer (a) is a copolymer having a structural unit derived from an alicyclic (meth)acrylate monomer and/or a structural unit derived from a linear or branched alkyl (meth)acrylate monomer having an alkyl group having 8 to 20 carbon atoms. An adhesive sheet for flexible displays, unwound from the adhesive sheet roll according to any one of claims 1 to 3 and punched.

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