JP2009046620A - Adhesive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive sheet being hardly deformed even if a picture surface is pressed and having an easily recovered recession even if it is deformed, when an optical film is stuck on PDP through an adhesive sheet. <P>SOLUTION: The adhesive sheet is prepared by crosslinking an adhesive composition containing a base polymer containing one kind or more of (meth)acrylate based polymer (including a copolymer), an acrylic based crosslinked monomer, and a crosslinking initiator. The adhesive sheet is provided, which has physical properties wherein storage shearing modulus of elasticity is within a range of larger than 1.0×10<SP>4</SP>Pa to 1.0×10<SP>5</SP>Pa in any of frequency 10<SP>-1</SP>Hz-10<SP>-5</SP>Hz of 20°C-reduced master curve, and that tanδ at frequency of 10<SP>-3</SP>Hz is 1.0×10<SP>-1</SP>or less. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention includes various window materials such as a multi-layer window, bonding of glass constituting various display panels, bonding of an optical film on the front side of a flat panel display, bonding of optical films, glass, plastic, etc. The present invention relates to a pressure-sensitive adhesive sheet that can be used for bonding various transparent members, such as bonding various transparent films to a transparent substrate.

  A flat panel display can be given as a typical example of a product in which a transparent member is bonded. In recent years, flat panel displays have been expected as alternatives to CRT televisions, and the market is rapidly rising. Among them, plasma display panels (referred to as “PDP”) and liquid crystal displays are typical examples.

  In such a flat panel display, an optical function film having various functions such as antireflection, near-infrared cut, visible toning, electromagnetic wave shielding, and an optical film filter obtained by bonding them are provided on a panel serving as a base. In addition, a structure that can be directly bonded with an adhesive without using an air layer has been studied, and an adhesive or an adhesive sheet used for the application has been developed.

For example, Patent Document 1 swells a three-dimensional crosslinked polymer with a liquid containing a plasticizer and inorganic fine particles as an adhesive sheet that can be bonded in a room temperature environment and can impart excellent buffering properties. A gel-like pressure-sensitive adhesive sheet is disclosed.
Patent Document 2 discloses a base polymer, a crosslinking monomer composed of a polyfunctional acrylate monomer, and a photoinitiator as a new pressure-sensitive adhesive sheet for bonding optical members having sufficient adhesive strength and excellent deformation recovery ability. A non-gel-like pressure-sensitive adhesive sheet obtained by forming a pressure-sensitive adhesive composition into a sheet and cross-linking it, and 50% at a tensile rate of 100 mm / min in an environment of 23 ° C. × 50% RH A pressure-sensitive adhesive sheet for bonding optical members is disclosed, which has a strain recovery rate of 60% or more when stretched and restored at the same speed.

JP 2004-359808 A JP 2006-169438 A

  Recently, in flat displays such as PDPs, an improvement in dent recovery on the screen has been further demanded. In a flat display with a configuration in which a plurality of optical films are laminated on a panel via an adhesive or an adhesive sheet, the adhesive sheet is easily indented and recessed when the screen is pressed with a finger when the adhesive sheet is inferior in resilience. It has been pointed out that not only does it take time to recover, but it also remains as a permanent distortion without being recovered, which is a cause of a decrease in visibility. For this reason, a rigid protective plate is also interposed between the optical film and the pressure-sensitive adhesive or pressure-sensitive adhesive sheet, but the mass of the filter itself is increased, which hinders weight reduction.

  The object of the present invention is, for example, that when an optical film is bonded to a flat display panel such as a PDP via an adhesive sheet, it is difficult to deform even if the screen surface is pressed with a finger or the like, and the dent is recovered even if deformed. It is in providing an easy-to-adhesive sheet.

The present invention crosslinks a pressure-sensitive adhesive composition containing a base polymer containing one or more kinds of (meth) acrylic acid ester polymers (including copolymers), an acrylic crosslinking monomer, and a crosslinking initiator. a pressure-sensitive adhesive sheet comprising Te, 20 ° C. level in all frequency 10 ^-1 Hz to 10 ^-5 Hz master curves, storage shear modulus exceed ^{1.0 × 10 4 Pa 1.0 × 10} 5 Provided is a pressure-sensitive adhesive sheet having physical properties that are in the range of Pa or less and tan δ (= loss shear modulus / storage shear modulus) at a frequency of 10 ⁻³ Hz is 1.0 × 10 ⁻¹ or less. is there.

In the pressure-sensitive adhesive sheet obtained by crosslinking a pressure-sensitive adhesive composition containing a base polymer containing one or more kinds of (meth) acrylic acid ester-based polymers, an acrylic crosslinking monomer, and a crosslinking initiator, The storage shear modulus of the low frequency region (frequency 10 ⁻¹ Hz to 10 ⁻⁵ Hz) is adjusted to a range of 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁵ Pa and less, and the frequency By adjusting tan δ (= loss shear modulus / storage shear modulus) at 10 ⁻³ Hz to 1.0 × 10 ⁻¹ or less, the storage shear modulus (G ′) of the low frequency region (low speed region) At the same time as increasing the absolute value, the absolute value of the loss shear modulus (G ″) is decreased to increase the difference between the two, thereby making it difficult for the screen surface to be deformed by an external force, particularly pressing at low speed. Even if the dent turns in a short time It could be found that the strain is not easily remain in.

  In general, "film" is a thin flat product whose thickness is extremely small compared to the length and width and whose maximum thickness is arbitrarily limited, and is usually supplied in the form of a roll. (Japanese Industrial Standard JISK6900), and “sheet” generally refers to a product that is thin by definition in JIS and generally has a thickness that is small and flat instead of length and width. However, since the boundary between the sheet and the film is not clear and it is not necessary to distinguish the two in terms of the present invention, in the present invention, even when the term “film” is used, the term “sheet” is included and the term “sheet” is used. In some cases, “film” is included.

BEST MODE FOR CARRYING OUT THE INVENTION

  The pressure-sensitive adhesive sheet according to the present embodiment (hereinafter referred to as “the pressure-sensitive adhesive sheet”) includes a base polymer, a crosslinking monomer, a crosslinking initiator, and an additive such as a plasticizer as necessary. Can be obtained by preparing a product, crosslinking the pressure-sensitive adhesive composition, and adjusting the dynamic viscoelasticity within a specific range.

(Base polymer)
Examples of the base polymer that can be used in the pressure-sensitive adhesive sheet include (meth) acrylic acid ester-based polymers (including copolymers).

  As the (meth) acrylate monomer component used for forming the (meth) acrylate polymer, that is, the alkyl acrylate monomer component or the alkyl methacrylate monomer component, the alkyl group is n-octyl, isooctyl, 2-ethylhexyl, n It is preferably one of alkyl acrylate or alkyl methacrylate monomers which are any one of butyl, isobutyl, methyl, ethyl and isopropyl, or a mixture of two or more selected from these.

  As other components, an acrylate or methacrylate monomer having an organic functional group such as a carboxyl group, a hydroxyl group, or a glycidyl group may be copolymerized. Specifically, the (meth) acrylate monomer component and the (meth) acrylate monomer component having such an organic functional group are selectively obtained and polymerized as a starting material (meth) Acrylic ester-based copolymer polymers can be mentioned.

  Preferably, one of alkyl acrylates such as iso-octyl acrylate, n-octyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate or a mixture of two or more selected from these, or α, β unsaturated carboxylic acid (Meth) acrylic acid ester-based copolymer containing acid, for example, copolymerization of at least one kind of acrylic acid with at least one of iso-octyl acrylate, n-octyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, etc. Can be mentioned.

The glass transition temperature (Tg) of the base polymer is preferably −20 ° C. or lower, particularly preferably −80 ° C. to −30 ° C.
The melt viscosity of the base polymer at 130 ° C. is 50,000 mPa · s or more, particularly 100,000 mPa · s to 500,000 mPa · s, and particularly preferably 100,000 mPa · s to 300,000 mPa · s.

  The glass transition temperature (Tg) can be measured using a viscoelasticity measuring device, for example, a viscoelasticity measuring device “Dynamic Analyzer RDAII” manufactured by Rheometrics. In that case, Tg should just read the temperature which shows the maximum value of Tan (delta) when measured by parallel plate 25mm (phi), distortion 3%, and frequency 1Hz. The melt viscosity can be measured with a B-type viscometer.

(Crosslinking monomer)
As the cross-linking monomer, it is preferable to use an acrylic cross-linking monomer. Above all, polyfunctional such as bifunctional (meth) acrylate, trifunctional (meth) acrylate, and tetrafunctional (meth) acrylate rather than monofunctional (meth) acrylate. A (meth) acrylate or a mixture formed by mixing two or more of monofunctional to tetrafunctional (meth) acrylates is preferable.

Here, as monofunctional (meth) acrylate, (meth) acrylic acids such as acrylic acid, methacrylic acid and crotonic acid, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4- Examples thereof include hydroxybutyl acrylate, tetrahydrofurfuryl acrylate, 1,6-hexanediol monoacrylate and dicyclopentane diene acrylate.
As the bifunctional (meth) acrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, diethylene glycol diacrylate, polyethylene Examples include glycol 400 diacrylate and tripropylene glycol diacrylate.
Examples of trifunctional (meth) acrylates include triacrylates such as pentaerythritol triacrylate, trimethylolpropane triacrylate, trimethylolpropane PO-modified triacrylate, trimethylolpropane EO-modified triacrylate, and trimethacrylates thereof. it can.
Examples of the tetrafunctional (meth) acrylate include ditrimethylolpropane tetraacrylate and pentaerythritol tetraacrylate.

  The crosslinking monomer is not limited to the (meth) acrylates exemplified above. For example, a (meth) acrylate monomer containing an organic functional group can be suitably used.

From the viewpoint of adjusting the viscoelastic characteristics to a desired range, the molecular weight of the crosslinking monomer is preferably relatively large. Specifically, a crosslinking monomer (including an oligomer) having a molecular weight of 300 to 2000, particularly 400 to 1500, and particularly 500 to 1000 is preferable.
In addition, “oligomer” is defined as “a substance composed of molecules including one or more kinds of atoms or atomic groups (structural units) that are repeatedly connected to each other” according to the definition according to JIS-K6900. According to the Dictionary of Polymers, “This definition does not necessarily distinguish polymers and oligomers based on absolute polymerization degree and molecular weight”. In general, the distinction between a monomer and an oligomer is also unclear, and even if there are repeating structural units in the molecule, it may be referred to as a monomer. Therefore, in this specification, the monomer and the oligomer are not distinguished, Even when “monomer” is described, “oligomer” is included.

  The content of the crosslinking monomer may be adjusted so that the storage shear modulus falls within a predetermined range, but is generally 0.01 to 40.0 parts by mass, preferably 0 with respect to 100 parts by mass of the base polymer. It is good to adjust within the range of the ratio of 1.0-40.0 mass parts, especially 1.0-30.0 mass parts. However, this range may be exceeded in balance with other elements.

(Crosslinking initiator)
As the crosslinking initiator, a photoinitiator or a thermal polymerization initiator can be used, and a photoinitiator is particularly preferable.
As the photoinitiator, either a cleavage type photoinitiator or a hydrogen abstraction type photoinitiator can be used, and among these, a hydrogen abstraction type photoinitiator is preferable.
As the hydrogen abstraction type photoinitiator, for example, any one of benzophenone, Michler's ketone, dibenzosuberone, 2-ethylanthraquinone, isobutylthioxanthone, or a mixed component composed of a combination of two or more of these can be used. However, the hydrogen abstraction type photoinitiator is not limited to the substances listed above. Further, the hydrogen abstraction type and the cleavage type may be used in various proportions.

  What is necessary is just to adjust the addition amount of a crosslinking initiator so that the said storage shear elastic modulus may enter in the predetermined range, Generally the range of the ratio of 0.05-5.0 mass parts with respect to 100 mass parts of base polymers. It is better to adjust within. However, this range may be exceeded in balance with other elements.

(Plasticizer)
The plasticizer is not necessarily an essential component in the pressure-sensitive adhesive sheet, but may be blended depending on the purpose. That is, the buffering force can be adjusted by adjusting the type and amount of the plasticizer, and the storage shear modulus of the pressure-sensitive adhesive sheet can be lowered as a whole, so that the storage shear modulus can be adjusted to a desired range. In some cases, it may be desirable to add a plasticizer.

  The plasticizer is preferably a liquid having a freezing point of −20 ° C. or less, particularly a liquid having a freezing point of −80 to −40 ° C., for example, adipic acid ester, phthalic acid ester, phosphoric acid ester, trimellitic acid (Meth) acrylic acid ester polymer that is a base polymer that can use any of ester, citrate ester, epoxy, polyester plasticizer, or a mixture of two or more of these. Those compatible with the polymer are preferred. However, the plasticizer is not limited to the substances listed above. In the case of ultraviolet photocrosslinking, it is preferable to use a plasticizer that does not absorb ultraviolet rays.

  What is necessary is just to set the compounding quantity of a plasticizer, adjusting at least so that the said storage shear elastic modulus may not remove | deviate from the predetermined range, Generally 1-150 mass parts with respect to 100 mass parts of base polymers, Preferably it is 10- It is good to adjust within the range of the ratio of 100 mass parts. However, this range may be exceeded in balance with other elements.

(Other additives)
In addition to the above components, pigments such as pigments and dyes having near-infrared absorption characteristics, tackifiers, antioxidants, antioxidants, hygroscopic agents, ultraviolet absorbers, silane coupling agents, natural products, Various additives such as synthetic resins, glass fibers and glass beads can be appropriately blended.

(Physical properties of adhesive sheet)
In this pressure-sensitive adhesive sheet, the storage shear modulus exceeds 1.0 × 10 ⁴ Pa and is not more than 1.0 × 10 ⁵ Pa at any of the frequencies of 10 ⁻¹ Hz to 10 ⁻⁵ Hz of the 20 ° C. standard master curve. It is important that tan δ (= loss shear modulus / storage shear modulus) at a frequency of 10 ⁻³ Hz is 1.0 × 10 ⁻¹ or less.
With such physical properties, the pressure-sensitive adhesive sheet is excellent in recoverability against dent deformation due to external force, particularly pressing at a low speed, and permanent distortion hardly remains. Conversely, if the storage shear modulus is greater than 1.0 × 10 ⁵ Pa at any frequency of 10 ⁻¹ Hz to 10 ⁻⁵ Hz, the flexibility of the pressure-sensitive adhesive sheet is poor and the wettability to the adherend is poor. turn into. In addition, when the storage shear modulus is less than 1.0 × 10 ⁴ Pa at any frequency of 10 ⁻¹ Hz to 10 ⁻⁵ Hz, it tends to be deformed by pressing, and the dent recoverability is poor. . In addition, at any frequency of 10 ^-1 Hz to 10 ^-5 Hz, even if the storage shear modulus is in the range of 1.0 x 10 ⁴ Pa to 1.0 x 10 ⁵ Pa, at 10 ^-3 Hz. If tan δ is greater than 1.0 × 10 ⁻¹ , the recoverability of dent deformation due to pressing is not sufficient and permanent distortion tends to remain.
From this point of view, the storage shear modulus is preferably more than 1.0 × 10 ⁴ Pa and not more than 1.0 × 10 ⁵ Pa at any frequency of 10 ⁻¹ Hz to 10 ⁻⁵ Hz. It is especially preferable that it is 0 * 10 < ⁴ > Pa-1.0 * 10 < ⁵ > Pa.
Further, tan δ at 10 ⁻³ Hz is more preferably 1.0 × 10 ⁻¹ or less, and particularly preferably 5.0 × 10 ⁻² or less.

In the present adhesive sheet, tan δ at a frequency of 10 ⁻¹ Hz of a 20 ° C. standard master curve is preferably 4.0 × 10 ⁻¹ or less, and more preferably 3.5 × 10 ⁻¹ or less.

Further, it is more preferable that the storage shear elastic modulus falls within the range of 3.0 × 10 ⁴ Pa to 6.0 × 10 ⁶ Pa at any of the frequencies 10 ³ Hz to 10 ⁴ Hz of the 20 ° C. standard master curve.
The storage shear elastic modulus in the frequency range of 10 ³ Hz to 10 ⁴ Hz affects the impact resistance, and the storage shear elastic modulus in the frequency range is adjusted to a range of 3.0 × 10 ⁴ Pa to 6.0 × 10 ⁶ Pa. By doing so, it can be made suitable also about the impact resistance of an adhesive sheet.
At this time, in order to bring the storage shear modulus in the frequency range of 10 ³ Hz to 10 ⁴ Hz into the predetermined range, for example, the glass transition temperature (Tg) of the base resin and, if necessary, the content of the plasticizer are set. Adjustment may be made, but the method is not limited to this.

(Method for producing adhesive sheet)
This pressure-sensitive adhesive sheet is prepared by, for example, preparing a pressure-sensitive adhesive composition by adding a crosslinking monomer and a crosslinking initiator and, if necessary, a plasticizer and other additives to a base polymer, and heating and melting the pressure-sensitive adhesive composition. The adhesive composition is applied to the release surface of the release film with a hot melt coater and sandwiched between the release films to form a laminated sheet, and then the laminated sheet is heated or irradiated with light. By making it bridge | crosslink, it can provide as an adhesive sheet of the state pinched | interposed into the release film.
In the case of photocrosslinking, light irradiation may be performed using, for example, a high-pressure mercury lamp or a metal halide lamp.

In such a production method, in order to adjust the viscoelastic properties of the pressure-sensitive adhesive sheet to a desired range, for example, a (meth) acrylic acid ester polymer having a glass transition temperature of −20 ° C. or lower is used as a base polymer, and a crosslinking monomer is used. As the cross-linking of the pressure-sensitive adhesive composition while adjusting the amount of the acrylic cross-linking monomer, the amount of the cross-linking initiator, the cross-linking strength, etc. At any of 10 ^-1 Hz to 10 ^-5 Hz, the storage shear modulus exhibits a value in the range of more than 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁵ Pa and a frequency of 10 ^-3. An adhesive sheet having a tan δ at Hz of 1.0 × 10 ⁻¹ or less can be produced. However, it is not limited to this method.
Note that the crosslinking strength can be adjusted by changing the integrated light amount in the case of photocrosslinking.

(Thickness of adhesive sheet)
The thickness of the pressure-sensitive adhesive sheet is preferably changed according to the use and necessity, but considering the use for a display body, it is preferably 50 μm to 5 mm, particularly 75 μm to 2 mm, and particularly preferably 75 μm to 1 mm.

(Use)
This adhesive sheet can be used to bond various window materials such as multi-layer windows and glass constituting various display panels, optical film bonding to the front side of flat panel displays, bonding of optical films, glass, plastic, etc. It can be used for laminating various transparent members such as laminating various transparent films to the transparent substrate.
In particular, if it is used for forming a display body such as a PDP, for example, an application for forming a display body by bonding an optical film on the display panel using the pressure-sensitive adhesive sheet, generation of distortion due to pressing can be suppressed. Therefore, it is possible to prevent a reduction in visibility and to reduce the weight because it is not necessary to interpose a rigid protective plate.

(Explanation of terms)
In the present invention, the expression “main component” includes the meaning of allowing other components to be contained within a range that does not hinder the function of the main component, unless otherwise specified. In particular, the content ratio of the main component is not specified, but the component (when two or more components are main components, the total amount thereof) is 50% by mass or more, particularly 70% by mass or more in the composition. Of these, 90% by mass or more (including 100%) is generally used.
Further, in this specification, when “X to Y” (X and Y are arbitrary numbers) is described, it means “preferably greater than X” or “within the meaning of“ X to Y ”unless otherwise specified. The term “preferably smaller than Y” is also included.

Next, an example is given and it demonstrates more concretely.
In the following, “parts” means “parts by mass”.

<Measurement of Storage Shear Modulus G ′, Loss Shear Modulus G ″, Tan δ>
The storage shear modulus G ′ of the pressure-sensitive adhesive sheet was measured as follows.
The measurement was performed under the following conditions using a viscoelasticity measuring apparatus dynamic analyzer (“RDAII” manufactured by Rheometrics).
・ Temperature: -50 ~ 200 ℃
Angular frequency: ω = 0.00005 to 4000000 rad / sec
・ Parallel plate: 25mmφ
・ Distortion amount: 3%

A master curve in temperature-time conversion is created using RDAII with 20 ° C. as the reference temperature, and the frequency f value is calculated from the following formula (1), and the frequencies are 10 ⁻⁵ Hz, 10 ⁻³ Hz, 10 ⁻¹ Hz, 10 The storage elastic modulus G ′ and loss shear elastic modulus G ″ at ³ Hz and 10 ⁴ Hz were read from the graph, and Tan δ (G ″ / G ′) was calculated.
f (Hz) = ω / (2π) (1)

<Measurement of integrated light intensity>
A photoreceiver “UVD-S365” was attached to a UV integrated light meter “UIT-150” manufactured by USHIO ELECTRIC CO., LTD, and the integrated light amount at a wavelength of 365 nm was measured.

Example 1
Base polymer: 100 parts by weight of Lamberti's product name “Esacure TZT” (mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone) as a photoinitiator: 0.8 part by weight and crosslinking Monomer (1): 20 parts by mass was added and melt-stirred to prepare an adhesive composition.
This pressure-sensitive adhesive composition was applied onto a release surface of a 75 μm-thick silicone release PET using a hot melt coater so as to have a thickness of 100 μm, and then a 50 μm-thick silicone release PET was applied thereon. Were laminated by irradiating UV energy (wavelength 365 mm equivalent) with an integrated light amount of 2,000 mJ / cm ² on both sides using a high-pressure mercury lamp from both sides to obtain an adhesive sheet.

The composition of the base polymer used was a copolymer of n-butyl acrylate: 78.4% by mass, 2-ethylhexyl acrylate: 19.6% by mass, acrylic acid: 2% by mass, Tg being −35 ° C. The 130 ° C. melt viscosity measured by a B-type viscometer was 240,000 mPa · sec.
The used crosslinking monomer (1) was a trifunctional acrylate monomer having a molecular weight of 530.

(Example 2)
Base polymer: 100 parts by mass, Laberti brand name “Esacure TZT” (mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone) as a photoinitiator: 0.8 parts by mass The same crosslinking monomer (1) as in Example 1: 20 parts by mass and crosslinking monomer (2): 5 parts by mass were added and melt-stirred to prepare an adhesive composition.
This pressure-sensitive adhesive composition was applied onto a release surface of a 75 μm-thick silicone release PET using a hot melt coater so as to have a thickness of 250 μm, and then a 50 μm-thick silicone release PET. Were laminated by irradiating UV energy (wavelength 365 mm equivalent) with a single-side integrated light amount of 3,000 mJ / cm ² from both sides using a high pressure mercury lamp to obtain an adhesive sheet.

The composition of the base polymer used was a copolymer of n-butyl acrylate: 50% by mass and 2-ethylhexyl acrylate: 50% by mass, Tg was -35 ° C, and 130 ° C melt viscosity by a B-type viscometer was 24. It was 10,000 mPa · sec.
The crosslinking monomer (2) used was a bifunctional acrylate monomer having a molecular weight of 650 and comprising polytetramethylene glycol diacrylate.

(Example 3)
The same base polymer as in Example 2: for 100 parts by mass, trade name “Esacure TZT” (mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone) manufactured by Lamberti as a photoinitiator: 3.0 Mass parts and the same crosslinking monomer (1) as in Example 1: 20 parts by mass and, as other additives, a silane coupling agent manufactured by Momentive Performance Materials Japan (formerly GE Toshiba Silicone), Inc. Product name “TSL8375” (Γ-methacryloxypropylmethyldimethoxysilane): 1.0 part by mass was added and melted and stirred to prepare an adhesive composition.
This pressure-sensitive adhesive composition was applied onto a release surface of a 75 μm-thick silicone release PET using a hot melt coater so as to have a thickness of 250 μm, and then a 50 μm-thick silicone release PET. Were laminated using a high-pressure mercury lamp and irradiated with ultraviolet energy (converted to a wavelength of 365 mm) with a single-side integrated light amount of 1,000 mJ / cm ² from both sides to obtain an adhesive sheet.

(Comparative Example 1)
Base polymer: 100 parts by mass, as plasticizer, trade name “DIDP” manufactured by Jay Plus Co .: 26 parts by mass, and as inorganic fine particles, product name “Aerosil 300” manufactured by Nippon Aerosil Co., Ltd .: 4 parts by mass, light Trade name “Esacure TZT” (mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone) manufactured by Lamberti as an initiator: 0.3 part by mass, and Osaka Organic Chemical Co., Ltd. as a crosslinking monomer (3) Product name “Biscoat # 260 (1,9-nonanediol diacrylate, molecular weight 267)”: 0.1 part by mass was added and melt-stirred to prepare an adhesive composition.
This pressure-sensitive adhesive composition was applied onto a release surface of a 75 μm-thick silicone release PET using a hot melt coater so as to have a thickness of 500 μm, and then a 50 μm-thick silicone release PET was applied thereon. Were laminated using a high-pressure mercury lamp and irradiated with ultraviolet energy (converted to a wavelength of 365 mm) with a single-side integrated light amount of 1,000 mJ / cm ² from both sides to obtain an adhesive sheet.

  The composition of the base polymer used was obtained by polymerizing 2-ethylhexyl acrylate: 100% by mass, Tg was −42 ° C., and the 130 ° C. melt viscosity measured by a B-type viscometer was 160,000 mPa · sec.

(Comparative Example 2)
Base polymer: 100 parts by weight of Lamberti's product name “Esacure TZT” (mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone) as a photoinitiator: 0.8 part by weight and crosslinking As a monomer (4), trade name “Biscoat # 295” (trimethylolpropane triacrylate, molecular weight 296) manufactured by Osaka Organic Chemical Industry Co., Ltd .: 2 parts by mass was added and melt-stirred to prepare an adhesive composition.
This pressure-sensitive adhesive composition was applied onto a release surface of a 75 μm-thick silicone release PET using a hot melt coater so as to have a thickness of 250 μm, and then a 50 μm-thick silicone release PET. Were laminated by irradiating ultraviolet energy (converted to a wavelength of 365 mm) with a light amount of 1,200 mJ / cm ² on one side from both sides using a high pressure mercury lamp to obtain an adhesive sheet.

  The composition of the base polymer used was a copolymer of 2-ethylhexyl acrylate: 80% by mass and methyl methacrylate: 20% by mass, Tg was −20 ° C., and 130 ° C. melt viscosity by a B-type viscometer was 200,000 mPa.・ It was sec.

(Comparative Example 3)
The same base polymer as in Comparative Example 2: 100 parts by mass, trade name “Esacure TZT” (mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone) manufactured by Lamberti as a photoinitiator: 0.8 A pressure-sensitive adhesive composition was prepared by adding 10 parts by mass of the same crosslinking monomer (1) as in Example 1 and 10 parts by mass with stirring.
This pressure-sensitive adhesive composition was applied onto a release surface of a 75 μm-thick silicone release PET using a hot melt coater so as to have a thickness of 250 μm, and then a 50 μm-thick silicone release PET. Were laminated using a high-pressure mercury lamp and irradiated with ultraviolet energy (converted to a wavelength of 365 mm) with a single-side integrated light amount of 1,000 mJ / cm ² from both sides to obtain an adhesive sheet.

(Comparative Example 4)
As a base polymer, 2-ethylhexyl acrylate: 77% by mass, vinyl acetate: 19% by mass, acrylic acid: 4% by mass were copolymerized, Tg was −15 ° C., and 130 ° C. melt viscosity by a B-type viscometer was 330,000. A pressure-sensitive adhesive sheet was obtained in the same manner as in Comparative Example 3 except that a polymer having mPa · sec was used.

(Comparative Example 5)
Adhesive manufactured by Soken Chemicals Co., Ltd. Stock solution of “SK Dyne 1882” (nonvolatile content: 15.5 to 17.5%, solvent composition: ethyl acetate, MEK, etc.): 100 parts by mass with respect to 100 parts by mass of isocyanate curing agent “ L-45 ”: 0.185 parts by mass and epoxy-based curing agent“ E-5XM ”: 0.05 parts by mass were added and stirred to prepare an adhesive composition.
This pressure-sensitive adhesive composition was applied on the release surface of a 75 μm-thick silicone release PET using a bar coater so as to have a dry thickness of 20 μm, and then left in a dryer at 90 ° C. for 3 minutes and dried. Then, a 50 μm thick silicone release PET was laminated thereon, and further aged at room temperature for 7 days to obtain an adhesive sheet.
The release film on one side of the pressure-sensitive adhesive sheet thus obtained is peeled off, and the pressure-sensitive adhesive surfaces are bonded together without bubbles with a hand roll, and 10 pressure-sensitive adhesive sheets having a thickness of 20 μm are stacked to form a pressure-sensitive adhesive sheet having a total thickness of 200 μm. Got.

(Comparative Example 6)
Base polymer: 100 parts by mass, Laberti brand name “Esacure TZT” (mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone) as a photoinitiator: 0.8 parts by mass The same crosslinking monomer (1) as in Example 1: 30 parts by mass was added, and the mixture was melted and stirred to prepare an adhesive composition.
This pressure-sensitive adhesive composition was applied onto a release surface of a 75 μm-thick silicone release PET using a hot melt coater so as to have a thickness of 250 μm, and then a 50 μm-thick silicone release PET. Were laminated using a high-pressure mercury lamp and irradiated with ultraviolet energy (converted to a wavelength of 365 mm) with a single-side integrated light amount of 1,000 mJ / cm ² from both sides to obtain an adhesive sheet.

  The composition of the base polymer used was a copolymer of 2-ethylhexyl acrylate: 77% by mass, vinyl acetate: 19% by mass, and acrylic acid: 4% by mass, Tg being −15 ° C., B-type viscosity. The 130 ° C. melt viscosity as measured was 330,000 mPa · sec.

(Comparative Example 7)
Base polymer: 100 parts by mass, photoinitiator: Trade name “Benzophenone” manufactured by Nacalai Tesque Co., Ltd .: 0.3 part by mass, and trade name “Biscoat #” manufactured by Osaka Organic Chemical Industry Co., Ltd. as a crosslinking monomer (3) 260 (1,9-nonanediol diacrylate, molecular weight 267) ": 0.1 part by mass was added and melt-stirred to prepare an adhesive composition.
This pressure-sensitive adhesive composition was applied onto a release surface of a 75 μm-thick silicone release PET using a hot melt coater so as to have a thickness of 250 μm, and then a 50 μm-thick silicone release PET. Were laminated by irradiating UV energy (wavelength 365 mm equivalent) with an integrated light amount of 2,000 mJ / cm ² on both sides using a high-pressure mercury lamp from both sides to obtain an adhesive sheet.

  The composition of the base polymer used was a copolymer of n-butyl acrylate: 78.4% by mass, 2-ethylhexyl acrylate: 19.6% by mass, acrylic acid: 2% by mass, and Tg was −35. The melt viscosity at 130 ° C. measured by a B-type viscometer was 240,000 mPa · sec.

(Comparative test)
About the adhesive sheet obtained by the above Example and comparative example, the presence or absence of the dent deformation | transformation by press was verified with the following test method.

Each pressure-sensitive adhesive sheet obtained in Examples and Comparative Examples was bonded onto a 10 cm × 10 cm soda lime glass (thickness 3 mm), and further a PET film 100 μm thick (Toyobo Cosmo Shine A4300) on the pressure-sensitive adhesive sheet. A film laminate formed by bonding two sheets together with an adhesive sheet having a thickness of 20 μm obtained in (Comparative Example 5) was used as a test sample.
A steel ball having a weight of 534 g was gently placed on the PET surface of the test sample and allowed to stand for 30 seconds, then unloaded and visually observed for the recovery of the dent, and evaluated according to the following criteria.

○: The dent recovered within 10 seconds after unloading and no visible distortion remained.
X: The distortion | strain which a dent did not recover within 10 seconds after unloading but the visible distortion produced.

(Comparative test results)
The results of the comparative test are shown in Table 1. When any pressure-sensitive adhesive sheet of Examples 1 to 3 was pressed from the surface, it was difficult for distortion to remain, and the result that the dent was easily recovered was obtained. The comparative test (dent deformation test) conducted this time is to inspect the dent deformation after unloading by placing a steel ball gently. For example, when the PDP screen is pressed slowly with a finger, The dent recoverability (that is, the dent recoverability in a low speed region) is inspected.
When the above comparative test results shown in Table 1 are compared with the value of the storage shear modulus (G ′) at a frequency of 10 ⁻¹ Hz to 10 ⁻⁵ Hz and the tan δ at a frequency of 10 ⁻³ Hz, In the frequency range (low speed range) of 10 ⁻¹ Hz to 10 ⁻⁵ Hz, the absolute value of the storage shear modulus (G ′) is increased while the absolute value of the loss shear modulus (G ″) is decreased. It has been found that by increasing the difference between the two, it is possible to significantly improve the dent recoverability when the pressure is applied slowly (that is, the dent recoverability in the low speed range).

Claims (5)

A pressure-sensitive adhesive sheet obtained by crosslinking a pressure-sensitive adhesive composition containing a base polymer containing one or more types of (meth) acrylic acid ester-based polymers, an acrylic crosslinking monomer, and a crosslinking initiator,
The storage shear elastic modulus is in the range of 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁵ Pa or less in any of the frequencies of 10 ⁻¹ Hz to 10 ⁻⁵ Hz of the 20 ° C. standard master curve, A pressure-sensitive adhesive sheet having physical properties such that tan δ at a frequency of 10 ⁻³ Hz is 1.0 × 10 ⁻¹ or less. The pressure-sensitive adhesive sheet according to claim 1, wherein tan δ at a frequency of 10 ^-1 Hz of a 20 ° C reference master curve is 4.0 x 10 ^-1 or less. The storage shear elastic modulus is in a range of 3.0 x 10 ⁴ Pa to 6.0 x 10 ⁶ Pa at a frequency of 10 ³ Hz to 10 ⁴ Hz of a 20 ° C reference master curve. 2. The adhesive sheet according to 2.   The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive sheet has a thickness of 50 μm to 5 mm. The display body provided with the structure formed by bonding an optical film using the adhesive sheet as described in any one of Claims 1-4.