JP2017200973A - Substrate-less double-sided adhesive sheet - Google Patents

Abstract

An object of the present invention is to provide a substrate-less double-sided pressure-sensitive adhesive sheet excellent in inspection property by a cross Nicol method. The substrate-less double-sided pressure-sensitive adhesive sheet has a first release film, a pressure-sensitive adhesive layer provided on the first release film, and a second release film provided on the pressure-sensitive adhesive layer. The first release film has a first biaxially stretched polyester film and a first release layer provided on the pressure-sensitive adhesive layer side of the first biaxially stretched polyester film, and the second release film A film has a second biaxially stretched polyester film and a second release layer provided on the pressure-sensitive adhesive layer side of the second biaxially stretched polyester film, and the first biaxially stretched polyester film And the thickness of the second biaxially stretched polyester film are all 19 to 50 μm, and the inclination of the main orientation axis of the substrate-less double-sided pressure-sensitive adhesive sheet is −12 degrees or more and 12 degrees or less. Lumber The double-sided pressure-sensitive adhesive sheet. [Selection diagram] Fig. 1

Description

  The present invention relates to a substrate-less double-sided pressure-sensitive adhesive sheet.

  Conventionally, various pressure-sensitive adhesive sheets for surface bonding between objects are known, and a base-less double-sided pressure-sensitive adhesive sheet is known as one of pressure-sensitive adhesive sheets. The substrate-less double-sided pressure-sensitive adhesive sheet is constituted by laminating a light release sheet having a relatively low peeling force and a heavy release sheet having a relatively high peeling force on both sides of the pressure-sensitive adhesive layer. The substrate-less double-sided PSA sheet is first peeled off from the light release sheet, and one side of the exposed PSA layer is bonded to the object surface. The other side of the layer is bonded to a different object surface, thereby surface bonding between the objects.

  For example, Patent Document 1 discloses a release film used for a substrate-less double-sided pressure-sensitive adhesive sheet for bonding a protective film having a hard coat layer to a panel substrate. The release film has a configuration in which a release layer is provided on one surface of a polyester film substrate having a thickness of 50 to 150 μm and an orientation angle of 12 degrees or less.

JP-A-2015-199265

As an application of the substrate-less double-sided pressure-sensitive adhesive sheet, there is bonding of optical films such as a polarizing film (polarizing plate) and a retardation film. When an adhesive is bonded to an optical film such as a polarizing plate, if the adhesive has a defect such as a minute foreign matter or a scratch, the defect appears as a bright spot visible in the display.
For this reason, in the optical film field, inspection standards for defects are strict, and it is important to improve inspection accuracy. The same inspection standard and improvement in inspection accuracy are also demanded for the base material-less double-sided pressure-sensitive adhesive sheet.

  For example, as a defect inspection in a polarizing plate, generally, defects are emphasized and inspected by a crossed Nicols method. In the crossed Nicols method, when two polarizing plates are overlapped so that their principal axes of orientation are perpendicular to each other and put into a quenching state, if there is a defect, that will appear as a bright spot, so that even a small defect can be inspected. That's it.

  This invention is made | formed in view of such a situation, and it aims at providing the base-material-free double-sided adhesive sheet excellent in the inspection property by the cross Nicol method.

As a result of intensive studies to solve the above-mentioned problems, the present inventors set the thickness of the first biaxially stretched polyester film and the thickness of the second biaxially stretched polyester film within a specific range, and the orientation main axis. It has been found that the above-mentioned problems can be solved by setting the inclination of the above to a specific range.
The present invention has been completed based on such findings.

That is, the present invention provides the following [1] to [6].
[1] A substrate-less double-sided pressure-sensitive adhesive sheet comprising a first release film, a pressure-sensitive adhesive layer provided on the first release film, and a second release film provided on the pressure-sensitive adhesive layer, The first release film has a first biaxially stretched polyester film and a first release layer provided on the pressure-sensitive adhesive layer side of the first biaxially stretched polyester film, and the second release film Has a second biaxially stretched polyester film and a second release layer provided on the pressure-sensitive adhesive layer side of the second biaxially stretched polyester film, and the first biaxially stretched polyester film A base material in which the thickness and the thickness of the second biaxially stretched polyester film are all 19-50 μm, and the inclination of the orientation main axis of the base material-less double-sided pressure-sensitive adhesive sheet is −12 degrees or more and 12 degrees or less. Less double-sided adhesive Sheet.
[2] The substrate-less double-sided pressure-sensitive adhesive sheet according to [1], wherein the pressure-sensitive adhesive layer has a thickness of 1 to 250 μm.
[3] The substrate-less double-sided adhesive according to [1] or [2], wherein each of the first biaxially stretched polyester film and the second biaxially stretched polyester film is a polyethylene terephthalate film. Sheet.
[4] The substrate-less double-sided pressure-sensitive adhesive sheet according to any one of [1] to [3], wherein each of the first release layer and the second release layer is a layer formed from a silicone resin. .
[5] The substrate-less double-sided pressure-sensitive adhesive sheet according to any one of [1] to [4], wherein the haze value is 25% or less.
[6] The substrate-less double-sided pressure-sensitive adhesive sheet according to any one of [1] to [5], wherein a difference in peeling force between the first release film and the second release film is 5 mN / 25 mm or more. .

  ADVANTAGE OF THE INVENTION According to this invention, the base material-less double-sided adhesive sheet excellent in the inspection property by the cross Nicol method can be provided.

It is sectional drawing which shows one Embodiment of the base material less double-sided adhesive sheet of this invention.

[Substrate-less double-sided adhesive sheet]
The base material-less double-sided pressure-sensitive adhesive sheet of the present invention has a first release film, a pressure-sensitive adhesive layer provided on the first release film, and a second release film provided on the pressure-sensitive adhesive layer. Further, the first release film has a first biaxially stretched polyester film and a first release layer provided on the pressure-sensitive adhesive layer side of the first biaxially stretched polyester film, and the second release film is And a second biaxially stretched polyester film and a second release layer provided on the pressure-sensitive adhesive layer side of the second biaxially stretched polyester film.
In the base material-less double-sided pressure-sensitive adhesive sheet of the present invention, the thickness of the first biaxially stretched polyester film and the thickness of the second biaxially stretched polyester film are both 19 to 50 μm. The inclination of the orientation main axis of the double-sided PSA sheet is -12 degrees or more and 12 degrees or less.

  FIG. 1 is a cross-sectional view showing an embodiment of a substrate-less double-sided pressure-sensitive adhesive sheet of the present invention. In the substrate-less double-sided pressure-sensitive adhesive sheet 10 of FIG. 1, the pressure-sensitive adhesive layer 1 is provided on the first release film 11, and the second release film 12 is provided on the pressure-sensitive adhesive layer 1. The first release film 11 has a first biaxially stretched polyester film 2 and a first release layer 3 provided on the pressure-sensitive adhesive layer side of the first biaxially stretched polyester film 2, and the first release film 11 The layer 3 is in contact with the pressure-sensitive adhesive layer 1. The second release film 12 has a second biaxially stretched polyester film 4 and a second release layer 5 provided on the pressure-sensitive adhesive layer side of the second biaxially stretched polyester film 4. The two peeling layers 5 are in contact with the pressure-sensitive adhesive layer 1.

In the substrate-less double-sided pressure-sensitive adhesive sheet of the present invention, the inclination of the orientation main axis is −12 degrees or more and 12 degrees or less.
Here, the “inclination of the orientation main axis” is also referred to as an orientation angle, and is the inclination of the main axis with respect to the width direction or the longitudinal direction of the sheet. When the inclination of the orientation main axis is less than −12 degrees and when it exceeds 12 degrees, the light leakage becomes large in the inspection by the crossed Nicols method, and there is a risk of hindering the detection of defects such as foreign matters and scratches.
The inclination of the orientation main axis is preferably −10 degrees to 10 degrees, more preferably −8 degrees to 8 degrees.

(First release film and second release film)
The first release film has a first biaxially stretched polyester film and a first release layer provided on the first biaxially stretched polyester film. The second release film has a second biaxially stretched polyester film and a second release layer provided on the second biaxially stretched polyester film.

In the present invention, the thickness of the first biaxially stretched polyester film and the thickness of the second biaxially stretched polyester film are both 19 to 50 μm. If it is less than 19 micrometers, there exists a possibility that dents, such as a deformation | transformation, an unevenness | corrugation, and a distortion, may arise on the adhesive layer surface. Moreover, the stiffness of the release film becomes weak and handling becomes difficult. If it exceeds 50 μm, the orientation angle of the biaxially stretched polyester film becomes large, the orientation angle cannot be lowered uniformly across the width direction of the formed biaxially stretched polyester film, and the influence on the cost is great. There is a risk of inspecting the product by the Nicol method.
The thickness of the first biaxially stretched polyester film and the thickness of the second biaxially stretched polyester film are preferably 25 to 48 μm.

The inclination (orientation angle) of the orientation main axis of the first biaxially stretched polyester film and the second biaxially stretched polyester film is desired to be the inclination (orientation angle) of the orientation principal axis of the substrate-less double-sided pressure-sensitive adhesive sheet of the present invention. Adjust so that it is within the range.
In the present invention, the orientation angle is defined as 0 degree when parallel to the film width direction, + as the clockwise inclination with respect to the film width direction, and-as the counterclockwise inclination. When the orientation angles of the first biaxially stretched polyester film and the second biaxially stretched polyester film are both +, the orientation angles of the first biaxially stretched polyester film and the second biaxially stretched polyester film are The first biaxially stretched polyester film and the second biaxial are preferably in the range of 0 to 12 degrees, more preferably 0 to 10 degrees, and still more preferably 0 to 8 degrees. When the orientation angles of the stretched polyester film are both −, the orientation angles of the first biaxially stretched polyester film and the second biaxially stretched polyester film are preferably −12 degrees or more and 0 degrees or less, and more preferably. Is in the range of -10 degrees to 0 degrees, more preferably -8 degrees to 0 degrees. Moreover, when the signs of the orientation angles of the first biaxially stretched polyester film and the second biaxially stretched polyester film are different, the orientation angle is not particularly limited. For example, the orientation angle of the first biaxially stretched polyester film Is preferably in the range of −40 ° to 0 °, and the orientation angle of the second biaxially stretched polyester film is preferably in the range of 0 ° to 40 °.

The hazes of the first biaxially stretched polyester film and the second biaxially stretched polyester film are both preferably 12% or less, and more preferably 10% or less. By setting it as 12% or less, the haze of the base material-less double-sided pressure-sensitive adhesive sheet can be adjusted to a desired value or less.
In addition, the said haze can be measured by the method based on JISK-7136 using a haze meter (Nippon Denshoku Industries Co., Ltd. make, NDH-5000).

Examples of the first biaxially stretched polyester film and the second biaxially stretched polyester film include a polyethylene terephthalate film, a polybutylene terephthalate film, and a polyethylene naphthalate film.
The first biaxially stretched polyester film and the second biaxially stretched polyester film may be the same film or different films. Among these, from the viewpoint of optical properties, it is preferable that both the first biaxially stretched polyester film and the second biaxially stretched polyester film are polyethylene terephthalate films.

  Examples of the method of biaxially stretching the polyester film include a method of stretching in the width direction after stretching in the longitudinal direction, a method of stretching in the longitudinal direction after stretching in the width direction, stretching in the longitudinal direction, and stretching in the width direction. Well-known methods, such as a method of combining two times or a method called simultaneous biaxial stretching in which stretching is performed simultaneously, can be mentioned.

The first release layer and the second release layer have a function of imparting peelability to the release film. A 1st peeling layer and a 2nd peeling layer are formed with the hardened | cured material of the composition for peeling layer formation containing a mold release agent, for example.
The release agent is not particularly limited, and examples thereof include a silicone resin, an alkyd resin, an acrylic resin, and a long-chain alkyl resin, and it is preferable to use a silicone resin.

  Examples of the silicone resin include silicone resins having dimethylpolysiloxane as a basic skeleton. Examples of the silicone resin include addition reaction type, condensation reaction type, ultraviolet curable type, and electron beam curable type. Among these, addition-reactive silicone resins are preferably used because they have high reactivity and excellent productivity, and have advantages such as less change in peel strength after production and no cure shrinkage compared to the condensation reaction type.

  Specific examples of the addition reaction type silicone resin include organos having two or more alkenyl groups having 2 to 10 carbon atoms such as vinyl group, allyl group, propenyl group and hexenyl group at the terminal and / or side chain of the molecule. Polysiloxane is mentioned. When such an addition reaction type silicone resin is used, it is preferable to use a crosslinking agent and a catalyst in combination.

  Examples of the crosslinking agent include, for example, organopolysiloxane having hydrogen atoms bonded to at least two silicon atoms in one molecule, specifically, a dimethylhydrogensiloxy group end-capped dimethylsiloxane-methylhydrogensiloxane copolymer. , Trimethylsiloxy group end-capped dimethylsiloxane-methylhydrogensiloxane copolymer, trimethylsiloxy group end-capped methylhydrogenpolysiloxane, poly (hydrogensilsesquioxane), and the like.

  Examples of the catalyst include fine platinum particles, fine platinum particles adsorbed on a carbon powder carrier, chloroplatinic acid, alcohol-modified chloroplatinic acid, olefin complexes of chloroplatinic acid, white metal compounds such as palladium and rhodium, and the like. Can be mentioned. By using such a catalyst, the curing reaction of the composition for forming a release layer can be advanced more efficiently.

When a silicone resin is used as the release agent, it is preferable to add a release adjusting agent such as MQ resin.
Moreover, you may mix | blend an additive suitably with the composition for peeling layer formation. Examples of the additive include dyes and dispersants. Further, the composition for forming a release layer may appropriately contain a dispersion medium or a solvent in order to bring the viscosity at the time of coating into an appropriate range.
Examples of the dispersion medium or solvent include aromatic solvents such as toluene, fatty acid esters such as ethyl acetate, ketones such as methyl ethyl ketone, and organic solvents such as aliphatic hydrocarbons such as hexane and heptane.

  Although content of the mold release agent contained in the composition for peeling layer formation is not specifically limited, It is preferable that it is 0.3-10 mass%.

Examples of the method for applying the release layer forming composition to the first or second biaxially stretched polyester film include a gravure coating method, a bar coating method, a spray coating method, a spin coating method, an air knife coating method, and a roll coating method. , Blade coating method, gate roll coating method, die coating method and the like. Among these, the gravure coating method and the bar coating method are preferable, and the bar coating method is more preferable.
Moreover, as a heating / drying method of the composition for forming a release layer, for example, a method of heat drying in a hot air drying furnace or the like can be mentioned. The drying temperature is, for example, 50 ° C. or higher and 150 ° C. or lower. Moreover, it is preferable that drying time is 10 second-5 minutes, for example.

  The thickness of the first release layer (when dried) and the thickness of the second release layer (when dried) are both preferably 40 nm to 1 μm, more preferably 50 nm to 0.5 μm, and 60 nm to 0 More preferably, it is 3 μm. By setting the thickness to 40 nm or more, it is possible to suppress the peeling force variation due to the fluctuation of the coating amount, and by setting the thickness to 1 μm or less, it is possible to suppress blocking.

  In the present invention, the difference in peel force between the first release film and the second release film is preferably 5 mN / 25 mm or more, more preferably 10 mN / 25 mm or more, and further preferably 20 mN / 25 mm or more. By setting it as 5 mN / 25 mm or more, when peeling a peeling film, it can make it difficult to generate | occur | produce the peeling defect which an adhesive transfers to the peeled film.

  When the first release film corresponds to the heavy release side, the release force of the first release film to the pressure-sensitive adhesive layer is preferably 30 to 300 mN / 25 mm, more preferably 50 to 200 mN / 25 mm, and still more preferably 50 to 100 mN / 25 mm. By setting it within the above range, when the first release film is peeled off, it is possible to make it difficult for the adhesive to transfer to the first release film.

  When the second release film corresponds to the light release side, the release force of the second release film to the adhesive layer is preferably 10 to 200 mN / 25 mm, more preferably 15 to 100 mN / 25 mm, and still more preferably 20 to 80 mN / 25 mm. By setting it within the above range, even if the peeling force of the first release film is suppressed, the difference in peel force between the first release film and the second release film can be increased.

(Adhesive layer)
The pressure-sensitive adhesive layer is formed using a pressure-sensitive adhesive. Examples of the adhesive include acrylic, rubber, polyester, urethane, and silicone. In the present invention, the pressure-sensitive adhesive preferably contains an acrylic pressure-sensitive adhesive, and preferably contains a (meth) acrylic acid ester copolymer from the viewpoint of adhesion durability.
In addition, as a form of an adhesive, a solvent type, an emulsion type, a solventless type etc. are mentioned.

  When the pressure-sensitive adhesive is a solvent-type or emulsion-type acrylic pressure-sensitive adhesive, the pressure-sensitive adhesive is composed of a main monomer component that provides tackiness, a comonomer component that provides adhesiveness and cohesive force, a crosslinking point, and an adhesive improvement agent. It can be comprised from the polymer or copolymer which has a functional group containing monomer component as a main. By including these components, the cohesive force and adhesive force of the resulting pressure-sensitive adhesive layer can be improved.

  The main monomer component includes, for example, alkyl groups such as butyl acrylate, amyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, cyclohexyl acrylate, benzyl acrylate, methoxyethyl acrylate and the like having 1 to 20 carbon atoms. Examples include alkyl acrylates and alkyl methacrylates having 1 to 20 carbon atoms in the alkyl group such as butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, and benzyl methacrylate.

  Examples of the comonomer component include methyl acrylate, methyl methacrylate, ethyl methacrylate, vinyl acetate, styrene, acrylonitrile, and the like.

  The functional group-containing monomer component preferably contains at least one of a hydroxyl group, a carboxyl group, and an amino group as the functional group. Specific examples include 2-hydroxyethyl (meth) acrylate, 2-methacrylic acid 2- (Meth) acrylic acid hydroxyalkyl esters such as hydroxypropyl; (meth) acrylic acid monomethylaminoethyl, (meth) acrylic acid monoethylaminoethyl, (meth) acrylic acid monoalkylaminoalkyl; acrylic acid, methacrylic acid, Examples thereof include ethylenically unsaturated carboxylic acids such as maleic acid.

  Further, the (meth) acrylic acid ester copolymer is not particularly limited as to its copolymerization form, and may be any of random, block, and graft copolymers.

  As the (meth) acrylic acid ester copolymer, those having a mass average molecular weight of 300,000 or more are preferable, those having 400,000 to 2,000,000 are more preferable, and those having 500,000 to 1,800,000 are used. More preferably, is used. Thereby, the adhesiveness and adhesion durability with respect to an adherend are sufficient, and the occurrence of floating and peeling can be more effectively prevented.

  In the present specification, the mass average molecular weight is a value in terms of polystyrene measured by a gel permeation chromatography (GPC) method.

  In the (meth) acrylic acid ester copolymer, the content of units derived from the functional group-containing monomer component is preferably 0.01% by mass or more and 10% by mass or less, and 0.05% by mass or more and 7.0% by mass. More preferably, it is at most 0.2 mass%, more preferably at least 0.2 mass% but no more than 6.0 mass%. When the content is within the above range, crosslinking is sufficient by reaction with a crosslinking agent described later. As a result, the pressure-sensitive adhesive layer is more excellent in flexibility and adhesion durability.

  In addition, 1 type may be used for such a (meth) acrylic acid ester copolymer, and it may use it in combination of 2 or more type.

  Examples of the organic solvent used for preparing the solvent-type acrylic pressure-sensitive adhesive composition include toluene, xylene, t-butanol, acetone, methyl ethyl ketone, tetrahydrofuran, and ethyl acetate.

  The solvent-type acrylic pressure-sensitive adhesive composition may be either a crosslinked type that undergoes crosslinking treatment or a non-crosslinked type that does not undergo crosslinking treatment, but a crosslinked type is preferred. In the case of a crosslinkable pressure-sensitive adhesive layer-forming composition, a pressure-sensitive adhesive layer with better cohesion can be formed.

  Examples of the crosslinking agent used in the crosslinked acrylic pressure-sensitive adhesive composition include isocyanate compounds, epoxy compounds, metal chelate compounds, metal alkoxides, metal salts, amine compounds, hydrazine compounds, and aldehyde compounds.

  Further, when the pressure-sensitive adhesive layer in the substrate-less double-sided pressure-sensitive adhesive sheet of the present invention is formed of a solventless acrylic pressure-sensitive adhesive, the side chain has a radically polymerizable unsaturated double bond group (meth) Adhesive containing at least one selected from acrylic ester polymer (A1), (meth) acrylate oligomer (A2), and (meth) acrylic ester monomer (A3), and photopolymerization initiator (B) The agent layer forming composition (i) can also be used.

  The number of radically polymerizable unsaturated double bond groups possessed by the polymer (A1) and the (meth) acrylate oligomer (A2) of the (meth) acrylate ester is from the viewpoint of increasing the strength and cohesive strength of the pressure-sensitive adhesive layer. Two or more are preferable.

  The polymer (A1) of the (meth) acrylic acid ester means a polymer having a polymer structure of (meth) acrylic acid ester and having a radical polymerizable unsaturated double bond in the side chain of the polymer structure. Specifically, a copolymer of a main monomer component disclosed in a solvent-type acrylic pressure-sensitive adhesive composition, a comonomer component disclosed in a solvent-type acrylic pressure-sensitive adhesive composition, and a monomer having a functional group having active hydrogen Preferred are those in which a radical polymerizable unsaturated double bond is introduced with respect to the functional group having the active hydrogen in.

  Examples of the monomer having a functional group having active hydrogen include monomers having a functional group such as a hydroxyl group, an amino group, and a carboxyl group. Specifically, the compound illustrated by the term of the functional group containing monomer disclosed by the solvent-type acrylic adhesive composition can be mentioned.

  A copolymer is obtained by polymerizing the above monomers by a conventional method. The copolymer of the (meth) acrylic acid ester may be used alone or in combination of two or more.

  Introducing a radical polymerizable unsaturated double bond group into a functional group having active hydrogen in the above copolymer, for example, adding a compound having both a radical polymerizable unsaturated double bond and an active hydrogen reactive group It can be performed by reacting. Examples of the active hydrogen reactive group include an isocyanate group and a glycidyl group.

  Specific examples of the compound having both a radically polymerizable unsaturated double bond and an active hydrogen reactive group include acryloyloxyethyl isocyanate, acryloyloxypropyl isocyanate, methacryloyloxyethyl isocyanate, methacryloyloxypropyl isocyanate, allyl isocyanate, Preferred examples include glycidyl (meth) acrylate.

  The addition reaction is preferably performed at a temperature of 25 to 60 ° C. for about 6 to 48 hours, for example. Moreover, in said addition reaction, it is also preferable to use organotin compounds, such as dibutyltin dilaurate, a substituted amine compound, etc. as a catalyst as needed.

Examples of the (meth) acrylate oligomer (A2) include various (meth) acrylates such as urethane (meth) acrylate oligomers, epoxy (meth) acrylate oligomers, polyester (meth) acrylate oligomers, and polyether (meth) acrylate oligomers. An oligomer etc. are mentioned. Among these, urethane (meth) acrylate oligomers can be preferably used. The urethane (meth) acrylate oligomer can be obtained, for example, by esterifying a polyurethane oligomer obtained by a reaction between a polyether polyol or a polyester polyol and a polyisocyanate by a reaction with (meth) acrylic acid.
As the (meth) acrylate oligomer (A2), one type may be used alone, or two or more types may be used in combination. Moreover, the polymer (A1) of a (meth) acrylic acid ester and the (meth) acrylate oligomer (A2) can be used in combination.

The weight average molecular weights of the (meth) acrylic acid ester polymer (A1) and the (meth) acrylate oligomer (A2) are respectively 20,000 or more, preferably 25,000 to 80,000, more preferably. Is 30,000-60,000.
The weight average molecular weight is a value in terms of polystyrene measured by a gel permeation chromatography (GPC) method.

  As said (meth) acrylic acid ester monomer (A3), it has two or more reactive sites, such as the monomer which comprises the polymer (A1) of the (meth) acrylic acid ester mentioned above, and a carbon-carbon double bond. Preferred examples include polyfunctional acrylates.

  Specific examples of the polyfunctional acrylate include 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, caprolactone-modified dicyclopentenyl di (meth) acrylate, and ethylene oxide-modified. Bifunctional type such as di (meth) phosphate; Trifunctional type such as trimethylolpropane tri (meth) acrylate and dipentaerythritol tri (meth) acrylate; Diglycerin tetra (meth) acrylate and pentaerythritol tetra (meth) 4-functional type such as acrylate; 5-functional type such as propionic acid-modified dipentaerythritol penta (meth) acrylate; dipentaerythritol hexa (meth) acrylate, caprolactone-modified dipentaerythritol hexa (meth) acrylate, etc. Functional type and the like.

  When the (meth) acrylic acid ester polymer (A1) or (meth) acrylate oligomer (A2) is used as the main raw material and the pressure-sensitive adhesive layer-forming composition (i) has a high viscosity, The (meth) acrylic acid ester monomer (A3) may be added to reduce the viscosity of the pressure-sensitive adhesive layer forming composition (i) and improve the coating property. The (meth) acrylic acid ester monomer (A3) is irradiated with (meth) acrylic acid ester monomers (A3), or the (meth) acrylic acid ester polymer (A1) and / or the (meth) acrylate oligomer ( Since the cross-linked structure is formed with A2), the cohesive force of the obtained pressure-sensitive adhesive layer can be increased, and problems such as bleeding can be effectively prevented.

  Said adhesive layer forming composition (i) can harden the ultraviolet curable component in adhesive layer forming composition (i) efficiently by containing a photoinitiator (B). In addition, the polymerization curing time and the amount of ultraviolet irradiation can be reduced.

  Examples of the photopolymerization initiator (B) include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, Benzophenone, p-phenylbenzophenone, 4,4′-diethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, benzyldimethyl ketal, acetophenone dimethyl ketal, p-dimethylamino Benzoic acid ester, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, etc. are mentioned. These may be used alone or in combination of two or more.

  The content of the photopolymerization initiator (B) contained in the pressure-sensitive adhesive layer forming composition (i) is the polymer (A1), (meth) acrylate oligomer (A2) and (meth) of (meth) acrylic acid ester. It is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and 0.2 to 2 parts by mass with respect to 100 parts by mass in total of the acrylate monomer (A3). More preferably.

  Moreover, the composition for forming an adhesive layer can be prepared by adding various additives usually used for an adhesive, for example, silane coupling agents, antistatic agents, tackifiers, antioxidants, ultraviolet absorbers, light stabilizers. An agent, a softening agent, a filler, a refractive index adjusting agent, a colorant and the like may be contained.

  The thickness of the pressure-sensitive adhesive layer is preferably 1 to 250 μm, more preferably 5 to 200 μm, and still more preferably 10 to 175 μm from the viewpoint of productivity and cost.

  Moreover, it is preferable from a viewpoint which applies the adhesive layer in this invention to an optical film that the skin (several micro unevenness | corrugation) does not generate | occur | produce on the adhesive layer surface. From such a viewpoint, the proportion of the unevenness outside the range of ± 0.2 μm from the reference surface on the surface of the pressure-sensitive adhesive layer is preferably 20% or less. By setting it within the above range, it is possible to more effectively prevent the appearance defect from occurring when the pressure-sensitive adhesive layer is attached to the adherend.

  In addition, the ratio for which the unevenness | corrugation outside the range of +/- 0.2 micrometer from the reference | standard surface in the surface of an adhesive layer can be calculated using a light interference type surface shape observation apparatus, for example. Specifically, using an optical interference type surface shape observation device, stitching is performed at 2.5 magnifications in the VSI mode, and ± 0 from the reference plane is obtained based on the obtained surface shape image in the range of 4 × 4 mm. The image is binarized with a portion outside the range of 2 μm and a portion within the range of ± 0.2 μm. Thereby, it can obtain by calculating the area ratio which the unevenness | corrugation of the part outside the range of +/- 0.2 micrometer from a reference plane occupies.

  The haze of the substrate-less double-sided pressure-sensitive adhesive sheet of the present invention is preferably 25% or less, more preferably 20% or less, and still more preferably 10% or less. The haze can be measured by a method based on JIS K-7136 using a haze meter (NDH-5000, manufactured by Nippon Denshoku Industries Co., Ltd.).

  Since the substrate-less double-sided pressure-sensitive adhesive sheet of the present invention is excellent in inspection by the crossed Nicols method, it can be suitably used for optical films such as polarizing plates.

(Manufacturing method of substrate-less double-sided PSA sheet)
Although there is no restriction | limiting in particular as a manufacturing method of a base material less double-sided adhesive sheet, For example, first, the 1st peeling film which formed the 1st peeling layer on the 1st biaxially stretched polyester film, and the 2nd biaxial A second release film having a second release layer formed on a stretched polyester film is prepared. Next, when using the above-mentioned solvent-type pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition is applied on the first release layer of the first release film by a known method, and then heated and dried to form a coating film. Form. Then, the base material-less double-sided pressure-sensitive adhesive sheet can be obtained by laminating the surface of the second release film on the second release layer side on the coating film and performing an aging treatment.
Examples of the method for applying the pressure-sensitive adhesive composition include spin coating, spray coating, bar coating, knife coating, roll coating, roll knife coating, blade coating, die coating, and gravure coating. Is mentioned.

  Moreover, when using the above-mentioned solventless type adhesive composition, after apply | coating this adhesive composition by the well-known method on the 1st release layer of a 1st peeling film, ultraviolet rays, an electron beam, etc. An adhesive layer is formed by irradiating active energy rays. In addition, in the irradiation with the active energy ray, the pressure-sensitive adhesive composition may be semi-cured or sufficiently cured. Subsequently, a base material-less double-sided pressure-sensitive adhesive sheet can be obtained by laminating the surface of the second release film on the second release layer side on the pressure-sensitive adhesive layer.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In addition, this invention is not limited to the form as described in an Example.

1. Cross Nicol inspection properties The substrate-less double-sided PSA sheet (20 cm x 20 cm) produced in the examples and comparative examples is sandwiched between two polarizing plates so that the polarization axes are perpendicular to each other, and a flat illuminator (Dentsu Sangyo Co., Ltd., (Product name: HF-SL-A312LC, illuminance: 26,000 Lux, luminance: 10,000 cd) and visually evaluated according to the following criteria.
<Evaluation criteria>
○: Cross Nicol (dark field) was sufficient, and the inspection level was sufficient ×: Cross Nicol was insufficient (light leaked), and the inspection level was insufficient

2. Inspection of foreign matter The second release film (light release film) of the substrate-less double-sided pressure-sensitive adhesive sheet (20 cm × 20 cm) prepared in Examples and Comparative Examples is peeled off, and about 20 μm between the second release film and the pressure-sensitive adhesive layer. After the black metal powder (foreign matter) having a size was mixed so as to be about 50, the second release film was bonded again. The base material-less double-sided PSA sheet mixed with the foreign matter thus obtained was visually observed from the second release film side, and the detection status of the mixed foreign matter was evaluated according to the following criteria.
<Evaluation criteria>
○: Foreign matter recognition was good and was sufficient as an inspection level for optical use. ×: Foreign matter was not confirmed and was an inappropriate inspection level for optical use.

3. Orientation main axis tilt (orientation angle)
Using a phase difference measuring device (manufactured by Oji Scientific Instruments, KOBRA-WR), the orientation of the biaxially stretched polyethylene terephthalate (PET) film used in Examples and Comparative Examples was observed, and the main orientation axis in the plane of the PET film The orientation angle was measured by measuring how many times the direction of the film was inclined with respect to the width direction of the PET film. The orientation angle is 0 degree when it is parallel to the film width direction, and the clockwise inclination with respect to the film width direction is +, and the counterclockwise inclination is-.

4). Haze The haze of the biaxially stretched polyethylene terephthalate (PET) film used in Examples and Comparative Examples, and the substrate-less double-sided pressure-sensitive adhesive sheets prepared in Examples and Comparative Examples is a haze meter (NDH-Nippon Denshoku Kogyo Co., Ltd., NDH- 5000) using a method according to JIS K-7136.

[Preparation of adhesive composition a]
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device and a nitrogen introduction tube, 95.0 parts by mass of n-butyl acrylate, 5.0 parts by mass of 2-hydroxyethyl acrylate, 200 parts by mass of ethyl acetate And 0.08 parts by mass of 2,2′-azobisisobutyronitrile were charged, and the air in the reaction vessel was replaced with nitrogen gas. While stirring in this nitrogen atmosphere, the reaction solution was heated to 60 ° C., reacted for 16 hours, and then cooled to room temperature. Here, a part of the obtained solution was subjected to GPC measurement, and production of a polymer (A) having a mass average molecular weight of 1.6 million was confirmed. 100 parts by mass (solid content) of the polymer (A), 4 parts by mass of a polyisocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name: Coronate L), and a silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., (Product name: KBM-403) 0.1 parts by mass added to the mixture, toluene is added as a solvent to adjust the solid content to 15% by mass, and a pressure-sensitive adhesive composition a which is a solvent-type acrylic pressure-sensitive adhesive is prepared. did.

[Preparation of adhesive composition b]
40 parts by mass of 2-ethylhexyl acrylate, 20 parts by mass of isobornyl acrylate, 10 parts by mass of 2-hydroxyethyl acrylate, 30 parts by mass of urethane acrylate oligomer, 1 part by mass of 1-hydroxycyclohexyl phenyl ketone, and 3-glycidoxypropyl A pressure-sensitive adhesive composition b, which is a solventless acrylic pressure-sensitive adhesive, was prepared by mixing 0.2 parts by mass of trimethoxysilane.
The urethane acrylate oligomer was synthesized as follows. First, 4 parts by mass of hexamethylene diisocyanate and 0.02 parts by mass of dioctyltin dilaurate are added to 100 parts by mass of polypropylene glycol having a weight average molecular weight of 3000, and the mixture is stirred for 6 hours at 80 ° C. I got a thing. Next, after confirming that the isocyanate group almost disappeared from the IR spectrum of the obtained first reaction product, 1 part by mass of 2-isocyanatoethyl acrylate was added, and the mixture was stirred at 80 ° C. for 3 hours. A reaction product was obtained. Next, it was confirmed from the IR spectrum of the obtained second reaction product that the isocyanate group had almost disappeared, and a urethane acrylate oligomer having a weight average molecular weight of 25,000 was obtained.

Example 1
1. Preparation of Release Layer Forming Composition (A) Silicone Resin Solution Containing Organopolysiloxane with Vinyl Group and Organopolysiloxane with Hydrosilyl Group (trade name: BY24-561, manufactured by Toray Dow Corning Co., Ltd., solid) 30 parts by mass in terms of solids) and 15 parts by mass in terms of solids in terms of MQ resin (made by Toray Dow Corning, product name: SD7292, solids 71% by mass) provided with vinyl groups. Was diluted and mixed with a toluene solvent so that the solid content concentration was 1.0% by mass. 2 parts by mass of a platinum-based catalyst (trade name: SRX-212, solid content: 100% by mass) manufactured by Toray Dow Corning Co., Ltd. was added to this solution to prepare a release layer forming composition (A).

2. Preparation of First Release Film A biaxially stretched polyethylene terephthalate (PET) film having a thickness of 38 μm, an orientation angle of 6 degrees, and a haze of 10% was prepared.
Next, on one surface of the biaxially stretched PET film (first biaxially stretched PET film), the release layer-forming composition (A) obtained above has a thickness after drying of 0.1 μm. Thus, it apply | coated with the bar coater and it dried at 120 degreeC for 1 minute, and formed the peeling layer (1st peeling layer), and obtained the 1st peeling film.

3. Preparation of Release Layer Forming Composition (B) Silicone Resin Solution Containing Organopolysiloxane with Vinyl Group and Organopolysiloxane with Hydrosilyl Group (trade name: BY24-561, manufactured by Toray Dow Corning Co., Ltd., solid) 30% by mass in terms of solid content was diluted and mixed with a toluene solvent so that the solid content concentration was 1.0% by mass. 2 parts by mass of a platinum-based catalyst (trade name: SRX-212, solid content: 100% by mass) manufactured by Toray Dow Corning Co., Ltd. was added to this solution to prepare a release layer forming composition (B).

4). Production of Second Release Film A biaxially stretched polyethylene terephthalate (PET) film having a thickness of 38 μm, an orientation angle of 6 degrees, and a haze of 10% was prepared.
Next, on one surface of the biaxially stretched PET film (second biaxially stretched PET film), the release layer-forming composition (B) obtained above has a thickness after drying of 0.1 μm. Thus, it apply | coated with the bar coater and it dried at 120 degreeC for 1 minute, and formed the peeling layer (2nd peeling layer), and obtained the 2nd peeling film.

5. Preparation of substrate-less double-sided pressure-sensitive adhesive sheet The surface of the first release film on the first release layer side was coated with an applicator so that the film thickness after drying was 20 μm, and the coating was applied at 105 ° C. for 2 minutes. Dried. Then, the surface by the side of the 2nd peeling layer of a 2nd peeling film was bonded, and it aged at 23 degreeC50RH for 1 week, and produced the base material-less double-sided adhesive sheet.

(Example 2)
1. Preparation of First Release Film and Second Release Film A first release film and a second release film were prepared in the same manner as in Example 1.

2. Preparation of base material-less double-sided pressure-sensitive adhesive sheet The pressure-sensitive adhesive composition b was applied to the surface of the first release film on the first release layer side with an applicator so as to have a film thickness of 125 μm to form a coating layer. Subsequently, ultraviolet rays were irradiated from the exposed surface side of the obtained coating layer under the following conditions to pre-cure the coating layer to obtain a pre-cured coating layer.
[UV irradiation conditions]
・ Lamp: High pressure mercury lamp ・ Integrated light quantity (wavelength 365 nm): 40 mJ / cm ²

Next, the surface on the second release layer side of the second release film was bonded to the exposed surface of the obtained precured coating layer. Thereafter, the pre-cured coating layer in the state where the second release film is laminated is irradiated with ultraviolet rays from the biaxially stretched PET film side of the second release film under the following conditions, and the pre-cured coating layer is fully cured to form a film. A pressure-sensitive adhesive layer having a thickness of 125 μm was obtained, and a substrate-less double-sided pressure-sensitive adhesive sheet having a layer structure of first release film / adhesive layer / second release film was obtained.
[UV irradiation conditions]
・ Lamp: High pressure mercury lamp ・ Integrated light quantity (wavelength 365 nm): 1200 mJ / cm ²

(Example 3)
A substrate-less double-sided pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the thickness of the first biaxially stretched PET film was 50 μm.

Example 4
A substrate-less double-sided pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the thickness of the second biaxially stretched PET film was 25 μm.

(Example 5)
A baseless double-sided PSA sheet was obtained in the same manner as in Example 1 except that the haze of the first biaxially stretched PET film and the second biaxially stretched PET film was 3%.

(Example 6)
A substrate-less double-sided pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the orientation angle of the first biaxially stretched PET film was 12 degrees and the orientation angle of the second biaxially stretched PET film was 0 degrees. It was.

(Example 7)
A substrate-less double-sided pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the orientation angles of the first biaxially stretched PET film and the second biaxially stretched PET film were both 0 °.

(Example 8)
A baseless double-sided pressure-sensitive adhesive sheet was prepared in the same manner as in Example 1 except that the orientation angle of the first biaxially stretched PET film was 36 degrees and the orientation angle of the second biaxially stretched PET film was -12 degrees. Obtained.

(Comparative Example 1)
Substrate-less double-sided pressure-sensitive adhesive sheet as in Example 1, except that the orientation angle of the first biaxially stretched PET film was −12 degrees and the orientation angle of the second biaxially stretched PET film was −18 degrees. Got.

(Comparative Example 2)
A substrate-less double-sided PSA sheet was obtained in the same manner as in Example 1 except that the orientation angles of the first biaxially stretched PET film and the second biaxially stretched PET film were both 15 degrees.

(Summary of results)
In Examples 1-8 using the substrate-less double-sided PSA sheet of the present invention, all were excellent in crossed Nicol inspection properties and foreign matter inspection properties.

DESCRIPTION OF SYMBOLS 10 Substrate-less double-sided adhesive sheet 11 First release film 12 Second release film 1 Adhesive layer 2 First biaxially stretched polyester film 3 First release layer 4 Second biaxially stretched polyester film 5 Second release layer

Claims (6)

A substrate-less double-sided pressure-sensitive adhesive sheet comprising a first release film, a pressure-sensitive adhesive layer provided on the first release film, and a second release film provided on the pressure-sensitive adhesive layer,
The first release film has a first biaxially stretched polyester film and a first release layer provided on the pressure-sensitive adhesive layer side of the first biaxially stretched polyester film,
The second release film has a second biaxially stretched polyester film and a second release layer provided on the pressure-sensitive adhesive layer side of the second biaxially stretched polyester film,
The thickness of the first biaxially stretched polyester film and the thickness of the second biaxially stretched polyester film are both 19 to 50 μm,
The substrate-less double-sided pressure-sensitive adhesive sheet, wherein the orientation principal axis of the substrate-less double-sided pressure-sensitive adhesive sheet has an inclination of -12 degrees or more and 12 degrees or less.   The base material-less double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer has a thickness of 1 to 250 µm.   The substrate-less double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, wherein each of the first biaxially stretched polyester film and the second biaxially stretched polyester film is a polyethylene terephthalate film.   The substrate-less double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein each of the first release layer and the second release layer is a layer formed from a silicone resin.   The base-material-free double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 4, having a haze value of 25% or less.   The base material-less double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein a difference in peeling force between the first release film and the second release film is 5 mN / 25 mm or more.