CN111793439A - Adhesive sheet for image display device - Google Patents

Adhesive sheet for image display device Download PDF

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Publication number
CN111793439A
CN111793439A CN202010235490.9A CN202010235490A CN111793439A CN 111793439 A CN111793439 A CN 111793439A CN 202010235490 A CN202010235490 A CN 202010235490A CN 111793439 A CN111793439 A CN 111793439A
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Prior art keywords
adhesive sheet
image display
display device
adhesive
meth
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CN202010235490.9A
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CN111793439B (en
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城下知辉
松原圭佑
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Gunze Ltd
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Gunze Ltd
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J7/00—Adhesives in the form of films or foils
    • C09J7/10—Adhesives in the form of films or foils without carriers
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J7/00—Adhesives in the form of films or foils
    • C09J7/30—Adhesives in the form of films or foils characterised by the adhesive composition
    • C09J7/38—Pressure-sensitive adhesives [PSA]
    • C09J7/381—Pressure-sensitive adhesives [PSA] based on macromolecular compounds obtained by reactions involving only carbon-to-carbon unsaturated bonds
    • C09J7/385—Acrylic polymers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
    • C08K5/0025—Crosslinking or vulcanising agents; including accelerators
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L93/00—Compositions of natural resins; Compositions of derivatives thereof
    • C08L93/04—Rosin
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J11/00—Features of adhesives not provided for in group C09J9/00, e.g. additives
    • C09J11/02—Non-macromolecular additives
    • C09J11/06—Non-macromolecular additives organic
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J11/00—Features of adhesives not provided for in group C09J9/00, e.g. additives
    • C09J11/08—Macromolecular additives
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J133/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Adhesives based on derivatives of such polymers
    • C09J133/04—Homopolymers or copolymers of esters
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J7/00—Adhesives in the form of films or foils
    • C09J7/30—Adhesives in the form of films or foils characterised by the adhesive composition
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J7/00—Adhesives in the form of films or foils
    • C09J7/40—Adhesives in the form of films or foils characterised by release liners
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J2203/00—Applications of adhesives in processes or use of adhesives in the form of films or foils
    • C09J2203/318—Applications of adhesives in processes or use of adhesives in the form of films or foils for the production of liquid crystal displays
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J2301/00—Additional features of adhesives in the form of films or foils
    • C09J2301/30—Additional features of adhesives in the form of films or foils characterized by the chemical, physicochemical or physical properties of the adhesive or the carrier
    • C09J2301/312—Additional features of adhesives in the form of films or foils characterized by the chemical, physicochemical or physical properties of the adhesive or the carrier parameters being the characterizing feature

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Adhesives Or Adhesive Processes (AREA)
  • Adhesive Tapes (AREA)
  • Laminated Bodies (AREA)

Abstract

The invention provides an adhesive sheet for an image display device and an adhesive sheet laminate for an image display device, which can prevent a coating film from cracking and peeling when the coating film is mounted on the image display device. The pressure-sensitive adhesive sheet for image display device of the present invention has a pressure-sensitive adhesive layer containing a crosslinked product of a pressure-sensitive adhesive composition containing, as a main componentThe adhesive composition comprises 1 to 40 parts by weight of a rosin ester-based tackifying resin per 100 parts by weight of a (meth) acrylate copolymer, wherein the adhesive composition has a tan maximum value at 1Hz of an adhesive layer of-20 ℃ or less and a storage elastic modulus at 1Hz and 25 ℃ of the adhesive layer of 1.0X 105Pa or less.

Description

Adhesive sheet for image display device
Technical Field
The present invention relates to an adhesive sheet for an image display device and an adhesive sheet laminate for an image display device.
Background
In recent years, for laminating a film, an electrode film, a housing, and the like constituting a touch panel display used in a smartphone or the like, an adhesive sheet described in patent document 1, for example, has been used.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open publication No. 2012-025808
Disclosure of Invention
Technical problem to be solved by the invention
However, in recent years, image display devices such as touch panel displays have curved surfaces or curved surfaces, and are sometimes used by being repeatedly curved, and therefore, a coating film or the like as a component thereof is required to be attached to follow the curved surface or the like. However, when a coating film is attached to such a curved surface, the coating film may be broken or peeled off, and improvement thereof is desired. The present invention has been made to solve the above problems, and an object of the present invention is to provide an adhesive sheet for an image display device and an adhesive sheet laminate for an image display device, which can prevent a coating film from being broken or peeled off when the coating film is attached to the image display device.
Technical solution for solving technical problem
An adhesive sheet for an image display device, having an adhesive layer containing a crosslinked product of an adhesive composition containing:
a (meth) acrylate copolymer as a main component;
an isocyanate-based crosslinking agent; and
the rosin ester-based tackifying resin,
the adhesive composition comprises 1 to 40 parts by weight of the rosin ester based adhesive resin per 100 parts by weight of the (meth) acrylate copolymer,
the adhesive layer has a maximum value of tan at 1Hz of-20 ℃ or lower,
the adhesive layer has a storage modulus of elasticity of 1.0X 10 at 1Hz and 25 DEG C5Pa or less.
Item 2 the pressure-sensitive adhesive sheet for image display devices according to item 1, wherein the storage modulus at 1Hz and-20 ℃ is 1.0X 105Pa or less.
Item 3 the pressure-sensitive adhesive sheet for image display devices according to item 1 or 2, wherein the thickness is 5 to 100 μm.
An adhesive sheet laminate for an image display device, comprising: the adhesive sheet for image display device of any one of items 1 to 3; and a base sheet for peeling attached to at least one surface of the adhesive sheet for image display device.
Effects of the invention
With the adhesive sheet according to the present invention, when a coating film is attached to an image display device, the coating film can be prevented from being broken or peeled.
Drawings
Fig. 1 is a sectional view of an adhesive sheet laminate according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a test piece for bending test.
Fig. 3 is a view showing a method of a bending test.
Description of the symbols
1 first Release sheet
2 adhesive sheet (adhesive layer)
3 second Release sheet
Detailed Description
An embodiment of the adhesive sheet according to the present invention will be described below. The adhesive sheet is used for mounting a film, an electrode film, a housing, and the like constituting an image display device such as a touch panel display, and is particularly suitable for mounting a film on a display having a curved or bent surface. The adhesive sheet is obtained by crosslinking an adhesive composition containing a (meth) acrylate copolymer as a main component, an isocyanate-based crosslinking agent, and a rosin ester-based tackifying resin. The following description is made in detail.
(meth) acrylate copolymer
The (meth) acrylate polymer preferably contains, as monomer units, an alkyl (meth) acrylate having an alkyl group and 2 to 20 carbon atoms and a monomer having a reactive functional group in a molecule (reactive functional group-containing monomer). This can exhibit preferable adhesiveness.
The alkyl (meth) acrylate having an alkyl group with 2 to 20 carbon atoms is preferably a compound having a glass transition temperature (Tg) of-40 ℃ or lower as a homopolymer (hereinafter, may be referred to as "specific acrylate"). By containing such a specific acrylate as a constituent monomer unit, the maximum value of tan of the adhesive sheet according to the present embodiment can be easily set to a range described later.
As the specific acrylic ester, for example, n-butyl acrylate (Tg-55 ℃ C.), n-octyl acrylate (Tg-65 ℃ C.), isooctyl acrylate (Tg-58 ℃ C.), 2-ethylhexyl acrylate (Tg-70 ℃ C.), isononyl acrylate (Tg-58 ℃ C.), isodecyl acrylate (Tg-60 ℃ C.), isodecyl methacrylate (Tg-41 ℃ C.), n-lauryl methacrylate (Tg-65 ℃ C.), tridecyl acrylate (Tg-55 ℃ C.), tridecyl methacrylate (-40 ℃ C.), etc. are preferably used. Among them, from the viewpoint of more effectively reducing the storage elastic modulus, the Tg of the homopolymer is more preferably-45 ℃ or less, particularly preferably-50 ℃ or less, as the specific acrylate. In particular, n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred. These acrylates may be used alone or in combination of 2 or more. Wherein the alkyl group in the alkyl (meth) acrylate in which the alkyl group has 2 to 20 carbon atoms is a linear, branched or cyclic alkyl group.
The (meth) acrylate ester polymer preferably contains 60% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more of a specific acrylate ester as a monomer unit. By containing 60 mass% or more of the specific acrylate, the maximum value of tan of the pressure-sensitive adhesive sheet according to the present embodiment can be set to a range described later more easily.
The (meth) acrylate polymer preferably contains 99.9% by mass or less, more preferably 99% by mass or less, and particularly preferably 98% by mass or less of the specific acrylate as a monomer unit. By containing 99.9 mass% or less of the above-mentioned specific acrylate, it is possible to introduce an appropriate amount of other monomer components (particularly, a monomer having a reactive functional group) into the (meth) acrylate polymer.
The (meth) acrylate polymer has a monomer having a reactive functional group as a monomer unit, and reacts with a crosslinking agent described later via the reactive functional group derived from the monomer having a reactive functional group to form a crosslinked structure (three-dimensional network structure), thereby obtaining an adhesive sheet having a desired cohesive force.
In the (meth) acrylate polymer, as the reactive functional group-containing monomer contained in the monomer unit, a monomer having a hydroxyl group in the molecule (hydroxyl group-containing monomer), a monomer having an amino group in the molecule (amino group-containing monomer), and the like are preferable. Among these, hydroxyl group-containing monomers are particularly preferred. The glass transition temperature (Tg) of the hydroxyl group-containing monomer is often 0 ℃ or lower, and it is easy to set the maximum value of tan of the pressure-sensitive adhesive sheet according to the present embodiment to the range described later.
Examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate. Among them, at least one of 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, and 4-hydroxybutyl acrylate is preferable from the viewpoint of the glass transition temperature (Tg), the reactivity of the hydroxyl group in the obtained (meth) acrylate polymer with a crosslinking agent, and the copolymerizability with other monomers. These hydroxyl group-containing monomers may be used alone or in combination of 2 or more.
The hydroxyl value of the (meth) acrylate copolymer is not particularly limited, and from the viewpoint of suppressing peeling from an adherend when the adhesive sheet is repeatedly bent in a state of being in close contact with the adherend, the lower limit thereof is preferably 5mgKOH/g or more, more preferably 10mgKOH/g or more. On the other hand, the upper limit is preferably 100mgKOH/g or less, more preferably 90mgKOH/g or less.
The (meth) acrylate polymer preferably contains 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more of a reactive functional group-containing monomer as a monomer unit. The (meth) acrylate polymer preferably contains 30% by mass or less, more preferably 20% by mass or less, and particularly preferably 8% by mass or less of a reactive functional group-containing monomer as a monomer unit.
The (meth) acrylate polymer according to the present embodiment does not contain a carboxyl group-containing monomer, particularly does not contain acrylic acid, as a monomer unit. Since the carboxyl group is an acid component, the carboxyl group-containing monomer is not contained, and thus, the occurrence of troubles due to an acid on the object to which the adhesive sheet is attached can be suppressed, and for example, even in the case where a transparent conductive film such as Indium Tin Oxide (ITO), a metal film, a metal mesh, or the like is present, troubles (corrosion, change in resistance value, or the like) due to an acid can be suppressed.
The polymerization mode of the (meth) acrylate polymer may be a random copolymer or a block copolymer.
The lower limit of the weight average molecular weight of the (meth) acrylate polymer is preferably 20 ten thousand or more, more preferably 30 ten thousand or more, and particularly preferably 40 ten thousand or more. When the lower limit of the weight average molecular weight of the (meth) acrylate polymer is not less than the above range, defects such as bleeding of the adhesive can be suppressed when the adhesive sheet is processed. The weight average molecular weight in the present specification is a value in terms of standard polystyrene measured by a Gel Permeation Chromatography (GPC) method.
The upper limit of the weight average molecular weight of the (meth) acrylate polymer is preferably 100 ten thousand or less, more preferably 90 ten thousand or less, and particularly preferably 80 ten thousand or less. When the upper limit value of the weight average molecular weight of the (meth) acrylate polymer is the above-mentioned or less, the adhesion force and storage elastic modulus between the obtained adhesive sheet and the adherend easily fall within the preferable ranges described later.
In the adhesive according to the present embodiment, 1 of the above-mentioned (meth) acrylate polymers may be used alone, or 2 or more of them may be used in combination.
< 2. isocyanate-based crosslinking agent
When the adhesive composition according to the present embodiment is heated, the isocyanate-based crosslinking agent crosslinks the (meth) acrylate polymer to form a three-dimensional network structure. This improves the cohesive force of the resulting adhesive sheet.
The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate, and biuret and isocyanurate products thereof, and adducts thereof with low molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane and castor oil. Among them, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate and trimethylolpropane-modified xylylene diisocyanate are preferable from the viewpoint of reactivity with hydroxyl groups.
The content of the isocyanate-based crosslinking agent in the adhesive composition is preferably 0.01 part by mass or more, particularly preferably 0.05 part by mass or more, and more preferably 0.1 part by mass or more, based on 100 parts by weight of the (meth) acrylate polymer. The content is preferably 10 parts by mass or less, particularly preferably 8 parts by mass or less, and further preferably 5 parts by mass or less.
< 3. rosin ester tackifying resins
The rosin ester based tackifying resin according to the present embodiment is a rosin ester based tackifying resin such as gum rosin, wood rosin, tall oil rosin and the like, which contains resin acids such as abietic acid, palustric acid, neoabietic acid, pimaric acid, isopimaric acid, dehydroabietic acid and the like as main components, and esters of various alcohols.
The content of the rosin ester-based tackifying resin in the adhesive composition is preferably 1 to 40 parts by weight, more preferably 1.5 to 35 parts by weight, and still more preferably 2 to 30 parts by weight, based on 100 parts by weight of the (meth) acrylate polymer. When the content is 1 part by weight or more, the bending resistance is improved when the coating film is attached to an image display device using the adhesive sheet. On the other hand, by setting the content to 40 parts by weight or less, the adhesive sheet can be inhibited from being clouded.
< 4. additive >
Various additives commonly used in acrylic adhesives, for example, silane coupling agents, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, fillers, refractive index adjusting agents, and the like may be added to the pressure-sensitive adhesive composition as needed. The polymerization solvent and the diluting solvent described later are not included in the additive constituting the adhesive composition.
< 5. Property of adhesive sheet >
< 5-1. thickness of adhesive sheet >
The thickness of the adhesive sheet is preferably 5 to 100 μm, and more preferably 10 to 50 μm. This is because when the thickness is less than 5 μm, the coating may be easily peeled off. On the other hand, if the thickness exceeds 100 μm, the coating may sink when pressed, and the pencil hardness may decrease.
< 5-2. storage modulus of elasticity and tan >)
The pressure-sensitive adhesive sheet according to the present embodiment has a maximum value of tan (glass transition temperature) of-20 ℃ or less at 1Hz, and a storage modulus of elasticity of 1.0X 10 at 1Hz and 25 ℃5Pa or less. the lower the tan maximum, the lower the storage elastic modulus, and the softer the adhesive sheet. Therefore, the adhesive sheet preferably has a maximum value of tan at 1Hz of-30 ℃ or less, more preferably-50 ℃ or less. The adhesive sheet preferably has a lower storage modulus of elasticity at 1Hz and 25 ℃, and preferably 1.0X 105Pa or less, more preferably 8.0X 104Pa or less, more preferably 5.0X 104Pa or less, particularly preferably 3.0X 104Pa or less. In additionIn addition, in order to maintain softness even at low temperatures, the adhesive sheet preferably has a storage elastic modulus of 1.0X 10 at 1Hz and-20 ℃5Pa or less, more preferably 7.0X 104Pa or less, particularly preferably 5.5X 104Pa or less.
The maximum value of tan can be measured, for example, using "Discovery HR-3" manufactured by TA Instruments, and the storage modulus of elasticity can be measured by a method based on JIS K7244-6.
< 6. method for producing adhesive sheet
The method for producing the pressure-sensitive adhesive sheet according to the present embodiment is not particularly limited, and may be performed, for example, as follows.
First, a (meth) acrylate polymer, an isocyanate-based crosslinking agent, and a rosin ester-based tackifying resin are mixed, and the above-mentioned additive is added as needed.
The (meth) acrylate polymer can be produced by polymerizing a mixture of monomers constituting the polymer by a general radical polymerization method. If necessary, the polymerization of the (meth) acrylate polymer is preferably carried out by a solution polymerization method using a polymerization initiator. Examples of the polymerization solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, and the like, and 2 or more kinds thereof may be used in combination.
The polymerization initiator may be an azo compound, an organic peroxide, or the like, and 2 or more kinds may be used in combination. Examples of the azo compound include 2,2' -azobisisobutyronitrile, 2' -azobis (2-methylbutyronitrile), 1' -azobis (cyclohexane 1-carbonitrile), 2' -azobis (2, 4-dimethylvaleronitrile), 2' -azobis (2, 4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2' -azobis (2-methylpropionate), 4' -azobis (4-cyanovaleric acid), 2' -azobis (2-hydroxymethylpropionitrile), and 2,2' -azobis [ 2- (2-imidazolin-2-yl) propane ].
Examples of the organic peroxide include benzoyl peroxide, tert-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, bis (2-ethoxyethyl) peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, (3,5, 5-trimethylhexanoyl) peroxide, dipropionyl peroxide, and diacetyl peroxide.
In the polymerization step, a chain transfer agent such as 2-mercaptoethanol is added to adjust the weight average molecular weight of the obtained polymer.
When the (meth) acrylate polymer is obtained, an isocyanate-based crosslinking agent, a rosin ester-based tackifying resin, a desired additive and a diluting solvent are added to a solution of the (meth) acrylate polymer and sufficiently mixed to obtain an adhesive composition (coating solution) diluted with the solvent.
In the case where a solid substance is used or when a solid substance is precipitated when the solid substance is mixed with another component in an undiluted state, any of the above components may be dissolved or diluted with a diluent solvent and then mixed with another component.
Examples of the diluent solvent include aliphatic hydrocarbons such as hexane, heptane and cyclohexane, aromatic hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as methylene chloride and dichloroethane, alcohols such as methanol, ethanol, propanol, butanol and 1-methoxy-2-propanol, ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone and cyclohexanone, esters such as ethyl acetate and butyl acetate, and cellosolve-based solvents such as ethyl cellosolve.
The concentration and viscosity of the coating solution prepared in this manner may be in a range in which the coating solution can be applied, and may be appropriately selected according to the situation. For example, the concentration of the adhesive composition may be diluted to 10 to 60 mass%. In addition, when obtaining a coating solution, the addition of a diluting solvent or the like is not an essential condition, and the diluting solvent may not be added as long as the adhesive composition has a coatable viscosity or the like. In this case, the adhesive composition is a coating solution in which the polymerization solvent of the (meth) acrylate polymer is directly used as a dilution solvent.
The crosslinking of the adhesive composition can be carried out by a heat treatment. The heat treatment may be performed as a drying treatment for evaporating a diluent solvent or the like from a coating film of the adhesive composition applied to a desired object.
The heating temperature of the heating treatment is preferably 50 to 150 ℃, and more preferably 70 to 120 ℃. The heating time is, for example, preferably 10 seconds to 10 minutes, and more preferably 50 seconds to 2 minutes.
After the heat treatment, a curing period of about 1 to 2 weeks at normal temperature (e.g., 23 ℃ C., 50% RH) may be set as necessary. When this curing period is required, an adhesive sheet is formed after the curing period. On the other hand, when the curing period is not required, the adhesive sheet is formed after the heat treatment is completed.
By the heat treatment (and curing), the (meth) acrylate polymer is sufficiently crosslinked with the isocyanate crosslinking agent to form a crosslinked structure, thereby obtaining an adhesive sheet.
< 7. adhesive sheet laminate >
Next, the adhesive sheet laminate according to the present embodiment will be described. As shown in fig. 1, the adhesive sheet laminate according to the present embodiment includes a first release sheet 1, an adhesive layer 2 laminated on the first release sheet 1, and a second release sheet 3 disposed on the adhesive layer 2. The first and second release sheets 1 and 3 are known release sheets, and at least one side thereof has a release surface.
The adhesive sheet laminate can be produced, for example, as follows. First, the first release sheet 1 is drawn out from the guide roller around which the first release sheet 1 is wound. Then, the coating solution of the adhesive composition described above is applied to the release surface of the first release sheet 1, and heat treatment is performed to thermally crosslink the adhesive composition, thereby forming the adhesive layer 2. The adhesive layer 2 corresponds to the adhesive sheet of the present invention. Thereafter, a second release sheet 3 is attached so as to cover the adhesive layer 2. At this time, the release surface of the second release sheet 3 is in contact with the adhesive layer 2. This forms the adhesive sheet laminate shown in fig. 1.
< 8. coating film >
The coating film to be attached to the image display device via the adhesive sheet is not particularly limited, and a known coating film may be used. There are various methods for attaching the adhesive sheet to the cover film. For example, the adhesive sheet laminate can be mounted on a cover film by peeling off the first or second release sheet and then transferring the exposed adhesive layer to the cover film. Alternatively, an adhesive layer (adhesive sheet) can be formed by applying the coating solution of the adhesive composition described above on one surface of the coating film, and performing heat treatment to thermally crosslink the adhesive composition.
< 9. feature >
The adhesive sheet according to the present invention has a low storage elastic modulus and contains a rosin ester-based adhesive resin, and therefore, when a film provided with the adhesive sheet is attached along an image display device having a bent portion, stress applied to the film due to bending can be relaxed by the adhesive sheet. Therefore, when the film is bent, cracking and peeling including cracks can be prevented from occurring.
Examples
Next, examples of the present invention will be explained. However, the present invention is not limited to the following examples.
< 1. production of examples and comparative examples >
Adhesive sheets according to examples 1 to 7 and comparative examples 1 to 4 were prepared. Then, a coating film was attached to the target film using each adhesive sheet to produce a laminate shown in fig. 2. The coating film and the object film are as follows.
(1) Film covering: acrylic resin film having a thickness of 100 μm and not causing cracks when R is 3.0mm in bending test
(2) Object membrane: polyimide resin film 30 μm thick
The target film is assumed to be an image display device to which the coating film is to be attached.
The compositions of the binders according to examples 1 to 7 and comparative examples 1 to 4 are as follows. Coronate L-55E, which constitutes an isocyanate-based crosslinking agent, is manufactured by Tosoh corporation, BXX8515 is manufactured by Toyo ink corporation, and Duranate TPA-100 is manufactured by Asahi Kasei corporation. PINECRYSTAL ME-GH constituting the rosin ester tackifier resin was manufactured by Kawakawa chemical industries, Ltd. For the acrylate copolymer, the weight average molecular weight and hydroxyl number are indicated.
[ Table 1]
Figure BDA0002430819820000101
The physical properties of the adhesive sheets of examples 1 to 7 and comparative examples 1 to 4 are as follows.
The storage modulus of elasticity and the loss tangent tan of the adhesive sheet were measured using "Discovery HR-3" manufactured by TA Instruments. The measurement conditions are as follows.
(measurement conditions)
Measurement mode: shear mode
Deformation: 0.1 percent of
Measuring frequency: 1Hz
Measuring temperature: -60 to 25 ℃ (5 ℃/min heating)
And (3) determining a sample: the adhesive layers of the adhesive sheets were overlapped and measured to have a total thickness of about 1 mm.
[ Table 2]
Figure BDA0002430819820000111
Each pressure-sensitive adhesive sheet was composed of a glass/pressure-sensitive adhesive sheet/PET film laminate, and the total light transmittance and haze were measured. The results of measuring the total light transmittance according to JIS K7136-1 and the results of measuring the haze according to JIS K7136 are shown in Table 3.
Further, a bending test was performed on the laminate shown in fig. 2 using each adhesive sheet. The bending test was performed using a no-load U-shaped tester shown in fig. 3. The testing machine has 2 movable plates that can be rotated, and the rotation axes of the movable plates are disposed close to each other so as to be parallel to each other. Then, a laminate as a sample piece was disposed on the movable plate in a horizontal state shown in fig. 3 (a). At this time, the laminate is disposed so that the film surface of the laminate contacts the movable plate. Next, as shown in fig. 3(b), the sample piece is bent into a U-shape by rotating both movable plates by 90 degrees. Such bending was repeated at a test speed of 0.85 sec/time at normal temperature. After the test, whether or not the film of the sample piece was cracked was checked, and the bending resistance was evaluated according to the following criteria (1) to (3). The test was performed so that the bending radius R of the sample piece was 2.5mm and 3.0mm, and as a result, whether the bending radius R corresponded to any of the following (1) to (3) was tested.
(1) The number of bending cycles was 10 ten thousand or more when R was 2.5mm, and no cracks were generated (when R was 2.5mm, no cracks were generated)
(2) When R is 2.5mm, cracks were generated with a bending frequency of less than 10 ten thousand, but when R is 3.0mm, cracks were not generated with a bending frequency of 10 ten thousand or more (when R is 3.0mm, cracks were not generated)
(3) When R is 3.0mm, the number of bending times is less than 10 ten thousand, and cracks are generated (when R is 3.0mm, cracks are generated)
[ Table 3]
Total light transmittance (%) Haze (%) Bending test
Example 1 90.6 0.7 (1) R2.5 has no crack
Example 2 90.6 0.7 (1) R2.5 has no crack
Example 3 90.4 0.8 (1) R2.5 has no crack
Example 4 90.5 0.7 (1) R2.5 has no crack
Example 5 90.2 0.7 (1) R2.5 has no crack
Example 6 90.6 0.7 (2) R3.0 has no crack
Example 7 90.2 1.1 (1) R2.5 has no crack
Comparative example 1 90.6 0.7 (3) R3.0 cracks
Comparative example 2 90.6 0.7 (3) R3.0 cracks
Comparative example 3 90.6 0.7 (3) R3.0 cracks
Comparative example 4 90.6 0.7 (3) R3.0 cracks
According to table 3, in examples 1 to 7, the number of times of bending was 10 ten thousand or more and no cracks were generated in the coating film when R was 2.5mm or 3.0mm, but in comparative examples 1 to 4, the number of times of bending was less than 10 ten thousand and cracks were generated when R was 3.0 mm. In example 6, the reason why the number of bending times is less than 10 ten thousand and cracks are generated when R is 2.5mm is considered to be that the content of the rosin ester based tackifying resin is small.
The flexural resistance was considered to be low in all of comparative examples 1 to 4 because they had a high modulus of elasticity at 25 ℃. Further, as described above, since comparative example 2 has a high storage elastic modulus, it is considered that the bending resistance is low even if the rosin ester based tackifying resin is contained.

Claims (4)

1. An adhesive sheet for an image display device, characterized in that,
which comprises an adhesive layer containing a crosslinked product of an adhesive composition,
the adhesive composition comprises:
a (meth) acrylate copolymer as a main component;
an isocyanate-based crosslinking agent; and
the rosin ester-based tackifying resin,
the adhesive composition contains 1 to 40 parts by weight of the rosin ester based tackifying resin per 100 parts by weight of the (meth) acrylate copolymer,
the adhesive layer has a maximum value of tan at 1Hz of-20 ℃ or lower,
the adhesive layer has a storage modulus of elasticity of 1.0X 10 at 1Hz and 25 DEG C5Pa or less.
2. The adhesive sheet for image display devices according to claim 1, wherein:
the storage elastic modulus at 1Hz and-20 ℃ is 1.0X 105Pa or less.
3. The adhesive sheet for image display devices according to claim 1 or 2, wherein: the thickness is 5 to 100 μm.
4. An adhesive sheet laminate for an image display device, comprising:
the adhesive sheet for image display device according to any one of claims 1 to 3; and
a release base sheet attached to at least one surface of the pressure-sensitive adhesive sheet for image display device.
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