CN109563391B - Acrylic adhesive composition, adhesive and adhesive sheet - Google Patents

Acrylic adhesive composition, adhesive and adhesive sheet Download PDF

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Publication number
CN109563391B
CN109563391B CN201780046953.3A CN201780046953A CN109563391B CN 109563391 B CN109563391 B CN 109563391B CN 201780046953 A CN201780046953 A CN 201780046953A CN 109563391 B CN109563391 B CN 109563391B
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meth
acrylate
alkyl
acrylic resin
monomer
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CN109563391A (en
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浅野铁也
中岛贵弘
野原一树
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Mitsubishi Kasei Corp
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Mitsubishi Chemical Corp
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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
    • 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
    • C09J133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
    • C09J133/08—Homopolymers or copolymers of acrylic acid esters
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/10—Esters
    • C08F220/26—Esters containing oxygen in addition to the carboxy oxygen
    • 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
    • C09J133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
    • 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
    • C09J133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
    • C09J133/10—Homopolymers or copolymers of methacrylic acid 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
    • 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
    • C09J133/14—Homopolymers or copolymers of esters of esters containing halogen, nitrogen, sulfur or oxygen atoms in addition to the carboxy oxygen
    • 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

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Adhesive Tapes (AREA)
  • Adhesives Or Adhesive Processes (AREA)
  • Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)

Abstract

An acrylic adhesive composition which is suitable for thick coating and which can give an adhesive having excellent heat stability and moist heat resistance and a low dielectric constant, which comprises an acrylic resin (A) which is a copolymer containing a copolymerization component of a hydroxyl group-containing (meth) acrylate monomer (a1) and an alkyl (meth) acrylate monomer (a2), wherein the alkyl (meth) acrylate monomer (a2) contains an alkyl (meth) acrylate monomer (a2-1) having a C10-24 linear alkyl group, the copolymerization component contains 5-15 wt% of hydroxyl group-containing (meth) acrylate monomer (a1) and 50-94 wt% of alkyl (meth) acrylate monomer (a2-1) having a C10-24 linear alkyl group.

Description

Acrylic adhesive composition, adhesive and adhesive sheet
Technical Field
The present invention relates to an acrylic adhesive composition, an adhesive containing the acrylic adhesive composition, and an adhesive sheet, and more particularly, to an acrylic adhesive composition which is excellent in thermal stability and moist heat resistance, exhibits a low dielectric constant, and is suitable for thick coating.
Background
In recent years, a touch panel in which a liquid crystal display and a position input device are combined has been widely used in mobile devices such as televisions, monitors for computers, notebook computers, mobile phones, tablet terminals, and the like, and among them, a capacitive touch panel has been increasing.
The touch panel is generally composed of a liquid crystal display, a transparent conductive film substrate (ITO substrate), and a protective film (glass), and a transparent adhesive sheet is used for bonding these members.
Such pressure-sensitive adhesives for transparent pressure-sensitive adhesive sheets are required to have not only pressure-sensitive adhesive properties such as adhesive strength, but also impact absorbability for preventing breakage of liquid crystal displays due to external impacts, excellent optical properties (transparency), and a low dielectric constant for suppressing erroneous operation of touch panels due to noise generated from display members and other peripheral members.
As low dielectric constant binders, for example: a binder using a (meth) acrylic polymer obtained by polymerizing a monomer component mainly containing an alkyl (meth) acrylate having a branched alkyl group having 10 to 18 carbon atoms at the end of an ester group (see patent document 1); an adhesive using a copolymer of a monomer mixture (a) comprising: specifically disclosed is a monomer containing a specific amount of each of an alkyl methacrylate monomer having a long-chain alkyl group having 10 or more carbon atoms at the alkyl ester moiety and an alkyl methacrylate monomer having an alkyl group having 1 to 9 carbon atoms at the alkyl ester moiety (see patent document 2).
On the other hand, in the adhesive for bonding optical members such as touch panels, a solvent-free adhesive using a photopolymerizable unsaturated monomer as a diluent monomer instead of a solvent used for adjusting viscosity or the like in a general acrylic adhesive is used in order to omit a drying step for volatilizing a solvent after applying the adhesive and to be suitable for thick coating application; for example, a solvent-free type active energy ray curable adhesive is known, which contains a diluent monomer and a polyfunctional compound as a curing component in an acrylic resin (see patent document 3).
However, the method using the diluent monomer has the following problems: the unreacted monomer remaining in the adhesive layer may cause a decrease in durability at high temperatures.
Therefore, even in the solvent-free type adhesives, hot melt type adhesives using no diluent monomer have been used. The hot-melt adhesive can more efficiently provide a thick adhesive layer having excellent durability at high temperatures.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open publication No. 2012-246477
Patent document 2: japanese patent laid-open publication No. 2015-40237
Patent document 3: japanese laid-open patent publication No. 2009-57550
Disclosure of Invention
Problems to be solved by the invention
However, since the resin is exposed to high temperature for a long time in the hot melt method, a resin having more excellent thermal stability is required.
Here, since hydrogen at the branched position of the alkyl (meth) acrylate having a branched alkyl group is easily taken away, the acrylic resin using a large amount of the alkyl (meth) acrylate having a branched alkyl group is poor in thermal stability, and the adhesive described in patent document 1 is insufficient in thermal stability when used in a hot melt adhesive.
In addition, since the acrylic resin described in patent document 2 uses a large amount of methacrylic acid ester having a small carbon number as a monomer of the acrylic resin, the acrylic resin has a high glass transition temperature and is difficult to handle when it is formed into a sheet by a hot-melt method, and therefore, it is difficult to increase the molecular weight, and the reliability of the adhesive is poor.
Further, when the content of the hydroxyl group-containing monomer as a monomer component of the acrylic resin is increased, although the moist heat resistance of the adhesive is improved, side reactions such as transesterification are likely to occur under high temperature conditions, the molecular weight tends to increase, gelation is likely to occur, and the thermal stability when the adhesive is used as a hot melt adhesive is poor.
Under such circumstances, the present invention provides an acrylic adhesive composition which can give an adhesive having excellent heat stability and moist heat resistance and a low dielectric constant and is suitable for thick coat application.
Means for solving the problems
However, the present inventors have made intensive studies in view of the above circumstances, and as a result, have found that by using: an acrylic adhesive composition suitable for thick coating applications, which is excellent in thermal stability and moist heat resistance and exhibits a low dielectric constant, can be obtained by copolymerizing an acrylic resin containing a specific amount of a hydroxyl group-containing (meth) acrylate monomer and an alkyl (meth) acrylate monomer having a long-chain and linear alkyl group having a constant or greater number of carbon atoms as a main component with the alkyl (meth) acrylate monomer.
That is, the present invention provides an acrylic adhesive composition comprising an acrylic resin (a) which is a copolymer containing a copolymerization component of a hydroxyl group-containing (meth) acrylate monomer (a1) and an alkyl (meth) acrylate monomer (a2), wherein the alkyl (meth) acrylate monomer (a2) contains an alkyl (meth) acrylate monomer (a2-1) having a linear alkyl group having 10 to 24 carbon atoms, and the copolymerization component contains 5 to 15 wt% of the hydroxyl group-containing (meth) acrylate monomer (a1) and 50 to 94 wt% of the alkyl (meth) acrylate monomer (a2-1) having a linear alkyl group having 10 to 24 carbon atoms.
The present invention also provides an adhesive comprising the acrylic adhesive composition, and an adhesive sheet having an adhesive layer comprising the acrylic adhesive composition.
ADVANTAGEOUS EFFECTS OF INVENTION
The acrylic adhesive composition of the present invention comprises an acrylic resin (A) which is a copolymer containing a hydroxyl group-containing (meth) acrylate monomer (a1) and an alkyl (meth) acrylate monomer (a2) as copolymerization components, wherein the alkyl (meth) acrylate monomer (a2) contains an alkyl (meth) acrylate monomer (a2-1) having a linear alkyl group having 10 to 24 carbon atoms, and the copolymerization components contain 5 to 15 wt% of the hydroxyl group-containing (meth) acrylate monomer (a1) and 50 to 94 wt% of the alkyl (meth) acrylate monomer (a2-1) having a linear alkyl group having 10 to 24 carbon atoms. Therefore, the adhesive containing the acrylic adhesive composition can be applied in a thick coat, is free from resin yellowing caused by heating, has excellent thermal stability, low dielectric constant, and further has excellent moist heat resistance, impact absorption, and step following property. In particular, the pressure-sensitive adhesive is useful as a pressure-sensitive adhesive used for bonding optical members constituting touch panels, image display devices, and the like.
Further, when the copolymerization component further contains 0.1 to 20 wt% of an alkyl methacrylate monomer (a2-2) having an alkyl group having 4 to 8 carbon atoms as the alkyl (meth) acrylate monomer (a2), the dielectric constant can be kept low and the cohesive force can be improved.
Further, the thermal stability is further excellent when the content ratio of the alkyl (meth) acrylate monomer having a linear alkyl group to the alkyl (meth) acrylate monomer having a branched alkyl group is 100/0 to 70/30 in terms of weight ratio among the alkyl (meth) acrylate monomers (a2) in the copolymerization component.
When the weight average molecular weight of the acrylic resin (a) is 15 to 150 ten thousand, the moist heat resistance, the impact absorption property, and the step following property are further excellent.
When the acrylic resin (a) has an active energy ray-crosslinkable structural site, the acrylic resin (a) can be effectively cured (crosslinked) to improve the cohesive force.
Further, when the active energy ray-crosslinkable structural moiety is a benzophenone-based crosslinkable structure, the reactivity is excellent and the cohesive force can be further improved.
When the volatile content in the acrylic resin (a) is 2 wt% or less, the coating can be further thick-coated.
Detailed Description
The present invention will be described in detail below, but these are examples of desirable embodiments.
In the present invention, (meth) acrylic acid means acrylic acid or methacrylic acid, (meth) acryloyl means acryloyl or methacryloyl, (meth) acrylate means acrylate or methacrylate, and acrylic resin means a resin obtained by polymerizing a monomer component containing at least 1 (meth) acrylic monomer, respectively. Further, "sheet" is intended to broadly include sheets, films, and tapes.
< acrylic adhesive composition >
The acrylic adhesive composition contains an acrylic resin (A) which is a copolymer containing 5 to 15 wt% of a hydroxyl group-containing (meth) acrylate monomer (a1) and 50 to 94 wt% of a copolymerized component of an alkyl (meth) acrylate monomer (a2-1) having a linear alkyl group having 10 to 24 carbon atoms as an alkyl (meth) acrylate monomer (a 2).
The hydroxyl group-containing (meth) acrylate monomer (a1) is generally a hydroxyl group-containing (meth) acrylate monomer having 5 to 12 carbon atoms, preferably 5 to 10 carbon atoms, and particularly preferably 5 to 8 carbon atoms, from the viewpoint of moisture and heat resistance, and specific examples thereof include: hydroxyalkyl acrylates such as 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, and 8-hydroxyoctyl (meth) acrylate; caprolactone-modified monomers such as 2-hydroxyethyl (meth) acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth) acrylate and polyethylene glycol (meth) acrylate; primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate, N-methylol (meth) acrylamide and hydroxyethyl acrylamide; secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and 3-chloro-2-hydroxypropyl (meth) acrylate; and tertiary hydroxyl group-containing monomers such as 2, 2-dimethyl-2-hydroxyethyl (meth) acrylate.
These may be used alone, or 2 or more kinds may be used in combination.
Among the above, a primary hydroxyl group-containing monomer is preferable, and a hydroxyalkyl acrylate is more preferable, from the viewpoint of excellent reactivity with a crosslinking agent and the viewpoint of improvement in resistance to wet-heat whitening. Among them, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferable, and 4-hydroxybutyl acrylate is particularly preferable, from the viewpoint of less impurities such as di (meth) acrylate and ease of production.
The content of the hydroxyl group-containing (meth) acrylate monomer (a1) in the copolymerization component is preferably 5 to 15 wt%, particularly preferably 8 to 14 wt%, and further preferably 10 to 13 wt% based on the whole copolymerization component.
When the content is too small, the wet-heat whitening resistance tends to decrease; when too much, the dielectric constant tends to be high.
The free acid contained in the hydroxyl group-containing (meth) acrylate monomer (a1) is preferably 1.0% or less, more preferably 0.5% or less, and still more preferably 0.1% or less.
When the content is too large, the thermal stability is lowered, and corrosion of the metal-based adherend tends to be increased easily when the pressure-sensitive adhesive sheet is produced.
Examples of the alkyl (meth) acrylate monomer (a2) include: methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, n-propyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, isotridecyl (meth) acrylate, isomyristyl (meth) acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, and isotetradecyl (meth) acrylate.
In the present invention, the alkyl (meth) acrylate monomer (a2) which is essentially an alkyl (meth) acrylate monomer (a2-1) containing a linear alkyl group having 10 to 24 carbon atoms includes, for example: decyl (meth) acrylate (having 10 carbon atoms in the alkyl group), lauryl (meth) acrylate (having 12 carbon atoms), tridecyl (meth) acrylate (having 13 carbon atoms), cetyl (meth) acrylate (having 16 carbon atoms), stearyl (meth) acrylate (having 18 carbon atoms), behenyl (meth) acrylate (having 22 carbon atoms), and the like.
These may be used alone, or 2 or more kinds may be used in combination.
In the alkyl (meth) acrylate monomer (a2-1) having a linear alkyl group having 10 to 24 carbon atoms, an alkyl methacrylate is preferably used from the viewpoint of reducing the dielectric constant and lowering the glass transition temperature of the acrylic resin (a), and stearyl methacrylate, lauryl methacrylate, and tridecyl methacrylate are particularly preferable.
The content of the alkyl (meth) acrylate monomer (a2-1) having a linear alkyl group having 10 to 24 carbon atoms is 50 to 94% by weight, preferably 60 to 83% by weight, and particularly preferably 70 to 80% by weight based on the total amount of the copolymerization components.
When the content is too small, the dielectric constant tends to be high, or the thermal stability of the acrylic resin (a) tends to be low.
In the present invention, the alkyl (meth) acrylate monomer (a2) is preferably an alkyl methacrylate monomer (a2-2) containing an alkyl group having 4 to 8 carbon atoms, from the viewpoint of improving the cohesive force. The alkyl group of the alkyl methacrylate monomer (a2-2) having an alkyl group having 4 to 8 carbon atoms may be a linear alkyl group or a branched alkyl group.
Examples of the alkyl methacrylate monomer (a2-2) having an alkyl group having 4 to 8 carbon atoms include: isobutyl methacrylate (having 4 carbon atoms in the alkyl group), tert-butyl methacrylate (having 4 carbon atoms), 2-ethylhexyl methacrylate (having 8 carbon atoms), and the like.
These may be used alone, or 2 or more kinds may be used in combination.
Among these, hydrogen abstraction in the case where a monomer having a tertiary carbon in an alkyl group is efficiently photocrosslinked can improve the cohesive force, and further, the monomer can improve the cohesive force because the glass transition temperature is high.
In addition, in the alkyl methacrylate monomer (a2-2) having an alkyl group having 4 to 8 carbon atoms, t-butyl methacrylate and 2-ethylhexyl methacrylate are preferably used from the viewpoint of keeping the dielectric constant low and improving the cohesive force.
The content of the alkyl methacrylate monomer (a2-2) having an alkyl group having 4 to 8 carbon atoms is preferably 0.1 to 20% by weight, particularly preferably 1 to 18% by weight, and more preferably 5 to 15% by weight, based on the whole copolymer component.
When the content is too small, the cohesive force tends to decrease; when too much, the thermal stability tends to be lowered and the handling property tends to be deteriorated.
In the present invention, the content ratio of the alkyl (meth) acrylate monomer having a linear alkyl group and the alkyl (meth) acrylate monomer having a branched alkyl group in the alkyl (meth) acrylate monomer (a2) in the copolymerization component is preferably 100/0 to 70/30, particularly preferably 100/0 to 80/20, and more preferably 90/10 to 85/15 in terms of weight ratio.
When the content ratio of the alkyl (meth) acrylate monomer having a branched alkyl group is too large, the thermal stability of the resin tends to be lowered; when the content of the alkyl (meth) acrylate monomer having a linear alkyl group is too large, adhesive properties tend to be lowered.
In the present invention, it is preferable that the copolymerization component contains a small amount of the alkyl (meth) acrylate monomer (a2) having a branched alkyl group such as a branched monomer having a tertiary carbon in the alkyl group and a branched monomer having a tertiary butyl group, from the viewpoint of keeping the dielectric constant low and efficiently improving the cohesive force.
Hydrogen abstraction in efficient photocrosslinking of a branched monomer having a tertiary carbon in an alkyl group can improve cohesion; the cohesive force can be increased by increasing the glass transition temperature of a branched monomer having a t-butyl group such as t-butyl (meth) acrylate.
Among them, as the alkyl (meth) acrylate monomer (a2) having a branched alkyl group, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and tert-butyl (meth) acrylate are preferably used, and 2-ethylhexyl (meth) acrylate or tert-butyl (meth) acrylate is particularly preferred.
The content of the alkyl (meth) acrylate monomer (a2) is preferably 51 to 95% by weight, more preferably 70 to 90% by weight, and particularly preferably 80 to 88% by weight based on the whole copolymer component.
When the content of the alkyl (meth) acrylate monomer (a2) is too small, the adhesive force tends to be insufficient.
In addition, the acrylic resin (a) used in the present invention preferably has an active energy ray-crosslinkable structural site from the viewpoint that the acrylic resin can be efficiently cured (crosslinked) to improve the cohesive force.
The active energy ray crosslinking structure part is as follows: and a structural site which can react with a part of the acrylic resin (a) or other curing component contained in the acrylic resin composition by irradiation with an active energy ray and form a crosslinked structure.
In the present invention, the active energy ray-crosslinkable structural moiety is preferably a benzophenone-based crosslinkable structure in terms of high reactivity and excellent improvement in cohesive force.
Therefore, in the present invention, it is preferable to further use (meth) acrylate monomer (a3) containing an active energy ray-crosslinkable structural site as a copolymerization component of the acrylic resin (a).
The (meth) acrylate monomer (a3) containing an active energy ray-crosslinkable structural site preferably contains a (meth) acrylate monomer having a benzophenone structure, and specifically, 4- (meth) acryloyloxybenzophenone and the like are mentioned, from the viewpoint that a crosslinked structure can be efficiently formed by active energy rays such as ultraviolet rays and electron beams.
The content of the (meth) acrylate monomer (a3) having an active energy ray-crosslinkable structural moiety is preferably 0.01 to 5% by weight based on the whole copolymerization component, and the content of the (meth) acrylate monomer having a benzophenone structure is preferably 0.01 to 5% by weight, particularly preferably 0.1 to 2% by weight, and further preferably 0.2 to 1% by weight based on the whole copolymerization component. When the content is too small, the holding power tends to decrease when a crosslinked structure is formed by active energy rays; further, the following tendency is exhibited: in order to form a crosslinked structure in order to produce a processable pressure-sensitive adhesive sheet, a large amount of active energy is required, and a large amount of energy is required in the production of the pressure-sensitive adhesive sheet, and it is difficult to produce the pressure-sensitive adhesive sheet efficiently. When the content is too large, the cohesive force of the entire system tends to be too large, and the adhesive force tends to be lowered.
In the present invention, if necessary, another copolymerizable ethylenically unsaturated monomer (a4) may be further contained as a copolymerization component.
Examples of other copolymerizable ethylenically unsaturated monomers (a4) include: aromatic ring-containing monomers such as phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenyldiethylene glycol (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, phenoxypolyethylene glycol-polypropylene glycol- (meth) acrylate, o-phenylphenoxyethyl (meth) acrylate, and nonylphenol ethylene oxide adduct (meth) acrylate; alicyclic-containing monomers such as cyclohexyl (meth) acrylate, cyclohexyloxyalkyl (meth) acrylate, t-butylcyclohexyloxyethyl (meth) acrylate, isobornyl (meth) acrylate, and dicyclopentanyl (meth) acrylate; ether chain-containing monomers such as 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2-butoxyethyl (meth) acrylate, 2-butoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, octyloxypolyethylene glycol-polypropylene glycol-mono (meth) acrylate, lauroxypolyethylene glycol mono (meth) acrylate, and stearoxypolyethylene glycol mono (meth) acrylate; acrylic acid dimers such as (meth) acrylic acid and β -carboxyethyl acrylate; carboxyl group-containing monomers such as crotonic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, N-glycolic acid, and cinnamic acid; amide group-containing monomers such as (meth) acrylamide, N- (N-butoxyalkyl) (meth) acrylamide, N-dimethyl (meth) acrylamide, N-diethyl (meth) acrylamide, and N, N-dimethylaminoalkyl (meth) acrylamide; amino group-containing monomers such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and quaternary ammonium compounds thereof; and acrylonitrile, methacrylonitrile, styrene, α -methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, dialkyl itaconate, dialkyl fumarate, allyl alcohol, acryloyl chloride, methyl vinyl ketone, N-acrylamidomethyltrimethyl ammonium chloride, allyltrimethyl ammonium chloride, dimethylallyl vinyl ketone, and the like.
These may be used alone, or 2 or more kinds may be used in combination.
In addition, for the purpose of high molecular weight of the acrylic resin (a), compounds having two or more ethylenically unsaturated groups such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, and divinylbenzene may be used in combination.
The content of the other copolymerizable ethylenically unsaturated monomer (a4) is preferably 0 to 20% by weight, more preferably 0 to 10% by weight, and still more preferably 0 to 5% by weight, based on the whole copolymer component.
When the content is too large, thermal stability tends to be lowered or adhesive force tends to be lowered.
When a carboxyl group-containing monomer is used as the other copolymerizable ethylenically unsaturated monomer (a4), the content is preferably 0 to 0.1% by weight, more preferably 0 to 0.07% by weight, and still more preferably 0 to 0.05% by weight, based on the whole copolymerizable components. When the content is too large, there is a possibility that a metal or a metal oxide of an adherend such as an ITO film is corroded or deteriorated.
The acrylic resin (a) used in the present invention can be produced by polymerizing the hydroxyl group-containing (meth) acrylate monomer (a1) and the alkyl (meth) acrylate monomer (a2-1) having a linear alkyl group having 10 to 24 carbon atoms as essential components, and by appropriately selecting any of the above-mentioned polymerization components.
As the polymerization method of the acrylic resin (a), conventionally known polymerization methods such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization and the like can be used, and in the present invention, it is preferable to produce the acrylic resin (a) by solution polymerization from the viewpoint that the acrylic resin (a) can be produced safely and stably with an arbitrary monomer composition.
An example of a preferable production method of the acrylic resin (a) used in the present invention is shown below.
First, a copolymerization component and a polymerization initiator are mixed or dropped into an organic solvent to carry out solution polymerization, thereby obtaining an acrylic resin (a) solution.
[ organic solvent ]
Examples of the organic solvent used in the polymerization reaction include: aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as n-hexane; esters such as methyl acetate, ethyl acetate, and butyl acetate; aliphatic alcohols such as methanol, ethanol, n-propanol, and isopropanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aliphatic ethers such as dimethyl ether and diethyl ether; aliphatic halogenated hydrocarbons such as methylene chloride and dichloroethane; cyclic ethers such as tetrahydrofuran, and the like. Among these solvents, it is preferable to use a solvent having a boiling point of 70 ℃ or less from the viewpoint of efficiently producing a solvent-free acrylic resin by distilling off the solvent from an acrylic resin solution obtained by solution polymerization.
Examples of the organic solvent having a boiling point of 70 ℃ or lower include: hydrocarbons such as n-hexane (67 ℃), aliphatic alcohols such as methanol (65 ℃), esters such as methyl acetate (54 ℃), ketones such as acetone (56 ℃), aliphatic ethers such as diethyl ether (35 ℃), aliphatic halogenated hydrocarbons such as dichloromethane (40 ℃), cyclic ethers such as tetrahydrofuran (66 ℃), and the like, among which acetone and methyl acetate are preferably used from the viewpoint of general versatility and safety, and acetone is particularly preferably used.
The numerical value in () described below in the name of each organic solvent is a boiling point.
[ polymerization initiator ]
As the polymerization initiator used in the above polymerization reaction, an azo polymerization initiator, a peroxide polymerization initiator, and the like, which are general radical polymerization initiators, can be used, and as the azo polymerization initiator, for example: 2,2 ' -azobis (2-methylbutyronitrile), 2 ' -azobisisobutyronitrile, (1-phenylethyl) azodiphenylmethane, 2 ' -azobis (2, 4-dimethylvaleronitrile), 2 ' -azobis (2-cyclopropylpropionitrile), 2 ' -azobis (4-methoxy-2, 4-dimethylvaleronitrile), and the like, and examples of the peroxide-based polymerization initiator include: benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, t-butyl peroxypivalate, t-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, diisobutyryl peroxide, and the like.
These may be used alone, or 2 or more kinds may be used in combination.
In the production of the acrylic resin (a) used in the present invention, it is preferable to use an organic solvent having a boiling point of 70 ℃ or lower as a reaction solvent for solution polymerization and to carry out polymerization at a relatively low temperature, and in this case, if a polymerization initiator having a high 10-hour half-life temperature is used, the polymerization initiator tends to remain. When the polymerization initiator remains, the following tendency is exhibited: in the step of distilling off the solvent from the acrylic resin (a) solution, which will be described later, gelation of the acrylic resin (a) occurs.
Accordingly, in the present invention, from the viewpoint of stably performing the step of distilling off the solvent from the acrylic resin (A) solution obtained by solution polymerization, it is preferable to use a polymerization initiator having a 10-hour half-life temperature of less than 60 ℃ among the polymerization initiators, and among them, 2 '-azobis (2, 4-dimethylvaleronitrile) (52 ℃), 2' -azobis (2-cyclopropylpropionitrile) (49.6 ℃), 2 '-azobis (4-methoxy 2, 4-dimethylvaleronitrile) (30 ℃), tert-butyl peroxypivalate (54.6 ℃), tert-hexyl peroxypivalate (53.2 ℃), tert-hexyl peroxyneodecanoate (44.5 ℃), diisopropyl peroxycarbonate (40.5 ℃), diisobutyroniyl peroxide (32.7 ℃), and particularly preferably 2, 2' -azobis (2, 4-Dimethylvaleronitrile) (52 ℃ C.), tert-hexyl peroxypivalate (53.2 ℃ C.).
The value in () described in the name of each compound is the 10-hour half-life temperature of each compound.
The amount of the polymerization initiator used is usually 0.001 to 10 parts by weight, preferably 0.1 to 8 parts by weight, particularly preferably 0.5 to 6 parts by weight, further preferably 1 to 4 parts by weight, particularly preferably 1.5 to 3 parts by weight, and most preferably 2 to 2.5 parts by weight, based on 100 parts by weight of the copolymerization component. When the amount of the polymerization initiator used is too small, the polymerization rate of the acrylic resin (a) tends to decrease, the amount of residual monomer tends to increase, or the weight-average molecular weight of the acrylic resin (a) tends to increase; when the amount is too large, gelation of the acrylic resin (a) tends to occur in a step of distilling off the solvent from the acrylic resin (a) solution, which will be described later.
[ polymerization conditions, etc. ]
The polymerization conditions for the solution polymerization may be any polymerization conditions known in the art, and for example, the polymerization may be carried out by mixing or dropping a copolymerization component containing a (meth) acrylic monomer and a polymerization initiator into a solvent and polymerizing them under predetermined polymerization conditions.
The polymerization temperature in the polymerization reaction is usually 40 to 120 ℃, and in the present invention, from the viewpoint of enabling the reaction to proceed stably, the polymerization temperature is preferably 50 to 90 ℃, more preferably 55 to 75 ℃, and particularly preferably 60 to 70 ℃. When the polymerization temperature is too high, the acrylic resin (a) tends to be easily gelled; if the amount is too low, the activity of the polymerization initiator decreases, and thus the polymerization rate tends to decrease and the amount of residual monomer tends to increase.
The polymerization time in the polymerization reaction (in the case of performing additional heating described later, the time to start the additional heating) is not particularly limited, and is 0.5 hours or more, preferably 1 hour or more, more preferably 2 hours or more, and particularly preferably 5 hours or more from the last addition of the polymerization initiator.
From the viewpoint of easy heat dissipation, it is preferable to carry out the polymerization reaction while refluxing the solvent.
In the production of the acrylic resin (a) of the present invention, it is preferable to additionally heat and decompose the polymerization initiator by heating in order to reduce the amount of the residual polymerization initiator.
The additional heating temperature is preferably higher than the 10-hour half-life temperature of the polymerization initiator, and specifically is usually 40 to 150 ℃, and from the viewpoint of gelation inhibition, is preferably 55 to 130 ℃, and particularly preferably 75 to 95 ℃. When the additional heating temperature is too high, the acrylic resin (a) tends to be yellowed; if the amount is too low, the polymerization monomer and the polymerization initiator remain, and the stability with time and thermal stability of the acrylic resin (a) tend to be lowered.
This gives an acrylic resin (A) solution.
The acrylic resin (a) solution may be used in the acrylic adhesive composition of the present invention in a state of containing a solvent to a certain extent, but in the present invention, the solvent is substantially completely distilled off from the acrylic adhesive composition and the acrylic resin (a) solution is used as a solvent-free adhesive, thereby exerting more excellent effects. Therefore, the solvent is usually distilled off from the obtained acrylic resin (a) solution.
The step of distilling the solvent out of the acrylic resin (a) solution can be carried out by a known and common method, and as a method of distilling the solvent, there are a method of distilling the solvent out by heating, a method of distilling the solvent out by reducing the pressure, and the like.
The temperature at which the solvent is distilled off by heating is preferably 60 to 150 ℃, and from the viewpoint of minimizing the amount of residual solvent, the following is particularly preferred: the reaction solution obtained by polymerizing the acrylic resin (A) is kept at 60 to 80 ℃ to distill off the solvent, and then the solvent is distilled off at 80 to 150 ℃. In view of suppressing gelation of the acrylic resin (a), it is preferable that the solvent is not distilled off at a temperature of 150 ℃.
The pressure at which the solvent is distilled off under reduced pressure is preferably 20 to 101.3kPa, and from the viewpoint of minimizing the amount of residual solvent, the following is particularly preferred: the reaction solution is held in a range of 50 to 101.3kPa to distill off the solvent in the reaction solution, and then the residual solvent is distilled off at a pressure of 20 to 50 kPa.
The acrylic resin (A) used in the present invention can be produced by this method.
The weight average molecular weight of the acrylic resin (a) used in the present invention is preferably 10 ten thousand or more, more preferably 15 to 150 ten thousand, particularly preferably 20 to 100 ten thousand, particularly preferably 25 to 80 ten thousand, and particularly preferably 30 to 60 ten thousand. When the weight average molecular weight is too large, the viscosity becomes too high, and the coatability and handling tend to be lowered; if the amount is too small, the cohesive force tends to decrease and the durability tends to decrease.
The weight average molecular weight of the acrylic resin (a) is a weight average molecular weight of the acrylic resin (a) at the time of production, and is a weight average molecular weight of the acrylic resin (a) after production without heating or the like.
The dispersion degree (weight average molecular weight/number average molecular weight) of the acrylic resin (a) is preferably 15 or less, more preferably 10 or less, particularly preferably 7 or less, and particularly preferably 5 or less. When the dispersion degree is too high, the durability of the adhesive layer tends to be lowered, and foaming tends to occur easily; when the amount is too low, the handling property tends to be lowered. From the viewpoint of production restrictions, the lower limit of the degree of dispersion is usually 1.1.
The weight average molecular weight obtained by conversion of the weight average molecular weight of the above-mentioned polystyrene resin to a standard polystyrene resin was determined by using 3 chromatographic columns connected in series to high performance liquid chromatography ("Waters 2695 (main body)" and "Waters 2414 (detector)") manufactured by japan Waters: shodex GPC KF-806L (exclusion limit molecular weight: 2X 10)7And separation range: 100 to 2 x 107Theoretical plate number: 10000/root, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm), and the number average molecular weight can be measured by the same method. The degree of dispersion was determined from the weight average molecular weight and the number average molecular weight.
The glass transition temperature (Tg) of the acrylic resin (A) used in the present invention is preferably-100 to 50 ℃, particularly preferably-50 to 20 ℃, and more preferably-20 to 0 ℃. When the glass transition temperature is too high, the melt viscosity of the acrylic resin (a) increases, and therefore the heating temperature required for coating increases, which may impair the stability of the acrylic resin (a), and may cause poor conformability and decrease in adhesive strength. When the glass transition temperature is too low, thermal durability tends to decrease.
The glass transition temperature (Tg) was determined by the following measurement method.
The release sheet was peeled from the pressure-sensitive adhesive sheet before the irradiation with active energy rays described later, and a plurality of pressure-sensitive adhesive sheets were laminated to prepare a pressure-sensitive adhesive sheet having a thickness of about 650 μm in an uncrosslinked state. The dynamic viscoelasticity of the sheet thus produced was measured under the following conditions, and the temperature at which the loss tangent (loss modulus G "/storage modulus G' ═ tan δ) reached the maximum was read as the Tg of the acrylic resin.
[ measurement conditions ]
Measurement equipment: DVA-225(I.T. manufactured by Keishku Seigyo Co., Ltd.)
Deformation mode: shearing
Strain: 0.1 percent of
Measuring temperature: -100 to 20 DEG C
Measuring frequency: 1Hz
The acrylic resin (A) preferably has a melt viscosity (mPas) at 100 ℃ of 1,000 to 10,000,000 mPas, particularly preferably 50,000 to 1,000,000 mPas, and more preferably 200,000 to 600,000 mPas. When the viscosity is too low, the durability tends to be lowered due to a decrease in molecular weight; when the viscosity is too high, the handling property tends to be lowered and the coating tends to be difficult.
The above viscosity was measured at a measurement temperature of 100 ℃ under a load of 30kg, a hole diameter of 1.0mm, a length of 10mm of a mold (Japanese: ダイ) using a "rheometer" manufactured by Shimadzu corporation.
The acrylic resin (a) of the present invention is preferably used as a solvent-free acrylic resin substantially free of a solvent, and in this case, the solvent content of the acrylic resin (a) is preferably 2% by weight or less, more preferably 0.00001 to 2% by weight, particularly preferably 0.0001 to 1% by weight, and particularly preferably 0.001 to 0.1% by weight. When the solvent content is too large, bubbles tend to be generated in the pressure-sensitive adhesive layer when the pressure-sensitive adhesive is used as a pressure-sensitive adhesive, and the durability tends to be lowered.
The amount of residual monomer in the acrylic resin (a) of the present invention is preferably 2% by weight or less, more preferably 0.00001 to 1.5% by weight, and still more preferably 0.0001 to 1.0% by weight. Too much residual monomer content tends to be as follows: when heated, the molecular weight increases to deteriorate the coating property and adhesive property, or the adhesive generates bubbles to deteriorate the durability.
The solvent content and the residual monomer amount in the acrylic resin (a) are as follows: the acrylic resin (A) was diluted 20-fold with toluene, and the value was measured by gas chromatography/mass spectrometry (GC: 7890A GCsystem manufactured by Agilent technologies, MSD: 5975 insert manufactured by Agilent technologies).
In the present invention, the content of volatile components (usually, solvent and residual monomer are main components) in the acrylic resin (a) is preferably 2 wt% or less, particularly preferably 0.00001 to 1.5 wt%, and more preferably 0.0001 to 1.0 wt%. Too much residual monomer content tends to be as follows: the acrylic resin (a) has a molecular weight increased during heating to lower coatability, or adhesive properties are lowered when it is used as an adhesive, or air bubbles are generated to lower durability.
The volatile content in the acrylic resin (a) is as follows: 1.5g of an acrylic resin was supported on a circular aluminum foil having a diameter of 50mm, and heated at 130 ℃ for 1 hour in a hot air dryer, and a value calculated from the weight change before and after heating was obtained.
The acrylic adhesive composition of the present invention preferably contains the acrylic resin (a) in an amount of 90 wt% or more based on the whole acrylic adhesive composition, more preferably 95 to 99.9 wt%, particularly 98 to 99.9 wt%, and particularly 99 to 99.9 wt%.
The acrylic pressure-sensitive adhesive composition of the present invention can be prepared by subjecting the acrylic pressure-sensitive adhesive composition to an active energy ray irradiation treatment and further aging as described below to cure (crosslink) the acrylic pressure-sensitive adhesive composition, and when curing is performed by an active energy ray, the photopolymerization initiator (B) can be added from the viewpoint of stabilizing the reaction at the time of active energy ray irradiation.
The photopolymerization initiator (B) is not particularly limited as long as it is an initiator that generates radicals by the action of light, and examples thereof include: as the photopolymerization initiator such as acetophenone type, benzoin type, benzophenone type, thioxanthone type, acylphosphine oxide type, etc., hydrogen abstraction type photopolymerization initiators of benzophenone type are preferably used from the viewpoint of efficiently crosslinking between molecules or within molecules.
Examples of benzophenone-based photopolymerization initiators include: benzophenone, benzoylbenzoic acid, 3' -dimethyl-4-methoxybenzophenone, polyvinyl benzophenone and the like.
These may be used alone, or 2 or more kinds may be used in combination.
In addition, as the auxiliary agent of the photopolymerization initiator (B), triethanolamine, triisopropanolamine, 4 ' -dimethylaminobenzophenone (michler's ketone), 4 ' -diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, ethyl 4-dimethylaminobenzoate, ethyl (n-butoxy) 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2, 4-diethylthioxanthone, 2, 4-diisopropylthioxanthone, and the like can be used in combination. These auxiliaries may also be used alone or in combination of 2 or more.
The amount of the photopolymerization initiator (B) is preferably 0.01 to 10 parts by weight, particularly preferably 0.1 to 5 parts by weight, and more preferably 0.5 to 2 parts by weight, based on 100 parts by weight of the acrylic resin (a). When the amount is too small, the curing rate tends to be low and the curing tends to be insufficient; even if the curing property is too high, the curability is not improved and the economical efficiency tends to be lowered.
When curing is performed by an active energy ray, an active energy ray-curable monomer such as a monofunctional monomer or a polyfunctional monomer may be further contained. This makes it possible to adjust the cohesive force of the entire pressure-sensitive adhesive layer and to obtain stable pressure-sensitive adhesive properties.
The active energy ray-curable monomer is preferably a polyfunctional monomer having 2 or more ethylenically unsaturated groups in 1 molecule, and examples thereof include: hexanediol di (meth) acrylate, butanediol di (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, ethylene oxide-modified tri (meth) acrylate isocyanurate, allyl (meth) acrylate, vinyl (meth) acrylate, urethane (meth) acrylate, and the like. The polyfunctional monomers may be used alone or in combination of 2 or more.
The polyfunctional monomer is preferably used in an amount of 0 to 5 parts by weight, particularly preferably 0.01 to 2 parts by weight, and more preferably 0.1 to 1 part by weight, based on 100 parts by weight of the acrylic resin (A).
The acrylic pressure-sensitive adhesive composition of the present invention may contain other pressure-sensitive adhesives, if necessary, or may contain conventionally known additives such as a crosslinking agent, a crosslinking accelerator, a silane coupling agent, an antistatic agent, a tackifier, and a functional pigment.
Thus, the acrylic adhesive composition of the present invention can be obtained by mixing the acrylic resin (a), the photopolymerization initiator (B) used as needed, and other optional components. The mixing method is not particularly limited, and various methods such as a method of mixing the respective components at once, a method of mixing optional components and then mixing the remaining components at once or sequentially, and the like can be employed.
The acrylic pressure-sensitive adhesive composition of the present invention has a melt viscosity (mPas) at 100 ℃ of preferably 1,000 to 10,000,000 mPas, particularly preferably 50,000 to 1,000,000 mPas, and more preferably 200,000 to 600,000 mPas. When the viscosity is too low, the durability tends to be insufficient due to a decrease in molecular weight; when the viscosity is too high, the handling property tends to be lowered and the coating tends to be difficult.
In the acrylic pressure-sensitive adhesive composition of the present invention, the solvent content is preferably 2% by weight or less, more preferably 0.00001 to 2% by weight, particularly preferably 0.0001 to 1% by weight, and particularly preferably 0.001 to 0.1% by weight. When the solvent content is too large, bubbles tend to be generated in the pressure-sensitive adhesive layer when the pressure-sensitive adhesive is used as a pressure-sensitive adhesive, and the durability tends to be lowered.
The amount of residual monomer in the acrylic adhesive composition is preferably 2% by weight or less, more preferably 0.00001 to 1.5% by weight, and still more preferably 0.0001 to 1.0% by weight. When the amount of the residual monomer is too large, the molecular weight increases upon heating to deteriorate the coatability and adhesive properties, or the adhesive tends to generate bubbles to deteriorate the durability.
In the present invention, the content of volatile components (usually, solvent and residual monomer as main components) in the acrylic adhesive composition is preferably 2 wt% or less, particularly preferably 0.00001 to 1.5 wt%, and more preferably 0.0001 to 1.0 wt%. Too much residual monomer content tends to be as follows: the acrylic resin (a) has a molecular weight increased during heating to lower coatability, or adhesive properties are lowered when it is used as an adhesive, or air bubbles are generated to lower durability.
The melt viscosity, solvent content, residual monomer content, and volatile content of the acrylic adhesive composition can be measured by the same methods as those for the acrylic resin (a).
The acrylic adhesive composition of the present invention is useful as an adhesive component for hot melt. Further, the adhesive containing the acrylic adhesive composition of the present invention is particularly useful as a solventless adhesive for optical members.
< adhesive sheet >
The acrylic adhesive composition of the present invention is preferably used in the form of: an adhesive sheet comprising a substrate sheet and an adhesive layer formed using the acrylic adhesive composition, a double-sided adhesive sheet comprising a release sheet and an adhesive layer formed on the release sheet, and an optical member with an adhesive layer comprising an optical member and an adhesive layer formed on the optical member.
The pressure-sensitive adhesive layer may be the acrylic pressure-sensitive adhesive composition of the present invention itself or may be a pressure-sensitive adhesive layer obtained by curing (crosslinking) the acrylic pressure-sensitive adhesive composition of the present invention.
As a curing method, there is a method of curing by an active energy ray, and irradiation of the active energy ray causes the acrylic resin (a) in the acrylic adhesive composition to form a crosslinked structure in at least one of the intramolecular and intermolecular sites.
The adhesive sheet can be produced, for example, as follows.
A method of first applying an acrylic adhesive composition to one or both surfaces of a base sheet in a state of being melted by heating, and then cooling; or a method in which an acrylic pressure-sensitive adhesive composition is melted by heating and extruded or laminated on a base sheet by a T die or the like, thereby forming a pressure-sensitive adhesive layer with a predetermined thickness on one surface or both surfaces of the base sheet. Then, a release sheet is bonded to the adhesive layer surface as needed, whereby an adhesive sheet can be produced.
After the pressure-sensitive adhesive layer is formed on the substrate sheet, the pressure-sensitive adhesive sheet may be subjected to an active energy ray irradiation treatment as needed and further cured, whereby a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer obtained by curing (crosslinking) the pressure-sensitive adhesive composition can be produced.
Alternatively, a double-sided pressure-sensitive adhesive sheet without a substrate may be produced by forming a pressure-sensitive adhesive layer on a release sheet and bonding the release sheet to the surface of the pressure-sensitive adhesive layer on the opposite side.
The obtained pressure-sensitive adhesive sheet or double-sided pressure-sensitive adhesive sheet was used after the release sheet was peeled from the pressure-sensitive adhesive layer.
Examples of the substrate sheet include: polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate/ethylene isophthalate copolymers; polyolefin resins such as polyethylene, polypropylene and polymethylpentene; polyvinyl Fluoride resins such as Polyvinyl Fluoride (pvdf), polyvinylidene Fluoride (pvdf), and Polyvinyl Fluoride (polyfluoroethylene); polyamides such as nylon 6 and nylon 6, 6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride/vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, vinylon and the like; cellulose resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; polystyrene; a polycarbonate; a polyarylate; synthetic resin sheets such as polyimide, metal foils of aluminum, copper, and iron, paper such as wood paper and cellophane, and woven or nonwoven fabrics made of glass fibers, natural fibers, synthetic fibers, and the like. These substrate sheets may be used in the form of a single layer or in the form of a multilayer body in which 2 or more kinds are laminated. Among these, synthetic resin sheets are preferable from the viewpoint of weight reduction and the like.
Further, as the release sheet, for example, a release sheet obtained by subjecting various synthetic resin sheets exemplified as the base sheet, paper, woven fabric, nonwoven fabric, and the like to release treatment can be used. As the release sheet, a silicon-based release sheet is preferably used.
The coating method of the acrylic pressure-sensitive adhesive composition is not particularly limited as long as it is a conventional coating method, and examples thereof include: roll coating, die coating, gravure coating, comma coating, slit coating, screen printing, and the like.
In the case of irradiation with active energy rays, rays such as far ultraviolet rays, near ultraviolet rays, and infrared rays, electromagnetic waves such as X rays and γ rays, and electron beams, proton beams, and neutron beams can be used, and curing by ultraviolet irradiation is advantageous in terms of curing speed, ease of use of an irradiation apparatus, cost, and the like.
In the present invention, the pressure-sensitive adhesive layer is laminated on the optical member to obtain an optical member with a pressure-sensitive adhesive layer. Further, the optical members may be bonded to each other using the double-sided adhesive sheet.
Examples of the optical member include a liquid crystal display, a transparent conductive film substrate (ITO substrate), and a protective film (glass) constituting a touch panel or an image display device.
The gel fraction of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is preferably 10 to 100% by weight, particularly preferably 30 to 90% by weight, and particularly preferably 50 to 80% by weight, from the viewpoint of durability and adhesive strength. When the gel fraction is too low, the cohesive force tends to decrease, and the durability tends to decrease. When the gel fraction is too high, the cohesive force tends to increase, and the adhesive force tends to decrease.
In addition, when the pressure-sensitive adhesive layer is formed by curing with an active energy ray, a mode in which the gel fraction is increased at a low irradiation dose is preferable from the viewpoint of economy and processability. Specifically, the cumulative light amount is preferably 1000mJ/cm2The lower gel fraction is 10 to 90 wt%, particularly preferably 30 to 85 wt%, and further preferably 50 to 80 wt%. If the gel fraction at a low irradiation dose is too low, a large amount of active energy rays is required until the adhesive layer is formed, and efficient production tends to be difficult. On the other hand, when a psa sheet is produced in a state of low gel fraction for economic reasons, the processability of the psa sheet tends to decrease.
When the gel fraction is adjusted to the above range, the gel fraction can be adjusted, for example, by adjusting the irradiation dose of the active energy ray, the content of the active energy ray-crosslinkable structural site in the acrylic resin (a), the amount of the photoinitiator, and the type and amount of the active energy ray-curable monomer.
The gel fraction is a standard of the degree of crosslinking (degree of curing), and is calculated, for example, by the following method. That is, an adhesive sheet (adhesive sheet without a release sheet) in which an adhesive layer is formed on a polymer sheet (for example, polyethylene terephthalate (PET) film) as a base material is wrapped with a 200-mesh SUS metal mesh, and immersed in toluene maintained at 23 ℃ for 24 hours, and the gel fraction is determined as the weight percentage of the insoluble adhesive component remaining in the metal mesh. In which the weight of the substrate is subtracted beforehand.
The thickness of the adhesive layer of the adhesive sheet is preferably 50 to 3000 μm, more preferably 100 to 1000 μm, and particularly preferably 175 to 350 μm. When the thickness of the adhesive layer is too thin, the impact absorbability tends to be lowered; if the thickness is too large, the thickness of the entire optical member tends to increase, and the practicability tends to decrease.
The thickness of the pressure-sensitive adhesive layer of the present invention was determined by subtracting the measured values of the thicknesses of the constituent members other than the pressure-sensitive adhesive layer from the measured value of the thickness of the entire pressure-sensitive adhesive layer-containing laminate obtained using "ID-C112B" manufactured by sanfeng corporation.
In the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention, the haze value when the thickness of the pressure-sensitive adhesive layer is 175 μm is preferably 2% or less, particularly preferably 0 to 1.5%, and more preferably 0 to 1%. When the haze value exceeds 2%, the adhesive layer tends to whiten and the transparency tends to decrease.
The adhesive layer of the present invention preferably has a relative dielectric constant of 3.5 or less, particularly preferably 3.0 or less at 100 Hz. The lower limit of the relative dielectric constant is usually 1.0.
When the relative dielectric constant is too high, the capacitance between electrodes mounted on the touch panel tends to increase, causing malfunction; if the capacitance is too low, the capacitance tends to be small, and the detection sensitivity tends to be low.
Examples
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the invention does not depart from the gist thereof. In the examples, "part" and "%" are based on weight except the haze value. The weight average molecular weight of the acrylic resin was measured by the method described above.
[ production example 1]
To a 2L flask equipped with a condenser were charged 100 parts of acetone (boiling point 56 ℃ C.) as a polymerization solvent, 0.6 part of 2, 2' -azobis (2, 4-dimethylvaleronitrile) (ADVN: 10-hour half-life temperature 52 ℃ C.) as a polymerization initiator, 50 parts (15% with respect to the whole copolymerization component) of a monomer solution (stearyl methacrylate (SMA: a2-1), 192 parts (57.6% with respect to the whole copolymerization component) of a mixture (SLMA: a2-1) of lauryl methacrylate and tridecyl methacrylate), 50 parts (15% with respect to the whole copolymerization component) of 2-ethylhexyl methacrylate (2 EHMA: a2-2), 40 parts (12% with respect to the whole copolymerization component) of 4-hydroxybutyl acrylate (4 HBA: a1), 1.5 parts (0.4% with respect to the whole copolymerization component) of a mixed solution of 4-methacryloxybenzophenone (MBP: a3) 20% of the monomer solution was refluxed in the flask, and the remaining 80% of the monomer solution was added dropwise over 2 hours. After 1 hour and 3 hours from the dropwise addition, 0.2 part and 0.6 part of ADVN were added, respectively, to carry out a reaction, thereby obtaining an acrylic resin [ a-1] solution.
The acrylic resin [ A-1] solution obtained above was kept at a jacket temperature of 80 ℃ for 1 hour, further reduced to 10kPa and kept at a jacket temperature of 90 ℃ for 2 hours by using a flask which was made so as to be able to remove the solvent by distillation using a "Bu" -shaped connecting tube, and the solvent was distilled off to obtain an acrylic resin [ A-1] (weight average molecular weight: 33.9 ten thousand, volatile content: 0.9%, glass transition temperature-8.9 ℃).
(production example 2, comparative production examples 1 to 2)
Acrylic resins [ A-2], [ A '-1 ] and [ A' -2] were produced in the same manner as in production example 1, except that the copolymerization components of the acrylic resins were set as shown in Table 1.
[ Table 1]
Figure BDA0001960780250000241
< example 1 >
The acrylic resin [ A-1] obtained in the above was reacted]The sheet was sandwiched between 2 polyester-based release sheets (thickness: 176 μm), and the pressure was applied while heating at 100 ℃ so that the thickness of the adhesive layer became 175 μm, and the sheet was irradiated with a high-pressure mercury UV irradiation apparatus at peak illuminance: 150mW/cm2Cumulative exposure amount: 1000mJ/cm2(500mJ/cm2X 2pass) by ultraviolet irradiation, thereby obtaining a resin compositionA double-sided pressure-sensitive adhesive sheet for substrates.
Further, the release sheet on one side was peeled from the adhesive layer of the double-sided adhesive sheet without a substrate obtained in the above, and pressed against an easy-adhesion treated polyethylene terephthalate (PET) film (thickness 125 μm) to obtain a PET film with an adhesive layer having an adhesive layer thickness of 175 μm.
< example 2 >
The substrate-less double-sided pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer-attached PET film of example 2 were obtained in the same manner as in example 1 except that the acrylic resin [ a-1] was changed to the acrylic resin [ a-2] in example 1.
< comparative example 1 >
A double-sided pressure-sensitive adhesive sheet without a substrate and a PET film with a pressure-sensitive adhesive layer of comparative example 1 were obtained in the same manner as in example 1, except that the acrylic resin [ a-1] was changed to the acrylic resin [ a' -1] in example 1.
< comparative example 2 >
A substrate-less double-sided pressure-sensitive adhesive sheet and a pressure-sensitive adhesive layer-attached PET film of comparative example 2 were obtained in the same manner as in example 1, except that the acrylic resin [ a-1] was changed to the acrylic resin [ a' -2] in example 1.
[ gel fraction (1) ]
The above-mentioned double-sided pressure-sensitive adhesive sheet without a substrate was cut to 40mm × 40mm, left to stand at 23 ℃ × 50% RH for 30 minutes, and then one release sheet was peeled off, and after the pressure-sensitive adhesive layer side was bonded to a 50mm × 100mm SUS mesh (200 mesh), the other release sheet was peeled off, and the sample was wrapped by folding back from the center in the longitudinal direction of the SUS mesh, and then immersed in a sealed container containing 250g of toluene kept at 23 ℃ for 24 hours, and the gel fraction (%) was measured from the change in weight at that time.
[ gel fraction (2) ]
After cutting the above double-sided adhesive sheet without a substrate into 40mm × 40mm, the resultant was irradiated with a high-pressure mercury UV irradiation device at peak illuminance: 150mW/cm2Cumulative exposure amount: 2000mJ/cm2(1000mJ/cm2X 2pass) under ultraviolet irradiation at 23 ℃ and 50% RHAfter 30 minutes, one release sheet was peeled off, and after the pressure-sensitive adhesive layer side was bonded to a 50mm × 100mm SUS mesh (200 mesh), the other release sheet was peeled off, and the sample was wrapped by folding back from the central portion in the longitudinal direction of the SUS mesh, and then immersed in a sealed container containing 250g of toluene kept at 23 ℃ for 24 hours, and the gel fraction (%) was measured from the change in weight at that time.
[ adhesive force ]
The pressure-sensitive adhesive layer-attached PET film was cut into a width of 25mm × a length of 100mm, and the release sheet was peeled off, and the pressure-sensitive adhesive layer side was pressure-bonded to alkali-free glass (EAGLE XG, thickness 1.1mm, manufactured by corning) by reciprocating 2 times with a 2kg rubber roller in an atmosphere of 23℃ × 50% RH, and after pressure-heating treatment at 50℃ × 0.5MPa × 20 minutes in an autoclave, the PET film side was irradiated with high-pressure mercury UV irradiation apparatus at peak illuminance: 150mW/cm2Cumulative exposure amount: 2000mJ/cm2(1000mJ/cm2X 2pass) was irradiated with ultraviolet rays, left to stand at 23 ℃ x 50% RH for 30 minutes, and then the 180-degree peel strength (N/25mm) was measured at a peel rate of 300 mm/min at normal temperature (23 ℃).
[ optical Properties of adhesive layer ]
The above substrate-free double-sided adhesive sheet was cut into 25mm × 25mm, and irradiated with a high-pressure mercury UV irradiation device at peak illuminance: 150mW/cm2Cumulative exposure amount: 2000mJ/cm2(1000mJ/cm2X 2pass) was irradiated with ultraviolet rays. Then, a release sheet was peeled off from the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer side was bonded to alkali-free glass ("EAGLE XG" manufactured by corning corporation, having a thickness of 1.1mm), and then, autoclave treatment (50 ℃. times.0.5 MPa. times.20 minutes) was performed, and the sheet was left to stand at 23 ℃. times.50% RH for 30 minutes. Finally, the other release sheet was peeled off to prepare a test piece having a "alkali-free glass/adhesive layer" structure.
The obtained test piece was used to measure a haze value, a total light transmittance, and a color difference b*Value, YI value.
[ haze value and Total light transmittance ]
The HAZE value was calculated by measuring the diffuse transmittance and the total light transmittance using a HAZE matrix NDH2000 (manufactured by japan electric color industry corporation) and substituting the obtained values of the diffuse transmittance and the total light transmittance into the following formula. The machine is based on JIS K7361-1.
Haze value (%) - (diffuse transmittance/total transmittance) × 100
[ color difference ]
Color difference b*The value was measured in accordance with JIS K7105 by using a spectrocolorimeter (SE 6000: manufactured by Nippon Denshoku industries Co., Ltd.) under a transmission condition.
[ YI value ]
The YI value was measured in accordance with JIS K7373 by using a spectral colorimeter (SE 6000: manufactured by Nippon Denshoku industries Co., Ltd.) under a transmission condition.
Note that, in the examples, haze, total light transmittance, color difference b*The value and YI value were measured by attaching only an adhesive layer to alkali-free glass (total light transmittance 93%, haze 0.06%, b)*Value 0.16) and measured.
[ Damp-heat resistance ]
The pressure-sensitive adhesive layer-attached PET film was cut into 30mm × 50mm, and a release sheet was peeled off, and after the pressure-sensitive adhesive layer side was bonded to alkali-free glass (EAGLE XG, manufactured by corning corporation, thickness 1.1mm), autoclave treatment (50 ℃ × 0.5MPa × 20 minutes) was performed, and the pressure-sensitive adhesive layer-attached PET film was irradiated with a high-pressure mercury UV irradiation apparatus from the PET film side at peak illuminance: 150mW/cm2Cumulative exposure amount: 2000mJ/cm2(1000mJ/cm2X 2pass) and left to stand at 23 ℃ x 50% RH for 30 minutes, thereby producing a test piece having a structure of "alkali-free glass/adhesive layer/PET film".
The obtained test piece was subjected to a wet heat resistance test for 168 hours in an atmosphere of 60 ℃ x 90% RH, and the haze values before the start of the wet heat resistance test and after the wet heat resistance test were measured and evaluated according to the following criteria. The haze value was measured by the same method as the measurement of the optical properties of the pressure-sensitive adhesive layer.
(evaluation)
Haze value after moist-heat resistance test of less than 2.0%, and rate of rise of haze value before and after the moist-heat resistance test of 20% or less
The haze value immediately after the delta wet-heat resistance test was less than 2.0%, and the rise ratio of the haze value before and after the wet-heat resistance test was more than 20%.
Haze value immediately after x moist-heat resistance test of 2.0% or more
The increase (%) in the haze value before and after the wet heat resistance test was determined by the following formula.
Percent increase (%) - (after-test haze value-before-test haze value)/before-test haze value × 100
[ thermal stability ]
The above substrate-free double-sided adhesive sheet was cut into 30mm × 50mm, and irradiated with a high-pressure mercury UV irradiation device at peak illuminance: 150mW/cm2Cumulative exposure amount: 2000mJ/cm2(1000mJ/cm2X 2pass) was irradiated with ultraviolet rays. Then, the release sheet on one side was peeled off from the adhesive layer, the adhesive layer side was bonded to alkali-free glass (EAGLE XG, 1.1mm in thickness, manufactured by corning corporation), and then the other release sheet was peeled off, and alkali-free glass (EAGLE XG, manufactured by corning corporation) was bonded to the other side, and autoclave treatment (50 ℃ c. × 0.5MPa × 20 minutes) was performed to prepare a test sheet having a structure of "alkali-free glass/adhesive layer/alkali-free glass".
Using the test piece obtained, a thermal stability test was conducted at 150 ℃ for 168 hours, and b after the thermal stability test was measured*The values were evaluated according to the following criteria. b*The value was measured by the same method as the measurement of the optical properties of the pressure-sensitive adhesive layer.
(evaluation)
O. b immediately after the thermal stability test*A value of 0.5 or less
B immediately after the thermal stability test*A value greater than 0.5
[ relative dielectric constant ]
The release sheet on one side was peeled from the adhesive layer of the above base-less double-sided adhesive sheet and pressed onto an untreated PET film (thickness: 50 μm), and then the other release sheet was peeled and pressed onto the same untreated PET film, thereby obtaining a PET film with an adhesive layer having a structure of "PET film/adhesive layer/PET film".
The above PET film with an adhesive layer was cut into 7cm × 7cm, and irradiated with a high-pressure mercury UV irradiation device at peak illuminance: 150mW/cm2Cumulative exposure amount: 2000mJ/cm2(1000mJ/cm2X 2pass) was irradiated with ultraviolet rays.
The dielectric constant of the adhesive layer was calculated from the change in capacitance between the electrodes by applying an electric field at a frequency of 100Hz to the test piece for measuring the dielectric constant between the electrodes in an atmosphere of 23 ℃ x 50% RH using a HP4284A precision LCR meter (Agilent). Then, the relative permittivity was calculated from the obtained permittivity.
(evaluation)
A relative dielectric constant of the adhesive layer at 100KHz of 3.0 or less
A relative dielectric constant of the adhesive layer at 100KHz of greater than 3.0
[ Table 2]
Figure BDA0001960780250000301
The pressure-sensitive adhesive sheets using the pressure-sensitive adhesive compositions of examples 1 and 2 had low dielectric constant and good balance between thermal stability and moist heat resistance.
On the other hand, comparative example 1, in which the content of the hydroxyl group-containing (meth) acrylate monomer (a1) was small, was inferior in moist heat resistance.
In addition, comparative example 2, in which the content of the alkyl (meth) acrylate monomer (a2-1) having a linear alkyl group having 10 to 24 carbon atoms was small, was poor in thermal stability and high in relative permittivity.
The above embodiments show specific modes of the present invention, but the above embodiments are merely illustrative and are not to be construed as limiting. It is intended that all such modifications as would be obvious to one skilled in the art are within the scope of this invention.
Industrial applicability
The acrylic adhesive composition of the present invention can be applied by thick coating, and the adhesive using the composition is free from yellowing of resin due to heating, has excellent thermal stability, low dielectric constant, and further excellent moist heat resistance, impact absorption, and step following properties, and is therefore useful particularly as an adhesive used for bonding optical members constituting touch panels, image display devices, and the like, sealing applications of organic EL displays, and the like.

Claims (8)

1. An acrylic adhesive composition comprising an acrylic resin (A) which is a copolymer containing a copolymerization component of a hydroxyl group-containing (meth) acrylate monomer (a1) and an alkyl (meth) acrylate monomer (a2),
the alkyl (meth) acrylate monomer (a2) contains an alkyl (meth) acrylate monomer (a2-1) having a C10-24 linear alkyl group and an alkyl methacrylate monomer (a2-2) having a C4-8 alkyl group,
the copolymerization component contains 5-15 wt% of hydroxyl group-containing (meth) acrylate monomer (a1), 50-94 wt% of alkyl (meth) acrylate monomer (a2-1) having a C10-24 linear alkyl group, 0.1-20 wt% of the alkyl methacrylate monomer (a2-2) having a C4-8 alkyl group,
the content ratio of the alkyl (meth) acrylate monomer having a linear alkyl group and the alkyl (meth) acrylate monomer having a branched alkyl group in the alkyl (meth) acrylate monomer (a2) in the copolymerization component is 100/0 to 70/30 in terms of weight ratio.
2. The acrylic adhesive composition according to claim 1, wherein the weight average molecular weight of the acrylic resin (a) is 15 to 150 ten thousand.
3. The acrylic adhesive composition according to claim 1 or 2, wherein the acrylic resin (a) has an active energy ray-crosslinkable structural moiety.
4. The acrylic adhesive composition according to claim 3, wherein the active energy ray-crosslinkable structural moiety is a benzophenone-based crosslinking structure.
5. The acrylic adhesive composition according to claim 1 or 2, wherein the volatile content in the acrylic resin (a) is 2% by weight or less.
6. An adhesive comprising the acrylic adhesive composition according to any one of claims 1 to 5.
7. An adhesive sheet comprising an adhesive layer formed from the acrylic adhesive composition according to any one of claims 1 to 5.
8. The adhesive sheet according to claim 7, wherein the adhesive layer is an adhesive layer obtained by curing an acrylic adhesive composition with an active energy ray.
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