Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2001-05-30
2003-11-11
Berman, Susan W. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S345000, C428S3550AC, C522S035000, C522S113000, C522S114000, C522S152000, C522S120000, C522S121000
Reexamination Certificate
active
06645617
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a solvent type or emulsion type pressure-sensitive adhesive composition which is curable with active energy beams, and relates to a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed of the above pressure-sensitive adhesive composition, which can be of great utility in the technical fields utilizing them.
BACKGROUND ART
Hitherto, pressure-sensitive adhesive compositions, particularly solvent type pressure-sensitive acrylic adhesive compositions, comprises acrylic polymers as main components which are often crosslinked for improvement of holding power. For performing the crosslinking, polyisocyanate compounds or the like that rapidly react at room temperature are generally used as crosslinking agents. In many cases, the pressure-sensitive adhesive compositions are coated on substrates and dried to form an adhesive layer, and thus these are used as pressure-sensitive adhesive sheets.
In the conventional pressure-sensitive adhesive compositions of the type of one-pack with which the crosslinking agent has been blended, however, polyisocyanate compounds as the crosslinking agent react at room temperature to cause deterioration of storage stability. Hence, in many cases, the compositions are used in a form of two-pack type according to which the acrylic polymer and the crosslinking agent are handled separately. However, the two-pack compositions still suffer from the problem that coatability is damaged because there are limitations in pot life or in some case the crosslinking partially proceeds before use.
Also, acrylic emulsion type pressure-sensitive adhesive compositions are often used together with crosslinking agents such as water-soluble epoxy resins and made into two-pack type compositions according to applications thereof for the purpose of improving cohesive strength of the adhesives. In this case, after being coated on a substrate, they require a heating step or an aging step for a long period, and thus are hard to produce.
Active energy beam-curable, pressure-sensitive adhesive compositions comprising (meth)acrylates are known as compositions which solve the problems in the conventional pressure-sensitive adhesive compositions. Since the pressure-sensitive compositions are crosslinked and cured by irradiation with active energy beams such as ultraviolet rays, electron beams, etc., they can be used as one-pack type compositions.
However, the compositions have the problem of odor of cured products. In other words, many of the conventional active energy beam-curable, pressure-sensitive adhesive compositions are insufficient in curability and sometimes generate an odor due to unreacted monomers remaining in the cured products. Moreover, when the compositions are cured with ultraviolet rays, a photopolymerization initiator must be added to the compositions. Even if the compositions curable with ultraviolet rays are excellent in curability, decomposition product of the photopolymerization initiator remains in the cured products and hence the cure products have an odor.
The inventors have conducted intensive researches in an attempt to find pressure-sensitive adhesive compositions and adhesive sheets which can be used as one-pack type, are excellent in storage stability, require no step for heating, aging or the like, and can give cured products that are excellent in adhesion and odorless.
DISCLOSURE OF INVENTION
As a result of various investigations, the inventors have found that a composition containing a copolymer having an imide (meth)acrylate of a specific structure as a constitutional monomer unit has excellent curability upon irradiation with ultraviolet rays without addition of a photopolymerization initiator or with addition of a small proportion of photopolymerization initiator and provides a cured product thereof which is substantially odorless, and besides the composition requires no steps such as for heating and aging, and is excellent in performance as a pressure-sensitive adhesive. Thus, the present invention has been accomplished.
The present invention will be explained in detail below.
In this specification, acrylate or methacrylate is called (meth)acrylate, and acrylic acid or methacrylic acid is called (meth)acrylic acid.
BEST MODE FOR CARRYING OUT THE INVENTION IMIDE (METH)ACRYLATE
The copolymer used in the composition of the present invention is a copolymer containing an imide (meth)acrylate represented by the following formula (1) (hereinafter referred to as merely “imide (meth)acrylate”) as a constitutional monomer unit.
In the above formula (1), R
1
and R
2
each independently is a hydrogen atom or an alkyl group of 4 or less carbon atoms, one of R
1
and R
2
is a hydrogen atom whilst another is an alkyl group of 4 or less carbon atoms, or R
1
and R
2
are bonded to each other to form a carbon ring; R
3
is an alkylene group of 1-6 carbon atoms; R
4
is a hydrogen atom or a methyl group; and n is an integer of 1-6.
In the above formula (1), n is preferably 1-2, more preferably 1 because the resulting copolymer is superior in curability.
Preferably, R
1
and R
2
each independently is an alkyl group of 4 or less carbon atoms or R
1
and R
2
are bonded to each other to form a carbon ring because of superior copolymerizability with an ethylenically unsaturated group-containing monomer. It is further preferred that R
1
and R
2
are bonded to each other to form a carbon ring, more preferably a group —CH
2
CH
2
CH
2
— or a group —CH
2
CH
2
CH
2
CH
2
—, especially preferably a group —CH
2
CH
2
CH
2
CH
2
— because the imide (meth)acrylate is easy to produce with high yield, and the resulting copolymer is superior in water resistance.
R
3
is an alkylene group of 1-6 carbon atoms, preferably an ethylene group, a propylene group or the like.
Preferable examples of imide (meth)acrylate include compounds represented by the following formula (2) and formula (3).
The compounds of the formula (2) are those of the formula (1) where R
1
and R
2
are boned to each other and represented by a group —CH
2
CH
2
CH
2
CH
2
— to form a carbon ring, R
3
is an ethylene group, R
4
is a hydrogen atom, and n is 1.
The compounds of the formula (3) are those of the formula (1) where R
1
and R
2
are bonded to each other and represented by a group —CH
2
CH
2
CH
2
CH
2
— to form a carbon ring, R
3
is an ethylene group, R
4
is a methyl group, and n is 1.
The imide (meth)acrylate can be produced from an acid anhydride, an amino alcohol and a (meth)acrylic acid by the processes disclosed in the following literatures and patent publications.
Kiyoshi Kato et al, “Journal of Synthetic Organic Chemistry Association (Yukigoseikagaku Kyokai-shi)”, 30 (10), 897, (1972).
Javier de Abajo et al, “Polymer”, vol.33 (5), (1992).
JP-A-56-53119
JP-A-1-242569
As the acid anhydride used as a starting material, mention may be made of 3,4,5,6-tetrahydrophthalic anhydride and derivatives thereof and dialkylmaleic anhydrides and derivatives thereof. Because of giving high yields, 3,4,5,6-tetrahydrophthalic anhydride and derivatives thereof are preferred.
Examples of the amino alcohol used as a starting material are alkanolamines such as ethanolamine, propanolamine and butanolamine, 2,2′-aminoethoxyethanol and the like.
Copolymers
The copolymers used in the present invention comprise 0.1-30% by weight of an imide (meth)acrylate and 70-99.9% by weight of an ethylenically unsaturated group-containing monomer (hereinafter referred to as “unsaturated monomer”) preferably 0.1-3% by weight of an imide (meth)acrylate and 97-99.9% by weight of an unsaturated monomer as constitutional monomer units. Since the copolymers used in the present invention have the maleimide group represented by the formula (1), they are readily cured with active energy beams, and besides even when they are cured with ultraviolet rays, they show excellent curability without addition of photopolymerization initiators or with addition of a small amount of photopolymerization initiators, and the crosslinked, cured products thereof provide pressur
Jitsumatsu Tetsuji
Okazaki Eiichi
Berman Susan W.
Fitch Even Tabin & Flannery
Toagosei Co. Ltd.
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