JP7292239B2 - Adhesive composition and adhesive sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to an adhesive composition and an adhesive sheet.

Conventionally, non-reactive (meth)acrylic pressure-sensitive adhesives that do not require a cross-linking agent that produces chemical bonds, such as hot-melt pressure-sensitive adhesives, are known (see, for example, Patent Document 1).

JP 2009-108185 A

Conventional non-reactive (meth)acrylic pressure-sensitive adhesives have low heat resistance, such as noticeable displacement in a holding power test in a high-temperature environment. According to the studies of the present inventors, if the glass transition temperature of the (meth)acrylic polymer is increased in order to impart heat resistance to the pressure-sensitive adhesive, another problem arises in that the initial adhesive strength (tack) of the pressure-sensitive adhesive is impaired. I found out.

An object of the present invention is to provide a (meth)acrylic pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet that are excellent in holding power in a high-temperature environment and have an appropriate initial adhesive strength (tack).

The present inventors have conducted studies to solve the above problems, and as a result, have found that the above problems can be solved by a pressure-sensitive adhesive composition having the following structure, and have completed the present invention. That is, the configuration of the present invention is, for example, as follows.

[1] A pressure-sensitive adhesive composition containing a (meth)acrylic triblock polymer (a), a (meth)acrylic polymer (b), and a tackifier (c), wherein the (meth)acrylic triblock polymer (a) has a block structure represented by ABA consisting of block A and block B (the two blocks A may be the same or different), and has a weight average molecular weight (Mw) of 50, 000 to 500,000, and block A is selected from structural units derived from the hydrogen-bonding functional group-containing monomer (a1), (meth)acrylic acid alkyl esters and (meth)acrylic acid alicyclic group-containing esters A polymer block having a structural unit derived from at least one monomer (a2) and having a glass transition temperature (Tg) of 0° C. or higher, wherein the block B is a (meth)acrylic acid alkyl ester (a3)-derived a polymer block having a Tg of −20° C. or less, a (meth)acrylic polymer (b) having a structural unit derived from a (meth)acrylic acid alkyl ester (b1), and an Mw of 1,000 to 10,000, the pressure-sensitive adhesive composition.

[2] In 100% by mass of the (meth)acrylic triblock polymer (a), the proportion of the structural unit derived from the monomer (a1) in the block A is 1 to 15% by mass, and The proportion of the structural unit is 4 to 39% by mass, and the total proportion of the structural unit derived from the monomer (a1) and the structural unit derived from the monomer (a2) is 5 to 40% by mass. , The pressure-sensitive adhesive composition according to [1] above, wherein the proportion of structural units derived from the (meth)acrylic acid alkyl ester (a3) is 60 to 95% by mass.

[3] The content of the (meth)acrylic polymer (b) is 5 to 100 parts by mass with respect to 100 parts by mass of the (meth)acrylic triblock polymer (a), and the tackifier (c) is contained. The pressure-sensitive adhesive composition according to [1] or [2], wherein the amount is 5 to 100 parts by mass.

[4] Block B of the (meth)acrylic triblock polymer (a) and the (meth)acrylic polymer (b) have at least 80% by mass of structural units derived from a common monomer, above [1] The pressure-sensitive adhesive composition according to any one of to [3].

[5] The pressure-sensitive adhesive composition according to any one of [1] to [4], further containing an organic solvent.
[6] The pressure-sensitive adhesive composition according to any one of [1] to [5], further containing a metal chelate compound.

[7] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of [1] to [6].
[8] The pressure-sensitive adhesive sheet according to [7], wherein the pressure-sensitive adhesive layer has a gel fraction of 0% by mass.

According to the present invention, it is possible to provide a (meth)acrylic pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet that are excellent in holding power in a high-temperature environment and have an appropriate initial adhesive strength (tack).

As used herein, (meth)acryl means acrylic and/or methacrylic, and (meth)acrylate means acrylate and/or methacrylate.

[Adhesive composition]
The pressure-sensitive adhesive composition of this embodiment contains a (meth)acrylic triblock polymer (a), a (meth)acrylic polymer (b), and a tackifier (c).

<(Meth)acrylic triblock polymer (a)>
The (meth)acrylic triblock polymer (a) (hereinafter also referred to as “triblock polymer (a)”) has a block structure represented by ABA consisting of block A and block B. Two blocks A may be the same or different.

≪Block A≫
Block A comprises a structural unit derived from a hydrogen-bonding functional group-containing monomer (a1) and at least one monomer (a2) selected from (meth)acrylic acid alkyl esters and (meth)acrylic acid alicyclic group-containing esters. and a polymer block having a glass transition temperature (Tg) of 0° C. or higher. Block A is thought to form a microphase-separated structure and exhibit cohesive force by causing pseudo-crosslinking, and exhibits high heat resistance because it is a polymer block with a high glass transition temperature.

Examples of the hydrogen-bonding functional group-containing monomer (a1) (hereinafter also referred to as "monomer (a1)") include monomers having a hydrogen-bonding functional group such as a carboxy group, a hydroxy group, and a nitrogen-containing group.

Carboxy group-containing monomers include, for example, β-carboxyethyl (meth)acrylate, 5-carboxypentyl (meth)acrylate, mono(meth)acryloyloxyethyl succinate, ω-carboxypolycaprolactone mono(meth)acrylate. carboxy group-containing (meth)acrylates such as; (meth)acrylic acid, itaconic acid, crotonic acid, fumaric acid and maleic acid.

Examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl ( Hydroxyalkyl (meth)acrylates such as meth)acrylates can be mentioned.

Monomers having a nitrogen-containing group include, for example, amino group-containing monomers, amide group-containing monomers, nitrogen-based heterocyclic ring-containing monomers, and cyano group-containing monomers. Examples of amino group-containing monomers include amino group-containing ( meth)acrylates. Examples of amide group-containing monomers include (meth)acrylamide, N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-hexyl(meth)acrylamide, diacetoneacrylamide, N-methylaminopropyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide. Nitrogen-based heterocyclic ring-containing monomers include, for example, vinylpyrrolidone, acryloylmorpholine, and vinylcaprolactam. Examples of cyano group-containing monomers include cyano(meth)acrylate and (meth)acrylonitrile.

Since the triblock polymer (a) has structural units derived from the monomer (a1), it has a high cohesive force even at a low gel fraction compared to ordinary (meth)acrylic pressure-sensitive adhesives. It has a sufficiently high cohesive strength without using a curing period.

The (meth)acrylic acid alkyl ester in the monomer (a2) includes, for example, a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 18 carbon atoms (CH ₂ ═CR ¹ —COOR ² ; R ¹ is a hydrogen atom or is a methyl group and R ² is an alkyl group having 1 to 18 carbon atoms), and a (meth)acrylic acid alkyl ester having a homopolymer Tg of 0° C. or higher is preferable. Specifically, methyl acrylate, n-propyl acrylate, t-butyl acrylate, pentyl acrylate, tetradecyl acrylate, hexadecyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, hexadecyl A methacrylate is mentioned.

Examples of the (meth)acrylic acid alicyclic group-containing ester in the monomer (a2) include cyclohexyl (meth)acrylate and isobornyl (meth)acrylate. Alicyclic group-containing esters are preferred.

For the Tg of the homopolymer of each monomer, the value described in the later-described Polymer Handbook or the value obtained by the method (DSC) described later can be adopted.

Block A may further have structural units derived from other monomers in addition to the structural units derived from the monomer (a1) and the structural units derived from the monomer (a2). Other monomers include, for example, alkoxyalkyl (meth)acrylates, alkoxypolyalkylene glycol mono(meth)acrylates, and aromatic ring-containing (meth)acrylates.

In 100% by mass of the triblock polymer (a), the proportion of structural units derived from the monomer (a1) in the block A is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, and more It is more preferably 7% by mass or more, preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 10% by mass or less. Block A has a structural unit derived from the monomer (a1) to improve heat resistance, and the structural unit can further improve heat resistance by interacting with a metal chelate compound described later. Become.

In addition, in the triblock polymer (a), self-organization occurs immediately after coating of the pressure-sensitive adhesive composition, and it is considered that blocks A having hydrogen-bonding functional groups are aggregated. As a result, the functional groups are brought closer to each other, and in the case of using a metal chelate compound, for example, it is thought that the reaction with the metal chelate compound accelerates the cross-linking between the polymers.

In 100% by mass of the triblock polymer (a), the proportion of structural units derived from the monomer (a2) in the block A is preferably 4% by mass or more, more preferably 10% by mass or more, and preferably 39% by mass or less. More preferably 35% by mass or less, still more preferably 30% by mass or less, and even more preferably 25% by mass or less.

In 100% by mass of the triblock polymer (a), the total ratio of the structural units derived from the monomer (a1) and the structural units derived from the monomer (a2) in the block A is preferably 5% by mass or more, more preferably 10% by mass. Above, more preferably 15% by mass or more, preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less.

Block A is a polymer block having a glass transition temperature (Tg) of 0° C. or higher, and the Tg is preferably 30° C. or higher, more preferably 50° C. or higher, still more preferably 100° C. or higher, and preferably 200° C. or higher. °C or less, more preferably 150°C or less. A polymer block having such a Tg is excellent in heat resistance and can exhibit cohesive force acting as a physical pseudo-crosslinking point.

In this specification, the glass transition temperature (Tg) of the polymer block can be calculated by the Fox formula. For example, the polymer block can be synthesized so that the glass transition temperature (Tg) determined by the Fox equation falls within the above range.
Fox's formula: 1/Tg=( _W1 / _Tg1 )+( _W2 / _Tg2 )+...+( _Wm / _Tgm )
_W1 + _W2 +...+ _Wm =1
In the above formula, Tg is the glass transition temperature (unit: K) of the polymer block, Tg _{1 ,} Tg ₂ , . W ₁ , W _{2 ,} . As the mass fraction of the constituent units derived from each monomer, the charging ratio of each monomer to all monomers at the time of polymer block synthesis can be used.

When calculating the Fox formula, the glass transition temperature (Tg) of the homopolymer formed from each monomer can adopt, for example, the value described in Polymer Handbook Fourth Edition (Wiley-Interscience 2003).

Tg, which is not described in the above literature, can be measured by, for example, a differential scanning calorimeter (DSC). The DSC measurement conditions were as follows: 5 mg of sample, under a nitrogen atmosphere. In the first measurement (1st RUN), the temperature was raised from -100°C to 200°C at a temperature increase rate of 20°C/min, and then the temperature decrease rate was 99.9°C. /min to -100°C, and in the second measurement (2nd RUN), the temperature is raised from -100°C to 200°C at a heating rate of 20°C/min. Here, the glass transition temperature is the region where the baseline of the DSC curve measured when the temperature is raised from −100° C. to 200° C. in the 2nd RUN changes to a sigmoid shape in the endothermic direction, which is lower than the region where it changes to a sigmoid shape. It refers to the intersection of the extension of the baseline on the side and the tangent to the point of inflection in the sigmoid.

≪Block B≫
Block B is a polymer block having a structural unit derived from (meth)acrylic acid alkyl ester (a3) and having a glass transition temperature (Tg) of −20° C. or lower. Block B must have a composition different from that of block A in order to form a microphase-separated structure, and must have a low glass transition temperature in order to develop an appropriate initial adhesive strength (tack). .

The (meth)acrylic acid alkyl ester (a3) includes, for example, a (meth)acrylic acid alkyl ester (CH ₂ ═CR ³ —COOR ⁴ ; R ³ is a hydrogen atom or a methyl group and R ⁴ is an alkyl group having 1 to 18 carbon atoms), and a (meth)acrylic acid alkyl ester having a homopolymer Tg of −20° C. or less is preferable. Specifically, ethyl acrylate, n -Butyl acrylate, isobutyl acrylate, hexyl acrylate, octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, octyl methacrylate, isooctyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tetradecyl methacrylate. For the Tg of the homopolymer of each monomer, the value described in the above-mentioned Polymer Handbook or the value obtained by the above-mentioned method (DSC) can be adopted.

As long as the Tg of the block B is -20°C or lower, the block B may have structural units derived from (meth)acrylic acid alkyl esters whose homopolymer Tg exceeds -20°C. For example, (meth)acrylic acid alkyl esters whose homopolymer Tg is above −20° C. and below 0° C. are preferred, and include isopropyl acrylate, lauryl acrylate, pentyl methacrylate, hexyl methacrylate, and 2-ethylhexyl methacrylate.

Block B may further have structural units derived from other monomers in addition to the structural units derived from the (meth)acrylic acid alkyl ester (a3). Other monomers include, for example, alkoxyalkyl (meth)acrylates, alkoxypolyalkylene glycol mono(meth)acrylates, alicyclic group-containing (meth)acrylates, and aromatic ring-containing (meth)acrylates.

In 100% by mass of the triblock polymer (a), the proportion of structural units derived from the (meth)acrylic acid alkyl ester (a3) in the block B is preferably 60% by mass or more, more preferably 65% by mass or more, and still more preferably It is 70% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

Block B is a polymer block having a glass transition temperature (Tg) of −20° C. or lower, preferably −30° C. or lower, preferably −80° C. or higher, more preferably −70° C. or higher, More preferably -60°C or higher. A polymer block having such a Tg is preferable from the viewpoint of exhibiting appropriate initial adhesive strength (tack) and adhesive strength at low temperatures. The Tg of block B can be obtained by a method similar to that of block A.

The difference between the Tg of block A and the Tg of block B is preferably 50°C or higher, more preferably 100°C or higher, even more preferably 130°C or higher, and even more preferably 150°C or higher. With such an aspect, it is believed that self-assembly of block A and self-assembly of block B between molecules of the triblock polymer (a) are promoted, thereby providing a microphase-separated structure in the pressure-sensitive adhesive. is self-organized and block A works as a pseudo cross-linking point.

Block B is preferably a polymer block substantially free of structural units derived from the hydrogen-bonding functional group-containing monomer (a1). The proportion of structural units derived from the hydrogen-bonding functional group-containing monomer (a1) in block B is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

<<Composition of triblock polymer (a)>>
The weight average molecular weight (Mw) of the triblock polymer (a) is 50,000 or more, preferably 70,000 or more, more preferably 100,000 or more, and 500,000 or less, preferably 450,000 or less, and more Preferably it is 400,000 or less.

The molecular weight distribution (weight average molecular weight (Mw)/number average molecular weight (Mn)) of the triblock polymer (a) is preferably 3.0 or less, more preferably 2.0 or less.
Mw and Mn can be determined by a gel permeation chromatography method (GPC method).

The proportion of block A in the triblock polymer (a) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass. % by mass or less, more preferably 30% by mass or less. The proportion of block A is the total proportion of two blocks A in the block structure represented by ABA.

The proportion of block B in the triblock polymer (a) is preferably 60% by mass or more, more preferably 65% by mass or more, still more preferably 70% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass. % by mass or less, more preferably 85% by mass or less.

When the proportion of block A is 5% by mass or more, the pressure-sensitive adhesive tends to favorably form a pseudo-crosslinked structure. When the proportion of block A is 40% by mass or less, the triblock polymer does not become too hard and tends to have an excellent balance of properties.

The triblock polymer (a) can be produced using general living radical polymerization, and among these, from the viewpoint of ease of control of the polymerization reaction, nitroxide-mediated radical polymerization and atom transfer radical polymerization are used. It can be suitably manufactured by The atom transfer radical polymerization method is a polymerization method using an organic halide or a sulfonyl halide compound as an initiator and a metal complex as a catalyst.

When the triblock polymer (a) is produced by a living radical polymerization method, a method of sequentially adding monomer units, a method of polymerizing the next polymer block using a polymer synthesized in advance as a polymer initiator, and a method of polymerizing separately polymerized Examples include a method of combining coalesced blocks by reaction, but it is preferable to produce the triblock polymer (a) by a method of sequential addition of monomer units.

When the triblock polymer (a) is produced by sequential addition of monomer units, the order of addition of the monomer components constituting block A and the monomer components constituting block B is not particularly limited, but block B is produced first. Thus, the production of block A from the polymerization end of block B facilitates polymerization control.

In addition, by producing the triblock polymer (a) by a bulk polymerization method, it can be used as a hot-melt pressure-sensitive adhesive that does not contain an organic solvent, or as an energy ray-curable pressure-sensitive adhesive by diluting it with a (meth)acrylic monomer. A product form is also possible, and it is also possible to use it as an environmentally friendly adhesive.
One or more triblock polymers (a) can be used.

The content of the triblock polymer (a) in the adhesive composition of the present embodiment is preferably 35% by mass or more, more preferably 40% by mass or more, and still more preferably 45% by mass or more in the solid content of the composition. is. The upper limit is defined by other components. The solid content is all components except the organic solvent described later. In addition, the pressure-sensitive adhesive composition of the present embodiment can be a hot-melt pressure-sensitive adhesive that does not contain an organic solvent. In that case, the content ratio of the triblock polymer (a) is The whole.

According to the present invention, by using a (meth)acrylic polymer (b) having good compatibility with the triblock polymer (a) and a tackifier (c) together with the triblock polymer (a), heat-resistant It is possible to obtain a PSA composition and a PSA sheet which are excellent in properties such as adhesiveness, initial adhesive strength (tack), and olefin adhesiveness and which do not require aging.

<(Meth)acrylic polymer (b)>
The (meth)acrylic polymer (b) has structural units derived from the (meth)acrylic acid alkyl ester (b1).
The (meth)acrylic acid alkyl ester (b1) includes, for example, a (meth)acrylic acid alkyl ester (CH ₂ ═CR ⁵ —COOR ⁶ ; R ⁵ is a hydrogen atom or a methyl group and R ⁶ is an alkyl group having 1 to 18 carbon atoms). -Butyl acrylate, isobutyl acrylate, hexyl acrylate, octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, octyl methacrylate, isooctyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tetradecyl methacrylate. For the Tg of each monomer homopolymer, the value described in the above-mentioned literature (Polymer Handbook) or the value obtained by the above-mentioned method (DSC) can be adopted.

Examples of the (meth)acrylic acid alkyl esters include (meth)acrylic acid alkyl esters having a homopolymer Tg of more than −20° C. and 0° C. or less, such as isopropyl acrylate, lauryl acrylate, pentyl methacrylate, and hexyl methacrylate. , 2-ethylhexyl methacrylate.

The proportion of structural units derived from the (meth)acrylic acid alkyl ester (b1) in the (meth)acrylic polymer (b) is preferably 90% by mass or more, more preferably 93% by mass or more, and still more preferably 95% by mass or more. is.

The (meth)acrylic polymer (b) is a component that improves the initial adhesive strength (tack) of the adhesive composition. Here, the (meth)acrylic polymer (b) has structural units derived from the (meth)acrylic acid alkyl ester (b1), and thus has excellent compatibility with the triblock polymer (a). In particular, the (meth)acrylic polymer (b) preferably has the same or similar composition as the block B constituting the triblock polymer (a). Such a (meth)acrylic polymer (b) has excellent compatibility with the triblock polymer (a) and exhibits high initial adhesive strength (tack). Poor compatibility between the (meth)acrylic polymer (b) and the triblock polymer (a) not only reduces the heat resistance, but also causes the (meth)acrylic polymer (b) to bleed out, resulting in adhesive strength. may decrease.

Therefore, the block B of the triblock polymer (a) and the (meth)acrylic polymer (b) preferably have a common monomer-derived structural unit in 80% by mass or more, more preferably 90% by mass or more. is. Specifically, the block B of the triblock polymer (a) and the (meth)acrylic polymer (b) may have a structural unit derived from a common (meth)acrylic acid alkyl ester in 80% by mass or more. It is preferably 90% by mass or more, more preferably 90% by mass or more.

The weight average molecular weight (Mw) of the (meth)acrylic polymer (b) is 1,000 or more, preferably 1,200 or more, more preferably 1,500 or more, from the viewpoint of improving the compatibility, It is 10,000 or less, preferably 8,000 or less, more preferably 5,000 or less.
Mw and Mn can be determined by a gel permeation chromatography method (GPC method).

The glass transition temperature (Tg) of the (meth)acrylic polymer (b) is preferably −20° C., more preferably −30° C. or lower, preferably −80° C. or higher, more preferably −70° C. or higher, and further It is preferably -60°C or higher. Tg can be calculated by the above-mentioned Fox formula.

The (meth)acrylic polymer (b) can be produced using a general polymerization method, for example, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. Specifically, a polymerization solvent and monomer components, a dispersion stabilizer and an emulsifier in the case of a suspension polymerization method or an emulsion polymerization method are charged into a reaction vessel, and a polymerization initiator is added under an inert gas atmosphere such as nitrogen gas. Then, the reaction initiation temperature is set to 50 to 90°C, the temperature of the reaction system is maintained at 50 to 90°C, and the reaction is carried out for 4 to 20 hours.
One or two or more (meth)acrylic polymers (b) can be used.

The content of the (meth)acrylic polymer (b) in the adhesive composition of the present embodiment is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, relative to 100 parts by mass of the triblock polymer (a). , more preferably 12 parts by mass or more, preferably 100 parts by mass or less, more preferably 90 parts by mass or less, and even more preferably 80 parts by mass or less.

<Tackifier (c)>
The tackifier (c) is a component that improves adhesion to low-polar adherends such as polyolefins (eg, polypropylene). The tackifier (c) is not particularly limited as long as it improves adhesive strength, and examples thereof include aliphatic petroleum resins (C5 petroleum resins), aromatic petroleum resins (C9 petroleum resins), and dicyclopentadiene. Alicyclic petroleum resins such as petroleum resins (DCPD petroleum resins), aliphatic/aromatic copolymer petroleum resins, alicyclic/aromatic copolymer petroleum resins, aliphatic/alicyclic copolymers Petroleum resins such as petroleum resins and hydrogenated petroleum resins obtained by hydrogenating these petroleum resins; terpene-based resins; rosin-based resins; tackifying resins such as coumarone-based resins and indene-based resins.
Among these, a terpene phenol-based tackifying resin is preferable because of its excellent compatibility with the triblock polymer (a).

The softening point of the tackifier (c) is preferably 50 to 200°C, more preferably 90 to 160°C, still more preferably 100 to 150°C. By using a tackifier having a softening point within the above range, the cohesive force of the composition is further improved, and a pressure-sensitive adhesive having excellent heat resistance can be obtained. The softening point is measured by the ring and ball method according to JIS K2207.
One or more tackifiers (c) can be used.

The content of the tackifier (c) in the pressure-sensitive adhesive composition of the present embodiment is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, relative to 100 parts by mass of the triblock polymer (a), It is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, and still more preferably 80 parts by mass.

<Metal chelate compound>
The triblock polymer (a) has sufficient cohesive force due to self-organization immediately after coating, and the pressure-sensitive adhesive composition containing the triblock polymer (a) becomes a pressure-sensitive adhesive that does not require a curing period. Therefore, the addition of a curing agent is not necessarily required, but from the viewpoint of further improving heat resistance, the pressure-sensitive adhesive composition of the present embodiment may further contain a metal chelate compound.

As metal chelate compounds, for example, polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium are coordinated with alkoxides, acetylacetone, ethyl acetoacetate, and the like. compound. Among these, aluminum chelate compounds are particularly preferred. Specific examples include aluminum iso-propylate, aluminum sec-butylate, aluminum ethylacetoacetate/diiso-propylate, aluminum trisethylacetoacetate and aluminum trisacetylacetonate.

The metal chelate compound crosslinks the triblock polymer (a) through coordinate bonds (pseudo-crosslinking). When a metal chelate compound is used, crosslinking is completed immediately after coating, and curing is not required.
One or more metal chelate compounds can be used.

When a metal chelate compound is used, the content of the metal chelate compound in the adhesive composition of the present embodiment is preferably 0.01 parts by mass or more, more preferably 0 parts by mass, relative to 100 parts by mass of the triblock polymer (a). .1 parts by mass or more, preferably 5 parts by mass or less, more preferably 2 parts by mass or less.

<Additive>
In addition to the above components, the pressure-sensitive adhesive composition of the present embodiment contains antioxidants, light stabilizers, metal corrosion inhibitors, plasticizers, cross-linking accelerators, nanoparticles, and silane cups within a range that does not impair the effects of the present invention. Additives such as ring agents may be contained. Additives can be used alone or in combination of two or more.

<Organic solvent>
The pressure-sensitive adhesive composition of the present embodiment is preferably a hot-melt pressure-sensitive adhesive that does not contain an organic solvent from the viewpoint of reducing environmental load. Even if the pressure-sensitive adhesive composition is diluted with a solvent, it exhibits sufficient performance as a one-component ageless pressure-sensitive adhesive composition.

Examples of organic solvents include aromatic hydrocarbons such as benzene, toluene and xylene; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane; cyclopentane, cyclohexane, cycloheptane, cyclo Alicyclic hydrocarbons such as octane; ethers such as diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, phenylethyl ether, diphenyl ether; chloroform, carbon tetrachloride, 1,2- Halogenated hydrocarbons such as dichloroethane and chlorobenzene; esters such as ethyl acetate, propyl acetate, butyl acetate and methyl propionate; ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone and cyclohexanone; N,N-dimethylformamide, N , N-dimethylacetamide and N-methylpyrrolidone; nitriles such as acetonitrile and benzonitrile; sulfoxides such as dimethylsulfoxide and sulfolane.
One or more organic solvents can be used.

<Preparation of adhesive composition>
The pressure-sensitive adhesive composition of the present embodiment can be prepared by mixing each component described above by a conventionally known method.
When the pressure-sensitive adhesive composition of the present embodiment is of a hot-melt type, the gel fraction of the pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition is preferably 0% by mass.

A gel fraction can be calculated|required as follows. About 0.1 g of the adhesive composition was collected in a sampling bottle, 30 mL of ethyl acetate was added, and the mixture was shaken for 4 hours. Dry at 100° C. for 2 hours and measure the dry mass. The gel fraction is calculated by the following formula.
Gel fraction (% by mass) = (dry mass/collected mass of pressure-sensitive adhesive composition) x 100 (%)

[Adhesive sheet]
The pressure-sensitive adhesive sheet of this embodiment has a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of this embodiment. Examples of the pressure-sensitive adhesive sheet include a double-sided pressure-sensitive adhesive sheet having only the pressure-sensitive adhesive layer, a double-sided pressure-sensitive adhesive sheet having a substrate and the pressure-sensitive adhesive layers formed on both sides of the substrate, and a substrate and one of the substrates. Single-sided pressure-sensitive adhesive sheets having the pressure-sensitive adhesive layer formed on one side, and pressure-sensitive adhesive sheets in which a release-treated cover film is attached to the side of the pressure-sensitive adhesive layer that is not in contact with the substrate.

As a method for applying the pressure-sensitive adhesive composition, known methods such as spin coating, knife coating, roll coating, bar coating, blade coating, die coating, and gravure coating may be used to obtain a predetermined thickness. A method of coating and drying can be used.

Examples of the substrate and cover film include polyester films such as polyethylene terephthalate (PET); and plastic films such as polyolefin films such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer.

The thickness of the pressure-sensitive adhesive layer is preferably 5 to 100 μm, more preferably 10 to 75 μm, from the viewpoint of maintaining adhesive performance and productivity. The thicknesses of the substrate and cover film are not particularly limited.

The pressure-sensitive adhesive sheet of the present embodiment can be used, for example, as an industrial pressure-sensitive adhesive sheet or for lamination of various resin films. It can be suitably used for fixing members that require heat resistance, such as members and members for electrical appliances. Moreover, the pressure-sensitive adhesive sheet of the present embodiment can also be suitably used as a decorative film.

EXAMPLES Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In the following descriptions of Examples and the like, "parts" means "parts by mass" unless otherwise specified.

[GPC]
The weight average molecular weight (Mw) and number average molecular weight (Mn) of (meth)acrylic triblock polymer and (meth)acrylic polymer were determined by gel permeation chromatography (GPC method) under the following conditions.
・ Measuring device: HLC-8320GPC (manufactured by Tosoh Corporation)
・ GPC column configuration: the following quadruple columns (all manufactured by Tosoh Corporation)
(1) TSKgel HxL-H (guard column)
(2) TSKgel GMHxL
(3) TSKgel GMHxL
(4) TSKgel G2500HxL
・Flow rate: 1.0 mL/min
・Column temperature: 40°C
・Sample concentration: 1.5% (w/v) (diluted with tetrahydrofuran)
・Mobile phase solvent: Tetrahydrofuran ・Converted to standard polystyrene

[Manufacturing example]
- (Meth) acrylic triblock polymer [Production Example 1]
75 parts of n-butyl acrylate (BA), 1,6-di[2-(N-tert-butyl-N-(1 -Diethylphosphono-2,2-dimethylpropyl)-N-oxyl)propionate] 1 part of hexylene alkoxyamine solution, N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) 0.07 part of the nitroxide solution was charged, the temperature was raised to 117° C. while nitrogen gas was introduced, and the polymerization reaction was carried out for 6 hours. After completion of the reaction, the mixture was diluted with 39 parts of toluene. Then, 22 parts of methyl methacrylate (MMA), 3 parts of methacrylic acid (MAA), and 108 parts of toluene were charged and reacted at 105° C. for 1 hour and 30 minutes while introducing nitrogen. After completion of the reaction, the solvent in the solution was volatilized using a dryer at 105 ° C. for 12 hours, the weight average molecular weight (Mw) was 200,000, and the molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn )) was 1.2 to obtain a (meth)acrylic triblock polymer (a-1).
The obtained (meth)acrylic triblock polymer is a triblock polymer having a structure in which block A and block B are represented by ABA, and the glass transition temperature of block A composed of MMA and MAA (Tg) was 113°C, and the glass transition temperature (Tg) of the B block composed of BA was -50°C.

[Production Examples 2, 5 to 15]
Except that the types and compounding ratios of the monomers (a1) and (a2), which are the components of block A, and the (meth)acrylic acid alkyl ester (a3), which is the component of block B, were changed as shown in Table 1. (Meth)acrylic triblock polymers (a-2), (a-5) to (a-12), and (a'-1) to (a'-3) were obtained in the same manner as in Production Example 1. .

[Production Example 3]
In the same manner as in Production Example 1, except that the N-tert-1-diethylphosphono-2,2-dimethylpropyl nitroxide solution was changed to 0.1 parts, MMA to 17 parts, and MAA to 8 parts, (meth ) An acrylic triblock polymer (a-3) was obtained.

[Production Example 4]
A (meth)acrylic triblock polymer (a-4 ).
・(Meth)acrylic polymer

[Production Example 16]
100 parts of n-butyl acrylate (BA) and 100 parts of ethyl acetate solvent were charged into a reactor equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen inlet tube, and heated to 75°C while introducing nitrogen gas. . Then, 7.0 parts of n-dodecylmercaptan (NDM) and 0.1 part of 2,2'-azobisisobutyronitrile (AIBN) were added to initiate a polymerization reaction at 75°C in a nitrogen gas atmosphere. Two hours later, 1.5 parts of AIBN was added, and 12 hours after the initiation of the polymerization reaction, the reaction was terminated to obtain a (meth)acrylic resin solution. After completion of the reaction, the solvent in the (meth)acrylic resin solution was volatilized using a dryer at 105° C. for 12 hours to obtain a weight average molecular weight (Mw) of 2,000 and a molecular weight distribution (weight average molecular weight (Mw )/number average molecular weight (Mn)) was 1.5 to obtain a (meth)acrylic polymer (b-1).

[Production Examples 17 to 20]
(Meth)acrylic polymers (b-2) to (b) were prepared in the same manner as in Production Example 16, except that the type and blending ratio of the (meth)acrylic acid alkyl ester (b1) were changed as shown in Table 1. -5) was obtained.
Abbreviations in Table 1 have the following meanings.
MMA: methyl methacrylate MA: methyl acrylate IBXA: isobornyl acrylate IBXMA: isobornyl methacrylate BA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate LA: lauryl acrylate MAA: methacrylic acid AA: acrylic acid 2HEA: 2-hydroxyethyl Acrylate AM: Acrylamide DMAEM: N,N-dimethylaminoethyl methacrylate

[Example 1]
The obtained (meth)acrylic triblock polymer (a-1) 100 parts, (meth)acrylic polymer (b-1) 15 parts, terpene phenol-based tackifying resin YS Polystar TH-130 (Yasuhara Chemical Co., Ltd. ) were mixed with 15 parts and melt-blended at 180° C. for 1 hour to obtain a hot-melt adhesive.

[Examples 2 to 16, Comparative Examples 1 to 3]
The types of the (meth)acrylic triblock polymer and the (meth)acrylic polymer, and the amounts of the (meth)acrylic polymer and the tackifying resin per 100 parts of the (meth)acrylic triblock polymer are as shown in Table 1. A hot-melt pressure-sensitive adhesive was obtained in the same manner as in Example 1, except for the changes. In Example 16, an aluminum chelate compound (M-5A (manufactured by Soken Chemical Co., Ltd.)) was also used as the metal chelate compound.

[Sample preparation]
The resulting hot-melt adhesive was sandwiched between 100 μm-thick release-treated PET films and hot-pressed at 200° C. for 1 hour at 1 MPa to form a 30 μm-thick adhesive layer. After that, the peel-treated PET film on one side was peeled off, and the exposed adhesive layer was attached to a PET film having a thickness of 25 μm to prepare an adhesive sheet.

[Adhesion test]
The prepared adhesive sheet was cut to a width of 25 mm and used as a test piece. It was pasted so as to be 100 mm, and crimped by reciprocating a 2 kg roller three times. After that, it was left in a 23° C. environment for 20 minutes, and under the same environment, the adhesive force was measured when peeled at a peel angle of 180 degrees and a tensile speed of 300 mm/min.
Criteria AA: 6.0 N/25 mm or more BB: 4.0 N/25 mm or more, less than 6.0 N/25 mm CC: 2.0 N/25 mm or more, less than 4.0 N/25 mm DD: less than 2.0 N/25 mm

[Holding force test]
The prepared adhesive sheet was cut to a width of 25 mm and used as a test piece, the peeled PET film was peeled off, and the exposed adhesive layer was attached to a stainless steel plate so that the attachment area was 25 mm × 25 mm. A 2-kg roller was reciprocated 3 times for crimping. After that, it is left to stand for 20 minutes in a 100 ° C./dry environment, a load of 1 kg is applied in the shear direction of the test piece under the same environment, and the amount of displacement of the test piece or the drop of the test piece after 1 hour from the start of load application. measured the time to
Criteria AA: The amount of deviation of the test piece is less than 0.1 mm (NC: non creeping)
BB: The amount of deviation of the test piece is 0.1 mm or more and less than 1.0 mm CC: The amount of deviation of the test piece is 1.0 mm or more and less than 2.0 mm DD: The amount of deviation of the test piece is 2.0 mm or more or the test piece Fall (denoted as ↓)

[Probe tack (PT)]
A 15 mm×15 mm cut piece of the produced pressure-sensitive adhesive sheet was used as a test piece, the release-treated PET film was peeled off, and the piece was attached to a test jig having a load of 20 g. Using a probe tack measuring device (manufactured by Tester Sangyo Co., Ltd.), a stainless steel probe with a diameter of 5 mm was applied to the surface of the exposed adhesive layer at 23° C. with a contact load of 1 N/cm ² and a contact speed of 10 mm/sec. The contact was made under the condition of a contact time of 1 second, and the probe peeling force was measured when the same probe was separated at a speed of 10 mm/second.

[Gel fraction]
About 0.1 g of the adhesive layer of the prepared adhesive sheet was collected in a sampling bottle, 30 mL of ethyl acetate was added and shaken for 4 hours. The above residue was dried at 100° C. for 2 hours and the dry weight was measured. The gel fraction was determined by the following formula.
Gel fraction (% by mass) = (dry mass/collected mass of pressure-sensitive adhesive layer) x 100 (%)
The above test results are shown in Table 2.

As shown in Table 2, the pressure-sensitive adhesive sheets obtained in Examples 1 to 16 were excellent in holding power in a high-temperature environment and had moderate initial adhesive strength (tack). Comparative Example 1, in which block A of the (meth)acrylic triblock polymer does not have a structural unit derived from the hydrogen-bonding functional group-containing monomer (a1), does not have sufficient holding power. Comparative Example 2, in which block A of the (meth)acrylic triblock polymer has a low Tg, does not have sufficient holding power. Comparative Example 3, in which block B of the (meth)acrylic triblock polymer has a high Tg, does not have sufficient adhesive strength and probe tack.

Claims (8)

A pressure-sensitive adhesive composition containing a (meth)acrylic triblock polymer (a), a (meth)acrylic polymer (b) and a tackifier (c),
(Meth)acrylic triblock polymer (a) has a block structure represented by ABA consisting of block A and block B (the two blocks A may be the same or different), and weight an average molecular weight (Mw) of 50,000 to 500,000,
Block A is a structural unit derived from a hydrogen-bonding functional group-containing monomer (a1), and at least one monomer (a2) selected from (meth)acrylic acid alkyl esters and (meth)acrylic acid alicyclic group-containing esters A polymer block having a structural unit derived from and having a glass transition temperature (Tg) of 0 ° C. or higher,
Block B is a polymer block having a structural unit derived from (meth)acrylic acid alkyl ester (a3) and having a Tg of −20° C. or less,
The (meth)acrylic polymer (b) has a structural unit derived from the (meth)acrylic acid alkyl ester (b1) and has an Mw of 1,000 to 10,000.
Adhesive composition. (Meth) acrylic triblock polymer (a) in 100% by mass,
In block A, the ratio of structural units derived from the monomer (a1) is 1 to 15% by mass, the ratio of structural units derived from the monomer (a2) is 4 to 39% by mass, and the monomer (a1 )-derived structural units and the monomer (a2)-derived structural units in a total ratio of 5 to 40% by mass,
In the block B, the ratio of structural units derived from the (meth)acrylic acid alkyl ester (a3) is 60 to 95% by mass.
The adhesive composition according to claim 1. The content of the (meth)acrylic polymer (b) is 5 to 100 parts by mass relative to 100 parts by mass of the (meth)acrylic triblock polymer (a), and the content of the tackifier (c) is 5 parts by mass. The pressure-sensitive adhesive composition according to claim 1 or 2, which is ~100 parts by mass. 4. Any one of claims 1 to 3, wherein block B of the (meth)acrylic triblock polymer (a) and the (meth)acrylic polymer (b) have at least 80% by mass of structural units derived from common monomers. 1. The pressure-sensitive adhesive composition according to claim 1. The pressure-sensitive adhesive composition according to any one of claims 1 to 4, further comprising an organic solvent. The pressure-sensitive adhesive composition according to any one of claims 1 to 5, further comprising a metal chelate compound. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 6. The pressure-sensitive adhesive sheet according to claim 7, wherein the pressure-sensitive adhesive layer has a gel fraction of 0% by mass.