JP6959779B2 - Adhesive composition for protective film and protective film - Google Patents

Description

The present invention relates to an adhesive composition for a protective film and a protective film.

Protective films for various optical members are widely used to protect optical members used in liquid crystal display devices, organic EL (electroluminescence) type display devices, and the like. The protective film is required to have no air entrainment between the protective film and the optical member in order to maintain the workability of the visual inspection of the optical member.

In recent years, as an optical member having an uneven structure on the surface, for example, a polarizing plate having enhanced antiglare (antireflection) property (hereinafter, may also be referred to as “AG polarizing plate”) has been used in a display device.
As an adhesive composition for an optical member protective film having improved adhesion to an optical member having irregularities on the surface, a protective film used for an optical film having fine irregularities such as a moth-eye type antireflection film is disclosed. (See, for example, Patent Document 1).
Further, a surface protective film having improved adhesion to an antiglare-treated polarizing plate is disclosed (see, for example, Patent Document 2).
A pressure-sensitive adhesive composition for a polarizing plate provided with a layer having fine irregularities such as an anti-glare layer is disclosed (see, for example, Patent Documents 3 and 4).

Japanese Unexamined Patent Publication No. 2011-88356 Japanese Unexamined Patent Publication No. 2011-168751 Japanese Unexamined Patent Publication No. 2009-275128 International Publication No. 2012/133343

In general, when the pressure-sensitive adhesive composition is softened, it is possible to improve the followability to a member having irregularities on the surface. However, when the pressure-sensitive adhesive composition is softened, the adhesive strength tends to be excessive, and the peeling power from the adherend tends to be too high. Therefore, problems such as deterioration of workability and adhesive remaining on the surface of the adherend are likely to occur.

Further, as a result of examination by the inventors, in Patent Documents 1 to 4, since an acrylic pressure-sensitive adhesive and an isocyanate-based cross-linking agent are used to form the pressure-sensitive adhesive layer of the protective film for an optical film, the adhesive strength is excessive. Adhesive may remain on the surface of the adherend at the time of peeling.
Therefore, it is difficult to achieve both followability and peeling force, that is, adhesive force suitable for the use of the protective film, particularly in an optical film that protects an optical member having an uneven surface such as an AG polarizing plate. rice field.

The present invention has been made in view of the above, and an object of the present invention is to provide an adhesive composition for a protective film and a protective film having excellent followability and peelability to a member having irregularities on the surface.

Specific means for solving the above problems include the following aspects.
<1> A (meth) acrylic resin (A) having at least a carboxy group and
Metal chelate cross-linking agent (B) and
Adhesive composition for protective film, including.

<2> The pressure-sensitive adhesive composition for a protective film according to <1>, wherein the (meth) acrylic resin (A) has an acid value of 9 mgKOH / g to 80 mgKOH / g.

<3> The pressure-sensitive adhesive composition for a protective film according to <1> or <2>, wherein the (meth) acrylic resin (A) does not contain a hydroxyl group.

<4> The pressure-sensitive adhesive composition for a protective film according to any one of <1> to <3>, which is used for an optical member.

<5> The pressure-sensitive adhesive composition for a protective film according to <4>, wherein the arithmetic average roughness Ra of the surface of the optical member is 0.1 μm to 3 μm.

<6> The pressure-sensitive adhesive composition for a protective film according to <5>, wherein the optical member has irregularities on its surface and the height difference of the irregularities is 1 μm to 20 μm.

<7> The pressure-sensitive adhesive composition for a protective film according to <6>, wherein the unevenness has at least an aspect ratio of the convex portion of 0.5 to 2.

<8> The pressure-sensitive adhesive composition for a protective film according to any one of <4> to <7>, wherein the optical member is an antiglare-treated polarizing plate.

<9> A protective film having a pressure-sensitive adhesive layer, which is a crosslinked product of the pressure-sensitive adhesive composition for a protective film according to any one of <1> to <8>, and a base material.

According to the present invention, it is possible to provide an adhesive composition for a protective film and a protective film having excellent followability and peelability to a member having irregularities on the surface.

It is a photograph which observed the surface of the anti-glare-treated polarizing plate (AG polarizing plate) which is one Embodiment of the adherend of the protective film which concerns on this invention with a laser microscope. It is a photograph which observed the surface of the polyethylene plate which is one Embodiment of the adherend of the protective film which concerns on this invention with a laser microscope. It is a photograph of the surface of the pressure-sensitive adhesive layer of the protective film according to the present invention after being peeled off from the AG polarizing plate, observed with a laser microscope.

Hereinafter, the pressure-sensitive adhesive composition of the present invention will be described in detail.
In the present invention, "-" in the numerical range means to include the numerical values before and after "-". In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described stepwise. Further, in the numerical range described in the present specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.
In the present specification, the amount of each component in the composition is the total amount of the plurality of substances present in the composition unless otherwise specified, when a plurality of substances corresponding to each component are present in the composition. Means.

In the present specification, the (meth) acrylic resin or the (meth) acrylic oligomer is a monomer in which at least the main component of the monomers constituting the resin has a (meth) acryloyl group. It means a resin or an oligomer formed by polymerization.
The main component of the (meth) acrylic resin or the (meth) acrylic oligomer means that the content (mass%) is the highest among the monomer components forming the resin or the oligomer. For example, in the case of a (meth) acrylic resin, it means that the content of the constituent units derived from the monomer having a (meth) acryloyl group as the main component is 50% by mass or more of all the constituent units.
As used herein, "(meth) acrylic" means at least one of "acrylic" and "methacrylic", and "(meth) acrylate" means at least one of "acrylate" and "methacrylate". "(Meta) acryloyl" means at least one of "acryloyl" and "methacrylic".

≪Adhesive composition for protective film≫
The adhesive composition for a protective film of the present invention (hereinafter, also simply referred to as “adhesive composition”) is a (meth) acrylic resin (A) having at least a carboxy group and a metal chelate-based cross-linking agent (B). And, including.

When the pressure-sensitive adhesive composition has the above-mentioned structure, it is possible to form a pressure-sensitive adhesive layer having excellent followability and peelability to a member having irregularities on the surface. This can be thought of as follows.

Usually, the adhesive composition for a protective film containing an isocyanate-based cross-linking agent has a gel fraction of 98% or more after cross-linking.
In a conventional pressure-sensitive adhesive composition containing an isocyanate-based cross-linking agent, a functional group in a resin that is reactive with an NCO (isocyanate) group and an NCO group in the cross-linking agent are covalently bonded to form a cross-linked structure.
The pressure-sensitive adhesive layer formed from such a pressure-sensitive adhesive composition for a protective film cannot follow the unevenness of the surface of a member having an uneven shape, and as a result, air is likely to be caught between the protective film and the member. The visibility, that is, the workability of the visual inspection of the member may be inferior.

On the other hand, since the pressure-sensitive adhesive composition of the present invention contains a (meth) acrylic resin (A) having at least a carboxy group and a metal chelate-based cross-linking agent (B), the (meth) acrylic resin (A) It is presumed that the carboxy group contained therein and the metal atom contained in the metal chelate-based crosslinking agent (B) are coordinated to form a crosslinked structure. As described above, the pressure-sensitive adhesive composition of the present invention containing at least a (meth) acrylic resin (A) having a carboxy group and a metal chelate-based cross-linking agent (B), and a pressure-sensitive adhesive for a protective film containing an isocyanate-based cross-linking agent. The cross-linked form is different from that of the composition, and the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention tends not to be too strong as compared with the cross-linked structure formed by covalent bonding, and the pressure-sensitive adhesive composition The gel fraction after cross-linking can be suppressed to about 80% to 90%. Therefore, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention does not become too hard. It may be called.) Excellent.
Further, the pressure-sensitive adhesive composition of the present invention does not have an excessive adhesive strength even though it is lower than the gel content of the pressure-sensitive adhesive composition for a protective film containing an isocyanate-based cross-linking agent, and is suitable for use as a protective film. While maintaining the adhesive strength, adhesive residue (hereinafter, may be referred to as "glue residue") is unlikely to occur, and peelability can be obtained.

From the above, the pressure-sensitive adhesive composition of the present invention is suitable for forming a pressure-sensitive adhesive layer having excellent step-following property and peelability.
Hereinafter, details of each component used in the pressure-sensitive adhesive composition of the present invention will be described.

<(Meta) Acrylic resin (A)>
The pressure-sensitive adhesive composition has a (meth) acrylic resin (A) having at least a carboxy group (hereinafter, also referred to as “specific (meth) acrylic resin”). The carboxy group in the specific (meth) acrylic resin reacts with the metal chelate-based cross-linking agent (B) described later to form a cross-linked structure appropriately, so that it does not become too hard and is formed from the pressure-sensitive adhesive composition. The adhesive layer can exhibit excellent step followability.

The specific (meth) acrylic resin has at least a carboxy group and a structure derived from the (meth) acryloyl group. The specific (meth) acrylic resin may be a resin formed by homopolymerizing a (meth) acrylic monomer having a carboxy group, and may be a resin formed by homopolymerizing a (meth) acrylic monomer having a carboxy group with a (meth) acrylic monomer having no carboxy group. , A resin formed by subjecting a monomer having a carboxy group to an addition polymerization reaction may be used.
The structural unit derived from the monomer having a carboxy group may contain one kind or two or more kinds.

The structural unit derived from the monomer having a carboxy group is not particularly limited, and examples thereof include a structural unit derived from a vinyl monomer having a carboxy group. Among these, as the structural unit derived from the vinyl monomer having a carboxy group, a (meth) acrylic acid ester having a carboxy group and a structural unit derived from (meth) acrylic acid are preferable.
As the structural unit derived from the vinyl monomer having a carboxy group, the structural unit derived from (meth) acrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, citraconic acid, cinnamic acid and the like is used. Can be mentioned.

As the structural unit derived from the (meth) acrylic acid ester having a carboxy group, monohydroxyethyl maleate (meth) acrylate, monohydroxyethyl fumarate (meth) acrylate, monohydroxyethyl phthalate (meth) acrylate, 1, Examples thereof include 2-dicarboxycyclohexane monohydroxyethyl (meth) acrylate, a structural unit derived from (meth) acrylic acid dimer, and a structural unit represented by the following general formula (1).

When the specific (meth) acrylic resin has a structural unit represented by the general formula (1), the adhesive strength can be suppressed low because the carboxy group is bonded via L.

In the structural unit represented by the general formula (1), L represents a divalent linking group composed of at least one selected from the group consisting of an alkylene group, an arylene group, a carbonyl group and an oxygen atom, and R ¹ Indicates a hydrogen atom or a methyl group. However, when L contains an oxygen atom, the oxygen atom forms a group bonded to at least one selected from the group consisting of an alkylene group, an arylene group and a carbonyl group, and is bonded to -COO- and -CO-. do.

The alkylene group in L may be linear, branched or cyclic. When the alkylene group in L is linear or branched, the alkylene group preferably has 1 to 12 carbon atoms, more preferably 2 to 10 carbon atoms, and even more preferably 2 to 6 carbon atoms. ..

When the alkylene group in L is cyclic, for example, the alkylene group may be a cyclic group having 3 to 5 carbon atoms.

The arylene group in L preferably has 6 to 10 carbon atoms, and more preferably a phenylene group. The bond position in the arylene group is not particularly limited. For example, when the arylene group is a phenylene group, the bonding positions may be any of the 1-position and the 4-position, the 1-position and the 2-position, and the 1-position and the 3-position, and are preferably the 1-position and the 2-position.

The alkylene group and the arylene group in L may have a substituent. Examples of the substituent include an alkyl group having 1 to 12 carbon atoms, a halogen atom, a hydroxyl group, an amino group, a nitro group, a phenyl group and the like.

The divalent linking group represented by L in the general formula (1) is preferably a divalent linking group represented by the following general formula (2a) or general formula (2b) from the viewpoint of peelability. ..

In the general formulas (2a) and (2b), R ^{21 to} R ²⁴ independently represent an alkylene group having 1 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms. n represents a number from 0 to 10, and m represents a number from 1 to 10.
The alkylene group in R ^{21 to} R ²⁴ may be linear, branched or cyclic, preferably linear or branched, and more preferably linear.
The bonding position of the arylene group in R ^{21 to} R ^{24 is not particularly limited.} For example, when the arylene group is a phenylene group or a cyclohexylene group, the bond position may be any of the 1st and 4th positions, the 1st and 2nd positions, and the 1st and 3rd positions, and is the 1st and 2nd positions. Is preferable.

The alkylene groups in R ²¹ and R ²² each independently preferably have 2 to 10 carbon atoms, and more preferably 2 to 6 carbon atoms. The alkylene groups in R ²¹ and R ²² may be the same or different.
The arylene group in R ²¹ and R ²² is preferably a phenylene group or a naphthylene group independently, and more preferably a phenylene group.

^{From the viewpoint of peelability, R 21} and R ²² in the general formula (2a) are preferably alkylene groups having 1 to 12 carbon atoms independently, and more preferably alkylene groups having 2 to 6 carbon atoms. It is preferably a linear or branched alkylene group having 2 to 6 carbon atoms.

In the general formula (2a), n represents a number from 0 to 10. When the specific (meth) acrylic resin contains only one type of structural unit represented by the general formula (1), n is an integer, and when it contains two or more types, n is an average value. It becomes. n is preferably 0 to 4, more preferably 0 to 2.

R ²³ is preferably an alkylene group having 1 to 12 carbon atoms, more preferably an alkylene group having 2 to 6 carbon atoms, and further preferably an alkylene group having 2 to 4 carbon atoms.

R ²⁴ is a linear or branched alkylene group having 2 to 6 carbon atoms, a cyclic alkylene group having 4 to 8 carbon atoms (divalent cyclocyclic group), or an arylene group having 6 to 10 carbon atoms. It is preferably a linear or branched alkylene group having 2 to 4 carbon atoms, a cyclic alkylene group having 5 to 6 carbon atoms, or a phenylene group, and a linear chain having 2 to 4 carbon atoms. Alternatively, it is more preferably a branched alkylene group, a cyclohexylene group, or a phenylene group.

In the general formula (2b), m represents a number from 1 to 10. When the specific (meth) acrylic resin contains only one type of structural unit represented by the general formula (1), m is an integer, and when it contains two or more types, m is an average value. It becomes. m is preferably 1 to 4, more preferably 1 to 2.

The structural unit represented by the general formula (1) is, for example, copolymerizing the monomer represented by the following general formula (1a) with other monomers constituting the specific (meth) acrylic resin. Therefore, it can be introduced into a specific (meth) acrylic resin.

In the general formula (1a), ^{R 1} and L are respectively the same as ^{R 1} and L in the general formula (1).

The monomer represented by the general formula (1a) may be produced by a conventional method or may be appropriately selected from commercially available monomers. Among the monomers represented by the general formula (1a), examples of the monomer in which L is represented by the general formula (2a) include, for example, a (meth) acrylic acid dimer (preferably n in the general formula (2a)). Ω-carboxy-polycaprolactone mono (meth) acrylate (preferably, the average value of n in the general formula (2a) is about 1.0). As these monomers, for example, those commercially available as "Aronix M-5600" and "Aronix M-5300" (all manufactured by Toagosei Co., Ltd., trade name) can be used.

Among the monomers represented by the general formula (1a), examples of the monomer in which L is represented by the general formula (2b) include 2- (meth) acryloyloxyethyl succinic acid and 2- (meth). ) Acryloyloxyethyl fumarate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, 2- (meth) acryloyloxyethyl phthalic acid. These monomers are, for example, "light ester HO-MS", "light acrylate HOA-MS (N)", "light acrylate HOA-HH (N)", "light acrylate HOA-MPL (N)" (above, above, A commercially available product (trade name) manufactured by Kyoeisha Chemical Co., Ltd. can be used.

From the viewpoint of adhesiveness, the structural unit derived from the vinyl monomer having a carboxy group is at least one of (meth) acrylic acid and the structural unit derived from the monomer represented by the above general formula (1). It is preferably present, and more preferably at least one of (meth) acrylic acid and the structural unit derived from the above general formula (1a), for (meth) acrylic acid and ω-carboxy-polycaprolactone mono (meth) acrylate. More preferably, it is at least one of the constituent units from which it is derived.

From the viewpoint of peelability, the content of the structural unit derived from the vinyl monomer having a carboxy group is preferably 3% by mass to 40% by mass, and 6% by mass to 20% by mass, based on all the structural units. It is more preferably mass%, and even more preferably 8% by mass to 10% by mass.

The specific (meth) acrylic resin preferably further contains at least one of the structural units derived from the alkyl (meth) acrylate in addition to the structural unit derived from the vinyl monomer having a carboxy group.

Examples of the structural unit derived from alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, and t. -Butyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-nonyl (meth) acrylate, isononyl (meth) acrylate, n-decyl (meth) acrylate , N-Dodecyl (meth) acrylate, isomyristyl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, and isobornyl (meth) acrylate-derived structural units.
The alkyl group of the alkyl (meth) acrylate may be linear, branched or cyclic.

The specific (meth) acrylic resin may contain one type alone or two or more types of structural units derived from alkyl (meth) acrylate, and preferably contains two or more types.

Among these, the structural unit derived from alkyl (meth) acrylate is preferably a structural unit derived from alkyl (meth) acrylate having a glass transition temperature of −30 ° C. or lower when used as a homopolymer.

A structural unit derived from an alkyl (meth) acrylate in which the specific (meth) acrylic resin is used (preferably a structural unit derived from an alkyl (meth) acrylate having a glass transition temperature of −30 ° C. or lower when used as a homopolymer). In the case of containing, the total content of the structural unit derived from the alkyl (meth) acrylate (preferably the structural unit derived from the alkyl (meth) acrylate having a glass transition temperature of −30 ° C. or lower when made into a homopolymer) is It is preferably 65% by mass to 99% by mass, more preferably 75% by mass to 97% by mass, and further preferably 80% by mass or more to 95% by mass with respect to all the constituent units.
When the total content of the constituent units derived from alkyl (meth) acrylate is 65% by mass or more, the compatibility (wetting property) tends to be better. Further, when the total content of the constituent units derived from alkyl (meth) acrylate is 99% by mass or less, the adhesive strength at the time of peeling does not become too high, and the peelability tends to be superior.

The structural unit derived from the alkyl (meth) acrylate includes a structural unit derived from at least one of n-butyl acrylate and 2-ethylhexyl acrylate from the viewpoint that the adhesive strength does not become too high and the peelability is excellent. Is preferable, and it is more preferable to contain a structural unit derived from n-butyl acrylate and 2-ethylhexyl acrylate.

The specific (meth) acrylic resin may further contain a structural unit derived from the vinyl monomer having a carboxy group described above and a structural unit other than the structural unit derived from the alkyl (meth) acrylate.
The other structural unit is not particularly limited as long as it can form a specific (meth) acrylic resin together with a structural unit derived from a vinyl monomer having a carboxy group, and can be appropriately selected depending on the intended purpose.
Examples of the monomer capable of forming other structural units include a monomer having a hydroxyl group, a monomer having an alkylene oxide chain, and a monomer having an aromatic ring.

Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 6-hydroxy. Hexyl (meth) acrylates include 10-hydroxydecyl (meth) acrylates, 12-hydroxylauryl (meth) acrylates and 3-methyl-3-hydroxybutyl (meth) acrylates.

When the specific (meth) acrylic resin further contains a structural unit derived from a monomer having a hydroxyl group, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition tends to leave the pressure-sensitive adhesive on the adherend after peeling. Tend.
Therefore, when the specific (meth) acrylic resin contains a structural unit derived from a monomer having a hydroxyl group, the content of the structural unit derived from the monomer having a hydroxyl group is a specific (meth) acrylic resin. It is preferably 5% by mass or less, more preferably 1% by mass or less, and further preferably substantially not contained, based on all the constituent units of the above.
It should be noted that "substantially free" means that the presence of a structural unit derived from a monomer having a hydroxyl group unavoidably mixed is allowed, but a structural unit derived from a monomer having a hydroxyl group intentionally added is allowed. Means that the presence of is unacceptable.

Examples of the monomer having an alkylene oxide chain include methoxyethyl (meth) acrylate, 2- (ethoxyethoxy) ethyl acrylate, polyethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, and methoxypolypropylene glycol (meth). Examples thereof include acrylates, polypropylene glycol (meth) acrylates and methoxypolyethylene glycol (meth) acrylates.

Examples of the monomer having an aromatic ring include benzyl (meth) acrylate and phenoxyethyl (meth) acrylate.

The acid value of the specific (meth) acrylic resin is preferably 9 mgKOH / g to 80 mgKOH / g, preferably 11 mgKOH / g to, from the viewpoint that the adhesive strength suitable for the use of the protective film can be more easily obtained. It is more preferably 40 mgKOH / g, and further preferably the acid value is 13 mgKOH / g to 30 mgKOH / g.
The acid value of the specific (meth) acrylic resin or the (meth) acrylic oligomer described later is calculated by the following formulas, respectively.

Acid value (mgKOH / g) = {(A / 100) ÷ B} × 56.1 × 1000 × C
A = Content (% by mass) of vinyl monomer having a carboxy group in all the monomers used for (meth) acrylic resin or (meth) acrylic oligomer.
B = Molecular weight of (meth) acrylic monomer C = Number of carboxy groups contained in one molecule of vinyl monomer having a carboxy group 56.1 is the molecular weight of KOH.
When there are a plurality of types of vinyl monomers having a carboxy group, the acid value can be obtained by adding up the values obtained from the above formulas for each monomer.

The glass transition temperature of the specific (meth) acrylic resin is preferably −40 ° C. or lower, more preferably −50 ° C. or lower, from the viewpoint of peelability.

The glass transition temperature (Tg) of the specific (meth) acrylic resin is the molar average glass transition temperature obtained by the calculation of the following formula.
1 / Tg = m ₁ / Tg ₁ + m ₂ / Tg ₂ + ... + m _(k-1) / Tg _(k-1) + m _k / Tg _k
... (Equation 1)
In Formula 1, Tg ₁ , Tg ₂ , ..., Tg _(k-1) , and Tg _k are the absolute temperatures when each monomer constituting the specific (meth) acrylic resin is used as a homopolymer (absolute temperature). It is a glass transition temperature represented by K). m ₁ , m ₂ , ..., m _(k-1) , m _k represent the mole fraction of each monomer constituting the specific (meth) acrylic resin, and m ₁ + m ₂ + ... -+ M _(k-1) + m _k = 1.

The "glass transition temperature represented by the absolute temperature (K) when made into a homopolymer" is the glass transition temperature represented by the absolute temperature (K) of the homopolymer produced by polymerizing the monomer alone. Refers to temperature. The glass transition temperature of the homopolymer uses a differential scanning calorimetry device (DSC) (EXSTAR6000, manufactured by Seiko Instruments Co., Ltd.) to measure the homopolymer in a nitrogen stream, a measurement sample of 10 mg, and a temperature rise rate of 10 ° C./min. The measurement was carried out under the conditions of (1), and the change point of the obtained DSC curve was taken as the glass transition temperature of the homopolymer.

The "glass transition temperature represented by the Celsius temperature (° C) of the homopolymer" of a typical monomer is 5 ° C for methyl acrylate, -27 ° C for ethyl acrylate, and 103 ° C for methyl methacrylate. Yes, n-butyl acrylate is -57 ° C, 2-ethylhexyl acrylate is -76 ° C, n-dodecyl methacrylate is -65 ° C, n-octyl acrylate is -65 ° C, and isooctyl acrylate is -65 ° C. -58 ° C., isononyl acrylate is -58 ° C., isomyristyl acrylate is -56 ° C., acrylic acid is 163 ° C. ° C., 2-acryloyloxyethyl-succinic acid is −40 ° C.
For example, by using these typical monomers, the above-mentioned glass transition temperature can be appropriately adjusted.

The weight average molecular weight (Mw) of the specific (meth) acrylic resin is not particularly limited, and is preferably 200,000 to 1,000,000, more preferably 300,000 to 800,000.
When the weight average molecular weight (Mw) of the specific (meth) acrylic resin is 200,000 or more, it is possible to more effectively suppress the adhesive from remaining on the adherend at the time of peeling. Further, when the weight average molecular weight (Mw) of the specific (meth) acrylic resin is 1 million or less, the followability and the familiarity (wetting property) tend to be more excellent.

The weight average molecular weight (Mw) of the specific (meth) acrylic resin is a value measured according to the following (1) to (3).
(1) A solution of a specific (meth) acrylic resin is applied to a release paper and dried at 100 ° C. for 2 minutes to obtain a film-like specific (meth) acrylic resin.
(2) Using the film-shaped specific (meth) acrylic resin obtained in (1) above and tetrahydrofuran (THF), a sample solution having a solid content concentration of 0.2% by mass is obtained.
(3) Under the following conditions, the weight average molecular weight (Mw) of the specific (meth) acrylic resin is measured as a standard polystyrene-equivalent value using gel permeation chromatography (GPC).

(conditions)
GPC: HLC-8220 GPC [manufactured by Tosoh Corporation]
Column: Use 4 TSK-GEL GMHXL Mobile phase solvent: Tetrahydrofuran (THF)
Flow rate: 0.6 mL / min Column temperature: 40 ° C

The content of the specific (meth) acrylic resin in the pressure-sensitive adhesive composition can be appropriately selected depending on the intended purpose. The content of the specific (meth) acrylic resin is preferably 80% by mass to 99% by mass, more preferably 85% by mass to 99% by mass, based on the total solid content of the pressure-sensitive adhesive composition. It is preferably 90% by mass to 98% by mass, more preferably 90% by mass.
The total mass of the solid content means the total mass of the residue obtained by removing volatile components such as a solvent from the pressure-sensitive adhesive composition.
The specific (meth) acrylic resin may be one type alone, or may be a combination of two or more types having different monomer compositions, weight average molecular weights, and the like.

The pressure-sensitive adhesive composition of the present invention may further contain a (meth) acrylic oligomer having a weight average molecular weight (Mw) of 3,000 to 30,000.
When the pressure-sensitive adhesive composition of the present invention contains a (meth) acrylic oligomer, for example, it is possible to easily impart antistatic properties or adjust the adhesive strength.
The (meth) acrylic oligomer may be used alone or in combination of two or more having different monomer compositions, weight average molecular weights, and the like.

The (meth) acrylic oligomer may contain a structural unit derived from an alkyl (meth) acrylate. Building blocks derived from alkyl (meth) acrylates tend to contribute to the adjustment of adhesive strength.
The alkyl (meth) acrylate has the same meaning as the alkyl (meth) acrylate in the above-mentioned specific (meth) acrylic resin, and the same applies to specific examples.
The alkyl (meth) acrylate is preferably an alkyl (meth) acrylate having 4 to 12 carbon atoms, because high durability is exhibited when the pressure-sensitive adhesive layer is exposed to a high-temperature and high-humidity environment. It is more preferably an alkyl (meth) acrylate having a branched chain and having 4 to 12 carbon atoms, and further preferably 2-ethylhexyl methacrylate.

The (meth) acrylic oligomer may contain a structural unit (other structural unit) other than the structural unit derived from the alkyl (meth) acrylate within the range in which the effect of the present invention is exhibited.

Examples of the monomer constituting the other structural unit include the above-mentioned monomer having an alkylene oxide chain, a monomer having a carboxy group, a monomer having a hydroxyl group, a monomer having an aromatic ring, and the like. The same applies to specific examples and preferred ranges.
When the (meth) acrylic oligomer contains a structural unit derived from a monomer having a carboxy group, the (meth) acrylic oligomer is covered with the (meth) acrylic oligomer at the time of peeling because the carboxy group reacts with the metal chelate-based cross-linking agent described later. It is preferable because it does not easily remain on the body.
When a structural unit derived from a monomer having a carboxy group is contained, the acid value of the (meth) acrylic oligomer can be calculated in the same manner as in the method described above.

Regarding the content of the (meth) acrylic oligomer, from the viewpoint of imparting the necessary adhesive force to the pressure-sensitive adhesive layer to the extent that it does not suddenly peel off from the adherend, and maintaining the peelability suitable for the use of the protective film. It is preferably 0.05 parts by mass to 2.00 parts by mass, more preferably 0.10 parts by mass to 1.50 parts by mass, and 0 parts by mass with respect to 100 parts by mass of the specific (meth) acrylic resin. It is more preferably .10 parts by mass to 1.20 parts by mass.

The weight average molecular weight (Mw) of the (meth) acrylic oligomer is preferably 3,000 or more from the viewpoint of preventing the (meth) acrylic oligomer from remaining on the adherend at the time of peeling. The above is more preferable, and 7,000 or more is further preferable. The weight average molecular weight (Mw) of the (meth) acrylic oligomer is preferably 30,000 or less, more preferably 25,000 or less, and 20, from the viewpoint of lowering the haze of the pressure-sensitive adhesive layer. It is more preferably 000 or less.

The weight average molecular weight (Mw) of the (meth) acrylic oligomer can be measured in the same manner as the method for measuring the weight average molecular weight (Mw) of the specific (meth) acrylic resin described above.

The glass transition temperature (Tg) of the (meth) acrylic oligomer is preferably 50 ° C. or lower. When the Tg of the (meth) acrylic oligomer is 50 ° C. or lower, an increase in adhesive strength due to heat treatment can be suppressed, so that the peelability tends to be more excellent.

The glass transition temperature of the (meth) acrylic oligomer can be calculated in the same manner as the method for calculating the glass transition temperature of the specific (meth) acrylic resin described above.

<Metal chelate cross-linking agent (B)>
The pressure-sensitive adhesive composition of the present invention contains a metal chelate-based cross-linking agent. The metal chelate-based cross-linking agent is contained in the resin by reacting the metal atom contained in the metal chelate-based cross-linking agent (B) with the carboxy group in the specific (meth) acrylic resin to form a coordination bond. A crosslinked structure is formed in the resin, and the gel fraction after crosslinking is suppressed to about 80% to 90%. Therefore, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition does not become too hard, an appropriate adhesive strength can be obtained, and excellent step-following property can be exhibited.
The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention and the pressure-sensitive adhesive layer formed by using an isocyanate-based cross-linking agent, an epoxy-based cross-linking agent, or the like are different in cross-linking form, and the pressure-sensitive adhesive of the present invention is used. The pressure-sensitive adhesive layer formed from the composition tends not to have excessive adhesive strength. Therefore, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention can obtain peelability in which the adhesive residue is suppressed while maintaining the adhesive strength suitable for the use of the protective film.

Examples of the metal chelate-based cross-linking agent include compounds in which polyvalent metal atoms and organic compounds are coordinated.
Examples of the polyvalent metal atom include Al, Zr, Co, Cu, Fe, Ni, V, Zn, In, Ca, Mg, Mn, Y, Ce, Sr, Ba, Mo, La, Sn and Ti. Be done. Among these, from the viewpoint of low cost and availability, the multivalent metal atom is preferably at least one selected from Al, Zr, and Ti, and more preferably Al.
Examples of the atom in the organic compound that coordinates with the polyvalent metal atom include an oxygen atom and the like. Examples of the organic compound having an oxygen atom include an alkyl ester, an alcohol compound, a carboxylic acid compound, an ether compound, and a ketone compound.

From the viewpoint of being relatively stable and easy to handle, aluminum trisacetylacetonate or the like can be preferably used as the metal chelate-based cross-linking agent.
The metal chelate-based cross-linking agent may be used alone or in combination of two or more.

From the viewpoint of imparting adhesive strength to the pressure-sensitive adhesive layer and being suitable for use as a protective film, the equivalent of the metal chelate-based cross-linking agent is the equivalent of 1 carboxy group of the specific (meth) acrylic resin. , 0.3 equivalents to 2.0 equivalents, more preferably 0.4 equivalents to 1.5 equivalents, and even more preferably 0.6 equivalents to 1.2 equivalents.

The equivalent of the metal chelate-based cross-linking agent is a value calculated from the following formula.
Eq = (A × B / C) / (D 1 × E 1 / F 1 + D 2 × E 2 / F 2 + ···· + D n × E n × F n)
A = Metal valence of metal chelate-based cross-linking agent B = Number of parts by mass of metal chelate-based cross-linking agent (amount as solid content)
C = Molecular weight of metal chelate cross-linking agent
D ₁ , D ₂ , ... D _n = Content rate (mass%) of each monomer having a carboxy group in all the monomers used for the specific (meth) acrylic resin and the (meth) acrylic oligomer. )
E _{1, E} 2, Number F ₁ of carboxy groups contained in one molecule of the monomer having a · · · _{E n} = a carboxy group, _F 2, ··· _{F n} = specific (meth) acrylic resin And the molecular weight of each monomer having a carboxy group used in the (meth) acrylic oligomer. In addition, n represents the number of types of monomers used, for example, the (meth) acrylic type used. When there is _{only one monomer, only D 1} is used in the calculation, and D ₂ ... D _n is not used in the calculation.

(Antistatic agent)
The pressure-sensitive adhesive composition may contain an antistatic agent.
Examples of the antistatic agent include ionic compounds. The ionic compound is not particularly limited, and examples thereof include alkali metal salts and organic salts.
Alkali metal salts and organic salts are preferable as antistatic agents because they have high ion dissociation and easily exhibit excellent antistatic properties even in a small amount.

The alkali metal salt is not particularly limited as long as it is a metal salt having ^{lithium ion (Li +} ), sodium ion (Na ⁺ ), potassium ion (K ⁺ ), rubidium (Rb ^{+) or the like as cations.}
For example, at least one cation selected from the group consisting of ^{Li +} , Na ⁺ and K ^{+ , and Cl −} , Br ⁻ , I ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , SCN ⁻ , ClO ₄ ⁻ , CF ₃ SO. _At least 1 selected from the group consisting of ^{3 −} , (FSO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ and (CF ₃ SO ₂ ) ₃ C ⁻ A metal salt composed of a seed anion can be preferably used.

Among them, the alkali metal salts include LiBr, LiI, LiBF ₄ , LiPF ₆ , LiSCN, LiClO ₄ , LiCF ₃ SO ₃ , Li (FSO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) from the viewpoint of antistatic property. _{Lithium salts such as 2} N, Li (C ₂ F ₅ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) ₃ C are preferable, and LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ It is more preferably N, Li (C ₂ F ₅ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) _{3 C.}
The alkali metal salt may be used alone or in combination of two or more.

The organic salt contains an organic cation and its counterion.
The organic salt preferably has a melting point of 30 ° C. or higher. When the melting point of the organic salt is 30 ° C. or higher, the transfer to the adherend is small and the contamination property is low, which is preferable.
The organic salt may be used alone or in combination of two or more.

Examples of the organic cation include an imidazolium cation, a pyridinium cation, an alkylpyrrolidinium cation, an ammonium cation having an organic group as a substituent, a sulfonium cation having an organic group as a substituent, and a phosphonium cation having an organic group as a substituent. Can be mentioned. Among these, from the viewpoint of antistatic property, the organic cation is preferably at least one of a pyridinium cation and an imidazolium cation.

The anion portion that becomes the counter ion of the organic cation is not particularly limited, and may be either an inorganic anion or an organic anion. Among them, the anion portion is preferably a fluorine-containing anion containing a fluorine atom, and more preferably a hexafluorophosphate anion (PF ₆ ⁻ ) because of its excellent antistatic property.

Pyridinium salt, imidazolium salt, alkylammonium salt, alkylpyrrolidinium salt, alkylphosphonium salt and the like are preferably used as examples of the organic salt. Among them, the organic salt is preferably at least one of a pyridinium salt and an imidazolium salt, and more preferably a salt of at least one of a pyridinium cation or an imidazolium cation and a fluorine-containing anion.

When the pressure-sensitive adhesive composition contains an antistatic agent, the content of the antistatic agent may be 0.05 parts by mass to 0.50 parts by mass with respect to 100 parts by mass of the specific (meth) acrylic resin. It is preferably 0.10 parts by mass to 0.30 parts by mass, more preferably.

<Other ingredients>
The pressure-sensitive adhesive composition includes a specific (meth) acrylic resin, a (meth) acrylic oligomer, a metal chelate-based cross-linking agent and an antistatic agent, as well as a cross-linking agent other than the metal chelate-based cross-linking agent and a poly, if necessary. It can appropriately contain ether-modified silicone, weather resistance stabilizer, crosslink, plasticizer, softener, peeling aid, dye, pigment, inorganic filler, surfactant and the like.
The pressure-sensitive adhesive composition preferably contains substantially no cross-linking agent other than the metal chelate-based cross-linking agent. Substantially free means that the presence of a cross-linking agent other than the metal chelate-based cross-linking agent unavoidably mixed is allowed, but the presence of a cross-linking agent other than the intentionally added metal chelate-based cross-linking agent is not allowed. Means.

[Use]
The pressure-sensitive adhesive composition of the present invention is preferably used for an optical member. Since the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention is excellent in step-following property and peelability, it can be suitably used for optical members having irregularities on the surface, and among them, anti-glare (antireflection) treatment is applied. It is more preferable to use it as a polarizing plate (AG polarizing plate). The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention is preferably used by being laminated with the uneven surface of the optical member.

The arithmetic mean roughness Ra of the surface of the optical member is preferably 0.1 μm to 3 μm, and more preferably 0.1 μm to 2.7 μm. The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition tends to exhibit better step-following property and adhesiveness with respect to an optical member having an arithmetic mean roughness Ra within the above range.

The arithmetic mean roughness Ra represents a parameter related to the height direction of the unevenness of the surface of the optical member, and is a value obtained by measuring according to JIS B 0601 (2001).
The arithmetic mean roughness Ra of the surface of the optical member can be calculated by hand calculation, for example, by observing with a laser microscope.

The unevenness of the surface of the optical member preferably has a height difference of 1 μm to 20 μm, and more preferably 1 μm to 3 μm.
The height difference of the unevenness on the surface of the optical member means the maximum value obtained by measuring, for example, 10 points of the Y-axis (height) distance in the entire range of the image acquired on the surface of the optical member using a laser microscope or the like. do.

The unevenness of the surface of the optical member preferably has an aspect ratio of at least the convex portion of 0.5 to 2.
As used herein, the aspect ratio of the convex portion means the ratio of the height of the convex portion to the length of the maximum width of the convex portion in the plane including the surface of the optical member.

[Protective film]
The protective film of the present invention has at least a pressure-sensitive adhesive layer which is a crosslinked product of the pressure-sensitive adhesive composition for a protective film, and a base material.
The adhesive layer of the protective film can exhibit excellent adhesiveness and followability (step followability) to members having irregularities on the surface.

The base material used for the protective film is not particularly limited as long as the pressure-sensitive adhesive layer can be formed on the base material.
From the viewpoint of inspection and management of optical members by fluoroscopy, the base materials include polyester resin, acetate resin, polyether sulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, and acrylic. Examples thereof include a film using a resin selected from based resins and the like.
Among them, the base material is preferably a film using a polyester resin from the viewpoint of surface protection performance, and more preferably a film using a polyethylene terephthalate (PET) resin in consideration of practicality.

The thickness of the base material can be generally 500 μm or less, preferably 5 μm to 300 μm, and more preferably 10 μm to 200 μm.

An antistatic layer may be provided on one side or both sides of the base material. Further, the surface of the base material on the side where the pressure-sensitive adhesive layer is provided may be subjected to a corona discharge treatment or the like in order to improve the adhesion between the pressure-sensitive adhesive layer and the base material.

A pressure-sensitive adhesive layer, which is a crosslinked product of the pressure-sensitive adhesive composition, is provided on the base material.
As a method for forming the pressure-sensitive adhesive layer, for example, a method is adopted in which the pressure-sensitive adhesive composition is diluted as it is or with an appropriate solvent as needed, applied to a base material, and then dried to remove the solvent. can do.
As a method for forming the pressure-sensitive adhesive layer, first, the pressure-sensitive adhesive composition is applied on a release sheet made of an appropriate film such as a paper or a polyester film that has been mold-released with a silicone resin or the like, and then heat-dried. It is also possible to adopt a method of forming the pressure-sensitive adhesive layer and then pressing the pressure-sensitive adhesive layer side of the release sheet against the base material to transfer the pressure-sensitive adhesive layer to the base material.

The thickness of the pressure-sensitive adhesive layer formed on the base material can be appropriately set according to the adhesive strength required for the protective film, the surface roughness of the optical member, and the like. The thickness of the pressure-sensitive adhesive layer is generally 1 μm to 100 μm, preferably 5 μm to 50 μm, and more preferably about 15 μm to 30 μm.

The pressure-sensitive adhesive layer (peeling force) at 180 ° peeling (peeling speed 0.3 m / min) is preferably 1 N / 25 mm or less, and more preferably 0.5 N / 25 mm or less.
Further, from the viewpoint of preventing unexpected peeling of the protective film, the adhesive force (peeling force) at a peeling speed of 0.3 m / min is preferably 0.05 N / 25 mm or more, and 0.2 N / 25 mm or more. Is more preferable.

The protective film of the present invention can be suitably used as a protective film for optical members.
The protective film is laminated on the surface of the optical member to protect the surface of the optical member from being contaminated or damaged, and when the optical member is processed into a liquid crystal display plate or the like, the protective film is used as the optical member. It is used for each process such as punching, inspection, transportation, and assembly of liquid crystal display boards while it is still laminated on the screen, and if necessary, it is subjected to heat and pressure treatment such as autoclave treatment and high temperature aging treatment. When the surface protection becomes unnecessary, it is peeled off from the optical member.

Examples of the optical member include a member constituting a device (optical device) such as an image display device and an input device, or a member used for these devices. Specific examples of the optical member include a polarizing plate, an AG polarizing plate, a wave plate, a retardation plate, an optical compensation film, a brightness improving film, a light guide plate, a reflective film, an antireflection film, and a transparent conductive film (ITO film, etc.). Can be mentioned.
The protective film of the present invention is preferably used for a polarizing plate, and more preferably used for an AG polarizing plate, from the viewpoint of exhibiting excellent step followability.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

(Manufacturing Example 1)
-Manufacture of (meth) acrylic resin-
70.0 parts by mass of ethyl acetate is placed in a reaction vessel equipped with a thermometer, a stirrer, a nitrogen introduction tube and a reflux cooler, and 60.0 parts by mass of n-butyl acrylate (BA) is placed in another container. Add 30.0 parts by mass of -ethylhexyl acrylate (2EHA) and 10.0 parts by mass of ω-carboxy-polycaprolactone (n≈2) monoacrylate (trade name: Aronix M-5300, manufactured by Toa Synthetic Co., Ltd.) and mix. Was prepared as a monomer mixture.
Of this monomer mixture, 20.0% by mass was added to the reaction vessel, and then the air in the reaction vessel was replaced with nitrogen gas, and then azobisisobutyronitrile (hereinafter, also referred to as "AIBN") was used as a polymerization initiator. The initial reaction was started by adding 0.01 parts by mass and raising the temperature of the mixture in the reaction vessel to 85 ° C. in a nitrogen atmosphere under stirring.
After the initial reaction was almost completed, the reaction was carried out for about 2 hours while sequentially adding 80.0% by mass of the remaining monomer mixture and 15.0 parts by mass of ethyl acetate and 0.10 parts by mass of AIBN, respectively, and subsequently. , The reaction was carried out for another 2 hours. Then, a solution prepared by dissolving 0.10 part by mass of t-butyl peroxypivalate in 25.0 parts by mass of ethyl acetate was added dropwise to the monomer mixture over 1 hour, and the mixture was further reacted for 1.5 hours. After completion of the reaction, a solution of the (meth) acrylic resin (A) was obtained.
Table 1 shows the acid value and weight average molecular weight (Mw) of the obtained (meth) acrylic resin (A) solution.
The acid value and the weight average molecular weight (Mw) are calculated by the method described above.

The acid value was calculated as follows.
Acid value (mgKOH / g) = {(A / 100) ÷ B} × 56.1 × 1000 × C
A = Content (% by mass) of vinyl monomer having a carboxy group in all the monomers used for (meth) acrylic resin: 10
B = Molecular weight of Aronix M-5300: 300.4
C = Number of carboxy groups contained in one molecule of vinyl monomer having a carboxy group: 1
Acid value = {(10/100) ÷ 300.4} x 56.1 x 1000 x 1 = about 18.7

(Production Examples 2 to 6)
A (meth) acrylic resin solution was produced in the same manner as in Production Example 1 except that the monomer composition was changed to the monomer composition shown in Table 1 and the amount of the initiator was appropriately adjusted. Table 1 shows the acid value and weight average molecular weight (Mw) of the obtained (meth) acrylic resin.
The acid value and the weight average molecular weight (Mw) are calculated by the method described above.

The abbreviations in Table 1 are as follows. In addition, "-" in Table 1 indicates that the corresponding component is not included.
BA: n-butyl acrylate, 2EHA: 2-ethylhexyl acrylate, M-5300: ω-carboxy-polycaprolactone (n≈2) monoacrylate (trade name: Aronix M-5300, manufactured by Toagosei Co., Ltd.) (general formula) Monomer represented by (1a))
・ AA: Acrylic acid ・ 4HBA: 4-Hydroxybutyl acrylate

(Example 1)
222.2 parts by mass (as solid content) of the solution (solid content 45%) of the (meth) acrylic resin (A) prepared above in a four-necked flask equipped with a stirring blade, a thermometer, a cooler and a dropping funnel. (100 parts by mass) was charged, and the liquid temperature in the flask was maintained at around 25 ° C., and the mixture was mixed and stirred for 4 hours. As a metal chelate-based cross-linking agent (B), an aluminum chelate diluted product (solid content 9.72% by mass) obtained by diluting aluminum tris acetylacetonate (trade name: aluminum chelate A, manufactured by Kawaken Fine Chemical Co., Ltd.) with acetylacetone and toluene. ) 25.7 parts by mass (2.5 parts by mass as a solid content) was added, and the mixture was sufficiently stirred to obtain a pressure-sensitive adhesive composition solution for a protective film.
The "solid content" is a residue obtained by removing the solvent from the solution of the (meth) acrylic resin.

-Making a protective film-
The pressure-sensitive adhesive composition solution prepared above is applied onto a polyethylene terephthalate (PET) film (trade name: Teijin Tetron Film Type G2, thickness 38 μm, manufactured by Teijin DuPont Film Co., Ltd.) after drying at a coating rate of 20 g / m. ^It was applied so as to be 2. Then, it was dried at 100 ° C. for 60 seconds in a hot air circulation type dryer to form an adhesive layer on the PET film, and a PET film with an adhesive layer was prepared.
After that, the pressure-sensitive adhesive layer is brought into contact with the peel-treated surface of the release film (trade name: Film Vina 100E-0010NO23, thickness 100 μm, manufactured by Fujimori Kogyo Co., Ltd.) that has been easily peeled with a silicone-based release treatment agent. A PET film with attachment was placed to form a laminated body. This laminate was passed through a pair of pressurized nip rolls, pressure-bonded and bonded, and then cured under the conditions of 23 ° C. and 50% RH for 1 hour to obtain a protective film.

[evaluation]
-Followability-
An uneven optical film (AG polarizing plate) having an arithmetic mean roughness Ra of 0.85 μm was prepared (see FIG. 1). The arithmetic mean roughness Ra is a value calculated by measuring a range of 283 μm × 212 μm using a laser microscope (device name: Laser microscope VK-X200, manufactured by KEYENCE CORPORATION).

The uneven optical film and the protective film produced above were superposed, and a 2 kg rubber roll was reciprocated twice and crimped to cut into a size of 5 cm × 2.5 cm. Then, it was allowed to stand for 24 hours in a 23 ° C. and 50% RH environment to obtain an optical film sample for evaluation.
Further, a polyethylene sample for evaluation was prepared by the same method as described above except that the concave-convex optical film was changed to a polyethylene (PE) plate (EL-N-AN grade, manufactured by Partec Co., Ltd.). The arithmetic mean roughness Ra of the surface of the PE plate was 2.88 μm (see FIG. 2). The arithmetic mean roughness Ra is a value calculated by measuring the entire acquired image (707 μm × 530 μm) as in the case of the uneven optical film.

The protective film was peeled off from each sample after standing, and the state of the adhesive layer of each protective film was visually observed to confirm the presence or absence of deformation of the adhesive layer.
Here, the deformation of the pressure-sensitive adhesive layer means that the pressure-sensitive adhesive layer is deformed when a concave or convex shape is observed on the surface of the pressure-sensitive adhesive layer of the protective film after peeling.

If deformation of the adhesive layer is visually confirmed, further observe the surface of the adhesive layer using a laser microscope (device name: Laser microscope VK-X200, manufactured by KEYENCE CORPORATION), and check the followability according to the following evaluation criteria. evaluated. The results are shown in Table 2.
If the evaluation standard is "A", it is judged that the followability is excellent.

<Evaluation criteria>
A: The deformation of the pressure-sensitive adhesive layer can be visually determined, and the deformation of the pressure-sensitive adhesive layer can be determined using a laser microscope.
B: Deformation of the adhesive layer cannot be visually determined.
C: The adhesive strength of the protective film is very low, the bonding itself is difficult, and the deformation of the adhesive layer cannot be visually confirmed.
D: There is adhesive residue on the adherend after the protective film is peeled off, and the deformation of the adhesive layer cannot be visually confirmed.

-Adhesive strength (peeling property)-
The concave-convex optical film (AG polarizing plate) and the protective film were brought into contact with the AG polarizing plate and the pressure-sensitive adhesive layer, and a 2 kg rubber roll was pressure-bonded twice to make a cut into a size of 15 cm × 2.5 cm. Then, it was allowed to stand for 24 hours in a 23 ° C. and 50% RH environment to obtain an optical film sample for evaluation.
A desktop material tester (model number: STA-1225, manufactured by Orientec Co., Ltd.) was used as the measuring device, and the protective film was removed from the evaluation optical film sample in the long side direction under the condition of a peeling speed of 0.3 m / min. The adhesive strength (unit: N / 25 mm) when peeled by 180 ° was measured.
When the adhesive strength was in the range of 0.05 N / 25 mm to less than 1 N / 25 mm, it was judged that the peelability to the member having irregularities on the surface was excellent.

(Examples 2 to 7 and Comparative Examples 1 to 7)
An adhesive composition for a protective film as shown in Table 2 was prepared in the same manner as in Example 1 except that the composition of Example 1 was changed to the composition shown in Table 2. Using the prepared pressure-sensitive adhesive composition, an optical film sample for evaluation and a polyethylene sample for evaluation were prepared in the same manner as in Example 1, and each was evaluated. The results obtained are shown in Table 2.
The DBTDL contained in the pressure-sensitive adhesive compositions of Comparative Examples 5 and 6 is a cross-linking catalyst and does not correspond to the metal chelate-based cross-linking agent (B).

The abbreviations in Table 2 are as follows. In addition, "-" in Table 2 indicates that the corresponding component is not contained or measurement is not possible.
・ LiTFSI: Li (CF ₃ SO ₂ ) ₂ N (manufactured by Morita Chemical Industries, Ltd.)
-DBTDL: Dibutyltin dilaurate (manufactured by Wako Pure Chemical Industries, Ltd., appropriately diluted with acetylacetone)
-Aluminum chelate A: Aluminum trisacetylacetonate (trade name: aluminum chelate A, manufactured by Kawaken Fine Chemical Co., Ltd., diluted to 9.7% by mass with toluene and acetylacetone)
-Coronate L: Adduct body of tolylene diisocyanate and trimethylolpropane (trade name: Coronate L, manufactured by Tosoh Corporation, solid content 100% by mass)
-Tetrad C: 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane (trade name: TETRAD-C, manufactured by Mitsubishi Gas Chemical Company, Inc.)
-Sumijour N3300: Isocyanurate-modified hexamethylene diisocyanate (manufactured by Sumika Cobestrourethane Co., Ltd., solid content 100% by mass)

The pressure-sensitive adhesive layer, which is a crosslinked product of the pressure-sensitive adhesive compositions of Examples 1 to 7, containing at least a (meth) acrylic resin having a carboxy group and a metal chelate-based cross-linking agent, has excellent step-following property and peelability. It was excellent.
In particular, the pressure-sensitive adhesive layer, which is a crosslinked product of the pressure-sensitive adhesive compositions of Examples 1 to 5, was particularly excellent in the balance of both step-following property and peelability.

On the other hand, in the pressure-sensitive adhesive layer which is a cross-linked product of the pressure-sensitive adhesive compositions of Comparative Example 1 and Comparative Example 2 containing an isocyanate-based cross-linking agent, the pressure-sensitive adhesive residue was observed on the adherend after peeling, and the step-following property was improved. It was inferior and had poor peelability because the adhesive strength was too high.
Further, the pressure-sensitive adhesive layer, which is a cross-linked product of the pressure-sensitive adhesive compositions of Comparative Examples 3 and 4 containing an epoxy-based cross-linking agent, was too hard and was inferior in step-following property.
In Comparative Example 5 containing a (meth) acrylic resin having no carboxy group and an isocyanate-based cross-linking agent, since a cross-linked structure is difficult to be formed, the adhesive strength is very low, the peelability is inferior, and the step tracking is performed. It was inferior in sex. Further, in Comparative Example 6 containing a (meth) acrylic resin having no carboxy group and increasing the content of the isocyanate-based cross-linking agent, the adhesive strength was obtained, but the step followability was inferior.
In Comparative Example 7, which contained a (meth) acrylic resin having no carboxy group and a metal chelate-based cross-linking agent, a cross-linked structure could not be formed, and the step followability and peelability were particularly inferior.

Further, as shown in FIGS. 1 and 3, it can be seen that the pressure-sensitive adhesive layer, which is a crosslinked product from the pressure-sensitive adhesive composition of the present invention, sufficiently follows the member having irregularities on the surface.

From the above, the pressure-sensitive adhesive layer, which is a crosslinked product of the pressure-sensitive adhesive composition of the present invention, is excellent in step-following property and peelability, and therefore can be suitably used as a protective film for an optical member having irregularities on its surface.

Claims (8)

A (meth) acrylic resin (A) having at least a carboxy group and
Metal chelate cross-linking agent (B) and
Only including,
The (meth) acrylic resin (A) has a structural unit represented by the following general formula (1) and does not contain a hydroxyl group.
Adhesive composition for protective film.

(In the general formula (1), L represents a divalent linking group composed of at least one selected from the group consisting of an alkylene group, an arylene group, a carbonyl group and an oxygen atom, and R ¹ is a hydrogen atom or a methyl group. However, when L contains an oxygen atom, the oxygen atom forms a group bonded to at least one selected from the group consisting of an alkylene group, an arylene group and a carbonyl group, and -COO- and -CO are formed. Combine with-.) The pressure-sensitive adhesive composition for a protective film according to claim 1, wherein the (meth) acrylic resin (A) has an acid value of 9 mgKOH / g to 80 mgKOH / g. The pressure-sensitive adhesive composition for a protective film according to claim 1 or 2 , which is used for an optical member. The pressure-sensitive adhesive composition for a protective film according to claim 3 , wherein the arithmetic average roughness Ra of the surface of the optical member is 0.1 μm to 3 μm. The pressure-sensitive adhesive composition for a protective film according to claim 4 , wherein the optical member has irregularities on its surface, and the height difference between the irregularities is 1 μm to 20 μm. The pressure-sensitive adhesive composition for a protective film according to claim 5 , wherein the unevenness has at least an aspect ratio of the convex portion of 0.5 to 2. The pressure-sensitive adhesive composition for a protective film according to any one of claims 3 to 6 , wherein the optical member is an antiglare-treated polarizing plate. A protective film having a pressure-sensitive adhesive layer which is a crosslinked product of the pressure-sensitive adhesive composition for a protective film according to any one of claims 1 to 7, and a base material.

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