JP6905476B2 - Adhesive composition and adhesive film for fluororesin base material - Google Patents

Description

The present invention relates to a pressure-sensitive adhesive composition for a fluororesin base material and a pressure-sensitive adhesive film.

Various display boards such as signs, advertisements, and signboards are provided with, for example, a printing layer formed by an inkjet method. On a display board installed outdoors, the surface of the print layer is likely to be soiled to reduce visibility, and the print layer is likely to fade due to deterioration over time. Therefore, a protective film is provided on the surface of the printing layer of the display board installed outdoors. An acrylic adhesive is used to attach the protective film to the display board.
The protective film provided with the pressure-sensitive adhesive layer formed of the acrylic pressure-sensitive adhesive is, for example, a pressure-sensitive adhesive film having a base material made of a fluororesin film and a pressure-sensitive adhesive layer containing an acrylic-based pressure-sensitive adhesive. However, a fluororesin-based adhesive film containing a triazine-based ultraviolet absorber is known (see, for example, Patent Document 1).

In addition, a reflective sheet may be attached to the surface of the display board installed outdoors for the purpose of enhancing visibility. In this case, the print layer is often provided on the outermost surface of the reflective sheet.
As the reflective sheet provided with the protective film, for example, a fluororesin film having a total light transmittance of 80% or more is mainly acrylic on the surface layer of the retroreflective sheet having a smooth surface layer on the light incident side. A retroreflective sheet formed by being laminated via an adhesive layer made of a based resin is known (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2012-17407 International Publication No. 97/22098

By the way, the protective film used for the display board installed outdoors is required to have weather resistance. For example, the pressure-sensitive adhesive layer included in the protective film is formed by using a pressure-sensitive adhesive composition containing a light stabilizer in order to enhance its weather resistance. In particular, a hindered amine-based light stabilizer (so-called HALS) is often used as a light stabilizer capable of forming a pressure-sensitive adhesive layer having excellent weather resistance.
However, when a protective film having an adhesive layer containing a hindered amine light stabilizer is used in a high humidity environment (for example, in an area with a large amount of rainfall), the adhesive layer may be whitened. Whitening of the adhesive layer included in the protective film can reduce the visibility of the information displayed on the display board, which can be a serious problem especially for road signs. Therefore, the pressure-sensitive adhesive composition used for the protective film of the display board is required to be able to form a pressure-sensitive adhesive layer that is difficult to whiten even in a high humidity environment.
Further, the pressure-sensitive adhesive composition used for the protective film of the display board is required to be able to form a pressure-sensitive adhesive layer that is difficult to peel off from the display board.
Further, in general, the pressure-sensitive adhesive layer included in a pressure-sensitive adhesive film such as a protective film is required to have excellent adhesion to a base material.

The problem to be solved by the present invention is that it contains a hindered amine-based light stabilizer, is difficult to whiten in a high-humidity environment, exhibits high adhesive strength to an adherend, and has adhesion to a fluorine-based resin base material. It is an object of the present invention to provide a pressure-sensitive adhesive composition for a fluororesin base material capable of forming an excellent pressure-sensitive pressure-sensitive adhesive layer.
Further, the problem to be solved by the present invention is that it contains a hindered amine-based light stabilizer, is difficult to whiten in a high-humidity environment, exhibits high adhesive strength to an adherend, and has a fluorine-based resin base material. It is an object of the present invention to provide an adhesive film provided with an adhesive layer having excellent adhesiveness.

Specific means for solving the problem include the following aspects.
<1> A pressure-sensitive adhesive composition for a fluorine-based resin base material, which comprises a (meth) acrylic polymer having a carboxy group, an isocyanate-based cross-linking agent, and a hindered amine-based light stabilizer having a molecular weight of 300 or more and 650 or less.
<2> The (meth) acrylic polymer according to <1>, wherein the (meth) acrylic polymer contains a structural unit derived from a monomer having a carboxy group, and the monomer having a carboxy group is acrylic acid. Adhesive composition for fluororesin base material.
<3> The (meth) acrylic polymer contains a structural unit derived from a monomer having a carboxy group, and the content of the structural unit derived from the monomer having a carboxy group is as described above ( Meta) The pressure-sensitive adhesive composition for a fluororesin base material according to <1> or <2>, which is 5% by mass or more and 15% by mass or less based on all the constituent units of the acrylic polymer.
<4> The fluororesin base material according to any one of <1> to <3>, wherein the (meth) acrylic polymer contains a structural unit derived from a (meth) acrylic acid alkyl ester monomer. Adhesive composition for.
<5> The adhesive composition for a fluorine-based resin base material provided on the fluorine-based resin base material and the above-mentioned fluorine-based resin base material and according to any one of <1> to <4>. An adhesive film comprising an adhesive layer.
<6> The adhesive film according to <5>, which is used as a surface protective film for a reflective sheet.

According to the present invention, a pressure-sensitive adhesive containing a hindered amine-based light stabilizer, which is difficult to whiten in a high-humidity environment, exhibits high adhesive strength to an adherend, and has excellent adhesion to a fluorine-based resin base material. A pressure-sensitive adhesive composition for a fluororesin base material capable of forming a layer is provided.
Further, according to the present invention, it contains a hindered amine-based light stabilizer, is difficult to whiten in a high-humidity environment, exhibits high adhesive strength to an adherend, and has excellent adhesion to a fluorine-based resin base material. An adhesive film with an adhesive layer is provided.

Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be carried out with appropriate modifications within the scope of the object of the present invention.

The numerical range indicated by using "~" in the present specification means a range including the numerical values before and after "~" as the minimum value and the maximum value, respectively.
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, a combination of two or more preferred embodiments is a more preferred embodiment.
In the present specification, the amount of each component means the total amount of a plurality of kinds of substances when a plurality of kinds of substances corresponding to each component are present, unless otherwise specified.

As used herein, the term "adhesive composition" means a liquid or paste-like substance after the (meth) acrylic polymer and the cross-linking agent are mixed and before the cross-linking reaction is completed.
As used herein, the term "adhesive layer" means a layer made of a substance after the cross-linking reaction in the pressure-sensitive adhesive composition is completed. The pressure-sensitive adhesive layer is, for example, a solid or gel-like layer.

As used herein, the term "(meth) acrylic polymer" means that the content of structural units derived from a monomer having a (meth) acryloyl group constitutes all structural units (that is, (meth) acrylic polymer). It means a polymer which is 50% by mass or more of the total constituent units.

In the present specification, "(meth) acrylic" is a term that includes both "acrylic" and "methacrylic", and "(meth) acrylate" is a term that includes both "acrylate" and "methacrylate". , "(Meta) acryloyl" is a term that includes both "acryloyl" and "methacrylic".

In the present specification, "difficult to whiten in a high humidity environment" may be referred to as "excellent in moisture resistance".
In the present specification, the "fluorine-based resin base material" means a base material containing a resin having a fluorine atom.

[Adhesive composition for fluororesin base material]
The pressure-sensitive adhesive composition for a fluororesin base material of the present invention (hereinafter, appropriately referred to as “pressure-sensitive adhesive composition”) is a (meth) acrylic polymer having a carboxy group (hereinafter, “specific (meth) acrylic”). It also includes a "polymer"), an isocyanate-based cross-linking agent, and a hindered amine-based light stabilizer having a molecular weight of 300 or more and 650 or less (hereinafter, also referred to as "specific light stabilizer").

Hindered amine-based light stabilizers are often used as light stabilizers capable of forming an adhesive layer having excellent weather resistance. However, when a protective film having an adhesive layer containing a hindered amine light stabilizer is used in a high humidity environment (for example, in an area with a large amount of rainfall), the adhesive layer may be whitened. Whitening of the adhesive layer included in the protective film can reduce the visibility of the information displayed on the display board, which can be a serious problem especially for road signs.
As a result of diligent studies by the present inventors, the pressure-sensitive adhesive layer is whitened by the action of water on the hindered amine-based light stabilizer, and the pressure-sensitive adhesive layer is whitened by using a hindered amine-based light stabilizer having a low molecular weight. It was found that it can suppress. However, as a result of further studies by the inventors, in the pressure-sensitive adhesive layer containing a hindered amine-based light stabilizer having a low molecular weight, the hindered amine-based light stabilizer is localized near the interface of the pressure-sensitive adhesive layer with the adherend. , It was found that the adhesive strength to the adherend tends to be low.
By the way, a fluorine-based resin film is often used as a base material used for a protective film for a display board. According to a further study by the present inventors, in the pressure-sensitive adhesive layer containing a hindered amine-based light stabilizer having a low molecular weight, the hindered amine-based light stabilizer is also localized near the interface of the pressure-sensitive adhesive layer with the base material. It was found that the adhesiveness between the pressure-sensitive adhesive layer and the base material tends to decrease with time, and such a tendency is remarkable in the fluororesin base material.

On the other hand, according to the pressure-sensitive adhesive composition of the present invention, although it contains a hindered amine-based light stabilizer, it is difficult to whiten in a high-humidity environment, exhibits high adhesive strength to an adherend, and is fluorine-based. A pressure-sensitive adhesive layer having excellent adhesion to a resin base material can be formed.
Although it is not clear why the pressure-sensitive adhesive composition of the present invention can exert such an effect, the present inventors speculate as follows. However, the following speculation does not limitly interpret the effect of the pressure-sensitive adhesive composition of the present invention, but is described as an example.

The pressure-sensitive adhesive composition of the present invention contains a relatively low molecular weight hindered amine-based light stabilizer (that is, a specific light stabilizer) having a molecular weight of 300 or more and 650 or less, so that the pressure-sensitive adhesive is difficult to whiten in a high humidity environment. Layers can be formed.
In the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention, the specific light stabilizer can be localized near the interface of the pressure-sensitive adhesive layer with the adherend. The pressure-sensitive adhesive layer in which the specific light stabilizer is localized near the interface of the pressure-sensitive adhesive layer with the adherend has a low adhesive force to the adherend, and thus easily peels off from the adherend. Since the pressure-sensitive adhesive composition of the present invention contains a (meth) acrylic polymer having a carboxy group (that is, a specific (meth) acrylic polymer), it is excellent in wettability to an adherend. As a result, it is considered that the pressure-sensitive adhesive composition of the present invention contains a hindered amine-based light stabilizer having a relatively low molecular weight, but the pressure-sensitive adhesive layer formed exhibits high adhesive strength to the adherend.
Further, in the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention, the specific light stabilizer can be localized near the interface of the pressure-sensitive adhesive layer with the fluorine-based resin base material. The pressure-sensitive adhesive layer in which the specific light stabilizer is localized near the interface of the pressure-sensitive adhesive layer with the base material has low adhesion to the base material and is easily peeled off from the base material. The pressure-sensitive adhesive composition of the present invention contains a specific (meth) acrylic polymer and an isocyanate-based cross-linking agent, and the specific light stabilizer acts on the cross-linking between the specific (meth) acrylic polymer and the isocyanate-based cross-linking agent. As a result, the cross-linking becomes appropriate, and the localization of the specific light stabilizer near the interface of the pressure-sensitive adhesive layer with the base material is suppressed. As a result, it is considered that the pressure-sensitive adhesive composition of the present invention contains a hindered amine-based light stabilizer having a relatively low molecular weight, but the pressure-sensitive adhesive layer formed has excellent adhesion to the fluorine-based resin base material.
Since the fluorine-based resin has a high melt processing temperature, it is difficult to add a hindered amine-based light stabilizer to the fluorine-based resin base material.

With respect to the pressure-sensitive adhesive composition of the present invention, the acrylic pressure-sensitive adhesives described in Patent Document 1 (Japanese Patent Laid-Open No. 2012-17407) and Patent Document 2 (International Publication No. 97/22098) have a molecular weight of 650. It is believed that the pressure-sensitive adhesive layer formed is whitened in a high humidity environment because it contains more hindered amine light stabilizers.

Hereinafter, each component of the pressure-sensitive adhesive composition of the present invention will be described.

[Specific (meth) acrylic polymer]
The (meth) acrylic polymer (that is, the specific (meth) acrylic polymer) contained in the pressure-sensitive adhesive composition of the present invention has a carboxy group.
In the present invention, in the specific (meth) acrylic polymer, the specific light stabilizer is localized near the surface of the pressure-sensitive adhesive layer (that is, near the interface with the adherend and near the interface with the substrate). Contributes to the improvement of the decrease in the adhesive force of the pressure-sensitive adhesive layer to the adherend and the decrease in the adhesion of the pressure-sensitive adhesive layer to the fluororesin base material.

The specific (meth) acrylic polymer may be a homopolymer or a copolymer. The specific (meth) acrylic polymer may be, for example, a homopolymer of a monomer having a carboxy group, and a carboxy group is introduced into the homopolymer of a monomer having no carboxy group by substitution. It may be a polymer of a monomer having a carboxy group and a monomer having no carboxy group.
The carboxy group of the specific (meth) acrylic polymer contributes to the formation of a crosslinked structure between the specific (meth) acrylic polymer and the isocyanate-based crosslinker. By the action of the specific light stabilizer on the cross-linking between the specific (meth) acrylic polymer and the isocyanate-based cross-linking agent, the cross-linking becomes appropriate and the adhesion between the pressure-sensitive adhesive layer and the fluorine-based resin base material can be improved. ..

<Constituent unit derived from a monomer having a carboxy group>
The specific (meth) acrylic polymer preferably contains a structural unit derived from a monomer having a carboxy group.
As used herein, the "constituent unit derived from a monomer having a carboxy group" means a structural unit formed by addition polymerization of a monomer having a carboxy group.

The type of monomer having a carboxy group is not particularly limited.
Examples of the monomer having a carboxy group include acrylic acid, methacrylic acid, crotonic acid, maleic anhydride, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, and ω-carboxy-polycaprolactone mono (meth) acrylate (for example, ω). -Carboxy-polycaprolactone (n≈2) monoacrylate), succinic acid ester (for example, 2-acryloyloxyethyl-succinic acid) and the like can be mentioned.
Among these, the monomer having a carboxy group is selected from the group consisting of acrylic acid, ω-carboxy-polycaprolactone mono (meth) acrylate, and succinic acid ester, for example, from the viewpoint of reactivity with a cross-linking agent. At least one monomer is preferable, and acrylic acid is more preferable from the viewpoint that the wettability of the pressure-sensitive adhesive composition to the adherend is improved and the pressure-sensitive adhesive layer can exhibit higher adhesive strength.

The specific (meth) acrylic polymer may contain only one type of structural unit derived from a monomer having a carboxy group, or may contain two or more types.

The content (ratio) of the structural units derived from the monomer having a carboxy group in the specific (meth) acrylic polymer is not particularly limited, but for example, all the structural units of the specific (meth) acrylic polymer (that is,). , 5% by mass or more and 15% by mass or less, more preferably 6% by mass or more and 12% by mass or less, more preferably 8% by mass, based on all the structural units constituting the specific (meth) acrylic polymer; hereinafter the same). More preferably 12% by mass or less.
When the content of the structural unit derived from the monomer having a carboxy group in the specific (meth) acrylic polymer is 5% by mass or more with respect to all the structural units of the specific (meth) acrylic polymer, the adhesive is adhered. Since the cohesive force of the agent layer is further improved, the pressure-sensitive adhesive layer may exhibit higher adhesive force to the adherend.
When the content of the structural unit derived from the monomer having a carboxy group in the specific (meth) acrylic polymer is 15% by mass or less with respect to all the structural units of the specific (meth) acrylic polymer, the adhesive is adhered. Since the adhesive layer exhibits sufficient wettability to the adherend in a state of high cohesive force, it is possible to better suppress a decrease in the adhesive force of the pressure-sensitive adhesive layer to the adherend.

<Constituent unit derived from (meth) acrylic acid alkyl ester monomer>
The specific (meth) acrylic polymer preferably contains a structural unit derived from the (meth) acrylic acid alkyl ester monomer.
The structural unit derived from the (meth) acrylic acid alkyl ester monomer contributes to the adjustment of the adhesive strength of the pressure-sensitive adhesive layer.

In the present specification, the “constituent unit derived from the (meth) acrylic acid alkyl ester monomer” means a structural unit formed by addition polymerization of the (meth) acrylic acid alkyl ester monomer.

As the (meth) acrylic acid alkyl ester monomer, an unsubstituted (meth) acrylic acid alkyl ester monomer is preferable, and an unsubstituted acrylic acid alkyl ester monomer is more preferable.
The type of (meth) acrylic acid alkyl ester monomer is not particularly limited.
The alkyl group of the (meth) acrylic acid alkyl ester monomer may be linear, branched or cyclic.
The carbon number of the alkyl group is preferably in the range of 1 to 18, more preferably in the range of 1 to 12, from the viewpoint of the adhesive force of the formed pressure-sensitive adhesive layer on the adherend and the adhesion to the substrate. ..

Examples of the (meth) acrylic acid alkyl ester monomer include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, s-butyl (meth) acrylate, and t. -Butyl (meth) acrylate, n-octyl (meth) acrylate, i-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-nonyl (meth) acrylate, i-nonyl (meth) acrylate, n-decyl Examples thereof include (meth) acrylate, n-dodecyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, and isobornyl (meth) acrylate.
Among these, as the (meth) acrylic acid alkyl ester monomer, for example, 2-ethylhexyl acrylate (2EHA) and n-butyl acrylate (n-BA) from the viewpoint that the adhesive strength of the pressure-sensitive adhesive layer can be easily adjusted. ) Is preferred. Further, as the (meth) acrylic acid alkyl ester monomer, for example, methyl is obtained from the viewpoint that the wettability of the pressure-sensitive adhesive composition to an adherend (particularly, an adherend containing an acrylic resin) can be improved. At least one selected from acrylate (MA) and ethyl acrylate (EA) is preferable.

When the specific (meth) acrylic polymer contains a structural unit derived from the (meth) acrylic acid alkyl ester monomer, the specific (meth) acrylic polymer contains only one structural unit derived from the (meth) acrylic acid alkyl ester monomer. It may be included, and two or more kinds may be included.

When the specific (meth) acrylic polymer contains a structural unit derived from the (meth) acrylic acid alkyl ester monomer, it is derived from the (meth) acrylic acid alkyl ester monomer in the specific (meth) acrylic polymer. The content rate (ratio) of the constituent units is preferably 30% by mass or more with respect to all the constituent units of the specific (meth) acrylic polymer, for example, from the viewpoint that the adhesive strength of the pressure-sensitive adhesive layer can be easily adjusted. 40% by mass or more is more preferable, and 50% by mass or more is further preferable.
The upper limit of the content (ratio) of the structural unit derived from the (meth) acrylic acid alkyl ester monomer in the specific (meth) acrylic polymer is not particularly limited, and for example, the specific (meth) acrylic polymer 90% by mass or less is preferable with respect to all the constituent units.

<Other building blocks>
The specific (meth) acrylic polymer is the above-mentioned structural unit, that is, the structural unit derived from the monomer having a carboxy group, and the (meth) acrylic acid within the range in which the effect of the present invention is exhibited. It may contain a structural unit (so-called other structural unit) other than the structural unit derived from the alkyl ester monomer.

The type of monomer constituting the other structural unit is not particularly limited.
Examples of the monomer constituting the other structural unit include a monomer having a hydroxyl group.
Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 6-hydroxyhexyl (6-hydroxyhexyl). Meta) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, 3-methyl-3-hydroxybutyl (meth) acrylate, 1,1-dimethyl-3-hydroxybutyl (meth) acrylate, 1,3-Dimethyl-3-hydroxybutyl (meth) acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth) acrylate, 2-ethyl-3-hydroxyhexyl (meth) acrylate, glycerin mono (meth) Examples thereof include acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, and poly (ethylene glycol-propylene glycol) mono (meth) acrylate.

Examples of the monomer constituting the other structural unit include (meth) acrylate having a cyclic group represented by benzyl (meth) acrylate and phenoxyethyl (meth) acrylate, methoxyethyl (meth) acrylate and ethoxyethyl (meth). Acrylic alkyl (meth) acrylate represented by meta) acrylate, styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and aromatic monovinyl represented by vinyltoluene, acrylonitrile and methacrylonitrile. Examples thereof include vinyl cyanate typified by nitrile, vinyl acrylate, vinyl acetate, vinyl propionate, vinyl esters typified by vinyl versaticate, and various derivatives of these monomers.

-Weight average molecular weight of specific (meth) acrylic polymer-
The weight average molecular weight (Mw) of the specific (meth) acrylic polymer is not particularly limited, but is preferably 300,000 or more and 2 million or less, more preferably 400,000 or more and 1.5 million or less, and 400,000 or more and 1.2 million or less. More preferably, it is more preferably 500,000 or more and 1.2 million or less.
When the weight average molecular weight (Mw) of the specific (meth) acrylic polymer is 300,000 or more, the cohesive force is further improved and higher adhesive force can be exhibited.
When the weight average molecular weight (Mw) of the specific (meth) acrylic polymer is 2 million or less, the wettability to the adherend can be further improved and higher adhesive strength can be exhibited.
The weight average molecular weight (Mw) of the specific (meth) acrylic polymer is desired by adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, and the like. Can be a value.

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

~conditions~
Measuring device: High-speed GPC (Model number: HLC-8220 GPC, Tosoh Corporation)
Detector: Differential refractometer (RI) (embedded in HLC-8220, Tosoh Corporation)
Column: 4 TSK-GEL GMHXL (Tosoh Corporation) connected in series Column temperature: 40 ° C
Eluent: tetrahydrofuran Sample concentration: 0.2% by mass
Injection volume: 100 μL
Flow rate: 0.6 mL / min

-Glass transition temperature of specific (meth) acrylic polymer-
The glass transition temperature (Tg) of the specific (meth) acrylic polymer is not particularly limited, but is, for example, preferably −50 ° C. or higher and −10 ° C. or lower, more preferably −45 ° C. or higher and −15 ° C. or lower, and −40 ° C. More preferably −20 ° C. or lower.
When the glass transition temperature (Tg) of the specific (meth) acrylic polymer is −50 ° C. or higher, the cohesive force is further improved and higher adhesive force can be exhibited.
When the glass transition temperature (Tg) of the specific (meth) acrylic polymer is −10 ° C. or lower, the wettability to the adherend can be further improved and higher adhesive strength can be exhibited.

The glass transition temperature (Tg) of the specific (meth) acrylic polymer is a value obtained by converting the absolute temperature (K) calculated from the following formula 1 into the Celsius temperature (° C.).
1 / Tg = m1 / Tg1 + m2 / Tg2 + ... + m (k-1) / Tg (k-1) + mk / Tgk (Equation 1)

In the formula 1, Tg1, Tg2, ..., Tg (k-1), and Tgk are the absolute temperatures (K) when each monomer constituting the specific (meth) acrylic polymer is used as a homopolymer. ) Represents the glass transition temperature (Tg). m1, m2, ..., M (k-1), and mk represent the mole fractions of each monomer constituting the specific (meth) acrylic polymer, and m1 + m2 + ... + m (k-). 1) + mk = 1.
The absolute temperature (K) can be converted to the Celsius temperature (° C) by subtracting 273 from the absolute temperature (K), and the Celsius temperature (° C) can be converted to the absolute temperature (K) by adding 273 to the Celsius temperature (° C). Can be converted to.

The "glass transition temperature (Tg) when made into a homopolymer" refers to the glass transition temperature (Tg) represented by the absolute temperature (K) of the homopolymer produced by polymerizing the monomer alone. say.
The glass transition temperature (Tg) of the homopolymer was measured using a differential scanning calorimetry device (DSC) (model number: EXSTAR6000, Seiko Instruments Co., Ltd.) in a nitrogen stream, a measurement sample of 10 mg, and a temperature rise rate of 10 ° C./min. The turning point of the obtained DSC curve was taken as the glass transition temperature (Tg) of the homopolymer.

The "glass transition temperature (Tg) represented by the Celsius temperature (° C.) when made into a homopolymer" of a typical monomer is that 2-ethylhexyl acrylate (2EHA) is -76 ° C. and 2-ethylhexyl methacrylate (2-ethylhexyl methacrylate). 2EHMA) is -10 ° C, n-butyl acrylate (n-BA) is -57 ° C, n-butyl methacrylate is 21 ° C, t-butyl acrylate (t-BA) is 41 ° C, t-butyl methacrylate is 107 ° C, Methyl acrylate (MA) at 5 ° C, methyl methacrylate (MMA) at 103 ° C, isobonyl methacrylate (IBMX) at 155 ° C, ethyl acrylate (EA) at -27 ° C, 2-ethylhexyl acrylate (2EHA) at -76 ° C, Methacrylate is 185 ° C, 4-hydroxybutyl acrylate (4HBA) is -39 ° C, 2-hydroxyethyl acrylate (2HEA) is -15 ° C, 2-hydroxyethyl methacrylate (2HEMA) is 55 ° C, acrylic acid (AA) is 163 ° C, isooctyl acrylate (i-OA) -75 ° C, dimethylaminoethyl methacrylate (DM) 18 ° C, trifluoroethyl methacrylate 72 ° C, trifluoroethyl acrylate -5 ° C, ω-carboxy- Polycaprolactone (n≈2) monoacrylate is −30 ° C. and 2-acryloyloxyethyl-succinic acid is −40 ° C.

The glass transition temperature (Tg) of the specific (meth) acrylic polymer can be appropriately adjusted by using, for example, monomers having different glass transition temperatures (Tg) when they are homopolymers.

-Manufacturing method of specific (meth) acrylic polymer-
The method for producing the specific (meth) acrylic polymer is not particularly limited.
The specific (meth) acrylic polymer can be produced by polymerizing a monomer by a known polymerization method typified by, for example, solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization.
Among these, as a polymerization method, for example, when preparing a pressure-sensitive adhesive composition after the production of a specific (meth) acrylic polymer, solution polymerization is relatively easy and can be performed in a short time. Is preferable.

In solution polymerization, generally, a predetermined organic solvent, a monomer, a polymerization initiator, and a chain transfer agent used as needed are charged in a polymerization tank, and the mixture is stirred in a nitrogen stream or at the reflux temperature of the organic solvent. While heating for several hours. In this case, at least a part of the organic solvent, the monomer, the polymerization initiator and / or the chain transfer agent may be added sequentially.

Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, alcohol compounds and the like.
At the time of the polymerization reaction, only one of these organic solvents may be used, or two or more of these organic solvents may be mixed and used.

More specific examples of the organic solvent used in the polymerization reaction include benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetraline, decalin, and aroma. Aromatic hydrocarbons represented by group naphtha, n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and fatty type represented by terepine oil or Alicyclic hydrocarbons, ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and esters typified by methyl benzoate, Acenes such as acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and For glycol ethers typified by diethylene glycol monobutyl ether, methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-butyl alcohol. Typical examples are alcohols.

In the production of the specific (meth) acrylic polymer, it is preferable to use an organic solvent that does not easily cause chain transfer during the polymerization reaction of esters, ketones, etc., and in particular, the solubility of the specific (meth) acrylic polymer. From the viewpoint of ease of polymerization reaction and the like, it is preferable to use ethyl acetate.

Examples of the polymerization initiator include organic peroxides and azo compounds used in ordinary solution polymerization.
Organic peroxides include t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propylperoxydicarbonate, and di-2-ethylhexylperoxydicarbonate. , T-butylperoxypivalate, 2,2-bis (4,5-di-t-butylperoxycyclohexyl) propane, 2,2-bis (4,5-di-t-amylperoxycyclohexyl) propane, 2, 2-bis (4,5-di-t-octylperoxycyclohexyl) propane, 2,2-bis (4,5-di-α-cumylperoxycyclohexyl) propane, 2,2-bis (4,5-di) Examples thereof include -t-butylperoxycyclohexyl) butane and 2,2-bis (4,5-di-t-octylperoxycyclohexyl) butane.
Examples of the azo compound include 2,2'-azobisisobutynitrile (AIBN), 2,2'-azobis (2,4-dimethylvaleronitrile) (ABVN), and 2,2'-azobis (4-methoxy-2, 4-Dimethylvaleronitrile), 1,1'-azobis (cyclohexane-1-carbonitrile), 2,2'-azobis (isobutyric acid) dimethyl and the like.

In the production of the specific (meth) acrylic polymer, it is preferable to use a polymerization initiator that does not cause a graft reaction during the polymerization reaction, and in particular, it is preferable to use an azobis-based polymerization initiator.

The amount of the polymerization initiator used is not particularly limited, and is appropriately set according to, for example, the molecular weight of the target specific (meth) acrylic polymer.

In the production of the specific (meth) acrylic polymer, a chain transfer agent may be used, if necessary, as long as the object and effect of the present invention are not impaired.
Examples of the chain transfer agent include cyanoacetic acid, alkyl esters having 1 to 8 carbon atoms of cyanoacetic acid, bromoacetic acid, alkyl esters having 1 to 8 carbon atoms of bromoacetic acid, α-methylstyrene, anthracene, phenanthrene, and fluorene. , And aromatic compounds typified by 9-phenylfluorene, p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and aromatic nitro compounds typified by p-nitrotoluene, Benzoquinone and benzoquinone derivatives typified by 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives typified by tributylborane, carbon tetrabromide, carbon tetrachloride, 1,1,2,2- Tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloromethane, tribromomethane, halogenated hydrocarbons typified by 3-chloro-1-propene, aldehydes typified by chloral and furaldehyde, carbon number 1 to 1 18 alkyl mercaptans, aromatic mercaptans typified by thiophenols and toluene mercaptans, mercaptoacetic acid, alkyl esters of mercaptoacetic acid having 1 to 10 carbon atoms, hydroxyalkyl mercaptans having 1 to 12 carbon atoms, and binen. And terpenes typified by turpinolene.

When a chain transfer agent is used in the production of the specific (meth) acrylic polymer, the amount of the chain transfer agent used is not particularly limited, and for example, it depends on the molecular weight of the specific (meth) acrylic polymer of interest. , Set as appropriate.

The polymerization temperature is not particularly limited, and is appropriately set according to, for example, the molecular weight of the target specific (meth) acrylic polymer.

[Isocyanate-based cross-linking agent]
The pressure-sensitive adhesive composition of the present invention contains an isocyanate-based cross-linking agent.
The isocyanate-based cross-linking agent is a coating of the pressure-sensitive adhesive layer due to the specific light stabilizer being localized near the surface of the pressure-sensitive adhesive layer (that is, near the interface with the adherend and near the interface with the substrate). It contributes to the improvement of the decrease in the adhesive force to the body and the decrease in the adhesion of the pressure-sensitive adhesive layer to the fluororesin base material.

Examples of the isocyanate-based cross-linking agent include xylylene diisocyanate (XDI), diphenylmethane diisocyanate, triphenylmethane triisocyanate, aromatic polyisocyanate compounds typified by tolylene diisocyanate (TDI), hexamethylene diisocyanate (HMDI), isophorone diisocyanate, and the like. And chain or cyclic aliphatic polyisocyanate compounds typified by the hydrogenated additives of the above aromatic polyisocyanate compounds, biuret, dimer, trimeric or pentamer of these polyisocyanate compounds, these. Examples thereof include isocyanate compounds such as adducts of polyisocyanate compounds and polyol compounds such as trimethylolpropane.

Among these, as the isocyanate-based cross-linking agent, for example, when a pressure-sensitive adhesive film provided with a pressure-sensitive adhesive layer is used outdoors, coloring (so-called yellowing) of the pressure-sensitive adhesive layer due to the isocyanate-based cross-linking agent is unlikely to occur. From the viewpoint, hexamethylene diisocyanate, hexamethylene diisocyanate dimer, hexamethylene diisocyanate and polyol adduct, hexamethylene diisocyanate trimeric or pentameric isocyanurate, hexamethylene diisocyanate biuret, etc. Hexamethylene diisocyanate compounds derived from various hexamethylene diisocyanates are preferable.

As the isocyanate-based cross-linking agent, a commercially available product can be used.
Examples of commercially available isocyanate-based cross-linking agents include "Coronate (registered trademark) HX", "Coronate (registered trademark) HL-S", "Coronate (registered trademark) L", and "Coronate (registered trademark)" of Toso Co., Ltd. "L-45E", "Coronate (registered trademark) 2031", "Coronate (registered trademark) 2030", "Coronate (registered trademark) 2234", "Coronate (registered trademark) 2785", "Aquanate (registered trademark)""200","Aquanate (registered trademark) 210", "Sumijuru (registered trademark) N3300", "Death Module (registered trademark) N3400", and "Sumijuru (registered trademark)" of Sumika Cobestro Urethane Co., Ltd. ) N-75 ”, Asahi Kasei Co., Ltd.“ Duranate® E-405-80T ”,“ Duranate® 24A-100 ”,“ Duranate® TSE-100 ”, and Mitsui Takeda Chemical Co., Ltd. "Takenate (registered trademark) D-110N", "Takenate (registered trademark) D-120N", "Takenate (registered trademark) M-631N" and "MT-Orester (registered trademark) NP1200" Those commercially available under the trade name of can be preferably used.

The pressure-sensitive adhesive composition of the present invention may contain only one type of isocyanate-based cross-linking agent, or may contain two or more types.

The content of the isocyanate-based cross-linking agent in the pressure-sensitive adhesive composition of the present invention is not particularly limited, but for example, from the viewpoint that the adhesive strength of the pressure-sensitive adhesive layer to the adherend can be further improved, a specific (meth) acrylic-based adhesive is used. With respect to 100 parts by mass of the polymer, 0.1 parts by mass to 0.6 parts by mass is preferable, and 0.1 parts by mass to 0.4 parts by mass is more preferable.

[Specific light stabilizer]
The pressure-sensitive adhesive composition of the present invention contains a hindered amine-based light stabilizer (that is, a specific light stabilizer) having a molecular weight of 300 or more and 650 or less.
Since the molecular weight of the hindered amine light stabilizer is 300 or more and 650 or less, the pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer that is difficult to whiten in a high humidity environment even though it contains the hindered amine-based light stabilizer.
Further, since the pressure-sensitive adhesive composition of the present invention contains a hindered amine-based light stabilizer, a pressure-sensitive adhesive layer having excellent weather resistance can be formed.

The molecular weight of the hindered amine light stabilizer is 300 or more and 650 or less, preferably 350 or more and 600 or less, and more preferably 400 or more and 600 or less.
When the molecular weight of the hindered amine light stabilizer is 300 or more, it is easy to obtain.
When the molecular weight of the hindered amine light stabilizer is 650 or less, an adhesive layer that is difficult to whiten can be formed in a high humidity environment.

Specific light stabilizers include bis sebacate (1,2,2,6,6-pentamethyl-4-piperidyl) [trade name: Tinuvin® 765, BASF], bis sebacate (2,2). 6,6-Tetramethyl-4-piperidyl) [trade name: Tinuvin (registered trademark) 770DF, BASF Corporation] and the like.

The pressure-sensitive adhesive composition of the present invention may contain only one type of specific light stabilizer, or may contain two or more types.

The content of the specific light stabilizer in the pressure-sensitive adhesive composition of the present invention is not particularly limited, and is appropriately set from the viewpoint of adhesive strength, for example.
The content of the specific light stabilizer in the pressure-sensitive adhesive composition of the present invention is preferably 0.5 parts by mass to 10 parts by mass, preferably 0.5 parts by mass to 100 parts by mass, based on 100 parts by mass of the specific (meth) acrylic polymer. 5 parts by mass is more preferable, and 1 part to 4 parts by mass is further preferable.

[UV absorber]
The pressure-sensitive adhesive composition of the present invention preferably contains, for example, an ultraviolet absorber from the viewpoint of improving weather resistance.
The ultraviolet absorber is not particularly limited.
Examples of the ultraviolet absorber include a benzotriazole-based ultraviolet absorber, a benzophenone-based ultraviolet absorber, a benzoate-based ultraviolet absorber, a hydroxyphenyltriazine-based ultraviolet absorber, and the like.
Among these, as the ultraviolet absorber, a benzotriazole-based ultraviolet absorber is preferable from the viewpoint of coloring the pressure-sensitive adhesive layer and weather resistance.

Examples of the benzotriazole-based ultraviolet absorber include 2- (3,5-di-tert-amyl-2-hydroxyphenyl) benzotriazole [trade name: Tinuvin (registered trademark) 328, BASF], 2- (2-hydroxy). -5-tert-octylphenyl) benzotriazole [trade name: Tinuvin® 329, BASF], 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H- Benzotriazole [trade name: Tinuvin (registered trademark) 234, BASF], 2- (2-hydroxy-5-tert-butylphenyl) -2H-benzotriazole [trade name: Tinuvin (registered trademark) PS, BASF] , 2- (2H-benzotriazole-2-yl) -4,6-bis (1-methyl-1-phenylethyl) phenol [trade name: tertwin® 900, BASF], 2- (2H-) Benzotriazole-2-yl) -6- (1-methyl-1-phenylethyl) -4- (1,1,3,3-tetramethylbutyl) phenol [trade name: Tinuvin® 928, BASF, Inc. ], 2- [5-Chloro (2H) -benzotriazole-2-yl] -4-methyl-6- (tert-butyl) phenol [trade name: Tinuvin® 326, BASF], 2-2 '-Methylenebis [6- (2H-benzotriazole-2-yl) -4- (1, 1, 3, 3-tetramethylbutyl) phenol] [trade name: Tinuvin (registered trademark) 360, BASF], etc. Can be mentioned.

When the pressure-sensitive adhesive composition of the present invention contains an ultraviolet absorber, it may contain only one type of ultraviolet absorber, or may contain two or more types of the ultraviolet absorber.

The content of the ultraviolet absorber in the pressure-sensitive adhesive composition of the present invention is not particularly limited.
When the pressure-sensitive adhesive composition of the present invention contains an ultraviolet absorber, the content of the ultraviolet absorber is preferably 1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the specific (meth) acrylic polymer, for example. ..

[Organic solvent]
The pressure-sensitive adhesive composition of the present invention may contain an organic solvent, for example, from the viewpoint of improving coatability.
Examples of the organic solvent include the same organic solvents as those used in the polymerization reaction of the specific (meth) acrylic polymer described above.

When the pressure-sensitive adhesive composition of the present invention contains an organic solvent, it may contain only one type of organic solvent, or may contain two or more types of organic solvent.

The content of the organic solvent in the pressure-sensitive adhesive composition of the present invention is not particularly limited and can be appropriately set.

[Other ingredients]
The pressure-sensitive adhesive composition of the present invention may contain components other than the above-mentioned components (so-called other components), if necessary, as long as the effects of the present invention are not impaired.
Examples of other components include polymers other than specific (meth) acrylic polymers, cross-linking catalysts, tackifiers, antioxidants, colorants (for example, dyes and pigments), and various additives such as antistatic agents. Be done.

[Gel fraction after cross-linking]
In the pressure-sensitive adhesive composition of the present invention, the gel content after cross-linking is preferably in the range of 5% by mass to 90% by mass, more preferably in the range of 10% by mass to 90% by mass, and 20% by mass. It is more preferably in the range of ~ 80% by mass.
When the gel fraction after cross-linking is within the above range, the permeation of water into the pressure-sensitive adhesive layer is further suppressed, so that the pressure-sensitive adhesive layer is more difficult to whiten.

In the present specification, the "gel fraction after cross-linking of the pressure-sensitive adhesive composition" is a value measured according to the following procedures (1) to (17).
(1) The pressure-sensitive adhesive composition is applied onto a polyethylene terephthalate (PET) film separator (release paper) having a thickness of 100 μm, air-dried at room temperature (23 ° C.) for 30 minutes, and then main-dried at an ambient temperature of 100 ° C. for 5 minutes. To form a pressure-sensitive adhesive layer to obtain a pressure-sensitive adhesive layer with a separator.
(2) The obtained pressure-sensitive adhesive layer with a separator is cured under the conditions of an atmospheric temperature of 23 ° C. and 65% RH for 10 days. Then, the pressure-sensitive adhesive layer with a separator is cut out to a size of 75 mm × 75 mm. The weight of the pressure-sensitive adhesive layer of the cut-out sample is about 0.2 g.

(3) Prepare a metal wire mesh of 250 mesh (wire diameter: 0.03 mm, opening: 72 μm, made of stainless steel), and cut the metal wire mesh into a size of 100 mm × 100 mm.
(4) The metal wire mesh is degreased with ethyl acetate and then dried. The metal wire mesh after degreasing and drying is stored in a desiccator. Further, the unraveling of the end portion of the metal wire mesh causes a measurement error, so it is removed in advance.
(5) Accurately measure the mass of the metal wire mesh. Let this mass be A.

(6) After attaching the pressure-sensitive adhesive layer with a separator of (2) cut out to a size of 75 mm × 75 mm to the center of the metal wire mesh, the PET film separator is peeled off from the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer is attached to the metal wire mesh so that the pressure-sensitive adhesive layer is arranged in the plane after the metal wire mesh is folded by the steps (7) to (9) described later.
(7) The metal wire mesh is folded in half from the back side to the front side with the side to which the film-like adhesive layer is attached inside.
(8) Fold the front one-third of the metal wire mesh folded in half (there are two ends on the front side) to the back side, and further fold the back one-third to the front side (100 mm in the vertical direction). Folded to 1/6 of the above, not folded in the horizontal direction).
(9) Fold the wire mesh to the right at the one-third part from the left, and similarly fold it to the left at the one-third part from the right. This is referred to as sample 1. In sample 1, due to the size of the original metal wire mesh, the vertical direction is folded to 1/6 and the horizontal direction is folded to 1/3.
(10) Accurately measure the mass of the above sample 1. Let this mass be B.

(11) Stapler the sample 1 so that the creases do not open. This is referred to as sample 2. The mass of sample 2 is measured. Let this mass be C.
(12) For each type of pressure-sensitive adhesive composition, two samples 2 for measuring the gel fraction are prepared.

(13) Sample 2 is placed in a glass bottle containing 80 g of ethyl acetate and covered.
(14) The glass bottle containing the sample 2 is left to stand for 3 days under the conditions of an atmospheric temperature of 23 ° C. and 65% RH.
(15) Sample 2 is taken out from the glass bottle and easily washed with ethyl acetate.
(16) After drying the sample 2 at 120 ° C. for 24 hours, the mass is accurately measured. Let this be D.

(17) Calculate the gel fraction by the following formula.
Gel fraction [mass%] = (D- (A + (CB))) / (BA) x 100

[Adhesive film]
The pressure-sensitive adhesive film of the present invention includes a fluorine-based resin base material and a pressure-sensitive adhesive layer provided on the fluorine-based resin base material and formed by the above-mentioned pressure-sensitive adhesive composition of the present invention. That is, in the pressure-sensitive adhesive film of the present invention, the fluorine-based resin base material and the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention are laminated.
In general, the pressure-sensitive adhesive layer containing a hindered amine-based light stabilizer has excellent weather resistance. However, when a pressure-sensitive adhesive film including a pressure-sensitive adhesive layer containing a hindered amine-based light stabilizer is used in a high-humidity environment, moisture may act on the hindered amine-based light stabilizer and the pressure-sensitive adhesive layer may be whitened. On the other hand, the pressure-sensitive adhesive layer included in the pressure-sensitive adhesive film of the present invention contains a hindered amine-based light stabilizer having a relatively low molecular weight, so that whitening of the pressure-sensitive adhesive layer is suppressed. Therefore, the adhesive film of the present invention is difficult to whiten even when used in a high humidity environment.
Further, in the pressure-sensitive adhesive layer containing a hindered amine-based light stabilizer having a low molecular weight, the hindered amine-based light stabilizer tends to be localized near the interface of the pressure-sensitive adhesive layer with the adherend, and the adhesive strength to the adherend tends to be low. There is. On the other hand, the pressure-sensitive adhesive film of the present invention contains a specific (meth) acrylic polymer and has a pressure-sensitive adhesive layer formed of a pressure-sensitive adhesive composition having excellent wettability to the adherend. Shows high adhesive strength.
Further, in the pressure-sensitive adhesive layer containing a hindered amine-based light stabilizer having a low molecular weight, the hindered amine-based light stabilizer is localized near the interface of the pressure-sensitive adhesive layer with the base material, and the adhesion with the fluorine-based resin base material is maintained over time. Tends to decline. On the other hand, in the pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive film of the present invention, the specific light stabilizer acts on the cross-linking between the specific (meth) acrylic polymer and the isocyanate-based cross-linking agent, so that the cross-linking becomes appropriate and the cross-linking becomes appropriate. Localization of the specific light stabilizer near the interface of the pressure-sensitive adhesive layer with the base material is suppressed. Therefore, the pressure-sensitive adhesive film of the present invention has excellent adhesion to a fluororesin base material.

The adhesive film of the present invention is suitably used as a surface protective film for a reflective sheet (also referred to as a "retroreflective sheet" or a "retroreflective sheet").
Reflective sheets are often attached to the surface of display boards such as signs (for example, road signs and public signs) and advertisements (for example, outdoor advertisements and indoor advertisements). The reflective sheet is used for the purpose of improving the visibility of signs, advertisements, etc. from the direction of the light source by a reflection phenomenon (so-called retroreflection) in which the incident light returns to the incident direction again. Further, in general, the outermost surface of the reflective sheet is a layer containing an acrylic resin.
Since the adhesive film of the present invention has an adhesive layer having high adhesive strength to an adherend (particularly an adherend containing an acrylic resin) and which is difficult to whiten in a high humidity environment, sunlight, snowfall, and rainfall Even if it is used as a surface protective film for a sign installed outdoors or a reflective sheet attached to an advertisement, etc., it may peel off during use, or the visibility of the sign or advertisement may decrease. Is unlikely to cause any problems.
By the way, a fluorine-based resin film is often used as the base material of the surface protective film of the reflective sheet. Since the pressure-sensitive adhesive film of the present invention includes a pressure-sensitive adhesive layer having excellent adhesion to a fluororesin base material, the base material and the pressure-sensitive adhesive layer are peeled off during use even when used as a surface protective film for a reflective sheet. It is unlikely that problems will occur.

The fluororesin base material is not particularly limited.
Examples of the fluororesin base material include ethylene / tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride / polyvinylidene fluoroethylene copolymer (PVdF), and ethylene fluoride / tetrafluoroethylene / hexafluoropropylene. Examples thereof include a polymer (FEP), a tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer (THV), and the like.

The fluororesin base material may contain various additives such as plasticizers, colorants (for example, dyes and pigments), heat stabilizers, fillers, antistatic agents, and flame retardants.
Further, the fluorine-based resin base material may be partially or entirely patterned.

The thickness of the fluororesin base material is generally 500 μm or less, preferably 300 μm or less, and more preferably 200 μm or less.
The lower limit of the thickness of the fluororesin base material is, for example, preferably 5 μm or more, more preferably 10 μm or more, from the viewpoint of the strength of the adhesive film.

The method for forming the pressure-sensitive adhesive layer is not particularly limited, and a commonly used method can be adopted.
As a method of forming the pressure-sensitive adhesive layer on the fluororesin base material, for example, the following method can be adopted.
The pressure-sensitive adhesive composition of the present invention is applied as it is or, if necessary, diluted with a solvent on a release film to form a coating film on the release film. Next, the formed coating film is dried to remove the solvent, and then bonded to the fluorine-based resin base material and cured to form a pressure-sensitive adhesive layer on the fluorine-based resin base material.
The release film is not particularly limited as long as it can be easily peeled off from the surface of the pressure-sensitive adhesive layer. Can be mentioned. Examples of the resin film include a polyester film typified by a polyethylene terephthalate film. Examples of the stripping agent include fluororesins, paraffin waxes, silicones, long-chain alkyl group compounds and the like.
The release film protects the surface of the pressure-sensitive adhesive layer until the pressure-sensitive adhesive film is put into practical use, and is peeled off during use.

As another method for forming the pressure-sensitive adhesive layer on the fluororesin base material, for example, the following method can be adopted.
The pressure-sensitive adhesive composition of the present invention is applied as it is or, if necessary, diluted with a solvent on a release film such as a paper or a resin film that has been easily peeled with a release agent. , A coating film is formed on the release film. Then, the formed coating film is dried to remove the solvent. Next, the surface of the release film on which the pressure-sensitive adhesive layer is formed is brought into contact with the fluorine-based resin base material and pressed, and the pressure-sensitive adhesive layer is transferred to the fluorine-based resin base material to be placed on the fluorine-based resin base material. Form a pressure-sensitive adhesive layer. Then, curing is performed.

The method of applying the pressure-sensitive adhesive composition on the fluororesin base material or the release film is not particularly limited, and for example, a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a knife coater, or a spray. Known methods using a coater, a bar coater, an applicator and the like can be mentioned.
The amount of the pressure-sensitive adhesive composition applied onto the fluororesin base material or the release film is appropriately set according to the thickness of the pressure-sensitive adhesive layer to be formed.

The method for drying the coating film formed on the fluororesin base material or the release film is not particularly limited, and examples thereof include natural drying, heat drying, hot air drying, and vacuum drying.
The drying temperature and drying time of the coating film are not particularly limited, and are appropriately set according to the thickness of the pressure-sensitive adhesive layer to be formed, the amount of the organic solvent in the pressure-sensitive adhesive composition, and the like.

The curing conditions are not particularly limited, and for example, the curing is carried out in an environment of 23 ° C. and 50% RH for 1 to 10 days.
Curing completes the cross-linking reaction of the pressure-sensitive adhesive composition to form a pressure-sensitive adhesive layer.

The thickness of the pressure-sensitive adhesive layer is not particularly limited and can be appropriately set according to the application of the pressure-sensitive adhesive film, the required performance, and the like.
For example, when the pressure-sensitive adhesive film is used as the surface protective film of the reflective sheet, the thickness of the pressure-sensitive adhesive layer is preferably 10 μm or more and 100 μm or less, more preferably 20 μm or more and 100 μm or less, and further preferably 30 μm or more and 100 μm or less.

Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

[Manufacture of (meth) acrylic polymer]
[Manufacturing Example 1]
24 parts by mass of ethyl acrylate (EA; (meth) acrylic acid alkyl ester monomer) and acrylic acid (AA; carboxy group) in a reactor equipped with a stirrer, a reflux cooler, a sequential dropping device, and a thermometer. After charging 10 parts by mass of a monomer (mono), 66 parts by mass of n-butyl acrylate (n-BA; (meth) acrylic acid alkyl ester monomer), and 150 parts by mass of ethyl acetate (EAc). , 2,2'-azobisisobutyronitrile (AIBN; azo compound) was added in an amount of 0.05 parts by mass as a polymerization initiator. After the addition of AIBN, the contents of the reactor were heated with stirring, raised until reflux occurred, and the temperature was maintained for 20 minutes. Hereinafter, the temperature at which reflux occurs is referred to as "reflux temperature".
Next, EA (75.6 parts by mass), AA (31 parts by mass), n-BA (206.3 parts by mass), and AIBN (0.5 parts by mass) were further added to the reactor in EAc (75.6 parts by mass). Solution A dissolved in 100 parts by mass) was sequentially added dropwise over 90 minutes. After the completion of the dropping of the solution A, the temperature of the contents in the reactor was further maintained at the reflux temperature for 60 minutes. Next, a solution B in which AIBN (1.0 part by mass) was dissolved in EAc (100 parts by mass) was sequentially added dropwise over 60 minutes, and then the temperature of the contents in the reactor was further maintained at the reflux temperature for 120 minutes. , Completed the reaction. After the reaction was completed, the mixture was diluted with EAc so that the solid content was 35% by mass, and then cooled to obtain a solution of the (meth) acrylic polymer.
The "solid content" in the solution of the (meth) acrylic polymer means the amount of residue obtained by removing volatile components such as a solvent from the solution of the (meth) acrylic polymer (hereinafter, the same applies).

(Meth) monomer composition of the acrylic polymer (unit: mass%), weight average molecular weight (Mw, ten thousand (in Table 1, denoted as "× 10 ^4")), and glass transition temperature (Tg , Unit: ° C) is shown in Table 1.
The weight average molecular weight (Mw) is measured by the method described above.
The glass transition temperature (Tg) is calculated by the method described above.

[Production Examples 2 to 13, and Production Examples 16 to 18]
In Production Examples 2 to 13 and Production Examples 16 to 18, the monomer composition in Production Example 1 is changed as shown in Table 1, and the amount of solvent, the amount of polymerization initiator, etc. are adjusted. Therefore, the (meth) acrylic having a solid content of 35% by mass was adjusted to the values shown in Table 1 by the same method as in Production Example 1 except that the weight average molecular weight (Mw) of the (meth) acrylic polymer was adjusted to the values shown in Table 1. A solution of the system polymer was prepared.
(Meth) monomer composition of the acrylic polymer (unit: mass%), weight average molecular weight (Mw, ten thousand (in Table 1, denoted as "× 10 ^4")), and glass transition temperature (Tg , Unit: ° C) is shown in Table 1.
The weight average molecular weight (Mw) is measured by the method described above.
The glass transition temperature (Tg) is calculated by the method described above.

[Production Example 14 and Production Example 15]
In Production Example 14 and Production Example 15, the weight average molecular weight (Mw) of the (meth) acrylic polymer was adjusted to the values shown in Table 1 by adjusting the amount of the solvent, the amount of the polymerization initiator, etc. in Production Example 1. A solution of the (meth) acrylic polymer having a solid content of 35% by mass was prepared by the same method as in Production Example 1 except that it was adjusted.
(Meth) monomer composition of the acrylic polymer (unit: mass%), weight average molecular weight (Mw, ten thousand (in Table 1, denoted as "× 10 ^4")), and glass transition temperature (Tg , Unit: ° C) is shown in Table 1.
The weight average molecular weight (Mw) is measured by the method described above.
The glass transition temperature (Tg) is calculated by the method described above.

Details of each monomer shown in Table 1 are as shown below.
"AA": Acrylic acid "M-5300": Aronix (registered trademark) M-5300 [Product name: ω-carboxy-polycaprolactone (n≈2) monoacrylate, Toagosei Co., Ltd.]
"HOA-MS": HOA-MS [trade name; 2-acryloyloxyethyl-succinic acid, succinic acid ester, Kyoeisha Chemical Co., Ltd.]
"2HEA": 2-hydroxyethyl acrylate "2EHA": 2-ethylhexyl acrylate "n-BA": n-butyl acrylate "EA": ethyl acrylate "MA": methyl acrylate In Table 1, "-" corresponds. It means that no monomer is used.

[Example 1]
-Preparation of adhesive composition-
100 parts by mass (solid content conversion value) of the solution of the (meth) acrylic polymer [specific (meth) acrylic polymer] prepared in Production Example 1 and the isocyanate compound as a cross-linking agent [trade name: Coronate (registered trademark) ) HX, isocyanurate compound of hexamethylene diisocyanate (HMDI), solid content: 100% by mass, Toso Co., Ltd.] 0.30 parts by mass, and light stabilizer [trade name: Tinuvin (registered trademark) 765, bis sebacate (1,2,2,6,6-pentamethyl-4-piperidyl), hindered amine-based light stabilizer, molecular weight: 509, BASF; specified light stabilizer] 2.0 parts by mass and ultraviolet absorber [trade name: Tinuvin® 329, 2- (2-hydroxy-5-tert-octylphenyl) benzotriazole, benzotriazole-based ultraviolet absorber, BASF] 3.0 parts by mass were mixed and thoroughly stirred. , A pressure-sensitive adhesive composition was obtained.
The gel fraction after cross-linking of the pressure-sensitive adhesive composition was measured by the method described above and found to be 30% by mass.

-Making an adhesive film-
Using the pressure-sensitive adhesive composition obtained above, a pressure-sensitive adhesive film was prepared as follows.
The thickness after drying (that is, on the peeling surface of a release film (trade name: Film Vina (registered trademark) 100E, Fujimori Kogyo Co., Ltd.)) that has been easily peeled with a silicone-based release treatment agent using a gravure coater. , The thickness of the pressure-sensitive adhesive layer; hereinafter referred to as “film thickness”) was applied so that the pressure-sensitive adhesive composition was 40 μm to form a coating film. Next, the coating film formed on the release film was dried at 100 ° C. for 1 minute using a hot air circulation type dryer. Next, the exposed surface of the coating film after drying and the base material (trade name: Aflex (registered trademark) 40NS, thickness: 40 μm, fluororesin film, Asahi Glass Co., Ltd.) are pressure-bonded with a pressure nip roll. And pasted together. Then, it was cured for 168 hours in an environment of 23 ° C. and 50% RH to prepare an adhesive film (base material / adhesive layer / release film).

[Example 2 and Example 3]
In Examples 2 and 3, the same as in Example 1 except that the type and blending amount of the cross-linking agent were changed to those shown in Table 2 in "-Preparation of Adhesive Composition-" of Example 1. To prepare an adhesive film.

[Examples 4 to 15, Example 22, Example 23, Example 27, and Example 28]
In Examples 4 to 15, Example 22, Example 23, Example 27, and Example 28, in "-Preparation of Adhesive Composition-" of Example 1, the (meth) acrylic polymer was used. An adhesive film was produced by performing the same operation as in Example 1 except that the type was changed to that shown in Table 2.

[Examples 16 to 19]
In Examples 16 to 19, in "-Preparation of Adhesive Film-" of Example 1, the pressure-sensitive adhesive composition is applied onto the base material so as to have the film thickness shown in Table 2 to form a coating film. An adhesive film was produced by performing the same operation as in Example 1 except for the above.

[Example 20 and Example 21]
In Example 20 and Example 21, the same operations as in Example 1 were performed except that the blending amount of the cross-linking agent was changed to the amount shown in Table 2 in "-Preparation of Adhesive Composition-" of Example 1. To prepare an adhesive film.

[Example 24]
In Example 24, the same operation as in Example 1 was performed except that the type of the ultraviolet absorber was changed to that shown in Table 2 in "-Preparation of Adhesive Composition-" of Example 1 to obtain adhesive. A film was made.

[Example 25]
In Example 25, the same operation as in Example 1 was performed except that the type of the light stabilizer was changed to that shown in Table 2 in "-Preparation of Adhesive Composition-" of Example 1 to obtain adhesive. A film was made.

[Example 26]
In Example 26, the same operation as in Example 1 was carried out except that the ultraviolet absorber was not blended in "-Preparation of Adhesive Composition-" of Example 1 to prepare an adhesive film.

[Comparative Example 1]
In Comparative Example 1, the same operation as in Example 1 was performed except that the type and blending amount of the cross-linking agent were changed to those shown in Table 3 in "-Preparation of Adhesive Composition-" of Example 1. , An adhesive film was prepared.

[Comparative Example 2 and Comparative Example 3]
In Comparative Example 2 and Comparative Example 3, the types of the (meth) acrylic polymer and the types and amounts of the cross-linking agents in "-Preparation of Adhesive Composition-" of Example 1 are shown in Table 3. An adhesive film was produced by performing the same operation as in Example 1 except that it was changed to.

[Comparative Example 4]
In Comparative Example 4, in "-Preparation of Adhesive Composition-" of Example 1, the types of (meth) acrylic polymers, the types of light stabilizers, and the types of ultraviolet absorbers are shown in Table 3. An adhesive film was produced by performing the same operation as in Example 1 except that the changes were made.
The gel fraction after cross-linking of the pressure-sensitive adhesive composition was measured by the method described above and found to be 44% by mass.

[Comparative Example 5]
In Comparative Example 5, except that the type of the (meth) acrylic polymer and the type of the light stabilizer were changed to those shown in Table 3 in "-Preparation of Adhesive Composition-" of Example 1. The same operation as in Example 1 was carried out to prepare an adhesive film.

[Comparative Example 6 to Comparative Example 9]
In Comparative Examples 6 to 9, the same operations as in Example 1 were performed except that the type of the light stabilizer was changed to that shown in Table 3 in "-Preparation of Adhesive Composition-" of Example 1. To prepare an adhesive film.

[Comparative Example 10]
In Comparative Example 10, the same operation as in Example 1 except that the type of the (meth) acrylic polymer was changed to that shown in Table 3 in "-Preparation of Adhesive Composition-" of Example 1. To prepare an adhesive film.

[evaluation]
1. 1. Moisture resistance A hot water test was conducted to evaluate the moisture resistance of the pressure-sensitive adhesive layer.
The adhesive film produced above was cut to a size of 40 mm × 50 mm using a cutter blade, and one adhesive film piece was prepared.
In an environment of an ambient temperature of 23 ° C. and 50% RH, the release film of the prepared adhesive film piece is peeled off, and the surface of the adhesive layer exposed by the peeling is a retroreflective sheet [trade name: Nikkalite ULS, capsule lens type height]. Bright retroreflective sheet, Nippon Carbide Industry Co., Ltd.] surface (acrylic resin) is overlaid and bonded, and then a 2 kg roller is reciprocated twice and crimped. Layer / base material) piece] was prepared.
First, the Y value (before the test) was measured using a spectrocolorimeter [model: SE 2000, Nippon Denshoku Kogyo Co., Ltd.] for the prepared evaluation sample. Next, the evaluation sample whose Y value (before the test) was measured was put into warm water at 50 ° C., left to stand for 7 days while maintaining the temperature, and then taken out. Then, the Y value (after the test) was measured using a spectrocolorimeter [model: SE 2000, Nippon Denshoku Kogyo Co., Ltd.] for the evaluation sample immediately after taking out.
The difference (ΔY) between the Y value (before the test) and the Y value (after the test) of the evaluation sample was calculated, and the moisture resistance of the pressure-sensitive adhesive layer was evaluated according to the following evaluation criteria.
When the evaluation result was "A", it was judged that the moisture resistance was excellent (that is, it was difficult to whiten in a high humidity environment).

-Evaluation criteria-
A: ΔY is less than 5.
B: ΔY is 5 or more.

2. Adhesiveness The adhesive film produced above was cut to a size of 25 mm × 150 mm using a cutter blade, and one adhesive film piece was prepared.
In an environment of an ambient temperature of 23 ° C. and 50% RH, the release film of the prepared adhesive film piece is peeled off, and the surface of the adhesive layer exposed by the peeling is a retroreflective sheet [trade name: Nikkalite ULS, capsule lens type height]. Bright retroreflective sheet, Nippon Carbide Industry Co., Ltd.] surface (acrylic resin) is overlaid and bonded, and then a 2 kg roller is reciprocated twice and crimped. Layer / base material) piece] was prepared.
Next, the prepared evaluation sample was left to stand for 24 hours in an environment of an atmospheric temperature of 23 ° C. and 50% RH, and then a single column type material tester (model number: STA-1225) of A & D Co., Ltd. was used. The adhesive film (adhesive layer / base material) piece was peeled 180 ° in the long side (150 mm) direction from the retroreflective sheet under the condition of an atmospheric temperature of 23 ° C. and a peeling speed of 500 mm / min. .. The peeled adhesive film piece was again crimped to the part to which the retroreflective sheet was attached by reciprocating a 2 kg roller twice, and left for 5 minutes in an environment of an atmospheric temperature of 23 ° C. and 50% RH. ) Using A &D's single column type material tester (model number: STA-1225), from a retroreflective sheet to an adhesive film under the condition of an ambient temperature of 23 ° C. and a peeling speed of 300 mm / min. The (adhesive layer / base material) piece was peeled off by 180 ° in the long side (150 mm) direction. After peeling, the surface of the retroreflective sheet was visually observed, and the adhesion of the pressure-sensitive adhesive layer to the substrate was evaluated according to the following evaluation criteria.
If the evaluation result is "A", it is judged that the pressure-sensitive adhesive layer contained in the pressure-sensitive adhesive film piece has excellent adhesion to the base material.

-Evaluation criteria-
A: Neither adhesive residue nor cloudiness is confirmed.
B: Adhesive residue is confirmed on a part of the bonded surface, or light cloudiness is confirmed only on the edge of the bonded surface.
C: Adhesive residue is confirmed on the entire surface of the bonded surface.

3. 3. Adhesive strength In order to evaluate the adhesive strength of the pressure-sensitive adhesive layer to the adherend, a 90 ° peel strength test, which is one of the constant load peeling tests, was performed.
The adhesive film produced above was cut to a size of 25 mm × 100 mm using a cutter blade, and one adhesive film piece was prepared.
The release film of the prepared adhesive film piece was peeled off to expose the surface of the adhesive layer by 25 mm × 50 mm. Next, the surface of the exposed adhesive layer was laminated on the surface (acrylic resin) of the retroreflective sheet [trade name: Nikkalite ULS, capsule lens type high-intensity retroreflective sheet, Nippon Carbide Industry Co., Ltd.]. After that, an evaluation sample in which the surface of the adhesive layer of the adhesive film piece was attached to the surface of the retroreflective sheet by reciprocating and crimping a 2 kg roller twice [retroreflective sheet / adhesive film (adhesive layer / base material) ) Piece, sticking area: 25 mm × 50 mm] was prepared. The operation from the exposure of the surface of the pressure-sensitive adhesive layer to the crimping was performed in an environment with an atmospheric temperature of 23 ° C. and 50% RH.
Next, the prepared evaluation sample was left for 24 hours in an environment of an atmospheric temperature of 23 ° C. and 50% RH, and then on one end side in the long side (100 mm) direction of the adhesive film piece attached to the retroreflective sheet. , The end portion on the side not attached to the retroreflective sheet was left for 10 minutes with a load of 800 g applied in the 90 ° direction. Then, after being left to stand, the peeling distance (unit: mm) in the long side (100 mm) direction of the adhesive film piece was measured.
The shorter the peeling distance of the adhesive film piece, the higher the adhesive force of the adhesive layer provided on the adhesive film piece to the adherend.

The composition, film thickness, measurement results, and evaluation results of the pressure-sensitive adhesive composition are shown in Tables 2 and 3.
In Table 2, "-" means that the corresponding component is not used.

Details of each component shown in Tables 2 and 3 are as shown below.
<Crosslinking agent>
-Isocyanate cross-linking agent-
"Coronate HX": Coronate (registered trademark) HX [trade name: isocyanurate of hexamethylene diisocyanate (HMDI), solid content: 100% by mass, Tosoh Corporation]
"Coronate L": Coronate (registered trademark) L [Product name: Adduct of toluene diisocyanate (TDI) and trimethylolpropane, solid content: 75% by mass, Tosoh Corporation]
"Takenate D110N": Takenate (registered trademark) D-110N [Product name: Adduct of xylylene diisocyanate (XDI) and trimethylolpropane, solid content: 75% by mass, Mitsui Chemicals, Inc.]
-Epoxy cross-linking agent-
"TETRAD-C": TETRAD®-C [trade name; 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, solid content: 100% by mass, Mitsubishi Gas Chemical Company, Inc.]
-Metal chelate cross-linking agent-
"Aluminum chelate A": Aluminum chelate A [Product name: Aluminum trisacetylacetone, Kawaken Fine Chemical Co., Ltd.]
<Light stabilizer>
"Tinuvin 765": Tinuvin® 765 [trade name: bissebacate (1,2,2,6,6-pentamethyl-4-piperidyl), molecular weight: 509, hindered amine light stabilizer, BASF]
"Tinuvin 770DF": Tinuvin® 770DF [trade name: bissebacate (2,2,6,6-tetramethyl-4-piperidyl), molecular weight: 481, hindered amine light stabilizer, BASF]
"Tinuvin 622LD": Tinuvin® 622LD [trade name; dimethyl 1- (2 hydroxyethyl) succinate-4-hydroxy-2,2,6,6-tetramethyl-4-piperidin polycondensate, molecular weight : 3550, hindered amine light stabilizer, BASF]
"LA-52": ADEKA STAB® LA-52 [trade name; tetrakis butane-1,2,3,4-tetracarboxylic dian (1,2,2,6,6-pentamethyl-4-piperidinyl), Molecular weight: 847, hindered amine-based light stabilizer, ADEKA Corporation]
"Tinuvin 123": Tinuvin® 123 [trade name; bisdecanedioate [2,2,6,6-tetramethyl-1- (octyloxy) piperidine-4-yl], molecular weight: 737, hindered amine system Light stabilizer, BASF]
"Tinuvin 144": Tinuvin® 144 [trade name; 2-[[3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl] methyl] -2-butylpropanediate bis [1] , 2,2,6,6-pentamethyl-4-piperidinyl], molecular weight: 685, hindered amine light stabilizer, BASF]
<UV absorber>
"Tinuvin 328": Tinuvin® 328 [trade name; 2- (3,5-di-tert-amyl-2-hydroxyphenyl) benzotriazole, benzotriazole-based UV absorber, BASF]
"Tinuvin 329": Tinuvin® 329 [trade name; 2- (2-hydroxy-5-tert-octylphenyl) benzotriazole, benzotriazole-based UV absorber, BASF]

As shown in Table 2, the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive compositions of Examples 1 to 28 contains a hindered amine-based light stabilizer, but is difficult to whiten in a high-humidity environment and has moisture resistance. It turned out to be excellent. Further, it was found that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive compositions of Examples 1 to 28 was excellent in adhesion to the fluororesin base material. Furthermore, it was found that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive compositions of Examples 1 to 28 exhibited high adhesive strength to the adherend.

On the other hand, as shown in Table 3, the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive compositions of Comparative Example 1 and Comparative Example 2 containing an epoxy-based cross-linking agent instead of the isocyanate-based cross-linking agent was the same as the fluorine-based resin base material. It was found that the adhesiveness of the epoxy was inferior and the adhesive strength to the adherend was low.
The pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 3 containing a metal chelate-based cross-linking agent instead of the isocyanate-based cross-linking agent is inferior in adhesion to a fluorine-based resin base material and has no adhesion to an adherend. It was found that the adhesive strength was low.
It is formed by the pressure-sensitive adhesive compositions of Comparative Examples 4 to 9 containing a hindered amine-based light stabilizer having a molecular weight of more than 650 instead of the hindered amine-based light stabilizer (specific light stabilizer) having a molecular weight of 300 or more and 650 or less. It was found that the adhesive layer whitened in a high humidity environment and was inferior in moisture resistance.
It was found that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 10 containing no (meth) acrylic polymer having a carboxy group had a significantly low adhesive force to the adherend.

Claims (6)

A (meth) acrylic polymer having a carboxy group and
Isocyanate cross-linking agent and
A hindered amine-based light stabilizer having a molecular weight of 300 or more and 650 or less,
Adhesive composition for fluororesin base material containing. The fluororesin according to claim 1, wherein the (meth) acrylic polymer contains a structural unit derived from a monomer having a carboxy group, and the monomer having a carboxy group is acrylic acid. Adhesive composition for substrate. The (meth) acrylic polymer contains a structural unit derived from a monomer having a carboxy group, and the content of the structural unit derived from the monomer having a carboxy group is the (meth) acrylic. The pressure-sensitive adhesive composition for a fluororesin base material according to claim 1 or 2, which is 5% by mass or more and 15% by mass or less based on all the constituent units of the polymer. The pressure-sensitive adhesive for a fluororesin base material according to any one of claims 1 to 3, wherein the (meth) acrylic polymer contains a structural unit derived from a (meth) acrylic acid alkyl ester monomer. Composition. A pressure-sensitive adhesive layer provided on a fluorine-based resin base material and the pressure-sensitive adhesive composition for a fluorine-based resin base material according to any one of claims 1 to 4. And with an adhesive film. The adhesive film according to claim 5, which is used as a surface protective film for a reflective sheet.