JP6832286B2 - Removable adhesive sheet - Google Patents

Description

The present invention relates to an adhesive sheet that can be peeled off after being attached to an adherend.

In recent years, so-called removable adhesive sheets have been used in various technical fields. The re-peelable pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer forming an adhesive surface that can be peeled off from the adherend after being attached to the adherend. Such a removable adhesive sheet protects the surface of the adherend in the process of manufacturing and processing various optical materials such as a polarizing film, a retardation film, and an antireflection film, and in the process of manufacturing and transporting furniture. It is used as a protective film for manufacturing. In the manufacturing and processing process of various optical materials, specifically, the removable adhesive sheet is applied to the surface of the optical material for the purpose of preventing scratches and stains on the surface of the optical material and suppressing cracks during the cutting process of the optical material. It is used by being pasted together. Then, the pressure-sensitive adhesive sheet is peeled off from the optical material at a predetermined time in the manufacturing / processing process of the optical material or before the use of the optical material. The removable adhesive sheet is described in, for example, Patent Documents 1 to 3 below.

Japanese Unexamined Patent Publication No. 10-046118 JP-A-11-000961 Japanese Unexamined Patent Publication No. 2001-064607

For example, in the re-peelable adhesive sheet used as described above, the degree of adhesive force to the adherend and the degree of peelability (easiness of peeling) from the adherend are required according to the application. There is. On the other hand, the pressure-sensitive adhesive layer of the removable pressure-sensitive adhesive sheet contains a polymer material as a main agent for developing adhesive strength, and the adhesive strength of such a pressure-sensitive adhesive layer changes with time (particularly, the adhesive strength). (Rise over time) may become apparent as a problem. An increase in the adhesive strength of the pressure-sensitive adhesive layer over time may reduce the peelability of the pressure-sensitive adhesive layer or the removable pressure-sensitive adhesive sheet.

The higher the degree of cross-linking of the polymer material in the pressure-sensitive adhesive layer of the removable pressure-sensitive adhesive sheet, that is, the higher the so-called gel content of the pressure-sensitive adhesive layer, the more the increase in the adhesive strength of the pressure-sensitive adhesive layer over time tends to be suppressed. It is in. However, the higher the gel fraction of the pressure-sensitive adhesive layer, the lower the adhesive strength of the pressure-sensitive adhesive layer tends to be. That is, from the viewpoint of the gel fraction of the pressure-sensitive adhesive layer, there is generally a trade-off relationship between the adhesive strength of the pressure-sensitive adhesive layer and the suppression of the increase in the pressure-sensitive adhesive strength. Therefore, if sufficient suppression of the increase in adhesive strength is realized only by increasing the gel fraction of the pressure-sensitive adhesive layer, it is difficult to obtain sufficient adhesive strength in the pressure-sensitive adhesive layer.

In addition, for the pressure-sensitive adhesive layer of the re-peelable pressure-sensitive adhesive sheet, the gel content is suppressed to ensure the adhesive strength, and the increase in the adhesive strength is suppressed by blending a release adjusting agent (surfactant, silicone-based release agent, etc.). It is also possible to do. However, according to such a measure, a residue of the release adjusting agent is likely to be generated on the surface of the adherend after the removable adhesive sheet is peeled off. That is, the release adjusting agent having a relatively low molecular weight tends to move in the pressure-sensitive adhesive layer and reach the surface of the adherend to contaminate the adherend. If the adherend is an optical material as described above, such contamination will affect the optical properties of the optical material.

The present invention has been conceived under such circumstances, and is low in contamination while realizing good adhesive strength and suppression of an increase in the adhesive strength over time (stability of the adhesive strength over time). It is an object of the present invention to provide a removable pressure-sensitive adhesive sheet suitable for realizing the properties.

According to the present invention, a removable pressure-sensitive adhesive sheet is provided. This pressure-sensitive adhesive sheet has a laminated structure including a base material and an acrylic pressure-sensitive adhesive layer. The acrylic pressure-sensitive adhesive layer has an adhesive surface that can be peeled off from the adherend after being attached to the adherend, and has a first acrylic polymer crosslinked by a cross-linking agent and a second acrylic-based weight. Including coalescence. In the acrylic pressure-sensitive adhesive layer, the proportion of the gel content insoluble in ethyl acetate is 30 to 80% by mass, and the weight average molecular weight of the sol content soluble in ethyl acetate is 700,000 or more. In the present invention, the acrylic polymer (first acrylic polymer, second acrylic polymer) is a monomer unit derived from an acrylic acid alkyl ester and / or a methacrylic acid alkyl ester, which is the most mass ratio. It refers to a polymer contained as a large number of main monomer units. In the present invention, the acrylic pressure-sensitive adhesive layer refers to a pressure-sensitive adhesive layer containing such an acrylic polymer as a polymer material having the largest mass ratio.

As described above, the acrylic pressure-sensitive adhesive layer of the removable pressure-sensitive adhesive sheet of the present invention contains a first acrylic-based polymer crosslinked by a cross-linking agent and a second acrylic-based polymer. The first acrylic polymer crosslinked by the cross-linking agent forms a three-dimensional network of polymer chains in the acrylic pressure-sensitive adhesive layer. Of the gel content (ethyl acetate insoluble content) of the acrylic pressure-sensitive adhesive layer, the structure of this polymer chain three-dimensional network has the largest mass ratio, and the ratio of the gel content is 30 to 80 mass as described above. %. On the other hand, the sol content (ethyl acetate-soluble content) of the acrylic pressure-sensitive adhesive layer is 20 to 70% by mass, and the second acrylic polymer has the largest mass ratio among the sol contents. This second acrylic polymer has a relatively large degree of polymerization and is long so that the weight average molecular weight of the sol of the acrylic pressure-sensitive adhesive layer is 700,000 or more. Such a second acrylic polymer is likely to be prevented from moving or changing its orientation by the above-mentioned three-dimensional network structure of polymer chains in the acrylic pressure-sensitive adhesive layer, and therefore, moving or changing its orientation in the acrylic pressure-sensitive adhesive layer. Hard to occur.

The lower the gel content of the pressure-sensitive adhesive layer, the higher the adhesive strength of the pressure-sensitive adhesive layer tends to be. However, in the acrylic pressure-sensitive adhesive layer of the present invention, the gel content is suppressed to 80% by mass or less as described above. Set. That is, the gel fraction of the acrylic pressure-sensitive adhesive layer is 80% by mass or less. Further, the larger the molecular weight of the polymer contained in the sol content in the pressure-sensitive adhesive layer and the larger the content ratio of the sol content in the pressure-sensitive adhesive layer, the higher the adhesive strength of the pressure-sensitive adhesive layer tends to be. As described above, the agent layer contains 20% by mass or more of a sol having a weight average molecular weight of 700,000 or more. The removable pressure-sensitive adhesive sheet or its acrylic pressure-sensitive adhesive layer, which has these configurations in a complex manner, is suitable for achieving good adhesive strength.

The higher the gel content of the pressure-sensitive adhesive layer, the more the increase in the adhesive strength of the pressure-sensitive adhesive layer with time tends to be suppressed. However, in the acrylic pressure-sensitive adhesive layer of the present invention, the gel content is 30 as described above. Set to mass% or more. That is, the gel fraction of the acrylic pressure-sensitive adhesive layer is 30% by mass or more. Further, as described above, the second acrylic polymer in the acrylic pressure-sensitive adhesive layer in the present invention is likely to be prevented from moving or changing its orientation by the three-dimensional network of the first acrylic polymer in the pressure-sensitive adhesive layer. Therefore, movement and orientation change are unlikely to occur in the acrylic pressure-sensitive adhesive layer. In such a configuration, the second acrylic polymer moves or changes its orientation in the pressure-sensitive adhesive layer, and the functional groups of the second acrylic polymer interact with the surface of the adherend. Contributes to suppressing the increase in the adhesive strength of the adhesive layer caused by the above. The removable pressure-sensitive adhesive sheet or the acrylic pressure-sensitive adhesive layer thereof, which comprises these configurations in a complex manner, is suitable for suppressing an increase in adhesive strength with time.

In addition, since the second acrylic polymer contained in the acrylic pressure-sensitive adhesive layer in the present invention is unlikely to move or change its orientation in the pressure-sensitive adhesive layer as described above, the re-peelable pressure-sensitive adhesive sheet or its acrylic pressure-sensitive adhesive. The layer is suitable for suppressing contamination of the adherend by components that move within the pressure-sensitive adhesive layer and reach the surface of the adherend.

As described above, the removable pressure-sensitive adhesive sheet according to the present invention realizes low pollution while achieving good adhesive strength and suppression of an increase in the adhesive strength with time (stability of the adhesive strength with time). However, it is suitable.

Preferably, the acrylic pressure-sensitive adhesive layer of the removable pressure-sensitive adhesive sheet is a dry culture of an water-dispersible pressure-sensitive adhesive composition containing a water-dispersible acrylic polymer and a water-soluble cross-linking agent. The dry curing of the pressure-sensitive adhesive composition is a pressure-sensitive adhesive composition containing a polymer component, a solvent, and the like that has been dried and cured (aged), and the pressure-sensitive adhesive composition contains a cross-linking agent. In the case, it means that the cross-linking reaction of the polymer component caused by the cross-linking agent has proceeded to a predetermined degree by drying curing. The configuration in which the acrylic pressure-sensitive adhesive layer is a dry nutrient of a water-dispersible pressure-sensitive adhesive composition containing a water-dispersible acrylic polymer and a water-soluble cross-linking agent is a structure of the pressure-sensitive adhesive composition in the production of the present pressure-sensitive adhesive sheet. It is suitable for avoiding the use of volatile organic compounds as a solvent for goods.

Preferably, the aqueous dispersion acrylic polymer contains a monomer unit derived from a nonionic reactive emulsifier and / or an anionic reactive emulsifier. Such a configuration appropriately produces an aqueous dispersion type acrylic polymer by emulsion polymerization in the manufacturing process of the present pressure-sensitive adhesive sheet, and moves in the pressure-sensitive adhesive layer to the surface of the adherend in the manufactured pressure-sensitive adhesive sheet. It is suitable for suppressing the contamination of the adherend by all the components.

Preferably, the acrylic polymer in the acrylic pressure-sensitive adhesive layer contains a (meth) acrylic acid alkyl ester and a carboxyl group-containing monomer of 0.5 to 5 parts by mass with respect to 100 parts by mass of the (meth) acrylic acid alkyl ester. It has a monomer unit composition derived from the monomer component composition including and. The (meth) acrylic acid alkyl ester for the acrylic polymer in the acrylic pressure-sensitive adhesive layer is preferably n-butyl acrylate and / or n-butyl methacrylate. The carboxyl group-containing monomer for the acrylic polymer in the acrylic pressure-sensitive adhesive layer is preferably acrylic acid and / or methacrylic acid. These configurations are suitable for setting the gel fraction of the acrylic pressure-sensitive adhesive layer to 30 to 80% by mass.

Preferably, the weight average molecular weight of the cross-linking agent in the acrylic pressure-sensitive adhesive layer is 3000 to 20000. Such a configuration is suitable for setting the weight average molecular weight of the sol content of the acrylic pressure-sensitive adhesive layer to 700,000 or more. From the viewpoint of increasing the molecular weight of the sol, the weight average molecular weight of the cross-linking agent in the acrylic pressure-sensitive adhesive layer is preferably 3000 or more. Regarding the cross-linking reaction with a cross-linking agent in a group of polymers having a wide molecular weight distribution, the larger the molecular weight or size of the cross-linking agent, the more the progress of the cross-linking reaction tends to be suppressed from the high molecular weight component of the polymer. Because it is in. On the other hand, from the viewpoint of efficient progress of the cross-linking reaction, the weight average molecular weight of the cross-linking agent in the acrylic pressure-sensitive adhesive layer is preferably 200,000 or less.

Preferably, the cross-linking agent in the acrylic pressure-sensitive adhesive layer is an oxazoline group-containing cross-linking agent. Such a configuration is suitable for setting the gel fraction to 30 to 80% by mass and the weight average molecular weight of the sol to 700,000 or more in the acrylic pressure-sensitive adhesive layer.

Preferably, the content of the cross-linking agent in the acrylic pressure-sensitive adhesive layer is 0.5 to 5 parts by mass with respect to 100 parts by mass of the total amount of the acrylic polymer. From the viewpoint of ensuring the gel fraction of the acrylic pressure-sensitive adhesive layer and suppressing the increase in adhesive strength with time, the content of the cross-linking agent is preferably 0.5 parts by mass or more. From the viewpoint of reducing the unreacted cross-linking agent in the acrylic pressure-sensitive adhesive layer and realizing low contamination of the pressure-sensitive adhesive sheet or the acrylic pressure-sensitive adhesive layer, the content of the cross-linking agent is preferably 5 parts by mass or less.

Preferably, the 180 ° peeling adhesive strength (against SUS304 plate, peeling temperature 23 ° C., peeling speed 0.3 m / min) of this re-peelable adhesive sheet is 1 N / 25 mm or more. Such a configuration is suitable for achieving good adhesive strength.

Preferably, the first 180 ° peeling adhesive force (against SUS304 plate, peeling temperature 23 ° C., peeling speed 3 m / min) of the present removable adhesive sheet is the second 180 ° peeling adhesive of the present removable adhesive sheet. Greater than the force (against SUS304 plate, peeling temperature 23 ° C., peeling speed 0.3 m / min). According to the viscoelastic theory, for a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive, peeling at a relatively high speed corresponds to peeling at a relatively low temperature, and peeling at a relatively low speed corresponds to peeling at a relatively high temperature. It can be attached and evaluated. The configuration in which the first 180 ° peeling adhesive force under high-speed conditions is larger than the second 180 ° peeling adhesive force under low-speed conditions is such that the acrylic pressure-sensitive adhesive layer of the re-peelable pressure-sensitive adhesive sheet and the adherend. It is suitable for suppressing peeling such as local peeling (floating) at the interface in a low temperature environment.

It is a partial cross-sectional schematic diagram of the removable pressure-sensitive adhesive sheet which concerns on one Embodiment of this invention.

FIG. 1 is a schematic partial cross-sectional view of an adhesive sheet 10 which is a removable adhesive sheet according to an embodiment of the present invention. The pressure-sensitive adhesive sheet 10 has a laminated structure including a base material 11 and a pressure-sensitive adhesive layer 12. The adhesive sheet 10 is a protective film for protecting the surface of the adherend in the process of manufacturing and processing various optical materials such as a polarizing film, a retardation film, and an antireflection film, and in the process of manufacturing and transporting furniture. It can be used as.

The base material 11 of the pressure-sensitive adhesive sheet 10 is a portion of the pressure-sensitive adhesive sheet 10 that functions as a support. The base material 11 is preferably a transparent resin base material from the viewpoint of achieving high transparency in the pressure-sensitive adhesive sheet 10 or the base material 11. Examples of the resin material for forming such a base material 11 include polyolefins such as polypropylene and polyethylene, polyesters such as polyethylene terephthalate (PET), polycarbonate, polyamide, polyimide, acrylic, polystyrene, acetate, polyether sulfone, and the like. Examples include triacetyl cellulose. The base material 11 may be made of one kind of material, may be made of two or more kinds of materials, or may contain an additive product other than the resin material. Further, the surface of the base material 11 on the pressure-sensitive adhesive layer side is preferably surface-treated to improve the adhesiveness with the pressure-sensitive adhesive layer 12. Examples of such a surface treatment include a physical treatment such as a corona treatment and a plasma treatment, and a chemical treatment such as an undercoat treatment. The thickness of such a base material 11 is, for example, 10 to 150 μm, preferably 15 to 100 μm, and more preferably 20 to 80 μm.

The pressure-sensitive adhesive layer 12 of the pressure-sensitive adhesive sheet 10 is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer as a polymer material having the largest mass ratio, and is a pressure-sensitive adhesive surface that can be peeled off from the adherend after being attached to the adherend. It has 12a. The pressure-sensitive adhesive layer 12 contains a first acrylic polymer crosslinked by a cross-linking agent and a second acrylic polymer, and the proportion of the gel insoluble in ethyl acetate is 30 to 80% by mass. The weight average molecular weight of the sol soluble in ethyl acetate is 700,000 or more. Such a pressure-sensitive adhesive layer 12 is, for example, a dry curing organism formed by drying and curing (aging) a pressure-sensitive adhesive composition containing an acrylic polymer, a cross-linking agent, and a solvent. From the viewpoint of avoiding the use of a volatile organic compound as a solvent of the pressure-sensitive adhesive composition for producing the pressure-sensitive adhesive sheet 10, the pressure-sensitive adhesive layer 12 is composed of an aqueous dispersion type acrylic polymer and a water-soluble cross-linking agent. It is preferably a dry nutrient composition of an aqueous dispersion type pressure-sensitive adhesive composition containing water as a solvent.

The acrylic polymer (first acrylic polymer, second acrylic polymer) in the pressure-sensitive adhesive layer 12 is a monomer unit derived from an acrylic acid alkyl ester and / or a methacrylate alkyl ester in terms of mass ratio. It is a polymer contained as the most abundant main monomer unit. In the following, "(meth) acrylic" is used to represent "acrylic" and / or "methacryl".

Examples of the (meth) acrylic acid alkyl ester for forming the monomer unit of the acrylic polymer include methyl (meth) acrylic acid, ethyl (meth) acrylic acid, propyl (meth) acrylic acid, and isopropyl (meth) acrylic acid. , (Meta) n-butyl acrylate, (meth) s-butyl acrylate, (meth) isobutyl acrylate, (meth) t-butyl acrylate, (meth) pentyl acrylate, (meth) isopentyl acrylate, ( Hexyl acrylate, (meth) heptyl acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, (Meta) decyl acrylate, (meth) isodecyl acrylate, (meth) undecyl acrylate, (meth) dodecyl acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, (meth) (Meta) having an alkyl group having 1 to 20 carbon atoms, such as hexadecyl acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, nonadecil (meth) acrylate, and eicosyl (meth) acrylate. Acrylic acid alkyl ester can be mentioned. Preferred (meth) acrylic acid alkyl esters for forming the monomer unit of the acrylic polymer in the pressure-sensitive adhesive layer 12 include n-butyl (meth) acrylic acid. As the (meth) acrylic acid alkyl ester for forming the monomer unit of the acrylic polymer in the pressure-sensitive adhesive layer 12, one kind of (meth) acrylic acid alkyl ester may be used, or two or more kinds of (meth) acrylic acid alkyl esters may be used. ) Acrylic acid alkyl ester may be used.

The content of the monomer unit derived from the (meth) acrylic acid alkyl ester in the acrylic polymer in the pressure-sensitive adhesive layer 12 is, for example, 50% by mass or more, preferably 60% by mass or more, and more preferably 70% by mass or more. , More preferably 80% by mass or more, more preferably 90% by mass or more, and more preferably 95% by mass or more. That is, the content of the (meth) acrylic acid alkyl ester in the monomer component composition of the raw material for forming the acrylic polymer in the pressure-sensitive adhesive layer 12 is, for example, 50% by mass or more, preferably 60% by mass or more. It is more preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The acrylic polymer in the pressure-sensitive adhesive layer 12 has a monomer unit structure derived from the monomer component composition with such a (meth) acrylic acid alkyl ester content. Such a configuration regarding the content of the (meth) acrylic acid alkyl ester is suitable for appropriately expressing the basic characteristics such as the adhesiveness of the acrylic pressure-sensitive adhesive in the pressure-sensitive adhesive layer 12.

The acrylic polymer (first acrylic polymer, second acrylic polymer) in the pressure-sensitive adhesive layer 12 preferably contains a monomer unit derived from a carboxyl group-containing monomer. The carboxyl group in the monomer unit of the acrylic polymer can function as a cross-linking point that causes a reaction with a cross-linking agent. Carboxylic group-containing monomers include, for example, (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Of these, acrylic acid (AA) and methacrylic acid (MAA) are preferred. As the carboxyl group-containing monomer for forming the monomer unit of the acrylic polymer in the pressure-sensitive adhesive layer 12, one type of carboxyl group-containing monomer may be used, or two or more types of carboxyl group-containing monomers may be used. Good.

The content of the monomer unit derived from the carboxyl group-containing monomer in the acrylic polymer in the pressure-sensitive adhesive layer 12 is, for example, 0.5 to 5 parts by mass with respect to 100 parts by mass of the monomer unit derived from the (meth) acrylic acid alkyl ester. It is preferably 0.8 to 4.5 parts by mass, more preferably 1 to 4 parts by mass, and more preferably 1.5 to 3 parts by mass. That is, the content of the carboxyl group-containing monomer in the monomer component composition of the raw material for forming the acrylic polymer in the pressure-sensitive adhesive layer 12 is, for example, 0.5 to 100 parts by mass with respect to 100 parts by mass of the (meth) acrylic acid alkyl ester. It is 5 parts by mass, preferably 0.8 to 4.5 parts by mass, more preferably 1 to 4 parts by mass, and more preferably 1.5 to 3 parts by mass. The acrylic polymer in the pressure-sensitive adhesive layer 12 has a monomer unit structure derived from the monomer component composition having such a carboxyl group-containing monomer content. Such a configuration regarding the content of the carboxyl group-containing monomer is suitable for the acrylic polymer to appropriately form a crosslinked structure.

The acrylic polymer in the pressure-sensitive adhesive layer 12 may contain a monomer unit derived from a monomer other than the (meth) acrylic acid alkyl ester and the carboxyl group-containing monomer described above. The copolymerizable monomer for such a monomer unit includes, for example, a hydroxyl group-containing monomer having at least one hydroxyl group in the monomer unit and at least one nitrogen atom in the monomer unit. Examples include nitrogen atom-containing monomers. As such a copolymerizable monomer for forming a monomer unit of the acrylic polymer in the pressure-sensitive adhesive layer 12, one kind of monomer may be used, or two or more kinds of monomers may be used. Further, when an acrylic polymer is formed by using a reactive emulsifier as described later, the reactive emulsifier also forms a monomer unit of the acrylic polymer.

The content of the acrylic polymer having the above structure in the pressure-sensitive adhesive layer 12 is, for example, 90 to 99.5% by mass.

As the above-mentioned cross-linking agent for cross-linking the acrylic polymer, a polymer-type cross-linking agent is preferable. The weight average molecular weight of the polymer cross-linking agent is, for example, 3000 to 20000. From the viewpoint of increasing the molecular weight of the ethyl acetate-soluble component (sol content) of the pressure-sensitive adhesive layer 12, the weight average molecular weight of the cross-linking agent in the pressure-sensitive adhesive layer 12 is preferably 3000 or more, more preferably 5000 or more, and more. It is preferably 15,000 or more, more preferably 25,000 or more, and more preferably 40,000 or more. Regarding the cross-linking reaction with a cross-linking agent in a group of polymers having a wide molecular weight distribution, the larger the molecular weight or size of the cross-linking agent, the more the progress of the cross-linking reaction tends to be suppressed from the high molecular weight component of the polymer. Because it is in. On the other hand, from the viewpoint of efficient progress of the crosslinking reaction, the weight average molecular weight of the crosslinking agent in the acrylic pressure-sensitive adhesive layer is preferably 200,000 or less, more preferably 150,000 or less, and even more preferably 100,000 or less. Examples of commercially available polymer-type cross-linking agents include "Epocross K series" and "Epocross WS series", which are oxazoline group-containing polymers manufactured by Nippon Shokubai Co., Ltd., and "PAA (polyallylamine)" manufactured by Nittobo Medical Co., Ltd. And "PAS (polyamine series)". An oxazoline group-containing cross-linking agent is preferable because the oxazoline group exhibits high reactivity with the carboxyl group.

The content of the cross-linking agent in the pressure-sensitive adhesive layer 12 is preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the total amount of the acrylic polymer (first acrylic polymer, second acrylic polymer). , More preferably 1 to 4 parts by mass, and more preferably 1.5 to 3 parts by mass. From the viewpoint of ensuring the gel fraction of the pressure-sensitive adhesive layer 12 and suppressing an increase in adhesive strength with time, the content of the cross-linking agent is preferably 0.5 parts by mass or more. From the viewpoint of reducing the unreacted cross-linking agent in the pressure-sensitive adhesive layer 12 and realizing low contamination of the pressure-sensitive adhesive sheet 10 or the pressure-sensitive adhesive layer 12, the content of the cross-linking agent is preferably 5 parts by mass or less. ..

The pressure-sensitive adhesive layer 12 may contain other components as long as the effects of the present invention are not impaired. Such components include, for example, tackifiers, silane coupling agents, colorants, pigments, dyes, release modifiers, surface lubricants, leveling agents, softeners, antioxidants, antioxidants, light stabilizers. , Polymerization inhibitors, inorganic or organic fillers, metal powders, particulates, and foils. The content of these components is determined according to the purpose of use, and is, for example, 10 parts by mass or less with respect to 100 parts by mass of the acrylic polymer as long as the effects of the present invention are not impaired.

In the pressure-sensitive adhesive layer 12, as described above, the proportion of the gel component insoluble in ethyl acetate (that is, the gel fraction) is set to 30 to 80% by mass. The gel fraction is preferably 40 to 77% by mass, more preferably 50 to 75% by mass. The gel fraction of the pressure-sensitive adhesive layer 12 can be calculated as follows.

_{First, a sample of about 0.1 g (mass: W 1} mg) is collected from the pressure-sensitive adhesive layer or the pressure-sensitive adhesive to be identified as a gel fraction, and a porous film made of tetrafluoroethylene resin (mass: W) having an average pore size of 0.2 μm is collected. _{Wrap in 2} mg) and tie with a kite string (mass: W ₃ mg) to obtain a wrap. The packet is then immersed in about 50 mL of ethyl acetate solution and allowed to stand in the ethyl acetate solution at room temperature (typically 23 ° C.) for 7 days. Next, the package containing the gel, which is an insoluble ethyl acetate, is removed from the ethyl acetate solution, and the package is dried at 130 ° C. for 1 hour. Then, the mass (W ₄ mg) of the whole package is measured. Then, the gel fraction is calculated by substituting the values of _{W 1 to} W _{4 into the following equation.}

Gel fraction (mass%) = [(W _4- W _2- W ₃ ) / W ₁ ] x 100

In the pressure-sensitive adhesive layer 12, as described above, the weight average molecular weight of the sol soluble in ethyl acetate is set to 700,000 or more. The weight average molecular weight of the sol is preferably 1,000,000 or more, more preferably 1200,000 or more. The weight average molecular weight of the sol can be determined as follows.

First, about 0.1 g of a sample is taken from the pressure-sensitive adhesive layer or the pressure-sensitive adhesive for which the sol component molecular weight is to be identified, wrapped in a porous film made of tetrafluoroethylene resin having an average pore size of 0.2 μm, and tied with a kite string to obtain a package. .. The packet is then immersed in about 50 mL of ethyl acetate solution and allowed to stand in the ethyl acetate solution at room temperature (typically 23 ° C.) for 7 days. Next, the package containing the ethyl acetate insoluble component and the ethyl acetate solution containing the sol component which is the ethyl acetate-soluble component are separated. Next, the sol-containing ethyl acetate solution is dried under reduced pressure at 30 ° C., and the ethyl acetate is evaporated to obtain a solid content. Next, this solid content is weighed. Next, the molecular weight of the sol content is measured by GPC (gel permeation chromatography). For example, using a GPC measuring device (trade name “HLC-8120GPC”, manufactured by Tosoh Corporation), the weight average molecular weight of the sol can be determined by the polystyrene conversion value under the following measurement conditions.
[GPC measurement conditions]
-Column: Two TSKgel GMH _HR- H (S) (manufactured by Tosoh Corporation) in series-Column size: 7.8 mmφ x 30 cm
-Column temperature: 40 ° C
-Eluent: tetrahydrofuran (THF)
・ Flow rate: 0.5 ml / min
-Sample injection amount: 100 μl
-Sample concentration: 0.1% by mass
・ Standard sample: Polystyrene ・ Detector: Differential refractometer (RI)

From the viewpoint of achieving good adhesive strength, the adhesive sheet 10 is set to have a 180 ° peeling adhesive strength (against SUS304 plate, peeling temperature 23 ° C., peeling speed 0.3 m / min) of 1 N / 25 mm or more. Is preferable. Further, in the adhesive sheet 10, the first 180 ° peeling adhesive force (against SUS304 plate, peeling temperature 23 ° C., peeling speed 3 m / min) is the second 180 ° peeling adhesive force (against SUS304 plate, peeling temperature 23). It is preferable that the temperature is set to be higher than ° C. and peeling speed of 0.3 m / min). According to the viscoelastic theory, for a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive, peeling at a relatively high speed corresponds to peeling at a relatively low temperature, and peeling at a relatively low speed corresponds to peeling at a relatively high temperature. It can be attached and evaluated. The configuration in which the first 180 ° peeling adhesive force under high-speed conditions is larger than the second 180 ° peeling adhesive force under low-speed conditions is localized at the interface between the pressure-sensitive adhesive layer 12 of the pressure-sensitive adhesive sheet 10 and the adherend. It is suitable for suppressing peeling such as peeling (floating) in a low temperature environment. The 180 ° peeling adhesive strength can be measured according to JIS Z 0237, for example, as follows.

First, a test piece (width 20 mm × length 100 mm) is prepared by cutting out from an adhesive sheet to be measured for adhesive strength. Next, the test piece is attached to a SUS304 plate which is an adherend, and the test piece and the adherend are crimped by reciprocating a 5 kg roller once. Then, after leaving it for 20 minutes in an environment of a temperature of 23 ° C. and a relative humidity of 60%, it is peeled off using a peeling adhesive force measuring device (trade name "Small desktop tester EXtest", manufactured by Shimadzu Corporation). Test under the conditions of temperature 23 ° C. and peeling speed 3 m / min (measurement condition related to the first 180 ° peeling adhesive strength) or peeling speed 0.3 m / min (measurement condition related to the second 180 ° peeling adhesive strength). For the piece, the 180 ° peeling adhesive force with respect to the SUS304 plate is measured.

The thickness of the pressure-sensitive adhesive layer 12 of the pressure-sensitive adhesive sheet 10 is, for example, 1 to 200 μm, preferably 1 to 50 μm, and more preferably 1 to 20 μm.

The pressure-sensitive adhesive sheet 10 may be provided with a separator (release liner) so as to cover the pressure-sensitive adhesive surface 12a of the pressure-sensitive adhesive layer 12. The separator is an element for protecting the pressure-sensitive adhesive layer 12 of the pressure-sensitive adhesive sheet 10 from being exposed, and is peeled off from the pressure-sensitive adhesive sheet 10 when the pressure-sensitive adhesive sheet 10 is attached to an adherend. On the other hand, the above-mentioned base material 11 is attached to the adherend together with the pressure-sensitive adhesive layer 12 when the pressure-sensitive adhesive sheet 10 is used. Examples of the separator include a base material having a peeling treatment layer, a low adhesive base material made of a fluoropolymer, and a low adhesive base material made of a non-polar polymer. The surface of the separator may be subjected to a mold release treatment, an antifouling treatment, or an antistatic treatment. The thickness of the separator is, for example, 5 to 200 μm.

For the pressure-sensitive adhesive sheet 10 having the above-described structure, for example, a pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer 12 is prepared, the pressure-sensitive adhesive composition is applied onto the base material 11, and the pressure-sensitive adhesive composition is applied. It can be produced by drying and aging the product. As the pressure-sensitive adhesive composition applied on the base material 11, from the viewpoint of avoiding the use of a volatile organic compound as the solvent, an aqueous dispersion type acrylic polymer, a water-soluble cross-linking agent, and water as a solvent are used. It is preferable that the composition is a water-dispersible pressure-sensitive adhesive composition containing. The water-dispersible pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer 12 can be produced, for example, as follows.

First, a mixture containing the monomer component necessary for forming the above-mentioned acrylic polymer, an emulsifier and water is stirred to prepare a monomer emulsion. In the manufactured pressure-sensitive adhesive sheet 10, the acrylic weight formed as the emulsifier is used from the viewpoint of suppressing the adherend from being contaminated by the components that move in the pressure-sensitive adhesive layer 12 and reach the surface of the adherend. It is preferable to use a nonionic reactive emulsifier and / or an anionic reactive emulsifier that is incorporated as a monomer unit into the coalescence. Next, a polymerization initiator is added to the monomer emulsion and heated to a predetermined temperature to carry out emulsion polymerization. The polymerization method may be a batch type or batch type emulsion polymerization, or may be a continuous type emulsion polymerization. Further, from the viewpoint of narrowing the molecular weight distribution of the obtained acrylic polymer to realize sharp physical properties, batch polymerization is preferable to so-called drop polymerization, and the polymerization time is set to be relatively short. Is preferable. The polymerization time is, for example, 0.5 to 3 hours. Examples of the polymerization initiator include an azo-based polymerization initiator, a peroxide-based polymerization initiator, and a redox-based polymerization initiator. As the azo-based polymerization initiator, for example, the azo-based polymerization initiator disclosed in JP-A-2002-69411 can be used. By undergoing such emulsion polymerization, an aqueous dispersion in which the acrylic polymer emulsion is dispersed in an aqueous solvent can be obtained. Next, a predetermined amount of a cross-linking agent is added to a predetermined amount of the aqueous dispersion and mixed. As described above, an aqueous dispersion type pressure-sensitive adhesive composition containing an acrylic polymer can be produced. The pressure-sensitive adhesive layer 12 formed from such a water-dispersible pressure-sensitive adhesive composition becomes a dry nutrient for the water-dispersion type pressure-sensitive adhesive composition containing the water-dispersible acrylic polymer and the water-soluble cross-linking agent.

As described above, the pressure-sensitive adhesive layer 12 of the pressure-sensitive adhesive sheet 10, which is a removable pressure-sensitive adhesive sheet, contains a first acrylic polymer crosslinked by a cross-linking agent and a second acrylic polymer. The first acrylic polymer crosslinked by the crosslinking agent forms a three-dimensional network of polymer chains in the pressure-sensitive adhesive layer 12. Of the gel content (ethyl acetate insoluble content) of the pressure-sensitive adhesive layer 12, the structure of this polymer chain three-dimensional network has the largest mass ratio, and the ratio of the gel content is 30 to 80 mass as described above. %. On the other hand, the sol content (ethyl acetate-soluble content) of the pressure-sensitive adhesive layer 12 is 20 to 70% by mass, and the second acrylic polymer has the largest mass ratio among the sol contents. This second acrylic polymer has a relatively large degree of polymerization and is long so that the weight average molecular weight of the sol of the pressure-sensitive adhesive layer 12 is 700,000 or more. Such a second acrylic polymer is likely to be prevented from moving or changing its orientation by the above-mentioned three-dimensional network structure of polymer chains in the pressure-sensitive adhesive layer 12, and therefore moving or changing its orientation in the pressure-sensitive adhesive layer 12. Hard to occur.

The lower the gel content of the pressure-sensitive adhesive layer, the higher the adhesive strength of the pressure-sensitive adhesive layer tends to be. However, in the pressure-sensitive adhesive layer 12 of the pressure-sensitive adhesive sheet 10, the gel content is suppressed to 80% by mass or less as described above. Set. Further, the adhesive strength of the pressure-sensitive adhesive layer tends to be higher as the molecular weight of the polymer contained in the sol content in the pressure-sensitive adhesive layer is larger and the content ratio of the sol content in the pressure-sensitive adhesive layer is larger. As described above, the agent layer 12 contains 20% by mass or more of a sol having a weight average molecular weight of 700,000 or more. The pressure-sensitive adhesive sheet 10 or the pressure-sensitive adhesive layer 12 thereof, which comprises these configurations in a complex manner, is suitable for realizing good adhesive strength.

The higher the gel content of the pressure-sensitive adhesive layer, the more the increase in the adhesive strength of the pressure-sensitive adhesive layer with time tends to be suppressed. However, in the pressure-sensitive adhesive layer 12 of the pressure-sensitive adhesive sheet 10, the gel content is 30 as described above. Set to mass% or more. Further, as described above, the second acrylic polymer in the pressure-sensitive adhesive layer 12 of the pressure-sensitive adhesive sheet 10 is prevented from moving or changing its orientation by the three-dimensional network of the first acrylic polymer in the pressure-sensitive adhesive layer. It is easy, and therefore, movement and orientation change are unlikely to occur in the pressure-sensitive adhesive layer 12. In such a configuration, the second acrylic polymer moves or changes its orientation in the pressure-sensitive adhesive layer 12, and the functional groups of the second acrylic polymer interact with the surface of the adherend. This contributes to suppressing the increase in the adhesive strength of the pressure-sensitive adhesive layer 12. The pressure-sensitive adhesive sheet 10 or the pressure-sensitive adhesive layer 12 thereof having these configurations in a complex manner is suitable for suppressing an increase in adhesive strength with time.

In addition, since the second acrylic polymer contained in the pressure-sensitive adhesive layer 12 of the pressure-sensitive adhesive sheet 10 is unlikely to move or change its orientation in the pressure-sensitive adhesive layer 12 as described above, the pressure-sensitive adhesive sheet 10 or its pressure-sensitive adhesive layer 12 Is suitable for suppressing contamination of the adherend by components that move in the pressure-sensitive adhesive layer 12 and reach the surface of the adherend.

As described above, the re-peelable adhesive sheet 10 is capable of achieving low pollution while achieving good adhesive strength and suppression of the increase in adhesive strength over time (stability of adhesive strength over time). , Suitable.

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to these Examples.

[Example 1]
In the container, 60 parts by mass of water, 55 parts by mass of n-butyl (BA) acrylate, 45 parts by mass of n-butyl methacrylate (BMA), 2 parts by mass of acrylic acid (AA), and anionic reactivity. A mixture containing 3 parts by mass of an emulsifier (trade name "Aquaron KH1025", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was stirred with a homomixer to prepare a monomer emulsion of Example 1. Next, in a reaction vessel equipped with a recirculation cooler, a nitrogen introduction tube, a thermometer, and a stirrer, 165 parts by mass of the monomer emulsion and a water-soluble azo polymerization initiator (trade name "V-50", Wako Pure Chemical Industries, Ltd.) A mixture of 0.03 parts by mass (manufactured by the company) was subjected to an emulsion polymerization reaction (batch polymerization) at 56 ° C. for 2 hours with stirring. Next, after cooling the reaction solution to 30 ° C., the reaction solution is adjusted to pH 8 by adding a 10% by mass aqueous ammonia solution, and then the acrylic polymer emulsion is dispersed in water. A liquid (40% by mass) was prepared.

Next, the aqueous dispersion of Example 1 and an oxazoline group-containing polymer cross-linking agent (trade name "Epocross WS-500", weight average molecular weight 70000, manufactured by Nippon Catalyst Co., Ltd.) were added to acrylic in the aqueous dispersion. The water-dispersed acrylic pressure-sensitive adhesive composition of Example 1 was prepared by mixing the cross-linking agent (solid content) in an amount ratio of 2 parts by mass with respect to 100 parts by mass of the system polymer.

Next, using a film casting knife (trade name "BYK Gardner Film Casting Knife", manufactured by Toyo Seiki Seisakusho Co., Ltd.), a film made of polyethylene terephthalate (PET) (trade name "Lumirror s10", manufactured by Toray Industries, Inc.) ), The water-dispersible acrylic pressure-sensitive adhesive composition of Example 1 was applied onto the corona-treated surface. Next, the water-dispersed acrylic pressure-sensitive adhesive composition on the PET film was dried at 130 ° C. for 3 minutes using a hot air circulation oven, and then cured (aging) at 50 ° C. for 3 days. Attached to. As described above, the adhesive sheet of Example 1 (adhesive layer thickness 10 μm) was produced.

[Example 2]
165 parts by mass of the monomer emulsion obtained in the same manner as in Example 1 and 0.03 parts by mass of ammonium peroxide (manufactured by Sigma Aldrich) as a polymerization initiator were added to a recirculation cooler, a nitrogen introduction tube, a thermometer, and a thermometer. The mixture was mixed in a reaction vessel equipped with a stirrer, and an emulsion polymerization reaction (batch polymerization) was carried out at 75 ° C. for 2 hours while stirring. Next, after cooling the reaction solution to 30 ° C., the reaction solution is adjusted to pH 8 by adding a 10% by mass aqueous ammonia solution, and then the acrylic polymer emulsion is dispersed in water. A liquid (40% by mass) was prepared. Next, the aqueous dispersion of Example 2 and an oxazoline group-containing polymer cross-linking agent (trade name “Epocross WS-500”, manufactured by Nippon Catalyst Co., Ltd.) were added to 100 mass of acrylic polymer in the aqueous dispersion. The water-dispersed acrylic pressure-sensitive adhesive composition of Example 2 was prepared by mixing the parts in an amount ratio of 1 part by mass of the cross-linking agent (solid content). Next, coating, drying, and curing were carried out in the same manner as in Example 1 except that the water-dispersed acrylic pressure-sensitive adhesive composition of Example 2 was used instead of the water-dispersed acrylic pressure-sensitive adhesive composition of Example 1. The adhesive sheet of Example 2 (adhesive layer thickness 10 μm) was produced.

[Comparative Example 1]
An aqueous dispersion (40% by mass) of Comparative Example 1 in which the acrylic polymer emulsion was dispersed in water was prepared through an emulsion polymerization reaction carried out using the same raw materials as in Example 1 and subsequent pH adjustment. Next, the aqueous dispersion of Comparative Example 1 and an aziridine cross-linking agent (trade name "CX-100", manufactured by DSM Coating Resins) are crosslinked with respect to 100 parts by mass of the acrylic polymer in the aqueous dispersion. The pressure-sensitive adhesive composition of Comparative Example 1 was prepared by mixing the agents (solid content) in an amount ratio of 0.5 parts by mass. Next, coating, drying, and curing were carried out in the same manner as in Example 1 except that the pressure-sensitive adhesive composition of Comparative Example 1 was used instead of the water-dispersed acrylic pressure-sensitive adhesive composition of Example 1, and Comparative Example. The adhesive sheet (adhesive layer thickness 10 μm) of No. 1 was produced.

[Comparative Example 2]
An aqueous dispersion (40% by mass) of Comparative Example 2 in which the acrylic polymer emulsion was dispersed in water was prepared through an emulsion polymerization reaction carried out using the same raw materials as in Example 2 and subsequent pH adjustment. Next, the mixture was applied, dried, and dried in the same manner as in Example 1 except that the aqueous dispersion of Comparative Example 2 (which does not contain a cross-linking agent) was used instead of the aqueous dispersion type acrylic pressure-sensitive adhesive composition of Example 1. Curing was performed to produce an adhesive sheet (adhesive layer thickness 10 μm) of Comparative Example 2.

[Comparative Example 3]
In the container, 40 parts by mass of water, 55 parts by mass of n-butyl (BA) acrylate, 45 parts by mass of n-butyl methacrylate (BMA), 2 parts by mass of acrylic acid (AA), and anionic reactivity. A mixture containing 3 parts by mass of an emulsifier (trade name "Aquaron KH1025", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was stirred with a homomixer to prepare a monomer emulsion of Comparative Example 3. Next, in a reaction vessel equipped with a recirculation cooler, a nitrogen introduction tube, a thermometer, and a stirrer, 20 parts by mass of water and a water-soluble azo polymerization initiator (trade name "V-50", manufactured by Wako Pure Chemical Industries, Ltd.) ) 0.03 parts by mass was mixed, and 145 parts by mass of the monomer emulsion of Comparative Example 3 was added dropwise to the mixture at 56 ° C. over 3 hours with stirring. Next, an emulsion polymerization reaction was carried out at 56 ° C. for 3 hours. Next, after cooling the reaction solution to 30 ° C., the reaction solution was adjusted to pH 8 by adding a 10% by mass aqueous ammonia solution, and then the acrylic polymer emulsion was dispersed in water. A liquid (40% by mass) was prepared. Next, the mixture was applied, dried, and dried in the same manner as in Example 1 except that the aqueous dispersion of Comparative Example 3 (which does not contain a cross-linking agent) was used instead of the aqueous dispersion type acrylic pressure-sensitive adhesive composition of Example 1. Curing was performed to produce an adhesive sheet (adhesive layer thickness 10 μm) of Comparative Example 3.

[Comparative Example 4]
In the container, 40 parts by mass of water, 55 parts by mass of n-butyl (BA) acrylate, 45 parts by mass of n-butyl methacrylate (BMA), 2 parts by mass of acrylic acid (AA), and anionic reactivity. A mixture containing 3 parts by mass of an emulsifier (trade name "Aquaron KH1025", manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was stirred with a homomixer to prepare a monomer emulsion of Comparative Example 4. Next, in a reaction vessel equipped with a recirculation cooler, a nitrogen introduction tube, a thermometer, and a stirrer, 20 parts by mass of water and a water-soluble azo polymerization initiator (trade name "V-50", manufactured by Wako Pure Chemical Industries, Ltd.) ) 0.3 parts by mass was mixed, and 145 parts by mass of the monomer emulsion of Comparative Example 4 was added dropwise to the mixture at 56 ° C. over 3 hours with stirring. Next, an emulsion polymerization reaction was carried out at 56 ° C. for 3 hours. Next, after cooling the reaction solution to 30 ° C., the reaction solution was adjusted to pH 8 by adding a 10% by mass aqueous ammonia solution, and then the acrylic polymer emulsion was dispersed in water. A liquid (40% by mass) was prepared. Next, the aqueous dispersion of Comparative Example 4 and an oxazoline group-containing polymer cross-linking agent (trade name “Epocross WS-500”, manufactured by Nippon Catalyst Co., Ltd.) were added to 100 mass of acrylic polymer in the aqueous dispersion. The pressure-sensitive adhesive composition of Comparative Example 4 was prepared by mixing the parts in an amount ratio of 2 parts by mass of the cross-linking agent (solid content). Next, coating, drying, and curing were carried out in the same manner as in Example 1 except that the pressure-sensitive adhesive composition of Comparative Example 4 was used instead of the water-dispersed acrylic pressure-sensitive adhesive composition of Example 1, and Comparative Example. The adhesive sheet of No. 4 (adhesive layer thickness 10 μm) was produced.

<Gel fraction>
For the pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets of Examples 1 and 2 and Comparative Examples 1 to 4, the gel fraction was determined as follows. _{First, a sample of about 0.1 g (mass: W 1} mg) was collected from the pressure-sensitive adhesive layer, and a porous film made of tetrafluoroethylene resin having an average pore size of 0.2 μm (trade name “Nitoflon NTF1122”, mass: W ₂ mg). , Nitto Denko Co., Ltd.) and tied with a kite string (mass: W ₃ mg) to obtain a package. The packet was then immersed in about 50 mL of ethyl acetate solution and allowed to stand in the ethyl acetate solution at room temperature (typically 23 ° C.) for 7 days. Next, the package containing the gel, which is an insoluble ethyl acetate, was removed from the ethyl acetate solution, and the package was dried at 130 ° C. for 1 hour. Then, the mass (W ₄ mg) of the whole package was measured. Then, the gel fraction (mass%) was calculated by substituting the values of _{W 1 to} W _{4 into the following equation.} The results are listed in Table 1.

Gel fraction (mass%) = [(W _4- W _2- W ₃ ) / W ₁ ] x 100

<Weight average molecular weight of sol>
For the pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets of Examples 1 and 2 and Comparative Examples 1 to 4, the weight average molecular weight of the sol content was determined as follows. Specifically, first, about 0.1 g of a sample is collected from the pressure-sensitive adhesive layer and a porous membrane made of tetrafluoroethylene resin (trade name "Nitoflon NTF1122", manufactured by Nitto Denko Co., Ltd.) having an average pore size of 0.2 μm is used. I wrapped it and tied it with a kite string to get the wrap. The packet was then immersed in about 50 mL of ethyl acetate solution and allowed to stand in the ethyl acetate solution at room temperature (typically 23 ° C.) for 7 days. Next, the package containing the insoluble ethyl acetate component and the ethyl acetate solution containing the sol component soluble in ethyl acetate were separated. Next, the sol-containing ethyl acetate solution was dried under reduced pressure at 30 ° C., and the ethyl acetate was evaporated to obtain a solid content. Next, this solid content was weighed. Next, using a GPC measuring device (trade name "HLC-8120 GPC", manufactured by Tosoh Corporation), the weight average molecular weight (Mw) of the sol content was determined by GPC (gel) under the following measurement conditions according to the polystyrene conversion value. It was determined by permeation chromatography). The results are listed in Table 1.
[GPC measurement conditions]
-Column: Two TSKgel GMH _HR- H (S) (manufactured by Tosoh Corporation) in series-Column size: 7.8 mmφ x 30 cm
-Column temperature: 40 ° C
-Eluent: tetrahydrofuran (THF)
・ Flow rate: 0.5 ml / min
-Sample injection amount: 100 μl
-Sample concentration: 0.1% by mass
・ Standard sample: Polystyrene ・ Detector: Differential refractometer (RI)

<Adhesive strength measurement>
The adhesive strength of each of the adhesive sheets of Examples 1 and 2 and Comparative Examples 1 to 4 was measured as follows. First, a test piece (width 20 mm × length 100 mm) to be subjected to the adhesive strength measurement was cut out from the adhesive sheet. Next, the test piece was attached to a SUS304 plate as an adherend, and the test piece and the adherend were crimped by reciprocating a 5 kg roller once. Then, after leaving it for 20 minutes in an environment of a temperature of 23 ° C. and a relative humidity of 60%, it is peeled off using a peeling adhesive force measuring device (trade name "Small desktop tester EXtest", manufactured by Shimadzu Corporation). Under the conditions of a temperature of 23 ° C. and a peeling speed of 0.3 m / min, 180 ° peeling adhesive strength (initial adhesive strength, second 180 ° peeling adhesive strength) to the SUS304 plate was measured for the test piece according to JIS Z 0237. .. Further, with respect to the pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets of Examples 1 and 2 and Comparative Examples 1 to 4, the peeling speed of 0.3 m / min was changed to a peeling speed of 3 m / min under the same conditions as above. Another 180 ° peeling adhesive force to the plate (first 180 ° peeling adhesive force) was measured. The results are listed in Table 1.

<Changes in adhesive strength over time>
For each of the pressure-sensitive adhesive sheets of Examples 1 and 2 and Comparative Examples 1 to 4, the change over time in the adhesive strength was examined as follows. First, a test piece (width 20 mm × length 100 mm) to be subjected to the adhesive strength measurement was cut out from the adhesive sheet. Next, the test piece was attached to a SUS304 plate as an adherend, and the test piece and the adherend were crimped by reciprocating a 5 kg roller once. Next, the test piece was allowed to stand at 80 ° C. for 24 hours. Then, after leaving it for 2 hours in an environment of a temperature of 23 ° C. and a relative humidity of 60%, it is peeled off using a peeling adhesive force measuring device (trade name "Small desktop tester EXtest", manufactured by Shimadzu Corporation). Under the conditions of a temperature of 23 ° C. and a peeling speed of 0.3 m / min, the 180 ° peeling adhesive strength (adhesive strength after standing at 80 ° C. for 24 hours) with respect to the SUS304 plate was measured for the test piece according to JIS Z 0237. .. The results are listed in Table 1.

<Pollutivity>
The stainability of each of the pressure-sensitive adhesive sheets of Examples 1 and 2 and Comparative Examples 1 to 4 was examined as follows. First, a test piece (width 25 mm × length 100 mm) was cut out from the adhesive sheet. Next, the test piece was attached to a SUS304 plate as an adherend, and the test piece and the adherend were crimped by reciprocating a 5 kg roller once. Next, after allowing the test piece to stand at 80 ° C. for 24 hours, the test piece was peeled off from the SUS304 plate, and the peeled portion on the SUS304 plate was visually observed. As a result, in the adhesive sheets of Examples 1 and 2 and Comparative Examples 1 and 4, no difference was observed between the portion where the adhesive sheet was attached (peeled portion) and the portion where the adhesive sheet was not attached on the SUS304 plate. .. On the other hand, in the adhesive sheets of Comparative Examples 2 and 3, the portion (peeled portion) to which the adhesive sheet was attached on the SUS304 plate was severely whitened. These results are listed in Table 1.

[Evaluation]
The adhesive sheets of Examples 1 and 2 showed a good initial adhesive force of 1.0 N / 25 mm or more, and the adhesive force increased with time (the adhesive force after standing at 80 ° C. for 24 hours and the initial adhesive force). The difference from the above) is suppressed to 1.5 N / 25 mm or less, and low pollution is realized. On the other hand, the adhesive sheets of Comparative Examples 1 and 4 had an increase in adhesive strength with time (difference between the adhesive strength and the initial adhesive strength after standing at 80 ° C. for 24 hours) of 1.5 N / 25 mm. It was bigger than that. Further, in the pressure-sensitive adhesive sheets of Comparative Examples 2 and 3, the pressure-sensitive adhesive layer was coagulated and broken in the pressure-sensitive adhesive strength measurement.

10 Adhesive sheet (removable adhesive sheet)
11 Base material 12 Adhesive layer (acrylic adhesive layer)
12a Adhesive surface

Claims (10)

It has a laminated structure including a base material and an acrylic pressure-sensitive adhesive layer.
The acrylic pressure-sensitive adhesive layer contains a first acrylic polymer crosslinked by a cross-linking agent and a second acrylic polymer.
In the acrylic pressure-sensitive adhesive layer, the ratio of toluene-insoluble gel fraction in ethyl acetate is 30 to 80 wt%, and a weight average molecular weight of soluble sol content in ethyl acetate Ri der 700,000 or more,
The acrylic pressure-sensitive adhesive layer, Ru dry curing product der water-dispersed PSA composition containing a water-dispersed acrylic polymer and the water-soluble crosslinking agent, the removable pressure-sensitive sheet. The removable pressure-sensitive adhesive sheet according to claim 1 , wherein the water-dispersible acrylic polymer contains a monomer unit derived from a nonionic reactive emulsifier and / or an anionic reactive emulsifier. The acrylic polymer has a monomer component composition containing a (meth) acrylic acid alkyl ester and a carboxyl group-containing monomer of 0.5 to 5 parts by mass with respect to 100 parts by mass of the (meth) acrylic acid alkyl ester. The removable pressure-sensitive adhesive sheet according to claim 1 or 2 , which has a derived monomer unit configuration. The removable pressure-sensitive adhesive sheet according to claim 3 , wherein the (meth) acrylic acid alkyl ester is n-butyl acrylate and / or n-butyl methacrylate. The removable pressure-sensitive adhesive sheet according to claim 3 or 4 , wherein the carboxyl group-containing monomer is acrylic acid and / or methacrylic acid. The removable pressure-sensitive adhesive sheet according to any one of claims 1 to 5 , wherein the cross-linking agent has a weight average molecular weight of 3000 to 20000. The removable pressure-sensitive adhesive sheet according to any one of claims 1 to 6, wherein the cross-linking agent is an oxazoline group-containing compound. The re-peeling according to any one of claims 1 to 7 , wherein the content of the cross-linking agent in the acrylic pressure-sensitive adhesive layer is 0.5 to 5 parts by mass with respect to 100 parts by mass of the acrylic polymer. Mold adhesive sheet. The re-peelable adhesive sheet according to any one of claims 1 to 8 , wherein the 180 ° peeling adhesive strength (against SUS304 plate, peeling temperature 23 ° C., peeling speed 0.3 m / min) is 1 N / 25 mm or more. The first 180 ° peeling adhesive strength (against SUS304 plate, peeling temperature 23 ° C., peeling speed 3 m / min) is the second 180 ° peeling adhesive strength (against SUS304 plate, peeling temperature 23 ° C., peeling speed 0.3 m / min). Minutes), the removable adhesive sheet according to any one of claims 1 to 9.

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