JP6849533B2 - Adhesive sheet - Google Patents

Description

The present invention relates to an adhesive sheet.

In general, a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive; the same applies hereinafter) exhibits a soft solid state (viscoelastic body) in a temperature range near room temperature, and has a property of easily adhering to an adherend by pressure. Taking advantage of these properties, the pressure-sensitive adhesive is, for example, in the form of a pressure-sensitive adhesive sheet with a base material having an pressure-sensitive adhesive layer on a supporting base material, for purposes such as joining, fixing, and protecting members in mobile phones and other mobile devices. Widely used in. Patent Documents 1 and 2 are examples of technical documents relating to double-sided adhesive tapes used for fixing parts of portable electronic devices.

Japanese Unexamined Patent Publication No. 2009-215355 Japanese Unexamined Patent Publication No. 2013-14985

Since portable devices are used by carrying them, secretions such as sebum and hand stains, chemicals such as cosmetics and hair styling products, moisturizing creams and sunscreens, and oils contained in foods and the like are likely to adhere. In particular, touch panel type mobile devices, which have become popular in recent years, are provided with a display unit / input unit in which the display unit also functions as an input unit, and are operated by the user directly touching the surface of the display unit / input unit with a fingertip. Therefore, there are many opportunities for oil to adhere through the fingertips. In addition, some so-called wearable devices are used by being worn in contact with the skin, and in such a usage pattern, there are many opportunities to be exposed to oils such as sebum and chemicals applied to the skin. When such an oil component comes into contact with the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet fixing the member, inconveniences such as a decrease in adhesive strength and protrusion of the pressure-sensitive adhesive may occur.

Regarding this point, for example, Patent Document 1 is studying a double-sided pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive does not easily soften and swell even when oil permeates, and the pressure-sensitive adhesive does not squeeze out when used for fixing parts. However, Patent Document 1 does not consider suppressing the decrease in adhesive strength due to contact with oil.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a pressure-sensitive adhesive sheet in which the adhesive strength is less reduced even when it comes into contact with oil and the protrusion of the pressure-sensitive adhesive is suppressed.

According to this specification, a pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive based on an acrylic polymer is provided. The surface free energy γ of the pressure-sensitive adhesive layer is less than ^{40 mJ / m 2.} Further, the pressure-sensitive adhesive layer has an oleic acid permeation amount of 1.5 g or more and 5.0 g or less per 1 g.

Since the surface energy γ of the pressure-sensitive adhesive layer is low in the pressure-sensitive adhesive sheet having such a structure, the pressure-sensitive adhesive layer tends to exhibit good wettability with respect to the adherend. As a result, the pressure-sensitive adhesive layer and the adherend can be suitably brought into close contact with each other, and the infiltration of oil from the outer edge of the pressure-sensitive adhesive sheet to the interface (adhesive interface) between the pressure-sensitive adhesive layer and the adherend can be suppressed. In addition, the pressure-sensitive adhesive layer has the ability to retain 1.5 g or more of oleic acid per gram in the oleic acid permeation amount measurement described later. By exhibiting such oil retention, even if oil penetrates into the adhesive interface from the outer edge of the pressure-sensitive adhesive sheet, the oil is absorbed (permeated) into the layer of the pressure-sensitive adhesive layer to make the adhesive interface oil. Can be kept low. In this way, by suppressing the infiltration of oil from the outer edge of the adhesive sheet into the adhesive interface and easily absorbing the infiltrated oil from the adhesive interface into the layer (bulk) of the adhesive layer, contact of oil It is possible to effectively suppress the decrease in adhesive strength due to the above. Then, by limiting the permeation amount of oleic acid per 1 g of the pressure-sensitive adhesive layer to 5.0 g or less, it is possible to prevent the phenomenon that the pressure-sensitive adhesive layer absorbs too much oil and the pressure-sensitive adhesive squeezes out.

In the pressure-sensitive adhesive sheet according to a preferred embodiment, the gel content of the pressure-sensitive adhesive layer is 30% or more and 70% or less. By setting the gel fraction in the above range, it tends to be easy to realize a pressure-sensitive adhesive layer in which the oleic acid permeation amount is in an appropriate range.

In another preferred embodiment, the pressure-sensitive adhesive layer is formed using a pressure-sensitive adhesive composition containing the acrylic polymer and a cross-linking agent. Such an embodiment has the advantage that the oleic acid permeation amount (or gel fraction) can be easily adjusted. As the cross-linking agent, a cross-linking agent containing at least an isocyanate-based cross-linking agent can be preferably used.

The pressure-sensitive adhesive sheet disclosed herein can be preferably implemented in a manner in which the pressure-sensitive adhesive layer contains a pressure-sensitive adhesive resin. By including the tackifier resin in the pressure-sensitive adhesive layer, the adhesion of the pressure-sensitive adhesive layer to the adherend can be improved, and the infiltration of oil from the outer edge of the pressure-sensitive adhesive sheet to the bonding interface can be better suppressed. Further, by selecting 50% by weight or more of the pressure-sensitive adhesive resin from the pressure-sensitive adhesive resins other than the rosin-based pressure-sensitive adhesive resin, it is easy to realize a pressure-sensitive adhesive layer in which the oleic acid permeation amount and the surface free energy γ are in an appropriate range. It tends to be.

In one aspect of the pressure-sensitive adhesive sheet disclosed herein, the monomer component constituting the acrylic polymer has 7 or more and 10 or less carbon atoms (hereinafter, such a range of carbon atoms is referred _{to as "C 7-10".} It contains more than 50% by weight of an alkyl (meth) acrylate having an alkyl group at the ester terminal. According to the technique disclosed herein _{, even in a configuration in which an acrylic polymer having a monomer composition containing a large amount of C 7-10} alkyl (meth) acrylate is used as the base polymer of the pressure-sensitive adhesive layer, the adhesive strength due to the oil content is maintained. A pressure-sensitive adhesive sheet can be realized in which the reduction and the protrusion of the pressure-sensitive adhesive are preferably suppressed.

The pressure-sensitive adhesive sheet disclosed herein can be preferably implemented in a manner in which the monomer component constituting the acrylic polymer contains a carboxy group-containing monomer in an amount of more than 5% by weight. According to the acrylic polymer having such a monomer composition, an oil component such as oleic acid can be well retained in the pressure-sensitive adhesive layer. As a result, the oil content present at the adhesive interface can be reduced, and the decrease in adhesive strength due to the oil content can be effectively suppressed. In _{an acrylic polymer having a monomer composition containing a large amount of C 7-10} alkyl (meth) acrylate, it is particularly effective to increase the content of the carboxy group-containing monomer in the monomer component.

The pressure-sensitive adhesive sheet disclosed herein can be preferably implemented in an embodiment in which the thickness of the pressure-sensitive adhesive layer is 25 μm or less. In such a pressure-sensitive adhesive sheet having a relatively small thickness of the pressure-sensitive adhesive layer, since the amount of pressure-sensitive adhesive per area of the pressure-sensitive adhesive sheet is small, it is particularly effective to set the amount of oleic acid permeation of the pressure-sensitive adhesive layer to a predetermined value or more. is there.

The pressure-sensitive adhesive sheet according to a preferred embodiment is configured as a double-sided pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer on one surface and the other surface of the base material. Since the double-sided adhesive sheet is used by attaching one surface and the other surface of the adhesive sheet to the adherends, oil easily penetrates into the adhesive interface with these adherends. Therefore, it is particularly meaningful to apply the technique disclosed herein to suppress the decrease in adhesive strength due to the oil content.

The pressure-sensitive adhesive sheet disclosed herein can be preferably used, for example, in an application for fixing a member in a mobile device. As described above, since mobile devices have many opportunities to come into contact with oil, it is particularly meaningful to apply the techniques disclosed herein to suppress the decrease in adhesive strength due to oil and the squeeze out of the adhesive.

It is sectional drawing which shows typically one structural example of the pressure-sensitive adhesive sheet. It is sectional drawing which shows the other structural example of the pressure-sensitive adhesive sheet schematically. It is sectional drawing which shows the other structural example of the pressure-sensitive adhesive sheet schematically. It is sectional drawing which shows the other structural example of the pressure-sensitive adhesive sheet schematically. It is sectional drawing which shows the other structural example of the pressure-sensitive adhesive sheet schematically. It is sectional drawing which shows the other structural example of the pressure-sensitive adhesive sheet schematically.

Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in the present specification and necessary for the implementation of the present invention are based on the teachings regarding the implementation of the invention described in the present specification and the common general knowledge at the time of filing. Can be understood by those skilled in the art. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art. Further, in the following drawings, members / parts having the same action may be described with the same reference numerals, and duplicate description may be omitted or simplified. Further, the embodiments described in the drawings are modeled for clearly explaining the present invention, and do not necessarily accurately represent the size and scale of the adhesive sheet of the present invention actually provided as a product. ..

As described above, the term "adhesive" as used herein refers to a material that exhibits a soft solid state (viscoelastic body) in a temperature range near room temperature and has the property of easily adhering to an adherend by pressure. .. ^{The adhesive referred to here is generally a complex tensile modulus E *} (1 Hz) as defined in "CA Dahlquist," Adhesion: Fundamentals and Practice ", McLaren & Sons, (1966) P. 143". <material having a property that meets the ¹⁰ 7 dyne / cm ² (typically, a material having the properties in 25 ° C.) may be.

As used herein, the term "(meth) acryloyl" is meant to comprehensively refer to acryloyl and methacryloyl. Similarly, "(meth) acrylate" means acrylate and methacrylate, and "(meth) acrylic" means acrylic and methacrylic, respectively.

As used herein, the term "acrylic polymer" refers to a polymer containing a monomer unit derived from a monomer having at least one (meth) acryloyl group in one molecule as a monomer unit constituting the polymer. Hereinafter, a monomer having at least one (meth) acryloyl group in one molecule is also referred to as an “acrylic monomer”. Acrylic polymers in this specification are defined as polymers containing monomer units derived from acrylic monomers.

The pressure-sensitive adhesive sheet disclosed herein includes a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive based on an acrylic polymer. Here, the base polymer refers to the main component of a rubber-like polymer (a polymer that exhibits rubber elasticity in a temperature range near room temperature) contained in the pressure-sensitive adhesive layer. Further, in this specification, the “main component” refers to a component contained in an amount of more than 50% by weight unless otherwise specified. The pressure-sensitive adhesive sheet disclosed herein may be a pressure-sensitive adhesive sheet with a base material having the pressure-sensitive adhesive layer on one side or both sides of the base material (support), and the pressure-sensitive adhesive layer is held by a release liner. It may be a base material-less adhesive sheet such as a form. The concept of an adhesive sheet referred to here may include what is called an adhesive tape, an adhesive label, an adhesive film, or the like. The pressure-sensitive adhesive sheet disclosed herein may be in the form of a roll or in the form of a single leaf. Alternatively, the pressure-sensitive adhesive sheet may be further processed into various shapes.

The pressure-sensitive adhesive sheet disclosed herein may have, for example, the cross-sectional structure schematically shown in FIGS. 1 to 6. Of these, FIGS. 1 and 2 are configuration examples of a double-sided adhesive type adhesive sheet with a base material. In the pressure-sensitive adhesive sheet 1 shown in FIG. 1, pressure-sensitive adhesive layers 21 and 22 are provided on each surface of the base material 10 (both are non-peelable), and the pressure-sensitive adhesive layers are such that at least the pressure-sensitive adhesive layer side is a peeling surface. It has a structure protected by the release liners 31 and 32, respectively. In the pressure-sensitive adhesive sheet 2 shown in FIG. 2, pressure-sensitive adhesive layers 21 and 22 are provided on each surface (both non-peelable) of the base material 10, and one of the pressure-sensitive adhesive layers 21 has a peeling surface on both sides. It has a structure protected by a peeling liner 31. The pressure-sensitive adhesive sheet 2 of this type has a structure in which the pressure-sensitive adhesive layer 22 is also protected by the release liner 31 by winding the pressure-sensitive adhesive sheet and bringing the other pressure-sensitive adhesive layer 22 into contact with the back surface of the release liner 31. be able to.

3 and 4 are configuration examples of a double-sided adhesive sheet without a base material. The pressure-sensitive adhesive sheet 3 shown in FIG. 3 has a structure in which both sides 21A and 21B of the base-less pressure-sensitive adhesive layer 21 are protected by at least the peel-off liners 31 and 32 having the pressure-sensitive adhesive layer side as the peel-off surface. The pressure-sensitive adhesive sheet 4 shown in FIG. 4 has a structure in which one surface (adhesive surface) 21A of the base-less pressure-sensitive adhesive layer 21 is protected by a release liner 31 having both sides as release surfaces. When wound, the other surface (adhesive surface) 21B of the pressure-sensitive adhesive layer 21 comes into contact with the back surface of the release liner 31, so that the other surface 21B can also be protected by the release liner 31.

5 and 6 are configuration examples of a single-sided adhesive type adhesive sheet with a base material. In the pressure-sensitive adhesive sheet 5 shown in FIG. 5, a pressure-sensitive adhesive layer 21 is provided on one surface 10A (non-peelable) of the base material 10, and the surface (adhesive surface) 21A of the pressure-sensitive adhesive layer 21 is peeled off at least on the pressure-sensitive adhesive layer side. It has a structure protected by a release liner 31 which is a surface. The pressure-sensitive adhesive sheet 6 shown in FIG. 6 has a structure in which the pressure-sensitive adhesive layer 21 is provided on one surface 10A (non-peelable) of the base material 10. The other surface 10B of the base material 10 is a peeling surface, and when the pressure-sensitive adhesive sheet 6 is wound, the pressure-sensitive adhesive layer 21 comes into contact with the other side surface 10B, and the surface (adhesive surface) 21B of the pressure-sensitive adhesive layer becomes the base material. It is protected by the other surface 10B.

<Adhesive layer>
In the pressure-sensitive adhesive sheet disclosed herein, the surface free energy γ of the pressure-sensitive adhesive layer ^{is less than 40 mJ / m 2} , and the amount of oleic acid permeated by the pressure-sensitive adhesive layer is 1.5 g / g or more and 5.0 g / g or less. Characterized by being.

(Surface free energy γ)
The surface free energy γ of the pressure-sensitive adhesive layer is a value represented by ^{the following equation: γ = γ d} + γ ^p + γ ^{h ;. Here, γ d} , γ ^p, and γ ^h in the above formula represent a dispersion component, a polar component, and a hydrogen bond component of surface free energy, respectively. For the surface free energy γ of the pressure-sensitive adhesive layer, water, diiodomethane and 1-bromonaphthalene are used as probe solutions, and the contact angle of each probe solution is determined by the Kitazaki-Hata formula (Journal of Japan Adhesive Association, Vol.8, No.3, 1972). , Pp.131-141). The contact angle can be measured using a commercially available contact angle meter. As the contact angle meter, the product name "CA-X" manufactured by Kyowa Interface Science Co., Ltd. can be used. The sessile drop method is used for the measurement, and the contact angle is measured from the shape of the droplet after 1500 ms of dripping. The same method is adopted in the examples described later.

When the surface free energy γ of the pressure-sensitive adhesive layer is low, the wettability of the pressure-sensitive adhesive layer with respect to the adherend tends to be improved, and the adhesion between the pressure-sensitive adhesive layer and the adherend (adhesive interface) tends to be high. .. By increasing the adhesion of the adhesive interface in this way, it is possible to suppress the infiltration of oil from the outer edge of the adhesive sheet into the adhesive interface.

In relation to the surface free energy of the adherend, the lower the surface free energy of the pressure-sensitive adhesive layer, the higher the wettability with respect to the adherend tends to be. Therefore, by lowering the surface free energy γ of the pressure-sensitive adhesive layer, the adhesion to a predetermined adherend can be further improved, and it is possible to adhere well to an adherend made of a wider variety of materials. It becomes. From this point of view, the surface free energy γ of the pressure-sensitive adhesive layer is preferably about 35 mJ / m ² or less, more preferably about 30 mJ / m ² or less. In one embodiment, the surface free energy γ of the pressure-sensitive adhesive layer may also be 27mJ / ^{m 2} or less, may also be 25 mJ / ^{m 2} or less, or even less 20 mJ / ^{m 2.} The lower limit of the surface free energy γ of the pressure-sensitive adhesive layer is not particularly limited, it is usually approximately 7 mJ / m ² or more, preferably about 10 mJ / m ² or more. The surface free energy γ of the pressure-sensitive adhesive layer is, for example, the composition of the monomer components constituting the acrylic polymer (the type and amount of the main monomer described later and the sub-monomer used as necessary, etc.), the type of the tackifier resin, and the pressure-sensitive adhesive resin. It can be adjusted according to the amount used.

(Oleic acid penetration)
In the technique disclosed herein, the amount of oleic acid permeated in the pressure-sensitive adhesive layer is measured by the following method.

[Oleic acid permeability evaluation]
The pressure-sensitive adhesive layer to be measured is prepared in the form of a single-sided pressure-sensitive adhesive sheet having the above-mentioned pressure-sensitive adhesive layer having a thickness of 20 μm on a non-peeling surface of a polyethylene terephthalate (PET) film having a thickness of about 10 μm to 100 μm (for example, 50 μm). For example, the single-sided pressure-sensitive adhesive sheet can be prepared by forming the pressure-sensitive adhesive layer on an appropriate peeling surface in a substrate-less form and bonding the pressure-sensitive adhesive layer to the non-peeling surface of the PET film. This single-sided adhesive sheet is cut into a square shape having a length of 25 mm and a width of 25 mm to prepare a test piece.
On the surface of a stainless steel plate (SUS304BA plate), two marked lines intersecting at an angle of 90 degrees at the center of the stainless steel plate are drawn with an oil-based pen. In an environment of 23 ° C. and 50% RH, the adhesive surface of the test piece is attached to the stainless steel plate on which the marked line is drawn to prepare a measurement sample. At this time, the test piece is attached so that the vertical and horizontal center lines of the test piece coincide with the above-mentioned marked line.
The measurement sample is kept in an environment of 23 ° C. and 50% RH for 12 hours. Next, after measuring the weight of the measurement sample (weight before immersion), the measurement sample is immersed in an oleic acid bath and kept in an environment of 40 ° C. and 90% RH for 2 weeks. Then, the measurement sample is pulled up from the oleic acid bath, the oleic acid adhering to the surroundings is lightly wiped off, and the weight of the measurement sample (weight after immersion) is measured. From the obtained measured values, the following formula:
Oleic acid permeation amount = (weight after immersion-weight before immersion) / weight of adhesive before permeation;
The amount of oleic acid permeation (g / g) per 1 g of the pressure-sensitive adhesive layer is calculated accordingly. The same evaluation method is adopted in the examples described later.

The pressure-sensitive adhesive layer having an oleic acid penetration amount of 1.5 g / g or more exhibits better oil retention than the pressure-sensitive adhesive layer having a smaller oleic acid penetration amount. As a result, even if oil penetrates into the adhesive interface from the outer edge of the pressure-sensitive adhesive sheet, the oil content can be absorbed into the layer (bulk) of the pressure-sensitive adhesive layer to keep the adhesive interface in a state of low oil content. As a result, it is possible to effectively suppress a decrease in the adhesive force due to the oil content present at the adhesive interface. Further, by absorbing the oil that has penetrated into the adhesive interface from the outer edge of the adhesive sheet into the bulk of the adhesive layer, it is possible to suppress the phenomenon that the oil component progresses to the inner part of the adhesive sheet sticking range along the adhesive interface. .. That is, the permeation distance of oil from the outer edge of the adhesive sheet can be suppressed. As a result, the influence of the oil content can be suppressed from the outer edge to the inner portion of the pressure-sensitive adhesive sheet, and the adhesive strength of the pressure-sensitive adhesive sheet as a whole can be better maintained. Further, the bulk of the pressure-sensitive adhesive layer appropriately absorbs the oil component, so that the pressure-sensitive adhesive layer is softened, and as a result, the peeling strength can be obtained by the deformation energy of the pressure-sensitive adhesive layer. This can also contribute advantageously to suppressing the decrease in adhesive strength due to the oil content. In this way, by suppressing the infiltration of oil from the outer edge of the adhesive sheet into the adhesive interface and easily absorbing the infiltrated oil from the adhesive interface into the bulk of the adhesive layer, the adhesive force due to contact with the oil is increased. The decrease can be effectively suppressed.

From the viewpoint of better exerting the above-mentioned effects, the permeation amount of oleic acid in the pressure-sensitive adhesive layer is preferably about 1.6 g / g or more, more preferably about 1.8 g / g or more. The technique disclosed herein is also preferably carried out in an embodiment in which the amount of oleic acid permeated in the pressure-sensitive adhesive layer is approximately 2.0 g / g or more (further, approximately 2.5 g / g or more, for example, approximately 3.0 g / g or more). Can be done. The upper limit of the oleic acid permeation amount of the pressure-sensitive adhesive layer is appropriately set to about 5.0 g / g or less from the viewpoint of preventing the phenomenon that the pressure-sensitive adhesive layer absorbs too much oil and the pressure-sensitive adhesive squeezes out. It is preferably 5.5 g / g or less (for example, about 4.0 g / g or less). In the pressure-sensitive adhesive sheet according to a preferred embodiment, the amount of oleic acid permeated by the pressure-sensitive adhesive layer is, for example, about 1.6 g / g or more and about 4.5 g / g or less, more preferably about 1.8 g / g or more and about 4.5 g. It can be less than / g. The amount of oleic acid permeated in the pressure-sensitive adhesive layer is, for example, the composition of the monomer components constituting the acrylic polymer (the type and amount of the main monomer described later and the submonomer used as necessary, etc.), the molecular weight of the acrylic polymer, and the like. It can be adjusted according to the type and amount of the cross-linking agent used, the type and amount of the tackifier resin used, and the like.

By the above-mentioned oleic acid permeability evaluation, it is possible to evaluate the squeeze-out prevention property of the pressure-sensitive adhesive. Specifically, in the oleic acid permeability evaluation, immediately after the measurement sample is pulled up from the oleic acid bath, the protrusion distance (protrusion width) of the adhesive from the outer edge of the PET film is visually measured. The same evaluation method is adopted in the examples described later.
In a preferred embodiment, the protrusion width of the pressure-sensitive adhesive may be less than about 1.0 mm (more preferably about 0.5 mm or less, still more preferably about 0.3 mm or less). The pressure-sensitive adhesive sheet provided with the pressure-sensitive adhesive layer having such a protrusion-preventing property is suitable for applications where bonding in a limited space is required, for example, for fixing members in a portable device. The smaller the protrusion width of the adhesive, the better, ideally about 0 mm.

In addition, the permeation distance of oleic acid into the pressure-sensitive adhesive sheet can be measured by the above-mentioned evaluation of oleic acid permeability. Specifically, after pulling up the measurement sample from the oleic acid bath and lightly wiping off the oleic acid adhering to the surroundings, the length from the outer edge of the PET film toward the inside where the marked line on the stainless steel disappears. Measure and use the length as the permeation distance of oleic acid. The same measurement method is adopted in the examples described later.
In a preferred embodiment, the permeation distance of the oleic acid is preferably about 0.5 mm or more, more preferably about 0.8 mm or more, and even more preferably about 1.0 mm or more. The permeation distance of the oleic acid is preferably about 7.0 mm or less, more preferably about 5.0 mm or less, still more preferably about 4.0 mm or less (for example, about 1.0 mm or more and about 4.0 mm or less). ). According to the pressure-sensitive adhesive layer in which the permeation distance of oleic acid is in the above range, the preferable permeation amount of oleic acid disclosed herein tends to be preferably realized.

(Acrylic polymer)
The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer contains an acrylic polymer as a base polymer. The acrylic polymer is preferably a monomer raw material polymer containing an alkyl (meth) acrylate as a main monomer and further containing a submonomer having copolymerizability with the main monomer. Here, the main monomer means a component contained in the monomer raw material in an amount of more than 50% by weight.

As the alkyl (meth) acrylate, for example, a compound represented by the following formula (1) can be preferably used.
CH ₂ = C (R ¹ ) COOR ² (1)
^{Here, R 1} in the above formula (1) is a hydrogen atom or a methyl group. Further, R ² is a chain alkyl group having 1 to 20 carbon atoms (hereinafter, such a range of carbon atoms may be referred _{to as “C 1-20”).} From the viewpoint of the storage elastic modulus of the pressure-sensitive adhesive, ^{alkyl (meth) acrylate in which R 2} is a C _1-14 chain alkyl group is preferable, and alkyl (meth) acrylate in which R ² is a C _1-10 chain alkyl group is preferable. ) Acrylate is more preferable, and ^{alkyl (meth) acrylate in which R 2} is a butyl group or a 2-ethylhexyl group is particularly preferable.

Examples of the alkyl (meth) acrylate in which R ² is a C _1-20 chain alkyl group include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, and n-butyl. (Meta) acrylate, isobutyl (meth) acrylate, s-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate , Octyl (meth) acrylate, Isooctyl (meth) acrylate, Nonyl (meth) acrylate, Isononyl (meth) acrylate, Decyl (meth) acrylate, Isodecyl (meth) acrylate, Undecyl (meth) acrylate, Dodecyl (meth) acrylate, Tridecyl Examples thereof include (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, nonadecil (meth) acrylate, and ecocil (meth) acrylate. .. These alkyl (meth) acrylates may be used alone or in combination of two or more. Particularly preferred alkyl (meth) acrylates include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA).

In the technique disclosed herein, the monomer component constituting the acrylic polymer contains at least one of BA and 2EHA, and the total amount of BA and 2EHA among the alkyl (meth) acrylates contained in the monomer component is 75 weight by weight. It can be preferably carried out in a mode in which% or more (usually 85% by weight or more, for example, 90% by weight or more, further 95% by weight or more) is occupied. The technique disclosed herein can be carried out, for example, in a mode in which the alkyl (meth) acrylate contained in the above-mentioned monomer component is BA alone, a mode in which 2EHA is alone, a mode in which BA and 2EHA are contained, and the like.

When the monomer component contains BA and 2EHA, the weight ratio of BA to 2EHA (BA / 2EHA) is not particularly limited, and may be, for example, 1/99 or more and 99/1 or less. In a preferred embodiment, BA / 2EHA can be 40/60 or less (eg 1/99 or more and 40/60 or less), 20/80 or less, and 10/90 or less (eg 1/99). It may be 10/90 or less).

The technique disclosed herein can be preferably carried out in a manner in which the monomer component constituting the acrylic polymer _{contains more than 50% by weight of C 7-10 alkyl (meth) acrylate.} As described above, _{the acrylic polymer containing C 7-10} alkyl (meth) acrylate as the main monomer generally has a high affinity for oil. Utilizing this high affinity for oil, the oil that has penetrated into the adhesive interface from the outer edge of the adhesive sheet is appropriately absorbed into the layer of the adhesive layer, which effectively reduces the adhesive strength due to contact with the oil. Can be suppressed. _{The ratio of C 7-10} alkyl (meth) acrylate in the monomer component may be 60% by weight or more, 70% by weight or more (for example, 80% by weight or more, and further 85% by weight or more). .. _{The upper limit of the ratio of C 7-10} alkyl (meth) acrylate to the monomer component is not particularly limited, and can be, for example, less than 98% by weight. Usually, from the viewpoint of facilitating compatibility with other properties, _{it is appropriate that the ratio of C 7-10} alkyl (meth) acrylate in the monomer component is 97% by weight or less, and 95% by weight or less (usually). Is less than 95% by weight, for example, 93% by weight or less). The C _7-10 alkyl (meth) acrylate may be used alone or in combination of two or more. Preferable examples of the C _{7-10 alkyl (meth) acrylate include C 7-10} alkyl acrylates such as 2EHA, isooctyl acrylate and isononyl acrylate. Of these, 2EHA is preferable.

The technique disclosed herein can also be preferably carried out in an embodiment in which the monomer component constituting the acrylic polymer _{contains more than 50% by weight of C 1-6 alkyl (meth) acrylate.} When _{an acrylic polymer containing C 1-6} alkyl (meth) acrylate as the main monomer is used as the base polymer as described above, for example, the type and amount of the submonomer, the type and amount of the cross-linking agent, and the tackifier resin are used. By appropriately setting conditions such as the type and amount of the oleic acid used, it is possible to obtain a pressure-sensitive adhesive layer showing a suitable amount of oleic acid permeation disclosed herein. _{The ratio of C 1-6} alkyl (meth) acrylate in the monomer component may be 60% by weight or more, or 70% by weight or more (for example, 85% by weight or more, and further 90% by weight or more). .. _{The upper limit of the ratio of C 1-6} alkyl (meth) acrylate to the monomer component is not particularly limited, and can be, for example, 99.5% by weight or less. Usually, from the viewpoint of facilitating compatibility with other properties, _{it is appropriate that the ratio of the above C 1-6} alkyl (meth) acrylate to the monomer component is 99% by weight or less, and 98% by weight or less ( For example, it is preferably 97% by weight or less). The C _1-6 alkyl (meth) acrylate may be used alone or in combination of two or more. BA is mentioned as a preferable example of C _{1-6 alkyl (meth) acrylate.}

A sub-monomer having copolymerizability with the main monomer, alkyl (meth) acrylate, can be useful for introducing cross-linking points into the acrylic polymer and enhancing the cohesive force of the acrylic polymer. As the submonomer, for example, the following functional group-containing monomers can be used alone or in combination of two or more.
Carboxy group-containing monomers: ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth) acrylate, crotonic acid, isocrotonic acid; maleic anhydride, itaconic acid, citraconic acid, etc. Ethylene unsaturated dicarboxylic acid and its anhydride (maleic anhydride, itaconic anhydride, etc.).
Hydroxyl-containing monomers: Hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate; Unsaturated alcohols such as vinyl alcohol and allyl alcohol; polypropylene glycol mono (meth) acrylate.
Amide group-containing monomers: For example, (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-butyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methylolpropane (meth) acrylamide, N-methoxymethyl (Meta) acrylamide, N-butoxymethyl (meth) acrylamide.
Amino group-containing monomer: For example, aminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate.
Monomers having an epoxy group: for example, glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, allyl glycidyl ether.
Cyanide-containing monomers: for example, acrylonitrile, methacrylonitrile.
Keto group-containing monomers: for example, diacetone (meth) acrylamide, diacetone (meth) acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetoacetate, vinyl acetoacetate.
Monomers having a nitrogen atom-containing ring: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazin, N-vinyl. Pyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, N- (meth) acryloylmorpholine.
Alkoxysilyl group-containing monomers: for example, 3- (meth) acryloxypropyltrimethoxysilane, 3- (meth) acryloxypropyltriethoxysilane, 3- (meth) acryloxypropylmethyldimethoxysilane, 3- (meth) acryloxy. Propylmethyldiethoxysilane.

The functional group-containing monomer may be used alone or in combination of two or more. Among the functional group-containing monomers, the carboxy group-containing monomer and the hydroxyl group-containing monomer can be preferably used because the introduction of the cross-linking point and the improvement of the cohesive force as described above can be suitably realized. Preferable examples of the carboxy group-containing monomer include acrylic acid and methacrylic acid. These can be used alone or in combination of two. Examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth) acrylates having a hydroxyl group at the end of a linear alkyl group having about 2 to 4 carbon atoms, such as 2-hydroxyethyl acrylate and 4-hydroxybutyl (meth) acrylate. Can be mentioned. The hydroxyl group-containing monomer may be used alone or in combination of two or more. A carboxy group-containing monomer and a hydroxyl group-containing monomer may be used in combination.

When the monomer component constituting the acrylic polymer contains a functional group-containing monomer, the ratio of the functional group-containing monomer to the monomer component is not particularly limited. Usually, the proportion of the functional group-containing monomer is 0.1% by weight or more and 40% by weight or less (for example, 0.5% by weight or more and 30% by weight) from the viewpoint of obtaining appropriate cohesiveness at the preferable oleic acid permeation amount disclosed herein. % Or less, usually 1% by weight or more and 20% by weight or less).

When the monomer component constituting the acrylic polymer contains a carboxy group-containing monomer, the ratio of the carboxy group-containing monomer to the monomer component is usually 0.5% by weight or more (preferably 1% by weight) from the viewpoint of cohesiveness and the like. % Or more, for example, 2% by weight or more, and 20% by weight or less (preferably 18% by weight or less, for example, 15% by weight or less).

The technique disclosed herein can be preferably carried out in a manner in which the monomer component contains a carboxy group-containing monomer in an amount of about 3% by weight or more (preferably about 5% by weight or more). According to the acrylic polymer having such a monomer composition, the absorbed oleic acid can be well retained in the layer (bulk) of the pressure-sensitive adhesive layer by the interaction between the carboxy group of the polymer and oleic acid. As a result, the adhesive interface can be maintained in a state of low oleic acid, and the decrease in adhesive strength due to the penetration of oleic acid can be effectively suppressed. From this point of view, the content of the carboxy group-containing monomer in the monomer component is preferably more than about 5% by weight, may be about 7% by weight or more, may be about 8% by weight or more, and further may be about 9% by weight. It may be% or more. The upper limit of the content of the carboxy group-containing monomer is not particularly limited, but it is usually appropriate to be about 18% by weight or less, and may be about 15% by weight or less (for example, about 12% by weight or less). In _{an acrylic polymer having a monomer composition containing a large amount of C 7-10} alkyl (meth) acrylate (for example, an acrylic polymer containing C _7-10 alkyl (meth) acrylate as a main monomer), a carboxy group-containing monomer in the monomer component (for example, It is particularly effective to increase the content of AA).

When the monomer component constituting the acrylic polymer contains a hydroxyl group-containing monomer, the content thereof is usually about 0.001% by weight or more and about 10% by weight or less (for example, about 0.01% by weight or more and about 5). It is appropriate that the weight is% or less, preferably about 0.02% by weight or more and about 2% by weight or less).

As the monomer component constituting the acrylic polymer, a copolymerization component other than the above-mentioned submonomer can be used for the purpose of enhancing the cohesive force of the acrylic polymer. Examples of such copolymerization components include vinyl ester-based monomers such as vinyl acetate, vinyl propionate, and vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrene (α-methylstyrene, etc.), and vinyltoluene; cyclohexyl (meth). ) Cycloalkyl (meth) acrylates such as acrylates, cyclopentyl (meth) acrylates, isobornyl (meth) acrylates; aryl (meth) acrylates (eg, phenyl (meth) acrylates), aryloxyalkyl (meth) acrylates (eg, phenoxyethyl (meth)). ) Acrylate), aromatic ring-containing (meth) acrylate such as arylalkyl (meth) acrylate (for example, benzyl (meth) acrylate); olefinic monomer such as ethylene, propylene, isoprene, butadiene, isobutylene; vinyl chloride, vinylidene chloride Chlorine-containing monomers such as 2- (meth) acryloyloxyethyl isocyanate and the like; isocyanate group-containing monomers such as 2- (meth) acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate; System monomer: 2 or more (for example, 3 or more) polymerizable functional groups (for example, (meth) acryloyl group) in one molecule such as 1,6-hexanediol di (meth) acrylate and trimethylpropantri (meth) acrylate. Polyfunctional monomer having the above; and the like.
The amount of the other copolymerization component may be appropriately selected depending on the purpose and application and is not particularly limited, but is usually preferably 10% by weight or less of the monomer component. For example, when a vinyl ester-based monomer (for example, vinyl acetate) is used as the other copolymerization component, the content thereof is, for example, about 0.1% by weight or more (usually about 0.5% by weight or more) of the monomer component. It is appropriate that the content is about 20% by weight or less (usually about 10% by weight or less).

The composition of the monomer components constituting the acrylic polymer is designed so that the glass transition temperature (Tg) of the acrylic polymer is approximately −15 ° C. or lower (for example, approximately −70 ° C. or higher and -15 ° C. or lower). Is appropriate. Here, the Tg of the acrylic polymer means the Tg obtained by the Fox formula based on the composition of the above-mentioned monomer component. As shown below, the Fox formula is a relational expression between the Tg of the copolymer and the glass transition temperature Tgi of the homopolymer in which each of the monomers constituting the copolymer is homopolymerized.
1 / Tg = Σ (Wi / Tgi)
In the Fox formula, Tg is the glass transition temperature (unit: K) of the copolymer, Wi is the weight fraction of the monomer i in the copolymer (copolymerization ratio based on the weight), and Tgi is the monomer i. Represents the glass transition temperature (unit: K) of the homopolymer.

As the glass transition temperature of the homopolymer used for calculating Tg, the value described in the publicly known material shall be used. For example, for the monomers listed below, the following values are used as the glass transition temperature of the homopolymer of the monomer.
2-Ethylhexyl acrylate-70 ° C
n-Butyl acrylate -55 ° C
Ethyl acrylate-22 ° C
Methyl acrylate 8 ℃
Methyl methacrylate 105 ° C
2-Hydroxyethyl acrylate -15 ° C
4-Hydroxybutyl acrylate-40 ° C
Vinyl acetate 32 ° C
Styrene 100 ° C
Acrylic acid 106 ℃
Methacrylic acid 228 ° C

For the glass transition temperature of homopolymers of monomers other than those exemplified above, the numerical values described in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. The highest value is adopted for the monomers for which a plurality of types of values are described in this document.

For monomers for which the glass transition temperature of the homopolymer is not described in the above document, the value obtained by the following measurement method shall be used.
Specifically, in a reactor equipped with a thermometer, a stirrer, a nitrogen introduction tube and a reflux condenser, 100 parts by weight of a monomer, 0.2 parts by weight of 2,2'-azobisisobutyronitrile and acetic acid as a polymerization solvent. Add 200 parts by weight of ethyl and stir for 1 hour while flowing nitrogen gas. After removing oxygen in the polymerization system in this way, the temperature is raised to 63 ° C. and the reaction is carried out for 10 hours. Then, the mixture is cooled to room temperature to obtain a homopolymer solution having a solid content concentration of 33% by weight. Next, this homopolymer solution is cast-coated on a release liner and dried to prepare a test sample (sheet-shaped homopolymer) having a thickness of about 2 mm. This test sample is punched into a disk shape with a diameter of 7.9 mm, sandwiched between parallel plates, and shear strain with a frequency of 1 Hz using a viscoelasticity tester (manufactured by TA Instruments Japan, model name "ARES"). The viscoelasticity is measured in a shear mode at a temperature range of −70 ° C. to 150 ° C. and a temperature rising rate of 5 ° C./min, and the temperature corresponding to the peak top temperature of tan δ is defined as Tg of the homopolymer.

Although not particularly limited, the Tg of the acrylic polymer is preferably about −25 ° C. or lower, preferably about −35 ° C. or lower, from the viewpoint of adhesion to the adherend or the base film. More preferably, it is about −40 ° C. or lower. Further, from the viewpoint of the cohesive force of the pressure-sensitive adhesive layer, the Tg of the acrylic polymer is usually about −75 ° C. or higher, preferably about −70 ° C. or higher. The technique disclosed herein can be preferably carried out in an embodiment in which the Tg of the acrylic polymer is approximately −65 ° C. or higher and approximately −40 ° C. or lower (for example, approximately −65 ° C. or higher and approximately −45 ° C. or lower). In a preferred embodiment, the Tg of the acrylic polymer can be approximately −65 ° C. or higher and approximately −55 ° C. or lower. The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (that is, the type and amount ratio of the monomers used in the synthesis of the polymer).

The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as synthetic methods for the acrylic polymer, such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, and a photopolymerization method. Can be adopted as appropriate. For example, a solution polymerization method can be preferably adopted. As a monomer supply method for solution polymerization, a batch charging method, a continuous supply (dropping) method, a divided feeding (dropping) method, or the like in which all the monomer raw materials are supplied at once can be appropriately adopted. The polymerization temperature can be appropriately selected depending on the type of the monomer and solvent used, the type of the polymerization initiator, and the like, and can be, for example, about 20 ° C. to 170 ° C. (usually about 40 ° C. to 140 ° C.). .. In a preferred embodiment, the polymerization temperature can be set to about 75 ° C. or lower (more preferably about 65 ° C. or lower, for example, about 45 ° C. to 65 ° C.).

The solvent (polymerization solvent) used for solution polymerization can be appropriately selected from conventionally known organic solvents. For example, aromatic compounds such as toluene and xylene (for example, aromatic hydrocarbons); acetate esters such as ethyl acetate and butyl acetate; aliphatic or alicyclic hydrocarbons such as hexane, cyclohexane and methylcyclohexane; 1 , 2-Alkane halides such as dichloroethane; Lower alcohols such as isopropyl alcohol (for example, monovalent alcohols having 1 to 4 carbon atoms); Ethers such as tert-butyl methyl ether; Ketones such as methyl ethyl ketone and acetone Any one solvent selected from the above; or a mixed solvent of two or more kinds can be used.

The initiator used for the polymerization can be appropriately selected from conventionally known polymerization initiators according to the type of polymerization method. For example, one or more azo polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other preferred examples of the polymerization initiator include peroxide-based initiators such as benzoyl peroxide (BPO) and hydrogen peroxide. Other polymerization initiators include persulfates such as potassium persulfate; substituted ethane initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; redox-based initiators in combination with peroxides and reducing agents; etc. Can be mentioned. Such a polymerization initiator can be used alone or in combination of two or more. The amount of the polymerization initiator used may be a normal amount, for example, about 0.005 to 1 part by weight (usually about 0.01 to 1 part by weight) with respect to 100 parts by weight of the monomer component. You can choose from a range.

According to the above solution polymerization, a polymerization reaction solution in which the acrylic polymer is dissolved in an organic solvent can be obtained. The pressure-sensitive adhesive layer in the technique disclosed herein may be formed from the above-mentioned polymerization reaction solution or a pressure-sensitive adhesive composition containing an acrylic polymer solution obtained by subjecting the reaction solution to an appropriate post-treatment. As the acrylic polymer solution, a solution prepared by preparing the polymerization reaction solution to an appropriate viscosity (concentration) can be used. Alternatively, an acrylic polymer solution prepared by synthesizing an acrylic polymer by a polymerization method other than solution polymerization (for example, emulsion polymerization, photopolymerization, bulk polymerization, etc.) and dissolving the acrylic polymer in an organic solvent may be used. Good.

The weight average molecular weight of the acrylic polymer (Mw) is not particularly limited, can be, for example, about 10 × 10 ⁴ or more 500 × 10 ⁴ or less. Here, Mw refers to a standard polystyrene-equivalent value obtained by GPC (gel permeation chromatography). As the GPC apparatus, for example, a model name "HLC-8320GPC" (column: TSKgelGMH-H (S), manufactured by Tosoh Corporation) can be used. From the viewpoint of adhesive performance and oil resistance, the Mw of the acrylic polymer is about 30 × 10 ⁴ or more and 200 × 10 ⁴ or less (more preferably about 45 × 10 ⁴ or more and 150 × 10 ⁴ or less, for example, about 65 × 10 ⁴ or more. It is preferably in the range of 150 × 10 ^{4 or less).} In a preferred embodiment, Mw of the acrylic polymer may be about 75 × 10 ⁴ or more about 140 × 10 ⁴ or less (e.g., about 90 × 10 ⁴ or more about 140 × 10 ⁴ or less).

(Crosslinking agent)
The pressure-sensitive adhesive composition (preferably a solvent-type pressure-sensitive adhesive composition) used for forming the pressure-sensitive adhesive layer preferably contains a cross-linking agent as an optional component. The pressure-sensitive adhesive layer in the technique disclosed herein contains the above-mentioned cross-linking agent in a form after the cross-linking reaction, a form before the cross-linking reaction, a form partially cross-linked, an intermediate or complex form thereof, and the like. obtain. The cross-linking agent is usually contained in the pressure-sensitive adhesive layer exclusively in the form after the cross-linking reaction.

The type of the cross-linking agent is not particularly limited, and a conventionally known cross-linking agent can be appropriately selected and used. Examples of such cross-linking agents include isocyanate-based cross-linking agents, epoxy-based cross-linking agents, oxazoline-based cross-linking agents, aziridine-based cross-linking agents, melamine-based cross-linking agents, carbodiimide-based cross-linking agents, hydrazine-based cross-linking agents, and amine-based cross-linking agents. Examples thereof include a peroxide-based cross-linking agent, a metal chelate-based cross-linking agent, a metal alkoxide-based cross-linking agent, and a metal salt-based cross-linking agent. The cross-linking agent may be used alone or in combination of two or more. The type and amount of cross-linking agent used can be set, for example, to form a pressure-sensitive adhesive layer exhibiting the preferred oleic acid penetrations disclosed herein. Examples of cross-linking agents that can be preferably used in the techniques disclosed herein include isocyanate-based cross-linking agents and epoxy-based cross-linking agents.

As the isocyanate-based cross-linking agent, polyfunctional isocyanate (a compound having an average of two or more isocyanate groups per molecule, including one having an isocyanurate structure) can be preferably used. The isocyanate-based cross-linking agent may be used alone or in combination of two or more.

Examples of polyfunctional isocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates and the like.
Specific examples of aliphatic polyisocyanes include 1,2-ethylene diisocyanate; 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, 1,4-tetramethylene diisocyanate and other tetramethylene diisocyanates; 1,2. -Hexamethylene diisocyanis such as 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,5-hexamethylene diisocyanate; Examples thereof include 2-methyl-1,5-pentanediisocyanate, 3-methyl-1,5-pentanediisocyanate and lysine diisocyanate.

Specific examples of alicyclic polyisocyanates include isophorone diisocyanates; 1,2-cyclohexyldiisocyanates, 1,3-cyclohexyldiisocyanates, cyclohexyldiisocyanates such as 1,4-cyclohexyldiisocyanates; 1,2-cyclopentyldiisocyanates, 1,3. Cyclopentyl diisocyanates such as −cyclopentyldiisocyanate; hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, and the like.

Specific examples of aromatic polyisocyanates include 2,4-tolylene diisocyanis, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, and 2,2'-diphenylmethane diisocyanate. , 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate , 4,4'-diphenylpropane diisocyanate, m-phenylenediisocyanide, p-phenylenediisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate , Xylylene-1,4-diisocyanate, xylylene-1,3-diisocyanate and the like.

As a preferable polyfunctional isocyanate, a polyfunctional isocyanate having an average of 3 or more isocyanate groups per molecule is exemplified. Such trifunctional or higher functional isocyanates are addition reactions of bifunctional or trifunctional or higher functional isocyanate multimers (eg, dimers or trimers), derivatives (eg, polyhydric alcohols and two or more molecules of polyfunctional isocyanates). Product), polymer, etc. For example, diphenylmethane diisocyanate dimer or trimeric, hexamethylene diisocyanate isocyanurate (isocyanurate structure trimeric adduct), reaction product of trimethylolpropane and tolylene diisocyanate, trimethylrolpropane and hexa. Examples thereof include reaction products with methylene diisocyanate, polyfunctional isocyanates such as polymethylene polyphenyl isocyanate, polyether polyisocyanate, and polyester polyisocyanate. Commercially available products of such polyfunctional isocyanates include the trade name "Duranate TPA-100" manufactured by Asahi Kasei Chemicals, the trade name "Coronate L", the same "Coronate HL", the same "Coronate HK", and the same "Coronate" manufactured by Tosoh Corporation. "HX", the same "Coronate 2096" and the like can be mentioned.

In the embodiment in which the isocyanate-based cross-linking agent is used, the amount used thereof is not particularly limited. The amount of the isocyanate-based cross-linking agent used can be, for example, approximately 0.5 parts by weight or more and approximately 10 parts by weight or less with respect to 100 parts by weight of the acrylic polymer. From the viewpoint of obtaining a preferable amount of oleic acid permeation disclosed herein, it is usually appropriate that the amount of the isocyanate-based cross-linking agent used with respect to 100 parts by weight of the acrylic polymer is about 1 part by weight or more, and is about 1.5 parts by weight. It is preferably parts by weight or more. Further, the amount of the isocyanate-based cross-linking agent used with respect to 100 parts by weight of the acrylic polymer is usually appropriately set to about 8 parts by weight or less, and may be set to about 5 parts by weight or less (for example, less than about 4 parts by weight). preferable.

As the epoxy-based cross-linking agent, a compound having two or more epoxy groups in one molecule can be used without particular limitation. An epoxy-based cross-linking agent having 3 to 5 epoxy groups in one molecule is preferable. The epoxy-based cross-linking agent may be used alone or in combination of two or more.

Although not particularly limited, specific examples of the epoxy-based cross-linking agent include, for example, N, N, N', N'-tetraglycidyl-m-xylene diamine, 1,3-bis (N, N-diglycidyl aminomethyl). ) Cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether and the like can be mentioned. Commercially available epoxy-based cross-linking agents include Mitsubishi Gas Chemical Company's product name "TETRAD-C" and product name "TETRAD-X", DIC's product name "Epicron CR-5L", and Nagase ChemteX's product. The product name "Denacol EX-512", the product name "TEPIC-G" manufactured by Nissan Chemical Industries, Ltd., and the like can be mentioned.

In the embodiment in which the epoxy-based cross-linking agent is used, the amount used thereof is not particularly limited. The amount of the epoxy-based cross-linking agent used may be, for example, more than 0 parts by weight and about 1 part by weight or less (preferably about 0.001 to 0.5 parts by weight) with respect to 100 parts by weight of the acrylic polymer. it can. From the viewpoint of preferably exerting the effect of improving the cohesive force, it is usually appropriate that the amount of the epoxy-based cross-linking agent used is about 0.002 parts by weight or more with respect to 100 parts by weight of the acrylic polymer, and is about 0. It is preferably .005 parts by weight or more, and more preferably about 0.008 parts by weight or more. Further, from the viewpoint of avoiding a shortage of the amount of oleic acid permeated due to excessive cross-linking, it is usually appropriate that the amount of the epoxy-based cross-linking agent used is about 0.2 parts by weight or less with respect to 100 parts by weight of the acrylic polymer. It is preferably about 0.1 parts by weight or less, and more preferably less than about 0.05 parts by weight.

The technique disclosed herein can be preferably carried out in an embodiment in which at least an isocyanate-based cross-linking agent is used as the cross-linking agent. Examples of such an embodiment include an embodiment in which the isocyanate-based cross-linking agent is used alone, and an embodiment in which the isocyanate-based cross-linking agent and another cross-linking agent are used in combination. In a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on at least one surface of the base film described later, it is particularly meaningful to use an isocyanate-based cross-linking agent from the viewpoint of improving anchoring property with respect to the base film.

An epoxy-based cross-linking agent is mentioned as a preferable example of a cross-linking agent used in combination with an isocyanate-based cross-linking agent. By using the epoxy-based cross-linking agent and the isocyanate-based cross-linking agent in combination, the preferable amount of oleic acid permeation disclosed herein can be preferably realized. Further, the cohesive force of the pressure-sensitive adhesive layer can be further improved while ensuring the adhesion to the base film (supporting base material).

In the embodiment containing the epoxy-based cross-linking agent and the isocyanate-based cross-linking agent, the relationship between the content of the epoxy-based cross-linking agent and the content of the isocyanate-based cross-linking agent is not particularly limited. The content of the epoxy-based cross-linking agent can be, for example, approximately 1/20 or less of the content of the isocyanate-based cross-linking agent. From the viewpoint of more preferably achieving both adhesion to the adherend and the base film and cohesive force, it is appropriate that the content of the epoxy-based cross-linking agent is about 1/30 or less of the content of the isocyanate-based cross-linking agent. It is preferably about 1/40 or less (for example, 1/50 or less). Further, from the viewpoint of preferably exerting the effect of using the epoxy-based cross-linking agent and the isocyanate-based cross-linking agent in combination, the content of the epoxy-based cross-linking agent is usually about 1/1000 of the content of the isocyanate-based cross-linking agent. As mentioned above, for example, it is appropriate to set it to about 1/500 or more.

(Adhesive-imparting resin)
Examples of the tackifier resin include phenol-based tackifier resins, terpene-based tackifier resins, modified terpene-based tackifier resins, rosin-based tackifier resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, and polyamide-based tackifier resins. , One or more selected from various known tackifier resins such as an elastomeric tackifier resin and a ketone tackifier resin can be used. By using the tackifier resin, the adhesion of the pressure-sensitive adhesive layer to the adherend can be improved, and the infiltration of oil from the outer edge of the pressure-sensitive adhesive sheet to the bonding interface can be effectively suppressed. For example, the permeation distance of oleic acid in the above-mentioned evaluation of oleic acid permeability can be shortened. The type and amount of the tackifier resin used can be set, for example, to form a pressure-sensitive adhesive layer that satisfies the preferred oleic acid permeation amount and surface free energy γ disclosed herein.

Examples of phenol-based tackifier resins include terpene phenol resins, hydrogenated terpene phenol resins, alkylphenol resins and rosinphenol resins.
The terpene phenol resin refers to a polymer containing terpene residues and phenol residues, and is a copolymer of terpenes and phenol compounds (terpene-phenol copolymer resin) and terpenes or homopolymers or copolymers thereof. It is a concept that includes both a polymer-modified mixture (phenol-modified terpene resin). Preferable examples of terpenes constituting such a terpene phenol resin are monoterpenes such as α-pinene, β-pinene, and limonene (including d-form, l-form, and d / l-form (dipentene)). Can be mentioned. The hydrogenated terpene phenol resin refers to a hydrogenated terpene phenol resin having a structure in which such a terpene phenol resin is hydrogenated. It is also called hydrogenated terpene phenol resin.
The alkylphenol resin is a resin (oil-based phenol resin) obtained from alkylphenol and formaldehyde. Examples of alkylphenol resins include novolak type and resol type ones.
The rosin phenolic resin is typically a phenolic modification of rosins or the various rosin derivatives described above (including rosin esters, unsaturated fatty acid modified rosins and unsaturated fatty acid modified rosin esters). Examples of the rosin phenol resin include a rosin phenol resin obtained by adding phenol to rosins or the above-mentioned various rosin derivatives with an acid catalyst and thermally polymerizing the resin.
Among these phenol-based tackifier resins, terpene phenol resins, hydrogenated terpene phenol resins and alkylphenol resins are preferable, terpene phenol resins and hydrogenated terpene phenol resins are more preferable, and terpene phenol resins are particularly preferable.

Examples of the terpene-based tackifier resin include polymers of terpenes (for example, monoterpenes) such as α-pinene, β-pinene, d-limonene, l-limonene, and dipentene. It may be a homopolymer of one kind of terpenes or a copolymer of two or more kinds of terpenes. Examples of the homopolymer of one kind of terpenes include α-pinene polymer, β-pinene polymer, dipentene polymer and the like.
Examples of the modified terpene resin include modified terpene resins. Specific examples thereof include styrene-modified terpene resin and hydrogenated terpene resin.

The concept of a rosin-based tackifier resin here includes both rosins and rosin derivative resins. Examples of rosins include unmodified rosins (raw rosins) such as gum rosins, wood rosins, and tall oil rosins; modified rosins obtained by modifying these unmodified rosins by hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosins, non-modified rosins) Normalized rosins, polymerized rosins, other chemically modified rosins, etc.);

The rosin derivative resin is typically a derivative of the rosins as described above. The concept of a rosin-based resin as used herein includes derivatives of unmodified rosins and derivatives of modified rosins (including hydrogenated rosins, disproportionated rosins and polymerized rosins). For example, rosin esters such as unmodified rosin esters, which are esters of unmodified rosins and alcohols, and modified rosin esters, which are esters of modified rosins and alcohols; for example, unmodified rosins modified with unsaturated fatty acids. Saturated fatty acid-modified rosins; for example, unsaturated fatty acid-modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids; for example, rosins or various rosin derivatives described above (rosin esters, unsaturated fatty acid-modified rosins and unsaturated). Examples thereof include rosin alcohols obtained by reducing the carboxy group of fatty acid-modified rosin esters; for example, metal salts of rosins or various rosin derivatives described above. Specific examples of rosin esters include methyl esters of unmodified rosins or modified rosins (hydrogenated rosins, disproportionated rosins, polymerized rosins, etc.), triethylene glycol esters, glycerin esters, pentaerythritol esters, and the like.

Examples of hydrocarbon-based tackifier resins include aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic / aromatic petroleum resins (styrene-olefin copolymers, etc.) ), Various hydrocarbon-based resins such as aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, kumaron-based resins, and kumaron-inden-based resins.

The softening point of the tackifier resin is not particularly limited. From the viewpoint of improving the cohesive force, in one embodiment, a tackifier resin having a softening point (softening temperature) of about 80 ° C. or higher (preferably about 100 ° C. or higher) can be preferably adopted. In the technique disclosed herein, the tackifier resin having the softening point is contained in an amount of more than 50% by weight (more preferably more than 70% by weight, for example, more than 90% by weight) of the entire tackifier resin contained in the pressure-sensitive adhesive layer. It can be preferably carried out in certain embodiments. For example, a phenol-based tackifier resin (terpene phenol resin or the like) having such a softening point can be preferably used. In a preferred embodiment, a terpene phenol resin having a softening point of about 135 ° C. or higher (further, about 140 ° C. or higher) can be used. The upper limit of the softening point of the tackifier resin is not particularly limited. From the viewpoint of adhesion to the adherend and the base film, in one embodiment, a tackifier resin having a softening point of about 200 ° C. or lower (more preferably about 180 ° C. or lower) can be preferably used. The softening point of the tackifier resin can be measured based on the softening point test method (ring ball method) specified in JIS K2207.

In the embodiment in which the tackifier resin is used, the content of the tackifier resin is not particularly limited. The content of the tackifier resin can be, for example, about 5 parts by weight or more with respect to 100 parts by weight of the acrylic polymer, and may be about 8 parts by weight or more (for example, about 10 parts by weight or more). The technique disclosed herein can also be preferably carried out in an embodiment in which the content of the tackifier resin with respect to 100 parts by weight of the acrylic polymer is approximately 15 parts by weight or more (for example, 25 parts by weight or more). The upper limit of the content of the tackifier resin is not particularly limited. From the viewpoint of compatibility with the acrylic polymer and initial adhesiveness, in one embodiment, it is usually appropriate that the content of the tackifier resin with respect to 100 parts by weight of the acrylic polymer is about 70 parts by weight or less. It is preferably 55 parts by weight or less, and more preferably about 45 parts by weight or less (for example, about 40 parts by weight or less).

In the embodiment in which the tackifier resin is used, it is preferable to select 50% by weight or less of the total amount of the tackifier resin from the tackifier resins other than the rosin-based tackifier resin. The ratio of the rosin-based tackifier resin to the total amount of the tackifier resin is preferably 25% by weight or less, and more preferably 10% by weight or less (for example, less than 5% by weight).
The amount of the rosin-based tackifier resin used is preferably less than 10 parts by weight, more preferably less than 5 parts by weight, based on 100 parts by weight of the acrylic polymer. The use of a rosin-based tackifier resin tends to cause an excessive increase in the amount of oleic acid permeation, depending on the type and amount used. In addition, the surface free energy γ tends to increase due to the use of the rosin-based tackifier resin. By limiting the amount of the rosin-based pressure-sensitive adhesive resin to 100 parts by weight of the acrylic polymer to less than 10 parts by weight, it becomes easy to obtain a pressure-sensitive adhesive layer in which the amount of oleic acid permeation and the surface free energy γ are in a suitable range. The technique disclosed herein can also be preferably carried out in an embodiment in which the pressure-sensitive adhesive layer substantially does not contain a rosin-based tackifier resin.

As a preferred embodiment, there is an embodiment in which the tackifier resin contains one or more phenol-based tackifier resins (for example, terpene phenol resin). Phenolic tackifier resins tend to have a lower affinity for oils than, for example, rosin tackifier resins. Therefore, by using the phenolic tackifier resin, the effect of improving the adhesion of the pressure-sensitive adhesive layer to the adherend (for example, the effect of shortening the permeation distance) is exhibited while suppressing an excessive increase in the amount of oleic acid permeation. obtain. The technique disclosed herein can be preferably carried out, for example, in an embodiment in which approximately 25% by weight or more (more preferably approximately 30% by weight or more) of the total amount of the tackifier resin is a terpene phenol resin. Approximately 50% by weight or more of the total amount of the tackifier resin may be terpene phenol resin, and approximately 80% by weight or more (for example, approximately 90% by weight or more) may be terpene phenol resin. Substantially all of the tackifier resin (for example, about 95% by weight or more and 100% by weight or less, and further about 99% by weight or more and 100% by weight or less) may be a terpene phenol resin. The content of the phenol-based tackifier resin (for example, terpene phenol resin) is about 5 parts by weight or more and about 45 parts by weight or less (for example, about 5 parts by weight or more and about 40 parts by weight or less) with respect to 100 parts by weight of the acrylic polymer. It is appropriate that the amount is about 8 parts by weight or more and about 35 parts by weight or less.

Although not particularly limited, as the tackifier resin in the technique disclosed herein, a tackifier resin having a hydroxyl value of less than 30 mgKOH / g (for example, less than 20 mgKOH / g) can be used. Hereinafter, the tackifier resin having a hydroxyl value of less than 30 mgKOH / g may be referred to as a “low hydroxyl value resin”. The hydroxyl value of the low hydroxyl value resin may be approximately 15 mgKOH / g or less, or may be approximately 10 mgKOH / g or less. The lower limit of the hydroxyl value of the low hydroxyl value resin is not particularly limited, and may be substantially 0 mgKOH / g. Such a low hydroxyl value resin (for example, a terpenphenol resin) is _{preferably used in combination with an acrylic polymer containing C 7-10} alkyl (meth) acrylate as a main monomer, and is used as an adhesive layer for an adherend. The effect of improving the adhesion of the resin (for example, the effect of shortening the permeation distance) can be satisfactorily exhibited.

Although not particularly limited, as the tackifier resin in the technique disclosed herein, a tackifier resin having a hydroxyl value of 30 mgKOH / g or more can be used. Hereinafter, a tackifier resin having a hydroxyl value of 30 mgKOH / g or more may be referred to as a “high hydroxyl value resin”. The upper limit of the hydroxyl value of the high hydroxyl value resin is not particularly limited. From the viewpoint of compatibility with the acrylic polymer, the hydroxyl value of the high hydroxyl value resin is usually about 200 mgKOH / g or less, preferably about 180 mgKOH / g or less, more preferably about 160 mgKOH / g or less. More preferably, it is about 140 mgKOH / g or less. A tackifier resin containing such a high hydroxyl value resin (for example, terpenephenol resin) is _{preferably used in combination with an acrylic polymer containing C 1-6} alkyl (meth) acrylate as a main monomer and adhered. The effect of improving the adhesion of the pressure-sensitive adhesive layer to the body (for example, the effect of shortening the permeation distance) can be satisfactorily exhibited.

Here, as the value of the hydroxyl value, a value measured by the potentiometric titration method specified in JIS K0070: 1992 can be adopted. The specific measurement method is as shown below.
[Measurement method of hydroxyl value]
1. 1. Reagent (1) As the acetylation reagent, about 12.5 g (about 11.8 mL) of acetic anhydride is taken, pyridine is added thereto to make the total volume 50 mL, and the reagent is sufficiently stirred. Alternatively, take about 25 g (about 23.5 mL) of acetic anhydride, add pyridine to this to make the total volume 100 mL, and use the one that has been sufficiently stirred.
(2) As a measurement reagent, a 0.5 mol / L potassium hydroxide ethanol solution is used.
(3) In addition, toluene, pyridine, ethanol and distilled water are prepared.
2. Operation (1) Approximately 2 g of a sample is precisely collected in a flat-bottomed flask, 5 mL of an acetylation reagent and 10 mL of pyridine are added, and an air cooling tube is attached.
(2) The flask is heated in a bath at 100 ° C. for 70 minutes, allowed to cool, 35 mL of toluene is added as a solvent from the upper part of the cooling pipe and stirred, and then 1 mL of distilled water is added and stirred to obtain acetic anhydride. Disassemble. Heat again in the bath for 10 minutes to complete the decomposition and allow to cool.
(3) Wash the cooling tube with 5 mL of ethanol and remove it. Then, 50 mL of pyridine is added as a solvent and stirred.
(4) Add 25 mL of 0.5 mol / L potassium hydroxide ethanol solution using a whole pipette.
(5) Potentiometric titration is performed with a 0.5 mol / L potassium hydroxide ethanol solution. The inflection point of the obtained titration curve is used as the end point.
(6) In the blank test, perform the above (1) to (5) without inserting a sample.
3. 3. Calculation Calculate the hydroxyl value by the following formula.
Hydroxy group value (mgKOH / g) = [(BC) × f × 28.05] / S + D
here,
B: Amount (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test,
C: Amount (mL) of 0.5 mol / L potassium hydroxide ethanol solution used for the sample,
f: Factor of 0.5 mol / L potassium hydroxide ethanol solution,
S: Sample weight (g),
D: Acid value,
28.05: 1/2 of the molecular weight of potassium hydroxide 56.11,
Is.

As the low hydroxyl value resin and the high hydroxyl value resin, those having the corresponding hydroxyl value among the various tackifier resins described above can be used. As the low hydroxyl value resin and the high hydroxyl value resin, one type may be used alone or two or more types may be used in combination, respectively. For example, as the low hydroxyl value resin, a phenolic tackifier resin having a hydroxyl value of less than 30 mgKOH / g can be preferably adopted. Further, for example, as the high hydroxyl value resin, a phenolic tackifier resin having a hydroxyl value of 30 mgKOH / g or more can be preferably adopted. Of these, terpene phenol resin is preferable. The terpene phenol resin is convenient because the hydroxyl value can be arbitrarily controlled by the copolymerization ratio of phenol.

(Other additives)
In addition to the above-mentioned components, the pressure-sensitive adhesive composition includes a leveling agent, a cross-linking aid, a plasticizer, a softening agent, an antistatic agent, an antioxidant, an ultraviolet absorber, an antioxidant, and a light stabilizer, if necessary. Various additives that are common in the field of adhesives such as, etc. may be contained. As for such various additives, conventionally known ones can be used by a conventional method and do not particularly characterize the present invention, and thus detailed description thereof will be omitted.

The pressure-sensitive adhesive layer disclosed herein may be a pressure-sensitive adhesive layer formed from a water-based pressure-sensitive adhesive composition, a solvent-type pressure-sensitive adhesive composition, a hot-melt type pressure-sensitive adhesive composition, and an active energy ray-curable pressure-sensitive adhesive composition. .. The water-based pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition in which a pressure-sensitive adhesive (sticking agent layer-forming component) is contained in a solvent containing water as a main component (water-based solvent), and is typically water-dispersed. A type pressure-sensitive adhesive composition (a composition in which at least a part of the pressure-sensitive adhesive is dispersed in water) and the like are included. Further, the solvent-type pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition in the form of containing a pressure-sensitive adhesive in an organic solvent. The technique disclosed herein can be particularly preferably carried out in an embodiment including a pressure-sensitive adhesive layer formed from a solvent-type pressure-sensitive adhesive composition from the viewpoint of pressure-sensitive adhesive properties and the like.

The pressure-sensitive adhesive layer disclosed herein can be formed by a conventionally known method. For example, a method (direct method) of forming a pressure-sensitive adhesive layer by directly applying (typically applying) the pressure-sensitive adhesive composition to a non-peelable base material and drying it can be adopted. Further, a method in which a pressure-sensitive adhesive composition is applied to a peelable surface (peeling surface) and dried to form a pressure-sensitive adhesive layer on the surface, and the pressure-sensitive adhesive layer is transferred to a non-peeling base material. (Transfer method) may be adopted. From the viewpoint of productivity, the transfer method is preferable. As the peeling surface, the surface of the peeling liner, the back surface of the base material that has been peeled off, or the like can be used. The pressure-sensitive adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form, and may have a regular or random pattern such as a dot shape or a striped shape. It may be a formed pressure-sensitive adhesive layer.

The pressure-sensitive adhesive composition can be applied by using a conventionally known coater such as a gravure roll coater, a die coater, or a bar coater. Alternatively, the pressure-sensitive adhesive composition may be applied by impregnation, a curtain coating method, or the like.
From the viewpoint of promoting the cross-linking reaction and improving the production efficiency, it is preferable that the pressure-sensitive adhesive composition is dried under heating. The drying temperature can be, for example, about 40 to 150 ° C., and is usually preferably about 60 to 130 ° C. After the pressure-sensitive adhesive composition is dried, aging is further performed for the purpose of adjusting the component transfer in the pressure-sensitive adhesive layer, advancing the cross-linking reaction, alleviating the strain that may exist in the base film or the pressure-sensitive adhesive layer, and the like. May be good.

The thickness of the pressure-sensitive adhesive layer is not particularly limited. From the viewpoint of avoiding excessive thickening of the pressure-sensitive adhesive sheet, the thickness of the pressure-sensitive adhesive layer is usually preferably about 100 μm or less, preferably about 70 μm or less, more preferably about 50 μm or less, and further preferably about 30 μm or less. Is. In the pressure-sensitive adhesive sheet according to a preferred embodiment, the thickness of the pressure-sensitive adhesive layer is about 25 μm or less (usually less than 25 μm, more preferably about 22 μm or less, for example, about 20 μm or less). In such a pressure-sensitive adhesive sheet having a relatively small thickness of the pressure-sensitive adhesive layer, since the amount of pressure-sensitive adhesive per area of the pressure-sensitive adhesive sheet is small, it is particularly effective to set the amount of oleic acid permeation of the pressure-sensitive adhesive layer to a predetermined value or more. Is. The lower limit of the thickness of the pressure-sensitive adhesive layer is not particularly limited, but from the viewpoint of adhesion to the adherend, it is advantageous to set it to about 4 μm or more, preferably about 6 μm or more, and more preferably about 10 μm or more (for example). Approximately 15 μm or more).
The technique disclosed herein can be suitably carried out, for example, in the form of a pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer having a thickness of about 10 μm or more and about 25 μm or less (preferably about 15 μm or more and about 22 μm or less). An adhesive sheet having an adhesive layer having such a thickness on both sides of the base material is preferable.

(Gel fraction)
Although not particularly limited, the gel fraction of the pressure-sensitive adhesive layer disclosed herein can be, for example, 20% or more on a weight basis, and usually 30% or more is appropriate, 35. % Or more is preferable. By increasing the gel fraction of the pressure-sensitive adhesive layer in an appropriate range, the appropriate amount of oleic acid permeation disclosed herein tends to be easily realized. On the other hand, if the gel fraction is too high, the amount of oleic acid permeated may tend to be insufficient. From this point of view, the gel fraction of the pressure-sensitive adhesive layer is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less (for example, 65% or less).

Here, the "gel fraction of the pressure-sensitive adhesive layer" means a value measured by the following method. The gel fraction can be grasped as the weight ratio of the ethyl acetate insoluble content in the pressure-sensitive adhesive layer.

[Gel fraction measurement method]
Approximately 0.1 g of adhesive sample (weight Wg _{1 ) is wrapped in a porous polytetrafluoroethylene film (weight Wg 2} ) having an average pore size of 0.2 μm in a purse-like shape, and the mouth is tied with octopus thread (weight Wg ₃ ). As the porous polytetrafluoroethylene (PTFE) film, the trade name "Nitoflon (registered trademark) NTF1122" (average pore diameter 0.2 μm, porosity 75%, thickness 85 μm) available from Nitto Denko KK or its own. Use an equivalent product.
This package is immersed in 50 mL of ethyl acetate and held at room temperature (typically 23 ° C.) for 7 days to elute only the sol component in the pressure-sensitive adhesive layer out of the film, and then the package is taken out and placed on the outer surface. The adhered ethyl acetate is wiped off, the wrap is dried at 130 ° C. for 2 hours, and the weight of the wrap (Wg ₄ ) is measured. Gel fraction F _G of the pressure-sensitive adhesive layer is determined by substituting each value into the following formula. The same method is adopted in the examples described later.
Gel fraction _{F G (%) = [(} Wg 4 -Wg 2 -Wg 3) / Wg 1] × 100

<Base material>
In the embodiment in which the pressure-sensitive adhesive sheet disclosed herein is in the form of a single-sided pressure-sensitive adhesive type or double-sided pressure-sensitive adhesive sheet with a base material, the base material for supporting (lining) the pressure-sensitive adhesive layer is a resin film, paper, cloth, or rubber. Sheets, foam sheets, metal foils, composites thereof and the like can be used. Examples of resin films include polyolefin films such as polyethylene (PE), polypropylene (PP), and ethylene / propylene copolymer; polyester films such as polyethylene terephthalate (PET); vinyl chloride resin film; vinyl acetate resin film; polyimide. Resin film; polyamide resin film; fluororesin film; cellophane and the like. Examples of paper include Japanese paper, kraft paper, glassin paper, high-quality paper, synthetic paper, top-coated paper and the like. Examples of the cloth include woven cloths and non-woven fabrics made by spinning various fibrous substances alone or in a blended manner. Examples of the fibrous material include cotton, sufu, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, polyolefin fiber and the like. Examples of the rubber sheet include a natural rubber sheet, a butyl rubber sheet and the like. Examples of the foam sheet include a foamed polyurethane sheet, a foamed polychloroprene rubber sheet, and the like. Examples of the metal foil include aluminum foil, copper foil and the like.

The non-woven fabric referred to here is a concept that mainly refers to a non-woven fabric for an adhesive sheet used in the field of adhesive tape and other adhesive sheets, and is typically a non-woven fabric produced by using a general paper machine. (Sometimes called "paper"). Further, the resin film referred to here is typically a non-porous resin sheet, and is a concept that is distinguished from, for example, a non-woven fabric (that is, does not include a non-woven fabric). The resin film may be a non-stretched film, a uniaxially stretched film, or a biaxially stretched film. Further, the surface of the base material on which the pressure-sensitive adhesive layer is provided may be subjected to surface treatment such as application of an undercoat agent, corona discharge treatment, and plasma treatment.

The technique disclosed herein can be preferably carried out in the form of a pressure-sensitive adhesive sheet with a base material having the pressure-sensitive adhesive layer on at least one surface of the base material film (support). For example, it can be preferably carried out in the form of a double-sided pressure-sensitive adhesive sheet with a base material having the pressure-sensitive adhesive layer on one surface and the other surface of the base material film.

As the base film, a base film containing a resin film can be preferably used. The base film is typically an independently shape-retainable (independent) member. The substrate film in the techniques disclosed herein may be substantially composed of such a base film. Alternatively, the base film may include an auxiliary layer in addition to the base film. Examples of the auxiliary layer include an undercoat layer, an antistatic layer, a colored layer and the like provided on the surface of the base film.

The resin film is a film containing a resin material as a main component (a component contained in the resin film in an amount of more than 50% by weight). Examples of resin films include polyethylene (PE), polypropylene (PP), ethylene / propylene copolymer and other polyolefin resin films; polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) and the like. Polyethylene resin film; vinyl chloride resin film; vinyl acetate resin film; polyimide resin film; polyamide resin film; fluororesin film; cellophane; and the like. The resin film may be a rubber-based film such as a natural rubber film or a butyl rubber film. Among them, a polyester film is preferable from the viewpoint of handleability and processability, and a PET film is particularly preferable. In the present specification, the "resin film" is typically a non-porous sheet, and is a concept that is distinguished from so-called non-woven fabrics and woven fabrics (in other words, a concept excluding non-woven fabrics and woven fabrics). is there.

The resin film (for example, PET film) may contain a filler (inorganic filler, organic filler, etc.), a colorant, a dispersant (surfactant, etc.), an antioxidant, an antioxidant, an ultraviolet ray, if necessary. Various additives such as absorbents, antistatic agents, lubricants, and plasticizers may be blended. The blending ratio of the various additives is usually about less than about 30% by weight (for example, less than about 20% by weight, preferably less than about 10% by weight).

The resin film may have a single-layer structure, or may have a multi-layer structure of two layers, three layers or more. From the viewpoint of shape stability, the resin film preferably has a single-layer structure. In the case of a multi-layer structure, it is preferable that at least one layer (preferably all layers) is a layer having a continuous structure of the above resin (for example, a polyester resin). The method for producing the resin film may appropriately adopt a conventionally known method, and is not particularly limited. For example, conventionally known general film molding methods such as extrusion molding, inflation molding, T-die casting molding, and calender roll molding can be appropriately adopted.

The thickness of the base film disclosed herein is not particularly limited. From the viewpoint of avoiding the pressure-sensitive adhesive sheet from becoming excessively thick, the thickness of the base film can be, for example, about 200 μm or less, preferably about 150 μm or less, and more preferably about 100 μm or less. Depending on the purpose and mode of use of the pressure-sensitive adhesive sheet, the thickness of the base film may be about 70 μm or less, about 50 μm or less, or about 30 μm or less (for example, about 25 μm or less). In one aspect, the thickness of the base film may be about 20 μm or less, about 15 μm or less, or about 10 μm or less (for example, about 5 μm or less). By reducing the thickness of the base film, the thickness of the pressure-sensitive adhesive layer can be further increased even if the total thickness of the pressure-sensitive adhesive sheets is the same. This can be advantageous from the viewpoint of improving the adhesion to the base material. The lower limit of the thickness of the base film is not particularly limited. From the viewpoint of handleability (handleability), processability, etc. of the pressure-sensitive adhesive sheet, the thickness of the base film is usually about 0.5 μm or more (for example, 1 μm or more), preferably about 2 μm or more, for example, about 4 μm or more. .. In one aspect, the thickness of the base film can be about 6 μm or more, may be about 8 μm or more, or may be about 10 μm or more (for example, more than 10 μm).

The surface of the base film may be subjected to conventionally known surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and application of an undercoat agent. Such a surface treatment may be a treatment for improving the adhesion between the base film and the pressure-sensitive adhesive layer, in other words, the anchoring property of the pressure-sensitive adhesive layer on the base film.

<Peeling liner>
In the technique disclosed herein, a release liner can be used when forming an adhesive layer, producing an adhesive sheet, storing the adhesive sheet before use, distributing the adhesive sheet, processing the shape, and the like. The release liner is not particularly limited, and for example, a release liner having a release treatment layer on the surface of a liner base material such as a resin film or paper, a fluoropolymer (polytetrafluoroethylene, etc.) or a polyolefin resin (polyethylene, etc.) A release liner or the like made of a low adhesive material (polypropylene or the like) can be used. The peeling treatment layer may be formed by surface-treating the liner base material with a peeling treatment agent such as silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide.

<Adhesive sheet>
The total thickness of the pressure-sensitive adhesive sheet (excluding the release liner) disclosed herein is not particularly limited. The total thickness of the pressure-sensitive adhesive sheet can be, for example, about 500 μm or less, and usually about 350 μm or less is suitable, and about 250 μm or less (for example, about 200 μm or less) is preferable. The technique disclosed herein is in the form of an adhesive sheet (typically a double-sided adhesive sheet) having a total thickness of approximately 150 μm or less (more preferably approximately 100 μm or less, even more preferably less than approximately 60 μm, eg, approximately 55 μm or less). It can be preferably carried out. The lower limit of the thickness of the pressure-sensitive adhesive sheet is not particularly limited, but usually, about 10 μm or more is suitable, about 20 μm or more is preferable, and about 30 μm or more is more preferable.

According to the technique disclosed herein, an adhesive sheet having an adhesive strength retention rate of more than 50% in the following oil resistance adhesiveness evaluation can be provided. In the pressure-sensitive adhesive sheet according to a preferred embodiment, the adhesive strength retention rate can be 60% or more (for example, 65% or more). The upper limit of the adhesive strength retention rate is not particularly limited, but is usually 150% or less, preferably 100% or less.

[Oil resistance and adhesiveness evaluation]
A sample piece is prepared by cutting the adhesive sheet into a size of 10 mm in width and 100 mm in length. Here, when the pressure-sensitive adhesive sheet of the measurement mode is a double-sided pressure-sensitive adhesive sheet, a PET film having a thickness of 50 μm is attached to one of the pressure-sensitive adhesive surfaces, lined with the adhesive sheet, and then cut to the above size.
In an environment of 23 ° C. and 50% RH, the adhesive surface of the sample piece is pressure-bonded to a stainless steel plate (SUS304BA plate) to prepare a measurement sample. The crimping is performed by reciprocating a 2 kg roller once. After leaving the above measurement sample in an environment of 23 ° C. and 50% RH for 30 minutes, a tensile tester is used under the conditions of a tensile speed of 150 mm / min and a peeling angle of 180 degrees according to JIS Z 0237: 2000. Then, the peel strength (N / 10 mm) is measured. This value is taken as the adhesive strength before immersion.
On the other hand, the measurement sample prepared in the same manner as above is left in an environment of 23 ° C. and 50% RH for 30 minutes, then immersed in an oleic acid bath, and kept in an environment of 40 ° C. and 90% RH for 2 weeks. .. Then, the measurement sample is pulled up from the oleic acid bath, the oleic acid adhering to the surroundings is lightly wiped off, and the mixture is left in an environment of 23 ° C. and 50% RH for 30 minutes. N / 10 mm) is measured. This value is taken as the adhesive strength after immersion.
From the obtained measured values, the following formula:
Adhesive strength retention rate (%) = (adhesive strength after immersion / adhesive strength before immersion) × 100;
The adhesive strength maintenance rate is calculated by.
As the tensile tester, for example, "Precision universal tester Autograph AG-IS 50N" manufactured by Shimadzu Corporation can be used. The same evaluation method is adopted in the examples described later.

In the pressure-sensitive adhesive sheet disclosed herein, the adhesive strength before immersion is not particularly limited. The pressure-sensitive adhesive sheet according to a preferred embodiment has a pre-immersion adhesive strength of about 3.0 N / 10 mm or more. The pressure-sensitive adhesive sheet exhibiting such pre-immersion adhesive strength has high adhesion to the adherend, and therefore can be excellent in performance of preventing oil from entering the adhesive interface from the outer edge of the pressure-sensitive adhesive sheet. A pressure-sensitive adhesive sheet having an adhesive strength before immersion of about 5.0 N / 10 mm or more (for example, about 6.0 N / 10 mm or more) is more preferable. The higher the adhesion to the adherend, the better. Therefore, the upper limit of the adhesive force before immersion is not particularly limited, but usually about 30 N / 10 mm or less (for example, about 20 N / 10 mm or less) is suitable.

Although not particularly limited, the adhesive strength after immersion is preferably 1.0 N / 10 mm or more from the viewpoint of suppressing the protrusion of the adhesive. The adhesive strength after immersion is preferably about 2.0 N / 10 mm or more, more preferably about 3.0 N / 10 mm or more, still more preferably about 4.0 N / 10 mm or more (for example, about 5.0 N / 10 mm or more, and further. Approximately 6.0 N / 10 mm or more). Such an adhesive sheet exhibiting adhesive strength after immersion is suitable for, for example, an application for fixing a member that can come into contact with oil.

<Use>
The pressure-sensitive adhesive sheet disclosed herein has little decrease in adhesive strength even when it comes into contact with oil, and the protrusion of the pressure-sensitive adhesive is suppressed. Taking advantage of these characteristics, the pressure-sensitive adhesive sheet can be preferably used for fixing various members that can come into contact with oil. A typical example of such an application is an application for fixing a member in various portable devices (portable devices). For example, it is suitable for fixing members in portable electronic devices. Non-limiting examples of the above-mentioned portable electronic devices include mobile phones, smartphones, tablet computers, laptop computers, various wearable devices (for example, wristwear type worn on the wrist like a wristwatch, clips, straps, etc.). Modular type to be attached to a part of, eyewear type including glasses type (monocular type and binocular type, including head mount type), clothes type to be attached to shirts, socks, hats, etc. in the form of accessories, earphones (Earwear type, etc. that can be attached to the ear), digital camera, digital video camera, audio equipment (portable music player, IC recorder, etc.), computer (computer, etc.), portable game equipment, electronic dictionary, electronic notebook, electronic book, in-vehicle Includes information devices, mobile radios, mobile TVs, mobile printers, mobile scanners, mobile modems, etc. Non-limiting examples of portable devices other than portable electronic devices include mechanical wristwatches and pocket watches, flashlights, hand mirrors, regular pockets, and the like. In addition, in this specification, "portable" means that it is not enough to be portable, but to have a level of portability that an individual (standard adult) can carry relatively easily. It shall mean.

The pressure-sensitive adhesive sheet (typically, a double-sided pressure-sensitive adhesive sheet) disclosed herein can be used for fixing a member constituting a portable device in the form of a bonding material processed into various outer shapes. A particularly preferable application is an application for fixing a member constituting a portable electronic device. Among them, it can be preferably used for a portable electronic device having a liquid crystal display device. For example, in such a portable electronic device, it is suitable for an application of joining a display unit (which may be a display unit of a liquid crystal display device) or a display unit protection member and a housing.

A preferred form of such a bonding material includes a form having a narrow portion having a width of 4.0 mm or less (for example, 2.0 mm or less, usually less than 2.0 mm). Since the adhesive sheet disclosed here is excellent in cohesive force in addition to oil resistance, even if it is used as a bonding material having a shape including such a narrow portion (for example, a frame shape), the member can be satisfactorily fixed. can do. In one aspect, the width of the narrow portion may be 1.5 mm or less, 1.0 mm or less, about 0.5 mm or less. The lower limit of the width of the narrow portion is not particularly limited, but from the viewpoint of handleability of the pressure-sensitive adhesive sheet, 0.1 mm or more (for example, 0.2 mm or more) is usually suitable.

The narrow portion is typically linear. Here, the linear shape is a concept that includes a linear shape, a curved line shape, a polygonal line shape (for example, an L-shape), an annular shape such as a frame shape or a circular shape, and a complex or intermediate shape thereof. .. The annular shape is not limited to the one formed by a curved line, and a part or all of the ring shape is formed in a straight line, for example, a shape along the outer circumference of a quadrangle (frame shape) or a shape along the outer circumference of a fan shape. It is a concept that includes a ring. The length of the narrow portion is not particularly limited. For example, in a form in which the length of the narrow portion is 10 mm or more (more preferably 20 mm or more, for example 30 mm or more), the effect of applying the technique disclosed herein can be suitably exhibited.

Matters disclosed by this specification include:
(1) A pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive using an acrylic polymer as a base polymer.
The pressure-sensitive adhesive layer is a pressure-sensitive adhesive sheet having a surface free energy γ of about 40 mJ / m ^{2 or} less and an oleic acid permeation amount of about 1.5 g or more and about 5.0 g or less.
(2) The pressure-sensitive adhesive sheet according to (1) above, wherein the gel fraction of the pressure-sensitive adhesive layer is about 30% or more and about 70% or less.
(3) The pressure-sensitive adhesive sheet according to (1) or (2) above, wherein the pressure-sensitive adhesive layer is formed by using a pressure-sensitive adhesive composition containing the acrylic polymer and a cross-linking agent.
(4) The pressure-sensitive adhesive sheet according to (3) above, wherein the cross-linking agent contains an isocyanate-based cross-linking agent.
(5) The pressure-sensitive adhesive layer according to any one of (1) to (4) above, wherein the pressure-sensitive adhesive layer contains a pressure-sensitive adhesive resin, and about 50% by weight or more of the pressure-sensitive adhesive resin is a pressure-sensitive adhesive resin other than a rosin-based resin. Adhesive sheet.

(6) The pressure-sensitive adhesive sheet according to any one of (1) to (5) above, wherein the monomer component constituting the acrylic polymer _{contains more than about 50% by weight of C 7-10 alkyl (meth) acrylate.}
(7) The pressure-sensitive adhesive sheet according to (6) above, wherein the monomer component constituting the acrylic polymer contains a carboxy group-containing monomer in an amount of approximately 5% by weight or more.
(8) The monomer component constituting the acrylic polymer contains about 70% by weight or more of C _7-10 alkyl (meth) acrylate and about 7% by weight or more and about 15% by weight or less of a carboxy group-containing monomer. The adhesive sheet according to any one of (1) to (7) above.
(9) The C _7-10 alkyl (meth) acrylate is one or more selected from 2-ethylhexyl acrylate, isooctyl acrylate and isononyl acrylate, and the carboxy group-containing monomer is acrylic acid and methacrylic acid. The pressure-sensitive adhesive sheet according to (8) above, which is an acid or a combination thereof.
(10) Any of the above (6) to (9), wherein the pressure-sensitive adhesive layer contains a pressure-sensitive adhesive resin, and about 50% by weight or more of the pressure-sensitive adhesive resin is a phenol-based pressure-sensitive adhesive resin (for example, terpenphenol resin). Adhesive sheet described in.
(11) The pressure-sensitive adhesive sheet according to (10) above, wherein the phenol-based pressure-sensitive adhesive resin contains a terpene phenol resin having a hydroxyl value of less than about 30 mgKOH / g.

(12) The pressure-sensitive adhesive sheet according to any one of (1) to (5) above, wherein the monomer component constituting the acrylic polymer _{contains more than about 50% by weight of C 1-6 alkyl (meth) acrylate.} ..
(13) The pressure-sensitive adhesive sheet according to (12) above, wherein the monomer component constituting the acrylic polymer contains a carboxy group-containing monomer in an amount of approximately 3% by weight or more.
(14) The C _1-6 alkyl (meth) acrylate is one or more selected from n-butyl acrylate, ethyl acrylate and methyl acrylate, and the carboxy group-containing monomer is acrylic acid or methacrylic acid. Alternatively, the adhesive sheet according to (13) above, which is a combination thereof.
(15) Any of the above (12) to (14), wherein the pressure-sensitive adhesive layer contains a pressure-sensitive adhesive resin, and about 50% by weight or more of the pressure-sensitive adhesive resin is a phenol-based pressure-sensitive adhesive resin (for example, terpenphenol resin). Adhesive sheet described in.
(16) The pressure-sensitive adhesive sheet according to (15) above, wherein the phenol-based pressure-sensitive adhesive resin contains a terpene phenol resin having a hydroxyl value of about 30 mgKOH / g or more.

(17) The pressure-sensitive adhesive sheet according to any one of (1) to (16) above, wherein the pressure-sensitive adhesive layer is formed by using a solvent-type pressure-sensitive adhesive composition containing a pressure-sensitive adhesive in an organic solvent.
(18) The pressure-sensitive adhesive sheet according to (17) above, wherein the organic solvent contains at least one of toluene and ethyl acetate.
(19) The pressure-sensitive adhesive sheet according to any one of (1) to (18) above, wherein the thickness of the pressure-sensitive adhesive layer is about 10 μm or more and about 25 μm or less.
(20) The pressure-sensitive adhesive sheet according to any one of (1) to (19) above, which is configured as a double-sided pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer on one surface and the other surface of the base material.
(21) The pressure-sensitive adhesive sheet according to (20) above, wherein the base material is a PET film having a single-layer structure.
(22) The adhesive sheet according to any one of (1) to (21) above, which is used for fixing a member in a portable device.

(23) A portable device having a member fixed by using the adhesive sheet according to any one of (1) to (22) above.
(24) The mobile device according to (23) above, wherein the mobile device is a wearable device (for example, a wristwear type wearable device).

Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to those shown in such examples. In the following description, "part" and "%" are based on weight unless otherwise specified.

<Preparation of acrylic polymer solution>
(Acrylic polymer A)
In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas introduction tube, a reflux condenser and a dropping funnel, 90 parts of 2EHA and 10 parts of AA as monomer components and 199 parts of ethyl acetate as a polymerization solvent were charged, and nitrogen gas was introduced. While stirring for 2 hours. After removing oxygen in the polymerization system in this manner, 0.2 part of benzoyl peroxide was added as a polymerization initiator, and solution polymerization was carried out at 60 ° C. for 6 hours to obtain a solution of acrylic polymer A. Mw of the acrylic polymer A was about 120 × 10 ^4.

(Acrylic polymer B)
In a reaction vessel equipped with a stirrer, thermometer, nitrogen gas introduction tube, reflux condenser and dropping funnel, 100 parts of 2EHA as a monomer component, 2 parts of methyl methacrylate (MMA) and 2 parts of AA, and 190 parts of toluene as a polymerization solvent. Was charged, and the mixture was stirred for 2 hours while introducing nitrogen gas. After removing oxygen in the polymerization system in this way, 0.3 parts of 2,2'-azobisisobutyronitrile was added as a polymerization initiator, and solution polymerization was carried out at 60 ° C. for 6 hours to carry out solution polymerization of acrylic polymer B. Solution was obtained. Mw of the acrylic polymer B was about 100 × 10 ^4.

(Acrylic polymer C)
In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas introduction tube, a reflux condenser and a dropping funnel, 95 parts of BA and 5 parts of AA as monomer components and 233 parts of ethyl acetate as a polymerization solvent were charged, and nitrogen gas was introduced. While stirring for 2 hours. After removing oxygen in the polymerization system in this way, 0.2 parts of 2,2'-azobisisobutyronitrile was added as a polymerization initiator and solution-polymerized at 60 ° C. for 8 hours to obtain an acrylic polymer. A solution was obtained. The Mw of the acrylic polymer was about 70 × 10 ^4.

<Preparation of adhesive composition>
(Example 1)
In the solution of the acrylic polymer A, 2 parts (nonvolatile content standard; the same applies hereinafter) of an isocyanate-based cross-linking agent (trade name "Coronate L", trimethylol propane /) with respect to 100 parts of the acrylic polymer A contained in the solution. A 75% ethyl acetate solution of the tolylene diisocyanate trimer adduct, manufactured by Toso Co., Ltd .; hereinafter referred to as "isocyanate-based cross-linking agent A") was added and mixed by stirring to prepare a pressure-sensitive adhesive composition according to this example.

(Example 2)
In the solution of the acrylic polymer A, 2 parts of the isocyanate-based cross-linking agent A and 0.01 part of the epoxy-based cross-linking agent (trade name "TETRAD-C") with respect to 100 parts of the acrylic polymer A contained in the solution. , 1,3-Bis (N, N-diglycidylaminomethyl) cyclohexane, manufactured by Mitsubishi Gas Chemicals, Inc .; hereinafter referred to as "epoxy-based cross-linking agent B"), and the mixture is stirred and mixed to obtain the adhesive according to this example. An agent composition was prepared.

(Example 3)
In the solution of the acrylic polymer A, 2 parts of the isocyanate-based cross-linking agent A, 0.035 parts of the epoxy-based cross-linking agent B, and 10 parts of the terpene phenol with respect to 100 parts of the acrylic polymer A contained in the solution. Resin A (trade name "Tamanol 803L", manufactured by Arakawa Chemical Industry Co., Ltd., softening point of about 145 to 160 ° C., hydroxyl value of 1 to 20 mgKOH / g) is added and mixed by stirring to prepare the pressure-sensitive adhesive composition according to this example. did.

(Example 4)
To the solution of the acrylic polymer C, two parts of the isocyanate-based cross-linking agent A was added to 100 parts of the acrylic polymer C contained in the solution, and the mixture was stirred and mixed to prepare the pressure-sensitive adhesive composition according to this example.

(Example 5)
30 parts of terpene phenol resin B (manufactured by Yasuhara Chemical Co., Ltd., trade name "YS Polystar S-145", softening point of about 145 ° C., hydroxyl value 70 to 110 mgKOH / g) was further added to 100 parts of acrylic polymer C. Prepared the pressure-sensitive adhesive composition according to this example in the same manner as in Example 4.

(Example 6)
The pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 5 except that the amount of terpene phenol resin B used with respect to 100 parts of the acrylic polymer C was changed to 40 parts.

(Example 7)
To the solution of the acrylic polymer B, 2 parts of the isocyanate-based cross-linking agent A was added to 100 parts of the acrylic polymer B contained in the solution, and the mixture was stirred and mixed to prepare the pressure-sensitive adhesive composition according to this example.

(Example 8)
The pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 4 except that the amount of the isocyanate-based cross-linking agent A used for 100 parts of the acrylic polymer C was changed to 1 part.

(Example 9)
Other examples include the addition of 10 parts of rosin-based pressure-sensitive adhesive resin A (trade name "Haritac SE10", hydrogenated rosing lycerin ester, manufactured by Harima Chemicals, softening point of about 80 ° C.) to 100 parts of acrylic polymer C. The pressure-sensitive adhesive composition according to this example was prepared in the same manner as in 4.

(Example 10)
To the solution of the acrylic polymer C, 2 parts of the isocyanate-based cross-linking agent A, 0.01 part of the epoxy-based cross-linking agent B, and 20 parts of the rosin-based adhesive to 100 parts of the acrylic polymer C contained in the solution. The imparting resin B (trade name “Pencel D125”, manufactured by Arakawa Chemical Industry Co., Ltd., pentaerythritol ester of polymerized rosin, softening point of about 125 ° C.) was added and mixed by stirring to prepare a pressure-sensitive adhesive composition according to this example.

<Making an adhesive sheet>
As the peeling liner, two polyester peeling films (trade name "Diafoil MRF", thickness 38 μm, manufactured by Mitsubishi Polyester Co., Ltd.) having a peeled surface on one side were prepared. The pressure-sensitive adhesive composition according to each example was applied to the peeled surface of these release liners and dried at 100 ° C. for 2 minutes to form a pressure-sensitive adhesive layer having a thickness of 19 μm. The pressure-sensitive adhesive layers formed on the above two release liners were bonded to the first surface and the second surface of a transparent base film having a thickness of 12 μm, respectively, to prepare a double-sided pressure-sensitive adhesive sheet having a total thickness of 50 μm. The release liner was left as it was on the pressure-sensitive adhesive layer and used to protect the surface (adhesive surface) of the pressure-sensitive adhesive layer. As the base film, a PET film (resin film) manufactured by Toray Industries, Inc. and a trade name of "Lumirror" were used. In this way, the double-sided pressure-sensitive adhesive sheets of Examples 1 to 10 corresponding to the pressure-sensitive adhesive compositions according to Examples 1 to 10 were produced.

<Evaluation test>
After curing the double-sided adhesive sheet according to Examples 1 to 10 in an environment of 50 ° C. and 50% RH for 1 day, the surface free energy γ, the gel fraction and the adhesive strength retention rate were determined by the above-mentioned method.
Further, the pressure-sensitive adhesive composition according to Examples 1 to 10 is applied to the peeling surface of the polyester release film (trade name "Diafoil MRF", thickness 38 μm, manufactured by Mitsubishi Polyester Co., Ltd.) and dried at 120 ° C. for 2 minutes. Then, a pressure-sensitive adhesive layer (base material-less pressure-sensitive adhesive layer) having a thickness of 20 μm was formed on the release film. This pressure-sensitive adhesive layer was attached to a PET film having a thickness of 50 μm (trade name “Lumilar”, manufactured by Toray Industries, Inc.) and cut into a square shape having a length of 25 mm and a width of 25 mm to prepare a test piece. By evaluating the permeability of oleic acid by the method described above using this test piece, the amount of oleic acid permeation and the permeation distance were determined, and the protrusion of the pressure-sensitive adhesive was evaluated.
The results obtained are shown in Tables 1 and 2.

^{As shown in Tables 1 and 2} , the adhesive layer has a surface free energy γ of less than 40 mJ / m 2 and an oleic acid permeation amount in the range of 1.5 g / g or more and 5.0 g / g or less. The adhesive sheets of Examples 1 to 6 all showed a good adhesive strength retention rate, and the adhesive did not squeeze out. On the other hand, the adhesive strength retention rate was low in Examples 7 and 8 in which the amount of oleic acid permeated was too small and in Example 10 in which the surface free energy γ was too high. In Example 9 in which the amount of oleic acid permeated was too large, the adhesive squeezed out significantly.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above.

1,2,3,4,5,6 Adhesive sheet 10 Base material 21,22 Adhesive layer 31,32 Release liner

Claims (6)

A pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive based on an acrylic polymer.
It is configured as a double-sided pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer on one surface and the other surface of the base material.
The base material is a base film using a resin film as a base film.
The pressure-sensitive adhesive layer has a surface free energy γ of ^{less than 40 mJ / m 2} and an oleic acid permeation amount per 1 g of 1.5 g or more and 5.0 g or less.
The thickness of the pressure-sensitive adhesive layer is 25 μm or less, and the thickness is 25 μm or less.
The pressure-sensitive adhesive layer is formed by using a pressure-sensitive adhesive composition containing the acrylic polymer, a cross-linking agent, and a pressure-sensitive adhesive resin.
The monomer component constituting the acrylic polymer contains more than 50% by weight of an alkyl (meth) acrylate having an alkyl group having 1 or more and 6 or less carbon atoms at the ester terminal, and 0.5% by weight of a carboxy group-containing monomer. Including at a ratio of 5% by weight or less
The cross-linking agent contains an isocyanate-based cross-linking agent, and the amount of the isocyanate-based cross-linking agent used is 0.5 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the acrylic polymer.
The tackifier resin contains a phenol-based tackifier resin, and the phenol-based tackifier resin contains a terpene phenol resin having a softening point of 135 ° C. or higher.
The pressure-sensitive adhesive sheet contains 8 parts by weight or more and 35 parts by weight or less with respect to 100 parts by weight of the acrylic polymer. The pressure-sensitive adhesive sheet according to claim 1, wherein the gel content of the pressure-sensitive adhesive layer is 30% or more and 70% or less. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein 50% by weight or more of the pressure-sensitive adhesive resin is a pressure-sensitive adhesive resin other than the rosin-based pressure-sensitive adhesive resin. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein 50% by weight or more of the pressure-sensitive adhesive resin is a terpene phenol-based resin. From the post-immersion adhesive strength measured after immersing in an oleic acid bath and holding in an environment of 40 ° C. and 90% RH for 2 weeks, and the pre-immersion adhesive strength measured before immersing in the oleic acid bath. The following formula:
Adhesive strength retention rate (%) = (adhesive strength after immersion / adhesive strength before immersion) × 100;
The adhesive sheet according to any one of claims 1 to 4, wherein the adhesive strength retention rate calculated by the above method is more than 50%. The adhesive sheet according to any one of claims 1 to 5 , which is used for fixing a member in a mobile device.

Images