JP2017165977A - Adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive sheet that is prevented from decreasing in adhesive capacity even in contact with an oil content, and also prevents the squeezing-out of an adhesive.SOLUTION: The present invention provides an adhesive sheet that comprises an adhesive layer composed of an adhesive using an acrylic polymer as a base polymer. The adhesive layer has a surface free energy γ of less than 40 mJ/mand also has an oleic acid permeation per 1g of 1.5g or more and 5.0g or less.SELECTED DRAWING: None

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 shall apply hereinafter) is in the form of a soft solid (viscoelastic body) in a temperature range near room temperature and has a property of easily adhering to an adherend by pressure. Taking advantage of such properties, the pressure-sensitive adhesive is, for example, in the form of a pressure-sensitive adhesive sheet with a base material having a pressure-sensitive adhesive layer on a supporting base material, and for purposes such as joining, fixing, and protection of members in mobile phones and other portable devices Widely used in Patent documents 1 and 2 are mentioned as technical literature about a double-sided adhesive tape used for component fixation of portable electronic equipment.

JP 2009-215355 A JP 2013-1000048 A1

  Since portable devices are used with carrying, oils contained in secretions such as sebum and dirt, cosmetics, hair styling agents, chemicals such as moisturizing creams, sunscreens, foods, etc. are likely to adhere. In particular, touch panel portable devices, which have been widely used in recent years, include a display unit / input unit whose display unit also functions as an input unit, and are operated when a user directly touches the surface of the display unit / input unit with a fingertip. Therefore, there are many opportunities for oil to adhere through the fingertips. Some so-called wearable devices are used while being in contact with the skin. In such usage, there are many opportunities to be exposed to oil 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 that fixes the member, problems such as a decrease in pressure-sensitive adhesive force and the pressure-sensitive adhesive protruding may occur.

  In this regard, for example, Patent Document 1 studies a double-sided pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive is not easily softened / swelled even when oil penetrates and the pressure-sensitive adhesive does not protrude when used for fixing components. However, in Patent Document 1, it is not considered to suppress a decrease in adhesive force due to contact with oil.

  This invention is made | formed in view of this situation, Comprising: It aims at providing the adhesive sheet with few fall of adhesive force even if it contacted with the oil component, and the protrusion of the adhesive being suppressed.

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

  Since the pressure-sensitive adhesive sheet having such a structure has a low surface energy γ of the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer tends to exhibit good wettability with respect to the adherend. Thereby, an adhesive layer and a to-be-adhered body are made to adhere | attach suitably, and the penetration | invasion of the oil from the outer edge of an adhesive sheet to the interface (adhesion interface) of an adhesive layer and an to-be-adhered body can be suppressed. Moreover, the said adhesive layer has the capability to hold | maintain an oleic acid 1.5g or more per 1g in the oleic acid penetration | permeation amount measurement mentioned later. By exhibiting such oil retention, even if oil enters the adhesion interface from the outer edge of the pressure-sensitive adhesive sheet, the oil content is absorbed (permeated) into the layer of the pressure-sensitive adhesive layer. It can be kept in a small state. In this way, the oil contact from the outer edge of the pressure-sensitive adhesive sheet is suppressed, and the oil content that has entered is easily absorbed from the adhesive interface into the pressure-sensitive adhesive layer (bulk). It is possible to effectively suppress a decrease in the adhesive strength due to. Then, by limiting the oleic acid permeation amount per 1 g of the pressure-sensitive adhesive layer to 5.0 g or less, an event where the pressure-sensitive adhesive layer absorbs oil excessively and the pressure-sensitive adhesive protrudes can be prevented.

  In the pressure-sensitive adhesive sheet according to a preferred embodiment, the pressure-sensitive adhesive layer has a gel fraction of 30% to 70%. By setting the gel fraction within the above range, a pressure-sensitive adhesive layer having an oleic acid permeation amount in an appropriate range tends to be realized.

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

  The pressure-sensitive adhesive sheet disclosed herein can be preferably implemented in a mode in which the pressure-sensitive adhesive layer contains a tackifying resin. By including a tackifier resin in the pressure-sensitive adhesive layer, the adhesiveness of the pressure-sensitive adhesive layer to the adherend can be improved, and oil penetration from the outer edge of the pressure-sensitive adhesive sheet to the adhesive interface can be better suppressed. Further, by selecting 50% by weight or more of the tackifying resin from a tackifying resin other than the rosin-based tackifying resin, a pressure-sensitive adhesive layer in which the oleic acid penetration amount and the surface free energy γ are in an appropriate range is easily realized. Tend to be.

In one embodiment of the pressure-sensitive adhesive sheet disclosed herein, the monomer component constituting the acrylic polymer has 7 to 10 carbon atoms (hereinafter, the range of such carbon atoms is expressed as “C _7-10 ”. The alkyl (meth) acrylate having an alkyl group at the ester terminal is contained in an amount of more than 50% by weight. According to the technology 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 oil is reduced. A pressure-sensitive adhesive sheet in which the decrease and the sticking-out of the pressure-sensitive adhesive are suitably suppressed can be realized.

The pressure-sensitive adhesive sheet disclosed herein can be preferably implemented in an embodiment in which the monomer component constituting the acrylic polymer contains more than 5% by weight of a carboxy group-containing monomer. According to the acrylic polymer having such a monomer composition, oil such as oleic acid can be favorably retained in the pressure-sensitive adhesive layer. Thereby, the oil component which exists in an adhesion interface can be reduced, and the fall of the adhesive force by an oil component can be suppressed effectively. In the 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 a mode 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 pressure-sensitive adhesive layer, since the amount of the pressure-sensitive adhesive per area of the pressure-sensitive adhesive sheet is small, it is particularly effective to set the oleic acid penetration amount 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 substrate. Since the double-sided PSA sheet is used by sticking one surface and the other surface of the PSA sheet to the adherend, the oil easily enters the adhesive interface with these adherends. Therefore, it is particularly meaningful to apply the technology disclosed herein to suppress a decrease in the adhesive strength due to the oil.

  The pressure-sensitive adhesive sheet disclosed herein can be preferably used for, for example, an application for fixing a member in a portable device. As described above, since there are many opportunities for the mobile device to come into contact with the oil, it is particularly meaningful to apply the technology disclosed herein to suppress the decrease in the adhesive force due to the oil and the protrusion of the adhesive.

It is sectional drawing which shows one structural example of an adhesive sheet typically. It is sectional drawing which shows the other structural example of an adhesive sheet typically. It is sectional drawing which shows the other structural example of an adhesive sheet typically. It is sectional drawing which shows the other structural example of an adhesive sheet typically. It is sectional drawing which shows the other structural example of an adhesive sheet typically. It is sectional drawing which shows the other structural example of an adhesive sheet typically.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention are based on the teachings on the implementation of the invention described in the present specification and the common general technical 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 this specification and common technical knowledge in the field. Further, in the following drawings, members / parts having the same action may be described with the same reference numerals, and overlapping descriptions may be omitted or simplified. In addition, the embodiment described in the drawings is schematically illustrated for clearly explaining the present invention, and does not necessarily accurately represent the size and scale of the pressure-sensitive adhesive sheet of the present invention that is actually provided as a product. .

In the present specification, the “pressure-sensitive adhesive” refers to a material that exhibits a soft solid (viscoelastic body) state in a temperature range near room temperature and has a property of easily adhering to an adherend by pressure as described above. . The adhesive here is generally defined as “CA Dahlquist,“ Adhesion: Fundamentals and Practice ”, McLaren & Sons, (1966) P. 143”, and generally has a complex tensile modulus E ^* (1 Hz). It may be a material having a property satisfying <10 ⁷ dyne / cm ² (typically, a material having the above property at 25 ° C.).

  In this specification, “(meth) acryloyl” means acryloyl and methacryloyl comprehensively. Similarly, “(meth) acrylate” means acrylate and methacrylate, and “(meth) acryl” generically means acrylic and methacryl.

  In this specification, the “acrylic polymer” refers to a polymer containing monomer units derived from a monomer having at least one (meth) acryloyl group in one molecule as monomer units constituting the polymer. Hereinafter, a monomer having at least one (meth) acryloyl group in one molecule is also referred to as an “acrylic monomer”. The acrylic polymer in this specification is defined as a polymer containing monomer units derived from an acrylic monomer.

  The pressure-sensitive adhesive sheet disclosed herein includes a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive having an acrylic polymer as a base polymer. Here, the base polymer refers to a main component of a rubber-like polymer (a polymer exhibiting rubber elasticity in a temperature range near room temperature) contained in the pressure-sensitive adhesive layer. Further, in this specification, “main component” refers to a component contained in an amount exceeding 50% by weight unless otherwise specified. The pressure-sensitive adhesive sheet disclosed herein may be a pressure-sensitive adhesive sheet with a substrate having the pressure-sensitive adhesive layer on one or both sides of the substrate (support), and the pressure-sensitive adhesive layer is held by a release liner. It may be a substrate-less pressure-sensitive adhesive sheet such as a form. The concept of the pressure-sensitive adhesive sheet herein may include what are called pressure-sensitive adhesive tapes, pressure-sensitive adhesive labels, pressure-sensitive adhesive films and the like. The pressure-sensitive adhesive sheet disclosed herein may be in the form of a roll or a single sheet. Or the adhesive sheet of the form processed into various shapes may be sufficient.

  The pressure-sensitive adhesive sheet disclosed herein may have, for example, a cross-sectional structure schematically shown in FIGS. Among these, FIG. 1, FIG. 2 is a structural example of the adhesive sheet with a base material of a double-sided adhesive type. The pressure-sensitive adhesive sheet 1 shown in FIG. 1 is provided with pressure-sensitive adhesive layers 21 and 22 on each surface (both non-peelable) of the base material 10, and these pressure-sensitive adhesive layers have at least the pressure-sensitive adhesive layer side as a release surface. It has the structure protected by the release liners 31 and 32 respectively. The pressure-sensitive adhesive sheet 2 shown in FIG. 2 is provided with pressure-sensitive adhesive layers 21 and 22 on each surface (both non-peelable) of the base material 10, respectively. It has a configuration protected by the release liner 31. This type of pressure-sensitive adhesive sheet 2 has a configuration 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 pressure-sensitive adhesive sheet without a base material. The pressure-sensitive adhesive sheet 3 shown in FIG. 3 has a configuration in which both surfaces 21A and 21B of a base material-less pressure-sensitive adhesive layer 21 are protected by release liners 31 and 32 having at least a pressure-sensitive adhesive layer side, respectively. The pressure-sensitive adhesive sheet 4 shown in FIG. 4 has a structure in which one surface (adhesive surface) 21A of the base material-less pressure-sensitive adhesive layer 21 is protected by a release liner 31 whose both surfaces are release surfaces. When wound, the other surface (adhesive surface) 21B of the pressure-sensitive adhesive layer 21 is brought into contact with the back surface of the release liner 31 so that the other surface 21B is also protected by the release liner 31.

  5 and 6 are configuration examples of a single-sided adhesive type adhesive sheet with a substrate. The pressure-sensitive adhesive sheet 5 shown in FIG. 5 is provided with a pressure-sensitive adhesive layer 21 on one surface 10A (non-peelable) of the substrate 10, and at least the surface (pressure-sensitive adhesive surface) 21A of the pressure-sensitive adhesive layer 21 is peeled off at the pressure-sensitive adhesive layer side. It has the structure protected with the release liner 31 used as the surface. The pressure-sensitive adhesive sheet 6 shown in FIG. 6 has a configuration in which a pressure-sensitive adhesive layer 21 is provided on one surface 10 </ b> A (non-peelable) of the substrate 10. The other surface 10B of the substrate 10 is a release surface. When the adhesive sheet 6 is wound, the adhesive layer 21 comes into contact with the other surface 10B, and the surface (adhesive surface) 21B of the adhesive layer is the substrate. 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 oleic acid permeation amount of the pressure-sensitive adhesive layer is 1.5 g / g or more and 5.0 g / g or less. It is 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 formula: γ = γ ^d + γ ^p + γ ^h ; Here, γ ^d , γ ^p and γ ^h in the above formulas represent a surface free energy dispersion component, a polar component and a hydrogen bonding component, respectively. The surface free energy γ of the pressure-sensitive adhesive layer was determined by using the water, diiodomethane, and 1-bromonaphthalene as probe liquids, and the contact angle of each probe liquid from Kitasaki-Hatashiki (Japan Adhesion Association Journal, Vol. 8, No. 3, 1972 , pp.131-141). The contact angle can be measured using a commercially available contact angle meter. As a contact angle meter, the product name “CA-X” manufactured by Kyowa Interface Science Co., Ltd. can be used. The droplet method is used for measurement, and the contact angle is measured from the droplet shape after 1500 ms of droplet landing. A similar method is employed in the embodiments described later.

  When the surface free energy γ of the pressure-sensitive adhesive layer is lowered, the wettability of the pressure-sensitive adhesive layer to the adherend is improved, and the adhesiveness at the interface (adhesion interface) between the pressure-sensitive adhesive layer and the adherend tends to be increased. . Thus, by increasing the adhesiveness of the adhesive interface, it is possible to suppress the infiltration of oil from the outer edge of the pressure-sensitive adhesive sheet into the adhesive interface.

In relation to the surface free energy of the adherend, when the surface free energy of the pressure-sensitive adhesive layer is lower, the wettability to the adherend tends to be higher. 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 adherends of various 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 monomer components constituting the acrylic polymer (the types and amounts of main monomers and sub-monomers used as necessary), the types of tackifying resins, and It can be adjusted according to the amount used.

(Oleic acid penetration)
In the technique disclosed herein, the amount of oleic acid permeation of 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 pressure-sensitive adhesive layer having a thickness of 20 μm on the 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 said single-sided adhesive sheet can be prepared by producing the said adhesive layer on a suitable peeling surface in the form of a base material-less, and bonding this to the non-peeling surface of the said PET film. The single-sided pressure-sensitive adhesive sheet is cut into a square shape having a length of 25 mm and a width of 25 mm to produce a test piece.
On the surface of a stainless steel plate (SUS304BA plate), two marked lines that intersect 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, a measurement sample is prepared by attaching the adhesive surface of the test piece to the stainless steel plate on which the marked line is drawn. At this time, the test piece is aligned and pasted so that the vertical and horizontal center lines of the test piece coincide with the marked line.
The measurement sample is held for 12 hours in an environment of 23 ° C. and 50% RH. Next, after measuring the weight (weight before immersion) of the measurement sample, the measurement sample is immersed in an oleic acid bath and kept in an environment of 40 ° C. and 90% RH for two weeks. Then, the said measurement sample is pulled up from an oleic acid bath, the oleic acid adhering to circumference | surroundings is wiped off lightly, and the weight (post-immersion weight) of this measurement sample is measured. From the measured value obtained, the following formula:
Oleic acid penetration amount = (weight after immersion−weight before immersion) / weight of adhesive before penetration;
Thus, the oleic acid permeation amount (g / g) per 1 g of the pressure-sensitive adhesive layer is calculated. A similar evaluation method is employed in the examples described later.

  A pressure-sensitive adhesive layer having an oleic acid penetration amount of 1.5 g / g or more exhibits better oil content retention than a pressure-sensitive adhesive layer having a lower oleic acid penetration amount. As a result, even if oil enters the adhesive interface from the outer edge of the pressure-sensitive adhesive sheet, the oil interface can be kept in a state where the oil content is low by absorbing the oil into the layer (bulk) of the pressure-sensitive adhesive layer. Thereby, the fall of the adhesive force by the oil component which exists in an adhesion interface can be suppressed effectively. In addition, by absorbing oil that has entered the adhesive interface from the outer edge of the pressure-sensitive adhesive sheet into the bulk of the pressure-sensitive adhesive layer, it is possible to suppress an event in which the oil component proceeds to the inner side of the adhesive sheet sticking range along the adhesive interface. . That is, the penetration distance of oil from the outer edge of the pressure-sensitive adhesive sheet can be suppressed. Thereby, it can suppress that the influence of an oil component reaches an inner part from the outer edge of an adhesive sheet, and can maintain the adhesive force as the whole adhesive sheet better. Furthermore, when the bulk of the pressure-sensitive adhesive layer absorbs oil appropriately, the pressure-sensitive adhesive layer is softened. As a result, the peel strength can be increased by the deformation energy of the pressure-sensitive adhesive layer. This can also advantageously contribute to the suppression of lowering of the adhesive strength due to oil. In this way, by suppressing the intrusion of oil from the outer edge of the pressure-sensitive adhesive sheet to the adhesive interface and making it easy to absorb the infiltrated oil from the adhesive interface into the bulk of the pressure-sensitive adhesive layer, Reduction can be effectively suppressed.

  From the viewpoint of better exerting the above-described effects, the oleic acid penetration amount of 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 implemented in an embodiment in which the oleic acid penetration amount of the pressure-sensitive adhesive layer is about 2.0 g / g or more (further about 2.5 g / g or more, for example, about 3.0 g / g or more). Can be done. The upper limit of the oleic acid penetration amount of the pressure-sensitive adhesive layer is suitably about 5.0 g / g or less from the viewpoint of preventing the pressure-sensitive adhesive layer from absorbing too much oil and causing the pressure-sensitive adhesive to protrude, and is about 4 or less. It is preferable to set it to 0.5 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 oleic acid permeation amount of 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. / G or less. The amount of oleic acid permeation of the pressure-sensitive adhesive layer is, for example, the composition of monomer components constituting the acrylic polymer (the types and amounts of main monomers to be described later and submonomer used if necessary), the molecular weight of the acrylic polymer, It can be adjusted according to the type and amount of the crosslinking agent, the type and amount of tackifier resin, and the like.

By the oleic acid permeability evaluation, it is possible to evaluate the anti-sticking 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 protruding distance (extruding width) of the adhesive from the outer edge of the PET film is measured visually. A similar evaluation method is employed in the examples described later.
In a preferred embodiment, the protruding width of the pressure-sensitive adhesive may be less than about 1.0 mm (more preferably about 0.5 mm or less, more preferably about 0.3 mm or less). Such a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having an anti-extrusion property is suitable for applications that require joining in a limited space, for example, applications that fix members in portable devices. The protrusion width of the adhesive is preferably as small as possible, and ideally it is about 0 mm.

Further, the penetration distance of oleic acid into the pressure-sensitive adhesive sheet can be measured by the oleic acid permeability evaluation. Specifically, after pulling up the measurement sample from the oleic acid bath and lightly wiping off the oleic acid adhering to the periphery, the length of the mark on the stainless steel disappeared from the outer edge of the PET film to the inside. Measure and set the length as the penetration distance of oleic acid. A similar measurement method is employed in the examples described later.
In a preferred embodiment, the penetration distance of the oleic acid is suitably about 0.5 mm or more, more preferably about 0.8 mm or more, and further preferably about 1.0 mm or more. The penetration distance of the oleic acid is preferably about 7.0 mm or less, more preferably about 5.0 mm or less, and 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 oleic acid permeation distance is in the above range, the preferred oleic acid permeation amount disclosed herein tends to be suitably 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 polymer of a monomer raw material that includes an alkyl (meth) acrylate as a main monomer and can further include a submonomer that is copolymerizable with the main monomer. Here, the main monomer refers to a component contained in the monomer raw material in an amount exceeding 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. R ² is a chain alkyl group having 1 to 20 carbon atoms (hereinafter, such a range of the number of carbon atoms may be represented as “C _1-20 ”). From the viewpoint of the storage elastic modulus and the like of the pressure-sensitive adhesive, an alkyl (meth) acrylate in which R ² is a C _1-14 chain alkyl group is preferable, and R ² is an alkyl (meta) that is a C _1-10 chain alkyl group. ) 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. (Meth) 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 (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, nonadecyl (meth) acrylate, And eicosyl (meth) acrylate. These alkyl (meth) acrylates can 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 in the alkyl (meth) acrylate contained in the monomer component is 75% by weight. % Or more (usually 85% by weight or more, for example 90% by weight or more, and further 95% by weight or more). The technique disclosed here can be implemented, for example, in an embodiment in which the alkyl (meth) acrylate contained in the monomer component is BA alone, an embodiment in which 2EHA is alone, an embodiment in which BA and 2EHA are formed, or the like.

  When the monomer component includes 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 (for example, 1/99 or more and 40/60 or less), or 20/80 or less, or 10/90 or less (for example, 1/99). 10/90 or less).

The technique disclosed here can be preferably implemented in an embodiment 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 having C _7-10 alkyl (meth) acrylate as a main monomer generally has high affinity for oil. Utilizing this high affinity for oil, the oil that has entered the adhesive interface from the outer edge of the pressure-sensitive adhesive sheet is absorbed properly into the pressure-sensitive adhesive layer, effectively reducing the adhesive strength due to contact with the oil. Can be suppressed. The proportion of C _7-10 alkyl (meth) acrylate in the monomer component may be 60% by weight or more, or 70% by weight or more (for example, 80% by weight or more, and further 85% by weight or more). . The upper limit of the proportion of C _7-10 alkyl (meth) acrylate in 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 characteristics, it is appropriate that the proportion 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 preferably less than 95% by weight, for example, 93% by weight or less. _C7-10 alkyl (meth) acrylate can be used individually by 1 type or in combination of 2 or more types. 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 here can also be preferably implemented 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. In this way, even when an acrylic polymer having a C _1-6 alkyl (meth) acrylate as a main monomer is used as a base polymer, for example, the type and amount of a secondary monomer, the type and amount of a crosslinking agent, a tackifier resin By appropriately setting the conditions such as the type and the amount used, a pressure-sensitive adhesive layer exhibiting a suitable amount of oleic acid permeation disclosed herein can be obtained. The proportion of the 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 proportion of C _1-6 alkyl (meth) acrylate in 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 characteristics, it is appropriate that the proportion of the C _1-6 alkyl (meth) acrylate in 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. C _1-6 alkyl (meth) acrylates may be used alone or in combination of two or more. A preferred example of C _1-6 alkyl (meth) acrylate is BA.

A submonomer having copolymerizability with the main monomer, alkyl (meth) acrylate, can be useful for introducing a crosslinking point into the acrylic polymer or increasing the cohesive strength of the acrylic polymer. As the secondary monomer, for example, the following functional group-containing monomers can be used singly or in combination of two or more.
Carboxy group-containing monomers: for example, ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth) acrylate, crotonic acid, and isocrotonic acid; maleic acid, itaconic acid, citraconic acid, etc. Ethylenically unsaturated dicarboxylic acid and its anhydride (maleic anhydride, itaconic anhydride, etc.).
Hydroxyl group-containing monomers: For example, 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 monomer: For example, (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-butyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methylolpropane (meth) acrylamide, N-methoxymethyl (Meth) 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.
Cyano group-containing monomer: 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-vinylpyrazine, N-vinyl Pyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, N- (meth) acryloylmorpholine.
Alkoxysilyl group-containing monomer: For example, 3- (meth) acryloxypropyltrimethoxysilane, 3- (meth) acryloxypropyltriethoxysilane, 3- (meth) acryloxypropylmethyldimethoxysilane, 3- (meth) acryloxy Propylmethyldiethoxysilane.

  The said functional group containing monomer can be used individually by 1 type or in combination of 2 or more types. Among the functional group-containing monomers, introduction of a crosslinking point and improvement of cohesion as described above can be suitably realized, and therefore a carboxy group-containing monomer and a hydroxyl group-containing monomer can be preferably used. Preferable examples of the carboxy group-containing monomer include acrylic acid and methacrylic acid. Any of these may be used alone or in combinations 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. A hydroxyl-containing monomer can be used individually by 1 type or in combination of 2 or more types. A carboxy group-containing monomer and a hydroxyl group-containing monomer may be used in combination.

  When the monomer component constituting the acrylic polymer includes a functional group-containing monomer, the ratio of the functional group-containing monomer in the monomer component is not particularly limited. Usually, from the viewpoint of obtaining appropriate cohesiveness at the preferred oleic acid penetration amount disclosed herein, the proportion of the functional group-containing monomer is 0.1 wt% or more and 40 wt% or less (eg, 0.5 wt% or more and 30 wt% % 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 proportion of the carboxy group-containing monomer in the monomer component is usually 0.5% by weight or more (preferably 1% by weight) from the viewpoint of cohesion and the like. % Or more, for example, 2% by weight or more), or 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 an embodiment in which the monomer component contains about 3% by weight or more (preferably about 5% by weight or more) of a carboxy group-containing monomer. According to the acrylic polymer having such a monomer composition, the absorbed oleic acid can be satisfactorily held in the pressure-sensitive adhesive layer (bulk) by the interaction between the carboxy group of the polymer and oleic acid. Thereby, an adhesion interface can be maintained in a state with few oleic acids, and the fall of the adhesive force by the penetration | invasion of an oleic acid can be suppressed effectively. From this viewpoint, 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 may be about 9% by weight. % Or more. The upper limit of the content of the carboxy group-containing monomer is not particularly limited, but it is usually suitably 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 having C _7-10 alkyl (meth) acrylate as a main monomer), a carboxy group-containing monomer (for example, a monomer component) Increasing the content of AA) is particularly effective.

  When the monomer component constituting the acrylic polymer includes a hydroxyl group-containing monomer, the content thereof is usually about 0.001% by weight to about 10% by weight of the monomer component (for example, about 0.01% by weight to about 5% by weight). % By weight 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, other copolymer components other than the above-mentioned submonomer can be used for the purpose of increasing the cohesive force of the acrylic polymer. Examples of such copolymerization components include vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl laurate; aromatic vinyl compounds such as styrene, substituted styrene (α-methylstyrene, etc.), vinyl toluene; cyclohexyl (meta ) Acrylate, cyclopentyl (meth) acrylate, isobornyl (meth) acrylate and other cycloalkyl (meth) acrylates; aryl (meth) acrylate (eg phenyl (meth) acrylate), aryloxyalkyl (meth) acrylate (eg phenoxyethyl (meth) ) Acrylate), arylalkyl (meth) acrylate (eg benzyl (meth) acrylate) and other aromatic ring-containing (meth) acrylates; ethylene, propylene, isoprene, butadiene, isobutylene Olefinic monomers such as: Chlorine-containing monomers such as vinyl chloride and vinylidene chloride; Isocyanate group-containing monomers such as 2- (meth) acryloyloxyethyl isocyanate; Alkoxy groups such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate Containing monomers; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, etc. 2 or more (for example, 3 or more) polymerization in one molecule Polyfunctional monomer having a functional group (for example, (meth) acryloyl group); and the like.
The amount of the other copolymer component is not particularly limited as long as it is appropriately selected depending on the purpose and application, but it is usually preferably 10% by weight or less of the monomer component. For example, when a vinyl ester monomer (for example, vinyl acetate) is used as the other copolymer 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. In addition, it is appropriate that the amount is about 20% by weight or less (usually about 10% by weight or less).

The composition of the monomer component constituting the acrylic polymer is designed so that the glass transition temperature (Tg) of the acrylic polymer is about −15 ° C. or lower (for example, about −70 ° C. or higher and −15 ° C. or lower). Is appropriate. Here, the Tg of the acrylic polymer refers to the Tg determined by the Fox equation based on the composition of the monomer component. The formula of Fox is a relational expression between Tg of a copolymer and glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below.
1 / Tg = Σ (Wi / Tgi)
In the above Fox equation, Tg is the glass transition temperature (unit: K) of the copolymer, Wi is the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), 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 the calculation of Tg, the values described in known materials are 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

  Regarding the glass transition temperature of homopolymers of monomers other than those exemplified above, the values described in “Polymer Handbook” (3rd edition, John Wiley & Sons, Inc., 1989) are used. The highest value is adopted for the monomer whose 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 is used.
Specifically, a reactor equipped with a thermometer, a stirrer, a nitrogen introduction tube and a reflux condenser is charged with 100 parts by weight of monomer, 0.2 part by weight of 2,2′-azobisisobutyronitrile and acetic acid as a polymerization solvent. 200 parts by weight of ethyl is added and stirred 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. Next, the mixture is cooled to room temperature to obtain a homopolymer solution having a solid concentration of 33% by weight. Next, this homopolymer solution is cast-coated on a release liner and dried to prepare a test sample (sheet-like 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 at a frequency of 1 Hz using a viscoelasticity tester (manufactured by TA Instruments Japan, model name “ARES”). The viscoelasticity is measured by the shear mode at a temperature rising rate of −70 ° C. to 150 ° C. and 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, from the viewpoint of adhesion to an adherend or a substrate film, the Tg of the acrylic polymer is advantageously about −25 ° C. or less, preferably about −35 ° C. or less. More preferably, it is about −40 ° C. or less. From the viewpoint of cohesive strength of the pressure-sensitive adhesive layer, the acrylic polymer Tg is usually about −75 ° C. or higher, and preferably about −70 ° C. or higher. The technique disclosed herein can be preferably implemented in an embodiment in which the Tg of the acrylic polymer is about −65 ° C. or higher and about −40 ° C. or lower (eg, about −65 ° C. or higher and about −45 ° C. or lower). In a preferred embodiment, the acrylic polymer may have a Tg of about −65 ° C. or more and about −55 ° C. or less. The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (that is, the type and amount ratio of monomers used for 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 acrylic polymers, such as solution polymerization method, emulsion polymerization method, bulk polymerization method, suspension polymerization method, photopolymerization method, etc. Can be adopted as appropriate. For example, a solution polymerization method can be preferably employed. As a monomer supply method when performing solution polymerization, a batch charging method, a continuous supply (dropping) method, a divided supply (dropping) method, or the like that supplies all monomer raw materials at once can be appropriately employed. The polymerization temperature can be appropriately selected according to the type of monomer and solvent to be used, the type of 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 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 the solution polymerization can be appropriately selected from conventionally known organic solvents. For example, aromatic compounds such as toluene and xylene (for example, aromatic hydrocarbons); acetates such as ethyl acetate and butyl acetate; aliphatic or alicyclic hydrocarbons such as hexane, cyclohexane and methylcyclohexane; 1 Halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (for example, monohydric alcohols having 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone and acetone Any one type of solvent selected from the group or the like, or a mixed solvent of two or more types can be used.

  The initiator used for the polymerization can be appropriately selected from conventionally known polymerization initiators according to the type of the 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 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 initiators in combination with peroxides and reducing agents; Can be mentioned. Such a polymerization initiator can be used individually by 1 type or in combination of 2 or more types. 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 solution polymerization, a polymerization reaction liquid in a form in which an acrylic polymer is dissolved in an organic solvent is obtained. The pressure-sensitive adhesive layer in the technology disclosed herein may be formed from a pressure-sensitive adhesive composition containing the above-mentioned polymerization reaction liquid or an acrylic polymer solution obtained by subjecting the reaction liquid to an appropriate post-treatment. As said acrylic polymer solution, what prepared the said polymerization reaction liquid to the appropriate viscosity (concentration) as needed 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 (Mw) of the acrylic polymer is not particularly limited, and may be, for example, about 10 × 10 ⁴ or more and 500 × 10 ⁴ or less. Here, Mw refers to a value in terms of standard polystyrene 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 viewpoints 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. 150 × 10 ⁴ or less). In a preferred embodiment, the Mw of the acrylic polymer may be about 75 × 10 ⁴ or more and about 140 × 10 ⁴ or less (eg, about 90 × 10 ⁴ or more and 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 crosslinking agent as an optional component. The pressure-sensitive adhesive layer in the technology disclosed herein contains the crosslinking agent in a form after the crosslinking reaction, a form before the crosslinking reaction, a partially crosslinked reaction, an intermediate or composite form thereof, and the like. obtain. The above-mentioned crosslinking agent is usually contained in the pressure-sensitive adhesive layer exclusively in the form after the crosslinking reaction.

  The kind in particular of a crosslinking agent is not restrict | limited, It can select from a conventionally well-known crosslinking agent suitably and can be used. Examples of such crosslinking agents include isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, melamine crosslinking agents, carbodiimide crosslinking agents, hydrazine crosslinking agents, amine crosslinking agents, Examples thereof include peroxide-based crosslinking agents, metal chelate-based crosslinking agents, metal alkoxide-based crosslinking agents, and metal salt-based crosslinking agents. A crosslinking agent can be used individually by 1 type or in combination of 2 or more types. The kind and amount of the crosslinking agent to be used can be set so that, for example, a pressure-sensitive adhesive layer showing a preferable oleic acid penetration amount disclosed herein is formed. Examples of the crosslinking agent that can be preferably used in the technology disclosed herein include an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent.

  As the isocyanate-based crosslinking agent, a polyfunctional isocyanate (refers to a compound having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. An isocyanate type crosslinking agent can be used individually by 1 type or in combination of 2 or more types.

Examples of the polyfunctional isocyanate include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates and the like.
Specific examples of the aliphatic polyisocyanates include 1,2-ethylene diisocyanate; tetramethylene diisocyanate such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, 1,4-tetramethylene diisocyanate; -Hexamethylene diisocyanate such as hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,5-hexamethylene diisocyanate; Examples include 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and lysine diisocyanate.

  Specific examples of alicyclic polyisocyanates include isophorone diisocyanate; cyclohexyl diisocyanates such as 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, 1,4-cyclohexyl diisocyanate; 1,2-cyclopentyl diisocyanate, 1,3 -Cyclopentyl diisocyanate such as cyclopentyl diisocyanate; hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and the like.

  Specific examples of the aromatic polyisocyanates include 2,4-tolylene diisocyanate, 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-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxy Diphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, xylylene-1,3-diisocyanate.

  Preferable polyfunctional isocyanates include polyfunctional isocyanates having an average of 3 or more isocyanate groups per molecule. Such trifunctional or higher functional isocyanate is a bifunctional or trifunctional or higher polymer (for example, dimer or trimer) or derivative (for example, addition reaction between polyhydric alcohol and two or more polyfunctional isocyanates). Product), polymer, and the like. For example, diphenylmethane diisocyanate dimer or trimer, hexamethylene diisocyanate isocyanurate (trimer adduct of isocyanurate structure), reaction product of trimethylolpropane and tolylene diisocyanate, trimethylolpropane and hexamer Examples of the reaction product with methylene diisocyanate include polyfunctional isocyanates such as polymethylene polyphenyl isocyanate, polyether polyisocyanate, and polyester polyisocyanate. As commercial products of such polyfunctional isocyanates, trade names “Duranate TPA-100” manufactured by Asahi Kasei Chemicals Corporation, trade names “Coronate L”, “Coronate HL”, “Coronate HK”, “Coronate HK” manufactured by Tosoh Corporation HX ”,“ Coronate 2096 ”and the like.

  In the embodiment using the isocyanate-based crosslinking agent, the amount used is not particularly limited. The amount of the isocyanate crosslinking agent used can be, for example, about 0.5 parts by weight or more and about 10 parts by weight or less with respect to 100 parts by weight of the acrylic polymer. From the viewpoint of obtaining the preferred oleic acid penetration amount disclosed herein, the amount of the isocyanate crosslinking agent used per 100 parts by weight of the acrylic polymer is usually suitably about 1 part by weight or more, and about 1.5 parts by weight. It is preferable to use at least parts by weight. In addition, the amount of the isocyanate crosslinking agent used per 100 parts by weight of the acrylic polymer is usually about 8 parts by weight or less, and about 5 parts by weight or less (for example, less than about 4 parts by weight). preferable.

  As the epoxy-based crosslinking agent, a compound having two or more epoxy groups in one molecule can be used without particular limitation. An epoxy-based crosslinking agent having 3 to 5 epoxy groups in one molecule is preferable. An epoxy type crosslinking agent can be used individually by 1 type or in combination of 2 or more types.

  Although it does not specifically limit, As a specific example of an epoxy-type crosslinking agent, for example, N, N, N ', N'-tetraglycidyl-m-xylenediamine, 1,3-bis (N, N-diglycidylaminomethyl) ) Cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, and the like. Commercially available epoxy crosslinking agents include trade names “TETRAD-C” and “TETRAD-X” manufactured by Mitsubishi Gas Chemical Company, “Epicron CR-5L” manufactured by DIC, and Nagase ChemteX Corp. Product name “Denacol EX-512”, product name “TEPIC-G” manufactured by Nissan Chemical Industries, Ltd., and the like.

  In the embodiment using the epoxy crosslinking agent, the amount used is not particularly limited. The amount of the epoxy-based crosslinking agent used is, 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 suitably exhibiting the effect of improving the cohesive force, it is usually appropriate that the amount of the epoxy crosslinking agent used is about 0.002 parts by weight or more with respect to 100 parts by weight of the acrylic polymer. 0.005 part by weight or more is preferable, and about 0.008 part by weight or more is more preferable. Further, from the viewpoint of avoiding insufficient oleic acid penetration due to excessive crosslinking, it is usually appropriate that the amount of the epoxy crosslinking agent used is about 0.2 parts by weight or less with respect to 100 parts by weight of the acrylic polymer. Yes, it is preferably about 0.1 parts by weight or less, more preferably less than about 0.05 parts by weight.

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

  One preferred example of the crosslinking agent used in combination with the isocyanate crosslinking agent is an epoxy crosslinking agent. By using a combination of an epoxy-based crosslinking agent and an isocyanate-based crosslinking agent, the preferred oleic acid penetration amount disclosed herein can be suitably realized. Moreover, the cohesive force of an adhesive layer can be further improved, ensuring the adhesiveness with respect to a base film (support base material).

  In an embodiment including an epoxy crosslinking agent and an isocyanate crosslinking agent, the relationship between the content of the epoxy crosslinking agent and the content of the isocyanate crosslinking agent is not particularly limited. The content of the epoxy crosslinking agent can be, for example, about 1/20 or less of the content of the isocyanate crosslinking agent. From the viewpoint of more suitably achieving both adhesion to the adherend and substrate film and cohesion, the content of the epoxy crosslinking agent is suitably about 1/30 or less of the content of the isocyanate crosslinking agent. It is preferably about 1/40 or less (for example, 1/50 or less). Also, from the viewpoint of suitably exhibiting the effect of using an epoxy crosslinking agent and an isocyanate crosslinking agent in combination, the content of the epoxy crosslinking agent is usually about 1/1000 of the content of the isocyanate crosslinking agent. For example, it is appropriate to set it to about 1/500 or more.

(Tackifying resin)
Examples of the tackifier resins include phenolic tackifier resins, terpene tackifier resins, modified terpene tackifier resins, rosin tackifier resins, hydrocarbon tackifier resins, epoxy tackifier resins, and polyamide tackifier resins. 1 type, or 2 or more types selected from well-known various tackifying resins, such as an elastomer type tackifying resin and a ketone type tackifying resin, can be used. By using the tackifying resin, the adhesiveness of the pressure-sensitive adhesive layer to the adherend can be improved, and oil penetration from the outer edge of the pressure-sensitive adhesive sheet to the adhesion interface can be effectively suppressed. For example, the penetration distance of oleic acid in the above-described oleic acid permeability evaluation can be shortened. The type and amount of tackifying resin to be used can be set so that, for example, a pressure-sensitive adhesive layer satisfying the preferred oleic acid penetration amount and surface free energy γ disclosed herein is formed.

Examples of the phenolic tackifier resin include terpene phenol resin, hydrogenated terpene phenol resin, alkylphenol resin, and rosin phenol resin.
A terpene phenol resin refers to a polymer containing a terpene residue and a phenol residue. It is a concept that includes both a phenol-modified product (phenol-modified terpene resin). Preferable examples of terpenes constituting such a terpene phenol resin include monoterpenes such as α-pinene, β-pinene and limonene (including d-form, l-form and d / l-form (dipentene)). Is mentioned. The hydrogenated terpene phenol resin refers to a hydrogenated terpene phenol resin having a structure obtained by hydrogenating such a terpene phenol resin. Sometimes referred to as hydrogenated terpene phenol resin.
The alkylphenol resin is a resin (oil-based phenol resin) obtained from alkylphenol and formaldehyde. Examples of the alkylphenol resin include those of novolak type and resol type.
The rosin phenolic resin is typically a phenol-modified product of rosins or the above-mentioned various rosin derivatives (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 a method in which phenol is added to a rosin or the above-mentioned various rosin derivatives with an acid catalyst and thermally polymerized.
Of these phenolic tackifier resins, terpene phenol resins, hydrogenated terpene phenol resins and alkylphenol resins are preferred, terpene phenol resins and hydrogenated terpene phenol resins are more preferred, and terpene phenol resins are particularly preferred.

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 terpene or a copolymer of two or more terpenes. Examples of the homopolymer of one kind of terpene include an α-pinene polymer, a β-pinene polymer, a dipentene polymer, and the like.
Examples of the modified terpene resin include those obtained by modifying the terpene resin. Specific examples include styrene-modified terpene resins and hydrogenated terpene resins.

  The concept of rosin-based tackifying resin here includes both rosins and rosin derivative resins. Examples of rosins include unmodified rosins such as gum rosin, wood rosin, tall oil rosin (raw rosin); modified rosins modified with hydrogenation, disproportionation, polymerization, etc. Averaged rosin, polymerized rosin, other chemically modified rosins, etc.).

  The rosin derivative resin is typically a derivative of rosins as described above. The concept of the rosin resin here includes derivatives of unmodified rosin and derivatives of modified rosin (including hydrogenated rosin, disproportionated rosin and polymerized rosin). For example, rosin esters such as an unmodified rosin ester that is an ester of an unmodified rosin and an alcohol, and a modified rosin ester that is an ester of a modified rosin and an alcohol; for example, an rosin modified with an unsaturated fatty acid. 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 Rosin alcohols obtained by reducing the carboxy group of fatty acid-modified rosin esters); for example, rosins or metal salts of the various rosin derivatives described above. Specific examples of rosin esters include unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.) methyl ester, triethylene glycol ester, glycerin ester, pentaerythritol ester and the like.

  Examples of hydrocarbon tackifying resins include aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic / aromatic petroleum resins (styrene-olefin copolymers, etc. ), Various hydrocarbon resins such as aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, coumarone indene resins, and the like.

  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 used. In the technology disclosed herein, the tackifying resin having the softening point is more than 50% by weight (more preferably more than 70% by weight, for example, more than 90% by weight) of the entire tackifying resin contained in the pressure-sensitive adhesive layer. It can be preferably implemented in some embodiments. For example, a phenolic 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 (or 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 an adherend or a substrate film, in one embodiment, a tackifying resin having a softening point of about 200 ° C. or lower (more preferably about 180 ° C. or lower) can be preferably used. In addition, the softening point of tackifying resin can be measured based on the softening point test method (ring ball method) prescribed | regulated to JISK2207.

  In the embodiment using the tackifying resin, the content of the tackifying resin is not particularly limited. The content of the tackifying resin can be, for example, about 5 parts by weight or more with respect to 100 parts by weight of the acrylic polymer, and can be about 8 parts by weight or more (for example, about 10 parts by weight or more). The technique disclosed here can also be preferably implemented in an embodiment in which the content of the tackifying resin with respect to 100 parts by weight of the acrylic polymer is about 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 viewpoints of compatibility with the acrylic polymer and initial adhesiveness, in one embodiment, the content of the tackifying resin with respect to 100 parts by weight of the acrylic polymer is usually suitably about 70 parts by weight or less. The amount 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 using the tackifying resin, 50% by weight or less of the total amount of the tackifying resin is preferably selected from tackifying resins other than the rosin-based tackifying resin. The proportion of the rosin-based tackifying resin in the total amount of the tackifying 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 tackifying resin used is preferably less than about 10 parts by weight and more preferably less than 5 parts by weight with respect to 100 parts by weight of the acrylic polymer. The use of a rosin-based tackifying resin tends to cause an excessive increase in the amount of oleic acid permeation depending on the type and amount used. Also, the surface free energy γ tends to increase due to the use of the rosin-based tackifying resin. By restricting the amount of the rosin-based tackifying resin used 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 oleic acid penetration amount and the surface free energy γ are in a suitable range. The technique disclosed here can be preferably implemented even in an embodiment in which the pressure-sensitive adhesive layer does not substantially contain a rosin-based tackifying resin.

  As a preferable aspect, the aspect in which the said tackifying resin contains 1 type, or 2 or more types of phenol type tackifying resin (for example, terpene phenol resin) is mentioned. Phenol-based tackifier resins tend to have a lower affinity for oil than, for example, rosin-based tackifier resins. Therefore, the use of phenolic tackifying resin exerts the effect of improving the adhesion of the pressure-sensitive adhesive layer to the adherend (for example, the effect of shortening the permeation distance) while suppressing an excessive increase in the amount of oleic acid permeation. obtain. The technology disclosed herein can be preferably implemented in a mode in which, for example, about 25% by weight or more (more preferably about 30% by weight or more) of the total amount of the tackifying resin is a terpene phenol resin. About 50% by weight or more of the total amount of the tackifying resin may be terpene phenol resin, and about 80% by weight or more (for example, about 90% by weight or more) may be terpene phenol resin. Substantially all of the tackifying resin (for example, about 95% by weight to 100% by weight, and further about 99% by weight to 100% by weight) may be a terpene phenol resin. The content of the phenolic tackifying resin (for example, terpene phenolic 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 suitable that the amount is about 8 parts by weight or more and about 35 parts by weight or less.

Although it does not specifically limit, As a tackifying resin in the technique disclosed here, a tackifying resin having a hydroxyl value of less than 30 mgKOH / g (for example, less than 20 mgKOH / g) can be used. Hereinafter, a tackifier resin having a hydroxyl value of less than 30 mg KOH / g may be referred to as a “low hydroxyl value resin”. The hydroxyl value of the low hydroxyl value resin may be about 15 mgKOH / g or less, or about 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, terpene phenol resin) is preferably used in combination with an acrylic polymer having a C _7-10 alkyl (meth) acrylate as a main monomer, for example, and is an adhesive layer for an adherend. The effect of improving the adhesiveness (for example, the effect of shortening the permeation distance) can be satisfactorily exhibited.

Although not particularly limited, a tackifier resin having a hydroxyl value of 30 mgKOH / g or more can be used as the tackifier resin in the technology disclosed herein. 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 an 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. Such a tackifying resin containing a high hydroxyl value resin (for example, a terpene phenol resin) is preferably used in combination with an acrylic polymer having a C _1-6 alkyl (meth) acrylate as a main monomer, for example. The effect of improving the adhesiveness of the pressure-sensitive adhesive layer to the body (for example, the effect of shortening the permeation distance) can be exhibited well.

Here, as the value of the hydroxyl value, a value measured by a potentiometric titration method defined in JIS K0070: 1992 can be adopted. The specific measurement method is as follows.
[Measurement method of hydroxyl value]
1. Reagent (1) As an acetylating reagent, about 12.5 g (about 11.8 mL) of acetic anhydride is taken, and pyridine is added thereto to make a total volume of 50 mL, and the mixture is sufficiently stirred. Alternatively, about 25 g (about 23.5 mL) of acetic anhydride is taken, and pyridine is added thereto to make a total volume of 100 mL, and the mixture is sufficiently stirred.
(2) As a measuring reagent, a 0.5 mol / L potassium hydroxide ethanol solution is used.
(3) Prepare toluene, pyridine, ethanol and distilled water.
2. Operation (1) About 2 g of a sample is accurately weighed in a flat bottom flask, 5 mL of an acetylating reagent and 10 mL of pyridine are added, and an air cooling tube is attached.
(2) The flask was heated in a bath at 100 ° C. for 70 minutes, allowed to cool, and 35 mL of toluene was added as a solvent from the top of the condenser and stirred, and then 1 mL of distilled water was added and stirred to acetic anhydride. Disassemble. Heat again in the bath for 10 minutes to complete decomposition and allow to cool.
(3) Wash the cooling tube with 5 mL of ethanol and remove it. Next, 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 with 0.5 mol / L potassium hydroxide ethanol solution. The inflection point of the obtained titration curve is the end point.
(6) In the blank test, the above (1) to (5) are performed without putting a sample.
3. Calculation The hydroxyl value is calculated by the following formula.
Hydroxyl value (mgKOH / g) = [(BC) × f × 28.05] / S + D
here,
B: Amount of 0.5 mol / L potassium hydroxide ethanol solution used for the blank test (mL),
C: The amount of 0.5 mol / L potassium hydroxide ethanol solution used for the sample (mL),
f: factor of 0.5 mol / L potassium hydroxide ethanol solution,
S: weight of the sample (g),
D: Acid value,
28.05: 1/2 of the molecular weight of potassium hydroxide 56.11,
It is.

  As low hydroxyl value resin and high hydroxyl value resin, what has the applicable hydroxyl value among the various tackifying resin mentioned above can be used. The low hydroxyl value resin and the high hydroxyl value resin can be used singly or in combination of two or more. For example, a phenolic tackifier resin having a hydroxyl value of less than 30 mg KOH / g can be preferably employed as the low hydroxyl value resin. For example, a phenolic tackifier resin having a hydroxyl value of 30 mgKOH / g or more can be preferably used as the high hydroxyl value resin. Of these, terpene phenol resins are preferred. The terpene phenol resin is advantageous because the hydroxyl value can be arbitrarily controlled by the copolymerization ratio of phenol.

(Other additives)
In addition to the above-described components, the pressure-sensitive adhesive composition includes a leveling agent, a crosslinking aid, a plasticizer, a softener, an antistatic agent, an anti-aging agent, an ultraviolet absorber, an antioxidant, and a light stabilizer as necessary. Various additives that are common in the field of pressure-sensitive adhesives may be included. About such various additives, conventionally well-known things can be used by a conventional method, and since it does not characterize this invention in particular, detailed description is abbreviate | 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 pressure-sensitive adhesive composition, or an active energy ray-curable pressure-sensitive adhesive composition. . The water-based pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition in a form containing a pressure-sensitive adhesive (pressure-sensitive adhesive layer forming component) in a water-based solvent (water-based solvent), and is typically dispersed in water. What is called 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. Moreover, a solvent-type adhesive composition means the adhesive composition of the form which contains an adhesive in an organic solvent. The technique disclosed herein can be particularly preferably implemented in an aspect 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 substrate and drying it can be employed. Also, a method for forming a pressure-sensitive adhesive layer on the surface by applying a pressure-sensitive adhesive composition to a surface having a peelable property (peeling surface) and drying it, and transferring the pressure-sensitive adhesive layer to a non-peelable substrate (Transfer method) may be adopted. From the viewpoint of productivity, the transfer method is preferred. As the release surface, the surface of the release liner, the back surface of the substrate after the release treatment, 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, for example, a regular or random pattern such as a dot or stripe. The formed adhesive layer may be sufficient.

The pressure-sensitive adhesive composition can be applied 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 or curtain coating.
From the viewpoint of promoting the crosslinking reaction and improving the production efficiency, the pressure-sensitive adhesive composition is preferably dried under heating. A drying temperature can be about 40-150 degreeC, for example, and it is preferable to usually be about 60-130 degreeC. After drying the pressure-sensitive adhesive composition, further aging is performed for the purpose of adjusting the component transfer in the pressure-sensitive adhesive layer, progress of the crosslinking reaction, alleviating the distortion that may exist in the base film or the pressure-sensitive adhesive layer, etc. Also good.

The thickness of the pressure-sensitive adhesive layer is not particularly limited. From the viewpoint of avoiding an excessively thick adhesive sheet, the thickness of the adhesive layer is usually about 100 μm or less, preferably about 70 μm or less, more preferably about 50 μm or less, more preferably about 30 μm or less. It 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 the pressure-sensitive adhesive per area of the pressure-sensitive adhesive sheet is small, it is particularly effective to set the oleic acid permeation amount of the pressure-sensitive adhesive layer to a predetermined value or more. It 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 be about 4 μm or more, preferably about 6 μm or more, more preferably about 10 μm or more (for example, About 15 μm or more).
The technique disclosed herein can be suitably implemented, for example, in the form of an adhesive sheet having an adhesive layer having a thickness of about 10 μm to about 25 μm (preferably about 15 μm to about 22 μm). A pressure-sensitive adhesive sheet having such a thickness of the pressure-sensitive adhesive layer on both sides of the substrate is preferred.

(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 is usually suitably 30% or more. % Or more is preferable. By increasing the gel fraction of the pressure-sensitive adhesive layer within an appropriate range, an appropriate amount of oleic acid permeation disclosed herein tends to be realized. On the other hand, if the gel fraction is too high, the amount of oleic acid permeation may tend to be insufficient. From this viewpoint, the gel fraction of the pressure-sensitive adhesive layer is preferably 90% or less, more preferably 80% or less, and further preferably 70% or less (for example, 65% or less).

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

[Gel fraction measurement method]
About 0.1 g of a pressure-sensitive adhesive sample (weight Wg ₁ ) is wrapped in a purse-like shape with a porous polytetrafluoroethylene membrane (weight Wg ₂ ) having an average pore diameter of 0.2 μm, and the mouth is bound with an octopus thread (weight Wg ₃ ). As the porous polytetrafluoroethylene (PTFE) membrane, a trade name “Nitoflon (registered trademark) NTF1122” (average pore diameter 0.2 μm, porosity 75%, thickness 85 μm) available from Nitto Denko Corporation or its Use an equivalent.
This packet is soaked in 50 mL of ethyl acetate and kept at room temperature (typically 23 ° C.) for 7 days to elute only the sol component in the pressure-sensitive adhesive layer outside the membrane, and then the packet is taken out to the outer surface. The adhered ethyl acetate is wiped off, the packet is dried at 130 ° C. for 2 hours, and the weight (Wg ₄ ) of the packet is measured. Gel fraction F _G of the pressure-sensitive adhesive layer is determined by substituting each value into the following formula. A similar method is employed in the embodiments 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, rubber Sheets, foam sheets, metal foils, composites of these, and the like can be used. Examples of resin films include polyolefin films such as polyethylene (PE), polypropylene (PP), and ethylene / propylene copolymers; polyester films such as polyethylene terephthalate (PET); vinyl chloride resin films; vinyl acetate resin films; Resin film; polyamide resin film; fluororesin film; cellophane and the like. Examples of paper include Japanese paper, kraft paper, glassine paper, high quality paper, synthetic paper, top coat paper, and the like. Examples of the fabric include woven fabrics and non-woven fabrics made of various fibrous substances alone or by blending. Examples of the fibrous material include cotton, suf, manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, polyolefin fiber and the like. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of the foam sheet include a foamed polyurethane sheet and a foamed polychloroprene rubber sheet. Examples of the metal foil include aluminum foil and copper foil.

  The term “nonwoven fabric” as used herein refers to a non-woven fabric for pressure-sensitive adhesive sheets mainly used in the field of pressure-sensitive adhesive tapes and other pressure-sensitive adhesive sheets, and is typically a non-woven fabric produced using a general paper machine. (Sometimes called "paper"). Moreover, the resin film here is typically a non-porous resin sheet, and is a concept that is distinguished from, for example, a nonwoven fabric (that is, does not include a nonwoven fabric). The resin film may be an unstretched film, a uniaxially stretched film, or a biaxially stretched film. The surface of the substrate on which the pressure-sensitive adhesive layer is provided may be subjected to a surface treatment such as application of a primer, corona discharge treatment, plasma treatment or the like.

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

  As a base film, what contains a resin film as a base film can be used preferably. The base film is typically a member capable of maintaining its shape independently (independent). The base film in the technology disclosed herein can 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, and a colored layer 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 exceeding 50% by weight). Examples of resin films include polyolefin resin films such as polyethylene (PE), polypropylene (PP), and ethylene / propylene copolymers; polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), etc. Polyester resin film; vinyl chloride resin film; vinyl acetate resin film; polyimide resin film; polyamide resin film; fluororesin film; The resin film may be a rubber film such as a natural rubber film or a butyl rubber film. Of these, a polyester film is preferable from the viewpoint of handling properties 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 a so-called nonwoven fabric or woven fabric (in other words, a concept that excludes nonwoven fabric or woven fabric). is there.

  For the resin film (for example, PET film), a filler (inorganic filler, organic filler, etc.), a colorant, a dispersant (surfactant, etc.), an anti-aging agent, an antioxidant, an ultraviolet ray, as necessary. Various additives such as an absorbent, an antistatic agent, a lubricant, and a plasticizer may be blended. The blending ratio of various additives is usually 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 multilayer 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 multilayer structure, at least one layer (preferably all layers) is preferably a layer having a continuous structure of the resin (for example, polyester resin). The method for producing the resin film is not particularly limited as long as a conventionally known method is appropriately employed. For example, conventionally known general film forming methods such as extrusion molding, inflation molding, T-die casting, and calendar roll molding can be appropriately employed.

  The thickness of the base film disclosed here is not particularly limited. From the viewpoint of avoiding an excessively thick adhesive sheet, the thickness of the base film can be, for example, about 200 μm or less, preferably about 150 μm or less, 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 embodiment, 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 increased even if the total thickness of the pressure-sensitive adhesive sheet is the same. This can be advantageous from the viewpoint of improving the adhesion to the substrate. The lower limit of the thickness of the base film is not particularly limited. From the viewpoint of handling property (handling property) and processability 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 embodiment, the thickness of the base film can be about 6 μm or more, about 8 μm or more, or 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 a primer. 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 to the base film.

<Release liner>
In the technology disclosed herein, a release liner can be used in forming the pressure-sensitive adhesive layer, preparing the pressure-sensitive adhesive sheet, storing the pressure-sensitive adhesive sheet before use, distributing it, and processing the shape. The release liner is not particularly limited. For example, a release liner having a release treatment layer on the surface of a liner substrate such as a resin film or paper, a fluoropolymer (polytetrafluoroethylene, etc.), a polyolefin resin (polyethylene, A release liner made of a low adhesion material such as polypropylene can be used. The release treatment layer may be formed, for example, by surface-treating the liner base material with a release 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 (not including 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, usually about 350 μm or less, and preferably about 250 μm or less (for example, about 200 μm or less). The technique disclosed herein is in the form of an adhesive sheet (typically a double-sided adhesive sheet) having a total thickness of about 150 μm or less (more preferably about 100 μm or less, more preferably about 60 μm or less, for example, about 55 μm or less). It can be preferably implemented. The lower limit of the thickness of the pressure-sensitive adhesive sheet is not particularly limited, but is usually about 10 μm or more, preferably about 20 μm or more, and more preferably about 30 μm or more.

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

[Evaluation of oil-resistant adhesion]
A pressure-sensitive adhesive sheet is cut into a size of 10 mm in width and 100 mm in length to prepare a sample piece. 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 pasted on the one pressure-sensitive adhesive surface, and then cut into the above size.
Under the 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 pressure bonding is performed by reciprocating a 2 kg roller once. The measurement sample was allowed to stand in an environment of 23 ° C. and 50% RH for 30 minutes, and then, using a tensile tester, conditions of a tensile speed of 150 mm / min and a peeling angle of 180 degrees according to JIS Z 0237: 2000. Then, peel strength (N / 10 mm) is measured. This value is defined as the adhesive strength before immersion.
On the other hand, a measurement sample prepared in the same manner as described above was 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. . Thereafter, the measurement sample was lifted from the oleic acid bath, the oleic acid adhering to the surroundings was gently wiped, left in an environment of 23 ° C. and 50% RH for 30 minutes, and peel strength ( N / 10 mm). This value is taken as the adhesive strength after immersion.
From the measured value obtained, the following formula:
Adhesive strength maintenance rate (%) = (adhesive strength after immersion / adhesive strength before immersion) × 100;
To calculate the adhesive strength maintenance rate.
As the tensile tester, for example, “Precision Universal Tester Autograph AG-IS 50N” manufactured by Shimadzu Corporation can be used. A similar evaluation method is employed in the examples described later.

  In the pressure-sensitive adhesive sheet disclosed herein, the adhesive force before immersion is not particularly limited. The pressure-sensitive adhesive sheet according to a preferred embodiment has an adhesive strength before immersion of about 3.0 N / 10 mm or more. Such a pressure-sensitive adhesive sheet exhibiting adhesive strength before immersion has high adhesion to an 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. An 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 strength before immersion is not particularly limited, but is usually about 30 N / 10 mm or less (for example, about 20 N / 10 mm or less).

  Although it does not specifically limit, It is preferable that the said post-immersion adhesive force is 1.0 N / 10mm or more from a viewpoint of suppressing the protrusion of an 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, more preferably about 4.0 N / 10 mm or more (for example, about 5.0 N / 10 mm or more, About 6.0 N / 10 mm or more). Such a pressure-sensitive adhesive sheet exhibiting post-immersion adhesive strength is suitable for, for example, a use for fixing a member that can come into contact with oil.

<Application>
The pressure-sensitive adhesive sheet disclosed here has little decrease in pressure-sensitive adhesive force even when it comes into contact with oil, and the pressure-sensitive adhesive is prevented from protruding. Taking advantage of such 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 a use is a use of fixing a member in various portable devices (portable devices). For example, it is suitable for a fixing application of a member in a portable electronic device. Non-limiting examples of the above-mentioned portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wrist wear devices that are worn on the wrist like watches, clips, straps, etc. Modular type, eyeglass type (monocular type or binocular type, including head mount type), clothing type that attaches to shirts, socks, hats, etc. in the form of accessories, earphones, etc. Earphone type that attaches to the ear, etc.), digital camera, digital video camera, audio equipment (portable music player, IC recorder, etc.), calculator (calculator, etc.), portable game device, electronic dictionary, electronic notebook, electronic book, in-vehicle Information equipment, portable radio, portable television, portable printer, portable scanner, portable modem, and the like. Non-limiting examples of portable devices other than portable electronic devices include mechanical wristwatches, pocket watches, flashlights, hand mirrors, time slots and the like. In this specification, “carrying” means that it is not sufficient to be able to carry it alone, but that it has a level of portability that allows an individual (standard adult) to carry it relatively easily. Shall mean.

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

  As a preferable form of such a bonding material, 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) can be given. The pressure-sensitive adhesive sheet disclosed here is excellent in cohesive strength in addition to oil resistance, so even if it is used as a bonding material with such a narrow width part (for example, frame shape), the member can be fixed well. can do. In one embodiment, the width of the narrow portion may be 1.5 mm or less, 1.0 mm or less, or about 0.5 mm or less. Although the minimum of the width | variety of a narrow part is not restrict | limited in particular, Usually, 0.1 mm or more (for example, 0.2 mm or more) is suitable from a viewpoint of the handleability of an adhesive sheet.

  The narrow portion is typically linear. Here, the term “linear” is a concept including a linear shape, a curved shape, a bent line shape (for example, an L shape), a ring shape such as a frame shape or a circular shape, or a composite or intermediate shape thereof. . The annular shape is not limited to a curved line, and a part or all of the shape is linearly formed, for example, a shape along the outer periphery of a square (frame shape) or a shape along a fan-shaped outer periphery. It is a concept that includes a ring. The length of the narrow portion is not particularly limited. For example, in the form in which the length of the narrow width 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.

The matters disclosed by this specification include the following.
(1) A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive having an acrylic polymer as a base polymer,
The pressure-sensitive adhesive layer has a surface free energy γ of less than about 40 mJ / m ² and an oleic acid penetration amount of about 1.5 g or more and about 5.0 g or less.
(2) The pressure-sensitive adhesive sheet according to (1), wherein the gel fraction of the pressure-sensitive adhesive layer is about 30% or more and about 70% or less.
(3) The said adhesive layer is an adhesive sheet as described in said (1) or (2) currently formed using the adhesive composition containing the said acrylic polymer and a crosslinking agent.
(4) The pressure-sensitive adhesive sheet according to (3), wherein the crosslinking agent includes an isocyanate-based crosslinking agent.
(5) The pressure-sensitive adhesive layer includes a tackifier resin, and about 50% by weight or more of the tackifier resin is a tackifier resin other than the rosin resin, according to any one of the above (1) to (4). 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), wherein the monomer component constituting the acrylic polymer contains more than about 5% by weight of a carboxy group-containing monomer.
(8) The monomer component constituting the acrylic polymer includes approximately 70% by weight or more of C _7-10 alkyl (meth) acrylate and approximately 7% by weight or more and approximately 15% by weight or less of a carboxy group-containing monomer. The pressure-sensitive 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, methacrylic acid, or the like. The pressure-sensitive adhesive sheet according to (8), which is an acid or a combination thereof.
(10) Any of the above (6) to (9), wherein the pressure-sensitive adhesive layer contains a tackifier resin, and about 50% by weight or more of the tackifier resin is a phenol-based tackifier resin (for example, terpene phenol resin). The pressure-sensitive adhesive sheet described in 1.
(11) The pressure-sensitive adhesive sheet according to (10), wherein the phenol-based tackifying resin includes 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), 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), wherein the monomer component constituting the acrylic polymer contains more than about 3% by weight of a carboxy group-containing monomer.
(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. Or the adhesive sheet as described in said (13) which is a combination of these.
(15) Any of the above (12) to (14), wherein the pressure-sensitive adhesive layer contains a tackifier resin, and about 50% by weight or more of the tackifier resin is a phenol-based tackifier resin (for example, terpene phenol resin). The pressure-sensitive adhesive sheet described in 1.
(16) The pressure-sensitive adhesive sheet according to (15), wherein the phenol-based tackifying resin includes 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), wherein the pressure-sensitive adhesive layer is formed using a solvent-type pressure-sensitive adhesive composition containing a pressure-sensitive adhesive in an organic solvent.
(18) The adhesive sheet according to (17), 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), 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), wherein the pressure-sensitive adhesive layer 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 substrate.
(21) The pressure-sensitive adhesive sheet according to (20), wherein the substrate is a PET film having a single layer structure.
(22) The pressure-sensitive adhesive sheet according to any one of (1) to (21), which is used for fixing a member in a portable device.

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

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples. In the following description, “parts” and “%” are based on weight unless otherwise specified.

<Preparation of acrylic polymer solution>
(Acrylic polymer A)
A reactor equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser and dropping funnel was charged with 90 parts of 2EHA and 10 parts of AA as monomer components and 199 parts of ethyl acetate as a polymerization solvent, and nitrogen gas was introduced. The mixture was stirred 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 performed at 60 ° C. for 6 hours to obtain an acrylic polymer A solution. Mw of this acrylic polymer A was about 120 × 10 ⁴ .

(Acrylic polymer B)
In a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet 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 And stirred for 2 hours while introducing nitrogen gas. After removing oxygen in the polymerization system in this way, 0.3 part of 2,2′-azobisisobutyronitrile was added as a polymerization initiator, and solution polymerization was performed at 60 ° C. for 6 hours to obtain acrylic polymer B. Solution was obtained. Mw of this acrylic polymer B was about 100 × 10 ⁴ .

(Acrylic polymer C)
A reactor equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser and dropping funnel was charged with 95 parts of BA and 5 parts of AA as monomer components and 233 parts of ethyl acetate as a polymerization solvent, and nitrogen gas was introduced. The mixture was stirred for 2 hours. After removing oxygen in the polymerization system in this way, 0.2 part of 2,2′-azobisisobutyronitrile was added as a polymerization initiator, and solution polymerization was performed at 60 ° C. for 8 hours to obtain an acrylic polymer. A solution was obtained. The acrylic polymer had an Mw of about 70 × 10 ⁴ .

<Preparation of pressure-sensitive adhesive composition>
(Example 1)
In the above acrylic polymer A solution, 2 parts (non-volatile content basis; the same applies hereinafter) of isocyanate crosslinking agent (trade name “Coronate L”, trimethylolpropane / 100 parts of acrylic polymer A contained in the solution) A 75% ethyl acetate solution of tolylene diisocyanate trimer adduct, manufactured by Tosoh Corporation; hereinafter referred to as “isocyanate-based crosslinking agent A”) was added and mixed by stirring to prepare a pressure-sensitive adhesive composition according to this example.

(Example 2)
In the above acrylic polymer A solution, 2 parts of isocyanate crosslinking agent A and 0.01 part of epoxy crosslinking agent (trade name “TETRAD-C”) with respect to 100 parts of acrylic polymer A contained in the solution. 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, manufactured by Mitsubishi Gas Chemical Company, Inc .; hereinafter referred to as “epoxy-based crosslinking agent B”), and mixed by stirring. An agent composition was prepared.

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

(Example 4)
To the acrylic polymer C solution, 2 parts of the isocyanate crosslinking 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 a 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 of 70 to 110 mg KOH / g) is added to 100 parts of acrylic polymer C Prepared an adhesive composition according to this example in the same manner as in Example 4.

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

(Example 7)
To the acrylic polymer B solution, 2 parts of the isocyanate crosslinking 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 a pressure-sensitive adhesive composition according to this example.

(Example 8)
A 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 crosslinking agent A used for 100 parts of the acrylic polymer C was changed to 1 part.

(Example 9)
Example in which 10 parts of rosin-based tackifier resin A (trade name “Halitac SE10”, hydrogenated rosin glycerin ester, manufactured by Harima Chemicals, softening point of about 80 ° C.) is further added to 100 parts of acrylic polymer C In the same manner as in Example 4, a pressure-sensitive adhesive composition according to this example was prepared.

(Example 10)
In the acrylic polymer C solution, 2 parts of isocyanate crosslinking agent A, 0.01 part of epoxy crosslinking agent B, and 20 parts of rosin-based adhesive with respect to 100 parts of acrylic polymer C contained in the solution. An adhesive resin B (trade name “Pencel D125”, manufactured by Arakawa Chemical Industries, Ltd., pentaerythritol ester of polymerized rosin, softening point of about 125 ° C.) was added and mixed by stirring to prepare an adhesive composition according to this example.

<Production of adhesive sheet>
Two release films made of polyester (trade name “Diafoil MRF”, thickness 38 μm, manufactured by Mitsubishi Polyester Co., Ltd.) were prepared as release liners. The pressure-sensitive adhesive composition according to each example was applied to the release 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 two release liners were bonded to the first and second surfaces of a transparent substrate 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 on the pressure-sensitive adhesive layer as it was and used for protecting the surface (adhesive surface) of the pressure-sensitive adhesive layer. As the base material film, a PET film (resin film) manufactured by Toray Industries, Inc. and a trade name “Lumirror” were used. Thus, the double-sided adhesive sheet of Examples 1-10 each corresponding to the adhesive composition which concerns on Examples 1-10 was produced.

<Evaluation test>
After the double-sided pressure-sensitive adhesive sheets according to Examples 1 to 10 were cured for 1 day in an environment of 50 ° C. and 50% RH, the surface free energy γ, the gel fraction, and the adhesive strength maintenance rate were determined by the methods described above.
Also, the pressure-sensitive adhesive composition according to Examples 1 to 10 was applied to the release surface of the polyester release film (trade name “Diafoil MRF”, thickness 38 μm, manufactured by Mitsubishi Polyester) and dried at 120 ° C. for 2 minutes. Thus, 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 bonded to a 50 μm-thick PET film (trade name “Lumirror”, 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 performing oleic acid permeability evaluation 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 obtained results are shown in Tables 1 and 2.

As shown in Tables 1 and ² , a pressure-sensitive adhesive layer having a surface free energy γ of less than 40 mJ / m ² and an oleic acid penetration amount in the range of 1.5 g / g to 5.0 g / g is provided. All of the pressure-sensitive adhesive sheets of Examples 1 to 6 exhibited a good adhesive strength maintenance rate, and the pressure-sensitive adhesive did not protrude much. On the other hand, in Examples 7 and 8 where the amount of oleic acid permeation was too small and Example 10 where the surface free energy γ was too high, the adhesive strength maintenance rate was low. In Example 9 in which the amount of oleic acid permeation was too large, the sticking out of the adhesive was large.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes 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 (10)

A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive based on an acrylic polymer,
The pressure-sensitive adhesive layer is a pressure-sensitive adhesive sheet having a surface free energy γ of less than 40 mJ / m ² and an oleic acid permeation amount per gram of 1.5 g or more and 5.0 g or less.   The pressure sensitive adhesive sheet according to claim 1 whose gel fraction of said pressure sensitive adhesive layer is 30% or more and 70% or less.   The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer is formed using a pressure-sensitive adhesive composition containing the acrylic polymer and a crosslinking agent.   The pressure-sensitive adhesive sheet according to claim 3, wherein the crosslinking agent includes an isocyanate-based crosslinking agent. The pressure-sensitive adhesive layer contains a tackifying resin,
The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein 50% by weight or more of the tackifying resin is a tackifying resin other than a rosin-based tackifying resin.   The monomer component constituting the acrylic polymer contains more than 50% by weight of an alkyl (meth) acrylate having an alkyl group having 7 to 10 carbon atoms at the ester end. The adhesive sheet as described.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, wherein the monomer component constituting the acrylic polymer contains more than 5% by weight of a carboxy group-containing monomer.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, wherein the pressure-sensitive adhesive layer has a thickness of 25 µm or less.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 8, wherein the pressure-sensitive adhesive sheet 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 substrate.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 9, which is used for fixing a member in a portable device.

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