Photocrosslinkable adhesive and its use

Abstract

To provide an adhesive which has good surface shape followability to an adherend and can form a bond having high deformation resistance, and to provide an adhesive sheet using the adhesive.SOLUTION: A photocrosslinkable adhesive containing a polymer having a benzophenone structure in a side chain is provided. The photocrosslinkable adhesive is a cured product of an adhesive composition containing an ethylenically unsaturated compound and a benzophenone structure-containing component. The amount of volatile organic compound emission of the photocrosslinkable adhesive is 500 μg / g or less. An adhesive sheet including an adhesive layer comprising the photocrosslinkable adhesive is also provided.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a photocrosslinkable pressure-sensitive adhesive, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing the photocrosslinkable pressure-sensitive adhesive, a method for producing a laminate using the photocrosslinkable pressure-sensitive adhesive, a method for producing the photocrosslinkable pressure-sensitive adhesive, and a pressure-sensitive adhesive composition used in producing the photocrosslinkable pressure-sensitive adhesive. [Background technology]

[0002] Generally, pressure-sensitive adhesives (also called pressure-sensitive adhesives; the same applies hereinafter) are in a soft solid (viscoelastic) state in a temperature range around room temperature, and have the property of easily adhering to an adherend when pressure is applied. Taking advantage of these properties, pressure-sensitive adhesives are widely used in a variety of fields. Patent Document 1 is an example of a technical document related to pressure-sensitive adhesives. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-140497 Summary of the Invention [Problem to be solved by the invention]

[0004] Pressure-sensitive adhesives are required to have various properties depending on their application. Some of these properties are difficult to achieve at a high level, as improving one property tends to reduce the other. One example of such properties that are difficult to achieve at the same time is the ability to deform in accordance with the surface shape of an adherend (hereinafter also referred to as "surface shape conformability") and the ability to resist deformation under stress (hereinafter also referred to as "deformation resistance").

[0005] Therefore, an object of the present invention is to provide a pressure-sensitive adhesive that has good conformability to the surface shape of an adherend and is capable of forming a bond that is highly resistant to deformation, and a pressure-sensitive adhesive sheet that uses the pressure-sensitive adhesive. [Means for solving the problem]

[0006] According to this specification, a photocrosslinkable pressure sensitive adhesive is provided which contains a polymer having a benzophenone structure in the side chain. The photocrosslinkable pressure-sensitive adhesive can be photocrosslinked using the benzophenone structure after application to an adherend, thereby increasing the deformation resistance of the pressure-sensitive adhesive. This allows the pressure-sensitive adhesive to conform well to the surface shape when applied to the adherend, and by photocrosslinking after application, a bond with high deformation resistance can be formed. A pressure-sensitive adhesive with good surface conformability can deform along (absorb) any unevenness that may exist on the surface of the adherend, thereby allowing it to adhere well to the surface of the adherend.

[0007] Furthermore, some adherends for pressure-sensitive adhesives may generate so-called outgassing under conditions such as high-temperature environments. Even if a satisfactory adhesion state without bubbles is achieved between the pressure-sensitive adhesive and the adherend with such an adherend, outgassing from the adherend may subsequently accumulate at the interface between the pressure-sensitive adhesive and the adherend, resulting in the formation of new bubbles. The generation of such bubbles (foaming) may reduce the adhesive contact area with the adherend, potentially reducing the reliability of the adhesive bonding. Therefore, a pressure-sensitive adhesive that is expected to be bonded to an adherend prone to outgassing is desirably configured to suppress the formation of such bubbles and ensure durable adhesion to the adherend even when maintained in a high-temperature environment after application to the adherend. Because the bubbles are formed by deformation of the pressure-sensitive adhesive, improving the deformation resistance of the pressure-sensitive adhesive can help prevent bubble formation. The photocrosslinkable pressure-sensitive adhesive disclosed herein can be photocrosslinked after application to an adherend to enhance the deformation resistance of the pressure-sensitive adhesive, thereby achieving both excellent surface conformability and adhesion durability.

[0008] In some embodiments of the technology disclosed herein (including photocrosslinkable adhesives, methods for producing adhesive sheets and laminates using the photocrosslinkable adhesives, methods for producing photocrosslinkable adhesives, adhesive compositions used in producing photocrosslinkable adhesives, etc.; the same applies hereinafter), the photocrosslinkable adhesives have a volatile organic compound emission level of 500 μg / g or less. Photocrosslinkable adhesives with low emission levels of volatile organic compounds (VOCs) (hereinafter also referred to as "VOC emission levels") have low odors and are preferred from the perspective of environmental hygiene.

[0009] The photocrosslinkable pressure-sensitive adhesive disclosed herein may be a cured product of a pressure-sensitive adhesive composition containing an ethylenically unsaturated compound and a benzophenone structure-containing component. Non-limiting examples of the benzophenone structure-containing component include a polymer having a benzophenone structure in its side chain (hereinafter also referred to as a "BP polymer") and a compound having an ethylenically unsaturated group and a benzophenone structure in its molecule (hereinafter also referred to as an "ethylenically unsaturated BP"). In some embodiments, a BP polymer may be preferably used as the benzophenone structure-containing component. The photocrosslinkable pressure-sensitive adhesive disclosed herein may be a cured product of a pressure-sensitive adhesive composition containing an ethylenically unsaturated compound and a BP polymer.

[0010] This specification also provides a photocrosslinkable pressure-sensitive adhesive containing two or more polymers with different monomer compositions, at least one of which is a BP polymer. With such a photocrosslinkable pressure-sensitive adhesive containing two or more polymers, the properties of the photocrosslinkable pressure-sensitive adhesive and the properties of the photocrosslinked product of the photocrosslinkable pressure-sensitive adhesive (i.e., the photocrosslinkable pressure-sensitive adhesive after photocrosslinking) can be appropriately adjusted by selecting and combining these polymers. The photocrosslinkable pressure-sensitive adhesive containing two or more polymers may be, for example, a cured product of a pressure-sensitive adhesive composition containing an ethylenically unsaturated compound and a BP polymer. The photocrosslinkable pressure-sensitive adhesive containing two or more polymers preferably has a VOC emission level of 500 μg / g or less.

[0011] In some embodiments, the photocrosslinkable pressure-sensitive adhesive disclosed herein has a shear storage modulus Gb' [kPa] at 80°C and an illuminance of 300 mW / cm using a high-pressure mercury lamp. 2 , cumulative light intensity 10,000mJ / cm 2 The relationship between the shear storage modulus Gc' [kPa] at 80°C of the photocrosslinked product obtained by irradiating ultraviolet light under the above conditions and the shear storage modulus Gc' [kPa] can satisfy the following formula: Gc' [kPa] - Gb' [kPa] ≥ 2 kPa. Hereinafter, the shear storage modulus Gb' may be referred to as the "modulus Gb' before photocrosslinking" or simply as the "modulus Gb'," and the shear storage modulus Gc' may be referred to as the "modulus Gc' after photocrosslinking" or simply as the "modulus Gc'." Hereinafter, Gc' [kPa] - Gb' [kPa], i.e., the increase in the shear storage modulus at 80°C due to photocrosslinking, may be referred to as "ΔG'" (unit: kPa). A photocrosslinkable pressure-sensitive adhesive having a ΔG' of 2 kPa or more is likely to exhibit the effect of improving deformation resistance due to photocrosslinking.

[0012] In some embodiments, the photocrosslinkable pressure-sensitive adhesive disclosed herein is exposed to a high-pressure mercury lamp at an illumination intensity of 300 mW / cm. 2 , cumulative light intensity 10,000mJ / cm 2 The photocrosslinked product obtained by irradiating with ultraviolet light under the above conditions may have a shear storage modulus Gc' [kPa] at 80°C of 40 kPa or more. A photocrosslinkable pressure-sensitive adhesive having a post-photocrosslinking modulus Gc' of 40 kPa or more is preferred because it tends to exhibit excellent adhesion durability to an adherend when photocrosslinked after application to the adherend.

[0013] This specification provides a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of any of the photocrosslinkable pressure-sensitive adhesives disclosed herein. When attached to an adherend, the pressure-sensitive adhesive sheet exhibits good conformability to the surface shape of the photocrosslinkable pressure-sensitive adhesive layer, and can form a bond with high deformation resistance by photocrosslinking the photocrosslinkable pressure-sensitive adhesive after attachment.

[0014] In some embodiments, the pressure-sensitive adhesive sheet may have a peel strength of 1.0 N / 10 mm or more, as measured by the following procedure. A pressure-sensitive adhesive sheet exhibiting such a peel strength can suitably achieve highly reliable bonding. [Peel strength measurement procedure] The surface of the adhesive layer was pressed against a glass plate by rolling a 2 kg rubber roller back and forth once, and then autoclaved (50°C, 0.5 MPa, 15 minutes). After that, a high-pressure mercury lamp was used to illuminate the glass plate side at an illumination intensity of 300 mW / cm. 2 , cumulative light intensity 10,000mJ / cm 2 Then, the pressure-sensitive adhesive sheet is peeled from the glass plate at a pulling rate of 300 mm / min and a peel angle of 180° in an atmosphere of 25° C., and the peel strength is measured.

[0015] This specification provides a method for producing a laminate, which includes, in this order, laminating any one of the photocrosslinkable pressure-sensitive adhesives disclosed herein with a member, and photocrosslinking the photocrosslinkable pressure-sensitive adhesive by reacting the benzophenone structure contained in the photocrosslinkable pressure-sensitive adhesive. This method allows the photocrosslinkable pressure-sensitive adhesive to conform well to the surface shape of the member when laminating the photocrosslinkable pressure-sensitive adhesive with the member, and photocrosslinks the photocrosslinkable pressure-sensitive adhesive after lamination to improve deformation resistance, thereby making it possible to obtain a laminate in which the photocrosslinked product of the photocrosslinkable pressure-sensitive adhesive and the member are reliably bonded.

[0016] This specification provides a method for producing a photocrosslinkable pressure-sensitive adhesive, which includes preparing a pressure-sensitive adhesive composition containing a BP polymer (A) and an ethylenically unsaturated compound (B) and irradiating the pressure-sensitive adhesive composition with active energy rays. The active energy rays are irradiated so as to react the ethylenically unsaturated groups in the ethylenically unsaturated compound (B) and to leave the benzophenone structure in the BP polymer (A). This allows a photocrosslinkable pressure-sensitive adhesive containing the BP polymer to be obtained as an active energy ray-cured product of the pressure-sensitive adhesive composition. This production method can be preferably used as a method for producing any of the photocrosslinkable pressure-sensitive adhesives disclosed herein.

[0017] In some embodiments, the pressure-sensitive adhesive composition may contain a compound (B1) having one ethylenically unsaturated group as the ethylenically unsaturated compound (B). According to the pressure-sensitive adhesive composition of such an embodiment, the properties of the photocrosslinkable pressure-sensitive adhesive formed from the composition can be appropriately adjusted by selecting the type and amount of the compound (B1).

[0018] In some embodiments, the pressure-sensitive adhesive composition may contain a compound (B2) having two or more ethylenically unsaturated groups as the ethylenically unsaturated compound (B). According to the pressure-sensitive adhesive composition of such an embodiment, the properties of the photocrosslinkable pressure-sensitive adhesive formed from the composition can be appropriately adjusted by selecting the type and amount of the compound (B2).

[0019] In some embodiments, the pressure-sensitive adhesive composition may further comprise a photoinitiator (C). Use of the photoinitiator (C) can promote the reaction of the ethylenically unsaturated group in the ethylenically unsaturated compound (B). As the photoinitiator (C), a compound that absorbs light with a wavelength of 300 nm to 500 nm to generate radicals can be preferably used. Since the excitation wavelength of a benzophenone structure is generally shorter than 300 nm, use of a photoinitiator that absorbs light with a wavelength of 300 nm or longer to generate radicals can effectively promote the reaction of the ethylenically unsaturated group while leaving the benzophenone structure intact.

[0020] The active energy rays irradiated onto the pressure-sensitive adhesive composition may preferably be, for example, ultraviolet light substantially free of components with wavelengths of less than 300 nm, which reacts with the ethylenically unsaturated groups while leaving the benzophenone structure intact to cure the pressure-sensitive adhesive composition, thereby enabling the production of a photocrosslinkable pressure-sensitive adhesive containing a BP polymer.

[0021] This specification provides a pressure-sensitive adhesive composition used to produce a photocrosslinkable pressure-sensitive adhesive containing a BP polymer. The pressure-sensitive adhesive composition contains a BP polymer (A) and an ethylenically unsaturated compound (B). The photocrosslinkable pressure-sensitive adhesive can be produced by reacting the ethylenically unsaturated group of the ethylenically unsaturated compound (B) with the pressure-sensitive adhesive composition and curing the composition so that the benzophenone structure of the BP polymer (A) remains. The pressure-sensitive adhesive composition can be cured, for example, by irradiating the pressure-sensitive adhesive composition with active energy rays.

[0022] In some embodiments, the pressure-sensitive adhesive composition may contain a photoinitiator (C) that absorbs light with a wavelength of 300 nm to 500 nm to generate radicals. Use of such a photoinitiator (C) can effectively promote the reaction of the ethylenically unsaturated group while leaving the benzophenone structure.

[0023] In some embodiments, the pressure-sensitive adhesive composition preferably contains a compound having two or more ethylenically unsaturated groups in an amount of less than 5 wt % of the total monomer components constituting the pressure-sensitive adhesive composition. A pressure-sensitive adhesive composition having such a composition tends to form a photocrosslinkable pressure-sensitive adhesive that exhibits good surface conformability before photocrosslinking.

[0024] In addition, any suitable combination of the above elements may also be included in the scope of the invention for which patent protection is sought through this patent application. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet according to one embodiment. [Figure 2] FIG. 10 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet according to another embodiment. [Figure 3] 1 is a cross-sectional view schematically showing an optical member with a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive sheet according to one embodiment is attached to an optical member. DETAILED DESCRIPTION OF THE INVENTION

[0026] Preferred embodiments of the present invention are described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings for carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. Furthermore, in the following drawings, components and parts that perform the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic for the purpose of clearly explaining the present invention, and do not necessarily accurately represent the size or scale of the actual product provided.

[0027] In this specification, the term "acrylic polymer" refers to a polymer derived from a monomer component containing more than 50% by weight (preferably more than 70% by weight, for example, more than 90% by weight) of an acrylic monomer. The acrylic monomer refers to a monomer having at least one (meth)acryloyl group per molecule. In this specification, "(meth)acryloyl" refers to acryloyl and methacryloyl in a comprehensive sense. Similarly, "(meth)acrylate" refers to acrylate and methacrylate in a comprehensive sense, and "(meth)acrylic" refers to acrylic and methacrylic in a comprehensive sense.

[0028] In this specification, the term "ethylenically unsaturated compound" refers to a compound having at least one ethylenically unsaturated group in the molecule. Examples of the ethylenically unsaturated group include a (meth)acryloyl group, a vinyl group, and an allyl group. Hereinafter, a compound having one ethylenically unsaturated group may be referred to as a "monofunctional monomer," and a compound having two or more ethylenically unsaturated groups may be referred to as a "polyfunctional monomer." Furthermore, among polyfunctional monomers, a compound having X ethylenically unsaturated groups may be referred to as an "X-functional monomer."

[0029] In this specification, unless otherwise specified, the PSA composition containing an ethylenically unsaturated compound means that the PSA composition contains the ethylenically unsaturated compound in the form of a partial polymer. Such a partial polymer is usually a mixture containing the ethylenically unsaturated compound in which the ethylenically unsaturated group is unreacted (unreacted monomer) and the ethylenically unsaturated compound in which the ethylenically unsaturated group has been polymerized.

[0030] In this specification, the total amount of monomer components constituting a pressure-sensitive adhesive composition refers to the total amount of monomer components constituting the polymer contained in the pressure-sensitive adhesive composition and monomer components contained in the pressure-sensitive adhesive composition in the form of unreacted monomers. The composition of the monomer components constituting the pressure-sensitive adhesive composition is usually roughly the same as the composition of the monomer components of the photocrosslinkable pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition and the composition of the monomer components constituting the photocrosslinked product.

[0031] In this specification, the term "active energy rays" is a concept that includes light such as ultraviolet rays, visible light, and infrared rays, and radioactive rays such as α rays, β rays, γ rays, electron beams, neutron beams, and X-rays.

[0032] <Photo-crosslinkable adhesive> This specification provides a photocrosslinkable pressure-sensitive adhesive containing a polymer (BP polymer) having a benzophenone structure in its side chain. The photocrosslinkable pressure-sensitive adhesive satisfies at least one of the following conditions: it is a cured product of a pressure-sensitive adhesive composition containing an ethylenically unsaturated compound and a component containing a benzophenone structure; it has a VOC emission level of 500 μg / g or less; and it contains two or more polymers with different monomer compositions, at least one of which is the BP polymer.

[0033] (BP polymer) A suitable example of the BP polymer in the technology disclosed herein (including the BP polymer contained in the photocrosslinkable pressure-sensitive adhesive disclosed herein and the BP polymer that can be used as a component of a pressure-sensitive adhesive composition for producing the photocrosslinkable pressure-sensitive adhesive; the same applies hereinafter) is an acrylic polymer having a benzophenone structure in the side chain. The BP polymer may or may not have an ethylenically unsaturated group. In some embodiments, the BP polymer is preferably a polymer that is substantially free of ethylenically unsaturated groups.

[0034] Here, in this specification, the term "benzophenone structure" refers to a compound represented by the general formula: Ar 1 -(C=O)-Ar 2 -; or -Ar 3 -(C=O)-Ar 2 -; where Ar in the above general formula is 1 is selected from phenyl groups which may have a substituent. 2 ,Ar 3 are each independently selected from phenylene groups which may have a substituent. 2 and Ar 3 and may be the same or different. The benzophenone structure-containing component refers to a compound having at least one such benzophenone structure in the molecule. The benzophenone structure can be excited by irradiation with ultraviolet light, and in the excited state, can abstract hydrogen radicals from other molecules or other parts of the molecule.

[0035] The photocrosslinkable adhesive disclosed herein contains a polymer (BP polymer) having a benzophenone structure in its side chain, and by exciting the benzophenone structure, it is possible to form a crosslinked structure by utilizing the abstraction reaction of the hydrogen radical. The polymer having the benzophenone structure in its side chain is a polymer having the above general formula: Ar 1 -(C=O)-Ar 2 -;Ar in 1 is an optionally substituted phenyl group, and Ar 2A polymer having a benzophenone structure, which is a phenylene group that may have a substituent, in a side chain is preferred. 1 and Ar 2 When at least one of the groups has one or more substituents, the substituents may be independently selected from the group consisting of an alkoxy group (e.g., an alkoxy group having 1 to 3 carbon atoms, preferably a methoxy group), a halogen atom (e.g., F, Cl, Br, etc., preferably Cl or Br), a hydroxyl group, an amino group, and a carboxy group, but are not limited to these.

[0036] The BP polymer in the technology disclosed herein may have a side chain in which the benzophenone structure described above is directly bonded to the main chain, or may have a side chain in which the side chain is bonded to the main chain via one or more of, for example, an ester bond or an oxyalkylene structure. A suitable example of a BP polymer is a polymer containing a repeating unit derived from an ethylenically unsaturated BP. The repeating unit may be a polymerized residue obtained by reacting the ethylenically unsaturated group of the corresponding ethylenically unsaturated BP.

[0037] Examples of ethylenically unsaturated BPs include acryloyloxybenzophenones which may have a substituent, such as 4-acryloyloxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, and 2-hydroxy-4-acryloyloxybenzophenone; acryloyloxyalkoxybenzophenones which may have a substituent, such as 4-[(2-acryloyloxy)ethoxy]benzophenone and 4-[(2-acryloyloxy)ethoxy]-4'-bromobenzophenone; 4-methacryloyloxybenzophenone, 4-methacryloyloxy-4'-methoxybenzophenone; Examples of methylbenzophenones that may have a substituent include 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone, and 2-hydroxy-4-methacryloyloxybenzophenone; methacryloyloxyalkoxybenzophenones that may have a substituent, such as 4-[(2-methacryloyloxy)ethoxy]benzophenone and 4-[(2-methacryloyloxy)ethoxy]-4'-methoxybenzophenone; and vinylbenzophenones that may have a substituent, such as 4-vinylbenzophenone, 4'-bromo-3-vinylbenzophenone, and 2-hydroxy-4-methoxy-4'-vinylbenzophenone. Ethylenically unsaturated BPs can be used alone or in combination to prepare BP polymers. Commercially available ethylenically unsaturated BPs can be used, or they can be synthesized by known methods. From the viewpoint of reactivity, etc., an ethylenically unsaturated BP having a (meth)acryloyl group, that is, an ethylenically unsaturated BP that is an acrylic monomer, can be preferably used.

[0038] A BP polymer may be a copolymer having repeating units derived from an ethylenically unsaturated BP and repeating units derived from an ethylenically unsaturated compound other than an ethylenically unsaturated BP (hereinafter also referred to as "other monomer"). Such a BP polymer may be a copolymer of monomer components including the ethylenically unsaturated BP and the other monomer. In some embodiments, one or more acrylic monomers may be preferably used as the other monomer. A suitable example of a BP polymer is an acrylic BP polymer in which more than 50 wt% (preferably more than 70 wt%, e.g., more than 90 wt%) of the monomer components constituting the BP polymer are acrylic monomers.

[0039] In some embodiments, the monomer components constituting the BP polymer may include, as the other monomer, one or more selected from (meth)acrylic acid alkyl esters having an alkyl group at the ester terminal. Hereinafter, a (meth)acrylic acid alkyl ester having a linear or branched alkyl group having from X to Y carbon atoms at the ester terminal will be referred to as "(meth)acrylic acid C X-Y The monomer components constituting the BP polymer include at least (meth)acrylic acid C as the other monomers mentioned above. 1-20 It is preferable that the (meth)acrylic acid C contains an alkyl ester. 4-20 It is more preferable that the (meth)acrylic acid C contains an alkyl ester. 4-18 Alkyl esters (e.g., acrylic acid C 4-9 It is more preferred that the hydroxyl group contains an alkyl ester.

[0040] (Meth)acrylic acid C 1-20Non-limiting examples of alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isopropyl (meth)acrylate. Examples of the alkyl (meth)acrylate include 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, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Particularly preferred alkyl (meth)acrylates include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), and isononyl acrylate. Other specific examples of (meth)acrylic acid alkyl esters that can be preferably used include n-butyl methacrylate (BMA), 2-ethylhexyl methacrylate (2EHMA), and isostearyl acrylate (iSTA). The (meth)acrylic acid alkyl esters can be used alone or in combination of two or more. The monomer components that constitute the BP polymer may contain, as the other monomer, one or more selected from the copolymerizable monomers described below.

[0041] The photocrosslinkable pressure-sensitive adhesive disclosed herein may be a photocrosslinkable acrylic pressure-sensitive adhesive in which more than 50 wt % (preferably more than 70 wt %, e.g., more than 90 wt %) of the total monomer components constituting the photocrosslinkable pressure-sensitive adhesive is an acrylic monomer. The photocrosslinkable acrylic pressure-sensitive adhesive forms a photocrosslinked acrylic product by photocrosslinking. The photocrosslinkable acrylic pressure-sensitive adhesive can have good transparency, and therefore can be preferably used, for example, in optical applications.

[0042] The weight average molecular weight (Mw) of the BP polymer is not particularly limited, and may be, for example, 0.5×10 4 ~500×10 4 In view of the cohesiveness of the photocrosslinkable pressure-sensitive adhesive and the handleability of a pressure-sensitive adhesive sheet having the photocrosslinkable pressure-sensitive adhesive, in some embodiments, the Mw of the BP polymer is generally about 1 × 10 4 It is appropriate that the value is 5×10 or more. 4 It is preferable that the value is 10×10 or more. 4 More than 15 x 10 4 More than 20 x 10 is also acceptable. 4 In addition, from the viewpoint of the conformability of the photocrosslinkable pressure-sensitive adhesive to the surface shape of the adherend (for example, an optical member), the Mw of the BP polymer contained in the photocrosslinkable pressure-sensitive adhesive is usually 200 × 10 4 It is appropriate that the value is less than 150 x 10 4 Preferably, it is less than 100 × 10 4 Less than 70 x 10 is fine. 4 Less than 50 x 10 is fine. 4 In some embodiments, the Mw of the BP polymer may be 40×10 or less. 4 Less than 30 x 10 is also acceptable. 4 Less than 25 x 10 is also acceptable. 4 Less than 20 x 10 is also acceptable. 4 The following is also acceptable. In this specification, the weight-average molecular weight (Mw) of a polymer refers to a value calculated as a standard polystyrene by gel permeation chromatography (GPC). As a GPC apparatus, for example, a model "HLC-8320GPC" (column: TSKgel GMH-H(S), manufactured by Tosoh Corporation) can be used.

[0043] In the technology disclosed herein, the glass transition temperature (Tg) of the BP polymer is not particularly limited. The Tg of the BP polymer may be, for example, from −80°C to 150°C, from −80°C to 50°C, or from −80°C to 10°C. From the viewpoint of the surface conformability of the photocrosslinkable pressure-sensitive adhesive, in some embodiments, the Tg of the BP polymer is suitably less than 0°C, preferably −10°C or less, and may be −20°C or less, −30°C or less, −35°C or less, −40°C or less, or −50°C or less. Furthermore, from the viewpoint of the cohesion of the photocrosslinkable pressure-sensitive adhesive and the deformation resistance after photocrosslinking (e.g., adhesion durability to an adherend), the Tg of the BP polymer is usually advantageously −75°C or higher, and may be −70°C or higher or −65°C or higher. In some embodiments, the Tg of the BP polymer may be −55°C or higher, −45°C or higher, or −40°C or higher. The Tg of the BP polymer can be adjusted by the type and amount of the monomer components that make up the BP polymer.

[0044] Here, the glass transition temperature (Tg) of a polymer in this specification refers to the glass transition temperature calculated by Fox's equation based on the composition of the monomer components that make up the polymer. The Fox's equation, as shown below, is a relational expression between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers that make up the copolymer. 1 / Tg=Σ(Wi / Tgi) In the above Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio by weight), and Tgi represents the glass transition temperature (unit: K) of the homopolymer of monomer i.

[0045] The glass transition temperature of the homopolymer used to calculate Tg is determined based on the value described in the publicly available literature. For example, for the following monomers, the following values are used as the glass transition temperatures of the homopolymers of the monomers: 2-Ethylhexyl acrylate -70℃ n-Butyl acrylate -55℃ Isostearyl acrylate -18℃ Methyl methacrylate 105℃ Methyl acrylate 8℃ Cyclohexyl acrylate 15℃ N-vinyl-2-pyrrolidone 54℃ 2-Hydroxyethyl acrylate -15℃ 4-Hydroxybutyl acrylate -40℃ Isobornyl acrylate 94℃ Acrylic acid 106℃ Methacrylic acid 228℃

[0046] For the glass transition temperatures of homopolymers of monomers other than those listed above, the values described in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. If multiple values are listed in this document, the highest value shall be used. For monomers for which the glass transition temperature of the homopolymer is not listed in the Polymer Handbook, the value obtained by the measurement method described in JP 2007-51271 A shall be used. Note that for polymers for which the nominal value of the glass transition temperature is provided by the manufacturer, etc., that nominal value may be used.

[0047] The BP polymer in the technology disclosed herein preferably contains, for example, approximately 0.5 mg or more of benzophenone structures per gram of polymer, calculated as 4-benzoylphenyl acrylate. Hereinafter, the number of benzophenone structures contained per gram of BP polymer, converted into the amount of 4-benzoylphenyl acrylate, is sometimes referred to as the BP equivalent (unit: mg / g) of the BP polymer. For example, if 40 μmol of benzophenone structures are contained per gram, the BP equivalent of the polymer is calculated to be 10 mg / g. In order to obtain a higher photocrosslinking effect (e.g., the effect of increasing deformation resistance through photocrosslinking), in some embodiments, the BP equivalent of the BP polymer is typically 1 mg / g or more, preferably 1.5 mg / g or more, and may be, for example, 2 mg / g or more, 5 mg / g or more, 8 mg / g or more, 10 mg / g or more, 15 mg / g or more, or 20 mg / g or more. In some embodiments, in order to improve the impact resistance and peel strength of the bonded joint formed by the photocrosslinked product, the BP equivalent of the BP polymer is typically 100 mg / g or less, and may be 80 mg / g or less, 60 mg / g or less, 40 mg / g or less, 25 mg / g or less, or 15 mg / g or less. In some embodiments, the BP equivalent of the BP polymer may be less than 10 mg / g or less. The BP equivalent of the BP polymer can be adjusted by the composition of the monomer components constituting the BP polymer.

[0048] The weight ratio of the BP polymer to the entire photocrosslinkable pressure-sensitive adhesive, i.e., the weight fraction of the BP polymer in the photocrosslinkable pressure-sensitive adhesive, is not particularly limited and can be set to achieve a favorable balance between the surface conformability of the photocrosslinkable pressure-sensitive adhesive and the deformation resistance of the photocrosslinked product. In some embodiments, the weight fraction of the BP polymer may be, for example, 1 wt% or more, typically 5 wt% or more, but may also be 10 wt% or more, 15 wt% or more, 25 wt% or more, 30 wt% or more, 35 wt% or more, 45 wt% or more, 50 wt% or more, or 55 wt% or more. As the weight fraction of the BP polymer increases, the ΔG′ (described below) tends to increase. The technology disclosed herein can also be implemented in an embodiment in which the weight fraction of the BP polymer in the photocrosslinkable pressure-sensitive adhesive is substantially 100 wt% (e.g., 99.5 wt% or more). Furthermore, from the viewpoint of the ease of adjusting adhesive performance and reducing VOCs, in some embodiments, the weight fraction of the BP polymer in the photocrosslinkable adhesive may be, for example, less than 99 wt%, less than 95 wt%, less than 85 wt%, less than 70 wt%, less than 60 wt%, less than 50 wt%, less than 40 wt%, or less than 35 wt%.

[0049] The photocrosslinkable adhesive disclosed herein preferably contains, for example, approximately 0.1 mg or more of a benzophenone structure, calculated as 4-benzoylphenyl acrylate, per gram of the photocrosslinkable adhesive. Hereinafter, the weight of the benzophenone structure contained per gram of the photocrosslinkable adhesive, calculated as 4-benzoylphenyl acrylate, may be referred to as the BP equivalent (unit: mg / g) of the photocrosslinkable adhesive. From the viewpoint of achieving a higher photocrosslinking effect (e.g., the effect of improving deformation resistance through photocrosslinking), in some embodiments, the BP equivalent of the photocrosslinkable adhesive is typically 0.3 mg / g or more, and may be 0.5 mg / g or more, 1 mg / g or more, 5 mg / g or more, 10 mg / g or more, or 20 mg / g or more. In some embodiments, from the viewpoint of the impact resistance of the joint formed by the photocrosslinked product and the suppression of distortion within the photocrosslinked product, the BP equivalent of the photocrosslinkable pressure-sensitive adhesive is typically suitably 100 mg / g or less, and may be 80 mg / g or less, 60 mg / g or less, 40 mg / g or less, 25 mg / g or less, or 15 mg / g or less.

[0050] The photocrosslinkable pressure-sensitive adhesive disclosed herein may be a cured product of a pressure-sensitive adhesive composition containing an ethylenically unsaturated compound and a benzophenone structure-containing component. The pressure-sensitive adhesive composition may contain, as the benzophenone structure-containing component, one or more monomers selected from the above-mentioned ethylenically unsaturated BPs, a pre-synthesized BP polymer, or both. The BP polymer contained in the photocrosslinkable pressure-sensitive adhesive may be, for example, the BP polymer contained in the pressure-sensitive adhesive composition or a modified version thereof, or may be formed by copolymerizing the ethylenically unsaturated BP contained in the pressure-sensitive adhesive composition with another monomer.

[0051] The photocrosslinkable pressure-sensitive adhesive disclosed herein may be a photocrosslinkable pressure-sensitive adhesive containing two or more polymers with different monomer compositions, at least one of which is the BP polymer. The photocrosslinkable pressure-sensitive adhesive may contain only two or more BP polymers as the two or more polymers, or may contain a combination of a polymer without a benzophenone structure (hereinafter also referred to as a "non-BP polymer") and a BP polymer. The non-BP polymer may be formed, for example, by using a pressure-sensitive adhesive composition containing an ethylenically unsaturated compound without a benzophenone structure and polymerizing the ethylenically unsaturated compound. From the standpoint of compatibility, it is preferable that both the BP polymer and the non-BP polymer are acrylic polymers.

[0052] The two or more polymers may or may not be chemically bonded. A photocrosslinkable pressure-sensitive adhesive according to some embodiments may contain at least one BP polymer in a form that is not chemically bonded to any polymer other than the BP polymer. By photocrosslinking the benzophenone structure of the BP polymer, the photocrosslinkable pressure-sensitive adhesive can form a photocrosslinked product in which the BP polymer is chemically bonded to a polymer other than the BP polymer.

[0053] The photocrosslinkable pressure-sensitive adhesive disclosed herein may contain other components that can be used in pressure-sensitive adhesives, as needed. A photocrosslinkable pressure-sensitive adhesive containing such optional components can be formed using a pressure-sensitive adhesive composition having a corresponding composition.

[0054] (VOC emission amount) The VOC emission amount of the photocrosslinkable pressure-sensitive adhesive disclosed herein is not particularly limited. The VOC emission amount may be, for example, 5000 μg / g or less, 3000 μg / g or less, or 1000 μg / g or less. In some embodiments, the VOC emission amount of the photocrosslinkable pressure-sensitive adhesive is preferably 500 μg / g or less, more preferably 300 μg / g or less, and even more preferably 100 μg / g or less. Photocrosslinkable pressure-sensitive adhesives with low VOC emission have low odor and are preferred from the viewpoint of environmental hygiene. A low VOC emission amount of a photocrosslinkable pressure-sensitive adhesive is also preferred from the viewpoints of suppressing foaming caused by volatile organic compounds (VOCs) in the photocrosslinkable pressure-sensitive adhesive and reducing contamination. The VOC emission amount of a photocrosslinkable pressure-sensitive adhesive is measured using an appropriate amount (e.g., approximately 1 mg to 2 mg) of the photocrosslinkable pressure-sensitive adhesive as a measurement sample by the following method. The thickness of the measurement sample is preferably 1 mm or less.

[0055] [VOC measurement test] The measurement sample is placed in a 20 mL vial and sealed. The vial is then heated at 80°C for 30 minutes, and 1.0 mL of the heated gas (sample gas) is injected into a gas chromatograph (GC) measurement device using a headspace autosampler (HSS). Based on the obtained gas chromatogram, the amount of gas generated from the measurement sample is calculated as an n-decane equivalent. From this value, the amount of VOC emitted per 1 g of measurement sample (μg / g) is calculated. Note that this n-decane equivalent is determined by considering the detection intensity of the generated gas obtained by GC Mass as the detection intensity of n-decane and applying a previously prepared n-decane calibration curve. The HSS and GC settings are as follows: HSS: Agilent Technologies model number "7694" Heating time: 30 minutes Pressurization time: 0.12 minutes Loop filling time: 0.12 minutes Loop equilibration time: 0.05 min Infusion time: 3 minutes Sample loop temperature: 160℃ Transfer line temperature: 200℃ GC device: Agilent Technologies model “6890” Column: GL Sciences J&W Capillary Column, product name "DB-ffAP" (inner diameter 0.533 mm x length 30 m, film thickness 1.0 μm) Column temperature: 250°C (heat from 40°C to 90°C at 10°C / min, then heat to 250°C at 20°C / min and hold for 5 minutes) Column pressure: 24.3 kPa (constant flow mode) Carrier gas: Helium (5.0 mL / min) Inlet: Split (split ratio 12:1) Inlet temperature: 250℃ Detector: FID Detector temperature: 250℃

[0056] Generally, volatile organic compounds that can increase the VOC emission level of a pressure-sensitive adhesive include organic solvents (e.g., residues of organic solvents contained in a pressure-sensitive adhesive composition used to prepare the photocrosslinkable pressure-sensitive adhesive) and unreacted ethylenically unsaturated compounds contained in the pressure-sensitive adhesive composition (e.g., unpolymerized acrylic monomers, hereinafter also referred to as "residual monomers"). The photocrosslinkable pressure-sensitive adhesives disclosed herein may have the content of such organic solvents or residual monomers suppressed to a level that satisfies any of the above-mentioned VOC emission levels. Despite having such a limited amount of residual monomers, the photocrosslinkable pressure-sensitive adhesives disclosed herein can utilize the benzophenone structure of the BP polymer to form new crosslinks within the system, thereby forming a photocrosslinked product with enhanced deformation resistance. In principle, the lower the VOC emission amount of the photocrosslinkable pressure-sensitive adhesive disclosed herein, the better. However, from the practical viewpoint of productivity, cost, etc., in some embodiments, the VOC emission amount may be, for example, 10 μg / g or more, 30 μg / g or more, 80 μg / g or more, 150 μg / g or more, or 200 μg / g or more.

[0057] (shear storage modulus) In the technology disclosed herein, the shear storage modulus Ga' [kPa] of the photocrosslinkable pressure-sensitive adhesive at 30°C is not particularly limited. The shear storage modulus Ga' [kPa] of the photocrosslinkable pressure-sensitive adhesive at 30°C is usually preferably greater than 1 kPa. Hereinafter, the shear storage modulus Ga' may be referred to as the "room-temperature modulus Ga' before photocrosslinking" or simply as the "room-temperature modulus Ga'." From the viewpoints of the cohesiveness of the photocrosslinkable pressure-sensitive adhesive and the handleability (e.g., processability) of a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the photocrosslinkable pressure-sensitive adhesive, the room-temperature modulus Ga' is preferably greater than 5 kPa, more preferably greater than 10 kPa, and may be greater than 15 kPa, 25 kPa, or 30 kPa. In some embodiments, the room-temperature modulus Ga' may be greater than 50 kPa, 65 kPa, or 75 kPa. In addition, from the viewpoint of conformability to the surface shape of the adherend, the room temperature modulus Ga' is usually suitably 500 kPa or less, preferably 200 kPa or less, and may be 100 kPa or less. In some embodiments, the room temperature modulus Ga' may be less than 80 kPa or may be less than 60 kPa. The room-temperature modulus Ga' of the photocrosslinkable pressure-sensitive adhesive can be determined by dynamic viscoelasticity measurement under the same conditions as those for the pre-photocrosslinking modulus Gb' described in the Examples below. The room-temperature modulus Ga' can be adjusted by the composition of the photocrosslinkable pressure-sensitive adhesive (e.g., the BP equivalent (Mw) of the BP polymer, the composition of the monomer components constituting the BP polymer, and the weight fraction of the BP polymer).

[0058] The shear storage modulus of the photocrosslinkable pressure-sensitive adhesive at 80°C (i.e., the modulus Gb' before photocrosslinking) is not particularly limited. From the viewpoints of the cohesiveness of the photocrosslinkable pressure-sensitive adhesive and the handleability of a pressure-sensitive adhesive sheet having the photocrosslinkable pressure-sensitive adhesive (e.g., the shelf life of the pressure-sensitive adhesive sheet), the modulus Gb' is usually suitably greater than 3 kPa, preferably greater than 5 kPa, more preferably greater than 10 kPa, and may even be greater than 15 kPa. In some embodiments, from the viewpoint of the processability of a pressure-sensitive adhesive sheet having the photocrosslinkable pressure-sensitive adhesive, the modulus Gb' may be greater than 30 kPa, greater than 40 kPa, greater than 50 kPa, or greater than 52 kPa. A photocrosslinkable pressure-sensitive adhesive having such a modulus Gb' can be preferably used, for example, as a component of a pressure-sensitive adhesive layer having a thickness of greater than 50 μm, greater than 70 μm, or greater than 90 μm, which is made of the photocrosslinkable pressure-sensitive adhesive, or a pressure-sensitive adhesive sheet having such a pressure-sensitive adhesive layer. The elastic modulus Gb' can be measured by the method described in the Examples below. The elastic modulus Gb' can be adjusted by the composition of the photocrosslinkable pressure-sensitive adhesive (e.g., the BP equivalent (Mw) of the BP polymer, the composition of the monomer components constituting the BP polymer, and the weight fraction of the BP polymer).

[0059] Photocrosslinkable adhesive is exposed to a high-pressure mercury lamp with an illumination intensity of 300mW / cm 2 , cumulative light intensity 10,000mJ / cm 2The shear storage modulus Gc' [kPa] at 80°C of the photocrosslinked product obtained by irradiating ultraviolet light under the above conditions (i.e., the post-photocrosslinking modulus Gc') is not particularly limited. From the viewpoint of suppressing cohesive failure of the bonded portion due to the photocrosslinked product, the modulus Gc' is usually advantageously 15 kPa or more, and preferably 25 kPa or more. From the viewpoint of improving adhesion durability to an adherend (particularly an adherend that is prone to outgassing, such as a polarizing plate), the modulus Gc' is advantageously 30 kPa or more, preferably 35 kPa or more, and more preferably 40 kPa or more. In some embodiments, the modulus Gc' may be 45 kPa or more, 50 kPa or more, 55 kPa or more, or 60 kPa or more. The modulus Gc' may also be, for example, 200 kPa or less, 150 kPa or less, or 120 kPa or less. From the viewpoint of easily achieving a good balance between adhesion durability to an adherend and other properties (e.g., peel strength), the elastic modulus Gc' is advantageously 100 kPa or less, preferably 80 kPa or less, and may be 70 kPa or less, or may be 65 kPa or less. When the elastic modulus Gc' is low, the peel strength from the adherend of the photocrosslinked product formed by laminating the photocrosslinkable pressure-sensitive adhesive to an adherend and then photocrosslinking the adhesive tends to generally be improved. In some embodiments, the elastic modulus Gc' may be less than 60 kPa, less than 55 kPa, less than 50 kPa, or less than 45 kPa. More specifically, the elastic modulus Gc' can be measured by the method described in the Examples below. The elastic modulus Gc' can be adjusted by the composition of the photocrosslinkable pressure-sensitive adhesive (e.g., the BP equivalent (Mw) of the BP polymer, the composition of the monomer components constituting the BP polymer, and the weight fraction of the BP polymer).

[0060] The relationship between the elastic modulus Gb' of a photocrosslinkable pressure-sensitive adhesive and the elastic modulus Gc' of its photocrosslinked product is not particularly limited, but typically satisfies Gc' [kPa] - Gb' [kPa] > 0 [kPa]. ΔG' may be, for example, 0.5 kPa or more, preferably 1 kPa or more, and more preferably 2 kPa or more. A photocrosslinkable pressure-sensitive adhesive having a ΔG' of 2 kPa or more is likely to exhibit favorable effects of improving deformation resistance due to photocrosslinking. From the viewpoint of obtaining a higher photocrosslinking effect, in some embodiments, ΔG' may be 3 kPa or more, or 5 kPa or more, for example, preferably 8 kPa or more, or may be 10 kPa or more, 15 kPa or more, 20 kPa or more, 25 kPa or more, or 30 kPa or more. The upper limit of ΔG' is not particularly limited, but from the viewpoint of achieving a good balance between the ability to follow the surface shape when attached to an adherend and the resistance to deformation after photocrosslinking, it is usually appropriate that the pressure is 150 kPa or less, preferably 100 kPa or less, or alternatively 80 kPa or less, 65 kPa or less, 50 kPa or less, or 40 kPa or less.

[0061] (gel fraction) The gel fraction of the photocrosslinkable pressure-sensitive adhesive disclosed herein is not particularly limited, but from the viewpoints of the cohesiveness of the photocrosslinkable pressure-sensitive adhesive and the handleability of a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the photocrosslinkable pressure-sensitive adhesive, it is usually appropriate to be 5% or more, preferably 15% or more, or may be 25% or more, or may be 35% or more. In principle, the gel fraction of the photocrosslinkable pressure-sensitive adhesive is 100% or less. Furthermore, from the viewpoint of conformability to the surface shape of the adherend, the gel fraction of the photocrosslinkable pressure-sensitive adhesive is preferably less than 85%, or may be less than 70%, or may be less than 55%, or may be less than 40%.

[0062] The gel fraction is measured by the following method. That is, about 0.5 g of a measurement sample is precisely weighed, and its weight is designated as W1. This measurement sample is wrapped in a porous PTFE (polytetrafluoroethylene) sheet and immersed in ethyl acetate at room temperature for one week, and then dried, and the weight W2 of the ethyl acetate-insoluble portion is measured, and W1 and W2 are calculated using the following formula: Gel fraction (%) = W2 / W1 × 100; The gel fraction is calculated by substituting the above formula: As the porous PTFE sheet, a product manufactured by Nitto Denko Corporation under the trade name "Nitoflon NTF1122" or an equivalent product can be used.

[0063] In some embodiments of the photocrosslinkable pressure-sensitive adhesive disclosed herein, the photocrosslinkable pressure-sensitive adhesive is exposed to an illuminance of 300 mW / cm using a high-pressure mercury lamp. 2 , cumulative light intensity 10,000mJ / cm 2 The gel fraction of the photocrosslinked product obtained by irradiating with ultraviolet light under the above conditions may be, for example, 70% or more, preferably 90% or more, or may be 95% or more, or may be 98% or more. In principle, the gel fraction of the photocrosslinked product is 100% or less. The gel fraction is measured by the above method.

[0064] (Formation of photocrosslinked product) The photocrosslinkable adhesive disclosed herein can be photocrosslinked, for example, by irradiating it with ultraviolet light containing a wavelength component capable of exciting the benzophenone structure. It is preferable to use a light source capable of irradiating ultraviolet light containing a component with a wavelength of less than 300 nm. Examples of such light sources include, but are not limited to, high-pressure mercury lamps, low-pressure mercury lamps, metal halide lamps, and super UV lamps. The light irradiated by the light source may contain a component with a wavelength of 300 nm or more.

[0065] Examples of light sources capable of irradiating ultraviolet light that does not contain or contains only a small amount of wavelength components (e.g., components with wavelengths less than 300 nm) capable of exciting the benzophenone structure include black lights and UV-LED lamps. These light sources can be preferably used as light sources for promoting the reaction (polymerization reaction or curing reaction) of ethylenically unsaturated groups by light irradiation in the presence of the benzophenone structure. In the ultraviolet irradiation for reacting the ethylenically unsaturated groups, a photoinitiator, which will be described later, can be used to promote the reaction.

[0066] The photocrosslinkable pressure-sensitive adhesive disclosed herein may be substantially free of photoinitiators that generate radicals upon absorbing light with a wavelength of 300 nm or longer. For example, it may be substantially free of photoinitiators that generate radicals upon absorbing visible light with a wavelength of 380 nm or longer (particularly 400 nm or longer). This may be advantageous in terms of the optical properties of the photocrosslinkable pressure-sensitive adhesive. "Not containing photoinitiators that generate radicals upon absorbing light with a wavelength of 300 nm or longer" refers to not containing the photoinitiator in a form capable of generating the radicals (i.e., a form having a site cleaved by the light), although the presence of cleavage residues of the photoinitiator is acceptable. A photocrosslinkable pressure-sensitive adhesive according to a preferred embodiment is substantially free of photoinitiators containing a phosphorus element in the molecule. The photocrosslinkable pressure-sensitive adhesive disclosed herein may be substantially free of both photoinitiators containing a phosphorus element in the molecule and cleavage residues of the photoinitiators.

[0067] <Adhesive composition> This specification provides a pressure-sensitive adhesive composition comprising a polymer (BP polymer) (A) having a benzophenone structure in its side chain and an ethylenically unsaturated compound (B). Such a pressure-sensitive adhesive composition can be used to produce any of the photocrosslinkable pressure-sensitive adhesives disclosed herein. In some embodiments, the pressure-sensitive adhesive composition can be an acrylic pressure-sensitive adhesive composition in which more than 50 wt % (preferably more than 70 wt %, e.g., more than 90 wt %) of the total monomer components constituting the pressure-sensitive adhesive composition are acrylic monomers.

[0068] The BP polymer (A) used as a constituent of the pressure-sensitive adhesive composition may be the same as the BP polymer contained in the photocrosslinkable pressure-sensitive adhesive, and therefore a duplicated description will be omitted.

[0069] (Ethylenically unsaturated compound (B)) Examples of compounds that can be used as the ethylenically unsaturated compound (B) include the above-mentioned (meth)acrylic acid alkyl esters and the above-mentioned ethylenically unsaturated BPs. Among these, at least the (meth)acrylic acid alkyl esters (e.g., (meth)acrylic acid C) are preferred. 1-20Alkyl esters, more preferably (meth)acrylic acid C 4-18 Alkyl esters, more preferably acrylic acid C 4-9 It is preferable to use (meth)acrylic acid alkyl esters (e.g., n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) as particularly preferred (meth)acrylic acid alkyl esters. Other specific examples of (meth)acrylic acid alkyl esters that can be preferably used include isononyl acrylate, n-butyl methacrylate (BMA), 2-ethylhexyl methacrylate (2EHMA), isostearyl acrylate (iSTA), and the like. The (meth)acrylic acid alkyl esters can be used alone or in combination of two or more. In some embodiments, the ethylenically unsaturated compound (B) preferably contains either one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA). In one embodiment, it is more preferable to contain at least 2EHA. In another embodiment, it is more preferable to contain at least BA.

[0070] In some embodiments, the ethylenically unsaturated compound (B) is acrylic acid C 4-9 The ethylenically unsaturated compound (B) may contain acrylic acid C in an amount of 40% by weight or more of alkyl ester. 4-9 The proportion of alkyl ester may be, for example, 50% by weight or more, 60% by weight or more, or 65% by weight or more. In addition, from the viewpoint of enhancing the cohesiveness of the photocrosslinkable pressure-sensitive adhesive, the proportion of acrylic acid C in the ethylenically unsaturated compound (B) may be 4-9 The proportion of alkyl ester is usually suitably 99.5% by weight or less, and may be 95% by weight or less, 85% by weight or less, 70% by weight or less, or 60% by weight or less.

[0071] Other examples of compounds that can be used as the ethylenically unsaturated compound (B) include ethylenically unsaturated compounds (copolymerizable monomers) copolymerizable with (meth)acrylic acid alkyl esters. Monomers having polar groups (e.g., carboxyl groups, hydroxyl groups, nitrogen atom-containing rings, etc.) can be suitably used as the copolymerizable monomers. Monomers having polar groups can be useful, for example, for introducing crosslinking points into polymers containing repeating units derived from the monomers, or for increasing the cohesive strength of photocrosslinkable pressure-sensitive adhesives. The copolymerizable monomers can be used alone or in combination of two or more.

[0072] Non-limiting examples of copolymerizable monomers include the following: Carboxy group-containing monomers: for example, acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc. Acid anhydride group-containing monomers: for example, maleic anhydride, itaconic anhydride. Hydroxyl group-containing monomers: for example, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. Monomers containing a sulfonic acid group or a phosphoric acid group: for example, styrenesulfonic acid, allylsulfonic acid, sodium vinylsulfonate, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, (meth)acryloyloxynaphthalenesulfonic acid, 2-hydroxyethyl acryloylphosphate, etc. Epoxy group-containing monomers: for example, epoxy group-containing acrylates such as glycidyl (meth)acrylate and 2-ethyl (meth)acrylate glycidyl ether, allyl glycidyl ether, glycidyl (meth)acrylate, etc. Cyano group-containing monomers: for example, acrylonitrile, methacrylonitrile, etc. Isocyanate group-containing monomers: for example, 2-(meth)acryloyloxyethyl isocyanate, (meth)acryloyl isocyanate, m-isopropenyl-α,α-dimethylbenzyl isocyanate, and the like. Amide group-containing monomers: for example, (meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, and N,N-di(t-butyl)(meth)acrylamide; N-alkyl(meth)acrylamides such as N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, and Nn-butyl(meth)acrylamide; N-vinylcarboxylic acid amides such as N-vinylacetamide; monomers having a hydroxyl group and an amide group, for example, N-(2-hydroxyethyl)(meth)acrylamide N-hydroxyalkyl (meth)acrylamides such as N-(2-hydroxypropyl) (meth)acrylamide, N-(1-hydroxypropyl) (meth)acrylamide, N-(3-hydroxypropyl) (meth)acrylamide, N-(2-hydroxybutyl) (meth)acrylamide, N-(3-hydroxybutyl) (meth)acrylamide, and N-(4-hydroxybutyl) (meth)acrylamide; monomers having an alkoxy group and an amide group, for example, N-alkoxyalkyl (meth)acrylamides such as N-methoxymethyl (meth)acrylamide, N-methoxyethyl (meth)acrylamide, and N-butoxymethyl (meth)acrylamide; and others such as N,N-dimethylaminopropyl (meth)acrylamide and N-(meth)acryloylmorpholine. Amino group-containing monomers: 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. 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-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine N-vinyl morpholine, N-(meth)acryloyl morpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinyl pyrazole, N-vinyl isoxazole, N-vinyl thiazole, N-vinyl isothiazole, N-vinyl pyridazine, and the like (for example, lactams such as N-vinyl-2-caprolactam). Monomers having a succinimide skeleton: for example, N-(meth)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxyhexamethylene succinimide, N-(meth)acryloyl-8-oxyhexamethylene succinimide, and the like. Maleimides: for example, N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide, etc. Itaconimides: for example, N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, N-laurylitaconimide, and the like. Aminoalkyl (meth)acrylates: for example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate. Alkoxy group-containing monomers: for example, alkoxyalkyl (meth)acrylates (alkoxyalkyl (meth)acrylates) such as 2-methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, and ethoxypropyl (meth)acrylate; alkoxyalkylene (meth)acrylates (for example, alkoxypolyalkylene glycol (meth)acrylates) such as methoxyethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate. Alkoxysilyl group-containing monomers: for example, alkoxysilyl group-containing (meth)acrylates such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane; and alkoxysilyl group-containing vinyl compounds such as vinyltrimethoxysilane and vinyltriethoxysilane. Vinyl esters: for example, vinyl acetate, vinyl propionate, etc. Vinyl ethers: for example, vinyl alkyl ethers such as methyl vinyl ether and ethyl vinyl ether. Aromatic vinyl compounds: for example, styrene, α-methylstyrene, vinyltoluene, etc. Olefins: for example, ethylene, butadiene, isoprene, isobutylene, etc. (Meth)acrylic acid esters having an alicyclic hydrocarbon group: for example, (meth)acrylates containing an alicyclic hydrocarbon group such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and adamantyl (meth)acrylate. (Meth)acrylic acid esters having an aromatic hydrocarbon group: for example, (meth)acrylates containing an aromatic hydrocarbon group such as phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, and benzyl (meth)acrylate. Other examples include heterocyclic ring-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, halogen atom-containing (meth)acrylates such as vinyl chloride and fluorine atom-containing (meth)acrylates, silicon atom-containing (meth)acrylates such as silicone (meth)acrylate, and (meth)acrylic acid esters obtained from terpene compound derivative alcohols.

[0073] When such a copolymerizable monomer is used, its amount is not particularly limited, but is usually suitably 0.01 wt% or more of the total monomer components constituting the pressure-sensitive adhesive composition. From the viewpoint of better exerting the effect of using the copolymerizable monomer, the amount of the copolymerizable monomer used (i.e., the weight fraction of the copolymerizable monomer in the total monomer components) may be 0.1 wt% or more, or even 0.5 wt% or more of the total monomer components. Furthermore, from the viewpoint of easily balancing the adhesive properties, the amount of the copolymerizable monomer used is usually suitably 50 wt% or less, and preferably 40 wt% or less, of the total monomer components.

[0074] In some embodiments, the copolymerizable monomer may include a monomer having a nitrogen atom. The use of a monomer having a nitrogen atom can increase the cohesive strength of the photocrosslinkable pressure-sensitive adhesive and preferably improve the peel strength after photocrosslinking. A suitable example of the monomer having a nitrogen atom is a monomer having a nitrogen atom-containing ring. The monomer having a nitrogen atom-containing ring may be one of those exemplified above, for example, a monomer represented by the general formula (1): [ka] In the general formula (1), an N-vinyl cyclic amide represented by the formula: 1 is a divalent organic group, specifically -(CH2) n-. n is an integer of 2 to 7 (preferably 2, 3, or 4). Of these, N-vinyl-2-pyrrolidone can be preferably used. Another suitable example of a monomer having a nitrogen atom is (meth)acrylamide.

[0075] When a nitrogen atom-containing monomer (preferably a monomer having a nitrogen atom-containing ring such as N-vinyl cyclic amide or N-(meth)acryloyl cyclic amide) is used, the amount used is not particularly limited and may be, for example, 1% by weight or more, 2% by weight or more, 3% by weight or more, or even 5% by weight or more, or 7% by weight or more of the total monomer components. In one embodiment, the amount of the nitrogen atom-containing monomer used may be 10% by weight or more, 15% by weight or more, or even 20% by weight or more of the total monomer components. Furthermore, the amount of the nitrogen atom-containing monomer used is suitably, for example, 40% by weight or less of the total monomer components, and may be 35% by weight or less, 30% by weight or less, or 25% by weight or less. In another embodiment, the amount of the nitrogen atom-containing monomer used may be, for example, 20% by weight or less, 15% by weight or less, or less than 10% by weight, or less than 6% by weight of the total monomer components.

[0076] In some embodiments, the copolymerizable monomer may include a hydroxyl group-containing monomer. The use of a hydroxyl group-containing monomer can favorably adjust the cohesive strength and degree of crosslinking (e.g., crosslinking with an isocyanate crosslinking agent) of the photocrosslinkable pressure-sensitive adhesive. When a hydroxyl group-containing monomer is used, the amount used is not particularly limited and may be, for example, 0.01 wt% or more, 0.1 wt% or more, 0.5 wt% or more, 1 wt% or more, 5 wt% or more, or 10 wt% or more of the total monomer components. Furthermore, from the viewpoint of suppressing water absorption of the photocrosslinkable pressure-sensitive adhesive or its photocrosslinked product, in some embodiments, the amount of the hydroxyl group-containing monomer used is suitably, for example, 40 wt% or less of the total monomer components, such as 30 wt% or less, 25 wt% or less, or 20 wt% or less. In another embodiment, the amount of the hydroxyl group-containing monomer used may be, for example, 15 wt% or less, 10 wt% or less, or 5 wt% or less of the total monomer components. Alternatively, a hydroxyl group-containing monomer need not be used as the copolymerizable monomer.

[0077] In some embodiments, the proportion of the carboxy group-containing monomer in the total monomer components may be, for example, 2 wt % or less, 1 wt % or less, or 0.5 wt % or less (e.g., less than 0.1 wt %). The pressure-sensitive adhesive composition may be substantially free of a carboxy group-containing monomer as a constituent monomer component. Here, "substantially free of a carboxy group-containing monomer" means that a carboxy group-containing monomer is not used at least intentionally. This can be advantageous from the viewpoint of, for example, the metal corrosion resistance of a photocrosslinkable pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition and its photocrosslinked product.

[0078] In some embodiments, the copolymerizable monomer may contain an alicyclic hydrocarbon group-containing (meth)acrylate. This can increase the cohesive strength of the pressure-sensitive adhesive and improve peel strength after photocrosslinking. Examples of the alicyclic hydrocarbon group-containing (meth)acrylate include those exemplified above. For example, cyclohexyl acrylate and isobornyl acrylate are preferred. When an alicyclic hydrocarbon group-containing (meth)acrylate is used, its amount is not particularly limited and can be, for example, 1% by weight or more, 3% by weight or more, or 5% by weight or more of the total monomer components. In one embodiment, the amount of the alicyclic hydrocarbon group-containing (meth)acrylate used may be 10% by weight or more, 15% by weight or more, more than 20% by weight, or even more than 25% by weight of the total monomer components. The upper limit of the amount of the alicyclic hydrocarbon group-containing (meth)acrylate used is suitably approximately 40% by weight or less, for example, 30% by weight or less, or 25% by weight or less (e.g., 15% by weight or less, or even 10% by weight or less).

[0079] In some embodiments, the copolymerizable monomer may include an alkoxysilyl group-containing monomer. The alkoxysilyl group-containing monomer is typically an ethylenically unsaturated compound having at least one (preferably two or more, e.g., two or three) alkoxysilyl group in one molecule, specific examples of which are as described above. The alkoxysilyl group-containing monomer may be used alone or in combination of two or more. The use of an alkoxysilyl group-containing monomer can introduce a crosslinked structure into the photocrosslinkable pressure-sensitive adhesive through a condensation reaction of silanol groups (silanol condensation). The alkoxysilyl group-containing monomer may also be useful for improving the peel strength of the adhesive to the adherend.

[0080] The amount of the alkoxysilyl group-containing monomer used is not particularly limited. In some embodiments, the amount of the alkoxysilyl group-containing monomer used can be, for example, 0.005 wt% or more of the total monomer components constituting the pressure-sensitive adhesive composition, and is usually 0.01 wt% or more. It may be 0.03 wt% or more, 0.05 wt% or more, or 0.07 wt% or more. From the viewpoint of obtaining a higher use effect, it may be more than 0.1 wt%, more than 0.2 wt%, or more than 0.3 wt%. Furthermore, from the viewpoint of the surface shape conformability of the photocrosslinkable pressure-sensitive adhesive, the amount of the alkoxysilyl group-containing monomer used is usually 1.0 wt% or less of the total monomer components, and may be 0.5 wt% or less, 0.35 wt% or less, 0.25 wt% or less, 0.1 wt% or less, or less than 0.1 wt%.

[0081] Further examples of compounds that can be used as the ethylenically unsaturated compound (B) include polyfunctional monomers. When a pressure-sensitive adhesive composition containing a polyfunctional monomer is used, the composition is cured to produce a photocrosslinkable pressure-sensitive adhesive, and the polyfunctional monomer is reacted to produce a photocrosslinkable pressure-sensitive adhesive crosslinked by the polyfunctional monomer. Examples of polyfunctional monomers include bifunctional monomers such as 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, and divinylbenzene; trifunctional or higher polyfunctional monomers such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; and others such as epoxy acrylate, polyester acrylate, and urethane acrylate. Among these, preferred examples include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. The polyfunctional monomers can be used alone or in combination of two or more.

[0082] When a polyfunctional monomer is used, the amount used is not particularly limited and can be set so as to form a photocrosslinkable pressure-sensitive adhesive that exhibits suitable properties. In some embodiments, the amount of polyfunctional monomer used can be less than 5.0 wt% of the total monomer components constituting the pressure-sensitive adhesive composition. This prevents the formation of an excessively crosslinked structure during the formation of the photocrosslinkable pressure-sensitive adhesive (i.e., before photocrosslinking), thereby improving the surface conformability of the photocrosslinkable pressure-sensitive adhesive. The amount of the polyfunctional monomer used can be, for example, 4.0 wt% or less, 3.0 wt% or less, 2.0 wt% or less, 1.0 wt% or less, 0.5 wt% or less, or 0.3 wt% or less of the total monomer components. It is not necessary to use a polyfunctional monomer. In some embodiments, from the viewpoint of imparting appropriate cohesiveness to the photocrosslinkable adhesive, the amount of polyfunctional monomer used relative to the total monomer components may be, for example, 0.001% by weight or more, 0.005% by weight or more, 0.01% by weight or more, or 0.03% by weight or more.

[0083] In some embodiments, a bifunctional monomer may be preferably used as the polyfunctional monomer from the viewpoint of the surface conformability of the photocrosslinkable pressure-sensitive adhesive, etc. The proportion of the bifunctional monomer in the total polyfunctional monomers used may be, for example, 50% by weight or more, 70% by weight or more, 90% by weight or more, or even 100% by weight.

[0084] The weight percentage of the BP polymer (A) relative to the total amount of the BP polymer (A) and the ethylenically unsaturated compound (B) contained in the PSA composition is not particularly limited and can be set so as to achieve a favorable balance between the surface conformability of the photocrosslinkable PSA formed from the PSA composition and the deformation resistance of the photocrosslinked product. In some embodiments, the weight percentage of the BP polymer may be, for example, 1 wt% or more, and typically 5 wt% or more. From the perspective of enhancing the photocrosslinking effect, it may be 10 wt% or more, 15 wt% or more, 25 wt% or more, 35 wt% or more, 45 wt% or more, or 55 wt% or more. Furthermore, from the perspective of ease of preparation and coatability of the PSA composition, in some embodiments, the weight percentage of the BP polymer relative to the total amount may be, for example, less than 99 wt%, less than 95 wt%, less than 85 wt%, less than 70 wt%, less than 50 wt%, or less than 40 wt%.

[0085] In the PSA composition disclosed herein, the weight ratio of the organic solvent to the total weight of the PSA composition may be, for example, 30 wt% or less, advantageously 20 wt% or less, preferably 10 wt% or less, and more preferably 5 wt% or less. In some embodiments, the weight ratio of the organic solvent may be 3 wt% or less, 1 wt% or less, 0.5 wt% or less, 0.1 wt% or less, or 0.05 wt% or less, or the PSA composition may be substantially free of organic solvent. Reducing the weight ratio of the organic solvent in the PSA composition is preferred from the viewpoint of reducing VOCs in the photocrosslinkable PSA formed from the PSA composition. The PSA composition disclosed herein contains an ethylenically unsaturated compound (B) in addition to the BP polymer (A), and therefore the ethylenically unsaturated compound (B) can be used as a diluent for the BP polymer (A). As a result, even in a pressure-sensitive adhesive composition containing a BP polymer (A) having a Mw of a certain level or more in a certain amount or more, an organic solvent is not required to improve the coatability of the pressure-sensitive adhesive composition in the normal temperature range (e.g., 20°C to 40°C), or the amount of the organic solvent used can be reduced.

[0086] In some embodiments of the PSA composition disclosed herein, from the viewpoint of coatability in the room temperature range, the PSA composition suitably has a viscosity (measured using a BH-type viscometer with a No. 5 rotor at 10 rpm and a measurement temperature of 30°C; the same applies hereinafter) of 1,000 Pa·s or less, preferably 100 Pa·s or less, and more preferably 50 Pa·s or less. The viscosity of the PSA composition may be, for example, 30 Pa·s or less, 20 Pa·s or less, 10 Pa·s or less, or 5 Pa·s or less. There are no particular restrictions on the lower limit of the viscosity of the PSA composition, but from the viewpoint of preventing repelling of the PSA composition within the coating area and protrusion of the PSA composition at the outer edges of the coating area, the viscosity is usually suitably 0.1 Pa·s or more, and may be 0.5 Pa·s or more, or may be 1 Pa·s or more.

[0087] The PSA composition according to some embodiments contains at least a compound (B1) having one ethylenically unsaturated group (i.e., a monofunctional monomer) as the ethylenically unsaturated compound (B). The monofunctional monomer (B1) can be selected from the above-mentioned examples of the ethylenically unsaturated compound (B). The monofunctional monomer (B1) can be used alone or in combination of two or more.

[0088] The weight proportion of the monofunctional monomer (B1) in the total amount of the BP polymer (A) and the ethylenically unsaturated compound (B) may be, for example, 1 wt% or more, 5 wt% or more, or 15 wt% or more. In some embodiments, from the viewpoint of ease of preparation and coatability of the PSA composition, the weight proportion of the monofunctional monomer (B1) may be 25 wt% or more, 35 wt% or more, or 45 wt% or more. Furthermore, the weight proportion of the monofunctional monomer (B1) in the total amount may be, for example, 99 wt% or less, and typically 95 wt% or less is suitable, but may also be 85 wt% or less, 75 wt% or less, 65 wt% or less, 55 wt% or less, or 45 wt% or less.

[0089] In embodiments in which the PSA composition contains a monofunctional monomer (B1), the glass transition temperature (Tg) calculated by the Fox equation based on the composition of the monofunctional monomer (B1) is not particularly limited and may be, for example, from -80°C to 250°C. From the viewpoint of compatibility between the polymer derived from the monofunctional monomer (B1) and other components, the Tg based on the composition of the monofunctional monomer (B1) is typically preferably 150°C or less, and may be 100°C or less, 70°C or less, 50°C or less, or 30°C or less. In some embodiments, from the viewpoint of the surface conformability of the photocrosslinkable PSA, the Tg based on the composition of the monofunctional monomer (B1) is preferably less than 0°C, more preferably -10°C or less, and may be -20°C or less, -30°C or less, or -40°C or less. Furthermore, from the viewpoint of the cohesion of the photocrosslinkable pressure-sensitive adhesive and the resistance to deformation after photocrosslinking (for example, adhesion durability to an adherend), the Tg based on the composition of the monofunctional monomer (B1) is usually advantageously −60° C. or higher, and may be −54° C. or higher, −50° C. or higher, −45° C. or higher, −35° C. or higher, or −25° C. The Tg can be adjusted by the compounds used as the monofunctional monomer (B1) and the ratio of their amounts used.

[0090] In a pressure-sensitive adhesive composition containing a BP polymer (A) and a monofunctional monomer (B1), a photocrosslinkable pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition, and a photocrosslinked product thereof, the Tg of the BP polymer (A) (hereinafter referred to as "Tg A ") and the Tg based on the monomer composition of the monofunctional monomer (B1) (hereinafter referred to as Tg B1 ") is also called Tg B1 [℃]-Tg AThe Tg difference [°C] (hereinafter also referred to as ΔTg) calculated by [°C] can be set to, for example, a range of -50°C or more and 70°C or less. It can be advantageous from the viewpoint of compatibility between the photocrosslinkable pressure-sensitive adhesive and its photocrosslinked product if the absolute value of the Tg difference is not too large. In some embodiments, ΔTg may be, for example, -10°C or more, preferably 0°C or more, 7°C or more, 10°C or more, 20°C or more, or 30°C or more. In some embodiments, ΔTg may be, for example, 50°C or less, 30°C or less, or 15°C or less.

[0091] The pressure-sensitive adhesive composition according to some embodiments contains at least a compound (B2) having two or more ethylenically unsaturated groups (i.e., a polyfunctional monomer) as the ethylenically unsaturated compound (B). The polyfunctional monomer (B2) may be one of the polyfunctional monomers listed above, or a combination of two or more thereof. The amount of the polyfunctional monomer (B2) used may be set to the same ratio as the proportion of the polyfunctional monomer in the total monomer components constituting the pressure-sensitive adhesive composition.

[0092] In an embodiment in which a monofunctional monomer (B1) and a polyfunctional monomer (B2) are used in combination as the ethylenically unsaturated compound (B), the weight proportion of the monofunctional monomer (B1) in the ethylenically unsaturated compound (B) may be, for example, 1% by weight or more, and typically 25% by weight or more, but may also be 50% by weight or more, 75% by weight or more, 95% by weight or more, or 99% by weight or more. Also, the weight proportion of the monofunctional monomer (B1) in the ethylenically unsaturated compound (B) may be, for example, 99.9% by weight or less, or 99.8% by weight or less.

[0093] In the pressure-sensitive adhesive composition disclosed herein, the ethylenically unsaturated compound (B) may be contained in the form of a partial polymer, or the entire amount may be contained in the form of an unreacted monomer. A preferred embodiment of the pressure-sensitive adhesive composition contains the ethylenically unsaturated compound (B) in the form of a partial polymer. The polymerization method for partially polymerizing the ethylenically unsaturated compound (B) is not particularly limited, and various conventionally known polymerization methods can be appropriately selected and used, such as photopolymerization performed by irradiating with light such as ultraviolet rays; radiation polymerization performed by irradiating with radiation such as beta rays or gamma rays; and thermal polymerization such as solution polymerization, emulsion polymerization, and bulk polymerization. From the viewpoints of efficiency and simplicity, photopolymerization is preferably employed. Photopolymerization allows the polymerization conversion rate (monomer conversion) to be easily controlled by adjusting polymerization conditions such as the light irradiation dose (light amount).

[0094] The polymerization conversion rate of the ethylenically unsaturated compound (B) in the partial polymer is not particularly limited. From the viewpoint of ease of preparation of the pressure-sensitive adhesive composition and coatability, the polymerization conversion rate is usually about 50% by weight or less, and preferably about 40% by weight or less (for example, about 35% by weight or less). The lower limit of the polymerization conversion rate is not particularly limited, but is typically about 1% by weight or more, and usually about 5% by weight or more.

[0095] A pressure-sensitive adhesive composition containing a partial polymer of an ethylenically unsaturated compound (B) can be obtained, for example, by partially polymerizing a monomer mixture containing the entire amount of the ethylenically unsaturated compound (B) used in preparing the pressure-sensitive adhesive composition by an appropriate polymerization method (e.g., photopolymerization). Alternatively, a pressure-sensitive adhesive composition containing a partial polymer of an ethylenically unsaturated compound (B) may be a mixture of a partial polymer of a monomer mixture containing a portion of the ethylenically unsaturated compound (B) used in preparing the pressure-sensitive adhesive composition and the remaining ethylenically unsaturated compound (B) or a partial polymer thereof. In this specification, the term "completely polymerized" refers to a polymer having a polymerization conversion rate of more than 95% by weight.

[0096] The partial polymer can be prepared, for example, by irradiating an ethylenically unsaturated compound with ultraviolet light. When the partial polymer is prepared in the presence of a BP polymer, a pressure-sensitive adhesive composition containing a partial polymer of an ethylenically unsaturated compound and a BP polymer can be obtained by setting the ultraviolet light irradiation conditions so that the ethylenically unsaturated groups react and the benzophenone structure is not photoexcited. The light source preferably used is a light source capable of irradiating ultraviolet light that does not contain or has a small amount of components with wavelengths shorter than 300 nm, such as the above-mentioned black light or UV-LED lamp.

[0097] Alternatively, a partial polymer of the ethylenically unsaturated compound (B) may be prepared in advance, and then the partial polymer may be mixed with the BP polymer to prepare the PSA composition. When the partial polymer is prepared by irradiating the ethylenically unsaturated compound with ultraviolet light in the absence of a benzophenone structure-containing component, the ultraviolet light source may be either a light source that does not excite the benzophenone structure or a light source that does excite the benzophenone structure.

[0098] In preparing the partial polymer of the ethylenically unsaturated compound (B), the reaction of the ethylenically unsaturated group can be promoted by using a photoinitiator. Examples of photoinitiators that can be used include ketal-based photoinitiators, acetophenone-based photoinitiators, benzoin ether-based photoinitiators, acylphosphine oxide-based photoinitiators, α-ketol-based photoinitiators, aromatic sulfonyl chloride-based photoinitiators, photoactive oxime-based photoinitiators, benzoin-based photoinitiators, benzyl-based photoinitiators, benzophenone-based photoinitiators, alkylphenone-based photoinitiators, and thioxanthone-based photoinitiators. Photoinitiators that absorb light with a wavelength of 300 nm or more (e.g., light with a wavelength of 300 nm or more but not greater than 500 nm) and generate radicals are preferably used. One photoinitiator can be used alone, or two or more photoinitiators can be used in appropriate combination.

[0099] (Photoinitiator (C)) The pressure-sensitive adhesive composition may contain a photoinitiator as needed to improve or impart photocurability. Examples of photoinitiators that can be used include ketal-based photoinitiators, acetophenone-based photoinitiators, benzoin ether-based photoinitiators, acylphosphine oxide-based photoinitiators, α-ketol-based photoinitiators, aromatic sulfonyl chloride-based photoinitiators, photoactive oxime-based photoinitiators, benzoin-based photoinitiators, benzyl-based photoinitiators, benzophenone-based photoinitiators, alkylphenone-based photoinitiators, and thioxanthone-based photoinitiators. One photoinitiator can be used alone, or two or more can be used in appropriate combination.

[0100] Specific examples of ketal-based photoinitiators include 2,2-dimethoxy-1,2-diphenylethan-1-one, and the like. Specific examples of acetophenone-based photoinitiators include 1-hydroxycyclohexyl-phenyl-ketone, 4-phenoxydichloroacetophenone, 4-t-butyl-dichloroacetophenone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, methoxyacetophenone, and the like. Specific examples of the benzoin ether photoinitiator include benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, and benzoin isobutyl ether, and substituted benzoin ethers such as anisole methyl ether. Specific examples of the acylphosphine oxide photoinitiator include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and the like. Specific examples of α-ketol-based photoinitiators include 2-methyl-2-hydroxypropiophenone, 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one, etc. Specific examples of aromatic sulfonyl chloride-based photoinitiators include 2-naphthalenesulfonyl chloride, etc. Specific examples of photoactive oxime-based photoinitiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime, etc. Specific examples of benzoin-based photoinitiators include benzoin, etc. Specific examples of benzyl-based photoinitiators include benzil, etc. Specific examples of the benzophenone-based photoinitiator include benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, α-hydroxycyclohexylphenyl ketone, and the like. Specific examples of the thioxanthone-based photoinitiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, dodecylthioxanthone, and the like.

[0101] As the photoinitiator (C) to be contained in the pressure-sensitive adhesive composition, a photoinitiator that absorbs light with a wavelength of 300 nm or more (for example, light with a wavelength of 300 nm or more and 500 nm or less) and generates radicals can be preferably used. The photoinitiators can be used alone or in appropriate combination of two or more. In some embodiments, a photoinitiator that does not contain a phosphorus element in the molecule can be preferably used. The pressure-sensitive adhesive composition disclosed herein can be substantially free of a photoinitiator that contains a phosphorus element in the molecule.

[0102] The content of the photoinitiator in the pressure-sensitive adhesive composition is not particularly limited and can be set so as to appropriately achieve the desired effect. In some embodiments, the content of the photoinitiator can be, for example, approximately 0.005 parts by weight or more, typically 0.01 parts by weight or more is appropriate, and preferably 0.05 parts by weight or more, and may be 0.10 parts by weight or more, 0.15 parts by weight or more, or even 0.20 parts by weight or more, relative to 100 parts by weight of the monomer components constituting the pressure-sensitive adhesive composition. Increasing the content of the photoinitiator improves the photocurability of the pressure-sensitive adhesive composition. Furthermore, the content of the photoinitiator relative to 100 parts by weight of the monomer components constituting the pressure-sensitive adhesive composition is typically 5 parts by weight or less, preferably 2 parts by weight or less, and may be 1 part by weight or less, 0.7 parts by weight or less, or 0.5 parts by weight or less. Not having an excessive photoinitiator content can be advantageous from the standpoint of suppressing gelation of the pressure-sensitive adhesive composition, for example.

[0103] (Crosslinking agent) The pressure-sensitive adhesive composition may contain known crosslinking agents, such as isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, melamine-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, hydrazine-based crosslinking agents, and amine-based crosslinking agents, as needed. Peroxides may also be used as crosslinking agents. These crosslinking agents may be used alone or in combination of two or more. Photocrosslinkable pressure-sensitive adhesives formed from pressure-sensitive adhesive compositions containing a crosslinking agent preferably contain the crosslinking agent primarily in the form after the crosslinking reaction. The use of a crosslinking agent allows the cohesive strength and other properties of the photocrosslinkable pressure-sensitive adhesive to be appropriately adjusted.

[0104] When a crosslinking agent is used, the amount used (the total amount when two or more crosslinking agents are used) is not particularly limited. From the viewpoint of realizing a PSA that exhibits well-balanced adhesive properties such as adhesive strength and cohesive strength, the amount of crosslinking agent used is usually approximately 5 parts by weight or less per 100 parts by weight of the monomer components constituting the PSA composition, and may be 3 parts by weight or less, 1 part by weight or less, 0.50 parts by weight or less, 0.30 parts by weight or less, or 0.20 parts by weight or less. The lower limit of the amount of crosslinking agent used is not particularly limited, and it may be an amount greater than 0 parts by weight per 100 parts by weight of the monomer components constituting the PSA composition. In some embodiments, the amount of crosslinking agent used may be, for example, 0.001 parts by weight or more, 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.10 parts by weight or more per 100 parts by weight of the monomer components constituting the PSA composition. The technology disclosed herein can also be preferably practiced in an embodiment in which a crosslinking agent is not used.

[0105] (chain transfer agent) The PSA composition may contain various conventionally known chain transfer agents. Examples of the chain transfer agent include mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, thioglycolic acid, and α-thioglycerol. Alternatively, a chain transfer agent that does not contain a sulfur atom (a non-sulfur chain transfer agent) may be used. Specific examples of non-sulfur chain transfer agents include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenoids such as α-pinene and terpinolene; styrenes such as α-methylstyrene and α-methylstyrene dimer; compounds having a benzylidenyl group such as dibenzylideneacetone, cinnamyl alcohol, and cinnamylaldehyde; hydroquinones such as hydroquinone and naphthohydroquinone; quinones such as benzoquinone and naphthoquinone; olefins such as 2,3-dimethyl-2-butene and 1,5-cyclooctadiene; alcohols such as phenol, benzyl alcohol, and allyl alcohol; and benzyl hydrogen compounds such as diphenylbenzene and triphenylbenzene. Chain transfer agents can be used alone or in combination. When a chain transfer agent is used, the amount used can be, for example, approximately 0.01 to 1 part by weight per 100 parts by weight of the monomer components. The technology disclosed herein can also be preferably practiced in an embodiment in which a chain transfer agent is not used.

[0106] Other components that can be contained in the pressure-sensitive adhesive composition include a silane coupling agent. Use of a silane coupling agent can improve the peel strength from an adherend (e.g., a glass plate). Furthermore, the photocrosslinkable pressure-sensitive adhesive disclosed herein can contain a silane coupling agent. A photocrosslinkable pressure-sensitive adhesive containing a silane coupling agent can be suitably formed using a pressure-sensitive adhesive composition containing a silane coupling agent. The silane coupling agents can be used alone or in combination of two or more. The PSA composition disclosed herein may contain, as necessary, various additives commonly used in the field of PSA, such as tackifying resins (e.g., rosin-based, petroleum-based, terpene-based, phenol-based, ketone-based, etc. tackifying resins), viscosity modifiers (e.g., thickeners), leveling agents, antioxidants, plasticizers, fillers, colorants such as pigments and dyes, stabilizers, preservatives, antioxidants, etc. As for such various additives, conventionally known ones can be used in the usual manner, and as they do not particularly characterize the present invention, detailed description thereof will be omitted. The technology disclosed herein can exhibit good adhesive strength without using the above-mentioned tackifier resin. Therefore, in some embodiments, the content of the tackifier resin in the PSA layer or PSA composition can be, for example, less than 10 parts by weight, or even less than 5 parts by weight, per 100 parts by weight of the monomer component. The content of the tackifier resin may be less than 1 part by weight (e.g., less than 0.5 parts by weight), or may be less than 0.1 parts by weight (0 parts by weight or more but less than 0.1 parts by weight). The PSA layer or PSA composition may not contain a tackifier resin.

[0107] (Formation of photocrosslinkable adhesive) The pressure-sensitive adhesive composition disclosed herein is configured so that, by curing the pressure-sensitive adhesive composition, a photocrosslinkable pressure-sensitive adhesive containing a BP polymer can be formed. The pressure-sensitive adhesive composition is preferably cured so as to react the ethylenically unsaturated groups contained in the pressure-sensitive adhesive composition and leave the benzophenone structure contained in the pressure-sensitive adhesive composition. The curing is preferably carried out by irradiation with active energy rays. The active energy rays used to form the photocrosslinkable pressure-sensitive adhesive are preferably ultraviolet rays, and more preferably ultraviolet rays that do not contain or contain only a small amount of wavelength components of 300 nm or less.

[0108] The photocrosslinkable pressure-sensitive adhesive disclosed herein may be produced using any of the pressure-sensitive adhesive compositions disclosed herein. Such a photocrosslinkable pressure-sensitive adhesive may contain a BP polymer (A) and a polymer (E) derived from an ethylenically unsaturated compound (B). In some preferred embodiments, the pressure-sensitive adhesive composition may be one in which the ethylenically unsaturated compound (B) does not contain an ethylenically unsaturated BP. Using a pressure-sensitive adhesive composition of this type, a photocrosslinkable pressure-sensitive adhesive may be produced that contains a BP polymer (A) and a polymer (E) derived from an ethylenically unsaturated compound (B), where the polymer (E) is a non-BP polymer.

[0109] This specification provides a method for producing a photocrosslinkable pressure-sensitive adhesive that can be photocrosslinked by a benzophenone structure. The production method includes preparing a pressure-sensitive adhesive composition containing an ethylenically unsaturated group and a benzophenone structure, and irradiating the pressure-sensitive adhesive composition with active energy rays (preferably ultraviolet rays). The pressure-sensitive adhesive composition may contain a photoinitiator. The active energy rays used to cure the pressure-sensitive adhesive composition are preferably irradiated so as to react the ethylenically unsaturated group and leave the benzophenone structure. A pressure-sensitive adhesive composition containing a BP polymer (A) and an ethylenically unsaturated compound (B) is preferably used as the pressure-sensitive adhesive composition. The photocrosslinkable pressure-sensitive adhesive production method can be preferably carried out using any of the pressure-sensitive adhesive compositions disclosed herein. As a light source for curing the pressure-sensitive adhesive composition to form a photocrosslinkable pressure-sensitive adhesive, a light source capable of irradiating ultraviolet rays that do not contain or contain only a small amount of components with wavelengths shorter than 300 nm, such as the above-mentioned black light or UV-LED lamp, is preferably used.

[0110] <Adhesive sheet> According to this specification, there is provided a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of any of the photocrosslinkable pressure-sensitive adhesives disclosed herein. FIG. 1 shows an example of the configuration of a pressure-sensitive adhesive sheet disclosed herein. This pressure-sensitive adhesive sheet 1 is configured as a single-sided pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer 10, one surface 10A of which serves as the surface to be attached to an adherend (adhesive surface), and a substrate 20 laminated on the other surface 10B of the pressure-sensitive adhesive layer 10. The pressure-sensitive adhesive layer 10 is bonded to one surface 20A of the substrate 20. A plastic film such as a polyester film can be used as the substrate 20. The substrate 20 may also be an optical film such as a polarizing plate. In the example shown in FIG. 1, the pressure-sensitive adhesive layer 10 has a single-layer structure. Before use (before attachment to an adherend), the pressure-sensitive adhesive sheet 1 can be in the form of a release-liner-attached pressure-sensitive adhesive sheet 50, in which the adhesive surface 10A is protected by a release liner 30, at least the pressure-sensitive adhesive layer side of which serves as a release surface (release surface), as shown in FIG. 1, for example. Alternatively, the second surface 20B of the substrate 20 (the surface opposite to the first surface 20A, also called the back surface) may be the release surface, and the adhesive surface 10A may be protected by being wound or laminated so that the adhesive surface 10A abuts against the second surface 20B of the substrate 20.

[0111] The release liner is not particularly limited, and examples thereof include release liners in which the surface of a liner substrate such as a resin film or paper has been release-treated, and release liners made of low-adhesion materials such as fluorine-based polymers (e.g., polytetrafluoroethylene) and polyolefin-based resins (e.g., polyethylene and polypropylene). For the release treatment, for example, a silicone-based or long-chain alkyl-based release treating agent can be used. In some embodiments, a release-treated resin film can be preferably used as the release liner.

[0112] The PSA sheet disclosed herein may be in the form of a substrate-less double-sided PSA sheet comprising a PSA layer. As shown in FIG. 2, before use, the substrate-less double-sided PSA sheet 2 may be in a form in which each side 10A, 10B of the PSA layer 10 is protected by release liners 31, 32, with at least the PSA layer side serving as a releasable surface (release surface). Alternatively, the back surface of the release liner 31 (the surface opposite the PSA side) may be the release surface, and the PSA surface 10B may be protected by being wound or laminated so that the PSA surface 10B abuts against the back surface of the release liner 31. Such a substrate-less double-sided PSA sheet may be used, for example, by bonding a substrate to either surface of the PSA layer.

[0113] The pressure-sensitive adhesive sheet disclosed herein may be a component of an optical member with a pressure-sensitive adhesive sheet, in which an optical member is bonded to one surface of the pressure-sensitive adhesive layer. For example, the pressure-sensitive adhesive sheet 1 shown in Fig. 1 may be a component of an optical member 100 with a pressure-sensitive adhesive sheet, in which an optical member 70 is bonded to one surface 10A of the pressure-sensitive adhesive layer 10, as shown in Fig. 3. The optical member may be, for example, a glass plate, a resin film, a metal plate, or the like.

[0114] The pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet disclosed herein may be a cured layer of the corresponding pressure-sensitive adhesive composition. For example, the pressure-sensitive adhesive layer may be formed by applying (e.g., coating) the pressure-sensitive adhesive composition to a suitable surface and then curing the pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition is preferably cured by irradiation with active energy rays. The active energy rays for forming the pressure-sensitive adhesive layer are preferably ultraviolet rays, and more preferably ultraviolet rays that do not contain or contain only a small amount of components with wavelengths of 300 nm or less.

[0115] The pressure-sensitive adhesive composition can be applied using a conventional coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, a spray coater, etc. In a pressure-sensitive adhesive sheet having a substrate, the method of providing a pressure-sensitive adhesive layer on the substrate may be a direct method in which the pressure-sensitive adhesive composition is directly applied to the substrate to form a pressure-sensitive adhesive layer, or a transfer method in which a pressure-sensitive adhesive layer formed on the release surface is transferred to the substrate.

[0116] The thickness of the pressure-sensitive adhesive layer is not particularly limited and may be, for example, approximately 3 μm to 2000 μm. From the viewpoint of adhesion to the adherend, such as surface conformability (e.g., conformability to unevenness), in some embodiments, the thickness of the pressure-sensitive adhesive layer may be, for example, 5 μm or more, suitably 10 μm or more, preferably 20 μm or more, and more preferably 30 μm or more. The thickness of the pressure-sensitive adhesive layer may be 50 μm or more, may be more than 50 μm, may be 70 μm or more, may be 100 μm or more, or may be 120 μm or more. Furthermore, from the viewpoint of preventing the occurrence of adhesive residue due to cohesive failure of the pressure-sensitive adhesive layer, in some embodiments, the thickness of the pressure-sensitive adhesive layer may be, for example, 1000 μm or less, may be 700 μm or less, may be 500 μm or less, may be 300 μm or less, or may even be 200 μm or less, or may be 170 μm or less. The technology disclosed herein can also be suitably implemented in the form of a pressure-sensitive adhesive sheet in which the thickness of the pressure-sensitive adhesive layer is 130 μm or less, 90 μm or less, 60 μm or less, or 40 μm or less. In a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with a multilayer structure of two or more layers, the thickness of the pressure-sensitive adhesive layer refers to the thickness from the adhesive surface attached to the adherend to the surface opposite the adhesive surface. From the viewpoint of surface conformability, the pressure-sensitive adhesive layer of the multilayer structure preferably does not contain any layer other than the pressure-sensitive adhesive layer (e.g., a resin film) within the thickness of the pressure-sensitive adhesive layer (i.e., between the adhesive surface attached to the adherend and the surface opposite the adhesive surface).

[0117] <Base material> The PSA sheet according to some embodiments may be in the form of a substrate-attached PSA sheet containing a substrate bonded to a PSA layer. The material of the substrate is not particularly limited and can be appropriately selected depending on the intended use and manner of use of the PSA sheet. Non-limiting examples of usable substrates include plastic films (resin films) such as polyolefin films primarily composed of polyolefins such as polypropylene and ethylene-propylene copolymers, polyester films primarily composed of polyesters such as polyethylene terephthalate and polybutylene terephthalate, and polyvinyl chloride films primarily composed of polyvinyl chloride; foam sheets made of foams such as polyurethane foam, polyethylene foam, and polychloroprene foam; woven and nonwoven fabrics made by spinning various fibrous materials (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, and semi-synthetic fibers such as acetate), either alone or in combination; paper such as Japanese paper, fine paper, kraft paper, and crepe paper; and metal foils such as aluminum foil and copper foil. Substrates having a composite structure of these materials may also be used. Examples of such a substrate having a composite structure include a substrate having a structure in which a metal foil and the above-mentioned plastic film are laminated together, and a plastic sheet reinforced with inorganic fibers such as glass cloth.

[0118] Various films (hereinafter also referred to as support films) can be preferably used as the substrate of the PSA sheet disclosed herein. The support film may be a porous film such as a foam film or a nonwoven fabric sheet, or a nonporous film, or may be a film having a structure in which a porous layer and a nonporous layer are laminated. In some embodiments, the support film preferably includes a base film that is an independently shape-retaining (self-supporting or independent) resin film. Here, the term "resin film" refers to a resin film with a nonporous structure that is typically substantially bubble-free (void-free). Therefore, the resin film is a concept that is distinct from foam films and nonwoven fabrics. The resin film may have a single-layer structure or a multi-layer structure of two or more layers (e.g., a three-layer structure).

[0119] Examples of resin materials that can be used to form the resin film include polyester, polyolefin, polycycloolefin derived from a monomer having an alicyclic structure such as a norbornene structure, polyamides (PA) such as nylon 6, nylon 66, and partially aromatic polyamides, polyimides (PI) such as transparent polyimide (CPI), polyamideimide (PAI), polyether ether ketone (PEEK), polyethersulfone (PES), polyphenylene sulfide (PPS), polycarbonate (PC), polyurethane (PU), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), polystyrene, ABS resin, fluororesins such as polyvinyl chloride, polyvinylidene chloride, and polytetrafluoroethylene (PTFE), acrylic resins such as polymethyl methacrylate, cellulose-based polymers such as diacetyl cellulose and triacetyl cellulose (TAC), vinyl butyral-based polymers, arylate-based polymers, polyoxymethylene-based polymers, and epoxy-based polymers. The resin film may be formed using a resin material containing one of these resins alone, or may be formed using a resin material in which two or more of these resins are blended. The resin film may be unstretched or stretched (for example, uniaxially or biaxially stretched).

[0120] Suitable examples of resin materials constituting the resin film include polyester-based resin, PPS resin, polyolefin-based resin, and polyimide resin. Here, polyester-based resin refers to a resin containing more than 50% by weight of polyester. Similarly, PPS resin refers to a resin containing more than 50% by weight of PPS, polyolefin-based resin refers to a resin containing more than 50% by weight of polyolefin, and polyimide resin refers to a resin containing more than 50% by weight of polyimide.

[0121] The polyester resin is typically a polyester resin containing, as a main component, a polyester obtained by polycondensation of a dicarboxylic acid and a diol. Specific examples of the polyester resin include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polybutylene naphthalate.

[0122] The polyolefin resin can be a single polyolefin or a combination of two or more polyolefins. The polyolefin can be, for example, an α-olefin homopolymer, a copolymer of two or more α-olefins, or a copolymer of one or more α-olefins with other vinyl monomers. Specific examples include polyethylene (PE), polypropylene (PP), poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymers such as ethylene-propylene rubber (EPR), ethylene-propylene-butene copolymers, ethylene-butene copolymers, ethylene-vinyl alcohol copolymers, and ethylene-ethyl acrylate copolymers. Both low-density (LD) and high-density (HD) polyolefins can be used. Examples of polyolefin resin films include unstretched polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, medium-density polyethylene (MDPE) film, high-density polyethylene (HDPE) film, polyethylene (PE) film made by blending two or more types of polyethylene (PE), and PP / PE blend film made by blending polypropylene (PP) and polyethylene (PE).

[0123] Specific examples of resin films that can be preferably used as the substrate include PET film, PEN film, PPS film, PEEK film, CPI film, CPP film, and OPP film. Preferred examples from the viewpoint of strength include PET film, PEN film, PPS film, PEEK film, and CPI film. Preferred examples from the viewpoints of availability, dimensional stability, optical properties, etc. include PET film, CPI film, and TAC film.

[0124] The resin film may contain known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, antiblocking agents, etc. The amount of additives added is not particularly limited and can be set appropriately depending on the application of the PSA sheet, etc.

[0125] The method for producing the resin film is not particularly limited, and for example, conventionally known general resin film forming methods such as extrusion molding, inflation molding, T-die casting, and calendar roll molding can be appropriately used.

[0126] The substrate may be substantially composed of such a resin film. Alternatively, the substrate may include an auxiliary layer in addition to the resin film. Examples of the auxiliary layer include an optical property adjusting layer (e.g., a coloring layer, an anti-reflection layer), a printing layer or a laminating layer for imparting a desired appearance to the substrate or pressure-sensitive adhesive sheet, an antistatic layer, an undercoat layer, a release layer, or other surface treatment layer. The substrate may also be an optical member (e.g., an optical film) described below.

[0127] The thickness of the substrate is not particularly limited and can be selected depending on the purpose and mode of use of the PSA sheet. The thickness of the substrate may be, for example, 1000 μm or less, 500 μm or less, 100 μm or less, 70 μm or less, 50 μm or less, 25 μm or less, 10 μm or less, or 5 μm or less. As the thickness of the substrate decreases, the flexibility of the PSA sheet and its ability to conform to the surface shape of the adherend tend to improve. Furthermore, from the viewpoint of handleability and processability, the thickness of the substrate may be, for example, 2 μm or more, or may be greater than 5 μm or greater than 10 μm. In some embodiments, the thickness of the substrate may be, for example, 20 μm or more, 35 μm or more, or 55 μm or more.

[0128] The surface of the substrate that is to be bonded to the pressure-sensitive adhesive layer may be subjected to conventional surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, application of a primer, and antistatic treatment, as necessary. Such surface treatments may be intended to improve the adhesion between the substrate and the pressure-sensitive adhesive layer, in other words, the anchoring ability of the pressure-sensitive adhesive layer to the substrate. The composition of the primer is not particularly limited and can be appropriately selected from known primers. The thickness of the primer layer is not particularly limited, but is generally approximately 0.01 μm to 1 μm, and preferably approximately 0.1 μm to 1 μm.

[0129] The surface of the substrate opposite to the side bonded to the pressure-sensitive adhesive layer (hereinafter also referred to as the back surface) may be subjected to a conventionally known surface treatment such as a release treatment, an adhesion or tackiness improving treatment, or an antistatic treatment, as necessary. For example, by surface treating the back surface of the substrate with a release agent, the unwinding force of the pressure-sensitive adhesive sheet wound into a roll can be reduced. Examples of release agents that can be used include silicone-based release agents, long-chain alkyl-based release agents, olefin-based release agents, fluorine-based release agents, fatty acid amide-based release agents, molybdenum sulfide, and silica powder.

[0130] <Characteristics of adhesive sheets> (peel strength) In the pressure-sensitive adhesive sheet disclosed herein, the peel strength measured by the peel strength measurement procedure described above, more specifically, the peel strength measured by the method described in the Examples below, may be, for example, approximately 0.5 N / 10 mm or more, and is usually approximately 1.0 N / 10 mm or more. From the viewpoint of improving bonding reliability, the peel strength is preferably, for example, approximately 1.5 N / 10 mm or more, and more preferably approximately 2.0 N / 10 mm or more. In the pressure-sensitive adhesive sheet according to one embodiment, the peel strength may be, for example, approximately 3.0 N / 10 mm or more, approximately 4.5 N / 10 mm or more, or approximately 5.5 N / 10 mm or more. The adhesive sheet disclosed herein can also be implemented in an embodiment in which the peel strength is approximately 5.7 N / 10 mm or more, approximately 6.5 N / 10 mm or more, approximately 7 N / 10 mm or more, approximately 8 N / 10 mm or more, approximately 9 N / 10 mm or more, approximately 10 N / 10 mm or more, approximately 11 N / 10 mm or more, approximately 12 N / 10 mm or more, or approximately 13 N / 10 mm or more. Such strong adhesive strength can be preferably achieved, for example, by using a silane coupling agent. The upper limit of the peel strength is not particularly limited, and may be, for example, 25 N / 10 mm or less, or, taking into account the balance with other physical properties, 20 N / 10 mm or less, 15 N / 10 mm or less, 10 N / 10 mm or less, or 8 N / 10 mm or less.

[0131] (Haze value) In the technology disclosed herein, the haze value of the pressure-sensitive adhesive sheet is suitably about 10% or less, and can be about 5% or less (e.g., about 3% or less). In some embodiments, the haze value of the pressure-sensitive adhesive sheet is preferably 1.0% or less. Such highly transparent pressure-sensitive adhesive sheets are suitable for optical applications requiring high light transmittance. The haze value of the pressure-sensitive adhesive sheet may be less than 1.0%, less than 0.7%, or 0.5% or less (e.g., 0 to 0.5%). These haze values can also be preferably applied to the haze value of a pressure-sensitive adhesive layer made of a photocrosslinkable pressure-sensitive adhesive.

[0132] Here, the "haze value" refers to the ratio of diffuse transmitted light to total transmitted light when visible light is irradiated onto the object to be measured. It is also called the cloudiness value. The haze value can be expressed by the following formula: Th[%]=Td / Tt×100 In the above formula, Th is the haze value [%], Td is the scattered light transmittance, and Tt is the total light transmittance. The haze value can be measured using a haze meter (for example, "MR-100" manufactured by Murakami Color Research Laboratory). The haze value can be adjusted, for example, by selecting the composition, thickness, etc. of the pressure-sensitive adhesive layer.

[0133] <Laminate manufacturing method> The photocrosslinkable pressure-sensitive adhesive disclosed herein can be preferably used in an embodiment in which the photocrosslinkable pressure-sensitive adhesive is laminated to a member serving as an adherend and then photocrosslinked. This allows for the production of a laminate in which the photocrosslinked product is reliably bonded to the adherend. The photocrosslinking of the photocrosslinkable pressure-sensitive adhesive can be achieved by irradiating the photocrosslinkable pressure-sensitive adhesive with active energy rays. The active energy rays are preferably ultraviolet light containing a wavelength component capable of exciting the benzophenone structure contained in the photocrosslinkable pressure-sensitive adhesive (e.g., ultraviolet light containing a component with a wavelength of less than 300 nm). The photocrosslinkable pressure-sensitive adhesive can be used in the production of the laminate in the form of an adhesive sheet having an adhesive layer made of the photocrosslinkable pressure-sensitive adhesive. Accordingly, this specification provides a laminate production method comprising, in this order, laminating an adhesive sheet having an adhesive layer made of any of the photocrosslinkable pressure-sensitive adhesives disclosed herein to an adherend, and irradiating the adhesive sheet with active energy rays to photocrosslink the photocrosslinkable pressure-sensitive adhesive. When the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet used in an embodiment in which photocrosslinking is performed after being attached to an adherend has a multilayer structure, the pressure-sensitive adhesive layer to be photocrosslinked may be a part of the layers (e.g., one layer) included in the multilayer structure, or may be all of the layers.

[0134] The photocrosslinkable pressure-sensitive adhesive disclosed herein can be used, for example, in the form of a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the photocrosslinkable pressure-sensitive adhesive, laminated on a surface having a step. The photocrosslinkable pressure-sensitive adhesive can exhibit good surface conformability (step-conforming ability) to the surface of an adherend having such a step. By laminating the photocrosslinkable pressure-sensitive adhesive and then photocrosslinking the photocrosslinkable pressure-sensitive adhesive, a highly reliable bond can be formed. The step can be, for example, a printed layer provided on the surface of the adherend. The height of the step can be, for example, 5 μm or more, 10 μm or more, 20 μm or more, or 30 μm or more. The height of the step can be, for example, 100 μm or less, preferably 70 μm or less.

[0135] <Application> The use of the photocrosslinkable pressure-sensitive adhesive disclosed herein is not particularly limited, and it can be used in a variety of applications. For example, the photocrosslinkable pressure-sensitive adhesive disclosed herein can be used in the form of a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the photocrosslinkable pressure-sensitive adhesive for applications such as fixing, joining, molding, decorating, protecting, and supporting components constituting various products. The material constituting at least the surface of the above-mentioned component can be, for example, glass such as alkali glass or alkali-free glass; metal materials such as stainless steel (SUS) and aluminum; ceramic materials such as alumina and silica; resin materials such as acrylic resin, ABS resin, polycarbonate resin, polystyrene resin, and transparent polyimide resin; etc. The above-mentioned component can be, for example, a component constituting various mobile devices (portable devices), automobiles, home appliances, etc. Furthermore, the surface of the above-mentioned component to which the pressure-sensitive adhesive sheet is attached can be a painted surface made of an acrylic, polyester, alkyd, melamine, urethane, acid-epoxy crosslinked paint, or a composite of these (e.g., acrylic-melamine, alkyd-melamine), or a plated surface such as a zinc-plated steel sheet. The member may be any of the support films (e.g., resin films) exemplified as materials that can be used for the substrate. The pressure-sensitive adhesive sheet disclosed herein may be, for example, a component of a member with a pressure-sensitive adhesive sheet in which such a member is bonded to at least one surface of the pressure-sensitive adhesive layer.

[0136] An example of a preferred application is an optical application. More specifically, the pressure-sensitive adhesive sheet disclosed herein can be preferably used as an optical pressure-sensitive adhesive sheet used for bonding optical members (for bonding optical members) or for manufacturing products (optical products) using the optical members.

[0137] The optical member refers to a member having optical properties (e.g., polarization, light refraction, light scattering, light reflectivity, light transmittance, light absorption, light diffraction, optical rotation, visibility, etc.). The optical member is not particularly limited as long as it has optical properties, and examples thereof include components constituting devices (optical devices) such as display devices (image display devices) and input devices, or components used in these devices, such as polarizing plates, wavelength plates, retardation plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflection films, hard coat (HC) films, impact absorbing films, antifouling films, photochromic films, light control films, transparent conductive films (ITO films), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and further components in which these are laminated (these may be collectively referred to as "functional films"). The above "plate" and "film" respectively include plate-like, film-like, sheet-like and other forms. For example, "polarizing film" includes "polarizing plate", "polarizing sheet", and the like.

[0138] Examples of the display device include a liquid crystal display device, an organic electroluminescence (EL) display device, a plasma display panel (PDP), and electronic paper, and are particularly suitable for use in foldable display devices and in-vehicle display devices that include expensive components. Examples of the input device include a touch panel.

[0139] The optical member is not particularly limited, but examples thereof include members (e.g., sheet-, film-, or plate-shaped members) made of glass, acrylic resin, polycarbonate, polyethylene terephthalate, metal thin film, etc. In this specification, the term "optical member" also includes members (such as design films, decorative films, and surface protection films) that serve to decorate or protect a display device or input device while maintaining its visibility.

[0140] The embodiment of bonding optical members using the pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and may include, for example, (1) bonding optical members to each other via the pressure-sensitive adhesive sheet disclosed herein, (2) bonding an optical member to a member other than an optical member via the pressure-sensitive adhesive sheet disclosed herein, or (3) bonding an optical member to a member other than an optical member in which the pressure-sensitive adhesive sheet disclosed herein includes an optical member. In the embodiment (3), the pressure-sensitive adhesive sheet including an optical member may be, for example, a pressure-sensitive adhesive sheet whose substrate is an optical member (e.g., an optical film). Such a pressure-sensitive adhesive sheet including an optical member as a substrate may also be considered a pressure-sensitive adhesive optical member (e.g., a pressure-sensitive adhesive optical film). Furthermore, when the pressure-sensitive adhesive sheet disclosed herein is a pressure-sensitive adhesive sheet having a substrate and the functional film is used as the substrate, the pressure-sensitive adhesive sheet disclosed herein may also be considered a "pressure-sensitive adhesive functional film" having the pressure-sensitive adhesive layer disclosed herein on at least one side of the functional film.

[0141] The peeling method disclosed herein can be preferably applied to peeling a pressure-sensitive adhesive sheet attached to a non-water-absorbent smooth surface such as a glass plate, a metal plate, a resin plate, etc. The peeling method disclosed herein can also be preferably used as a method for peeling a pressure-sensitive adhesive sheet from any of the optical components described above. In particular, the peeling method is suitable as a method for peeling a pressure-sensitive adhesive sheet attached to a glass plate such as an alkali glass or alkali-free glass.

[0142] The matters disclosed in this specification include the following: (1) A polymer having a benzophenone structure in a side chain, A cured product of a pressure-sensitive adhesive composition containing an ethylenically unsaturated compound and a benzophenone structure-containing component, A photo-crosslinkable adhesive that emits volatile organic compounds of 500 μg / g or less. (2) The photocrosslinkable pressure-sensitive adhesive according to (1) above, wherein the benzophenone structure-containing component is a polymer having a benzophenone structure in a side chain. (3) The shear storage modulus Gb' [kPa] of the photocrosslinkable pressure-sensitive adhesive at 80°C and the illuminance of the photocrosslinkable pressure-sensitive adhesive using a high-pressure mercury lamp at 300 mW / cm 2 , cumulative light intensity 10,000mJ / cm 2 The relationship between the shear storage modulus Gc' [kPa] at 80°C of the photocrosslinked product obtained by irradiating ultraviolet rays under the conditions above is expressed by the following formula: Gc' [kPa] - Gb' [kPa] ≥ 2 kPa; The photocrosslinkable pressure-sensitive adhesive according to (1) or (2) above, which satisfies the above. (4) The photocrosslinkable adhesive is exposed to a high-pressure mercury lamp at an illumination intensity of 300 mW / cm. 2 , cumulative light intensity 10,000mJ / cm 2 The photocrosslinkable pressure-sensitive adhesive according to any one of (1) to (3) above, wherein the photocrosslinked product obtained by irradiating with ultraviolet light under the conditions above has a shear storage modulus Gc' [kPa] at 80°C of 40 kPa or more. (5) A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the photocrosslinkable pressure-sensitive adhesive described in any one of (1) to (4) above and (13) to (18) below. (6) The pressure-sensitive adhesive sheet according to (5) above, which has a peel strength of 1.0 N / 10 mm or more as measured by the following procedure. [Peel strength measurement procedure] The surface of the adhesive layer was pressed against a glass plate by rolling a 2 kg rubber roller back and forth once, and then autoclaved (50°C, 0.5 MPa, 15 minutes). After that, a high-pressure mercury lamp was used to illuminate the glass plate side at an illumination intensity of 300 mW / cm. 2 , cumulative light intensity 10,000mJ / cm 2Then, the pressure-sensitive adhesive sheet is peeled from the glass plate at a pulling rate of 300 mm / min and a peel angle of 180° in an atmosphere of 25° C., and the peel strength is measured. (7) Laminating the photocrosslinkable pressure-sensitive adhesive according to any one of (1) to (4) above and (13) to (18) below on a member; reacting the benzophenone structure contained in the photocrosslinkable pressure-sensitive adhesive to photocrosslink the photocrosslinkable pressure-sensitive adhesive; A method for manufacturing a laminate, comprising the steps of: (8) preparing a pressure-sensitive adhesive composition containing a polymer (A) having a benzophenone structure in a side chain and an ethylenically unsaturated compound (B); and irradiating the pressure-sensitive adhesive composition with active energy rays; It encompasses Here, the irradiation of the active energy rays is carried out so as to react the ethylenically unsaturated group of the ethylenically unsaturated compound (B) and leave the benzophenone structure of the polymer (A). (9) The method according to (8) above, wherein the pressure-sensitive adhesive composition contains, as the ethylenically unsaturated compound (B), a compound (B1) having one ethylenically unsaturated group. (10) The method according to (8) or (9) above, wherein the pressure-sensitive adhesive composition contains, as the ethylenically unsaturated compound (B), a compound (B2) having two or more ethylenically unsaturated groups. (11) The method according to any one of (8) to (10) above, wherein the pressure-sensitive adhesive composition further contains a photoinitiator (C). (12) A pressure-sensitive adhesive composition used for producing a photocrosslinkable pressure-sensitive adhesive containing a polymer having a benzophenone structure in a side chain (for example, the photocrosslinkable pressure-sensitive adhesive described in any one of (1) to (4) above and (13) to (18) below), comprising: A polymer (A) having a benzophenone structure in a side chain; an ethylenically unsaturated compound (B); A photoinitiator (C) that absorbs light with a wavelength of 300 nm to 500 nm and generates radicals. Including, A pressure-sensitive adhesive composition, wherein the weight fraction of the compound (B2) having two or more ethylenically unsaturated groups in all the monomer components constituting the pressure-sensitive adhesive composition is less than 5 wt %.

[0143] (13) A photocrosslinkable pressure-sensitive adhesive comprising a polymer having a benzophenone structure in the side chain. (14) The photocrosslinkable pressure-sensitive adhesive according to (13) above, which comprises two or more polymers having different monomer compositions, at least one of which has a benzophenone structure in its side chain. (15) The photocrosslinkable pressure-sensitive adhesive according to (12) or (13) above, which has an emission amount of volatile organic compounds of 500 μg / g or less. (16) The photocrosslinkable pressure-sensitive adhesive according to any one of (13) to (15) above, which is a cured product of a pressure-sensitive adhesive composition containing an ethylenically unsaturated compound and a benzophenone structure-containing component. (17) The shear storage modulus Gb' [kPa] of the photocrosslinkable pressure-sensitive adhesive at 80°C and the irradiance of the photocrosslinkable pressure-sensitive adhesive using a high-pressure mercury lamp at an illumination intensity of 300 mW / cm 2 , cumulative light intensity 10,000mJ / cm 2 The relationship between the shear storage modulus Gc' [kPa] at 80°C of the photocrosslinked product obtained by irradiating ultraviolet rays under the conditions above is expressed by the following formula: Gc' [kPa] - Gb' [kPa] ≥ 2 kPa; The photocrosslinkable pressure-sensitive adhesive according to any one of the above (13) to (16), which satisfies the above conditions. (18) The photocrosslinkable adhesive is exposed to a high-pressure mercury lamp at an illumination intensity of 300 mW / cm 2 , cumulative light intensity 10,000mJ / cm 2 The photocrosslinkable pressure-sensitive adhesive according to any one of (13) to (17) above, wherein the photocrosslinked product obtained by irradiating with ultraviolet light under the conditions above has a shear storage modulus Gc' [kPa] at 80°C of 40 kPa or more.

[0144] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

[0145] <Example 1> (Preparation of Pressure-Sensitive Adhesive Composition) An acrylic copolymer with a benzophenone structure in the side chain (BASF, product name: acResin UV3532, Tg: -60°C, Mw: 25 × 10 4 A pressure-sensitive adhesive composition C1 for producing a photocrosslinkable pressure-sensitive adhesive was prepared by mixing 60 parts of methylparaben (BP equivalent: 10 mg / g), 30 parts of 2-ethylhexyl acrylate (2EHA), 10 parts of N-vinyl-2-pyrrolidone (NVP), 0.2 parts of 1,6-hexanediol diacrylate (HDDA), and 0.15 parts of a photoinitiator P1 (manufactured by IGM Regins, trade name: Omnirad 651) with an absorption peak in the wavelength range of 300 nm to 500 nm. The viscosity of this pressure-sensitive adhesive composition C1 (BH-type viscometer, No. 5 rotor, 10 rpm, measurement temperature 30°C) was 2.4 Pa s, and the organic solvent content was less than 1 wt%.

[0146] (Preparation of photocrosslinkable adhesive) The pressure-sensitive adhesive composition C1 prepared above was applied to the release surface of a 38 μm-thick release film R1 (Mitsubishi Plastics, Inc., MRF#38), one side of which is a polyester film, and then covered with a release film R2 (Mitsubishi Plastics, Inc., MRE#38), one side of which is a polyester film, to block air. A black light (Toshiba, product name FL15BL) was used from one side of this laminate to illuminate the laminate at an illuminance of 5 mW / cm. 2 , cumulative light intensity 800mJ / cm 2 This resulted in a photocrosslinkable pressure-sensitive adhesive A1, which was a cured product of the pressure-sensitive adhesive composition C1, in the form of a 150 μm-thick pressure-sensitive adhesive layer (substrate-less pressure-sensitive adhesive sheet) sandwiched between the release films R1 and R2. The illuminance value of the black light is a value measured using an industrial UV checker (manufactured by Topcon Corporation, product name: UVR-T1, light receiving unit model UD-T36) with a peak sensitivity wavelength of approximately 350 nm.

[0147] (Preparation of laminate) The release film R2 was peeled off from the photocrosslinkable pressure-sensitive adhesive A1 obtained above, and the resulting sheet was attached to a 75 μm-thick corona-treated polyethylene terephthalate (PET) film, thereby obtaining a single-sided pressure-sensitive adhesive sheet S1 with a substrate, in which one side of the pressure-sensitive adhesive layer made of the photocrosslinkable pressure-sensitive adhesive A1 was adhered to the PET film (substrate). The release film R1 was removed from the adhesive surface of this single-sided pressure-sensitive adhesive sheet, and the exposed adhesive surface was pressed against a glass plate (Corning Gorilla Glass 3) using a 2 kg rubber roller, which was rolled back and forth once. After autoclaving (50°C, 0.5 MPa, 15 minutes), a high-pressure mercury lamp (Toshiba, product name H3000L / 22N) was used to irradiate the sheet from the glass plate side at an illuminance of 300 mW / cm. 2 , cumulative light intensity 10,000mJ / cm 2 The pressure-sensitive adhesive A1 was photocrosslinked by irradiating it with ultraviolet light under the conditions of: In this way, a laminate having a structure of PET film / pressure-sensitive adhesive layer / glass plate was produced. The illuminance value of the high-pressure mercury lamp is a value measured by an industrial UV checker (manufactured by Topcon Corporation, product name: UVR-T1, light receiving unit model UD-T25) with a peak sensitivity wavelength of about 350 nm.

[0148] <Example 2> A photocrosslinkable adhesive composition C2 was prepared by mixing 30 parts of an acrylic copolymer with a benzophenone structure in the side chain (BASF, product name: acResin UV3532), 38 parts of 2EHA, 4 parts of NVP, 28 parts of isobornyl acrylate (IBXA), 0.04 parts of HDDA, 0.08 parts of 3-acryloxypropyltrimethoxysilane (Shin-Etsu Silicones, product name: KBM-5103), and 0.2 parts of photoinitiator P2 (IGM Regins, product name: Omnirad 184) with an absorption peak in the wavelength range of 300 to 500 nm. The viscosity of this adhesive composition C2 (BH-type viscometer, No. 5 rotor, 10 rpm, measurement temperature 30°C) was 0.4 Pa·s, and the organic solvent content was less than 1 wt%. In the same manner as in Example 1, except that adhesive composition C2 was used instead of adhesive composition C1, a photocrosslinkable adhesive A2, which was a cured product of adhesive composition C2, was obtained in the form of a 150 μm thick adhesive layer (substrate-less adhesive sheet) sandwiched between release films R1 and R2. Using this photocrosslinkable pressure-sensitive adhesive A2, a laminate having a structure of PET film / pressure-sensitive adhesive layer / glass plate was produced in the same manner as in Example 1.

[0149] <Example 3> A monomer mixture consisting of 78 parts of 2EHA, 18 parts of NVP, and 4 parts of 2-hydroxyethyl acrylate (HEA) was placed in a four-neck flask along with 0.07 parts of a 1:1 mixture of photoinitiators P1 and P2. The mixture was photopolymerized under a nitrogen atmosphere by irradiating ultraviolet light using the high-pressure mercury lamp described above until the viscosity reached approximately 15 Pa·s (BH-type viscometer, No. 5 rotor, 10 rpm, 30°C). A monomer syrup containing a partial polymer of the monomer mixture was prepared. 10 parts of NVP, 20 parts of IBXA, 0.15 parts of HDDA, 0.2 parts of α-methylstyrene dimer (NOF Corporation, trade name: Nofumer MSD) as a chain transfer agent, and 0.5 parts of photoinitiator P1 (Omnirad 651) were added to the monomer syrup and mixed to prepare PSA composition C3. The pressure-sensitive adhesive composition C3 prepared above was applied to the release surface of release film R1 (Mitsubishi Plastics, Inc., MRF#38), and then release film R2 (Mitsubishi Plastics, Inc., MRE#38) was placed over the laminate to block air. The black light was used from one side of the laminate to illuminate at an intensity of 5 mW / cm. 2 The adhesive composition C3 was then irradiated with ultraviolet light for 100 seconds. The ultraviolet irradiation time was adjusted so that approximately 5% of the total ethylenically unsaturated compounds used in preparing the adhesive composition C3 remained unreacted (i.e., so that the polymerization conversion rate was approximately 95%). In this way, an adhesive A3, which was a cured product of the adhesive composition C3, was obtained in the form of a 150 μm thick adhesive layer (substrate-less adhesive sheet) sandwiched between the release films R1 and R2. Using this adhesive A3, a laminate having a structure of PET film / adhesive layer / glass plate was produced in the same manner as in Example 1.

[0150] <Example 4> An acrylic copolymer with a benzophenone structure in the side chain (BASF, product name: acResin A260UV, Tg: -39°C, Mw: 19 × 10 4 Pressure-sensitive adhesive composition C4 for producing a photocrosslinkable pressure-sensitive adhesive was prepared by mixing 50 parts of methylparaben (BP equivalent: 2 mg / g), 34 parts of n-butyl acrylate (BA), 16 parts of NVP, and 0.2 parts of photoinitiator P2 (Omnirad 184). The viscosity of this pressure-sensitive adhesive composition C4 (BH-type viscometer, No. 5 rotor, 10 rpm, measurement temperature 30°C) was 27 Pa s, and the organic solvent content was less than 1 wt%. In the same manner as in Example 1, except that adhesive composition C4 was used instead of adhesive composition C1, a photocrosslinkable adhesive A4, which was a cured product of adhesive composition C4, was obtained in the form of an adhesive layer (substrate-less adhesive sheet) with a thickness of 150 μm sandwiched between release films R1 and R2. Using this photocrosslinkable pressure-sensitive adhesive A4, a laminate having a structure of PET film / pressure-sensitive adhesive layer / glass plate was produced in the same manner as in Example 1.

[0151] <Measurement and Evaluation> (1) Measurement of elastic modulus Gb' before photocrosslinking The pressure-sensitive adhesives (substrate-less pressure-sensitive adhesive sheets) according to each example were stacked to a thickness of approximately 1.5 mm and punched out into disks with a diameter of 7.9 mm to prepare measurement samples. The measurement samples were sandwiched between parallel plates, and dynamic viscoelasticity measurements were performed in shear mode using a viscoelasticity tester (ARES, manufactured by Rheometrics) at a temperature range of -70 to 150°C and a heating rate of 5°C / min while applying a shear strain of 1 Hz, and the shear storage modulus Gb' at 80°C was determined. The results are shown in Table 1.

[0152] (2) Measurement of elastic modulus Gc' after photocrosslinking The adhesive (substrate-less adhesive sheet) according to each example was sandwiched between release films R1 and R2 and illuminated from one side with the above-mentioned high-pressure mercury lamp at an illumination intensity of 300 mW / cm 2 , cumulative light intensity 10,000mJ / cm 2After photocrosslinking by irradiating with ultraviolet light under the conditions, the sheets were stacked to a thickness of approximately 1.5 mm, excluding the release films R1 and R2, and then punched into a disk with a diameter of 7.9 mm to prepare a measurement sample. This measurement sample was subjected to dynamic viscoelasticity measurement in the same manner as in the measurement of the pre-photocrosslinking modulus Gb', and the shear storage modulus Gc' at 80°C was determined. The results are shown in Table 1.

[0153] (3) Measurement of VOC emission amount The VOC emission amount of each example of the pressure-sensitive adhesive (substrate-less pressure-sensitive adhesive sheet) was measured according to the VOC measurement test described above. The results are shown in Table 1.

[0154] (4) Durability evaluation A polarizing plate (manufactured by Nitto Denko, product name "REGQ-HC3", thickness 92 mm) was attached to one surface with aluminum foil (manufactured by Mitsubishi Aluminum Foil, product name "Nippaku Foil", thickness 12 μm) using a 15 μm thick adhesive, and this was used as an adherend to be bonded to one surface of the substrateless adhesive sheet. The adhesive (substrate-less adhesive sheet) according to each example was cut to a size of 60 mm x 120 mm together with the release films R1 and R2, and then the release film R2 was peeled off, and the exposed adhesive surface was attached to the polarizing plate side of the adherend using a hand roller. Next, the release liner R2 was peeled off from the adhesive, and the exposed adhesive surface was attached to a glass plate (manufactured by Matsunami Glass Industry Co., Ltd., product name "MICRO SLIDE GLASS", product number "S", thickness 1.3 mm, haze 0.1%, water-polished edge). In this way, a laminate having a configuration of glass plate / adhesive / polarizing plate / aluminum foil was obtained. This laminate was subjected to autoclave treatment (50°C, 0.5 MPa, 15 minutes), and then irradiated from the glass plate side with the high-pressure mercury lamp at an illumination intensity of 300 mW / cm 2 , cumulative light intensity 10,000mJ / cm 2 The sample was irradiated with ultraviolet light under the above conditions and used as a sample for durability evaluation. The evaluation samples were stored in an environment at 85°C for 24 hours, and then visually observed in an environment at 23°C and 50% RH, and durability was evaluated using the following two criteria. The results are shown in the "Adhesion durability" column in Table 1. In addition, no air bubbles were observed immediately after the preparation of the durability evaluation samples using the pressure-sensitive adhesive sheets according to any of the examples. E (Excellent): No bubbles were observed (excellent adhesion durability). P (Poor): Air bubbles were clearly observed (poor adhesion durability).

[0155] (5) Peel strength The release film R2 was peeled off from each PSA (substrate-less PSA sheet) and attached to a corona-treated PET film with a thickness of 75 μm to produce a single-sided PSA sheet, which was then cut to a width of 20 mm and a length of 100 mm to produce a test specimen. In an environment of 23°C and 50% RH, the release film R1 was peeled off from the test piece, and the exposed adhesive surface was pressed against a glass plate (Corning Gorilla Glass 3) as an adherend by rolling a 2 kg rubber roller back and forth once. After autoclaving (50°C, 0.5 MPa, 15 minutes), the test piece was exposed to light from the glass plate side using the high-pressure mercury lamp at an illuminance of 300 mW / cm. 2 , cumulative light intensity 10,000mJ / cm 2 The sample was irradiated with ultraviolet light under the following conditions. The peel strength of the test piece from the glass plate was then measured at a tension speed of 300 mm / min and a peel angle of 180° using a tensile tester (Minebea Co., Ltd., universal tension-compression tester, device name "Tension-Compression Tester, TCM-1kNB") in an environment of 23°C and 50% RH. The measurement was carried out three times, and the average value was converted into a value per 10 mm width (unit: N / 10 mm) and is shown in Table 1.

[0156] [Table 1]

[0157] As shown in Table 1, the photocrosslinkable pressure-sensitive adhesives of Examples 1, 2, and 4 exhibited significantly superior adhesion durability compared to the pressure-sensitive adhesive of Example 3. Furthermore, the photocrosslinkable pressure-sensitive adhesives of Examples 1, 2, and 4 emitted less VOC than the pressure-sensitive adhesive of Example 3, and had significantly lower odor.

[0158] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0159] 1,2 Adhesive sheet 10 adhesive layer 10A One surface (adhesive side) 10B Other surface 20 Base material 20A front page 20B Second side (back) 30, 31, 32 Release liner 50 adhesive sheets with release liner 70 Optical Components 100 Adhesive sheet attached material

Claims

1. A photocrosslinkable pressure-sensitive adhesive comprising a cured product of a pressure-sensitive adhesive composition containing an ethylenically unsaturated compound and a benzophenone structure-containing component, the pressure-sensitive adhesive comprising a polymer having a benzophenone structure in a side chain, the pressure-sensitive adhesive composition contains, as the ethylenically unsaturated compound, a compound (B1) having one ethylenically unsaturated group and a compound (B2) having two or more ethylenically unsaturated groups; The amount of volatile organic compounds emitted is 500 μg / g or less, A photocrosslinkable pressure-sensitive adhesive, wherein the photocrosslinkable pressure-sensitive adhesive is irradiated with ultraviolet light using a high-pressure mercury lamp under conditions of an illuminance of 300 mW / cm 2 and an accumulated light quantity of 10,000 mJ / cm 2, and the photocrosslinked product obtained has a shear storage modulus Gc' [kPa] at 80°C of 40 kPa or more.

2. The photocrosslinkable pressure-sensitive adhesive according to claim 1 , wherein the benzophenone structure-containing component is a polymer having a benzophenone structure in a side chain.

3. The shear storage modulus Gb' [kPa] of the photocrosslinkable pressure-sensitive adhesive at 80°C and the illuminance of the photocrosslinkable pressure-sensitive adhesive using a high-pressure mercury lamp at 300 mW / cm ２ , cumulative light intensity 10,000 mJ / cm ２ The relationship between the shear storage modulus Gc′ [kPa] at 80° C. of the photocrosslinked product obtained by irradiating ultraviolet rays under the conditions of Gc'[kPa]-Gb'[kPa]≧2kPa; The photocrosslinkable pressure-sensitive adhesive according to claim 1 or 2, which satisfies the above.

4. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the photocrosslinkable pressure-sensitive adhesive according to any one of claims 1 to 3.

5. The pressure-sensitive adhesive sheet according to claim 4, which has a peel strength of 1.0 N / 10 mm or more as measured by the following procedure. [Procedure for measuring peel strength] The surface of the adhesive layer was pressed against a glass plate by rolling a 2 kg rubber roller back and forth once, and then autoclaved (50°C, 0.5 MPa, 15 minutes). After that, a high-pressure mercury lamp was used from the glass plate side at an illuminance of 300 mW / cm. ２ , cumulative light intensity 10,000 mJ / cm ２ Thereafter, the peel strength is measured when the pressure-sensitive adhesive sheet is peeled from the glass plate in an atmosphere of 25° C. at a pulling rate of 300 mm / min and a peel angle of 180°.

6. Laminating the photocrosslinkable pressure-sensitive adhesive according to any one of claims 1 to 3 and a member; reacting the benzophenone structure contained in the photocrosslinkable pressure-sensitive adhesive to photocrosslink the photocrosslinkable pressure-sensitive adhesive; A method for manufacturing a laminate, comprising the steps of:

7. A method for producing the photocrosslinkable adhesive according to any one of claims 1 to 3, comprising: Preparing a pressure-sensitive adhesive composition containing a polymer (A) having a benzophenone structure in a side chain and an ethylenically unsaturated compound (B); and irradiating the pressure-sensitive adhesive composition with active energy rays; It encompasses Here, the method for producing a photocrosslinkable pressure-sensitive adhesive is such that the irradiation of the active energy rays is carried out so as to react the ethylenically unsaturated group of the ethylenically unsaturated compound (B) and leave the benzophenone structure of the polymer (A).

8. The method according to claim 7, wherein the pressure-sensitive adhesive composition comprises, as the ethylenically unsaturated compound (B), a compound (B1) having one ethylenically unsaturated group.

9. The method according to claim 7 or 8, wherein the pressure-sensitive adhesive composition comprises, as the ethylenically unsaturated compound (B), a compound (B2) having two or more ethylenically unsaturated groups.

10. The method according to any one of claims 7 to 9, wherein the pressure-sensitive adhesive composition further comprises a photoinitiator (C).

11. A pressure-sensitive adhesive composition used for producing a photocrosslinkable pressure-sensitive adhesive, comprising a polymer having a benzophenone structure in a side chain, A polymer (A) having a benzophenone structure in a side chain; an ethylenically unsaturated compound (B); a photoinitiator (C) that absorbs light with a wavelength of 300 nm to 500 nm and generates radicals; Including, The ethylenically unsaturated compound (B) includes a compound (B1) having one ethylenically unsaturated group and a compound (B2) having two or more ethylenically unsaturated groups, The pressure-sensitive adhesive composition does not contain a photoinitiator containing a phosphorus element in the molecule, A pressure-sensitive adhesive composition, wherein the weight fraction of the compound having two or more ethylenically unsaturated groups in all the monomer components constituting the pressure-sensitive adhesive composition is less than 5 wt %.

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