JP2016017113A - Adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive sheet having further improved drop resistance, with good repulsion resistance being maintained.SOLUTION: An adhesive sheet includes an adhesive layer mainly composed of an acrylic polymer. The acrylic polymer includes a polar group-containing monomer as the constituent monomer component in a content of 15 wt.% or more relative to the whole monomer components to constitute the acrylic polymer. The polar group-containing monomer further includes a nitrogen atom-containing monomer in a content of 40 wt.% or more. The adhesive layer is formed of an adhesive composition including an acrylic polymer component and an acrylic oligomer.SELECTED DRAWING: None

Description

  The present invention relates to an adhesive sheet.

  In general, a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive; the same shall apply hereinafter) is in the form of a soft solid (viscoelastic body) in a temperature range near room temperature and has a property of easily adhering to an adherend by pressure. Above all, pressure-sensitive adhesives containing acrylic polymers are easy to design polymer molecules and have various properties (light resistance, weather resistance, oil resistance, etc.), so they can be joined and fixed in various fields in the form of pressure-sensitive adhesive sheets. It is widely used for such purposes. For example, it is also preferably used for portable electronic devices such as mobile phones and smartphones that have been widely used in recent years. Patent documents 1 and 2 are mentioned as technical literature about this kind of adhesive sheet.

Japanese Patent No. 4825992 JP 2014-51644 A

  For example, a portable electronic device is required to have a characteristic that does not cause breakage or malfunction of a main body due to an impact at the time of dropping because of a usage form of carrying. The demand for this characteristic has been increasing year by year from the viewpoints of durability, long life, safety, and the like. Therefore, the pressure-sensitive adhesive sheet applied to this type of application is also required to have a performance (drop impact resistance) that does not cause a bonding failure such as peeling even under a drop impact under more severe conditions. However, in general, in order to further improve the drop impact resistance, other characteristics required for the adhesive (specifically, one of typical adhesive characteristics, repelling resistance) must be sacrificed to some extent. For this reason, it has been difficult to achieve both a drop impact resistance and a repulsion resistance at a higher level.

  The present invention was created in view of the above circumstances, and an object thereof is to provide a pressure-sensitive adhesive sheet having further improved drop impact resistance while maintaining good repulsion resistance.

  According to this invention, an adhesive sheet provided with the adhesive layer which contains an acrylic polymer as a main component is provided. The acrylic polymer contains a polar group-containing monomer as a constituent monomer component. The polar group-containing monomer is contained in a proportion of 15% by weight or more of all monomer components constituting the acrylic polymer. Furthermore, the polar group-containing monomer contains a nitrogen atom-containing monomer in a proportion of 40% by weight or more. And the said adhesive layer is formed using the adhesive composition containing an acrylic polymerization component and an acrylic oligomer.

  According to such a configuration, the acrylic polymer that is the main component of the pressure-sensitive adhesive contains a polar group-containing monomer unit at a predetermined ratio or more, and therefore, good repulsion resistance can be realized. In addition, the acrylic polymer contains a nitrogen atom-containing monomer unit at a predetermined ratio, and an acrylic oligomer is used for the pressure-sensitive adhesive, so that it has a drop impact resistance while maintaining a high level of repulsion resistance. Further improvements can be made.

  In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the polar group-containing monomer further includes at least one of a carboxy group-containing monomer and a hydroxyl group-containing monomer. By using the above-mentioned polar group-containing monomer, it is possible to preferably realize a configuration in which both drop impact resistance and repulsion resistance are compatible at a high level. Especially, it is preferable that the said polar group containing monomer contains a carboxy group containing monomer. In a more preferred embodiment, from the viewpoint of improving drop impact resistance, the acrylic polymer contains the carboxy group-containing monomer in a proportion of less than 5% by weight as a constituent monomer component.

  In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the polar group-containing monomer includes a monomer having a nitrogen atom-containing ring as the nitrogen atom-containing monomer. By using a polar group-containing monomer including a monomer having a nitrogen atom-containing ring, it is possible to preferably realize a configuration in which both drop impact resistance and repulsion resistance are achieved at a high level.

In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the content of the acrylic oligomer is 5 parts by weight or less with respect to 100 parts by weight of the acrylic polymerization component. By adding a limited amount of the acrylic oligomer, the drop impact resistance and the repulsion resistance can be further improved. The acrylic oligomer preferably has a weight average molecular weight in the range of 0.1 × 10 ^{4 to} 3 × 10 ⁴ .

  According to the pressure-sensitive adhesive sheet disclosed herein, the drop impact resistance can be further improved while maintaining good repulsion resistance. Therefore, the pressure-sensitive adhesive sheet disclosed herein is preferably used for portable electronic devices that require a high level of drop impact resistance and repulsion resistance.

It is sectional drawing which shows one structural example of an adhesive sheet typically. It is sectional drawing which shows typically another structural example of an adhesive sheet. It is explanatory drawing which shows the sample for evaluation used when evaluating drop impact resistance. It is a schematic diagram which shows the initial state of the test piece affixed on the to-be-adhered body in repelling resistance evaluation. It is a schematic diagram which shows the state which the edge part of the test piece affixed on the to-be-adhered body floated from this to-be-adhered body in evaluation of repulsion resistance.

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

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

  As used herein, “(meth) acryloyl” is a generic term for acryloyl and methacryloyl. Similarly, “(meth) acrylate” means acrylate and methacrylate, and “(meth) acryl” generically means acrylic and methacryl. In the present specification, the “acrylic monomer” refers to a monomer having at least one (meth) acryloyl group in one molecule. The “acrylic polymer” refers to a polymer containing an acrylic monomer as a monomer unit (constituent monomer component) constituting the polymer. That is, it refers to a polymer containing monomer units derived from acrylic monomers.

  In the present specification, the “main component” refers to a component contained in the largest proportion unless otherwise specified, and typically refers to a component contained in an amount exceeding 50% by weight. For example, “the pressure-sensitive adhesive layer containing an acrylic polymer as a main component” means that the acrylic polymer is contained in the largest proportion among all the components included in the pressure-sensitive adhesive layer, Typically, it refers to a pressure-sensitive adhesive layer containing 50% by weight or more of an acrylic polymer. Similarly, “the main component of the total monomer component (typically the monomer mixture) is an alkyl (meth) acrylate” means that the component contained in the largest proportion of all the monomer components (for example, exceeding 50% by weight) It means that the component (included in proportion) is an alkyl (meth) acrylate.

  In the present specification, the “active energy ray” refers to an energy ray having an energy capable of causing a chemical reaction such as a polymerization reaction, a crosslinking reaction, and decomposition of an initiator. Examples of active energy rays here include light such as ultraviolet rays (UV), visible rays, and infrared rays, and radiation such as α rays, β rays, γ rays, electron rays, neutron rays, and X rays. It is.

<Configuration of adhesive sheet>
The pressure-sensitive adhesive sheet disclosed herein includes a pressure-sensitive adhesive layer. This pressure-sensitive adhesive layer typically constitutes at least one surface (for example, both surfaces) of the pressure-sensitive adhesive sheet. The pressure-sensitive adhesive sheet may be a pressure-sensitive adhesive sheet with a substrate having the above-mentioned pressure-sensitive adhesive layer on one side or both sides of the substrate (support), and the pressure-sensitive adhesive layer may be a release liner (a substrate having a release surface). It may be grasped.) It may be a substrate-less pressure-sensitive adhesive sheet such as a form held in (1). In this case, the pressure-sensitive adhesive sheet may consist of only a pressure-sensitive adhesive layer. The concept of the pressure-sensitive adhesive sheet here includes what is called a pressure-sensitive adhesive tape, a pressure-sensitive adhesive label, a pressure-sensitive adhesive film, and the like. The pressure-sensitive adhesive sheet provided by the present specification may be in the form of a roll or a single sheet. Or the adhesive sheet of the form processed into various shapes may be sufficient.

  1 and 2 are configuration examples of a baseless double-sided adhesive pressure-sensitive adhesive sheet. The pressure-sensitive adhesive sheet 1 shown in FIG. 1 has a configuration in which both surfaces 21A and 21B of a base material-less pressure-sensitive adhesive layer 21 are protected by release liners 31 and 32 having at least a pressure-sensitive adhesive layer side, respectively. The pressure-sensitive adhesive sheet 2 shown in FIG. 2 has a configuration in which one surface (adhesion surface) 21A of a base material-less pressure-sensitive adhesive layer 21 is protected by a release liner 31 whose both surfaces are release surfaces. When wound, the other surface (contact surface) 21B of the pressure-sensitive adhesive layer 21 comes into contact with the back surface of the release liner 31, so that the other surface 21B is also protected by the release liner 31.

<Adhesive composition>
(Acrylic polymerization component)
The pressure-sensitive adhesive composition used for forming the pressure-sensitive adhesive layer disclosed herein contains an acrylic polymerizing component. The acrylic polymerization component is a concept that includes an unreacted product (unpolymerized product, that is, a monomer component) and a reaction product (partially polymerized product and complete polymer product) of a monomer component containing an acrylic monomer. For example by partial or complete polymerization.

Examples of the monomer component constituting the acrylic polymerization component include a chain alkyl (meth) acrylate. As the chain alkyl (meth) acrylate, one or more chain alkyl (meth) acrylates represented by the following formula (1) can be used.
CH ₂ = CR ¹ COOR ² (1)
In the above formula (1), R ¹ is a hydrogen atom or a methyl group. R ² is a chain alkyl group, typically a chain alkyl group having 1 to 20 carbon atoms (hereinafter sometimes abbreviated as “C _1-20 ”). From the viewpoint of the storage elastic modulus and the like of the pressure-sensitive adhesive, a chain alkyl (meth) acrylate in which R ² is C _1-14 (for example, C _1-12 , typically C _1-10 ) can be preferably used. The alkyl group can be linear or branched. Specific examples of chain alkyl (meth) acrylates preferably used include methyl acrylate, methyl methacrylate (MMA), ethyl acrylate (EA), n-butyl acrylate (BA), isobutyl methacrylate (IBMA), t-butyl acrylate ( t-BA), 2-ethylhexyl acrylate (2EHA), isooctyl acrylate (IOA), nonyl acrylate (NA), isononyl acrylate (INA), lauryl acrylate (LA), lauryl methacrylate (LMA), and the like.

From the viewpoint of adhesive properties (particularly, compatibility between drop impact resistance and other adhesive properties), R ² is C _4-12 (for example, C _6-10 , typically C _{6-8 in the} above formula (1)). A linear alkyl (meth) acrylate (typically an alkyl acrylate) that is) may be preferably used. Preferable examples of the chain alkyl (meth) acrylate include BA, IBMA, t-BA, 2EHA, IOA, LA, and LMA. Of these, 2EHA is particularly preferable.

In the above formula (1), the chain alkyl (meth) acrylate in which R ² is C _4-12 is 50% by weight of the total chain alkyl (meth) acrylate contained as a constituent monomer component of the acrylic polymerization component. It is preferable to occupy more than 70% by weight (typically 80% by weight or more typically). In addition, the upper limit of the total chain alkyl (meth) acrylate is typically 100% by weight or less (for example, 95% by weight or less).

  The chain alkyl (meth) acrylate contained in the acrylic polymerization component is suitably the main component of the monomer component constituting the acrylic polymerization component from the viewpoint of achieving good adhesive properties. It is preferable to occupy about 50% by weight or more of the total monomer component), and more preferably about 60% by weight or more (eg, 70% by weight or more, typically 75% by weight or more). The upper limit of the content of the chain alkyl (meth) acrylate is approximately 90% by weight or less (for example, 85% by weight or less, typically 80% by weight or less, from the viewpoint of sufficiently expressing the effect of the polar group-containing monomer described later. ) Is appropriate.

  In a preferred embodiment, the acrylic polymerization component contains a polar group-containing monomer as its constituent monomer component. In other words, a polar group-containing monomer can be copolymerized with the acrylic polymerization component. By including the polar group-containing monomer, the cohesive force of the pressure-sensitive adhesive layer is improved. The polar group-containing monomer disclosed herein typically includes a nitrogen atom-containing monomer (hereinafter also referred to as “N-containing monomer”).

Examples of the N-containing monomer include a monomer having a nitrogen atom (N) -containing ring, an amino group-containing monomer, an amide group-containing monomer, a cyano group-containing monomer, an imide group-containing monomer, and an isocyanate group-containing monomer.
Examples of the monomer having an N-containing ring (typically an N-containing heterocyclic ring) include N-vinyl-2-pyrrolidone (NVP), N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, and N-vinylpyrimidine. N-vinyl piperazine, N-vinyl pyrazine, N-vinyl pyrrole, N-vinyl imidazole, N-vinyl oxazole, 2-vinyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl -2-oxazoline, N-vinylmorpholine, N-vinylcaprolactam, N- (meth) acryloylmorpholine and the like.
Examples of amino group-containing monomers include N, N-dialkylaminoalkyl such as N, N-dimethylaminomethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, and N, N-diethylaminoethyl (meth) acrylate. (Meth) acrylate; N-alkylaminoalkyl (meth) acrylate such as N-methylaminoethyl (meth) acrylate and N-ethylaminoethyl (meth) acrylate; N such as N, N-dimethylamino (meth) acrylate N-dialkylamino (meth) acrylate; N-alkylamino (meth) acrylate such as N-methylamino (meth) acrylate; aminoalkyl (meth) acrylate such as aminomethyl (meth) acrylate; amino (meth) acrylate; Is mentioned.
Examples of the amide group-containing monomer include (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N-butyl (meth) acrylamide, N-methylol (meth) acrylamide, N -Methylolpropane (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, hydroxyethyl (meth) acrylamide and the like.
Examples of the cyano group-containing monomer include acrylonitrile and methacrylonitrile.
Examples of the imide group-containing monomer include maleimide monomers such as N-cyclohexylmaleimide and N-phenylmaleimide; itaconimide monomers such as N-methylitaconimide; succinimide monomers such as N- (meth) acryloxymethylenesuccinimide; Is mentioned.
Examples of the isocyanate group-containing monomer include (meth) acryloyl isocyanate and 2- (meth) acryloyloxyethyl isocyanate.
These can be used alone or in combination of two or more. Among them, a monomer having an N-containing ring (typically NVP, N-acryloylmorpholine (ACMO)), an amino group-containing monomer (typically N, N-dimethylaminomethyl (meth) acrylate), an amide group-containing Monomers (typically N, N-diethylacrylamide (DEAA), N- (2-hydroxyethyl) acrylamide (HEAA)) are preferred.

The polar group-containing monomer may include one or more polar group-containing monomers other than the N-containing monomer (other polar group-containing monomers). Examples of other polar group-containing monomers include the following.
Carboxy group-containing monomers: ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA) and crotonic acid; ethylenically unsaturated dicarboxylic acids such as maleic acid, itaconic acid and citraconic acid and anhydrides thereof (Maleic anhydride, itaconic anhydride, etc.).
Hydroxyl group-containing monomers: For example, hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate; Unsaturated alcohols such as vinyl alcohol and allyl alcohol.
Sulfonic acid group-containing monomers: for example, styrene sulfonic acid, allyl sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, (meth) acrylamide propane sulfonic acid, sulfopropyl (meth) acrylate, (meth) acryloyloxynaphthalene Sulfonic acid.
Phosphoric acid group-containing monomer: for example 2-hydroxyethylacryloyl phosphate.
Aziridine group-containing monomer: for example, (meth) acryloylaziridine, 2-aziridinylethyl (meth) acrylate.
Epoxy group-containing monomer: for example, glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, allyl glycidyl ether.
Keto group-containing monomers: for example, diacetone (meth) acrylamide, diacetone (meth) acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetoacetate, vinyl acetoacetate.
Alkoxy group-containing monomer: for example, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, propoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, ethoxypropyl (meth) acrylate.
Alkoxysilyl group-containing monomer: For example, 3- (meth) acryloxypropyltrimethoxysilane, 3- (meth) acryloxypropyltriethoxysilane, 3- (meth) acryloxypropylmethyldimethoxysilane, 3- (meth) acryloxy Propylmethyldiethoxysilane.
A macromonomer having a radical polymerizable vinyl group at the terminal of a monomer obtained by polymerizing a vinyl group.

  When the N-containing monomer is used as the polar group-containing monomer constituting the acrylic polymerization component, the proportion of the N-containing monomer in the total monomer components constituting the acrylic polymerization component is about 5% by weight or more (for example, 10% by weight or more, Typically, it is preferably 15% by weight or more. This increases the tendency to achieve both a drop impact resistance and a repulsion resistance at a high level. In addition, the compatibility with the acrylic oligomer can be improved by selecting the type and use ratio of the N-containing monomer (for example, a monomer having an N-containing ring) corresponding to the composition of the acrylic oligomer described later. From the same point of view, the upper limit of the proportion of the N-containing monomer in all monomer components constituting the acrylic polymerization component should be less than about 50% by weight (for example, 30% by weight or less, typically 25% by weight or less). Is appropriate.

  When other polar group-containing monomer is used as the polar group-containing monomer constituting the acrylic polymerization component, the proportion of the other polar group-containing monomer in the total monomer components constituting the acrylic polymerization component is other polarities. From the viewpoint of satisfactorily expressing the effect of the group-containing monomer, it is preferably about 0.1% by weight or more (for example, 1% by weight or more, typically 2% by weight or more). The upper limit of the proportion of the other polar group-containing monomer is suitably about 30% by weight or less (eg, 10% by weight or less, typically 5% by weight or less). As other polar group-containing monomers, carboxy group-containing monomers (for example, AA, MAA) and hydroxyl group-containing monomers (for example, 2-hydroxyethyl acrylate (HEA), 4-hydroxybutyl acrylate (4HBA)) are preferable.

  When the carboxy group-containing monomer is copolymerized with the acrylic polymerization component, the proportion of the carboxy group-containing monomer in all the monomer components constituting the acrylic polymerization component is 5% by weight from the viewpoint of improving the drop impact resistance. Is suitably less than 5% by weight (eg less than 4% by weight, typically less than 3% by weight), more preferably less than 2.5% by weight (typically 2% by weight). % Or less). From the viewpoint of maintaining repulsion resistance, the proportion of the carboxy group-containing monomer is preferably 0.5% by weight or more (eg, 1% by weight or more, typically 1.5% by weight or more).

  The acrylic polymerization component is other copolymer different from the chain acrylic (meth) acrylate and the polar group-containing monomer as a constituent monomer component for the purpose of adjusting the glass transition temperature (Tg) and improving cohesive force. May contain a functional monomer. Examples of such other copolymerizable monomers include cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentenyl (meth) acrylate, and dicyclopentanyl (meth) acrylate. Aliphatic hydrocarbon group-containing (meth) acrylates; vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl cyclohexanecarboxylate, vinyl benzoate, etc .; styrene, substituted styrene (α-methylstyrene) Etc.), aromatic vinyl compounds such as vinyl toluene; aromatic ring-containing (meth) acrylates such as aryl (meth) acrylate, aryloxyalkyl (meth) acrylate, arylalkyl (meth) acrylate; ethylene, May be used alone or two or more of the like; vinyl chloride, chlorine-containing monomers such as vinylidene chloride; propylene, isoprene, butadiene, olefin monomer isobutylene and methyl vinyl ether, vinyl ether monomers such as ethyl vinyl ether.

  When the acrylic polymerization component contains other copolymerizable monomer as a constituent monomer component, the content thereof is 20% by weight or less (for example, 10% by weight or less) of all monomer components constituting the acrylic polymerization component. (Typically 5% by weight or less). The acrylic polymerization component disclosed herein may contain substantially no other copolymerizable monomer as a structural unit.

  In a preferred embodiment, the acrylic polymerization component can be prepared by at least partially polymerizing the monomer component described above. The polymerization method of the monomer component is not particularly limited, and various conventionally known polymerization methods can be appropriately employed. For example, thermal polymerization such as solution polymerization, emulsion polymerization and bulk polymerization (typically performed in the presence of a thermal polymerization initiator); photopolymerization performed by irradiation with light such as UV (typically It is carried out in the presence of a photopolymerization initiator.), And active energy ray irradiation polymerization such as radiation polymerization performed by irradiation with radiation such as β-rays and γ-rays can be appropriately employed. Of these, active energy ray irradiation polymerization (particularly photopolymerization) is preferred.

  The mode of polymerization is not particularly limited, and conventionally known monomer supply methods, polymerization conditions (temperature, time, pressure, active energy ray irradiation amount, etc.), materials used other than monomers (polymerization initiator, surfactant, etc.), etc. It can be selected as appropriate. For example, as a monomer supply method, all the monomer components may be supplied to the reaction vessel at once (collective supply), or may be gradually added dropwise (continuous supply), or may be divided into several batches to be predetermined. Each amount may be supplied (divided supply) every time. A part or all of the monomer component may be supplied as a solution dissolved in a solvent or a dispersion emulsified in water.

  In the polymerization of the monomer component, one or more known or commonly used polymerization initiators can be appropriately selected and used according to the polymerization method, polymerization mode, and the like.

  The initiator for thermal polymerization is not particularly limited. For example, an azo polymerization initiator such as azobisisobutyronitrile (AIBN), a peroxide initiator, a peroxide and a reducing agent, A redox initiator, a substituted ethane initiator, or the like can be used. Thermal polymerization can be preferably carried out at a temperature of, for example, about 20 to 100 ° C. (typically 40 to 80 ° C.).

  Various photopolymerization initiators can be used for active energy ray irradiation polymerization (typically photopolymerization). Although it does not specifically limit as a photoinitiator, For example, ketal type photoinitiators, such as 2, 2- dimethoxy- 1, 2- diphenyl ethane- 1-one (brand name "Irgacure 651" etc.), etc. 1-hydroxycyclohexyl-phenyl-ketone (trade name “Irgacure 184” etc.), 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one ( Acetophenone photopolymerization initiators such as trade name “Irgacure 2959”, 2-hydroxy-2-methyl-1-phenyl-propan-1-one (trade name “Darocur 1173” etc.); benzoin such as benzoin methyl ether Benzoin ether photopolymerization initiators such as ethers, substituted benzoin ethers such as anisole methyl ether; bis (2, , 6-trimethylbenzoyl) phenylphosphine oxide (trade name “Irgacure 819” etc.), 2,4,6-trimethylbenzoyl diphenylphosphine oxide (trade name “Lucirin TPO” etc.), etc .; Α-ketol photopolymerization initiators such as 2-methyl-2-hydroxypropiophenone and 1- [4- (2-hydroxyethyl) phenyl] -2-methylpropan-1-one; 2-naphthalenesulfonyl chloride and the like Aromatic sulfonyl chloride photopolymerization initiators; photoactive oxime photopolymerization initiators such as 1-phenyl-1,1-propanedione-2- (o-ethoxycarbonyl) -oxime; benzoin photopolymerization such as benzoin Initiator; benzyl photopolymerization initiator such as benzyl; benzophenone, benzoy Benzophenone photopolymerization initiators such as benzoic acid; thioxanthone, 2-chloro thioxanthone photopolymerization initiators such as thioxanthone; and the like (any of the above product is available from BASF).

  The amount of such thermal polymerization initiator or photopolymerization initiator used is not particularly limited, and can be used according to the polymerization method and polymerization mode. For example, the initiator is 0.001 to 5 parts by weight (typically 0.01 to 2 parts by weight, for example 0.01 to 1 part by weight) with respect to 100 parts by weight of the constituent monomer component of the acrylic polymerization component. be able to.

  The polymerization conversion rate (monomer conversion) of the monomer in the acrylic polymerization component is not particularly limited. Therefore, the acrylic polymerization component may contain an unreacted (unpolymerized) monomer or may not contain substantially. Here, “substantially free of unreacted monomer” means that the content ratio of the unreacted monomer is less than 1% by weight (typically less than 0.1% by weight) of the acrylic polymerization component. In addition, the acrylic polymerization component may include a material (for example, a polymerization initiator, a solvent, a dispersion medium, etc.) other than the monomer used in the polymerization for obtaining the polymerization component.

  In a preferred embodiment, the acrylic polymerization component may be a partial polymer obtained by partially polymerizing the monomer component. Here, the “partially polymerized product” refers to a polymerization reaction product obtained by partially polymerizing the constituent monomer components. Such a partial polymer typically has a syrup shape (viscous liquid) in which a polymer formed from a part of the monomer component and an unreacted monomer are mixed. Hereinafter, such a partially polymerized product may be referred to as “polymer syrup” or simply “syrup”.

  The polymerization conversion rate of the monomer component in such a partially polymerized product is suitably about 70% by weight or less, and preferably 60% by weight or less. From the viewpoint of ease of preparation of the pressure-sensitive adhesive composition, coating property, and the like, the polymerization conversion rate is more preferably 50% by weight or less (for example, 40% by weight or less, typically 30% by weight or less). The lower limit of the polymerization conversion rate is not particularly limited, but is suitably 1% by weight or more, and preferably 5% by weight or more (for example, 10% by weight or more) from the viewpoint of adhesive performance and the like.

The polymerization conversion rate of the acrylic polymerization component (polymerization reaction product) is determined by the following method.
[Measurement of polymerization conversion]
A sample of about 0.5 g is collected from the polymerization reaction product and accurately weighed (weight Wp ₁ ). Next, the unreacted monomer is volatilized by heating the sample to 130 ° C. for 2 hours, and the weight of the sample remaining after the heating is precisely weighed (weight Wp ₂ ). The polymerization conversion rate is obtained by substituting each value into the following equation.
Polymerization conversion [%] = (Wp ₂ / Wp ₁ ) × 100

  A polymerization method for partially polymerizing the monomer component is not particularly limited, but from the viewpoint of efficiency and simplicity, an active energy ray irradiation polymerization method (for example, a photopolymerization method) can be preferably employed. For example, according to photopolymerization, the polymerization conversion rate of the monomer component can be controlled by polymerization conditions such as light irradiation amount (light quantity).

  The pressure-sensitive adhesive composition containing the partial polymer is a form containing a polymer formed from a part of the monomer component in the unreacted monomer (typically, a form in which the polymer is dissolved in the unreacted monomer). Therefore, even if it is not diluted with a solvent or a dispersion medium, it may have a viscosity that can be applied at room temperature. Therefore, it is suitable as a pressure-sensitive adhesive composition that does not substantially contain a solvent (solvent-free pressure-sensitive adhesive composition). Such a solventless pressure-sensitive adhesive composition can form a pressure-sensitive adhesive layer by applying an appropriate curing means (polymerization means) such as light irradiation or radiation irradiation. The solvent-free adhesive composition is substantially environmentally friendly because it does not contain any organic solvent, and does not require any adhesive composition drying equipment or organic solvent recovery equipment, or downsize the equipment. It is also advantageous in that it can be simplified. The pressure-sensitive adhesive composition substantially does not contain a solvent when the content of the solvent in the pressure-sensitive adhesive composition is 5% by weight or less (typically 2% by weight or less, preferably 1% by weight or less). Say something.

  In a preferred embodiment, the pressure-sensitive adhesive composition contains an additional monomer component in addition to the polymer (for example, a partial polymer) as an acrylic polymerization component. The additional monomer component can be added to the polymer after obtaining the polymer.

  The additional monomer component may be any of the chain alkyl (meth) acrylates exemplified above, polar group-containing monomers (N-containing monomers, carboxy group-containing monomers, hydroxyl group-containing monomers, etc.), and other copolymerizable monomers. . As the additional monomer component, one or more of the various monomers exemplified above can be used. Among these, polar group-containing monomers are preferable, and carboxy group-containing monomers (typically AA) are more preferable.

  When using an additional monomer component, the content of the additional monomer component in the pressure-sensitive adhesive composition takes into consideration the action of the additional monomer component (eg, cohesiveness in the case of a polar group-containing monomer), coating properties, and the like. The total amount of the acrylic polymerization component is preferably about 0.1 to 10% by weight (for example, 0.5 to 5% by weight, typically 1 to 3% by weight).

  Moreover, it is preferable that an adhesive composition contains a polyfunctional monomer as another copolymerizable monomer for the purpose of crosslinking or the like. Examples of such polyfunctional monomers include 1,6-hexanediol di (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and polypropylene glycol di ( (Meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, 2 or more (typically 3 or more) weights per molecule such as dipentaerythritol penta (meth) acrylate and dipentaerythritol hexa (meth) acrylate (Typically (meth) acryloyl group) sexually functional group include monomers having a. These can be used alone or in combination of two or more.

  When the pressure-sensitive adhesive composition disclosed herein contains a polyfunctional monomer, the content thereof is 0.01 to 1% by weight (for example, 0.02 to 1%) of all monomer components constituting the acrylic polymerization component. % By weight, typically 0.05 to 0.5% by weight).

  The polyfunctional monomer may be added to the pressure-sensitive adhesive composition before, for example, partial polymerization of the acrylic polymerization component, or may be added after the polymerization (after at least partial polymerization). When a polyfunctional monomer is added after forming an acrylic polymer (for example, a partial polymer), the pressure-sensitive adhesive composition is subjected to a treatment that reacts (typically a crosslinking reaction) after the addition. In one embodiment using a polyfunctional monomer, from the viewpoint of reliably increasing the cohesiveness, a pressure-sensitive adhesive composition to which a polyfunctional monomer is added after forming a partial polymer of an acrylic polymerization component is preferably used.

  A pressure-sensitive adhesive composition (for example, a solventless pressure-sensitive adhesive composition) containing a partial polymer as an acrylic polymerization component is, for example, a partial polymer obtained by partially polymerizing the monomer component by an appropriate polymerization method. , An acrylic oligomer described later, and other components used as necessary (for example, unreacted monomer, the above-mentioned photopolymerization initiator, additional monomer, polyfunctional monomer, a tackifier described later, a crosslinking agent, etc.) It can be prepared by mixing.

In another aspect, the acrylic polymerization component may be a fully polymerized product with a polymerization conversion of greater than 95% by weight (typically greater than 99% by weight). It is preferable that the pressure-sensitive adhesive composition containing such a completely polymerized acrylic polymerization component does not substantially contain unreacted monomers. For example, the content of unreacted monomer is preferably less than 1% by weight (typically less than 0.5% by weight). When the acrylic polymerization component is a complete polymer, its weight average molecular weight (Mw) is 20 × 10 ⁴ to 200 × 10 ⁴ (for example, 30) from the viewpoint of ease of preparation of the pressure-sensitive adhesive composition, coating property, and the like. × 10 ^{4 to} 150 × 10 ⁴ ). In the present specification, Mw of a polymer (including a partial polymer and a complete polymer) can be measured by gel permeation chromatography (GPC). More specifically, for example, the product name “HLC-8120GPC” (manufactured by Tosoh Corporation) can be used as a GPC measuring apparatus, and the above polymer can be used as a sample to calculate a standard polystyrene equivalent value. In addition, it is noted that the unreacted monomer that can be included in the partially polymerized product hardly affects the value of Mw obtained from the GPC measurement.

  The completely polymerized product is diluted to an appropriate viscosity with a solvent, such as a solvent-type pressure-sensitive adhesive composition or a water-dispersed pressure-sensitive adhesive composition (typically an emulsion-type pressure-sensitive adhesive composition). It can be preferably applied to a pressure-sensitive adhesive composition in a dissolved (dispersed or dispersed) form. By including a relatively high molecular weight complete polymer, the pressure-sensitive adhesive composition can form a high-performance pressure-sensitive adhesive layer by a simple curing treatment such as drying the composition.

  The solvent-type pressure-sensitive adhesive composition can be prepared, for example, by subjecting a monomer component having a composition corresponding to the constituent monomer component of the acrylic polymerization component to solution polymerization. As the polymerization solvent, conventionally known various organic solvents can be used in solution polymerization of acrylic polymers such as ethyl acetate, toluene, hexane, and mixed solvents thereof. The aspect of solution polymerization is not specifically limited, A conventionally well-known aspect should just be employ | adopted suitably. The type and amount of the polymerization initiator are generally as described above. Alternatively, a solvent-type pressure-sensitive adhesive composition may be prepared by dissolving a polymerization reaction product obtained by a polymerization method other than solution polymerization in an appropriate organic solvent.

  The emulsion-like pressure-sensitive adhesive composition can be prepared, for example, by subjecting a monomer component having a composition corresponding to the constituent monomer component of the acrylic polymerization component to emulsion polymerization. The aspect of emulsion polymerization is not particularly limited, and a conventionally known aspect may be adopted as appropriate. The type and amount of the polymerization initiator are generally as described above. In addition, an emulsion-like pressure-sensitive adhesive composition is obtained by emulsifying a polymerization reaction product obtained by a polymerization method other than emulsion polymerization in an aqueous solvent (typically water), typically in the presence of a suitable emulsifier. It may be prepared.

  The composition of all constituent monomer components of the acrylic polymerization component can be set so that the Tg of the completely polymerized product is −60 ° C. or higher and −10 ° C. or lower. From the viewpoint of drop impact resistance and repulsion resistance, Tg calculated from the composition of all constituent monomer components of the acrylic polymerization component is −15 ° C. or lower (eg, −20 ° C. or lower, typically −25 ° C. or lower). It is preferable that From the viewpoint of the cohesiveness of the pressure-sensitive adhesive, it is appropriate that the Tg is −60 ° C. or higher (eg, −55 ° C. or higher). In a preferred embodiment, the Tg calculated from the composition of all the constituent monomer components can be −60 ° C. to −30 ° C. (typically −55 ° C. to −35 ° C.).

  Here, the above Tg means the Fox (Fox) based on the Tg of a homopolymer of each monomer constituting the acrylic polymerization component and the weight fraction of the monomer (copolymerization ratio on a weight basis). A value obtained from an expression. Therefore, the Tg can be adjusted by appropriately changing the composition of the constituent monomer components. As the Tg of the homopolymer, the value described in known materials is adopted.

In the technique disclosed here, the following values are specifically used as the Tg of the homopolymer.
2-Ethylhexyl acrylate -70 ° C
Methyl methacrylate 105 ° C
Dicyclopentanyl methacrylate 175 ° C
N-vinyl-2-pyrrolidone 54 ° C
2-hydroxyethyl acrylate -15 ° C
N- (2-hydroxyethyl) acrylamide 98 ° C
2-Methoxyethyl acrylate-50 ° C
1,6-hexanediol diacrylate 43 ° C
Acrylic acid 106 ℃
For the Tg of homopolymers other than those exemplified above, the numerical values described in “Polymer Handbook” (3rd edition, John Wiley & Sons, Inc., 1989) are used. When not described in the above Polymer Handbook, values obtained by the measuring method described in JP-A-2007-51271 are used.

(Acrylic oligomer)
The pressure-sensitive adhesive composition disclosed herein contains an acrylic oligomer. By adopting the acrylic oligomer, it is possible to improve the drop impact resistance and the repellent property in a well-balanced manner. In addition, acrylic oligomers are used for tackifying resins such as rosin-based and terpene-based adhesives for general acrylic pressure-sensitive adhesives when the pressure-sensitive adhesive composition is cured by active energy ray irradiation (for example, UV irradiation). It has the advantage that it is less likely to cause curing inhibition (for example, polymerization inhibition of unreacted monomer) than resin. The acrylic oligomer is a polymer containing an acrylic monomer as a constituent monomer component, and is defined as a polymer having a smaller Mw than the acrylic polymer formed from the acrylic polymerization component.

  The proportion of the acrylic monomer in the total monomer components constituting the acrylic oligomer is typically more than 50% by weight, preferably 60% by weight or more, more preferably 70% by weight or more (for example, 80% by weight). Or more and 90% by weight or more). In a preferred embodiment, the acrylic oligomer has a monomer composition consisting essentially only of acrylic monomers.

  As a constituent monomer component of the acrylic oligomer, a chain alkyl (meth) acrylate exemplified as a monomer that can be used for the acrylic polymerization component, a polar group-containing monomer, and other copolymerizable monomers (for example, an alicyclic hydrocarbon group) Containing (meth) acrylates). As a monomer component which comprises an acryl-type oligomer, the 1 type (s) or 2 or more types of the various monomers illustrated above can be used.

The chain alkyl (meth) acrylate that can be used as a constituent monomer component of the acrylic oligomer is a chain alkyl (meth) acrylate in which R ² is C _1-12 (for example, C _1-8 ) in the above formula (1). Are preferably used. Preferable examples thereof include MMA, EA, BA, IBMA, t-BA, and 2EHA. Of these, MMA is more preferable.

  Preferable examples of the polar group-containing monomer that can be used as a constituent monomer component of the acrylic oligomer include a monomer having an N-containing ring (typically an N-containing heterocycle) such as NVP or ACMO; N, N-dimethylaminoethyl Examples thereof include amino group-containing monomers such as (meth) acrylate; amide group-containing monomers such as N, N-diethyl (meth) acrylamide; carboxy group-containing monomers such as AA and MAA; hydroxyl group-containing monomers such as HEA.

  Preferable examples of the other copolymerizable monomer that can be used as the constituent monomer component of the acrylic oligomer include one or more of the alicyclic hydrocarbon group-containing (meth) acrylates exemplified above. The number of carbon atoms in the alicyclic hydrocarbon group of the alicyclic hydrocarbon group-containing (meth) acrylate is suitably 4-20. The number of carbon atoms is preferably 5 or more (for example, 6 or more, typically 8 or more), and preferably 16 or less (for example, 12 or less, typically 10 or less). Specifically, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentenyl (meth) acrylate, and dicyclopentanyl (meth) acrylate are more preferable, and dicyclopentanyl methacrylate (DCPMA) is particularly preferable.

  In a preferred embodiment, the acrylic oligomer contains a chain alkyl (meth) acrylate and / or an alicyclic hydrocarbon group-containing (meth) acrylate as a constituent monomer component. In this embodiment, the proportion of the chain alkyl group-containing and alicyclic hydrocarbon group-containing (meth) acrylic acid ester in the total monomer components constituting the acrylic oligomer is about 80% by weight or more (for example, 90 to 100). % By weight, typically 95 to 100% by weight). The monomer component constituting the acrylic oligomer is more preferably substantially composed of a chain alkyl (meth) acrylate and / or an alicyclic hydrocarbon group-containing (meth) acrylate.

  The acrylic oligomer preferably contains an alicyclic hydrocarbon group-containing (meth) acrylate as a constituent monomer component. In this embodiment, the ratio of the alicyclic hydrocarbon group-containing (meth) acrylate (that is, the copolymerization ratio) in the total monomer components constituting the acrylic oligomer is about 30 to from the viewpoint of adhesiveness and cohesiveness. It is preferably 90% by weight (for example, 50 to 80% by weight, typically 55 to 70% by weight). In addition, an acrylic oligomer using an alicyclic hydrocarbon group-containing (meth) acrylate as a constituent monomer component can be selected by appropriately selecting the type of the monomer so that a polar group-containing monomer (for example, an N-containing monomer, typically There is an advantage that the tendency to be compatible with an acrylic polymerization component having a monomer having an N-containing ring as a constituent monomer component is increased.

When the acrylic oligomer is a copolymer of a monomer mixture containing a chain alkyl (meth) acrylate and an alicyclic hydrocarbon group-containing (meth) acrylate, the chain alkyl (meth) acrylate and the alicyclic hydrocarbon The ratio with the group-containing (meth) acrylate is not particularly limited. In one preferred embodiment, the weight ratio of the weight percentage of the chain alkyl (meth) weight ratio of acrylate (W _A) and the alicyclic hydrocarbon group-containing (meth) acrylate in the constituent monomer components of the acrylic oligomer (W _B) (W _A : W _B ) is 1: 9 to 9: 1, preferably 2: 8 to 7: 3 (eg, 3: 7 to 6: 4, typically 3: 7 to 5: 5). It is.

  Although it does not specifically limit, the composition (namely, superposition | polymerization composition) of the structural monomer component of an acrylic oligomer can be set so that Tg of this acrylic oligomer may be 10 to 300 degreeC. Here, the Tg of the acrylic oligomer refers to a value obtained in the same manner as the Tg based on the constituent monomer composition of the acrylic polymerization component based on the composition of the constituent monomer component of the acrylic oligomer. The Tg of the acrylic oligomer is preferably 180 ° C. or lower (for example, 160 ° C. or lower) from the viewpoint of initial adhesiveness. Moreover, it is preferable that said Tg is 60 degreeC or more (for example, 100 degreeC or more typically 120 degreeC or more) from a cohesive viewpoint of an adhesive.

The Mw of the acrylic oligomer is not particularly limited, but is typically about 0.1 × 10 ^{4 to} 3 × 10 ⁴ . From the viewpoint of improving adhesive properties (for example, adhesive strength and repulsion resistance), Mw of the acrylic oligomer is preferably 1.5 × 10 ⁴ or less, more preferably 1 × 10 ⁴ or less, and 0.8 × 10 ⁴ or less. (For example, 0.6 × 10 ⁴ or less) is more preferable. Further, from the viewpoint of cohesiveness of the pressure-sensitive adhesive, the Mw is preferably 0.2 × 10 ⁴ or more (for example, 0.3 × 10 ⁴ or more).

  The acrylic oligomer can be formed by polymerizing its constituent monomer components. The polymerization method and the polymerization mode are not particularly limited, and various conventionally known polymerization methods (for example, solution polymerization, emulsion polymerization, bulk polymerization, photopolymerization, radiation polymerization, etc.) can be employed in an appropriate mode. Since the types and amounts of polymerization initiators that can be used as needed (for example, azo polymerization initiators such as AIBN) are generally as described above, the description thereof will not be repeated here.

  In order to adjust the molecular weight of the acrylic oligomer, a chain transfer agent can be used in the polymerization. Examples of chain transfer agents that can be used include compounds having a mercapto group, thioglycolic acid and its derivatives. Specific examples of the compound having a mercapto group include octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan and the like. Specific examples of thioglycolic acid and its derivatives include thioglycolic acid, ethyl thioglycolate, propyl thioglycolate, butyl thioglycolate, t-butyl thioglycolate, 2-ethylhexyl thioglycolate, thioglycolic acid Examples include octyl, decyl thioglycolate, dodecyl thioglycolate, thioglycolate of ethylene glycol, thioglycolate of neopentyl glycol, thioglycolate of pentaerythritol, and the like. Among these, a preferred chain transfer agent is thioglycolic acid.

  The amount of the chain transfer agent used is not particularly limited and can be appropriately adjusted according to the Mw of the target acrylic oligomer. Usually, the chain transfer agent is 0.1 to 20 parts by weight (preferably 0.2 to 15 parts by weight, more preferably 0.3 to 10 parts by weight) with respect to 100 parts by weight of the constituent monomer component of the acrylic oligomer. It is preferable to use a degree.

  The content of the acrylic oligomer in the pressure-sensitive adhesive composition disclosed herein is suitably 0.5 parts by weight or more with respect to 100 parts by weight of the acrylic polymerization component. From the viewpoint of better exerting the effect of the acrylic oligomer, the content of the acrylic oligomer is preferably 1 part by weight or more (eg, 1.5 parts by weight or more, typically 2 parts by weight or more). . From the viewpoint of the curability of the pressure-sensitive adhesive composition and the compatibility with the acrylic polymerization component, the content of the acrylic oligomer is suitably less than 50 parts by weight (for example, less than 10 parts by weight). And less than 8 parts by weight (for example, less than 7 parts by weight, typically 5 parts by weight or less). Even with such a small amount of addition, the effect of improving the repulsion resistance by using the acrylic oligomer can be realized.

(Tackifier)
The pressure-sensitive adhesive composition disclosed herein may be a composition containing a tackifier. Although it does not restrict | limit especially as a tackifier, For example, rosin type, terpene type, hydrocarbon type, various tackifying resins, such as a phenol type, can be used. Such tackifiers can be used singly or in combination of two or more.

  In a preferred embodiment, the pressure-sensitive adhesive composition contains a hydrocarbon-based tackifier resin as a tackifier. Examples of the hydrocarbon-based tackifying resin include aliphatics such as olefins having about 4 to 5 carbon atoms (1-butene, isobutylene, 1-pentene, etc.) and dienes (butadiene, 1,3-pentadiene, isoprene, etc.). An aromatic hydrocarbon resin such as a polymer of a vinyl group-containing aromatic hydrocarbon having about 8 to 10 carbon atoms (styrene, vinyltoluene, α-methylstyrene, indene, methylindene, etc.); Alicyclic hydrocarbon resins polymerized after cyclization and dimerization of so-called “C4 petroleum fraction” or “C5 petroleum fraction”, cyclic diene compounds (cyclopentadiene, dicyclopentadiene, ethylidene norbornene, dipentene, etc. ) Polymer or its hydrogenated product, aromatic hydrocarbon resin or aliphatic / aromatic petroleum resin aromatic ring hydrogenated alicyclic charcoal Aliphatic cyclic hydrocarbon resins such as hydrogen resins; Aliphatic and aromatic petroleum resins (styrene-olefin copolymers, etc.); Aliphatic and alicyclic petroleum resins; Hydrogenated hydrocarbon resins; Coumarone Resin; coumarone indene resin; and the like. Of these, hydrogenated products of aliphatic cyclic hydrocarbon resins are preferable. This type of tackifying resin can be prepared by subjecting a petroleum resin to a hydrogenation treatment.

  In the technology disclosed herein, a tackifying resin having a softening point (softening temperature) of about 60 ° C. or higher (preferably about 80 ° C. or higher, typically 100 ° C. or higher) can be preferably used. According to the tackifying resin having the softening point, a higher-performance (for example, highly adhesive) pressure-sensitive adhesive sheet can be realized. The upper limit of the softening point of the tackifying resin is not particularly limited, and can be about 180 ° C. or lower (for example, about 140 ° C. or lower). In addition, the softening point of the tackifier resin here is defined as a value measured by a softening point test method (ring ball method) defined in either JIS K 5902: 2006 and JIS K 2207: 2006.

  The amount of tackifier used is not particularly limited, but is usually based on 100 parts by weight of the acrylic polymerization component in consideration of the balance between the tackiness of the pressure-sensitive adhesive (for example, tackiness and repulsion resistance) and cohesiveness. About 0.5 to 50 parts by weight (more preferably 1 to 10 parts by weight, still more preferably 1 to 3 parts by weight) is appropriate. The method for adding a tackifier to the pressure-sensitive adhesive composition is not particularly limited. For example, the tackifier can be added after obtaining a polymer of an acrylic polymerization component (for example, a partial polymer). In addition, the technique disclosed here can be implemented in the aspect using the adhesive which does not contain tackifying components (tackifier) other than an acrylic oligomer substantially.

(Other additive components)
The solvent-type or water-dispersed pressure-sensitive adhesive composition may contain various crosslinking agents as required in addition to the acrylic polymerization component and the acrylic oligomer. Examples of the crosslinking agent include an epoxy crosslinking agent, an isocyanate crosslinking agent, a silicone crosslinking agent, an oxazoline crosslinking agent, an aziridine crosslinking agent, a silane crosslinking agent, an alkyl etherified melamine crosslinking agent, and a metal chelate crosslinking agent. 1 type (s) or 2 or more types can be used. The cross-linking agent may be used in an appropriate amount based on the common general knowledge of those skilled in the art so that the desired adhesive properties can be obtained. In addition, the technique disclosed here can be implemented in the aspect using the adhesive composition which does not contain crosslinking components (crosslinking agent) other than the said polyfunctional monomer substantially.

  The pressure-sensitive adhesive composition disclosed herein may contain various colorants (pigments, dyes, etc.) depending on the purpose and application location. For example, when a pressure-sensitive adhesive composition is cured by a photopolymerization method to form a pressure-sensitive adhesive layer, in order to color the pressure-sensitive adhesive layer, it is possible to use as a colorant a pigment that does not alienate photopolymerization. it can. When black is desired as the color of the pressure-sensitive adhesive layer, for example, carbon black can be preferably used as the colorant. The amount of the colorant used is selected from the range of 10% by weight or less (for example, 0.001 to 5% by weight), preferably 0.01 to 3% by weight in the pressure-sensitive adhesive layer in consideration of the degree of coloring and the like. It is desirable.

  The pressure-sensitive adhesive composition disclosed herein may contain various conventionally known fillers that can be included in the pressure-sensitive adhesive. As the filler, various particulate materials and fibrous materials can be used. The constituent material of the particulate matter can be, for example, a metal, a metal oxide, a carbide such as calcium carbonate, a hydroxide such as aluminum hydroxide, an inorganic material such as nitride; an organic material such as a polymer; Alternatively, natural raw material particles such as clay may be used. Furthermore, the pressure-sensitive adhesive composition may contain a particulate material having a hollow structure (for example, a hollow glass balloon) and various foaming agents (for example, thermally expandable microspheres). As the fibrous substance, various synthetic fiber materials and natural fiber materials can be used. These can be used alone or in combination of two or more. The addition amount of such a filler is not particularly limited, and an appropriate amount may be added based on the purpose and technical common knowledge of those skilled in the art.

  The pressure-sensitive adhesive composition disclosed herein is used for acrylic pressure-sensitive adhesives such as plasticizers, softeners, antioxidants, leveling agents, stabilizers, preservatives, etc., as long as the effects of the present invention are not significantly hindered. You may further contain the well-known additive which can be obtained, and various arbitrary polymer components as needed.

  The form of the pressure-sensitive adhesive composition disclosed herein is not particularly limited. For example, as described above, a composition prepared by curing with an active energy ray such as UV or radiation to form a pressure-sensitive adhesive (active energy) Wire curable pressure-sensitive adhesive composition), composition in a form containing a pressure-sensitive adhesive (adhesive component) in an organic solvent (solvent-type pressure-sensitive adhesive composition), composition in a form in which the pressure-sensitive adhesive is dispersed in an aqueous solvent (water-dispersed type) Adhesive composition) may be used, and may be various forms of adhesive compositions such as a hot-melt adhesive composition that is applied in a heated and melted state and forms an adhesive when cooled to near room temperature.

<Adhesive layer>
The pressure-sensitive adhesive layer disclosed herein contains an acrylic polymer as a main component. Here, the acrylic polymer is not only a polymer derived from an acrylic polymerization component (acrylic polymer) but also a relatively low degree of polymerization that is generally referred to as an oligomer (including an acrylic oligomer). It is also a concept that includes the polymerized product.

  Examples of the constituent monomer component of the acrylic polymer include various monomers exemplified as the constituent monomer component of the acrylic polymer component and the acrylic oligomer. Typically, a chain alkyl (meth) acrylate is used as the main component of the monomer component constituting the acrylic polymer. From the viewpoint of realizing good adhesive properties, the chain alkyl (meth) acrylate is 50% by weight or more (preferably 60% by weight or more, for example 70% by weight or more) of all monomer components constituting the acrylic polymer. It is appropriate to include them in proportions. As the chain alkyl (meth) acrylate, those exemplified as the constituent monomer component of the acrylic polymerization component can be preferably used.

From the viewpoint of adhesive properties (particularly, compatibility between drop impact resistance and other adhesive properties), R ² is C _4-12 (for example, C _6-10 , typically C _{6-8 in the} above formula (1)). A linear alkyl (meth) acrylate that is) can be preferably used. In the formula (1), the chain alkyl (meth) acrylate in which R ² is C _4-12 is 50% by weight of the total chain alkyl (meth) acrylate contained as a constituent monomer component of the acrylic polymer. It is preferable to occupy more than 70% by weight (typically 80% by weight or more typically). Moreover, the upper limit may be 100 weight% or less (for example, 95 weight% or less) in the said all-chain alkyl (meth) acrylate.

  The acrylic polymer contains a polar group-containing monomer as a constituent monomer component. By including the polar group-containing monomer, the cohesive force of the pressure-sensitive adhesive layer is improved. The technique disclosed here is characterized in that the polar group-containing monomer contains an N-containing monomer.

  As the N-containing monomer, one or more of a monomer having an N-containing ring exemplified as a constituent monomer component of the acrylic polymerization component, an amino group-containing monomer, an amide group-containing monomer and the like can be preferably used. Among these, NVP and ACMO are preferable as the monomer having an N-containing ring, N, N-dimethylaminomethyl (meth) acrylate is preferable as the amino group-containing monomer, and DEAA and HEAA are preferable as the amide group-containing monomer.

  The polar group-containing monomer may further include other polar group-containing monomers. As other polar group-containing monomers, one or more of carboxy group-containing monomers and hydroxyl group-containing monomers exemplified as constituent monomer components of the acrylic polymerization component can be used.

  The technique disclosed here is characterized by the ratio of the N-containing monomer in the total polar group-containing monomer component constituting the acrylic polymer being 40% by weight or more. By using the N-containing monomer in the above-described ratio, a configuration that achieves both a drop impact resistance and a repulsion resistance at a high level is realized. Moreover, the adhesiveness to resin-made to-be-adhered bodies, such as a polycarbonate, improves by using N containing monomer as a polar group containing monomer. The proportion of the N-containing monomer in the total polar group-containing monomer component constituting the acrylic polymer is preferably more than about 50% by weight (for example, 60% by weight or more, typically 70% by weight or more). The upper limit of the ratio of the N-containing monomer in the total polar group-containing monomer component is not particularly limited, but may be, for example, 100% by weight or less, and from the viewpoint of favorably expressing the effects of other polar group-containing monomers. It may be 90% by weight or less (for example, 80% by weight or less).

  In a preferred embodiment, an N-containing monomer (for example, a monomer having an N-containing ring, typically NVP) and a carboxy group-containing monomer (for example, AA) are used in combination as the polar group-containing monomer. Thereby, the tendency for cohesiveness of adhesive force to develop stably increases. When the N-containing monomer and the carboxy group-containing monomer are used in combination, the ratio of the N-containing monomer content to the total content of the N-containing monomer and the carboxy group-containing monomer is approximately 50% by weight or more (for example, 70% by weight or more). , Typically 80% by weight or more). The ratio is preferably less than about 100% by weight (for example, 95% by weight or less). Thereby, there exists a tendency for an acid / base to be balanced, and aggregation can be improved efficiently by adding a small amount of a polar group-containing monomer.

  Corresponding to the content of the N-containing monomer, the proportion of the other polar group-containing monomer in the total polar group-containing monomer component constituting the acrylic polymer is 60% by weight or less and less than 50% by weight (for example, 40 % By weight or less, typically 30% by weight or less), and may be about 10% by weight or less.

  As the other polar group-containing monomer described above, a carboxy group-containing monomer is preferably included. Of these, AA and MAA are preferable, and AA is more preferable. From the viewpoint of drop impact resistance, the proportion of the carboxy group-containing monomer in the total polar group-containing monomer component constituting the acrylic polymer is preferably 15% by weight or less, more preferably 12% by weight or less. More preferably, it is 10% by weight or less. From the viewpoint of improving repulsion resistance, the proportion of the carboxy group-containing monomer in the total polar group-containing monomer component should be about 1% by weight (for example, 3% by weight or more, typically 6% by weight or more). Is preferred.

  When a carboxy group-containing monomer (for example, AA) is copolymerized with the acrylic polymer as another polar group-containing monomer, the ratio of the carboxy group-containing monomer in the total monomer components constituting the acrylic polymer is From the viewpoint of improving the drop impact resistance, the content is suitably 5% by weight or less, preferably less than 5% by weight (for example, less than 4% by weight, typically less than 3% by weight), more preferably 2.5% by weight or less (typically 2% by weight or less). From the viewpoint of improving repulsion resistance, the proportion of the carboxy group-containing monomer is preferably 0.5% by weight or more (eg, 1% by weight or more, typically 1.5% by weight or more).

  Moreover, it is preferable that a hydroxyl-containing monomer is included as another polar group containing monomer. Of these, HEA and 4HBA are preferable. From the viewpoint of cohesiveness of the pressure-sensitive adhesive, the proportion of the hydroxyl group-containing monomer in the total polar group-containing monomer component constituting the acrylic polymer is approximately 1 to 40% by weight (for example, 3 to 30% by weight, typically 5 to 20% by weight) is appropriate.

  The polar group-containing monomer is sufficiently contained in a proportion of 15% by weight or more of the total monomer components constituting the acrylic polymer in order to fully express its effect and contribute to the adhesive properties. The total amount of polar group-containing monomers in all monomer components constituting the acrylic polymer is preferably about 18% by weight or more (for example, 20% by weight or more, typically 22% by weight or more), and about 40% by weight. % Or less (for example, 30% by weight or less, typically 25% by weight or less).

  The acrylic polymer may contain other copolymerizable monomers different from the above-mentioned chain acrylic (meth) acrylate and the polar group-containing monomer for the purpose of adjusting Tg and improving cohesion as a constituent monomer component. Good. Examples of such other copolymerizable monomers include alicyclic hydrocarbon group-containing (meth) acrylates, carboxylic acid vinyl esters, aromatic vinyl compounds, aromatic rings exemplified as constituent monomer components of the above-mentioned acrylic polymerization components. 1 type (s) or 2 or more types, such as containing (meth) acrylate, can be used. When the constituent monomer component of the acrylic polymer disclosed herein contains another copolymerizable monomer (for example, (alicyclic hydrocarbon group-containing (meth) acrylate)), the content thereof is acrylic polymer. It is appropriate that it is 20% by weight or less (for example, 10% by weight or less, typically 5% by weight or less) of all the monomer components constituting the above. Further, the content is 0.5% by weight or more (for example, 1% by weight or more, typically 2% by weight) when, for example, an alicyclic hydrocarbon group-containing (meth) acrylate is used as another copolymerizable monomer. % Or more).

  In addition, as the other copolymerizable monomer, a polyfunctional monomer may be included as necessary for the purpose of crosslinking or the like. As such a polyfunctional monomer, 2 or more (typically 3 or more) polymerizable functional groups (typically (meth) acryloyl) per molecule as exemplified as the constituent monomer component of the acrylic polymerization component. One or more monomers having a group) can be used. When the constituent monomer component of the acrylic polymer disclosed herein contains a polyfunctional monomer, the content thereof is 0.01 to 1% by weight (for example, 0%) of all monomer components constituting the acrylic polymer. 0.02 to 1% by weight, typically 0.05 to 0.5% by weight).

The pressure-sensitive adhesive layer disclosed herein contains an acrylic polymer that is a completely polymerized product of an acrylic polymerization component. Since the monomer composition of the acrylic polymer (monomer type, use ratio, etc.) is the same as the description regarding the monomer composition of the acrylic polymerization component, the description will not be repeated here. The Mw of the acrylic polymer is preferably 20 × 10 ⁴ or more, more preferably 30 × 10 ⁴ or more, for example, 40 × 10 ⁴ or more. The upper limit of the Mw is not particularly limited, from the viewpoint of preparation ease and coatability of the pressure-sensitive adhesive composition, usually, it is preferable that Mw is 200 × 10 ⁴ or less, is 0.99 × 10 ⁴ or less It is more preferable.

  The pressure-sensitive adhesive layer disclosed herein contains an acrylic oligomer as in the above-described pressure-sensitive adhesive composition. Since matters (monomer composition and the like) related to the acrylic oligomer are the same as those described in the pressure-sensitive adhesive composition, description thereof will not be repeated here.

  Moreover, the adhesive layer disclosed here may contain various additive components (tackifier, a coloring agent, etc.) illustrated as an additive component contained in the above-mentioned adhesive composition as needed. The details (compound name, blending ratio, etc.) are basically the same as the contents described in the pressure-sensitive adhesive composition, and therefore the description will not be repeated here.

  The pressure-sensitive adhesive in the technology disclosed herein comprises all the constituent monomer components having the above-described composition, polymer (for example, acrylic polymer or acrylic oligomer), unpolymerized (that is, the polymerizable functional group is unreacted). A certain form), or a pressure-sensitive adhesive composition containing them in the form of a mixture thereof. When the pressure-sensitive adhesive composition disclosed herein contains a partially polymerized product, the pressure-sensitive adhesive composition polymerizes unreacted monomers (for example, an additional monomer) contained in the composition by an appropriate means. To cure. In this embodiment, the polymerization method for curing the pressure-sensitive adhesive composition to form a pressure-sensitive adhesive (pressure-sensitive adhesive layer) is not particularly limited, and is the same polymerization method used when partially polymerizing the monomer components. Alternatively, different methods can be employed as appropriate.

  The pressure-sensitive adhesive layer disclosed herein can be formed by a conventionally known method. For example, a method of forming a pressure-sensitive adhesive layer by applying (typically applying) a pressure-sensitive adhesive composition to a peelable surface (peeling surface) and curing (curing reaction, drying, etc.) is preferably employed. be able to. Alternatively, the pressure-sensitive adhesive composition is directly applied (typically applied) to the substrate and cured to form a pressure-sensitive adhesive layer (direct method), or the pressure-sensitive adhesive composition is applied to the release surface. You may employ | adopt the method (transfer method) which forms an adhesive layer on this surface by making it harden | cure, and transfers the adhesive layer to a base material. As the release surface, the surface of the release liner, the back surface of the substrate after the release treatment, or the like can be used. The coating may be performed using a known or conventional coater such as a gravure roll coater or a reverse roll coater. The pressure-sensitive adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form, and is formed in a regular or random pattern such as a spot or stripe. It may be an adhesive layer.

In a preferred embodiment, the polymerization (typically photopolymerization) in forming the pressure-sensitive adhesive from the pressure-sensitive adhesive composition can be performed by UV irradiation. As a UV lamp used for UV irradiation, a lamp having a spectral distribution in a wavelength region of 300 to 400 nm is preferably used. For example, a chemical lamp, a black light (for example, a black light manufactured by Toshiba Lighting & Technology), a metal halide lamp, or the like can be used as the light source. In particular, it is preferable to irradiate UV so that the illuminance at a wavelength of 300 to 400 nm is 1 to 50 mW / cm ² . Setting the illuminance of UV to 50 mW / cm ² or less (typically 40 mW / cm ² or less, for example, 30 mW / cm ² or less) is advantageous from the viewpoint of obtaining better adhesive properties. The illuminance of the UV 1 mW / cm ² or more (more preferably 2 mW / cm ² or more, for example 3 mW / cm ² or higher) and that is advantageous from the viewpoint of productivity. The UV illuminance can be measured using an industrial UV checker (trade name “UVR-T1”, light receiving unit type UD-T36, manufactured by Topcon Corporation) having a peak sensitivity wavelength of about 350 nm. When forming the pressure-sensitive adhesive layer using UV irradiation, it is cured with both sides of the pressure-sensitive adhesive layer covered with a release liner or substrate from the viewpoint of suppressing reaction inhibition by oxygen in the atmosphere. It is preferable to carry out the reaction.

  The gel fraction of the pressure-sensitive adhesive layer disclosed herein is suitably about 10% by weight or more. From the viewpoint of cohesiveness, the gel fraction is preferably 30% by weight or more (eg, 50% by weight or more, typically 60% by weight or more). From the viewpoint of tackiness, the gel fraction is suitably 90% by weight or less (for example, 85% by weight or less, typically 80% by weight or less). The gel fraction is adjusted by the monomer composition, the polymerization conversion rate of the constituent monomer components, the Mw of the polymer, the formation conditions of the pressure-sensitive adhesive layer (curing conditions of the pressure-sensitive adhesive composition, such as light irradiation conditions and drying conditions), etc. Can do.

The gel fraction can be measured by the following method. That is, about 0.1 g of a measurement sample is wrapped in a purse-like shape with a porous sheet made of tetrafluoroethylene resin having an average pore diameter of 0.2 μm, and the mouth is tied with a kite string. The total weight Wa (mg) of the porous sheet made of tetrafluoroethylene resin and the kite string is measured in advance. Then, the weight of the wrap (total weight of the adhesive and the wrap) Wb (mg) is measured. Place this packet in a 50 mL screw tube (use one screw tube per packet) and fill the screw tube with ethyl acetate. This is allowed to stand at room temperature (typically 23 ° C.) for 7 days, then the packet is taken out and dried at 120 ° C. for 2 hours, and the weight Wc (mg) of the package after drying is measured. The gel fraction (%) of the pressure-sensitive adhesive is the above-mentioned Wa, Wb and Wc:
Gel fraction [%] = (Wc−Wa) / (Wb−Wa) × 100;
By substituting for. As the porous sheet made of tetrafluoroethylene resin, trade name “Nitoflon NTF1122” (average pore diameter 0.2 μm, porosity 75%, thickness 85 μm) manufactured by Nitto Denko Corporation or its equivalent can be used. The same applies to the gel fraction in Examples described later.

  The thickness of the pressure-sensitive adhesive layer disclosed here is suitably 10 μm or more. From the viewpoint of adhesive properties (particularly drop impact resistance and repulsion resistance), the thickness is preferably 60 μm or more (for example, 90 μm or more, typically 140 μm or more). The upper limit of the thickness is suitably about 5 mm or less. From the viewpoint of cohesion and the like, the thickness is preferably 1500 μm or less (for example, 600 μm or less, typically 400 μm or less). When the pressure-sensitive adhesive sheet disclosed herein is a double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on both sides of the substrate, the thickness of each pressure-sensitive adhesive layer may be the same or different. Moreover, the pressure-sensitive adhesive sheet may include a pressure-sensitive adhesive layer having a multilayer structure. In that case, the plurality of pressure-sensitive adhesive layers may have a laminated structure of the pressure-sensitive adhesive layer disclosed herein and a conventionally known pressure-sensitive adhesive layer.

<Base material>
When the pressure-sensitive adhesive sheet disclosed herein is a pressure-sensitive adhesive sheet with a base material, various sheet-like base materials can be used as a base material for supporting (lining) the pressure-sensitive adhesive layer. As the substrate, for example, a resin film, paper, cloth, rubber sheet, foam sheet, metal foil, a composite of these, or the like can be used. The surface (adhesive layer side surface) on which the adhesive layer of the substrate (for example, a resin film substrate, a rubber sheet substrate, a foam sheet substrate, etc.) is disposed is corona discharge treatment, plasma treatment, UV irradiation. Known or conventional surface treatments such as treatment, acid treatment, alkali treatment, and application of a primer may be performed. Alternatively, when the pressure-sensitive adhesive sheet disclosed herein is a single-sided adhesive pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer is provided on one side of the substrate, the release treatment agent is provided on the surface of the substrate where the pressure-sensitive adhesive layer is not formed (back surface). A peeling treatment with (back treatment agent) may be performed.

<Release liner>
A conventional release paper or the like can be used as the release liner, and is not particularly limited. For example, it consists of a release liner having a release treatment layer on the surface of a liner substrate such as a resin film or paper, or a low adhesive material such as a fluorine-based polymer (polytetrafluoroethylene, etc.) or a polyolefin resin (polyethylene, polypropylene, etc.). A release liner or the like can be used. The release treatment layer may be formed, for example, by surface-treating the liner base material with a release treatment agent such as silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide.

<Characteristics of adhesive sheet>
According to a preferred embodiment, in the drop impact resistance evaluation of dropping 60 times, a drop impact resistance level at which no joint failure such as peeling is observed until it is dropped 25 times (preferably 40 times, more preferably 50 times). A pressure-sensitive adhesive sheet (typically a double-sided pressure-sensitive adhesive sheet) can be realized. A pressure-sensitive adhesive sheet that satisfies this characteristic is excellent in the ability to withstand an impact such as a drop and maintain bonding (ie, a drop impact resistance). For example, in an application that is expected to be dropped during use, such as a portable electronic device. It is suitable as an adhesive sheet used for joining parts. According to a particularly preferred embodiment of the pressure-sensitive adhesive sheet, a drop impact resistance level at which no bonding failure is observed even when dropped 60 times in the drop impact resistance evaluation is realized. The drop impact resistance evaluation is performed by the method described in the examples described later.

  According to a preferred embodiment, in the repulsion resistance test, a pressure-sensitive adhesive sheet exhibiting a level of repulsion resistance that satisfies a test piece float of 15 mm or less (preferably 10 mm or less, more preferably 5 mm or less) is realized. The pressure-sensitive adhesive sheet exhibiting the above characteristics can be excellent in step following ability. According to the pressure-sensitive adhesive sheet according to a particularly preferred embodiment, a level of repulsion resistance that realizes substantially no floating of the test piece in the repulsion resistance test is realized. Specifically, the repulsion resistance test is performed by the method described in Examples described later.

  The pressure-sensitive adhesive sheet disclosed herein preferably exhibits a 180-degree peel strength (against polycarbonate (PC) pressure-sensitive adhesive strength) of 12 N / 20 mm or more. The pressure-sensitive adhesive sheet exhibiting the above characteristics can firmly adhere to an adherend (particularly, a resin adherend such as a PC) and can be preferably used for joining and fixing. For example, high adhesion reliability can be maintained in applications where the adhesion area tends to be reduced, such as a double-sided PSA sheet used in portable electronic devices. The PC adhesive strength is more preferably 15 N / 20 mm or more (for example, 18 N / 20 mm or more, typically 22 N / 20 mm or more). The adhesion to PC is measured by the method described in the examples described later.

  The pressure-sensitive adhesive sheet disclosed herein may have desired optical characteristics (transmittance, reflectance, etc.). For example, the pressure-sensitive adhesive sheet used for light shielding applications preferably has a total light transmittance of 0% to 20% (more preferably 0% to 10%). The total light transmittance is measured by the method described in Examples described later. The optical characteristics of the pressure-sensitive adhesive sheet can be adjusted, for example, by coloring the pressure-sensitive adhesive layer or the base material.

  The total thickness of the pressure-sensitive adhesive sheet disclosed here (which may include a pressure-sensitive adhesive layer and a base material but does not include a release liner) is not particularly limited, and is suitably in the range of about 10 μm to 5 mm. The total thickness of the pressure-sensitive adhesive sheet is preferably about 60 to 1500 μm (for example, 90 to 800 μm, typically 140 to 500 μm) in consideration of pressure-sensitive adhesive properties such as drop impact resistance. When the total thickness of the pressure-sensitive adhesive sheet is set to a predetermined value or less, it can be advantageous in terms of thinning, downsizing, lightening, and resource saving of a product to which the pressure-sensitive adhesive sheet is applied.

<Application>
The pressure-sensitive adhesive sheet disclosed herein is compatible with both high levels of drop impact resistance and repulsion resistance. Moreover, in one suitable aspect, it is excellent in adhesive force. For this reason, it can be suitable as a pressure-sensitive adhesive sheet (typically a double-sided pressure-sensitive adhesive sheet) used for the purpose of joining, fixing, shock absorption, etc. in a portable device that is susceptible to impact due to dropping or the like. In addition, taking advantage of the above features, for electronic device applications, for example, for fixing a protective panel (lens) that protects the display of portable electronic devices (for example, mobile phones, smartphones, tablet computers, laptop computers, cameras, etc.) It can be preferably applied to applications such as fixing a mobile phone key module member, fixing a television decoration panel, fixing a battery pack of a personal computer, and waterproofing a lens of a digital video camera. A particularly preferred application is a portable electronic device. In particular, it can be preferably used for a portable electronic device incorporating a liquid crystal display device. For example, in such a portable electronic device, it is suitable for applications such as joining a protective panel (lens) that protects the display unit and a housing. In the present specification, “portable” means that it is not sufficient to be able to carry it alone, and that it is portable enough for an individual (standard adult) to carry it relatively easily. Shall mean. In addition, the “lens” in the present specification is a concept including both a transparent body showing a light refraction action and a transparent body having no light refraction action. In other words, the “lens” in the present specification includes a protective panel that has no refractive action and simply protects a display portion of a portable electronic device.

  The adhesion target of the adhesive sheet disclosed here is not particularly limited. The pressure-sensitive adhesive sheet includes, for example, metal materials such as stainless steel (SUS) and aluminum; inorganic materials such as glass and ceramics; resin materials such as PC, polymethyl methacrylate, polypropylene, and polyethylene terephthalate (PET); natural rubber, butyl rubber, and the like A rubber material; and a composite material or the like, and affixed to an adherend having a surface made of such a composite material.

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

[Evaluation method]
(1) Drop impact resistance The double-sided pressure-sensitive adhesive sheet was cut into a window frame shape (frame shape) having a width of 53 mm, a height of 116 mm, and a width of 1 mm as shown in FIG. Using this window frame-shaped double-sided pressure-sensitive adhesive sheet, a PC board (width 70 mm, length: 130 mm, thickness 2 mm) and a glass plate (width 53 mm, height 116 mm, thickness 1 mm, weight 18 g) are reciprocated once by a 5 kg roller. The samples for evaluation were obtained by pressure bonding under conditions (see FIGS. 3A and 3B).
FIG. 3 is a schematic view of the sample for evaluation, wherein (a) is a top view and (b) is a cross-sectional view taken along the line BB ′. In FIG. 3, reference numeral 50 denotes a window frame-shaped double-sided pressure-sensitive adhesive sheet, reference numeral 51 denotes a PC plate, and reference numeral 52 denotes a glass plate.
A 110 g weight was attached to the back surface (surface opposite to the surface bonded to the glass plate) of the PC plate of these evaluation samples. About the sample for evaluation with the said weight, the drop test which makes it fall freely to a concrete board 60 times from the height of 1.2 m at normal temperature (about 23 degreeC) was done. At this time, the direction of the fall was adjusted so that the six surfaces of the sample for evaluation became sequentially lower. That is, 10 cycles of one drop pattern were performed for each of the six surfaces.
Each time it was dropped, it was visually checked whether or not peeling occurred between the PC plate and the glass plate, and the number of drops until peeling occurred was evaluated as drop impact resistance. When peeling was not recognized even after dropping 60 times, “60 times or more” is displayed.

(2) Repulsion resistance Each double-sided adhesive sheet was cut to a size of 20 mm in width and 180 mm in length, and the 0.5 mm-thick aluminum was cut to the same size on the exposed first adhesive surface by peeling off the first release liner A test piece was prepared by attaching and backing a plate. The test piece was pressed against a 2 mm thick PC plate cut into a size of 30 mm × 200 mm using a laminator in an environment of 23 ° C. and RH 50%, and then held in the same environment for 24 hours. Next, as shown in FIG. 4, the PC plate to which the test piece was attached was bent in an arc shape having a chord length of 190 mm. This was held for 72 hours under an atmosphere of 70 ° C., and the distance h (mm) at which the end of the test piece lifted from the PC plate surface was measured (FIG. 5). 4-5, the code | symbol 100, 200, 300 shows the double-sided adhesive sheet except the 1st and 2nd release liner, an aluminum plate, and a PC board, respectively.

(3) Adhesive strength against polycarbonate The release liner covering one adhesive surface of the double-sided adhesive sheet was peeled off, and a 50 μm thick PET film was bonded to the one adhesive surface. This was cut into a size of 20 mm in width and 100 mm in length to produce a measurement sample.
In an environment of 23 ° C. and 50% RH, the other adhesive surface of the measurement sample was exposed, and the other adhesive surface was pressed against the surface of the PC plate by reciprocating a 2 kg roller once. After leaving this in the same environment for 30 minutes, using a universal tensile compression tester (product name “TG-1kN”, manufactured by Minebea Co., Ltd.), in accordance with JIS Z 0237, tensile speed of 300 mm / min, peeling angle The peel strength [N / 20 mm width] was measured under the condition of 180 degrees.

(4) Light transmission The total light transmittance of the double-sided pressure-sensitive adhesive sheet after peeling off the release liner is measured using a haze meter (trade name “HM-150”, manufactured by Murakami Color Research Laboratory) in accordance with JIS K 7361. Measured. When the total light transmittance was 20% or less, it was evaluated as “No”, and when the total light transmittance exceeded 20%, it was evaluated as “Yes”.

<Example 1>
[Preparation of pressure-sensitive adhesive composition]
A monomer mixture consisting of 78 parts of 2-ethylhexyl acrylate (2EHA), 18 parts of N-vinyl-2-pyrrolidone (NVP) and 4 parts of 2-hydroxyethyl acrylate (HEA) was converted into 2,2-dimethoxy as a photopolymerization initiator. 0.05 parts of -1,2-diphenylethane-1-one (trade name “Irgacure 651” manufactured by BASF) and 1-hydroxycyclohexyl-phenyl-ketone (trade name “Irgacure 184” manufactured by BASF) A syrup A containing a partially polymerized product was obtained by putting it into a four-necked flask together with 05 parts and subjecting it to partial photopolymerization by irradiation with UV in a nitrogen atmosphere. The polymerization conversion of the monomer mixture in syrup A was about 10%.
To 100 parts of this syrup A, 2 parts of acrylic acid (AA) as an additional monomer, 0.12 part of 1,6-hexanediol diacrylate (HDDA), 3 parts of an acrylic oligomer, and a black colorant (Daiichi Seisen) A pressure-sensitive adhesive composition according to this example was prepared by adding and mixing 0.8 parts of a product name “AT DN101 Black” manufactured by Kagaku Kogyo Co., Ltd.
As the acrylic oligomer, one prepared by the following method was used. 60 parts of dicyclopentanyl methacrylate (DCPMA: Hitachi Chemical Co., Ltd., trade name “FA-513M”) and 40 parts of methyl methacrylate (MMA), 3 parts of thioglycolic acid as a chain transfer agent, and toluene as a solvent And dissolved oxygen was removed by blowing nitrogen gas. The mixture was then heated to 70 ° C. and stirred at 70 ° C. for 1 hour, and 0.2 part of azobisisobutyronitrile as a polymerization initiator was added. This was reacted at 70 ° C. for 2 hours and then at 80 ° C. for 2 hours. Thereafter, the pressure was reduced at 130 ° C., and the mixture was stirred for 1 hour to remove the residual monomer to obtain an acrylic oligomer having an Mw of about 0.55 × 10 ⁴ and a Tg of about 144 ° C.

[Production of adhesive sheet]
Two PET films having a thickness of 38 μm, each having a release surface treated with a silicone-based release treatment agent, were prepared. Of these, the pressure-sensitive adhesive composition was applied onto the release surface of the first PET film. By covering the peeled surface of the second PET film on the applied pressure-sensitive adhesive composition and irradiating it with UV, the pressure-sensitive adhesive composition is cured to form a pressure-sensitive adhesive layer having a thickness of 230 μm. Formed. For UV irradiation, a black light (15 W / cm) was used, and an illumination intensity of 5 mW / cm ² (industrial UV checker having a peak sensitivity wavelength of about 350 nm (trade name “UVR-T1” manufactured by Topcon Corporation), light receiving unit type UD- Measured by T36), and the light quantity was 1500 mJ / cm ² . Thus, the double-sided adhesive sheet which consists of an adhesive layer was obtained. The first adhesive surface and the second adhesive surface of this adhesive sheet are protected by the two PET films (release liners), respectively. The gel fraction of the pressure-sensitive adhesive layer according to this example was about 70% by weight.

<Examples 2 to 6>
Same as Example 1 except that the amount of additional monomer used, the amount of acrylic oligomer used, the presence or absence of other additives (tackifier, black colorant) and the amount used were changed to the contents shown in Table 1. Thus, a pressure-sensitive adhesive composition according to each example was prepared. Using the pressure-sensitive adhesive composition, double-sided pressure-sensitive adhesive sheets according to Examples 2 to 6 including pressure-sensitive adhesive layers having thicknesses shown in Table 1 were produced in the same manner as Example 1.

<Example 7>
A monomer mixture consisting of 80 parts of 2EHA, 11.5 parts of 2-methoxyethyl acrylate (2MEA), 7 parts of NVP and 1.5 parts of N- (2-hydroxyethyl) acrylamide (HEAA) was used as a photopolymerization initiator. -Dimethoxy-1,2-diphenylethane-1-one (BASF, trade name “Irgacure 651”) 0.05 part and 1-hydroxycyclohexyl-phenyl-ketone (BASF, trade name “Irgacure 184”) 0.05 part was put into a four-necked flask and irradiated with UV in a nitrogen atmosphere and partially photopolymerized to obtain syrup B containing a partially polymerized product. The polymerization conversion of the monomer mixture in syrup B was about 10%.
A pressure-sensitive adhesive composition according to this example was prepared by adding 3 parts of AA as an additional monomer, 0.12 part of HDDA, and 5 parts of an acrylic oligomer to 100 parts of this syrup B and mixing them. The same type of acrylic oligomer as that used in Example 1 was used. A double-sided PSA sheet according to this example was prepared in the same manner as Example 1 except that this PSA composition was used.

  Table 1 shows the results of the above measurement evaluations for the pressure-sensitive adhesive sheets according to Examples 1 to 7. Table 1 also shows a schematic configuration of the pressure-sensitive adhesive sheet according to each example. In the table, “-” indicates no addition.

  As shown in Table 1, an example of using an acrylic polymer containing N-containing monomer units at a predetermined ratio or more as a polar group-containing monomer unit and using an acrylic oligomer as one component of the acrylic polymer The pressure-sensitive adhesive sheets of Examples 1 to 4 were able to improve the drop impact resistance while maintaining the repulsion resistance at a high level. On the other hand, in Examples 5 and 6, it was not possible to realize both the drop impact resistance and the repulsion resistance. One reason for this is that in these examples, acrylic oligomers were not used, and therefore, adhesive properties contributing to drop impact resistance and repulsion resistance could not be obtained. Further, in Example 7 in which the amount of the N-containing monomer used was small, a tendency for the repulsion resistance to decrease was observed. This suggests that a predetermined amount or more of N-containing monomer is necessary to maintain the repulsion resistance at a high level.

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

1, 2 Adhesive sheet 21 Adhesive layers 31, 32 Release liner

Claims (8)

Provided with an adhesive layer containing an acrylic polymer as a main component,
The acrylic polymer includes a polar group-containing monomer as a constituent monomer component,
The polar group-containing monomer is contained in a ratio of 15% by weight or more of all monomer components constituting the acrylic polymer,
The polar group-containing monomer contains a nitrogen atom-containing monomer in a proportion of 40% by weight or more,
The pressure-sensitive adhesive layer is a pressure-sensitive adhesive sheet formed using a pressure-sensitive adhesive composition containing an acrylic polymerization component and an acrylic oligomer.   The pressure-sensitive adhesive sheet according to claim 1, wherein the polar group-containing monomer further comprises at least one of a carboxy group-containing monomer and a hydroxyl group-containing monomer.   The pressure-sensitive adhesive sheet according to claim 2, wherein the polar group-containing monomer includes a carboxy group-containing monomer.   The pressure-sensitive adhesive sheet according to claim 3, wherein the acrylic polymer contains the carboxy group-containing monomer in a proportion of less than 5% by weight as a constituent monomer component.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the polar group-containing monomer includes a monomer having a nitrogen atom-containing ring as the nitrogen atom-containing monomer.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein the content of the acrylic oligomer is 5 parts by weight or less with respect to 100 parts by weight of the acrylic polymerization component. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, wherein the acrylic oligomer has a weight average molecular weight in the range of 0.1 x 10 ^{4 to} 3 x 10 ⁴ .   The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, which is used for a portable electronic device.

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