JP2017066243A - Adhesive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive composition excellent in wet heat resistance with hardly changing appearance even under wet heat condition, low dielectric constant with capable of suppressing transmission delay of electronic devices and further gas barrier property.SOLUTION: There is provided an adhesive composition containing (a) a (meth)acrylic acid alkyl ester monomer having an alkyl group having 10 to 24 carbon atoms, (b) a (meth)acrylic acid ester monomer having a substituent capable of forming a cyclic ether structure during polymerization and (c) an acryl polymer obtained by polymerizing a monomer containing an amide group-containing (meth)acrylic acid ester monomer, an isocyanate compound and a tackifier resin.SELECTED DRAWING: None

Description

  The present invention relates to a pressure-sensitive adhesive composition. More specifically, the present invention relates to a pressure-sensitive adhesive composition that is less likely to change even under wet heat conditions, has a low dielectric constant so that transmission delay of electronic devices can be suppressed, and has excellent gas barrier properties. .

  In recent years, in information equipment terminals such as smartphones, device miniaturization has progressed, and high-speed data transmission has been demanded. As part of this, the frequency of electrical signals is increasing, but if high frequency components increase in the electrical signals, the transmission path is likely to be delayed. In order to suppress the transmission delay, it is effective to lower the dielectric constant of the member. Therefore, the adhesive used is required to have a low dielectric constant. In order to reduce the dielectric constant of the pressure-sensitive adhesive, the proportion of the hydrophobic monomer may be increased as a constituent component of the polymer.

  On the other hand, in an electronic device, since an adhesive is also used for a visually recognizable part such as a display, transparency is strongly required. Further, it is required that appearance changes such as discoloration do not occur even under severe conditions such as high temperature and high humidity. As a method for improving the heat and moisture resistance, pressure-sensitive adhesives using various hydrophilic monomers are known. On the other hand, since the use of a hydrophobic monomer is effective for reducing the dielectric constant, it has been difficult to achieve both heat and moisture resistance and a low dielectric constant.

  In addition, if moisture is mixed into an electronic device, it may cause a failure or malfunction, so the member is also required to have a gas barrier property. If the proportion of the hydrophobic monomer is increased as a constituent component of the polymer, the gas barrier property can be improved. However, as described above, the heat and moisture resistance acts in a disadvantageous direction. Therefore, it has been difficult to satisfy these required performances with a high balance.

Patent Document 1 discloses a pressure-sensitive adhesive having a low dielectric constant, but has not been examined for heat-and-moisture resistance. Patent Document 2 discloses an adhesive with improved resistance to moisture and heat, but does not discuss the reduction of dielectric constant. Patent Document 3 discloses a pressure-sensitive adhesive having excellent transparency, but gas barrier properties and low dielectric constant have not been studied.
JP 2012-246477 JP 2011-195651 Japanese Unexamined Patent Publication No. 2015-3959

  An object of the present invention is to provide a pressure-sensitive adhesive composition excellent in moisture and heat resistance, the appearance of which hardly changes even under wet heat conditions, a low dielectric constant capable of suppressing transmission delay of an electronic device, and an excellent gas barrier property.

  The present invention includes (a) a (meth) acrylic acid alkyl ester monomer having an alkyl group having 10 to 24 carbon atoms, and (b) a (meth) acrylic acid ester having a substituent capable of forming a cyclic ether structure upon polymerization. A pressure-sensitive adhesive composition comprising an acrylic polymer obtained by polymerizing a monomer containing a monomer.

  Since the pressure-sensitive adhesive composition of the present invention is excellent in moisture and heat resistance, it can maintain transparency even when used in an electronic device and is excellent in appearance. In addition, since the device has a low dielectric constant, the device can be miniaturized and the transmission delay can be suppressed even if the data transmission speed is increased, and it is useful as an adhesive used in information equipment terminals such as smartphones. In addition, since the gas barrier property is excellent, failure or malfunction of the electronic device can be reduced.

  The pressure-sensitive adhesive composition of the present invention has (a) a (meth) acrylic acid alkyl ester monomer having an alkyl group having 10 to 24 carbon atoms, and (b) a substituent capable of forming a cyclic ether structure upon polymerization. Contains an acrylic polymer obtained by polymerizing monomers, including (meth) acrylic acid ester monomers.

(A) As a (meth) acrylic acid alkyl ester monomer having an alkyl group having 10 to 24 carbon atoms, a monomer having a linear alkyl group, a monomer having a branched alkyl group, and a cyclic alkyl group And the like.
Monomers having a linear alkyl group include undecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl ( Examples include meth) acrylate, stearyl (meth) acrylate, and behenyl (meth) acrylate.

  Monomers having a branched alkyl group include isodecyl (meth) acrylate, isomistyryl (meth) acrylate, isostearyl (meth) acrylate, propylheptyl (meth) acrylate, isoundecyl (meth) acrylate, isododecyl (meth) acrylate, isotridecyl (Meth) acrylate, isopentadecyl (meth) acrylate, isohexadecyl (meth) acrylate, isoheptadecyl (meth) acrylate, etc. are mentioned.

  Examples of the monomer having a cyclic alkyl group include isobornyl (meth) acrylate, terpene (meth) acrylate, and dicyclopentanyl (meth) acrylate.

  It is preferable to use 30 to 99% by weight of the (meth) acrylic monomer having a substituent having 10 to 24 carbon atoms based on the whole monomer constituting the acrylic polymer, and 40 to 99% by weight. More preferably, it is used. The dielectric constant and water vapor permeability of the pressure-sensitive adhesive obtained by using 30% by weight or more can be kept low, and when it is 99% by weight or less, there is no adverse effect on the heat and moisture resistance.

  (B) The (meth) acrylic acid ester monomer having a substituent capable of forming a cyclic ether structure at the time of polymerization is a single monomer capable of forming a cyclic ether structure by a (meth) acryloyl group and an intramolecular polymerizable unsaturated group at the time of polymerization. It is a mer. Since a 5-membered ring or a 6-membered ring can be formed stably, it preferably has a substituent capable of forming such a cyclic ether structure. Specific examples include 2- (allyloxymethyl) alkyl acrylate. Such monomer production methods are disclosed in JP 2010-168539 A, JP 2010-235546 A, JP 2010-254665 A, JP 2010-254685 A, and the like.

  By polymerizing an acrylic polymer using a (meth) acrylic acid ester monomer having a substituent capable of forming a cyclic ether structure at the time of polymerization, discoloration under wet heat conditions can be suppressed. It is preferable to use 0.1 to 5% by weight, and more preferably 0.5 to 4% by weight, based on the whole monomer constituting the acrylic polymer. By using 0.1 weight or more, the discoloration suppressing effect under wet heat conditions is remarkably exhibited, and by setting it to 5 weight% or less, it is possible to suppress an increase in the dielectric constant.

  An acrylic polymer is polymerized using a (meth) acrylate monomer having a substituent having a cyclic ether structure instead of a (meth) acrylate monomer having a substituent capable of forming a cyclic ether structure. In such a case, a sufficient discoloration suppressing effect under wet heat conditions cannot be obtained. The reason for this is not clear, but in the former, the cyclic ether structure is part of the main chain of the acrylic polymer, but in the latter, the cyclic ether structure is the side chain of the acrylic polymer. it is conceivable that.

  As a monomer constituting the acrylic polymer, it is preferable to further contain (c) an amide group-containing (meth) acrylic acid ester monomer. Specifically, (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-butyl (meth) acrylamide, diacetone acrylamide, N, N- Dimethylacrylamide, N, N-diethylacrylamide, N, N-dipropyl (meth) acrylamide, acryloylmorpholine, Nn-butoxymethyl (meth) acrylamide, N-isobutoxymethyl (meth) acrylamide, N-methoxymethyl ( And meth) acrylamide and N-vinylpyrrolidone.

  By polymerizing an acrylic polymer using an amide group-containing (meth) acrylic acid ester monomer, discoloration under wet heat conditions can be suppressed. It is preferable to use 0.1 to 10% by weight, and more preferable to use 1 to 10% by weight with respect to the whole monomer constituting the acrylic polymer. When it is used in an amount of 0.1% by weight or more, moisture and heat whitening resistance is exhibited, and when it is 10% by weight or less, an increase in dielectric constant and water vapor permeability can be suppressed.

As the monomer constituting the acrylic polymer, other known (meth) acrylic monomers and monomers copolymerizable with (meth) acrylic monomers can be used.
As a (meth) acrylic acid alkyl ester monomer having an alkyl group having 9 or less carbon atoms, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n -Butyl (meth) acrylate, sec-butyl (meth) acrylate, t-butyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, etc. are mentioned.

Examples of the hydroxyl group-containing (meth) acrylic monomer include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, and methacrylic acid. 3-hydroxypropyl, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 2-hydroxy-3-chloropropyl acrylate, 2-hydroxy-3-chloropropyl methacrylate, 2-hydroxy-3-phenoxy acrylate And propyl, 2-hydroxy-3-phenoxypropyl methacrylate and the like.
By using a hydroxyl group-containing (meth) acrylic monomer, when an isocyanate compound is added, a crosslinking reaction proceeds with the acrylic polymer, so that the cohesive force is increased and the adhesive force can be improved.

  Examples of (meth) acrylic acid alkoxyesters include 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 2-methoxypropyl methacrylate, 3-methoxypropyl methacrylate, 2-methoxybutyl methacrylate, 4-methoxy methacrylate. Examples include butyl.

  As (meth) acrylic acid alkylene glycol, ethylene glycol acrylate, polyethylene glycol acrylate, propylene glycol acrylate, polypropylene glycol acrylate, ethylene glycol methacrylate, polyethylene glycol methacrylate, propylene glycol methacrylate, polypropylene glycol methacrylate, etc. Is mentioned.

  Examples of the aryl (meth) acrylate include benzyl acrylate, phenoxyethyl acrylate, phenyl acrylate, benzyl methacrylate, phenoxyethyl methacrylate, and phenyl methacrylate.

  In addition, aromatic vinyl monomers such as styrene, α-methylstyrene, vinyl toluene, ethyl vinyl benzene, saturated fatty acid vinyl monomers such as vinyl acetate, vinyl propionate, vinyl versatate, ethylene, propylene, butadiene Olefinic monomers such as, carboxyl group-containing monomers such as acrylic acid, methacrylic acid and itaconic acid, and polyfunctional monomers such as divinylbenzene, ethylene glycol dimethacrylate and diallyl phthalate.

An acrylic polymer can be synthesized by heating the acrylic monomer together with a polymerization initiator in a solvent, for example. The weight average molecular weight of the acrylic polymer is preferably 700,000 or less. If it exceeds 700,000, the viscosity of the resin solution becomes high, and the coatability with a thick film may be lowered.
In addition, the weight average molecular weight in this invention means the value measured by GPC (gel permeation chromatography) and calculated by polystyrene conversion. The sample used was a filtrate obtained by dissolving the sample in tetrahydrofuran to make a 0.1 wt% solution, leaving it in an ultrasonic cleaning apparatus to which water was added for 10 minutes, and then filtering through a 0.20 μm membrane filter.
Analyzer: SHIMADZU, LC20AD
Column: GPC-80M x2 made by SHIMADZU
Column size: 8.0mmφ x 300mm each 600mm in total
Eluent: Tetrahydrofuran Flow rate: 1.0 ml / min
Inlet pressure: 10kgf
Detector: Differential refractometer (RI)
Column temperature: 40 ° C
Injection volume: 50 μl
Eluent: Tetrahydrofuran Detector: Differential refractometer Standard sample: Polystyrene

  Solvents used for acrylic polymer synthesis include methyl acetate, ethyl acetate, butyl acetate, benzene, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, n-hexane, isopropyl alcohol, n-butanol, propylene glycol monomethyl ether, propylene Examples include organic solvents such as glycol dimethyl ether, propylene glycol monomethyl ether acetate, and propylene carbonate. However, other solvents may be used, and two or more solvents may be used in combination.

Examples of the polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis (2,4-dimethyl). Valeronitrile), dimethyl-2,2′-azobis (2-methylpropionate), 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile) 2,2′-azobis [N- (2-propenyl) -2-methoxypropionamide], 1-[(1-cyano-1-methylethyl) azo] formamide, 2,2′-azobis (N-butyl) -2-methylpropionamide), 2,2′-azobis (N-cyclohexyl-2-methylpropionamide), [1,1′-azobis (1-acetoxy-1-phenylethane)], and the like Zo compounds, lauroyl peroxide, octanoyl peroxide, benzoyl peroxide, ethyl methyl ketone peroxide, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, cumyl peroxyneodecanoate, t- Hexylperoxyneodecanoate, t-butylperoxy-2-ethylhexanoate, dicumyl peroxide, isobutyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, t-butylperoxy Benzoate, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, di (2-ethylhexyl) peroxydicarbonate, 1,1-bis (t-butylperoxy) -3,3 5-trimethylcyclohexa , It can be used 3,3,5 organic peroxide compounds such as trimethyl cyclohexanoyl peroxide and the like.
In addition, the peroxide compound can be subjected to redox polymerization by using a reducing agent such as N, N-dimethyltoluidine, N, N-diethyltoluidine or the like in combination.
The polymerization initiator is usually used in an amount of 0.05 to 3 parts by weight based on 100 parts by weight of the acrylic monomer. Increasing the amount of polymerization initiator used tends to decrease the molecular weight of the polymer obtained, and decreasing the amount of polymerization initiator used tends to increase the molecular weight of the polymer obtained.

The pressure-sensitive adhesive composition of the present invention preferably has a relative dielectric constant of 3.5 or less at a frequency of 1 MHz. As a method for measuring the relative dielectric constant, a pressure-sensitive adhesive layer (a film obtained by peeling a PET film subjected to silicone treatment from a pressure-sensitive adhesive sheet) is laminated to form a laminated pressure-sensitive adhesive layer of about 200 μm. The relative dielectric constant was measured by the following apparatus. In the measurement, the average of the measured values of the three samples was taken as the dielectric constant.
Measurement method: LCR meter (Device: Wayne Kerr 6440B using impedance analyzer)
Frequency: 1MHz
Bias voltage: 2V
Measurement environment: 23 ± 1 ℃, 50 ± 1% RH

Gas barrier property can be improved by mix | blending a tackifier with the adhesive composition of this invention. Usually, when a tackifier is blended, discoloration easily occurs under wet heat conditions. In the present invention, (b) (meth) acrylic acid ester having a substituent capable of forming a cyclic ether structure during polymerization (b) By including a body, discoloration can be suppressed.
Specific examples of tackifiers include gum rosin, tall rosin, wood rosin, disproportionated rosin, polymerized rosin, glycerin ester and pentaerythritol ester of these rosins, rosin resins such as hydrogenated products thereof, terpene resins, hydrocarbon-modified terpenes Resins, terpene resins such as these hydrogenated products, terpene phenol resins, terpene phenol resins such as hydrogenated terpene phenol resins, aliphatic petroleum resins, alicyclic petroleum resins, aromatic petroleum resins, Copolymer petroleum resin, dicyclopentadiene petroleum resin, pure monomer petroleum resin, petroleum resins such as these hydrogenated products, styrene resin, coumarone indene resin, alkylphenol resin, xylene resin, dammar, Examples include copal and shellac.

  The blending amount of the tackifier is preferably 2 to 25 parts by weight and more preferably 5 to 20 parts by weight with respect to 100 parts by weight of the acrylic polymer. The gas barrier property is remarkably improved by using 2 parts by weight or more, and the compatibility with the acrylic polymer is maintained by using 25 parts by weight or less.

By adding an isocyanate compound to the pressure-sensitive adhesive composition of the present invention, the cohesive force is increased by the progress of a crosslinking reaction with the hydroxyl group of the acrylic polymer, and the pressure-sensitive adhesive force can be improved. Isocyanate compounds include aromatic isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, and p-phenylene diisocyanate, and aliphatic isocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, nobornene diisocyanate, and dicyclohexylmethane diisocyanate. And hydrogenated products of the above aromatic diisocyanates such as isophorone diisocyanate and hydrogenated xylene diisocyanate. Also, reaction products of polyfunctionalized polyisocyanate structures such as adduct type, isocyanurate type, biuret type, polymethylene polyphenyl polyisocyanate, polyester polyisocyanate, polyether polyisocyanate, trimethylolpropane modified polyisocyanate, etc. It may be a thing.
As a compounding quantity of an isocyanate compound, 0.01-0.5 weight part is preferable with respect to 100 weight part of said acrylic polymers.

  In addition, a metal complex compound may be added. Examples of the metal complex compound include compounds in which acetylacetone, ethyl acetoacetate, and the like are coordinated to a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium. Specific examples include nursem aluminum (trade name, manufactured by Nippon Kagaku Sangyo Co., Ltd.) in which acetylseton is coordinated to aluminum.

  The pressure-sensitive adhesive composition of the present invention includes various additives such as ultraviolet absorbers, near-infrared absorbers, antioxidants, antiseptics, antifungal agents, plasticizers, antifoaming agents, and wettability adjusting agents. May be.

  The pressure-sensitive adhesive composition of the present invention can be used for various applications, and is particularly useful as an optical pressure-sensitive adhesive for liquid crystal panels, organic EL panels, touch panels, electronic paper, solar cells, and these members.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and demonstrated in detail about this invention, a specific example is shown and it does not specifically limit to these.

Synthelizable flask equipped with acrylic polymer synthesis stirrer and reflux condenser. As monomers, 30 parts by weight of 2-ethylhexyl acrylate (2EHA), 30 parts by weight of n-decyl methacrylate (DMA), and isostearyl acrylate (ISTA) 15 Parts by weight, acrylamide (AAm) 3 parts by weight, methyl acrylate (MA) 20 parts by weight and 2-hydroxyethyl acrylate (2HEA) 1 part by weight, 2- (allyloxymethyl) methyl acrylate (MeAMA, manufactured by Nippon Shokubai Co., Ltd.) Name) 1 part by weight, 0.30 part of azobisisobutyronitrile as a polymerization initiator, 90 parts of ethyl acetate as a solvent were added, and nitrogen gas was introduced for 30 minutes or more to remove oxygen in the polymerization system. The temperature was raised to 65 ° C. at a rate of 1 ° C./1 min, and the mixture was stirred for 12 hours while maintaining the temperature at 65 ± 1 ° C. After completion of the reaction, the reaction solution was diluted with ethyl acetate to obtain an acrylic polymer solution AP1 which was a pale yellow transparent viscous liquid. The viscosity was 4000 mPa · s, the solid content was 50%, and the weight average molecular weight was 330,000.

  In addition to the materials used in the synthesis of AP1, as monomers, lauryl methacrylate (LMA), lauryl acrylate (LA), dimethylacrylamide (DMAA), NVP (N-vinylpyrrolidone), methyl methacrylate (MMA), t-butyl acrylate (TBMA), 4-hydroxybutyl acrylate (4HBA), tetrahydrofurfuryl methacrylate (THFMA), cyclohexyl methacrylate (CHMA), dicyclopentanyl acrylate (DCPA), etc. Were prepared in the same manner as AP1, and acrylic polymer solutions AP2 to AP9 having a solid content of 50% were prepared.

Example 1
To 100 parts by weight of the solid content of the acrylic polymer solution AP1, 10 parts by weight of YS Polystar TH130 (manufactured by Yashara Chemical, trade name) as a tackifier, and Coronate HX (manufactured by Nippon Polyurethane Industry Co., Ltd.), which is a polyfunctional isocyanate compound as a crosslinking agent, Product name) 0.1 part by weight was added to prepare an adhesive composition of Example 1.

Examples 2-4, Comparative Examples 1-5
A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 with the formulation shown in Table 1. For 100 parts by weight of the solid content of each acrylic polymer solution, YS Polystar TH130 and YS Polystar TO125 (trade name, manufactured by Yasuhara Chemical) as tackifiers, Coronate HX as a cross-linking agent and Coronate L (Nippon Polyurethane Industry) which is a polyfunctional isocyanate compound. (Trade name, product name) was added according to the formulation shown in Table 1.

  The pressure sensitive adhesive compositions of Examples and Comparative Examples were evaluated by the following methods.

Preparation of pressure-sensitive adhesive sheet Each pressure-sensitive adhesive composition was applied on a release film (silicone-treated PET film) so that the thickness after drying was 100 μm, dried at 90 ° C. for 20 minutes, and then another It was bonded to a release film and further aged at 23 ° C. for 7 days to prepare a substrate-less pressure-sensitive adhesive sheet.

Peel strength Each pressure-sensitive adhesive sheet was bonded to a PET film (trade name A4100, manufactured by Toyobo Co., Ltd., thickness 50 μm) to form a film piece having a width of 25 mm and a length of 100 mm. The release film of the film piece is peeled off, and pasted on glass at 23 ° C. and 50% RH atmosphere using a laminator, and left in an atmosphere of 23 ° C. and relative humidity 50% RH for 1 day, then for testing The pressure-sensitive adhesive tape was pulled in a 180 ° direction at a pulling speed of 300 mm / min, and the center value was defined as a 180 ° peel adhesive strength. If the peel adhesive strength is 10 N / 25 mm or more, it does not peel off during use and has a sufficient adhesive force.

The moisture permeability was measured according to JIS Z0208 cup method. The 100 μm-thick coating film prepared as described above is placed in a test cup that weighs 5 g of calcium chloride, and the periphery is sealed with wax. The weight of the sealed specimen is weighed and allowed to stand for 24 hours in an environment of 40 ° C. and 90% RH. Then, the weight of the specimen is weighed again, and the water vapor transmission rate is calculated from the weight increase. An adhesive having a water vapor transmission rate of 200 g / m ² · 24 hr or less is used as a gas barrier adhesive.

The wet and heat resistant adhesive sheets were bonded to a PET film (trade name A4100, manufactured by Toyobo Co., Ltd., thickness 50 μm) to prepare a film piece having a width of 25 mm and a length of 100 mm. The release film of the film piece was peeled off and stuck on glass at 23 ° C. and 50% RH atmosphere using a laminator. This was allowed to stand for 500 hours in an environment of 60 ° C. and 95% RH, and after cooling at 23 ° C. and 50% RH for 1 hour, measurement of haze and the presence or absence of yellowing were confirmed. In addition, haze was measured using Toyo Seiki Seisakusho Co., Ltd. HAZE-GARDII. The evaluation criteria are as follows.
◯: Haze is less than 1.5 (almost no whitening is confirmed and moisture and heat whitening resistance is good)
X: Haze is 1.5 or more (cannot be used due to poor whitening property)
○: No yellowing ×: Yellowing

  As shown in Table 2, each of the pressure-sensitive adhesive compositions of Examples had a low relative dielectric constant and water vapor permeability, and was good without whitening and yellowing even under wet heat conditions. On the other hand, none of the pressure-sensitive adhesive sheets using the respective pressure-sensitive adhesive compositions of Comparative Examples satisfied all the performances.

Claims (8)

  (A) (meth) acrylic acid alkyl ester monomer having an alkyl group having 10 to 24 carbon atoms, (b) (meth) acrylic acid ester monomer having a substituent capable of forming a cyclic ether structure upon polymerization A pressure-sensitive adhesive composition comprising an acrylic polymer obtained by polymerizing a monomer containing.   The pressure-sensitive adhesive composition according to claim 1, further comprising (c) an amide group-containing (meth) acrylic acid ester monomer as a monomer constituting the acrylic polymer.   3. The (b) monomer (meth) acrylate ester having a substituent capable of forming a cyclic ether structure during polymerization is methyl 2- (allyloxymethyl) acrylate. Adhesive composition.   In the monomer constituting the acrylic polymer, (a) the proportion of the (meth) acrylic acid alkyl ester monomer having an alkyl group having 10 to 24 carbon atoms is 30 to 90% by weight, (b) 2- The proportion of (meth) acrylic acid ester monomer having allyloxymethyl is 0.1 to 5% by weight, and the proportion of (c) amide group-containing (meth) acrylic acid ester monomer is 0.1 to 10% by weight. The pressure-sensitive adhesive composition according to claim 2 or 3, wherein   Furthermore, an isocyanate compound is contained, The adhesive composition in any one of Claims 1-4 characterized by the above-mentioned.   The pressure-sensitive adhesive composition according to claim 1, further comprising a tackifier.   The pressure-sensitive adhesive composition according to any one of claims 1 to 6, comprising 2 to 25 parts by weight of the tackifier with respect to 100 parts by weight of the acrylic polymer.   The pressure-sensitive adhesive composition according to claim 1, wherein the dry film has a relative dielectric constant of 3.5 or less at a frequency of 1 MHz.