JP7698971B2 - Double-sided adhesive tape - Google Patents

Description

The present invention relates to a double-sided adhesive tape.

Devices with displays have the problem that if they are dropped or subjected to impact, the display screen can crack.

In order to absorb such shocks, the use of double-sided adhesive tape with excellent shock absorption properties has been proposed (for example, Patent Document 1).

However, conventional shock-absorbing adhesive tapes have the problem that their shock-absorbing properties decrease over a wide temperature range, especially in the low temperature range.

JP 2014-94575 A

The objective of the present invention is to provide a double-sided adhesive tape that has excellent shock absorption properties over a wide temperature range, particularly in the low temperature range.

The double-sided adhesive tape of the present invention is
A double-sided pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer on both sides of a base layer,
The double-sided pressure-sensitive adhesive tape as a whole has a storage modulus E' of 1.0 x 10 ⁵ Pa to 1.0 x 10 ⁸ Pa measured at -25°C to 120°C and a frequency of 1 Hz.

In one embodiment, the base layer has a storage modulus E' of 1.0 x 10 ⁵ Pa to 1.0 x 10 ⁸ Pa measured at -25°C to 120°C and a frequency of 1 Hz.

In one embodiment, the pressure-sensitive adhesive layer has a maximum storage modulus G' of 1.0 x 10 ¹⁰ Pa or less, measured at -25°C to 120°C and a frequency of 1 Hz.

In one embodiment, the adhesive layer has an adhesive strength of 5 N/20 mm or more to a SUS plate at 23°C, 50% RH, a tensile speed of 300 mm/min, and a 180-degree peel.

In one embodiment, the substrate layer contains at least one polar functional group-containing polymer selected from condensation polymers and polyaddition polymers.

In one embodiment, the polar functional group-containing polymer is at least one selected from polyamide, polyurethane, and polyurea.

In one embodiment, the polar functional group-containing polymer has at least one bond selected from an ether bond and an ester bond.

In one embodiment, the adhesive layer includes at least one adhesive selected from an acrylic adhesive, a rubber adhesive, a silicone adhesive, and a urethane adhesive.

In one embodiment, the adhesive tape of the present invention is an impact absorbing tape for displays.

The present invention provides a double-sided adhesive tape that has excellent shock absorption properties over a wide temperature range, particularly in the low temperature range.

FIG. 1 is a schematic cross-sectional view showing one embodiment of the double-sided pressure-sensitive adhesive tape of the present invention.

<<Double-sided adhesive tape>>
The double-sided adhesive tape according to the embodiment of the present invention is an adhesive tape having adhesive layers on both sides of a base layer, that is, the double-sided adhesive tape 1000 according to the embodiment of the present invention is a double-sided adhesive tape having adhesive layers 200a, 200b on both sides of a base layer 100, as shown in FIG.

The adhesive layer 200a and the adhesive layer 200b may be adhesive layers of the same composition or adhesive layers of different compositions.

The adhesive layer 200a and the adhesive layer 200b may have the same thickness or different thicknesses.

The substrate layer may be one layer or two or more layers. The substrate layer is preferably one layer, since this allows the effects of the present invention to be more effectively exhibited.

The adhesive layer may be one layer or two or more layers. The adhesive layer is preferably one layer, since this allows the effects of the present invention to be more effectively exhibited.

The double-sided adhesive tape according to the embodiment of the present invention may have any suitable layers other than the substrate layer and the adhesive layer, as long as the effects of the present invention are not impaired.

The double-sided adhesive tape according to the embodiment of the present invention may be provided with any suitable release liner on the surface of the adhesive layer opposite the substrate layer for protection until use, etc.

Examples of release liners include release liners in which the surface of a substrate (liner substrate) such as paper or plastic film is silicone-treated, and release liners in which the surface of a substrate (liner substrate) such as paper or plastic film is laminated with a polyolefin resin. Examples of plastic films as liner substrates include polyethylene films, polypropylene films, polybutene films, polybutadiene films, polymethylpentene films, polyvinyl chloride films, vinyl chloride copolymer films, polyethylene terephthalate films, polybutylene terephthalate films, polyurethane films, and ethylene-vinyl acetate copolymer films.

The thickness of the release liner is preferably 1 μm to 500 μm, more preferably 3 μm to 450 μm, even more preferably 5 μm to 400 μm, and particularly preferably 10 μm to 300 μm.

It is preferable that the release liner has at least one surface subjected to a release treatment. Any suitable release treatment may be used as long as it does not impair the effects of the present invention.

The double-sided adhesive tape according to the embodiment of the present invention has a total thickness d of preferably 1 μm to 500 μm, more preferably 5 μm to 450 μm, even more preferably 10 μm to 400 μm, particularly preferably 15 μm to 350 μm, and most preferably 30 μm to 300 μm. If the total thickness d of the double-sided adhesive tape according to the embodiment of the present invention is within the above range, the effects of the present invention can be more effectively achieved.

In the double-sided pressure-sensitive adhesive tape according to the embodiment of the present invention, the storage modulus E' of ^{the entire double-sided pressure-sensitive adhesive tape, measured at -25°C to 120°C and a frequency of 1 Hz, is within the range of 1.0 x 10 5 Pa} to 1.0 x 10 ⁸ Pa. The storage modulus E' is preferably within the range of 3.0 x 10 5 Pa to 1.0 x 10 8 Pa, more preferably within the range of ⁵ x 10 ⁵ Pa to 1.0 x 10 ⁸ Pa, even more preferably within the range of 8.0 x 10 ⁵ Pa to 9.9 x 10 ⁷ Pa, and particularly preferably within the range of 1.0 x 10 ⁶ Pa to 9.85 x 10 ⁷ Pa. If the storage modulus E' of the entire double-sided pressure-sensitive adhesive tape is within the above range, it is possible to provide a double-sided pressure-sensitive adhesive tape that has excellent impact absorption properties over a wide temperature range, particularly in the low temperature region.

In the double-sided pressure-sensitive adhesive tape according to the embodiment of the present invention, the storage modulus E' of the entire double-sided pressure-sensitive adhesive tape measured at -25°C and a frequency of 1 Hz is preferably 1.0 x 10 ⁸ Pa or less, more preferably 9.9 x 10 ⁷ Pa or less, even more preferably 9.75 x 10 ⁷ Pa or less, and particularly preferably 9.6 x 10 ⁷ Pa or less. The lower limit of the storage modulus E' measured at -25°C and a frequency of 1 Hz is preferably 5.0 x 10 ⁶ Pa or more. If the storage modulus E' of the entire double-sided pressure-sensitive adhesive tape measured at -25°C and a frequency of 1 Hz is within the above range, a double-sided pressure-sensitive adhesive tape having excellent impact absorption properties can be provided over a wide temperature range, particularly in the low temperature region.

In the double-sided pressure-sensitive adhesive tape according to the embodiment of the present invention, the storage modulus E' of the entire double-sided pressure-sensitive adhesive tape measured at 23° C. and a frequency of 1 Hz is preferably 1.0×10 ⁸ Pa or less, more preferably 3.0×10 ⁶ Pa or less, even more preferably 2.5×10 ⁶ Pa or less, and particularly preferably 2.3×10 ⁶ Pa or less. The lower limit of the storage modulus E' measured at 23° C. and a frequency of 1 Hz is preferably 5.0×10 ⁵ Pa or more. If the storage modulus E' of the entire double-sided pressure-sensitive adhesive tape measured at 23° C. and a frequency of 1 Hz is within the above range, a double-sided pressure-sensitive adhesive tape having excellent impact absorption properties can be provided over a wide temperature range, particularly in the low temperature region.

In the double-sided pressure-sensitive adhesive tape according to the embodiment of the present invention, the storage modulus E' of the entire double-sided pressure-sensitive adhesive tape measured at 80° C. and a frequency of 1 Hz is preferably 1.0×10 ⁸ Pa or less, more preferably 3.0×10 ⁶ Pa or less, and even more preferably 2.9×10 ⁶ Pa or less. The lower limit of the storage modulus E' measured at 80° C. and a frequency of 1 Hz is preferably 5.0×10 ⁵ Pa or more. If the storage modulus E' of the entire double-sided pressure-sensitive adhesive tape measured at 80° C. and a frequency of 1 Hz is within the above range, a double-sided pressure-sensitive adhesive tape having excellent impact absorption properties can be provided over a wide temperature range, particularly in the low temperature region.

In the double-sided adhesive tape according to the embodiment of the present invention, the ratio of the storage modulus E' measured at a frequency of 1 Hz at -25°C to the storage modulus E' measured at a frequency of 1 Hz at 0°C (storage modulus E'(-25°C)/storage modulus E'(80°C)) of the entire double-sided adhesive tape is preferably 40.0 or less, more preferably 35.0 or less, even more preferably 30.0 or less, and particularly preferably 18.0 or less. The lower limit of the above ratio (storage modulus E'(-25°C)/storage modulus E'(80°C)) is preferably 1.0 or more. If the ratio of the storage modulus E' measured at a frequency of 1 Hz at -25°C to the storage modulus E' measured at a frequency of 1 Hz at 0°C (storage modulus E'(-25°C)/storage modulus E'(80°C)) of the entire double-sided adhesive tape is within the above range, a double-sided adhesive tape having excellent impact absorption properties can be provided over a wide temperature range, particularly in the low temperature range.

In the double-sided pressure-sensitive adhesive tape according to the embodiment of the present invention, the storage modulus E' of the base material layer measured at -25°C to 120°C and a frequency of 1 Hz is preferably within the range of 1.0 x ¹⁰⁵ Pa to 1.0 x ¹⁰⁸ Pa, more preferably within the range of 3.0 x ¹⁰⁵ Pa to 8.0 x ¹⁰⁷ Pa, even more preferably within the range of 5.0 x ¹⁰⁵ Pa to 5.0 x ¹⁰⁷ Pa, and particularly preferably within the range of 1.0 x ¹⁰⁶ Pa to 2.0 x ¹⁰⁷ Pa. When the storage modulus E' of the base material layer is within the above range, it is possible to provide a double-sided pressure-sensitive adhesive tape having excellent impact absorption properties over a wide temperature range, particularly in the low temperature region.

In the double-sided pressure-sensitive adhesive tape according to the embodiment of the present invention, the pressure-sensitive adhesive layer has a maximum storage modulus G' measured at -25°C to 120°C and a frequency of 1 Hz of preferably 1.0 x ¹⁰¹⁰ Pa or less, more preferably in the range of 1.0 x ¹⁰² Pa to 5.0 x ¹⁰⁹ Pa, even more preferably in the range of 5.0 x ¹⁰² Pa to 1.0 x ¹⁰⁹ Pa, and particularly preferably in the range of 1.0 x ¹⁰³ Pa to 7.0 x ¹⁰⁸ Pa. When the maximum storage modulus G' of the pressure-sensitive adhesive layer is within the above range, a double-sided pressure-sensitive adhesive tape having excellent impact absorption properties can be provided over a wide temperature range, particularly in the low temperature region.

In the double-sided adhesive tape according to the embodiment of the present invention, the adhesive layer has an adhesive strength to a SUS plate at 23°C, 50% RH, a tensile speed of 300 mm/min, and a peel angle of 180 degrees, of preferably 5 N/20 mm or more, more preferably 5 N/20 mm to 100 N/20 mm, even more preferably 5 N/20 mm to 50 N/20 mm, particularly preferably 5 N/20 mm to 30 N/20 mm, and most preferably 5 N/20 mm to 20 N/20 mm. If the adhesive layer has an adhesive strength to a SUS plate at 23°C, 50% RH, a tensile speed of 300 mm/min, and a peel angle of 180 degrees, within the above range, a double-sided adhesive tape with excellent impact absorption properties can be provided over a wide temperature range, particularly in the low temperature range.

≪Base material layer≫
The thickness of the substrate layer is preferably 1 μm to 500 μm, more preferably 2 μm to 400 μm, further preferably 3 μm to 300 μm, and particularly preferably 5 μm to 200 μm. When the thickness of the substrate layer is within the above range, it is possible to provide a double-sided pressure-sensitive adhesive tape having excellent impact absorption properties over a wide temperature range, particularly in the low temperature region.

As the material for the substrate layer, any appropriate material may be used as long as it does not impair the effects of the present invention. Such a material preferably includes at least one polar functional group-containing polymer selected from condensation polymers and polyaddition polymers. That is, the substrate layer preferably includes at least one polar functional group-containing polymer selected from condensation polymers and polyaddition polymers.

The content of at least one polar functional group-containing polymer selected from condensation polymers and polyaddition polymers in the base layer is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, even more preferably 90% by weight to 100% by weight, particularly preferably 95% by weight to 100% by weight, and most preferably 98% by weight to 100% by weight, in order to further exert the effects of the present invention.

At least one polar functional group-containing polymer selected from condensation polymers and polyaddition polymers has a polar functional group such as a carbonyl group in the polymer main chain, and can have a network structure that is not based on covalent bonds due to the action of stronger intermolecular forces than radical polymerization polymers. A polymer that has a large number of network structures based on covalent bonds can have too high elasticity and poor conformability. In condensation polymers and polyaddition polymers that have a network structure that is not based on covalent bonds, the intermolecular forces due to polar functional groups are weaker than the intermolecular forces generated by covalent bonds, and stress is easily relieved by deformation, etc. even with smaller energy (energy such as work done by stress, etc.), and after the relaxation, intermolecular forces again act between the polar functional groups (for example, the combination of polar functional groups that generates intermolecular forces changes), making it possible to provide a double-sided adhesive tape with excellent impact absorption over a wide temperature range, especially in the low temperature range.

The polar functional group-containing polymer is preferably at least one selected from polyamide, polyurethane, and polyurea. It is believed that the intermolecular force of a polymer containing a hydrogen-bonding polar functional group (more precisely, a hydrogen-bonding polar functional group having hydrogen donor properties) such as polyamide, polyurethane, and polyurea can be broken with approximately 1/10 the energy of a covalent bond (the combination of hydrogen-bonding functional groups that generates the intermolecular force changes), and the intermolecular force can be effectively broken by the energy generated by the work done by thermal energy applied at about room temperature or stress generated by bending, etc. For this reason, it is possible to provide a double-sided pressure-sensitive adhesive tape with excellent shock absorption properties over a wide temperature range, especially in the low temperature range.

More preferably, the base layer contains a polar functional group-containing polymer that is a polyaddition polymer. In polyaddition polymers, monomers having various functional groups can be used, and the operation of converting the monomer into a polymer is easy. By utilizing these characteristics, it is possible to impart various properties to the polyaddition polymer.

The polar functional group-containing polymer, which is a polyaddition polymer, may have at least one bond selected from an ether bond and an ester bond. The ether bond can be introduced by employing a monomer having an ether bond when obtaining the polyaddition polymer. The ester bond can be introduced by employing a monomer having an ester bond when obtaining the polyaddition polymer. For example, when polyurethane is employed as the polar functional group-containing polymer, examples of the polyurethane having an ether bond include ether-based polyurethanes. Examples of the polyurethane having an ester bond include ester-based polyurethanes.

An example of an ether-based polyurethane is a urethane acrylate resin. For example, a precursor containing a polyether segment, a (meth)acrylic segment, and a urethane segment is polymerized under conditions in which the molecular weight can be controlled to produce an oligomer, and then various additives are added to the oligomer to produce a coating composition for forming a resin film. This coating composition is then applied to a supporting substrate and crosslinked to produce a urethane acrylate resin film on the supporting substrate. More specifically, a polyether polyol, a compound containing an isocyanate group, and a hydroxyalkyl (meth)acrylate, or an acrylic-modified polyether polyol and a compound containing an isocyanate group, etc. are polymerized in advance to produce a urethane acrylate oligomer, and additives are added to the oligomer to produce a coating composition for forming a resin film. This coating composition is then applied to a supporting substrate and crosslinked to produce a urethane acrylate resin film on the supporting substrate.

Examples of polyether polyols include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, as well as various derivatives thereof.

Examples of hydroxyalkyl (meth)acrylates include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate.

Examples of compounds containing an isocyanate group include resins containing an isocyanate group, oligomers containing an isocyanate group, and monomers containing an isocyanate group. Examples of compounds containing an isocyanate group include (poly)isocyanates such as methylene bis-4-cyclohexyl isocyanate, trimethylolpropane adduct of tolylene diisocyanate, trimethylolpropane adduct of hexamethylene diisocyanate, trimethylolpropane adduct of isophorone diisocyanate, isocyanurate of tolylene diisocyanate, isocyanurate of hexamethylene diisocyanate, and biuret of hexamethylene isocyanate, as well as block products of these isocyanates.

Examples of ester-based polyurethanes include adipate-based (ester-based) polyurethanes and polycaprolactone-based (ester-based) polyurethanes.

When a monomer having an ether bond is used to obtain a polyaddition polymer, the elasticity of the polyaddition polymer can be weakened and molecular flexibility can be imparted. When a monomer having an ester bond is used to obtain a polyaddition polymer, rigidity can be imparted to the polyaddition polymer. Therefore, for example, by appropriately combining a monomer having an ether bond with a monomer having an ester bond to obtain a polyaddition polymer, or by using them alone, the elasticity and rigidity of the polyaddition polymer can be adjusted, and a double-sided adhesive tape with excellent impact absorption properties can be provided over a wide temperature range, particularly in the low temperature range.

When a polyurethane (preferably an ether-based polyurethane or an ester-based polyurethane) is used as the polar functional group-containing polymer, a hydroxyl group-containing monomer may be used when obtaining the polyurethane. When a hydroxyl group-containing monomer is used when obtaining the polyurethane, the isocyanate monomer used in the polyaddition reaction when obtaining the polyurethane reacts with the hydroxyl group-containing monomer to introduce a covalent network structure. In addition, the hydroxyl group-containing monomer can be added all at once as a polyurethane raw material, which can simplify the work of adding the polyurethane raw material after preparation.

As the polar functional group-containing polymer, polyurethane (preferably ether-based polyurethane or ester-based polyurethane) is preferred in that it can further exert the effects of the present invention. Polyurethane is a polymer compound synthesized by polyaddition reaction of polyol (e.g., diol) and polyisocyanate (e.g., diisocyanate) in a predetermined ratio.

Polyurethanes (preferably ether-based polyurethanes, ester-based polyurethanes) include thermoplastic polyurethanes (TPUs) and thermosetting polyurethanes, with thermosetting polyurethanes being preferred in that they can provide double-sided adhesive tapes with superior shock absorption over a wide temperature range, particularly in the low temperature range. In that they can better demonstrate the effects of the present invention, the thermosetting polyurethane is preferably at least one selected from the group consisting of thermosetting ether-based polyurethanes and thermosetting ester-based polyurethanes, and more preferably at least one selected from thermosetting urethane acrylate resins and thermosetting polycaprolactone-based (ester-based) polyurethane resins.

Examples of polyols that can be used in the synthesis of polyurethane include diols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, polyoxytetramethylene glycol, diethylene glycol, polyethylene glycol, and polypropylene glycol; polyester polyols which are polycondensates of the above diols and dicarboxylic acids (e.g., adipic acid, azelaic acid, and sebacic acid); and carbonate diols such as polyalkylene carbonate diols. These may be used alone or in combination of two or more kinds.

Polyisocyanates that can be used in the synthesis of polyurethanes include aromatic, aliphatic, and alicyclic diisocyanates, as well as polymers of these diisocyanates (e.g., dimers, trimers, etc.). Examples of the diisocyanate include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, butane-1,4-diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, 1,3-bis(isocyanatemethyl)cyclohexane, methylcyclohexane diisocyanate, and m-tetramethylxylylene diisocyanate. These may be one type or two or more types.

In addition to the polyol and polyisocyanate, other copolymerization components may be introduced into the polyurethane. Examples of the other copolymerization components include monocarboxylic acids, dicarboxylic acids, trifunctional or higher polycarboxylic acids, hydroxycarboxylic acids, alkoxycarboxylic acids, and derivatives thereof. The other copolymerization components may be one type only, or two or more types. The content of the other copolymerization components in the polyurethane is preferably less than 30% by weight, more preferably less than 10% by weight, and even more preferably less than 5% by weight.

<Adhesive layer>
The thickness of the pressure-sensitive adhesive layer is preferably 1 μm to 500 μm, more preferably 3 μm to 300 μm, even more preferably 5 μm to 200 μm, and particularly preferably 10 μm to 120 μm. If the thickness of the pressure-sensitive adhesive layer is within the above range, it is possible to provide a double-sided pressure-sensitive adhesive tape that has excellent impact absorption properties over a wide temperature range, particularly in the low temperature region.

The adhesive layer contains a base polymer. The base polymer may be of only one type, or may be of two or more types. The content of the base polymer in the adhesive layer is preferably 30% by weight to 95% by weight, more preferably 40% by weight to 90% by weight, and even more preferably 50% by weight to 80% by weight, in order to further exert the effects of the present invention.

The base polymer is preferably at least one selected from an acrylic polymer, a rubber polymer, a silicone polymer, and a urethane polymer, in terms of being able to more effectively exert the effects of the present invention. That is, the adhesive layer preferably contains at least one selected from an acrylic adhesive containing an acrylic polymer, a rubber adhesive containing a rubber polymer, a silicone adhesive containing a silicone polymer, and a urethane adhesive containing a urethane polymer. In the following, an acrylic adhesive will be described in detail as a representative example.

<Acrylic adhesive>
The acrylic adhesive contains an acrylic polymer as a base polymer. The acrylic adhesive may contain a tackifier resin. The acrylic adhesive may contain a crosslinking agent.

When the acrylic adhesive contains an acrylic polymer, a tackifier resin, and a crosslinking agent, the content ratio of the total amount of the acrylic polymer, the tackifier resin, and the crosslinking agent to the total amount of the acrylic adhesive is preferably 95% by weight or more, more preferably 97% by weight or more, and even more preferably 99% by weight or more, in order to further exert the effects of the present invention.

(Acrylic polymer)
The acrylic polymer is preferably a polymer of monomer components that contain an alkyl (meth)acrylate as a main monomer and may further contain a sub-monomer copolymerizable with the main monomer, where the main monomer is a component that accounts for more than 50% by weight of the total monomer components.

As the alkyl(meth)acrylate, for example, a compound represented by the following formula (1) can be suitably used.
CH ₂ =C(R ¹ )COOR ² (1)

Here, in the above formula (1), R ¹ is a hydrogen atom or a methyl group, and R ² is a chain alkyl group having 1 to 20 carbon atoms (hereinafter, such a range of carbon atoms may be referred to as "C1-20"). From the viewpoint of the storage elastic modulus of the pressure-sensitive adhesive layer, etc., R ² is preferably a chain alkyl group having C1-14, more preferably a chain alkyl group having C2-10, and even more preferably a chain alkyl group having C4-8. Here, chain includes linear and branched chains.

Examples of alkyl(meth)acrylates in which R ² is a C1-20 chain alkyl group include methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, s-butyl(meth)acrylate, pentyl(meth)acrylate, isopentyl(meth)acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, isooctyl(meth)acrylate, and isooctyl(meth)acrylate. Examples of the alkyl (meth)acrylate include acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. These alkyl (meth)acrylates may be used alone or in combination of two or more kinds.

As alkyl (meth)acrylates, n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) are preferred, as they can better demonstrate the effects of the present invention.

The content of alkyl (meth)acrylate in the total monomer components used in the synthesis of the acrylic polymer is preferably 55% by weight or more, more preferably 60% by weight or more, even more preferably 65% by weight or more, even more preferably 70% by weight or more, particularly preferably 85% by weight or more, and most preferably 90% by weight or more, in order to further exert the effects of the present invention. The upper limit of the content of alkyl (meth)acrylate is preferably 99.5% by weight or less, more preferably 99% by weight or less. However, the acrylic polymer may be obtained by polymerizing substantially only alkyl (meth)acrylate.

When an alkyl(meth)acrylate in which R ² is a C4-8 linear alkyl group is used, the proportion of the alkyl(meth)acrylate in which R ² is a C4-8 linear alkyl group among the alkyl(meth)acrylates contained in the monomer component is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, particularly preferably 95% by weight or more, and most preferably 99% by weight to 100% by weight, in terms of being able to further exhibit the effects of the present invention.

One embodiment (I) of the acrylic polymer is an acrylic polymer in which 80% by weight or more of the total monomer components is n-butyl acrylate (BA). In this case, the content of n-butyl acrylate (BA) in the total monomer components is preferably 82% by weight to 99% by weight, more preferably 85% by weight to 98% by weight, even more preferably 87% by weight to 97% by weight, particularly preferably 89% by weight to 96% by weight, and most preferably 91% by weight to 95% by weight, in order to further exert the effects of the present invention.

Another embodiment (II) of the acrylic polymer is an acrylic polymer in which 50% by weight or more and less than 80% by weight of the total monomer components is n-butyl acrylate (BA). In this case, the content of n-butyl acrylate (BA) in the total monomer components is preferably 52% by weight to 80% by weight or less, more preferably 55% by weight to 80% by weight, even more preferably 60% by weight to 80% by weight, particularly preferably 63% by weight to 80% by weight, and most preferably 65% by weight to 80% by weight, in order to further exert the effects of the present invention. In this embodiment, the total monomer components may further contain 2-ethylhexyl acrylate (2EHA) in a proportion less than n-butyl acrylate (BA).

Another embodiment (III) of the acrylic polymer is an acrylic polymer in which less than 50% by weight of the total monomer components is 2-ethylhexyl acrylate (2EHA). In this case, the content of 2-ethylhexyl acrylate (2EHA) in the total monomer components is preferably more than 0% by weight and not more than 48% by weight, more preferably 5% to 45% by weight, even more preferably 10% to 43% by weight, particularly preferably 15% to 40% by weight, and most preferably 20% to 35% by weight, in order to further exert the effects of the present invention. The total monomer components may further contain n-butyl acrylate (BA) in a proportion greater than 2-ethylhexyl acrylate (2EHA).

Another embodiment (IV) of the acrylic polymer is an acrylic polymer in which 50% by weight or more of the total monomer components is n-butyl acrylate (BA) and less than 50% by weight of the total monomer components is 2-ethylhexyl acrylate (2EHA). In this case, the content of n-butyl acrylate (BA) in the total monomer components is preferably 52% by weight to 80% by weight or less, more preferably 55% by weight to 80% by weight, even more preferably 60% by weight to 80% by weight, particularly preferably 63% by weight to 80% by weight, and most preferably 65% by weight to 80% by weight, in order to further exhibit the effects of the present invention. In this case, the content of 2-ethylhexyl acrylate (2EHA) in all monomer components is preferably more than 0% by weight and not more than 48% by weight, more preferably 5% by weight to 45% by weight, even more preferably 10% by weight to 43% by weight, particularly preferably 15% by weight to 40% by weight, and most preferably 20% by weight to 35% by weight, in order to better demonstrate the effects of the present invention.

The acrylic polymer may be copolymerized with other monomers (A) to the extent that the effect of the present invention is not impaired. The other monomers (A) may be one type only, or two or more types. The other monomers (A) can be used for the purpose of adjusting the glass transition temperature (Tg) of the acrylic polymer, adjusting the adhesive performance, etc. Examples of other monomers (A) that can improve the cohesive strength and heat resistance of the adhesive include, for example, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, cyano group-containing monomers, vinyl esters, aromatic vinyl compounds, etc., with vinyl esters being preferred. Specific examples of vinyl esters include, for example, vinyl acetate (VAc), vinyl propionate, vinyl laurate, etc., with vinyl acetate (VAc) being preferred.

The content of other monomer (A) in the total monomer components is preferably 0.001% by weight to 40% by weight, more preferably 0.01% by weight to 40% by weight, even more preferably 0.1% by weight to 20% by weight, particularly preferably 0.5% by weight to 10% by weight, and most preferably 1% by weight to 5% by weight.

The acrylic polymer may be copolymerized with other monomers (B) to the extent that the effect of the present invention is not impaired. The other monomers (B) may be one type only, or two or more types. The other monomers (B) are other monomers that introduce functional groups that can be crosslinking base points into the acrylic polymer or contribute to improving adhesive strength, and examples of such monomers include hydroxyl group (OH group)-containing monomers, carboxy group-containing monomers, acid anhydride group-containing monomers, amide group-containing monomers, amino group-containing monomers, imide group-containing monomers, epoxy group-containing monomers, (meth)acryloylmorpholine, vinyl ethers, etc.

One embodiment of the acrylic polymer is an acrylic polymer in which a carboxyl group-containing monomer is copolymerized as the other monomer (B). Examples of the carboxyl group-containing monomer include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Among these, the carboxyl group-containing monomer is preferably acrylic acid (AA) or methacrylic acid (MAA), and more preferably acrylic acid (AA), in terms of being able to more effectively exhibit the effects of the present invention.

When a carboxyl group-containing monomer is used as the other monomer (B), the content of the other monomer (B) in the total monomer components is preferably 0.1% by weight to 10% by weight, more preferably 0.2% by weight to 8% by weight, even more preferably 0.5% by weight to 5% by weight, particularly preferably 0.7% by weight to 4% by weight, and most preferably 1% by weight to 3% by weight, in order to further exert the effects of the present invention.

The acrylic polymer may be copolymerized with other monomers (C) to the extent that the effect of the present invention is not impaired. The other monomers (C) may be one type only, or two or more types. Examples of the other monomers (C) include hydroxyl group-containing monomers. Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; polypropylene glycol mono(meth)acrylate; N-hydroxyethyl (meth)acrylamide; and the like. Among these, the hydroxyl group-containing monomer is preferably a hydroxyalkyl (meth)acrylate in which the alkyl group is linear and has 2 to 4 carbon atoms, in terms of being able to further express the effect of the present invention. Specifically, examples of the hydroxyl group-containing monomer include 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA).

When a hydroxyl group-containing monomer is used as the other monomer (C), the content of the other monomer (C) in the total monomer components is preferably 0.001% by weight to 10% by weight, more preferably 0.01% by weight to 5% by weight, even more preferably 0.02% by weight to 2% by weight, particularly preferably 0.03% by weight to 1% by weight, and most preferably 0.04% by weight to 0.5% by weight, in order to further exert the effects of the present invention.

The Tg of the base polymer may be, for example, -80°C or higher, from the viewpoint of further exerting the effects of the present invention. The base polymer (preferably an acrylic polymer) is designed so that the Tg is preferably -15°C or lower, from the viewpoint of increasing the deformability of the adhesive layer in the shear direction. In some embodiments, the Tg of the base polymer is, for example, preferably -25°C or lower, more preferably -40°C or lower, and even more preferably -50°C or lower. The Tg of the base polymer is designed so that the Tg is, for example, preferably -70°C or higher (more preferably -65°C or higher, and even more preferably -60°C or higher), from the viewpoint of increasing the cohesiveness and shape recovery.

The Tg of the base polymer refers to a value calculated from the Fox formula based on the Tg of the homopolymer of each monomer constituting the base polymer and the weight fraction (copolymerization ratio based on weight) of the monomer. The Fox formula is a relational expression between the Tg of the copolymer and the glass transition temperature Tgi of the homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below.
1/Tg=Σ(Wi/Tgi)

In the above Fox formula, Tg is the glass transition temperature (unit: K) of the copolymer, Wi is the weight fraction (copolymerization ratio by weight) of monomer i in the copolymer, and Tgi is the glass transition temperature (unit: K) of the homopolymer of monomer i. The Tg of the homopolymer is a value listed in publicly available documents.

As the Tg of the homopolymer, for example, the following values can be specifically used:
2-Ethylhexyl acrylate -70℃
n-Butyl acrylate -55℃
Acrylic acid 106℃
2-Hydroxyethyl acrylate -15℃
4-Hydroxybutyl acrylate -40℃

For the Tg of homopolymers other than those exemplified above, the values listed in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989) can be used. If multiple values are listed in the "Polymer Handbook," the conventional values are used. For monomers not listed in the "Polymer Handbook," the catalog values of the monomer manufacturers are used. For the Tg of homopolymers of monomers not listed in the "Polymer Handbook" and for which no catalog values are provided by the monomer manufacturers, the values obtained by the measurement method described in JP 2007-51271 A are used.

As a method for obtaining an acrylic polymer, various polymerization methods known as a synthesis method for an acrylic polymer, such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, etc., can be appropriately adopted. Among these polymerization methods, a solution polymerization method can be preferably used. As a monomer supply method when performing solution polymerization, a lump-sum charging method in which the entire amount of the monomer component is supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, etc. can be appropriately adopted. The polymerization temperature can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and is preferably 20°C or higher, more preferably 30°C or higher, even more preferably 40°C or higher, preferably 170°C or lower, more preferably 160°C or lower, and even more preferably 140°C or lower. As a method for obtaining an acrylic polymer, photopolymerization (typically performed in the presence of a photopolymerization initiator) performed by irradiating light such as UV rays, or radiation polymerization performed by irradiating radiation such as β rays or γ rays, etc., may be adopted.

The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from any suitable organic solvent. Examples include aromatic compounds (typically aromatic hydrocarbons) such as toluene, acetate esters such as ethyl acetate, and aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane.

The initiator (polymerization initiator) used in the polymerization can be appropriately selected from any suitable polymerization initiator depending on the type of polymerization method. The polymerization initiator may be one type or two or more types. Examples of such polymerization initiators include azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN); persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and the like. Other examples of polymerization initiators include redox-based initiators that are a combination of a peroxide and a reducing agent.

The amount of polymerization initiator used is preferably 0.005 to 1 part by weight, and more preferably 0.01 to 1 part by weight, per 100 parts by weight of the total monomer components.

The Mw of the acrylic polymer is preferably 10×10 ⁴ to 500×10 ⁴ , more preferably 10×10 ⁴ to 150×10 ⁴ , further preferably 20×10 ⁴ to 75×10 ⁴ , and particularly preferably 35×10 ⁴ to 65×10 ^4. Here, Mw refers to a value calculated in terms of standard polystyrene obtained by GPC (gel permeation chromatography). As the GPC device, for example, a model named "HLC-8320GPC" (column: TSKgel GMH-H(S), manufactured by Tosoh Corporation) can be used.

(Tackifier resin)
The acrylic adhesive may contain a tackifier resin in order to further exert the effects of the present invention. Examples of the tackifier resin include rosin-based tackifier resins, terpene-based tackifier resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, polyamide-based tackifier resins, elastomer-based tackifier resins, phenol-based tackifier resins, and ketone-based tackifier resins. The tackifier resin may be one type or two or more types.

The amount of tackifier resin used is preferably 5 to 70 parts by weight, more preferably 10 to 60 parts by weight, even more preferably 15 to 50 parts by weight, even more preferably 20 to 45 parts by weight, and particularly preferably 25 to 40 parts by weight, per 100 parts by weight of base polymer, in order to further exert the effects of the present invention.

The tackifier resin preferably contains a tackifier resin TL having a softening point of less than 105°C, in order to further exert the effects of the present invention. The tackifier resin TL can effectively contribute to improving the deformability in the planar direction (shear direction) of the pressure-sensitive adhesive layer. From the viewpoint of obtaining a higher effect of improving deformability, the softening point of the tackifier resin used as the tackifier resin TL is preferably 50°C to 103°C, more preferably 60°C to 100°C, even more preferably 65°C to 95°C, particularly preferably 70°C to 90°C, and most preferably 75°C to 85°C.

The softening point of a tackifier resin is defined as a value measured based on the softening point test method (ring and ball method) specified in JIS K5902 and JIS K2207. Specifically, the sample is melted as quickly as possible at the lowest possible temperature, and is carefully filled into a ring placed on a flat metal plate, taking care not to create bubbles. After cooling, the part that protrudes from the flat surface, including the top end of the ring, is cut off with a slightly heated knife. Next, a support (ring stand) is placed in a glass container (heating bath) with a diameter of 85 mm or more and a height of 127 mm or more, and glycerin is poured to a depth of 90 mm or more. Next, a steel ball (diameter 9.5 mm, weight 3.5 g) and the ring filled with the sample are immersed in glycerin without touching each other, and the temperature of the glycerin is kept at 20°C ± 5°C for 15 minutes. Next, a steel ball is placed in the center of the surface of the sample in the ring, and this is placed in a fixed position on the support. Next, keeping the distance from the top of the ring to the glycerin surface at 50 mm, place a thermometer, align the center of the thermometer's mercury bulb to the same height as the center of the ring, and heat the container. The flame of the Bunsen burner used for heating should be midway between the center of the bottom of the container and its edge, and heat evenly. After heating begins and the temperature reaches 40°C, the rate of increase in the bath temperature must be 5.0 ± 0.5°C per minute. The sample gradually softens and flows down the ring, and the temperature is read when it finally touches the bottom plate, and this is the softening point. The softening point is measured for two or more samples at the same time, and the average value is used.

The amount of tackifier resin TL used is preferably 5 to 50 parts by weight, more preferably 10 to 45 parts by weight, even more preferably 15 to 40 parts by weight, particularly preferably 20 to 35 parts by weight, and most preferably 25 to 32 parts by weight, relative to 100 parts by weight of base polymer, in order to further exert the effects of the present invention.

As the tackifier resin TL, one or more types appropriately selected from the tackifier resins exemplified above having a softening point of less than 105°C may be used. The tackifier resin TL preferably contains a rosin-based resin.

Examples of rosin-based resins that can be preferably used as the tackifier resin TL include rosin esters such as unmodified rosin ester and modified rosin ester. Examples of modified rosin esters include hydrogenated rosin ester.

The tackifier resin TL preferably contains a hydrogenated rosin ester, which can further exert the effects of the present invention. The hydrogenated rosin ester preferably has a softening point of less than 105°C, more preferably 50°C to 100°C, even more preferably 60°C to 90°C, particularly preferably 70°C to 85°C, and most preferably 75°C to 85°C, which can further exert the effects of the present invention.

The tackifier resin TL may contain a non-hydrogenated rosin ester. Here, the term "non-hydrogenated rosin ester" is a general concept that refers to the above-mentioned rosin esters other than the hydrogenated rosin ester. Examples of non-hydrogenated rosin esters include unmodified rosin ester, disproportionated rosin ester, and polymerized rosin ester.

For non-hydrogenated rosin esters, the softening point is preferably less than 105°C, more preferably 50°C to 100°C, even more preferably 60°C to 90°C, particularly preferably 70°C to 85°C, and most preferably 75°C to 85°C, in order to better demonstrate the effects of the present invention.

The tackifier resin TL may contain other tackifier resins in addition to the rosin resin. As the other tackifier resins, one or more types appropriately selected from the tackifier resins exemplified above having a softening point of less than 105°C may be used. The tackifier resin TL may contain, for example, a rosin resin and a terpene resin.

The content of the rosin-based resin in the entire tackifier resin TL is preferably more than 50% by weight, more preferably 55% to 100% by weight, even more preferably 60% to 99% by weight, particularly preferably 65% to 97% by weight, and most preferably 75% to 97% by weight, in order to further exert the effects of the present invention.

The tackifier resin may contain a combination of tackifier resin TL and tackifier resin TH having a softening point of 105°C or higher (preferably 105°C to 170°C), in order to further exert the effects of the present invention.

As the tackifier resin TH, one or more types appropriately selected from the tackifier resins exemplified above having a softening point of 105°C or higher may be used. The tackifier resin TH may include at least one type selected from rosin-based tackifier resins (e.g., rosin esters) and terpene-based tackifier resins (e.g., terpene phenol resins).

(Crosslinking Agent)
The acrylic adhesive can contain a crosslinking agent. The crosslinking agent may be one type or two or more types. The use of the crosslinking agent can impart an appropriate cohesive force to the acrylic adhesive. The crosslinking agent can also be useful for adjusting the slippage distance and return distance in the holding power test. The acrylic adhesive containing the crosslinking agent can be obtained, for example, by forming an adhesive layer using an adhesive composition containing the crosslinking agent. The crosslinking agent can be contained in the acrylic adhesive in the form after crosslinking reaction, the form before crosslinking reaction, the form partially crosslinked, or an intermediate or composite form thereof. The crosslinking agent is typically contained in the acrylic adhesive exclusively in the form after crosslinking reaction.

The amount of the crosslinking agent used is preferably 0.005 to 10 parts by weight, more preferably 0.01 to 7 parts by weight, even more preferably 0.05 to 5 parts by weight, particularly preferably 0.1 to 4 parts by weight, and most preferably 1 to 3 parts by weight, relative to 100 parts by weight of the base polymer, in order to further exert the effects of the present invention.

Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, silicone-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, silane-based crosslinking agents, alkyl etherified melamine-based crosslinking agents, metal chelate-based crosslinking agents, peroxide-based crosslinking agents, etc., and from the viewpoint of being able to more effectively exert the effects of the present invention, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred, and isocyanate-based crosslinking agents are more preferred.

As the isocyanate-based crosslinking agent, a compound having two or more isocyanate groups (including isocyanate regenerating functional groups in which the isocyanate group is temporarily protected by a blocking agent or oligomerization) in one molecule can be used. Examples of isocyanate-based crosslinking agents include aromatic isocyanates such as tolylene diisocyanate and xylylene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate.

More specifically, examples of isocyanate-based crosslinking agents include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic diisocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and polymethylene polyphenyl isocyanate; trimethylolpropane/tolylene diisocyanate trimer adduct (e.g., manufactured by Tosoh Corporation, product name: Coronate L), trimethylolpropane/hexamethylene diisocyanate trimer adduct (e.g., manufactured by Tosoh Corporation, product name: Coronate HL), and isocyanurate of hexamethylene diisocyanate (e.g., manufactured by Tosoh Corporation, product name: Coronate HL). isocyanate adducts such as CORONATE HX (manufactured by Mitsui Chemicals, Inc.); trimethylolpropane adducts of xylylene diisocyanate (e.g., Takenate D110N, manufactured by Mitsui Chemicals, Inc.), trimethylolpropane adducts of xylylene diisocyanate (e.g., Takenate D120N, manufactured by Mitsui Chemicals, Inc.), trimethylolpropane adducts of isophorone diisocyanate (e.g., Takenate D140N, manufactured by Mitsui Chemicals, Inc.), trimethylolpropane adducts of hexamethylene diisocyanate (e.g., Takenate D160N, manufactured by Mitsui Chemicals, Inc.); polyether polyisocyanates, polyester polyisocyanates, and adducts of these with various polyols; polyisocyanates multifunctionalized with isocyanurate bonds, biuret bonds, allophanate bonds, etc.; Among these, aromatic isocyanates and alicyclic isocyanates are preferred because they provide a good balance between deformability and cohesive strength.

The amount of isocyanate-based crosslinking agent used is preferably 0.005 to 10 parts by weight, more preferably 0.01 to 7 parts by weight, even more preferably 0.05 to 5 parts by weight, particularly preferably 0.1 to 4 parts by weight, and most preferably 1 to 3 parts by weight, per 100 parts by weight of base polymer, in order to further exert the effects of the present invention.

When the monomer components constituting the acrylic polymer contain a hydroxyl group-containing monomer, the weight ratio of the isocyanate-based crosslinking agent to the hydroxyl group-containing monomer is preferably more than 20 and less than 50, more preferably 22 to 45, even more preferably 25 to 40, particularly preferably 27 to 40, and most preferably 30 to 35, in order to further exert the effects of the present invention.

When the acrylic adhesive contains a tackifier resin TL with a softening point of 105°C or less, the weight ratio of tackifier resin TL/isocyanate-based crosslinking agent is preferably more than 2 and less than 15, more preferably 5 to 13, even more preferably 7 to 12, and particularly preferably 7 to 11, in order to better demonstrate the effects of the present invention.

As the epoxy crosslinking agent, a multifunctional epoxy compound having two or more epoxy groups in one molecule can be used. Examples of the epoxy crosslinking agent include N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and sorbitol polyglycidyl ether. Examples of epoxy crosslinking agents include glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, and epoxy resins having two or more epoxy groups in the molecule. Commercially available epoxy crosslinking agents include, for example, Mitsubishi Gas Chemical Company's products under the trade names "Tetrad C" and "Tetrad X."

The amount of epoxy crosslinking agent used is preferably 0.005 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, even more preferably 0.015 to 1 part by weight, still more preferably 0.015 to 0.5 parts by weight, particularly preferably 0.015 to 0.3 parts by weight, and most preferably 0.15 to 0.3 parts by weight, relative to 100 parts by weight of the base polymer, in order to further exert the effects of the present invention.

(Other ingredients)
The acrylic adhesive may contain, as necessary, various additives commonly used in the field of adhesives, such as colorants (pigments, dyes, etc.), leveling agents, crosslinking assistants, plasticizers, softeners, fillers, antistatic agents, antiaging agents, ultraviolet absorbers, antioxidants, light stabilizers, etc. As for such various additives, conventionally known ones can be used in the usual manner.

When a colorant (pigment, dye, etc.) is used as an additional component, the amount used is preferably 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, even more preferably 0.05 to 1 part by weight, and particularly preferably 0.1 to 1 part by weight, per 100 parts by weight of the base polymer.

≪≪Applications≫≫
The double-sided pressure-sensitive adhesive tape according to the embodiment of the present invention has excellent shock absorbing properties over a wide temperature range, particularly in the low temperature range. Taking advantage of this characteristic, the double-sided pressure-sensitive adhesive tape according to the embodiment of the present invention can be used, for example, as a shock absorbing tape for displays.

The present invention will be explained in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples. In the following explanation, "parts" and "%" are by weight unless otherwise specified.

<Measurement of storage modulus E' of entire double-sided adhesive tape>
Using RSA-G2 (TA Instruments Japan, Inc.) as a dynamic viscoelasticity measuring device, a sample with a sheet width of 10 mm was placed on the tensile jig of the measuring device at a measurement interval of 20 mm, and the measurement environment oven was changed to the measurement start temperature. After confirming that the temperature of the measurement environment was stable, the temperature was increased from the lower limit temperature of the predetermined temperature range of the measurement at a temperature increase rate of 5°C/min. The frequency during measurement was 1 Hz, and tensile deformation was applied, and the deformation strain amount was controlled in a range where the sheet was not permanently deformed, and the generated stress was calculated as the storage elastic modulus E'.

<Measurement of storage modulus E′ of substrate layer>
Using RSA-G2 (TA Instruments Japan, Inc.) as a dynamic viscoelasticity measuring device, a sample with a sheet width of 10 mm was placed on the tensile jig of the measuring device at a measurement interval of 20 mm, and the measurement environment oven was changed to the measurement start temperature. After confirming that the temperature of the measurement environment was stable, the temperature was increased from the lower limit temperature of the predetermined temperature range of the measurement at a temperature increase rate of 5°C/min. The frequency during measurement was 1 Hz, and tensile deformation was applied, and the deformation strain amount was controlled in a range where the sheet was not permanently deformed, and the generated stress was calculated as the storage elastic modulus E'.

<Measurement of storage modulus G' of pressure-sensitive adhesive layer>
Using an ARES-G2 (TA Instruments Japan, Inc.) as a dynamic viscoelasticity measuring device, a sample with a sheet thickness of 1 mm to 2 mm was placed on a predetermined measuring device jig, and the measurement environment oven was changed to the measurement start temperature. After confirming that the temperature of the measurement environment had stabilized, the temperature was increased from the lower limit temperature in the predetermined temperature range of the measurement at a temperature increase rate of 5°C/min. The frequency during measurement was 1 Hz, shear deformation was applied, and the deformation strain amount was controlled in a range where the sheet was not permanently deformed, and the generated stress was calculated as the storage elastic modulus G'.

<Adhesive strength>
The adhesive strength refers to the 180-degree peel strength (180-degree peel adhesion) against a stainless steel plate. The 180-degree peel strength was measured by attaching a single-sided adhesive tape (product name "No. 31B", manufactured by Nitto Denko Corporation, total thickness 50 μm) to the surface of one of the two adhesive layers of the adhesive sheet, and then cutting the adhesive sheet into a size of 20 mm wide and 100 mm long for a measurement sample. The adhesive surface of the measurement sample was pressed against the surface of a stainless steel plate (SUS304BA plate) by rolling a 2 kg roll back and forth once under an environment of 23°C and 50% RH. After leaving it in the same environment for 30 minutes, the peel strength (N/20 mm) was measured using a universal tension and compression tester in accordance with JIS Z 0237:2000 under the conditions of a tensile speed of 300 mm/min and a peel angle of 180 degrees. The universal tensile/compression tester used was an "Autograph AG-10G tensile tester" manufactured by Shimadzu Corporation.

<Shock absorption>
The impact absorption is indicated by the pressure when an iron ball is dropped. A double-sided adhesive tape cut to 70 mm x 70 mm with the center aligned on a stainless steel plate (SUS plate: 10 mm x 150 mm x 150 mm) is placed, a pressure measurement film (manufactured by Fujifilm, Prescale (Type MS)) with the center aligned on top of it, a stainless steel plate (SUS plate: 5 mm x 70 mm x 70 mm) is placed on top of it with the center aligned, and an iron ball (96 g) is dropped from a height of 40 cm with the center aligned. Next, the pressure measurement film is removed, an image is captured with a pressure image analyzer scanner GT-F740 (manufactured by Fujifilm), and the pressure is analyzed with a Prescale pressure image analysis system FPD-8010J (manufactured by Fujifilm).

Example 1
A reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a cooler was charged with 68 parts of n-butyl acrylate (BA), 29 parts of 2-ethylhexyl acrylate (2EHA), 3 parts of acrylic acid (AA), and 0.04 parts of 4-hydroxybutyl acrylate (4HBA) as monomer components, 0.07 parts of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 151 parts of toluene as a polymerization solvent, and the mixture was solution polymerized at 65°C for 5 hours and then at 80°C for 2 hours to obtain a toluene solution of an acrylic polymer (A). The weight average molecular weight of this acrylic polymer (A) was 440,000.
To 100 parts of the acrylic polymer (A) contained in the toluene solution, 30 parts of a tackifier resin (hydrogenated rosin glycerin ester, manufactured by Harima Chemical Industries, Ltd., product name "Haritac SE10") and 3 parts of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, product name "Coronate L") were added to prepare a pressure-sensitive adhesive composition (A).
Two commercially available release liners (manufactured by Mitsubishi Chemical, product name "Diafoil MRF #50" (biaxially oriented polyester film-based release liner with one-sided release treatment layer, thickness 50 μm)) were prepared. The above-mentioned adhesive composition (A) was applied to one side (release surface) of each release liner so that the thickness after drying was 50 μm, and dried at 120 ° C. for 5 minutes. In this way, adhesive layers (first adhesive layer and second adhesive layer) with a thickness of 50 μm composed of the acrylic adhesive (A) corresponding to the adhesive composition (A) were formed on the release surfaces of the two release liners.
A 100 μm thick thermosetting polyurethane resin film (Toray Industries, 100 μm thick polycaprolactone (ester) polyurethane resin film (100% modulus = 1.8 MPa)) was prepared as the substrate layer. The first and second adhesive layers formed on the two release liners were attached to the first and second surfaces of this substrate layer. The release liner was left on the adhesive layer as it was and used to protect the surface (adhesive surface) of the adhesive layer. The obtained structure was passed through a laminator (0.3 MPa, speed 0.5 m/min) at 80°C once, and then aged in an oven at 50°C for 3 days. In this way, an adhesive tape (1) was obtained.
The results are shown in Table 1.

Example 2
A reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a cooler was charged with 100 parts of n-butyl acrylate (BA), 5 parts of vinyl acetate (VAc), 3 parts of acrylic acid (AA), and 0.1 parts of 2-hydroxyethyl acrylate (HEA) as monomer components, 0.25 parts of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 200 parts of toluene as a polymerization solvent, and the mixture was solution polymerized at 60°C for 6 hours and then at 75°C for 3 hours to obtain a toluene solution of an acrylic polymer (B). The weight average molecular weight of this acrylic polymer (B) was 550,000.
To 100 parts of the acrylic polymer (B) contained in the toluene solution, 10 parts of a tackifier resin (Harima Chemical Industries, Ltd., polymerized rosin ester, product name "Haritac PCJ"), 10 parts of a tackifier resin (Harima Chemical Industries, Ltd., hydrogenated rosin glycerin ester, product name "Haritac SE10"), 5 parts of a tackifier resin (Rika Hercules Corporation, product name "Hercolin D"), 15 parts of a phenol-modified rosin (Sumitomo Bakelite Co., Ltd., product name "SUMILITE PR12603N"), and 2 parts of an isocyanate-based crosslinking agent (Tosoh Corporation, product name "Coronate L") were added to prepare a pressure-sensitive adhesive composition (B).
Two sheets of commercially available release liners (manufactured by Mitsubishi Chemical, product name "Diafoil MRF #50" (biaxially stretched polyester film-based release liner with one-sided release treatment layer, thickness 50 μm)) were prepared. The above-mentioned adhesive composition (B) was applied to one side (release surface) of each release liner so that the thickness after drying was 50 μm, and dried at 120 ° C. for 5 minutes. In this way, adhesive layers (first adhesive layer and second adhesive layer) with a thickness of 50 μm composed of the acrylic adhesive (B) corresponding to the adhesive composition (B) were formed on the release surfaces of the two release liners, respectively.
A thermosetting polyurethane resin film (Toray Industries, 100 μm thick polycaprolactone (ester) polyurethane resin film (100% modulus = 1.8 MPa)) was prepared as the substrate layer. The first and second pressure-sensitive adhesive layers formed on the two release liners were attached to the first and second surfaces of this substrate layer. The release liner was left on the pressure-sensitive adhesive layer as it was and used to protect the surface (adhesive surface) of the pressure-sensitive adhesive layer. The resulting structure was passed through a laminator (0.3 MPa, speed 0.5 m/min) at 80°C once, and then aged in an oven at 50°C for 3 days. In this way, a pressure-sensitive adhesive tape (2) was obtained.
The results are shown in Table 1.

Example 3
In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a cooler, 100 parts of n-butyl acrylate (BA), 3 parts of vinyl acetate (VAc), 2 parts of acrylic acid (AA), and 0.2 parts of 2-hydroxyethyl acrylate (HEA) as monomer components, 0.25 parts of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 200 parts of toluene as a polymerization solvent were charged, and the mixture was solution polymerized at 60°C for 6 hours and then at 75°C for 3 hours to obtain a toluene solution of an acrylic polymer (C). The weight average molecular weight of this acrylic polymer (C) was 600,000.
To 100 parts of the acrylic polymer (C) contained in the toluene solution, 10 parts of a tackifier resin (Harima Chemical Industries, Ltd., polymerized rosin ester, product name "Haritac PCJ"), 10 parts of a tackifier resin (Harima Chemical Industries, Ltd., hydrogenated rosin glycerin ester, product name "Haritac SE10"), 5 parts of a tackifier resin (Rika Hercules Corporation, product name "Hercolin D"), 15 parts of a phenol-modified rosin (Sumitomo Bakelite Co., Ltd., product name "SUMILITE PR12603N"), 2 parts of an isocyanate-based crosslinking agent (Tosoh Corporation, product name "Coronate L"), and 0.2 parts of a black pigment (Dainichiseika Chemicals Mfg. Co., Ltd., "NAF-5091 Black") were added to prepare a pressure-sensitive adhesive composition (C).
Two sheets of commercially available release liners (manufactured by Mitsubishi Chemical, product name "Diafoil MRF #50" (biaxially stretched polyester film-based release liner with one-sided release treatment layer, thickness 50 μm)) were prepared. The above-mentioned adhesive composition (C) was applied to one side (release surface) of each release liner so that the thickness after drying was 50 μm, and dried at 120 ° C. for 5 minutes. In this way, adhesive layers (first adhesive layer and second adhesive layer) with a thickness of 50 μm composed of the acrylic adhesive (C) corresponding to the adhesive composition (C) were formed on the release surfaces of the two release liners, respectively.
50 parts of toluene, 330 parts of polytetramethylene glycol (PTMG2000, manufactured by Mitsubishi Chemical Corporation), 50 parts of hexamethylene diisocyanate, 2 parts of hexamethylene diisocyanate isocyanurate modified type (Takenate (registered trademark) D-170N, manufactured by Mitsui Chemicals, Inc.), 0.02 parts of dibutyltin laurate, 0.02 parts of hydroquinone monomethyl ether, and 11 parts of 2-hydroxyethyl acrylate were mixed and kept at 70° C. for 5 hours, and then diluted with toluene to obtain a toluene solution of oligomer A having a solids concentration of 60% by weight. A toluene solution of the obtained oligomer (P) with a solid content of 60% by weight: 100 parts, a hindered phenol-based antioxidant (IRGANOX1010, manufactured by BASF Japan Ltd.): 5 parts, and a photopolymerization initiator (IRGACURE184, manufactured by BASF Japan Ltd.): 1.5 parts were mixed and diluted with methyl ethyl ketone to obtain a coating composition (Q) for forming a resin film with a solid content of 40% by weight.
A 50 μm thick polyester film (manufactured by Toray Industries, Inc., product name "Lumirror (registered trademark) R75X") with a release layer was used as the support substrate, and a continuous coating device with a slot die coater was used to apply the resin film forming coating composition (Q) onto the release layer of the support substrate, adjusting the discharge flow rate so that the thickness of the cured resin film was 100 μm, and the coating composition was dried and cured. The resin film was peeled off from the support substrate to obtain a thermosetting urethane acrylate resin film (R) (100% modulus = 2.0 MPa) with a thickness of 100 μm. The drying temperature was 80° C., and the curing conditions of the ultraviolet ray (UV ray) were an irradiation output of 400 mW/cm ² and an accumulated light amount of 1200 mJ/cm ² .
The obtained thermosetting urethane acrylate resin film (R) was used as a substrate layer, and the first and second surfaces of this substrate layer were laminated with the first and second adhesive layers formed on the two release liners. The release liners were left on the adhesive layer as they were and used to protect the surface (adhesive surface) of the adhesive layer. The obtained structure was passed through a laminator (0.3 MPa, speed 0.5 m/min) at 80°C once, and then aged in an oven at 50°C for 3 days. In this way, an adhesive tape (3) was obtained.
The results are shown in Table 1.

Example 4
An adhesive tape (4) was obtained in the same manner as in Example 3, except that the amount of black pigment (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., "NAF-5091 Black") was changed to 0.6 parts.
The results are shown in Table 1.

Example 5
An adhesive tape (5) was obtained in the same manner as in Example 3, except that the base layer was changed to a thermosetting polyurethane resin film (manufactured by Toray Industries, Inc., 100 μm thick polycaprolactone-based (ester-based) polyurethane resin film (100% modulus = 1.8 MPa).
The results are shown in Table 1.

Example 6
An adhesive tape (6) was obtained in the same manner as in Example 5, except that the amount of black pigment (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., "NAF-5091 Black") was changed to 0.6 parts.
The results are shown in Table 1.

Comparative Example 1
An adhesive tape (C1) was obtained in the same manner as in Example 1, except that a thermoplastic polyurethane resin film having a thickness of 100 μm (urethane elastomer film, product name "Silclon", manufactured by Okura Kogyo Co., Ltd.) was used as the base layer.
The results are shown in Table 1.

Comparative Example 2
An adhesive tape (C2) was obtained in the same manner as in Example 2, except that a 100 μm-thick thermoplastic polyurethane resin film (urethane elastomer film, product name "Silclon", manufactured by Okura Kogyo Co., Ltd.) was used as the base layer.
The results are shown in Table 1.

Comparative Example 3
A reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a cooler was charged with 95 parts of n-butyl acrylate (BA) as monomer components, 5 parts by weight of acrylic acid (AA), 0.25 parts of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 234 parts of ethyl acetate as a polymerization solvent, and solution polymerization was carried out at 65°C for 9 hours to obtain an ethyl acetate solution of acrylic polymer (D). The weight average molecular weight of this acrylic polymer (D) was 600,000.
To 100 parts of the acrylic polymer (D) contained in the toluene solution, 30 parts of a tackifier resin (terpene phenol resin, manufactured by Yasuhara Chemical Co., Ltd., product name "YS Polystar S145"), 2 parts of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, product name "Coronate L"), and 0.01 part of an epoxy-based crosslinking agent (manufactured by Mitsubishi Gas Chemical Company, Inc., product name "Tetrad C") were added to prepare a pressure-sensitive adhesive composition (D).
Two sheets of commercially available release liners (manufactured by Mitsubishi Chemical, product name "Diafoil MRF #50" (biaxially oriented polyester film-based release liner with one-sided release treatment layer, thickness 50 μm)) were prepared. The above-mentioned adhesive composition (D) was applied to one side (release surface) of each release liner so that the thickness after drying was 50 μm, and dried at 120 ° C. for 5 minutes. In this way, adhesive layers (first adhesive layer and second adhesive layer) with a thickness of 50 μm composed of the acrylic adhesive (D) corresponding to the adhesive composition (D) were formed on the release surfaces of the two release liners, respectively.
A 100 μm thick thermosetting polyurethane resin film (Toray Industries, 100 μm thick caprolactam (ester) polyurethane resin film (100% modulus = 1.8 MPa)) was prepared as the substrate layer. The first and second adhesive layers formed on the two release liners were attached to the first and second surfaces of this substrate layer. The release liner was left on the adhesive layer as it was and used to protect the surface (adhesive surface) of the adhesive layer. The obtained structure was passed through a laminator (0.3 MPa, speed 0.5 m/min) at 80 ° C once, and then aged in an oven at 50 ° C for 3 days. In this way, an adhesive tape (C3) was obtained.
The results are shown in Table 1.

The double-sided adhesive tape according to the embodiment of the present invention has excellent shock absorption properties over a wide temperature range, especially in the low temperature range. Taking advantage of this characteristic, the double-sided adhesive tape according to the embodiment of the present invention can be used, for example, as a shock absorbing tape for displays.

1000 Double-sided adhesive tape 100 Base material layer 200a Adhesive layer 200b Adhesive layer

Claims (8)

A double-sided pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer on both sides of a base layer,
the substrate layer contains at least one polar functional group-containing polymer selected from a condensation polymer and a polyaddition polymer,
the polar functional group-containing polymer has a carbonyl group as a polar functional group in a polymer main chain,
the storage modulus E' of the entire double-sided pressure-sensitive adhesive tape, measured at -25°C to 120°C and a frequency of 1 Hz, is within the range of 1.0 x ¹⁰⁵ Pa to 1.0 x ¹⁰⁸ Pa;
Double-sided adhesive tape. 2. The double-sided pressure-sensitive adhesive tape according to claim 1, wherein the base layer has a storage modulus E' of 1.0 x 10 ⁵ Pa to 1.0 x 10 ⁸ Pa measured at -25°C to 120°C and a frequency of 1 Hz. 3. The double-sided pressure-sensitive adhesive tape according to claim 1, wherein the pressure-sensitive adhesive layer has a maximum storage modulus G' of 1.0 x 10 ¹⁰ Pa or less, measured at -25°C to 120°C and a frequency of 1 Hz. The double-sided adhesive tape according to any one of claims 1 to 3, wherein the adhesive layer has an adhesive strength of 5 N/20 mm or more to a stainless steel plate at 23°C, 50% RH, a tensile speed of 300 mm/min, and a peel angle of 180 degrees. The double-sided pressure-sensitive adhesive tape according to claim 1 , wherein the polar functional group-containing polymer is at least one selected from the group consisting of polyamide, polyurethane, and polyurea. The double-sided pressure-sensitive adhesive tape according to claim 1 , wherein the polar functional group-containing polymer has at least one bond selected from an ether bond and an ester bond. 7. The double-sided pressure-sensitive adhesive tape according to claim 1, wherein the pressure-sensitive adhesive layer comprises at least one selected from the group consisting of an acrylic pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, a silicone pressure-sensitive adhesive, and a urethane pressure-sensitive adhesive. The double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 7 , which is an impact absorbing tape for a display.

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