Reinforcing film, device with reinforcing film, and method for manufacturing same

Abstract

To provide a reinforcing film having both transparency and impact relaxation properties to an adherend.SOLUTION: The reinforcing film (10) includes a pressure-sensitive adhesive layer (2) fixedly laminated on one main surface of a film base material (1). In the film base material, the filler content obtained from the area ratio of the cross section is 0 to 300ppm. The pressure-sensitive adhesive layer may have photocurability. The loss tangent of the pressure sensitive adhesive layer (after photocuring in a case where the pressure sensitive adhesive layer is photocurable) at a temperature of 25 °C and a frequency of 1.0 * 106Hz is 0.3 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a reinforced film having a pressure-sensitive adhesive layer fixedly laminated onto a film substrate.The present invention also relates to a device with a reinforced film bonded to a surface thereof, and a method for producing the same. [Background technology]

[0002] An adhesive film may be attached to the surface of an optical device such as a display or an electronic device for the purpose of surface protection, imparting impact resistance, etc. Such an adhesive film usually has an adhesive layer fixedly laminated on the main surface of a film substrate, and is attached to the device surface via this adhesive layer.

[0003] By temporarily attaching an adhesive film to the surface of a device or device component before use during device assembly, processing, transportation, etc., it is possible to prevent the adherend from being scratched or damaged. Patent Document 1 discloses a reinforcing film provided on a film substrate with a photocurable adhesive layer containing an acrylic-based polymer, a multifunctional (meth)acrylate as a photocuring agent, and a photopolymerization initiator.

[0004] This reinforcing film has low adhesiveness immediately after application to the adherend, making it easy to peel off from the adherend. This allows for reworking from the adherend, and also allows for selective peeling and removal of the reinforcing film from areas of the adherend that do not require reinforcement. The adhesive of the reinforcing film firmly bonds to the adherend upon photocuring, leaving the film substrate permanently bonded to the surface of the adherend, making it usable as a reinforcing material for protecting the surface of devices, etc.

[0005] From the viewpoint of improving the visibility of a display and the appearance of a device, high transparency is sometimes required for a reinforcing film to be attached to the surface of a device. Patent Documents 2 and 3 propose that in a surface protection film to be attached to the surface of a device or optical film, a film substrate that is substantially free of filler is used to increase transparency and improve the visibility of the adherend and the efficiency of appearance inspection. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-41113 [Patent Document 2] International Publication No. 2021 / 235078 [Patent Document 3] Japanese Patent Application Publication No. 2019-127526 Summary of the Invention [Problem to be solved by the invention]

[0007] By using a film that is substantially free of filler as the film substrate of the reinforced film, the reinforced film has low haze, which can contribute to improving the visibility and appearance of the adherend. However, a film substrate that does not contain filler has a lower effect of absorbing external impact than a film substrate that contains filler, and the impact resistance of an adherend to which the reinforced film is attached tends to be inferior.

[0008] In view of the above, an object of the present invention is to provide a reinforcing film that has both transparency and impact mitigation properties. [Means for solving the problem]

[0009] The reinforcing film of the present invention comprises a pressure-sensitive adhesive layer fixedly laminated on one main surface of a film substrate, the film substrate having a filler content of 0 to 300 ppm as determined from the area ratio of the cross section.

[0010] The adhesive layer may be photocurable. The adhesive layer is heated at a temperature of 25° C. and a frequency of 1.0×10 6 If the adhesive layer is photocurable, the loss tangent at 25°C after photocuring is 0.3 or more. 6 The loss tangent in Hz is 0.3 or greater.

[0011] The pressure-sensitive adhesive layer (after photo-curing, if photo-curable) preferably has a shear storage modulus of 30 kPa or more at a temperature of 85°C and a frequency of 1 Hz. The adhesive strength of the pressure-sensitive adhesive layer (after photo-curing, if photo-curable) to the polyimide film is preferably 5 N / 25 mm or more.

[0012] The adhesive composition constituting the adhesive layer preferably contains an acrylic-based polymer. The acrylic-based polymer preferably contains one or more monomer units selected from the group consisting of hydroxyl group-containing monomers and carboxyl group-containing monomers, and has a crosslinked structure introduced therein. The photocurable adhesive composition preferably contains, in addition to the acrylic-based polymer, a photocuring agent having two or more photopolymerizable functional groups, and a photopolymerization initiator.

[0013] A device with a reinforced film is formed by bonding the reinforced film to the surface of the device. The device may be foldable. If the adhesive layer of the reinforced film is photocurable, the reinforced film is temporarily bonded to the surface of the device as an adherend, and then the adhesive layer is photocured to form a device with a reinforced film. [Effects of the Invention]

[0014] The reinforcing film of the present invention has low haze because the film substrate does not substantially contain a filler, which can contribute to improving the visibility and appearance of the adherend. In addition, the pressure-sensitive adhesive layer has a large loss tangent (tan δ) at high frequencies, which means that the reinforcing film has excellent impact absorption properties, achieving both transparency and impact absorption properties. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a cross-sectional view showing a laminated structure of a reinforcing film. [Figure 2] FIG. 2 is a cross-sectional view showing a laminated structure of a reinforcing film. [Figure 3] FIG. 10 is a cross-sectional view showing a device to which a reinforcing film is attached. DETAILED DESCRIPTION OF THE INVENTION

[0016] Fig. 1 is a cross-sectional view showing one embodiment of a reinforced film. Reinforced film 10 has a pressure-sensitive adhesive layer 2 on one main surface of a film substrate 1. The pressure-sensitive adhesive layer 2 is fixedly laminated on one main surface of the film substrate 1. Fig. 2 is a cross-sectional view of the reinforced film in which a release liner 5 is temporarily attached onto the main surface of the pressure-sensitive adhesive layer 2.

[0017] "Fixed" means that the two laminated layers are firmly bonded together, making it difficult or impossible to separate them at their interface. "Temporary adhesion" means that the adhesive strength between the two laminated layers is weak, making them easy to separate at their interface.

[0018] 3 is a cross-sectional view showing a state in which a reinforcing film 10 is attached to the surface of a device 20. The release liner 5 is peeled off and removed from the surface of the pressure-sensitive adhesive layer 2, and the exposed surface of the pressure-sensitive adhesive layer 2 is attached to the surface of the device 20, thereby attaching the reinforcing film 10 to the surface of the device 20.

[0019] The pressure-sensitive adhesive layer 2 may be photocurable. When the pressure-sensitive adhesive layer 2 is photocurable, the pressure-sensitive adhesive layer 2 is photocured in a state where the reinforcing film 10 (pressure-sensitive adhesive layer 2) is attached to the device 20, thereby increasing the adhesive strength at the interface between the device 20 and the pressure-sensitive adhesive layer 2 and fixing the device 20 to the reinforcing film 10.

[0020] [Structure of the reinforcing film] <Film substrate> A plastic film is used as the film substrate 1. In order to bond the film substrate 1 and the pressure-sensitive adhesive layer 2 together, it is preferable that the surface of the film substrate 1 to which the pressure-sensitive adhesive layer 2 is to be attached is not subjected to a release treatment.

[0021] Examples of plastic materials constituting the film substrate 1 include polyester resins, polyolefin resins, cyclic polyolefin resins, polyamide resins, polyimide resins, and polyether ether ketone resins. In a reinforcing film for an optical device such as a display, the film substrate 1 is preferably a transparent film. Polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate are preferred because they combine mechanical strength and transparency, with polyethylene terephthalate being particularly preferred.

[0022] It is preferable that the film substrate 1 does not substantially contain fillers (fine particles). When the film substrate does not contain fillers, light scattering by the film substrate is less likely to occur, and haze tends to be reduced. As a result, the visibility, appearance, and design of the device to which the reinforcement film is attached tend to be improved.

[0023] The filler content calculated from the cross-sectional area ratio of the film substrate 1 is 0 to 300 ppm. The lower the filler content, the less light scattering occurs, and the haze tends to be smaller. The filler content of the film substrate 1 is preferably 250 ppm or less, more preferably 220 ppm or less, and even more preferably 200 ppm or less, and may be 150 ppm or less or 100 ppm or less. The film substrate 1 may contain a small amount of filler from the viewpoint of improving slip properties, etc. The filler content of the film substrate 1 may be 10 ppm or more, 20 ppm or more, 30 ppm or more, or 40 ppm or more.

[0024] The filler content of the film substrate can be determined from a cross-sectional TEM image of the film substrate or reinforcing film. The filler content is defined as the ratio of the total area of ​​the filler to the thickness of the film substrate x the observation width (500 μm).

[0025] A film containing no filler at all has a smooth surface and poor slipperiness, which can lead to blocking or poor transport or winding in a roll-to-roll process. As described above, when a film substrate contains a small amount of filler, fine irregularities are formed on the surface, which tends to improve slipperiness. To improve slipperiness while suppressing an increase in haze, a filler-containing layer may be provided on one or both sides of a filler-free substrate (core layer). This filler-containing layer functions as a slip-promoting layer. When the film substrate has a filler-containing layer, the filler content is calculated from the ratio of the total area of ​​the filler to the total area of ​​the core layer and filler-containing layer in the cross section.

[0026] When the film substrate contains a filler, examples of the filler include inorganic fillers and organic fillers. Examples of inorganic fillers include inorganic oxides such as silica and alumina. Examples of organic fillers include silicone resins and acrylic resins. The filler may be of one type or two or more types. The average particle size of the filler is not particularly limited, but from the viewpoint of suppressing light scattering and enhancing slipperiness, it is preferably 10 to 400 nm, more preferably 20 nm to 350 nm, and even more preferably 30 nm to 300 nm, and may be 50 to 250 nm or 70 to 220 nm. The average particle size of the filler can be determined from a cross-sectional TEM observation image.

[0027] The thickness of the film substrate 1 is, for example, about 4 to 150 μm. From the viewpoint of reinforcing the device by imparting rigidity and cushioning impact, the thickness of the film substrate 1 is preferably 5 μm or more, more preferably 12 μm or more, even more preferably 20 μm or more, and particularly preferably 25 μm or more. From the viewpoint of imparting flexibility to the reinforcing film to make it foldable, the thickness of the film substrate 1 is preferably 125 μm or less, more preferably 100 μm or less. To impart flexibility to the reinforcing film to make it foldable, the thickness of the film substrate 1 is preferably 125 μm or less, more preferably 100 μm or less.

[0028] The haze of the film substrate 1 is preferably 2.0% or less, more preferably 1.5% or less, and even more preferably 1.0% or less. The haze tends to decrease as the amount of filler contained in the film substrate 1 decreases.

[0029] The surface of the film substrate 1 may be provided with a functional coating such as an easy-adhesion layer, an easy-slip layer, a release layer, an antistatic layer, a hard coat layer, or an antireflection layer. As described above, the surface of the film substrate 1 may be provided with an easy-slip layer containing a filler. This easy-slip layer may also have the functions of an easy-adhesion layer, an antistatic layer, a hard coat layer, etc. As described above, in order to bond the film substrate 1 and the pressure-sensitive adhesive layer 2 together, it is preferable that no release layer is provided on the surface of the film substrate 1 to which the pressure-sensitive adhesive layer 2 is to be attached.

[0030] <Adhesive layer> The thickness of the pressure-sensitive adhesive layer 2 fixedly laminated on the film substrate 1 is, for example, about 1 to 300 μm. The thicker the pressure-sensitive adhesive layer 2, the more likely it is to have improved adhesion to an adherend. On the other hand, if the pressure-sensitive adhesive layer 2 is too thick, the fluidity of the pressure-sensitive adhesive may be high, making handling difficult. Therefore, the thickness of the pressure-sensitive adhesive layer 2 is preferably 3 to 100 μm, more preferably 5 to 50 μm, even more preferably 6 to 40 μm, and particularly preferably 8 to 30 μm. From the viewpoint of achieving a thinner thickness, the thickness of the pressure-sensitive adhesive layer 2 may be 25 μm or less, 20 μm or less, or 18 μm or less.

[0031] The total light transmittance of the pressure-sensitive adhesive layer 2 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The haze of the pressure-sensitive adhesive layer 2 is preferably 2% or less, more preferably 1% or less, even more preferably 0.7% or less, and particularly preferably 0.5% or less.

[0032] The adhesive layer 2 is subjected to a temperature of 25°C and a frequency of 1.0 x 10 6 The loss tangent (tanδ) at 100 Hz is 0.3 or more. The tanδ of the pressure-sensitive adhesive layer 2 is preferably 0.4 or more, more preferably 0.5 or more, even more preferably 0.6 or more, and may be 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, or 1.1 or more. The greater the tanδ at high frequencies, the higher the impact mitigation properties of the reinforcing film, and the more likely it is that the impact resistance of the adherend to which the reinforcing film is bonded will be improved.

[0033] As described above, by using a film that is substantially filler-free (filler content of 300 ppm or less) as the film substrate 1, the haze of the reinforced film is low, which is excellent from the viewpoint of improving visibility, etc. On the other hand, if the film substrate 1 does not contain a filler, the stress relaxation and impact force dispersion effects of the filler cannot be obtained, and the impact relaxation properties of the reinforced film tend to be reduced. Since the pressure-sensitive adhesive layer 2 has a large tan δ at high frequencies, the pressure-sensitive adhesive layer has a high impact relaxation effect, so impact resistance can be ensured even when a film substrate that is substantially filler-free is used.

[0034] Loss tangent tanδ is the ratio G" / G' of shear storage modulus G' to loss modulus G". Storage modulus G' corresponds to the portion stored as elastic energy when a material is deformed, and is an index that indicates the degree of hardness. Loss modulus G" corresponds to the portion of energy lost that is dissipated due to internal friction, etc. when a material is deformed, and indicates the degree of viscosity. The larger tanδ, the stronger the tendency for viscosity, the more liquid-like the deformation behavior, and the smaller the rebound elastic energy.

[0035] Generally, viscoelasticity such as G' and tanδ is often evaluated at a frequency of 1 Hz. On the other hand, the impact of a flying or falling foreign object is a deformation in a short time (high speed), so it is evaluated at a high frequency (10 6 It is believed that the value of tan δ at high frequencies (Hz) is highly correlated with shock absorption properties, and the larger the tan δ at high frequencies, the stronger the shock absorption effect.

[0036] Tan δ at high frequencies can be determined by performing viscoelasticity measurements while changing the frequency at multiple temperatures. Specifically, a master curve at 25°C is created from a curve plotting frequency and tan δ at each temperature based on the temperature-time conversion rule, and a 1.0 x 10 6 The value of tan δ in Hz is read. When the pressure-sensitive adhesive layer 2 is photocurable, the viscoelasticity measurement is carried out using the pressure-sensitive adhesive after photocuring. That is, when the pressure-sensitive adhesive layer 2 is photocurable, it is preferable that the tan δ of the pressure-sensitive adhesive after photocuring is in the above range.

[0037] There are no particular limitations on the composition of the pressure-sensitive adhesive layer 2, so long as the tan δ at high frequencies is within the above range. As described above, the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer 2 may be photocurable.

[0038] (base polymer) The base polymer of the pressure-sensitive adhesive may be appropriately selected from acrylic polymers, silicone polymers, urethane polymers, rubber polymers, etc. Acrylic polymers are preferred as the base polymer because they have excellent optical transparency and adhesive properties and allow easy control of viscoelasticity, and it is preferable that 50 wt % or more of the pressure-sensitive adhesive composition be acrylic polymers.

[0039] The acrylic polymer preferably contains an alkyl (meth)acrylate ester as a main monomer component. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0040] As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having an alkyl group with a carbon number of 1 to 20 is preferably used. The (meth)acrylic acid alkyl ester may have a branched alkyl group or may have a cyclic alkyl group (alicyclic alkyl group).

[0041] Specific examples of the (meth)acrylic acid alkyl ester having a chain alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and (meth) Examples of the acrylate include nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0042] Specific examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; and (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring such as dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate. The (meth)acrylic acid alkyl esters having an alicyclic alkyl group may have a substituent on the ring, such as 3,3,5-trimethylcyclohexyl (meth)acrylate. The (meth)acrylic acid alkyl ester having an alicyclic alkyl group may also be a (meth)acrylic acid ester containing a condensed ring of an alicyclic structure and a ring structure having an unsaturated bond, such as dicyclopentenyl (meth)acrylate.

[0043] The content of the (meth)acrylic acid alkyl ester is preferably 50 parts by weight or more, more preferably 60 parts by weight or more, and may be 70 parts by weight or more, 80 parts by weight or more, 90 parts by weight or more, or 95 parts by weight or more, relative to 100 parts by weight of the total amount of the monomer components constituting the polymer.

[0044] In order to lower the glass transition temperature (Tg) of the acrylic base polymer and increase adhesive strength over a wide temperature range, the alkyl group of the (meth)acrylic acid alkyl ester is preferably a chain alkyl group, which may be linear or branched.

[0045] Among the exemplified (meth)acrylic acid alkyl esters, from the viewpoint of lowering the Tg of the base polymer, (meth)acrylic acid C having an alkyl group with 1 to 9 carbon atoms is preferred. 1-9The (meth)acrylic acid alkyl ester is preferably one having a homopolymer glass transition temperature of −50° C. or less, and among these, (meth)acrylic acid C esters having an alkyl group with 6 to 9 carbon atoms are preferred. 6-9 Alkyl esters are preferred.

[0046] (Meth)acrylic acid C, the glass transition temperature of which homopolymer is -50°C or less 6-9 Specific examples of alkyl esters include 2-ethylhexyl acrylate (Tg: -70°C), n-hexyl acrylate (Tg: -65°C), n-octyl acrylate (Tg: -65°C), isononyl acrylate (Tg: -60°C), n-nonyl acrylate (Tg: -58°C), isooctyl acrylate (Tg: -58°C), etc. Among these, 2-ethylhexyl acrylate and n-octyl acrylate are preferred because they have a low Tg and can provide a pressure-sensitive adhesive with a low storage modulus.

[0047] The most abundant monomer (main monomer) in the acrylic base polymer is (meth)acrylic acid C 6-9 Preferably, it is an alkyl ester. (Meth)acrylic acid C 6-9 The amount of alkyl ester is preferably 40 parts by weight or more, more preferably 50 parts by weight or more, and may be 55 parts by weight or more, 60 parts by weight or more, or 65 parts by weight or more, relative to 100 parts by weight of the total amount of the constituent monomer components of the polymer.

[0048] The acrylic base polymer may contain two or more kinds of (meth)acrylic acid alkyl esters as monomer components, and (meth)acrylic acid C 1-9 Alkyl ester and (meth)acrylic acid C 10-20 The homopolymer of a (meth)acrylic acid alkyl ester having a long-chain alkyl group having 10 or more carbon atoms has a temperature range (plateau region) above Tg where the temperature dependence of viscoelasticity is small. Therefore, when the base polymer contains (meth)acrylic acid C as a monomer component, 10-20By including an alkyl ester, the temperature dependency of the storage modulus is reduced, which may prevent the adherend from warping due to temperature changes and the reinforcing film from peeling off from the adherend.

[0049] Since the temperature range of the plateau region is wide and the storage modulus in the plateau region is small, (meth)acrylic acid C 10-20 Among the chain alkyl esters, (meth)acrylic acid C 12-18 Alkyl esters are preferred, among which dodecyl (meth)acrylate and isostearyl (meth)acrylate are preferred, and dodecyl acrylate (lauryl acrylate) is particularly preferred.

[0050] The acrylic base polymer contains (meth)acrylic acid C as a monomer component. 10-20 If it contains alkyl ester, (meth)acrylic acid C 10-20 The amount of alkyl ester is preferably 1 to 40 parts by weight, more preferably 2 to 30 parts by weight, and even more preferably 3 to 25 parts by weight, and may be 4 to 20 parts by weight or 5 to 15 parts by weight, relative to 100 parts by weight of the total amount of the constituent monomer components of the polymer.

[0051] The acrylic base polymer preferably contains, as a constituent monomer component, a monomer component having a crosslinkable functional group in addition to a (meth)acrylic acid alkyl ester. Examples of the monomer having a crosslinkable functional group include a hydroxy group-containing monomer and a carboxy group-containing monomer. The hydroxy group or carboxy group of the base polymer serves as a reaction site with the crosslinking agent described below. For example, when an isocyanate-based crosslinking agent is used, it is preferable to contain a hydroxy group-containing monomer as a monomer component of the base polymer. When an epoxy-based crosslinking agent is used, it is preferable to contain a carboxy group-containing monomer as a monomer component of the base polymer. The introduction of a crosslinked structure into the base polymer tends to improve cohesive strength and increase adhesive strength to an adherend.

[0052] Examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 4-(hydroxymethyl)cyclohexylmethyl (meth)acrylate, etc. Among these, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred because they contribute significantly to improving the adhesive strength of the pressure-sensitive adhesive.

[0053] Examples of the carboxy group-containing monomer include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc. Among these, acrylic acid and methacrylic acid are preferred, with acrylic acid being particularly preferred, since they tend to increase the cohesiveness of the pressure-sensitive adhesive, thereby improving the adhesive strength and adhesive retention.

[0054] From the viewpoint of appropriately introducing a crosslinked structure using a crosslinking agent such as an isocyanate-based crosslinking agent or an epoxy-based crosslinking agent, the total amount of the hydroxy group-containing monomer and the carboxy group-containing monomer relative to 100 parts by weight of the total amount of the constituent monomer components of the acrylic base polymer is preferably 0.3 parts by weight or more, more preferably 0.5 parts by weight or more, and may be 0.7 parts by weight or more, or 1.0 part by weight or more.

[0055] The acrylic base polymer may contain, as a constituent monomer component, a nitrogen-containing monomer such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acryloylmorpholine, N-vinylcarboxylic acid amides, or N-vinylcaprolactam.

[0056] When the acrylic base polymer contains a monomer (highly polar monomer) having a highly polar functional group, such as a hydroxyl group-containing monomer, a carboxyl group-containing monomer, or a nitrogen-containing monomer, the cohesive strength of the polymer increases, and the pressure-sensitive adhesive layer tends to have a high storage modulus at high temperatures and excellent adhesive retention. On the other hand, if the proportion of the highly polar monomer is high, the tan δ at high frequencies decreases and impact absorption properties may be poor. Therefore, the amount of the highly polar monomer (the total of the hydroxyl group-containing monomer, the carboxyl group-containing monomer, and the nitrogen-containing monomer) per 100 parts by weight of the total monomer components constituting the acrylic base polymer is preferably 0.3 to 30 parts by weight, more preferably 0.5 to 15 parts by weight, even more preferably 0.8 to 10 parts by weight, and may be 1 to 5 parts by weight or 1.5 to 4 parts by weight.

[0057] The higher the content of high Tg monomer components in the base polymer's constituents, the higher the storage modulus of the adhesive layer at high temperatures and the more excellent the adhesive retention. High Tg monomers are monomers whose homopolymer glass transition temperatures (Tg) are 40°C or higher, and include dicyclopentanyl methacrylate (Tg: 175°C), dicyclopentanyl acrylate (Tg: 120°C), isobornyl methacrylate (Tg: 173°C), isobornyl acrylate (Tg: 97°C), methyl methacrylate (Tg: 105°C), 1-adamantyl methacrylate (Tg: 250°C), and 1-adamantyl acrylate (Tg (meth)acrylic monomers such as acryloylmorpholine (Tg: 145°C), dimethylacrylamide (Tg: 119°C), diethylacrylamide (Tg: 81°C), dimethylaminopropylacrylamide (Tg: 134°C), isopropylacrylamide (Tg: 134°C), and hydroxyethylacrylamide (Tg: 98°C); and N-vinylpyrrolidone (Tg: 54°C).

[0058] If the ratio of high Tg monomers is high, tan δ at high frequencies may be small, resulting in poor impact absorption. Therefore, the amount of high Tg monomers (total of monomers whose homopolymer Tg is 40°C or higher) relative to 100 parts by weight of the total constituent monomer components of the acrylic base polymer is preferably 30 parts by weight or less, more preferably 15 parts by weight or less, and even more preferably 10 parts by weight or less, and may be 5 parts by weight or less, or 4 parts by weight or less. The amount of high Tg monomers relative to 100 parts by weight of the total constituent monomer components of the acrylic base polymer may be 0 parts by weight or more, 0.5 parts by weight or more, 0.8 parts by weight or more, 1 part by weight or more, or 1.5 parts by weight or more.

[0059] The acrylic base polymer may contain, as a constituent monomer component, a (meth)acrylic acid ester having an alkylene oxide chain. The (meth)acrylic acid ester having an alkylene oxide chain is represented by the following general formula (1). CH2=CR 1 -COO-(R 2 -O) m -R 3 (1)

[0060] R in general formula (1) 1 is a hydrogen atom or a methyl group, and R 1 is a hydrogen atom, the compound of formula (1) is an acrylate, 1 Compounds of formula (1) where is a methyl group are methacrylates.

[0061] R in general formula (1) 2 is an alkylene group such as ethylene, propylene, or butylene, and -R 2 -O- is an alkylene oxide chain. -R 2 Specific examples of -O- include ethylene oxide (-CH2CH2-O-), propylene oxide (-CH(CH3)CH2-O-), and butylene oxide (-CH2CH2CH2CH2-O-).

[0062] In general formula (1), m is the number of repeating alkylene oxide units and is an integer of 1 or more. m is preferably 1 to 5. If m is too large, the (meth)acrylate compound represented by general formula (1) tends to act as a chain transfer agent, and the molecular weight of the acrylic base polymer as a polymer does not become sufficiently large, which may result in insufficient adhesive strength of the pressure-sensitive adhesive. 3 is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 20 carbon atoms. From the viewpoint of lowering the Tg of the acrylic base polymer and improving compatibility with the photocuring agent described later, R 3 is preferably an alkyl group having 1 to 3 carbon atoms, and a methyl group or an ethyl group is particularly preferred.

[0063] Specific examples of the compound represented by general formula (1) include methoxyethyl acrylate, phenoxyethyl acrylate, ethoxyethoxyethyl acrylate, and methoxytriethylene glycol acrylate.

[0064] The acrylic base polymer may contain other monomer components, such as vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfo group-containing monomers, phosphate group-containing monomers, and acid anhydride group-containing monomers.

[0065] From the viewpoint of imparting excellent adhesive properties to the PSA, the glass transition temperature of the acrylic base polymer is preferably −10° C. or lower, more preferably −20° C. or lower, even more preferably −30° C. or lower, and may be −40° C. or lower, −50° C. or lower, −55° C. or lower, or −60° C. or lower. The glass transition temperature of the acrylic base polymer is generally −100° C. or higher, and may be −80° C. or higher, or −70° C. or higher.

[0066] The glass transition temperature (Tg) is the temperature (peak top temperature) at which the loss tangent tanδ in viscoelasticity measurement is maximized. The theoretical glass transition temperature may be used instead of the glass transition temperature determined by viscoelasticity measurement. The theoretical Tg is the glass transition temperature Tg of a homopolymer of the constituent monomer components of a polymer. i and the weight fraction W of each monomer component i It is calculated using the following Fox formula: 1 / Tg=Σ(W i / Tg i )

[0067] Tg is the theoretical glass transition temperature of the polymer (unit: K), W i is the weight fraction of monomer component i (copolymerization ratio by weight), Tg i is the glass transition temperature (unit: K) of the homopolymer of monomer component i. The glass transition temperature of the homopolymer can be determined from the values ​​listed in Polymer Handbook, 3rd Edition (John Wiley & Sons, Inc., 1989). The glass transition temperature of the homopolymer of a monomer not listed in the above literature can be determined from the peak top temperature of tan δ measured by dynamic viscoelasticity measurement.

[0068] The above monomer components are polymerized by various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization to obtain an acrylic polymer as a base polymer. Solution polymerization is preferred from the viewpoints of cost and the balance of adhesive strength, holding power, and other properties of the pressure-sensitive adhesive. Ethyl acetate, toluene, etc. are used as the solvent for solution polymerization. The solution concentration is usually about 20 to 80% by weight. Various known polymerization initiators such as azo-based and peroxide-based initiators can be used for solution polymerization. A chain transfer agent may be used to adjust the molecular weight. The reaction temperature is usually about 50 to 80°C, and the reaction time is usually about 1 to 8 hours.

[0069] The weight-average molecular weight of the acrylic base polymer is preferably 200,000 or more, more preferably 300,000 or more, and even more preferably 500,000 or more. The higher the weight-average molecular weight of the base polymer, the higher the adhesive strength at high temperatures tends to be. If the weight-average molecular weight of the base polymer is excessively high, the pressure-sensitive adhesive tends to have a high storage modulus and a low tan δ. Therefore, the weight-average molecular weight of the acrylic base polymer is preferably 3,000,000 or less, more preferably 2,500,000 or less, and may be 2,200,000 or less or 2,000,000 or less. When a crosslinked structure is introduced into the base polymer, the molecular weight of the base polymer refers to the molecular weight before the crosslinked structure is introduced.

[0070] (Crosslinking agent) From the viewpoint of providing the pressure-sensitive adhesive with an appropriate cohesive strength and exhibiting adhesive strength, it is preferable to introduce a crosslinked structure into the base polymer. For example, the crosslinked structure is introduced by adding a crosslinking agent to a solution obtained after polymerizing the base polymer and heating it as necessary. The crosslinking agent has two or more crosslinkable functional groups per molecule. The crosslinking agent may also have three or more crosslinkable functional groups per molecule.

[0071] Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. These crosslinking agents react with functional groups such as hydroxy groups and carboxy groups introduced into the acrylic base polymer to form a crosslinked structure. Isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred because they have high reactivity with the hydroxy groups and carboxy groups of the acrylic base polymer and allow for easy introduction of a crosslinked structure.

[0072] As the isocyanate-based crosslinking agent, a polyisocyanate having two or more isocyanate groups per molecule is used. The isocyanate-based crosslinking agent may be one having three or more isocyanate groups per molecule. Examples of the isocyanate-based crosslinking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate and xylylene diisocyanate; trimethylolpropane / trilene diisocyanate; Examples of suitable isocyanate crosslinking agents include isocyanate adducts such as a diisocyanate trimer adduct (e.g., "Takenate D101E" manufactured by Mitsui Chemicals), a trimethylolpropane / hexamethylene diisocyanate trimer adduct (e.g., "Coronate HL" manufactured by Tosoh), a trimethylolpropane adduct of xylylene diisocyanate (e.g., "Takenate D110N" manufactured by Mitsui Chemicals), and an isocyanurate of hexamethylene diisocyanate (e.g., "Coronate HX" manufactured by Tosoh). Examples of suitable isocyanate crosslinking agents include isocyanate compounds having a biuret group (e.g., "Duranate 24A-100" manufactured by Asahi Kasei) and isocyanate compounds having an allophanate group.

[0073] The epoxy crosslinking agent is a multifunctional epoxy compound having two or more epoxy groups in one molecule. The epoxy crosslinking agent may have three or more or four or more epoxy groups in one molecule. The epoxy group of the epoxy crosslinking agent may be a glycidyl group. Examples of epoxy crosslinking agents 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, sorbitol polyglycidyl ether, 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, and bisphenol-S-diglycidyl ether. As the epoxy-based crosslinking agent, commercially available products such as "Denacol" manufactured by Nagase ChemteX, and "Tetrad X" and "Tetrad C" manufactured by Mitsubishi Gas Chemical may be used.

[0074] The amount of crosslinking agent used can be adjusted appropriately depending on the composition and molecular weight of the acrylic base polymer, and is preferably about 0.01 to 3 parts by weight per 100 parts by weight of the acrylic base polymer. The greater the amount of crosslinking agent, the higher the crosslink density of the base polymer, and the greater the tendency for adhesive strength retention to be enhanced. On the other hand, an excessively large amount of crosslinking agent can cause a decrease in tan δ and a decrease in adhesive strength at high temperatures. From the viewpoint of achieving high adhesive strength and high tan δ, the amount of crosslinking agent is preferably 0.05 to 1.5 parts by weight, more preferably 0.1 to 1.0 parts by weight, and may be 0.15 to 0.6 parts by weight, 0.2 to 0.5 parts by weight, or 0.25 to 0.4 parts by weight per 100 parts by weight of the acrylic base polymer.

[0075] (light curing agent) The adhesive constituting the adhesive layer 2 may be a photocurable adhesive composition containing a photocuring agent in addition to a base polymer. The photocuring agent is a compound having two or more photopolymerizable functional groups in one molecule. The photocurable adhesive improves its adhesive strength to the adherend by photocuring after lamination with the adherend.

[0076] From the viewpoint of compatibility with the base polymer, the photocuring agent is preferably a liquid at room temperature. The photopolymerizable functional group of the photocuring agent is preferably one that is polymerizable by a photoradical reaction. The photocuring agent is preferably a compound having two or more ethylenically unsaturated bonds in one molecule, and polyfunctional (meth)acrylates are preferred because they exhibit appropriate compatibility with the acrylic base polymer.

[0077] The polyfunctional (meth)acrylate is typically an ester of a polyol and (meth)acrylic acid. Specific examples of the polyfunctional (meth)acrylate include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, isocyanuric acid di(meth)acrylate, isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, and trimethylolpropanediol di(meth)acrylate. Examples of the acrylate include ethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin di(meth)acrylate, urethane (meth)acrylate, epoxy (meth)acrylate, butadiene (meth)acrylate, and isoprene (meth)acrylate.

[0078] The polyfunctional (meth)acrylate may be an ester of an alkylene oxide-modified polyol and (meth)acrylic acid. Examples of the alkylene oxide include ethylene oxide (EO) and propylene oxide (PO). The alkylene oxide may be a polyalkylene oxide such as polyethylene glycol or polypropylene glycol.

[0079] Specific examples of alkylene oxide-modified polyfunctional (meth)acrylates include bisphenol A ethylene oxide-modified di(meth)acrylate, bisphenol A propylene oxide-modified di(meth)acrylate, trimethylolpropane ethylene oxide-modified tri(meth)acrylate, trimethylolpropane propylene oxide-modified tri(meth)acrylate, isocyanuric acid ethylene oxide-modified di(meth)acrylate, isocyanuric acid propylene oxide-modified di(meth)acrylate, isocyanuric acid ethylene oxide-modified tri(meth)acrylate, isocyanuric acid propylene oxide-modified tri(meth)acrylate, pentaerythritol ethylene oxide-modified tetra(meth)acrylate, and pentaerythritol propylene oxide-modified tetra(meth)acrylate.

[0080] In polyfunctional (meth)acrylates containing alkylene oxide chains, such as polyalkylene glycol di(meth)acrylates and alkylene oxide-modified polyfunctional (meth)acrylates, the alkylene oxide is preferably (poly)ethylene oxide or (poly)propylene oxide, with (poly)ethylene oxide being particularly preferred. The chain length (n) of the alkylene oxide (the number of repeating units of the alkylene oxide) is approximately 1 to 15. When multiple alkylene oxide chains are contained in one molecule, the average chain length n is preferably 1 to 15. The (average) chain length n of the alkylene oxide chain may be 12 or less, 10 or less, 8 or less, 6 or less, 5 or less, 4 or less, or 3 or less. By adjusting the type and chain length of the alkylene oxide, the compatibility with the acrylic base polymer can be adjusted within an appropriate range.

[0081] Polyfunctional (meth)acrylates having alkylene oxide chains tend to have lower compatibility with acrylic base polymers as the alkylene oxide chain length n increases, and when n is 4 or greater, they have lower compatibility with acrylic base polymers than the acrylic oligomers described below. Therefore, polyfunctional (meth)acrylates having alkylene oxide chains, particularly polyalkylene glycol di(meth)acrylates in which the alkylene oxide chain length n is 4 or greater, tend to be unevenly distributed on the surface of the pressure-sensitive adhesive layer (near the adhesive interface with the adherend), and the photocuring agent unevenly distributed at the adhesive interface with the adherend is likely to form an adhesion-inhibiting layer (Weak Boundary Layer; WBL).

[0082] When a WBL is formed, the adhesive layer retains its bulk properties, such as storage modulus, while the liquid properties of the surface (adhesive interface) become stronger, which tends to reduce the adhesive strength with the adherend, and the adhesive layer before photocuring is easy to peel from the adherend. When a WBL is formed on an adhesive layer where the photocuring agent is unevenly distributed near the adhesive interface with the adherend, the curing reaction of the photocuring agent is more likely to proceed near the adhesive interface where the photocuring agent is present at a higher density, which tends to increase the cohesive force near the adhesive interface and increase the adhesive strength. Furthermore, when a WBL is formed, the increase in the storage modulus, which is a bulk property, of the adhesive after photocuring is suppressed, and as a result, tan δ tends to increase.

[0083] Polyfunctional (meth)acrylates with alkylene oxide chains whose chain length n is 3 or less are highly compatible with acrylic base polymers and therefore do not easily form WBLs. On the other hand, polyfunctional (meth)acrylates with alkylene oxide chains whose chain length n is short have a small functional group equivalent weight of the (meth)acryloyl group, so the pressure-sensitive adhesive layer after photocuring tends to have a high crosslinking density and high adhesive strength.

[0084] As described above, when a polyfunctional (meth)acrylate having an alkylene oxide chain with a long chain length n (particularly n = 4 or greater) is used as a photocuring agent, the adhesive strength of the pressure-sensitive adhesive layer before photocuring tends to be low, whereas when a polyfunctional (meth)acrylate having an alkylene oxide chain with a short chain length n (particularly n = 3 or less) is used, the adhesive strength of the pressure-sensitive adhesive layer after photocuring tends to be high. For the purpose of adjusting the adhesive strength of the pressure-sensitive adhesive layer before and after photocuring, multiple polyfunctional (meth)acrylates having alkylene oxide chains with different chain lengths n may be used. For example, a polyfunctional (meth)acrylate having an alkylene oxide chain with a chain length n = 3 or less may be used in combination with a polyfunctional (meth)acrylate having an alkylene oxide chain with a chain length n = 4 or greater. Alternatively, two or more polyfunctional (meth)acrylates having an alkylene oxide chain with a chain length n = 3 or less may be used.

[0085] From the viewpoint of maintaining adequate compatibility with the acrylic base polymer, the molecular weight of the polyfunctional (meth)acrylate used as the photocuring agent, particularly the polyfunctional (meth)acrylate containing an alkylene oxide chain, is preferably 1500 or less, more preferably 1000 or less, and may be 800 or less, 500 or less, or 400 or less. From the viewpoint of achieving both compatibility with the acrylic base polymer and improved adhesive strength after photocuring, the functional group equivalent (g / eq) of the polyfunctional (meth)acrylate is preferably 500 or less, more preferably 400 or less, and may be 300 or less, 250 or less, 200 or less, 180 or less, or 160 or less. On the other hand, if the functional group equivalent of the polyfunctional (meth)acrylate is too small, the crosslinking density of the pressure-sensitive adhesive layer after photocuring increases, resulting in an increased storage modulus and reduced adhesiveness at low temperatures. Therefore, the functional group equivalent of the photocuring agent is preferably 80 or more, more preferably 100 or more, and may be 120 or more or 130 or more.

[0086] Two or more types of photocuring agents may be used in combination. For example, two or more types of polyfunctional (meth)acrylates having an alkylene oxide chain may be used as the photocuring agent, or a polyfunctional (meth)acrylate having an alkylene oxide chain and a polyfunctional (meth)acrylate having no alkylene oxide chain may be used. Furthermore, polyfunctional (meth)acrylates having different numbers of functional groups (the number of (meth)acryloyl groups in one molecule) may be used as the photocuring agent. For example, a bifunctional (meth)acrylate and a trifunctional or higher polyfunctional (meth)acrylate may be used in combination as the photocuring agent for the purpose of adjusting the adhesive strength and storage modulus of the pressure-sensitive adhesive layer after photocuring.

[0087] As the photocuring agent, a polyfunctional (meth)acrylate having an alkylene oxide chain and a urethane (meth)acrylate may be used. The urethane (meth)acrylate is a compound having one or more urethane bonds and two or more (meth)acryloyl groups in one molecule, and preferably contains two or more urethane bonds in one molecule.

[0088] By including urethane (meth)acrylate as a photocuring agent in addition to a polyfunctional (meth)acrylate with an alkylene oxide chain, the adhesive strength of the adhesive layer before photocuring may be low and the adhesive strength of the adhesive layer after photocuring may be high. Because the compatibility behavior of urethane (meth)acrylate with acrylic base polymers differs from that of polyfunctional (meth)acrylate with an alkylene oxide chain, the inclusion of urethane (meth)acrylate is thought to promote the formation of WBL, contributing to the reduction in the adhesive strength of the adhesive layer before photocuring and the improvement in the adhesive strength of the adhesive layer after photocuring.

[0089] Urethane (meth)acrylates having two or more urethane bonds can be obtained, for example, by reacting a polyisocyanate with a (meth)acrylic compound having a hydroxy group, where the isocyanate group of the polyisocyanate bonds with the hydroxy group of the (meth)acrylic compound to form a urethane bond. Urethane (meth)acrylates having two or more urethane bonds can also be obtained by reacting a polyisocyanate with a polyol to prepare a prepolymer having an isocyanate group at its terminal, and then bonding a (meth)acrylic compound having a hydroxy group to the isocyanate group at the terminal of the prepolymer. Alternatively, urethane (meth)acrylates having two or more urethane bonds can be obtained by reacting a polyisocyanate with a (meth)acrylic compound having a hydroxy group, and then reacting the resulting reaction product with a polyol.

[0090] From the viewpoint of reducing the adhesive strength of the pressure-sensitive adhesive layer before photocuring and increasing the adhesive strength by photocuring, the molecular weight of the urethane (meth)acrylate is preferably 1,000 to 50,000, more preferably 1,500 to 30,000, and may be 2,000 to 20,000, 2,500 to 15,000, or 3,000 to 10,000. The functional group equivalent (g / eq) of the (meth)acryloyl group of the urethane (meth)acrylate is preferably 500 to 20,000, more preferably 800 to 10,000, and even more preferably 1,000 to 7,000, and may be 1,200 to 5,000 or 1,500 to 4,000.

[0091] The urethane (meth)acrylate may be commercially available from Kyoeisha Chemical, Shin-Nakamura Chemical, Negami Chemical Industries, Mitsubishi Chemical, Daicel Allnex, Resonac, or the like.

[0092] The smaller the functional group equivalent weight of the photocuring agent and the greater the content of the photocuring agent, the higher the crosslink density upon photocuring, and therefore the greater the storage modulus of the pressure-sensitive adhesive layer after photocuring and the smaller the tan δ. From the viewpoint of increasing the adhesive strength of the pressure-sensitive adhesive after photocuring and increasing tan δ, the content of the photocuring agent in the pressure-sensitive adhesive composition is preferably 1 to 30 parts by weight, more preferably 3 to 20 parts by weight, even more preferably 5 to 15 parts by weight, or even 7 to 13 parts by weight or 8 to 12 parts by weight, per 100 parts by weight of the acrylic base polymer. As described above, if a WBL is formed on the surface (adhesion interface) of the pressure-sensitive adhesive layer by adjusting the compatibility between the acrylic base polymer and the photocuring agent, the adhesive strength is likely to increase upon photocuring even with a small amount of photocuring agent, and high adhesive strength can be achieved.

[0093] When the photocurable composition constituting the pressure-sensitive adhesive layer contains a urethane (meth)acrylate as a photocuring agent in addition to a polyfunctional (meth)acrylate without a urethane bond (particularly a polyfunctional (meth)acrylate with an alkylene oxide chain), the content of the urethane (meth)acrylate is preferably 0.01 parts by weight or more, more preferably 0.0.5 parts by weight or more, and even more preferably 0.1 parts by weight or more, per 100 parts by weight of the acrylic base polymer. If the content of the urethane (meth)acrylate is excessively high, the photocuring agent may bleed out onto the surface of the pressure-sensitive adhesive layer (the adhesive interface with the adherend), causing contamination of the adherend. Furthermore, if the amount of urethane (meth)acrylate is excessively high, the increase in adhesive strength of the pressure-sensitive adhesive upon photocuring tends to be insufficient. Therefore, the content of urethane (meth)acrylate in the pressure-sensitive adhesive composition is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and may be 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, or 0.5 parts by weight or less, relative to 100 parts by weight of the acrylic base polymer.

[0094] (Photopolymerization initiator) The photocurable pressure-sensitive adhesive composition preferably contains a photopolymerization initiator. The photopolymerization initiator is preferably a photoradical polymerization initiator (photoradical generator). The photoradical polymerization initiator is preferably one that generates radicals upon irradiation with visible light or ultraviolet light having a wavelength shorter than 450 nm, and examples of the photoradical polymerization initiator include hydroxyketones, benzyl dimethyl ketals, aminoketones, acylphosphine oxides, benzophenones, and trichloromethyl group-containing triazine derivatives. The photopolymerization initiator may be used alone or in combination of two or more.

[0095] When the pressure-sensitive adhesive composition is photocurable, the content of the photopolymerization initiator is preferably 0.01 to 5 parts by weight, more preferably 0.02 to 3 parts by weight, and even more preferably 0.03 to 2 parts by weight, relative to 100 parts by weight of the base polymer. The content of the photopolymerization initiator is preferably 0.02 to 20 parts by weight, more preferably 0.05 to 10 parts by weight, and even more preferably 0.1 to 7 parts by weight, relative to 100 parts by weight of the photocuring agent.

[0096] (Other ingredients) The pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer 2 may contain components other than those described above. For example, the pressure-sensitive adhesive composition may contain an oligomer having a lower molecular weight than the base polymer for the purpose of adjusting adhesive strength, viscosity, etc. The weight-average molecular weight of the oligomer is about 1,000 to 30,000, and acrylic oligomers are preferred because they have excellent compatibility with the acrylic base polymer.

[0097] The acrylic oligomer contains a (meth)acrylic acid alkyl ester as the main constituent monomer component. Among them, those containing a (meth)acrylic acid alkyl ester having a chain alkyl group (chain alkyl (meth)acrylate) and a (meth)acrylic acid alkyl ester having an alicyclic alkyl group (alicyclic alkyl (meth)acrylate) as the constituent monomer component are preferred. Specific examples of the chain alkyl (meth)acrylate and the alicyclic alkyl (meth)acrylate are as exemplified above as the constituent monomers of the acrylic base polymer.

[0098] The glass transition temperature of the acrylic oligomer is preferably 20°C or higher, more preferably 30°C or higher, and even more preferably 40°C or higher. Combining a low-Tg acrylic base polymer with a high-Tg acrylic oligomer tends to improve adhesive strength over a wide temperature range, and when the pressure-sensitive adhesive composition is not photocurable, it is preferable to increase adhesive strength by blending an acrylic oligomer. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, but is generally 200°C or lower, preferably 180°C or lower, and more preferably 160°C or lower. The glass transition temperature of the acrylic oligomer is calculated using the Fox formula described above.

[0099] Among the exemplified alkyl (meth)acrylates, methyl methacrylate is preferred as the chain alkyl (meth)acrylate because it has a high glass transition temperature and excellent compatibility with the base polymer. Dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred as the alicyclic alkyl (meth)acrylate. That is, the acrylic oligomer preferably contains, as constituent monomer components, one or more selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate.

[0100] The amount of the alicyclic alkyl (meth)acrylate relative to the total amount of the monomer components constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and even more preferably 30 to 70% by weight. The amount of the chain alkyl (meth)acrylate relative to the total amount of the monomer components constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and even more preferably 30 to 70% by weight.

[0101] The weight average molecular weight of the acrylic oligomer is preferably from 1,000 to 30,000, more preferably from 1,500 to 10,000, and even more preferably from 2,000 to 8,000. By using an acrylic oligomer having a molecular weight within this range, the adhesive strength and adhesive retention power of the pressure-sensitive adhesive tend to be improved.

[0102] The acrylic oligomer can be obtained by polymerizing the above-mentioned monomer components by various polymerization methods. Various polymerization initiators may be used in the polymerization of the acrylic oligomer. Furthermore, a chain transfer agent may be used to adjust the molecular weight.

[0103] When the pressure-sensitive adhesive composition contains an oligomer component such as an acrylic oligomer, the content thereof is preferably 0.5 to 30 parts by weight, more preferably 1 to 25 parts by weight, and even more preferably 2 to 20 parts by weight, relative to 100 parts by weight of the base polymer. When the content of the oligomer in the pressure-sensitive adhesive composition is within the above range, the adhesiveness and adhesive retention at high temperatures tend to be improved. On the other hand, the greater the amount of oligomer with a higher glass transition temperature, the smaller the tan δ and the lower the impact relaxation properties tend to be.

[0104] A silane coupling agent may be added to the pressure-sensitive adhesive composition for the purpose of adjusting the adhesive strength. When a silane coupling agent is added to the pressure-sensitive adhesive composition, the amount added is usually about 0.01 to 5.0 parts by weight, and preferably about 0.03 to 2.0 parts by weight, per 100 parts by weight of the base polymer.

[0105] In addition to the above-mentioned components, the pressure-sensitive adhesive composition may contain additives such as a tackifier, a crosslinking accelerator, a crosslinking retarder, a plasticizer, a softener, an antioxidant, an antidegradant, a filler, a colorant, an ultraviolet absorber, a surfactant, and an antistatic agent, within a range that does not impair the properties of the present invention.

[0106] [Preparation of reinforcing film] A reinforcing film is obtained by laminating a pressure-sensitive adhesive layer 2 on a film substrate 1. The pressure-sensitive adhesive layer 2 may be formed directly on the film substrate 1, or a pressure-sensitive adhesive layer formed in sheet form on another substrate may be transferred onto the film substrate 1.

[0107] The pressure-sensitive adhesive composition is applied to a substrate by roll coating, kiss roll coating, gravure coating, reverse coating, roll brush, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coating, or the like, and the solvent is dried and removed as necessary to form a pressure-sensitive adhesive layer. A suitable drying method can be adopted as appropriate. The heating and drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and even more preferably 70°C to 170°C. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and even more preferably 10 seconds to 10 minutes.

[0108] When the pressure-sensitive adhesive composition contains a crosslinking agent, it is preferable to promote crosslinking by heating or aging simultaneously with or after drying of the solvent. The heating temperature and heating time are appropriately set depending on the type of crosslinking agent used, and crosslinking is usually achieved by heating in the range of 20°C to 160°C for about 1 minute to 7 days. The heating for drying and removing the solvent may also serve as the heating for crosslinking.

[0109] In a photocurable pressure-sensitive adhesive composition, even after a crosslinked structure is introduced into the polymer by a crosslinking agent, the photocuring agent remains unreacted. Therefore, the photocurable pressure-sensitive adhesive layer 2 is made of a photocurable pressure-sensitive adhesive composition containing a base polymer with a crosslinked structure introduced therein, a photocuring agent, and a photopolymerization initiator. When forming the pressure-sensitive adhesive layer 2 on the film substrate 1, it is preferable to apply a release liner 5 on the pressure-sensitive adhesive layer 2 for purposes such as protecting the pressure-sensitive adhesive layer 2. Crosslinking may be performed after applying the release liner 5 on the pressure-sensitive adhesive layer 2.

[0110] When the pressure-sensitive adhesive layer 2 is formed on another substrate, the reinforcing film is obtained by transferring the pressure-sensitive adhesive layer 2 onto the film substrate 1 after drying the solvent. The substrate used to form the pressure-sensitive adhesive layer may be used as the release liner 5 as is.

[0111] As the release liner 5, a plastic film such as polyethylene, polypropylene, polyethylene terephthalate, or polyester film is preferably used. The thickness of the release liner is typically 3 to 200 μm, preferably about 10 to 100 μm. The surface of the release liner 5 that comes into contact with the pressure-sensitive adhesive layer 2 is preferably treated with a release agent such as a silicone-based, fluorine-based, long-chain alkyl-based, or fatty acid amide-based release agent, or with silica powder or the like. By treating the surface of the release liner 5 with a release treatment, when the release liner 5 is peeled from the film substrate 1, peeling occurs at the interface between the pressure-sensitive adhesive layer 2 and the release liner 5, maintaining the pressure-sensitive adhesive layer 2 adhered to the film substrate 1. The release liner 5 may be antistatically treated on either or both of the release-treated and untreated surfaces. By treating the release liner 5 with an antistatic treatment, charging when the release liner is peeled from the pressure-sensitive adhesive layer can be suppressed.

[0112] [Characteristics of the reinforcing film and use of the reinforcing film] The reinforced film of the present invention is used by being attached to a device or a device component. The adherend to which the reinforced film is attached is not particularly limited, and examples thereof include various electronic devices, optical devices, and their component parts. In one embodiment, the reinforced film is attached to the surface of a foldable flexible device. The foldable device has a hinge portion and can be folded around this hinge portion. The folding angle can be set arbitrarily, and the device may be bent (folded) 180°. When the device is a display device, the reinforced film may be attached to the surface on the screen side, or to the back side (housing). A flexible device that is configured to be bendable at a predetermined location such as a hinge portion repeatedly bends and stretches at the same location during use.

[0113] The reinforcing film may be attached to the entire surface of the adherend, or may be selectively attached only to the areas requiring reinforcement (reinforcement target areas). After the reinforcing film is attached to the entire areas requiring reinforcement (reinforcement target areas) and areas not requiring reinforcement (non-reinforcement target areas), the reinforcing film is cut and peeled off from the non-reinforcement target areas, thereby producing a device in which the reinforcing film is attached only to the areas requiring reinforcement. If the adhesive layer 2 is photocurable, the adhesive layer has low adhesive strength before photocuring, and the reinforcing film is temporarily attached to the surface of the adherend, so the reinforcing film can be easily peeled off and removed from the surface of the adherend.

[0114] By laminating a reinforcing film, appropriate rigidity is imparted, which is expected to improve the handleability and prevent breakage of thin members such as flexible devices. When a reinforcing film is laminated to a work-in-progress in the device manufacturing process, the reinforcing film may be laminated to a large-sized work-in-progress before it is cut to the product size. The reinforcing film may also be laminated roll-to-roll to the mother roll of a device manufactured by a roll-to-roll process.

[0115] For example, a reinforcing film is laminated to a mother roll of a device or a work-in-progress thereof using a roll-to-roll method, and then the mother roll to which the reinforcing film is laminated is cut and separated into individual products. Only the reinforcing film is cut using a half cut, and the reinforcing film in the non-reinforced area is peeled off, thereby obtaining a device in which the reinforcing film is laminated to the area to be reinforced. The cutting method is not particularly limited, and any appropriate cutting method such as a rotary cutter, a push blade (e.g., a Thomson blade), or a laser cutter can be used.

[0116] When the pressure-sensitive adhesive layer 2 is photocurable, the pressure-sensitive adhesive layer 2 is irradiated with actinic rays after laminating a reinforcing film to the adherend, thereby photocuring the pressure-sensitive adhesive layer, thereby increasing the adhesive strength to the adherend. Ultraviolet rays are preferred as the actinic rays. The irradiation intensity and irradiation time of the actinic rays may be appropriately set depending on the composition, thickness, etc. of the pressure-sensitive adhesive layer 2. The pressure-sensitive adhesive layer 2 may be irradiated with actinic rays from either the film substrate 1 side or the adherend side, or may be irradiated with actinic rays from both sides.

[0117] From the viewpoint of adhesive reliability during device use, the adhesive strength between the adhesive layer and the adherend (polyimide film) at a temperature of 25°C is preferably 5 N / 25 mm or more, more preferably 6 N / 25 mm or more, even more preferably 8 N / 25 mm or more, and may be 10 N / 25 mm or more, 12 N / 25 mm or more, 14 N / 25 mm or more, or 15 N / 25 mm or more. The adhesive strength is determined by a peel test using a polyimide film as the adherend at a tensile speed of 300 mm / min and a peel angle of 180°. Unless otherwise specified, the adhesive strength is measured at a temperature of 25°C and a relative humidity of 50%. If the adhesive is photocurable, the reinforcing film is attached to the polyimide film and then photocured, and the peel strength at the interface between the adhesive layer and the polyimide film after photocuring is taken as the adhesive strength.

[0118] From the viewpoint of realizing high adhesive strength with the adherend and increasing adhesive retention at high temperatures, the shear storage modulus G' of the pressure-sensitive adhesive layer at a temperature of 85°C and a frequency of 1 Hz is preferably 30 kPa or more, more preferably 40 kPa or more, even more preferably 50 kPa or more, and may be 60 kPa or more, 65 kPa or more, 70 kPa or more, or 75 kPa or more. A large G' at high temperatures tends to suppress peeling of the reinforced film from a flexible device to which the reinforced film is bonded in a high-temperature environment when the device is repeatedly bent and stretched at the same location or when the device is held in a bent state.

[0119] As the G' of the pressure-sensitive adhesive increases, tan δ tends to decrease and impact relaxation properties tend to decrease. Therefore, the shear storage modulus G' of the pressure-sensitive adhesive layer at a temperature of 85°C and a frequency of 1 Hz is preferably 200 kPa or less, more preferably 150 kPa or less, even more preferably 120 kPa or less, and may be 110 kPa or less, 100 kPa or less, or 90 kPa or less.

[0120] The storage modulus of the pressure-sensitive adhesive layer is determined by reading the value at a predetermined temperature when measuring at a frequency of 1 Hz in the range of -70 to 200°C at a heating rate of 5°C / min according to the method described in JIS K7244-1 "Plastics - Test methods for dynamic mechanical properties." If the pressure-sensitive adhesive is photocurable, the storage modulus is measured using the photocured pressure-sensitive adhesive as a sample.

[0121] As the amount of the crosslinking agent and the amount of the photocuring agent increase, the storage modulus G' of the pressure-sensitive adhesive layer tends to increase and the tan δ tends to decrease. 6 The tan δ in Hz is 0.3 or greater, preferably 0.4 or greater, more preferably 0.5 or greater, even more preferably 0.6 or greater, and may be 0.7 or greater, 0.8 or greater, 0.9 or greater, 1.0 or greater, or 1.1 or greater.

[0122] The haze of the reinforced film is preferably 2.0% or less, more preferably 1.5% or less. As described above, by using a low-haze film that is substantially filler-free as the film substrate 1, a reinforced film with low haze that is unlikely to deteriorate the visibility and appearance of a device to which it is adhered can be obtained.

[0123] By attaching the reinforced film, appropriate rigidity is imparted to the adherend and stress is alleviated and dispersed, thereby suppressing various problems that may occur during the device manufacturing process and use. The reinforced film of the present invention has a large high-frequency tan δ of the pressure-sensitive adhesive layer and excellent stress relaxation properties, so even if the film substrate does not substantially contain a filler, the reinforced film has an excellent effect of improving impact resistance. [Example]

[0124] The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0125] [Preparation of base polymer] <Polymer A> A reaction vessel equipped with a thermometer, stirrer, reflux condenser, and nitrogen gas inlet tube was charged with 20 parts by weight of butyl acrylate (BA), 70 parts by weight of 2-ethylhexyl acrylate (2EHA), 8 parts by weight of lauryl acrylate (LA), 1 part by weight of 4-hydroxybutyl acrylate (4HBA), and 1 part by weight of N-vinyl-2-pyrrolidone (NVP), 0.1 parts by weight of azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and 233 parts by weight of ethyl acetate as a solvent. Nitrogen gas was introduced and the mixture was stirred for about 1 hour while nitrogen substitution was performed. The mixture was then heated to 60°C and reacted for 7 hours to obtain a solution of acrylic polymer A with a weight-average molecular weight of 1.8 million.

[0126] <Polymers B to D> The amounts of monomers charged were changed as shown in Table 1. In the polymerization of polymers B and D, 0.2 parts by weight of a thermal polymerization initiator was used, and in the polymerization of polymer C, 0.1 parts by weight of a thermal polymerization initiator was used. Except for these changes, solutions of polymers B, C, and D were obtained in the same manner as in the polymerization of polymer A.

[0127] The monomer ratios used for acrylic polymers A to D and the weight average molecular weights (Mw) of the polymers are listed in Table 1. The weight average molecular weights (polystyrene equivalent) were measured using GPC ("HLC-8220GPC" manufactured by Tosoh) under the following conditions. Sample concentration: 0.2 wt% (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent:THF Flow rate: 0.6mL / min Measurement temperature: 40℃ Sample column: TSKguardcolumn SuperHZ-H (1 column) + TSKgel SuperHZM-H (2 columns) Reference column: TSKgel SuperH-RC (1 column)

[0128] In Table 1, the monomers are described by the following abbreviations. BA: butyl acrylate 2EHA: 2-ethylhexyl acrylate MMA: methyl methacrylate LA: Lauryl acrylate MEA: methoxyethyl acrylate AA: Acrylic acid 4HBA: 4-hydroxybutyl acrylate NVP: N-vinyl-2-pyrrolidone

[0129] [Table 1]

[0130] [Preparation of acrylic oligomers] A reaction vessel equipped with a thermometer, stirrer, reflux condenser, and nitrogen gas inlet tube was charged with 96 parts by weight of cyclohexyl methacrylate (CHMA) and 4 parts by weight of acrylic acid (AA) as monomers, 3 parts by weight of 2-mercaptoethanol as a chain transfer agent, 0.2 parts by weight of AIBN as a thermal polymerization initiator, and 103.2 parts by weight of toluene as a solvent. Nitrogen gas was introduced and the mixture was purged with nitrogen for approximately 1 hour while stirring. The mixture was then heated to 70°C and reacted for 3 hours, and then further reacted at 75°C for 2 hours to obtain a solution of acrylic oligomer E with a weight-average molecular weight of 4000.

[0131] [Preparation of reinforcing film] Example 1 (Preparation of Pressure-Sensitive Adhesive Composition) To a solution of acrylic polymer A (100 parts by weight as polymer solids), 0.3 parts by weight of a trifunctional isocyanate-based crosslinking agent (Tosoh's "Coronate HX") as a crosslinking agent, a multifunctional acrylate (having no urethane bond) and a urethane acrylate shown in Table 2 as photocuring agents, and 0.3 parts by weight of IGM Resins' "Omnirad 651" as a photopolymerization initiator were added and mixed uniformly to prepare a pressure-sensitive adhesive composition.

[0132] (application of adhesive solution and cross-linking) The adhesive composition was applied to a polyethylene terephthalate (PET) film (Toray Industries, Inc., "Lumirror #50-U48"; hereafter referred to as "U48") with a filler-free, 50-μm-thick core layer and nanoparticle-containing, easy-adhesion layers (90 nm thick) on both sides. The adhesive composition was applied using a fountain roll to a dry thickness of 15 μm. After drying at 130°C for 1 minute to remove the solvent, the release-treated surface of a release liner (a 25-μm-thick polyethylene terephthalate film with antistatic treatment on both sides and a silicone release treatment on one side) was bonded to the adhesive-coated surface. The film was then aged for 4 days in an atmosphere at 25°C to promote crosslinking, resulting in a reinforced film in which a photocurable adhesive sheet was fixedly laminated onto a polyethylene terephthalate film substrate, with a release liner temporarily attached thereto.

[0133] <Examples 2 to 8> In preparing the pressure-sensitive adhesive composition, the amounts of the crosslinking agent and the polyfunctional acrylate added were changed as shown in Table 2. Except for this, a reinforcing film was prepared in the same manner as in Example 1.

[0134] <Comparative Example 1> A 50 μm thick PET film (Mitsubishi Chemical's "Diafoil T100-C50"; hereinafter referred to as "T100") that had not been surface-treated and contained 630 ppm of filler was used as the film substrate, and a reinforced film was produced in the same manner as in Example 4.

[0135] <Examples 9 and 10> In preparing the pressure-sensitive adhesive, acrylic polymer B was used instead of acrylic polymer A, 0.5 parts by weight of a tetrafunctional epoxy crosslinking agent ("Tetrad C" manufactured by Mitsubishi Gas Chemical Company) was used as the crosslinking agent, and the type and amount of photocuring agent added were changed as shown in Table 2. Aside from these changes, a reinforcing film was produced in the same manner as in Example 1.

[0136] Example 11 A non-photocurable adhesive composition was prepared by adding 0.05 parts by weight of a tetrafunctional epoxy crosslinking agent ("Tetrad C" manufactured by Mitsubishi Gas Chemical Co., Ltd.) as a crosslinking agent, 15 parts by weight of acrylic oligomer E, and 0.15 parts by weight of a silane coupling agent ("KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd.) to a solution of acrylic polymer C. Using this adhesive composition, a reinforcing film was produced in the same manner as in Example 1.

[0137] <Comparative Example 2> A non-photocurable adhesive composition was prepared by adding 0.05 parts by weight of a tetrafunctional epoxy crosslinking agent ("Tetrad C" manufactured by Mitsubishi Gas Chemical Co., Ltd.) as a crosslinking agent, 15 parts by weight of acrylic oligomer E, and 0.15 parts by weight of a silane coupling agent ("KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd.) to a solution of acrylic polymer D. Using this adhesive composition, a reinforcing film was produced in the same manner as in Example 1.

[0138] <Comparative Example 3> A reinforced film was produced in the same manner as in Comparative Example 2, except that T100 was used as the film substrate instead of U48.

[0139] [evaluation] <Filler content in film substrate> The two types of PET films (U48 and T100) used in the examples and comparative examples were embedded in resin and subjected to ultrathin sectioning, including precious metal staining, to prepare test specimens. Cross-sectional TEM observations were performed using a transmission electron microscope (Hitachi High-Technologies Corporation, "HT7820") at an accelerating voltage of 100 kV and a magnification of 1,000,000 times. A 500 μm wide region was extracted from the obtained TEM image, and the filler area percentage in the cross section was calculated from the filler diameter and number, and the average of the two regions was calculated.

[0140] For U48, the PET film substrate contained no filler, and the adhesive layer contained filler with an average particle size of 150 nm, with the filler area occupancy rate in the adhesive layer being 14,915 ppm. The filler area occupancy rate for the entire film was 53.5 ppm. For T100, filler with an average particle size of 113 nm was contained, with the filler area occupancy rate being 630 ppm.

[0141] <Haze of reinforcement film> The release liner was peeled off from the pressure-sensitive adhesive layer of the reinforcing film of each of the Examples and Comparative Examples, and the pressure-sensitive adhesive layer was attached to a glass plate. In Examples 1 to 8 and Comparative Example 1, 4000 mJ / cm was irradiated from an LED lamp with a wavelength of 365 nm on the surface of the PET film substrate side. 2 The adhesive was photocured by irradiating it with ultraviolet light of 1000 kJ / cm. The haze of the sample in which the reinforcing film was attached to the glass plate was measured using a haze meter ("NDH-5000" manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136.

[0142] <Storage modulus of adhesive layer> The adhesive composition was applied to a release liner and crosslinked in the same manner as in the above Examples and Comparative Examples to prepare an adhesive layer. In Examples 1 to 8 and Comparative Example 1, a release liner was attached to the surface of the adhesive layer to shield it from oxygen, and the adhesive layer was exposed to 4000 mJ / cm 2 of light from a 365 nm LED lamp. 2The adhesive layer was laminated to prepare a measurement sample having a thickness of approximately 1.0 mm, and dynamic viscoelasticity measurement was carried out under the following conditions using a rotational rheometer (TA Instruments, "Discovery-HR2"), and the shear storage modulus G' at 85°C was read. (Measurement conditions) Deformation mode: Torsion Measurement frequency: 1Hz Heating rate: 5°C / min Measurement temperature: -70~200℃ Shape: Parallel plate 8.0mmφ Distortion: 0.1%

[0143] <Tan δ of adhesive layer> Measurement samples were prepared in the same manner as in the measurement of storage modulus described above, except that the laminate thickness of the adhesive layer was changed to 2.0 mm. Dynamic viscoelasticity measurements were performed using a viscoelasticity measuring device (TA Instruments, "ARES") under the following conditions: temperatures from -50°C to 200°C in 10°C increments, at frequencies of 0.0159 to 15.9 Hz (0.1 to 100 rad / s). A master curve at 25°C was obtained from a curve plotting the loss tangent (tanδ) against frequency at each temperature based on the temperature-time conversion rule. The master curve was then used to measure the storage modulus at 1 Hz and 1.0 x 10 6 The value of tan δ in Hz was read. (Measurement conditions) Deformation mode: Torsion Measurement frequency: 0.0159 to 15.9 Hz Measurement temperature: -70 to 200°C (measured in 10°C increments) Shape: Parallel plate 8.0mmφ Distortion: 0.3%

[0144] <Adhesion strength to polyimide film> A 25 μm thick polyimide film (UBE "Upilex 25S") was attached to a glass plate via double-sided adhesive tape (Nitto Denko "No. 531") to obtain a polyimide film substrate for measurement. The release liner was peeled off from the surface of a reinforcing film cut to a width of 25 mm and a length of 100 mm, and the film was then attached to the polyimide film substrate for measurement using a hand roller. In Examples 1 to 8 and Comparative Example 1, an LED lamp with a wavelength of 365 nm was used to irradiate the film from the surface facing the PET film substrate at 4000 mJ / cm. 2 The adhesive was photocured by irradiating ultraviolet light of 1000 nm. Using a test sample in which a reinforcing film was bonded to a polyimide film, the edge of the film substrate of the reinforcing film was held with a chuck, and the reinforcing film was peeled at a 180° angle at a pulling speed of 300 mm / min, and the peel strength was measured.

[0145] <Shock absorption> The release liner was peeled off and removed from the surface of the reinforcing film, and the film was laminated to a 25 μm-thick polyimide film (UBE's "Upilex 25S") using a hand roller. In Examples 1 to 8 and Comparative Example 1, the adhesive was photocured in the same manner as above. This sample was cut into a 50 mm x 50 mm piece and placed on a stage with the polyimide film facing downwards. A 40 g metal ball was dropped from a height of 300 mm, and the test force F1 applied to the stage was measured using a piezoelectric sensor (PCB Piezotronics' "MODEL 480C02"). A similar test was performed using a polyimide film without a reinforcing film placed on the stage, and the test force F0 was determined. The impact absorption rate was calculated using the following formula: Impact absorption rate (%) = 100 x (F0 - F1) / F0

[0146] [Evaluation results] Table 2 shows the types of substrates and adhesive compositions of the reinforcing films of the examples and comparative examples, as well as the evaluation results.

[0147] Details of the crosslinking agent and photocuring agent in Table 2 are as follows: (Crosslinking agent) C / HX: Isocyanurate of hexamethylene diisocyanate (Tosoh's "Coronate HX") D110N: 75% ethyl acetate solution of xylylene diisocyanate trimethylolpropane adduct (Mitsui Chemicals "Takenate D110N") T / C: N,N,N',N'-tetraglycidyl-m-xylylenediamine ("Tetrad C" manufactured by Mitsubishi Gas Chemical Company) (light curing agent) M350: Trimethylolpropane EO-modified (n=1) triacrylate (Toagosei "Aronix M-350", functional group equivalent weight 143g / eq) A200: Polyethylene glycol #200 (n=4) diacrylate ("NK Ester A200" manufactured by Shin-Nakamura Chemical Co., Ltd., functional group equivalent: 154 g / eq) 306T: Pentaerythritol triacrylate-tolylene diisocyanate adduct (Kyoeisha Chemical Co., Ltd. "UA-306T", functional group equivalent: 128 g / eq)

[0148] [Table 2]

[0149] The reinforced film of Comparative Example 3, which had a pressure-sensitive adhesive layer on a PET film substrate (T100) containing a filler, had high haze and poor visibility. The reinforced film of Comparative Example 2, in which the film substrate was changed to a PET film substrate (U48) containing substantially no filler, had low haze and improved transparency, but the impact relaxation rate was lower than that of Comparative Example 3. A comparison between Example 4 and Comparative Example 1 also shows that when a PET film substrate containing substantially no filler is used, the haze is reduced but the impact relaxation rate tends to be lower.

[0150] Examples 1 to 11, in which the composition of the adhesive layer formed on a PET film substrate (U48) containing substantially no filler was changed, had low haze and an impact relaxation rate of 13% or more, achieving both transparency and impact relaxation properties.

[0151] Regarding the relationship between the tan δ and the impact relaxation rate of the pressure-sensitive adhesive layers of Examples 1 to 11 and Comparative Example 1, no clear correlation was observed between the tan δ at a frequency of 1 Hz and the impact relaxation rate. 6 There was a positive correlation between tanδ in Hz and the impact relaxation rate, and the larger the tanδ, the higher the impact relaxation rate tended to be.

[0152] From the comparison of Examples 1 to 6, it can be seen that in the case of the photocurable adhesive, the smaller the amount of the photocurable adhesive, the shorter the frequency 10 6 It can be seen that the tan δ at Hz is large and that there is a tendency for the impact absorption to be excellent. A similar tendency was observed when comparing Example 9 and Example 10. In Examples 1 to 4, there was a tendency for the adhesive strength to the polyimide film to increase as the amount of photocuring agent increased. On the other hand, in Examples 4 to 6, there was a tendency for the adhesive strength to decrease as the amount of photocuring agent increased. When the amount of photocuring agent is excessively large, it is thought that one of the causes of the decrease in adhesive strength is the decrease in viscosity of the adhesive after photocuring.

[0153] From the comparison of Examples 4, 7, and 8, the smaller the amount of crosslinking agent, the lower the frequency of 10 6 It can be seen that there is a tendency for tan δ at Hz to be large, for shock absorption to be excellent, and for adhesive strength to polyimide film to be high.

[0154] The results of the above examples and comparative examples show that by providing an adhesive layer with a large tan δ at high frequencies on a film substrate that does not substantially contain filler, it is possible to achieve both transparency and impact mitigation properties (improved impact resistance) for the reinforced film. [Explanation of symbols]

[0155] 1. Film substrate 2. Adhesive layer 10 Reinforcement film 5 Release liner 20 Adherent

Claims

1. The adhesive tape comprises a film substrate and a photocurable pressure-sensitive adhesive layer fixedly laminated on one main surface of the film substrate, The film substrate has a filler content of 0 to 300 ppm as determined from the cross-sectional area ratio, After photocuring, the pressure-sensitive adhesive layer was subjected to a temperature of 25° C. and a frequency of 1.0×10 ６ The loss tangent in Hz is 0.3 or more, Reinforcement film.

2. The reinforced film according to claim 1 , wherein the pressure-sensitive adhesive layer has a shear storage modulus of 30 kPa or more at a temperature of 85° C. and a frequency of 1 Hz after photocuring.

3. The reinforcing film according to claim 1 , wherein the adhesive layer has an adhesive strength to a polyimide film of 5 N / 25 mm or more after photocuring.

4. the pressure-sensitive adhesive layer is made of a photocurable composition including an acrylic base polymer, a photocuring agent having two or more photopolymerizable functional groups, and a photopolymerization initiator; the acrylic base polymer contains, as a monomer unit, one or more selected from the group consisting of a hydroxy group-containing monomer and a carboxy group-containing monomer, and a crosslinked structure is introduced into the acrylic base polymer; The reinforcing film according to claim 1 .

5. A film substrate and a pressure-sensitive adhesive layer fixedly laminated on one main surface of the film substrate, The film substrate has a filler content of 0 to 300 ppm as determined from the cross-sectional area ratio, The pressure-sensitive adhesive layer was subjected to a temperature test at 25°C and a frequency test at 1.0 x 10 ６ The loss tangent in Hz is 0.3 or more, Reinforcement film.

6. The reinforced film according to claim 5 , wherein the pressure-sensitive adhesive layer has a shear storage modulus of 30 kPa or more at a temperature of 85° C. and a frequency of 1 Hz.

7. The reinforcing film according to claim 5 , wherein the adhesive layer has an adhesive strength to the polyimide film of 5 N / 25 mm or more.

8. the pressure-sensitive adhesive layer contains an acrylic-based polymer, the acrylic base polymer contains, as a monomer unit, one or more selected from the group consisting of a hydroxy group-containing monomer and a carboxy group-containing monomer, and has a crosslinked structure introduced therein; The reinforcing film according to claim 5 .

9. A device with a reinforcing film, in which a reinforcing film is attached to the surface of the device, The reinforcing film includes a film substrate and a pressure-sensitive adhesive layer fixedly laminated on one main surface of the film substrate, the pressure-sensitive adhesive layer is attached to a device surface, The film substrate has a filler content of 0 to 300 ppm as determined from the cross-sectional area ratio, The pressure-sensitive adhesive layer was subjected to a temperature test at 25°C and a frequency test at 1.0 x 10 ６ The loss tangent in Hz is 0.3 or more, Device with reinforced film.

10. The device with a reinforced film according to claim 9 , wherein the pressure-sensitive adhesive layer has a shear storage modulus of 30 kPa or more at a temperature of 85° C. and a frequency of 1 Hz.

11. The device with a reinforced film according to claim 9 or 10, which is foldable.

12. A method for manufacturing a device with a reinforced film having a surface to which a reinforced film is attached, comprising the steps of: After the pressure-sensitive adhesive layer of the reinforcing film according to any one of claims 1 to 4 is temporarily attached to the surface of an adherend, A method for producing a device with a reinforced film, comprising irradiating the pressure-sensitive adhesive layer with active light rays to photocure the pressure-sensitive adhesive layer, thereby increasing the adhesive strength between the reinforced film and the adherend.

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