JP5428158B2 - Double-sided adhesive tape - Google Patents

Description

  The present invention relates to a double-sided pressure-sensitive adhesive tape for sticking and fixing a transparent panel provided with a decorative portion to the surface of an image display device.

  Display elements such as LCD modules (liquid crystal display devices) are used in a wide range of fields including word processors and personal computers. In particular, electronic notebooks, cellular phones, portable audio players, and the like are becoming increasingly smaller and thinner in recent years, and there is a high demand for higher definition due to the compatibility with moving image playback functions and the like.

  As an example of the configuration of the image display unit of such a small electronic device, an image display device in which an LCD module and an image display panel are fixed with a frame-like double-sided tape is used (for example, see Patent Document 1). However, since the image display device having the above configuration has a gap due to the air layer between the LCD module and the image display panel, a decrease in reflectance due to the air layer is inevitable.

  As a liquid crystal display device having a structure having no gap as described above, a structure in which a display element unit and a protective panel are entirely bonded has been studied. In such a configuration, a liquid adhesive (for example, see Patent Document 2) is often applied to the adhesion between the display element unit and the protective panel. However, in the process of assembling various parts, if a liquid adhesive coating or curing process is included, the manufacturing process is complicated, which causes an increase in manufacturing cost. Therefore, there is a demand for an adhesive tape that can easily fix the display element unit and the protection panel as described above.

  For example, in the field of touch panels, a conductive polyethylene terephthalate film (PET film) and a polycarbonate, which is a reinforcing material, are used as adhesive tapes for fixing components of small electronic devices such as LCD modules, for safety reasons such as weight reduction and crack prevention. A double-sided pressure-sensitive adhesive tape that is colorless and transparent and has excellent peeling resistance and foam resistance has been proposed (see Patent Document 3).

The double-sided pressure-sensitive adhesive tape has excellent peeling resistance and foam resistance due to the specific pressure-sensitive adhesive layer. However, in recent protection panels for small electronic devices, particularly protection panels for mobile phones, a printed layer or the like is used on the frame portion other than the image display portion on the back side so that decorations of various characters and designs can be visually recognized from the front surface. In many cases, a decorative layer is provided. When a conventional adhesive tape for component fixing is applied to the transparent panel and the image display device, air bubbles are generated between the image display part and the part other than the decorative part of the transparent panel due to the level difference of the decorative part of the transparent panel. There was a problem that bubbles were generated even after the heat and pressure treatment.
JP 2006-186239 A JP 2007-297582 A JP 2005-255877 A

  Therefore, the problem to be solved by the present invention is that the transparent panel provided with the decorative portion and the surface of the image display device can be suitably fixed, and the transparent panel having a step due to the decorative portion is bonded to the flat surface of the image display device. An object of the present invention is to provide a double-sided pressure-sensitive adhesive tape that can suppress the generation of bubbles at the step portion during the bonding, suppress the foaming with the passage of time, and has excellent drop impact resistance.

  In the present invention, the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive tape has a loss tangent peak in the low temperature range, and has a loss tangent and storage elastic modulus in the high temperature range within a specific range, thereby bonding the members together. Sometimes, the pressure-sensitive adhesive layer has a high fluidity and can be a double-sided pressure-sensitive adhesive tape with good vibration absorption when an impact occurs. As a result, the double-sided pressure-sensitive adhesive tape of the present invention can suppress the generation of air bubbles that are visible even when fixing a member having a step or after aging, and is less likely to peel off even during a drop impact. .

That is, the present invention is a double-sided pressure-sensitive adhesive tape for sticking and fixing a transparent panel provided with a decorative portion to the surface of an image display device, and is a light mainly composed of (meth) acrylic acid alkyl ester having 1 to 12 carbon atoms. It consists of a pressure-sensitive adhesive layer obtained by curing a curable pressure-sensitive adhesive composition, and the loss tangent at 70 ° C. of the dynamic viscoelastic spectrum at a frequency of 1 Hz of the pressure-sensitive adhesive layer is 0.43 to 0.98. The storage elastic modulus is 0.8 × 10 ^{4 to} 3.4 × 10 ⁴ Pa, and the adhesive layer has a maximum value of loss tangent in a temperature range of −40 to −10 ° C. The present invention provides a double-sided pressure-sensitive adhesive tape characterized in that the thickness of the agent layer is 100 to 250 μm.

The double-sided pressure-sensitive adhesive tape of the present invention has a high loss tangent of the pressure-sensitive adhesive layer under a high temperature condition, a low storage elastic modulus, and a thickness of the double-sided pressure-sensitive adhesive tape is 100 to 250 μm. It is excellent in air bleedability of bubbles to be generated, and foaming over time can be suppressed.
Further, this double-sided pressure-sensitive adhesive tape has excellent drop impact resistance because the pressure-sensitive adhesive layer has a maximum value of loss tangent in a temperature range of −40 to −10 ° C.

The double-sided pressure-sensitive adhesive tape of the present invention is a double-sided pressure-sensitive adhesive tape for sticking and fixing a transparent panel provided with a decorative part to the surface of an image display device, and is a light mainly composed of (meth) acrylic acid alkyl ester having 1 to 12 carbon atoms. It is a double-sided pressure-sensitive adhesive tape formed from a pressure-sensitive adhesive layer made of a cured product obtained by curing a curable pressure-sensitive adhesive composition and having a total thickness of 100 to 250 μm. The pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive tape has a loss tangent at 70 ° C. of the dynamic viscoelastic spectrum at a frequency of 1 Hz of 0.43 to 0.98, and a storage elastic modulus at 70 ° C. of 0.8 × 10 ^{4 to} 3. 4 × 10 ⁴ Pa, and has a maximum value of loss tangent in a temperature range of −40 to −10 ° C.

[Photocurable adhesive composition]
The photocurable pressure-sensitive adhesive composition used in the present invention contains a C1-C12 (meth) acrylic acid alkyl ester as a main component. By using the said photocurable adhesive composition, it is easy to adjust the thickness of a double-sided adhesive tape to a suitable range. Moreover, the adhesive force required in the fixation between members can be provided by making the said C1-C12 (meth) acrylic-acid alkylester into a main component.
In the present specification, acrylic acid and methacrylic acid are collectively referred to as (meth) acrylic acid, and these derivatives are also represented in the same manner.

  Specific examples of the (meth) acrylic acid alkyl ester having an alkyl side chain having 1 to 12 carbon atoms include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, and sec-butyl acrylate. , T-butyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, Isopropyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, t-butyl methacrylate, n-hexylme Acrylate, cyclohexyl methacrylate, n- octyl methacrylate, isooctyl methacrylate, 2-ethylhexyl methacrylate, isononyl methacrylate, isodecyl methacrylate, lauryl methacrylate and the like.

  Among them, a methacrylic acid alkyl ester having an alkyl side chain having 4 to 9 carbon atoms or an acrylic acid alkyl ester having an alkyl side chain having 4 to 9 carbon atoms is preferable, and the alkyl side having 4 to 9 carbon atoms is preferred. More preferred are alkyl acrylates having a chain. By using a (meth) acrylic acid alkyl ester having an alkyl side chain with a carbon number within the range, suitable flexibility can be imparted to the resulting adhesive tape, which is useful for improving the step following ability.

It is preferable that content of the said (meth) acrylic-acid alkylester in a photocurable adhesive composition shall be 50-85 mass% with respect to the total amount of the photocurable compound contained in the said composition, 60- It is more preferable to set it as 85 mass%. By making the content of the above (meth) acrylic acid alkyl ester in the photocurable pressure-sensitive adhesive composition in this range, it is advantageous in improving the adhesive force.

  In the photocurable pressure-sensitive adhesive composition used in the present invention, it is preferable to use a monomer having a polar group in combination as a monomer other than the (meth) acrylic acid alkyl ester. Examples of the monomer having a polar group include a monomer containing a hydroxyl group, a monomer containing a carboxyl group, and a monomer containing a nitrogen atom. Among these, it is preferable to use a monomer containing a hydroxy group or a monomer containing a carboxyl group. Moreover, it is also preferable to use together the monomer containing a hydroxyl group, and the monomer containing a carboxyl group. A monomer containing a hydroxy group and a monomer containing a carboxyl group can improve the cohesive strength of the pressure-sensitive adhesive layer, and easily reduce adhesive residue at the time of peeling.

  Examples of the monomer containing a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, hydroxypropyl (meth) acrylate, caprolactone-modified (meth) acrylate, Examples include polyethylene glycol mono (meth) acrylate and polypropylene glycol (meth) acrylate.

  When the monomer containing a hydroxyl group is used, the content of the monomer containing a hydroxyl group in the photocurable pressure-sensitive adhesive composition is 0. 0 relative to the total amount of the photocurable compound contained in the composition. It is preferable to set it as 01-1.0 mass%, and it is more preferable to set it as 0.01-0.8 mass%. By adjusting the content of the monomer containing the hydroxyl group, the cohesive force of the pressure-sensitive adhesive layer can be easily adjusted.

  Examples of the monomer containing a carboxyl group include acrylic acid, methacrylic acid, itaconic acid, maleic acid, crotonic acid, acrylic acid dimer, and ethylene oxide-modified succinic acrylate.

  When the monomer containing a carboxyl group is used, the content of the monomer containing a carboxyl group in the photocurable pressure-sensitive adhesive composition is 0. 0 relative to the total amount of the photocurable compound contained in the composition. It is preferable to set it as 1-8.0 mass%, It is more preferable to set it as 0.5-7.0 mass%, It is further more preferable to set it as 1.0-6.0 mass%. It becomes easy to adjust the cohesion force of an adhesive layer by making it content of the monomer containing said carboxyl group.

  In addition, the photocurable pressure-sensitive adhesive composition preferably contains a crosslinking agent in order to increase the cohesive strength of the resulting pressure-sensitive adhesive layer.

  Examples of the crosslinking agent used include isocyanate crosslinking agents, epoxy crosslinking agents, chelating crosslinking agents, azirine crosslinking agents, and polyfunctional acrylates. Among them, an isocyanate-based crosslinking agent rich in reactivity with the (meth) acrylic copolymer or a polyfunctional acrylate-based crosslinking agent that can be crosslinked by light irradiation is preferable.

  0.1-5 mass parts is preferable, as for the compounding quantity of the crosslinking agent in the photocurable adhesive composition at the time of adding a crosslinking agent, 0.1-3 mass parts is more preferable, and 0.1-1. 5 parts by mass is more preferable. By setting the content of the crosslinking agent in this range, it is easy to adjust the gel fraction of the pressure-sensitive adhesive layer to a suitable range.

  Moreover, the method of adding various additives is mentioned as a means to adjust the molecular weight of an adhesive layer to a suitable range. Examples of the various additives include hydrogenated rosin esters, hydrogenated terpene phenols, polar aliphatic saturated hydrocarbon resins, and acrylic copolymers with little photopolymerization inhibition. Among these, a colorless and transparent polar aliphatic saturated hydrocarbon resin and hydrogenated terpene phenol are preferable.

  5-40 mass parts is preferable, as for the compounding quantity of the additive in a photocurable adhesive composition, 5-30 mass parts is more preferable, and 5-20 mass parts is further more preferable. By setting the content of the additive in this range, it is easy to adjust the molecular weight of the pressure-sensitive adhesive layer to a suitable range.

  Moreover, you may add antioxidant, a filler, a pigment, a thickener, etc. to the adhesive in the range which does not inhibit performance as needed.

  The photocurable composition used in the present invention preferably contains a (meth) acrylic acid alkyl ester polymer obtained by previously polymerizing the (meth) acrylic acid alkyl ester. By containing the polymer in the photocurable composition, it is easy to adjust the adhesive coating liquid to a viscosity suitable for coating.

  The mass average molecular weight (Mw) of the polymer is preferably 100,000 to 2,000,000, and more preferably 150,000 to 1,500,000. By setting the blending amount of the polymer in this range, the double-sided pressure-sensitive adhesive tape can be easily imparted with pressure-sensitive adhesive properties under high-temperature and high-humidity conditions, in particular, foam resistance and peeling resistance under high-temperature and high-humidity conditions.

  Moreover, 5-40 mass parts is preferable with respect to the (meth) acrylic-acid alkylester contained in a photocurable composition, and, as for content of the said polymer, 10-30 mass parts is more preferable. By setting the content of the polymer in this range, it is easy to adjust the pressure-sensitive adhesive coating liquid to a viscosity suitable for coating.

  The photopolymerization initiator used in the photocurable composition used in the present invention is not particularly limited, but acetophenone, methoxyacetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophenone, 2,2- Dimethoxy-2-phenylacetophenone, α-hydroxy-α, α′-dimethylacetophenone, 2-hydroxy-2-cyclohexylacetophenone, 2-methyl-1 [4- (methylthio) phenyl] -2-monforinopropanone- 1, acetophenones, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin ethers such as benzoin isopropyl butyl ether, benzophenone, 2-chlorobenzophenone, p, p'-dichlorobenzophenone, N, N'-tetramethyl-4, '-Diaminobenzophenone, ketones such as 4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone, thioxanthones such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, bisacyl Examples include phosphine oxides such as phosphine oxide and benzoylphosphine oxide, ketals such as benzyldimethyl ketal, and quinones such as camphane-2,3-dione and phenanthrenequinone.

  0.01-5 mass parts is preferable and, as for the compounding quantity of a photoinitiator, 0.1-3 mass parts is more preferable. By setting the content of the photopolymerization initiator in this range, it is easy to adjust the double-sided pressure-sensitive adhesive tape with little residual monomer.

  Examples of a method for curing the photocurable pressure-sensitive adhesive composition include an ultraviolet irradiation method and an electron beam irradiation method. From the viewpoint of easily adjusting the mass average molecular weight of the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive tape of the present invention within a suitable range, the ultraviolet irradiation method is preferable.

[Adhesive layer]
The pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive tape of the present invention is a pressure-sensitive adhesive layer obtained by curing the photocurable composition. In the present invention, the loss tangent (tan δ) at 70 ° C. of the dynamic viscoelastic spectrum of the pressure-sensitive adhesive layer is 0.43 to 0.98, and the storage elastic modulus at 70 ° C. is 0.8 × 10 ^{4 to} 3. 4 × 10 ⁴ Pa. By having a pressure-sensitive adhesive layer with a loss tangent and storage elastic modulus in the above range, the double-sided pressure-sensitive adhesive tape of the present invention has high fluidity of the pressure-sensitive adhesive layer during heating and pressurizing treatment, and is due to the decorative part provided on the transparent panel. Excellent ability to remove bubbles generated by steps. Furthermore, the fluidity is improved during the heat and pressure treatment, whereby the adhesion between the pressure-sensitive adhesive layer and the adherend is improved and the foaming over time is excellently suppressed. Adjustment of these viscoelastic characteristics can be suitably adjusted by adjusting the mass average molecular weight, gel fraction, and the like of the pressure-sensitive adhesive layer.

  The loss tangent at 70 ° C. of the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive tape of the present invention is preferably 0.45 to 0.75, more preferably 0.5 to 0.70. If the loss tangent is in the above range, the transparent panel and the image are excellent because the adhesive layer has excellent fluidity during the heat and pressure treatment after the transparent panel provided with the decoration is pasted and fixed to the surface of the image display device. It is possible to improve the detachability of bubbles generated at the stepped portion when bonded to the display device surface.

The storage elastic modulus at 70 ° C. is preferably 1.2 × 10 ^{4 to} 3.4 × 10 ⁴ Pa, and more preferably 1.5 × 10 ^{4 to} 3.1 × 10 ⁴ Pa. When the storage elastic modulus is within the above range, the elasticity of the pressure-sensitive adhesive is lowered during the heat and pressure treatment after the transparent panel provided with the decorative portion is pasted and fixed on the surface of the image display device, and is provided on the transparent panel. The adhesiveness to the location where adhesion between the pressure-sensitive adhesive layer and the adherend is difficult can be improved by the step of the decorative portion.

  The dynamic viscoelasticity of the pressure-sensitive adhesive layer in the present invention is obtained by sandwiching a test piece between parallel disks, which are measuring parts of the tester, using a viscoelasticity tester (manufactured by Rheometrics, trade name: Ares 2KSTD). Then, the storage elastic modulus (G ′) and the loss elastic modulus (G ″) at a frequency of 1 Hz are measured, and the loss tangent is calculated by an expression represented by tan δ = (G ″) / (G ′). The test piece is obtained by sandwiching an adhesive having a thickness of 0.5 to 2.5 mm between parallel disks.

[Double-sided adhesive tape]
The double-sided pressure-sensitive adhesive tape of the present invention is a pressure-sensitive adhesive tape comprising the above-mentioned pressure-sensitive adhesive layer, and is a double-sided pressure-sensitive adhesive tape having no core substrate. The double-sided pressure-sensitive adhesive tape may be a single-layer pressure-sensitive adhesive layer or may be a laminate of a plurality of pressure-sensitive adhesive layers.

  The thickness of the double-sided pressure-sensitive adhesive tape of the present invention is 100 to 250 μm, preferably 125 to 225 μm, more preferably 150 to 200 μm. By setting the thickness of the double-sided pressure-sensitive adhesive tape within the above range, it becomes easy to absorb an impact generated when dropping or the like, and it is easy to follow a step generated by a decorative portion provided on the transparent panel. When the thickness of the double-sided pressure-sensitive adhesive tape is less than 100 μm, the stress relaxation property of the pressure-sensitive adhesive layer is lowered, and it becomes difficult to follow the step caused by the decorative portion provided on the transparent panel. It becomes difficult to reduce the thickness of small portable electronic devices.

In the double-sided pressure-sensitive adhesive tape of the present invention, the gel fraction represented by the following formula when immersed in toluene for 24 hours is preferably 30 to 70%, more preferably 30 to 60%, 30 ~ 50% is most preferred. When the gel fraction of the pressure-sensitive adhesive layer is within the above range, it is easy to adjust the loss tangent and storage elastic modulus at 70 ° C. of the pressure-sensitive adhesive layer to suitable ranges and to improve the cohesive force of the pressure-sensitive adhesive layer.
Gel fraction = [(mass after dipping toluene in double-sided pressure-sensitive adhesive tape) / (mass before dipping toluene in double-sided pressure-sensitive adhesive tape)] × 100

  The mass average molecular weight (Mw) of the pressure-sensitive adhesive layer in the double-sided pressure-sensitive adhesive tape of the present invention is preferably 300,000 to 1,500,000, more preferably 300,000 to 1,300,000, and further preferably 300,000 to 1,000,000. When the mass average molecular weight Mw of the pressure-sensitive adhesive layer in the double-sided pressure-sensitive adhesive tape of the present invention is within the above range, the loss tangent and storage elastic modulus at 70 ° C. of the pressure-sensitive adhesive layer can be adjusted to a suitable range.

In the present invention, the mass average molecular weight (Mw) of the pressure-sensitive adhesive layer in the double-sided pressure-sensitive adhesive tape of the present invention can be measured by gel permeation chromatography (GPC). More specifically, as a GPC measurement device, “SC8020” manufactured by Tosoh Corporation can be used to measure and obtain the following GPC measurement conditions based on polystyrene conversion values.
(GPC measurement conditions)
Sample concentration: 0.5% by weight (tetrahydrofuran solution)
Sample injection volume: 100 μL
Eluent: Tetrahydrofuran (THF)
Flow rate: 1.0 mL / min
Column temperature (measurement temperature): 40 ° C
Column: “TSKgel GMHHR-H” manufactured by Tosoh Corporation
Detector: Differential refraction

  The double-sided pressure-sensitive adhesive tape of the present invention preferably has high transparency from the viewpoint of use in an image display device.

  The total light transmittance (JIS K 7361) in the visible light wavelength region of the double-sided pressure-sensitive adhesive tape of the present invention is preferably 85% or more, more preferably 90% or more, and further preferably 95% or more. When the total light transmittance is within the above range, the double-sided pressure-sensitive adhesive tape has high transparency, and high definition of the display screen is possible.

  Further, the haze (JIS K 7136) of the double-sided pressure-sensitive adhesive tape of the present invention is preferably 2.0 or less, more preferably 1.5% or less, and further preferably 1.0% or less. When the haze is within the above range, the double-sided pressure-sensitive adhesive tape has high transparency, and high definition of the display screen is possible.

  The adhesive strength (JIS-Z0237 (2000)) of the double-sided pressure-sensitive adhesive tape of the present invention is suitable for fixing between parts when it is 5 N / 20 mm or more with respect to the glass plate, preferably 5 to 20 N / 20 mm, 7 -20N / 20mm is more preferable, and 10-20N / 20mm is more preferable. When the adhesive force of the double-sided pressure-sensitive adhesive tape of the present invention is within the above range, peeling from the pressure-sensitive adhesive layer of the transparent panel can be suppressed.

[Create double-sided adhesive tape]
The photocurable pressure-sensitive adhesive composition is, for example, coated on a release-treated polyethylene terephthalate (PET) film, laminated with the release-treated PET film, and irradiated with ultraviolet rays, and the above-mentioned photocurable pressure-sensitive adhesive composition. Can be cured to create a double-sided adhesive tape. In addition, it is preferable to perform ultraviolet irradiation with the low energy amount ultraviolet lamp which can reduce a residual monomer and can adjust the mass mean molecular weight of the double-sided adhesive tape of this invention in the suitable range.

Ultraviolet irradiation intensity is preferably 0.3~2.0mW / cm ^2, more preferably 0.3~1.5mW / cm ^2, more preferably 0.3~1.2mW / cm ^2. Within the above range, the residual monomer is small and the double-sided pressure-sensitive adhesive tape can be adjusted efficiently. If it is less than 0.3 mW / cm ² , the irradiation intensity is insufficient and a lot of ultraviolet irradiation time is required, and the productivity is remarkably lowered. This is because if it exceeds 2.0 mW / cm ² , the irradiation intensity is high, the residual monomer is increased, and the adhesive performance is significantly reduced.

The ultraviolet cumulative amount of light is preferably from 100 to 500 mJ / cm ^2, more preferably 100 to 400 mJ / cm ^2, more preferably 100~300mJ / cm ^2. Within the above range, the photopolymerization initiator is consumed, the residual monomer is small, and the double-sided adhesive tape can be adjusted efficiently.

[Usage]
The double-sided pressure-sensitive adhesive tape of the present invention can be suitably used when sticking and fixing a transparent panel provided with a decorative portion on the surface of an image display device. As a specific embodiment, for example, there is an image display panel as shown in FIG. In FIG. 1, 1 is a transparent panel, 2 is a decorative part attached to the transparent panel, 3 is a double-sided adhesive tape, and 4 is an image display device.

  The transparent panel is not particularly limited, but a transparent panel made of (meth) acrylic resin, polycarbonate resin, glass or the like can be suitably used. A glass panel with higher transparency is preferred.

  The thickness of the transparent panel is preferably 100 μm to 3.0 mm, more preferably 250 μm to 2.0 mm, and even more preferably 500 μm to 1.0 mm. When the thickness of the transparent panel is within the above range, it is possible to reduce the thickness when applied to a small electronic terminal while maintaining the strength of the transparent panel.

  The decorative part provided on the transparent panel includes characters and figures visually recognized around the screen display part of the portable electronic terminal, or a black or white background provided on the back of these. These decorative portions are preferable because they can be easily provided by printing on a transparent panel. The printing method and printing ink are not particularly limited, and a commonly used printing method such as silk printing or pad printing or printing ink can be used.

  5-30 micrometers is preferable, as for the thickness of the decoration part provided in the transparent panel at the time of using the double-sided adhesive tape of this invention, 5-25 micrometers is more preferable, and 5-20 micrometers is more preferable. When the thickness of the decorative portion provided on the transparent panel is within the above range, the step following property of the double-sided pressure-sensitive adhesive tape of the present invention is particularly suitable, and the effect of suppressing the generation of bubbles is also effective when applied to a thin electronic terminal. It can be suitably expressed. Moreover, the decoration part may be laminated | stacked by the some decoration part, and the magnitude | size and shape of the decoration part laminated | stacked may differ. In the case where a plurality of decorative portions are stacked, the effects of the present invention are easily achieved when the maximum thickness of the stacked decorative portions is within the above range.

  Although it does not specifically limit as an image display apparatus, For example, the LCD module, organic EL module, etc. which are used for image displays, such as a small electronic terminal, are mentioned. Since the double-sided pressure-sensitive adhesive tape of the present invention can reduce the thickness of a portable electronic device, it is preferably used for an LCD module that tends to be thickened by a backlight. In such an LCD module, a polarizing film is often provided on the surface to be bonded with the transparent panel and the double-sided adhesive tape. The double-sided pressure-sensitive adhesive tape of the present invention is excellent in the step following of a member having the other step when the surface of one member to be bonded is a flat surface such as the surface of the polarizing film. It can be suitably applied to a configuration in which the surfaces to be bonded do not have a step. Further, even when the surface of the image display device has a step, the thickness of the double-sided pressure-sensitive adhesive tape can be suitably adjusted to appropriately follow the step on the surface of the image display device.

[Panel fixing method]
When fixing the transparent panel and the image display device, it is preferable to perform a heating and pressurizing process in order to remove bubbles mixed in due to the step of the decorative portion of the transparent panel.

  40-85 degreeC is preferable, as for the conditions of the temperature which performs said heat pressurization process, 50-80 degreeC is more preferable, and 60-80 degreeC is further more preferable. This is because when the temperature at which the heat and pressure treatment is performed is within the above range, the fluidity of the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive tape of the present invention is enhanced, and it is easy to efficiently remove mixed bubbles to the outside of the apparatus.

  The pressure condition for performing the heating and pressing treatment is preferably 3 to 5 atm, more preferably 4 to 5 atm, and further preferably 4.5 to 5 atm. This is because the pressure-sensitive adhesive layer easily adheres to the transparent panel and the image display device when the pressure for performing the heating and pressurizing treatment is within the above range.

  10-50 minutes are preferable, as for the conditions of the time which performs said heat pressurization process, 10-40 minutes are more preferable, and 10 minutes-30 minutes are further more preferable. This is because when the time for performing the heating and pressing treatment is within the above range, the pressure-sensitive adhesive layer, the transparent panel, and the image display device can be efficiently fixed.

  Hereinafter, the present invention will be described specifically by way of examples. In addition, the description of "part" in an Example all represents "mass part".

[Example 1]
70 parts of 2-ethylhexyl acrylate, 4.5 parts of acrylic acid, 0.1 part of 4-hydroxybutyl acrylate, 25 parts of a polymer having a weight average molecular weight of 760,000 based on 2-ethylhexyl acrylate, Ciba Specialty as a polymerization initiator Add 1.2 parts of “DAROCUR1173” manufactured by Chemical Co., Ltd. and 0.5 parts of “Coronate L-75” manufactured by Nippon Polyurethane Co., Ltd. (isocyanate-based cross-linking agent, solid content: 75%) as a cross-linking agent. After defoaming, coating was performed on a PET film having a thickness of 75 μm after the release treatment so that the thickness after drying was 175 μm, and then laminated with a PET film having a thickness of 25 μm after being subjected to a release treatment. Irradiation was performed using a “chemical lamp FL20SBL” manufactured by Toshiba Corporation for 5 minutes. Then, it left still at 40 degreeC for 2 days, and obtained the double-sided adhesive tape of thickness 175 micrometers.

[Example 2]
70 parts of 2-ethylhexyl acrylate, 4.5 parts of acrylic acid, 0.1 part of 4-hydroxybutyl acrylate, 25 parts of a polymer having a weight average molecular weight of 760,000 based on 2-ethylhexyl acrylate, Ciba Specialty as a polymerization initiator Chemical "DAROCUR1173" 0.3 parts, Shin-Nakamura Chemical Co., Ltd. "APG700" (acrylate-based crosslinking agent, solid content 75%) 0.3 parts, additive Arakawa Chemical "KR1840" ( Polar aliphatic saturated hydrocarbon resin) 20 parts added, stirred for 15 minutes, degassed under vacuum conditions, and then dried on a 75 μm thick PET film to a thickness of 175 μm after drying After being coated in this way, it is laminated with a 25 μm thick PET film that has been subjected to mold release treatment, and UV irradiation is made by Toshiba Chemical Using the pump FL20SBL ", to obtain a double-sided adhesive tape having a thickness of 175μm was irradiated for 10 minutes ultraviolet rays.

[Example 3]
70 parts of 2-ethylhexyl acrylate, 4.5 parts of acrylic acid, 0.1 part of 4-hydroxybutyl acrylate, 25 parts of a polymer having a weight average molecular weight of 760,000 based on 2-ethylhexyl acrylate, Ciba Specialty as a polymerization initiator After adding 0.3 parts of “DAROCUR1173” manufactured by Chemical Co., Ltd. and 20 parts of “UH115” (terpene phenol) manufactured by Yashara Chemical Co., Ltd. as an additive, the mixture was stirred for 15 minutes, defoamed under vacuum conditions, and then subjected to mold release treatment. After coating on a 75 μm thick PET film to a thickness of 175 μm after drying, it is laminated with a 25 μm thick PET film that has been subjected to mold release treatment, and UV irradiation is performed by “Chemical Lamp FL20SBL” manufactured by Toshiba Corporation. Used, and irradiated with ultraviolet rays for 10 minutes to obtain a double-sided adhesive tape having a thickness of 175 μm.

[Example 4]
70 parts of 2-ethylhexyl acrylate, 4.5 parts of acrylic acid, 0.1 part of 4-hydroxybutyl acrylate, 25 parts of a polymer having a weight average molecular weight of 760,000 based on 2-ethylhexyl acrylate, Ciba Specialty as a polymerization initiator 1.2 parts of “DAROCUR1173” manufactured by Chemical Co., Ltd. “APG700” manufactured by Shin-Nakamura Chemical Co., Ltd. (acrylate crosslinker, solid content 75%) as a cross-linking agent, and “KR1840” manufactured by Arakawa Chemical Co., Ltd. as an additive ( Polar aliphatic saturated hydrocarbon resin) 10 parts added, stirred for 15 minutes, degassed under vacuum conditions, and then dried on a 75 μm thick PET film to a thickness of 175 μm after drying After being coated in this way, it is laminated with a 25 μm thick PET film that has been subjected to mold release treatment, and UV irradiation is made by Toshiba Chemical Using the pump FL20SBL ", to obtain a double-sided adhesive tape having a thickness of 175μm was irradiated for 10 minutes ultraviolet rays.

[Example 5]
A polymer having a weight average molecular weight of 1.06 million with a composition of 37 parts butyl acrylate, 25 parts 2-ethylhexyl acrylate, 1 part acrylic acid, 0.1 part 4-hydroxybutyl acrylate, butyl acrylate / 2-ethylhexyl acrylate = 3/1. 16 parts, 17 parts of a polymer having a weight average molecular weight of 5000 based on cyclohexyl methacrylate, 0.3 parts of “DAROCUR1173” manufactured by Ciba Specialty Chemicals as a polymerization initiator, and “Coronate L-75” manufactured by Nippon Polyurethane as a crosslinking agent “(Isocyanate-based crosslinking agent, solid content: 75%) 0.5 part was added, stirred for 15 minutes, degassed under vacuum conditions, and then dried on a 75 μm-thick PET film. 25 μm thick after the mold release treatment after coating to a thickness of 175 μm And laminated with a PET film, ultraviolet irradiation using a "chemical lamp FL20SBL" manufactured by Toshiba Corporation, was irradiated for 5 minutes ultraviolet rays. Then, it left still at 40 degreeC for 2 days, and obtained the double-sided adhesive tape of thickness 175 micrometers.

[Comparative Example 1]
70 parts of 2-ethylhexyl acrylate, 4.5 parts of acrylic acid, 0.1 part of 4-hydroxybutyl acrylate, 25 parts of a polymer having a weight average molecular weight of 760,000 based on 2-ethylhexyl acrylate, Ciba Specialty as a polymerization initiator Add 0.3 parts of “DAROCUR1173” manufactured by Chemical Co., Ltd. and 1.5 parts of “Coronate L-75” manufactured by Nippon Polyurethane Co., Ltd. (isocyanate-based crosslinking agent, solid content: 75%) as a cross-linking agent. After defoaming under conditions, it was coated on a 75 μm-thick PET film that had been subjected to mold release treatment, and then dried to a thickness of 175 μm, and then laminated with a 25 μm-thick PET film that had been mold-released. For the ultraviolet irradiation, “Chemical Lamp FL20SBL” manufactured by Toshiba was used, and ultraviolet irradiation was performed for 5 minutes. Then, it left still at 40 degreeC for 2 days, and obtained the double-sided adhesive tape of thickness 175 micrometers.

[Comparative Example 2]
70 parts of 2-ethylhexyl acrylate, 4.5 parts of acrylic acid, 0.1 part of 4-hydroxybutyl acrylate, 25 parts of a polymer having a weight average molecular weight of 760,000 based on 2-ethylhexyl acrylate, Ciba Specialty as a polymerization initiator Add 0.3 part of “DAROCUR1173” manufactured by Chemical Co., Ltd. and 0.1 part of “Coronate L-75” (isocyanate-based cross-linking agent, solid content: 75%) manufactured by Nippon Polyurethane Co., Ltd. as a cross-linking agent. After defoaming under conditions, it was coated on a 75 μm-thick PET film that had been subjected to mold release treatment, and then dried to a thickness of 175 μm, and then laminated with a 25 μm-thick PET film that had been mold-released. For the ultraviolet irradiation, “Chemical Lamp FL20SBL” manufactured by Toshiba was used, and ultraviolet irradiation was performed for 5 minutes. Then, it left still at 40 degreeC for 2 days, and obtained the double-sided adhesive tape of thickness 175 micrometers.

[Comparative Example 3]
A polymer having a weight average molecular weight of 1.06 million with a composition of 37 parts butyl acrylate, 25 parts 2-ethylhexyl acrylate, 1 part acrylic acid, 0.1 part 4-hydroxybutyl acrylate, butyl acrylate / 2-ethylhexyl acrylate = 3/1. 16 parts, 17 parts of a polymer having a weight average molecular weight of 5000 based on cyclohexyl methacrylate, 0.3 parts of “DAROCUR1173” manufactured by Ciba Specialty Chemicals as a polymerization initiator, and “Coronate L-75” manufactured by Nippon Polyurethane as a crosslinking agent “(Isocyanate-based crosslinking agent, solid content: 75%) 1.5 parts added, stirred for 15 minutes, degassed under vacuum conditions, and then dried on a 75 μm-thick PET film after release treatment 25 μm thick after the mold release treatment after coating to a thickness of 175 μm And laminated with a PET film, ultraviolet irradiation using a "chemical lamp FL20SBL" manufactured by Toshiba Corporation, was irradiated for 5 minutes ultraviolet rays. Then, it left still at 40 degreeC for 2 days, and obtained the double-sided adhesive tape of thickness 175 micrometers.

[Comparative Example 4]
A polymer having a mass average molecular weight of 1.06 million with a composition of 45 parts butyl acrylate, 15 parts 2-ethylhexyl acrylate, 3 parts acrylic acid, 0.1 part 4-hydroxybutyl acrylate, butyl acrylate / 2-ethylhexyl acrylate = 3/1. 18 parts, 19 parts of a polymer having a weight average molecular weight of 5000 based on cyclohexyl methacrylate, 0.3 parts of “DAROCUR1173” manufactured by Ciba Specialty Chemicals as a polymerization initiator, and “Coronate L-75” manufactured by Nippon Polyurethane as a crosslinking agent “(Isocyanate-based crosslinking agent, solid content: 75%) 1.5 parts added, stirred for 15 minutes, degassed under vacuum conditions, and then dried on a 75 μm-thick PET film after release treatment 25 μm thick after the mold release treatment after coating to a thickness of 175 μm It was laminated with a PET film, ultraviolet irradiation using the "chemical lamp FL20SBL" manufactured by Toshiba Corporation, and a double-sided adhesive tape was irradiated with 5 minutes UV. Then, it left still at 40 degreeC for 2 days, and obtained the double-sided adhesive tape of thickness 175 micrometers.

[Comparative Example 5]
70 parts of 2-ethylhexyl acrylate, 4.5 parts of acrylic acid, 0.1 part of 4-hydroxybutyl acrylate, 25 parts of a polymer having a weight average molecular weight of 760,000 based on 2-ethylhexyl acrylate, Ciba Specialty as a polymerization initiator Add 1.2 parts of “DAROCUR1173” manufactured by Chemical Co., Ltd. and 0.5 part of “Coronate L-75” (isocyanate-based cross-linking agent, solid content: 75%) manufactured by Nippon Polyurethane Co., Ltd. as a cross-linking agent. After defoaming under conditions, it was coated on a 75 μm-thick PET film that had been subjected to mold release treatment, and then dried to a thickness of 175 μm, and then laminated with a 25 μm-thick PET film that had been mold-released. For the ultraviolet irradiation, “Chemical Lamp FL20SBL” manufactured by Toshiba was used, and ultraviolet irradiation was performed for 5 minutes. Then, it left still at 40 degreeC for 2 days, and obtained the double-sided adhesive tape of thickness 125 micrometers.

[Comparative Example 6]
70 parts 2-ethylhexyl acrylate, 4.5 parts acrylic acid, 0.1 part 4-hydroxybutyl acrylate, 25 parts polymer having a weight average molecular weight of 760,000 based on 2-ethylhexyl acrylate, cyclohexyl methacrylate / acrylic acid = 20 parts of a polymer having a mass average molecular weight of 6600 with a composition of 97/3, 1.2 parts of “DAROCUR1173” manufactured by Ciba Specialty Chemicals as a polymerization initiator, and “Coronate L-75” (isocyanate type) manufactured by Nippon Polyurethane as a crosslinking agent After adding 0.5 parts (crosslinking agent, solid content: 75%), stirring for 15 minutes, defoaming under vacuum conditions, and release on a 75 μm thick PET film, the thickness after drying is 175 μm. And coated with a 25μm thick PET film after release. Te, ultraviolet irradiation using a "chemical lamp FL20SBL" manufactured by Toshiba Corporation, was irradiated for 5 minutes ultraviolet rays. Then, it left still at 40 degreeC for 2 days, and obtained the double-sided adhesive tape of thickness 175 micrometers.

(Evaluation of double-sided adhesive tape)
The following evaluation was performed about the double-sided tape created in Examples 1-5 and Comparative Examples 1-6, and the obtained result was shown to Tables 1-2.

(1) Measurement of dynamic viscoelasticity of pressure-sensitive adhesive layer Aged pressure-sensitive adhesive layer was laminated to a thickness of about 2 mm to obtain a test piece. A parallel plate having a diameter of 7.9 mm was attached to a viscoelasticity testing machine (ARES 2kSTD) manufactured by T.A. Instruments Japan, and the test piece was sandwiched with a compression load of 40 to 60 g. A temperature range of −60 to 100 ° C. was measured at a frequency of 1 Hz, and a temperature showing a maximum value (M 1) of loss tangent (tan δ) was measured.

(2) Gel fraction measurement The composition of the pressure-sensitive adhesive layer after aging is immersed in toluene, the mass after drying of the insoluble matter remaining after being allowed to stand at 23 ° C. for 24 hours is measured, and is expressed as a percentage of the original mass. expressed.

(3) Air bubble releasing properties Examples 1 to 5 and Comparative Examples 1 to 5 from a printing surface side to a glass plate with printing having a thickness of 0.5 mm, a length of 50 mm, a width of 40 mm, and a window frame shape of a thickness of 15 μm and a width of 5 mm. After pasting each double-sided adhesive tape of No. 6, it is bonded to a glass plate having a thickness of 0.5 mm, a length of 50 mm, and a width of 40 mm, and is heated and pressurized under conditions of 5 atm, 70 ° C. and 20 minutes. After performing and fixing, the presence or absence of bubbles was visually confirmed.
The evaluation criteria for the bubble releasing property were as follows.
○: No bubbles.
X: Air bubbles are present.

  Moreover, the presence or absence of air bubbles in the double-sided pressure-sensitive adhesive tapes of Example 1 and Comparative Example 2 was observed at a magnification of 50 times with an optical microscope “Powerscope KH-2700” manufactured by Hilox. The observation result of Example 1 is shown in FIG. 2, and the observation result of Comparative Example 2 is shown in FIG.

(4) Foam resistance After laminating each double-sided adhesive tape to a polyethylene terephthalate film (PET film) having a thickness of 25 μm, a length of 50 mm, and a width of 50 mm, this is 2.5 mm thick, 50 mm long, and wide. Affixed to a 50 mm polymethylmethacrylate plate (PMMA plate), fixed by heat and pressure treatment under conditions of 5 atm, 70 ° C., 20 minutes, and the configuration of the PET film / adhesive layer / PMMA plate layer A sample with was prepared. This sample was put in a heater at 85 ° C. for 500 hours to conduct a foam resistance test. After the foam resistance test, the presence or absence of bubbles was confirmed by visual observation.
The evaluation criteria for foam resistance were as follows.
○: No bubbles.
X: Air bubbles are present.

(5) Drop impact resistance test (DuPont impact resistance tester)
(I) Double-sided pressure-sensitive adhesive tapes having a length of 50 mm and a width of 40 mm were attached to a glass plate having a thickness of 0.5 mm, a length of 50 mm, and a width of 40 mm under 23 ° C. conditions.
(Ii) A glass plate with a double-sided adhesive tape of (i) was attached to a PC plate having a thickness of 2 mm, a length of 150 mm, and a width of 100 mm, and subjected to heat and pressure treatment at 5 atm, 70 ° C. for 20 minutes. Then, it left still at 23 degreeC for 1 hour.
(Iii) On the pedestal of the DuPont impact tester, the plate prepared in (ii) was allowed to stand so that the glass plate was on the lower side.
Next, a stainless steel strike core (tip diameter: 12.7 mm) having a diameter of 25 mm and a mass of 300 g was dropped from the top surface of the plate from a position having a height of 10 cm. An impact was applied to the central portion of the plate, and it was evaluated whether or not the glass plate attached to the side opposite to the surface to which the impact was applied dropped. When it did not fall off, the height of the hitting core was raised by 10 cm, an impact test was performed again, and finally the hitting height until dropping was measured. In addition, "50 <" was displayed when it did not fall even if it dropped from the height of 50cm.

(6) Total light transmittance After a double-sided pressure-sensitive adhesive tape is attached to a glass plate having a thickness of 0.5 mm, a length of 50 mm, and a width of 40 mm, this is formed into a glass having a thickness of 0.5 mm, a length of 50 mm, and a width of 40 mm. A sample having a structure of glass plate / adhesive layer / glass plate was prepared by bonding to a plate and fixing it by heating and pressing under conditions of 5 atm and 70 ° C. for 20 minutes. The total light transmittance was measured based on JIS K 7105 and JIS K 7136 of the sample using “HR-100 Model” manufactured by Murakami Color Research Laboratory.

  As shown in Tables 1 and 2 and FIGS. 2 to 3, the double-sided pressure-sensitive adhesive tapes of the present invention of Examples 1 to 5 can suppress the bubble-removability at the time of bonding and foaming with time after bonding, and are visually recognized. No bubbles were seen. Also, in the drop impact test, the member did not fall off, and it was clear that it was suitable for fixing a component provided with a step. On the other hand, in the double-sided pressure-sensitive adhesive tapes of Comparative Examples 1 to 6, it is difficult to suppress foaming at the time of bonding, and in the double-sided pressure-sensitive adhesive tapes of Comparative Examples 1, 2, 5, and 6, the generation of bubbles over time is also difficult. Many were confirmed.

It is a schematic sectional drawing of the image display panel which fixed the transparent panel which has a decoration part, and the image display apparatus using the double-sided adhesive sheet of this invention. It is an observation result with an optical microscope about the presence or absence of the bubble at the time of using the double-sided adhesive tape of Example 1. FIG. It is an observation result with an optical microscope about the presence or absence of the bubble at the time of using the double-sided adhesive tape of the comparative example 2. FIG.

Explanation of symbols

1: Transparent panel 2: Decoration part 3: Double-sided adhesive tape 4: Image display device

Claims (5)

A double-sided pressure-sensitive adhesive tape for sticking and fixing a transparent panel provided with a decorative portion on the surface of an image display device,
It consists of a pressure-sensitive adhesive layer formed by curing a photocurable pressure-sensitive adhesive composition containing a C1-C12 (meth) acrylic acid alkyl ester as a main component,
The loss tangent at 70 ° C. of the dynamic viscoelastic spectrum at a frequency of 1 Hz of the pressure-sensitive adhesive layer is 0.43 to 0.98, and the storage elastic modulus at 70 ° C. is 0.8 × 10 ^{4 to} 3.4 × 10. ⁴ Pa,
The pressure-sensitive adhesive layer has a maximum value of loss tangent in a temperature range of −40 to −10 ° C.,
A double-sided pressure-sensitive adhesive tape having a total thickness of 100 to 250 μm. The transparent panel provided with the decorative part is a transparent panel provided with a decorative part by printing or the like, and is used when fixing a transparent panel having a level difference of 5 to 30 μm from the decorative part. Double-sided adhesive tape. The double-sided pressure-sensitive adhesive tape according to claim 1 or 2, wherein a gel fraction represented by the following formula when the double-sided pressure-sensitive adhesive tape is immersed in toluene for 24 hours is 30 to 70%.
Gel fraction = [(mass after dipping toluene in double-sided pressure-sensitive adhesive tape) / (mass before dipping toluene in double-sided pressure-sensitive adhesive tape)] × 100 The double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive layer has a mass average molecular weight (Mw) of 300,000 to 1,500,000. The double-sided pressure-sensitive adhesive tape according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer has a total light transmittance in a visible light wavelength region of 90% or more and a haze of 1.0% or less.

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