Double-sided adhesive sheet and display device for touch panel including same

Abstract

The embodiment examples of the present invention relate to a double-sided adhesive sheet and a display device for a touch panel including the same. The double-sided adhesive sheet, according to the embodiment examples of the present invention, comprises a transparent acryl-based resin layer as a substrate, can provide a double-sided adhesive sheet which can be detached and recycled after attaching to the touch panel and a display device module, by means of the adhesive agent layers that are formed on both sides having different detaching force, can improve visibility of the display device by being coupled between the touch panel and the display device module for eliminating an air gap, and can minimize the difference in the bending rate of each layer of the double-sided adhesive sheet for eliminating visibility exhaustion as much as possible.

Claims

1. A double-sided adhesive sheet sequentially including a first adhesive layer, a transparent acrylic resin layer and a second adhesive layer, wherein each of the first adhesive layer and the second adhesive layer comprises an acrylic adhesive; the first adhesive layer is disposed to adjoin a touch panel; the second adhesive layer is disposed to adjoin a display device module; and adhesive strength between the first adhesive layer and the touch panel is higher than adhesive strength between the second adhesive layer and the display device module, wherein the first adhesive layer, the transparent acrylic resin layer and the second adhesive layer have an index of refraction ranging from 1.44 to 1.55, wherein the first adhesive layer has a 180 peel strength of 800 g/in to 3000 g/in with respect to a substrate at a peeling rate of 300 mm/min and a temperature of 23 C., and the second adhesive layer has a 180 peel strength of 0 to 80 g/in with respect to a polarizing film at a peeling speed of 300 mm/min and a temperature of 23 C., wherein the first adhesive layer has a thickness of 130 m to 180 m and the second adhesive layer has a thickness of 8 m to 20 m, and wherein the double-sided adhesive sheet has a total thickness of 100 m to 300 m.

2. The double-sided adhesive sheet according to claim 1, wherein the acrylic adhesive included in the first adhesive layer comprises an acrylate monomer having a C.sub.1-C.sub.12 alkyl group and a functional group-containing copolymerizable monomer, wherein the functional group-containing monomer is present in an amount of 5 wt % or more in the acrylic copolymer.

3. The double-sided adhesive sheet according to claim 1, wherein the acrylic adhesive included in the second adhesive layer comprises an acrylate monomer having a C.sub.1-C.sub.12 alkyl group and a functional group-containing copolymerizable monomer, wherein the functional group-containing monomer is present in an amount of 5 wt % or less in the acrylic copolymer.

4. The double-sided adhesive sheet according to claim 1, wherein the first adhesive layer is formed of a solventless adhesive and the second adhesive layer is formed of a solvent adhesive.

5. The double-sided adhesive sheet according to claim 1, wherein the second adhesive layer is formed of an acrylic monomer having at least one functional group selected from the group consisting of hydroxyl and amide functional groups.

6. The double-sided adhesive sheet according to claim 1, wherein the transparent acrylic resin layer has an optical transmittance of 92% or more.

7. The double-sided adhesive sheet according to claim 1, wherein at least one surface of the transparent acrylic resin layer adjoining the first adhesive layer or the second adhesive layer is subjected to at least one of primer treatment, corona treatment, plasma treatment, heat treatment, and hard coating treatment.

8. The double-sided adhesive sheet according to claim 1, wherein the double-sided adhesive sheet has a CIE lightness index L* value of 97 or more and a b* value of 0.5 or less, based on JIS Z 8729.

9. The double-sided adhesive sheet according to claim 1, wherein the double-sided adhesive sheet has a haze value of 1% or less.

10. A touch panel display device including: a touch panel; a display module; the double-sided adhesive sheet according to claim 1, disposed between the touch panel and the display module; the first pressure sensitive adhesive layer disposed between the touch panel and the display module and attached to a first side of the double-sided adhesive sheet; and the second pressure sensitive adhesive layer disposed between the touch panel and the display module and attached to a second side of the double-sided adhesive sheet, wherein the first adhesive layer of the double-sided adhesive sheet is bonded to an overall surface of the touch panel, the second adhesive layer of the double-sided adhesive sheet is bonded to an overall surface of the display device module, and the double-sided adhesive sheet is peelable and re-bondable with respect to the touch panel or the display device module.

11. A method of securing a touch panel type display device module, comprising: bonding the second adhesive layer of the double-sided adhesive sheet according to claim 1 to the display device module; and bonding the first adhesive layer of the double-sided adhesive sheet to the touch panel.

12. The double-sided adhesive sheet according to claim 1, wherein at least one surface of the transparent acrylic resin layer adjoining the first adhesive layer or the second adhesive layer is subjected to plasma treatment.

13. The double-sided adhesive sheet according to claim 1, wherein at least one surface of the transparent acrylic resin layer adjoining the first adhesive layer or the second adhesive layer is subjected to hard coating treatment.

14. The double-sided adhesive sheet according to claim 1, wherein the transparent acrylic resin layer is formed of at least one selected from the group consisting of methyl methacrylate, urethane acrylate, epoxy acrylate, silicone acrylate, ethylhexyl acrylate, butyl acrylate, ethyl acrylate, isobonyl acrylate, cyclohexyl methacrylate, glycidyl methacrylate, glycidyl acrylate, behenyl acrylate, ethyl acrylate, lauryl acrylate, stearyl acrylate, acrylic acid, hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, phenoxy acrylate, methylacrylate, and hexanediol diacrylate.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic sectional view of a conventional touch panel type display device;

(2) FIG. 2 is a schematic sectional view of a double-sided adhesive sheet in accordance with one embodiment of the present invention; and

(3) FIG. 3 is a schematic sectional view of a touch panel type display device in accordance with one embodiment of the present invention.

MODE FOR INVENTION

(4) The present invention will be described in more detail with reference to examples, and it should be understood that the following examples are provided for illustration only and are not to be construed in any way as limiting the scope of the present invention.

PREPARATIVE EXAMPLE 1

Preparation of First Adhesive Layer

(5) To prepare a first adhesive layer, 90 parts by weight of an ethylhexyl acrylate monomer and 10 parts by weight of an acrylic acid monomer were mixed in a 1 L reactor, and a heat initiator was added to the mixture, followed by heating the mixture to 60 C., thereby preparing a partially polymerized resin having a viscosity of 1000 to 5000 cps. Then, 1.0 part by weight of a photoinitiator (Irgacure 184) and 0.2 parts by weight of hexanediol diacrylate were mixed with the partially polymerized resin. Then, the mixture was coated on a PET release film and dried for 3 minutes under a fluorescent blacklight produced by Osram Sylvania Inc., thereby forming adhesive sheets having thicknesses of 130 m and 180 m, respectively.

PREPARATIVE EXAMPLE 2

Preparation of Second Adhesive Layer

(6) To prepare a second adhesive layer, 98 parts by weight of ethylhexyl acrylate and 2 parts by weight of hydroxy ethyl acrylate were mixed in ethyl acetate, and then a heat initiator was added to the mixture, followed by heating the mixture to 60 C., thereby preparing a polymer adhesive resin having a molecular weight of 500,000. Then, the polymer adhesive resin was mixed with 1.0 part by weight of a toluene diisocyanate curing agent, followed by coating the mixture on a PET release film by taking drying-induced reduction in thickness into account. Then, the prepared film was dried at 110 C. in a hot air oven for 1 minute, and left at 40 C. for 1 day, thereby preparing adhesive sheets having thicknesses of 8 m and 20 m, respectively.

PREPARATIVE EXAMPLE 3

Preparation of Transparent Acrylic Resin Layer

(7) To prepare a transparent acryl film as a base film, an urethane acrylate oligomer (molecular weight: 1000) and an isobonyl acrylate monomer were mixed in a ratio of 50:50, and 1.0 part by weight of a photoinitiator (Irgacure 184) was added to the mixture, which in turn was coated to thicknesses of 12 m, 50 m and 100 m on a PET release film and dried for 3 minutes under a fluorescent blacklight produced by Osram Sylvania Inc., thereby forming an acryl film.

COMPARATIVE PREPARATION EXAMPLE 1

Preparation of First Adhesive Layer

(8) To prepare a first adhesive layer, 80 parts by weight of an ethylhexyl acrylate monomer, 18 parts by weight of glycidyl methacrylate and 2 parts by weight of an acrylic acid monomer were mixed in a 1 L reactor, and a heat initiator was added to the mixture, followed by heating the mixture to 60 C., thereby preparing a partially polymerized resin having a viscosity of 1000 to 5000 cps. Then, 1.0 part by weight of a photoinitiator (Irgacure 184) and 0.2 parts by weight of hexanediol diacrylate were mixed with the partially polymerized resin. Then, the mixture was coated on a PET release film and dried for 3 minutes under a fluorescent blacklight produced by Osram Sylvania Inc., thereby forming an adhesive sheet having a thickness of 130 m.

COMPARATIVE PREPARATION EXAMPLE 2

Preparation of Second Adhesive Layer

(9) To prepare a second adhesive layer, 60 parts by weight of ethylhexyl acrylate, 30 parts by weight of silicone acrylate and 10 parts by weight of an acrylic acid monomer were mixed in ethyl acetate, and then a heat initiator was added to the mixture, followed by heating the mixture to 60 C., thereby preparing a polymer adhesive resin having a molecular weight of 500,000. Then, the polymer adhesive resin is mixed with 0.6 parts by weight of an aziridine curing agent having two functional groups, followed by coating the mixture on a PET release film by taking drying-induced reduction in thickness into account. Then, the prepared film was dried at 110 C. in a hot air oven for 1 minute, and left at 40 C. for 1 day, thereby preparing an adhesive sheet having a thickness of 20 m.

EXAMPLE 1

(10) A 180 m thick acrylic adhesive layer prepared in Preparative Example 1 was transferred to one side of a 50 m thick transparent acryl film prepared in Preparative Example 3 through roll lamination to form a first adhesive layer, and a 20 m thick acrylic adhesive layer prepared in Preparative Example 2 was transferred to the other side of the transparent acryl film through roll lamination to form a second adhesive layer, thereby preparing a double-sided adhesive sheet having a total thickness of 250 m.

EXAMPLE 2

(11) A double-sided adhesive sheet was prepared in the same manner as in Example 1 except that a 100 m thick transparent acryl film prepared in Preparative Example 3 was used to prepare a double-sided adhesive sheet having a total thickness of 300 m.

EXAMPLE 3

(12) A double-sided adhesive sheet was prepared in the same manner as in Example 1 except that a 12 m thick transparent acryl film prepared in Preparative Example 3, a 130 m thick first adhesive layer prepared in Preparative Example 1, and a 8 m thick second layer prepared in Preparative Example 2 were used to prepare a double-sided adhesive sheet having a total thickness of 150 m.

COMPARATIVE EXAMPLE 1

(13) Instead of using the transparent acryl film of Preparative Example 3, a 180 m thick first adhesive layer prepared in Preparative Example 1 and a 20 m thick second layer prepared in Preparative Example 2 were transferred through roll lamination, thereby preparing a double-sided adhesive sheet having a total thickness of 200 m.

COMPARATIVE EXAMPLE 2

(14) A double-sided adhesive sheet was prepared in the same manner as in Example 1 except that a 50 m thick polyethylene terephthalate (PET) film was used as the base film instead of using the transparent acryl film of Preparative Example 3.

COMPARATIVE EXAMPLE 3

(15) A double-sided adhesive sheet was prepared in the same manner as in Example 1 except that a 180 m thick first adhesive layer prepared in Comparative Preparation Example 1 was used as the first adhesive layer.

COMPARATIVE EXAMPLE 4

(16) A double-sided adhesive sheet was prepared in the same manner as in Example 2 except that a 20 m thick second adhesive layer prepared in Comparative Preparation Example 2 was used as the second adhesive layer.

EXPERIMENTAL EXAMPLE

Measurement of Physical Properties

(17) 1) Evaluation of Visibility

(18) In each of the double-sided adhesive sheets prepared in Examples 1 to 3 and Comparative Examples 1 to 4, the indices of refraction of the first adhesive layer, the transparent acrylic resin layer and the second adhesive layer were measured (using an Abbe Refractometer) and differences therebetween were analyzed to evaluate improvement in visibility through suppression of optical distortion. Good improvement in visibility is indicated by O, normal improvement in visibility is indicated by , and insufficient improvement in visibility is indicated by X.

(19) 2) Measurement of Peel Strength

(20) For each of the double-sided adhesive sheets prepared in Examples 1 to 3 and Comparative Examples 1 to 4, one side of the adhesive sheet facing the first adhesive layer was bonded to an about 1 mm thick polycarbonate film by reciprocating a 2 kg roller twice to prepare a specimen, which in turn was subjected to measurement of peel strength, and the other side of the adhesive sheet facing the second adhesive layer was bonded to a triacetylcellulose (TAC) polarizing film in the same manner to prepare a specimen, which in turn was subjected to measurement of peel strength.

(21) 180 peel strength was measured by peeling the double-sided adhesive sheet from the polycarbonate and TAC films at 23 C. and at a peeling rate of 300 mm/min and a peeling angle of 180 using a small tensile tester (Texture Analyzer, TA instrument). Results are shown in Table 1.

(22) 3) Evaluation of Reworkability (Repeelability)

(23) For each of the double-sided adhesive sheets prepared in Examples 1 to 3 and Comparative Examples 1 to 4, one side of the adhesive sheet facing the first adhesive layer was bonded to an about 1 mm thick polycarbonate film by reciprocating a 2 kg roller twice and the other side of the adhesive sheet facing the second adhesive layer was bonded to an about 1 mm thick glass surface on a triacetylcellulose (TAC) polarizing film, followed by complete removal of bubbles from the specimen in an autoclave at 60 C. and 5 atm. for 30 minutes.

(24) Then, the specimen was left in an oven at 60 C. for 1 minute, and within 1 minute after removing the specimen from the oven, whether the second adhesive layer could be naturally separated from the specimen by hand was determined Easy separation is indicated by , normal separation is indicated by , and difficult separation is indicated by . Results are shown in Table 1.

(25) 4) Measurement of CIE L*a*b* Color System

(26) After attaching the adhesive sheet onto a 1.1 mm thick soda lime glass using SHIMADZU 3700N and removing the PET release film, the color system was measured. For measurement, each sample had a size of 10 cm10 cm and an average value was obtained by measuring at 5 points on the sample.

(27) 5) Measurement of Haze

(28) A haze value (%) of each of the double-sided adhesive sheets prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured using a Haze-Gard plus device produced by BYK Gardner Inc., according to ASTM D1003. Results are shown in Table 2.

(29) 6) Measurement of Optical Transmittance (Ts)

(30) Optical transmittance was measured in an optical transmittance mode according to the same method as in measurement of the color system.

(31) TABLE-US-00001 TABLE 1 180 180 Index of Index of peel peel Index of refraction refraction strength of strength of refraction of first of second first second Base of base adhesive adhesive adhesive adhesive film film layer layer Visibility layer (g/in) layer (g/in) Reworkability Ex. 1 Acryl 1.49 1.48 1.46 1250 10 Ex. 2 Acryl 1.49 1.46 1.45 1107 5 Ex. 3 Acryl 1.49 1.48 1.46 965 5 Com. 1.48 1.46 X 3865 90 Ex. 1 Com. PET 1.62 1.48 1.45 X 706 89 Ex. 2 Com. Acryl 1.49 1.57 1.46 3209 65 X Ex. 3 Com. Acryl 1.49 1.48 1.42 2252 176 X Ex. 4

(32) TABLE-US-00002 TABLE 2 Ts (%) Haze (%) L* a* b* Ex. 1 93.5 0.99 97.3 0.03 0.26 Ex. 2 94.8 0.68 97.5 0.04 0.15 Ex. 3 93.1 0.86 98.1 0.02 0.33 Com. Ex. 1 94.9 0.65 95.2 0.01 0.19 Com. Ex. 2 89.5 1.56 97.0 0.03 0.68 Com. Ex. 3 92.4 1.01 96.8 0.01 0.45 Com. Ex. 4 91.6 1.15 96.9 0.03 0.46

(33) From the results of the experimental results for examples and comparative examples, it can be seen that the double-sided adhesive sheets according to the examples of the present invention exhibit superior reworkability to the double-sided adhesive sheets prepared in the comparative examples, and had a minimized difference in index of refraction between the first adhesive layer, the transparent acrylic resin layer and the second adhesive layer and thus did not deteriorate optical characteristics of the display device.

(34) Although some embodiments have been described herein, it will be understood by those skilled in the art that these embodiments are provided for illustration only, and various modifications, changes, alterations and equivalent embodiments can be made without departing from the scope of the present invention. Therefore, the scope and sprit of the present invention should be defined only by the accompanying claims and equivalents thereof.