INTERLAYER FILLER MATERIAL FOR TOUCH PANELS, AND TOUCH PANEL LAMINATE

Abstract

The present invention aims to provide an interlayer filling material for a touch panel which is used for filling an interlayer space between a touch panel and another component or an interlayer space between transparent conductive films included in the touch panel in production of a personal digital assistant and enables production of a touch panel laminate that is less likely to suffer cracks or breakage in a surface protection panel or a glass substrate. The present invention also aims to provide a touch panel laminate produced using the interlayer filling material for a touch panel. The present invention relates to an interlayer filling material for a touch panel used for filling an interlayer space between a touch panel and another component, or at least one interlayer spaces included in the touch panel between transparent conductive films, between a glass sheet and one of the transparent conductive films, between a glass sheet and another glass sheet, between a glass sheet and a polarizing film, between a substrate and a glass sheet, between a substrate and one of the transparent conductive films, and between a substrate and a polarizing film, the interlayer filling material containing: a polyvinyl acetal; and a plasticizer, the interlayer filling material having a flexural modulus at 25 C. of 2.410.sup.9 Pa or higher.

Claims

1. An interlayer filling material for a touch panel used for filling an interlayer space between a touch panel and another component, or at least one interlayer spaces included in the touch panel between transparent conductive films, between a glass sheet and one of the transparent conductive films, between a glass sheet and another glass sheet, between a glass sheet and a polarizing film, between a substrate and a glass sheet, between a substrate and one of the transparent conductive films, and between a substrate and a polarizing film, the interlayer filling material comprising: a polyvinyl acetal; and a plasticizer, the interlayer filling material having a flexural modulus at 25 C. of 2.410.sup.9 Pa or higher.

2. The interlayer filling material for a touch panel according to claim 1, wherein the polyvinyl acetal is polyvinyl butyral.

3. The interlayer filling material for a touch panel according to claim 1, wherein the amount of the plasticizer relative to 100 parts by weight of the polyvinyl acetal is 1 to 30 parts by weight.

4. The interlayer filling material for a touch panel according to claim 1, further comprising: a reactive diluent; and a photopolymerization initiator.

5. The interlayer filling material for a touch panel according to claim 4, wherein the reactive diluent is a (meth)acrylic reactive diluent, an epoxy reactive diluent, or a silicone reactive diluent.

6. The interlayer filling material for a touch panel according to claim 4, wherein the amount of the reactive diluent relative to 100 parts by weight of the polyvinyl acetal is 0.1 to 30 parts by weight.

7. A touch panel laminate comprising: a touch panel comprising transparent conductive films; and the interlayer filling material for a touch panel according to claim 1, the interlayer filling material for a touch panel filling at least one interlayer space selected from the group consisting of an interlayer space between a surface protection panel and the touch panel, an interlayer space between the touch panel and a polarizing film, and interlayer spaces included in the touch panel between transparent conducive films, between a glass sheet and one of the transparent conducive films, between a glass sheet and another glass sheet, between a glass sheet and a polarizing film, between a substrate and a glass sheet, between a substrate and one of the transparent conducive films, and between a substrate and a polarizing film.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0073] FIG. 1 is a cross-sectional view schematically illustrating an exemplary application of the interlayer filling material for a touch panel of the present invention.

DESCRIPTION OF EMBODIMENTS

[0074] Embodiments of the present invention will be specifically described in the following with reference to, but not limited to, the examples.

<Preparation of Polyvinyl Butyral>

[0075] A reactor equipped with a stirrer was charged with 2,700 mL of ion exchange water and 300 g of polyvinyl alcohol having an average degree of polymerization of 1,700 and a degree of saponification of 99.3 mol %, and the contents were heated with stirring to be dissolved, thereby preparing a solution. To the obtained solution was added as a catalyst 35% by weight hydrochloric acid such that the hydrochloric acid concentration was set to 0.2% by weight. The temperature of the mixture was adjusted to 15 C., and 21 g of n-butyraldehyde (n-BA) was added thereto with stirring. Then, 145 g of n-butyraldehyde (n-BA) was further added, so that a polyvinyl butyral resin in the form of white particles was precipitated. Fifteen minutes after the precipitation, 35% by weight hydrochloric acid was added such that the hydrochloric acid concentration was set to 1.8% by weight. The mixture was heated to 50 C. and aged at 50 C. for two hours. After cooling and neutralization of the solution, the polyvinyl butyral resin was washed with water and then dried, thereby preparing polyvinyl butyral 1 (PVB 1).

[0076] The obtained PVB 1 had an average degree of polymerization of 1,700, a hydroxy group content of 31.3 mol %, an acetyl group content of 0.7 mol %, and a degree of butyralization (Bu degree) of 68.0 mol %.

[0077] Further, polyvinyl butyral 2 (PVB 2) to polyvinyl butyral 5 (PVB 5) were prepared by selecting the type of polyvinyl alcohol as a raw material and setting the conditions for butyralization.

[0078] Table 1 shows each polyvinyl butyral obtained.

TABLE-US-00001 TABLE 1 PVB 1 PVB 2 PVB 3 PVB 4 PVB 5 Hydroxy group 31.3 31.3 31.3 31.3 31.3 content (mol %) Butyralization 68.0 68.0 68.0 68.0 68.0 degree (mol %) Acetyl group 0.7 0.7 0.7 0.7 0.7 content (mol %) Average degree 1700 850 650 250 2500 of polyemrization

Example 1

[0079] To 100 parts by weight of PVB 1 was added 15 parts by weight of triethylene glycol-di-2-ethylhexanoate (3GO) as a plasticizer, and the mixture was sufficiently kneaded, thereby preparing an interlayer filling material for a touch panel.

[0080] The obtained interlayer filling material for a touch panel was pressed between mold release-treated surfaces of mold release polyethylene terephthalate (PET) films each with a thickness of 50 m under the conditions of 120 C. and 10 MP to have a thickness of 200 m, and further pressurized with a press machine under the conditions of 20 C. and 10 MPa to be cooled. Thus, an evaluation sample having a mold release PET film attached to each surface was obtained.

[0081] The obtained evaluation sample was cut to a size of 70 mm in width100 mm in length, and attached to a glass of 0.7 mm (70 mm in width100 mm in length0.2 mm in thickness). A liquid crystal panel (3 mm) was placed on the other surface of the evaluation sample on the side opposite the surface where the glass was attached. They were attached to each other using a vacuum laminator under the conditions of 100 Pa and 75 C. The resulting laminate was further pressure-bonded in an autoclave under the conditions of 75 C. and 0.5 MPa for 30 minutes, thereby preparing an evaluation sample.

[0082] The flexural modulus at 25 C. of the obtained evaluation sample was measured by the method A of JIS-K7171 under the conditions of the loading speed of 500 ram/min and the distance between the fulcrums of 50 mm. The load and displacement were measured using Tensilon UTA-500 available from Orientec Co., Ltd.

Examples 2 to 5, Comparative Examples 1 to 3

[0083] An interlayer filling material for a touch panel was prepared in the same manner as in Example 1 except that the type of the polyvinyl butyral and the amount of the plasticizer were changed as shown in Tables 2 or 3. Using the obtained interlayer filling material for a touch panel, the flexural modulus at 25 C. was measured.

Example 6

[0084] To 100 parts by weight of PVB 1 were added 25 parts by weight of triethylene glycol-di-2-ethylhexanoate (3GO) as a plasticizer and 4 parts by weight of trimethylolpropane triacrylate (TMPA) as a reactive diluent. The mixture was sufficiently stirred, thereby obtaining a mixture composition. The mixture composition was sufficiently mixed with benzophenone (BP) as a photopolymerization initiator in an amount of 1 part by weight relative to 100 parts by weight of the reactive diluent, thereby obtaining an interlayer filling material for a touch panel.

[0085] The obtained interlayer filling material for a touch panel was applied to a mold release-treated surface of a mold release polyethylene terephthalate (PET) film with a thickness of 50 m to have a thickness of 800 m. On the obtained interlayer filling material layer was placed another mold release PET film in such a manner that the mold release-treated surface thereof was in contact with the interlayer filling material layer, thereby preparing a laminate. The resulting sheet was left to stand at 23 C. for five days to give an evaluation sample having a mold release PET film attached to each surface.

[0086] The evaluation sample was irradiated with light at a wavelength of 365 nm and a dose of 4,000 mJ/cm.sup.2 using an ultra-high pressure mercury lamp.

[0087] The flexural modulus (after irradiation with light) at 25 C. of the evaluation sample after irradiation with light was measured in the same manner as in Example 1.

Examples 7 to 11, Comparative Example 4

[0088] An interlayer filling material for a touch panel was prepared in the same manner as in Example 6 except that the composition was set as shown in Tables 2 or 3, and the flexural modulus (after irradiation with light) at 25 C. thereof was measured.

Comparative Example 5

(1) Preparation of an Acrylic Copolymer

[0089] An amount of 65.0 parts by weight of n-butyl acrylate, 26.0 parts by weight of methyl methacrylate, 4.0 parts by weight of ethyl acrylate, 1.0 part by weight of hydroxy ethyl acrylate, 4.0 parts by weight of acrylic acid, and 0.2 parts by weight of 2,2-azobisisobutyronitrile as a polymerization initiator were dissolved in 100 parts by weight of ethyl acetate in a reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas inlet. After the air inside the reaction vessel was substituted with nitrogen, the solution was polymerized at 80 C. for eight hours to give an acrylic copolymer.

[0090] The obtained acrylic copolymer was diluted with tetrahydrofuran (THF) by a factor of 50 times. The resulting diluted solution was passed through a filter (material: polytetrafluoroethylene, pore size: 0.2 m) to prepare a measurement sample. The obtained measurement sample was placed in a gel permeation chromatograph (produced by Waters, 2690 Separations Model) and subjected to GPC measurement under the conditions of a sample flow rate of 1 ml/min and a column temperature of 40 C. The molecular weight of the acrylic copolymer in terms of polystyrene was thus determined. Based on the measurement result, the weight average molecular weight (Mw) was obtained. The obtained acrylic copolymer had a weight average molecular weight of 650,000.

[0091] The column used was GPC LF-804 (Showa Denko K.K.) and the detector used was a differential refractometer.

(2) Preparation of an Interlayer Filling Material for a Touch Panel

[0092] An amount of 100 parts by weight of the obtained acrylic copolymer was diluted with ethyl acetate to give an adhesive solution with a resin solid content of 45%. An amount of 100 parts by weight of the adhesive solution was blended with 1 part by weight of an isocyanate crosslinking agent (produced by Nippon Polyurethane Industry Co., Ltd., Coronate L-45, solid content: 45%), stirred for 15 minutes, applied to a mold release-treated surface of a mold release PET film with a thickness of 50 m to a dry thickness of 200 m, and dried at 80 C. for 15 minutes. On the obtained adhesive layer was placed another mold release PET film in such a manner that the mold release-treated surface thereof was in contact with the adhesive layer, thereby preparing a laminate. The resulting sheet was left to stand at 23 C. for five days to give an interlayer filling material for a touch panel (thickness: 200 m) having a mold release PET film attached to each surface.

(Evaluation)

[0093] The interlayer filling materials for a touch panel obtained in the examples and comparative examples were evaluated by the following methods.

[0094] Tables 2 and 3 show the results. In Tables 2 and 3, the number of parts of the photopolymerization initiator is a value relative to 100 parts by weight of the reactive diluent.

(1) Evaluation of Adhesiveness

[0095] The interlayer filling material for a touch panel was cut to a size of 25 mm100 mm and attached to glass. A plasma-treated polyethylene terephthalate (PET) film (25 mm100 mm) was attached thereto and the laminate was vacuum-laminated at 25 C., followed by pressure bonding with heat in an autoclave at 75 C. and 0.5 MPa for 30 minutes. An evaluation sample was thus prepared.

[0096] The obtained evaluation sample was subjected to 180 peel test at 300 ram/min in conformity with JIS K 6854:1994. The case where the peel strength was 5 N/25 mm or more was rated o (Good) and the case where the peel strength was less than 5 N/25 mm was rated x (Poor).

(2) Evaluation of Impact Resistance

[0097] The interlayer filling material for a touch panel was attached to a tempered glass sheet with a size of 10 cm7.0 cm and a thickness of 0.7 mm. To the other surface of the interlayer filling material for a touch panel was attached a corona-treated polycarbonate sheet with a size of 10 cm7.0 cm and a thickness of 3 mm, thereby preparing a tempered glass/interlayer filling material for a touch panel/polycarbonate laminate. This laminate was treated in an autoclave at 75 C. and 0.5 MPa for 30 minutes.

[0098] The laminates obtained using the interlayer filling materials of Examples 6 to 11 and Comparative Example 4 were irradiated with light having a wavelength of 365 nm at a dose of 4,000 mJ/cm.sup.2 using an ultra-high pressure mercury lamp.

[0099] The obtained laminate was fixed in a stainless-steel frame (inner size: 60 cm90 cm), and an iron ball (240 g) was dropped to the central portion of the laminate from the height of 100 cm in an environment of 23 C. The laminate having no cracks after the dropping was rated o (Good) and the laminate having cracks after the dropping was rated x (Poor).

TABLE-US-00002 TABLE 2 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Polyvinyl acetal Type PVB1 PVB1 PVB1 PVB2 PVB2 PVB1 Degree of 1700 1700 1700 850 850 1700 polymerization Number of parts 100 100 100 100 100 100 (parts by weight) Plasticizer Type 3GO 3GO 3GO 3GO 3GO 3GO Number of parts 15 20 30 15 25 25 (parts by weight) Reactive diluent Type TMPA Number of parts 4 (parts by weight) Photopolymerization Type BP initiator Number of parts 1 (parts by weight) Flexural modulus at Without irradiation 4.6 10.sup.9 3.7 10.sup.9 2.4 10.sup.9 3.9 10.sup.9 2.5 10.sup.9 25 C. (Pa) with light After irradiation 3.6 10.sup.9 with light Evaluation Adhesiveness Impact resistance Example 7 Example 8 Example 9 Example 10 Example 11 Polyvinyl acetal Type PVB1 PVB2 PVB2 PVB3 PVB4 Degree of 1700 850 850 650 250 polymerization Number of parts 100 100 100 100 100 (parts by weight) Plasticizer Type 3GO 3GO 3GO 3GO 3GO Number of parts 30 12 20 12 10 (parts by weight) Reactive diluent Type TMPA TMPA TMPA TMPA TMPA Number of parts 4 4 8 4 15 (parts by weight) Photopolymerization Type BP BP BP BP BP initiator Number of parts 1 1 1 1 1 (parts by weight) Flexural modulus at Without irradiation 25 C. (Pa) with light After irradiation 2.4 10.sup.9 5.3 10.sup.9 4.0 10.sup.9 5.6 10.sup.9 5.9 10.sup.9 with light Evaluation Adhesiveness Impact resistance * Number of parts of photopolymerization initiator is a value relative to 100 parts by weight of reactive diluent

TABLE-US-00003 TABLE 3 Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Polyvinyl acetal Type PVB1 PVB2 PVB5 PVB4 Acrylic Degree of 1700 850 2500 250 copolymer polymerization Number of parts 100 100 100 100 (parts by weight) Plasticizer Type 3GO 3GO 3GO 3GO Number of parts 40 40 60 35 (parts by weight) Reactive diluent Type TMPA Number of parts 0.05 (parts by weight) Photopolymerization Type BP initiator Number of parts 1 (parts by weight) Flexural modulus at Without irradiation 2.1 10.sup.9 1.9 10.sup.9 1.7 10.sup.9 1.4 10.sup.9 25 C. (Pa) with light After irradiation 1.0 10.sup.9 with light Evaluation Adhesiveness Impact resistance X X X X X * Number of parts of photopolymerization initiator is a value relative to 100 parts by weight of reactive diluent

INDUSTRIAL APPLICABILITY

[0100] The present invention can provide an interlayer filling material for a touch panel which is used for filling an interlayer space between a touch panel and another component or an interlayer space between transparent conductive films included in the touch panel in production of a personal digital assistant and enables production of a touch panel laminate that is less likely to suffer cracks or breakage in a surface protection panel or a glass substrate. The present invention can also provide a touch panel laminate produced using the interlayer filling material for a touch panel.

REFERENCE SIGNS LIST

[0101] 1: Interlayer filling material for a touch panel of the present invention [0102] 2: Touch panel [0103] 3: Surface protection panel [0104] 4: Polarizing film [0105] 5: Decorative printing portion