JP4650003B2 - Transparent composite sheet and display element substrate using the same - Google Patents

Description

  The present invention relates to an optical sheet having a small linear expansion coefficient, excellent optical characteristics, and capable of replacing glass, and to a display element substrate using the same.

  In general, glass plates are widely used as display element substrates (particularly active matrix type) for liquid crystal display elements and organic EL display elements, color filter substrates, solar cell substrates and the like. However, in recent years, plastic materials have been studied as an alternative to glass plates because they are easily broken, cannot be bent, have a large specific gravity, and are not suitable for weight reduction.

  For example, Patent Documents 1 and 2 describe a transparent resin substrate for a liquid crystal display element comprising a cured product obtained by curing an epoxy resin composition containing an epoxy resin, an acid anhydride curing agent and a curing catalyst. . However, these conventional plastic materials for glass substitutes have a larger coefficient of linear expansion than glass plates, and particularly when used for active matrix display element substrates, problems such as warping and disconnection of aluminum wiring occur in the manufacturing process. It is difficult to use. Accordingly, there is a need for a plastic material having a low linear expansion coefficient while satisfying the transparency, solvent resistance, liquid crystal resistance, heat resistance, etc. required for display element substrates, particularly active matrix display element substrates.

  In order to reduce the linear expansion coefficient, various composites of materials in which an inorganic filler such as glass powder or glass fiber is mixed with a resin have been conventionally performed. However, since these resins and inorganic fillers have different refractive indexes, the light transmitted through the resin is irregularly refracted, and the transparency of the base material in the composite material is often impaired. Accordingly, various studies have been made to make the refractive index of the resin and the inorganic filler transparent. For example, Patent Document 3 discloses a light-transmitting epoxy resin composition comprising a filler having substantially the same refractive index as that of an epoxy resin cured with an acid anhydride. Various epoxy resin compositions that have been made transparent by combining them have been reported.

  Moreover, the biggest problem in the transparent composite composition comprising the composite of the transparent resin and the inorganic filler as described above is the micro-level optical anisotropy inside the composite. In the composite material, since the thermal expansion coefficient differs between the resin and the filler, micro level internal stress is generated at the interface, and as a result, molecular orientation occurs inside the resin due to the stress, resulting in micro level optical anisotropy. It is difficult to apply a substrate having optical anisotropy to a liquid crystal display element, particularly a liquid crystal display element that requires very fine pixels.

JP-A-6-337408 JP-A-7-120740 JP-A-4-236217

  An object of the present invention is to provide a transparent composite sheet having a small linear expansion coefficient, excellent in transparency and heat resistance, and having reduced optical anisotropy due to internal stress generated in the composite material, which can be substituted for glass. There is.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have made a transparent composite sheet comprising a transparent resin (a) and an inorganic filler (b), and the volume hardening shrinkage of the transparent resin (a) is 5% or less. However, since the internal stress generated in the material due to shrinkage due to curing is small, the optical anisotropy is small, the rigidity is low with a low linear expansion coefficient, and it is excellent in transparency, heat resistance and solvent resistance. It is found to be suitably used for optical sheets such as liquid crystal display element substrates, organic EL display element substrates, color filter substrates, touch panel substrates, solar cell substrates, transparent plates, optical lenses, optical elements, and optical waveguides. The present invention has been reached.

That is, the present invention comprises (1) a transparent composite sheet comprising a transparent resin (a) and an inorganic filler (b), and the volume hardening shrinkage of the transparent resin (a) is 5% or less,
(2) The transparent composite sheet according to (1), wherein the transparent resin (a) contains an epoxy resin,
(3) The transparent composite sheet according to (2), wherein the epoxy resin contains an alicyclic epoxy resin represented by the following chemical formula (1):
(In the formula, X represents —CH ₂ —, —CH (CH ₃ ) —, or — (CH ₃ ) ₂ —).
(4) The transparent composite sheet according to (2), wherein the epoxy resin contains an alicyclic epoxy resin represented by the following chemical formula (2):
(5) The transparent composite sheet according to (2) to (4), which contains a cationic curing catalyst (d) as a curing agent for the epoxy resin,
(6) The transparent composite sheet of (1) to (5), wherein the difference between the refractive index after curing of the transparent resin (a) and the refractive index of the inorganic filler (b) is 0.01 or less,
(7) The transparent composite sheet according to (1) to (6), wherein the Abbe number after curing of the transparent resin (a) is 45 or more,
(8) The transparent composite sheet according to (1) to (7), wherein the inorganic filler (b) includes a glass fiber cloth,
(9) The transparent composite sheet according to (1) to (8), wherein the light transmittance at a wavelength of 550 nm is 80% or more,
(10) The transparent composite sheet according to (1) to (9), wherein an average linear expansion coefficient at 30 to 150 ° C. is 40 ppm or less,
(11) A display element substrate comprising the transparent composite sheet of (1) to (10),
It is.

Hereinafter, the present invention will be described in detail.
The volume hardening shrinkage of the transparent resin (a) in the transparent composite sheet of the present invention needs to be 5% or less. Preferably it is 4% or less, more preferably 3% or less, and most preferably 2% or less. The volume cure shrinkage referred to here is a volume shrinkage calculated from the specific gravity of the uncured resin at normal temperature and the specific gravity of the cured resin at normal temperature. When a resin and a filler are combined and cured and then returned to room temperature, generally a tensile stress is applied to the resin and a compressive stress is applied to the filler. This internal stress causes molecular orientation inside the resin, resulting in micro optical anisotropy in the material. The present inventors have found that the smaller the internal stress generated in the material, the smaller the optical anisotropy resulting therefrom, and in order to reduce the optical anisotropy, the volume hardening shrinkage of the resin can be reduced. It is important, and when this value is not more than the upper limit value, it has been found that a transparent composite sheet suitably used for an optical sheet, a transparent plate, an optical lens, an optical element, an optical waveguide and the like can be provided.

  The transparent resin (a) used in the present invention is not particularly limited as long as the volume hardening shrinkage is 5% or less. Examples of transparent resins having a volume hardening shrinkage of 5% or less include thermosetting resins such as epoxy resins and oxetane resins and photocurable resins. An alicyclic epoxy resin is preferred, and among them, an alicyclic epoxy resin represented by the general formula (1) or an alicyclic epoxy resin represented by the general formula (2) (bicyclohexyl 3,3 ′ dioxide) This is particularly preferable because the volume hardening shrinkage is small.

(In the formula, X represents —CH ₂ —, —CH (CH ₃ ) —, or — (CH ₃ ) ₂ —).

  The curing agent for the epoxy resin used in the present invention is not particularly limited as long as the volume curing shrinkage is 5% or less, but a cationic curing catalyst (d) is preferable because a cured product having high heat resistance is obtained. . Examples of the cationic curing catalyst (d) include an initiator that releases a substance that initiates cationic polymerization by heating and an initiator that releases a substance that initiates cationic polymerization by active energy rays. In particular, an initiator that releases a substance that initiates cationic polymerization upon heating, that is, a thermal cationic curing catalyst, is preferable because a product is obtained.

  Preferred thermal cation curing catalysts include aromatic sulfonium salts, aromatic iodonium salts, aluminum chelates and the like. Specific examples include aromatic sulfonium salts such as SI-60L, SI-80L, SI-100L manufactured by Sanshin Chemical Industry, CP-66, CP-77 manufactured by Asahi Denka Kogyo Co., Ltd. Is Daicel Chemical Industries' DAICAT EX-1.

  The transparency of the transparent resin (a) of the present invention is preferably such that the light transmittance at 550 nm when formed into a sheet is 80% or more, more preferably 85% or more, and most preferably 90% or more. When used as a display element substrate, 85% or more is preferable.

  The transparent resin (a) used in the present invention is desirable for maintaining excellent transparency that the Abbe number after curing is 45 or more. The Abbe number is a parameter indicating the wavelength dependence of the refractive index. The larger this value, the smaller the wavelength dependence of the refractive index. For inorganic materials such as glass, the Abbe number is relatively large, and for organic materials such as plastic, it is relatively small. In order to maintain transparency in any wavelength region in the transparent composite substrate, it is necessary to match the wavelength dependence of the refractive indexes of the transparent resin and the glass filler as much as possible. Since it is technically difficult to reduce the Abbe number of glass, it has been found that it is sometimes necessary to bring the Abbe numbers closer to each other by increasing the Abbe number of the transparent resin. When a transparent resin having an Abbe number of less than 45 is used, the transparency of the transparent composite resin may be inferior.

  Examples of the inorganic filler (b) used in the present invention include glass fiber cloth such as glass fiber, glass cloth, and glass nonwoven fabric. Among them, glass cloth is most preferable because it has a high effect of reducing the linear expansion coefficient. Although the thickness of a fiber is not specifically limited, It is preferable that it is 30-300 micrometers. Examples of the glass include E glass, C glass, A glass, S glass, D glass, NE glass, and T glass. Among them, E glass, S glass, T glass, and NE glass with few alkali metals are preferable. The refractive index of the fibrous inorganic filler (b) is not particularly limited, but in order for the transparent composite sheet to exhibit excellent transparency, the difference from the refractive index after curing of the transparent resin (a) is 0.01 or less. Desirably, 0.005 or less is more preferable.

  When the composite transparent sheet of the present invention is used as a transparent plate, an optical lens, a liquid crystal display element plastic substrate, a color filter substrate, an organic EL display element plastic substrate, a solar cell substrate, a touch panel, an optical element, an optical waveguide, etc. The light transmittance at a wavelength of 550 nm is preferably 80% or more, and more preferably 85% or more. When the light transmittance at a wavelength of 550 nm is less than the lower limit value, the efficiency of using light is lowered, which is not preferable for applications where light efficiency is important.

  When the transparent composite sheet of the present invention is used as a transparent plate, an optical lens, a liquid crystal display element plastic substrate, a color filter substrate, an organic EL display element plastic substrate, a solar cell substrate, a touch panel, an optical element, an optical waveguide, etc. The average linear expansion coefficient at 30 to 150 ° C. is preferably 40 ppm or less, more preferably 30 ppm or less, and most preferably 20 ppm or less. For example, when this composite composition is used for an active matrix display element substrate, if this upper limit is exceeded, problems such as warpage and disconnection of aluminum wiring may occur in the manufacturing process.

  There is no limitation on the molding method of the transparent composite sheet in the present invention, for example, a method in which a transparent resin and a glass filler are directly mixed, cast into a required mold and then cross-linked to form a sheet, and the resin is dissolved in a solvent and glass Examples include a method in which a filler is dispersed and cast and then cross-linked to form a sheet, a method in which an epoxy resin is impregnated into glass cloth or a glass nonwoven fabric, and then cross-linked to form a sheet.

  In the present invention, as the inorganic filler and the resin are in close contact with each other, the transparency of the composite sheet of the present invention is improved. Therefore, the surface of the inorganic filler is treated with a known surface treatment agent such as a silane coupling agent. It is preferable. Examples of the silane coupling agent include an epoxy silane coupling agent, a titanate coupling agent, an aminosilane coupling agent, and a silicone oil type coupling agent. These may be used alone or in combination. Good.

  The transparent composite sheet of the present invention may be provided with a resin coating layer on both sides in order to improve smoothness. The resin to be coated preferably has excellent transparency, heat resistance and chemical resistance, and specific examples include polyfunctional acrylates and epoxy resins. As thickness of resin to coat, 0.1-50 micrometers is preferred and 0.5-30 micrometers is more preferred.

The transparent composite sheet of the present invention may be provided with a gas barrier layer or a transparent electrode layer against water vapor or oxygen as necessary.
In the transparent composite sheet of the present invention, if necessary, a small amount of antioxidant, ultraviolet absorber, dye / pigment, and the like, as long as the properties such as transparency, solvent resistance and heat resistance are not impaired. It may contain a filler such as an inorganic filler.

  Hereinafter, the contents of the present invention will be described in detail by way of examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

Example 1
A NE glass-based glass cloth (NEA2319E manufactured by Nittobo Co., Ltd.) having a thickness of 80 μm and a refractive index of 1.51 was baked to remove organic substances, and then treated with glycidoxypropyltrimethoxysilane (epoxysilane). On this glass cloth, 75 parts by weight of hydrogenated biphenyl type alicyclic epoxy resin (E-BP manufactured by Daicel Chemical Industries), 25 parts by weight of silxesquioxane having oxetanyl group (OX-SQ manufactured by Toagosei Co., Ltd.), aromatic sulfonium-based It impregnated and degassed with a resin (refractive index of cured resin 1.51, Abbe number 56) obtained by melting and mixing 1 part by weight of a thermal cation catalyst (SI-100L, manufactured by Sanshin Chemical Co., Ltd.). This glass cloth impregnated with resin is sandwiched between release-treated glass plates and heated at 80 ° C. for 2 hours while pressing at a pressure of 30 kg / cm ² using a vacuum press, and further heated at 200 ° C. for 2 hours. And cured to obtain a transparent composite sheet having a thickness of 0.1 mm.

(Example 2)
80 parts by weight of an alicyclic epoxy resin (EHPE3150 manufactured by Daicel Chemical Industries), 20 parts by weight of a bisphenol S type epoxy resin (Epiclon EXA1514 manufactured by Dainippon Ink and Chemicals), methylhexahydrophthalic anhydride (Rikacid MH-700 manufactured by Shin Nippon Chemical Co., Ltd.) ) 75 parts by weight, tetraphenylphosphonium bromide (TPP-PB manufactured by Hokuko Chemical Co., Ltd.) 0.5 parts by weight, 1,3 dioxolane 60 parts by weight, and varnish (refractive index of cured resin 1.51, Abbe number) 55). This was impregnated into the glass cloth described in Example 1, dried at 125 ° C. for 5 minutes, and then sandwiched between the release-treated glass plates, and at 200 ° C. while being pressed at a pressure of 30 kg / cm ² using a vacuum press. It was cured by heating for 2 hours to obtain a transparent composite sheet having a thickness of 0.1 mm.

(Example 3)
A NE glass-based glass cloth (NEA2319E manufactured by Nittobo Co., Ltd.) having a thickness of 80 μm and a refractive index of 1.51 was baked to remove organic substances, and then treated with glycidoxypropyltrimethoxysilane (epoxysilane). 2,2'-bis (3,4'-epoxycyclohexyl) propane (E-DOA manufactured by Daicel Chemical Industries), aromatic sulfonium-based thermal cation catalyst (SI-100L manufactured by Sanshin Chemical) 1 Impregnation was performed by impregnating a resin (refractive index of cured resin 1.512, Abbe number 57) obtained by melting and mixing parts by weight. This glass cloth impregnated with resin is sandwiched between release-treated glass plates and heated at 80 ° C. for 2 hours while pressing at a pressure of 30 kg / cm ² using a vacuum press, and further heated at 200 ° C. for 2 hours. And cured to obtain a transparent composite sheet having a thickness of 0.1 mm.

Example 4
NE glass powder having an average particle diameter of 3.2 μm (refractive index: 1.510, manufactured by Nittobo) was baked to remove organic substances, and then treated with glycidoxypropyltrimethoxysilane (epoxysilane). 100 parts by weight of this glass powder, 100 parts by weight of 2,2-bis (3 ′, 4′-epoxycyclohexyl) propane (E-DOA manufactured by Daicel Chemical Industries), an aromatic sulfonium-based thermal cation catalyst (manufactured by Sanshin Chemical Co., Ltd.) (SI-100L) 1 part by weight was dispersed in a melt-mixed resin (refractive index of cured resin 1.512, Abbe number 57) and defoamed. This is sandwiched between glass plates with an aluminum foil having a thickness of 80 μm as a spacer, heated in an oven at 80 ° C. for 2 hours, and further heated at 200 ° C. for 2 hours to obtain a transparent sheet having a thickness of 0.1 mm. It was.

(Comparative Example 1)
100 parts by weight of triglycidyl isocyanurate (TEPIC manufactured by Nissan Chemical Industries), 147 parts by weight of methylhexahydrophthalic anhydride (Rikacid MH-700 manufactured by Shin Nippon Chemical Co., Ltd.), 2 parts by weight of tetraphenylphosphonium bromide (TPP-PB manufactured by Hokuko Chemical) A resin obtained by melt-mixing a part at 110 ° C. (refractive index of cured resin 1.51, Abbe number 54) is impregnated into a glass cloth described in Example 1, and then sandwiched between release-treated glass plates, and a vacuum press machine Was cured by heating at 200 ° C. for 2 hours while pressing at a pressure of 30 kg / cm ² to obtain a transparent composite sheet having a thickness of 0.1 mm.

About the transparent composite sheet produced as mentioned above, various characteristics were evaluated by the evaluation method shown below.
(A) Light transmittance The light transmittance at 550 nm was measured with a spectrophotometer U3200 (manufactured by Hitachi, Ltd.).

(B) Average linear expansion coefficient Using a TMA / SS120C type thermal stress strain measuring device manufactured by Seiko Electronics Co., Ltd., the temperature was increased from 30 ° C. to 400 ° C. at a rate of 5 ° C. per minute in a nitrogen atmosphere. It was hold | maintained for minutes and measured and calculated | required the value at the time of 30 to 150 degreeC. The load was 5 g and the measurement was performed in the tensile mode. For the measurement, an independently designed quartz tension chuck (material: quartz, coefficient of linear expansion 0.5 ppm) was used. Commonly used Inconel chucks have high linear expansion per se and defects in the sample support form. When applied to thick sheets exceeding 100 μm, the linear expansion coefficient is larger than the result measured in the compression mode. And there was a problem that measurement variation became large. Therefore, we decided to design a quartz tensile chuck and use it to measure the linear expansion coefficient. By using this tension chuck, it has been confirmed that it can be measured with a value almost the same as that measured in the compression mode.

(C) Volume cure shrinkage of resin Specific gravity of uncured resin and cured resin was measured at room temperature using a density bottle, and the volume reduction rate per unit weight was calculated in% from the measured value. .

(D) Optical anisotropy The prepared transparent composite sheet was observed with a polarizing microscope in crossed Nicols. The sample was rotated while the optical axis of the polarizing microscope was fixed and the intensity of the light source was constant, and the sample was set at an angle at which part or all of the sheet became brightest. An observation portion of 2.4 mm × 1.8 mm was converted into an image (number of pixels: 640 × 480) and captured on a PC, which was converted into a black and white image with each pixel having a gradation of 0 to 255. The gradation of each pixel in this black-and-white image was summed up, and this was used as the optical anisotropy evaluation value. When this evaluation value was less than 10 million, it was judged that the transparent composite sheet had small optical anisotropy and good quality.

Example 1 has a light transmittance of 91%, an average linear expansion coefficient of 14 ppm, a volume hardening shrinkage of the resin of 0.5%, and an optical anisotropy evaluation value as small as 4 million. It was usable.
Example 2 has a light transmittance of 89%, an average linear expansion coefficient of 16 ppm, a volume cure shrinkage of the resin of 4%, and an optical anisotropy evaluation value as small as 8.1 million, which can be used as a display element substrate. It was a thing.
Example 3 has a light transmittance of 91%, an average linear expansion coefficient of 13 ppm, a volume hardening shrinkage of the resin of -1%, and an optical anisotropy evaluation value as small as 5 million, which is used as a display element substrate. It was possible.
Example 4 has a light transmittance of 89%, an average linear expansion coefficient of 31 ppm, a volume cure shrinkage of the resin of -1%, and an optical anisotropy evaluation value as small as 3 million, which is used as a display element substrate. It was possible.
In Comparative Example 1, the light transmittance was 90% and the average linear expansion coefficient was 15 ppm, but the evaluation value of the optical anisotropy was as large as 12 million because the volume hardening shrinkage of the resin was as large as 6.5%. It was insufficient for use as a display element substrate.

The transparent composite sheet of the present invention has a low coefficient of linear expansion and is excellent in transparency, heat resistance, and the like. For example, it is preferable for a display element such as a liquid crystal display element substrate or an organic EL element substrate (particularly an active matrix type), a transparent plate, It can be suitably used for optical lenses, color filter substrates, solar cell substrates, touch panels, optical elements, optical waveguides, and the like.

Claims (6)

Transparent containing a cycloaliphatic epoxy resin represented by the following chemical formula (1) or a hydrogenated biphenyl type alicyclic epoxy resin represented by the following chemical formula (1) having a volume hardening shrinkage measured by the following measurement method 1 of 5% or less Transparent composite sheet for display element substrate comprising resin (a) and inorganic filler (b) [Measuring method 1: Specific gravity of uncured resin and cured resin is measured at room temperature using a specific gravity bottle and measured. From the value, the volume reduction rate per unit weight is calculated in unit%. ]


(In the formula, X represents —CH ₂ —, —CH (CH ₃ ) —, or —C (CH ₃ ) ₂ —).


The transparent composite sheet for a display element substrate according to claim 1, comprising a cationic curing catalyst (d) as a curing agent for the alicyclic epoxy resin (a). Wherein the inorganic filler (b) is according to claim 1 or 2 display device a transparent composite sheet according a fiberglass cloth. The transparent composite sheet for display element substrates according to any one of claims 1 to 3, wherein the light transmittance ( measured wavelength: 550 nm, measured with a spectrophotometer) is 80% or more. The average linear expansion coefficient (measured temperature 30 ° C. to 400 ° C., heating rate 5 ° C. / 1min, tensile was measured by thermal stress strain measuring apparatus in mode) any one of claims 1 to 4 is 40ppm or less The transparent composite sheet for display element substrates as described . A display element substrate produced using the transparent composite sheet for a display element substrate according to any one of claims 1 to 5.