JP2006278034A - Touch panel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a touch panel material in which birefringence due to extension is small, birefringence due to flow orientation of a resin is small and refringence variation due to external force is small. <P>SOLUTION: This touch panel material formed of a resin composition comprising an acrylic resin (a) and a polylactic acid-based resin (b) is used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a touch panel material made of a resin composition having excellent optical characteristics.

  In recent years, liquid crystal display elements have attracted attention as image display elements, and one of their uses is to personal computer displays, televisions, portable electronic notebooks, information terminals, video camera viewing finders, car navigation monitors, etc. Applied. In recent years, an input method in which a transparent touch panel as an input device is mounted on a liquid crystal display element and an input is performed while looking at the screen has been desired for these devices. A touch panel usually has a structure in which two electrodes coated with a transparent conductive film are stacked with the transparent electrode side inward, and when the panel is pressed from the outside, it contacts the other electrode due to deformation of the electrode, and the resistance value changes. This is a method for reading the position. For example, a combination of a glass fixed electrode substrate and a polyethylene terephthalate (PET) movable electrode film is known as a touch panel (see, for example, Patent Document 1). There was a problem that the decrease occurred.

When a polymer material is used as a touch panel material, it is molded by injection molding, extrusion molding, or the like, but orientation birefringence due to resin stretching or flow causes the polarization of the liquid crystal display element to change. Therefore, a low birefringence touch panel material that hardly changes the polarization has been demanded.
In addition, in order to reduce the distribution of birefringence generated in the touch panel material due to the bias of external force during manufacture and use of the touch panel, a material having a small change in birefringence due to the external force is required. For this purpose, a polymer optical material having a low photoelastic coefficient is required as a new required characteristic, and methyl methacrylate homopolymer (PMMA) and amorphous polyolefin (APO) are known as materials having a low photoelastic coefficient. (For example, refer nonpatent literature 1). However, even with these materials, a material having a large change in birefringence due to an external force and a small change in birefringence due to an external force has been desired.
Also, a blend of PMMA and polylactic acid is known (for example, see Non-Patent Document 2). However, there was no description or suggestion that these blends were excellent in optical properties.
JP-A-9-262925 Chemical Review, No. 39, 1998 (published by Academic Publishing Center) POLYMER Vol.39 No.26, 1998

  An object of the present invention is to provide a touch panel material that has a small change in birefringence due to stretching, a small birefringence due to flow orientation of a resin, and a small change in birefringence due to external force.

The present inventors have found that a combination of resin compositions has a small change in birefringence due to stretching, a small birefringence due to flow orientation of the resin, and a small change in birefringence due to external force, leading to the completion of the present invention. It was.
That is, the present invention
[1] A touch panel material comprising a resin composition comprising an acrylic resin (a) and an aliphatic polyester resin (b),
[2] The relationship between the birefringence (Δn (S)) and the draw ratio (S) when the resin composition is stretched is characterized in that the value of the slope K obtained from the least square approximation satisfies the following equation: The touch panel material according to [1],
K = Δn (S) / S
−8.0 × 10 ⁻⁶ <K <6.5 × 10 ⁻⁵
[3] The touch panel material according to [1] or [2], which is a film formed by extrusion molding,
[4] The touch panel material according to [1] or [2], which is a film formed by cast molding,
[5] The touch panel material according to [1], which is a molded body molded by injection molding,
[6] The touch elastic material according to any one of [1] to [5], wherein the photoelastic coefficient is greater than −13 × 10 ⁻¹² / Pa and less than 12 × 10 ⁻¹² / Pa,
[7] The touch panel material according to any one of [1] to [6], wherein a transparent electrode film is laminated on the surface,
It is.

  According to the present invention, it is possible to provide a touch panel material in which the change in birefringence when stretched is small, the birefringence due to resin flow orientation is small, and the change in birefringence due to external force is small.

Hereinafter, the present invention will be specifically described.
(A) Acrylic resin of the present invention includes methacrylic acid esters such as cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, methyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate, acrylic acid 2 -A polymer obtained by polymerizing one or more monomers selected from acrylic acid esters such as ethylhexyl. Of these, a homopolymer of methyl methacrylate or a copolymer with other monomers is preferable. Examples of monomers copolymerizable with methyl methacrylate include other alkyl methallylic esters, alkyl acrylates, aromatic vinyl compounds such as styrene, vinyl toluene and α-methyl styrene, acrylonitrile, methacrylonitrile, etc. And vinyl cyanides, maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide, unsaturated carboxylic acid anhydrides such as maleic anhydride, and unsaturated acids such as acrylic acid, methacrylic acid and maleic acid.

  Among these monomers copolymerizable with methyl methacrylate, acrylic acid alkyl esters are particularly excellent in thermal decomposition resistance, and methacrylic resins obtained by copolymerizing alkyl acrylates are flowable during molding. Highly preferable. The amount of alkyl acrylates used when methyl acrylate is copolymerized with methyl methacrylate is preferably 0.1% by weight or more from the viewpoint of thermal decomposition resistance, and 15% from the viewpoint of heat resistance. % Or less is preferable. The content is more preferably 0.2% by weight or more and 14% by weight or less, and particularly preferably 1% by weight or more and 12% by weight or less. Among these alkyl acrylates, especially methyl acrylate and ethyl acrylate are remarkably most preferable even when they are copolymerized with a small amount of methyl methacrylate. The said monomer which can be copolymerized with methyl methacrylate can also be used 1 type or in combination of 2 or more types.

The acrylic resin (a) preferably has a weight average molecular weight of 50,000 to 200,000. The weight average molecular weight is desirably 50,000 or more from the viewpoint of the strength of the molded product, and desirably 200,000 or less from the viewpoint of molding processability and fluidity. A more desirable range is 70,000 to 150,000. In the present invention, isotactic polymethacrylate and syndiotactic polymethacrylate can be used simultaneously.
As a method for producing an acrylic resin, for example, generally used polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, and anionic polymerization can be used. It is preferable to avoid mixing of foreign substances as much as possible. From this viewpoint, bulk polymerization or solution polymerization without using a suspending agent or an emulsifier is desirable. When solution polymerization is performed, a solution prepared by dissolving a mixture of monomers in an aromatic hydrocarbon solvent such as toluene or ethylbenzene can be used. In the case of polymerization by bulk polymerization, the polymerization can be started by irradiation with free radicals generated by heating or ionizing radiation as is usually done.

As the initiator used in the polymerization reaction, any initiator generally used in radical polymerization can be used. For example, an azo compound such as azobisisobutylnitrile, benzoyl peroxide, lauroyl peroxide, t-butylperoxy -When an organic peroxide such as 2-ethylhexanoate is used and the polymerization is carried out particularly at a high temperature of 90 ° C or higher, solution polymerization is common, so the 10-hour half-life temperature is 80 Peroxides and azobis initiators that are soluble in the organic solvent to be used are preferable, and specifically, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, cyclohexane par. Oxide, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 1,1-azobis (1-cyclohexane) Sun-carbonitrile), and 2- (carbamoylazo) isobutyronitrile. These initiators are used in the range of 0.005 to 5 wt%.
As the molecular weight regulator used as necessary in the polymerization reaction, any one used in general radical polymerization is used, for example, mercaptan compounds such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-ethylhexyl thioglycolate and the like. It is mentioned as preferable. These molecular weight regulators are added in a concentration range such that the degree of polymerization is controlled within the above range.

  Examples of the (b) aliphatic polyester-based resin of the present invention include polymers having aliphatic hydroxycarboxylic acids as main constituent components, polymers having aliphatic polyvalent carboxylic acids and aliphatic polyhydric alcohols as main constituent components, and the like. Can be mentioned. Specifically, polymers having aliphatic hydroxycarboxylic acid as a main component include polyglycolic acid, polylactic acid, poly-3-hydroxybutyric acid, poly-4-hydroxybutyric acid, poly-4-hydroxyvaleric acid, poly-3- Hydroxyhexanoic acid and polycaprolactone are listed. Polymers mainly composed of aliphatic polycarboxylic acid and aliphatic polyhydric alcohol include polyethylene adipate, polyethylene succinate, polybutylene adipate, and polybutylene succinate. Is mentioned. These aliphatic polyesters can be used alone or in combination of two or more. Among these aliphatic polyesters, a polymer containing hydroxycarboxylic acid as a main constituent is preferable, and a polylactic acid resin is particularly preferably used. These (b) components can use 1 or more types.

  The polylactic acid-based resin is a polymer having L-lactic acid and / or D-lactic acid as a main constituent component, but within a range not impairing the object of the present invention, other copolymer components other than lactic acid 0.1 It may contain 30% by weight. Examples of such other copolymer component units include polyvalent carboxylic acids, polyhydric alcohols, hydroxycarboxylic acids, lactones, and the like. Specifically, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid , Azelaic acid, sebacic acid, dodecanedioic acid, fumaric acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, 5-tetrabutylphosphonium sulfoisophthalic acid Polyhydric carboxylic acids such as ethylene glycol, propylene glycol, butanediol, heptanediol, hexanediol, octanediol, nonanediol, decanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, glycerin, trimethyl Rupuropan, pentaerythritol, bisphenol - Le A can be mentioned.

  Also, polyhydric alcohols such as aromatic polyhydric alcohols obtained by addition reaction of bisphenol with ethylene oxide, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, glycolic acid, 3-hydroxybutyric acid, 4-hydroxy Hydroxycarboxylic acids such as butyric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid, hydroxybenzoic acid, glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone , Lactones such as pivalolactone and δ-valerolactone can be used. These copolymer components can be used alone or in combination of two or more.

  (B) As a method for producing an aliphatic polyester-based resin, a known polymerization method can be used. In particular, for a polylactic acid-based resin, a direct polymerization method from lactic acid, a ring-opening polymerization method via lactide, or the like is employed. be able to. The polylactic acid (b) in the present invention is a polymer mainly composed of lactic acid, that is, L-lactic acid and D-lactic acid. In the polylactic acid-based resin, the constituent molar ratio of the L-lactic acid unit and the D-lactic acid unit is preferably 100% for both the L-form and the D-form, and either the L-form or the D-form is preferably 85% or more. More preferably, one is 90% or more, and more preferably one is a 94% or more polymer. In the present invention, poly-L lactic acid mainly composed of L-lactic acid and poly-D lactic acid mainly composed of D-lactic acid can be used simultaneously.

The heat of crystal melting of polylactic acid is preferably less than 15 J / g. More preferably, it is less than 10 J / g, and particularly preferably less than 7 J / g. When the crystal melting heat amount of polylactic acid exceeds 15 J / g, the transparency of the film is lowered.
The polylactic acid-based resin may be copolymerized with lactic acid derivative monomers other than L-form or D-form or other components copolymerizable with lactide. Examples of such components include dicarboxylic acids, polyhydric alcohols, hydroxycarboxylic acids. Examples include acids and lactones. The polylactic acid resin can be polymerized by a known polymerization method such as direct dehydration condensation or ring-opening polymerization of lactide. If necessary, the molecular weight can be increased by using a binder such as polyisocyanate.

The preferred weight average molecular weight range of the polylactic acid-based resin is preferably a weight average molecular weight of 30,000 or more from the viewpoint of mechanical properties, and preferably 1,000,000 or less from the viewpoint of processability. More preferably, it is 50,000-500,000, Most preferably, it is 100,000-280,000.
In the present invention, the range (parts by weight) of the acrylic resin (a) in the resin composition comprising the acrylic resin (a) and the aliphatic polyester resin (b) is the range of the component (a) and the component (b). From the viewpoint of birefringence, strength, heat resistance, etc., the total amount is preferably from 0.1 to 99.9 parts by weight, more preferably from 20 to 95 parts by weight. More preferably, it is 40 parts by weight or more and 90 parts by weight or less.

In the touch panel material made of the resin composition of the present invention, the photoelastic coefficient is preferably more than −13 × 10 ⁻¹² / Pa and less than 12 × 10 ⁻¹² / Pa. The photoelastic coefficient is described in various documents (see, for example, Non-Patent Document 1) and is defined by the following equation.
C _R = Δn / σ _R Δn = nx−ny
( _Wherein , C _R : photoelastic coefficient, σ _R : stretching stress, Δn: birefringence, nx: refractive index in the stretching direction, ny: refractive index perpendicular to the stretching direction)
The closer the value of the photoelastic coefficient is to zero, the smaller the change in birefringence due to external force, which means that the change in birefringence designed for each application is small. The value of the photoelasticity is more preferably −10 × 10 ⁻¹² / Pa and less than 9 × 10 ⁻¹² / Pa, more preferably −5 × 10 ⁻¹² / Pa and less than 5 × 10 ⁻¹² / Pa. It is particularly preferred that there is.

In the production of the touch panel material of the present invention, it is composed of an acrylic resin (a) and an aliphatic polyester resin (b), and in the relationship between birefringence (Δn (S)) and stretch ratio (S) when stretched, It is preferable to use a resin composition in which the value of the slope K obtained from the least square approximation satisfies the following formula.
K = Δn (S) / S
−8.0 × 10 ⁻⁶ <K <6.5 × 10 ⁻⁵
The draw ratio (S) is a value represented by the following equation, where L0 is the distance between chucks before stretching and L1 is the distance between chucks after stretching.
L1-L0
S = ――――――― × 100 (%)
L0
A more preferable range of the slope K is −5.0 × 10 ⁻⁶ <K <5 × 10 ⁻⁵ , and a particularly preferable range is −3.0 × 10 ⁻⁶ <K <2 × 10 ⁻⁵ . . When used for a touch panel material, a material having a K value in this range is preferable because the change in birefringence due to stretching or orientation is small, and the required birefringence design is easy.

  In the present invention, by further adding a hydrolysis resistance inhibitor to the resin composition of the component (a) and the component (b), it is possible to suppress a decrease in molecular weight due to hydrolysis of the component (b). A decrease or the like can be suppressed. As the hydrolysis resistance inhibitor, compounds having reactivity with carboxylic acid and hydroxyl group, which are terminal functional groups of aliphatic polyester resins, such as carbodiimide compounds, isocyanate compounds, oxozoline compounds, and the like can be applied. A carbodiimide compound (including a polycarbodiimide compound) is preferable because it can be melt-kneaded well with a polyester resin and hydrolysis can be suppressed by adding a small amount. As a carbodiimide compound (including a polycarbodiimide compound) having one or more carbodiimide groups in the molecule, for example, an organic phosphorus compound or an organometallic compound is used as a catalyst, and various polymer isocyanates are used at a temperature of about 70 ° C. or higher. What can be synthesize | combined by attaching | subjecting a decarboxylation condensation reaction in a non-solvent or an inert solvent is mentioned.

  As the polycarbodiimide, those produced by various methods can be used. Basically, a conventional method for producing polycarbodiimide (US Pat. No. 2,941,956, Japanese Patent Publication No. 47-33279, J. Pat. Chem. 28, 2069-2075 (196 3), Chemical Review 981, Vol. 81 No. 4, p619-621) can be used. Examples of the organic diisocyanate that is a raw material for producing polycarbodiimide include aromatic diisocyanate, aliphatic diisocyanate, alicyclic diisocyanate and mixtures thereof. Specifically, 1,5-naphthalene diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-diphenyldimethylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2, Mixture of 4-tolylene diisocyanate and 2,6-tolylene diisocyanate, hexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate , Dicyclohexylmethane-4,4′-diisocyanate, methylcyclohexane diisocyanate, tetramethylxylylene diisocyanate, 2,6-diisopropylphenyl isocyanate, 1,3,5-triisopropylbenzene-2,4-diisocyanate Can do.

A preferable amount of the hydrolysis-resistant inhibitor is 0.01 to 50 parts by weight of the hydrolysis-resistant inhibitor with respect to 100 parts by weight of the components (a) and (b). 0.01 weight or more is preferable from the viewpoint of expression of the hydrolysis resistance suppressing effect, and 50 weight part or less is preferable from the viewpoint of optical characteristics. A more preferable range is a range of 0.01 to 30 parts by weight, and a further preferable range is 0.1 to 30 parts by weight.
Moreover, in this invention, polymers other than (a) component and (b) component can be mixed in the range which does not impair the objective of this invention. Examples of the polymer other than the component (a) and the component (b) include polyolefins such as polyethylene and polypropylene, styrene resins such as polystyrene and styrene acrylonitrile copolymers, polyamide, polyphenylene sulfide resin, polyether ether ketone resin, polyester, At least one or more of thermoplastic resins such as polysulfone, polyphenylene oxide, polyimide, polyetherimide, and polyacetal, and thermosetting resins such as phenol resin, melamine resin, silicone resin, and epoxy resin can be further added.

  Furthermore, arbitrary additives can be mix | blended according to various objectives within the range which does not impair the effect of this invention remarkably. The type of additive is not particularly limited as long as it is generally used for blending resins and rubber-like polymers. Inorganic fillers, pigments such as iron oxide, stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, ethylene bisstearamide, lubricants, mold release agents, paraffinic process oil, naphthenic process oil, Softeners and plasticizers such as aromatic process oil, paraffin, organic polysiloxane, mineral oil, hindered phenol antioxidants, antioxidants such as phosphorus heat stabilizers, hindered amine light stabilizers, benzotriazoles Examples include ultraviolet absorbers, flame retardants, antistatic agents, reinforcing agents such as organic fibers, glass fibers, carbon fibers, and metal whiskers, coloring agents, other additives, and mixtures thereof.

The production method of the unstretched molded product in the present invention is not particularly limited, and a known method can be used. For example, it can be produced using a melt kneader such as a single screw extruder, a twin screw extruder, a Banbury mixer, a Brabender, or various kneaders. Further, the unstretched molded product in the present invention can be molded by a known method such as injection molding, sheet molding, blow molding, injection blow molding, inflation molding, extrusion molding, foam molding, etc. Secondary processing molding methods such as these can also be used.
When the form of the touch panel material of the present invention is a film or a sheet, techniques such as extrusion molding and cast molding are used. For example, an unstretched film can be extruded by using an extruder equipped with a T die, a circular die, or the like. When a molded product is obtained by extrusion molding, a material in which the components (a) and (b) are melted and kneaded in advance can be used, or molding can be performed through melt-kneading at the time of extrusion molding. In addition, by using a solvent common to component (a) and component (b), for example, a solvent such as chloroform and methylene dichloride, the component (a) and component (b) are dissolved, cast and dried to solidify. The film can also be cast.

  Unstretched film can be uniaxially stretched longitudinally in the direction of mechanical flow and transversely uniaxially stretched in the direction perpendicular to the direction of mechanical flow. Simultaneous biaxial stretching by roll and tenter stretching, and simultaneous biaxial stretching by tenter stretching A biaxially stretched film can be produced by stretching by a biaxial stretching method using a method such as tubular stretching. The strength of the film can be improved by stretching. The final draw ratio can be determined from the heat shrinkage rate of the obtained molded body. The draw ratio is preferably 0.1% or more and 1000% or less in at least one direction, more preferably 0.2% or more and 600% or less, and more preferably 0.3% or more and 300% or less. Especially preferred. By designing in this range, a touch panel material preferable in terms of birefringence, heat resistance, and strength can be obtained.

  The main method of the touch panel is a two-electrode method. The structure of the touch panel is described in various documents (for example, new development of transparent conductive film, 1999 (issued by CMC)). The two-electrode system has a structure in which two electrodes coated with a transparent conductive film are overlapped with the transparent electrode side inward, and when the panel is pressed from the outside, it contacts the other electrode due to deformation of the electrode. This is a method of reading a position from a change in value. The touch panel material of the present invention is used for a molded body of a touch panel electrode substrate. The touch panel material can be formed by injection molding, extrusion molding, cast molding, or the like. The two electrodes of the touch panel include a combination of electrode film / electrode film and electrode film / electrode support plate. The thickness of the electrode film is preferably 10 to 500 μm, more preferably 20 to 300 μm, and particularly preferably 30 to 200 μm. The electrode film can be formed by extrusion molding, cast molding, or the like. The thickness of the electrode support plate is preferably from 0.1 to 5 mm, more preferably from 0.2 to 4 mm, and particularly preferably from 0.3 to 3 mm. The electrode support plate can be formed by injection molding, extrusion molding or the like.

  By laminating a transparent electrode film on the touch panel material of the present invention, it can be used as an electrode of a touch panel. The transparent conductive film is not particularly limited, and metal films such as gold, silver, copper, palladium, aluminum, chromium, and rhodium, and metal oxide films such as indium oxide, tin oxide, zinc oxide, and titanium oxide can be applied. In particular, in terms of transparency, conductivity, etching, and mechanical properties, composite oxides in which zinc oxide is doped with gallium, composite oxides in which zinc oxide is doped with aluminum, indium oxide and tin oxide in which indium oxide is doped with tin A composite oxide (ITO) thin film is preferred. The method for forming the transparent conductive film is not particularly limited, and examples thereof include a spray method, a gas phase reaction method (CVD method), a coating method, a vacuum deposition method, a sputtering method, an ion beam sputtering method, and an ion plating method. The details of the method for forming a transparent conductive film are described in literature (for example, see Journal of Applied Electronics Physical Properties, Vol. 11, No. 1, 2005 (published by Applied Physics Society of Applied Electronic Properties)). The method can be used.

  The touch panel material of the present invention can be used for a touch panel combined with a display element such as a liquid crystal display, a plasma display, an organic EL display, or a field emission display. It can also be used as a touch panel material for personal computer displays, televisions, portable electronic notebooks, information terminals, video camera viewing finder, car navigation, game machines, mobile phones and the like. The touch panel material of the present invention can be subjected to surface functionalization treatment such as antireflection treatment, electromagnetic wave shielding treatment, and gas barrier treatment.

Next, the present invention will be described by way of examples.
First, the evaluation methods used in the present invention and examples will be described.
(I) Evaluation.
(I) Measurement of photoelastic coefficient
A birefringence measuring apparatus described in detail in Polymer Engineering and Science 1999, 39, 2349-2357 was used. A film tensioning device was placed in the laser beam path, and birefringence was measured while applying a tensile stress at 23 ° C. The strain rate during stretching was 50% / min (between chucks: 10 mm, chuck moving speed: 5 mm / min), and the test piece width was 8 mm. From the relationship between birefringence (Δn) and tensile stress (σ _R ), the photoelastic coefficient (C _R ) was calculated by obtaining the slope of the straight line by least square approximation. A graph of the relationship is shown in FIG. The smaller the absolute value of the slope is, the closer the photoelastic coefficient is to 0, indicating a preferable optical characteristic.
C _R = Δn / σ _R Δn = nx−ny
(C _R : photoelastic coefficient, σ _R : stretching stress, Δn: birefringence, nx: refractive index in the stretching direction, ny: refractive index perpendicular to the stretching direction)
The absolute value (| Δn |) of birefringence (Δn) was determined as follows.
| Δn | = | nx−ny |

(Ii) Measurement of total light transmittance Measurement was performed in accordance with ASTM D1003.
(Iii) Molecular weight GPC [GPC-8020 manufactured by Tosoh Corp., detection RI, column Shodex K-805, 801 linked by Showa Denko] was used, the solvent was chloroform, the measurement temperature was 40 ° C., and the weight average molecular weight was calculated in terms of commercial standard polystyrene. It was.
(Iv) Specific rotation
The specific rotation [α] was determined by the method described in Macromolecules 1991, 24, 5657-5662.

(II) Raw materials used (i) (Methyl methacrylate / methyl acrylate) copolymer (A-1)
1,1-di-t-butylperoxy-3,3,5-trimethyl was added to a monomer mixture consisting of 89.2 parts by weight of methyl methacrylate, 5.8 parts by weight of methyl acrylate, and 5 parts by weight of xylene. Add 0.0294 parts by weight of cyclohexane and 0.115 parts by weight of n-octyl mercaptan and mix uniformly.
This solution is continuously supplied to a sealed pressure resistant reactor having an internal volume of 10 liters, polymerized with stirring at an average temperature of 130 ° C. and an average residence time of 2 hours, and then continuously sent to a storage tank connected to the reactor. Acrylic resin (a) used for the following examples in which the volatile components are removed under a certain condition and further transferred to the extruder in a molten state and used in the following examples in the extruder (methyl methacrylate / acrylic acid) Methyl) copolymer pellets were obtained. The resulting copolymer had a methyl acrylate content of 6.0% by weight, a weight average molecular weight of 145,000, a melt flow rate value of 230 ° C. and a load of 3.8 kilograms measured in accordance with ASTM-D1238 was 1. 0.0 g / min.

(Ii) Polylactic acid (B-1)
The polylactic acid-based resin, which is the aliphatic polyester-based resin (b) used in the following examples, is known from, for example, “Polylactide” in Biopolymers Vol. 4 (Wiley-VCH 2002) PP 129-178 and polylactic acid (copolymer of L lactic acid and D lactic acid) by a ring-opening polymerization method of lactide using a tin-based catalyst according to JP-A-05-504731 Got ready. The weight average molecular weight and specific rotation of (B-1) were 176,000 and -150.6 °, respectively.

[Examples 1-3 and Comparative Examples 1-2]
The dry blend of each component of (a) component and (b) component is put into the hopper of Technobel's T die mounting extruder (KZW15TW-25MG-NH type / width 150 mm T die mounting / lip thickness 0.5 mm). did. The unstretched films of Examples 1 to 3 and Comparative Examples 1 to 2 were obtained by adjusting the resin temperature in the cylinder of the extruder and the temperature of the T die and performing extrusion molding. Table 1 shows the composition, extrusion conditions, film thickness, total light transmittance, and photoelastic coefficient. Moreover, the relationship between (DELTA) n and the extension stress of the unstretched film of Examples 1-2 and Comparative Examples 1-2 is shown in FIG.
Next, uniaxial stretching (stretching speed 5% / min) of the unstretched films of Examples 1 to 3 and Comparative Examples 1 and 2 obtained was performed using a tensile tester, and birefringence (Δn (S )) And the draw ratio (S) were plotted, the value of K was determined by least square approximation, and the results are shown in Table 1. FIG. 2 is a graph plotting the relationship between birefringence (Δn (S)) and stretch ratio (S) when stretched.
Further, nx necessary for obtaining | Δn | = | nx−ny | is a refractive index in a uniaxial tensile direction, and ny is a refractive index in a direction perpendicular to the uniaxial tensile direction. The nx-ny value of the film made of A-1 in Comparative Example 1 was negative.
The compositions of Examples 1-3 and Comparative Examples 1-2, extrusion conditions, stretching conditions, film thickness, and absolute values of birefringence are shown in Tables 2-6, respectively.

  The touch panel material of the present invention has excellent optical properties such as a small change in birefringence due to stretching, a small birefringence due to resin flow orientation, and a small change in birefringence due to external force. A liquid crystal display, a plasma display, and an organic EL display. It can be used for a touch panel combined with a display element such as a field emission display. It can also be used as a touch panel material for personal computer displays, televisions, portable electronic notebooks, information terminals, video camera viewing finder, car navigation, game machines, mobile phones and the like.

It is a graph which shows the relationship of (DELTA) n of Examples 1, 2 and Comparative Examples 1, 2 and an extensional stress. It is the graph which plotted the relationship of birefringence ((DELTA) n (S)) at the time of extending | stretching the unstretched film of Examples 1-3 and Comparative Examples 1-2, and a draw ratio (S).

Claims (7)

  A touch panel material comprising a resin composition comprising an acrylic resin (a) and an aliphatic polyester resin (b). The relationship between the birefringence (Δn (S)) and the draw ratio (S) when the resin composition is stretched, and the value of the slope K obtained from the least square approximation thereof satisfies the following equation: The touch panel material according to 1.
K = Δn (S) / S
−8.0 × 10 ⁻⁶ <K <6.5 × 10 ⁻⁵   The touch panel material according to claim 1, wherein the touch panel material is a film formed by extrusion molding.   The touch panel material according to claim 1, wherein the touch panel material is a film formed by cast molding.   The touch panel material according to claim 1, which is a molded body molded by injection molding. The touch panel material according to any one of claims 1 to 5, wherein the photoelastic coefficient is greater than -13 x ^10-12 / Pa and less than 12 x ^10-12 / Pa.   The touch panel material according to claim 1, wherein a transparent electrode film is laminated on the surface.

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