JP2010059280A - Hardcoat coating liquid, hardcoat film, and upper electrode plate for touch panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive hardcoat coating liquid for forming a hardcoat layer that hardly shows interference nonuniformity and is excellent in visual recognizability, and to provide a hardcoat film, and an upper electrode plate for a touch panel. <P>SOLUTION: The hardcoat coating liquid comprises at least an ionizing radiation-curable material and a solvent, where the solvent has a surface tension of at least 28 mN/m and at most 40 mN/m at 25°C. The hardcoat film 1 comprises a film substrate 11 and a hardcoat layer 12 provided on at least one face thereof, where the hardcoat layer 12 is formed by a step of applying the hardcoat coating liquid on the film substrate 11 to form a coating film, a step of drying the coating film to remove the solvent and a step of curing the coating film by irradiating it with an ionizing radiation. The upper electrode plate for a touch panel comprises the hardcoat film 1 having at least a transparent electroconductive layer laminated on the opposite face side to the hardcoat layer 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hard coat coating solution for forming a hard coat layer having low visibility and less noticeable interference unevenness and excellent visibility. Moreover, this invention relates to a hard coat film provided with the hard-coat layer formed using this hard-coat coating liquid. The present invention further relates to an upper electrode plate for a touch panel using the hard coat film.

  In recent years, plastic products are good in terms of processability and weight reduction, so various products are being replaced from glass products to plastic products, but the surface of these plastic products is easily damaged, so surface hardness and scratch resistance In many cases, a hard coat layer is provided on the surface or a film provided with a hard coat layer is used by bonding.

In addition, for conventional glass products, plastic films are increasingly being bonded to prevent scattering when broken, and a hard coat layer is formed on the surface of these films in order to strengthen their hardness. In particular, it is used for display devices such as LCD, PDP, FED, and EL, and the outermost surface of touch panels and the like.
In such a configuration, when the hard coat is visually recognized, rainbow-colored unevenness (interference unevenness) occurs, and the visibility is often deteriorated or the appearance is impaired.

Here, the cause of interference unevenness will be described. When a transparent layer on the surface of the base material is installed and there is a difference in refractive index between them, for example, the light reflected from the surface of the transparent layer with respect to the incident light from the transparent layer side and the base material that passes through the transparent layer The light reflected at the interface of the transparent layer causes interference due to the optical path difference (film thickness of the transparent layer). Waviness (ripple) occurs in the reflection spectrum. Here, when there is variation in the film thickness of the transparent layer, the reflection spectrum changes corresponding to the film thickness, and a portion having a different reflection color is generated.
For example, the hard coat layer is often produced by applying an acrylic ionizing radiation curable resin having a hardness higher than that of the base material on the base material. This general acrylic ionizing radiation curable resin cured product has a refractive index of about 1.51 to 1.54. However, the refractive index of a polyethylene terephthalate (PET) film generally used as a highly transparent film is about 1.62, and the refractive index of a triacetyl cellulose (TAC) film used in the same manner is 1.49. There is a difference from the refractive index of the above-mentioned cured product of ionizing radiation curable resin. Moreover, it is difficult to adjust the refractive index equivalent to that of the above-mentioned ionizing radiation-cured resin cured product even in various base materials in terms of compatibility with other functions and productivity. In order to suppress this interference unevenness, the following techniques are invented and disclosed (Patent Documents 1 to 4).
JP-A-8-197670 JP 2000-111706 A JP-A-7-151902 JP 2003-205563 A

  The interference unevenness reduction technique described in Patent Document 1 is a technique for scattering light reflection at the interface between the hard coat layer and the substrate by providing irregularities on the substrate. However, before applying the hard coat layer to provide unevenness on the substrate, a step of providing unevenness on the surface of the substrate is included, and this method increases the number of steps, leading to increased costs, and the surface There is a problem that the sharpness of the image is lowered due to the uneven structure.

Moreover, the interference nonuniformity prevention technique described in Patent Document 2 is to provide a refractive index intermediate layer between the base material and the hard coat layer in order to alleviate the refractive index difference between the base material and the hard coat layer. In this technique, even if an intermediate layer is provided, the refractive index changes only in stages, and interference unevenness does not disappear even if it decreases. Moreover, since the process of providing an intermediate | middle layer is needed, there existed a malfunction of leading to a cost increase.
Patent Document 3 discloses a technique for forming a hard coat layer using an ionizing radiation curable resin containing ultrafine metal oxide particles in order to match the refractive index of the hard coat layer to that of the substrate. However, when metal oxide ultrafine particles having a particle size of several tens of nanometers are dispersed in an ionizing radiation curable resin, both the ultrafine particle material and the dispersion process must be increased in cost.
Note that the problem of interference unevenness has not been completely solved by the above-described conventional technology.
As an example of eliminating interference unevenness, Patent Document 4 discloses that there is no reflection from the layer interface by applying a hard coat layer to the substrate using a resin containing a solvent that dissolves or swells the substrate. A technique for preventing unevenness is disclosed. However, in a biaxially oriented polyester film that is difficult to dissolve and swell by the dissolution and swelling methods, the applicable solvent is limited to a special and highly harmful solvent such as chlorophenol. In addition, triacetyl cellulose (TAC) films that are easily dissolved and swelled have a problem that the hardness of the hard coat is reduced by dissolution of the base material.

  An object of the present invention is to provide a hard coat coating solution for forming a hard coat layer having low visibility and less noticeable unevenness of interference and having excellent visibility, and a hard coat comprising a hard coat layer formed using the hard coat coating solution An object is to provide a film and an upper electrode plate for a touch panel using the hard coat film.

The invention according to claim 1 is a hard coat coating liquid containing at least an ionizing radiation curable material and a solvent,
A hard coat coating solution comprising a solvent having a surface tension at 25 ° C. of 28 mN / m or more and 40 mN / m or less as the solvent.
The invention according to claim 2 is characterized in that the solvent of the hard coat coating liquid is at least one selected from cyclohexanone, cyclopentanone, dioxolane and ethylene glycol monomethyl ether. Hard coat coating solution.
The invention according to claim 3 is a hard coat film comprising a hard coat layer on at least one surface of the film substrate,
The hard coat layer is a step of applying the hard coat coating solution according to claim 1 or 2 on the film substrate to form a coating film, a step of drying the coating film to remove a solvent, A hard coat film formed by a step of irradiating with ionizing radiation and curing.
The invention according to claim 4 is the hard coat film according to claim 3, wherein the hard coat layer has a thickness of 4 μm or more and 25 μm or less.
The invention according to claim 5 is an upper electrode plate for a touch panel, wherein at least a transparent conductive layer is laminated on the opposite side of the hard coat layer of the hard coat film according to claim 3 or 4. is there.
The invention described in claim 6 is characterized in that an adhesive layer, a transparent resin film, and a transparent conductive layer are provided in this order on the opposite surface side of the hard coat layer. It is an electrode plate.

  According to the present invention, a hard coat coating liquid for forming a hard coat layer that is low-cost and in which interference unevenness is not conspicuous and has excellent visibility, and a hard coat provided with a hard coat layer formed using the hard coat coating liquid It is possible to provide an upper electrode plate for a touch panel using the film and the hard coat film, which is low-cost and in which interference unevenness is not noticeable and has excellent visibility.

  Hereinafter, the hard coat coating liquid, hard coat film, and upper electrode plate for touch panel of the present invention will be described.

  The hard coat coating liquid of the present invention includes at least an ionizing radiation curable material and a solvent, and the solvent includes a solvent having a surface tension at 25 ° C. of 28 mN / m or more and 40 mN / m or less.

  The inventors of the present invention have formed a transparent hard coat layer with excellent visibility by making the solvent component of the hard coat coating solution have a surface tension at 25 ° C. of 28 mN / m or more and 40 mN / m or less so that interference unevenness is not noticeable. Found that you can. A more preferable surface tension is 31 mN / m or more and 37 mN / m or less. Here, the surface tension measured by the Wilhelmi method was used.

  In the present invention, at least one of the solvents contained in the hard coat coating solution may be 28 mN / m or more and 40 mN / m or less, and the following solvents are particularly preferable.

Surface tension (mN / m) Boiling point (℃)
Cyclopentanone 36.2 131
Cyclohexanone 34.5 156
Dioxolane 34.1 76
Ethylene glycol monomethyl ether 31.8 125

  In the present invention, one of the reasons that interference unevenness due to film thickness variation can be eliminated is that local surface tension differences are hardly generated in the coating liquid during the coating film drying process. In the case where a solvent having a surface tension of less than 28 mN / m is used, the film is formed by a local surface tension difference in the coating film in the drying step after the hard coat coating solution is applied to the film substrate. Thickness unevenness occurs, resulting in interference unevenness.

  In the present invention, the solvent contained in the hard coat coating solution may contain a solvent not included in the range of 28 mN / m or more and 40 mN / m or less. At this time, it is preferable that the solvent within the range of 28 mN / m or more and 40 mN / m or less is contained by 50 wt% or more with respect to the total solvent of the hard coat coating solution.

In the present invention, a surface conditioner may be added to the hard coat coating solution. Surface modifiers are also called leveling agents, antifoaming agents, interfacial tension modifiers, and surface tension modifiers depending on their function. For the purpose of reducing the surface tension of the coating film formed by applying a hard coat coating solution to suppress coating film defects such as repellency and unevenness, or to impart antifouling properties to the formed hard coat layer It is added to the coating liquid.
The decrease in surface tension due to the surface conditioner does not affect the interference unevenness.

FIG. 1 is a schematic cross-sectional view of a hard coat film formed using the hard coat coating liquid of the present invention. In the hard coat film 1 of the present invention, the hard coat layer 12 is provided on the film substrate 11. The hard coat layer 12 is a step of applying the hard coat coating solution of the present invention on the film substrate 11 to form a coating film, a step of drying the coating film to remove the solvent, and irradiating the coating film with ionizing radiation. It can be formed by a curing step.
In the hard coat film of the present invention, another functional layer may be provided between the hard coat layer 12 and the film base 11 or on the surface of the film base on the side where the hard coat layer 12 is not provided. . As the functional layer, a functional layer having antistatic performance, electromagnetic wave shielding performance, infrared absorption performance, ultraviolet absorption performance, color correction performance, polarization performance, hard coat performance, cushion performance, antiglare brain and the like is provided. Examples of these functional layers include an antistatic layer, an antifouling layer, an electromagnetic wave shielding layer, an infrared absorption layer, an ultraviolet absorption layer, a color correction layer, a polarizing layer, a hard coat layer, a cushion layer, and an antiglare layer. A plurality of functional layers may be provided.

  Moreover, in the hard coat film of this invention, it is preferable that the layer thickness of a hard-coat layer exists in the range of 4 micrometers or more and 25 micrometers or less. When the thickness of the hard coat layer is less than 4 μm, it may be difficult for the hard coat layer to have sufficient scratch resistance. On the other hand, when the layer thickness of the hard coat layer exceeds 25 μm, the degree of curling of the hard coat film to be formed increases due to the curing shrinkage of the hard coat layer, and handling properties are reduced during the production of the hard coat film. There is. Moreover, although a hard coat film is used by bonding with other members, it may be difficult to bond with other members.

  The hard coat film of the present invention can be suitably provided on a display device such as an LCD, PDP, FED, EL, or touch panel. Particularly preferred is a touch panel.

  The material used for the hard coat coating liquid of the present invention will be described. The hard coat coating liquid of the present invention contains at least an ionizing radiation curable material and a solvent.

  Examples of the ionizing radiation curable material include polyfunctional (meth) acrylates having two or more, more preferably three or more acrylic groups and methacrylic groups in the molecule and curable by ionizing radiation. Specific examples include trimethylolpropane tri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol di (meth) acrylate, dipentaerythritol. By reacting polyol polyacrylate such as hexaa (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol tetraa (meth) acrylate, polyhydric alcohol, polyvalent isocyanate and hydroxyl group-containing (meth) acrylate Obtained by esterifying the resulting urethane (meth) acrylate polyhydric alcohol and polyhydric carboxylic acid and / or anhydride thereof and acrylic acid Kill polyester (meth) acrylate, polysiloxane polyacrylate, and the like.

  In the present invention, “(meth) acrylate” refers to both “acrylate” and “methacrylate”. For example, “urethane (meth) acrylate” indicates both “urethane acrylate” and “urethane methacrylate”.

  In addition, a polyfunctional (meth) acrylate may be used independently or may be used in mixture of 2 or more types. The content thereof is preferably in the range of 50 parts by weight or less and 100 parts by weight or less with respect to 100 parts by weight of the solid content excluding the surface conditioner of the hard coat coating solution. When the polyfunctional (meth) acrylate is less than 50 parts by weight, the hardness of the hard coat is not sufficient, and when the hard coat layer is made sufficiently hard, a hard coat layer having a larger layer thickness is required, and the cost It leads to up.

  Moreover, polyfunctional (meth) acrylate shrinks by curing. Therefore, when a hard coat coating solution is applied, dried, and cured on a film substrate, the resulting hard coat film may curl, and the subsequent workability may become a problem. Therefore, a non-polymerizable polymer or a polymerizable polymer having an acrylic group or a methacryl group in the molecule can be added to the hard coat coating liquid for the purpose of adjusting the shrinkage as required. The content thereof is preferably 50 parts by weight or less with respect to 100 parts by weight of the solid content excluding the surface conditioner of the hard coat coating liquid. When the non-polymerizable polymer or the polymer component is more than 50 parts by weight with respect to 100 parts by weight of the solid content excluding the surface conditioner of the hard coat coating liquid, the hardness of the hard coat layer is not sufficient, When the hardness is sufficient, a hard coat layer having a larger layer thickness is required, which may lead to an increase in cost. Furthermore, when it exceeds 50%, the viscosity of the polymer is high and uniform coating becomes difficult.

  It is preferable to add a fluorine-based surface conditioner or a silicone-based surface conditioner to the hard coat coating liquid of the present invention. A compound having a perfluoroalkyl group is used as the fluorine-based surface conditioner. The silicone-based surface conditioner is a derivative having polydimethylsiloxane as a basic structure, and a polydimethylsiloxane structure having a modified side chain can be used. These fluorine-based surface conditioners and silicone-based surface conditioners preferably have a carbon-carbon unsaturated double bond in the molecule. By having a carbon-carbon unsaturated double bond in the molecule and using a crosslinkable surface conditioner, the acrylic or methacrylic group of the ionizing radiation curable material when curing a coating film comprising a hard coat coating solution Can form a matrix by reacting with and chemically bond, so that the surface conditioner can be made difficult to fall off from the formed hard coat layer.

  Further, in the hard coat coating liquid of the present invention, other additives can be added. Examples of other additives that can be used include an antistatic agent, an ultraviolet absorber, an infrared absorber, a refractive index adjusting agent, an adhesion improver, a curing agent, and other surface adjusting agents. In addition, by including particles in the hard coat coating liquid, irregularities may be formed on the surface of the hard coat layer, and an antiglare function may be imparted to the hard coat layer. Inclusion of particles in the hard coat layer can suppress the glare of the reflected image formed on the surface and transferred to the film surface. Also, by diffusing the transmitted light using particles having a refractive index difference from the hard coat material, it is possible to suppress glare in the display image, color change when viewed from an oblique direction peculiar to liquid crystal display devices, Tonal change can be suppressed.

  When ultraviolet rays are used as ionizing radiation for curing the ionizing radiation curable material, a photopolymerization initiator is added to the hard coat coating solution. Although a well-known photoinitiator can be used for a photoinitiator, it is preferable to use what was suitable for the ionizing radiation curable material to be used. As a photopolymerization initiator, it is desirable to mix acetophenones, benzophenones, α-hydroxyketone, benzyldimethyl ketal, α-aminoketone, acylphosphine oxide, and the like. The amount of the photopolymerization initiator used is preferably in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the ionizing radiation curable material. Furthermore, it is preferably within the range of 1 part by weight or more and 5 parts by weight or less.

  The hard coat film of the present invention will be described. The hard coat film of the present invention comprises a hard coat layer on at least one surface of a film substrate, the step of applying the hard coat coating liquid of the present invention on the film substrate to form a coating film, and drying the coating film It is formed by a step of removing the solvent and a step of irradiating the coating film with ionizing radiation and curing.

  At this time, glass, a plastic film, etc. can be used as a film base material. The plastic film only needs to have appropriate transparency and mechanical strength. For example, polyethylene terephthalate (PET), triacetyl cellulose (TAC), diacetyl cellulose, acetyl cellulose butyrate, polyethylene naphthalate (PEN), cycloolefin polymer, polyimide, polyethersulfone (PES), polymethyl methacrylate (PMMA), A film such as polycarbonate (PC) can be used.

  Especially, a polyethylene terephthalate (PET) film can be used suitably as a film base material of this invention. The polyethylene terephthalate film has characteristics such as high transparency, good handling properties, and low cost. However, the refractive index of the polyethylene terephthalate (PET) film is 1.62, and the refractive index of the hard coat layer obtained by curing the ionizing radiation curable material made of polyfunctional (meth) acrylate is 1.51 to 1.54. And a large refractive index difference of about 0.1. When a polyethylene terephthalate (PET) film is used as the transparent film substrate, interference unevenness due to non-uniformity in the thickness of the hard coat layer, which is the subject of the present invention, is likely to occur. By using the hard coat film of the present invention, a hard coat layer without interference unevenness can be formed even when a polyethylene terephthalate (PET) film is used as the transparent film substrate.

The hard coat coating solution is applied on the film substrate, and a coating film is formed on the film substrate. Coating methods for film bases include dip coating, spin coating, flow coating, spray coating, roll coating, gravure roll coating, air doctor coating, blade coating, wire doctor coating, knife coating A method such as a method, a reverse coating method, a transfer roll coating method, a bar coating method, a micro gravure coating method, a kiss coating method, a cast coating method, a slot orifice coating method, a calendar coating method, a die coating method and the like can be used.
The solid content of the hard coat coating liquid at the time of application is preferably adjusted to, for example, 30 to 70% by weight.

  The hard coat coating solution is applied, and the coating film formed on the film substrate is dried to remove the solvent. A drying step is provided to remove the solvent in the coating. Examples of the drying means include heating, air blowing, and hot air. It is also possible to remove the solvent by natural drying.

  Subsequently, the coating film on the film substrate is irradiated with ionizing radiation, whereby the coating film is cured and a hard coat layer is formed. As the ionizing radiation, ultraviolet rays, electron beams, gamma rays, or the like can be used. When an electron beam or gamma ray is used as the ionizing radiation, it is not always necessary to contain a photopolymerization initiator or a photoinitiator auxiliary in the first hard coat layer forming coating solution. As a light source for generating ultraviolet rays, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, a carbon arc lamp, a metal halide lamp, a xenon lamp, an electrodeless discharge tube, or the like can be used. Moreover, as an electron beam, the electron beam emitted from various electron beam accelerators, such as a Cockloftwald type, a bande graph type, a resonance transformation type, an insulated core transformer type, a linear type, a dynamitron type, a high frequency type, can be used. Thus, the hard coat film of the present invention is formed.

Next, the upper electrode plate for a touch panel of the present invention will be described. In the upper electrode plate for a touch panel of the present invention, at least a transparent conductive layer is laminated on the opposite side of the hard coat layer of the hard coat film. In addition, an adhesive layer, a transparent resin film, and a transparent conductive layer may be provided in this order on the opposite side of the hard coat layer to form an upper electrode plate for a touch panel.
As an adhesive layer, the layer which consists of an acrylic adhesive or a rubber-type adhesive can be mentioned, and thickness is 10-50 micrometers. Furthermore, the layer which consists of an acrylic adhesive can be used suitably.
Moreover, as a transparent resin film, polyethylene terephthalate (PET), triacetyl cellulose (TAC), diacetyl cellulose, acetyl cellulose butyrate, polyethylene naphthalate (PEN), cycloolefin polymer, polyimide, polyethersulfone (PES), poly A film such as methyl methacrylate (PMMA) or polycarbonate (PC) can be used, and among them, a polyethylene terephthalate (PET) film can be preferably used.
Moreover, as a transparent conductive layer, the layer which consists of electroconductive materials, such as oxides, such as an indium oxide, a tin oxide, a zinc oxide, or those mixed oxides, can be mentioned. In particular, a mixed oxide (ITO) of indium oxide and tin oxide is preferably used. Further, the conductive material can contain additives such as Al, Zr, Ga, Si, and W as required. The transparent conductive layer is formed by a vacuum film forming method such as a sputtering method, a vapor deposition method, an ion plating method, or a CVD method.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not restrict | limited to the following example.

A PET film (A4300-125 μm manufactured by Toyobo Co., Ltd.) was used as the film substrate. In (Example 1) to (Example 6) and (Comparative Example 1) to (Comparative Example 5), each was prepared using the ionizing radiation curable material, photopolymerization initiator, and solvent shown in (Table 1). . It is coated on a PET film with a die coater and dried to remove the solvent contained in the coating film, and then irradiated with ultraviolet light at 400 mJ / cm ^{2 in} an atmosphere having an oxygen concentration of 0.03% or less using a high-pressure mercury lamp. Thus, the coating film was cured to prepare a hard coat film.

The following evaluations were made.
[Interference unevenness]
In order to eliminate the influence of back surface reflection, the back surface of the measurement surface (hard coat layer surface side) was roughened with sandpaper, and then colored with a black matte spray to prepare a sample. When the sample is placed in a dark room at 40 cm directly under a three-wavelength fluorescent lamp (National Parrook three-wave fluorescent lamp (FLR40S / EX-N / MX) manufactured by Matsushita Electric Industrial Co., Ltd.) The results are shown in Table 1.

Interference unevenness is not visible: ◎
Very weak interference unevenness is visible: ○
Weak interference unevenness is visible: △
Interference unevenness is clearly visible: ×

In Table 1, the materials used are as follows.
PE-3A: (Pentaerythritol triacrylate) Kyoeisha Chemical Co., Ltd.
UA-306I: (urethane acrylate) Kyoeisha Chemical Co., Ltd.
IRGACURE184: (Photopolymerization initiator) Ciba Japan Co., Ltd.

It is a schematic cross section of the hard coat film formed using the hard coat coating liquid of the present invention.

Explanation of symbols

1 Hard Coat Film 11 Film Base 12 Hard Coat Layer

Claims (6)

A hard coat coating solution containing at least an ionizing radiation curable material and a solvent,
A hard coat coating liquid comprising a solvent having a surface tension at 25 ° C. of 28 mN / m or more and 40 mN / m or less as the solvent.   The hard coat coating solution according to claim 1, wherein the solvent of the hard coat coating solution is at least one selected from cyclohexanone, cyclopentanone, dioxolane, and ethylene glycol monomethyl ether. A hard coat film comprising a hard coat layer on at least one surface of a film substrate,
The hard coat layer is a step of applying the hard coat coating solution according to claim 1 or 2 on the film substrate to form a coating film, a step of drying the coating film to remove a solvent, A hard coat film formed by a process of irradiating with ionizing radiation and curing.   The hard coat film according to claim 3, wherein the hard coat layer has a thickness of 4 μm or more and 25 μm or less.   An upper electrode plate for a touch panel, wherein at least a transparent conductive layer is laminated on the opposite side of the hard coat layer of the hard coat film according to claim 3 or 4.   The upper electrode plate for a touch panel according to claim 5, wherein an adhesive layer, a transparent resin film, and a transparent conductive layer are provided in this order on the opposite side of the hard coat layer.

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