JP2009265548A - Method of manufacturing optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress, in a method of manufacturing an optical film comprising a step of providing a hard coat layer on one surface of a transparent resin film, curling caused in the manufacturing process without taking a complicate and expensive measure such as: detailed adjustment of the film thickness, molecular weight or hardness of a hard coat used; the composition of an additive; the structure of a resin used or the like; treatment of the whole film surface with solvent or gas; or application of a back coat layer. <P>SOLUTION: In the method of manufacturing the optical film 1 including the step of providing the hard coat layer 12 on one surface of the transparent resin film 11, solvent treatment is performed to the optical film backside which is a surface opposite to the surface having the hard coat layer 12 formed thereon. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an optical film, and more particularly to a method for manufacturing an optical film that is prevented from curling.

  In an image display device such as a liquid crystal display device (LCD) or a plasma display panel (PDP), an optical film for imparting various characteristics is generally provided on the outermost surface. For example, an antireflection film (antireflection film) that reduces the reflectivity by using the principle of optical interference and prevents contrast reduction or image reflection due to reflection of external light is an example. Since such an optical film is usually disposed on the outermost surface of a display device, a hard coat layer is provided for the purpose of surface protection.

  The hard coat layer is required to have high hardness and high scratch resistance, and in order to improve the film hardness, there are methods such as increasing the thickness of the hard coat layer and increasing the degree of cure of the resin forming the hard coat layer. However, this increases the curl of the optical film and often causes a problem of deterioration in handling.

  In particular, due to the recent increase in the size of image display devices, a wider optical film has been demanded than in the past. Yield and productivity decrease. In order to suppress the occurrence of curling, in addition to limiting the film thickness of the hard coat layer, there have been devised various adjustments such as molecular weight, degree of cure, additive composition, resin structure used (Patent Document 1). -3), it is difficult to achieve both the curl reduction of the film, the high hardness and the high scratch resistance only by adjusting the hard coat layer.

  As a curling mitigation method other than the adjustment of the hard coat layer, a treatment with a solvent or a gas is performed on the back side of the surface on which the hard coat layer is provided (see Patent Document 4), and a back coat layer for preventing curling is provided. However, when processing is performed on the entire back surface, it is necessary to consider the influence of the processing on performance such as haze and transmitted light amount. Furthermore, the method of providing the backcoat layer also greatly increases the cost of equipment and materials for that purpose.

Moreover, when creating an optical film, particularly strong curled portions are both ends of the film, and this leads to a deterioration in the overall handling. The method cannot avoid the yield reduction.
Japanese Patent Laid-Open No. 2005-288921 JP 2002-233501 A JP 2005-181996 A JP-A-9-218302 JP-A-9-201912 JP 2004-250614 A

  Therefore, an object of the present invention is to provide an optical film manufacturing method that does not affect the performance required as an optical film, such as physical strength and optical properties, and suppresses curling of the film during the process inexpensively and easily. It is to be.

Invention of Claim 1 is a manufacturing method of the optical film which has the process of providing a hard-coat layer in the single side | surface of a transparent resin film, It is a solvent with respect to the optical film back surface on the opposite side to the surface where the said hard-coat layer is provided. It is a manufacturing method of the optical film characterized by performing a process.
Invention of Claim 2 is a manufacturing method of the optical film characterized by performing a solvent process with respect to the edge part of the said optical film back surface in the manufacturing method of the optical film of Claim 1.
Invention of Claim 3 is a manufacturing method of the optical film of Claim 2, It is a manufacturing method of the optical film characterized by performing a solvent process using the solvent which swells or melt | dissolves the said transparent resin film. is there.

  According to the present invention, in the method for producing an optical film having a step of providing a hard coat layer on one side of a transparent resin film, a solvent treatment is performed on the other side which is the back side of the other side instead of the surface on which the hard coat layer is provided. Therefore, the hard coat layer and other various thin film layers existing on the same side as the surface on which the hard coat layer is provided, such as an antireflection layer, an antistatic layer, an infrared absorption layer, an antifouling layer, an electromagnetic wave shielding layer, etc. It is possible to suppress curling without directly acting and without affecting the physical strength and required performance.

  In addition, according to the present invention, the solvent treatment is performed by narrowing the narrow range at both ends of the film, which is particularly strong in curl and causes the entire handling deterioration. There is little influence on the product performance such as the amount of light, and curling can be effectively suppressed at low cost.

Embodiments of the present invention will be described below.
FIG. 1 shows a schematic cross-sectional view of the present invention. The optical film 1 in the present invention refers to a transparent resin film 11 provided with a hard coat layer 12 on one side, and has various functions such as antireflection, infrared absorption, antifouling, and electromagnetic wave shielding in addition to the hard coat layer. Also included are those having one or more functional layers for application.

  The transparent resin film used as a base material in the present invention is an acetyl cellulose resin film typified by triacetyl cellulose (TAC), but can be used as an optical film such as a polyester film or a polycarbonate film. Any of them can be used.

  The solvent treatment performed in the present invention refers to the solvent, specifically the transparent resin film as the base material, with respect to the optical film back surface opposite to the surface on which the hard coat layer is provided of the transparent resin film as the base material. It is carried out by spraying or applying a coating solution containing a solvent that swells or dissolves the solution. This gives the base film the property of curling with the treated surface inside.

  The main cause of curling that occurs in an optical film having a hard coat layer is the curing shrinkage of the resin used in the hard coat layer, and the surface on which the hard coat layer exists is on the inside. Therefore, if curling in the reverse direction with the back surface being the inner side is generated on the back surface of the base film, the entire curl can be reduced.

  There is no particular limitation on the method for performing the solvent treatment in the present invention. For example, any of the methods of spraying using a spray, applying using a roll, a wire bar, a blade, a die coater, etc. may be used. A method may be used.

  Further, the solvent treatment step may be performed before or after the hard coat layer is provided, or at the same time as the step of providing the hard coat layer.

  The solvent used for the solvent treatment in the present invention may be any solvent that swells or dissolves the transparent resin film used as the base film. Examples of triacetyl cellulose (TAC) include methyl ethyl ketone, ethyl acetate and dimethyl carbonate as solvents that swell the same, and methyl acetate, 1,3-dioxolane, and methylene chloride as solvents that dissolve. However, other solvents such as chloroform, toluene, and acetone can be used depending on the properties of the transparent resin film used as the substrate. Moreover, these may be used not only individually but also in a mixture, and in addition to these, a solvent appropriately mixed with a solvent that does not swell or dissolve the base film may be used.

  The resin used for forming the hard coat layer in the present invention is mainly an active energy ray curable resin typified by an ultraviolet curable resin and an electron beam curable resin, but also has a high hardness and a high scratch resistance. Any material may be used as long as it has physical strength and optical performance required for a hard coat, such as adhesion to a substrate and transparency. These may be used alone or in admixture with monomers or prepolymers. Depending on the purpose and application, organic or inorganic fine particles, antioxidants, surface modifiers and other additives other than resins may be added. Also good.

  In the optical film of the present invention, a hard coat layer is formed by applying a coating liquid for forming a hard coat layer containing an active energy ray-curable resin and irradiating ultraviolet rays or electron beams after the application. The optical film of the present invention uses a web-like transparent resin film and is continuously formed by a roll-to-roll system using a coating apparatus.

  In the case of the optical film, it is preferable that the solvent treatment is performed only on the end portion. By performing the solvent treatment only on the end portion where the degree of curling is strong, curling can be effectively reduced. In forming the hard coat layer by the roll-to-roll method, it is preferable to perform the solvent treatment only on the end portion in the direction perpendicular to the traveling direction of the transparent resin film. Moreover, it is preferable that only the end portion is subjected to solvent treatment, and the end portion subjected to the solvent treatment when the obtained optical film is provided in the image display device is an unnecessary portion. In the manufactured optical film, the solvent-treated portion may have changed optical characteristics, and the end portion is preferably not used when provided in the image display device.

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

  A hard coat coating solution is applied on a 40 μm thick triacetyl cellulose film by a bar coating method, dried in an oven, and then irradiated with ultraviolet rays to form a hard coat layer having a thickness of about 6 to 7 μm. A standard sample was used.

  The hard coat coating solution used was a UV-curable polyfunctional urethane acrylate prepolymer added with a radical polymerization initiator and diluted to 45% solids with ethyl acetate.

  Methyl ethyl ketone was applied on a 40 μm thick triacetyl cellulose film by a bar coating method and dried in an oven. Then, a hard coat coating solution is applied to the other side, which is the reverse side of the solvent-treated side, by a bar coating method, dried in an oven, and then irradiated with ultraviolet rays to form a hard coat having a thickness of about 6 to 7 μm. A layer was formed and used as Comparative Sample 1.

  A hard coat coating solution was applied onto a 40 μm thick triacetylcellulose film by a bar coating method, dried in an oven, and then irradiated with ultraviolet rays to form a hard coat layer having a thickness of about 6 to 7 μm. Thereafter, methyl ethyl ketone was applied to the other surface corresponding to the back side of the surface coated with the hard coat by a bar coating method and dried in an oven.

  A test piece of 1.5 mm × 15 mm having a long side in the width direction of the base film was cut out from the standard sample and comparative samples 1 and 2, and the curvature radius was determined by regarding the curl of the test piece as an arc. The results are shown in Table 1.

[Table 1]

  Both comparative samples 1 and 2 had a larger radius of curvature than the standard sample, and the effect of curling reduction by solvent treatment was recognized.

  Furthermore, after forming a hard coat layer on the triacetyl cellulose film in the same manner as the standard sample, on the other side of the side where the hard coat layer was applied, methyl ethyl ketone was applied only to the end 20 mm range. Then, it was dried in an oven, and this was used as Comparative Sample 3.

  A test piece (1) having a width of 1.5 mm was cut out from the standard sample and the comparative sample 3 in parallel with the width direction of the base film, and placed on the horizontal surface (2) so that the hard coat layer side was on the top. As shown in Fig. 3, the height (3) from the horizontal plane to the edge was measured. The results are shown in Table 2.

[Table 2]

  In Comparative Sample 3, the height from the horizontal plane to the end portion was reduced as compared with the standard sample, and the effect of curling reduction by solvent treatment was recognized.

Industrial applicability

  According to the present invention, in the production of an optical film provided with a hard coat layer on one side of a transparent resin film, without affecting the physical strength or other required performance of various thin film layers including the hard coat layer, and Curling can be effectively suppressed at low cost, thereby contributing to stabilization of the quality of the optical film, improvement of productivity and yield, and reduction of manufacturing costs.

It is a schematic cross section of the optical film of the present invention. It is a schematic diagram of curl evaluation in the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Hard coat film 11 ... Transparent resin film 12 ... Hard coat layer 2 ... Horizontal surface 3 ... Height from a horizontal surface to a sample edge part

Claims (3)

  An optical film manufacturing method comprising a step of providing a hard coat layer on one side of a transparent resin film, wherein a solvent treatment is performed on the back side of the optical film opposite to the side on which the hard coat layer is provided. A method for producing a film.   The method for producing an optical film according to claim 1, wherein a solvent treatment is performed on an end of the back surface of the optical film.   The method for producing an optical film according to claim 2, wherein a solvent treatment is performed using a solvent that swells or dissolves the transparent resin film.

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