JP2013000693A - Production method for moth-eye film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method for a moth-eye film which surely forms a fine moth-eye structure even if using no mold.SOLUTION: The production method includes an applying step of applying a coating liquid for a moth-eye layer onto a transparent base-material film, a moth-eye layer forming step of drying the coating liquid for the moth-eye layer to form the moth-eye structure, and a moth-eye layer curing step of curing the moth-eye layer by irradiation of an active-energy ray. The moth-eye layer has 60-97 wt.% of an active-energy ray curing type resin, 1-35 wt.% of a polymer component and 1-10 wt.% of a photopolymerization initiator, and also the sum of the active-energy ray curing type resin, the polymer component and the photopolymerization initiator is 99-100 wt.%. In the moth-eye layer forming step, far-infrared containing any of wavelengths of 2-20 μm is radiated to the coating liquid for the moth-eye layer to dry it.

Description

  The present invention relates to a method for producing a moth-eye film having a moth-eye structure on the surface.

  It is known that a film having a fine uneven structure on the surface exhibits an antireflection effect and a lotus effect. In particular, when the period of the concavo-convex structure (distance between convex portions or concave portions) is equal to or less than the wavelength of visible light (approximately 380 nm or less), the antireflection effect and the lotus effect are enhanced. In particular, a moth-eye film, which is called a moth-eye structure, in which a fine concavo-convex structure in which a plurality of conical or pyramidal projections are densely turbulent is formed on a substrate, has a refractive index of the substrate from the refractive index of air. By increasing the refractive index continuously, it becomes an effective antireflection means.

  There exists patent document 1 as a manufacturing method of the moth-eye film provided with such a moth-eye structure. In Patent Document 1, a base film having a surface having an arithmetic average roughness Ra of 0.06 to 0.4 μm by roughening, and a difference in refractive index from the cured layer is within ± 0.05. A step of sandwiching the active energy ray-curable resin composition between the surface and the surface of the mold having the inverted structure of the moth-eye structure on the surface, and irradiating the active energy ray-curable resin composition with the active energy ray The moth-eye film is manufactured through a process of obtaining a moth-eye film having a moth-eye layer to which the uneven shape of the mold is transferred by curing the active energy ray-curable resin composition, and a step of separating the moth-eye film and the mold. Yes.

  Patent Document 2 is also available as a film having irregularities on the surface. In Patent Document 2, the surface uneven layer is a plurality of styrene resins, (meth) acrylic resins, alicyclic olefin resins, polyester resins, aliphatic organic acid cellulose esters, and aromatic organic acid cellulose esters. And at least selected from epoxy (meth) acrylate, urethane (meth) acrylate, polyester (meth) acrylate, silicone (meth) acrylate, and a polyfunctional monomer having at least two polymerizable unsaturated bonds It is comprised with one curable resin precursor. Then, at least two components of the polymer are phase-separated by spinodal decomposition from the liquid phase, thereby forming irregularities on the surface, and subsequently curing the precursor to produce an antiglare film. At this time, in Patent Document 2, the polymer is phase-separated by hot air drying to form irregularities.

JP 2010-16441 A JP 2004-126495 A

  In the method of Patent Document 1, in order to produce a moth-eye film, it is necessary to use a mold having an inverted structure of the moth-eye structure and to transfer the structure to an active energy ray-curable resin composition, which is complicated to produce. It is.

  On the other hand, in Patent Document 2, irregularities are formed on the surface using phase separation by spinodal decomposition, but when the irregularities are formed, hot air is dried, and the average distance between domains of the phase separation structure is 1 to 70 μm. ing. That is, when drying is performed using convection as in Patent Document 2, a fine uneven structure having a period equal to or shorter than the wavelength of visible light cannot be produced, and an excellent antireflection effect or lotus effect cannot be obtained.

  Then, the place made into the objective of this invention is providing the manufacturing method of the moth-eye film which can form a fine moth-eye structure reliably, without using a mold.

  As a means for that purpose, the present invention provides a coating step for applying a moth-eye layer coating solution on a transparent substrate film, and a moth-eye structure for drying a moth-eye layer coating solution on the transparent substrate film to form a moth-eye structure. A method for producing a moth-eye film in which a moth-eye layer is formed on a transparent substrate film, comprising: a layer forming step; and a moth-eye layer curing step in which the moth-eye layer having the moth-eye structure formed is cured by irradiation with active energy rays. The moth-eye layer contains 60 to 97 wt% of the active energy ray curable resin, 1 to 35 wt% of the polymer component, and 1 to 10 wt% of the photopolymerization initiator, and the active energy ray curable resin and the polymer component. And the photopolymerization initiator is 99 to 100 wt%. In addition, in the moth-eye layer forming step, the moth-eye layer coating liquid is dried by radiating far-infrared rays having any wavelength of 2 to 20 μm.

  According to the present invention, the moth-eye layer coating liquid having a predetermined composition is dried by heat radiation, so that a fine concavo-convex moth-eye structure can be formed reliably and easily without the need for a mold. be able to. Therefore, a moth-eye film having an excellent antireflection effect, lotus effect, etc. can be easily produced.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described in detail. In the moth-eye film of this embodiment, a moth-eye layer is laminated on a transparent substrate film.

[Transparent substrate film]
The transparent substrate film serves as a moth-eye film substrate (base material), and a transparent resin film or the like is used. The resin material forming the moth-eye film is not particularly limited as long as it is a transparent resin. For example, poly (meth) acrylic resin, triacetate cellulose (TAC) resin, polyethylene terephthalate (PET) resin, polycarbonate (PC) resin Examples thereof include resins. Among them, triacetate cellulose (TAC) resin or polyethylene terephthalate (PET) resin is preferable from the viewpoint of versatility. The thickness of the transparent substrate film is usually 10 to 500 μm, preferably 25 to 200 μm.

[Moss eye layer]
The moth eye layer is a layer laminated directly on the transparent base film, and has a moth eye structure on the surface thereof. The moth-eye structure is a concavo-convex structure in which a plurality of conical or pyramidal protrusions are densely lumped. The period of the moth-eye structure formed in this embodiment (the distance between the convex portions or the concave portions) is at least the wavelength of visible light (about 380 nm or less). Thereby, an antireflection effect and a lotus effect become high. Specifically, the arithmetic average roughness Ra (JIS B0601-1994) of the moth-eye layer is 0.05 to 0.30 μm, and the average interval Sm (JIS B0601-1994) of the unevenness is 0.001 mm or less. . When Ra of the moth-eye layer is less than 0.05 μm and Sm is 0.001 mm or less, the refractive index is insufficient to continuously increase from the refractive index of air to the refractive index of the transparent base film, and the reflection The prevention effect cannot be obtained. Further, when Ra of the moth-eye layer is larger than 0.30 μm, Sm is larger than 0.001 mm, and only a concavo-convex structure having a period larger than the wavelength of visible light can be formed, and a sufficient antireflection effect cannot be obtained. . Furthermore, even if Ra is 0.05 to 0.30 μm, when Sm is larger than 0.001 mm, only a concavo-convex structure having a period longer than the wavelength of visible light can be formed, and a sufficient antireflection effect can be obtained. I can't.

  The moth-eye layer is formed by a cured product obtained by curing a moth-eye layer coating liquid containing an active energy ray-curable resin, a polymer component, and a photopolymerization initiator. The sum of the active energy ray-curable resin, the polymer component, and the photopolymerization initiator is 99 to 100 wt% with respect to 100 wt% of the cured moth-eye layer. It can be added in a range. As other components, a leveling agent and the like are blended. The moth-eye layer coating liquid usually contains a diluting solvent from the viewpoint of coating properties. In the present invention, fine particles that actively form irregularities are not included.

(Active energy ray-curable resin)
The active energy ray-curable resin is a main component of the moth-eye layer coating liquid for expressing unevenness. As such an active energy ray-curable resin, one or more kinds selected from a monofunctional monomer and a polyfunctional monomer are used. Specifically, (meth) acrylic acid alkyl ester, (meth) acrylic acid (poly) ethylene glycol group-containing (meth) acrylic acid ester and the like are preferable as the monofunctional monomer. Examples of the polyfunctional monomer include ester compounds of polyhydric alcohol and (meth) acrylic acid, polyfunctional polymerizable compounds containing two or more (meth) acryloyl groups such as urethane-modified acrylate, and the like. In the present specification, “(meth) acrylic acid” means acrylic acid or methacrylic acid. The same applies to “(meth) acryloyl group” and “(meth) acrylic resin”.

  The blending amount of the active energy ray-curable resin is 60 to 97 wt% with respect to 100 wt% of the moth eye layer. When the amount is less than 60 wt%, the unevenness of the moth-eye structure tends to be reduced, and the coating film strength becomes weak. On the other hand, when it is more than 97 wt%, the blending amount of the photopolymerization initiator is relatively reduced, and the coating strength tends to be weakened.

(Polymer component)
The polymer component is a compound that dissolves in the moth-eye layer coating solution. Examples of such a polymer component include a thermoplastic resin having a weight average molecular weight of 1,000 to 500,000, a polymer having a (meth) acryloyl group, and the like. Examples of thermoplastic resins include styrene resins, styrene / (meth) acrylic resins, (meth) acrylic resins, organic acid vinyl ester resins, vinyl ether resins, polyester resins, thermoplastic polyurethane resins, and cellulose derivatives. Can be mentioned. Examples of the polymer having a (meth) acryloyl group include a resin obtained by polymerizing or copolymerizing a (meth) acrylic monomer, and a resin obtained by copolymerizing a (meth) acrylic monomer and another monomer having an ethylenically unsaturated double bond. , A resin obtained by reacting a (meth) acryl monomer with another monomer having an ethylenically unsaturated double bond and an epoxy group, a monomer having a (meth) acryl monomer and another ethylenically unsaturated double bond and an isocyanate group And the like. Among these, styrene / (meth) acrylic resins are preferable from the viewpoint of optimally expressing the moth-eye structure (antireflection effect).

  The blending amount of the polymer component is 1 to 35 wt% with respect to 100 wt% of the moth eye layer. As the blending amount of the polymer component is smaller, the unevenness of the moth-eye structure tends to increase, but when it is less than 1 wt%, the unevenness does not appear and antireflection properties cannot be obtained. On the other hand, when it exceeds 35 wt%, the unevenness, that is, Ra becomes small.

(Photopolymerization initiator)
The photopolymerization initiator is used as an initiator for forming a coating film by curing the moth-eye layer coating liquid with active energy rays such as ultraviolet rays (UV). The photopolymerization initiator is not particularly limited as long as it initiates polymerization upon irradiation with active energy rays, and known compounds can be used. For example, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropane-1 -One, acetophenone polymerization initiators such as 1- [4- (2-hydroxyethoxy) phenyl] -2-hydroxy-2-methyl-1-propan-1-one, benzoin, 2,2-dimethoxy 1,2 -Benzoin polymerization initiators such as diphenylethane-1-one, benzophenone, [4- (methylphenylthio) phenyl] phenylmethanone, 4-hydroxybenzophenone, 4-phenylbenzophenone, 3,3 ', 4,4' -Benzophenone polymerization initiators such as tetra (t-butylperoxycarbonyl) benzophenone, 2-chlorothio Sandton, such thioxanthone type polymerization initiators such as 2,4-diethyl thioxanthone, and the like.

  The compounding quantity of a photoinitiator shall be 1-10 wt% with respect to 100 wt% of moth-eye layers. When the blending amount of the photopolymerization initiator is less than 1 wt%, it is not preferable because the moth-eye layer coating liquid does not harden even when irradiated with active energy rays. On the other hand, a compounding amount exceeding 10 wt% is not preferable because it is unnecessarily large for curing.

[Formation of moth eye layer]
The moth-eye layer is produced by the following process.
Step 1: Application step of applying a moth-eye layer coating solution on a transparent substrate film Step 2: Drying the moth-eye layer coating solution on the transparent substrate film to form a moth-eye structure Step 3: A moth-eye layer curing process in which the moth-eye layer formed with the moth-eye structure is cured by irradiation with active energy rays.

(Process 1)
The application method of the moth-eye layer coating liquid is not particularly limited, and is known, for example, roll coating method, spin coating method, dip coating method, spray coating method, bar coating method, knife coating method, die coating method, ink jet method, gravure coating method, etc. Any method is adopted. In addition, in order to improve adhesiveness, it is also possible to perform pre-treatments such as corona discharge treatment on the surface of the transparent substrate film in advance.

(Process 2)
As a drying method used in the moth-eye layer forming step, a method of radiating light having a wavelength of 2 to 20 μm in a far infrared drying furnace is used. The far-infrared drying furnace here is different from convection in which heated fluid is heated using a fluid such as air or heat transfer in which the heat source is in contact with the object to be heated. Contact heating is a drying furnace that utilizes radiation using electromagnetic waves. In addition, among infrared rays which are a kind of electromagnetic waves, those in the wavelength region of 1 to 1000 μm are called far infrared rays. In order to form a moth-eye layer, light containing any wavelength of 2 to 20 μm is used. It is necessary to use it. By radiating light of this wavelength, the coating layer undergoes molecular motion, and as a result, unlike the drying using convection or heat transfer, the surface temperature of the coating layer is not increased, that is, the surface temperature of the coating layer is low. While maintaining this state, the coating layer can be dried in a short time. Therefore, a fine moth-eye structure in which the period of the concavo-convex structure is not more than the wavelength of visible light can be formed.

  Generally, when drying a coating layer prepared by wet coating, a hot-air drying furnace (convection) is used. In this case, hot air at the hot air set temperature directly hits the coating layer, and the surface temperature of the coating layer is high. Thus, the coating layer is dried. When a hot air drying furnace is used in the present invention, the surface of the moth-eye layer is directly heated. As a result, the uneven shape of the moth-eye structure becomes gentle, Ra on the surface of the moth-eye layer is small, and Sm is large.

(Process 3)
As an active energy ray source for curing the moth-eye layer, for example, a high-pressure mercury lamp, a halogen lamp, a xenon lamp, a nitrogen laser, an electron beam accelerator, a radioactive element or the like is used. In this case, it is preferable that the irradiation amount of an active energy ray is 50-5000 mJ / cm < ² > as an integrated light quantity in ultraviolet wavelength 365nm. When the irradiation amount is less than 50 mJ / cm ² , curing of the coating liquid becomes insufficient, which is not preferable. On the other hand, when it exceeds 5000 mJ / cm ² , the active energy ray-curable resin tends to be colored, which is not preferable. In addition, in order to improve the hardening degree of a coating layer, it is also possible to perform ultraviolet irradiation in nitrogen atmosphere.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. Here, the moth-eye films of the examples and comparative examples have a structure in which a moth-eye layer is laminated on one surface of the transparent substrate film. Moreover, the visibility reflectance, Ra, and Sm in each example were measured by the following methods.

<Visibility reflectance>
In order to remove the back surface reflection of the measurement surface, a film whose surface was roughened with sandpaper and painted with a black paint was measured with a spectrophotometer [manufactured by JASCO Corporation, product name: U-best 560] at a wavelength of light of 380 to 380. A 5 ° and −5 ° specular reflection spectrum at 780 nm was measured. Using the obtained spectral reflectance of 380 to 780 nm and the relative spectral distribution of CIE standard illuminant D65, the tristimulus value Y of the object color due to reflection in the XYZ color system defined by JIS Z8701 is obtained as the luminous reflectance. It was.

<Arithmetic mean roughness (Ra)>
Arithmetic average roughness in accordance with the provisions of JIS B0601-1994, using a surface roughness measuring instrument (manufactured by Kosaka Laboratory, model name Surfcoder SE500) under the conditions of a scanning range of 4 mm and a scanning speed of 0.2 mm / s. Ra (μm) was measured.

<Average interval of unevenness (Sm)>
Using a surface roughness measuring instrument (manufactured by Kosaka Laboratory Co., Ltd., model name Surfcorder SE500) under the conditions of a scanning range of 4 mm and a scanning speed of 0.2 mm / s, the average spacing of irregularities according to the provisions of JIS B0601-1994 (Mm) was measured.

[Preparation of moth-eye layer coating solution]
The following raw materials were used as the moth-eye layer coating liquid, and the respective raw materials were mixed in the composition shown in Table 1 to prepare moth-eye layer coating liquids M-1 and M-2. The numerical values in Table 1 are wt%.
Active energy ray curable resin: Hexafunctional urethane acrylate (purple light UV-7600B manufactured by Nippon Synthetic Chemical Industry Co., Ltd.)
Polymer component: Styrene (meth) acrylic resin (BR-50 manufactured by Mitsubishi Rayon Co., Ltd.)
Photopolymerization initiator: I-184 manufactured by Ciba Specialty Chemicals Co., Ltd.
Solvent: methyl isobutyl ketone

Example 1
The moth-eye layer coating solution (M-1) was applied on a 100 μm-thick polyethylene terephthalate (PET) film as a transparent substrate film with a bar coater so that the thickness of the cured moth-eye layer was 3.0 μm. (Step 1). Subsequently, light containing a wavelength of 6 to 20 μm was radiated by a far infrared heating furnace [DIR631 manufactured by Yamato Scientific Co., Ltd.] and dried at 50 ° C. for 10 seconds (step 2). Thereafter, ultraviolet light was irradiated with a 120 W high-pressure mercury lamp (manufactured by Nippon Battery Co., Ltd.) under a nitrogen atmosphere (accumulated light amount 400 mJ / cm ² ) to cure the moth-eye layer (Step 3) to produce a moth-eye film.

(Comparative Example 1)
The same method as in Example 1 except that the far-infrared heating furnace was changed to a hot air drying furnace [F0-30W (WT) manufactured by Tokyo Glass Instruments Co., Ltd.] in Step 2 (same drying temperature and time). A moth-eye film was prepared.

(Comparative Example 2)
In Step 1, an active energy ray cured film was produced in the same manner as in Example 1 except that the moth-eye layer coating liquid was changed to M-2.

Table 2 shows the configurations and test results of the examples and comparative examples.

From the results shown in Table 2, in Example 1, the surface irregularities (Ra, Sm) are appropriately formed, and the visibility reflectance, that is, the antireflection effect is excellent. On the other hand, in Comparative Example 1, since a hot air drying furnace was used when forming the moth-eye structure, Sm was wide and the visibility reflectance was poor. In Comparative Example 2, Ra is small and the visibility reflectance is poor because the polymer component is not properly blended in the moth-eye layer coating liquid.

Claims (1)

An application step of applying a moth-eye layer coating liquid on the transparent substrate film;
A moth-eye layer forming step of drying a moth-eye layer coating liquid on the transparent substrate film to form a moth-eye structure;
A moth-eye layer curing step for curing the moth-eye layer formed with the moth-eye structure by irradiation with active energy rays;
A method for producing a moth-eye film in which a moth-eye layer is formed on a transparent substrate film,
The moth-eye layer contains 60 to 97 wt% of active energy ray curable resin, 1 to 35 wt% of a polymer component, and 1 to 10 wt% of a photopolymerization initiator, and the active energy ray curable resin, the polymer component, and the The sum with the photopolymerization initiator is 99 to 100 wt%,
In the moth-eye layer forming step, far-infrared radiation including any wavelength of 2 to 20 μm is radiated to the moth-eye layer coating solution.