JP6658255B2 - Optical film manufacturing method - Google Patents

Description

  The present invention relates to a method for producing an optical film, and more particularly, to a method for producing an optical film provided with an optical function by applying a coating solution to a film substrate.

  The optical film has a function of transmitting or reflecting light of various wavelengths. Such an optical film is formed by applying a coating liquid for imparting a function of transmitting or reflecting a specific wavelength to a film-like substrate. Above all, in recent years, there is a transparent infrared shielding film as an optical film that transmits or reflects a specific wavelength simply by being attached to a window or the like. The transparent infrared shielding film has a function of transmitting a wavelength in a visible light region and reflecting a wavelength in an infrared region. In such a method for producing an optical film, simultaneous multilayer coating using a slide surface is used in terms of performance and cost.

  Conventionally, a slide hopper type coating apparatus has been used for simultaneous multilayer coating. The slide hopper type coating apparatus is suitably used for the production of a multilayer laminated film as a wet film forming apparatus capable of simultaneously applying a plurality of coating liquids in multiple layers. There is a demand for a manufacturing method that reduces unevenness in the manufacturing process.

  For example, in Patent Document 1, a distance (hereinafter, referred to as a slit portion) from a portion (hereinafter, referred to as a chamber) where a coating solution in a slide hopper type coating device is widened to a coating width in a width direction of a base film (hereinafter, referred to as a chamber) is described. A manufacturing method for improving the uniformity of the quality of a coating film by setting the length (noted as length) to 40 mm or more is disclosed. According to this manufacturing method, it is possible to provide a small and lightweight slide hopper type coating apparatus having high uniformity of coating film quality.

JP 2009-28604 A

  However, high uniformity is required for the method of manufacturing an optical film because of the need to transmit or reflect a specific wavelength. In particular, due to uneven coating or uneven coating such as streaks, transmitted light is refracted or irregularly reflected, causing a reduction in visibility when the optical film is attached to a window. In this regard, the prior art still has room for improvement.

  Therefore, an object of the present invention is to provide a method for manufacturing an optical film that can suppress the occurrence of uneven coating.

  The above object of the present invention is achieved by the following means.

(1) A method for producing an optical film in which an optical functional layer is formed by simultaneously coating at least two or more layers on a substrate,
When a droplet of the coating liquid used for the simultaneous multilayer coating is vertically dropped on the substrate, the contact angle of the droplet at the time of 50 msec after the contact of the droplet with the substrate is 70 degrees or less. A method for producing an optical film, comprising applying the coating liquid as the lowermost coating liquid during the simultaneous multi-layer coating.

  (2) When a droplet of a coating liquid used in the simultaneous multi-layer coating is vertically dropped on the substrate, the contact angle of the droplet at a time of 50 msec after the droplet contacts the substrate is (1) The method for producing an optical film according to (1), wherein the coating liquid having a temperature of 70 ° or less is applied as the uppermost coating liquid during the simultaneous multi-layer coating.

(3) The lowermost layer coating liquid has a viscosity of 0.5 cp to 30 cp,
The method for producing an optical film according to (1) or (2), wherein the amount of the lowermost layer coating solution is 10 to 50 g / m ² .

(4) The method for producing an optical film according to any one of (1) to (3), wherein the coating amount of the entire optical functional layer is 50 to 150 g / m ² .

  (5) The method for producing an optical film according to any one of (1) to (4), wherein a coating speed during the simultaneous multilayer coating is 5 to 200 m / min.

  (6) The method for producing an optical film according to any one of (1) to (5), wherein the optical functional layer includes polyvinyl alcohol having different degrees of saponification.

  (7) The method for producing an optical film according to any one of (1) to (6), wherein the optical functional layer is an infrared reflective layer.

  According to the present invention, since the coating liquid having a contact angle of 70 degrees or less at the time of 50 msec after the droplet of the coating liquid comes into contact with the base material is used for the lowermost layer of the simultaneous multi-layer coating, it is applied to the base material. Since the liquid can be applied with a uniform thickness, the occurrence of application unevenness can be suppressed.

It is sectional drawing which shows the structure of the optical film formed by the simultaneous multilayer coating in embodiment to which this invention is applied. It is a schematic diagram for explaining a contact angle. It is the schematic which shows the whole structure of the coating device for performing simultaneous multilayer coating. It is the schematic which shows the detail of the application part of an application device. It is a schematic diagram for demonstrating the moment when a coating liquid contacts a base material at the time of the start of simultaneous multilayer coating. It is a schematic diagram for demonstrating the state after a coating liquid contacts a base material in simultaneous multilayer coating. 4 is a graph showing the measurement results of the contact angle over time with respect to the lowermost coating solution used in Examples 1, 2 and 4.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. In addition, the dimensional ratios in the drawings are exaggerated for convenience of description, and may be different from the actual ratios.

  FIG. 1 is a cross-sectional view showing a structure of an optical film formed by simultaneous multilayer coating in an embodiment to which the present invention is applied.

  The optical film 10 has a coating layer 30 applied on a film-like base material 20. The coating layer 30 is a simultaneous multi-layer coating layer that becomes an optical functional layer. Here, the high-refractive-index layers 32 and the low-refractive-index layers 34 are alternately and simultaneously applied by the simultaneous multilayer application method. The coating layer 30 is a coating film 40 applied on the base material 20 by a coating device. The details of the coating apparatus for performing the simultaneous multi-layer coating will be described later (see FIG. 3). However, the number of the coating layers 30 to be stacked on the base material 20 being transported (moved) by the transport system 110 is set so as to be predetermined. The coating liquid 300 flows out from the die coater 120 so as to form a plurality of layers, and is applied.

The number of layers of the coating layer 30 is preferably 200 layers or less, more preferably 100 layers or less, and still more preferably 50 layers or less from the viewpoint of productivity. The thickness per layer is 1 to 1000 nm. The amount of the coating solution for all such layers is 50 to 150 g / m ² .

  In the following, the terms “high refractive index layer” and “low refractive index layer” mean the higher refractive index and the lower refractive index, respectively, when comparing the refractive index difference between two adjacent layers.

  The lowermost layer of the coating layer 30 adjacent to the base material 20 and the uppermost layer exposed to the outside are formed of the low refractive index layer 34. In the intermediate layer located between the lowermost layer and the uppermost layer, the high refractive index layers 32 and the low refractive index layers 34 are alternately arranged.

  In the present embodiment, the initial contact angle with the substrate 20 is 70 degrees or less, preferably 60 degrees or less, as the coating liquid 300 forming the lowermost layer 351 of the coating layer 30 formed by such simultaneous multilayer coating. .

In the present embodiment, the initial contact angle with the base material 20 of the coating liquid 300 forming the uppermost layer 352 of the coating layer 30 is also preferably 70 degrees or less. In the multilayer structure shown in FIG. 1, the lowermost layer 351 and the uppermost layer 352 are both low refractive index layers 34. The liquid 300 may be used. Of course, the present invention is not limited to such a multilayer structure, and the lowermost layer 351 and the uppermost layer 352 may use coating liquids having different functions, components, or compositions. In that case, the lowermost layer of the coating liquid has an initial contact angle with the substrate 20 of 70 degrees or less, and preferably, the uppermost layer 352 of the coating liquid 300 also has an initial contact angle with the substrate 20 of 70 degrees or less. It is better to

  FIG. 2 is a schematic diagram for explaining a contact angle. As is well known, the contact angle itself is defined as the angle between the liquid surface and the solid surface (takes an angle inside the liquid) where the free surface of the stationary liquid contacts the solid wall. If this is applied to the present embodiment, as shown in FIG. 2, the contact angle is such that a droplet 301 of the coating liquid 300 is vertically dropped on the substrate 20, and the liquid surface of the droplet 301 is And the angle θ formed by The “initial contact angle” used in the present embodiment is a contact angle of a droplet 301 at a time point of 50 msec from the moment (0 msec) when the droplet 301 of the coating liquid 300 contacts the substrate 20. When the droplet 301 is dropped on the substrate 20, the shape of the coating liquid changes over time. Therefore, in order to define the characteristics of the coating liquid by the contact angle, it cannot be specified unless a time scale is used. Therefore, as described above, the initial contact angle is specified.

  The contact angle changes depending not only on the characteristics of the coating liquid but also on the state of the surface of the substrate 20. Therefore, it is also possible to change (modify) the state of the substrate surface in order to reduce the initial contact angle to 70 degrees or less. For example, the initial contact angle of the coating liquid with the substrate can be reduced to 70 degrees or less by performing a plasma treatment on the surface of the substrate, that is, a plasma treatment for improving so-called wettability.

  However, in the case of an optical film, if the surface of the substrate is modified, the optical characteristics also change. For example, in an optical film that reflects a specific wavelength and transmits another wavelength, the transparency may decrease, and there is a limit to the modification of the substrate surface.

  Therefore, in the present embodiment, the initial contact angle is set to 70 degrees or less mainly by changing the characteristics of the coating liquid.

  In order to reduce the initial contact angle of the coating solution to 70 degrees or less, for example, a surfactant is added. The initial contact angle can be reduced by increasing the amount of the surfactant added. As the surfactant, various anionic, cationic or nonionic surfactants can be used.

  Also, the initial contact angle can be reduced by adding an organic solvent. The organic solvent used may be the same as the solvent for preparing the coating solution for the high refractive index layer and the coating solution for the low refractive index layer, and is not particularly limited. Examples of the organic solvent include alcohols such as methanol, ethanol, 2-propanol (isopropyl alcohol) and 1-butanol; esters such as ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; Examples include ethers such as diethyl ether, propylene glycol monomethyl ether, and ethylene glycol monoethyl ether; amides such as dimethylformamide and N-methylpyrrolidone; and ketones such as acetone, methyl ethyl ketone, acetylacetone, and cyclohexanone. These organic solvents may be used alone or in combination of two or more.

  To control the initial contact angle using an organic solvent, the initial contact angle can be reduced by increasing the amount of the organic solvent added.

  The addition amount of the surfactant and the organic solvent varies depending on the components of the coating solution, and is not limited. The addition amount is adjusted so that the initial contact angle is 70 degrees or less, preferably 60 degrees or less. Further, a surfactant and an organic solvent may be added respectively, or only one of them may be added.

  Note that the lower limit of the initial contact angle may be 0 (zero) degrees, and the lower limit is not limited.

  The viscosity of the lowermost layer coating solution (after the initial contact angle is adjusted to 70 ° or less) is preferably 0.5 to 30 cp. By using a coating liquid having such a viscosity range, the liquid adhesion to the base material during coating is improved, and high-speed coating can be performed. The viscosity can be adjusted by adding water (pure water). When water is added, the viscosity can be lowered by increasing the amount of water. On the other hand, the viscosity can be increased by reducing the amount of added water or evaporating and concentrating water.

Further, it is preferable that the application amount of the lowermost coating liquid applied at the time of simultaneous multilayer coating is 5 to 50 g / m ² . More preferably, it is 10 to 50 g / m ² . If the coating amount of the lowermost layer is less than 5 g / m ² , the layer thickness as the lowermost layer may be too thin to be applied uniformly. On the other hand, if it is applied in excess of 50 g / m ² , there is a possibility that only the lowermost layer becomes too thick due to the relationship with the adjacent layer, so that desired optical characteristics cannot be obtained. However, such an application amount is not limited to the above range. In particular, the upper limit may not be affected even if the thickness is increased (even if the layer thickness is increased) in consideration of the thickness of the adjacent layer and the like, and may be appropriately adjusted according to the optical film to be manufactured.

  Here, specific examples of the material of the coating liquid 300 (the components excluding the above-described surfactant for adjusting the contact angle and viscosity, the organic solvent, and water) will be described.

  An optical reflection film that reflects a specific wavelength will be described as an example of the optical film. The optical reflection film has a configuration in which a laminate including a high refractive index layer and a low refractive index layer is disposed on at least a substrate. With such a configuration, a light beam having a specific wavelength is reflected by appropriately controlling the optical film thickness (film thickness × refractive index) of the high refractive index layer and the low refractive index layer.

  The optical reflection film becomes, for example, an ultraviolet shielding film when reflecting a light ray (ultraviolet light) having a wavelength of 200 to 400 nm, and becomes a visible light coloring film when reflecting a light ray (visible light) having a wavelength of 400 to 700 nm. In the case of reflecting a light beam (infrared ray) of 700 to 1200 nm, it can be an infrared shielding film.

  In addition, by appropriately designing the optical film thickness and the like of the laminate, the wavelength and the reflectance of the reflected light can be controlled to obtain a metallic glossy film. Among these, the light that can be blocked by the optical reflection film is preferably a light in the ultraviolet to infrared region having a wavelength of 200 nm to 1000 μm, more preferably a light having a wavelength of 250 to 2500 nm, and a wavelength of 700 to 1200 nm. Is more preferably a near infrared ray.

  Further, an infrared shielding film will be described below as a typical example of the optical reflection film, but the invention is not limited thereto.

  The infrared shielding film has an infrared reflective layer as an optical functional layer on a substrate. It is preferable that the infrared reflective layer includes at least one unit composed of two layers having different refractive indexes, that is, a high refractive index layer and a low refractive index layer. For example, when the high refractive index layer and the low refractive index layer each include metal oxide particles, the metal oxide particles contained in the low refractive index layer (hereinafter, referred to as “first metal oxide particles”), Metal oxide particles contained in the high refractive index layer (hereinafter, referred to as “second metal oxide particles”) are mixed at an interface between the two layers, and the first metal oxide particles and the second metal oxide are mixed. A layer containing oxide particles may be formed. In that case, the layer is regarded as a low refractive index layer or a high refractive index layer depending on the abundance ratio of the first metal oxide particles and the second metal oxide particles. Specifically, the low refractive index layer means that the first metal oxide particles are 50 to 100% by mass based on the total mass of the first metal oxide particles and the second metal oxide particles. Means the layers included. The high refractive index layer means that the second metal oxide particles exceed 50% by mass and 100% by mass or less based on the total mass of the first metal oxide particles and the second metal oxide particles. Means the layers included. The type and amount of metal oxide particles contained in the refractive index layer can be analyzed by energy dispersive X-ray spectroscopy (EDX).

The metal oxide particles are not particularly limited, but titanium oxide (TiO ₂ ), zinc oxide (ZnO), zirconium oxide (ZrO ₂ ), niobium oxide (Nb ₂ O ₅ ), aluminum oxide (Al ₂ O ₃ ), Examples include silicon oxide (SiO ₂ ), calcium fluoride (CaF ₂ ), magnesium fluoride (MgF ₂ ), indium tin oxide (ITO), and antimony tin oxide (ATO). Among these, titanium oxide (TiO ₂ ) is used as the second metal oxide particles contained in the coating liquid for the high refractive index layer, and silicon oxide is used as the first metal oxide particles contained in the coating liquid for the low refractive index layer. (SiO ₂ ) is preferably used.

  Further, the titanium oxide particles may be coated with a silicon-containing hydrated oxide. The coating amount of the silicon-containing hydrate compound is preferably 3 to 30% by mass, more preferably 3 to 10% by mass, and still more preferably 3 to 8% by mass. When the coating amount is 30% by mass or less, a desired refractive index of the high refractive index layer is obtained, and when the coating amount is 3% by mass or more, particles can be formed stably.

As a method for coating the titanium oxide particles with a silicon-containing hydrated oxide, a conventional method can be used. For example, Japanese Unexamined Patent Publication No. 10-158015 (Si / Al hydrated oxide treatment of rutile type titanium oxide; hydrated silicon and / or aluminum oxide on the surface of titanium oxide after peptization in the alkali region of titanic acid cake) For producing a titanium oxide sol for precipitating and surface-treating), JP-A-2000-204301 (sol in which rutile-type titanium oxide is coated with a composite oxide of Si, Zr and / or Al oxide, hydrothermal treatment). ), JP and 2007-246351 JP (hydrous titanium oxide to hydrosols of titanium oxide obtained by peptization, wherein ^R ₁ n _{SiX 4-n} (wherein ^{R 1} as stabilizer C1-C8 alkyl group, glycidyl An oxy-substituted C1-C8 alkyl group or a C2-C8 alkenyl group, X is an alkoxy group, and n is 1 or 2. Titanium oxide hydrosol coated with hydrated oxide of silicon by adding a compound having a complexing action to silane or titanium oxide, adding to a solution of sodium silicate or silica sol in an alkaline region, adjusting pH, and aging And the like).

  Generally, in the infrared shielding film, it is preferable to design a large difference in the refractive index between the low refractive index layer and the high refractive index layer from the viewpoint that the infrared reflectance can be increased with a small number of layers. In the infrared shielding film, in at least one of the units composed of the low refractive index layer and the high refractive index layer, the difference in refractive index between the adjacent low refractive index layer and high refractive index layer is 0.1 or more. Is preferably 0.3 or more, more preferably 0.35 or more, and particularly preferably 0.4 or more. When the infrared shielding film has a plurality of units of a high refractive index layer and a low refractive index layer, the refractive index difference between the high refractive index layer and the low refractive index layer in all units is within the above preferred range. Is preferred. However, the outermost layer and the lowermost layer may have a configuration outside the above preferred range. In the infrared shielding film, the low refractive index layer preferably has a refractive index of 1.10 to 1.60, and more preferably 1.30 to 1.50. The preferred refractive index of the high refractive index layer is from 1.80 to 2.50, and more preferably from 1.90 to 2.20.

  The refractive indexes of the high refractive index layer and the low refractive index layer are determined according to the following method.

  A sample in which each refractive index layer for measuring a refractive index is applied as a single layer on a substrate is prepared, and this sample is cut into 10 cm × 10 cm, and then the refractive index is determined according to the following method. Using a U-4000 type spectrophotometer (manufactured by Hitachi, Ltd.) as a spectrophotometer, after roughening the back surface on the measurement side of each sample, light absorption treatment was performed with a black spray, and light on the back surface was measured. The reflection is prevented, and the reflectance in the visible light region (400 nm to 700 nm) is measured at 25 points under the condition of regular reflection at 5 degrees to determine the average value, and the average refractive index is determined from the measurement result.

  The reflectance in the specific wavelength region is determined by the difference in the refractive index between the two adjacent layers and the number of layers. The greater the difference in the refractive index, the more the same reflectance can be obtained with a smaller number of layers. The difference between the refractive index and the required number of layers can be calculated using commercially available optical design software. For example, in order to obtain an infrared reflectance of 90% or more, if the difference in refractive index is less than 0.1, a stack of 200 or more layers is required, which not only reduces the productivity but also causes scattering at the interface of the stack. , The transparency is reduced, and it is difficult to manufacture without failure. From the viewpoint of improving the reflectance and reducing the number of layers, there is no upper limit to the difference in the refractive index, but the limit is practically about 1.4.

  The number of layers of the infrared shielding film is, for example, 10 to 40 layers, preferably 10 to 34 layers, and more preferably 10 to 26 layers. Further, the infrared shielding film may be, for example, a laminated film in which both the outermost layer and the lowermost layer of the laminated film are a high refractive index layer or a low refractive index layer. The infrared shielding film preferably has a layer configuration in which the lowermost layer adjacent to the substrate is a low refractive index layer and the outermost layer is also a low refractive index layer.

  The total thickness of the infrared shielding film is preferably 12 μm to 315 μm, more preferably 15 μm to 200 μm, and still more preferably 20 μm to 150 μm. The thickness of the low refractive index layer excluding the lowermost layer after drying per one layer is preferably 30 to 500 nm, more preferably 30 to 300 nm. On the other hand, the thickness of one layer of the high refractive index layer excluding the lowermost layer after drying is preferably from 30 to 500 nm, more preferably from 30 to 300 nm. The thickness of the lowermost layer after drying is preferably 300 to 1500 nm, more preferably 400 to 1200 nm, regardless of whether the lowermost layer is a low refractive index layer or a high refractive index layer.

  Further, as the optical characteristics of the infrared shielding film, the transmittance in the visible light region indicated by JIS R3106: 1998 is preferably 50% or more, more preferably 75% or more, and further preferably 85% or more. It is preferable to have a region having a reflectance of more than 50% in a wavelength region of 900 nm to 1400 nm.

  The infrared shielding film is provided below the base material or on the outermost surface layer on the opposite side of the base material for the purpose of adding further functions, such as a conductive layer, an antistatic layer, a gas barrier layer, and an easy-adhesion layer (adhesion layer). , Antifouling layer, deodorant layer, drip layer, lubricating layer, hard coat layer, abrasion resistant layer, antireflection layer, electromagnetic wave shielding layer, ultraviolet absorbing layer, infrared absorbing layer, printing layer, fluorescent light emitting layer, Used for hologram layer, release layer, adhesive layer, adhesive layer, infrared cut layer (metal layer, liquid crystal layer) other than high refractive index layer and low refractive index layer of the present invention, colored layer (visible light absorbing layer), laminated glass It may have one or more functional layers such as an intermediate film layer to be formed.

  As the coating solution for the low refractive index layer and the coating solution for the high refractive index layer, a water-soluble polymer such as polyvinyl alcohol, and water or water can be used to set a coating film after application and suppress mixing between layers. It is preferable to use an aqueous coating solution containing an aqueous solvent containing a water-soluble organic solvent.

  The solid content of the coating solution is preferably 0.1 to 10% by mass, more preferably 0.1 to 5% by mass. This is because if the content is in this range, the solid content is low and the uniformity of the coating solution is high, so that the film thickness uniformity is considered to be further improved.

  The concentration of the water-soluble polymer in the coating solution for the low refractive index layer is preferably 0.1 to 10% by mass. Further, the concentration of the first metal oxide particles in the coating solution for the low refractive index layer is preferably 1 to 60% by mass.

  The concentration of the water-soluble polymer in the coating solution for the high refractive index layer is preferably 0.5 to 10% by mass. Further, the concentration of the second metal oxide particles in the coating solution for the high refractive index layer is preferably 1 to 60% by mass.

  The second metal oxide particles used in the coating solution for the high refractive index layer are preferably prepared separately in the form of a dispersion before preparing the coating solution. That is, it is preferable to form the high refractive index layer using an aqueous high refractive index layer coating solution prepared by adding and dispersing rutile type titanium oxide having a volume average particle diameter of 100 nm or less. Further, it is more preferable to form the high refractive index layer using an aqueous high refractive index layer coating solution prepared by adding and dispersing titanium oxide particles coated with a silicon-containing hydrated oxide. When a dispersion is used, the dispersion may be appropriately added so as to have an arbitrary concentration in each layer.

(solvent)
The solvent for preparing the coating liquid for the high refractive index layer and the coating liquid for the low refractive index layer is not particularly limited, but water, an organic solvent, or a mixed solvent thereof is preferable.

  Examples of the organic solvent include alcohols such as methanol, ethanol, 2-propanol and 1-butanol; esters such as ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; diethyl ether and propylene. Examples thereof include ethers such as glycol monomethyl ether and ethylene glycol monoethyl ether, amides such as dimethylformamide and N-methylpyrrolidone, and ketones such as acetone, methyl ethyl ketone, acetylacetone, and cyclohexanone. These organic solvents may be used alone or in combination of two or more.

From the viewpoint of environment, simplicity of operation, and the like, the solvent for the coating solution is particularly preferably water or a mixed solvent of water and methanol, ethanol, or ethyl acetate.

(Water-soluble polymer)
Examples of the water-soluble polymer include polyvinyl alcohols, polyvinylpyrrolidones, polyvinyl butyral, polyacrylic acid, acrylic acid-acrylonitrile copolymer, potassium acrylate-acrylonitrile copolymer, and vinyl acetate-acrylate copolymer. Polymer, or acrylic resin such as acrylic acid-acrylic acid ester copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid ester copolymer, styrene-α Styrene acrylate resin such as -methylstyrene-acrylic acid copolymer or styrene-α-methylstyrene-acrylic acid-acrylate copolymer, styrene-sodium styrenesulfonate copolymer, styrene-2-hydroxyethyl Ace relay Copolymer, styrene-2-hydroxyethyl acrylate-potassium styrenesulfonate copolymer, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, vinylnaphthalene-acrylic acid copolymer, vinylnaphthalene- Synthetic water-soluble polymers such as maleic acid copolymers, vinyl acetate-maleic acid ester copolymers, vinyl acetate-crotonic acid copolymers, vinyl acetate-acrylic acid copolymers and vinyl acetate copolymers and salts thereof Polymers: natural water-soluble polymers such as gelatin and thickening polysaccharides, and the like. Among these, particularly preferred examples are polyvinyl alcohols, polyvinylpyrrolidones, and copolymers containing them, polyvinyl butyral, gelatin, thickening polysaccharides, from the viewpoint of handling during production and flexibility of the film. (Especially celluloses). These water-soluble polymers may be used alone or in combination of two or more.

  The polyvinyl alcohol includes modified polyvinyl alcohol in addition to ordinary polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate. Examples of the modified polyvinyl alcohol include cation-modified polyvinyl alcohol, anion-modified polyvinyl alcohol, nonionic-modified polyvinyl alcohol, and vinyl alcohol-based polymers.

  The polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate preferably has an average degree of polymerization of 1,000 or more, and particularly preferably has an average degree of polymerization of 1,500 to 5,000, and 5,000 are more preferably used. When the polymerization degree of polyvinyl alcohol is 1,000 or more, there is no crack in the coating film, and when the polymerization degree is 5,000 or less, the coating liquid is stabilized. In addition, that the coating liquid is stable means that the coating liquid is stabilized with time. Hereinafter, the same applies.

  The saponification degree is preferably from 70 to 100%, and more preferably from 80 to 99.5% from the viewpoint of solubility in water. Further, a plurality of water-soluble polymers having different degrees of saponification may be used.

  For example, in addition to a polyvinyl alcohol having an average degree of polymerization of 1,000 or more, a low degree of polymerization and a high saponified polyvinyl alcohol having a degree of polymerization of 100 to 500 and a degree of saponification of 95 mol% or more are used for forming a high refractive index layer and a low refractive index layer. It is preferable that at least one of them contains. By containing such a low-polymerization degree high saponified polyvinyl alcohol, the stability of the coating solution is improved.

  Further, as long as the effects of the present invention are not impaired, at least one of the high refractive index layer and the low refractive index layer is partially modified in addition to ordinary polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate. It may contain polyvinyl alcohol. Examples of such modified polyvinyl alcohol include cation-modified polyvinyl alcohol, anion-modified polyvinyl alcohol, nonionic-modified polyvinyl alcohol, and vinyl alcohol-based polymers.

  As the cation-modified polyvinyl alcohol, for example, as described in JP-A-61-10483, a primary to tertiary amino group or quaternary ammonium group is contained in the main chain or side chain of the polyvinyl alcohol. Which is obtained by saponifying a copolymer of an ethylenically unsaturated monomer having a cationic group and vinyl acetate.

  Examples of the ethylenically unsaturated monomer having a cationic group include trimethyl- (2-acrylamido-2,2-dimethylethyl) ammonium chloride and trimethyl- (3-acrylamido-3,3-dimethylpropyl) ammonium chloride. N-vinylimidazole, N-vinyl-2-methylimidazole, N- (3-dimethylaminopropyl) methacrylamide, hydroxylethyltrimethylammonium chloride, trimethyl- (2-methacrylamidopropyl) ammonium chloride, N- (1, 1-dimethyl-3-dimethylaminopropyl) acrylamide and the like. The ratio of the cation-modified group-containing monomer of the cation-modified polyvinyl alcohol is preferably 0.1 to 10 mol%, more preferably 0.2 to 5 mol%, based on vinyl acetate.

  Anion-modified polyvinyl alcohol is described in, for example, polyvinyl alcohol having an anionic group as described in JP-A-1-2060888, JP-A-61-237681 and JP-A-63-307979. Such copolymers of vinyl alcohol and a vinyl compound having a water-soluble group, and modified polyvinyl alcohol having a water-soluble group as described in JP-A-7-285265.

  Examples of the nonionic modified polyvinyl alcohol include, for example, a polyvinyl alcohol derivative in which a polyalkylene oxide group is added to a part of vinyl alcohol as described in JP-A-7-9758, and JP-A-8-25795. Block copolymer of vinyl compound and vinyl alcohol having a hydrophobic group described, silanol-modified polyvinyl alcohol having a silanol group, reactive group modification having a reactive group such as an acetoacetyl group, a carbonyl group, and a carboxyl group Polyvinyl alcohol and the like.

  These polyvinyl alcohols may be used alone or in combination of two or more kinds having different degrees of polymerization and types of modification. As the polyvinyl alcohol, a commercially available product or a synthetic product may be used. Examples of commercially available products include, for example, PVA-102, PVA-103, PVA-105, PVA-110, PVA-117, PVA-120, PVA-124, PVA-135, PVA-203, PVA-205, and PVA-210. , PVA-217, PVA-220, PVA-224, PVA-235, and PVA-617 (manufactured by Kuraray Co., Ltd.), Exeval (registered trademark, manufactured by Kuraray Co., Ltd.), Nichigo G Polymer (registered trademark, Nippon Gosei) Chemical Industry Co., Ltd.).

(Additive)
Various additives may be added to the low refractive index layer coating liquid and the high refractive index layer coating liquid as needed. Hereinafter, the additives will be described.

(Curing agent)
In the low refractive index layer and the high refractive index layer, it is preferable to add a curing agent. Examples of the curing agent include, for example, a curing agent that causes a curing reaction with polyvinyl alcohol suitable as the water-soluble polymer described above. Specifically, boric acid and its salts are preferred. Known compounds other than boric acid and salts thereof can be used, and generally, a compound having a group capable of reacting with polyvinyl alcohols or a compound which promotes a reaction between different groups of polyvinyl alcohols, It is appropriately selected and used. Specific examples of curing agents other than boric acid and salts thereof include, for example, epoxy curing agents (diglycidyl ethyl ether, ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-diglycidyl cyclohexane) , N, N-diglycidyl-4-glycidyloxyaniline, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, etc., aldehyde curing agents (formaldehyde, glyoxal, etc.), active halogen curing agents (2,4-dichloro-4-) Hydroxy-1,3,5-s-triazine, etc.), active vinyl compounds (1,3,5-trisacryloyl-hexahydro-s-triazine, bisvinylsulfonylmethyl ether, etc.), aluminum alum and the like.

  Boric acid and salts thereof refer to oxyacids and salts thereof having a boron atom as a central atom, and specifically, orthoboric acid, diboric acid, metaboric acid, tetraboric acid, pentaboric acid and octaboric acid. Acids and their salts.

  Boric acid having a boron atom and a salt thereof as a curing agent may be used alone or in a mixture of two or more. Particularly preferred is a mixed aqueous solution of boric acid and borax.

  The aqueous solutions of boric acid and borax can be added only as relatively dilute aqueous solutions, respectively, but by mixing them, a concentrated aqueous solution can be obtained, and the coating solution can be concentrated. Further, there is an advantage that the pH of the aqueous solution to be added can be controlled relatively freely.

  It is preferable to use boric acid and its salt and / or borax from the viewpoint of further suppressing interlayer mixing in simultaneous multilayer coating. When boric acid and its salts and / or borax are used, the metal oxide particles and the OH groups of polyvinyl alcohols, which are water-soluble binder resins, form a hydrogen bonding network, resulting in a high refractive index layer. It is considered that interlayer mixing between the layer and the low refractive index layer is suppressed, and preferable near-infrared shielding characteristics are achieved. In particular, when using a set application process in which after coating a multilayer multilayer of a high refractive index layer and a low refractive index layer with a coater, the film surface temperature of the coating film is once cooled to about 15 ° C., and then the film surface is dried. Can more preferably exert the effect.

  The total amount of the curing agent used is preferably 1 to 600 mg per 1 g of polyvinyl alcohol, and more preferably 100 to 600 mg per 1 g of polyvinyl alcohol.

  In addition, various additives that can be added to the coating liquid for the high refractive index layer and the coating liquid for the low refractive index layer are listed below. For example, ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, JP-A-57-74192, and JP-A-57-87989 JP-A-60-72785, JP-A-61-146591, JP-A-1-95091, JP-A-3-13376, etc., anti-fading agents, anions and cations Or various nonionic surfactants, JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-242871, and JP-A-4-219266. Fluorescent whitening agents described in Japanese Patent Application Publication Nos. JP-A-2005-209, sulfuric acid, phosphoric acid, acetic acid, citric acid, sodium hydroxide, potassium hydroxide, potassium carbonate, sodium acetate PH adjusters, defoamers, lubricants such as diethylene glycol, preservatives, fungicides, antistatic agents, matting agents, heat stabilizers, antioxidants, flame retardants, crystal nucleating agents, inorganic particles, organic particles, Known various additives such as a viscosity reducing agent, a lubricant, an infrared absorber, a coloring matter, a pigment and the like can be mentioned.

  Next, the operation of the present embodiment will be described. Here, in order to understand the present embodiment, first, a coating apparatus for simultaneous multilayer coating will be described.

  FIG. 3 is a schematic view showing the overall configuration of a coating apparatus for performing simultaneous multilayer coating. FIG. 4 is a schematic diagram showing the details of the coating section of the coating apparatus. Note that such a coating device is an example of a coating device used to carry out the present invention, and the present invention is not limited to the case where such a coating device is used.

  As shown in FIG. 3, the coating apparatus 100 includes storage units 201 to 204 that store the coating liquid, and a die coater 120 that simultaneously applies the coating liquid supplied from the storage units 201 to 204 onto the base material 20 in a multi-layer manner. (Coating unit), a coating liquid supply system 150 that distributes the coating liquid from the storage units 201 to 204 to the die coater 120, and a transport system 110 that transports the substrate 20.

  The storage units 201 to 204 are facilities for temporarily storing the coating liquid for stable supply to the die coater 120. Various components are mixed in the coating liquid. The mixing and preparation of the components may be performed in different places (equipment), or the necessary components may be mixed in the respective reservoirs.

  The die coater 120 is of a slide type, and simultaneously applies multiple coating layers corresponding to each layer of the optical film. For this purpose, the die coater 120 has a stacked body 122 in which rectangular bars 130 are sequentially stacked.

  The bar 130 includes a front bar 132, a plurality of intermediate bars 134, and a back bar 136. The front bar 132 is the bar 130 occupying the lowermost layer of the laminate 122 and is positioned near the base material 20. The back bar 136 is the bar 130 occupying the uppermost layer of the laminate 122. The middle bar 134 is the bar 130 occupying the middle layer located between the front bar 132 and the back bar 136. The application width direction is orthogonal to the transport direction (arrow F in the figure).

  The bar 130 has a proximal end 140, a pocket 143, and a distal end 146, as shown in FIG.

  The base end 140 has a through hole 142 communicating with the application liquid supply system 150. The through hole 142 is located at the center of the base end 140 in the application width direction, and extends from the end face of the base end 140 toward the pocket 143.

  The thickness t1 of the base portion 140 is set to be larger than the thickness t2 of the tip portion 146. Thus, when the bars 130 are stacked, the proximal end 140 abuts the proximal end 140 of another adjacent bar 130. On the other hand, a slit (gap) 148 having a thickness t1-t2 is formed between the distal end portion 146 and the distal end portion 146 of the adjacent bar 130.

  The slit 148 functions as a passage through which the coating liquid passes. The coating liquid is discharged from the tip of the slit 148 and flows down the end face 147 of the tip 146. Therefore, the end surface 147 functions as a slide surface on which the coating liquid flows down. The number of slits 148 provided corresponds to the number of layers of the optical film, and the number of intermediate bars 134 is adjusted according to the number of layers of the optical film.

  The pocket portion 143 has a concave portion 144 formed to extend in the application width direction of the bar 130. The concave portion 144 is a coating liquid reservoir communicating with the slit 148 and the through hole 142. The pocket portion 143 is used to spread the application liquid evenly in the application width direction and supply the liquid to the slit 148 stably.

  The coating liquid supply system 150 has piping systems 151 to 154 communicating with the through holes 142 of the die coater 120 (the bar 130 of the laminate 122).

  Here, in the coating apparatus shown in FIG. 3, the coating liquid for the lowermost layer is supplied from the storage unit 201, and the coating liquid for one layer (for example, a low refractive index layer) for the intermediate layer is supplied from the storage unit 202. The coating liquid for one adjacent layer (for example, a high refractive index layer) for the intermediate layer is supplied from the storage unit 203, and the coating liquid for the uppermost layer is supplied from the storage unit 204. For this reason, each pipe is arranged as follows. The piping system 151 is connected to the storage unit 201 via the liquid sending device 156. The piping system 152 is connected to the storage unit 202 via the liquid sending device 157. The piping system 153 is connected to the storage unit 203 via the liquid sending device 158. The piping system 154 is connected to the storage unit 204 via the liquid sending device 159.

  The connection relationship between each storage section and each piping system may be freely changed according to each layer coating liquid desired as a coating layer, and is not limited to such a connection form.

  In the piping systems 151 to 154, for example, a filtering device, a flow meter, and the like can be appropriately arranged in the path (all are not shown). The filtering device is used to remove foreign substances mixed in the coating liquid, aggregates of the coating liquid components, and the like. The flow meter is used to measure the flow rate of the coating solution passing through the piping system. As the flow meter, for example, a flap type, a hot wire type, a Karman vortex type, and a negative pressure sensing type can be applied. In addition to or instead of the flow meter, a pressure gauge for measuring the pressure of the coating solution can be provided.

  When the coating liquid is water-based, it is preferable to further arrange a dispersing device in the path. The dispersing device performs a dispersing process (including a shearing process) on the coating solution to break bonds (van der Waals bonds, etc.) between water-soluble polymers and between terminal groups in the molecules, and entangle the molecules. And is used to adjust the physical properties of the coating solution. The dispersing device is, for example, a milder dispersing machine, a pressure type homogenizer, or a high-speed rotation shearing type homogenizer.

  The coating liquid is uniformly spread in the coating width direction in the concave portion 144 of the pocket portion 143, and is introduced into the slit 148. The coating solution that has passed through the slit 148 flows down the end surface 147 of the tip portion 146 of the bar 130 as shown in FIG. 4 and flows down the end surface 147 of the tip portion 146 of another bar 130 located below. And overlap sequentially. Then, the coating solution flowing down, when overlapping with the coating solution passing through the slit 148 of the front bar 132, is composed of the same number of layers as the optical film.

  Then, the coating liquid is separated from the front bar 132 which is the lowermost bar 130, flows down to the base material 20, and is simultaneously multi-layer coated to form the coating film 40.

  If necessary, a thickening step for increasing (thickening) the viscosity of the coating solution may be arranged immediately after the simultaneous multilayer coating to suppress interlayer mixing. After coating, the viscosity of the coating solution is applied by cooling, flash freeze drying with liquid nitrogen, heating drying, drying under reduced pressure, or the like. For example, the coating liquid is cooled by blowing cooling air against the coating liquid flowing on the slide surface, or the coating liquid on the substrate 20 is indirectly contacted by contact between the cooled back roll 112 and the substrate 20. The coating liquid is dried by cooling the coating liquid, blowing hot air against the coating liquid flowing on the slide surface, or heating the coating liquid with an infrared heater, or providing a heating / decompression drying zone immediately after the back roll 112. By drying the liquid, the viscosity of the coating liquid can be increased (increased).

  The transport system 110 has a back roll 112. The back roll 112 is arranged inside the substrate 20 and is configured to convey the substrate 20 by being driven to rotate. The arrow F indicates the transport direction of the substrate 20. The transport speed is, for example, 5 to 200 m / min. This transfer speed is the coating speed in the simultaneous multi-layer coating as it is. If it is 5 m / min or more, the amount of liquid will not decrease and the thickness of the coating film will not become non-uniform, and if it is less than 200 m / min, the speed will be too fast to prevent drying in the drying step. Note that a decompression mechanism that suctions the substrate 20 and corrects the shape distortion thereof may be disposed near the back roll 112. Thereby, the clearance accuracy between the die coater 120 and the substrate 20 can be improved.

  A drying device (not shown) is provided downstream of the transport system 110. Since the temperature of the coating solution and the base material 20 are raised at the time of coating, the coating solution applied to the base material 20 is once cooled to 1 to 15 ° C., and then 10 ° C. or more (for example, a wet bulb temperature of 5 to 5 ° C.). It is dried at 50 ° C. and a coating surface temperature of 10 to 50 ° C.). By drying the coating film 40 with this drying device, an optical film in which the coating layer 30 is formed on the base material 20 is completed.

  Next, the operation of the present embodiment will be described. FIG. 5 is a schematic diagram for explaining the moment when the coating liquid comes into contact with the base material at the start of simultaneous multilayer coating. FIG. 6 is a schematic diagram for explaining a state after the coating liquid comes into contact with the base material in the simultaneous multilayer coating. In FIGS. 5 and 6, the downward direction in the figures is the vertical downward direction.

  As shown in FIG. 5, in the simultaneous multi-layer coating, at the beginning of the coating, when the layered coating liquid 300 is sent out, the coating liquid 300 flows out from the tip 146 side of the die coater 120 so as to hang down. Then, the coating liquid 300 comes into contact with the substrate 20. At the moment when the overlaid coating liquid 300 comes into contact with the substrate 20, the coating liquid 300 to be the uppermost layer 352 comes into contact with the substrate 20 first. At this moment, the intermediate layer 353 and the lowermost layer 351 are not in contact with the base material 20.

  Thereafter, as shown in FIG. 6, when the base material 20 moves over time, the middle layer 353 portion, and subsequently the lowermost layer 351 come into contact with the base material 20 so as to be drawn into the uppermost layer 352.

  From this, for example, when the coating liquid 300 of the uppermost layer 352 first comes into contact with the base material 20, if the thickness of the uppermost layer 352 is disturbed, or if partial fading or streaking occurs, The influence is exerted on the intermediate layer 353 and the lowermost layer 351, which may cause uneven coating.

  In the present embodiment, the coating liquid 300 of the uppermost layer 352 is also set to have an initial contact angle of 70 degrees or less, so that the coating liquid 300 of the uppermost layer 352 is first uniformly contacted with the base material 20 from the moment of contact. Coating can be performed with a uniform thickness without uneven coating. Therefore, the intermediate layer 353 and the lowermost layer 351 that are applied after the uppermost layer 352 are also formed to have a uniform thickness and are applied in a multilayered manner without application unevenness.

  After that, after all the coating liquids 300 of each layer come into contact with the substrate 20 (after FIG. 6), the lowermost layer 351 comes into contact with the substrate 20 as shown in FIG. For this reason, by setting the initial contact angle of the coating liquid 300 of the lowermost layer 351 to 70 degrees or less, the coating film 40 being continuously applied is applied with a uniform thickness, and the completed coating layer 30 is formed. Application unevenness is suppressed.

  As described above, in the present embodiment, it is possible to suppress the occurrence of coating unevenness in simultaneous multilayer coating in which a plurality of layers can be simultaneously coated at high speed. Further, the optical film obtained thereby has a good appearance (appearance) because the coating film in the portion to be the optical functional layer has a uniform thickness and has no troubles such as streaks.

  Hereinafter, results of experiments actually performed according to the above-described embodiment will be described as examples. For comparison, an experimental result when the embodiment is not applied will be described as a comparative example.

  The optical films of Examples and Comparative Examples were prepared by preparing a coating solution for a low refractive index layer and a coating solution for a high refractive index layer, and simultaneously coating these two types of coating solutions on a substrate to form an infrared shielding film. Produced.

[Preparation of coating solution for lowermost layer and uppermost layer]
(Preparation of coating liquid precursor 1)
Colloidal silica (Snowtex OXS, manufactured by Nissan Chemical Industries, Ltd., solid content 10% by mass), 5% by mass polyvinyl alcohol (PVA-103, degree of polymerization 300, degree of saponification 98.5 mol%, manufactured by Kuraray Co., Ltd.) ) 200 parts by weight of an aqueous solution and 1000 parts by weight of a 3% by weight aqueous solution of boric acid were added, respectively, and then heated to 45 ° C and stirred with 5% by weight of polyvinyl alcohol (PVA-117, degree of polymerization 1700, degree of saponification 98.5 mol). %, Manufactured by Kuraray Co., Ltd.) 2000 parts by mass of an aqueous solution and 10500 parts by mass of pure water were added to prepare 15,000 parts by mass of a coating liquid precursor 1.

(Preparation of coating liquid precursor 2)
2400 parts by mass of colloidal silica, 400 parts by mass of a 5% by mass aqueous solution of polyvinyl alcohol (PVA-103), 1500 parts by mass of a 3% by mass aqueous solution of boric acid, and 4000 parts by mass of a 5% by mass aqueous solution of polyvinyl alcohol (PVA-117) Coating liquid precursor 2 was prepared in the same manner as coating liquid precursor 1 except that the amount of pure water was changed to 6600 parts by mass.

(Addition of activator and alcohol)
For the prepared coating liquid precursors 1 and 2, 5% by mass of a surfactant (Sofdazoline LMEB-R, manufactured by Kawaken Fine Chemical Co., Ltd.) and isopropyl alcohol were added so as to have the addition amounts shown in Table 1, respectively. A liquid was prepared.

(Shearing)
The coating solution prepared by adding the surfactant and the alcohol was subjected to a shear treatment to prepare a coating solution. The details of the shearing treatment are as follows.

Shearing A shearing treatment was performed using CLEARMIX CLM-0.8S (manufactured by M Technique Co., Ltd.), which is a high-speed stirring type dispersion apparatus. The coating liquid was supplied to a processing vessel for dispersion (350 cc vessel) at a flow rate of 1 L / min using a rotary pump. The shearing treatment was performed at a rotation speed of 18000 rpm, R2 was used for the rotor, and S2.0-24 was used for the screen.

(Preparation of base material)
As a substrate for coating, a PET substrate (Cosmoshine A4300, manufactured by Toyobo Co., Ltd.) having a thickness of 50 μm was used.

(Measurement of initial contact angle)
With respect to the coating liquid obtained above, a coating liquid sample and a coating PET substrate left standing at room temperature for 24 hours or more were set on a contact angle meter LSE-B100W (manufactured by Nick), and the contact angle was measured at room temperature. , 50 msec. As a result of this extraction, those having an initial contact angle of 70 ° or less were regarded as examples, and those exceeding 70 ° were regarded as comparative examples.

[Preparation of coating liquid for high refractive index layer]
After adding 20,000 parts by mass of pure water to 5000 parts by mass of 15.0% by mass titanium oxide sol (SRD-W, volume average particle size 5 nm, rutile type titanium dioxide particles, manufactured by Sakai Chemical Industry Co., Ltd.), the mixture was heated to 90 ° C. . Then, 13000 parts by mass of a silicic acid aqueous solution (a solution obtained by diluting sodium silicate No. 4 (manufactured by Nippon Chemical Industry Co., Ltd.) with pure water so that the SiO ₂ concentration becomes 2.0% by mass) was gradually added, and the autoclave was added. 175 ° C. for 18 hours. After cooling, the mixture was concentrated with an ultrafiltration membrane to obtain a titanium dioxide sol having a solid content of 20% by mass and having SiO ₂ attached to the surface (hereinafter, anion-treated titanium dioxide sol).

200 mass parts of 5 mass% polyvinyl alcohol (PVA-103, degree of polymerization 300, degree of saponification 98.5 mol%, manufactured by Kuraray Co., Ltd.) aqueous solution in 3000 mass parts of anion-treated titanium dioxide sol (solid content 20.0 mass%) After adding 1000 parts by mass of a 3% by mass aqueous solution of boric acid and 1000 parts by mass of a 2% by mass aqueous solution of citric acid, 5% by mass of polyvinyl alcohol (PVA-617, polymerization degree 1700, A saponification degree of 95.0 mol%, 2,000 parts by mass of an aqueous solution (manufactured by Kuraray Co., Ltd.), 100 parts by mass of a 1% by mass surfactant (Lapisol A30, manufactured by NOF CORPORATION), and 2700 parts by mass of pure water are added. 10,000 parts by mass of a coating solution for a refractive index layer was prepared. The average spinning length of the obtained coating liquid for a high refractive index layer was 0 cm.
[Preparation of coating liquid for low refractive index layer]
1800 parts by mass of colloidal silica, 300 parts by mass of a 5% by mass aqueous solution of polyvinyl alcohol (PVA-103), 1250 parts by mass of a 3% by mass aqueous solution of boric acid, and 3000 of 5% by mass aqueous solution of polyvinyl alcohol (PVA-117) A coating liquid precursor was prepared in the same manner as in the coating liquid precursor 1, except that the amount of pure water was changed to 3550 parts by mass. The precursor subjected to the above-mentioned shearing treatment was used as a coating liquid.

[Production of infrared shielding film]
The coating liquid prepared for the lowermost layer is disposed in the lowermost layer, and the coating liquid for the high refractive index layer and the coating liquid for the low refractive index layer are kept at 45 ° C., and a 50 μm-thick PET substrate (Cosmoshine A4300, Toyo (Spinning Co., Ltd.), a low-refractive-index layer and a high-refractive-index layer are alternately laminated nine layers at a time at a speed of 6 m / min by using a slide hopper coating device to obtain nine layers simultaneously. The obtained coating film was dried to produce an infrared shielding film. The average thickness of the dried layers was 150 nm for each low refractive index layer, and 150 nm for each high refractive index layer.

[Evaluation of infrared shielding film]
The following performance evaluation was performed about the produced infrared shielding film.

(Evaluation of visibility of pasted window glass)
The formed film was affixed to a window glass, and the visibility outside the window was visually evaluated by the number of samples N = 20 in each of Examples and Comparative Examples.

◎: No visibility problem in all films,
：: There is no visibility problem with 18 or more films,
Δ: No visibility problem with 10 or more films,
X: Less than 10 films without visibility problems.

  The results obtained are shown in Table 1 below. In Table 1, the surfactant is described as “activator”.

  From Table 1, Examples 1 to 13 in which the initial contact angle of the lowermost layer coating solution is 70 or less than Comparative Examples 1 to 3 in which the initial contact angle of the lowermost layer coating solution exceeds 70 degrees. The result of evaluation of the visibility of the attached window glass is good. Therefore, it can be seen that setting the initial contact angle of the lowermost coating liquid to 70 degrees or less is effective in eliminating coating unevenness.

  In Example 4, and Examples 5 and 6, a coating liquid having the same initial contact angle of 58.05 degrees as the lowermost coating liquid was used. On the other hand, as for the uppermost layer coating solution, Example 4 has an initial contact angle of 70 degrees or less, while Examples 5 and 6 have an initial contact angle of 70 degrees or more. The evaluation result of the pasted window glass visibility is better in Example 4 than in Examples 5 and 6. From this, it can be seen that the coating unevenness is further suppressed by setting the initial contact angle to 70 degrees or less for the uppermost coating liquid.

  However, even when the initial contact angle of only the uppermost coating liquid is 70 degrees or less as in Comparative Examples 1 to 3, if the initial contact angle of the lowermost coating liquid exceeds 70 degrees, the affixed window glass is visible. It turns out that the sex evaluation result is not good. This indicates that setting the initial contact angle of the lowermost coating liquid to 70 degrees or less is effective for suppressing coating unevenness.

  Further, from Comparative Examples 1 to 3, Examples 1 and 2, it can be seen that the initial contact angle of the lowermost coating liquid is reduced by increasing the amount of the surfactant added. Similarly, when isopropyl alcohol (IPA) is added together with a surfactant from the absence of isopropyl alcohol of Example 2 and Examples 3 and 4, the initial amount of the coating solution in the lowermost layer is increased by increasing the amount of isopropyl alcohol added. It can be seen that the contact angle becomes smaller.

  It can be seen from Examples 9 to 13 that the lower the viscosity, the better the result of the evaluation of the visibility of the attached window glass. In this respect, the viscosities of Comparative Examples 1 to 3 are lower than those of Examples 11 to 13. However, the evaluation results of the attached windowpane visibility are not better in Comparative Examples 1 to 3 than in Examples 11 to 13. From this fact, it can be seen that although it is effective to lower the viscosity for suppressing the coating unevenness in the initial contact angle, it is most effective to set the initial contact angle of the lowermost coating liquid to 70 degrees or less.

  From Examples 1, 2 and 8, the lower the initial contact angle of the lowermost coating liquid, the better the evaluation results of the attached windowpane visibility. This shows that the smaller the initial contact angle of the lowermost coating liquid, the higher the effect of suppressing the coating unevenness.

  Next, FIG. 7 is a graph showing the measurement results of the contact angle of the lowermost coating liquid used in Examples 1, 2 and 4 with the passage of time.

  As can be seen from FIG. 7, it can be seen that the contact angle decreases with the passage of time from the time when the droplet comes into contact with the substrate surface (0 msec). This is the same tendency in all the embodiments shown in FIG. Above all, even if the contact angle exceeds 70 degrees at the time when the droplet contacts the substrate surface (0 msec) as in Examples 1 and 2, if the contact angle is 70 degrees or less after the prescribed 50 msec, As shown in Table 1, in Examples 1 and 2, coating unevenness was eliminated. Therefore, it is meaningful to prepare the coating liquid by defining the contact angle at the time (50 msec) after the elapse of a certain time as the initial contact angle.

  The embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment. In particular, the infrared shielding film has been described, but the present invention is not limited to the coating liquid for the infrared shielding film. The present invention can be variously modified within the scope of the claims.

10 optical films,
20 base material,
30 coating layer 100 coating device,
110 transport system,
120 die coater,
122 laminate,
130 bar,
140 proximal end,
142 through hole,
143 pocket part,
146 tip,
148 slits,
150 coating liquid supply system,
201-204 storage unit,
300 coating liquid,
301 droplets,
351 The lowest layer,
352 Top layer,
353 middle layer.

Claims (7)

A method for producing an optical film in which an optical functional layer is formed by simultaneously coating at least two layers on a substrate,
When a droplet of the coating liquid used for the simultaneous multilayer coating is vertically dropped on the substrate, the contact angle of the droplet at the time of 50 msec after the contact of the droplet with the substrate is 70 degrees or less. A method for producing an optical film, comprising applying the coating liquid as the lowermost coating liquid during the simultaneous multi-layer coating.   When a droplet of the coating liquid used for the simultaneous multilayer coating is vertically dropped on the substrate, the contact angle of the droplet at the time of 50 msec after the contact of the droplet with the substrate is 70 degrees or less. The method for producing an optical film according to claim 1, wherein a coating liquid to be used is applied as a coating liquid for an uppermost layer when the simultaneous multi-layer coating is performed. The coating liquid of the lowermost layer has a viscosity of 0.5 cp to 30 cp,
The method for producing an optical film according to claim 1, wherein the amount of the lowermost layer coating solution is 10 to 50 g / m ² . Wherein the optical functional layer, the coating solution of the entire layer is 50 to 150 g / m ^2, The method for producing an optical film according to any one of claims 1 to 3.   The method for producing an optical film according to any one of claims 1 to 4, wherein a coating speed during the simultaneous multilayer coating is 5 to 200 m / min.   The method for manufacturing an optical film according to claim 1, wherein the optical functional layer includes polyvinyl alcohol having different degrees of saponification.   The method for producing an optical film according to claim 1, wherein the optical function layer is an infrared reflection layer.