Coating film manufacturing method

Abstract

To provide a coating method and a film formation apparatus for suppressing occurrence of poor appearance such as streaks.SOLUTION: A film formation apparatus includes a coating part (30) and a surface treatment part (35) positioned on the downstream of the coating part. A coating liquid is coated onto a main surface of a base material by the coating part while continuously conveying a belt-like base material (1) in a longitudinal direction and a coated film (311) is formed, and the surface of the coated film is treated by a surface treatment part. The surface treatment part includes a first bar (351), and a second bar (352). The first bar is a rotor that is arranged so as to contact the surface of the coated film (311) and has a circular cross section. The second bar is arranged in close contact with the downstream side of the first bar so as to scrape off the coating liquid attached to the surface of the first bar. The second bar also contacts the coated film.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to the formation of a coating film on a substrate. [Background technology]

[0002] In recent years, curved displays and foldable displays (flexible displays, foldable displays) have been developed, and flexible resin films have come to be used instead of glass as materials for substrates and cover windows. In order to give the resin film a hardness comparable to that of glass, a hard coat film having a hard coat layer provided on the surface of the resin film is used.

[0003] The hard coat layer is formed by applying a photocurable or thermosetting coating liquid (hard coat composition) to the surface of a resin film to form a coating film, removing the solvent as necessary, and then curing the composition. A coating film such as a hard coat layer may cause streaky coating defects during application, and coating defects tend to occur easily with an increase in the viscosity of the coating liquid or an increase in the coating speed.

[0004] Various attempts have been made to reduce appearance defects such as streaks in solution coating. For example, Patent Document 1 describes that a coating rod rotated in the opposite direction to the conveying direction is brought into contact with the coated film to scrape off excess coating liquid, and the rotation speed is adjusted to enable good coating. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2001-029871 A Summary of the Invention [Problem to be solved by the invention]

[0006] A high hardness is required for components arranged on the display surface, such as a cover window, and in order to increase the hardness, it is necessary to increase the thickness of the hard coat layer. In order to increase the thickness of the coating film, it is necessary to use a composition with a higher concentration, which increases the viscosity of the composition, and is likely to cause appearance defects such as streaks.

[0007] In optical materials for displays and the like, since defects in appearance such as streaks can cause display defects, a higher degree of uniformity is required, and it is difficult to ensure sufficient quality with conventional coating methods. In view of this problem, the present invention aims to provide a coating method in which defects in appearance such as streaks are reduced. [Means for solving the problem]

[0008] The present invention relates to a method for producing a coating film, which forms a coating film on a main surface of a belt-shaped substrate while continuously transporting the substrate in the longitudinal direction, and a film forming apparatus used for forming the coating film. The film forming apparatus includes a coating section that applies a coating liquid onto the main surface of the substrate to form a coating film, and a surface treatment section located downstream of the coating section. The formation of the coating film includes a step of applying the coating liquid onto the main surface of the substrate to form a coating film in the coating section, and a step of treating the surface of the coating film in the surface treatment section.

[0009] When the coating liquid contains a solvent, the solvent may be dried and removed after the treatment in the surface treatment section. The viscosity of the coating liquid may be 10 to 100 poise. The thickness of the coating film may be 10 μm or more. When the coating liquid contains a solvent, the thickness after removing the solvent is defined as the thickness of the coating film.

[0010] The coating liquid may be a hard coat composition containing a curable resin. When the coating liquid is a hard coat composition, the hard coat composition is cured after the surface treatment of the coating film to form a hard coat layer as a coating film. When the hard coat composition contains a solvent, it is preferable to dry and remove the solvent between the surface treatment of the coating film and the curing.

[0011] The surface treatment section includes a first bar and a second bar, and the surface treatment of the coating film is performed by these two bars. The first bar is a rotating body having a circular cross section and arranged so as to contact the surface of the coating film. The first bar may be a wire bar.

[0012] The second bar is disposed downstream of and adjacent to the first bar so as to scrape off the coating liquid adhering to the surface of the first bar. The second bar also comes into contact with the coating film. The shape of the second bar is not particularly limited as long as it can scrape off the coating liquid adhering to the surface of the first bar, but it may have a circular cross section like the first bar. The second bar may be a wire bar.

[0013] The peripheral speed Vb of the rotation of the first bar is preferably greater than the transport speed Va of the substrate, and Vb / Va may be equal to or greater than 2. The second bar is preferably fixed and does not rotate. Effect of the Invention

[0014] After applying the coating liquid to form a coating film, the coating film is subjected to surface treatment in the surface treatment section. This makes it possible to reduce or eliminate appearance defects such as streaks without reducing the thickness of the coating film, thereby forming a high-quality coating film. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view of a hard coat film according to an embodiment. [Diagram 2] FIG. 1 is a conceptual diagram showing an outline of a film-forming apparatus for forming a coating film on a film substrate and the process thereof. [Diagram 3] FIG. 2 is a schematic diagram showing the configuration of a surface treatment section and the state of surface treatment of a coating film. [Figure 4] FIG. 1 is a schematic diagram showing the surface treatment of a coating film using a single rotating bar. [Diagram 5] 1 shows projected images in an appearance test of hard coat films of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] [Process overview] The present invention relates to the formation of a coating film on a substrate. Fig. 1 is a cross-sectional view showing a layered structure of a laminate 8 having a coating film 3 on a first main surface 1A of a substrate 1. In one embodiment, the laminate 8 is a hard coat film having a hard coat layer 3 as a coating film on a film substrate 1.

[0017] 2 is a conceptual diagram showing an overview of a film-forming apparatus and film-forming process for forming a coating film 3 on a film substrate 1. The film-forming apparatus includes a coating section and a surface treatment section located downstream thereof, and forms a coating film on the strip-shaped film substrate while transporting the film substrate in the longitudinal direction. In FIG. 2, a roll 10 of a long film substrate wound in a roll shape is wound around an unwinding roll 11. The strip-shaped film substrate 1 unwound from the roll 10 is transported to the coating section 30.

[0018] In the coating section 30, a coating liquid is applied to the surface of the film substrate 1 to form a coating film. The film substrate 1 on which the coating film of the coating liquid has been formed is transported downstream, and in the surface treatment section 35, the surface treatment of the coating film is performed by two bars 351, 352. By performing this surface treatment, a coating film with reduced appearance defects such as streaks is formed.

[0019] The coating film after the surface treatment is transported together with the substrate 1 to the heating furnace 50, where the solvent in the coating film is dried and removed by heating. If the coating liquid (composition) is photocurable or thermocurable, the coating film is cured by light or heat in the curing section 60. If the composition is thermocurable, the heating furnace 50 may be used to perform thermal curing together with drying and removing the solvent.

[0020] The laminate 8 in which the coating film 3 is formed on the film substrate 1 is wound up by a winding roll 81 to obtain a roll 80 of a long film.

[0021] Hereinafter, the method and apparatus of the present invention will be described in more detail based on an embodiment in which a hard coat layer is formed by applying a photocurable hard coat composition onto a film substrate.

[0022] [Hard coat film materials] <Film substrate> For example, a transparent film is used as the film substrate 1 of the hard coat film. The visible light transmittance (total light transmittance) of the transparent film is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0023] The resin material constituting the transparent film is preferably one having excellent transparency, mechanical strength, and thermal stability. Specific examples of the resin material include polyester resin, (meth)acrylic resin, polyethersulfone resin, polysulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, cyclic polyolefin resin, polyarylate resin, polystyrene resin, and cellulose resin.

[0024] When the hard coat film is used as a cover window of a display, the film substrate is required to have excellent heat resistance and mechanical strength, and a preferred example of the resin material is transparent polyimide. While general wholly aromatic polyimides are colored yellow or brown, transparent polyimides with high visible light transmittance can be obtained by introducing an alicyclic structure, a bent structure, or a fluorine substituent.

[0025] The thickness of the film substrate is not particularly limited, but from the viewpoints of strength, workability such as handleability, thin layer property, etc., it is preferably about 5 to 300 μm, more preferably 10 to 250 μm, and even more preferably 20 to 200 μm.

[0026] <Hard Coat Composition> The hard coat layer is a cured resin layer, and is formed by applying a hard coat composition containing a curable resin onto a film substrate and curing the resin component.

[0027] (curable resin) The curable resin (binder resin) may be a thermosetting resin or a photocurable resin. The hard coat composition is preferably photocurable, and the curable resin is preferably photocurable, since it can be cured in a short time by irradiation with active light such as ultraviolet light and has excellent productivity.

[0028] The photocurable resin is a polyfunctional compound having two or more photopolymerizable (preferably ultraviolet-polymerizable) functional groups. The polyfunctional compound may be a monomer or an oligomer. Examples of the photopolymerizable functional group include a functional group having an ethylenically unsaturated double bond, such as a vinyl group or a (meth)acryloyl group, and a cyclic ether group, such as an epoxy group or an oxetane group.

[0029] Specific examples of the photocurable resin include acrylic urethane resin, polyester acrylate resin, epoxy acrylate resin, polyol acrylate resin, and epoxy resin. As the photocurable resin, polysiloxane resin having an epoxy group as a photopolymerizable functional group, as disclosed in WO2018 / 096729, WO2014 / 204010, JP2017-8142A, etc., may be used.

[0030] (Photopolymerization initiator) It is preferable to blend a photopolymerization initiator in the photocurable hard coat composition. As the photopolymerization initiator, a photoradical polymerization initiator, a photocationic polymerization initiator (photoacid generator), etc. may be used depending on the polymerizability of the curable resin. As the photoradical polymerization initiator, acetophenones, benzophenones, Michler's benzoyl benzoate, α-aminoxime ester, thioxanthones, propiophenones, benzils, benzoins, and acylphosphine oxides may be mentioned. As the photocationic polymerization initiator, strong acids such as toluenesulfonic acid or boron tetrafluoride; onium salts such as sulfonium salts, ammonium salts, phosphonium salts, iodonium salts, and selenium salts; iron-arene complexes; silanol-metal chelate complexes; sulfonic acid derivatives such as disulfones, disulfonyldiazomethanes, disulfonylmethanes, sulfonylbenzoylmethanes, imidosulfonates, and benzoin sulfonates; and organic halogen compounds may be mentioned.

[0031] The content of the photopolymerization initiator in the hard coat composition is about 0.05 to 10 parts by weight, and may be 0.1 to 5 parts by weight, or 0.2 to 2 parts by weight, based on 100 parts by weight of the curable resin.

[0032] (Photosensitizer) The hard coat composition may contain a photosensitizer for the purpose of improving photosensitivity, etc. Examples of the photosensitizer include anthracene derivatives, benzophenone derivatives, thioxanthone derivatives, anthraquinone derivatives, and benzoin derivatives. Among them, anthracene derivatives, thioxanthone derivatives, and benzophenone derivatives are preferred from the viewpoint of photoinduced electron donative properties.

[0033] (Reactive diluent) The hard coat composition may contain a reactive diluent (photocurable monomer) in addition to the photocurable resin. By adding a reactive diluent to the composition, the density of the photopolymerization reaction points (crosslinking points) increases, and the curing speed may be increased.

[0034] (Additives) The hard coat composition may contain additives such as fine particles, colorants, plasticizers, dispersants, wetting agents, thickeners, leveling agents, defoamers, flame retardants, antistatic agents, antioxidants, ultraviolet absorbers, polymerization inhibitors, etc. The hard coat composition may also contain a thermoplastic or thermosetting resin material in addition to the above-mentioned photocurable resin.

[0035] (solvent) The hard coat composition may be solvent-free or may contain a solvent. The solvent is preferably one that does not dissolve the film substrate. On the other hand, by using a solvent that has a degree of solubility that swells the film substrate, the adhesion between the film substrate and the hard coat layer may be improved.

[0036] Examples of the solvent include ketones such as acetone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, etc.; alcohols such as ethanol, isopropyl alcohol, butanol, cyclohexanol, etc.; esters such as methyl acetate, ethyl acetate, butyl acetate, isopropyl acetate, etc.; ethers such as dioxane, tetrahydrofuran, diethylene glycol methyl ether, propylene glycol methyl ether, etc.; aliphatic hydrocarbons such as hexane, etc.; alicyclic hydrocarbons such as cyclohexane, etc.; aromatic hydrocarbons such as toluene and xylene, etc.; amides such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, etc.; alkyl halides such as chloroform, dichloromethane, dichloroethane, etc.; sulfoxides such as dimethyl sulfoxide, etc.; and cellosolves such as methyl cellosolve, ethyl cellosolve, etc.

[0037] (Preparation of Hard Coat Composition) The method for preparing the hard coat composition is not particularly limited. For example, the above-mentioned components may be mixed and mixed with a hand mixer or a static mixer, or kneaded with a planetary mixer, disperser, roll, kneader, or the like.

[0038] The solid content of the hard coat composition is usually about 5 to 80% by weight, and may be about 10 to 70% by weight. Considering the film-forming property and the efficiency of drying and removing the solvent, the solid content of the hard coat composition is preferably 15% by weight or more, more preferably 20% by weight or more, and may be 25% by weight or more, 30% by weight or more, 35% by weight or more, or 40% by weight or more. As described above, the hard coat composition may be a solvent-free type.

[0039] The viscosity of the hard coat composition (coating liquid) is not particularly limited and may be set according to the coating method, etc., but is usually about 1 to 200 poise, and may be 5 to 150 poise or 10 to 100 poise. If the solid concentration of the coating liquid is high and the viscosity is high, the leveling effect of the coating film surface decreases, and coating defects such as streaks and stepped thickness unevenness are likely to occur. As described later, these appearance defects can be reduced or eliminated by carrying out a specified surface treatment after forming a coating film on a substrate.

[0040] [Formation of hard coat layer] 2, a strip-shaped film substrate 1 is unwound from a winding roll 11 and transported continuously in the longitudinal direction, while a hard coat composition is applied as a coating liquid in a coating section 30 to form a coating film, and the solvent is dried and removed in a heating furnace 50 as necessary, and then the composition is cured in a curing section 60 to form a hard coat layer 3 on the film substrate 1. In the present invention, a surface treatment section 35 arranged downstream of the coating section 30 brings a bar into contact with the coating film, thereby treating the surface of the coating film.

[0041] The strip-shaped film substrate 1 unwound from the unwinding roll 11 moves continuously downstream of the transport path formed by the transport rolls 41, 42, 43 and the pair of nip rolls 45, and is transported to the coating section 30, transported along the transport path formed by the transport rolls 37, 38 and the transport rolls 71, 71 arranged before and after the heating furnace to the curing section 60, transported along the pair of nip rolls 75 and the transport rolls 73, 74, and taken up by the take-up roll 81. Although not shown, a transport roll may also be provided inside the heating furnace 50.

[0042] Nip roll 45 and nip roll 75 sandwich the film between the two rolls and transport it downstream. At least one of the two rolls constituting the nip roll is a drive roll, and the transport speed of the film is kept constant by adjusting its rotation speed. The transport roll may be a drive roll or a free rotating roll.

[0043] The conveying speed Va of the film substrate is not particularly limited and may be appropriately set in consideration of the coating thickness, the time required for drying the solvent and curing the composition, etc. The conveying speed Va of the film substrate is generally about 0.1 to 100 m / min, and may be 0.3 to 50 m / min, 0.5 to 30 m / min, or 1 to 20 m / min.

[0044] <Formation of coating film> A hard coat composition is applied as a coating liquid onto the first main surface 1A of the film substrate 1 transported to the coating unit 30, thereby forming a coating film 311. In the embodiment shown in Fig. 2, the coating liquid discharged from a die 33 is applied onto the first main surface 1A of the film substrate 1 with the second main surface 1B of the film substrate 1 in contact with the backup roll 31.

[0045] There is no particular limitation on the method for applying the coating liquid onto the film substrate 1. Examples of the application method include die coating, gravure coating, wire bar coating, knife roll coating, blade coating, and spray coating. The application thickness D1 of the coating liquid (thickness of the coating film 311) may be appropriately set according to the thickness of the coating film 3 after the solvent is dried and removed.

[0046] <Surface treatment of coating film> The laminate in which the coating film 311 is formed on the substrate 1 is transported to the surface treatment section 35 arranged downstream of the coating section 30, where the surface treatment of the coating film 311 is performed. Fig. 3 is a schematic diagram showing the state of treatment in the surface treatment section.

[0047] Surface treatment section 35 includes a first bar 351 and a second bar 352 disposed adjacent to the downstream side of first bar 351. First bar 351 is a rotating body (roll) having a circular cross section, and is disposed so as to be in contact with coating film 311 formed in coating section 30. The surface of first bar 351 may be a smooth surface, or may have an uneven surface like a wire bar roll or a gravure roll. The diameter of first bar 351 is, for example, about 5 to 500 mm, and may be 10 to 300 mm, or may be 100 mm or less, 50 mm or less, or 30 mm or less.

[0048] The first bar 351 comes into contact with the surface of the coating film 311, thereby leveling the surface of the coating liquid and eliminating defects such as streaks formed on the coating film 311 during coating in the coating unit 30. From the viewpoint of enhancing the smoothing effect on the coating film surface, it is preferable to rotate the first bar 351. The rotation direction of the first bar 351 may be the forward direction (normal rotation) or the reverse direction (reverse rotation). From the viewpoint of enhancing the effect of scraping off the coating liquid by the second bar 352 described below, the rotation direction of the first bar 351 is preferably the forward direction.

[0049] The rotation speed of the first bar 351 is not particularly limited, but the higher the rotation speed, the greater the effect of smoothing the coating film. The peripheral speed Vb=πRφ of the rotation of the first bar 351 is preferably greater than the conveying speed Va of the film substrate 1. π is the ratio of the circumference of the circle to its circumference, R is the number of rotations (rpm), and φ is the diameter.

[0050] When the first bar 351 is rotating in the forward direction, if the circumferential speed Vb is greater than the conveying speed Va of the substrate 1, a shear force in the conveying direction acts on the surface of the coating 311. The higher the rotation speed (circumferential speed) of the first bar 351 and the greater the shear force on the coating surface, the greater the smoothing effect of the coating tends to be. The ratio Vb / Va of the circumferential speed Vb of the first bar to the conveying speed Va of the film substrate 1 is preferably 2 or more, and may be 3 or more, 4 or more, or 5 or more.

[0051] If the rotation speed is excessively high, the coating film may have a reduced thickness or step-like unevenness due to the coating liquid being lifted up by shear force on the coating film surface. Therefore, Vb / Va is preferably 500 or less, and may be 300 or less, 100 or less, 50 or less, or 30 or less.

[0052] The second bar 352, which is disposed close to the downstream side of the first bar 351, has the role of scraping off the coating liquid stirred up by the first bar 351 to maintain the thickness of the coating film. Figure 4 shows a schematic diagram of the case where the surface of the coating film 311 is treated with only one rotating bar 359.

[0053] When the rotating bar 359 comes into contact with the surface of the coating film 311, the coating liquid on the surface of the coating film is rolled up by the rotating bar 359 due to a shearing action, and the thickness of the coating film 315 is reduced. The higher the viscosity of the coating liquid and the higher the rotation speed (circumferential speed) of the bar, the greater the amount of coating liquid rolled up by the rotating bar, and the greater the amount of thickness reduction (D1-D5) tends to be. Furthermore, when the rotating bar 359 is a wire bar, the smaller the wire bar number (wire diameter) (i.e., the smaller the volume of the space between the substrate 1 and the rotating bar 359), the greater the effect of improving the appearance by the surface treatment, but the greater the amount of coating liquid rolled up and the greater the amount of thickness reduction tends to be.

[0054] When the coating liquid of the coating film 311 is wound up by the rotating bar 359, a pool 319 of the wound up coating liquid is formed between the coating film 311 and the rotating bar 359 on the upstream side of the rotating bar 359. The coating liquid intermittently flows from this pool to the downstream side, which may cause step-like unevenness in thickness.

[0055] 3, by arranging second bar 352 close to the downstream side of first bar 351, the coating liquid rolled up by first bar 351 is scraped off by second bar 352. Therefore, immediately after coating film 311 comes into contact with first bar 351, the film thickness is temporarily reduced, but the coating liquid scraped off by second bar 352 returns to the surface of the coating film and is recoated between second bar 352 and substrate 1, so that the film thickness of the coating film can be maintained.

[0056] figure 3 In the figure, second bar 352 is shown to be a roll having a circular cross section like first bar 351, but the shape of second bar 352 is not limited as long as it is capable of scraping off the coating liquid rolled up by first bar 351. For example, second bar 352 may be a plate-like body such as a doctor blade.

[0057] The second bar 352 may be in contact with the first bar 351. If the second bar 352 is in contact with the first bar 351, the rotation of the first bar may be hindered. Therefore, the second bar 352 may be arranged slightly away from the first bar 351. When the first bar 351 and the second bar 352 are apart, the arrangement of the second bar 352 may be adjusted so that the second bar 352 comes into contact with the coating liquid attached to the first bar 351 and has the effect of scraping off the coating liquid from the first bar 351. The distance d between the first bar 351 and the second bar 352 is preferably 1 mm or less, and may be 500 μm or less, 300 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. The distance d may be 1 μm or more, 3 μm or more, or 5 μm or more.

[0058] As described above, the second bar 352 may be a roll having a circular cross section. When the second bar 352 is a roll, it is preferable that the second bar is arranged without rotating. Since the fixed second bar 352 is arranged close to the first bar 351 without rotating, the second bar 352 does not scoop up the coating liquid, and therefore a decrease in the thickness of the coating film 313 after passing through the second bar 352 can be suppressed. Furthermore, since the second bar 352 does not rotate, liquid pools are unlikely to form, and the occurrence of step-like unevenness in the coating film 313 is suppressed.

[0059] The difference (D1-D3) between the thickness D1 of the coating film 311 before contacting the first bar 351 and the thickness D3 of the coating film 313 after passing through the second bar 352, i.e., the change in the thickness of the coating film before and after treatment in the surface treatment section 35, is preferably 5 μm or less, more preferably 3 μm or less, and may be 2 μm or less or 1 μm or less.

[0060] As described above, in surface treatment section 35 arranged downstream of coating section 30, the surface of coating film 311 is smoothed by contacting the surface of first bar 351, which is a rotating body. In addition, second bar 352 arranged close to the downstream side of first bar 351 has the function of scraping off the coating liquid stirred up by first bar 351 and recoating it on the substrate surface, so that defects such as streaks can be eliminated without reducing the thickness of the coating film.

[0061] From the viewpoint of making the thickness of the coating film 313 after treatment in the surface treatment unit 35 uniform, the second bar 352 preferably functions as a bar coater. The second bar may be one having an uneven surface, such as a wire bar roll or a gravure roll. For example, by using a wire bar or gravure roll having a number (wire diameter, cell volume) corresponding to the thickness D1 of the coating film 311 (and the thickness D3 of the coating film 313) as the second bar 352 and arranging the roll so that the outer periphery is in contact with the film substrate 1, the thickness of the coating film 313 can be made uniform.

[0062] The second bar 352 may be a roll bar, a knife coater, a blade coater, or the like having a smooth surface (surface in contact with the coating film). In this case, it is preferable to arrange the second bar 352 so that the distance (clearance) between the film substrate and the second bar 352 coincides with the thickness D1 of the coating film 311 and the thickness D3 of the coating film 313.

[0063] <Drying> When the hard coat composition contains a solvent, the solvent is dried after the surface treatment of the coating film. Drying may be performed at room temperature, but from the viewpoint of increasing the efficiency of removing the solvent, it is preferable to heat the laminate in which the coating film is formed on the film substrate in a heating furnace 50. The heating temperature is not particularly limited, but is about 30 to 200°C, and may be increased stepwise. The heating time is about 10 seconds to 10 minutes.

[0064] As described above, in this embodiment, before the solvent is dried and removed from the coating film, the coating film is treated in the surface treatment section 35, and defects such as streaks on the coating film surface are reduced or eliminated. Therefore, even after the solvent is dried and removed, the surface of the coating film remains highly smooth, and coating defects such as streaks are reduced.

[0065] <Curing> When the hard coat composition contains a photocurable resin, it is preferable to dry and remove the solvent from the coating film, and then perform photocuring in the curing section 60. Photocuring is performed by irradiating the coating film with active energy rays from a light source 65. Fig. 2 illustrates a form in which the film substrate is irradiated with active light rays from a light source 65 while being transported on a backup roll 63.

[0066] Examples of active energy rays irradiated during photocuring include visible light, ultraviolet light, infrared light, X-rays, α-rays, β-rays, γ-rays, and electron beams. UV light is preferred as the active light, since it has a high curing reaction rate and is excellent in energy efficiency. Examples of light sources include low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, carbon arc lamps, LEDs, black lights, and chemical lamps.

[0067] The cumulative dose of active energy rays is, for example, 50 to 10,000 mJ / cm 2 The heating temperature is about 120° C., and may be set according to the type and amount of the curable resin and photopolymerization initiator contained in the hard coat composition, the thickness of the coating film, etc. Photocuring may be performed under heating conditions for the purpose of promoting the photocuring reaction, etc. The heating temperature is not particularly limited, but is usually 120° C. or less.

[0068] <Characteristics of hard coat film> As described above, a hard coat film 8 is obtained by forming a hard coat layer 3 on a strip-shaped film substrate 1. The thickness of the hard coat layer 3 is about 1 to 100 μm, and preferably 2 to 80 μm. The thickness of the hard coat layer may be 3 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more. The thicker the hard coat layer, the higher the surface hardness tends to be. The pencil hardness of the surface of the hard coat film 8 on which the hard coat layer 3 is formed is preferably H or more, and may be 2H or more, 3H or more, or 4H or more.

[0069] In order to increase the thickness of the hard coat layer, it is necessary to increase the thickness of the coating film of the hard coat composition, but if the coating film is too thick, it may cause a decrease in the efficiency of drying and removing the solvent or a coating defect. The thickness of the coating film can be reduced by reducing the amount of solvent in the hard coat composition and increasing the solid content concentration. On the other hand, if the solid content concentration is increased, the viscosity of the coating liquid increases, so that coating defects such as streaks are likely to occur. As described above, in the present invention, after forming the coating film in the coating section 30, a treatment is performed in the surface treatment section 35, so that a hard coat layer with a large thickness and few defects such as streaks can be formed even when the viscosity of the coating liquid is high (for example, 10 poise or more).

[0070] [Application to other coating films] Although the embodiment in which a hard coat layer is formed as the coating film 3 on the film substrate 1 has been described above, the present invention can be applied to the formation of various coating films on a substrate. The coating film may be a functional layer that imparts a predetermined function to the surface of the film substrate, such as an anti-reflection layer, an antistatic layer, an easy-adhesion layer, or an adhesive layer. The coating film may also be a film that is self-supporting in itself. When the coating film is a film that is self-supporting, the coating film 3 may be peeled off from the substrate 1, and then only the coating film may be wound up to form a roll. EXAMPLES

[0071] The present invention will be specifically described below by comparing examples and comparative examples, but the present invention is not limited to the following examples.

[0072] [Preparation of hard coat resin composition] A reaction vessel was charged with 100 parts by weight of β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane ("SILQUEST A-186" manufactured by Momentive Performance Materials), 0.12 parts by weight of magnesium chloride, 11 parts by weight of water, and 11 parts by weight of propylene glycol monomethyl ether, and the mixture was stirred at 130°C for 3 hours and then devolatilized under reduced pressure at 60°C to obtain a condensation product (siloxane resin having an alicyclic epoxy group).

[0073] A hard coat composition (viscosity 20 poise) was obtained by blending 100 parts by weight of the above siloxane resin, 2 parts by weight of a photoacid generator ("CPI-101A" manufactured by San-Apro), and 0.2 parts by weight (as solids) of a leveling agent ("BYK-300" manufactured by BYK).

[0074] [Comparative Example 1] A long transparent polyimide film (manufactured by Kaneka) with a thickness of 80 μm was set on the unwinding roll of a coating device as shown in FIG. 2. The hard coat resin composition was applied from a die coater while the polyimide film was transported downstream at a transport speed of 0.5 m / min. The film was heated at 120° C. for 2 minutes, and then applied with 1000 mJ / cm 2 .2 The hard coat composition was cured by irradiation with ultraviolet light of 1000 nm to obtain a hard coat film having a hard coat layer having a thickness of 47 μm on a transparent polyimide film.

[0075] [Comparative Example 2] Immediately after forming the coating film with the die coater, a first bar (a wire bar with a shaft diameter of 15 mm and wire size #56) was rotated in the forward direction at a rotation speed of 250 rpm (circumferential speed of 11.8 m / min) and brought into contact with the coating film to perform surface treatment. A hard coat film was obtained in the same manner as in Comparative Example 1 except for the above.

[0076] [Example 1] A second bar (a wire bar with a shaft diameter of 15 mm and wire size #34) was brought into contact with the downstream side of the first bar to perform surface treatment. The first bar was rotated at 250 rpm, and the second bar was not rotated. Otherwise, a hard coat film was obtained in the same manner as in Comparative Example 2.

[0077] [Comparative Example 3] A hard coat film was obtained in the same manner as in Example 1, except that the first bar was not rotated.

[0078] [evaluation] <Appearance> In a darkroom, an appearance inspection light ("S-light SA" manufactured by Nippon Gijutsu Center) was placed 140 cm away from a white screen, and a hard-coated film was placed at an equal distance from the light and the white screen (70 cm from each). The light from the light was irradiated onto the hard-coated film, and the projected light was projected onto the white screen to check for the presence or absence of streaky shadows (streaks) extending in the conveying direction and stepped unevenness (step unevenness) extending in the width direction.

[0079] For both streaks and step unevenness, those that were clearly observed were given a C, those that were slight or not observed were given an A, and those that were intermediate between the two were given a B.

[0080] <Thickness of hard coat layer> The thickness of the hard coat film was measured using a dial type thickness gauge, and the thickness of the hard coat layer was determined by subtracting the thickness of the polyimide film (80 μm).

[0081] [Evaluation Results] The treatment conditions and evaluation results of the coatings of the hard coat compositions in the examples and comparative examples are shown in Table 1. Moreover, projected images of the appearance inspection of the hard coat films of Comparative Examples 1 and 2 and Example 1 are shown in FIG.

[0082] [Table 1]

[0083] In Comparative Example 1, in which the hard coat composition was applied using a die coater, then dried and cured without surface treatment of the coating, obvious streaks extending in the longitudinal direction (MD) were observed (see FIG. 5(A)). In Comparative Example 2, in which the coating was surface treated using a single rotating bar, the MD streaks were eliminated, but the thickness of the hard coat layer was reduced, and stepped thickness unevenness extending in the width direction became noticeable (see FIG. 5(B)).

[0084] In Example 1, in which the surface treatment was performed by arranging the second bar downstream of the first bar, the MD streaks were eliminated, and the step unevenness was also improved compared to Comparative Example 1. Furthermore, the thickness of the hard coat layer in Example 1 was 47 μm, the same as that of the hard coat layer in Comparative Example 1, in which the surface treatment was not performed, and no reduction in the thickness of the hard coat layer due to the surface treatment as in Comparative Example 2 was observed.

[0085] In Comparative Example 3, in which the first bar was used without rotation, the step unevenness and MD streaks were reduced compared to Comparative Example 1, but the MD streaks remained, and the appearance improvement effect was not sufficient.

[0086] From the above results, it can be seen that MD streaks can be reduced by contacting the surface of the coating with a rotating bar to apply shear force, and that by placing another bar behind the rotating bar to scrape off the coating liquid adhering to the rotating bar, it is possible to reduce step-like unevenness without reducing the thickness of the coating, resulting in a coating film with excellent appearance. [Explanation of symbols]

[0087] 1 Base material 3 Coating film (hard coat layer) 8 Laminate (hard coat film) 11 Unwinding roll 81 Winding roll 30 Coating Section 33 Backup Role 31 Dice 35 Surface treatment section 351 First Bar 352 Second Bar 311,313 Coating 50 Furnace 60 Hardened part 65 Light source 63 Backup Roll 45,75 Nip roll 41~43 Transport roll 37,38 Transport roll 71~74 Transport roll

Claims

1. A method for producing a coating film, comprising the steps of: forming a coating film on a main surface of a belt-shaped substrate while continuously transporting the substrate in a transport direction parallel to the longitudinal direction of the substrate; and drying and / or curing the coating film, A step of applying a coating liquid onto a main surface of the substrate in a coating section to form a coating film; a step of surface-treating the coating film formed in the coating section in a surface treatment section located downstream in the conveying direction away from the coating section; and A step of drying and / or curing the coating film to form a coating film, The surface treatment section includes a first bar and a second bar, the first bar is a rotating body having a circular cross section and arranged so as to contact the surface of the coating film, and rotates in a forward direction relative to a conveying direction of the substrate, and a ratio Vb / Va of a peripheral speed Vb (m / min) of rotation of the first bar to a conveying speed Va (m / min) of the substrate is 2 or more, the second bar is disposed adjacent to the first bar on the downstream side in the conveying direction so as to scrape off the coating liquid adhering to the surface of the first bar, and the second bar also comes into contact with the coating film; A method for producing a coating film.

2. The method for producing a coating film according to claim 1 , wherein the second bar has a circular cross section and is fixed without rotating.

3. The method for producing a coating film according to claim 1 or 2, wherein the second bar is a wire bar.

4. The method for producing a coating film according to any one of claims 1 to 3, wherein the first bar is a wire bar.

5. The method for producing a coating film according to any one of claims 1 to 4, wherein a difference between a thickness of the coating film before the surface treatment step and a thickness of the coating film after the surface treatment step is 5 µm or less.

6. The method for producing a coating film according to any one of claims 1 to 5, wherein the coating liquid has a viscosity of 10 to 100 poise.

7. The coating liquid is a hard coat composition containing a curable resin, The method for producing a coating film according to any one of claims 1 to 6, wherein after the surface treatment step, the hard coat composition is cured to form a hard coat layer as the coating film.

8. The hard coat composition comprises a solvent, The method for producing a coating film according to claim 7 , wherein after the surface treatment step, the solvent is removed by drying before the hard coat composition is cured.

9. The method for producing a coating film according to any one of claims 1 to 8, wherein the coating film has a thickness of 10 µm or more.

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