JP2016179458A - Coating applicator and coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating applicator capable of flattening a coating film stably without applying mechanical vibration thereto, in order to remove dispersion of a film thickness distribution such as ribbing irregularity or step irregularity in high-speed coating.SOLUTION: A coating applicator 10 for forming a coating film on a substrate 1, by coating out a coating body 2 from a coating head 3, includes a film thickness fluctuation detector 4 for measuring the thickness of a coating film just after being formed, an electrode 5 in parallel with a coated surface arranged in the non-contact state with the coated surface, and a voltage source 6 connected to the electrode 5, for applying a voltage in accordance with film thickness fluctuation.SELECTED DRAWING: Figure 1

Description

  The present invention is used in the manufacture of members that require a uniform film thickness distribution, such as color filters and optical films, and in the manufacture of barrier films that require high speed and mass production. The present invention relates to a coating apparatus and a coating method to be formed.

  In recent years, application of a coating / printing technique has been actively performed in the manufacture of display device components. For example, in a color filter, a color coater is uniformly applied on a substrate using a die coater or the like, and a desired RGB pattern is formed by photolithography.

  A color resist formed with a film thickness of less than 1 μm has a color density that varies depending on the thickness, and therefore requires a uniform film thickness at the sub-μm level.

  Moreover, in the production of optical films such as antireflection films, a coating film having a thickness of several μm is formed on a substrate using a gravure coater or the like. High speed application is required.

  In addition, in the production of barrier films that have become indispensable for our daily lives by improving the storage stability and designability of foods, high-speed coating one order of magnitude on optical films is required.

  However, in high-speed coating, it is known that a periodic film thickness distribution is generally likely to occur in the coating width direction, which is generally called “living”.

  FIG. 6 is a front conceptual view (a) and a side conceptual view (b) showing the occurrence of living unevenness in a conventional coating apparatus.

  FIG. 6 shows a coating process using a die coater as an example of a typical coating apparatus. When the coating film 2 applied to the substrate 1 is seen in the width direction as the coating speed increases, the substrate 1 is shown in FIG. A periodic thickness distribution is generated in the width direction (FIG. 2B).

  This is mainly caused by the pressure distribution occurring inside the coating bead on which the coating film is formed. The film thickness distribution due to this phenomenon (living) is called living unevenness 9.

  FIG. 7 is a front conceptual view (a) and a side conceptual view (b) showing the occurrence of step unevenness in a conventional coating apparatus, which may be uniform in the substrate width direction and have a thickness distribution in the traveling direction. This is called step unevenness 11.

  This step unevenness 11 is caused by a change in the distance between the coating outlet of the die coater and the base material 1 due to vibration of the coating apparatus, a change in the transport speed of the base material transport path, and the like. 2 is a phenomenon caused by fluctuations in the amount of liquid due to the pulsation of the pump that feeds 2.

  These film thickness distributions cause uneven defects in the above-described color filter and optical film, and lead to a decrease in barrier properties in the barrier film.

  In order to apply the coating at a high speed while suppressing the living unevenness 9, a pressure reducing mechanism is provided on the upstream side of the application bead to equalize the pressure distribution at the tip of the coating head, and to control the unevenness of the coating apparatus. The use of vibration or pulsating pumps has been implemented.

  However, the vibration and control of the apparatus are likely to become unstable due to the high-speed coating, and it is difficult to suppress the occurrence of the film thickness distribution.

  Also, as a method of eliminating the film thickness distribution, there is a method of improving the coating apparatus, mechanically vibrating the substrate after coating, improving the fluidity of the coating film on the substrate, and leveling by leveling. It has been devised (Patent Document 1).

  However, this method is effective for living and other unevenness, structural defects, etc. However, since a part of the coating apparatus is replaced with a member having a vibration function, a vibration source is added to the coating apparatus, which is not effective. There is a problem of stabilization.

JP 2005-144414 A

  The present invention is proposed in view of the above-mentioned problems, and is stable without mechanical vibrations in order to eliminate variations in film thickness distribution such as living unevenness and step unevenness that occur in high-speed coating. An object of the present invention is to provide a coating apparatus capable of flattening a coating film.

As means for solving the above-mentioned problems, the invention according to claim 1 is a coating apparatus for coating a substrate with a coating liquid from a coating head to form a coating film,
A film thickness variation detector for measuring the film thickness immediately after formation of the coating film,
An electrode parallel to the coating surface arranged in non-contact with the coating surface;
And a voltage source for applying a voltage in accordance with the film thickness variation.

  The invention according to claim 2 is characterized in that the shape of the electrode is plate-like or blade-like, and the side facing the application surface has a sharp tip. It is a coating device.

  The invention according to claim 3 is the coating apparatus according to claim 1, wherein the electrode has a linear shape.

  The invention according to claim 4 further comprises an angle adjusting mechanism for adjusting the angle of the electrode with respect to the transport direction of the substrate or the coating head. It is a coating device as described in above.

  In addition, the invention described in claim 5 is a film that exists immediately after coating by applying a voltage to the electrode using the coating apparatus according to any one of claims 1 to 4 to swell the coating film directly under the electrode. This coating method is characterized in that the thickness distribution is eliminated.

The present invention is a coating apparatus that applies a liquid to a desired base material, and includes a coating mechanism that forms a coating film on the base material, and a downstream side from a coating portion where the liquid is applied to the base material to be coated in the coating mechanism. By applying a voltage to the electrode in accordance with the film thickness variation, it was possible to eliminate film thickness distribution defects due to living unevenness and step unevenness caused by high-speed coating without mechanically applying vibration.

It is the front conceptual diagram (a) and side conceptual diagram (b) which showed the structure of the coating device of this invention. It is the front conceptual diagram (a) side conceptual diagram (b) which showed the change of the coating liquid by the effect | action of an electric field in the coating device of this invention. The conceptual diagram (a) which showed arrangement | positioning of the electrode corresponding to the generated living nonuniformity in the coating device of this invention, and the conceptual diagram which showed the film thickness distribution before and after letting a voltage be applied to an electrode and let it pass directly under an electrode ( b). The conceptual diagram (a) which showed arrangement | positioning of the electrode corresponding to the generated step nonuniformity in the coating apparatus of this invention, and the conceptual diagram which showed the film thickness distribution before and after letting a voltage be applied to an electrode and let it pass directly under an electrode ( b). It is the conceptual diagram which showed the elimination mechanism of the nonuniformity by the application of a voltage in the coating device of this invention. It is the front conceptual diagram (a) and side conceptual diagram (b) which showed living nonuniformity generation | occurrence | production in the conventional coating device. It is the front conceptual diagram (a) and side conceptual diagram (b) which showed generation | occurrence | production of the step unevenness in the conventional coating device.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 shows the configuration of the coating apparatus of the present invention as a front view (a) and a side view (b).

  The coating apparatus 10 of the present invention includes a coating head 3, a film thickness variation detector 4, an electrode 5, and a voltage source 6, and forms a coating film on the substrate 1. The coating liquid 2 is applied and applied.

  A film thickness variation detector 4 that detects the film thickness variation of the coating liquid 2 formed on the base material 1 is provided downstream from the coating head 3, and the electrode 5 extends in the width direction of the base material 1. It has a spread, is disposed on the application surface side of the coating liquid 2 without contact with the application surface, and is connected to a voltage source 6 for applying a voltage.

  In addition, an electrode angle adjusting mechanism 8 that adjusts an angle θ between the electrode 5 and the traveling direction of the substrate 1 by moving the electrode 5 is provided.

  The coating head 3 is a coating part of the coating apparatus 10, and examples thereof include a die coater, a gravure coater, a reverse roll coater, a knife coater, and a comma coater. A bead is formed between the substrate 1 and the coating head 3. A coating apparatus that is formed and continuously supplies the coating liquid is suitable, and a coating film may be formed by intermittently ejecting liquid droplets such as inkjet.

  The base material 1 corresponds to a flexible resin film used in a glass substrate, an optical film, a packaging material, or the like.

  The electrode 5 is a flat plate or a wire made of metal. In the case of a flat plate, it is better that the long side facing the coating film is processed at an acute angle so that the electric field distribution is concentrated directly under the electrode.

  In the case of a wire, it is installed so that the wire is stretched in the width direction of the substrate. The distance between the wire and the base material is the same as the distance between the flat plate tip and the base material in the case of the flat electrode. When the wire diameter is as thin as possible, the electric field distribution tends to concentrate directly under the electrode.

  As the wire, for example, a thin metal wire of about several tens of μm can be used, and a wire tosmicron NANO (manufactured by Toxen Industries) having a wire diameter of 10 μm or less is suitable.

  As the voltage source 6, a voltage generated by a function generator or a pulse generator amplified by a high-voltage amplifier can be used.

  The film thickness variation detector 4 detects the film thickness variation of the coating film applied on the substrate 1 conveyed at high speed on the line. The substrate is obtained by attaching a polarizing lens to a high-speed camera. And detecting the distribution by image processing the difference in brightness when the substrate is irradiated with white light, or detecting the film thickness directly with a spectral interference film thickness meter is preferred.

  The electrode angle adjustment mechanism 7 is formed between the axis of the electrode 5 extending in the width direction of the base material 1 and the direction of travel of the base material according to the state of the film thickness distribution detected by the film thickness variation detector 4. The angle θ is adjusted.

  As the angle adjusting mechanism 7, for example, one end of the electrode 5 in the width direction of the substrate to be coated and the center in the width direction of the substrate are held, and the substrate 1 and the electrode 5 are kept horizontal with the holding portion as the center. A rotating mechanism may be used.

  Next, a method for eliminating film thickness unevenness using the coating apparatus 10 of the present invention will be described. FIG. 2 shows changes in the liquid level due to the action of an electric field in the coating apparatus 10 of the present invention. The coating liquid 2 applied from the coating head 3 forms a coating film on the substrate 1 and is conveyed downstream.

  When the coating liquid 2 passes under the electrode 5, Maxwell stress is applied to the interface between the air layer and the coating liquid 2 by the action of an electric field generated from the electrode 5 by applying a voltage from the voltage source 6 connected to the electrode 5. And the coating liquid 2 just below the electrode 5 is lifted by an electric field. Since Maxwell stress is generated directly under the electrode 5, the lifted coating film is flattened by the action of gravity and surface tension on the downstream side of the electrode 5.

  As the film thickness unevenness caused by high-speed application, there are a living unevenness 9 shown in FIG. 3 and a step unevenness 11 shown in FIG. 3 is a phenomenon in which a thick portion 12 and a thin portion of the film periodically appear in the width direction of the substrate 1 downstream from the application portion. 4 is a phenomenon that is uniform with respect to the width direction of the substrate 1 and that a thick portion 12 and a thin portion of the film appear periodically in the traveling direction of the substrate 1.

  The occurrence of the unevenness is detected by the film thickness fluctuation detector 4. When it is determined by the film thickness variation detector 4 that unevenness has occurred, the type of unevenness is the living unevenness 9 or the step unevenness 11, and the electrode 5 angle adjustment mechanism 7 indicates the axis AB of the electrode 5 and the substrate 1. The angle is adjusted and a voltage is applied from a voltage source 6 connected to the electrode 5.

  If the angle of the electrode 5 is the living unevenness 9, the axis AB of the electrode 5 is made parallel to the width direction of the substrate 1 as shown in FIG. In the case of the step unevenness 11, as shown in FIG. 4, the angle is adjusted in a range in which the axis AB of the electrode 5 is non-parallel and non-perpendicular to the width direction of the substrate 1.

  FIG. 5 shows a cross-sectional view of the coating liquid 2 when no voltage is applied by the voltage source 6 in a state where each of the above unevenness occurs. When unevenness of the film thickness occurs (FIG. 5A), thick and thin portions of the coating liquid 2 appear periodically in the cross section of the coating liquid 2 along the axis AB of the electrode 5.

  When the voltage of the voltage source 6 is applied to the electrode 5 (FIG. 5B), the coating liquid 2 is lifted just below the electrode 5 until the Maxwell stress, the surface tension, and the gravity are balanced. At this time, the periodic film thickness distribution that has occurred in the direction of the axis AB of the electrode 5 is eliminated.

  In the present invention, not only the thin part is lifted, but the thick part and the thin part are all pulled up, and finally the deformation of the coating stops when the height reaches the balance between Maxwell stress and surface tension. I use that.

  When the substrate 1 moves downstream and moves away from the effective range of Maxwell stress, the lifted coating liquid 2 is relaxed by the action of gravity and surface tension, and is flattened as shown by the cross section of the broken line Z part. For the sake of explanation, the width of the electrode 5 is narrowly described, but actually, the coating liquid 2 on the substrate 1 is flattened in the entire width direction by making it wider than the width of the substrate 1 (c).

  The height at which the coating liquid 2 is lifted becomes higher in a narrower range as the relative dielectric constant of the coating liquid is larger than that of air, and depends on the strength of the electric field. Therefore, it is necessary to adjust the distance between the electrode 5 and the coating liquid, the magnitude of the applied voltage, and the frequency depending on the physical properties of the coating liquid.

  In addition, when the coating liquid 2 is a liquid that is easily charged, the liquid level may not rise well if the waveform voltage is positive or negative unipolar. In this case, the burst waveform voltage that reverses the positive and negative polarities. May be applied.

  Further, the higher the viscosity of the coating liquid 2 is, the slower the liquid surface rises, so that the liquid surface does not sufficiently rise when only one electrode 5 is provided, and the flattening effect may not be obtained. That is, when the speed of lifting is insufficient, such as when the conveyance speed is high or the viscosity of the coating liquid is high, a plurality of auxiliary electrodes similar to the electrode 5 are further provided on the downstream side of the electrode 5. The effect can be supplemented.

  When a burst waveform with an amplitude of several hundred volts is applied to a liquid having a viscosity of about 100 mPa · s and the gap between the tip of the electrode 5 and the coating liquid is 100 μm, the liquid surface having a vertex number of 10 μm and a width of about 1 mm in several milliseconds. A swell is formed.

  At a coating speed of 100 m / min, the movement of 1 mm takes about 600 μs, so that a calculation of several μm per electrode is possible.

  Since the amount of deformation changes approximately linearly depending on the viscosity, the number of auxiliary electrodes required can be determined according to the thickness of the film to be flattened by the above estimation.

  The present invention generally includes a liquid in which a solute such as a polymer resin is mixed with an organic solvent generally used for industrial use, a coating liquid in which a water-soluble polymer is mixed in water, and a mixture of microparticles therein. It can be applied to various coating liquids.

DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Coating liquid 3 ... Coating head 4 ... Film thickness variation detector 5 ... Electrode 6 ... Voltage source 7 ... Angle adjustment mechanism 8 of an electrode ..Control device 9 for angle adjustment mechanism ... Living unevenness 10 ... Coating device 11 ... Step unevenness 12 ... Thick portion 13 of film ... Coating liquid lifted by electric field

Claims (5)

A coating device that coats a substrate with a coating liquid from a coating head to form a coating film,
A film thickness variation detector for measuring the film thickness immediately after formation of the coating film,
An electrode parallel to the coating surface arranged in non-contact with the coating surface;
And a voltage source that is connected to an electrode and applies a voltage in accordance with the film thickness variation.   The coating apparatus according to claim 1, wherein the electrode has a plate shape or a blade shape, and a side facing the coating surface has a sharp tip.   The coating apparatus according to claim 1, wherein the electrode has a linear shape.   The coating apparatus according to any one of claims 1 to 3, further comprising an angle adjusting mechanism that adjusts an angle of the electrode with respect to a conveyance direction of the substrate or the coating head.   Using the coating apparatus according to any one of claims 1 to 4, a voltage is applied to the electrode, the coating film directly under the electrode is raised, and the distribution of the film thickness existing immediately after coating is eliminated. Application method.

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