JPH05293428A - Method for smoothing resin film - Google Patents

Abstract

PURPOSE:To efficiently smooth a resin film without leaving a damage or unevenness on the surface of the smoothed resin film. CONSTITUTION:A release film 27 with a thickness of 25-100mum coated with a silicone-based release agent 30 with peel strength of 10-50g/50mm is placed on the surface of a resin film 13 and heated and pressed by a roller 25 to smooth the resin film. Thereafter, the release film 27 is peeled off to obtain the smoothed resin film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for smoothing a resin film applied on a supporting substrate.

[0002]

2. Description of the Related Art In recent years, organic materials have been widely used in various electronic devices. For example, a high resistance substrate of a thermal head (thermal printing head) or a hybrid I
An electronic device such as a multi-layer circuit board for C, which is required to have high reliability against heat, has a structure in which a heat-resistant polyimide resin is coated on a supporting substrate as an insulating layer or a heat-resistant layer.
Color filters used in liquid crystal display devices or the like have various patterns of colored color ink coatings printed or applied directly on the translucent substrate or via other layers. The surface of these resin coatings is smoothed before use.

Taking a thermal head as an example, in the past, instead of a high resistance substrate formed as a heat insulating layer for controlling heat dissipation and heat storage, a glaze glass layer was formed on a ceramic substrate or a polyimide on a ceramic substrate or a metal substrate. A heat-resistant insulating substrate formed of resin as a heat insulating layer is becoming practical. A thermal head using such a heat-resistant insulating substrate has a polyimide resin layer as a heat insulating layer, so that the thermal diffusivity of the polyimide resin is 1/3 to 1/6 that of a conventional glaze glass layer. Since it becomes extremely small, the thermal efficiency becomes excellent. Also, such as metal substrates
When a flexible substrate is used, bending can be performed, and a compact, inexpensive high-performance thermal head can be manufactured.

In such a thermal head, since it is necessary to form an inorganic thin film or a metal thin film for forming a heating resistor or an electrode on the polyimide resin layer of the heat retaining layer,
It is necessary to minimize defects such as voids and protrusions and surface irregularities. As this means, in the method for producing a resin substrate for coating a polyimide resin layer on a supporting substrate, a polyamic acid varnish of a polyimide precursor is applied to the supporting substrate, and a temperature at which the polyamic acid varnish applied to the supporting substrate is not imidized. And heat to remove the solvent in the polyamic acid varnish. Thereafter, the polyamic acid varnish coating film is smoothed by heating and pressurizing it with a smoothing roller through a peeling member, and the smoothed polyamic acid varnish coating film is heat-treated to imidize the polyamic acid to form a polyimide resin layer. A method of forming the is proposed.

Further, a color filter used in a color liquid crystal display device is formed by printing and coating a color ink in which a pigment or a dye is dispersed in a resin binder on a glass substrate surface,
If necessary, a transparent resin protective layer is further formed on the protective layer, and a transparent electrode is formed on the protective layer.
In this case, in order to maintain the cell spacing of the liquid crystal display device and prevent various optical losses, defects such as voids and projections and surface irregularities are formed on the colored ink film in a dry state in which the solvent contained in the colored ink film is evaporated. A method is known in which a colored ink film is heat-cured after being heated and pressed by a smoothing roller via a peeling member to be smoothed. Further, a transparent protective layer such as an epoxy resin or an acrylic resin is formed on the colored ink film, and in a dry state in which the solvent contained in the transparent protective layer is evaporated, the transparent protective layer is heated with a smoothing roller through a peeling member, A method is also known in which pressure is applied to smooth the surface, and then heat curing is performed.

For example, in Japanese Unexamined Patent Publication No. 63-216028 or Japanese Unexamined Patent Publication No. 1-167807, a roller made of rubber or a mirror-finished metal is heated and pressed to crush the convex portion of the colored ink film. A method of smoothing is disclosed. In addition, a method of applying the colored ink coating side of the color filter to a flat plate or a flat surface plate directly or through a film that is difficult to adhere to them, and smoothing by pressing with a roller or a surface plate for pressing from the glass substrate side, Japanese Patent Laid-Open No. 2-25
No. 1816 or Japanese Patent Laid-Open No. 62-280805.

[0007]

The latter method out of the above has the advantage that a substantially uniform pressure is applied to the entire surface of the colored ink film surface, and the entire surface is likely to be uniformly smoothed.
However, since the pressing pressure is applied through the glass substrate on which the colored ink film is formed, it is necessary to keep the pressing force to a relatively small pressure within the range where the glass substrate is not damaged. In particular, when pressure is applied by the press roller, the glass substrate is likely to be damaged, so it is necessary to keep the pressure to a lower level. The method of applying pressure by applying a flat surface plate on the glass substrate is convenient because it does not easily damage the substrate, but the pressing force to obtain the necessary and sufficient crushing amount over the entire surface is a large value. I will end up. Therefore, according to these methods, gaps that cannot be crushed easily remain between the color ink coatings. When such a gap is left, when assembled as a liquid crystal display device, voids or bubbles are formed on the bonding surface with another substrate such as a thin glass plate for electrode formation or a polarizing plate glass, or glass is parallel and even. Sticking becomes impossible. Further, when an ITO film (indium-tin oxide film) which is a transparent conductive film is formed on the colored ink film attached to the filter substrate directly or through an overcoat layer by sputtering or the like. In addition, if the surface of the colored ink coating film has irregularities, the sputter-formed coating film becomes insufficient in the thick portion of the coating film, or the sputtered coating film is not formed and disconnection is likely to occur. Thus, the manufacturing and characteristics of the color liquid crystal display device are likely to be hindered. Furthermore, the light diffusion phenomenon due to the unevenness of the surface of the colored ink coating film impairs the transparency and causes other optical loss and the like. To completely eliminate such a gap between the colored ink coatings, a higher pressing pressure is required, or a considerably long pressing time is required. This is a problem in production efficiency because the temperature control and the viscosity control of the colored ink coating become complicated. Also,
The film is apt to adhere to the colored ink film, and if peeled off without difficulty, streaky scratches or wrinkles are likely to occur on the surface of the colored ink film. As described above, the conventional smoothing method has a considerable number of advantages, but has the above-described disadvantages to be improved. It is an object of the present invention to provide a method for smoothing a resin coating which has excellent smoothness without causing scratches or irregularities on the smoothed resin coating surface.

[0008]

According to the present invention, the peeling force is 1
A release film having a thickness in the range of 25 to 100 μm coated with a silicon release agent in the range of 0 to 50 g / 50 mm is placed on the resin coating surface, and heated by a roller or the like from above the release film. This is a method for smoothing a resin film in which pressure is applied to smoothen the release film and then the release film is peeled off.

[0009]

According to the present invention, the release film can be smoothed while applying an appropriately controlled tension, and the resin coating may be peeled off at the time of peeling or a flaw such as scratches, irregularities, or wrinkles may be generated on the smooth surface. There is almost no. Therefore, the resin coating surface having excellent smoothness can be efficiently manufactured.

[0010]

Embodiments will be described below with reference to the drawings.
The same parts are denoted by the same reference numerals. The embodiment shown in FIG. 1 is a case where the present invention is applied to manufacture of a color filter used in a color liquid crystal display device. The figure shows a part of it in an enlarged manner. First, a light blocking layer 12 made of chromium was attached in a matrix on one surface of a transparent glass substrate 11 having a side of 30 cm and a thickness of 1.1 mm. Next, after cleaning the surface of the substrate, using an intaglio offset printing machine, a colored ink mainly composed of an epoxy resin varnish containing a pigment and a solvent was used, and a stripe-shaped colored ink film was formed according to an intaglio cell pattern using an intaglio plate. 13
Was printed on the substrate surface. The colored ink film 13 was formed by sequentially printing three primary colors of red (R), green (G), and blue (B).
Then, since each of the colored ink coatings R, G, and B has viscoelasticity, a portion in the vicinity of the center, which is slightly biased toward the rear end side in the printing direction, has a mountain-like shape. The film thickness near the top is 4 to 5 μm.

After forming this colored ink coating 13, 85
The solvent was removed by drying at a temperature in the range of ˜105 ° C. where thermosetting of the colored ink coating did not occur. This solvent removal amount is
The amount of the solvent initially added to the colored ink is 60% or more, and more preferably 80% or more. If the amount of the solvent removed is 60% or less, bubbles may be entrained due to foaming due to evaporation of the solvent when the colored ink film is smoothed later. Therefore, the above range is set in order to avoid it.

Next, the glass substrate 11 side of the color filter on which the colored ink coating 13 was printed and dried was placed on the heating platen 24, adsorbed and fixed by a vacuum suction chuck (not shown). A heating heater 28 is embedded in the heating platen 24, whereby the surface plate surface is set to a predetermined temperature. A heating and pressing roller 25 is installed above the surface plate 24. A heater (not shown) is built in the roller 25, and the surface of the roller 25 is set to a temperature in the range of 80 to 105 ° C. The diameter of the heating / pressurizing roller 25 is 12 cm.
The surface JIS-A hardness is 70 and the surface roughness Ra is 0.
It is a silicone rubber of 1 μm or less. The hardness of the roller surface depends on the hardness of the resin component in the ink, but the hardness is 4
It is preferably 0 or more and 90 or less. If the hardness is lower than 40 degrees,
It is difficult to control the surface roughness of the smoothed colored ink coating to 0.1 μm or less. Further, if the hardness is higher than 90, the glass substrate is easily damaged.

Therefore, the colored ink film of the color filter
A release film 27 is interposed between the heating roller 13 and the heating pressure roller 25. The release film 27 is a resin film 29 having a predetermined thickness, which is a base material, and a thin release agent 30 applied to the lower surface in the drawing. The base resin film 29 is
The thickness is in the range of 25 to 100 μm, more preferably 35.
To 80 μm, for example, 50 μm polyethylene terephthalate (PET) or polyethylene naphthalate (PEN). The release agent 30 is a silicon-based release agent that does not easily adhere to the colored ink film and is 1 μm.
m or less, for example, a thickness of several thousand angstroms. The release agent 30 also has a peeling force of 10 to 5
0g / 50mm range, more preferably 25-35g
It is in the range of / 50 mm.

The peeling force is defined as a value obtained by the following well-known measuring method. That is, a standard tape having a width of 50 mm on the surface coated with the release agent 30 (for example, double-sided adhesive tape No. 59 manufactured by Sekisui Chemical Co., Ltd.).
5) Laminate them so that no bubbles enter. Then, it is lined with a polyester film (No. 25), sandwiched between glass plates, and a load of 20 g / cm @ 2 is applied at 65 DEG C. ± 3 DEG C. and left for 20 hours. After that, after leaving for 1 hour under a standard condition of 25 ° C. and a humidity of 65%, the test piece is 300 mm at an angle of 180 degrees using an Instron type tester.
Peel at a peeling speed of 1 / min. The force required for this peeling is the peeling force.

The color ink coating of the color filter
While heating 13 to about 90 ° C, move the heating roller 25 to the arrow Fa
The colored ink film 25 was crushed through the release film 27 while being pressed down, and was rotationally moved as indicated by arrow Fb. That is, the striped colored ink film 13 was continuously smoothed by the heating and pressing roller 25 in the direction of arrow Fc in the pattern direction, that is, the longitudinal direction thereof.
In this smoothing process, the release film 27 is inclined at an angle with respect to the surface of the colored ink coating 13 to be smoothed. Thereby, the colored ink film
The air present in the depressions of 13 is pushed out smoothly, and the ink film is smoothed by the heating and pressing roller 25. The angle between the surface of the colored ink film to be smoothed and the resin film may be 5 degrees or more and 80 degrees or less.
After smoothing by the heating / pressurizing roller 25, the release film 27 is kept on the surface of the smoothed colored ink coating 13a, so that the surface of the colored ink coating is kept warm to cause uneven temperature. No wrinkles or streaks are formed on the surface of the coating in the subsequent peeling step. The pressing force (linear pressure) by the heating / pressurizing roller 25 is 10 to 15 kg /
cm, and the feed rate was 15 to 30 cm / min.

Immediately after smoothing the entire surface of the colored ink film 13 in this manner, a release roller (not shown) was operated to lift the release film 27 obliquely upward and release it from the surface of the colored ink film. Then, after that, the glass substrate 11 of the color filter was removed from the surface plate 24 and heated at 200 to 250 ° C. for several hours to thermally cure the colored ink film. As a result, a color filter in which the surface 13a of the colored ink coating 13 was smoothed was obtained. The smoothed color ink coating had a thickness of 3.0 μm.

The pattern of the colored ink film is not limited to a stripe pattern, and may be a regular array pattern in which pixels of each color are rectangular. In that case, the heating roller is rotated in the longitudinal direction of the color pixels to smooth the color pixels. Is desirable. Alternatively, it may be a pattern of square or circular color pixels. In that case, smoothing toward the same color direction is desirable because there is less possibility of color mixing.

The embodiment shown in FIGS. 2 to 6 shows a case where an apparatus capable of automatically and efficiently performing this smoothing processing is used. The glass substrate 11 of the color filter, on which the color ink was printed and dried, was mounted on the smoothing processing device 20 for smoothing the surface of the color ink film and smoothed. The smoothing processing device 20 has a base on which a heating platen 24 is placed and moves. Above the position where this heating platen 14 passes,
A roller 25 for heating and pressing is installed. Also,
A release film transport device is provided, and a release film 27 is provided between the heating platen 24 and the heating / pressurizing roller 25 by an arrow Fd.
It can be transported like.

A heating heater 28 is embedded in the heating platen 24, and a vacuum suction chuck (not shown) is further provided. The heating / pressurizing roller 25 also has a built-in heating heater, and can be moved up and down. The film transport device 26 automatically supplies the release film 27,
A film feed roll made of plastic that has an unused release film 27 wound around the heating pressure roller 25 diagonally above the left side in the figure.
31 are arranged. Between the film feed roll 31 and the heating / pressurizing roller 25, an ion blow device 32 and a suction device 3 for removing foreign matter adhering to the film.
3. A meandering prevention roller 34 is provided. They are,
It constitutes a release film supply unit. The release film feed roll 31 includes a reverse rotation driving device (not shown) and a powder.
A braking mechanism such as a brake is provided and is controlled by the control device. On the right side of the heating and pressing roller 25 in the drawing, a movable release film peeling roller 35, a guide roller 36, a movable film pulling roller 37, a meandering prevention roller 38, and a release film take-up roller. A roll 39 is provided. A release film is hung on each of these rollers as shown in the drawing and conveyed. The release film winding roll 39 is also provided with a torque motor and a braking device, and is controlled by the control device. In this way, a predetermined tension is applied to the release film 27 and controlled. Therefore, first, the surface of the heating platen 24 is set to a temperature in the range of 80 to 105 ° C, and the heating and pressure roller is set.
The surface temperature of 25 was set to a temperature in the range of 80 to 105 ° C. Then, as shown in FIG. 2, the colored color ink film is formed.
The glass substrate 11 on which 13 was printed was advanced on the heating platen 24 with the colored ink film facing upward while vacuum adsorption and preheating to proceed as indicated by arrow Fe. Until the heating platen 24 reaches below the heating / pressurizing roller 25, the roller 25 and the film peeling roller 35 are in the upper position. Then, at a time point A (see FIG. 6, the same applies hereinafter) when the heating platen 24 approaches near the heating and pressing roller 25, the take-up roll 39 is rotationally driven and the release film 27 is moved to the right in the figure. Proceed to.
Thereby, the unused release agent surface of the release film is
Face the colored ink coating 13 to be smoothed.

Next, at the time B when the heating platen 24 reaches below the heating and pressing roller 25, as shown in FIG. 3, the heating roller 25 and the film peeling roller 35 descend from the original position indicated by the dotted line. Then, from the time point C, the heating / pressurizing roller 25 crushes the colored ink film 13 at a predetermined pressure as shown by the arrow Fa and rotationally moves as shown by the arrow Fb to smooth it. Colored ink film 13
Is heated to about 90 ° C., softened and smoothed. During that time, the release film 27 travels in the right direction in the drawing together with the movement of the heating platen 24 and the rotation of the heating and pressing roller 25. Appropriate tension is applied to the release film 27 by the feed roll 31 and the winding roll 39 to absorb the thermal expansion of the film. On the side of the feed roll 31, the release film 27 is arranged in an oblique direction with respect to the surface of the colored ink film 13 to be smoothed, and the smoothed ink film surface is completely smoothed. It is kept close until you do.

Then, as shown in FIG. 4, the colored ink film 13 on the glass substrate is smoothed. This state corresponds to FIG. That is, the release film 27 is interposed between the colored ink film 13 and the heating / pressurizing roller 25, and the striped colored ink film is continuously formed in the pattern direction, that is, in the longitudinal direction thereof in the direction of arrow Fc. Smoothed. In this smoothing step, the release film 27 is inclined at a predetermined angle with respect to the surface of the colored ink coating film to be smoothed, whereby the air present in the recesses of the colored ink coating film 13 is smoothly moved. While being extruded, the ink film is smoothed by the heating and pressing roller 25. After smoothing by the heating / pressurizing roller 25, the release film 27 is kept on the surface of the smoothed colored ink coating 13a, so that the surface of the colored ink coating is kept warm to cause uneven temperature. No wrinkles or streaks were formed on the surface of the coating in the subsequent peeling step.
The pressing force (linear pressure) by the heating and pressing roller 25 is 10 to 15 Kg / cm as described above, and the feeding speed is 15 to 30.
cm / min.

Next, the colored ink film 13 on the glass substrate surface
After the entire surface has been smoothed, the film peeling roller 35 is pushed up as indicated by arrow Ff and the film pulling roller 37 is moved from the original position indicated by the dotted line as indicated by arrow Fg as shown in FIG. As shown in the figure, the release film 27 is moved in the upper left direction, and while the release film 27 is prevented from sagging, the release film is strongly pulled diagonally upward from one end of the colored ink coating surface 13a to the other end on the heating and pressure roller side. It peeled off at once. Alternatively, the take-up roll 39 may be instantaneously strongly rotated forward without applying a tension roller to apply a strong tension to the release film to perform peeling. The peeling speed of this release film is 2 seconds to 5 per 1 m of the peeling distance of the colored ink film surface.
When it was carried out within the range of 0 seconds, no streaky traces remained on the smoothed colored ink film surface, and good results were obtained.

In this way, at the time point G after the release film is peeled off, the film pulling roller 37 is returned to its original position, and the heating and pressing roller 25 and the film peeling roller are
35 is raised, and the subsequent smoothing process of the color filter on the heating platen 24 is performed. Such operation is automatically controlled by a sequence control device using a well-known microcomputer. Then, mass production can be performed at a relatively high processing speed. In this way, the glass substrate 11 of the color filter which has been smoothed is removed from the heating platen 24, and
The colored ink film was thermally cured by heating at 0 to 250 ° C. for several hours. It was 3.0 μm. An ITO film to be a counter electrode of a liquid crystal display device was formed on the colored ink film directly or through an overcoat layer. According to the present invention, since the smoothness of the colored ink film is extremely good,
Good optical and electrical properties were obtained even when the ITO film was directly deposited without the bar coat layer.

As described above, while the smoothing treatment is being carried out, an appropriate tension is applied to the release film by the release film supply section and the release film winding section to heat the release film. It absorbs elongation caused by pressurization and prevents unevenness on the smooth surface of the colored ink film. When the thickness of the release film is less than 25 μm, it becomes difficult to apply sufficient tension. If it is thicker than 100 μm, the heat transfer from the heating / pressurizing roller to the colored ink film is deteriorated and the smoothing efficiency is lowered. By keeping the release film in close contact with the smoothed coating surface until the smoothing of the entire surface is completed, the effect of preventing the occurrence of horizontal stripes on the coating surface can be obtained. In order to maintain this, the release film needs to have a peeling force in the range of 10 to 50 g / 50 mm as described above. This peel force is 50g / 50
If it is larger than mm, peeling of the colored ink film from the glass substrate may be induced.

The embodiment shown in FIGS. 7 to 9 is a case where the smoothing processing device 20 is further simplified. A cleaning device 41 including an electrostatic removal unit for removing foreign matter that may be attached to the unused release film 27, an ultrasonic wave oscillation unit, and a suction device is provided diagonally above and to the left of the heating and pressing roller 25 in the drawing. Is installed. The film feed roll 31 may have a simple mechanism that applies braking so as to prevent excessive slack in the film. And
On the right side of the heating / pressurizing roller 25 in the figure, a guide roller 42 that is vertically moved between the position shown by the dotted line is arranged. The film winding roll 39 may have a simple structure controlled by a torque motor.

Using this apparatus, the heating platen 24 and the heating / pressurizing roller 25 are respectively provided in the same manner as in the above-mentioned embodiment.
The temperature is set in the range of 0 to 105 ° C, and the colored ink film 13
The glass substrate 11 of the color filter, which had been printed and dried, was adsorbed by a vacuum suction chuck with the ink film on the heating platen 24, and allowed to proceed while preheating. And FIG.
As described above, the colored ink film surface was crushed and smoothed by the heating and pressing roller 25 through the release film 27. The release film 27 used in this example has a peeling force in the range of 25 to 50 g / 50 mm and a thickness in the range of 38 to 100 μm. In this case, since the adhesive force between the release film 27 and the colored ink film 13 is relatively large, the adhesive portion and the guide roller 42 as well as the portion pressed by the heating and pressing roller 25 and the film feed roll 31 are. Appropriate tension is also applied between them, and the thermal expansion of the release film is absorbed.

Subsequently, the colored ink film 13 on the glass substrate
As shown in FIG. 8, when the entire surface of the
The heating / pressurizing roller 25 and the guide roller 42 are raised as shown by the arrow. In that state, the release film 27 remains attached to the entire surface of the colored ink film surface. Therefore, FIG.
As shown in FIG. 7, the film winding roll 39 is rotated at a low speed, and the release film 27 is continuously peeled from the right side of the colored ink coating surface as indicated by symbols a, b and c from the right side in the drawing.
When the peeling is completed, the release film 27 is held between the meandering prevention roller 34 and the guide roller 34. In this way, smoothing and peeling of the release film are automatically performed, and the smoothing process of the next color filter is performed. According to this method, by setting the peeling force and the thickness of the release film in a predetermined range, a relatively simple device can be used, which is free from wrinkles, streak-like traces, etc., and has excellent smoothness. A color filter having a coated surface is obtained.

The above is the case of the color filter. Next, an example of a thermal head in which a resin film is attached on the surface of a metal substrate will be described. A 0.5 mm thick metal substrate made of an iron alloy containing 16 to 18% by weight of chromium was prepared. 40 ~
It was activated in dilute sulfuric acid at 60 ° C. for 1 to 2 minutes. Polyamic acid, which is a polyimide precursor, was applied onto the surface of the substrate using a roll coater. 60 to 120
The solvent in the coating was removed by treatment at a temperature of ℃ which did not cause imidization. After that, smoothing treatment was performed under the following conditions.

The release film is a biaxially stretched PET having a thickness of 80 μm coated with additional silicone, and has a thickness of about 3 μm.
It has a peel force of 0 g / 50 mm. The smoothing condition is that the preheating temperature is 85 to 90 ° C. and the pressure roller temperature is 90 to 1
05 ℃, pressure 10-15kg / cm, feed rate 2
It is 0 to 50 cm / min.

[0030]

As described above, according to the present invention,
The release film can be smoothed while applying an appropriately controlled tension, and there is almost no risk that the resin film will peel off during peeling or that defects such as scratches, unevenness, and wrinkles will occur on the smooth surface.
Therefore, the resin coating surface having excellent smoothness can be efficiently manufactured.

[Brief description of drawings]

FIG. 1 is an enlarged perspective view of an essential part showing an embodiment of the present invention.

FIG. 2 is a schematic side view showing a state in an initial stage of the process of FIG.

FIG. 3 is a schematic side view showing a state in a step subsequent to FIG.

FIG. 4 is a schematic side view showing a state in a step subsequent to FIG.

5 is a schematic side view showing a state in a step subsequent to FIG.

FIG. 6 is a diagram showing a continuous operation of each member in the steps shown in FIGS.

FIG. 7 is a schematic side view showing a state of a smoothing process of another embodiment of the present invention.

8 is a schematic side view showing a state in a step subsequent to FIG. 7.

9 is a schematic side view showing a state in a film peeling process after FIG.

[Explanation of symbols]

11 ... Translucent substrate, 13 ... Colored color ink film, 24 ... Heating platen, 25 ... Heating roller, 26 ... Release film conveying device, 27
… Release film, 35… Film peeling roller, 37… Film pulling roller.

Claims (1)

[Claims] 1. A step of depositing a resin coating on one surface of a supporting substrate directly or via another layer, and a step of thereafter applying pressure while heating the resin coating to smooth the coating surface. In the method of smoothing a resin coating, comprising: a release film having a release force of 25 to 100 μm and coated with a silicone release agent having a release force of 10 to 50 g / 50 mm, is placed on the resin coating surface, A method for smoothing a resin coating, comprising heating and pressurizing the release film to smooth it, and then peeling the release film.