JPH07184B2 - Coating method and coating device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a coating method and a coating apparatus, and more particularly to solvent coating.

BACKGROUND OF THE INVENTION There are various methods and apparatuses as a coating method and a coating apparatus for forming a coating liquid layer on a support. The choice depends on the surface condition of the substrate to be coated, the properties of the paint such as absorbency and strength, the rheological properties of the paint, and most importantly the properties of the dry coating required. For example, air doctors, blade coaters, knife coaters, reverse roll coaters, transfer roll coaters, gravure coaters, cast coaters, curtain coaters, extrusion coaters, bead coaters and the like are known. Of these coating methods, a reverse roll coater is often used when, for example, a magnetic recording material is coated on a support to produce a magnetic recording material. The reverse roll coater is composed of an applicator roll, a back roll and the like, and the width of the applicator roll is usually made wider than the width of the support in view of coating properties. In such a case, the coating material remains on both sides of the coating material attached to the applicator roll outside the width of the support. Therefore, particularly when a low boiling point organic solvent is used as a solvent in the paint, the solvent of the paint remaining on the applicator roll is evaporated, the applicator roll is cooled by this heat of vaporization, The diameter shrinks. Therefore, the gap between the metering roll or blade that adjusts the liquid thickness on the applicator roll and the applicator roll changes, the gap on both sides expands, and the liquid thickness on the applicator roll becomes thicker on both sides. Therefore, the coating film thickness becomes thicker on both sides.
Therefore, the coating stability may be impaired and the yield may be significantly reduced.

[Problems to be Solved by the Invention]

The purpose of the present invention is a reverse roll coater consisting of a back roll and an applicator roll as described above, particularly by improving the coating gap accuracy when applying a coating liquid containing a low boiling point solvent, and a stable coating method of film thickness accuracy and An object is to provide a coating device. Another object of the present invention is to provide a coating method and a coating device that can improve the coating yield by stabilizing the coating.

[Means for solving problems]

The above object of the present invention is a method of applying a coating material onto a support by using a reverse roll coater consisting of at least an applicator roll and a back roll, wherein the coating is performed while heating both sides of the applicator roll. It has been found that the above-mentioned coating method and the above-mentioned coating method can be achieved by a coating apparatus having heating means on both sides of the applicator roll. Next, the details of the present invention will be specifically described with reference to the drawings. First
The figure is a cross-sectional view of a reverse roll coater. FIG. 3A shows an example in which a fountain coater 6 is used to attach the coating material to the applicator roll 2 and a metering roll is used to regulate the film thickness. FIG. 2B shows an example in which the big up roll 7 is used instead of the fountain coater. Further, FIG. 7C shows an example in which a doctor using a blade is used instead of the metering roll. In the reverse roll coater, the coating liquid adhered to the applicator roll 2 via the fountain coater or the pickup roll has the nip width set correctly by the counter-rotating metering roll 3 in the case of FIGS. 1 (a) and 1 (b). To be scraped. In this case, the amount of the coating liquid on the applicator roll depends on the nip width between the applicator roll and the metering roll and these
Adjusted by the relative surface speed of the two rolls. In the case of FIG. 1 (c), the amount of coating liquid is controlled by adjusting the gap between the blade and the applicator roll. Then, the coating liquid is attached to the support conveyed by the back roll by the nip pressure between the back roll and the applicator roll. FIG. 2 (a) is a perspective view showing the relationship among the applicator roll 2, the back roll 1, and the support 4. As shown in the figure, the width of the support is narrower than the entire width of the back roll. On the other hand, the coating liquid is applied to the applicator roll over almost the entire width. This is because both sides of the applicator roll are vacant due to the problem of coatability on the support, but for this reason, the coating liquid on the applicator roll remains on both sides. When this coating liquid contains a low boiling point solvent, the solvent evaporates, and the heat of vaporization causes both sides of the applicator roll to contract. FIG. 2 (b) is a perspective view showing the relationship between the applicator roll and the blade (the same applies to the case of the metering roll) as the coating liquid amount adjusting means. As shown in FIG. Therefore, the liquid volume on both sides of the applicator roll increases. The liquid on the applicator roll is attached to the support by the nip with the back roll, so that the coating film thickness increases toward both sides. FIG. 3 (a) is an example showing the variation of the film thickness in the width direction of the support under the above-mentioned conditions, and the coating film thickness is clearly thicker on both sides than in the central portion. For example, in the case of a magnetic recording medium, the thickness of the magnetic layer differs depending on the application such as audio, floppy disk, video, etc., but it is about several μm, and the practically acceptable film thickness is about ± 5 of the magnetic layer film thickness. Must be within%. The density of floppy disks, which have recently been densified, is about ± 0.1 μm. Therefore, in such a case, the coating yield is greatly impaired. Therefore, in the present invention, it is intended to prevent the deformation of the applicator roll by compensating the heat deprived by the heat of vaporization by heating. Various methods are conceivable as means for heating both sides of the applicator roll. For example, there are the following means. Hot air, hot water heater, infrared induction heating, etc. An example of an embodiment in which hot air is used is shown in FIG. In this method, the air flow sent by the blower 15 is heated by the heater 14, and the warm air thus obtained is blown by the flexible pipes 16 to both side surfaces of the applicator roll to heat the air. Of course, as the means for heating the airflow, a heating method may be used in addition to the heater by various heat exchange methods using a known heat medium. An example of an embodiment in which hot water is used is shown in FIG. 4 (b). This is a method of circulating hot water inside the applicator roll. Hot water is introduced from the hot water introduction pipe 12 at the center of the roll, both sides of the applicator roll are heated by the hot water jacket 11, and the hot water is circulated through the hot water discharge pipe 13 outside the hot water introduction pipe at the center of the roll. In this case, other heat medium can be used instead of hot water. Heating with a heater is a method of placing a heater near the applicator roll and heating directly. A heater may be built in on both sides of the applicator roll. Infrared heating is a method of heating by placing infrared light bulbs on both sides of the applicator roll. The induction heating jacket roll is a method in which the heat medium enclosed in the roll is heated by low-frequency induction heating to make the surface temperature of the roll uniform. Although several examples of the heating means of the present invention have been given, the present invention is not limited to this, and any heating means may be used as long as it can heat both sides of the applicator roll. The control of these heating controls the film thickness after coating and drying on-line or off.
It can be done by measuring with -line and feeding back this information.

【Example】

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. Example 1 A coating having the following composition was applied on a 13 μm polyethylene terephthalate support to a dry thickness of 4.2 μm while using the reverse roll coater of FIG. 1 (a) and heating with warm air shown in FIG. 4 (a). It was applied so that Structure of Magnetic Paint First, the following magnetic paint containing no curing agent was prepared. Co-containing γ-Fe ₂ O ₃ 300 parts Partly hydrolyzed vinyl chloride-vinyl acetate copolymer (“VAGH” 40 parts by Union Carbide Co., Ltd. 40 parts polyurethane (“Nipporan N-3022” by Nippon Polyurethane Co., Ltd.) Silicone oil 4 parts Toluene / methyl ethyl ketone = 1/1 800 parts The above composition was put into a ball mill, dispersed for 48 hours and filtered with a filter having an average particle size of 3 μm to obtain a magnetic paint.18 kg of this magnetic paint was put into a tank and stirred. However, 25 parts of isocyanate compound (“Coronate L” manufactured by Nippon Polyurethane Company) 10 parts of terminal NCO urethane prepolymer Toluene / methyl ethyl ketone = 1/1 Add 0.6 kg of a curing agent having a composition of 105 parts and leave for 10 hours, then cure as described above. 0.6 kg of the agent was added, and the mixture was stirred for 10 minutes and then applied.The results are shown in Fig. 3. The results are shown by the film thickness distribution in the width direction of the support after drying. A If not delivered, the thickness of both sides is thicker. (B) whereas at room temperature the hot air, 10 ° C.
This is the case when coating is performed while blowing air at a high air pressure of 50 mmH ₂ O, and the film thickness is smooth over the entire width. From this result, it is understood that the film thickness can be stabilized by the method of heating the side surface of the applicator roll under appropriate warm air conditions. Example 2 Instead of using the warm air of Example 1, heating was performed with the warm water shown in FIG. 4 (b). The hot water jacket 11 had a width of 5 cm from the end of the applicator roll having a width of 400 mm and a diameter of 30 cm, the water temperature was set to the roll surface temperature + 3 ° C., and the flow rate was 1.0 m ³ / H. As a result, the film thickness distribution was uniform as in FIG. 3 (b) of Example 1.

【The invention's effect】

By a reverse roll coater comprising a back roll and an applicator roll according to the present invention, in a method of applying a coating material containing a low boiling point solvent, by improving the roll gap accuracy, to provide a stable coating method and coating apparatus of film thickness accuracy, As a result, it was possible to provide a coating method and a coating apparatus capable of improving the coating yield.

[Brief description of drawings]

FIG. 1 is a sectional view of a reverse roll coater used in the present invention. FIG. 2 (a) is a perspective view showing the relationship between the deformed applicator roll and the support. Fig. 2 (b)
FIG. 3 is a perspective view illustrating a gap between a deformed applicator roll and a doctor blade. FIG. 3 is a view showing the film thickness distribution in the width direction after coating and drying. FIG. 4 is a perspective view or a sectional view showing an embodiment of the heating method for both sides of the applicator roll according to the present invention. 1: Back roll 2: Applicator roll 3: Metalling roll 4: Support, 5: Cleaning doctor 6: Fountain coater 7: Pickup roll 8: Doctor blade, 9: Axial roll 11: Hot water jacket, 12: Hot water introduction pipe 13: Hot water discharge pipe 14: Heater, 15: Blower 16: Flexible pipe

Claims (2)

[Claims] 1. A method for applying a coating solution onto a support using a reverse roll coater comprising at least an applicator roll and a back roll, characterized in that the application is performed while heating both sides of the applicator roll. How to apply. 2. A coating apparatus comprising a reverse roll coater comprising at least an applicator roll and a back roll, wherein heating means is provided on both sides of the applicator roll.