Patent Grant
7018474
1. Field of the Invention
The present invention relates to a coating apparatus and, more particularly, to an improvement in extrusion type coating apparatus that is used for manufacturing photosensitive materials and magnetic recording media.
2. Description of the Related Art
Photosensitive materials and magnetic recording media are manufactured through a coating step of forming a coating film by applying a coating liquid, such as a magnetic liquid, to a continuously running substrate sheet (hereinafter referred to as “web”). In recent years, magnetic recording media such as magnetic recording tapes particularly for broadcasting and computer use have been rapidly improved in capacity and recording density, and there has been needed a coating technology capable of providing a magnetic layer which has an extremely thin film thickness and a smooth surface.
Coating apparatuses for applying a coating liquid to the surface of a web include, for example, apparatuses of types such as roll coater, gravure coating, roll coating plus doctor roll, extrusion coating, and slide coating. In recent years, an apparatus of extrusion type has been commonly used to apply a magnetic coating liquid.
One method employing an extrusion type coating apparatus in which the tip of a coating head is pushed against a web, as described in Japanese Patent Application Publication No. 58-109162, has been commonly used in the field of manufacturing magnetic recording media because a thin and uniform coating layer can be obtained by increasing the liquid pressure at the tip of the coating head utilizing the web tension, thereby eliminating the air accompanying the web. However, even in the method of applying a single coat of liquid using this type of coating head, the reduction in coating thickness is limited.
As a method for forming a much thinner coating layer, there is a method in which a very thin coating layer can be formed by applying an excess amount of coating liquid to a web using a web-pushing type extrusion coating apparatus and then scraping off the excess coating liquid with a blade disposed on the downstream side of the extrusion coating apparatus, as described in Japanese Patent Application Publication No. 7-287843. In this case, a device which applies an excess amount of coating liquid to a web is not necessarily limited to the web-pushing type extrusion coating apparatus, but coating apparatuses such as roller coater, gravure coater, and extrusion coater equipped with a back-up roll can be used.
In the scraping-off type coating apparatus as disclosed in Japanese Patent Application Publication No. 7-287843, however, since the coating liquid recovered by being scraped off with the blade has once been exposed to the atmosphere in a process from the coating apparatus to the blade, the solvent contained in the coating liquid volatilizes, whereby the liquid physical properties such as viscosity and solid content concentration are changed. Thus, the apparatus has a disadvantage in that the recovered liquid must undergo treatment for adjusting its physical properties such as viscosity and solid content concentration before being reused. Further, the apparatus has a disadvantage in that dust is liable to be included in the coating liquid having been applied to the web because the recovered liquid comes once into contact with the atmosphere, so that the recovered liquid cannot be reused because dust cannot be removed even if an excess liquid recovered with the blade is filtered.
With such a background, the present inventors have proposed coating method and apparatus in Japanese Patent Application Nos. 2001-302401 and 2001-302402 corresponding to U.S. patent application Ser. No. 10/253,427 and German Patent Application No. 102 44 882.5 such that two slits of a coating slit and a recovering slit are provided so that an excess of coating liquid that has been discharged excessively from the coating slit and applied to a web is scraped off with the recovering slit or an excess of coating liquid is sucked up into the recovering slit. According to the coating method and apparatus, the recovered coating liquid can be reused without any one of liquid-adjusting treatment and filtering treatment.
However, the coating apparatus having two slits of the coating slit and recovering slit is a novel coating apparatus exceeding the limit of conventional idea. The optimization of slit clearance of the coating slit and recovering slit is of importance in obtaining a coating layer with a very small and even thickness.
The present invention has been made in view of the above situation, and an object thereof is to provide a coating apparatus in which in coating with two slits of a coating slit and a recovering slit, the slit clearance of the coating slit and recovering slit is optimized so that a coating layer with a very small and even thickness can be obtained.
To attain the above object, the present invention is directed to a coating apparatus in which in a state where a continuously running web is brought close to a lip surface at a tip of a coating head, a coating liquid sent into the coating head in excess of a desired amount is discharged through a coating slit and is applied to the web, and an excess of coating liquid applied to excess is scraped off with a recovering slit provided on a downstream side of the coating slit in a running direction of the web, wherein: there is provided a slit clearance adjusting device which adjusts a width of at least one of the coating slit and the recovering slit.
According to the present invention, in the coating apparatus in which after the coating liquid is applied to excess through the coating slit, an excess of coating liquid is scraped off with the recovering slit to apply the desired amount of coating liquid to the web, there is provided a slit clearance adjusting device which adjusts the clearance of at least one of the coating slit and the recovering slit. Thus, by changing the clearance of at least one of the coating slit and the recovering slit, the amount of coating liquid applied through the coating slit or the amount of coating liquid scraped off with the recovering slit can be adjusted. Therefore, the thickness of coating layer formed finally to the web can be adjusted with high accuracy. Also, by adjusting the slit clearance in the web width direction of at least one of the coating slit and the recovering slit by using the slit clearance adjusting device, the distribution of coating amount and scraping-off amount in the web width direction can be adjusted. Thereby, a coating layer with a very small and even thickness can be obtained.
To attain the above object, the present invention is also directed to a coating apparatus in which in a state where a continuously running web is brought close to a lip surface at a tip of a coating head, a coating liquid sent into the coating head in excess of a desired amount is discharged through a coating slit and is applied to the web, and an excess of coating liquid applied to excess is sucked up with a sucking-up device through a recovering slit provided on a downstream side of the coating slit in a running direction of the web, wherein: there is provided a slit clearance adjusting device which adjusts a width of at least one of the coating slit and the recovering slit.
According to the present invention, in the coating apparatus in which after the coating liquid is applied to excess through the coating slit, an excess of coating liquid is sucked up with the sucking-up device through the recovering silt to apply the desired amount of coating liquid to the web, there is provided a slit clearance adjusting device which adjusts the clearance of at least one of the coating slit and the recovering slit. Thus, by changing the clearance of at least one of the coating slit and the recovering slit, the amount of coating liquid applied through the coating slit or the amount of coating liquid sucked up through the recovering slit can be adjusted. Therefore, the thickness of coating layer formed finally to the web can be adjusted with high accuracy. Also, by adjusting the slit clearance in the web width direction of at least one of the coating slit and the recovering slit by using the slit clearance adjusting device, the distribution of coating amount and sucking-up amount in the web width direction can be adjusted. Thereby, a coating layer with a very small and even thickness can be obtained.
As a preferred mode of the present invention, it is preferable that two or more slit clearance adjusting devices be arranged in the web width direction of the slit.
The coating slit and the recovering slit may be formed in the same coating head. Alternatively, the configuration may be such that the coating head is formed with the coating slit only, and the recovering head formed with the recovering slit is provided separately to integrally arrange the coating head and the recovering head. Also, as a web used in the present invention, a web in which an undercoat is applied and solidified in advance may be used.
The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures and wherein:
a) and 8(b) are graphs showing coat thickness distribution and clearance distribution in the web width direction before and after a recovering slit is adjusted by a slit clearance adjusting device; and
a) and 9(b) are graphs showing coat thickness distribution and clearance distribution in the web width direction before and after a coating slit is adjusted by a slit clearance adjusting device.
Preferred embodiments of a coating apparatus in accordance with the present invention will now be described in detail with reference to the accompanying drawings.
As shown in
As shown in
The coating head 16 is constructed by combining three blocks 23, 25 and 27, and the pocket portions 26, 28 and the slits 30, 32 are formed by assembling the blocks 23, 25 and 27. The pocket portions 26, 28 must be formed so as to have a cross-sectional shape which prevents stagnation of coating liquid. The cross-sectional shape thereof should preferably be circular. The slits 30, 32 are generally parallel with each other in the range from the pocket portion 26, 28 to the discharge port 30A or the recovering port 32A. However, the slits 30, 32 may be formed so that the distance therebetween decreases or increases toward the discharge port 30A or the recovering port 32A. The slit clearance of the slit 30, 32 is preferably set in the range of 0.05 to 2 mm at the position of the discharge port 30A or the recovering port 32A. The coating slit 30 further preferably has a slit clearance in the range of 0.1 to 0.3 mm, and the recovering slit 32 in the range of 0.2 to 2 mm.
The lip surface 24 of the coating head 16 preferably uses an ultrahard material with Rockwell hardness of HRA85 such as cemented carbide and ceramics to increase the working accuracy and to restrain abrasion at the time of long-term use. Regarding the shape of the lip surface 24, as shown in
The slit clearance adjusting device 15 comprises a yoke 60, an urging screw 62 installed in the yoke 62, a supporting point screw 64, and a fixing screw 66. As shown in
Although explanation has been given by taking an example in which the slit clearance of the recovering slit 32 is adjusted as shown in
The supplying line 18 is such that its supplying piping 34 connects a coating liquid tank 36 and the coating pocket portion 26 of the coating head 16 and in the middle of the supplying piping 34 are provided a supplying pump 38 for supplying a coating liquid to the coating pocket portion 26 and a supplying flowmeter 40 for measuring the amount of coating liquid flowing through the supplying piping 34 as shown in
The recovering line 20 in the case of the scraping-off type shown in
On the other hand, in the case of the sucking-up type shown in
As the supplying pump 38 and the suction pump 44, a metering gear pump is preferably used.
The support rollers 14 are provided as a pair on both of the upstream and downstream sides relative to the coating head 16 in the web running direction, and arranged at positions lower than the tip of the coating head 16 as shown in
Into the controller 22 are input the measured values of the amount of the coating liquid supplied and the amount of the coating liquid recovered, which are measured with the supplying flowmeter 40 and the recovering flowmeter 46, respectively. Further, in the controller 22, an operation is conducted to determine whether or not a difference between the amount of the coating liquid supplied Q1 and the amount of the coating liquid recovered Q2 agrees with the desired amount Q of the coating liquid applied to the web 12. If the difference does not agree with the desired amount, the controller 22 controls the rotational speed of the driving motor for the supplying pump 38 in the case of the scraping-off type shown in
In the case of the scraping-off type, the coating liquid having been applied to the web 12 to excess at the discharge port 30A of the coating slit 30 reaches the recovering port 32A of the recovering slit 32 while accompanying the web 12, and an excess of coating liquid is scraped off by an edge portion of recovering port 32A. Thus, the coating liquid applied to the web to excess is divided into two: coating liquid flowing through the recovering slit 32, and coating liquid decreased to the desired amount and successively accompanying the web 12. Therefore, by controlling the rotational speed of the driving motor for the supplying pump 38 by using the controller 22, the amount of the coating liquid accompanying the web 12 is adjusted so as to be the desired coating liquid amount Q. By decreasing the amount of the coating liquid accompanying the web 12, a very thin coating layer can be obtained.
In the case of the sucking-up type, by driving the supplying pump 38 and the suction pump 44, a circulation flow of coating liquid from the coating liquid tank 36 to the supplying piping 34 to the coating pocket portion 26 to the coating slit 30 to the recovering slit 32 to the recovering pocket portion 28 to the recovering piping 42 to the coating liquid tank 36 is formed. Since the amount of the coating liquid supplied by the supplying pump 38 is larger than the amount of the coating liquid recovered by the suction pump 44, the applied coating liquid is divided into coating liquid flowing through the recovering slit 32 and coating liquid flowing while accompanying the web 12 at the recovering port 32A. Therefore, by controlling at least one of the rotational speeds of the driving motors for the supplying pump 38 and the suction pump 44 by using the controller 22, the amount of the coating liquid accompanying the web 12 is adjusted so as to be the desired coating liquid amount Q. By decreasing the amount of the coating liquid accompanying the web 12, a very thin coating layer can be obtained.
In both cases of the scraping-off type and the sucked-up type, as shown in
The following is a description of the operation of the coating apparatus 10 constructed as described above.
The coating liquid pumped out in excess from the coating liquid tank 36 by the supplying pump 38, flowing through the supplying piping 34 and supplied to the coating pocket portion 26 of the coating head 16, rises up through the coating slit 30 and is discharged from the discharge port 30A. The coating liquid discharged to excess from the discharge port 30A is applied to the web 12 while forming beads 50 between the lip surface 24 of the coating head 16 and the web 12 running adjacently to the lip surface 24. In other words, the coating liquid supplied to excess is applied to the web 12 in such a state that a discharge force which discharges the coating liquid from the discharge port 30A and a pushing force of the web 12 against the lip surface 24 of the coating head 16 are well balanced. Meanwhile, at the recovering port 32A of the recovering slit 32 formed in the lip surface 24 on the downstream side relative to the discharge port 30A in the web running direction, an excess of coating liquid is recovered into the recovering slit 32 by scraping off or sucking up. Thereby, a coating layer is formed on the web 12.
In forming this coating layer, the slip clearance of at least one of the coating slit 30 and the recovering slit 32 is adjusted by the slip clearance adjusting device 15 according to the coating conditions such as coating speed, coating thickness, and kind and viscosity of coating liquid. In this case, the adjustment is preferably made considering the rotational speeds of the driving motors for the supplying pump 38 and the suction pump 44. For example, when the thickness of the coating layer formed finally on the web 12 is adjusted, it is preferable that coating operation be started after the relation between the coating amount and the recovering amount is adjusted so as to obtain a desired coating layer thickness by the adjustment of the rotational speeds of the driving motors for the supplying pump 38 and the suction pump 44, and fine adjustment of the coating layer thickness, in which only the relation between the coating amount and the recovering amount does not suffice, be made by the slit clearance adjusting device 15. In this case, the slit clearance adjusting device 15, which comprises the yoke 60 provided on the outside wall of the coating head 16, the urging screw 62, the supporting point screw 64, and the fixing screw 66, which are installed to the yoke 60, can easily make adjustment of slip clearance of the slits 30, 32 even during the coating operation.
Also, the slit clearance in the web width direction of at least one of the coating slit 30 and the recovering slit 32 is adjusted by three slit clearance adjusting devices 15 arranged in the widthwise direction of the web 12, by which the coating amount distribution and the scraping-off amount distribution in the web width direction can be adjusted. Thereby, the coating thickness distribution in the web width direction of the coating layer finally formed on the web 12 can be corrected.
Thus, in coating with two slits of the coating slit 30 and the recovering slit 32, by optimizing the slit clearances of the coating slit 30 and the recovering slit 32, a coating layer with a very small and even thickness can be obtained. Thereupon, the coating apparatus 10 in accordance with the present invention is suitable as a coating apparatus for obtaining an even and very thin magnetic layer required in manufacturing magnetic recording media, and is especially suitable for a very thin coat in which the wet thickness of magnetic coating liquid applied to the web 12 is 2 μm or smaller.
a) and 8(b) show the result of a test in which a scraping-off type coating apparatus shown in
a) and 9(b) show the result of a test in which a scraping-off type coating apparatus shown in
The composition of the coating liquid subjected to the test was as given in Table 1, and the coating conditions were as given in Table 2. The thickness of the coating layer formed on the web was set at 2 μm in wet thickness.
After a coating liquid having the composition given in Table 1 was kneaded and dispersed in a prescribed manner, an organic solvent was added appropriately and mixed homogeneously, and the obtained coating liquid was used for the test. Although a magnetic coating liquid was used in this example, the type of coating liquid is not limited to this type.
Test 1: Adjustment of Recovering Slit
In test 1, the coating liquid was applied to the web by using the coating apparatus in a state in which the recovering slit is not adjusted by three slit clearance adjusting devices, and the coating thickness distribution (%) in the web width direction of the sample before adjustment and the slit clearance distribution (%) in the web width direction of the recovering slit at this time were measured. The measured coating thickness distribution (%) is shown by a solid line in
Next, the slit clearance distribution in the web width direction of the recovering slit was individually adjusted by the three slit clearance adjusting devices so as to correct the coating thickness distribution shown by the solid line in
As seen from this result, in coating with two slits of the coating slit and the recovering slit, by adjusting the clearance distribution in the web width direction of the recovering slit by using the slit clearance adjusting devices, the coating thickness distribution in the web width direction of the coating layer formed on the web can be adjusted with high accuracy.
Test 2: Adjustment of Coating Slit
In test 2, the coating liquid was applied to the web by using the coating apparatus in a state in which the coating slit is not adjusted by three slit clearance adjusting devices, and the coating thickness distribution (%) in the web width direction of the sample before adjustment and the slit clearance distribution (%) in the web width direction of the coating slit at this time were measured. The measured coating thickness distribution (%) is shown by a solid line in
Next, the slit clearance distribution in the web width direction of the coating slit was individually adjusted by the three slit clearance adjusting devices so as to correct the coating thickness distribution shown by the solid line in
As seen from this result, in coating with two slits of the coating slit and the recovering slit, by adjusting the clearance distribution in the web width direction of the coating slit by using the slit clearance adjusting devices, the coating thickness distribution in the web width direction of the coating layer formed on the web can be adjusted with high accuracy.
Although either one of the recovering slit and the coating slit was adjusted in this example, both of these slits may be adjusted. Also, although explanation was given by taking a scraping-off type coating apparatus as an example, a similar result can be obtained in the case of the sucking-up type coating apparatus shown in
According to the coating apparatus in accordance with the present invention, in coating with two slits of the coating slit and the recovering slit, by optimizing the slit clearance of the coating slit and the recovering slit, a coating layer with a very small and even thickness can be obtained.
Thereupon, the coating apparatus in accordance with the present invention is suitable as a coating apparatus for obtaining an even and very thin magnetic layer required in manufacturing magnetic recording media, and is especially suitable for a very thin coat in which the wet thickness of magnetic coating liquid applied to the web is 2 μm or smaller.
It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, alternate constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002-041010 | Feb 2002 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4102299 | Wallsten | Jul 1978 | A |
| 4944808 | Sugiyama et al. | Jul 1990 | A |
| 4984533 | Takahashi et al. | Jan 1991 | A |
| 6582768 | Mandai et al. | Jun 2003 | B1 |
| 20030099769 | Mandai et al. | May 2003 | A1 |
| 20030157251 | Mandai et al. | Aug 2003 | A1 |
| Number | Date | Country |
|---|---|---|
| 58-109162 | Jun 1983 | JP |
| 7-287843 | Oct 1995 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20030154918 A1 | Aug 2003 | US |
