JPH0338909B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention is applicable to the continuous production of recording materials such as photographic film and photographic paper, photolithographic materials, magnetic recording materials such as magnetic recording tape, pressure-sensitive recording paper, heat-sensitive recording paper, etc. The present invention relates to an improvement in the process of applying a liquid coating composition to a traveling elongated flexible support (hereinafter referred to as a "web"), and more specifically to an improved bar coating method. [Prior Art] Various methods have been proposed for applying a coating liquid to a continuously running web. In general, the coating process includes a part that transfers the coating liquid onto the web (hereinafter referred to as the "application system") and a part that measures the coating liquid transferred to the web to a desired coating amount (hereinafter referred to as the "measuring system"). ), the coating methods were classified based on the differences in application and metering systems.
Based on differences in application systems, roller coating methods, dip coating methods, fountain coating methods, etc. have been known, and based on differences in metering systems, air knife coating methods, blade coating methods, bar coating methods, etc. have been known. Additionally, extrusion coating methods, beat coating methods, and curtain coating methods have been known as methods in which application and metering are performed in the same part. Among these coating methods, the bar coating method transfers excess coating liquid to the web, and then scrapes off the excess coating liquid with a bar that is stationary or rotating at a slower circumferential speed in the opposite direction to the web. It has been widely used because it allows a desired amount of coating to be applied and can achieve high-speed, thin-layer coating with simple equipment and operations. Although any application method can be used in the bar coating method, the roller coating method, especially the kiss coating method, has been most commonly used to take advantage of its simplicity. However, in the conventional bar coating method,
Since the application system and metering system were completely independent, it was necessary to set conditions for each separately when applying, which was not only complicated, but also
It has the disadvantage that it requires a large amount of space and is uneconomical in terms of space utilization. Japanese Unexamined Patent Publication No. 53-22543 proposes a method in which the coating liquid is applied by the bar by supplying the coating liquid so that a pool of liquid is formed just before the contact area between the bar and the web, and the operation is easy. It is used as an improved coating method that is easy to use, does not require a large amount of space, and can form a coating film with excellent surface properties. In the above-mentioned coating process, due to the action of the surface tension of the liquid coating composition, a thick coated film part is generated at both edges in the width direction of the web, and this thick film part is dried in the subsequent drying process. Since it causes non-uniformity, it is desirable to remove it before the drying process. U.S. Pat. No. 2,899,339 discloses that in such a process, nozzles are provided at both edges in the width direction of the web for sucking up the coating liquid, and the nozzles have an L-shaped double tube structure, and the outer circumference of the nozzles is A method and apparatus are disclosed for supplying a spray or jet stream of diluent or solvent from a central portion and sucking up the coating liquid along with the diluent and solvent from a central portion. [Object of the Invention] The present invention provides an improved coating method that does not require removing the thick film coating solution using a nozzle or the like as described above, and does not generate thick film parts on both edges in the width direction. The purpose is to provide The present invention also aims to provide an improved coating method that allows stripe coating. [Structure and operation of the invention] An object of the present invention is to supply the coating liquid to the web so that a pool of liquid is formed just before the contact portion between the rotating bar and the continuously running web. This is achieved by a method of applying a liquid, characterized in that a blade is provided in contact with a part of the surface of the rotating bar at a position separated from the web, and the amount of application is partially adjusted. . DESCRIPTION OF THE PREFERRED EMBODIMENTS The content of the present invention will be explained in more detail below in comparison with the prior art based on the accompanying drawings. FIG. 1 is a schematic diagram of a bar coating device disclosed in Japanese Unexamined Patent Publication No. 53-22543. In Fig. 1, 1 is a wire bar or a grooving bar, and a web 2 is continuously run.
is rotated in the same direction. Reference numeral 4 denotes a bar support member, which is provided over the entire length of the bar 1, and has the function of preventing the bar 1 from being bent and serving as a liquid supply device for supplying the coating liquid 3 to the bar 1. That is, the coating liquid 3 is supplied from the liquid supply port 5 provided on the bar support member 4 into the liquid supply guide groove 7 formed between the bar support member 4 and the weir member 6, and is picked up by the rotating bar and applied to the web 2. However, at this time, the coating liquid 3 is measured at the contact area between the web 2 and the bar 1, and only the desired coating amount is applied to the web 2, while the rest flows down and is replaced by the newly supplied coating liquid. 3 and a liquid pool 8 is formed. Therefore, in a steady state, the coating liquid 3 is in the liquid pool 8.
It will be applied to the web 2 through the. When the coating liquid 3 was applied to the web 2 from the liquid pool 8 in this manner, it was surprisingly observed that the surface properties of the coating film 9 were improved compared to the conventional method. Moreover, since the bar 1 has both the function of transferring and applying the coating liquid onto the web and the function of measuring the desired amount of coating liquid, the entire device can be made compact and space can be used effectively. This makes it easier to set and operate various conditions. Conventional methods for preventing thick coated edges in such coating methods include scraping off the excess liquid on the edges of the support with a metal doctor before the drying process, or completely drying the thickly coated areas. In order to do this, methods such as blowing heated air to the thickly coated areas and forcibly drying them are used in addition to normal drying. However, in the former method, the doctor is in contact with the support, so the surface of the support is The latter requires large-scale equipment, which is very troublesome to operate, and other problems. Therefore, as shown in Figure 2, by inserting a thin base material 10 between the support and the coating bar at the edge of the support, the amount of thick coating at the edge has been reduced (wiper method). However, there were still problems such as the coating being a little thick and the base material being constantly rubbed by the support and bar, resulting in poor durability. The thickness and material of the base material 10 used in this method are not particularly limited. FIG. 3 is a sectional view when the blade 11 is attached to the bar coater in the present invention, and 12 is a blade holder. FIG. 4 is a perspective view when the blade is attached. 13 indicates that it is not coated. That is, in FIGS. 3 and 4, a blade 11 that contacts a part of the surface of the rotating bar 1 is provided at a position apart from the web 2, and only the part of the blade 11 is partially supplied with liquid to the support. Can be stopped. Therefore, the blade part can be left uncoated. In reality, the liquid pool is stretched in the width direction of the support due to the influence of the liquid pool 8 described above, so that the uncoated width becomes narrower than the blade width. This width varies depending on the physical properties of the coating liquid used, the running speed of the support, etc. By using this blade, it is possible to completely prevent thick coating by leaving the ears of the support uncoated. It was also found that stripe coating is possible by using the blade of the present invention. That is, by attaching a blade wider than the width of the uncoated area to the area to be left uncoated, stripe coating can be performed to leave the target area uncoated by the desired width. FIG. 6 shows a schematic diagram of stripe coating using the blade 11. The material of the blade used in the present invention is not particularly limited. Further, the thickness and shape of the blade are not particularly limited as long as it can fit within the coater without contacting the support. It has been found that the same effect can be obtained by scraping off the coating liquid by bringing the blade 11 into contact with the bar as shown in FIG. [Examples of the Invention] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the Examples. Example 1 To Canadian Freeness 300c.c. beaten wood pulp (LBKP), 1.0% sodium stearate was added based on the weight of bone-dry pulp, then 1.5% aluminum sulfate and polyamide polyamine epichlorohydrin (LBKP) were added. By adding 0.5% of Kymen 557 (trade name, manufactured by Kyures) and 0.3% of alkyl ketene dimer (trade name: Acopel, manufactured by Deitsku Harkyures), both based on the weight of bone-dry pulp, the basis weight was determined by a normal papermaking method. The paper was made to have a weight of 150 g/m ² . Next, calcium chloride of 1% based on the base paper was applied depending on the surface size, and after drying, the thickness was adjusted to 160 μm using a calender.
The back side of this base paper is coated with polyethylene with a density of about 0.930 g/cm ³ to a thickness of about 0.33 mm, and the surface is coated with polyethylene with a density of about 0.960 g/cm ³ containing 10 weight percent titanium oxide. A long flexible support for photographic paper having a thickness of 230 μm and a width of 1400 mm was obtained by coating with a thickness of 0.3 mm. The following composition (Table 1) was applied to the back side of this support using a wire bar coating device shown in Figures 3 and 4 at a coating speed of 150.
6 c.c./m ² was applied at m/min.

〔Effect of the invention〕

According to the present invention, it is possible to prevent the occurrence of thick coated film portions on both edges in the width direction as described in the embodiments, thereby reducing the drying load and improving the yield in the production of recording materials that have a coating and drying process.・Maintenance work will be streamlined. Furthermore, by appropriately selecting and setting the dimensions, number, and widthwise positions of the blades 11, it is possible to perform stripe coating with a high degree of freedom.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams of a conventional bar coating device, and FIGS. 3 and 4 are schematic diagrams of a bar coating device showing an embodiment of the present invention. 5 and 6 are both schematic diagrams of a bar coating device showing another embodiment of the present invention. 7 and 8 are diagrams showing example data. 1... Applicator roll, 2... Web,
3... Coating liquid, 4... Bar support member, 5... Liquid supply port, 6... Weir member, 8... Liquid pool, 11... Blade, 12... Blade holder.

Claims (1)

[Claims] 1. In a method of applying the coating liquid to the web by supplying the coating liquid so that a liquid pool is formed just before the contact portion between the rotating bar and the continuously running web, A coating method characterized in that a blade is provided at a position that contacts a part of the surface of the rotating bar to partially adjust the coating amount.