JPH0427462A - Coating method and applicator - Google Patents

Abstract

PURPOSE:To coat a web with a desired amt. of a coating liq. with a uniform profile by dropping the coating liq. on the surface of a rotating roll in the form of a curtain and bringing the web into contact with a uniform layer of the coating liq. formed on the surface of the roll. CONSTITUTION:A curtain header 1 has a pocket at the inside and a high accuracy slit at the bottom. A coating liq. flows out uniformly from the slit and drops on the surface of a rotating roll 2 in the form of a curtain. Scraping doctors 3 set on the roll 2 scrapes an excess of the coating liq. so as to form dry edges at both edges of a web. An air intercepting doctor 4 is set near the bottom of the curtain. A layer of the coating liq. formed on the roll 2 is transferred to the web travelling along the roll 2 at the same speed.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a coating method and a coating device for a running web, and in particular, a method for receiving a coating liquid dropped in a curtain shape with a rotating roll and transferring it onto the web. The present invention relates to a coating method and apparatus.

[Conventional technology]

Generally, air knife coating methods, blade coating methods, and the like are well known as methods for applying a coating liquid to a web.

In all of these coating methods, after applying excess coating liquid to the web, the excess coating liquid is scraped off with an air knife or blade, and the target coating amount is measured, and the scraped coating liquid is collected and circulated. It is meant to be reused.

These coating methods are widely used in the production of processed paper and are typical coating methods. However, these coating methods have the following problems.

In other words, the air knife coating method involves blowing high-speed air (air knife) onto the coating surface coated on the web to remove excess coating liquid in order to obtain a uniform coating layer as described above. However, due to the influence of the surface of the base paper, uneven surfaces are likely to occur on the coated surface.Also, since air is used, a high-pressure blower is required, resulting in high running costs.

Furthermore, the air knife coating method is said to have a maximum coating speed of about 600 m/min due to the air flow velocity limit. Incidentally, if the speed is higher than this, there is a problem that mist of the coating liquid is generated and operation becomes difficult.

Next, the blade coating method is a method in which the blade is pressed against the coated surface of the web to scrape off excess coating liquid in order to obtain a constant coating layer as described above. Since they are usually made of steel, the plates tend to wear out when they come into contact with the web (for this reason, stable operation cannot be maintained unless they are replaced frequently).

Therefore, there are drawbacks to the cost of the blade and the reduction in operational efficiency. Further, if foreign matter is mixed in the coating liquid, there is a problem in that the foreign matter is caught between the web and the blade, and scratches (streaks) are likely to occur on the web surface. Furthermore, there is also the problem that uneven coating tends to occur due to the inclusion of air bubbles in the coating liquid. Furthermore, when used in the production of pressure-sensitive copying paper, there is a problem that the microcapsules are destroyed when scraping off excess microcapsule coating liquid, impairing the quality of the pressure-sensitive copying paper. Furthermore, when heat-sensitive recording paper is used for production, the coating liquid develops color due to frictional heat between the blade and the web, resulting in a decrease in whiteness, which impairs the quality of the heat-sensitive recording paper.

Furthermore, the air knife application method and blade application method are
In both cases, it is necessary to send several tens of times the amount of liquid applied and recirculate the scraped off liquid, so screens, etc. must be installed to separate foreign substances, and the problem is that it requires a large amount of equipment costs. For this reason, a curtain coating method (for example, Japanese Patent Laid-Open No. 53-2108
No. 1, JP-A-54-74762, JP-A-57-
212094) is also proposed.

The curtain coating method described in these publications is a method in which the coating solution is coated under a falling curtain by crossing a running web.

This curtain coating method differs from the air knife coating method and blade coating method described above, in that it forms a falling curtain of the amount of coating liquid necessary for the target coating amount, and allows this to fall onto the running web to achieve a uniform coating. It forms a coating layer.

The advantages of this coating method are that all of the supplied coating solution can be coated without circulation; 1. Unlike the blade application method, there is no mechanical scraping, so a uniform surface can be obtained, and the application speed can be significantly improved compared to the blade application method, approximately 1000 m. Coating for more than 1 minute is also possible. Moreover, since there is no need to replace the blades, there are advantages in terms of equipment maintenance costs, labor for replacement, operability, etc. However, while the curtain coating method has the excellent effects mentioned above, it also has the following disadvantages because it involves dropping a curtain of coating liquid directly onto a parallel web. There is.

■ Because the coating liquid falls like a curtain and falls directly onto the nib as it travels, the impact of the fall causes the web to swing and become unstable, which tends to disturb the coated surface. ■Since the coating liquid that falls like a curtain falls directly onto the running web, it is necessary to prevent the coating liquid from being splashed when it falls. For this purpose, the height of the curtain fall is delicately adjusted by changing the coating speed and the amount of liquid sent.
It is difficult to obtain a uniform coating surface unless you always maintain an appropriate falling height.

■ For many coated papers, 10 to 20 mm on both ends of the web.
It is common practice to cut and remove the portions in a subsequent process according to the specified dimensions of the web. Therefore, coating on both ends is meaningless, so in order to improve the yield of the coating solution, the uncoated area (
However, since the curtain coating method involves dropping the curtain directly onto the web, it is difficult to coat while forming uncoated areas (dry edges).
Yes.

■ In the coating method using a blade coater, in order to check the target coating amount and the uniformity (profile) in the width direction of the coated surface, the coating liquid is coated on a roll in advance and checked before coating on the paper. A method is adopted to do so.

However, in the case of the curtain coating method, it is structurally impossible to make adjustments as in the coating method using a blade coater, and check adjustment is only possible after coating on the paper surface. Therefore, there is a problem that a large amount of defective webs are likely to occur during adjustment at the initial stage.

■ Another disadvantage of the curtain coating method is the web that passes under the coating liquid that falls in the form of a curtain. This is not a problem at low speeds, but at high speeds, at least 500 m/min or higher, the air film (air rim) attached to the surface layer of the web collides with the curtain film, disturbs the curtain at the point where the curtain falls, and traps air, causing the liquid to drop. The problem is that there are areas where the product cannot be applied, making it impossible to apply it. For this reason, it is conceivable to install an air film removing doctor, but applying the doctor directly to the web tends to cause paper breakage and scratches on the paper surface, so it is actually impossible.

Although the curtain coating method has many advantages as described above, it also has many disadvantages.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the drawbacks of current curtain coating methods and to provide a curtain coating method and coating device that can coat a web with a desired coating amount and a uniform profile.

[Means to solve the problem]

The present invention involves dropping a coating liquid onto the surface of a rotating roll in the form of a single or multi-layer curtain to form a uniform coating liquid layer on the roll surface, and bringing the web into contact with this coating liquid layer. This is a coating method characterized by transferring the coating liquid onto the web.

Furthermore, the present invention includes a curtain header l for causing the coating liquid to fall in a curtain shape, and a rotating roll 2 for receiving the fallen coating liquid to form a coating liquid layer and transferring this coating liquid layer to the web. This is a coating device characterized by having the following as a basic configuration.

[Function] In the above configuration, first, the curtain coating method will be explained.

The coating liquid is dropped from the curtain header onto the surface of the rotating roll in a curtain-like manner. ), coating speed, slit width of the curtain header for causing the coating liquid to fall in a curtain shape, etc., and adjust as appropriate. Incidentally, when making this adjustment, it is also possible to configure the curtain header so that internal pressure can be applied to it as necessary, and to push it out from the curtain header using pressure means.

The coating liquid to be dropped in a curtain-like manner may be in a single layer, or if necessary, a curtain header may be installed on the surface of each of the two rotating rolls that are in contact with each other to drop the coating liquid (for example, a sizing agent liquid). It is also possible to drop it like a curtain and transfer it to both sides of the web (Figure 3).

Additionally, a plurality of curtain headers are installed on one rotating roll, and a plurality of coating liquids (for example, a coating liquid for forming a curse recording layer and a coating liquid for forming an overcoat layer, or a coating liquid for forming an undercoat layer) are used. It is also possible to make a multilayer coating liquid layer by dropping the coating liquid for forming the swear recording layer and the coating liquid for forming the swearing recording layer in a curtain shape (FIGS. 4 and 5).

It goes without saying that the coating method of the present invention can also be used in the production of heat-sensitive recording materials, pressure-sensitive copying paper, coated paper for printing, adhesive paper, photographic paper, etc., or in size presses.

Next, the coating apparatus of the present invention will be explained based on the drawings.

The coating device of the present invention includes a curtain header 1 for causing the coating liquid to fall in a curtain shape toward a rotating roll, and a curtain header 1 for receiving the fallen coating liquid to form a coating liquid layer, and transferring this coating liquid layer to a web. The curtain header 1 is characterized in that it has a rotating roll 2 as a basic structure, and the curtain header 1 has a pocket inside and a high-precision slit below.

The supplied coating liquid fills the pocket, flows out uniformly from the slit, and falls like a curtain onto the surface of the rotating roll.

The width of the slint provided in the curtain header 1 is also related to the amount of coating liquid supplied, and is selected appropriately in relation to the properties of the coating liquid and the target coating amount, but is usually 0. 1
-1.0 am, preferably 0.2-0.5 am, especially 0.2-0.4 ml are suitable.

The length of the slit is selected appropriately in relation to the web width.

The height of the curtain varies depending on the amount of liquid supplied, but is preferably 30 cm or less, particularly preferably about 10 to 20 cm.

The rotating roll is usually a metal roll coated with rubber or a metal roll coated with chrome. It is also preferable to provide a doctor 3 for scraping the coating liquid and a doctor 4 for blocking air flow on the rotating roll.

The purpose of the scraping doctor 3 installed on the rotating roll 2 is to scrape off excess paint to form dry edges on both ends of the web.The installation location of the air blocking doctor 4 is at the point where the curtain falls. It is preferable to install it near the airflow because it will not be affected by airflow.

The web 5 contacts the rotating roll 2 in a tangential direction, or runs the rotating roll 2 at the same speed as the rotating roll 2 in the range of 0° to 300°, and the coating liquid is applied onto the rotating roll surface. Transfer the layer to the web.

The curtain header 1 is supplied with coating liquid by a separately installed pump 6.

Further, the curtain header position on the rotating roll 2 can be moved horizontally or in the circumferential direction of the rotating roll 2 within the roll diameter.

Next, the driving situation will be explained.

First, from the slit in the curtain header 1, an amount of coating liquid corresponding to the target coating amount falls in a curtain shape onto a rotating roll 2 that runs at the same speed as the paper surface with a width larger than the width of the web (paper, film, etc.). Next, the excess coating liquid is scraped off by a scraping doctor 3 that can be moved to the width to be coated on the paper surface on the rotating roll 2, that is, the width necessary to remove the dry edge. Therefore, at this point, the coating liquid applied to the rotating roll 2 is transferred to the web running in contact with or being held by the rotating roll 2 at the same speed. At this time, it is also possible to install backup rolls that sandwich the web in order to ensure transfer.

Further, the air blocking doctor 4 is installed on the rotating roll 2 to block the air flow across the entire width in the roll rotation direction. At this time, in order to protect the rubber layer of the rotating roll 2, it is desirable to supply water so that the plate has the ability to lubricate the rubber layer and to clean the roll.

〔effect〕

By adopting the coating method and coating device of the present invention,
The problems associated with the direct application of a conventional curtain coating liquid to a web can be improved, namely: (1) There is no impact of the curtain falling onto the web, and a stable coating layer can be obtained. ■
A dry edge, which is difficult to achieve with conventional curtain coating methods, can be easily formed on a rotating roll in the present invention. (2) Since the coating liquid is applied onto the transfer roll before being applied to the web, it is easy to check and adjust the coating amount and coating unevenness in the width direction. (2) After adjusting and obtaining a uniform surface, the coating is transferred from a transfer roll to the web, resulting in less loss of web and paint compared to conventional curtain coating methods.

■Compared to conventional curtain coating methods, the curtain is stabilized because the air rim that rotates on the rotating roll can be blocked. ■Apply the coating liquid onto the rotating roll,
Since the coating is then transferred to a web, the roughness of the roll surface will appear on the surface, but if a chrome plated metal roll or the like is used, a coated surface with the same gloss as the plated layer can be obtained.

■Since the coating is applied once on a rotating roll, a stable coating layer is formed and a sufficient coating speed can be obtained, approximately 1500 m /
Application speeds on the order of minutes are also possible.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a coating device according to the present invention. Second
The figure is a perspective view of the coating device. FIG. 3 is an explanatory view showing a structure in which curtain headers are installed on the surfaces of two rotating rolls that are in contact with each other so that the coating liquid falls in a curtain shape and can be transferred to both sides of the web. FIGS. 4 and 5 are explanatory diagrams showing a state in which a plurality of curtain headers are installed for one rotating roll. 1... Curtain header 2... Rotating roll 3... Scraping doctor 4... Air blocking doctor 5... Web 6... ... Pump 7 ... Curtain coating liquid 8 ... Coating liquid tank 9 ... Backup roll

Claims (4)

[Claims] (1) By dropping the coating liquid in a single layer or multilayer curtain shape onto the rotating roll surface to form a uniform coating layer on the roll surface, and by bringing the web into contact with the coating layer. A coating method characterized by transferring a coating liquid layer onto a web. (2) The basic configuration includes a curtain header 1 for dropping the coating liquid in a curtain shape, and a rotating roll 2 for receiving the fallen coating liquid to form a coating liquid layer and transferring this coating liquid layer to the web. A coating device comprising: (3) The coating apparatus according to claim (2), wherein a curtain header is installed for each of the two rotating rolls that come into contact with each other. (4) The coating device according to claim (2), wherein a plurality of curtain headers are installed for one rotating roll.