JPH01224077A - Coating method - Google Patents

Abstract

PURPOSE:To prevent deposition of the dissolved air in a coating liquid in the form of fine bubbles and to form a uniform coated film on a web by passing the coating liquid through the inside of specific tubes under pressurization and reducing the pressure on the outside thereof so that >=10% of the satd. and dissolved air in the coating liquid is removed. CONSTITUTION:The coating liquid 30a is pressurized to >=0.5kg/cm<2> and is supplied from a liquid inlet 24a of a deaeration device 10 where the liquid is introduced into the inlet 20a of the tubular porous high-polymer film tubes 21 so as to pass the inside of the tubes 21 which are wound to a spiral shape. The inside of a reduced pressure chamber 23 in which a core 20 and the tubes 21 are housed is evacuated by a vacuum pump 26 through a discharge pipe 25 and is kept at a desired vacuum degree by a pressure sensor 27 and a control circuit 28. The dissolved air in the coating liquid 30a is thereby deaerated while the liquid passes the inside of the tubes 21. The coating liquid 30b from which >=10% of the satd. and dissolved air is removed in such a manner is supplied to a bar coater and is coated on the traveling web.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to continuous running in the production of recording materials such as photographic film and photographic paper, photolithographic materials, pressure-sensitive recording paper, and heat-sensitive recording paper. Regarding a coating method for improving the coated surface quality when applying a liquid coating composition (hereinafter referred to as "coating liquid") to a long flexible support (hereinafter referred to as "web") using a coating device, More specifically, the present invention relates to a bar coating method for applying a coating liquid from which dissolved air has been removed.

[Conventional technology]

Conventionally, various methods have been proposed as methods for applying a coating liquid to a continuously running web. Generally, the coating process involves the part where the coating liquid is transferred to the web (hereinafter referred to as "
"Application system". ) and a part that measures the coating liquid transferred to the web to the desired coating amount (hereinafter referred to as the "measuring system"), so coating methods are classified according to the differences between the application system and the measuring system. Ta.

Based on the difference in application system, roller coating method,
Known methods include dip coating, fountain coating, and air knife coating, blade coating, bar coating, etc. based on differences in metering systems.

In addition, extrusion coating methods, bead coating methods, and curtain coating methods are known as methods in which application and measurement 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. The desired amount of application is achieved,
simple:! ! It was widely used because it has the characteristic of being able to apply a thin layer at high speed by placing and manipulating it.

For example, FIG. 4 is a schematic diagram showing an example of a bar coating device using a coating rod for a conventional coating device according to the present invention. 2 is rotated. Reference numeral 3 denotes a λ-supporting member, which is provided over the entire length of the bar 2, and has the function of preventing the bar 2 from being bent and serving as a liquid supply device for supplying the coating liquid 4 to the bar 2. That is, the coating liquid 4 is supplied from the liquid supply port 5 provided in the bar support member 3 to the supply port 5 formed between the weir member 6 and the weir member 6.
It is supplied within 7 hours, pinked up by the rotating bar 2, and applied to the web 2. At this time, the coating amount is measured at the contact area between the web 1 and the bar 2 to achieve the desired coating. Only a small amount of the coating liquid is applied to the web 1, and the rest flows down to form a liquid pool 8 together with the newly supplied coating liquid 4. Therefore, in a steady state, the coating liquid 4 is applied to the web 1 via the liquid reservoir B.

In this coating method, when the rotation of the coating rod 2 becomes large, bubbles are generated between the coating rod 2 and the bar support member 30 depending on the 40 types of coating liquid, and the bubbles adhere to the surface of the coating rod 2 and coat the coating. Transferring bubbles to the membrane part 10 or coating rod 2 and web 1
Bubbles may accumulate near the downstream side of the contact area, causing streaks. It is believed that these bubbles are generated when the air existing between the coating rod 2 and the bar support member 3 is drawn in by the rotation of the coating rod 2. In order to prevent this, Japanese Patent Publication No. 58-4589, Publication No. 59-123568 and JP-A No. 60-2256
69, as shown in FIG. 5, the coating 14 is also supplied toward the coating rod 2 on the downstream side and overflows from the weir member 6b, forming a bubble-preventing liquid pool 9 and preventing air from flowing out. A method is disclosed to avoid being caught upstream.

[Problems to be Solved by the Invention] However, as the coating speed increases, the web 1 may come into contact with the liquid pool 8 at high speed, or the coating rod 2 may come into contact with the coating rod 2.
Because the rotation of the web 1 becomes high speed, the web 1 applies a high shear force to the coating liquid at the contact part between the web 1 and the coating liquid in the liquid reservoir 8, and pressure is applied to the coating liquid. On the other hand, in the vicinity of the contact portion on the downstream side, rapid separation of the web 1 and the coating rod 2 occurs via the coating liquid. That is, on the upstream side of the coating rod, due to the high shear force,
Also, on the downstream side, fine bubbles are precipitated due to the reduced pressure caused by peeling.
As a result, the coating liquid containing minute air bubbles is applied to the web 1, and the coating film 10 contains the air bubbles, which may result in failures such as pinholes, or in extreme cases. However, there is a problem in that air bubbles accumulate near the contact part on the downstream side of the coaching bean rod, causing streaks.

The present invention has been made based on the above circumstances, and its purpose is to solve the conventional problems when supplying a coating liquid to a coating device using a coating rod and coating a web running at high speed. In order to prevent dissolved air in the coating liquid from precipitating as fine bubbles (resulting in coating failure), and to form a uniform coating film on the web, a bar coating method is used. be.

[Means and effects for solving the problems] The above-mentioned object of the present invention is to provide a method for supplying a coating liquid to a coating device using a coating rod and continuously coating a moving support with the coating liquid. The coating solution is passed through the inside of a porous polymer membrane tube under pressure, and the outside of the tube is depressurized to remove 10% or more of the saturated dissolved air amount in the coating solution (hereinafter referred to as "deaeration treatment"). This is achieved by a coating method characterized in that the coating is applied after

In that case, it is preferable that the pressure of the coating liquid passed through the inside of the porous polymer membrane tube is 0.5 kg/cd gauge pressure or more.

Furthermore, in consideration of the degassing treatment of organic solvent-based coating liquids, the material of the porous polymer membrane tube of the present invention is most preferably polytetrafluoroethylene resin.

The present invention is a method for applying a coating liquid onto a web at high speed using a bar coating device using a coating rod, and the coating solution is degassed before being supplied to the bar coating device to reduce dissolved air. The greatest feature of the present invention is that it has been found that dissolved air in the liquid can be prevented from precipitating as fine bubbles even under high shear force or peeling at the part where the web and coating rod come into contact. . Degassing the coating solution before it is supplied to the coating device eliminates dissolved air during the coating process, even if high shear forces are applied before and after the coating rod, or if pressure is reduced due to peeling. This is thought to be due to the fact that it has the effect of suppressing precipitation since it has a small amount. Therefore, the degree of deaeration treatment is as high as possible (in the direction of reducing dissolved air).
is preferable.

The coating liquid in the present invention is not particularly limited, and may include a water or organic solvent solution of a polymer compound, a colloid, etc. 8 liquid etc. can be used. The physical properties of the coating solution are also not particularly limited, but considering that it will be passed through a porous polymer membrane tube, there are
Since the viscosity affects the loss of pressure tn, these factors need to be selected appropriately depending on the degree of degassing required of the coating liquid.

The web in the present invention includes paper, plastic film, resin coated paper, aluminum web, synthetic paper and the like. The material of the plastic film is
For example, polyethylene.

Polyolefins such as polypropylene, polyvinyl acetate,
Vinyl polymers such as polyvinyl chloride and polystyrene, 6,
Polyamides such as 6-nylon and 6-nylon, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polycarbonate, and cellulose triacetate.

Cellulose acetates such as cellulose diacetate are used. Further, the resin used for resin coated paper is typically polyolefin such as polyethylene, but is not necessarily limited thereto.

The thickness of the web is also not particularly limited, but is 0.01 mu
, 0 m is advantageous in terms of handling versatility.

In the present invention, the coating rod may be rotated in the same direction as the web or in the opposite direction.

Further, the coating rod used in the coating method of the present invention includes a coating rod member made of stainless steel material, iron material, brass material, etc., and a wire material such as stainless wire, piano wire, nylon wire, Teflon wire material wrapped around the coating rod member. Alternatively, a carved version of the above rod member can be used.

Next, a deaeration process for removing dissolved air in the coating liquid will be described. Many methods are known for removing air dissolved in a liquid, and a typical example is a method of placing the liquid under reduced pressure. However, although this method can remove the air dissolved in the liquid, there is a phenomenon in which fine bubbles are generated in the liquid, and it is necessary to extract the liquid from under reduced pressure or release the reduced pressure. Even in this case, there are still some microbubbles in the liquid. Therefore, in this method of degassing the coating liquid under reduced pressure, the coating liquid contains fine bubbles, and coating failure may occur if the coating liquid is coated onto a web using a bar coating device.

Therefore, it is desirable for the degassing treatment to be a method that does not generate fine bubbles, and a suitable method is to pass the coating solution through a porous polymer membrane tube and reduce the pressure on the outside.

-C The conventional deaerator A using a porous polymer membrane tube has a flow sheet as shown in Fig. 3, and has a built-in porous polymer membrane tube 11 through which the liquid to be deaerated is passed. A pressure reducing chamber 12 and a pressure sensor 15 measure the degree of vacuum.
It is comprised of a vacuum pump 14 which is detected by the sensor and activated or stopped by the control circuit 13, and a liquid delivery system for the liquid to be degassed. When removing gas dissolved in the liquid 16 using the deaerator JA, the decompression chamber 12
The night body 16 is pumped 17 by adjusting the hull lever 18 while maintaining the pressure within a predetermined range of reduced pressure.
The sample is passed through the tube at a predetermined speed while being pressurized.

When gas dissolved in a liquid is degassed, "degree of deaeration" is defined as a term expressing the degree of deaeration, and when a large amount of dissolved gas is deaerated, it is said that the degree of deaeration is high. When it is low, it is said that the degree of deaeration is low.

Regarding the tube, among the factors that affect the degree of deaeration, the smaller the inner diameter, the thinner the wall thickness, and the larger the surface area in contact with the liquid, the easier it is to be degassed.

On the other hand, although the degree of vacuum inside the decompression chamber is high, is it easy to degas?
Liquid may permeate depending on the pore size and porosity of the tube. In this case, the higher the surface tension of the liquid, the smaller the pore size of the tube in terms of pore size and porosity, and the lower the porosity, the less likely liquid permeation will occur. Therefore, once the material, pore diameter and porosity of the tube are determined, liquid permeation through the tube is closely related to the pressure difference inside and outside the tube and the surface tension of the liquid.

The material of the tube, as long as the liquid does not pass through the tube.
When the inner diameter and wall thickness are the same, the degree of deaeration is determined by the degree of vacuum inside the decompression chamber. However, the longer the tube, the higher the degree of deaeration, but conversely the pressure loss of the liquid to be deaerated within the tube becomes greater, so this pressure loss must be taken into consideration. Next, regarding the liquid to be degassed, the lower the flow rate of the liquid, the easier it is to be degassed. This can be understood from the fact that the longer the liquid stays in the tube, the more easily it is degassed. Also, if the residence time is the same, the flow rate inside the tube is higher, and the gas is more likely to be degassed. Furthermore, the lower the viscosity of the liquid, the easier it is to degas. This can be understood from the fact that the thickness of the membrane layer on the tube wall becomes thinner and the diffusion coefficient increases.

Above we have discussed the case of passing liquid through a tube, but
In the case of a coating liquid, if its viscosity is high or the pressure loss in the flow path following the acid tube is large, excessive pressure will be applied to the tube, exceeding the pressure resistance of the tube and causing it to burst. This may make it impossible to process the coating liquid.

Therefore, when processing a coating liquid, it is important to reduce the pressure loss in the flow path following the tube, and to reduce the pressure loss in the tube, but if this is difficult, It is necessary to improve the pressure resistance of the tube.

As a means for this, there is a method of providing a reinforcing material on the outside of the tube, but in this case, it is necessary to have a structure that does not impair the processing ability of the tube as much as possible.

From the above point of view, it is generally preferable that the reinforcing material provided on the outside of the tube has a porous structure, and its material is preferably a polymeric material.

The pressure resistance of a degassing composite tube provided with a reinforcing material on the outside of the tube depends mostly on the strength of the reinforcing material.

It should be noted that pressurizing the coating liquid inside the tube where the degassing process is being performed also produces the effect that the inflowing air bubbles are dissolved in the degassing coating liquid and the degassing process is carried out. It was found that the pressure level was 0.5k.
g/cd gauge pressure or higher is preferable.

Any method may be used to reduce the pressure on the outside of the tube, and the pressure for one night of application is usually 300 Torr to I
Torr is preferred.

The degassing treatment using porous polymer membrane tubes has been described above, but in order to process a large amount of coating liquid, it is common to use a module in which a large number of such tubes are arranged in parallel. How much length, inner diameter.

The number of tubes to be used is appropriately selected depending on the amount of coating liquid required for degassing, the degree of degassing of the coating liquid, etc.

The coating solution deaerated in this way is supplied to a coating device, particularly a coating device using a coating rod, and even when coated on a web running at high speed, it is possible to prevent dissolved air from precipitating. As a result, coating defects such as pinholes and vertical streaks can be prevented, so a uniform coating film can be obtained.

Next, regarding the degassing treatment of the embodiments of this invention, the second
The degassing process shown in the figure and the coating by the bar coating device will be explained based on the flow shown in FIG. 1. However, the present invention is not limited to this example.

The degassing device 19 shown in FIG. 2 has a module 22. which is spirally wound around a core 20 and formed of a number of tubes 21 made of tubular porous molecular membranes. Decompression chamber 23. Application liquid inlet 24a, outlet 24b, exhaust pipe 25
．． Vacuum pump 26° pressure sensor 27. and a control circuit 28, and the module 22 is housed in a decompression chamber 23.

Inlets and outlets 29a and 29b of the tube 21 open to liquid inlets and outlets 24a and 24b, respectively. The decompression chamber 23 is evacuated by a vacuum pump 26 through an exhaust pipe 25, and can be maintained at a desired degree of vacuum by a pressure sensor 27 and a control circuit 28. The coating liquid 30a is supplied from the liquid inlet 24a at 0.5k.
Dissolved air in the coating liquid 30a is supplied under pressure of g/crM or more, and is guided to the tube inlet 29a and passed through the tube 21 having an inner diameter of about 6a+m, which is spirally wound around the core 20. is degassed and module 2
The application that reached the exit 29b of No. 2 and was degassed? (130
It becomes b. The dissolved air removed while passing through the module 22 lowers the degree of vacuum in the decompression chamber 23, but at this time the pressure sensor 27 detects the degree of vacuum and the control circuit 28
The vacuum pump 26 is operated to maintain the decompression chamber 23 at a desired degree of vacuum.

The material of the spiral porous polymer membrane tube that forms the module 22 is polytetrafluoroethylene resin, and the inner diameter is 6 mm and the wall thickness is 0.2 mm. In order to improve pressure resistance, a reinforcing material made of polytetrafluoroethylene resin is provided on the outside of this tube.
It is a composite form.

FIG. 1 shows the flow of a coating liquid delivery system including a bar coating device and the above-mentioned deaerator. In the figure, 31 is a pump;
2 is a filter, 19 is a deaerator, 33 is a valve, 35
is a bar coating device.

The coating solution is prepared in a preparation tank (not shown) and pump 3
1 and is supplied to the inlet side of filter 32 by pump 31.
is supplied to The coating liquid is free from foreign matter, dirt, and
After removing insoluble matters, the coating liquid 30 shown in FIG.
a and is supplied to the deaerator 19.

The coating liquid 30a supplied to the deaerator 19 is deaerated as shown in FIG. After being applied to the substrate, it is introduced into a drying device (not shown).

In order to adjust the pressure applied to the coating liquid 30a to be deaerated, a valve 33 is provided on the outlet side of the deaerator 19, and a pressure gauge 36 is provided on the outlet side of the pump 31. Further, a sampling valve 34 is provided between the valve 33 and the bar coating device 350 in order to measure the degassed layer, and the coating liquid 30b is sampled from the valve 34.

This is intended to investigate the state of the coating film when coating is performed by changing the deaeration layer or by changing the running speed of the web.

〔Example〕

One embodiment of the present invention will be described below, but the present invention is not limited to this embodiment.

Example 1 Using the liquid feeding system and bar coating device shown in Fig. 1, a photosensitive coating liquid (liquid temperature 20°C) having the composition and physical properties shown in Table 1 was coated in advance with a thickness of 0.24 mm and a width of 1003 mm. Aluminum web with a roughened surface using an abrasive material No. 1
Table (Photosensitive coating liquid-1) ■ Specifications and conditions of the deaerator a Decompression chamber vacuum degree Adjust to obtain the desired deaerated dust b Tube (composite type) Material: polytetrafluoroethylene resin Inner diameter: 6 mm Wall thickness : 0.25 cm The results of examining the coating film dried by the drying device under the above conditions when changing the running speed of the web, the deaerating dust of the photosensitive coating liquid, and the pressure applied to the tube in the degassing device. Shown in Table 2.

Furthermore, in order to examine the deaerated dust in the photosensitive coating liquid deaerated by the deaerator, the deaerated liquid was sampled from the sampling pulp and dissolved oxygen was measured using a dissolved oxygen concentration meter.

The term ``relative dissolved air amount'' is defined as follows to express deaerated dust.

100% relative dissolved air content means that the liquid to be degassed is sufficiently stirred at a certain temperature (20"C in this case) to saturate the dissolved air, and the dissolved oxygen concentration is measured using a dissolved oxygen meter. Regarding the amount of dissolved air in the degassed liquid, the degassed liquid is brought to the same temperature as the liquid containing saturated dissolved air before being degassed (20°C in this case), and the amount of dissolved air is The oxygen concentration is measured with a dissolved oxygen concentration meter, and the value at this time is expressed as a relative value to a liquid with a relative dissolved air amount of 100%, and is called the relative dissolved air amount and is expressed as a percentage. Therefore, the smaller the relative dissolved air amount, the lower the relative dissolved air amount. It can be said that the amount of degassed dust is high.

As shown in Table 2, the photosensitive coating liquid that has been deaerated is supplied to the bar coating device and coated on the continuously running aluminum web to prevent coating film defects, especially pinholes, etc. Surface quality can be improved.

It was also found that the coating surface quality could be improved by pressurizing the photosensitive coating liquid in the module.

〔Effect of the invention〕

As described above, the present invention provides a method in which a coating liquid is supplied to a coating device using a coating rod, and the coating liquid is continuously applied to a moving support. The amount of saturated dissolved air in the coating liquid was reduced to 10 by passing it through the inside of the molecular membrane tube and reducing the pressure on the outside of the tube.
The coating method, which is characterized by applying after removing more than % of the coating, prevents the dissolved air in the coating solution from precipitating as minute bubbles, and enables uniform coating even at high speed coating without causing failures such as pinholes or streaks. This has contributed to improvements in quality, yield, and productivity. The coating quality can be further improved by pressurizing the coating solution passed through the inside of the tube to 0.5 g/cal gauge pressure or higher, and polytetrafluoroethylene resin is used as the material for the porous polymer membrane. This made it possible to widen the scope of application of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of one embodiment of a coating system using the bar coating method of the present invention, and FIG. Figure 3 is an explanatory diagram of a general flow sheet of a conventional degassing device using a tube made of a porous polymer membrane, Figure 4 is a side sectional view of a conventional bar coating device, and Figure 5 is an improved type. FIG. 3 is a side sectional view of the bar coating device of FIG. I9... Deaerator 21... Spiral tubular porous polymer membrane 22...
・Module -23... Residual pressure chamber 26... Vacuum pump 4.30a, 30b...-Coating liquid 31... Pump 32... Filter 33... Pressurized pulp 35...
・Bar coating device 36...pressure gauge (3 idiots) Figure 32 tz 4 Crocodile and 31V-Support material Figure 5

Claims (3)

[Claims] (1) In a method in which a coating liquid is supplied to a coating device using a coating rod and the coating liquid is continuously applied to a moving support, the coating liquid is applied to the inside of a porous polymer membrane tube while pressurizing the coating liquid. A coating method characterized in that coating is carried out after removing 10% or more of the saturated dissolved air amount in the coating liquid by applying a vacuum to the outside of the tube. (2) The coating method according to claim 1, characterized in that the pressure of the coating liquid passed through the inside of the porous polymer membrane tube is 0.5 kg/cm^2 gauge pressure or more. . (3) The coating method according to claim 1, wherein the material of the porous polymer membrane tube is polytetrafluoroethylene resin.