JPH0290972A - Coating method - Google Patents

Abstract

PURPOSE:To prevent streak defect from being caused on a coated surface by setting the gap between a weir member forming a liquid trap and a bar at the interval not smaller than at least 1/12 of the circumference of the bar and performing coating. CONSTITUTION:The inner wall 11 of a weir member which forms the gap be tween the weir member 6 and a bar 2 is partially worked at inner diameter dimension 20% larger than outer diameter dimension of the bar 2. The gap between the weir member 6 and the bar 2 is set in a range of such interval that (l) is equalized to 1/8. If this gap (d0-d1) is made excessively large, distur bance is caused in a liquid trap 8 and generation of a coating streak is caused. Therefor the gap d0-d1 in this interval is set to 2.5-1.5mm. Thereby high-velocity coating can be realized and productivity can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to photographic light-sensitive materials such as photographic film and photographic paper, and photolithography materials.1 Magnetic recording materials such as magnetic recording tape, pressure-sensitive recording paper, and heat-sensitive recording paper. Regarding the improvement of the process of applying a liquid coating composition (hereinafter referred to as coating liquid) to a continuously running long flexible support (hereinafter referred to as "web") in the production of recording materials, more specifically, the improved The present invention relates to a bar coating method.

(Prior Art) Various methods have been proposed for applying a coating liquid to a continuously running web.Generally, the coating process consists of a 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, blade coating methods, bar coating methods, and the like have been known as methods in which application and measurement are performed in the same part.

Among these coating methods, the bar coating method or the roller coating method transfers excess coating liquid to the web, and then removes the excess coating liquid using a bar or roller that is stationary or rotating at a slower circumferential speed in the opposite direction to the web. The coating liquid is scraped off to achieve the desired coating amount, and it has been widely used because it has the feature of being able to apply a thin layer at high speed with a simple device and operation.

For example, FIG. 4 is a schematic diagram showing an example of a bar coating device using a conventional coach-in-blonde coating device disclosed in Japanese Patent Publication No. 58-4589, in which a web is continuously run. A coating rod (hereinafter referred to as bar) 2 is rotated in the same direction or in the opposite direction. 3 is a bar support member provided over the entire length of the bar 2, which prevents the bar 2 from being bent and supplies the coating liquid 4 to the bar 2. It has the function of a vessel. That is, the coating liquid 4 is supplied from the liquid supply port 5 provided in the bar support member 3 into the liquid supply guide groove 7 formed between the bar support member 3 and the weir member 6, and is picked up by the rotating bar 2 and applied to the web 1. However, at this time, the coating liquid 4 is measured at the contact area between the web 1 and the bar 2, and only the desired coating amount is applied to the web 1, while the rest flows down and the newly supplied coating liquid 4 is applied. At the same time, a liquid reservoir 8 is formed.

Therefore, in a steady state, the coating liquid 4 is applied to the web 1 via the liquid reservoir 8.

[Problem to be solved by the invention]

However, when applying coating liquid with high color density,
In some cases, the disturbance in the liquid flow that occurs in the liquid reservoir 8, which is the application part, manifests itself as uneven metering, that is, a line failure on the application surface.

On the other hand, if the coating method disclosed in JP-A-59-123568, which is characterized by providing a rectifying plate in the liquid pool, is used, the above-mentioned streak failure on the coated surface can be prevented to a certain extent. However, when the coating solution contains many low-boiling components or when coating a coating solution with low fluidity, as the coating speed to the support is gradually increased, even if the above improved method is used, Streak defects on the coating surface of the coating solution became apparent and became a problem.

The present invention solves the above-mentioned problems and provides a coating method that does not cause streaks on the coated surface even when coating a coating liquid with low fluidity.

[Means and operations for solving the problems] An object of the present invention is to supply the coating liquid so that a liquid pool is formed just before the contact portion between the rotating bar and the continuously running web. In the method of applying the coating liquid to the web, the gap between the weir member forming the liquid pool and the bar is set to an area of 1/12 or more of the circumference of the bar (5 mm to 0.3 m
m).

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a side cross-sectional view (a) and a partially enlarged view (b) of one embodiment of a coating apparatus for explaining the coating method of the present invention.

In FIG. 1, the inner wall 11 that forms the gap between the weir member 6 and the bar 2 is partially machined to have an inner diameter that is 20% larger than the outer diameter of the bar 2, and the gap between the weir member 6 and the bar 2 is N
= 1/8 (circumference of the bar) (d0 to d1) is (
It is set to 2.5 mm ~ l, 5 fences).

The entire bar coating device shown in FIG. 1(a) is M49 different from the conventional coating device shown in FIG.
The gap (aO to a+) is narrower than before and is set over a length l, thereby rectifying the liquid flow in that section and further suppressing the occurrence of turbulence in the liquid flow. Figure 1 (b
) is a partially enlarged view of the relationship between the weir member 6 and the bar 2,
N=1/8. (circumference of the bar), weir member 6
The gap (d, -d,) between and bar 2 is (2.5mm ~ 1
．． 5mm), but this gap (d0~d1)
If it is too large, turbulence will occur in the liquid reservoir 8, causing coating streaks. Also, the section as well! A similar phenomenon occurs even if the length of is short.

Also, the gap between the sections is, for example, 2.51111 mm from the liquid supply guide groove 7.
n to 1. It is formed in a direction that reduces to 5 mm.

FIG. 2 is a side sectional view (al) and a partially enlarged view (b) of a coating device showing another embodiment of the present invention.The inner wall 11 of the weir member 6 has a linear shape; The gap between 6 and bar 6 is !!, = 1/8 (circumference of bar), (
dS~ar) is set to (2.5~1.0 mm).

FIG. 3 is a sectional view of a coating device showing yet another embodiment, in which the portion of the inner wall of the weir member that maintains a narrow gap is formed by two straight lines. = 1/8 (circumference of bar)
It is set to (aS~dl)-(4mm~2mm) in the interval.

In the coating device of the present invention, the liquid pool 8 is much smaller than in the conventional coating device.

The coating liquid in the present invention is not particularly limited, and includes water or an organic solvent 1&1 pigment aqueous dispersion of a polymer compound, a colloidal solution, and the like.

In addition, the physical properties of the coating liquid are not particularly limited, but
As for the conditions of the liquid applied on the web, it is suitable that the viscosity is low, and a state of 100 cp or less, particularly 50 cp or less is suitable. Surface tension is also not particularly limited, but 50dy
Favorable results can be obtained at ne/cm or less.

In the present invention, the web refers to paper, plastic film,
Contains resin coated paper, aluminum web, synthetic paper, etc. Examples of the material of the plastic film include polyolefins such as polyethylene and polypropylene, vinyl polymers such as polyvinyl acetate, polyvinyl chloride, and polystyrene, polyamides such as 66-nylon and 16-nylon, polyethylene terephthalate, and polyethylene terephthalate.
Polyesters such as 26-naphthalate, polycarbonates, and cellulose acetates such as cellulose triacetate and 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 0.0IIIf
We handle fl-1.0ffII11, which is advantageous in terms of versatility.

The bars used in the present invention include wire bars and grooved bars.

When a wire bar is used in the present invention, a suitable bar diameter is 6II11 to 25-1, preferably 6m to 15-1
It is. If the diameter is larger than this, vertical streaks are likely to occur in the coating film, which is undesirable. Moreover, if the diameter is smaller than this, it will be difficult to manufacture. The diameter of the wire is 0.07~1. 0+nl11, preferably 0.07~
0.4 mm is appropriate. If it is larger than this, the amount of coating will be too large and it is not appropriate to use the bar coating method, which is effective for high-speed thin layer coating, and if it is smaller than this, it will be difficult to wind the wire to create a wire bar. Along with this, problems also arise in terms of strength. Although metal is used as the material for the wire, stainless steel is most suitable from the viewpoints of corrosion resistance, abrasion resistance, strength, etc. This wire can also be plated on its surface to further improve wear resistance. Heart chrome plating is especially suitable.

Further, when using a groove cutting bar in the present invention, the pinch of the groove is 0.1 to 0.5111ffl, preferably 0.2 to 0.5111ffl.
A value of 0.3++++n is appropriate, and a cross-sectional shape approximating a sine curve is particularly suitable. However, the cross-sectional shape is not necessarily limited to this, and other cross-sectional shapes can also be used. In general, there is a certain correspondence between the grooving bar and the wire bar, and if the area per unit length of the space below the line connecting the tops of the convex parts in the cross section is the same, then the same application under the same conditions is possible. It is said to be suitable for applying large amounts. Therefore, based on such a correspondence relationship, an appropriate groove cutting bar can be determined based on knowledge regarding wire bars.

As the material of the bar, metal is preferable from the viewpoint of corrosion resistance and strength, and stainless steel is particularly suitable.

Further, as the material for the groove cutting bar, metal, particularly stainless steel, is suitable in terms of corrosion resistance, strength, and wear resistance.

Since the bar rotates at high speed, the bar support member must be made of a material that has low frictional resistance with the bar (wire in the case of a wire bar). Materials for the bar support member and weir member preferably used in the present invention include, for example, fluorine resin, polyacecool resin, polyethylene resin, polystyrene resin, etc.
Among these, polytetrafluoroethylene known as Teflon (trade name of DuPont, USA) and polyacetal resin known as Delrin (trade name of DuPont, USA) are particularly suitable in terms of friction coefficient and strength. Furthermore, it is also possible to use these plastic materials to which fillers such as glass fiber, graphite, and molybdenum disulfide are added.

Furthermore, after the bar support member is made of a metal material, the surface of the bar support member may be coated with or affixed with the above-mentioned plastic material to reduce the coefficient of friction between it and the bar. A metal material impregnated with the aforementioned plastic material, for example, aluminum impregnated with polytetrafluoroethylene, can also be used for the bar support member.

(Example) In order to make the effects of the present invention clearer, examples will be given below.

Example-1 A coating solution having the composition and physical properties shown in Table 1 was applied to the surface of a polyethylene terephthalate film having a thickness of 200 μm and a width of 1000 mm using the coating device shown in FIG. 1 at a coating speed of 40 m/min and 70 m/min. min100m/
The coating amount was changed to 36 cc/rd.

At this time, the gap between the weir member 6 and the bar 2 is f = 1/8 (circumference of the bar) and d0 to d1 is 2.5 to 1.5 mm. Table 1 Wire diameter of the wire bar used here is 0.5 m
m, and its diameter is 12 mm.

The rod was rotated at the same speed in the traveling direction of the web.

When the surface of the coating film coated by this coating method was inspected, no coating streaks were generated on the wet surface immediately after coating at any speed, and no coating streaks were generated on the dry coating surface.

When the coating speed is 40m/min or 70m/min, the coating liquid does not overflow on the plate, and the coating speed is 100m/min.
Overflow occurred at min.

Comparative Example The coating liquid shown in Example-1 was applied using the coating apparatus shown in FIG. 4 using the same rod as shown in Example-1.

At this time, the gap between the weir member 6 and the rod 2 is 1111II1
It was 1.

Slight streaks occurred at 40m/min, and at 70m/min.
At min, about 10 strong streaks were generated in the width direction, and at room/min, even stronger streaks were generated all over the width direction.

[Effects of the Invention] As explained above, the coating method of the present invention prevents streaks from occurring on the coated surface even when coating a coating liquid with low fluidity, and enables high-speed coating. , we were able to obtain improvements in productivity and product quality.

[Brief explanation of drawings]

Section 1.2. Figures 3 and 3 are a side sectional view (a) and a partially enlarged view (bl) of an embodiment of a coating device for explaining the bar coating method of the present invention. Figure 4 shows an example of a conventional bar coating method. It is a side cross-sectional view of the coating device to be explained. ■・・・・・・・・・・・・・・・・・・・・・・・・・・・Bar support member 4 ・・・Coating liquid 5・・・Liquid supply port 6・・・Weir member 7...Liquid supply guide groove 8...?U
ali 9...Bath roll 10...Coating layer 1
1...Inner wall of weir member (d0~dt)...Gap/Length l between gaps (a, -a,) ・Figure (b) Figure (b) Figure (b)

Claims (1)

[Claims] A weir that forms the liquid pool in a method of supplying a coating liquid and applying the coating liquid to the web so that a liquid pool is formed immediately before a contact portion between a rotating bar and a continuously running web. The gap between the member and the bar should be at least 1/12 of the circumference of the bar (5 m) along the bar.
A coating method characterized in that coating is performed by setting the coating thickness to 0.3 mm.