JPH11104547A - Prevention of streak of web coating surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the streaks generated on the coating surface of a web traveling on the surface of a coating roll by sucking the part near the front end of a die head while continuing operation in the case a coating liquid is extruded from a die coater and is applied on the web. SOLUTION: When streaks 5 occur on the coating surface 4, the front end of the suction nozzle 6 is brought near to the position where the streaks occur at the front end of the lip 7 of a slot die 3 in the case the coating liquid is extruded from the slot die 3 and is applied atop the web 2 traveling on the surface of the coating roll 1. A vacuum pump 8 is then operated to execute suction usually for one to two seconds. The degree of the pressure reduction of this time is usually set at about 10<3> Pa. A liquid reservoir 9 is disposed between the suction nozzle 6 and the vacuum pump 8 to separate the sucked coating liquid. As a result, the cause for the generation of the streaks 5 may be removed without stopping the operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing streaks on a web-applied surface, and more particularly, to a method for preventing streaks on a web-applied surface by sucking the vicinity of the tip of a die head and removing the cause of streaks. It is about the method.

[0002]

2. Description of the Related Art When a coating liquid is applied to the surface of a web using a die coater such as a slot die or a slide coater, a streak-like unevenness called "streak" may appear on a coating surface in a flow direction. As a cause thereof, it is conceivable that foreign matters and bubbles contained in the coating liquid, dust in the air, foreign substances attached to the web, etc. adhere to the head portion and locally change the flow state of the coating liquid. . The thickness of the coating layer in the portion where the streak occurred is not necessarily significantly different from other portions, and there is no problem in terms of the mechanical properties of the product, but in applications such as photography, magnetic recording, or optics, The presence of streaks is not preferable because unevenness or abnormal recording is often detected. Conventionally, when a streak has occurred, insert a thin piece of plastic between the die head and the web for cleaning while continuing operation, sharply change the discharge amount of the coating liquid, use bead vacuum In such a case, the cause of streak generation is removed by means such as abruptly changing the degree of pressure reduction. If the streak does not disappear after taking these measures, retract the die and insert a thin plastic piece between the lips to clean. If streaking still occurs with this method, the operation is stopped, the die is disassembled, and the inside is cleaned. In the conventional method, it takes a long time for the streak to completely disappear, even if streak measures are taken while continuing operation,
The generation of defective products causes a great loss. On the other hand, when the operation is stopped, it is unknown whether the streak has been eliminated or not until the operation is restarted, and the result cannot be immediately confirmed, which is extremely inconvenient. Therefore, it is desired to develop a method for simply eliminating streaks while continuing operation.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and has as its object to provide a method for easily preventing streaks generated on a coating surface of a web without stopping operation. I do.

[0004]

Means for Solving the Problems The present inventor has conducted studies in accordance with the above-mentioned object, and as a result, has found that the cause of the occurrence of streaks can be eliminated by sucking the vicinity of the die head to complete the present invention. . That is, in the present invention, when the coating liquid is extruded from a die coater and applied to the surface of a web running on the surface of a coating roll, the web coating is characterized by sucking the vicinity of the tip of the die head while continuing the operation. The present invention relates to a method for preventing streaks on a surface.

Hereinafter, the present invention will be further described. The web in the present invention is polyethylene terephthalate,
Sheets and films made of plastics such as polycarbonate and acrylic resin; papers; metal sheets such as aluminum; and sheets and films obtained by laminating them. Web thickness is 1-50
The range is 0 μm.

The components of the coating liquid used in the present invention vary widely depending on whether the final product is used for optical films, photographic films, photographic printing papers, magnetic tapes, magnetic disks, adhesive tapes, wallpapers, etc. Generally contains an organic high-molecular or low-molecular binder or an inorganic binder, a solvent, an additive such as a surfactant or a softener, a filler, and the like. After the application, the product is solidified as it is, or the solvent is volatilized by heating or heating under reduced pressure, leaving only a solid layer on the web to obtain a product.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention is achieved by sucking the vicinity of the tip of a die head at a portion where a streak has occurred. This operation can be performed without stopping the coating operation. The die coater has a structure in which a coating solution is extruded from a die through a die head onto an arbitrary substrate with a constant thickness and width. As a mechanism for pushing out the coating liquid from the die, an appropriate pressure transfer mechanism such as a pump or an extruder is used. The width of the die head is usually
The range is from several tens of cm to about 10 m. The device used for suction is arbitrary, but it is preferable to use a suction nozzle or the like having a flat cross section so as to facilitate local suction at a narrow place at the tip of the head. The size of the nozzle is greatly affected by the size of the head, the gap between the head and the web, and the like.
m, an elliptical shape with a minor axis of about 1 mm. As the material of the suction nozzle, a material that is softer than the die, for example, copper or hard plastic, is preferable so as to be easily processed and to prevent damage to the die. A normal vacuum pump can be used for suction. Although the degree of reduced pressure of suction is not particularly limited, for example, a range of 10 ² to 10 ⁵ Pa is preferable. The suction time is not particularly limited, either, and is selected, for example, from the range of 0.1 to 10 seconds. Note that the tip of the suction nozzle is held so as not to come into direct contact with the application liquid.However, when performing suction, the cause of the streak is generated by locally sucking the application liquid itself near the streak generation position. Remove. Therefore, the streak can be prevented without stopping the operation and only losing a very limited portion where the streak exists.

Next, an example of the present invention will be described in more detail with reference to the drawings. FIG. 1A is a schematic perspective view illustrating a streak prevention method of the present invention. When the coating liquid is extruded from the slot die 3 and applied on the upper surface of the web 2 running on the surface of the coating roll 1, when a streak 5 occurs on the application surface 4, the tip of the suction nozzle 6 is moved to the lip 7 of the slot die. , And the vacuum pump 8 is operated to normally perform suction for 1 to 2 seconds. The degree of pressure reduction is usually about 10 ³ Pa. It is preferable to provide a liquid reservoir 9 between the suction nozzle 6 and the vacuum pump 8 to separate the suctioned application liquid. In addition,
When the coating solution contains a harmful solvent or the like, the vacuum pump 8
A method can be used as appropriate, such as providing a filter at the discharge port, or, when containing a water-soluble substance, discharging into water. FIGS. 1 (b) and 1 (c) correspond to FIG.
FIG. 4 is a partially enlarged view of the nozzle tip of FIG. The cross section of the nozzle tip 6a is flattened and formed into an elliptical shape so as to facilitate local suction. FIG. 2 is a partially schematic longitudinal sectional view illustrating the usage state of the nozzle tip. It is preferable to provide a notch 6b at the end of the nozzle tip 6a so that the lip 7 of the slot die 3 and both surfaces of the coating liquid 10 can be easily approached. It should be noted that the lower side of the lip 7 can also be appropriately suctioned to reduce the pressure if necessary.

[0009]

The following effects can be obtained by using the method of the present invention. (1) The cause of the streak can be eliminated without stopping the operation, and the effect can be immediately confirmed. Therefore, the coating liquid, the web, and the waiting time consumed before the recovery are small, and the productivity is low. high. (2) Since there is no need for disassembly and cleaning, there is little risk of damaging the head.

[Brief description of the drawings]

FIG. 1A is a schematic perspective view illustrating a streak prevention method. 1 (b) and 1 (c) show FIG.
It is the elements on larger scale which looked at the nozzle tip part of (a) from arrow b and c direction, respectively.

FIG. 2 is a partially schematic longitudinal sectional view illustrating a use state of a nozzle tip.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coating roll 2 Web 3 Slot die 4 Coating surface 5 Streak 6 Suction nozzle 6a Nozzle tip 6b Notch 7 Lip 8 Vacuum pump 9 Liquid reservoir 10 Coating liquid

Claims (1)

[Claims] 1. A web application surface wherein a coating liquid is extruded from a die coater and applied to the surface of a web running on the surface of a coating roll, wherein the vicinity of the tip of a die head is sucked while the operation is continued. Streak prevention method.