Coating processes – With post-treatment of coating or coating material – Solid treating member or material contacts coating
Reexamination Certificate
2003-04-07
2004-08-31
Bareford, Katherine A. (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Solid treating member or material contacts coating
C427S358000, C427S256000, C118S610000, C118S410000, C118S429000
Reexamination Certificate
active
06783803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a leaf coater and a method for producing leaf type coated substrates. In more detail, it relates to a leaf coater and a method for producing leaf type coated substrates, which allow the production of coated substrates excellent in the uniformity of the film thickness of an applied coating material.
2. Description of Related Art
A leaf coating refers to a method for coating a blank substrate in such a process that the blank substrate having a limited length in the coating direction of a coating solution are supplied one by one to a coater; each supplied blank substrate is coated with the coating solution in a predetermined length; the coated substrate completely coated with the coating solution is taken out of the coater; and the next blank substrate is supplied to the coater and coated as before to produce a coated substrate.
Coating relatively small blank substrates having a length of less than 2 m in the coating direction with a desired coating material, i.e., a leaf coating is used to produce plastic substrates for optical filters, glass substrates for liquid crystal display devices and glass substrates for color filters. In some cases, it is highly demanded that the coated substrates produced by leaf coating are thin and uniform in the coating thickness of the coating solution applied to the substrates.
Known leaf coating methods include spin coating method, roll coating method, bar coating method, die coating method and combinations of these methods.
In the spin coating method, a coating solution is dropped onto the center of the surface of a rotating substrate, and the dropped coating solution is spread on the surface of the substrate using the rotation of the substrate, to form a coating film on the surface of the substrate. A device used for producing coated substrates by the spin coating method is generally called a spin coater.
Spin coaters are widely used for photo resist coating of semiconductor wafers. A case of using a spin coater for the production of color filters is disclosed in JP-63107769-A. The coating film obtained by a spin coater can be very accurately uniformed in the thickness over the entire range of the substrate, if the rheological property of the coating solution is made Newtonian, as disclosed in JP-06348023-A and JP-07261378-A. In the case where the coating solution is non-Newtonian or has a high viscosity, a thick film portion is formed in the central portion of rotation, to degrade the uniformity of the film thickness. Furthermore, a spin coater spends the coating solution in a very large amount for obtaining a predetermined coating film thickness, to raise the production cost disadvantageously.
In the roll coating method, a rotating application roll is interposed between a coating solution pan containing a coating solution and a blank substrate, and the coating solution deposited on the application roll is transferred onto the blank substrate. A device used for producing coated substrates by the roll coating method is generally called a roll coater.
Roll coaters are often used in the case where long blank substrates are coated or where a blank substrate wound as a roll is coated, and they are also used for a leaf coating. Since the coating solution is transferred from the coating solution pan to the application roll, and then to the blank substrate, the coating solution is exposed to air for a long period of time and is likely to absorb moisture and to be deteriorated, and furthermore, the ingress of objects is likely to occur during the period of time disadvantageously.
In the bar coating method, a bar comprising a rod having thin wire wound around thereon is used to coat the substrate with a paste. A device used for producing coated substrates by the bar coating method is generally called a bar coater.
A bar coater is disclosed in JP-02258081-A. In the case of a bar coater, since the wire wound around the rod is kept in direct contact with the blank substrate, the leveling is poor in the case where the coating solution is non-Newtonian or has a high viscosity, and the marks of wire remain on the coated substrates disadvantageously.
In the die coating method, the coating solution is extruded from a slit formed in a die onto the substrate in opposite to the slit with a clearance kept between them, and the slit and the substrate are moved relatively to each other, to form a coating film on the substrate. A device used for producing coated substrates by the die coating method is generally called a die coater. A method of using a spray instead of the slit of the die is known as the spray coating method, and a method of using a nozzle instead of the slit of the die is known as the nozzle coating method.
Die coaters are widely used for thick film coating and continuous coating of a coating material having a high viscosity. Cases of using a die coater for the production of color filters are disclosed in JP-05011105-A, JP-05142407-A, JP-06339656-A, JP-08229482-A and JP-08229497-A. In the case where a coating film is formed using a die coater, the coating solution can be supplied to the blank substrate by the curtain flow method, extrusion method or bead method, as described in U.S. Pat. No. 4,230,793, U.S. Pat. No. 4,696,885 and U.S. Pat. No. 2,761,791.
In the bead method, a coating material reservoir called a coating material bead is formed between the slit and the blank substrate, and the coating material is drawn from the slip with the movement of the blank substrate or the movement of the die, to form a coating film on the blank substrate. According to the bead method, since the coating material as much as the coating material spent for the formation of the coating film is supplied from the slit, the formed coating film is very good in the uniformity of the film thickness. The coating material is little wasted, and since the coating material feed passage till the coating material is discharged from the slit is closed, the deterioration of the coating material and contamination of objects can be prevented. So, the quality of the obtained coating film can be kept high.
However, as described in JP-08229482-A and JP-08229497-A, it is very difficult to form a further more uniform coating film using a die coater. To form a further more uniform coating film, the coater becomes complicated.
For forming a further more uniform coating film, JP-08332436-A proposes a leaf coating method, in which the coating method for applying a coating solution in a straight direction by the roll coating method, bar coating method or die coating method is combined with a method of applying a coating solution by the spin coating. However, also in this case, the complication of the coater cannot be avoided.
At present, a technique that allows a further more uniform coating film to be formed using a less complicated coater is being demanded for the production of color filters for color liquid crystal display devices. If a color filter for a color liquid crystal display has any abnormal projections on the surface of the coating film that must be flat, the color filter substrate contacts the opposite board, to cause conduction, and a phenomenon called common shorts occurs, to cause display failures such as luminescent points and lines or black points and lines.
To avoid such events, it is necessary to develop a leaf coater that can prevent the formation of projections to cause common shorts on the coated substrate.
A leaf coater intended to inhibit, as far as possible, the formation of projections on the surface of the coating film caused depending on the conditions of the coating solution in the coating film forming step is proposed in JP-08229497-A.
The leaf coater comprises a coating solution supply source, a predetermined coating solution quantity intermittent supply means, a coating solution applying means for applying a coating solution to each blank substrate, a first coating solution flow pipeline connecting said coating solution supply means with said predetermined coating solution
Hashimoto Kazuyuki
Kawatake Hiroshi
Kobayashi Hirofumi
Tomimatsu Shinji
Tsujii Masaya
Bareford Katherine A.
Piper Rudnick LLP
Toray Industries Inc.
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