Coating method, coating apparatus, and coating die

Abstract: The present invention is to provide a method for coating an advancing web (W) on a backup roller (6), which enables to measure and control a coating gap between a lip surface of a coating die (1) and the backup roller (6). The method comprises the steps of forming an extended portion (2A,2B) which extends outward from each end of a slit portion of the coating die and has a reference surface parallel to the lip surface, locating the coating die (1) slidably on a frame, fixing a distance sensing means (9) on each side of the backup roller (6), measuring a distance from the distance sensing means (9) to the surface of the extended portion (2A,2B) and controlling the coating gap by sliding the coating die (1) in a radial direction of the backup roller (6).

Description: BACKGROUND OF THE INVENTION The present invention relates to a coating method and apparatus by which a coater gap can be set accurately, quickly and easily and further the reproducing accuracy can be improved. The invention also relates to a coating die as defined in the preamble of claim 5. In an extrusion type or a slide hopper type coating apparatus, the setting of a coater gap between a coater edge and a web is one of the most important factors from the viewpoints of uniformity and stability of coating, and it is also important to improve quality and productivity. However, a method to directly detect the coater edge position has as yet not been proposed. Conventionally, the coater gap setting or adjusting operation is conducted by a skilled worker in the following manner before a coating operation is started or when the coating apparatus or coating roller is replaced: the skilled worker adjusts a gap between a coater edge and a web, or a gap between the coater edge and a coating roller using a thickness gauge; or a displacement of the web or coating roller with respect to the frame of the device is measured by a dial gauge or distance sensor mounted on the frame, and the skilled worker adjusts the gap in accordance with the detected value. However, according to the aforementioned method, the position of the coater edge during coating, that is, the coater gap, can not be detected, and further in the case of replacement of a coating die, the adjusting operation must be carried out again. Therefore, working efficiency is lowered, and there is a possibility that the reproducibility is lowered. When the coater gap is fluctuated or the coater gap is in an abnormal condition, the coated layer is of inferior quality, that is, streaks and stripes are caused on the coated layer, and further the layer thickness is deviated. Japanese Patent Application Open to Public Inspection No. 40258/1990 discloses the following means in which the positional sensor is disposed in such a manner that: the angle formed by the positional sensor axis and the horizontal line is the same as that formed by the moving axis of the coating die and the horizontal line. Until now, there has not been proposed a coater edge position detecting means by which the coater edge position can be directly detected so as to stably obtain excellent coating properties. A prior art coating method and coating die are described in GB-A-1 439 604. In this known coating die flat plates serving as the reference surfaces used for measuring and controlling the coating gap are respectively mounted to sliding feed of the coating die. These sliding feed are slidingly mounted on support frame of the coating apparatus such that the coating device may move towards or away from the coating roller. Accordingly, the reference surface is not directly mounted to the coating die and is moreover not coplanar with the coating edge surface, i.e. the lip surface of the die. Upon replacement of the coating die in this prior art several positional changes in the positional relation between the coating edge surface of the die and the reference surface are caused. Accordingly, delicate adjustment work using feeler gauges and jacking screws is necessary in this prior art in order to eliminate positional changes, particularly upon each replacement of the coating die. Another coating die for the application of liquids is described in DE 39 27 680 A1. This known coating die has endplates mounted to the die, wherein these plates serve to close the die gap to the sides of the die in a transverse direction but not as reference surfaces for the coating gap adjustment. SUMMARY OF THE INVENTION It is a primary object of the present invention to provide a coating method, apparatus and die by which it is pssible to more simply and accurately measure and set a coater gap and to thereby improve reproduction accuracy and efficiency. In order to solve the aforementioned object, the present invention provides a method of coating a web on a backup roller with a coating solution fed from a slit portion on a lip surface of a coating die, comprising the steps of forming an end plate with the coating die in one body so that a reference surface formed by the end plate and the lip surface of the coating die are made to be coplanar, slidably locating the coating die in close proximity to the backup roller so that the lip surface of the coating die faces the peripheral surface of the backup roller and a coating gap is formed between the lip surface and the peripheral surface of the backup roller, measuring a distance between a predetermined position of a distance measuring means and the reference surface of the coating die, sliding the coating die toward or away from the backup roller based on the measured distance so that a desired coating gap ist formed between the lip surface and the peripheral surface of the backup roller, and coating the web on the backup roller with the coating solution fed from the slit portion on the lip surface. According to the present invention there is also provided a method of coating a web on a backup roller with a coating solution fed from a slit portion on a lip surface of a coating die, comprising the steps of forming an end plate with the coating die in one body so that a reference surface formed by the end plate and the lip surface of the coating die are made to be coplanar, slidably locating the coating die in close proximity to a coating roller so that the lip surface of the coating die faces the peripheral surface of the coating roller and a coating gap is formed between the lip surface and the peripheral surface of the coating roller, measuring a distance between a predetermined position of a distance measuring means and the reference surface, sliding the coating die toward or away from the coating roller based on the measured distance so that a desired coating gap is formed between the lip surface and the peripheral surface of the coating roller, feeding the coating solution from the slit portion on the lip surface to the coating roller, and transferring the coating solution from the coating roller to the web on the backup roller. Moreover, the invention provides a coating die for applying a coating solution, said coating die comprising a lip surface adapted to face a peripheral surface of an object to be coated and a slit provided on the lip surface, the coating solution being applicable through the slit onto the object, and a distance measuring means for measuring a distance between a predetermined position of the distance measuring means and a reference surface of the coating die, and the coating die being slidable toward and away from the object based on the measured distance so that a desired coating gap is formed between the lip surface and the peripheral surface of the object, characterized in that the reference surface is formed by an end plate mounted on the coating die so as to form one body so that the reference surface of the end plate and the lip surface of the coating die are made to be coplanar. Finally, the invention also provides an apparatus for coating a web as defined in claims 7 and 8 which employs such coating die as proposed by the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic illustration showing the entire structure of the coater gap control apparatus of the present invention; Fig. 2 is a side view showing the state of installation of the distance measuring means of the present invention; Fig. 3 is a perspective view showing the coating die of the present invention; Fig. 4 is a schematic illustration showing a coating apparatus to execute the present invention; and Fig. 5 is a schematic illustration showing a coating apparatus to execute the present invention. DETAILED DESCRIPTION OF THE INVENTION Fig. 1 is a schematic illustration showing the entire structure of the coater gap control device of the present invention. Fig. 2 is a side view showing the state of installation of the distance measuring means of the present invention. Fig. 3 is a perspective view showing the coating die of the present invention. In Figs. 1 to 3, numeral 1 is an extrusion type coating die. A coating solution is extruded from a slit 5 that is formed by a front edge 3 and a back edge 4 so that the coating solution can be coated on the surface of continuously running web W supported by a backup roller 6. In the aforementioned coating apparatus, it is important to control a gap between the surface of front edge 3 or the surface of back edge 4 and surface of web W, that is, a coating gap. Therefore, it is necessary to directly detect the position of the front edge 3 or the back edge 4. As shown in Figs. 2 and 3, in the present invention, when the lengths of the end plates 2A and 2B of the coating die 1 are extended, the coating die 1 is made longer than the backup roller 6. The surface to be measured of the extended portion, that is, the end plates 2A and 2B in this example, is ground together with the edge surface of the tip of the coating die 1, that is, the surface of the front edge 3 and that of the back edge 4, so that the surface to be measured can be ground to be the same surface as the front edge 3 and the back edge 4 of the coating die 1. Provided to oppose the surfaces of the end plates 2A and 2B to be measured, the distance measuring means composed of the distance sensors 9A and 9B are arranged on both sides of the backup roller 6. More preferable is a concurrent finishing of the surfaces of the end plates and the lip portion (the front edge and the back edge) as one surface after the assembly of the main body and the end plates. Further, it is also possible to make the coating die 1 longer than the backup roller 6, and to provide sealing members to both sides of the slit in order to prevent the solution from leaking, so that the coating width can be reduced to be narrower than web W. In this case, the front edge 3 or the back edge 4 of the coating die 1 can be used for measuring. A contact type distance sensor such as "Magnescale" made by Sony Magnescale Co. is used for the distance sensor 9. It is preferable to use a noncontact type distance sensor such as a laser type distance sensor, an ultrasonic type distance sensor or an eddy-current type distance sensor. The coating die is mounted on the coater frame 7. The coating die can be moved in the radial direction of the backup roller 6 by a positional control means composed of a positional control motor 8 connected with the coating die 1, wherein a servo motor is used for the positional control motor 8. Numeral 10 is a calculation processing unit that is operated in the following manner: in accordance with the distances measured by the distance sensors 9A, 9B, the calculation processing unit 10 calculates a moving distance necessary for accomplishing a target coating gap; the calculation processing unit 10 outputs a positional correction signal to the positional control motor 8 so that the coater edge of the coating die 1 can be placed in a position separated from web W by a predetermined distance; and the coating die 1 is moved on the coater frame 7 through a rear holding member 11 so that the coater gap can be adjusted to be a predetermined value. In the aforementioned apparatus, the initial value of the coater gap, that is, the zero point of distance measuring can be determined in the following manner: the coating die 1 is advanced by the positional control motor 8; and when the coater edge comes into contact with the surface of web W, the initial value of distance measuring can be obtained. Instead of the servo motor 8, a hydraulic cylinder may be applied to the positional control means of the present invention in order to supply power. In order to prevent slippage of the end plates 2A, 2B, it is preferable that a packing member is not provided between the end plate 2A and the coating die 1, or between the end plate 2B and the coating die 1. In this case, in order to prevent leakage of the coating solution from between the coating die 1 and the end plates 2A, 2B, it is preferable that the surface of the coating die 1 and that of the end plates 2A, 2B are ground to obtain a smooth surface. In the above example, the present invention is applied to the apparatus of the extrusion coating method in which the coating solution is coated on the web continuously conveyed and held by the backup roller. The present invention can be also applied to the apparatus of the transfer type extrusion coating method in which a gap formed between the coating die 1 and the coating roller 12 is adjusted as shown in Fig. 4. The present invention can be applied to not only the extrusion type coating die but also the slide hopper type coating die 1 as shown in Fig. 5, and the coater edge gap detection means can be provided to the coating die 1 in the same manner as described before so as to control the gap. As explained above, according to the present invention, the coating gap can be directly detected. Therefore, the coating gap can be accurately set at a predetermined value, and further its reproducibility can be improved. Consequently, the coating operation can be stably carried out while the accuracy of coated layer thickness is improved. In the apparatus of the present invention, the coating die is made longer than the length of the roller surface, and the extended portion of the coating die is provided with the distance measuring means in order to measure the distance from the surface of the extended portion, and according to the result of the measurement, the distance can be controlled. Therefore, the distance between the coater edge and the web, or the distance between the coater edge and the backup roller is directly detected, so that the gap adjusting operation can be accurately carried out. Accordingly, the occurrence of inferior coating quality such as streaks and stripes of a coated layer and defective thickness of a coated layer can be prevented. In this case, the surface to be measured on the extended portion of the coating die is made to be the same as the edge surface of the tip of the coating die. When the surface to be measured on the extended portion and the edge surface of the tip of the coating die are ground concurrently, gap adjustment can be accurately carried out. When the positional control means controls the moving distance of the coating die in the radial direction of the backup roller, a predetermined gap can be automatically obtained very quickly during coating while the web is running and also after the exchange of the coating die. As explained above, according to the present invention, the coater gap can be directly detected. Therefore, the coater gap can be accurately set at a predetermined value, and further its reproducibility can be improved. Consequently, the coating operation can be stably carried out while the accuracy of coated layer thickness is improved.

Claims: A method of coating a web (W) on a backup roller (6) with a coating solution fed from a slit portion (5) on a lip surface (3, 4) of a coating die (1), comprising the steps of forming an end plate (2A, 2B) with the coating die (1) in one body so that a reference surface formed by the end plate and the lip surface (3, 4) of the coating die (1) are made to be coplanar; slidably locating the coating die (1) in close proximity to the backup roller (6) so that the lip surface (3, 4) of the coating die (1) faces the peripheral surface of the backup roller (6) and a coating gap is formed between the lip surface (3, 4) and the peripheral surface of the backup roller (6); measuring a distance between a predetermined position of a distance measuring means (9A, 9B) and the reference surface of the coating die (1); sliding the coating die (1) toward or away from the backup roller (6) based on the measured distance so that a desired coating gap is formed between the lip surface (3, 4) and the peripheral surface of the backup roller (6); and coating the web on the backup roller (6) with the coating solution fed from the slit portion (5) on the lip surface (3, 4). A method of coating a web (W) on a backup roller (6) with a coating solution fed from a slit portion (5) on a lip surface (3, 4) of a coating die (1), comprising the steps of forming an end plate (2A, 2B) with the coating die (1) in one body so that a reference surface formed by the end plate and the lip surface (3, 4) of the coating die (1) are made to be coplanar; slidably locating the coating die (1) in close proximity to a coating roller (12) so that the lip surface (3, 4) of the coating die (1) faces the peripheral surface of the coating roller (12) and a coating gap is formed between the lip surface (3, 4) and the peripheral surface of the coating roller (12); measuring a distance between a predetermined position of a distance measuring means (9A, 9B) and the reference surface; sliding the coating die (1) toward or away from the coating roller based on the measured distance so that a desired coating gap is formed between the lip surface (3, 4) and the peripheral surface of the coating roller (12); feeding the coating solution from the slit portion (5) on the lip surface (3, 4) to the coating roller (12); and transferring the coating solution from the coating roller (12) to the web on the backup roller. The method of claim 1 or 2, wherein the lip surface (3, 4) and the reference surface are made to be coplanar by grinding the lip surface (3, 4) and the reference surface together so as to form a plane surface. The method of claim 1, 2 or 3, wherein the coating die (1) provided with the end plate (2A, 2B) is formed wider than the web width so that the end plate (2A, 2B) forms an extended portion on which the reference surface is located. A coating die for applying a coating solution, said coating die (1) comprising a lip surface (3,4) adapted to face a peripheral surface of an object (6,12) to be coated and a slit (5) provided on the lip surface (3,4), the coating solution being applicable through the slit (5) onto the object (6,12), and a distance measuring means (9A,9B) for measuring a distance between a predetermined position of the distance measuring means (9A,9B) and a reference surface of the coating die (1), and the coating die (1) being slidable toward and away from the object (6,12) based on the measured distance so that a desired coating gap is formed between the lip surface (3,4) and the peripheral surface of the object (6,12), characterized in that the reference surface is formed by an end plate (2A,2B) mounted on the coating die (1) so as to form one body so that the reference surface of the end plate (2A,2B) and the lip surface (3,4) of the coating die (1) are made to be coplanar. The coating die of claim 5, characterised in that the lip surface (3,4) of the coating die (1) and the reference surface of the end plate (2A,2B) are ground together so as to be coplanar. An apparatus for coating a web (W) with a coating solution, said apparatus comprising the coating die (1) as defined in claim 5 or 6, wherein the object (6) to be coated by the coating die (1) is the web (W) trained around a backup roller (6) and the coating die (1) is slidable toward and away from the backup roller (6) such that the desired coating gap is formed between the lip surface (3,4) and the peripheral surface of the backup roller (6). An apparatus for coating a web (W) with a coating solution, said apparatus comprising the coating die (1) as defined in claim 5 or 6, wherein the object (6) to be coated by the coating die (1) is a coating roller (12) and the coating die (1) is slidable toward and away from the coating roller (12) such that the desired coating gap is formed between the lip surface (3,4) and the peripheral surface of the coating roller (6), wherein the coating solution is transferred from said coating roller (12) to the web (W) on a backup roller.

Inventors: FUJIMORI MASATO, MORITA EIICHI, SHIMIZU KAZUYUKI, TANAKA HIROMI, YOSHIDA MAKOTO, FUJIMORI, MASATO, MORITA, EIICHI, SHIMIZU, KAZUYUKI, TANAKA, HIROMI, YOSHIDA, MAKOTO
Applicants: KONISHIROKU PHOTO IND, KONICA CORPORATION
Application year: 1992
Main classification: B05C5
IPC codes: B05C5, B05D1, B05C1, B05C11