Coating apparatus

Abstract: The known coating apparatus of the type including a device for blowing off and applying coat liquid onto a web which is being transported as wrapped around a backing roller and a blade for averaging the applied coat liquid into a constant thickness, is improved. A partition plate for dividing in the web traveling direction the inside of a chamber for storing and blowing off coat liquid, is provided. A plate-like body resiliently held in contact with the web is mounted to an upper portion of the partition plate, and a plurality of holes are formed in a lower portion of the same partition plate.

Description: The present invention relates to a coating apparatus of coat liquid which is applicable to a paper coater in a paper making machine. Such a coating apparatus is known from the document DE-A-36 16 645 wherein a dam plate disposed at an upstream side of the apparatus with respect to the web transport direction and a blade are provided, which is disposed downstream of said dam plate with respect to said web transport direction. The blade is biased in a direction toward the outer circumferential surface of a roll and a chamber is defined between the blade and the dam plate. Between a flat plate extending crosswise to the dam plate and the surface of the roll a gap space is provided. As a result, the effect of uniforming a flow of coat liquid by means of the flat plate is small. The flat plate is connected with a dam plate and a support bed. However, an unevenness of coating may be easily caused depending on this connecting mode. Furthermore, the shape of this coating apparatus is complicated, and therefore it is very difficult to provide side seals. During the operation the internal pressure of the chamber is also too low to guarantee an uniform thickness of the coat. Accordingly, some skip coating - such an uneveness of coating as the surface of a paper web is exposed - may be easily caused. A coating machine (short dwell coater) is also known from the document GB-A-21 58 371. The principle construction of this machine is shown in Fig. 3, in which a web (of paper) 3 is adapted to be transported as wrapped around an outer circumference of a backing roller 2 having an elastic material such as rubber or the like wrapped around its outer circumferential surface. At a lower position of the outer circumference of the aforementioned backing roller 2 a blow-off section 5 for making coat liquid adhere onto a paper surface by blowing off the coat liquid vertically upward towards a lower surface of the web of paper 3 is provided. Integrally with this blow-off section 5 and at the downstream with respect to the paper web transport direction thereof a blade 7 for removing surplus coat liquid to form a coat liquid layer having a constant thickness is provided. In addition, for the purpose of damming up the coat liquid within a chamber 4, a dam plate 8 is disposed at the upstream with respect to the paper web transport direction of the chamber 4. With regard to the short dwell time blade coater, as shown in Fig. 3 coat liquid blown off from a liquid feeder 9 is transferred onto the web 3, the coat liquid having reached the blade 7 as a result of transportation of the same web becomes surplus liquid and is mixed coat with the coat liquid newly blown off, and the mixed coat liquid circulates within the chamber 4 as indicated at 12, but a part thereof would flow out beyond the dam plate 8. In such coating apparatus, in the case of employing coat liquid having a lot of hydrophobic pigment mixed therein, in the case of employing coat liquid containing a binder at a small proportion, or in the case of raising a web speed to a high speed (800m/min. or higher) when a water absorptivity of a web has been lowered by pretreatment, a coating thickness would become uneven in the widthwise direction of the web even if metering is effected by means of the blade 7, and hence a coat film thickness of a product would be also influenced thereby. That is, in the case where a coated web is looked under a fluorescence exciting lamp in the case of coat liquid containing fluorescent dye, in some cases belt-like uneveness of coating is observed. The coat liquid blown off from the liquid feeder 9 in the prior art as shown in Fig. 3 would circulate within the chamber, and what serves as a propelling force for pressurizing the coat liquid and transferring it onto the web is an upward pressure of the circulating flow and a speed of the coat liquid scraped out by the blade 7. However, the circulating flow is not uniform along the widthwise direction of the web, especially as the machine is speeded up to a high speed, the uniformity is lost, and in some cases due to the unevenness the coat liquid layer could not be averaged evenly. Another embodiment of such a coating machine is also disclosed in the document GB-A-21 58 371. Between the blade and the dam plate a partition plate extending parallel to the dam plate and defining a gap between the surface of the backing roller and the plate is disposed. This embodiment of an coating machine is very complicated because it has two liquid outlets. In order to support the partition plate the support bed thereof is connected with the main body of the coating machine. Accordingly, an unevenness of coating may be caused by a pitch of the support bed. It is therefore one object of the present invention to provide an improved coating apparatus which can apply coat liquid onto a web at a uniform thickness, especially at a more uniform thickness along the widthwise direction of the web. According to one feature of the present invention, there is provided a coating apparatus confronting an outer circumferential surface of a backing roller for coating a web traveling in a web transport direction over said surface with a coating liquid, said apparatus including a plate-like member disposed at an upstream side of the apparatus with respect to the web transport direction, said plate-like member extending toward the outer circumferential surface of said backing roller, a blade disposed downstream of said plate-like member with respect to said web transport direction and biased in a direction toward the outer circumferential surface of said backing roller such that a chamber is defined between said blade and said plate-like member, a liquid feed passageway serving as a blow-off section defining a bottom of said chamber remote from the outer circumferential surface of said backing roller and being open to said chamber at the bottom thereof; according to the invention a partition plate having upper and lower portions extending substantially parallel to said blade through said chamber toward the outer circumferential surface of said backing roller and being spaced from said plate-like member and said blade in the web transport direction so as to divide said chamber into a first section delimited by said plate-like member and the partition plate on the upstream side of the apparatus and a second section delimited by said blade and the partition plate on the downstream side of the apparatus, and a resilient body are provided, which is fixed to the upper portion of said partition plate adjacent said backing roller and disposed so as to resiliently engage a web travelling in said circumferential surface of said backing roller, said resilient body being oriented at an inclination relative to said partition plate and extending from said upper portion of the partition plate in a direction toward said blade, said resilient body and the outer circumferential surface of said backing roller defining a wedge-shaped space therebetween, said partition plate having holes extending through the lower portion thereof which place said first and said second sections in communication with one another, said liquid feed passageway having an inlet end open to the bottom of said second section of said chamber at a location adjacent the lower portion of said partition plate, said blow-off section defining a bottom of said second section of the chamber extending between the inlet end of said liquid feed passageway and said blade such that the inlet end of said liquid feed passageway is spaced from the downstream side of the second section of said chamber with respect to the web transport direction, and said chamber being open at the bottom thereof only to said liquid feed passageway such that when liquid is being fed into said chamber from said liquid feed passageway the liquid must pass out of said first section of the chamber only toward the outer circumferential surface of said backing roller. According to the present invention, owing to the above-mentioned structural feature, coat liquid delivered from the liquid feed passageway serving as blow-off section is mixed with the coat liquid in the chamber section on the downstream side with respect to the web traveling direction, and then enters the chamber section on the upstream side through the plurality of holes formed in the partition plate. The coat liquid having reached and adhered to the web in the above-described chamber section on the upstream side, would forcibly open the plate-like body resiliently held in contact with the web due to the traveling speed of the web, and would reach the blade. At this time, surplus coat liquid would descend along the blade and fills the chamber section on the downstream side, at the same time the surplus coat liquid raises the pressure in that chamber section and is mixed with coat liquid fed from the blow-off section, and a most part of the mixed coat liquid would flow out into the chamber section on the upstream side through the plurality of holes in the partition plate. As per such operation principle, the coat liquid can be transferred onto the web uniformly along the widthwise direction of the web by making the flow of the coat liquid uniform along the widthwise direction with the aid of the array of holes in the partition plate, and by making the back pressure applied to the plate-like body resiliently held in contact with the web uniform as a result of adjustment of the cross-section area of the holes. The above-mentioned and other objects, features and advantages of the present invention will become more apparent by reference to the following description of preferred embodiments of the invention taken in conjunction with the acompanying drawings. In the acompanying drawings: Fig. 1 is a cross-section side view of a coating apparatus according to a first preferred embodiment of the present invention; Fig. 2 is a cross-section side view of a coating apparatus according to a second preferred embodiment of the present invention; and Fig. 3 is a cross-section side view of one example of a coating apparatus in the prior art. Now the present invention will be described in greater detail in connection to the preferred embodiments illustrated in Figs. 1 and 2. In these figures, reference numeral 2 designates a backing roller, numeral 3 designates a web, numeral 4 designates a chamber for storing and blowing off coat liquid, numeral 5 designates a liquid feed passageway serving as a coat liquid blow-off section of the chamber 4, numeral 7 designates a blade, and numeral 8 designates a dam plate. In addition, reference numeral 10 designates a partition plate having a large number of holes formed therein, this partition plate 10 is fixed in a coat liquid feeding device so as to divide the inside of the chamber 4 in the traveling direction of the web into an upstream side chamber section A and a downstream side chamber section B, and provision is made such that by mounting a resilient body 11 to an upper portion of the partition plate as directed in the same direction as the traveling of the web, coat liquid fed from a lower portion of the chamber 4 and surplus coat liquid scraped down from the surface of the web 3 by the blade 7 may be separated. Next, operations of the above-described coating apparatus will be explained. When coat liquid is made to flow, the coat liquid having flowed out from the blow-off section 5 is filled in the chamber section A on the upstream side with respect to the web traveling direction and in the chamber section B on the downstream side with respect to the same direction, and coat liquid coming into contact with the web 3 forcibly opens the resilient body 11 as a result of the propelling force of the web 3, passes through the gap space between the web and the resilient body 11 and reaches the blade 7. While a coat liquid film controlled in a film thickness by the blade 7 so as to have a predetermined film thickness passes the blade portion jointly with the web 3, surplus coat liquid flows down along the blade 7 and is mixed with newly fed coat liquid, a part of the mixed coat liquid passes through the holes in the partition plate 10, thus enters the chamber section A and again reaches the web 3, but the remainder of the mixed coat liquid circulates in the chamber section B. Surplus coat liquid in the chamber section A is discharged to the outside of the coating apparatus through a gap space between the dam plate 8 and the web 3. It is to be noted that the holes formed in the partition plate 10 could be circular holes, elongated holes or a combination of these. Fig. 2 shows another preferred embodiment of the present invention. While the operation principle of this modified embodiment is nearly the same as that of the first preferred embodiment shown in Fig. 1, in this modification a blow-off section 5 is inclined as shown at 5a to direct the flow direction towards the portion of the partition plate 10 where a plurality of holes are formed, and thereby newly fed coat liquid is introduced into the chamber section A so that coat liquid in the chamber section A may be made to flow as mixed with and driven by the newly fed coat liquid. With regard to effects and advantages, significant differences are not observed between the two preferred embodiments. As will be obvious from the detailed description of the preferred embodiments above, according to the present invention, owing to the facts that a partition plate for dividing in the web traveling direction the inside of a chamber for storing and blowing off coat liquid is provided, that a plate-like body resiliently held in contact with the web is mounted to an upper portion of the partition plate, and that a plurality of holes are formed in a lower portion of the partition plate, coat liquid scraped down by a blade and newly fed coat liquid can be mixed uniformly along the widthwise direction of the web with the aid of an array of holes in the partition plate. In addition, thanks to the above-mentioned operation, uneven swirl flows within the chamber can be prevented. Furthermore, by adjusting the cross-section area of the holes in the partition plate, the pressure in the downstream side chamber section can be varied, hence the back pressure of the resilient plate can be regulated, also an osmotic pressure of the coat liquid to be transferred to the web is regulated to transfer the coat liquid to the web uniformly along its widthwise direction, and air accompanied from the outside along the backing roller is intercepted. On the other hand, the coat liquid scraped down by the blade and distributed unevenly along the widthwise direction circulates within the downstream side chamber section, but this coat liquid can be intercepted from the web by the resilient body. Furthermore, the subject coating apparatus has an advantage that the coat liquid having a property uneven along the widthwise direction within the downstream side chamber section is given a viscosity uniform along the widthwise direction after it has passed the holes in the partition plate because a shearing effect is applied to the liquid when it passes the holes. Accordingly, even if the web traveling speed is raised to 800 m/min. or higher, the coat liquid film would have a uniform profile from the above-mentioned reasons, and an osmotic pressure of the coat liquid also can be made uniform.

Claims: A coating apparatus confronting an outer circumferential surface of a backing roller (2) for coating a web (3) traveling in a web transport direction over said surface with a coating liquid, said apparatus including a plate-like member (8) disposed at an upstream side of the apparatus with respect to the web transport direction, said plate-like member (8) extending toward the outer circumferential surface of said backing roller (2), a blade (7) disposed downstream of said plate-like member (8) with respect to said web transport direction and biased in a direction toward the outer circumferential surface of said backing roller (2) such that a chamber (4) is defined between said blade (7) and said plate-like member (8), a liquid feed passageway serving as a blow-off section (5) defining a bottom of said chamber (4) remote from the outer circumferential surface of said backing roller (2) and being open to said chamber (4) at the bottom thereof, characterized in that a partition plate (10) having upper and lower portions extending substantially parallel to said blade (7) through said chamber (4) toward the outer circumferential surface of said backing roller (2) and being spaced from said plate-like member (8) and said blade (7) in the web transport direction so as to divide said chamber (4) into a first section (A) delimited by said plate-like member (8) and the partition plate (10) on the upstream side of the apparatus and a second section (B) delimited by said blade (7) and the partition plate (10) on the downstream side of the apparatus, and a resilient body (11) are provided, which is fixed to the upper portion of said partition plate (10) adjacent said backing roller (2) and disposed so as to resiliently engage a web (3) travelling in said circumferential surface of said backing roller (2), said resilient body (11) being oriented at an inclination relative to said partition plate (10) and extending from said upper portion of the partition plate (10) in a direction toward said blade (7), said resilient body (11) and the outer circumferential surface of said backing roller (2) defining a wedge-shaped space therebetween, said partition plate (10) having holes extending through the lower portion thereof which place said first and said second sections (A,B) in communication with one another, said liquid feed passageway having an inlet end open to the bottom of said second section (B) of said chamber (4) at a location adjacent the lower portion of said partition plate (10), said blow-off section (5) defining a bottom of said second section (B) of the chamber (4) extending between the inlet end of said liquid feed passageway and said blade (7) such that the inlet end of said liquid feed passageway is spaced from the downstream side of the second section (B) of said chamber (4) with respect to the web transport direction, and said chamber (4) being open at the bottom thereof only to said liquid feed passageway such that when liquid is being fed into said chamber (4) from said liquid feed passageway the liquid must pass out of said first section (A) of the chamber (4) only toward the outer circumferential surface of said backing roller (2). A coating apparatus as claimed in claim 1, characterized in that said liquid feed passageway is open to the second section (B) of said chamber (4) and extends obliquely relative to said partition plate (10) in a direction toward said lower portion of the partition plate (10). A coating apparatus as claimed in claim 1, characterized in that said plate-like member (8) is a dam plate having a terminal end spaced from the outer circumferential surface of said backing roller (2) so as to define a gap therebetween, whereby excess coating liquid passing out of the first section (A) of said chamber (4) toward a web (3) traveling in the web transport direction over said backing roller (2) is allowed to flow in a direction opposite to said web transport direction.

Inventors: HIROTA KAZUO TAKASAGO TECHNICA, JAKUNEN HIROTO HIROSHIMA TECHN, SUZUMURA HIROSHI HIROSHIMA TEC, YAMAMOTO MITSUO MIHARA MACHINE, HIROTA, KAZUO, TAKASAGO TECHNICAL INST. OF, JAKUNEN, HIROTO, HIROSHIMA TECHNICAL INST. OF, SUZUMURA, HIROSHI, HIROSHIMA TECHNICAL INST. OF, YAMAMOTO, MITSUO, MIHARA MACHINERY WORKS OF
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1990
Main classification: D21H23
IPC codes: B05C3, B67B7, B05C5, C12M1, G01N1, C12N15, B05C11, D21H23