EP2474369B1

EP2474369B1 - Curtain coating method

Info

Publication number: EP2474369B1
Application number: EP10811687.2A
Authority: EP
Inventors: Hirofumi Morita; Akio Hirano; Hiroyuki Kohno; Toshihiro Katano
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2009-08-31
Filing date: 2010-08-09
Publication date: 2019-05-01
Anticipated expiration: 2030-08-09
Also published as: WO2011024637A1; CN102574147A; JP2011050817A; EP2474369A4; CN102574147B; EP2474369A1

Description

TECHNICAL FIELD

The present invention relates to a curtain coating method for supplying a curtain film of a coating material onto a surface of a web being conveyed to coat the surface of the web with the coating material.

BACKGROUND ART

For example, as one of the apparatuses for manufacturing thermal recording paper, etc. to coat a surface of a web (base material) such as coating base papers with a heat-sensitive coating material, there has been a curtain coating apparatus in which a curtain film of a coating material is supplied from a curtain head, which is a chamber provided with a nozzle and forms a curtain film of curtain material, onto a surface of a web being conveyed, thereby to coat the surface of the web with the coating material (refer, for example, to Patent document 1).
Figure 5 illustrates an example of such conventional curtain coating apparatuses. The curtain coating apparatus A includes a supply tank Ts for storing a coating material C supplied through a piping h. The coating material C stored in the supply tank Ts is supplied to a vacuum defoaming device Da via a piping a with a pump P1 being interposed. The coating material C having undergone a defoaming process at the vacuum defoaming device Da is supplied to a curtain head H via a piping b with a pump P2 being interposed.
The curtain head H is disposed above a web W being conveyed, and is provided with a head portion Hh and a nozzle portion Hn as shown in Figure 6. The head portion Hh is provided with a coating material supply channel Hp that extends in a longitudinal direction, and the nozzle portion Hn is provided with a slot Hs that communicates with the coating material supply channel Hp and is open downward.
The coating material C supplied into the coating material supply channel Hp of the curtain head H passes through the slot Hs to be formed as a curtain film V that extends in a web width direction. By supplying the curtain film V of the coating material C from the curtain head H onto the surface of the web W being conveyed in a direction shown by an arrow F, the coating material C is coated on the surface of the web W continuously.
Figure 7 illustrates another configuration of the curtain head. This curtain head H' is provided with a head portion Hh' and a nozzle portion Hn'. The head portion Hh' is provided with a coating material supply channel Hp' that extends in a longitudinal direction, and the nozzle portion Hn' is provided with a slot Hs' that communicates with the coating material supply channel Hp' and is open upward.
The coating material C supplied into the coating material supply channel Hp' of the curtain head H' passes through the slot Hs' and then flows down along a guide face Hg' so as to be formed as a curtain film V that extends in a web width direction. By supplying the curtain film V of the coating material C from the curtain head H' onto the surface of the web W being conveyed in a direction shown by an arrow F, the coating material C is coated on the surface of the web W continuously.
Hereinafter, description is made in regard to the curtain coating apparatus using the curtain head H shown in Figure 6. It goes without saying that description would be the same in regard to the curtain coating apparatus using the curtain head H' shown in Figure 7.
Referring to Figure 5, a return pan I is disposed below the web W together with the curtain head H arranged above the web W. The curtain head H and the return pan I are accommodated inside a heat insulating room R disposed along a convey line of the web W.
Upper side of the heat insulating room R whose peripheral wall is made of a heat insulating material is disposed an air duct Ad. A cool wind from an air conditioner Ac is sent into the air duct Ad by a blower fan Af. Cooling down of the curtain head H is performed by a cool wind (arrows w) blowing out from the air duct Ad.
Meanwhile, a part of the coating material C that might contain air bubbles and that flows out from the upper portion of the curtain head H during performing the coating on the web W in the heat insulating room R is discharged into the return pan I as shown by an arrowed line v. The coating material C accumulated in the return pan I is stored in a return tank Tr via a piping d.
The coating material C stored in the return tank Tr is supplied to a centrifugal defoaming device Db of a simple construction via a piping e with a pump P3 being interposed. After being defoamed by centrifugal defoaming device Db, the coating material C is sent into the supply tank Ts via a piping f. Thereafter, a circulation of the supply tank Ts →the vacuum defoaming device Da →the curtain head H→the return pan I→the return tank Tr→the centrifugal defoaming device Db→the supply tank Ts is repeated.
In the above-described curtain coating apparatus A, the curtain head H accommodated inside the heat insulating room R is cooled by the air conditioner Ac. This is done for the purpose of improving the coating quality as described below.
Specifically, in the curtain coating apparatus A, a heat source such as a dryer is used on the production line. As a result, if the heat insulating room R is not cooled, the curtain head H would be heated to approximately 30 - 40°C.
On the other hand, the temperature of the coating material C supplied to the curtain head H is approximately 20°C, which is lower even compared with an ordinary temperature of the ambient atmosphere. This is because the coating material C is supplied via the vacuum defoaming device Da.
At the vacuum defoaming device Da, since the coating material C is supplied into an extremely low-pressure container of 15 - 50Torr, the coating material C would boil if the temperature is high. Therefore, it is necessary for the coating material C to be cooled to around 20°C before it is supplied into the container. Thus, the temperature of the coating material C after the defoamation is performed is also approximately 20°C. Incidentally, the temperature of the coating material C is lower after the defoamation is performed than before the deformation is performed. This is due to the cooling phenomenon caused by an adiabatic expansion occurring during the defoamation.
For the above reason, if the curtain head H is not cooled, the coating material C having the temperature of approximately 20°C would be supplied to the curtain head H having the temperature of approximately 30 - 40°C. This causes a problem that the curtain head H is thermally deformed due to the temperature difference between the curtain head H and the coating material C.
Especially, when the width of the slot Hs in the nozzle portion Hn varies, flow rate of the coating material C in the curtain film V varies as time passes, and the web W becomes uneven in the web width direction. This might cause a variation in coating amount (supplied amount of the coating material C onto the surface of the web W), which might incur a tremendous decrease in the quality of coating.
Therefore, the above-described conventional curtain coating apparatus A is constructed so that the curtain head H is accommodated in the heat insulating room R and the curtain head H is cooled by the air conditioner Ac, thereby to make equal temperatures of the curtain head H and the coating material C, whereby deformation of the curtain head H, especially deformation of the slot Hs in the nozzle portion Hn, is prevented from occurring, and lowering of the coating quality is suppressed.

[Related art documents]

[Patent documents]

[Patent document 1] Japanese patent application publication no. 2001-18526
[Patent document 2] US patent application publication no. US 2004/173093

[Summary of the invention]

[Problems to be solved by the invention]

Incidentally, in the curtain coating apparatus A in which the curtain head H is cooled in order to prevent the deterioration in the coating quality as described above, several problems occur as detailed below.
Specifically, in the curtain coating apparatus, a cool wind is supplied inside the heat insulating room R in order for the curtain head H accommodated in the heat insulating room R to be cooled. However, the cool wind may hit the coating material curtain V causing the coating material curtain V to swing, resulting in that a poor coating on the web W might be incurred.
In addition, when the curtain head H is cooled, water vapor contained in the surrounding air will condense to generate dew on the surface of the curtain head H. This dew might incur a problem of poor coating when the dew drops on the web W during the course of coating. To solve the problem, it is essential to dehumidify the air inside the heat insulating room R more than necessary.
Further, such problems cannot be prevented from occurring not only that a tremendous amount of energy is required for cooling of air to be supplied inside the heat insulating room R in order to cool the curtain head H, and for dehumidifying of the air inside the heat insulating room R in order to prevent dew from generating onto the curtain head H, but also that a tremendous capital investment is required for installation of the air conditioner Ac, the blower fan Af, the air duct Ad, the heat insulating room R, and various related equipment and facility.
In view of the forgoing situation, an object of the present invention is to provide a curtain coating method capable of reducing consumption of energy in the coating operations and of achieving a large amount of reduction in the capital investment as well as capable of achieving improvements in the coating quality.

[Measure to solve the problems]

In order to achieve the above object, a curtain coating method according to the invention recited in claim 1.
A suitable curtain coating apparatus for the claimed method that supplies a coating material having been processed at a vacuum defoaming device to a curtain head, and supplies a curtain film of the coating material formed by the curtain head onto a surface of a web that is being conveyed to coat the surface of the web with the coating material, characterized in that a heating device is provided at a piping for supplying the coating material from the vacuum defoaming device to the curtain head to heat the coating material so that temperature of the coating material approximates to temperature of the curtain head is disclosed but not claimed
A suitable curtain coating apparatus to perform the invention may be characterized in that, in the curtain coating apparatus the temperature of the coating material heated by the heating device and to be supplied to the curtain head is set to be within a range of ± 5°C relative to the temperature of the curtain head.
A suitable curtain coating apparatus to perform the invention may be characterized in that, in the curtain coating apparatus there are provided a temperature sensor that detects temperature of the curtain head, and a control device that controls operations of the heating device based on the temperature detected by the temperature sensor so that the temperature of the coating material to be supplied to the curtain head is heated to approximate to the temperature of the curtain head.
A curtain coating method according to the invention recited in claim 1 that supplies a coating material having been processed at a vacuum defoaming device to a curtain head, and supplies a curtain film of the coating material formed by the curtain head onto a surface of a web that is being conveyed to coat the surface of the web with the coating material, is characterized in that the coating material supplied from the vacuum defoaming device to the curtain head is heated by a heating device so that temperature of the coating material approximates to temperature of the curtain head.
The temperature of the coating material heated by the heating device and to be supplied to the curtain head is set to be within a range of ± 5°C relative to the temperature of the curtain head.
A curtain coating method according to the invention recited in claim 2, is characterized in that, in the invention recited in claim 1, operations of the heating device is controlled based on the temperature of the curtain head so that the temperature of the coating material to be supplied to the curtain head approximates to the temperature of the curtain head.

[Advantageous effect of the invention]

In a curtain coating apparatus suitable for the invention recited in claim 1, a heating device is provided at the piping for supplying the coating material from the vacuum defoaming device to the curtain head, the temperature of the coating material is heated to approximate to the temperature of the curtain head, whereby the temperature difference between the curtain head and the coating material can be suppressed without cooling the curtain head forcibly. Since the temperature difference between the curtain head and the coating material can be suppressed in the above manner, and there occurs no swing in the curtain film of coating material caused by the wind for the cooling of the curtain head, it becomes possible to achieve a large improvement in the coating quality.
Further, equipment and facilities for cooling the curtain head becomes unnecessary, and capital investment required for installation of the cooling equipment and facilities can be reduced. In addition, it become possible to achieve a great decrease in the consumption of energy required during the coating operations.
In another curtain coating apparatus according suitable for the invention recited in claim 1, the temperature of the coating material heated by the heating device and to be supplied to the curtain head is set to be within a range of ± 5°C relative to the temperature of the curtain head, whereby the temperature difference between the curtain head and the coating material can be suppressed to be small, and deformation of the curtain head due to the above temperature difference can be prevented. Therefore, it becomes possible to achieve a large improvement in the coating quality.
In another curtain coating apparatus suitable for the invention, since the operation of the heating device is controlled by the control device based on the temperature detected by the temperature sensor, the coating material is heated so that the temperature of the coating material approximates to the temperature of the curtain head. As a result, the temperature difference between the curtain head and the coating material can be suppressed as small as possible, deformation of the curtain head due to the above temperature difference can be prevented from occurring, and it becomes possible to achieve a large improvement in the coating quality.
In the curtain coating method according to the invention recited in claim 1, the temperature of the coating material is heated to approximate to the temperature of the curtain head by the heating device provided at the piping for supplying the coating material from the vacuum defoaming device to the curtain head, whereby the temperature difference between the curtain head and the coating material can be suppressed without cooling the curtain head forcibly. Since the temperature difference between the curtain head and the coating material can be suppressed, and there occurs no swing in the curtain film of coating material caused by the wind for the cooling of the curtain head, it becomes possible to achieve a large improvement in the coating quality. Further, equipment for cooling the curtain head becomes unnecessary, and therefore capital investment required for installation of the cooling equipment and facilities can be reduced. In addition, it become possible to greatly reduce the consumption of energy in the coating operations.
Additionally, the temperature of the coating material heated by the heating device and to be supplied to the curtain head is set to be within a range of ± 5°C relative to the temperature of the curtain head, the temperature difference between the curtain head and the coating material can be suppressed to be small, and deformation of the curtain head due to the above temperature difference can be prevented. Therefore, it becomes possible to achieve a large improvement in the coating quality.
In the curtain coating method according to the invention recited in claim 2, since the operation of the heating device is controlled based on the temperature of the curtain head so that the temperature of the coating material to be supplied to the curtain head approximates to the temperature of the curtain head, the temperature difference between the curtain head and the coating material can be suppressed as small as possible. Thus, deformation of the curtain head due to the above temperature difference can be prevented from occurring, and therefore it becomes possible to achieve a large improvement in the coating quality.

[Brief description of the drawings]

Figure 1 is a conceptual overall view illustrating a first embodiment of a curtain coating apparatus suitable for the present invention.
Figure 2 is a conceptual overall view illustrating a second embodiment of a curtain coating apparatus suitable for the present invention.
Figure 3 is a conceptual overall view illustrating a third embodiment of a curtain coating apparatus suitable for the present invention.
Figure 4 is a conceptual overall view illustrating a fourth embodiment of a curtain coating apparatus suitable for the present invention.
Figure 5 is a conceptual overall view illustrating a conventional curtain head.
Figure 6A is a conceptual front view illustrating a curtain head; and Figure 6B illustrates a cross-section surface of the curtain head taken along a line b - b in Figure 6A.
Figure 7 is a cross sectional view illustrating another embodiment of the curtain head.

[Exemplary embodiments of the invention]

Description is now made in detail to curtain coating apparatus and curtain coating method according to the present invention in reference to the accompanying drawings illustrating exemplary embodiments of the present invention.
Figure 1 illustrates a first embodiment of a curtain coating apparatus suitable to perform the present invention. A curtain coating apparatus 1 of this embodiment is an apparatus that is used for manufacturing thermal recording paper in which a heat-sensitive coating material is coated on the surface of a web (base material) such as coating base papers.
The curtain coating apparatus 1 includes a supply tank 2 for storing a coating material C supplied through a piping 1a. The coating material C stored in the supply tank 2 is supplied to a vacuum defoaming device 3 via a piping 1b with a pump P1 being interposed. The coating material C having undergone a defoaming process at the vacuum defoaming device 3 is supplied to a curtain head 4 via a piping 1c with a pump P2 and a heating device 10 that is described later being interposed.
The curtain head 4 is disposed above a web W being conveyed, and is provided with a head portion and a nozzle portion not shown in the drawings. The head portion is provided with a coating material supply channel that extends in a longitudinal direction, and the nozzle portion is provided with a slot that communicates with the coating material supply channel and is open downward. The curtain head 4 is not different from the conventional curtain head H as shown in Figure 6.
In the same manner as in the coating material C supplied to the conventional curtain head H shown in Figure 6, the coating material C supplied to the curtain head 4 is formed as a curtain film V that extends in a web width direction. By supplying the curtain film V of the coating material C from the curtain head 4 onto the surface of the web W being conveyed, the coating material C is coated on the surface of the web W continuously.
A return pan 5 is disposed below the web W while the curtain head 4 arranged above the web W as described above. The curtain head H and the return pan 5 are accommodated inside a room 6 disposed along a convey line of the web W.
The room 6 is disposed for blocking a wind blowing from outside so as not to swing the curtain film V of the coating material that has been formed in the curtain head 4. Since the room 6 is constructed with a low-cost material such as a plastic sheet in a simply way, the capital investment is at an extremely low.
Apart of the coating material C, which might contain air bubbles and flows out from the upper portion of the curtain head 4 during performing the coating on the web W in the room 6, is discharged into the return pan 5 as shown by an arrowed line v. The coating material C accumulated in the return pan 5 is stored in a return tank 7 via a piping 1d.
The coating material C stored in the return tank 7 is supplied to a centrifugal defoaming device 8 of a simple construction via a piping 1e with a pump P3 being interposed. After being defoamed by centrifugal defoaming device 8, the coating material C is sent into the supply tank 2 via a piping 1f. Thereafter, a circulation of the supply tank 2 →the vacuum defoaming device 8 →the curtain head 4→the return pan 5→the return tank 7→the centrifugal defoaming device 8→the supply tank 2 is repeated.
Incidentally, in the above-described curtain coating apparatus 1, a heat source such as a dryer is used on the production line. Therefore, the curtain head 4 is in a state of being heated to approximately 30 - 40°C.
Meanwhile, the coating material C supplied to the curtain head 4 from the vacuum deforming device 3 via the piping 1c has been heated to a temperature approximating to that of the curtain head 4 by the above-mentioned heating device 10 disposed in the piping 1c.
In other words, the heating device 10 is adapted for heating the coating material C flowing through the piping c to a temperature approximating to that of the curtain head 4. Specifically, the heating device 10 is so constructed that a circumference of the piping 1c is covered with a jacket, and a heating medium such as heated air or heated water is supplied into the jacket to heat the coating material to an adequate temperature.
Incidentally, in the heating device 10, it is effective that the circumference of the piping 1c is formed to be in a spiral shape in order to widen the heat transfer interface area between the piping 1c and the heating medium (heated air, heated water), and the heating medium is supplied to the circumference of the piping 1c.
It is of course possible that, as an actual construction of the heating device 10, various constructions such as providing an electric heater or lamp heater in the circumference of the piping 1c may be adoptable other than the above-mentioned construction that uses heated air or heated water.
As described above, according to this embodiment of the curtain coating apparatus 1 and the curtain coating method, by heating the coating material to be supplied to the curtain head 4, temperature difference between the coating material C and the curtain head 4 is suppressed, whereby thermal deformation of the curtain head 4 caused by the temperature difference can be prevented from occurring. Thus, variation in the amount of coating material supplied onto the web W is suppressed so as to enable to achieve improvements of the coating quality.
Further, according to the above-described construction of the embodiment, since the temperature difference from the curtain head 4 is suppressed by heating the coating material C, in other words, since the temperature difference between the coating material C and the curtain head 4 is suppressed without adopting the conventional constitution in which the curtain head is cooled (see Figure 5), such problems that a curtain film of coating material unfavourably swings caused by a wind accompanying the cooling down of the curtain head or the like will not occur. Therefore, it becomes possible to achieve a large improvement in the coating quality.
Further, since the curtain head 4 is not cooled in the above-described construction of the embodiment, there occurs no inconvenience such as that "dew generated on the surface of the curtain head when water vapor contained in the surrounding air condense incurs a poor coating when it drops on the web W during the course of coating" or the like as in the conventional curtain coating apparatus in which the curtain head is cooled (see Figure 5).
Further, in the above-described construction of the embodiment, there is no need to conduct dehumidification for the purpose of preventing dew condensation in the curtain head 4 since the curtain head 4 is not cooled, and in addition, there is no need to provide equipment and facilities for cooling the curtain head. Therefore, the heating device 10 of this embodiment is more compact and requires smaller amount of heat compared with the conventional cooling device using cool wind (see Figure 5). As a result, capital investment required for the construction of the curtain coating apparatus 1 can be reduced, as well as it become possible to achieve a large decrease in the consumption of energy in the coating operations.
Further, in the above-described embodiment, the coating material C is heated to suppress the temperature difference from the curtain head 4. Specifically, the coating material C is heated to around 35°C in this embodiment, whereas, in the conventional curtain coating apparatus, the temperature of the coating material C is around 20°C because the curtain head is cooled. As a result, the coating material C in this embodiment is lower in viscosity, and has a better fluidity so as to be extendable smoothly compared with the conventional construction, which generates an advantageous effect to greatly improve the coating quality.
Incidentally, in a case where the coating material is heated by the heating device 10, it is extremely effective to build a construction in which an observation is conducted beforehand to perceive an actual temperature of the curtain head 4 to which the coating material C is to be supplied, and the coating material C is heated to a temperature approximating to the actual temperature as closer as possible, preferably within a range of ± 5°C relative to the temperature of the curtain head 4.
By setting the temperature of the coating material C having heated by the heating device 10 and to be supplied to the curtain head 4 within a range of ± 5°C relative to the temperature of the curtain head 4 as described above, the temperature difference between the curtain head 4 and the coating material C is suppressed to be small. This makes possible to prevent the deformation of the curtain head 4 caused by the above temperature difference, and as a result, to achieve a great improvement in the coating quality.
Further, concerning the temperature of the coating material C to be supplied to the curtain head 4, in a case where the temperature of the coating material C is substantially high relative to that of the curtain head 4, an unfavorable event may occur in which a coating material C that has been dried and solidified is attached to the nozzle portion to damage the curtain film V, resulting in a flaw in the form of lines on the coated surface, etc. Considering the occurrence of such an unfavorable event in that case, it is ideal that the temperature of the coating material C is determined to be within a range between approximately -5°C relative to the temperature of the curtain head 4 and a temperature a little smaller than the temperature of the curtain head 4, in other words, a temperature not higher than the temperature of the curtain head 4.
Figure 2 illustrates a second embodiment of the curtain coating apparatus according to the present invention. In the curtain coating apparatus 1A in this embodiment, the coating material C having undergone a defoaming process at the vacuum defoaming device 3 is supplied to the curtain head 4 via a piping 1g with the pump P2 being interposed. The piping 1g is formed to be in a spiral shape in order to expand its overall length.
Inside the room of a factory building where the curtain coating apparatus 1A is installed, a heat source such as a dryer is used as having been mentioned already, which raises the temperature of ambient atmosphere inside the factory building to approximately 30 - 40°C. Thus, the coating material C supplied from the vacuum defoaming device 3 to the curtain head 4 via the piping 1 g is heated by the ambient atmosphere temperature inside the factory building when the coating material C flows through the piping 1g formed in a spiral shape.
In other words, the piping 1g formed in a spiral shape as described above constitutes a heating device utilizing the temperature of the ambient atmosphere inside the factory building as a heat source. By passing though the piping 1g, the coating material C is heated to a temperature approximating to the temperature of the curtain head 4 that is exposed to the same ambient atmosphere temperature inside the factory building.
Incidentally, the construction of the above-described curtain coating apparatus 1A is basically the same as that of the curtain coating apparatus 1 of the first embodiment except for the piping 1g formed in a spiral shape. Therefore, the same reference symbols as in Figure 1 are assigned to the components in Figure 2 having the same functions as those in the curtain coating apparatus 1, and detailed description thereof is omitted.
According to the construction of the second embodiment as described above, just like the curtain coating apparatus and the curtain coating method of the first embodiment, a large decrease in the consumption energy in the coating operations can be achieved, and capital investment can be substantially reduced, as well as it become possible to achieve an improvement in the coating quality.
Figure 3 illustrates a third embodiment of the curtain coating apparatus according to the present invention. In the curtain coating apparatus 1B in this embodiment, the coating material C having undergone a defoaming process at the vacuum defoaming device 3 is supplied to a storage tank 9 via a piping 1h with the pump P2 being interposed. The coating material C stored in the storage tank 9 is supplied to the curtain head 4 via a piping 1i.
Inside the room of a factory building where the curtain coating apparatus 1A is installed, a heat source such as a dryer is used as having been mentioned already, and therefore the temperature of ambient atmosphere inside the factory building is approximately 30 - 40°C. Thus, the coating material C supplied from the vacuum defoaming device 3 to the storage tank 9 via the piping 1h is heated by the ambient atmosphere temperature inside the factory building while the coating material C is being stored temporarily in the storage tank 9.
In other words, the storage tank 9 installed for the purpose of storing the coating material C from the vacuum defoaming device 3 as described above constitutes a heating device utilizing the ambient atmosphere temperature inside the factory building as a heat source. While being accumulated in the storage tank 9, the coating material C is heated to a temperature approximating to the temperature of the curtain head 4 that is exposed to the same ambient atmosphere temperature inside the factory building, and the coating material C thus heated is supplied to the curtain head 4 via the piping 1i.
Incidentally, the construction of the above-described curtain coating apparatus 1B is basically the same as that of the curtain coating apparatus 1 of the first embodiment except for the storage tank 9 and the piping 1h and the piping 1i. Therefore, the same reference symbols as in Figure 1 are assigned to the components in Figure 3 having the same functions as those in the curtain coating apparatus 1, and detailed description thereof is omitted.
According to the construction of the third embodiment as described above, just like the curtain coating apparatus and the curtain coating method of the first embodiment, a large decrease in the consumption energy in the coating operations can be achieved, and capital investment can be substantially reduced, as well as it become possible to achieve an improvement in the coating quality.
Figure 4 illustrates a fourth embodiment of the curtain coating apparatus according to the present invention. The curtain coating apparatus 1' in this embodiment comprises a temperature sensor S for detecting the temperature of the curtain head 4', and a control device 100' for controlling operations of the heating device 10' based on the temperature detected by the temperature sensor S.
The temperature sensor S is disposed at a location suitable for measuring the substantial temperature of the curtain head 4', such as at the head portion or the nozzle portion of the curtain head 4' or the like. A detection signal from the temperature sensor S is input to the control device 100'.
The control device 100' controls the operations (i.e., performs feedback control) of the heating device 10' to heat the coating material C to be supplied to the curtain head 4' based on the temperature detected by the temperature sensor S so that the temperature of the coating material C to be supplied to the curtain head 4' approximates to the temperature of the curtain head 4'.
Here, the heating device 10' is so constructed that a circumference of the piping 1c' is covered with a jacket and a heating medium such as heated air or heated water is supplied into the jacket to heat the coating material at an adequate temperature like the heating device 10 shown in Figure 1 does, and supply amount and/or temperature of the heating medium to be supplied inside the jacket is adjusted on the basis of commands from the control device 100' to heat the coating material C to a temperature approximating to the temperature of the curtain head 4'.
Incidentally, the construction of the above-described curtain coating apparatus 1' is basically the same as that of the curtain coating apparatus 1 shown in Figure 1 except for the sensor S and the control device 100 of the curtain coating apparatus 1'. Therefore, the same reference symbols in Figure 1 followed by ' (apostrophe) are assigned to the components in Figure 3 having the same functions as those in the curtain coating apparatus 1, and detailed description thereof is omitted.
According to the construction of this embodiment as described above, just like the curtain coating apparatus and the curtain coating method of the embodiment shown in Figure 1, a large decrease in the consumption energy in the coating operations can be achieved, and capital investment can be substantially reduced, as well as it become possible to achieve an improvement in the coating quality.
In addition, according to the construction of the above-described embodiment, the control device 100' controls operations of the heating device 10' based on the temperature detected by the temperature sensor S to heat the coating material C so that the temperature of the coating material C approximates to the temperature of the curtain head 4', whereby the temperature difference between the curtain head 4' and the coating material C can be suppressed as small as possible, and deformation of the curtain head 4' due to the temperature difference can be prevented from occurring. Thus, it becomes possible to achieve a large improvement in the coating quality.
Incidentally, in the above-described embodiment, even in the construction in which the heating device 10' is constituted by an electric heater or lamp heater arranged in the circumference of the piping 1c', it is of course possible to adjust the temperature of the coating material C to be approximate to the temperature of the curtain head 4' by controlling the amount of electric power to be supplied to the electric heater or lamp heater on the basis of commands from the control device 100'.
In addition, although the curtain coating apparatus 1 as shown in Figure 1, the curtain coating apparatus 1A as shown in Figure 2, the curtain coating apparatus 1B as shown in Figure 3 and the curtain coating apparatus 1' as shown in Figure 4 are all to be employed for a manufacture of thermal recording paper, it goes without saying that technology in the curtain coating apparatus and the curtain coating method according to the present invention is applicable effectively to a manufacture of various papers such as art paper and coated paper as well as pressure-sensitive paper and paper board.
Further, although the curtain coating apparatus 1 as shown in Figure 1, the curtain coating apparatus 1A as shown in Figure 2, the curtain coating apparatus 1B as shown in Figure 3 and the curtain coating apparatus 1' as shown in Figure 4 are all to coat the surface of a web with one layer of a coating material, it goes without saying that technology in the curtain coating apparatus and the curtain coating method according to the present invention is applicable effectively even to a situation where a two-layer coating material curtain film constituted by the first coating material and the second coating material is supplied to a surface of a web that is being conveyed, to coat the surface of the web with a two-layer coating material, with the first and the second coating materials one on top of another.

[Explanation of the reference symbols and numerals]

1, 1A, 1B, 1' ... curtain coating apparatus
1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i,
1a', 1b', 1c', 1d', 1e', 1f' ... piping
2, 2' ... supply tank
3, 3' ... vacuum defoaming device
4, 4' ... curtain head
5, 5' ... return pan
6, 6' ... room
7, 7' ... return tank
8, 8' ... centrifugal defoaming device
9 ... storage tank
10' ... heating device
100' ... control device
C ... coating material
V ... curtain film
W ... web

Claims

A curtain coating method that supplies a coating material (C) having been processed at a vacuum defoaming device (3) to a curtain head (4), and supplies a curtain film of the coating material (C) formed by the curtain head (4) onto a surface of a web (W) that is being conveyed to coat the surface of the web with the coating material (C), characterized in that the coating material (C) supplied from the vacuum defoaming device (3) to the curtain head (4) is heated by a heating device (10) so that temperature of the coating material (C) approximates to temperature of the curtain head (4), wherein the temperature of the coating material (C) heated by the heating device (10) and to be supplied to the curtain head (4) is set to be within a range of +- 5° C relative to the temperature of the curtain head (4).
The curtain coating method according to claim 1, characterized in that operations of the heating device (10) are controlled based on the temperature of the curtain head (4) so that the temperature of the coating material (C) to be supplied to the curtain head (4) approximates to temperature of the curtain head (4).