Application method and application device

Abstract

 In an application method and an application device, a liquid (3) to be applied is supplied to form a liquid reservoir (8) immediately upstream of the contact portion between a rotating bar (1) and a continuously-­moving web (2) so as to apply the liquid (3) to the web (2). The effective application length of the bar (1) is set to be shorter than the width of the web (2) so as to prevent the liquid (3) from flying away and suction openings (11) are provided at both the end faces (10) of the effective application length part of the bar (1) so as to suck the excess portion of the liquid (3) along the end faces (10) of the bar (1).

Description

[0001] The present invention relates to the improvement of a process for applying a liquid composition to a continuously-moving long flexible carrier (hereinafter often simply referred to as web) in manufacturing a photographic material such as a photographic film and printing paper, a magnetic recording material such as a magnetic recording tape, or a recording material such as pressure-sensitive paper and thermosensitive recording paper, and more particularly relates to an improved method and an improved device, both of which a liquid is applied by a bar.

[0002] Various conventional methods of applying a coating solution or liquid to a continuously-moving web were proposed. Since a liquid application process is generally considered consisting of a part (hereinafter referred to as application part) wherein a liquid is transferred to a web, and another part (hereinafter referred to as measuring part) wherein the liquid transferred to the web is measured out to a desired quantity, the application methods are classified in terms of the differences in the application part and the measuring part. A roller application method, a dipping application method, a fountain application method and so forth are classified in terms of the difference in the application part, while an air knife application method, a blade application method, a bar applicatin method and so forth are classified in terms of the difference in the measuring part. An extrusion application method, a bead coating method and a curtain application method are known as those in which application and measuring-out are performed in an identical part.

[0003] In the bar application method among others, more than a desired quantity of a liquid is transferred to a web, and the excess portion of the liquid is thereafter scraped down by a bar being at a standstill or rotating in the opposite direction to the moving direction of the web at a lower circumferential velocity than the movement of web, so that the applied liquid is adjusted to the desired quantity. Since the bar application method is characterized in that a thin layer of a liquid can be rapidly applied by a simple device and simple operation, the method is widely used. Though an optional method can be adopted as the application part of the bar application method, a roller application method, particularly a kissing application method, is most widely adopted as the application part in order to utilize the simpleness of the method.

[0004] However, since the application part and measuring part of the conventional bar application method are completely independent of each other, conditions need to be separately set for the parts to apply the liquid. For that reason, the method is not only troublesome but also requires a large space, which means that the space utilization is uneconomical.

[0005] Disclosed in the British 1,582,485 or USP 4,263,870 is a method in which a liquid to be applied is supplied to form a liquid accumulation immediately upstream of the contact portion between a bar and a web so as to apply the liquid to the web by the bar. The operation in the method is easy, a large space is not required, and a coating film with a good surface is produced.

[0006] In the above-mentioned application process, the thickness of the film of the applied liquid becomes larger at both the side edges of the web than at its other portion due to the surface tension of the liquid composition. Since the following drying of the liquid is caused to be nonuniform by the larger thickness of the film, it is desirable to make the thickness of the film uniform along the total width of the web before the liquid is dried.

[0007] Disclosed in the United States Patent No. 2,899,339 are a method and a device, in which a nozzle for sucking off an applied liquid portion is provided at each side edge of a web. The nozzle is defined by L-shaped double tubes. A spray or jet of a diluting liquid or solvent is supplied from the peripheral portion of the nozzle and the applied liquid portion is sucked off together with the diluting liquid or solvent by the central portion thereof.

[0008] It is an object of the present invention to provide an improved application method in which an applied liquid portion does not need to be removed from the thicker section of an applied liquid film by a nozzle or the like as described above, and such thicker section is not produced at each side edge of a web.

[0009] The above-mentioned object of the present invention is achieved with an application method and an application device. In the application method, a liquid to be applied is supplied to form a liquid accumulation immediately upstream of the contact portion between a rotating bar and a continuously-moving web so as to apply the liquid to the web. The method and the device are characterized in that the effective application length of the bar is set to be shorter than the width of the web so as to prevent the liquid from flying away, and the excess portion of the liquid is sucked along the end faces of the bar.

Figs. 1 and 2 show schematic views of a bar application device which indicate the way how the present invention is embodied;

Figs. 3 and 4 show sectional front views of the main portion of an application part according to the present invention;

Figs. 5, 6 and 7 show sectional front views of main portions, which indicate bar end face forms according to the present invention; and

Figs. 8 and 9 show experimental data.

[0010] The way how the present invention is embodied is now described in detail with reference to the drawings. Fig. 1 shows a wire bar or grooved bar 1 which is rotated in the same direction as the moving direction of a continuously-moving web 2. A bar supporting member 4 is disposed along the total length of the bar 1 so as to prevent the bar 1 from sagging and to serve as a liquid feeder for supplying the bar 1 with a liquid 3 to be applied. The liquid 3 is supplied into a liquid guide groove 7 defined between the bar supporting member 4 and a weir member 6, through a liquid supply port 5 of the bar supporting member 4, and is then taken up by the rotating bar 1 and applied to the web 2. At that time, the quantity of the liquid 3 is measured out at the contact portions of the bar 1 and the web 2 so that only a desired quantity of the liquid 3 is applied to the web 2 and the other quantity of the liquid flows down. The flowed-down liquid and the newly supplied liquid form a liquid reservoir 8. For that reason, the liquid 3 is applied to the web 2 through the liquid reservoir 8, in a stationary state. Since the liquid 3 is applied to the web 2 from the liquid reservoir 8, the surface of the film 9 of the applied liquid 3 is improved in comparison with conventional methods. Furthermore, since the bar 1 has not only a function of transferring the liquid 3 and applying it to the web 2 but also a function of measuring out the applied liquid to a desired quantity, the whole equipment for the application is made compact, the space for the equipment is efficiently utilized, and the setting of various conditions and operation are facilitated.

[0011] In one of conventional methods which serve to prevent the thickness of an applied liquid film from becoming larger at each side edge of a carrier, the excess liquid portion at the side edge is scraped down by a metal doctor or the like before the applied liquid film is dried. However, since the doctor is located in contact with the carrier, the surface of the carrier is damaged. In the other conventional method, heating air is blown to the applied liquid film portion of larger thickness so as to forcibly dry the portion completely. However, the latter method requires a larger equipment whose operation is very troublesome.

[0012] To solve such problems, the effective application length of the bar 1 is made shorter than the width of the web 2 in accordance with the present invention, as shown in Fig. 2, to prevent the liquid 3 from flying away from the bar 1 due to the centrifugal force thereof. In addition, the excess portion 12 of the liquid 3 is sucked through suction openings 11 along the end faces 10 of the bar 1, as shown in Fig. 3. The thickness of the applied liquid film on the web 2 is thus kept from becoming larger at both the side edges of the web.

[0013] In the embodiment of the present invention, each end face 10 of the bar 1 has a recess almost concentric with the bar as shown in Fig. 4. An outer portion defining each suction opening 11 is of a static type and is provided with such a contour that the outer portion is kept fitted with the bar 1, As a result, the excess liquid portion 12 can bridge very little. The form of each end face 10 of the bar 1 may be otherwise determined as shown Figs. 5, 6 and 7. The thickness t of each peripheral edge portion of the bar 1 is set at 1 mm or less, preferably at 0.1 to 0.5 mm.

[0014] A preferred embodiment of the present invention is described in detail below. However, the present invention is not confined to the embodiment.

Preferred embodiment

[0015] Wood pulp (LBKP) is beaten in 300 cc. of Canadian freeness. Sodium stearate is added to the wood pulp so that the weight of the sodium stearate is equal to 1.0 % of the completely dry weight of the pulp. After that, 1.5 % (by weight to the completely dry weight of the pulp) of aluminum sulfate and 0.5 % of a polyamide polyamine epichlorohydrin (Kymene 557 which is a commercial product made by Dick Hercules) are added to the mixture. 0.3 % of an alkyl ketene dimer (Aquapel which is a commercial product made by Dick Hercules) is then added to the mixture. The mixture is thereafter made into paper in a conventional method so that the paper has an area quantity of 150 g/m². 1 % (by weight to the of the paper) of calcium chloride is caused to cling to the paper by surface sizing. After the paper is dried, it is calendered to a thickness of 160 µ. The reverse side of the paper is coated with a polyethylene of about 0.930 g/cm³ in density so that the thickness of the polyethylene is set at about 0.033 mm. The obverse side of the paper is coated with a polyethylene which has a density of about 0.960 g/cm³ and which contains 10 % by weight of titanium oxide, so that the thickness of the polyethylene is set at about 0.030 mm. A long flexible carrier, which has a thickness of 230 µ and a width of 1,400 mm and is to be used to make printing paper, is thus obtained. A liquid having a composition shown in Table 1 below is applied to the reverse side of the carrier, at an application speed of 180 m/min. and a quantity ratio of 6 cc./m², by a wire bar application device shown in Figs. 1, 2, 3 and 4.

[0016] The wire bar and wire of the application device are made of stainless steel and have diameters of 50 mm and 0.08 mm, respectively. The wire bar and the wire are rotated at a circumferential velocity equal to the application speed. The effective application length of the bar is set at 1,374 mm as against the carrier's width of 1,400 mm. The bar support of the device is made of a polytetrafluoroethylen. The thickness t of each peripheral edge portion of the bar is 0.5 mm. Each suction opening is defined by a high-density polyethylene and has an effective diameter of 2mm. The pressure for sucking the liquid is 100 mmHg. After the applied film of the liquid is dried, the quantity of the colloidal silica contained in the film is detected by a fluorescent X-ray measuring instrument so as to plot the standardized ratio (along the axis of the ordinate) of the applied liquid quantity in the direction (along the axis of the abscissa) of the width of the carrier, as shown in Fig. 8.

Comparative example

[0017] A liquid of the same composition as that shown in Table 1 is applied, at an application speed of 180 m/min. and a quantity ratio of 6 cc./m², to the reverse side of the same long flexible carrier as that obtained in the above-described embodiment of the present invention, by a conventional wire bar application device. The effective application length of the wire bar of the device is set at 1,460 mm. Suction openings as provided according to the present invention are not provided in the comparative example. The other conditions are the same as that of the above-described embodiment. After the applied film of the liquid is dried, applied quantity data corresponding to those shown in Fig. 8 are obtained as shown in Fig. 9. By comparing the data shown in Fig. 8 with those shown in Fig. 9, it is found out that according to the present invention, the thickness of the applied film does not become larger at both the side edges of carrier.

[0018] According to the present invention, the thickness of the applied film is kept from becoming larger at both the side edges of the carrier, as described above. For that reason, the reduction of load of drying, the improvement of yield and the rationalization of maintenance work can be realized in the production of a recording material, which includes an application process and a drying process.

Claims

1. A method of application, in which a liquid (3) to be applied is supplied to form a liquid reservoir (8) immediately upstream of the contact portion between a rotating bar (1) and a continuously-moving web (2) so as to apply said liquid (3) to said web (2), characterized in that the effective application length of said bar (1) is set to be shorter than the width of said web (2) so as to prevent said liquid (3) from flying away; and the excess portion (12) of said liquid (3) is sucked along the end faces (10) of said bar (1).

2. A device for application, in which a liquid (3) to be applied is supplied to form a liquid reservoir (8) immediately upstream to the contact portions of a rotating bar (1) and a continuously-moving web (2) so as to apply said liquid (3) to said web (2), characterized in that suction openings (11) are provided at both the end faces (10) of said effective application length part of said bar (1) which is set to be shorter than the width of said web (2).

3. A device for application as claimed in claim 2, characterized in that both the end faces (10) of the effective application length part of said bar (1) have recesses almost concentric with said bar (1); and outer portions which define said suction openings (11) have such contours that said outer portions are fitted with said recesses.

4. A device for application as claimed in claim 3, characterized in that said outer portions defining said suction openings (11) are of the static type.

5. A device for application as claimed in claim 2, 3 or 4, characterized in that each peripheral edge portion of said bar (1) has a thickness of 1 mm or less.

6. A device for application as claimed in claim 2, 3 or 4, characterized in that each peripheral edge portion of said bar (1) has a thickness of 0.1 mm to 0.5 mm.

Drawing