JP2005205362A - Coating apparatus and coating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating apparatus and a coating method which suppresses striping unevenness and coating troubles and enables the spraying of a coating solution in form of droplets with an excellent coating uniformity. <P>SOLUTION: The coating apparatus comprises a slot nozzle spray apparatus having a coating solution nozzle part for supplying a coating solution in the full length of the coating width in the direction crossing the transportation direction of a transported object to be coated and a gas nozzle part for jetting a gas in the vicinity of the aperture part of the coating solution nozzle part and applies a coating solution to the object to be coated by spraying the coating solution while forming droplets of the coating solution by causing collision of the gas against the coating solution. The coating solution nozzle part for supplying the coating solution pinches a shim having a plurality of coating solution discharge parts formed by grooves not penetrating in the thickness direction and supplies the coating solution from the coating solution discharge part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a coating apparatus and a coating method for coating by spraying a coating liquid as droplets.

  Conventionally, various methods for applying a coating solution on a substrate are known. For example, as a method of applying a coating solution with high accuracy onto a long belt-like substrate (hereinafter also simply referred to as a substrate) to be conveyed, it is described in “MODERN COATING AND DRYING TECHNOLOGY” by Edward Cohen, Edgar Gutoff. Various methods have been proposed, for example, dip coating method, blade coating method, air knife coating method, wire bar coating method, gravure coating method, reverse coating method, reverse roll coating method, extrusion coating method. A slide bead coating method, a curtain coating method, and the like are known. In these coating methods, in order to obtain a uniform dry film thickness with high accuracy in the width direction of the substrate, attention is paid to the coating film thickness accuracy and uniformity during coating (after coating and before drying). , Applying.

  Among these coating methods, in particular, a coating device having a flow rate control die can perform high-speed, thin film, and multilayer simultaneous coating, and coating devices for photographic photosensitive materials, ink jet recording materials, magnetic recording materials, and the like due to their characteristics. Is widely used.

  As a preferred example, a slide bead coating device or an extrusion coating device proposed by Russell et al. In US Pat. No. 2,761,791 is widely used. The curtain coating device is also a flow regulation type coating device having a die, but is also widely used.

  For example, in the case of this slide bead coating device, a coating liquid reservoir called a bead is formed between the tip of the coating device and the substrate to be conveyed, and coating is performed via this bead. In the case of a curtain coating apparatus, the curtain-shaped coating liquid film is freely dropped from the coating apparatus, and coating is performed by positioning the substrate at the destination. These are very useful for obtaining a uniform dry film thickness with high accuracy.

  However, the coating by the coating device having these dies, in principle, continuously connects the coating device and the substrate, such as a bead or a curtain film, with the coating liquid. In order to form a coating film having a uniform thickness on the substrate, the flow rate of the coating solution from the coating apparatus is always constant and must not be interrupted. That is, in order to form a coating film continuously and to make the coating film thickness highly accurate and constant, a predetermined amount or more of coating solution is required. Therefore, in these methods, it is difficult to extremely reduce the amount of the coating liquid discharged from the coating apparatus for the purpose of obtaining a uniform film thickness.

  Therefore, when forming a film having a small dissolved mass per coating layer, that is, a very thin wet film thickness (for example, about 1 to 50 μm) before coating and drying the coating liquid, the solvent amount of the coating liquid is set. It is necessary to increase the total amount of the coating liquid. In particular, when the viscosity of the coating solution is low, the coating solution flows on the substrate, so that it is difficult to form a stable coating film, and the amount of the coating solution must be increased.

  However, if the amount of the solvent is increased, the load (drying load) for drying the solvent after application increases, which is not preferable in terms of production efficiency. In addition, when the amount of solvent is large or drying takes a long time, when another constituent layer is present under the coating layer, the coating layer coating solution excessively penetrates and diffuses into the constituent layer, May have adverse effects.

  Therefore, there is a demand for a coating method in which a thin film is provided with high accuracy in coating thickness, low drying load, and high productivity.

  There are various coating products in which a thin film having a uniform coating thickness with such a high accuracy needs to be provided on the constituent layers, and examples thereof include a void-type recording medium for ink jet as described below. .

  The recording medium used in the ink jet recording method is such that the ink absorption layer is a paper itself such as plain paper, or an ink absorption layer is coated on a substrate that also serves as an absorber such as coated paper. Or a non-absorbable base material such as a resin-coated paper or a polyester film coated with an ink absorbing layer.

  Among them, the recording medium of the type in which an ink absorbing layer is coated on a non-absorbing substrate is a silver salt such as glossy, glossy, deep due to the high surface smoothness of the substrate and less waviness. It is preferably used for an output that requires a high quality texture such as a photograph. Furthermore, as a glossy recording medium with high glossiness and glossiness, a swelling type recording medium in which a water-soluble binder such as polyvinylpyrrolidone or polyvinyl alcohol is coated as an ink absorbing layer on a non-absorbent substrate, A so-called void-type recording medium is used in which a fine void structure is formed with a pigment or a pigment and a binder as the ink absorption layer, and the ink is absorbed into the void.

  In a void type recording medium, the porous ink absorbing layer having this void structure is mainly formed of a hydrophilic binder and fine particles, and inorganic or organic fine particles are known as fine particles. Inorganic fine particles with higher gloss and higher glossiness are used. Then, by using a relatively small amount of a hydrophilic binder for the fine particles, voids are formed between the fine particles, and a porous ink absorbing layer is obtained.

  In general, various properties are required for the above porous ink absorbing layer, and in order to improve these various properties, use of each additive described below has been proposed.

1: Stable fine particles that form a porous of about 0.1 μm or less in order to achieve high color developability and gloss. 2: Low swellable hydrophilic property that has high fine particle retention and does not decrease the ink absorption rate. Binder 3: Hydrophilic binder crosslinker to improve ink absorption speed and water resistance of coating 4: Surfactant and hydrophilic polymer distributed on the surface to achieve optimum dot diameter 5: Dye bleed Cationic fixing agent for improving water resistance and polyvalent metal compound 6: Anti-fading agent for improving fading due to light or oxidizing gas of dye image 7: Fluorescence enhancement for improving white background Whitening agent and color tone adjusting agent (redness agent, bluing agent, etc.)
8: Matting agent and slip agent for improving surface slipperiness 9: Various oil components and latex particles or water-soluble plasticizer for imparting flexibility to the porous ink absorption layer 10: Dye bleeding and water resistance Various inorganic salts (polyvalent metal salts) for improving the weatherability or weather resistance
11: Acids and alkalis for adjusting the film surface pH of the porous ink absorbing layer may be mentioned.

  However, when each additive used for the above-mentioned various purposes is added to the coating solution for forming the porous ink absorbing layer, many additives are subject to various restrictions from the viewpoint of the stability of the manufacturing process. There are many.

  As one of the solutions to the above-mentioned problems, the additive is not included in the coating liquid for the porous ink absorption layer, but is first applied as a constituent layer on the base material, and the additive is included before drying at a reduced rate. There has been proposed a method of providing a so-called overcoat layer in which a coating solution is applied to the upper part of the constituent layer (for example, see Patent Document 1 and Patent Document 2). The additive contained in the coating liquid for the overcoat layer is expected to permeate appropriately into a component layer (for example, a porous ink absorbing layer) provided in advance and to provide a preferable function without causing the above problem. Is done. In other words, it is expected to work as a function-imparting compound. Originally, the purpose is to impregnate the porous ink-absorbing layer with the function-imparting compound, so the overcoat layer itself may be very thin. Also, a very thin one is preferable. In addition, after applying a water-soluble coating solution that forms a porous layer containing a hydrophilic binder and fine particles, the moisture content of the coating film becomes less than the void volume of the porous layer after drying, and then additives are added online An ink jet recording paper that overcoats a solution has been proposed (see, for example, Patent Document 3).

  However, when two layers of a constituent layer and an overcoat layer are provided, first, the constituent layer is applied and dried, then once wound on a roll, and again fed out from the roll to apply and dry the overcoat layer in two steps (two lines). If it does, there exists a problem which manufacturing cost increases significantly. In addition, after a while after forming the constituent layer, not only does the quality stability cause problems due to temperature history and variations in time, but also problems such as uneven coating tend to occur when an overcoat layer is provided. .

  As a result, the application of the overcoat layer further results in a large amount of solvent (water or organic solvent) being applied to the surface of the ink absorption layer, and the cost is increased due to the drying time and the drying zone being extended, and the drying capacity is specified. In some cases, the coating speed must be reduced. Furthermore, by applying a thick overcoat layer, the degree of diffusion and penetration into the ink absorption layer is large before drying, and it takes time to dry completely. The effect of adding the additive directly to the coating solution is not sufficient, and the advantages of the overcoat layer cannot be fully exhibited.

  On the other hand, in order to improve bleeding resistance or water resistance in the above-described inkjet recording paper, a water-soluble polyvalent metal ion is previously added to the inkjet recording paper as a cross-linking agent, and the dye is aggregated and fixed during inkjet recording. There is a known method of immobilization.

  For example, it is already known that a compound containing a zirconium atom or an aluminum atom is used for an inkjet recording paper as a polyvalent metal compound. For example, JP-A-55-53591, JP-A-55-150396, JP-A-56-86789, JP-A-58-89391 and JP-A-58-94491 disclose a water-soluble salt that forms a sparingly soluble salt by binding with a water-soluble dye. An ink jet recording paper to which a functional polyvalent metal salt is added is disclosed. JP-A-60-67190, 61-10484, and 61-57379 disclose ink jet recording paper to which a cationic polymer and a water-soluble polyvalent metal salt are added. JP-A-60-257286 discloses an ink jet recording paper containing a basic polyaluminum hydroxide compound.

Usually, these polyvalent metal compounds, especially those containing aluminum atoms, are added to the ink absorbing layer for the purpose of preventing colorant bleeding under high humidity and improving water resistance after printing on the surface of the recording medium. However, when a large amount is added to the ink absorbing layer, if the prepared coating solution is held for a long period of time, the coating solution will greatly thicken and gel, or conversely, it will remarkably decrease in viscosity. As a result, the coating liquid tends to flow, and as a result, stable coating becomes difficult, and it becomes difficult to obtain a uniform coating film. Therefore, the current situation is that the amount of addition is naturally limited.
Japanese Patent Laid-Open No. 11-115308 Japanese Patent Laid-Open No. 11-192777 JP 2002-331745 A

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a coating apparatus and a coating method for spraying and coating a coating liquid having excellent coating uniformity with reduced unevenness and coating failure. It is to be.

  The above object of the present invention is achieved by the following configurations.

(Claim 1)
A coating liquid nozzle unit that transports the coated body and supplies a coating liquid over a coating width in a direction that intersects the transport direction of the coated body, and a gas nozzle that ejects gas in the vicinity of the opening of the coating liquid nozzle In a coating apparatus that applies a coating liquid onto the object to be coated by spraying the gas by colliding with the coating liquid to form a droplet by using a slot nozzle spray device having a portion A coating liquid nozzle section for supplying a liquid sandwiches a shim having a plurality of coating liquid discharge sections formed by grooves that do not penetrate in the thickness direction, and supplies the coating liquid from the coating liquid discharge section apparatus.

(Claim 2)
When the length of the coating liquid discharge part in the longitudinal direction of the shim is L ₁ and the distance between the coating liquid discharge parts is L ₂ , the opening ratio (L ₁ / L ₁ + L ₂ ) is 0.2 or more. The coating apparatus according to claim 1, wherein

(Claim 3)
The coating apparatus according to claim 2, wherein a distance L ₂ between the coating liquid discharge units is 1 mm or less.

(Claim 4)
The coating apparatus according to claim 1, wherein a thickness t of the shim is 0.5 mm or less.

(Claim 5)
5. The coating apparatus according to claim 1, comprising a plurality of coating liquid discharge portions formed by grooves that do not penetrate in the thickness direction on both surfaces of the shim.

(Claim 6)
The coating apparatus according to claim 1, wherein a shape of the coating liquid discharge unit is a square, a rectangle, a semicircle, a triangle, or a circle.

(Claim 7)
The object to be coated is an ink jet recording paper having an ink absorbing layer on a substrate, and the coating liquid contains a function-imparting compound for the ink absorbing layer. The coating apparatus of any one of Claims.

(Claim 8)
8. The function-imparting compound is at least one selected from a pH adjuster, a surfactant, a hydrophilic binder cross-linking agent, an image stabilizer, and a water-soluble polyvalent metal compound. Coating device.

(Claim 9)
Application | coating method characterized by performing application | coating on a to-be-coated body using the coating device of any one of Claims 1-8.

  ADVANTAGE OF THE INVENTION According to this invention, a coating apparatus and the coating method which spray and apply | coat the coating liquid excellent in the uniformity of application | coating with the smoothing and the coating failure reduced as a droplet can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  For example, Japanese Patent Application Nos. 2002-49715, 2002-253172, and 2002 are related to a method of manufacturing an inkjet recording paper by spraying a coating liquid as droplets using a slot nozzle spray device. Nos. 272943 and 2002-272944 describe details of manufacturing conditions for ink jet recording paper using a slot nozzle spray device. Japanese Patent Application No. 2003-409981 proposes a method that uses a slot nozzle spray device to define the shape of the coating liquid discharge port of the coating liquid nozzle and the gas discharge port of the gas nozzle, and so on. Although it is an effective coating method for realizing this, as a result of further investigation on a coating method for stably forming a thin film coating film at a higher speed, not only the shape of the slot nozzle spray device but also a more uniform In order to realize stable spraying of the coating liquid, it has been found that the shim shape constituting the coating liquid flow path of the coating liquid nozzle portion for supplying the coating liquid has a great influence.

  As a result of examining the shim shape constituting the slot nozzle spray device in more detail, the present inventor transports the object to be coated and supplies the coating liquid over the coating width in the direction intersecting the transport direction of the object to be coated. Using a slot nozzle spray device having a coating liquid nozzle section and a gas nozzle section for ejecting gas in the vicinity of the opening of the coating liquid nozzle, the gas is collided with the coating liquid to form droplets and spray In the coating apparatus for applying the coating liquid onto the object to be coated, the coating liquid nozzle section for supplying the coating liquid has a plurality of coating liquid discharge sections formed by grooves that do not penetrate in the thickness direction. The coating apparatus and the coating apparatus for spraying and coating the coating liquid as liquid droplets with reduced coating unevenness and coating failure and excellent coating uniformity by the coating apparatus that supplies the coating liquid from the coating liquid discharge unit. It found to be able to implement the method, a completed the invention.

  That is, as a shim shape for forming a coating liquid flow path which has been conventionally known or proposed in the above specifications, a comb-shaped shim penetrating in the thickness direction is disclosed.

  Normally, when using a shim that forms a plurality of coating liquid discharge portions, the uniformity of the interval between the coating liquid discharge portions is a very important factor in order to achieve the coating uniformity. Further, in order to cope with higher speed application, it is necessary to dispose a larger number of higher-density application liquid discharge units in the width direction of the slot nozzle spray device. In response to the above-mentioned demand, it has been difficult to produce a high processing accuracy of the coating liquid flow path with a comb-shaped shim that has been conventionally used in the thickness direction. When a shim is incorporated into a slot nozzle spray device, it is difficult to ensure high mounting accuracy. In particular, in the case of a comb-shaped shim provided with a larger number of application liquid discharge portions at a high density as described above, the difficulty level is further increased.

  In response to the above problems, the shim according to the present invention is provided with a plurality of groove-like or tunnel-like coating liquid channels in the substrate so as not to penetrate the plate-like shim substrate in the thickness direction. It is a feature. The shim of the present invention having such a configuration can form the coating liquid flow path with high accuracy and can arrange the coating liquid flow path with high density, so that it has excellent coating uniformity and high efficiency. It becomes possible to apply by.

  Details of the present invention will be described below.

  First, the details of the slot nozzle spray device which is the coating device of the present invention will be described with reference to the drawings. However, the coating apparatus of this invention is not limited only to the structure shown with the figure illustrated here.

  The coating method of the present invention includes a coating liquid nozzle that transports an object to be coated and supplies a coating liquid over a coating width in a direction that intersects the transport direction of the body to be coated, and an opening end of the coating liquid nozzle. A slot nozzle spray device having a gas nozzle for jetting gas and a shim that forms a coating liquid flow path in the coating liquid nozzle, and spraying by forming droplets by colliding the gas with the coating liquid Thus, a coating solution is applied onto the substrate.

  Here, the to-be-coated body in the present invention refers to an object to be coated to be coated by applying a coating liquid in the form of droplets using the coating method of the present invention and spraying the coating liquid. Although there is no long belt-like support, or an inkjet recording paper having a constituent layer, for example, an ink absorbing layer, etc. already on the belt-like support, the effect of the present invention can be sufficiently achieved, It is not limited to this. The coated body may be a plate-like support or a three-dimensional shape as long as the coated portion has an area.

  Moreover, in this invention, a to-be-coated body is moved (conveyed) relatively with respect to the coating liquid nozzle of a coating device, and performs coating manufacture continuously. The coating liquid nozzle of the coating device has a length corresponding to at least the coating width of the coated body (refers to the length of the coated portion of the coated body in a direction intersecting the transport direction of the coated body). And by arrange | positioning so that it may cross | intersect the conveyance direction of a to-be-coated body, a coating liquid is apply | coated on a to-be-coated body only by conveying a to-be-coated body with respect to a coating device. When the object to be coated is a long belt-like support, the belt-like support itself is transported in the longitudinal direction of the belt-like support, and the coating liquid nozzle of the coating device is placed in the width direction of the belt-like support (perpendicular to the longitudinal direction). Preferably in the direction of An extremely thin coating film can be applied with high film thickness uniformity without a drying load by conveying the object to be coated in one direction to the coating apparatus and spraying the coating liquid as droplets over the coating width.

In addition, the droplets sprayed from the coating liquid nozzle of the coating device, in the coating width direction,
1: the droplet size distribution is uniform,
2: The area range in which the droplets fall on the coated body has a uniform drop length in the transport direction,
3: The angle falling on the coated body is uniform,
4: The collision speed falling on the coated body is uniform,
Thus, it is possible to ensure more uniform coating film thickness.

  That the droplet diameter distribution is uniform in the coating width direction specifically means that the variation of the average droplet diameter is ± 20% or less in the coating width direction. More preferably, it is ± 10% or less.

  The variation of the average droplet diameter can be measured and calculated using a laser diffraction particle size distribution measuring apparatus. Specifically, the following measurement method is used.

  First, the coating liquid is sprayed from a spray device such as a slot nozzle spray device that sprays the coating liquid as droplets, and the spray state is stabilized. Immediately after the start of spraying, the discharge amount of the coating liquid and the gas pressure are not constant, and the spray state is not stable. Therefore, it can be stabilized by continuing spraying for a predetermined time.

  Next, spray droplet RTS5123 (manufactured by Malvern Co., Ltd.) is used as a laser diffraction particle size distribution measuring device for the droplet group in which the spray state is stable, and the average droplet diameter is measured at five locations at equal intervals in the coating width direction. . At both ends (application ends) of the droplet width falling on the substrate to be coated, the spray concentration is usually extremely low, so that the effective coating width is not counted. Therefore, the both ends of the effective coating width are the two ends of the measurement point. Specifically, two points at both ends of the measurement point are 1 cm inside from the coating end, and three points at equal intervals inside are added to obtain a total of five points, which are used as measurement points. The variation rate is calculated from the average droplet diameter measured at these five locations.

  The average droplet diameter can be easily measured by using a spray tech RTS5123. However, when each droplet diameter of the droplet group at the measurement location is measured and the droplet diameter is plotted on the horizontal axis, This refers to the droplet diameter at 50%.

  In addition, that the length in the transport direction of the area range in which the droplets fall on the coated body is uniform means that the variation in the length in the coating width direction is ± 10% or less. More preferably, it is ± 5% or less.

  Further, the spread angle of the liquid droplets falling on the coated body is uniform, the fluctuation of the falling angle of the liquid droplets falling on the coated body in the coating width direction with the coating liquid nozzle of the coating device as a base point, It means ± 10% or less. More preferably, it is ± 5% or less.

  Further, that the spatial density of the droplet group falling on the coated body is uniform means that the variation in the spatial density of the droplet group falling on the coated body in the coating width direction is ± 10% or less. say. More preferably, it is ± 5% or less.

  In order to achieve uniform spraying as described above, the present invention is characterized by the use of a slot nozzle spray device. The slot nozzle spray device has a plurality of coating liquid discharge portions for discharging the coating liquid in the coating width direction. The coating liquid discharge units may be arranged in a line in the coating width direction or in a staggered manner. And a gas nozzle hole for ejecting gas in the vicinity of the coating liquid discharge portion, and a mechanism for forming droplets by colliding the gas ejected from the nozzle with the coating liquid discharged from the coating liquid nozzle hole. Have.

  As a slot nozzle spray device that can be preferably used in the present invention, for example, a device described in JP-A-6-170308 can be applied. Japanese Patent Laid-Open No. 6-170308 discloses an example in which an adhesive for disposable diapers is applied onto a fiber using this slot nozzle spray device. However, an extremely high viscosity coating liquid (adhesive) is applied to the slot nozzle. It is dropped in a fiber form from a coating liquid nozzle (coating liquid discharge portion) of the spray device, and the coating apparatus and the object to be coated (fiber) are connected by the fiber-shaped coating liquid. That is, unlike the coating method of the present invention, it is not applied as a discontinuous droplet on the object to be coated. The fiber-like coating liquid falling in parallel from each of the plurality of coating liquid nozzles provided over the coating width is disturbed by the gas ejected from the gas nozzle provided in the vicinity of the coating liquid nozzle, preventing vertical drop. And only land randomly within a certain area on the coated body. Without the gas nozzle, the fiber-like coating liquid falls vertically as it is, but by spraying the gas from the gas nozzle, it is possible to disperse and land the coating liquid over a wider range, The coating layer is simply spread and placed, and is not a coating that requires strictly uniform coating film thickness over the entire surface of the coated body as described in the example of the ink jet recording paper. Further, since the adhesive is applied, the formed coating film is extremely thick.

  Further, a slot nozzle spray coating apparatus disclosed in JP-A-5-309310 can also be preferably used in the present invention. In the example disclosed in Japanese Patent Laid-Open No. 5-309310, a hot melt type adhesive is applied onto an object to be coated, as in the above-mentioned Japanese Patent Laid-Open No. 6-170308. Since this is also a very high viscosity coating liquid (adhesive), it is a method of continuously discharging the coating liquid to the surface of the coated body in the form of fibers, and there is no strict film thickness uniformity. The coating film to be formed is also very thick.

  As described above, using such a slot nozzle spray device to increase the uniformity of the spray state over the coating width, the viscosity of the coating solution is relatively low, and the gas pressure ejected from the gas nozzle is increased. Is possible. Further, the uniformity of spraying can be enhanced by reducing the area of the opening end of the coating liquid nozzle of the slot nozzle spray device, or by reducing the pitch of the opening end.

  The viscosity of the coating solution is preferably 0.1 to 250 mPa · s, more preferably 0.1 to 50 mPa · s, and still more preferably 0.1 to 20 mPa · s. By applying to a slot nozzle spray device, it is possible to spray droplets uniformly over the coating width.

  In order to spray droplets uniformly over the coating width, the surface tension of the coating solution is adjusted to 20 to 70 mN / m, preferably 20 to 50 mN / m, more preferably 20 to 30 mN / m. That is.

  Further, when the gas internal pressure is 10 kPa or more, preferably 20 kPa or more, and more preferably 50 kPa or more when a gas is collided with the coating liquid to form a droplet using a slot nozzle spray device or the like, uniform spraying is performed. easy. The gas flow rate is 3.5 CMM / m or more, preferably 7 CMM / m or more, and more preferably 10 CMM / m or more.

  By using the above-mentioned means, the coating liquid can be uniformly supplied onto the object to be coated even if the amount of the coating liquid is small by scattering in the form of discontinuous droplets instead of continuous fibers over the coating width. . As a result, the coating film thickness can be made uniform. In addition, since discontinuous droplets are supplied onto the object to be coated and the amount of the coating liquid is reduced, no drying load is applied.

  Next, a specific form of the slot nozzle spray coating apparatus used in the coating apparatus of the present invention will be described.

  FIG. 1 is a schematic view for explaining the coating method of the present invention. In the figure, reference numeral 1 is a slot nozzle spray portion of a slot nozzle spray device (the whole is not shown), and 9 is a long belt-like support-type coated body.

  The coated body 9 is transported at a constant speed by a transport means (not shown) in the transport direction indicated by the arrow in the drawing, which is the longitudinal direction of the coated body 9. The coating liquid nozzle C of the slot nozzle spray unit 1 has a length in the width direction of the object 9 to be applied, which is a direction orthogonal to the transport direction, and is disposed so as to face the application surface of the object 9 to be applied. Yes. The coating liquid is sprayed in the form of droplets from the coating liquid nozzle C, and the coating is performed by landing the droplets on the object 9 to be transported. At this time, the length to which the coating solution in the width direction of the substrate 9 is applied corresponds to the coating width indicated by the arrow in the figure. In FIG. 1, the application width is shorter than the length in the width direction of the article 9 to be applied, but it may of course be the same.

  FIG. 2 is a schematic cross-sectional view showing an example of a slot nozzle spray device including the slot nozzle spray unit described in FIG.

  The slot nozzle spray unit 1 includes a pair of internal die blocks 3a and 3b and external die blocks 2a and 2b on the outside of the pair of internal die blocks 3a and 3b. Further, a coating liquid nozzle C (coating liquid flow path) is formed by sandwiching the shim 1a, and a gas nozzle D is provided between the internal die block 3a and the external die block 2a, and between the internal die block 3b and the external die block 2b. It is configured.

  In FIG. 2, the slot nozzle spray unit 1 has a pair of gas nozzles D having a gas pocket A and a coating liquid nozzle C having a coating liquid pocket B. The coating solution has a viscosity (preferably 0.1 to 250 mPa · s) capable of forming droplets without forming a fiber shape. For example, a coating solution such as a function-imparting compound-containing solution is placed in the preparation kettle 4, and the pump 5, It is supplied to the coating liquid pocket B through the flow meter 6 and guided to the coating liquid nozzle 3 formed by the shim 1d. On the other hand, pressurized air is supplied from the pressurized air source 7 to the gas pocket A via the valve 8 to the gas nozzle 2. At the time of application, the application liquid is supplied from the preparation kettle 4 so that the specified application amount is applied from the application liquid nozzle C, and at the same time, pressurized air is sprayed from the pair of gas nozzles D to form the application liquid in the form of droplets. It is sprayed and deposited on the body 9. In the coating method of the present invention, it is a great feature that the coating liquid can be sprayed as fine droplets instead of fibers. By supplying the coating liquid as fine droplets onto the surface of the object 9 to be coated, a highly uniform thin film can be formed at high speed without a drying load.

  Next, with reference to FIG. 3, the slot nozzle spray section and the formation and flying state of the droplets formed there will be described.

  In FIG. 3, the coating liquid E discharged from the coating liquid nozzle C formed by the shim 1d is subdivided by compressed air G supplied from the gas nozzle D provided in the vicinity of both sides of the coating liquid nozzle C. The droplet particles 12 are formed into droplets 12 having a nearly spherical shape, and then fly and land uniformly on the surface of the object 9 across the gap L5. In FIG. 3, the substrate 9 is shown as a model in which the ink absorbing layer 11 is applied as a constituent layer on the substrate 10. The area range of the droplet particles 12 of the coating liquid that lands on the substrate 9 is preferably always uniform, but in particular, the length in the transport direction (denoted by the drop length L5 in the figure) is the coating width. It is preferable to be uniform over the entire area. Further, it is preferable that the spread angle of the droplet group sprayed on the object to be coated with the opening end of the coating liquid nozzle C as a base point is uniform over the coating width.

  FIG. 4 is an exploded perspective view of a slot nozzle spray unit having a shim according to the present invention. In the figure, reference numerals 3a and 3b are internal die blocks for forming a coating liquid slit having a predetermined distance and causing the coating liquid to flow down the slit. One die block 3 a has a coating liquid supply pipe 61 that receives a coating liquid supplied from a coating liquid supply source (not shown) and communicates with the coating liquid pocket B. The coating liquid staying in the coating liquid pocket B flows down through the coating liquid slit formed between the internal die blocks 3a and 3b. 1d is a shim sandwiched between the internal blocks 3a and 3b, and a plurality of coating liquid nozzles in the coating width direction by dividing the coating liquid slit formed in the gap between the two internal die blocks 3a and 3b in the vertical direction. d is formed.

  Reference numerals 2a and 2b denote gas supply external die blocks that form gas nozzles D (not shown) through which compressed gas flows in the gaps between the external die blocks 2a and 2b. The gas nozzle D in this case is a slit extending in the coating width direction. Compressed air is supplied from an air supply source (not shown) to each air supply pipe 81 of each of the external die blocks 2a and 2b and stays in the gas pocket A, and then formed in a gap between the internal die block and the external die block. The gas nozzle D (not shown) flows down with pressure.

  The coating liquid flowing down the groove-shaped or tunnel-shaped coating liquid flow path formed in the shim 1d and the compressed air flowing down the two gas nozzles collide with each other at the coating liquid nozzle which is the bottom of the slot nozzle spray unit 1. Then, droplets are formed and fly on the object to be coated, which is the object to be coated.

  Next, details of the shim shape according to the present invention will be described.

  FIG. 5 is a diagram illustrating an example of a conventional comb-shaped shim.

  FIG. 5 is a comb-shaped shim 1d in which a plurality of grooves penetrating in the thickness direction are provided in a plate-shaped shim base to form a coating solution flow path. FIG. 5A is a perspective view thereof. 5 b) is a sectional view thereof. In the shim 1d having the shape shown in FIG. 5, the most part including the tip of the comb-like coating liquid channel wall 14 is not fixed. Therefore, the processing accuracy at the time of slit formation and the shim between the internal blocks 3a and 3b are not fixed. It becomes difficult to maintain the mounting accuracy when holding the lens.

  FIG. 6 is a diagram showing an example of a shim shape according to the present invention.

  FIG. 6 shows a shim 1d in which a large number of groove-like coating liquid channels are formed on one surface side of a plate-like shim base material without penetrating in the thickness direction. FIG. 6a is a perspective view thereof. 6b) is a cross-sectional view thereof.

  In the shim having the configuration shown in FIG. 6, a plurality of coating liquid channels provided can be accurately formed using known cutting means at arbitrary intervals, and the coating liquid channel walls are shim substrates. Therefore, when the shim is sandwiched between the internal blocks 3a and 3b, it can be attached with extremely high accuracy without being subjected to fluctuations or distortions of the coating liquid discharge unit 13. By using the slot nozzle spray device having a shim according to the present invention, it is possible to realize coating with excellent coating uniformity, reduced unevenness and coating failure.

In the shim according to the present invention, as shown in FIG. 6 b), the length of the coating liquid discharge section 13 in the longitudinal direction of the shim is L _1, and the distance between the coating liquid discharge sections 13 is L ₂ . When the opening ratio (L ₁ / L ₁ + L ₂ ) is preferably 0.2 or more, more preferably 0.2 to 0.75. By disposing the coating liquid discharge section 13 with such an opening ratio at a high density, it is possible to enable uniform coating and to impart high-speed coating suitability.

Further, the distance L ₂ between the coating solution discharge section 13, is preferably 1mm or less, more preferably 0.1 to 1.0 mm. In the shim according to the present invention, the thickness t of the shim base material is preferably 0.5 mm or less, more preferably 0.1 to 0.5 mm.

  Although FIG. 6 shows an example in which a plurality of coating liquid channels are provided on one side of the shim base, a plurality of coating liquid channels are provided on both sides of the shim base as shown in FIG. The provided shim is a more preferable embodiment.

  FIG. 7 is a shim 1d in which a large number of groove-like coating liquid channels are formed on both surfaces of a plate-like shim base material without penetrating in the thickness direction, and a) in FIG. 7 is a perspective view thereof. FIG. 7 b is a cross-sectional view thereof. As shown in FIG. 7, when a slot nozzle spray device is configured by arranging a plurality of coating liquid channels on both sides of the shim base material and arranging each coating solution channel in a staggered manner, both ends of the shim Therefore, the balance with the gas nozzle portion disposed on the surface becomes better, and more stable spraying of the coating liquid can be performed.

  6 and 7, the coating liquid discharge unit 13 has been described as an example of a square shape. However, the shape of the coating liquid discharge unit is not limited to a square, and is rectangular or as shown in FIG. 8. A shim shape provided with a semicircular coating liquid flow path, a shim shape provided with a triangular coating liquid flow path as shown in FIG. 9, or a tunnel-like shape inside the shim substrate as shown in FIG. A shim shape provided with a circular coating liquid channel is also preferable. 8 and 9, an example in which each coating liquid flow path is provided on one surface of the shim base material is shown, but a specification provided on both sides of the shim base material as shown in FIG. 7 is also preferable. Also, in FIG. 10, an example in which circular coating liquid ejection units are arranged in a row is shown, but a configuration in which a plurality of coating liquid ejection units are arranged as necessary may be used.

  On the other hand, in the slot nozzle spray device according to the present invention, the shape of the opening end of the gas nozzle may be a circle or a slit extending to the coating width, and the diameter or slit interval at this time is approximately 50 to 500 μm. It can be used in the range. The angle of the gas nozzle with respect to the coating solution nozzle is preferably in the range of 15 to 60 degrees, more preferably 15 to 45 degrees. Further, the distance between the coating liquid nozzle of the slot nozzle spray section and the object to be coated is preferably in the range of approximately 0.2 to 10 cm, more preferably 0.5 to 6.0 cm, and still more preferably 1.0 to 3.5 cm.

  11 and 12 are schematic views of the slot nozzle spray portion of FIG. 2 as viewed from the coating liquid nozzle C side. An opening end of a plurality of coating liquid nozzles C and an opening end of a gas nozzle D arranged in the coating width direction are shown.

  In the coating liquid nozzle shown in FIG. 11, the shim 1d having the configuration shown in FIG. 10 is sandwiched between the internal die blocks 3a and 3b, and the circular coating liquid discharge portions 13 are arranged in the coating width direction. Shows the configuration. And it is the aspect in which the slit-shaped gas nozzle D is provided adjacent to both sides of each coating liquid discharge part 13. Each coating liquid discharge part 13 is arranged at equal intervals, respectively. Here, the two gas nozzles D corresponding to the shim 1d provided with one coating liquid discharge part 13 are arranged in a straight line in a direction perpendicular to the coating width direction, but the shim 1d and the gas nozzle D are alternately arranged. Alternatively, they may be arranged in a zigzag pattern. In FIG. 11, the gas nozzle D has a slit-like shape, but it may be configured to be positioned at a constant interval (pitch) between the circular gas discharge portions similar to the shim 1 d.

  The coating liquid nozzle shown in FIG. 12 is different from the form shown in FIG. 11, and a shim 1d having a configuration in which a coating liquid flow path is provided on both sides of the shim base shown in FIG. A configuration is shown in which the circular coating liquid discharge sections 13 are arranged in the coating width direction, sandwiched between the die blocks 3a and 3b.

Although the supply amount of the coating liquid from the coating liquid nozzle cannot be defined unconditionally depending on the desired coating film thickness, coating liquid concentration, coating speed, etc., the coating amount on the coated body is generally 1 to 50 g / m. A range of ² is preferred. If it is less than 1 g / m ^2, it is difficult to form a stable and uniform coating film. Conversely, if it exceeds 50 g / m ² , the drying load will be affected, making it difficult to exhibit the effects of the present invention effectively. . The wet film thickness of the coating solution is 1 to 50 μm, and preferably 5 to 30 μm.

  On the other hand, the gas ejected from the gas nozzle may be any gas suitable for application, and generally air (air) is used, but the gas supply condition is generally 1 to 50 CMM / m (flow rate per application width). The internal pressure at the gas nozzle at that time is preferably 10 kPa or more from the viewpoint of coating uniformity.

  The air linear velocity v is preferably 100 to 400 m / s from the viewpoint that the object of the present invention can be remarkably achieved. In particular, if v is 100 m / s or more, it is preferable from the viewpoint of coating dryness, and if it is 400 m / s or less, it is preferable from the viewpoint of coating yield.

  The air linear velocity referred to in the present invention is the air linear velocity immediately after the gas nozzle exit, and can be determined by measuring with a laser Doppler anemometer or the like. Further, the coating yield is the amount of coating liquid applied on the substrate to be coated / the total amount of coating liquid supplied × 100 (%), and is calculated by a mass method. That is, the amount of coating liquid applied on the coated body is calculated from the change in mass before and after coating on the coated body, and the total amount of coating liquid fed is fed to the coating liquid nozzle and supplied mass, that is, It can be determined from the liquid feed flow rate x the coating time.

  In this case, the average particle diameter of the droplets of the coating liquid is preferably 10 to 70 μm from the viewpoint that the object of the present invention can be remarkably achieved. The average particle size of the droplets referred to in the present invention is the average particle size at the position of the application gap (distance L5 between the application liquid nozzle and the object to be applied), and is a laser diffraction type particle size measuring device such as manufactured by MALVAN. It can be determined by measuring with RTS114.

  FIG. 13 shows an example of a coating production line in which the slot nozzle spray device as described above is arranged. In this case, the object to be coated is one in which a constituent layer is coated on a support. A plurality of (multi-stage) slot nozzle spray devices were arranged in the step of drying after applying the constituent layers. Thus, on the same line, forming the constituent layers and applying the overcoat layer (outermost layer) according to the present invention is called online coating.

  A porous material supplied from the flow-regulating slide bead coating device 20 in the process of passing the support roller 21 from the original winding of the support by a transport means (not shown) and further reversely transporting at the position of the backup roll 22. A coating liquid for the quality ink absorbing layer (constituting layer) is applied. Since the coating liquid for the porous ink absorbing layer contains a hydrophilic binder, it is cooled once in the cooling zone 30 and fixed. The to-be-coated body 9 having a constituent layer on the support is conveyed to a drying process. In the drying process, a reverser 23 that blows air and reversely conveys the coating film surface in a non-contact manner and a normal conveyance roller 24 that reversely conveys the reverse surface of the coated object 9 are provided alternately. Is meandering. In this drying step, hot air is blown to dry (the hot air blowing means is not shown). In the course of this drying process, preferably at the position after the reduced rate drying, application by droplet spraying as described above of the present invention is performed by the two slot nozzle spray devices 1. Of the two slot nozzle sprays, at least one is preferably placed at a position after the drying end point from the viewpoint of drying properties. In this example, two slot nozzle spray devices are used, but one or of course three or more nozzles may be used. It was found that application by droplet spraying in multiple stages reduces the drying load and at the same time increases the film thickness uniformity.

  Using the coating method of the present invention, the coating speed when forming a thin film on an object to be coated varies depending on the type, concentration, solvent content, drying ability, etc. of the coating solution to be used. Although not possible, the coating speed is preferably 50 to 500 m / min, more preferably 100 to 300 m / min.

  As a coating time when coating is performed on an object to be coated having at least one component layer on the support using the coating method of the present invention, the component layer formed on the support is subjected to reduction rate drying or later. Preferably, after the end point of drying. Moreover, it is preferable that the coating process performed by using the slide nozzle coating and the like and the coating process performed by using the slot nozzle spray device of the present invention are continuously performed on the same production line (online coating and say). Since the coating method according to the present invention can be applied even with a small amount of a coating solution, even if it is performed in a state where the constituent layer is not completely dried, the drying load is small, and there is also an adverse effect on the constituent layer. Few. It has also been found that the application of the present invention before the constituent layer is completely dried can prevent the disadvantages such as cracking of the constituent layer.

  Since the coating method of the present invention has a small drying load, it can be carried out in the drying step of the constituent layers. In the drying step, it is usually preferable to dry the coating film in a wet state by blowing dry air controlled to a specific temperature and humidity condition from the front surface or the back surface thereof while continuously conveying the coating film.

  The drying process of the wet coating film can be classified mainly as follows. In the initial stage of drying, it is called a constant rate drying section, and water and solvent, which are solvents of the coating solution, evaporate while taking away latent heat of evaporation, so that the surface temperature of the constituent layers is almost constant. This period of constant temperature is called a constant rate drying section. After the constant rate drying section, the water and the solvent that interact with the solute of the coating solution are evaporated, so that energy for solving the interaction is required in addition to the latent heat of vaporization, so that the surface temperature rises. This period is referred to as a reduced rate drying unit. Decreasing drying is a phenomenon that occurs when the evaporation of the solvent from the surface excels the moisture transfer in the coating film in the layer. Next, when the reduction rate drying is completed, a region where the temperature of the drying air coincides with the surface temperature of the inkjet recording paper is entered. This point is called the drying end point.

  The confirmation method of the constant rate drying unit, the reduction rate drying unit, and the drying end point described above is not particularly limited. For example, the surface temperature is monitored, and the region where the surface temperature is constant is defined as the constant rate drying unit, the surface The point in time when the temperature rising region becomes the same as the reduction rate drying unit and the drying temperature can be obtained as the drying end point.

  As another method, a water content meter can be installed in each region, the water content of the coating film can be monitored, and the region where the water content decrease curve becomes flat can be defined as the drying end point.

  The viscosity of the coating solution in the coating method of the present invention is preferably 0.1 to 250 mPa · s. More preferably, it is 0.1-50 mPa * s. More preferably, it is 0.1-20 mPa * s.

  The coating method of the present invention can form a thin layer uniformly and can be applied to a wide range of fields, for example, formation of an antireflection film that imparts a functional layer to the outermost surface of a general silver salt photosensitive material, Although it can be used for the application of a charge generation layer, a charge transport layer, and application on an inkjet recording paper of a photoreceptor used in electrophotography, it is particularly preferably applied to application of an overcoat layer on an inkjet recording paper. It is.

  An inkjet recording paper to which the coating method of the present invention can be preferably applied has a porous ink absorbing layer containing a hydrophilic binder and fine particles as a constituent layer on a support, and an overcoat layer formed thereon by the coating method of the present invention. Is provided.

  The porous ink absorbing layer is mainly formed from fine particles and a hydrophilic binder. As the fine particles, fine particle silica synthesized by a vapor phase method is preferably used, and as the hydrophilic binder, polyvinyl alcohol or the like is preferably used.

  As the support used for such an ink jet recording paper, a water-absorbing support (for example, paper) or a non-water-absorbing support can be used. From the viewpoint of obtaining a higher-quality print, An ionic support is preferred. As such a support, there is a paper support in which both sides of paper are laminated with a polyolefin resin.

  The coating liquid for the porous ink absorption layer (for the constituent layer) containing the polyvinyl alcohol and fine particle silica tends to be low viscosity at high temperature and high viscosity at low temperature. Therefore, after coating the water-soluble coating liquid on the support, it is preferable to cool the coating liquid and increase the viscosity significantly.

  The coating temperature of the porous ink absorbing layer is generally 30 to 60 ° C., and the cooling temperature after coating may be such that the coating film temperature is approximately 20 ° C. or less, and particularly 15 ° C. or less. It is preferable to do.

  The cooling step can be performed by passing a zone cooled to, for example, 15 ° C. or lower after the coating for a certain period of time (preferably 5 seconds or more). At the time of cooling, it is preferable not to blow too strong wind from the viewpoint of obtaining a uniform and uniform coating without causing liquid twist.

  Once cooled, even if a strong wind is blown, the coating liquid itself is thickened, so that the liquid twist is less likely to occur, and the generation of the liquid twist can be suppressed even if the strong wind is blown. Moreover, although the temperature of the strong wind to blow can blow the wind of 20 degreeC or more, it is preferable to raise the temperature of a wind gradually.

  The drying step after applying the coating liquid for the porous ink absorbing layer on the support is performed by blowing air, passing through a zone in a high temperature state, or using both in combination.

  When drying by passing through a high temperature zone, it passes through a drying zone of 50 to 150 ° C. At this time, it is preferable to select an appropriate drying temperature in consideration of the heat resistance of the support and the adverse effect on the coating film. The drying wind is usually carried out with a relative humidity of 10 to 50%, preferably 15 to 40%. Although depending on the wet film thickness, the drying time is preferably within about 10 minutes, and particularly preferably within 5 minutes.

  The coating speed depends on the wet film thickness and the drying capacity of the equipment, but is generally 10 to 1000 m per minute, preferably 20 to 500 m.

  The method for applying the coating liquid for the porous ink absorbing layer can be appropriately selected from known methods, for example, gravure coating method, roll coating method, rod bar coating method, air knife coating method, extrusion coating. The extrusion coating method using a hopper described in US Pat. No. 2,681,294 is preferably used.

  Next, the coating liquid for the overcoat layer when the overcoat layer is provided on the porous ink absorbing layer of the inkjet recording paper using the slot nozzle spray device of the present invention will be described below.

  The coating liquid for the overcoat layer is characterized by containing a function-imparting compound for the surface of the constituent layer of the ink jet recording paper.

  Organic or inorganic acids whose pH changes depending on the use of the function-imparting compound, or various alkaline additives, water-soluble salts of water-soluble polyvalent metal ions, various anionic, cationic, amphoteric or nonionic surface activity Agents, anti-fading agents, cationic fixing agents, crosslinking agents for hydrophilic binders, and the like.

  Examples of acids that can be used for the purpose of lowering the film surface pH of the porous ink absorbing layer include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, citric acid, formic acid, acetic acid, phthalic acid, succinic acid, oxalic acid, poly Mention may be made of organic acids such as acrylic acid.

  Examples of the alkali used for the purpose of increasing the film surface pH of the porous ink absorption layer include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, borax, sodium phosphate, calcium hydroxide, and organic amine. Is mentioned.

  The pH adjusting agent is particularly preferred when the pH in the coating solution for forming a porous film is different from the preferred film surface pH of the recording medium.

  The film surface pH of the porous ink absorbing layer of the recording medium varies depending on the type of ink, but generally the water resistance and bleeding of the dye are improved on the acidic side, but the light resistance is improved on the higher pH side. Therefore, the optimum pH is selected in combination with the ink to be used. The membrane surface pH of the porous surface is preferably 3 to 7, and particularly preferably 3.5 to 6.5. The film surface pH referred to here is J.I. It is a value measured in accordance with the paper surface pH measurement method specified in TAPPI 49. Specifically, 50 μl of pure water (pH = 6.2 to 7.3) is dropped onto the surface of the recording medium, and is commercially available. The value measured using a plane electrode.

  The function-imparting compound may be a surfactant.

The surfactant can control the dot diameter during ink jet recording, and examples of such a surfactant include anionic, cationic, amphoteric, and nonionic surfactants. Moreover, 2 or more types of surfactant can also be used together. The addition amount of the surfactant is approximately 0.01 to 50 mg per 1 m ² of the recording medium. If it exceeds 50 mg, it tends to cause uneven spots during ink jet recording.

  The function-imparting compound may be a hydrophilic binder crosslinking agent.

  As such a cross-linking agent, known ones can be used, and preferred are the aforementioned boric acids, zirconium salts, aluminum salts or epoxy-based cross-linking agents.

The function-imparting compound may be an image stabilizer (hereinafter also referred to as an anti-fading agent). The anti-fading agent suppresses fading caused by light irradiation and fading caused by various oxidizing gases such as ozone, active oxygen, NO _x , and SO _x .

  As the function-imparting compound, a cationic polymer can be used.

In general, the cationic polymer acts as a dye fixing agent and is preferably added in advance to a coating solution for forming a porous receiving layer in order to prevent water resistance and bleeding, but is added to the coating solution. If a problem occurs, the overcoat method can be used. For example, when a cationic polymer is added to increase the viscosity of the coating solution over time or to improve the color developability by providing a distribution of the cationic polymer in the porous layer, it is supplied by an overcoat method. It is preferable. When the cationic polymer is supplied by the overcoat method, the amount is generally in the range of 0.1 to 5 g per 1 m ^{2 of} the recording medium.

  The function-imparting compound may be a water-soluble polyvalent metal compound.

  Water-soluble polyvalent metal compounds generally tend to agglomerate when present in a coating solution containing inorganic fine particles, and this tends to cause minor coating failure and loss of glossiness. preferable.

Examples of such polyvalent metal compounds include sulfates such as Mg ₂ ⁺ , Ca ₂ ⁺ , Zn ₂ ⁺ , Zr ₂ ⁺ , Ni ₂ ⁺ and Al ₃ ⁺ , chlorides, nitrates and acetates. It is done.

  Each of the above functionality-imparting compounds can be used alone or in combination of two or more. Specifically, it is also possible to use an aqueous solution containing two or more types of anti-fading agent, a solution containing an anti-fading agent and a crosslinking agent, a solution containing an anti-fading agent and a surfactant, and further a crosslinking agent, an aqueous solution. The polyvalent metal compound and anti-fading agent can also be used in combination.

  The solvent for the functional compound can be water or a mixed solution of water-miscible organic solvent and water, and it is particularly preferable to use water. A mixed solvent of water and a water-miscible low-boiling organic solvent (for example, methanol, ethanol, i-propanol, n-propanol, acetone, methyl ethyl ketone, etc.) is also a preferable solvent. When water and a water-miscible organic solvent are used in combination, the content of water is preferably 50% by mass or more by mass ratio.

  Here, the low-boiling organic solvent having water miscibility refers to an organic solvent having a solubility of 10% by mass or more with respect to water at room temperature and a boiling point of about 120 ° C. or lower.

  The surface tension of the coating solution used in the coating method of the present invention is preferably 20 to 60 mN / m at room temperature from the viewpoint of obtaining uniform coating properties.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1
<< Preparation of the object 1 to be coated >>
A substrate 1 to be coated, which was formed on a support using a four-layered porous ink absorbing layer as a constituent layer, was prepared.

(Production of support)
Low density polyethylene having a density of 0.92 was applied to the back side of a photographic base paper having a water content of 6% and a basis weight of 200 g / m ² by a thickness of 35 μm by extrusion coating. Next, a low density polyethylene containing 5.5% anatase-type titanium oxide on the surface side and having a density of 0.92 was applied by extrusion coating with a thickness of 40 μm to prepare a support having both sides coated with polyethylene. Corona discharge was performed on the front side, the undercoating layer made of polyvinyl alcohol was 0.03 g / m ² , and the corona discharge was also performed on the back side, and then the latex layer was applied at 0.12 g / m ² .

(Preparation of each dispersion)
(Preparation of silica dispersion 1)
Using a jet stream inductor mixer TDS manufactured by Mitamura Riken Kogyo Co., Ltd., 160 kg of gas phase method silica (Tokuyama: Leolosil QS-20) having an average primary particle size of about 12 nm, the pH is adjusted to 2. After suction-dispersing in 480 L of pure water (containing 10 L of ethanol) adjusted to 5 at room temperature, the entire amount was finished with 600 L with pure water to prepare silica dispersion 1.

(Preparation of silica dispersion 2)
Stir 60.0 L of the silica dispersion 1 in 15 L of an aqueous solution (pH = 2.3) containing 2.12 kg of the cationic polymer (HP-1), 2.2 L of ethanol, and 1.1 L of n-propanol. Then, 8.0 L of an aqueous solution containing 320 g of boric acid and 190 g of borax was added, and 200 ml of an aqueous solution containing 2 g of Sanbuco Co., Ltd. antifoam SN381 was added.

  This mixed liquid was dispersed with a high-pressure homogenizer manufactured by Sanwa Kogyo Co., Ltd., and the entire amount was finished to 85 L with pure water to prepare silica dispersion 2.

(Preparation of oil dispersion)
210 kg of an aqueous gelatin solution containing 20 kg of diisodecyl phthalate and 20 kg of an antioxidant (AO-1) heated in 45 kg of ethyl acetate and containing 8 kg of acid-treated gelatin, 2.9 kg of the cationic polymer HP-1 and 5 kg of saponin; After mixing at 55 ° C. and emulsifying and dispersing with a high-pressure homogenizer, the entire amount was finished to 300 L with pure water to prepare an oil dispersion.

[Preparation of coating liquid for ink absorbing layer]
Each coating solution for an ink absorbing layer having the following constitution was prepared. In addition, the addition amount of each layer was displayed by the quantity per 1L of coating liquids. In the examples, “%” represents mass% unless otherwise specified.

<First layer coating solution: bottom layer>
Silica dispersion 2 580ml
Polyvinyl alcohol (Kuraray Co., Ltd .: PVA203) 10% aqueous solution 5 ml
6.5% aqueous solution of polyvinyl alcohol (average polymerization degree: 3800 saponification degree 88%)
290ml
Oil dispersion 30ml
Latex dispersion (Showa Polymer Co., Ltd .: AE803) 42ml
8.5 ml of ethanol
Finish the whole volume with pure water to 1000ml <Second layer coating solution>
Silica dispersion 2 600ml
Polyvinyl alcohol (Kuraray Co., Ltd .: PVA203) 10% aqueous solution 5 ml
6.5% aqueous solution of polyvinyl alcohol (average polymerization degree: 3800 saponification degree 88%)
270ml
Oil dispersion 20ml
Latex dispersion (Showa Polymer Co., Ltd .: AE803) 22ml
8 ml of ethanol
Finish the whole volume to 1000ml with pure water <Coating liquid for third layer>
Silica dispersion 2 630ml
Polyvinyl alcohol (Kuraray Co., Ltd .: PVA203) 10% aqueous solution 5 ml
6.5% aqueous solution of polyvinyl alcohol (average polymerization degree: 3800 saponification degree 88%)
270ml
Oil dispersion 10ml
Latex dispersion (Showa Polymer Co., Ltd .: AE803) 5ml
Ethanol 3ml
Finish the whole volume to 1000ml with pure water. <Fourth layer coating solution: top layer>
Silica dispersion 2 660ml
Polyvinyl alcohol (Kuraray Co., Ltd .: PVA203) 10% aqueous solution 5 ml
6.5% aqueous solution of polyvinyl alcohol (average polymerization degree: 3800 saponification degree 88%)
250ml
3% 4% aqueous solution of betaine surfactant
2 ml of 25% aqueous solution of saponin
Ethanol 3ml
Finish the whole volume to 1000ml with pure water.

[Application of ink absorbing layer]
Next, four layers are simultaneously formed on the support at 40 ° C. using a coating line consisting of the steps shown in FIG. It apply | coated and the to-be-coated body 1 was produced.

<Wet film thickness>
First layer: 42 μm
Second layer: 39 μm
Third layer: 44 μm
Fourth layer: 38 μm
After applying the ink absorbing layer coating liquid, the film surface temperature is decreased to 13 ° C. by passing through a cooling zone maintained at 5 ° C. for 15 seconds, and then the following temperature winds are sequentially applied to the surface of the ink absorbing layer. While spraying, each zone of the drying step 30 was passed through and dried.

  The total drying step was 360 seconds, and the average relative humidity of the blowing wind was 30% or less for the first 270 seconds. After 270 seconds, the humidity was adjusted to a relative humidity of 40 to 60%.

《Overcoat implementation》
[Preparation of Sample 101]
(Preparation of overcoat solution 1)
An aqueous solution containing 1.0% by mass of the following water-soluble dye was prepared, and this was designated as overcoat solution 1.

(Overcoat)
In the coating line shown in FIG. 13 (using the second half of the overcoat zone shown in FIG. 13 and having one coater), the slot nozzle spray device having the configuration shown in FIG. A comb-like shim is attached, and the overcoat liquid 1 prepared above is applied onto the prepared object 1 so that the coating speed is 150 m / min and the wet film thickness is 10.0 μm. Was designated as Sample 101. The shim shown in FIG. 5 used for coating 101 has a coating liquid discharge part length L ₁ of 0.15 mm, a distance L ₂ between the coating liquid discharge parts of 0.35 mm, and a shim substrate thickness t. Was 0.15 mm. Further, the distance between the bottom surface of the external die block and the surface of the object to be coated was 2 cm, and the gas supplied from the gas nozzle was air, and was supplied from the gas nozzle at a wind speed of 160 m / sec.

[Production of Samples 102 to 112]
In the preparation of the sample 101, the type of shim shape, the length L _{1 of} the coating liquid discharge part, the distance L ₂ between the coating liquid discharge parts, the depth L ₃ of the coating liquid supply path, and the thickness t of the shim base material are set. Samples 102 to 112 were produced in the same manner except that the changes were made as described in Table 1.

<Evaluation of coating properties>
When the samples 101 to 112 were prepared, the coating liquid flying state and the coating surface quality of the slot nozzle spray device were visually observed, the coating properties were evaluated according to the following criteria, and the obtained results were obtained. Table 1 shows.

◎: The flying of the coating liquid is stable, there is no occurrence of uneven stripes or coating failures, and the coating property is extremely uniform. ○: The generation of extremely weak uneven stripes is observed, but the flying of the coating liquid is stable. Almost good coating uniformity Δ: Slight unevenness is observed, but practically acceptable coating quality ×: Application of the coating solution is unstable, frequent strong unevenness occurs, and lacks uniformity Is quality

As is clear from the results shown in Table 1, the coating method of the present invention using a shim having a plurality of coating liquid discharge portions formed by grooves not penetrating in the thickness direction is free from the occurrence of uneven stripes compared to the comparative example. It can be seen that it has good coating properties. Among the coating methods of the present invention, a shim having a coating liquid discharge part provided on both sides of a shim base material, a shim having an opening ratio (L ₁ / L ₁ + L ₂ ) of 0.2 or more, and between the coating liquid discharge parts It can be seen that a coating method using a shim having a distance L ₂ of 1 mm or less or a shim having a thickness t of 0.5 mm or less has better coating uniformity.

Example 2
<< Preparation of Samples 201-212 >>
In the preparation of the samples 101 to 112 described in Example 1, a 4% boric acid solution having a viscosity of 1.5 mPa · s at 23 ° C. and a surface tension of 60 to 70 mN / m was used as the overcoat layer coating solution. Samples 201 to 212 were produced in the same manner except for the above.

《Image printing and evaluation》
A magenta solid image having a density of about 1.0 is printed on each of the prepared samples with genuine ink using a PM-980C printer manufactured by Seiko Epson Corporation, and the density uniformity of the solid image is visually observed. Then, the uniformity of the image was evaluated, and the results obtained are shown in Table 2.

A: There is no density unevenness, and the image is extremely good. ○: Extremely weak density unevenness is observed, but the image is good. Δ: Weak density unevenness is observed, but an image that is practically acceptable. Quality x: Strong streak-like density unevenness is recognized and the image lacks uniformity.

As is clear from the results shown in Table 2, the sample produced by the coating method of the present invention using a shim having a plurality of coating liquid discharge portions formed by grooves that do not penetrate in the thickness direction is printed on the comparative example. It can be seen that the density uniformity of the obtained image is excellent. Among the samples of the present invention, a shim having a coating liquid discharge part provided on both sides of a shim base material, a shim having an opening ratio (L ₁ / L ₁ + L ₂ ) of 0.2 or more, and a coating liquid discharge part It can be seen that a sample produced by a coating method using a shim having a distance L ₂ of 1 mm or less or a shim having a thickness t of 0.5 mm or less has better image uniformity.

Example 3
In the preparation of the samples 201 to 212 described in Example 2, as a coating solution for the overcoat layer, instead of the 4% boric acid solution, an anti-fading agent (HO-N (C ₂ H ₄ SO ₃ Na) ₂ ) Each sample was prepared in the same manner except that a 4% aqueous solution was used, and after printing a magenta solid image according to the method described in Example 2, the image was stored outdoors for 2 months to evaluate image stability. As a result, it was confirmed that the sample produced according to the coating method of the present invention had excellent image density uniformity with little density unevenness compared to the comparative example.

Example 4
In the production of samples 201 to 212 described in Example 2, the same procedure was performed except that a 4% aqueous solution of a polyvalent metal compound (zirconium acetate) was used as the overcoat layer coating solution instead of the 4% boric acid solution. After each sample was prepared and a magenta solid image was formed according to the method described in Example 2, the bleeding resistance was evaluated by a well-known method. As a result, the sample prepared according to the coating method of the present invention was compared with the comparative example. It was confirmed that the uniformity of the bleeding resistance effect was excellent.

It is the schematic for demonstrating the coating method of this invention. It is a schematic sectional drawing which shows an example of the slot nozzle spray apparatus containing a slot nozzle spray part. It is a schematic diagram explaining the formation and flight state of a slot nozzle spray part and the droplet formed there. It is a disassembled perspective view of the slot nozzle spray part which has the shim which concerns on this invention. It is a figure showing an example of the conventional comb-tooth shaped shim. It is a figure which shows an example of the shim shape which concerns on this invention. It is a figure which shows an example of the shim which formed many groove-shaped coating liquid flow paths in the state which does not penetrate in the thickness direction on both surfaces of the plate-shaped shim base material which concerns on this invention. It is a figure which shows an example of the shim shape which provided the semicircular coating liquid flow path which concerns on this invention. It is a figure which shows an example of the shim shape which provided the triangular coating liquid flow path which concerns on this invention. It is a figure which shows an example of the shim shape which provided the tunnel-shaped circular coating liquid flow path inside the mu base material which concerns on this invention. FIG. 3 is a schematic view showing an example of the slot nozzle spray portion of FIG. 2 viewed from the coating liquid nozzle C side. FIG. 6 is a schematic view showing another example of the slot nozzle spray portion of FIG. 2 viewed from the coating liquid nozzle C side. It is a schematic diagram which shows an example of the coating production line which has arrange | positioned the slot nozzle spray apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Slot nozzle spray part 1d Shim 2a, 2b External die block 2c, 2d Bottom face of external die block 3a, 3b Internal die block 3c, 3d Bottom face of internal die block 4 Adjustment pot 5 Pump 6 Flow meter 7 Pressurized air source 8 Valve DESCRIPTION OF SYMBOLS 9 To-be-coated body 10 Base material 11 Ink absorption layer 12 Droplet particle 13 Coating liquid discharge part 14 Coating liquid flow path wall 20 Slide bead coating device 30 Cooling zone A Gas pocket B Coating liquid pocket C Coating liquid nozzle D Gas nozzle E Coating liquid G Compressed air

Claims (9)

A coating liquid nozzle unit that transports the coated body and supplies a coating liquid over a coating width in a direction that intersects the transport direction of the coated body, and a gas nozzle that ejects gas in the vicinity of the opening of the coating liquid nozzle In a coating apparatus that applies a coating liquid onto the object to be coated by spraying the gas by colliding with the coating liquid to form a droplet by using a slot nozzle spray device having a portion A coating liquid nozzle section for supplying a liquid sandwiches a shim having a plurality of coating liquid discharge sections formed by grooves that do not penetrate in the thickness direction, and supplies the coating liquid from the coating liquid discharge section apparatus. When the length of the coating liquid discharge part in the longitudinal direction of the shim is L ₁ and the distance between the coating liquid discharge parts is L ₂ , the opening ratio (L ₁ / L ₁ + L ₂ ) is 0.2 or more. The coating apparatus according to claim 1, wherein The coating apparatus according to claim 2, wherein a distance L ₂ between the coating liquid discharge units is 1 mm or less. The coating apparatus according to claim 1, wherein a thickness t of the shim is 0.5 mm or less. 5. The coating apparatus according to claim 1, comprising a plurality of coating liquid discharge portions formed by grooves that do not penetrate in the thickness direction on both surfaces of the shim. The coating apparatus according to claim 1, wherein a shape of the coating liquid discharge unit is a square, a rectangle, a semicircle, a triangle, or a circle. The object to be coated is an ink jet recording paper having an ink absorbing layer on a substrate, and the coating liquid contains a function-imparting compound for the ink absorbing layer. The coating apparatus of any one of Claims. 8. The function-imparting compound is at least one selected from a pH adjuster, a surfactant, a hydrophilic binder cross-linking agent, an image stabilizer, and a water-soluble polyvalent metal compound. Coating device. Application | coating method characterized by performing application | coating on a to-be-coated body using the coating device of any one of Claims 1-8.

Images