JP2006346516A - Coating liquid applying method and coating applicator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating liquid applying method and a coating applicator, each of which is used for uniformly applying a coating liquid having low viscosity at room temperature to form a thin coating film. <P>SOLUTION: The coating liquid applying method comprises the steps of: applying a coating liquid (A) containing an inorganic fine particle and a water-soluble binder onto a substrate (9) being conveyed continuously; and applying another coating liquid (B) having 0.1-10 mPa-sec viscosity at 25°C onto the applied coating liquid (A) by using a coater (1). The temperature of the coating liquid (B) to be supplied to the coater (1) is kept within 35-55°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a coating method and a coating apparatus for uniformly coating a low-viscosity coating liquid.

  The ink jet recording method is a method in which fine droplets of ink are ejected by various operating principles and adhered to an ink jet recording material such as paper to record images and characters. It has the advantage that it can be easily colored, and is now rapidly spreading in various fields such as various printers, facsimiles, and computer terminals.

  In particular, ink jet recording materials have been rapidly improved in image quality and approaching photographic image quality. In particular, in order to achieve image quality comparable to that of photographic image quality by inkjet recording, improvements have been made from the aspect of inkjet recording paper, and inorganic fine particles typified by silica and a water-soluble binder on a highly smooth support. A void-type inkjet recording paper provided with a porous ink absorbing layer having a minute void structure made of the above has high gloss, vivid color, and in addition, has excellent ink absorbability and drying properties. Therefore, it is becoming one of the closest to photo quality.

  On the other hand, in the method for producing ink jet recording paper, various properties are required for the porous ink absorbing layer, and in order to improve these various properties, various additives such as those described below are used. Use is suggested.

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 And cationic fixing agent for improving water resistance 6: anti-fading agent for improving fading due to light and oxidizing gas of dye image 7: fluorescent whitening agent and color tone adjustment for improving white background Agents (redness and bluing agents)
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 absorbing 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 such a problem, for example,
A: Coating liquid pot that aggregates between fine particles and additives or phase separation in the coating liquid makes stable coating without unevenness difficult, gloss decreases, and matte Life is shortened and production efficiency is drastically reduced. B: When the prepared coating solution is stagnated for a long time, the coating solution thickens and gels. The liquid easily flows, and as a result, stable coating becomes difficult, and it becomes difficult to obtain a uniform coating film. C: Cracks on the surface increase when the porous ink absorbing layer is applied and dried. D: Porous ink absorbing layer For example, the porosity of the resin is reduced.

  The problems related to the above A and B terms are often based mainly on the electrical interaction of the additive. For example, the cationic fixing agent is the main cause, and reacts with various raw materials having an anionic group. As a result, it causes various problems.

  As one of the solutions to the above problems, the coating liquid for the porous ink absorption layer does not contain the additive, but is first applied as a constituent layer on a support, and then the coating liquid containing the additive is added. A so-called overcoat coating method in which the coating is applied to the upper part of the constituent layer is disclosed (for example, see Patent Document 1). 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 of impregnating the porous ink-absorbing layer with the function-imparting compound is that the overcoat layer itself may be very thin.

  The function required for the coating liquid used for the overcoat application as described above is only necessary to give a new function to the already formed ink absorption layer, and does not reduce the void volume of the ink absorption layer. Need to be low concentration. From such a viewpoint, many coating solutions used for overcoat coating have a relatively low viscosity (for example, a viscosity at 25 ° C. of about 0.1 to 10 mPa · sec). Moreover, it is necessary to apply | coat with a thin film (for example, 1-50 micrometers as a wet film thickness).

  As a method of applying an overcoat layer that requires the above-described characteristics as a thin film, for example, a coating method using a slot nozzle spray device is disclosed (for example, see Patent Document 2). This coating method includes a coating liquid nozzle that transports a base material and supplies a coating liquid over a coating width in a direction that intersects the transport direction of the base material, and a gas nozzle that ejects gas in the vicinity of the opening end of the coating liquid nozzle The coating method is to apply the coating liquid onto the thin film by spraying the gas by colliding the gas with the coating liquid, and spraying the low-viscosity coating liquid under the thin film conditions. It was a suitable method for coating.

In recent years, due to the rapid development of inkjet printers, ink droplets flying from inkjet recording heads have been remarkably advanced from the viewpoint of improving printing speed or improving image quality, and inkjet recorded images are comparable to photographic image quality. It is up to. However, as a result of the progress of miniaturization and high density of ink droplets in such an ink jet printer, even if there is a slight unevenness on the surface of the ink jet recording paper used for printing, the obtained print quality is lowered. The problem has become apparent. Therefore, in order to obtain a high-quality inkjet recording image with extremely high uniformity, various functions for achieving high image quality are imparted to the inkjet recording paper, and a higher coating film uniformity than before. There is a demand for development of an ink jet recording paper having good properties.
JP 2002-331745 A Japanese Patent Laid-Open No. 2004-906

  This invention is made | formed in view of the said subject, The objective is to provide the coating method and coating device which apply | coat a low-viscosity coating liquid uniformly with a thin film at room temperature.

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

(Claim 1)
After coating a coating liquid (A) containing inorganic fine particles and a water-soluble binder on a substrate that is continuously conveyed, a coating liquid (B) having a viscosity at 25 ° C. of 0.1 mPa · sec to 10 mPa · sec is coated. In the coating method of coating using (b), the temperature of the coating liquid (B) supplied to the coater (b) is 35 ° C. or more and 55 ° C. or less.

(Claim 2)
The coating method according to claim 1, wherein the coating liquid (B) is defoamed before being supplied to the coater (b).

(Claim 3)
The absolute value ΔT ₁ of the temperature difference between the temperature T ₁ immediately before the coating liquid (B) is supplied to the coater (b) and the temperature T ₂ of the coater (b) is 10 ° C. or less. The coating method according to claim 1 or 2.

(Claim 4)
The absolute value ΔT ₂ of the temperature difference between the temperature T ₁ immediately before the coating liquid (B) is supplied to the coater (b) and the ambient temperature T _{3 of the} room where the coater (b) is installed is 10 ° C. The coating method according to claim 1, wherein the coating method is as follows.

(Claim 5)
The coating method according to claim 1, wherein the coater (b) is a slot nozzle spray device.

(Claim 6)
A coater for applying a coating solution (B) having a viscosity at 25 ° C. of 0.1 mPa · sec or more and 10 mPa · sec or less onto a substrate on which a coating solution (A) containing inorganic fine particles and a water-soluble binder is applied on a support. (B) and a coating liquid supply source for supplying the coating liquid (B) to the coater (b), the coating liquid from the coating liquid supply source or the coating liquid supply source to the coater (b) The supply apparatus for supplying (B) has a temperature adjusting means, and keeps the coating solution (B) at 35 ° C. or higher and 55 ° C. or lower.

(Claim 7)
The coating apparatus according to claim 6, wherein a defoaming device is provided in the middle of the supply pipe for supplying the coating liquid (B) to the coater (b).

(Claim 8)
The coating apparatus according to claim 6 or 7, wherein the coater (b) includes a temperature adjusting means.

(Claim 9)
The coating apparatus according to any one of claims 6 to 8, wherein a room in which the coater (b) is installed includes a temperature adjusting means.

(Claim 10)
The coating device according to any one of claims 6 to 9, wherein the coater (b) is a slot nozzle spray device.

  ADVANTAGE OF THE INVENTION According to this invention, the coating method and coating device which apply | coat the coating liquid of low viscosity at room temperature uniformly with a thin film can be provided.

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

  As a result of intensive studies in view of the above problems, the present inventor 1) after applying a coating liquid (A) containing inorganic fine particles and a water-soluble binder onto a substrate that is continuously conveyed, the viscosity at 25 ° C. is 0. In the coating method in which the coating liquid (B) of 1 mPa · sec or more and 10 mPa · sec or less is applied using the coater (b), the temperature of the coating liquid (B) supplied to the coater (b) is 35 ° C. The coating method is characterized by being 55 ° C. or lower, or 2) The viscosity at 25 ° C. is 0.1 mPas on a substrate on which a coating liquid (A) containing inorganic fine particles and a water-soluble binder is coated on a support. A coating apparatus having a coater (b) for coating a coating liquid (B) of not less than 10 mPa · sec and a coating liquid supply source for supplying the coating liquid (B) to the coater (b). Liquid source or the The supply pipe for supplying the coating liquid (B) from the cloth liquid supply source to the coater (b) has a temperature adjusting means, and keeps the coating liquid (B) at 35 ° C. or more and 55 ° C. or less. It has been found that a coating method or a coating apparatus for uniformly coating a coating solution having a low viscosity at room temperature with a thin film can be realized by the coating apparatus described above.

  Conventionally, when applying a highly viscous coating liquid that has temperature dependence of viscosity, a close relationship has been known between the temperature of the coating liquid at the time of coating and the quality of the coating film obtained. A wide range of studies have been conducted on various coating conditions for forming a coated film. For example, in the case of application using a low-viscosity coating solution of 0.1 to 10 mPa · sec, the temperature dependence of the viscosity is small, and in many cases, it is considered unnecessary to heat the coating solution or the like. It was done.

  A coating solution having a high viscosity at room temperature, for example, a coating solution containing a water-soluble binder at a high concentration, can be stably coated by greatly reducing the viscosity by heating. Therefore, for example, as described in paragraph [0079] of JP-A No. 2002-331745, it is preferable to apply the coating solution by heating it to a certain temperature. In addition, when the binder used in the coating solution is solidified at room temperature depending on the type and amount thereof, for example, in a coating solution using gelatin or the like as a binder, heating is an indispensable requirement. In the case of application of a hot melt adhesive or the like, for example, as described in JP-A-7-299394, it is proposed to apply using a device for heating and melting a hot melt liquid. The method of heating these coating liquids is a method for reducing the viscosity when a high-viscosity (for example, tens of thousands mPa · sec at room temperature) or solid coating liquid is applied at room temperature.

  On the other hand, if it is a low-viscosity coating solution of about 0.1 to 10 mPa · sec at room temperature, there is no need to heat it separately. In other words, there has been no recognition of the special advantage of heating.

  However, the present inventor paid attention to the wettability and diffusibility of the coating liquid to the substrate in the coating using the low viscosity coating liquid, and as a result of earnestly examining the heat retention effect of the low viscosity coating liquid, Even if it is a liquid, it has been found that by heating the coating liquid, the coating property, particularly the coating unevenness resistance and the coating film uniformity in the direction of the coating width, are dramatically improved.

  As described above, the detailed meganism has not been clarified at the present time regarding the effects on the coating unevenness resistance and the uniformity in the coating width direction by heating the low-viscosity coating liquid at the time of coating. I guess.

  Even with a low-viscosity coating solution, setting the coating solution temperature at the time of coating to a certain temperature makes the coating solution more active in thermal motion and changes the surface tension, etc., as a result. It is presumed that the wettability to the substrate is improved and the coating film formation is stabilized. In addition, by heating the coating liquid to a temperature of, for example, 35 to 55 ° C., it is assumed that leveling of the formed coating film (also referred to as leveling) is likely to occur due to spreading of the coating film even after being applied to the substrate. Is done. Further, in the coating method using a slide hopper coater, a roll coater, a bar coater, etc., it is considered that wetting and spreading are stabilized in the coater or in the region where the coater part and the substrate are in contact with each other. Also, in a coating method using a dip coating method or the like, by heating the coating liquid, convection of the coating liquid becomes active in the liquid holding portion for transferring the coating liquid to the substrate. As a result, the coating liquid Is likely to be uniform. Therefore, it is presumed that a coating method excellent in coating uniformity could be realized by heating the coating solution even if it was a low viscosity coating solution.

  Details of the present invention will be described below.

  In the coating method of the present invention, after the ink absorbing layer coating liquid, which is a coating liquid (A) containing inorganic fine particles and a water-soluble binder, is coated on the substrate to form the ink absorbing layer, the viscosity at 25 ° C. The coating liquid (B) of 0.1 mPa · sec or more and 10 mPa · sec or less is heated in a range of 35 ° C. or more and 55 ° C. or less and supplied to the coater (b) for application, From the viewpoint of further improving the coating quality, it is preferable to heat the coating solution (B) in the range of 38 ° C. or higher and 50 ° C. or lower, and in the range of 40 ° C. or higher and 45 ° C. or lower. Particularly preferred. If the temperature at which the coating liquid (B) is heated is 30 ° C. or higher, the effect of uniforming the coating by heating can be sufficiently exerted, and if it is 55 ° C. or lower, unnecessary heating energy is not required. In addition, coating nonuniformity due to convection of the coating solution is not caused, and a highly uniform coating film can be obtained stably.

  Next, an overall outline of a coating process to which the coating method or the coating apparatus of the present invention is applied will be described.

  FIG. 1 shows an example of a coating production line in which a coater (b) for applying a low-viscosity coating liquid (B) of 0.1 mPa · sec or more and 10 mPa · sec or less according to the present invention is arranged. In the present invention, as an object to be coated, an ink absorbing layer is formed by applying a coating liquid (A) containing inorganic fine particles and a water-soluble binder on a substrate using a coater (a) as a first coating machine. Use things. A plurality of (multi-stage) coaters (b) were arranged in the step of drying after applying the ink absorbing layer. In this way, continuously forming the ink absorbing layer and applying the overcoat layer (outermost layer) by the coater (b) according to the present invention on the same line is called online coating.

  Pores supplied from the flow rate regulation type coater (a) 20 in the process of passing the support roller 21 from the original winding of the support body by a transport means (not shown) and then 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 water-soluble binder, it is cooled once in the cooling zone 30 and fixed. The substrate 9 having the ink absorption layer on the support is conveyed to the drying process. In the drying process, a reverser 23 that reversely conveys air without blowing it to the surface of the coating film and an ordinary conveying roller 24 that reversely conveys while contacting the back surface of the coated body 9 are provided alternately. Is meandering. In this drying step, hot air is blown to dry (the hot air blowing means is not shown). Application by the two coaters (b) 1 is performed in the middle of the drying process, preferably at a position after the decreasing rate drying. At this time, the temperature of the coating liquid (B) applied by the coater (b) is heated in the range of 38 ° C. or higher and 50 ° C. or lower.

  Of the two coaters (b), at least one is preferably placed at a position after the drying end point from the viewpoint of drying properties. Although FIG. 1 shows an example in which two coaters (b) are used, one may naturally be used, or different types of functional compounds may be applied using three or more coaters (b). . It was found that by performing the coating in multiple stages, the drying load is reduced and the film thickness uniformity is also increased.

  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.

  When the coating liquid (B) is applied by the coater (b) on the substrate having at least one ink absorbing layer on the support using the coating method of the present invention, the support is used. It is after the reduction rate drying of the ink absorbing layer formed above, preferably after the drying end point. Moreover, it is preferable that the coating process performed by using the coater (a) and the coating process performed by the coater (b) according to the present invention are continuously performed on the same production line.

  Since the coating method of the present invention can be applied even with a small amount of coating liquid, the drying load is small even when the ink absorbing layer is not completely dried, and the adverse effect on the ink absorbing layer is also small. . In addition, it is preferable to perform coating by the coating method of the present invention before the ink absorbing layer is completely dried, in order to prevent disadvantages such as cracking of the formed ink absorbing layer.

  Since the coating method of the present invention has a small drying load, it can be carried out even during the drying step of the ink absorbing layer. 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.

  In FIG. 1, the coater (a) used for applying the coating liquid (A) containing inorganic fine particles and a water-soluble binder on the substrate is not particularly limited, and conventionally, the coating liquid is applied on the substrate. An applicator known as a method can be applied. For example, as a method of applying the coating liquid (A) with high accuracy onto a long belt-like substrate to be conveyed (hereinafter also simply referred to as a substrate), “MODERN COATING AND DRYING TECHNOLOGY” by Edward Cohen, Edgar Gutoff. Various methods have been proposed, such as dip coating, blade coating, air knife coating, wire bar coating, gravure coating, reverse coating, reverse roll coating, ext A rhodium coating method, a slide bead coating method, a curtain coating method, or the like can be applied. Also, a slide bead coating method proposed by Russell et al. In US Pat. No. 2,761,791, an extrusion coating method, etc., and a curtain coating method can also use a flow regulation type coating method using a die. .

  The coater (b) used for coating the coating liquid (B) having a viscosity at 25 ° C. of 0.1 mPa · sec to 10 mPa · sec and a temperature of 35 ° C. to 55 ° C. according to the present invention is described above. In addition to various coating machines applicable to the coater (a), a coating method using a reverse roll coater, a gravure roll coater, or a slot nozzle spray device from the viewpoint of stably coating a low-viscosity coating solution with a thin film. Among these, a coating method using a slot nozzle spray device is particularly preferable from the viewpoint of stably forming a highly uniform coating film.

  FIG. 2 is a schematic view showing an example of a reverse roll coater applicable to the present invention.

  The reverse roll coater 101 includes a backup roller 112, a casing 113, an applicator roller 114, a metering roller 115, and a collection roller 116.

  The backup roller 112 is provided with adjusting means including a solenoid for adjusting the distance between the backup roller 112 and the applicator roller 114. Here, the film thickness of the coating liquid P applied to the sheet-like base material B can be changed depending on the relationship between the transport speed of the base material B and the peripheral speed of the applicator roller 114.

  The casing 113 accommodates the coating liquid P therein and is disposed on the backup roller 112. In the casing 113, substantially L-shaped blades 129 are attached to both front and rear sides of the lower extraction port 128. The casing 113 is provided with a stirring means 130 for stirring the coating solution P. The stirring means 130 includes a drive motor 131 and a wing member 132 immersed in the coating liquid P in the casing 113.

  The applicator roller 114 is disposed at the center of the extraction port 128 of the casing 113 so as to be opposed to the backup roller 112, and is in a Y direction opposite to the conveyance direction X of the sheet base material B by a conveyance unit (not shown). It is designed to rotate.

  The metering roller 115 is disposed on the downstream side in the transport direction X at the extraction port 128 of the casing 113 so as to face the applicator roller 114 and to contact the blade 129. The metering roller 115 is rotated in the reverse direction at the nip portion between the metering roller 115 and the applicator roller 114 by a drive motor (not shown) in order to make the amount of the coating liquid P dispensed in the casing 113 constant.

  The coating liquid P extruded from between the applicator roller 114 and the metering roller 115 is applied to the surface of the base material B by a roll coating method. Further, on the collection roller 116 side, the gap with the applicator roller 114 is in an open state, and the coating liquid P remaining on the surface of the applicator roller 114 due to the rotation of the collection roller 116 is not leaked from the gap, and the casing. It is collected in 113.

  FIG. 3 is a schematic view showing an example of a gravure roll coater applicable to the present invention.

  A backup roll 202 is disposed at a position corresponding to the application position of the base material B so as to contact one surface of the base material B. The backup roll 202 is provided with adjusting means including a solenoid 221 for adjusting the distance between the backup roll 202 and the gravure roll.

  Further, a gravure roll 203 is supported on the opposite surface side of the backup roll 202 across the base material B so that the rotation direction thereof is orthogonal to the traveling direction of the base material B. The gravure roll 3 is shown in the figure. The drive motor is driven to rotate in the direction opposite to the traveling direction of the base material B through a coupling. Further, on the outer peripheral surface of the gravure roll 203, a cell pattern (not shown) having a width narrower than the entire width of the base material B is engraved over the entire circumference.

  On the side of the gravure roll 203, there is disposed a coating liquid storage case 204 for storing the coating liquid 7 whose surface facing the gravure roll 203 is open, and on the open surface of the coating liquid storage case 204. Two holders 205 that extend from the lower end of the coating liquid storage case 204 toward the center of the coating liquid storage case 204 and are inclined toward the gravure roll 203 are attached. In each of these holders 205, doctor blades 206 whose tips are in contact with the outer peripheral surface of the gravure roll 203 are arranged symmetrically, and a part of the peripheral surfaces of the doctor blade 206, the holder 205 and the gravure roll 203 is arranged. Thus, a closed space is formed inside the coating liquid storage case 204. The coating liquid storage case 204 is provided with a stirring means 230 for stirring the coating liquid 207. The stirring means 230 includes a drive motor 231 and a wing member 232 immersed in the coating liquid 207.

  By supplying the coating liquid 207 to the inside of the coating liquid storage case 204, the coating liquid 207 is stored inside the coating liquid storage case 204, and in this state, the gravure roll 203 is rotated to drive the gravure roll 203. The coating liquid 207 is applied to the surface, and the doctor blade 206 wipes off the excess coating liquid 207 applied to the cell pattern, and fills the cell pattern of the gravure roll 203 with an appropriate amount of the coating liquid 207 over the entire width. At the same time, the coating liquid 207 on the outer side is also wiped from both ends of the cell pattern.

  As a method of applying the coating liquid 207 using a gravure roll coater, first, the coating liquid 207 is stored inside the coating liquid storage case 204, and the coating liquid in the coating liquid storage case 204 by the wing member 232 of the stirring means 230. 207 is agitated, and the substance that precipitates in the coating liquid 207 is scraped up. The peripheral surface of the engraving part of the gravure roll 203 located in the internal space of the coating liquid storage case 204 is immersed in the coating liquid 207, and the coating liquid 207 is filled and supplied to the inside of the engraving part of the gravure roll 203. Then, by rotating the gravure roll 203 in the clockwise direction in the figure, the doctor blade 206 wipes off the excess coating liquid 207 and fills and supplies only an appropriate amount to the entire width of the cell pattern. The surplus coating liquid 207 is returned to the inside of the coating liquid storage case 204.

  When an appropriate amount of coating liquid 207 is supplied into the cell pattern of the gravure roll 203 in this way, the gravure roll 203 is moved toward the surface of the substrate B, and the cell pattern of the gravure roll 203 is moved to the substrate. The coating liquid 207 in the cell pattern is applied to the surface of the substrate B in contact with the surface of B.

  In the coating method of the present invention, the coating liquid (B) having a viscosity at 25 ° C. of 0.1 to 10 mPa · sec and a temperature of 35 to 55 ° C. according to the present invention is used. As the coater (b), it is particularly preferable to use a slot nozzle spray device from the viewpoint of further achieving the object effect of the present invention. As a slot nozzle spray device preferably used in the present invention, for example, a device described in JP-A-2004-906 can be exemplified.

  Hereinafter, an example of the slot nozzle spray device according to the present invention will be described with reference to the drawings.

  FIG. 4 is a schematic view for explaining a coating method using the slot nozzle spray device according to the present invention.

  In FIG. 4, reference numeral 1 is a slot nozzle spray unit 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. From the coating liquid nozzle C, the coating liquid (B) is sprayed in the form of droplets, and coating is performed by landing the droplets on the object 9 to be transported. At this time, the length to which the coating liquid (B) in the width direction of the substrate 9 is applied corresponds to the coating width indicated by the arrow in the figure. In FIG. 4, the application width is shorter than the length in the width direction of the object 9 to be applied, but it may of course be the same.

  FIG. 5 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. The coating liquid nozzle C is formed in the gas nozzle D 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.

  In FIG. 5, 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. For example, the coating solution (B) such as a function-imparting compound-containing solution having a viscosity (preferably 0.1 to 250 mPa · s) capable of forming droplets without forming a fiber shape is placed in the preparation kettle 4 and the pump 5 Then, it is supplied to the coating liquid pocket B through the decapsulating tank 6 and guided to the coating liquid nozzle 3. 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 coating, the coating liquid (B) is supplied from the preparation kettle 4 so as to have a prescribed coating amount from the coating liquid nozzle C, and at the same time, pressurized air is sprayed from the pair of gas nozzles D to drop the coating liquid (B) into droplets. It is sprayed and deposited on the body 9 to be coated. The coating method of the present invention is characterized in that the viscosity of the coating solution is 0.1 mPa · sec to 10 mPa · sec, and the coating solution is sprayed as fine droplets. 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, the formation and flying state of the slot nozzle spray portion and the droplets formed there will be described with reference to FIG.

  In FIG. 6, the coating liquid E discharged from the coating liquid nozzle C is subdivided into droplets by a compressed air G supplied from a gas nozzle D provided close to both sides of the coating liquid nozzle C. Droplet particles 12 that are close to each other, fly, and land uniformly on the surface of the object 9 across the gap L5. In FIG. 6, the to-be-coated body 9 is shown as a model in which the ink absorbing layer 11 is coated on the substrate 10 as a constituent layer. The area range of the droplets 12 of the coating liquid landing on the substrate 9 is preferably always uniform, but in particular, the drop length in the transport direction (denoted by the drop length L7 in the figure) is applied. Preferably it is uniform across the width. Further, it is preferable that the spread angle θ 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.

  Moreover, in order to spray uniform droplets over the coating width using the above-described slot nozzle spray device, it is preferable to adjust the dynamic surface tension (DST) of the coating liquid to 20 to 55 mN / m, Preferably it is 20-50 mN / m, More preferably, it is 20-40 mN / m.

  Using the slot nozzle spray device or the like, when the gas is collided with the coating liquid to form a droplet, the gas internal pressure is 10 kPa or more, preferably 20 kPa or more, more preferably 50 kPa or more, and uniform spraying is easily performed. . 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.

  In the coating method of the present invention, the coating liquid (B) according to the present invention has a viscosity at 25 ° C. of 0.1 to 10 mPa · sec, and the coating liquid (B) according to the present invention includes It is preferable not to contain a water-soluble binder having an effect of increasing the viscosity. Furthermore, the viscosity is more preferably 0.5 mPa · sec or more and 5.0 mPa · sec or less, and particularly preferably 0.7 mPa · sec or more and 2.0 mPa · sec or less.

  When such a low-viscosity coating liquid is stably applied, by applying the above-described slot nozzle spray device, it is possible to spray droplets uniformly over the coating width. In addition, in order to measure the viscosity of the coating liquid (B) in the present invention, there is no particular limitation as long as it is tested with a viscometer calibration standard liquid specified in JIS Z 8809. A viscometer of a formula or a thin tube type can be used. As a viscometer, it can measure with a Saybolt viscometer, a Redwood viscometer, etc., for example, Tokimec Co., Ltd., a conical plate type E-type viscometer, Toki Sangyo Co., Ltd. E Type Viscometer, Tokyo Keiki Co., Ltd. make No. B type viscometer BL, FVM-80A manufactured by Yamaichi Electronics Co., Ltd., Viscoliner manufactured by Nametore Industries Co., Ltd., VISCO MATE MODEL VM-1A manufactured by Yamaichi Electric Co., Ltd., and VM1G-L.

  In the coating method of the present invention, it is preferable to defoam the coating solution (B) before supplying the coating solution (B) to the coater (b). Moreover, in the coating device of this invention, it is preferable that the defoaming device is provided in the middle of supply piping which supplies a coating liquid (B) to a coater (b).

  Conventionally, in a low-viscosity coating solution, bubbles or the like mixed in the preparation process are easily removed from the coating solution by natural levitation, etc., and there is almost no bubble at the time of coating. It was. However, when the surface of the prepared coated product was inspected in detail, it was found that circular or elliptical coating failures having a diameter of about 1 to 10 mm were sporadic. As a result of detailed examination of this coating failure, it was estimated that the bubbles contained in the coating solution were applied. Therefore, even when such a low-viscosity coating solution is used, it is preferable to perform a defoaming treatment of the coating solution before coating.

  The coating method of the present invention is characterized in that the coating liquid (B) is heated in the range of 35 to 55 ° C. When the coating liquid is heated in this way, the solubility of the gas in the coating liquid Decreases and bubbles are easily generated in the coating solution. For this reason, in the coating method in which the coating solution is heated to a certain temperature as in the present invention, it is preferable to perform defoaming treatment before coating.

  Before the coating liquid (B) is supplied to the coater (b) in the present invention, for example, in FIG. 5, the slot nozzle spray unit 1 (coater ( b)) refers to the period until it is supplied, and it is preferable to install a decapsulation tank 6 between the pump 5 and the slot nozzle spray section 1 as shown in FIG. Further, the defoaming time is to defoam within 15 minutes from immediately before feeding the coating liquid (B) to the coater (b) (several seconds to several tens of seconds before), and more preferably the coating liquid ( B) is within 10 minutes immediately before feeding (several seconds to several tens of seconds before), and particularly preferably within 5 minutes from immediately before feeding the coating liquid (B) (several seconds to several tens of seconds before).

  In general, defoaming means, in a narrow sense, separation / removal or dissolution / disappearance of bubbles in a liquid, and in a broad sense, in addition to the narrow meaning, a gas such as air once dissolved in a liquid once again in a use stage. The operation to prevent the phenomenon of appearing as bubbles is also included.

  In the narrow sense, defoaming is achieved by performing either one or both of the operations of removing bubbles or dissolving and extinguishing bubbles.

  As described above, there are two types of processes for defoaming, but either one may be selected, two processes may be performed simultaneously, or a separation and removal process may be performed after the dissolution and extinction process. For example, only the large bubbles may be separated and removed in the first process, and then only the small bubbles that could not be separated and removed in the first process may be dissolved and extinguished.

  In the defoaming process as described above, as a method for separating and removing only relatively large bubbles, centrifugal defoaming method for removing bubbles in the liquid using centrifugal force, or ultrasonic energy is applied to the liquid in the liquid. May include the ultrasonic defoaming method for fusing together bubbles, dissolving the fine bubbles, or depressurizing the container containing the coating solution to float and remove the bubbles in the solution. it can. Examples of the method for dissolving and extinguishing fine bubbles in the liquid include the ultrasonic defoaming method and the pressure defoaming method described above. In the present invention, the characteristics of the coating liquid (B) to be used are described. Depending on the situation, it can be appropriately selected.

  In the coating method of the present invention, when the coating liquid (B) is applied using the coater (b), the temperature of the environment in which the coating liquid (B) and the coater (b) or the coater (b) are installed. The difference is preferably defined within a specific range.

As one temperature regulation condition, the absolute value ΔT ₁ of the temperature difference between the temperature T ₁ immediately before supplying the coating liquid (B) to the coater (b) and the temperature T ₂ of the coater (b) is set to 10 ° C. or less. From the viewpoint of improving the coating film quality, it is more preferably 5 ° C. or lower, and particularly preferably 0 ° C. to 3 ° C.

As another temperature regulation condition, the temperature difference between the temperature T ₁ immediately before the coating liquid (B) is supplied to the coater (b) and the environmental temperature T _{3 of the} room where the coater (b) is installed. The absolute value ΔT ₂ is preferably 10 ° C. or lower, and more preferably 5 ° C. or lower, particularly preferably 0 ° C. to 3 ° C. from the viewpoint of further improving the coating film quality.

By setting the absolute value ΔT _{1 of} the temperature difference and the absolute value ΔT ₂ of the temperature difference as defined above, the temperature change in the process of coating from the preparation of the coating liquid (B) can be suppressed to a low level. As a result, stable application can be realized.

The coating apparatus of the present invention has a coating liquid supply source for supplying the coating liquid (B) to the coater (b), and the coating liquid (B) is applied to the coater (b) from the coating liquid supply source or the coating liquid supply source. The supply pipe to be supplied has a temperature adjusting means. By this temperature adjusting means, the absolute value ΔT _{1 of} the temperature difference and the absolute value ΔT ₂ of the temperature difference specified above are the conditions of 10 ° C. or less. Can be controlled.

  The coating liquid supply source as used in the present invention is the adjustment pot 4 for preparing the coating liquid (B) as shown in FIG. 5 or a stock tank that is temporarily stored before coating, and the coater (b) from the coating liquid supply source. The supply pipe for supplying the coating liquid (B) to the pipe means a pipe line from the coating liquid discharge port at the bottom of the preparation kettle 4 shown in FIG. 5 to the supply port of the slot nozzle spray unit 1 (coater (b)). .

  There are no particular restrictions on the temperature control method for these coating liquid supply sources and supply pipes, but a method of providing a heat insulation jacket on the outer periphery of the coating liquid supply source and supply pipe and circulating cold water or hot water inside the heat insulation jacket Alternatively, a method of controlling the coating liquid (B) to a desired temperature by wrapping a ribbon heater around the outer periphery of the coating liquid supply source or the supply pipe can be mentioned.

  Examples of the temperature control method of the coater (b) include a method of circulating hot water in the coater (b) or the outer periphery, a method of providing a ribbon heater or the like in the coater (b) or the outer periphery, and the like. However, from the viewpoint that the temperature of the entire coater (b) becomes uniform, a method of circulating hot water inside the coater is preferable.

  Moreover, the temperature of the coating liquid (B) as used in the field of this invention means the temperature of the coating liquid (B) just before supplying to a coater (b), and this temperature is measured suitably by installing a thermometer in the line. be able to.

The ambient temperature T _{3 of the} room in which the coater (b) is installed is an average temperature of the coating chamber measured within 1 m from the point where the coater (b) is installed. More preferably, the temperature is controlled uniformly. At this time, the room in which the coater (b) is installed is preferably a room provided with air conditioning equipment having a temperature adjustment function.

  Next, the configuration of the coating liquid (B) will be described in detail.

  In the coating method of the present invention, there is no particular limitation on the coating liquid to be applied to the coated body using the slot nozzle spray device according to the present invention, but the function for the porous ink absorbing layer of the ink jet recording paper described later is used. It preferably contains an imparting compound.

  Although there is no restriction | limiting in particular as a function provision compound with respect to a porous ink absorption layer, It may be at least 1 chosen from the crosslinking agent of a hydrophilic binder, an image stabilizer, a water-soluble polyvalent metal compound, a mordant, and a pH adjuster. preferable.

  Acids that can be used for the purpose of lowering the film surface pH of the porous ink absorbing layer include, for example, 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 absorbing 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 preferable when the pH of the coating solution for forming a porous film is different from the preferable film surface pH of the recording paper.

  The film surface pH of the porous ink absorbing layer of the recording paper 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 paper, and is commercially available. The value measured using a plane electrode.

  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, it is generally in the range of 0.1 to 5 g per 1 m ^{2 of} recording paper.

  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, which can easily cause minor coating failures 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, a cross-linking agent, 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 function-imparting compound may be a mordant.

  In the present invention, a compound containing an aluminum atom can be suitably used as a mordant. The compound containing an aluminum atom may be any of a single salt and double salt of an inorganic acid or an organic acid, an organic metal compound, a metal complex, etc., but a polyaluminum chloride compound, a polyaluminum sulfate compound, a polyaluminum sulfate silicate Particularly preferred are compounds.

The polyaluminum chloride compound is represented by the general formula [Al ₂ (OH) _n Cl _6-n ] m, [Al (OH) ₃ ] n · AlCl ₃ , for example, [Al ₆ (OH) ₁₅ ] ³⁺ , [Al ₈ (OH) ₂₀ ] ⁴⁺ , [Al ₁₃ (OH) ₃₄ ] ⁵⁺ and other basic and highly positively charged polynuclear condensed ions (polymeric) as active ingredients, It is a polyaluminum chloride containing stably.

Examples of commercially available products of polyaluminum chloride include polyaluminum hydroxide (Paho) manufactured by Asada Chemical Co., Ltd., polyaluminum chloride (PAC) manufactured by Taki Chemical Co., Ltd., and Pukeram manufactured by Riken Green Co., Ltd. WT. The polyaluminum sulfate compound is represented by the general formula [Al ₂ (OH) _n (SO ₄ ) _{6-n / 2} ] m (where 0 <n <6). Examples include basic aluminum sulfate (AHS) manufactured by Chemical Co., Ltd. As a commercial item of a polysulfuric acid aluminum silicate compound, PASS made from Nippon Light Metal Co., Ltd. is mentioned.

  In the coating method of the present invention, the coated body has a porous ink absorbing layer mainly composed of inorganic fine particles and a water-soluble binder on a substrate.

  Examples of inorganic fine particles that can be used in the present invention include light calcium carbonate, heavy calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc hydroxide, and zinc sulfide. , Zinc carbonate, hydrotalcite, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, alumina, colloidal alumina, pseudoboehmite, aluminum hydroxide, lithopone, zeolite, magnesium hydroxide, etc. A white inorganic pigment etc. can be mentioned. Moreover, each may be used independently and multiple types may be used together.

  In the present invention, from the viewpoint of obtaining a high-quality print on an inkjet recording paper, the inorganic fine particles are preferably alumina, pseudoboehmite, colloidal silica, or fine particle silica synthesized by a gas phase method, and fine particles synthesized by a gas phase method. Silica is particularly preferred. The silica synthesized by this vapor phase method may have a surface modified with Al. The Al content of vapor-phase process silica whose surface is modified with Al is preferably 0.05 to 5% by mass with respect to silica.

  The particle size of the inorganic fine particles is preferably 30 nm or less as an average primary particle size for obtaining a structure having a large porosity, and particularly preferably 3 to 10 nm for enhancing the transparency of the film.

  The average particle size of the inorganic fine particles is obtained as a simple average value (number average) by observing the cross section and surface of the porous material layer with an electron microscope and determining the particle size of 100 arbitrary particles. Here, each particle size is expressed by a diameter assuming a circle equal to the projected area.

  The hydrophilic binder that can be used in the porous ink absorbing layer according to the present invention is not particularly limited, and examples thereof include polyvinyl alcohol, gelatin, polyethylene oxide, polyvinyl pyrrolidone, polyacrylic acid, polyacrylamide, polyurethane, and dextran. , Dextrin, color ginnan (κ, ι, λ, etc.), agar, pullulan, water-soluble polyvinyl butyral, hydroxyethyl cellulose, carboxymethyl cellulose and the like.

  Polyvinyl alcohol is particularly preferable as the hydrophilic binder. The polyvinyl alcohol preferably used in the present invention includes, in addition to ordinary polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate, modified polyvinyl alcohol such as polyvinyl alcohol having a cation-modified terminal and anion-modified polyvinyl alcohol having an anionic group. Alcohol is also included.

  As the polyvinyl alcohol obtained by hydrolyzing vinyl acetate, those having an average degree of polymerization of 1000 or more are preferably used, and those having an average degree of polymerization of 1500 to 5000 are particularly preferably used.

  The saponification degree is preferably 70 to 100%, particularly preferably 80 to 99.5%.

  Examples of the cation-modified polyvinyl alcohol include a polyvinyl alcohol having a primary to tertiary amino group or a quaternary ammonium group in the main chain or side chain of the polyvinyl alcohol, as described in, for example, JP-A-61-110483. The alcohol is obtained by saponifying a copolymer of an ethylenically unsaturated monomer having a cationic group and vinyl acetate.

  Examples of the ethylenically unsaturated monomer having a cationic group include trimethyl- (2-acrylamide-2,2-dimethylethyl) ammonium chloride, trimethyl- (3-acrylamide-3,3-dimethylpropyl) ammonium chloride, N-vinylimidazole, N-vinyl-2-methylimidazole, N- (3-dimethylaminopropyl) methacrylamide, hydroxylethyltrimethylammonium chloride, trimethyl- (2-methacrylamidopropyl) ammonium chloride, N- (1,1 -Dimethyl-3-dimethylaminopropyl) acrylamide and the like.

  The ratio of the cation-modified group-containing monomer of the cation-modified polyvinyl alcohol is usually 0.1 to 10 mol%, preferably 0.2 to 5 mol%, relative to vinyl acetate.

  Examples of the anion-modified polyvinyl alcohol include polyvinyl alcohol having an anionic group as described in JP-A-1-206088, JP-A-61-237681, and JP-A-63-307979. Examples thereof include a copolymer of vinyl alcohol and a vinyl compound having a water-soluble group, and modified polyvinyl alcohol having a water-soluble group as described in JP-A-7-285265.

The amount of inorganic fine particles used in the ink absorption layer depends largely on the required ink absorption capacity, the porosity of the void layer, the type of inorganic fine particles, and the type of hydrophilic binder, but in general, per 1 m ² of recording paper, Usually 5 to 30 g, preferably 10 to 25 g.

  The ratio of the inorganic fine particles and the hydrophilic binder used in the ink absorbing layer is usually 2: 1 to 20: 1 by mass ratio, and particularly preferably 3: 1 to 10: 1.

  The substrate that can be used in the present invention may be a water-absorbing support or a non-absorbing support, but a non-water-absorbing support is used from the viewpoint of obtaining a higher-quality print. It is preferable.

  The non-absorbent support preferably used in the present invention is a transparent polyester film, an opaque polyester film, an opaque polyolefin resin film, and a paper support in which both surfaces of paper are laminated with a polyolefin resin.

  A paper support laminated with such a polyolefin resin will be described below.

  The base paper used for the paper support is made from wood pulp as a main raw material, and if necessary, paper is made using synthetic pulp such as polypropylene or synthetic fiber such as nylon or polyester in addition to wood pulp. As wood pulp, any of LBKP, LBSP, NBKP, NBSP, LDP, NDP, LUKP, and NUKP can be used, but it is preferable to use more LBKP, NBSP, LBSP, NDP, and LDP with a large amount of short fibers. However, the ratio of LBSP and / or LDP is preferably 10% by mass to 70% by mass.

  The pulp is preferably a chemical pulp (sulfate pulp or sulfite pulp) with few impurities, and a pulp having a whiteness improved by bleaching is also useful.

  In the base paper, sizing agents such as higher fatty acids and alkyl ketene dimers, white pigments such as calcium carbonate, talc and titanium oxide, paper strength enhancing agents such as starch, polyacrylamide and polyvinyl alcohol, fluorescent whitening agents, polyethylene glycols A water retaining agent such as a dispersant, a softening agent such as a quaternary ammonium, and the like can be appropriately added.

  The freeness of pulp used in papermaking is preferably 200 to 500 ml as defined by CSF, and the fiber length after beating is 24% by mass as defined in JIS-P-8207, and 42 mesh residue. The sum of 30% and 70% by mass is preferable. In addition, it is preferable that the mass% of 4 mesh remainder is 20 mass% or less.

  The basis weight of the base paper is preferably 30 to 250 g, particularly preferably 50 to 200 g. The thickness of the base paper is preferably 40 to 250 μm.

The base paper can be given high smoothness by calendering at the paper making stage or after paper making. The density of the base paper is generally 0.7 to 1.2 g / cm ³ (JIS-P-8118). Furthermore, the base paper stiffness is preferably 20 to 200 g under the conditions specified in JIS-P-8143.

  A surface sizing agent may be applied to the surface of the base paper. As the surface sizing agent, a sizing agent similar to the size that can be added to the base paper can be used.

  The pH of the base paper is preferably 5 to 9 when measured by the hot water extraction method defined in JIS-P-8113.

  The polyethylene covering the front and back surfaces of the base paper is mainly low-density polyethylene (LDPE) and / or high-density polyethylene (HDPE), but some other LLDPE, polypropylene, etc. can also be used.

  In particular, the polyethylene layer on the ink absorbing layer side is preferably one in which rutile or anatase type titanium oxide is added to polyethylene to improve opacity and whiteness, as is widely done in photographic paper. The content of titanium oxide is usually 3% by mass to 20% by mass, preferably 4% by mass to 13% by mass with respect to polyethylene.

  Polyethylene-coated paper can be used as glossy paper. Also, when polyethylene is melt-extruded on the surface of the base paper and coated, a so-called molding process is performed to form a matte or silky surface that can be obtained with ordinary photographic paper. These can also be used in the present invention.

  In the polyethylene-coated paper, the moisture content in the paper is particularly preferably maintained at 3% by mass to 10% by mass.

  Various additives can be added to the porous ink absorbing layer according to the present invention. For example, polystyrene, polyacrylates, polymethacrylates, polyacrylamides, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, or copolymers thereof, or organic latex fine particles such as melamine resin, cation or Nonionic surfactants, UV absorbers described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, JP-A-57-74192, JP-A-57-87989, JP-A-60- No. 72785, 61-146591, anti-fading agents described in JP-A-1-95091 and JP-A-3-13376, JP-A-59-42993, 59-52689, 62-280069 , 61-242871, and JP-A-4-219266. Such as fluorescent brighteners, sulfuric acid, phosphoric acid, citric acid, sodium hydroxide, potassium hydroxide, potassium carbonate, pH adjusters, antifoaming agents, preservatives, thickeners, antistatic agents, matting agents, etc. Various known additives can also be contained.

  The temperature at which the porous ink absorbing layer is applied on the non-absorbing support is generally 30 to 60 ° C., and the cooling temperature after coating is about 20 ° C. or less. In particular, the temperature is preferably set to 15 ° C. or lower.

  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.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

Example 1
<Preparation of recording paper 101>
(Production of support)
1 part by mass of polyacrylamide, 4 parts by mass of ash (talc), 2 parts by mass of cationized starch and 0. 0% of polyamide epichlorohydrin resin per 100 parts by mass of wood pulp (LBKP / NBSP = 50/50). Slurry liquid containing 5 parts by mass and various addition amounts of alkyl ketene dimer (sizing agent) was prepared, and a base paper was made with a long paper machine so that the basis weight was 170 g / m ² . After calendering this, a low-density polyethylene resin having a density of 0.92 containing 7% by mass of anatase-type titanium oxide and a small amount of a color tone adjusting agent was melt extruded at a temperature of 320 ° C. to a thickness of 28 μm. One side of the paper was coated and cooled immediately with a mirror cooling roller. Then, the opposite surface is coated with a mixed melt of high density polyethylene with a density of 0.96 / low density polyethylene with a density of 0.92 = 70/30 by the same melt extrusion method to a thickness of 32 μm. did.

  The surface on the side where the ink absorbing layer is provided had a 60 ° glossiness of 56% and a centerline average roughness Ra of 0.12 μm.

After corona discharge on the titanium oxide-containing layer side of the support, 0.05 g / m ² of gelatin was applied as an undercoat layer.

  On the other side, a styrene / acrylic emulsion containing silica fine particles (matting agent) having an average particle diameter of about 1.0 μm and a small amount of cationic polymer (conductive agent) has a dry film thickness of about 0.5 μm. Thus, a support for applying the ink absorbing layer was prepared.

  On the back surface side, the glossiness was about 18%, the centerline average roughness Ra was about 4.5 μm, and the Beck smoothness was 160 to 200 seconds.

  The moisture content of the base paper of the support thus obtained was 7.0 to 7.2%.

The support had an opacity of 96.5% and whiteness of L ^* = 95.2, a ^* = 0.56, and b ^* = − 4.35.

[Preparation of ink absorbing layer coating solution]
According to the following procedure, a coating liquid for an ink absorbing layer having the following composition was prepared.

(Preparation of titanium oxide dispersion 1)
20 kg of titanium oxide having an average particle size of about 0.25 μm (Ishihara Sangyo: W-10), 150 g of sodium tripolyphosphate with pH = 7.5, 500 g of polyvinyl alcohol (Kuraray Co., Ltd .: PVA235), cationic polymer (P-1) was added to 90 L of an aqueous solution containing 150 g and 10 g of the defoaming agent SN381 from Sannobuco, and dispersed with a high-pressure homogenizer (manufactured by Sanwa Kogyo Co., Ltd.). A titanium dispersion 1 was obtained.

(Preparation of silica dispersion 1)
Water 71L
Boric acid 0.27kg
Borax 0.24kg
Ethanol 2.2L
Cationic polymer (P-1) 25% aqueous solution 17L
Anti-fading agent (AF1 * 1) 10% aqueous solution 8.5L
Optical brightener aqueous solution (* 2) 0.1L
The entire amount was finished to 100 L with pure water.

  As inorganic fine particles, 50 kg of vapor phase method silica (average primary particle diameter of about 12 nm) is prepared, and the above additives are added thereto, followed by dispersion by the dispersion method described in Example 5 of JP-A-2002-47454. Thus, a silica dispersion 1 was obtained.

* 1: anti-fading agent (AF-1) HO-N (C 2 H 4 SO 3 Na) 2
* 2: UVITEX NFW LIQUID manufactured by Ciba Specialty Chemicals
(Preparation of silica dispersion 2)
In the preparation of the silica dispersion 1, the silica dispersion 2 was prepared in the same manner except that the cationic polymer (P-1) was changed to the cationic polymer (P-2).

(Preparation of ink absorbing layer coating solution)
The coating liquid for each ink absorption layer of the first layer, the second layer, the third layer, and the fourth layer was prepared by the following procedure.

<Coating liquid for first layer>
The following additives were sequentially mixed with 610 ml of silica dispersion 1 while stirring at 40 ° C.

5% aqueous solution of polyvinyl alcohol (Kuraray Industrial Co., Ltd .: PVA235)
220ml
5% aqueous solution of polyvinyl alcohol (Kuraray Industrial Co., Ltd .: PVA245)
80ml
Titanium oxide dispersion 30ml
15 ml of polybutadiene dispersion (average particle size: about 0.5 μm, solid content: 40%)
Surfactant (SF1) 5% aqueous solution 1.5ml
The whole amount was finished to 1000 ml with pure water.

<Second layer coating solution>
The following additives were sequentially mixed with 630 ml of silica dispersion 1 while stirring at 40 ° C.

5% aqueous solution of polyvinyl alcohol (Kuraray Industrial Co., Ltd .: PVA235)
180ml
5% aqueous solution of polyvinyl alcohol (Kuraray Industrial Co., Ltd .: PVA245)
80ml
15 ml of polybutadiene dispersion (average particle size: about 0.5 μm, solid content: 40%)
The whole amount was finished to 1000 ml with pure water.

<Coating liquid for third layer>
The following additives were sequentially mixed with 650 ml of silica dispersion 2 while stirring at 40 ° C.
5% aqueous solution of polyvinyl alcohol (Kuraray Industrial Co., Ltd .: PVA235)
180ml
5% aqueous solution of polyvinyl alcohol (Kuraray Industrial Co., Ltd .: PVA245)
80ml
The whole amount was finished to 1000 ml with pure water.

<Fourth layer coating solution>
The following additives were sequentially mixed with 650 ml of silica dispersion 2 while stirring at 40 ° C.

5% aqueous solution of polyvinyl alcohol (Kuraray Industrial Co., Ltd .: PVA235)
180ml
5% aqueous solution of polyvinyl alcohol (Kuraray Industrial Co., Ltd .: PVA245)
80ml
Saponin 50% aqueous solution 4ml
Surfactant (SF1) 5% aqueous solution 6ml
The whole amount was finished to 1000 ml with pure water.

  Each coating solution prepared as described above was subjected to two-stage filtration with a filter capable of collecting 20 μm.

  Each of the above coating solutions is 30 to 80 mPa · s at 40 ° C. and 30000 to 100,000 mPa.s at 15 ° C. The viscosity characteristic of s was shown.

[Preparation of Overcoat Liquid 1 (Coating Liquid (B))]
Overcoat liquid 1 was prepared by sequentially adding and dissolving the following additives in 500 ml of stirring water.

Water-soluble dye Basonyl Red 560 (manufactured by BASF) 3.0 g
Surfactant (Nissin Chemical Orphine E1010) 3.0g
Finish up to 1000 ml with water.

  The viscosity of this overcoat liquid 1 was 1.0 mPa · s at 25 ° C., the static surface tension was 35 mN / m, and the dynamic surface tension was 40 mN / m.

  The dynamic surface tension (DST) is measured by using BP2 made by Cruz at a coating solution temperature of 25 ° C., and continuously generating bubbles, and measuring the value of the surface tension at 50 ms by the bubble pressure method. did. Moreover, the surface tension value by the platinum plate method at the time of 25 degreeC was measured for the static surface tension (SST) using the surface tension meter (Kyowa Interface Science make: CBVP-Z). The viscosity was measured using a vibration viscometer (manufactured by Yamaichi Denki: VM1G-L).

[Application]
The coating production line shown in FIG. 1 was used, the coater (a) used a four-layer curtain coater, and the coater (b) used only one slot nozzle spray device shown in FIGS. In addition, the slot nozzle spray device is provided with temperature control means using cold / hot water, and the overcoat liquid adjustment kettle is provided with a temperature control jacket on the outer peripheral portion thereof to enable temperature control. Further, the supply pipe from the preparation kettle to the supply port of the slot nozzle spray device is provided with a heat insulation jacket on the outer peripheral portion thereof so that arbitrary temperature control can be performed. Further, the coating area where the slot nozzle spray device is arranged is provided with a partition to be an independent coating chamber, and the entire coating chamber can be controlled to a predetermined temperature. Note that in the production of the recording paper 101, the defoaming tank shown in FIG.

  Using the coating production line as described above, the coating liquid for each ink absorbing layer prepared above was coated on the front side of the support coated on both sides with the polyolefin prepared above on the first layer (35 μm) and the second layer (45 μm). Each layer was simultaneously applied so that the third layer (45 μm) and the fourth layer (40 μm) were in this order. In addition, the numerical value in the parenthesis of each layer shows each wet film thickness. The coating was carried out simultaneously at a coating width of about 1.5 m and a coating speed of 150 m / min using a four-layer curtain coater at 40 ° C. for each ink absorbing layer coating solution.

  Immediately after coating, the film is cooled for 20 seconds in a cooling zone maintained at 8 ° C., then 20 to 30 ° C., relative humidity 20% or less for 30 seconds, 60 ° C., relative humidity 20% or less for 120 seconds, 55 ° C., relative humidity 20%. It dried by blowing each drying wind for 60 seconds below.

  Next, using the slot nozzle spray device having the structure shown in FIGS. 4 to 6 as the drying end point of the ink absorbing layer, the overcoat liquid temperature is 5 ° C., the slot nozzle spray device temperature is 25 ° C., and the overcoat coating is performed. The chamber temperature was set to 25 ° C., and the above-prepared overcoat liquid 1 was applied onto the multilayer ink absorption layer at a coating speed of 150 m / min, a wet film thickness (hw) of 10.0 μm, and a liquid outlet linear velocity of the overcoat liquid 1 Coating was performed under the condition of 62.5 cm / sec to produce a recording paper 101.

  In the slot nozzle spray device, the coating liquid nozzle has a 40 μm slit shape, the gas nozzle has a 150 μm wide slit shape, the angle formed by the bottom surface of the external die block is 180 degrees, and the coating liquid discharge port of the coating liquid nozzle and the gas nozzle gas The angle formed by the discharge ports was 30 degrees, the bottom surface of the external die block was 40 mm, and the distance between the bottom surface of the external die block and the surface of the coated body was 10 mm. The gas supplied from the gas nozzle was air, and was supplied from the gas nozzle at an air volume of 200 m / sec.

[Preparation of recording sheets 102 to 111]
In the production of the recording paper 101, the recording paper was similarly prepared except that the temperature at the time of supplying the overcoat liquid 1 (coating liquid (B)) to the coater (b) was changed as shown in Table 1. 102-111 were produced.

[Preparation of recording sheets 112 and 113]
In the production of the recording sheets 107 and 111, an ultrasonic defoaming tank (Bronson ultrasonic wave) is provided between the pump 5 of the supply pipe and the coating liquid supply port to the overcoat liquid 1 as shown in FIG. Recording sheets 112 and 113 were produced in the same manner except that the transmitter was installed at the bottom of the defoaming tank and the defoaming process was started 5 minutes before supplying the overcoat liquid 1 to the coater (b).

<Evaluation of recording paper>
Each of the produced recording papers was evaluated for uneven coating resistance and foam failure resistance according to the following methods.

[Evaluation of uneven coating resistance]
Each of the prepared recording sheets is cut into a size of 3 cm in length and 3 cm in width, read by a scanner (Epson ES-8000), converted into density by a scanner data vs density conversion table prepared in advance, and further obtained separately. From the relationship between the amount of dye and the concentration of the dye, the amount was converted to an RMS, and the RMS of the amount of change at 300 points was calculated by the following formula (1).

  In the formula, Xi represents each concentration value, X represents a concentration average value, and n represents the number of measurement points.

  This is a quantification of coating unevenness from the mean square of the density difference at each point with respect to the average density. The smaller the coating unevenness, the smaller the RMS value. In the present invention, from the correlation between the RMS calculated value and the visual evaluation, if the RMS value is 3.0 or less, it is determined that there is no practical problem.

[Evaluation of foam failure resistance]
Each of the recording papers was applied three times, the coating surface was observed for each of the recording papers for 5 m and a total of 15 m, and the number of occurrences of density variation portions having a circular or elliptical shape with a diameter of 1 to 10 mm was measured. The foam failure resistance was evaluated according to the criteria of

A: No circular or elliptical failure was found B: One circular or elliptical failure occurred C: Two or five circular or elliptical failures occurred D: Circular or Six or more elliptical faults have occurred. In the above evaluation, the acceptable quality level is A or B.

  The results obtained as described above are shown in Table 1.

  From the results shown in Table 1, even in a low-viscosity overcoat solution, the occurrence of coating unevenness is reduced and the coating uniformity is improved by heating the temperature of the coating solution to 35 to 55 degrees. I understand. It can also be seen that there is no occurrence of a circular or elliptical failure by further defoaming treatment.

Example 2
<< Preparation of recording sheets 201-209 >>
In the preparation of the recording sheet 112 as described in Example 1, changes the retained temperature of the slot nozzle spray device (coater (b)), the coating liquid between the temperature T ₂ of the temperature T ₁ of the coater (B) (b) Recording sheets 201 to 209 were produced in the same manner except that the absolute value ΔT ₁ of the temperature difference was changed as shown in Table 2.

<Evaluation of recording paper>
The recording paper 112 produced in Example 1 and the produced recording papers 201 to 209 were evaluated in the same manner as in Example 1 for evaluation of coating unevenness resistance and bubble failure resistance, and in accordance with the following method. The coating uniformity was evaluated.

[Evaluation of width application uniformity]
Each recording sheet is cut out in a conveyance direction of 3 cm × application width direction of 140 cm, data is read for 100 points with a scanner (Epson ES-8000), and converted into a density using a scanner data vs density conversion table prepared in advance. Further, the amount was converted from the relationship between the amount of the dye and the concentration obtained separately. Next, the maximum value, the minimum value, and the average value of the converted weights were obtained for 100 measurement points, and the fluctuation range was calculated according to the following formula.

Fluctuation width = [(maximum weight value−minimum weight value) / average weight value] × 100 (%)
If the fluctuation range was within 7%, it was judged that there was no practical problem.

  The results obtained as described above are shown in Table 2.

As apparent from the results shown in Table 2, warmed coater (b), the absolute value [Delta] T ₁ of the temperature difference between the temperature T ₂ of the temperature T ₁ of the coater of the coating solution (B) (b) 10 It can be seen that by setting the temperature to not higher than 5 ° C., preferably not higher than 5 ° C., particularly preferably 0 ° C., good coating unevenness resistance and foam failure resistance can be maintained, and the uniform coating uniformity can be further improved.

Example 3
<< Preparation of recording sheets 301-309 >>
In the production of the recording paper 205 described in Example 2, the air conditioning temperature of the coating chamber in which the slot nozzle spray device (coater (b)) is installed is changed, and the temperature T ₁ of the coating liquid (B) and the coater (b The recording sheets 301 to 309 were prepared in the same manner except that the absolute value ΔT ₂ of the temperature difference from the environmental temperature T ₃ of the coating chamber in which () was installed was changed as shown in Table 3.

<Evaluation of recording paper>
For the recording paper 204 produced in Example 2 and the produced recording papers 301 to 309, evaluation of coating unevenness resistance, bubble failure resistance and width application uniformity was performed in the same manner as in the methods described in Examples 1 and 2. The results obtained are shown in Table 3.

As is apparent from the results shown in Table 3, the air conditioning temperature of the coating chamber in which the coater (b) is installed is changed, and the temperature T ₁ of the coating liquid (B) and the coating in which the coater (b) is installed. By maintaining the absolute value ΔT ₂ of the temperature difference from the ambient temperature T _{3 of the} room to 10 ° C. or less, preferably 5 ° C. or less, particularly preferably 0 ° C., it is possible to maintain good coating unevenness resistance and foam failure resistance, It can be seen that the application uniformity of the width is further improved.

Example 4
<< Preparation of recording sheets 401-405 >>
Table 4 shows the type and temperature of the coater (b), the temperature at which the coating liquid (B) is supplied to the coater (b), and the air conditioning temperature of the coating chamber in the production of the recording paper 305 described in Example 3. Recording sheets 401 to 405 were produced in the same manner except that the combination was changed.

  The reverse roll coater used for producing the recording sheets 402 and 403 uses the coater shown in FIG. 2, and the gravure roll coater used for producing the recording sheets 404 and 405 uses the coater shown in FIG. did.

<Evaluation of recording paper>
With respect to the recording paper 305 produced in Example 3 and the recording papers 401 to 405 produced above, the coating unevenness resistance and width application uniformity were evaluated in the same manner as in the methods described in Examples 1 and 2, and obtained. Table 4 shows the results.

  As is apparent from the results shown in Table 4, the temperature of the coating liquid (B) is 35 to 55 degrees even when a reverse roll coater or a gravure roll coater is used as the coater (b) in addition to the slot nozzle spray device. It can be seen that by heating to a high temperature, results of excellent coating unevenness resistance and wide coating uniformity can be obtained. Among various coaters, it can be seen that excellent effects can be obtained particularly when a slot nozzle spray device is used.

Example 5
In each of the coating methods described in Examples 1 to 4, each overcoat solution containing a hydrophilic binder cross-linking agent, an image stabilizer, and a water-soluble polyvalent metal compound as a functional compound instead of an aqueous dye solution. And the same coating was performed.

  As a result of performing the same performance evaluation on each of the obtained recording papers, the coating method of the present invention is similar to the comparative example in that the coating method of the present invention has coating unevenness resistance and uniform width coating. It was confirmed that the coating performance was improved, coating failure was reduced, and stable and good film surface performance could be obtained.

It is the schematic which shows an example of the coating production line which has arrange | positioned the coater (b) which apply | coats the low-viscosity coating liquid (B) based on this invention. It is the schematic which shows an example of the reverse roll coater applicable to this invention. It is the schematic which shows an example of the gravure roll coater applicable to this invention. It is the schematic for demonstrating the coating method using the slot nozzle spray apparatus which concerns on this invention. It is a schematic sectional drawing which shows an example of the slot nozzle spray apparatus containing the slot nozzle spray part demonstrated in FIG. It is a schematic diagram explaining the formation and flight state of a slot nozzle spray part and the droplet formed there.

Explanation of symbols

1 Slot nozzle spray section (coater (b))
2a, 2b External die block 2c, 2d Bottom surface of external die block 3a, 3b Internal die block 3c, 3d Bottom surface of internal die block 4 Adjustment hook 5 Pump 6 Defoaming tank 7 Pressurized air source 8 Valve 9 Substrate 10 Base Material 11 Ink absorbing layer 12 Droplet particle 20 Coater (a)
DESCRIPTION OF SYMBOLS 30 Cooling zone A Gas pocket B Coating liquid pocket C Coating liquid nozzle D Gas nozzle E Coating liquid G Compressed air 101 Reverse roll coater 111 Conveying means 112 Backup roller 113 Casing 114 Applicator roller 115 Metalling roller 116 Collection roller 201 Gravure roll coater 202 Backup roll 203 Gravure roll 204 Coating solution storage case 205 Holder 206 Doctor blade 207 Coating solution 230 Stirring means

Claims (10)

After coating a coating liquid (A) containing inorganic fine particles and a water-soluble binder on a substrate that is continuously conveyed, a coating liquid (B) having a viscosity at 25 ° C. of 0.1 mPa · sec to 10 mPa · sec is coated. In the coating method of coating using (b), the temperature of the coating liquid (B) supplied to the coater (b) is 35 ° C. or more and 55 ° C. or less. The coating method according to claim 1, wherein the coating liquid (B) is defoamed before being supplied to the coater (b). The absolute value ΔT ₁ of the temperature difference between the temperature T ₁ immediately before the coating liquid (B) is supplied to the coater (b) and the temperature T ₂ of the coater (b) is 10 ° C. or less. The coating method according to claim 1 or 2. The absolute value ΔT ₂ of the temperature difference between the temperature T ₁ immediately before the coating liquid (B) is supplied to the coater (b) and the ambient temperature T _{3 of the} room where the coater (b) is installed is 10 ° C. The coating method according to claim 1, wherein the coating method is as follows. The coating method according to claim 1, wherein the coater (b) is a slot nozzle spray device. A coater for applying a coating solution (B) having a viscosity at 25 ° C. of 0.1 mPa · sec or more and 10 mPa · sec or less onto a substrate on which a coating solution (A) containing inorganic fine particles and a water-soluble binder is applied on a support. (B) and a coating liquid supply source for supplying the coating liquid (B) to the coater (b), the coating liquid from the coating liquid supply source or the coating liquid supply source to the coater (b) The supply apparatus for supplying (B) has a temperature adjusting means, and keeps the coating solution (B) at 35 ° C. or higher and 55 ° C. or lower. The coating apparatus according to claim 6, wherein a defoaming device is provided in the middle of the supply pipe for supplying the coating liquid (B) to the coater (b). The coating apparatus according to claim 6 or 7, wherein the coater (b) includes a temperature adjusting means. The coating apparatus according to any one of claims 6 to 8, wherein a room in which the coater (b) is installed includes a temperature adjusting means. The coating device according to any one of claims 6 to 9, wherein the coater (b) is a slot nozzle spray device.

Images