JP2003275664A - Coating method, coated product, and ink-jet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating method for forming a thin film at a high coating speed with excellent drying property, to provide a product coated by the coating method, and to provide an ink-jet recording medium. <P>SOLUTION: In the coating method for applying a coating liquid to a substrate, the substrate has at least one constituent layer on a support and the coating method comprises a step of applying the coating liquid to the constituent layer by using a reverse roll coater after decreasing the rate of drying of the constituent layer after application of the constituent layer on a support. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method for coating a coating solution using a reverse roll, a coating product coated and manufactured using the coating method, and an inkjet recording medium.

[0002]

2. Description of the Related Art Conventionally, various methods for coating a coating liquid on a substrate have been known. For example, as a method for applying a coating liquid on a long strip-shaped substrate (hereinafter, also simply referred to as a substrate) that is conveyed with high accuracy, Edward Cohen, E
dgar Gutoff "MODERN COATI
NG AND DRYING TECHNOLOGY "
Various methods have been proposed, as described in
For example, a dip coating method, a blade coating method, an air knife coating method, a wire bar coating method, an extrusion coating method, a slide bead coating method, a curtain coating method and the like are known. Then, in these coating methods, in order to obtain a uniform dry film thickness in the width direction of the substrate with high accuracy, pay attention to the coating film thickness accuracy (after coating and before drying), uniformity, etc. during coating, Applying.

Among these coating methods, a coating apparatus having a flow rate controlling die is capable of high-speed, thin-film and multi-layer simultaneous coating, and is characterized by its photographic light-sensitive material, ink jet recording material, magnetic recording material and the like. It is widely used as a coating device.

As a preferable example thereof, Russel
The slide bead coating device proposed by US Pat. No. 2,761,791, the extrusion coating device, etc. are widely used. Also, the curtain coating device is a flow regulation type coating device having a die,
Widely used as well.

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 through this bead. Further, in the case of a curtain coating apparatus, coating is performed by allowing a curtain-shaped coating liquid film to freely fall from the coating apparatus and positioning the substrate at the drop destination. They are,
It is very useful to obtain a uniform dry film thickness with high accuracy.

However, in principle, the coating by means of the coating device having these dies is to continuously connect the coating device such as beads and curtain films between the coating device and the substrate with the coating liquid. To form a coating film of uniform thickness on a substrate,
The coating liquid flow rate from the coating device is always constant and must not be interrupted. That is, in order to continuously form the coating film and to keep the coating film thickness constant with high accuracy, a predetermined amount or more of the coating liquid is required. Therefore, in these methods, it is difficult to extremely reduce the amount of the coating liquid discharged from the coating device for the purpose of obtaining a uniform film thickness.

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

However, if the amount of solvent is increased, the load (drying load) for removing the solvent and drying after coating increases,
Not preferable in terms of production efficiency. Also, the amount of solvent is large,
If it takes a long time to dry, when another constituent layer exists below the coating layer, the coating solution for the coating layer may excessively penetrate and diffuse into the constituent layer, which may have an adverse effect.

Therefore, as a thin film coating method, there is a demand for a coating method having high accuracy of coating film thickness, less drying load, and high productivity.

There are various coating products which require the provision of such a thin film having a uniform coating film thickness with high accuracy on the constituent layers. For example, the following void type recording medium for ink jet is used. Can be mentioned.

The recording medium used in the ink jet recording method has an ink absorbing layer which is a paper itself such as plain paper, or an ink absorbing layer on a support which also serves as an absorbent such as coated paper. There are those coated, or those coated with an ink absorbing layer on a non-absorbent support such as resin-coated paper or polyester film.

Among them, a recording medium of a type in which an ink absorbing layer is coated on a non-absorbent support has a high glossiness, a glossy feeling, and a deep feel because of the high surface smoothness of the support and the small waviness. It is preferably used for output that requires high-quality texture such as silver salt photography. Furthermore, as a glossy recording medium having a 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 support, A so-called void type recording medium is used as an ink absorbing layer in which a fine void structure is formed by a pigment or a pigment and a binder and the ink is absorbed in the voids.

In the void type recording medium, the porous ink absorbing layer having this void structure is mainly composed of a hydrophilic binder and fine particles, and as the fine particles, inorganic or organic fine particles are known. Generally, fine inorganic particles having high gloss are used. By using a relatively small amount of hydrophilic binder with respect to the fine particles, voids are formed between the fine particles and a porous ink absorption layer is obtained.

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

1: To achieve high color developability and gloss,
Stable fine particles forming a porosity of about 0.1 μm or less 2: High retention of fine particles and low swelling hydrophilic binder for not lowering ink absorption speed 3: Ink absorption speed and water resistance of coating film Crosslinking agent for hydrophilic binder for improvement 4: Surfactant or hydrophilic polymer distributed on the surface to achieve optimum dot diameter 5: Cationic fixing agent for improving dye bleeding and water resistance 6: Anti-fading agent for improving fading of dye image due to light or oxidizing gas 7: Optical brightening agent and color tone adjusting agent for improving white background (reddish or bluing agent) 8: Surface Matting agent or slip agent for improving slipperiness 9: various oil components or latex particles or water-soluble plasticizer 10 for imparting flexibility to the porous ink absorption layer 10: bleeding of dye, water resistance or weather resistance Breaks Various inorganic salts for (polyvalent metal salt) 11: acid, alkali, etc. for adjusting the surface pH of the porous ink absorbing layer.

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

As such problems, for example, A: agglomeration occurs between fine particles and additives, or phase separation occurs in the coating liquid, which makes it difficult to perform stable coating without unevenness. There are problems such as a decrease in gloss and mattization, a shortened pot life of the coating liquid, and a significant decrease in production efficiency. B: If the prepared coating liquid is stagnated for a long time, the coating liquid will thicken significantly. Gelling or conversely significantly reducing the viscosity, the coating solution easily flows on the support, resulting in difficulty in stable coating and difficulty in obtaining a uniform coating C: coating porous ink absorption layer When dried, cracks on the surface increase. D: Porosity of the porous ink absorption layer decreases. The above problems relating to the items A and B may be mainly due to electrical interaction of the additive. Many, for example, cationic fixatives The main cause is that it reacts with various raw materials having anionic groups, resulting in various problems.

As one of the solutions to the above problems, the coating solution for the porous ink absorbing layer does not contain the above-mentioned additive, but is first coated as a constituent layer on the support, and then contains the above-mentioned additive. A method of forming a so-called overcoat layer, in which the coating liquid is applied to the upper part of the constituent layer, is conceivable. The additive contained in the coating liquid for the overcoat layer is expected to appropriately permeate the constituent layers (for example, the porous ink absorbing layer) provided in advance and to impart a preferable function without causing the above problems. To be done. That is, it is expected to function as a function-imparting compound. Since the purpose is originally to impregnate the porous ink absorbing layer with the function-imparting compound, the overcoat layer itself may be very thin. In addition, it is preferable that it is very thin.

However, in the case of providing two layers of a constituent layer and an overcoat layer, first, the constituent layer is applied and dried, then wound up on a roll and then unreeled again to apply and dry the overcoat layer. If it is performed in two lines, there is a problem that the manufacturing cost increases significantly. In addition, after a certain time has passed after forming the constituent layers, not only problems in quality stability will occur due to variations in temperature history and time, but also problems such as uneven coating tend to occur when the overcoat layer is provided. .

Further, in order to apply the above-mentioned overcoat layer, it is usual to use the extrusion coating method, the slide bead coating method and the curtain coating method using the above-mentioned flow rate controlling die. When using these coating methods to form a highly uniform film thickness, increase the coating film thickness or add a large amount of solvent to the coating solution to establish stable coating conditions. I have to.

As a result, by coating the overcoat layer, a large amount of solvent (water or organic solvent) is further applied to the surface of the ink absorbing layer, and the drying time and the drying zone are extended to increase the cost and the drying ability. If so, the coating speed must be reduced. Furthermore, by applying a thick hot overcoat layer, the degree of diffusion and penetration into the ink absorption layer is large before drying, and it takes time to completely dry the porous ink. There is an effect that an additive is directly added to the coating solution for the layer, and the advantage of the overcoat layer cannot be fully exhibited.

[0022]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems, and an object of the present invention is to provide a coating method for realizing a thin film having a uniform film thickness with high accuracy at high speed and with a low drying load. It is intended to provide a coated product and an inkjet recording medium which are coated and manufactured by the coating method. Also,
It is an object of the present invention to provide a coating method in which, when a thin film is provided on a constituent layer that has already been formed by coating, the constituent layer is not adversely affected and total production efficiency is high. In particular, in coating production of an inkjet recording medium, when an ink absorbing layer was used as a constituent layer and a thin overcoat layer was provided thereon, various properties of the recording medium, coating film uniformity, and coating liquid stability were excellent. It is to provide a coating method.

[0023]

The above object of the present invention has been achieved by the following constitution.

(1) In a coating method of coating a coating liquid on a substrate, the substrate has at least one constituent layer on a support, and after the constituent layer is applied on the support, A coating method comprising applying the coating liquid on the constituent layer using a reverse roll coater after the rate-decreasing drying of the constituent layer.

(2) After the constituent layer is applied onto the support, the coating liquid is applied onto the constituent layer using a reverse roll coater after the drying end point of the constituent layer. The coating method according to (1).

(3) The coating method according to (1) or (2), characterized in that a plurality of the reverse roll coaters are provided in the conveying direction of the substrate and coating is performed in multiple stages.

(4) The viscosity of the coating solution is 0.1 to 25.
It is 0 mPa * s, The coating method as described in any one of (1)-(3) characterized by the above-mentioned.

(5) The viscosity of the coating solution is 0.1 to 50.
The coating method according to any one of (1) to (3), wherein the coating method is mPa · s.

(6) The viscosity of the coating solution is 0.1 to 20.
The coating method according to any one of (1) to (3), wherein the coating method is mPa · s.

(7) The coating according to any one of (1) to (6), wherein the solvent of the coating liquid is water or a mixed solution of water and a water-miscible organic solvent. Method.

(8) The wet film thickness of the coating solution is 1 to 5
It is 0 micrometer, The coating method as described in any one of (1)-(7) characterized by the above-mentioned.

(9) The coating speed of the coating is 50 to 3
It is characterized in that it is 00 m / min (1) to (8)
The coating method according to any one of 1.

(10) The coating method as described in any one of (1) to (9), wherein the coating liquid contains a compound that imparts a function to the constituent layers.

(11) The function-imparting compound is selected from the group consisting of a surfactant, a crosslinking agent for hydrophilic binders, an image stabilizer, and a water-soluble polyvalent metal compound. Application method.

(12) The coating method according to any one of (1) to (11), wherein the coating solution is a coating solution for the outermost layer of an inkjet recording paper.

(13) The coating method according to any one of (1) to (12), wherein the constituent layer is an ink absorbing layer.

(14) The coating method according to any one of (1) to (13), wherein the support is a support having both surfaces of paper coated with a polyolefin resin.

(15) Any one of (1) to (14)
A coated product produced by coating using the coating method according to the item.

(16) Any one of (1) to (14)
An inkjet recording medium produced by coating using the coating method described in the item 1.

As a result of earnest studies, the present inventors have found that in a coating method for coating a coating liquid on a substrate, the substrate has at least one constituent layer on a support, and this constituent layer is provided on the support. After the rate-reduced drying of the applied constituent layer, by applying the coating liquid on the constituent layer using a reverse roll coater, a thin film of uniform thickness can be applied with high accuracy at high speed and with low drying load. I found that I can.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an example of a reverse roll coater 1 used in the present invention. The reverse roll coater 1 generally includes a backup roller 12, a casing 13, an applicator roller 14, and a metering roller 1.
5 and a collection roller 16.

The backup roller 12 is provided with an adjusting means composed of a solenoid 26 for adjusting a gap between the backup roller 12 and an applicator roller 14 which will be described later.
Here, the film thickness of the coating liquid P applied to the sheet base material B can be changed by the relationship between the transport speed of the base material B and the peripheral speed of the applicator roller 14 described later.

The casing 13 contains the coating liquid P therein and is arranged above the backup roller 12. In the casing 13, substantially L-shaped blades 29 are attached to both front and rear sides of a lower end extraction port 28. Further, the casing 13 is provided with a stirring means 30 for stirring the coating liquid P. The stirring means 30 comprises a drive motor 31 and a blade member 32 immersed in the coating liquid P in the casing 13.

The applicator roller 14 is disposed at the center of the extraction port 28 of the casing 13 so as to face the backup roller 12, and is opposed to the conveying direction X of the sheet base material B by a conveying means (not shown). Reverse Y
It is designed to rotate in the direction.

The metering roller 15 faces the applicator roller 14, and the blade 2
9 so that it comes into contact with the outlet port 28 of the casing 13.
Is arranged on the downstream side in the transport direction X in. The metering roller 15 applies the coating liquid P in the casing 13.
In order to make the pouring amount of (1) constant, the driving motors (not shown) rotate in opposite directions at the nip portion with the applicator roller 14. Further, the metering roller 15 is provided with a moving means composed of a solenoid 34, and from a state of being in contact with the applicator roller 14, the applicator roller 14 and a predetermined distance t1 (see FIG. 2).
(See (A)) of FIG.

The collecting roller 16 is arranged on the upstream side of the extraction port 28 of the casing 13 in the carrying direction X so as to face the applicator roller 14. The collecting roller 16 is the applicator roller 1
In order to collect the coating liquid P adhering to the surface of No. 4 in the casing 13 without leakage, the driving motor (not shown) rotates in the same direction at the nip portion with the applicator roller 14. Similarly to the metering roller 15, the collecting roller 16 is provided with a moving means including a solenoid 35, and from the state where the collecting roller 16 is in contact with the applicator roller 14, the applicator roller 14 and a predetermined distance t2 (FIG. 2). (See (A)) of FIG.

When a start switch (not shown) is turned on, the coating liquid supply unit 37 operates and the stirring means 3 is operated.
The coating liquid P in the casing 13 is agitated by the blade member 32 of 0 to scrape up substances and the like that precipitate in the coating liquid P. Further, the intervals t1 and t2 between the metering roller 15 and the collecting roller 16 with respect to the applicator roller 14 are 0 (zero).
In this state, the rollers 14, 15 and 16 rotate. The intervals t1 and t2 are the same as those of the solenoids 34 and 3
5 may be opened to the extent that the coating liquid P does not flow out.
Next, the base material B is supplied.

Then, as shown in FIG. 2A, the solenoids 34 and 35, which are moving means of the metering roller 15 and the collecting roller 16, operate to operate the metering roller 15 and the collecting roller with respect to the applicator roller 14. The 16 intervals t1 and t2 are open. The timing at which the solenoids 34 and 35 operate is determined by the base material B.
Until the tip of the reaches the backup roller 12,
It is set so that the applicator roller 14 can rotate once or twice.

When the intervals t1 and t2 are opened, the application liquid P may drip from the applicator roller 14 if it is too early, and the application liquid P is applied to the surface of the applicator roller if it is too late. The liquid P may not adhere with a uniform thickness. Further, in the above state, the coating liquid P is quantitatively extracted and adhered to the outer peripheral portion of the applicator roller 14 by the metering roller 15. Further, the applied coating liquid P is collected in the casing 13 by the collecting roller 16 without leakage.

Then, when the base material B is conveyed, FIG.
As shown in (B), the solenoid 26 operates at the timing when the front end of the base material B is just conveyed onto the backup roller 12, and the backup roller 12 is pressed against the applicator roller 14.

As a result, the applicator roller 14 is
And the coating liquid P extracted between the metalling roller 15 and
Is applied to the surface of the base material B by a rolling coating method. On the collecting roller 16 side, a gap t2 with the applicator roller 14 is open, and the coating liquid P remaining on the surface of the applicator roller 14 leaks from the gap t2 due to the rotation of the collecting roller 16. Instead, it is collected in the casing 13.

In the present invention, the substrate is an object to be coated on which the coating liquid is applied by using the coating method of the present invention, and its form is not limited. The long strip-shaped support described above,
It is preferable that the belt-shaped support already has a constituent layer so that the effects of the present invention can be sufficiently exhibited,
It is not limited to this. The substrate may be a plate-shaped support or a three-dimensional support as long as the coated portion has an area.

In the coating method of the present invention, coating is performed using a reverse roll coater. FIG. 3 shows an example of a coating production line in which the reverse roll coater 1 as described above is arranged. Here, as the base, a support having a constituent layer coated thereon is used. After coating the constituent layers, a plurality of reverse roll coaters were arranged in the step of drying. Thus, the formation of the constituent layers and the coating of the overcoat layer (outermost layer) according to the present invention on the same line are called online coating.

Supplied from the flow-regulating slide bead coating device 50 in the process in which the support passes from the original winding of the support by the transport means (not shown), passes through the transport roller 51, and is reversed and transported at the position of the backup roll 52. The coating liquid for the porous ink absorption layer (constituent layer) is applied.
Since the coating liquid for the porous ink absorbing layer contains the hydrophilic binder, it is once cooled by the cooling device 60 and fixed. The substrate B having the constituent layers on this support is transported to the drying step. In the drying step, the reverser 53 and the base B for blowing air to reversely convey the non-contacted surface of the coating film.
A normal conveying roller 54 that makes contact with the back surface of the sheet and reverses the sheet.
And are alternately provided, and the substrate B is meandered and conveyed. In this drying step, hot air is blown to dry (a hot air blowing means is not shown). During this drying process,
The coating as described above according to the present invention is preferably performed by the two reverse roll coaters at the position after the rate-decreasing drying. At least one of the two reverse roll coaters is preferably placed at a position after the drying end point. Two reverse roll coaters are used here, but one may of course be used and three or more may be used.
By performing the coating in multiple stages, the drying load is reduced and at the same time the film thickness uniformity is improved.

The coating speed when the coating solution is applied onto a substrate to form a thin film by using the coating method of the present invention varies depending on the type of the coating solution used, the concentration, the solvent content, the drying ability and the like. However, the coating speed is preferably 50 to 300 m / min, and more preferably 100 to 300 m / min.

Using the coating method of the present invention, at least 1
When coating is performed on a substrate having constituent layers of a layer on a support, the coating time is after the rate-reduced drying of the constituent layer formed on the support, preferably after the drying end point. Further, it is preferable that the coating step of applying the above-mentioned constituent layers using slide bead coating or the like and the coating step of using the reverse roll coater of the present invention are continuously performed on the same production line (referred to as online coating). . Since the coating method according to the present invention can coat even a small amount of coating liquid, the drying load is small even when the composition layer is not completely dried, and the composition layer is not adversely affected. Few. Further, it has been found that applying the coating according to the present invention before the constituent layers are completely dried can prevent the disadvantages such as cracking of the constituent layers.

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

The drying process of the wet coating film can be classified as follows. In the initial stage of drying, which is called a constant-rate drying section, the solvent of the coating liquid, such as water and the solvent, evaporates while taking away latent heat of vaporization, so that the surface temperature of the constituent layer is almost constant. This constant temperature period is referred to as a constant rate drying unit. After the constant-rate drying section, water and a solvent having an interaction with the solute of the coating solution are evaporated, and therefore energy for releasing the interaction is required in addition to the latent heat of evaporation, so that the surface temperature rises. This period is called the rate-reducing section. In the rate-decreasing section, the evaporation of the solvent from the surface is a phenomenon that occurs when the water movement in the coating film in the layer is superior. Then, when the reduction rate drying is completed, the area enters a region where the temperature of the drying air and the surface temperature of the inkjet recording medium match. This time point is called the end of drying.

There are no particular restrictions on the method for confirming the constant rate drying section, the decreasing rate drying section, and the drying end point, but for example, by monitoring the surface temperature, the area where the surface temperature is constant is subjected to constant rate drying. The time point at which the area where the temperature rises and the surface temperature become the same as the rate-decrease drying section and the drying temperature can be determined as the drying end point.

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

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

In the present invention, the wet film thickness of the coating solution is from 1 to
It is preferably 50 μm, more preferably 5 to 3
It is 0 μm.

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, an antireflection film for imparting a functional layer to the outermost surface of a general silver salt photosensitive material. It can be used for forming a charge generation layer of a photoreceptor used in electrophotography, coating of a charge transport layer, coating on an inkjet recording medium, etc., but particularly preferably for coating an overcoat layer on an inkjet recording medium. Is to apply.

The ink jet recording medium 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 the coating method of the present invention is applied thereon. An overcoat layer is provided.

The porous ink absorbing layer is mainly composed of fine particles and a hydrophilic binder. The fine particles are preferably fine particle silica synthesized by a gas phase method, and the hydrophilic binder is preferably polyvinyl alcohol.

As the support used for such an ink jet recording medium, a water-absorbent support (for example, paper) or a non-water-absorbent support can be used, but from the viewpoint of obtaining higher quality prints. A non-water absorbent support is preferred. As such a support, there is a paper support in which both surfaces of paper are laminated with a polyolefin resin.

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

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 about 20 ° C. or less, and particularly 1
It is preferably 5 ° C. or lower.

In the cooling step, after coating, the zone cooled to, for example, 15 ° C. or lower is kept for a predetermined time (preferably 5 seconds or longer).
It can be done by passing it. At the time of this cooling, it is preferable not to blow a very strong wind from the viewpoint of obtaining a uniform and even coating film without causing liquid twist.

After cooling once, even if a strong wind is blown, the viscosity of the coating liquid itself is increased, so that liquid twist hardly occurs, and even if a strong wind is blown, the generation of liquid twist can be suppressed. The temperature of the strong wind to be blown can be 20 ° C. or higher, but it is preferable to gradually raise the temperature of the wind.

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

When passing through a high temperature zone for drying,
Pass through a drying zone at 50-150 ° 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 air usually has a relative humidity of 10 to 50%, preferably 1
It is performed with a wind of 5 to 40%. Although the drying time depends on the wet film thickness, it is preferably within 10 minutes, 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, preferably 20 to 500 m per minute.

Next, in the coating method of the present invention, the coating liquid for the overcoat layer when the overcoat layer is provided on the porous ink absorbing layer of the ink jet recording medium will be described below.

The coating liquid for the overcoat layer is characterized in that it contains a function-imparting compound for the surface of the constituent layers of the ink jet recording medium.

By the use of the function-imparting compound, an organic or inorganic acid whose pH changes, or various alkaline additives, water-soluble salts of water-soluble polyvalent metal ions, anions, cations, amphoteric or nonionic compounds. Examples include various surfactants, anti-fading agents, cationic fixing agents, and crosslinking agents for hydrophilic binders.

Acids which can be used for lowering the surface pH of the porous ink absorption layer include, for example, sulfuric acid, hydrochloric acid,
Examples thereof include inorganic acids such as nitric acid and phosphoric acid, and organic acids such as citric acid, formic acid, acetic acid, phthalic acid, succinic acid, oxalic acid, and polyacrylic acid.

Examples of the alkali used for 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,
Organic amine etc. are mentioned.

The above pH adjusting agent is particularly preferable when the pH of the coating solution for forming the porous layer is different from the preferable film surface pH of the recording medium.

Film surface pH of the porous ink absorption layer of the recording medium
Is different depending on the type of ink, but generally, the water resistance and bleeding of the dye are improved on the more acidic side, but the light resistance tends to be improved on the higher pH side. The optimum pH is selected in combination. The film surface pH of the preferable porous surface is 3 to 7, and particularly 3.
5 to 6.5 is preferable. The term "membrane surface pH" as used herein refers to J.
It is a value measured according to the paper surface pH measuring method specified in TAPPI 49. Specifically, 50 μl of pure water (pH = 6.2 to 7.3) is dropped on the surface of the recording medium to obtain a commercially available product. The value measured using a plane electrode.

The function-imparting compound may be a surfactant. The surfactant can control the dot diameter at the time of inkjet recording, and as such a surfactant, anionic, cationic,
An amphoteric or nonionic surfactant can be mentioned. Further, two or more kinds of surfactants can be used in combination. The addition amount of the surfactant is generally 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 inkjet recording.

The function-imparting compound may be a crosslinking agent for a hydrophilic binder. As such a cross-linking agent, known ones can be used, and preferable ones include
The above-mentioned boric acid, zirconium salt, aluminum salt or epoxy-based cross-linking agent.

The function-imparting compound may be an image stabilizer (hereinafter, also referred to as anti-fading agent). Anti-fading agents include fading due to light irradiation, ozone, active oxygen, N
It suppresses discoloration due to various oxidizing gases such as O _x and SO _x .

A cationic polymer can be used as the function-imparting compound. Generally, the cationic polymer acts as a fixing agent for the dye and is preferably added in advance to the coating solution for forming the porous receiving layer in order to prevent water resistance and bleeding, but it was added to the coating solution. If a problem occurs, it can be supplied by the overcoat method. For example, in the case of adding a cationic polymer to increase the viscosity of the coating solution over time, or to improve the color developability by giving a distribution of the cationic polymer in the porous layer, the coating solution is supplied by the overcoat method. It is preferable. When the cationic polymer is supplied by the overcoat method, it is in the range of about 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 are generally prone to agglomeration when they are present in a coating solution containing inorganic fine particles, and this tends to cause minute coating failures and deterioration of glossiness. Preferably.

As such a polyvalent metal compound, for example,
For example, Mg₂ ⁺, Ca₂ ⁺, Zn₂ ⁺, Zr ₂ ⁺, Ni₂ ⁺, Al₃ ⁺
Used in sulfates, chlorides, nitrates, acetates, etc.
It

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

As the solvent of the above-mentioned functionality imparting compound, water or a mixed solution of water-miscible organic solvent and water is preferable, and water is particularly preferably used. Further, a mixed solvent of water and a low-boiling organic solvent having water miscibility (for example, methanol, ethanol, i-propanol, n-propanol, acetone, methyl ethyl ketone, etc.) is also a particularly preferable solvent. When water and a water-miscible organic solvent are used together, the content of water is 50% by mass.
It is preferable to contain the above.

The water-miscible low boiling point organic solvent has a solubility of 10% by mass or more in water at room temperature,
An organic solvent having a boiling point of about 120 ° C. or lower.

The surface tension of the coating liquid used in the coating method of the present invention is 20 to 60 mN / m at room temperature.
It is preferable from the viewpoint of obtaining uniform coatability.

[0091]

[Examples] Hereinafter, examples of forming an overcoat layer of an ink jet recording medium by the coating method of the present invention will be described.
The invention is illustrated, but the invention is not limited to these examples.

Example 1 [Preparation of Substrate] A substrate having a four-layered porous ink absorbing layer as a constituent layer and formed on a support was prepared.

First, the following coating liquids for constituent layers were prepared.
The silica in the silica dispersion has an average primary particle size of about 0.
012 μm vapor phase silica (Aerosil 200 manufactured by Nippon Aerosil Co., Ltd.) was used. Further, the oil dispersion liquid contains an antioxidant. Each addition amount is coating liquid 1
The amount is shown per L. In the examples, "%" represents mass% unless otherwise specified.

[0094]   <First layer coating liquid: bottom layer>   Silica dispersion 580 ml   Polyvinyl alcohol (Kuraray: PVA203) 10% aqueous solution                                                               5 ml   Polyvinyl alcohol (average degree of polymerization: 3800, saponification degree 88%)     290 ml of 6.5% aqueous solution   Oil dispersion 30ml   Latex dispersion (Showa High Polymer Co., Ltd .: AE803) 42 ml   8.5 ml of ethanol   Finish with 1000ml of pure water   <Second layer coating liquid>   Silica dispersion 600 ml   Polyvinyl alcohol (Kuraray: PVA203) 10% aqueous solution                                                               5 ml   Polyvinyl alcohol (average degree of polymerization: 3800, saponification degree 88%)     270 ml of 6.5% aqueous solution   Oil dispersion 20ml   Latex dispersion (Showa High Polymer Co., Ltd .: AE803) 22 ml   8 ml of ethanol   Finish with 1000ml of pure water   <Coating liquid for third layer>   Silica dispersion 630ml   Polyvinyl alcohol (Kuraray: PVA203) 10% aqueous solution                                                               5 ml   Polyvinyl alcohol (average degree of polymerization: 3800, saponification degree 88%)     270 ml of 6.5% aqueous solution   Oil dispersion 10ml   Latex dispersion (Showa High Polymer Co., Ltd .: AE803) 5 ml   3 ml of ethanol   Finish with 1000ml of pure water   <4th layer coating liquid: top layer>   Silica dispersion 660 ml   Polyvinyl alcohol (Kuraray: PVA203) 10% aqueous solution                                                               5 ml   Polyvinyl alcohol (average degree of polymerization: 3800, saponification degree 88%)     250% 6.5% aqueous solution   Betaine type surfactant 4% aqueous solution 3 ml   2 ml of a 25% aqueous solution of saponin   3 ml of ethanol   Make up to 1000 ml with pure water.

Next, four layers of the above coating solutions were simultaneously coated at 40 ° C. on a paper support coated with polyethylene at 40 ° C. using a slide bead type coating device so as to obtain the following wet film thickness. A substrate was prepared.

<Wet Film Thickness> First layer: 42 μm Second layer: 39 μm Third layer: 44 μm Fourth layer: 38 μm After application of the coating liquid for the ink absorbing layer, it passed through a cooling zone kept at 5 ° C. for 15 seconds. Then, the temperature of the film surface was lowered to 13 ° C., and then the air was blown to the surface of the ink absorption layer in sequence while passing through each zone of the drying step to be dried.

The total drying step was 360 seconds, of which 270 seconds in the first half was 3 seconds when the average relative humidity of the blowing air was 3 seconds.
It was set to 0% or less. After 270 seconds, the relative humidity is 40 to 6
The humidity was adjusted to 0%.

As a result of measuring the film surface temperature, the constant rate drying part is shown up to 150 seconds in the first half, and the decreasing rate drying part is shown after that, and the drying end point (the part where the film surface temperature matches the temperature of the wind) is 240 seconds. there were.

[Coating Method 1] A 4% boric acid solution was used as a coating liquid for the overcoat layer. The viscosity of this coating solution is 1.5 mPa · s at room temperature, and the surface tension is 60 to 70.
It was mN / m.

The coating production line was the same as in FIG. However, one reverse roll coater 1 was provided, and the reverse roll coater 1 was arranged at a position of 200 seconds in the drying step of the porous ink absorbing layer (reduction rate drying section, before the drying end point).

As coating conditions, overcoating was performed at a coating speed of 150 m / min so that the wet film thickness was 15 μm.

[Coating Method 2] In the above coating method 1,
The coating method 2 was carried out in the same manner except that the disposition of the reverse roll coater 1 was changed to the position of 300 seconds in the drying step (after the drying end point).

[Coating Method 3] In the above coating method 1,
The coating method 3 was carried out in the same manner except that the number of the reverse roll coater 1 was changed to two and the reverse roll coater 1 was arranged at the position of 200 seconds and the position of 300 seconds in the drying step.

[Coating Method 4] The following was changed in Coating Method 1 above.

As a coating solution for the overcoat layer, polyvinyl alcohol (average degree of polymerization: 3800, degree of saponification: 88%) was added to the composition of the boric acid solution so that the viscosity was increased. The viscosity of the coating solution at this time is 3 at room temperature.
It was 00 mPa · s. The surface tension is 40 mN /
It was m.

[Coating Method 5] In the above coating method 1,
Coating was performed in the same manner except that the reverse roll coater 1 was changed to an extrusion coating device. At this time, the coating liquid formed a bead-shaped liquid film from the coating device to the substrate.

Table 1 shows the results of the following evaluations for each ink jet recording medium obtained by each of the above coating methods.
Shown in.

(Evaluation of coating property) The surface of each recording medium after coating and drying was visually observed, and the coating property was evaluated according to the criteria described below.

A: No coating unevenness was observed on the coated surface B: Microscopic coating unevenness was observed on the coated surface, but was slight C: Some coating unevenness could be confirmed on the coated surface, but practically acceptable D: Moderately strong coating unevenness is recognized on the coated surface and there is a problem in practical use E: Extremely strong coating unevenness is recognized on the coated surface (evaluation of drying property) Each record after coating and drying The surface of the medium was visually observed, and the drying property was evaluated according to the criteria described below.

A: The coating surface is completely dry B: The coating surface is almost dry C: A weak undried portion is observed at the end of the coating surface, but it is within the allowable range D: A slightly strong undried portion is observed at the end of the coated surface, which is a problem in practical use. E: A undried portion occurs on the entire coated surface.

[0111]

[Table 1]

From the results shown in Table 1, it was found that the ink jet recording media prepared by the coating methods 1 to 4 were excellent in coating property and drying property.

Example 2 In the coating methods 1 to 5 described in Example 1, coating was carried out in the same manner except that a betaine type surfactant was used instead of the 4% boric acid solution. It showed a similar tendency to.

Example 3 In the coating methods 1 to 5 described in Example 1, coating was carried out in the same manner as in Example 1 except that a 4% boric acid solution was used instead of the anti-fading agent. Showed a tendency.

Example 4 In the coating methods 1 to 5 described in Example 1, coating was performed in the same manner except that the 4% boric acid solution was changed to a polyvalent metal-containing aqueous solution, and Example 1 was used. It showed a similar tendency to.

Example 5 In Example 1, the coating method 5 was changed to the coating method 5 in which only the wet film thickness (before drying) was changed to 60 μm. In coating method 6, the coating property was slightly improved with C, but was not at a practical level, and similarly the drying property was deteriorated to E.

Example 6 In the coating methods 1 to 5 of Example 1, the coating speed was changed from 150 m / s to 300 m / s, and the coating methods 7 to 11 were used. In the coating methods 7 to 10, the results were substantially the same as those in the coating methods 1 to 4, but in the coating method 11, the coating property was further deteriorated.

[0118]

According to the present invention, it is possible to provide a coating method which realizes high-speed coating of a thin film and high drying property, a coating product thereof, and an inkjet recording medium.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a reverse roll coater.

2A and 2B are process diagrams showing application of a coating liquid onto a substrate by a reverse roll coater.

FIG. 3 is a schematic view showing an example of a coating production line in which a reverse roll coater is arranged.

[Explanation of symbols]

1 Reverse roll coater 11 Transport means 12 Backup roller 13 casing 14 Applicator roller 15 Metalling roller 16 Collection roller 50 Slide bead coating device 60 cooling system

Claims (16)

[Claims] 1. A coating method for applying a coating liquid onto a substrate, wherein the substrate has at least one constituent layer on a support, and the constituent layer is coated on the support, and then the composition is formed. A coating method comprising applying the coating liquid on the constituent layers using a reverse roll coater after the layer is subjected to rate reduction drying. 2. The coating liquid is applied onto the constituent layer using a reverse roll coater after the constituent layer is applied onto the support and after the drying end point of the constituent layer. The coating method according to claim 1. 3. The coating method according to claim 1, wherein a plurality of the reverse roll coaters are provided in the transport direction of the substrate, and the coating is performed in multiple stages. 4. The coating solution has a viscosity of 0.1 to 250 mP.
It is a * s, The coating method of any one of Claims 1-3 characterized by the above-mentioned. 5. The viscosity of the coating liquid is 0.1 to 50 mPas.
-S is any one of Claims 1-3 characterized by the above-mentioned.
The coating method according to item. 6. The viscosity of the coating liquid is 0.1 to 20 mPas.
-S is any one of Claims 1-3 characterized by the above-mentioned.
The coating method according to item. 7. The coating method according to claim 1, wherein the solvent of the coating liquid is water or a mixed solution of water and a water-miscible organic solvent. 8. The wet film thickness of the coating liquid is 1 to 50 μm.
The coating method according to any one of claims 1 to 7, wherein: 9. The coating speed of the coating is 50 to 300 m.
/ Min, The coating method according to claim 1. 10. The coating solution contains a function-imparting compound for the constituent layer.
10. The coating method according to any one of 9 to 10. 11. The function-imparting compound is a surfactant,
11. The coating method according to claim 10, wherein the coating agent is selected from a crosslinking agent for hydrophilic binders, an image stabilizer, and a water-soluble polyvalent metal compound. 12. The coating liquid is a coating liquid for the outermost layer of an inkjet recording paper, wherein the coating liquid is a coating liquid for the outermost layer.
11. The coating method according to any one of 11 above. 13. The coating method according to claim 1, wherein the constituent layer is an ink absorbing layer. 14. The coating method according to any one of claims 1 to 13, wherein the support is a support in which both surfaces of paper are coated with a polyolefin resin. 15. A coated product, which is manufactured by coating using the coating method according to any one of claims 1 to 14. 16. An ink jet recording medium, which is manufactured by coating using the coating method according to any one of claims 1 to 14.