JP2010094832A - Manufacturing method for coating liquid used in formation of ink receiving layer of inkjet recording medium and manufacturing method for inkjet recording medium using this coating liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method whereby a coating liquid of a high concentration of a solid content is manufactured while the problem of a viscosity increase and gelation is suppressed in relation to the manufacturing of the coating liquid used in the formation of an ink receiving layer of an inkjet recording medium. <P>SOLUTION: In the manufacturing method for the coating liquid used in the formation of the ink receiving layer of the inkjet recording medium, the method has a preparation process of preparing a polyvinyl alcohol aqueous solution of pH 5.0 or lower, and an addition process of adding an alumina hydrate as a powdered matter to the polyvinyl alcohol aqueous solution. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a manufacturing method of a coating liquid used for forming an ink receiving layer of an inkjet recording medium, and a manufacturing method of an inkjet recording medium using the coating liquid.

  Various types of recording media such as those having an ink receiving layer made of a hydrophilic resin and those having a porous ink receiving layer made of an inorganic pigment and a binder have been proposed as recording media used for ink jet recording. Has been.

  An ink jet recording medium can be generally obtained by coating inorganic fine particles on a support. The following proposals have been made for a coating liquid for applying such an inkjet recording medium and a method for producing the recording medium.

  An inorganic fine particle dispersion containing a cationic polymer is heated for 0.5 to 5 hours under conditions of 45 ° C. or higher and 60 ° C. or lower, and then stagnation for 0.5 to 5 hours under conditions of 10 ° C. or higher and 40 ° C. or lower. . Next, a method for manufacturing a recording medium in which a coating liquid is prepared by mixing with a water-soluble binder has been proposed (see Patent Document 1).

Moreover, the manufacturing method of the inorganic fine particle coating liquid which mixes the inorganic fine particle aqueous dispersion adjusted to 5-34 degreeC and the polyvinyl alcohol aqueous solution adjusted to 60-80 degreeC is known (refer patent document 2).
JP 2006-224498 A JP 2008-001054 A

  The coating liquid used for forming the ink receiving layer is preferably increased in solid content concentration of the coating liquid in order to improve the properties of the ink receiving layer, for example, by giving the ink receiving layer a thickness.

  However, in the method for producing a coating liquid as described in Patent Documents 1 and 2, the inorganic fine particle dispersion and the aqueous binder are prepared in advance in separate tanks, and then the inorganic fine particle dispersion and the aqueous binder are fed. It is a method of mixing by liquid. In these methods, since the coating liquid contains a lot of water, it is difficult to increase the solid content concentration of the coating liquid. Furthermore, when the solid content of the inorganic fine particle dispersion or the aqueous binder is increased for the purpose of increasing the solid content concentration of the coating liquid, the dispersion or the binder-containing aqueous solution may be thickened or gelled. For this reason, handling of liquid feeding etc. became difficult and it discovered that there existed a subject that it was difficult to manufacture a coating liquid with high solid content concentration.

  Accordingly, the present invention produces a coating liquid having a high solid content concentration while suppressing the occurrence of problems such as thickening and gelation with respect to the production of a coating liquid used for forming an ink receiving layer of an inkjet recording medium. The purpose is to do.

  The above object is achieved by the present invention described below.

  That is, the present invention relates to a method for producing a coating liquid used for forming an ink receiving layer of an ink jet recording medium, comprising a preparation step of preparing a polyvinyl alcohol aqueous solution having a pH of 5.0 or less, and hydration of alumina in the polyvinyl alcohol aqueous solution. And an addition step of adding the product as a powder.

  Another embodiment of the present invention is a method for producing an ink jet recording medium having an ink receiving layer, wherein the ink receiving layer is formed using the coating liquid produced by the above production method. This is a method for producing an inkjet recording medium.

  According to the present invention, a coating liquid having a high solid content concentration is produced while suppressing the occurrence of problems such as thickening and gelation with respect to the production of a coating liquid used for forming an ink receiving layer of an inkjet recording medium. Can be manufactured.

  An ink jet recording medium forms a porous ink-receiving layer having a void layer or a curl adjusting layer by applying inorganic fine particles to a support. The porous ink receiving layer and the curl adjusting layer are coated as a coating liquid by mixing inorganic fine particles and a water-soluble polymer.

  Since the ink receiving layer needs to sufficiently absorb the ink component at the time of recording, for example, a solvent for ink, when forming an ink receiving layer having excellent printing characteristics, the dry coating amount of the ink receiving layer should be reduced. It is preferable to increase, that is, to increase the solid content concentration of the coating liquid.

  On the other hand, since the curl adjusting layer needs to adjust the curl according to the balance with the dry coating amount of the ink receiving layer, the dry coating amount needs to be arbitrarily controlled. From the viewpoint of drying, the coating liquid used for coating the ink receiving layer and the curl adjusting layer must be made to have harsh drying conditions unless the solids concentration is as high as possible. Cracks will occur. Therefore, it is preferable to increase the solid concentration of the coating liquid used for forming the ink receiving layer.

  In order to increase the solid content concentration of the coating liquid, a method of reducing the amount of water in the coating liquid can be considered. In the conventional method for producing a coating liquid, an inorganic fine particle dispersion and a water-soluble binder are prepared in separate tanks, and the inorganic fine particle dispersion and the aqueous water-soluble binder solution are separately fed and mixed with stirring. When the solid content concentration of the coating liquid is increased by these methods, it is necessary to increase the solid content concentration of the inorganic fine particle dispersion or to increase the solid content concentration of the water-soluble binder.

  However, in both cases, when the solid content concentration is increased, thickening occurs, and in some cases, there is a problem of gelation. Especially for alumina dispersions, this tendency appears remarkably, and when the solid content concentration is increased, the viscosity suddenly increases from a certain solid content concentration, and eventually gelled. If such thickening occurs, when the dispersion and the aqueous binder aqueous solution are added separately, it is difficult to supply the liquid and it becomes difficult to produce the coating liquid.

  As a result of intensive studies on this point, the present inventors have added alumina hydrate as a powder in a polyvinyl alcohol aqueous solution and dispersed it, thereby suppressing the thickening, while reducing the solid content concentration. I found that it can be enhanced. This is thought to be due to the suppression of the thickening due to aggregation caused when the solid content concentration of the inorganic fine particles is increased by the adsorption of polyvinyl alcohol on the surface of the alumina hydrate due to the steric hindrance of the polyvinyl alcohol. .

  Hereinafter, embodiments of the present invention will be described more specifically.

<Support>
The ink receiving layer formed with the coating liquid of the present invention is provided on a support. Examples of the support include paper such as high-quality paper, medium-quality paper, coated paper, art paper, cast-coated paper, synthetic paper, white plastic film, transparent plastic film, or translucent plastic film, resin-coated paper, and the like. It is done. Of these, paper such as cast-coated paper, laminated paper (resin-coated paper) in which a thermoplastic resin composition is coated on a base paper, a white plastic film, and the like are preferable. Further, a gas-permeable support made of an opaque material such as paper or a polyolefin resin-coated paper coated with at least one surface provided with an ink receiving layer is preferable. Further, a gas-permeable support made of an opaque material and a polyolefin-coated paper coated on both sides are preferable. In particular, when a fibrous support, that is, a gas-permeable support made of paper, is used, after forming a porous ink receiving layer described later on the support, by performing a gloss treatment such as casting, This is preferable because high surface gloss comparable to silver salt photography can be obtained.

  Examples of the air-permeable support made of paper include those obtained by subjecting a base paper to size press with starch, polyvinyl alcohol, etc., art paper, coated paper, cast coated paper, etc. provided with a coat layer on the base paper Coated paper and the like.

When paper is used as the air-permeable support, it is preferable that a coat layer having a thickness that completely covers the cellulose pulp fibers and texture of the paper (base paper) is provided as an undercoat layer of the ink receiving layer. When the ink receiving layer is not covered, uneven coating (such as streaks) due to the fibers and texture tends to occur when the ink receiving layer is applied. In this case, since the cellulose pulp fiber is present in the ink receiving layer or in the vicinity of the surface of the ink receiving layer or on the surface, even if the surface of the recording medium is cast, a good and uniform cast surface, That is, it may be difficult to obtain a photo-like high gloss surface. In order to cover the cellulose pulp of the air-permeable support made of paper, the dry coating amount of the coat layer is preferably 10 g / m ² or more, more preferably 13 g / m ² or more.

  The air permeability of the air-permeable support made of paper is preferably 6000 seconds or less, and more preferably 5500 seconds or less from the viewpoint of suitability for gloss treatment in the gloss treatment step described later.

When a gas-permeable support made of paper is used, it is preferable that the Steecht sizing degree is 100 to 400 seconds, the Beck smoothness is 100 to 500 seconds, and the underwater elongation is 1.2 to 2.5%. Further, in order to obtain a recording medium having the same texture and high quality as a silver salt photograph, the basis weight of the air-permeable support made of paper is 160 to 230 g / m ² , Gurley stiffness (J. Tappi No. 40, It is preferable that the longitudinal dimension is 7 to 15 mN.

<Surface treatment process of support>
It is preferable to apply a surface treatment liquid on the support.

  The surface treatment step of the support is a step of applying a precoat liquid containing a cross-linking agent that causes a cross-linking reaction with the binder to be cured, and is performed as necessary. The addition of the crosslinking agent is preferable in order to further strengthen the structure of the porous layer in the ink receiving layer as a desired ink receiving layer. The surface treatment step is a step of applying a surface treatment liquid containing a crosslinking agent that cures by causing a crosslinking reaction with the binder, and contains at least one selected from the group consisting of boric acid and borate. This is a step of applying a surface treatment liquid, which is a coating liquid, to a support.

  In the surface treatment step, the substrate surface is not dried after applying the surface treatment liquid to the air-permeable support, and the substrate surface is kept in a certain wet state (coating liquid state or thickened state may be maintained) It is preferable to perform the next step of applying the ink receiving layer forming coating solution.

  The surface treatment liquid is an aqueous solution containing the crosslinking agent, and preferably contains 1% by mass or more and 10% by mass of the crosslinking agent. Further, in order to improve the wettability of the surface treatment liquid, a surfactant, alcohol, or the like may be added to the surface treatment liquid to adjust the surface tension and water absorption.

The coating amount of the surface treatment liquid in the surface treatment step is on a solid basis of boric acid and borate 0.05 g / ^{m 2} or more 3.0 g / ^{m 2} or less.

<Ink-receiving layer forming step>
The ink receiving layer of the inkjet recording medium is formed by applying the coating liquid produced by the production method of the present invention on a support and drying it.

  The material for forming the ink receiving layer used in the present invention will be described in detail. The ink receiving layer is formed by applying a coating liquid containing alumina hydrate and polyvinyl alcohol. Alumina hydrate has high ink absorbability, excellent color development, can form high-quality images, and can be easily reduced in particle size, with relatively low viscosity and stable dispersion even at high solids concentrations. Preferred is an alumina hydrate having a boehmite structure or pseudoboehmite structure.

As said alumina hydrate, what is represented by the following general formula (X) can be used suitably, for example.
Al ₂ O _3-n (OH) _2n · mH ₂ O (X)
(In the above formula, n represents any of 0, 1, 2, or 3, and m represents a value in the range of 0 to 10, preferably 0 to 5. However, m and n are not 0 at the same time. MH ₂ O often represents a detachable aqueous phase that is not involved in the formation of the crystal lattice, so m can take an integer or non-integer value. M can reach a value of 0 when heated.)
Suitable alumina hydrates in the present invention are described, for example, in JP-A-7-232473, JP-A-8-132931, JP-A-9-66664, JP-A-9-76628, and the like. And alumina hydrate.

In the production process of the alumina hydrate, the pore properties are adjusted. In order to satisfy the BET specific surface area and the pore volume of the ink receiving layer, the pore volume is 0.3 to 1.0 ml / It is preferable to use alumina hydrate which is g. More preferably, it is 0.35-0.9 ml / g. Alumina hydrate having a pore volume in this range is more suitable for bringing the pore volume of the ink receiving layer within the specified range. Also, the BET specific surface area, it is preferable to use alumina hydrate is 50~350m ² / g, more preferably 100 to 250 m ² / g. Alumina hydrate having a BET specific surface area within this range is more suitable for setting the specific surface area of the ink receiving layer within the specified range. The BET method referred to in the present invention is one of powder surface area measurement methods by vapor phase adsorption, and is a method for determining the total surface area, that is, the specific surface area of a 1 g sample from the adsorption isotherm. Usually, nitrogen gas is often used as the adsorbed gas, and the most frequently used method is to measure the amount of adsorption from the change in pressure or volume of the gas to be adsorbed. The most prominent expression for representing the isotherm of multimolecular adsorption is the Brunauer, Emmett, and Teller equation, called the BET equation, which is widely used for determining the specific surface area. The adsorption amount is obtained based on the BET formula, and the specific surface area is obtained by multiplying the area occupied by one adsorbed molecule on the surface.

  Moreover, as a suitable shape of the alumina hydrate in this invention, what is flat form and whose average aspect-ratio is 3-10 and the aspect ratio of a flat plate surface is 0.6-1.0 is preferable. The definition of the aspect ratio can be obtained by the method described in Japanese Patent Publication No. 5-16015. The aspect ratio is expressed as the ratio of the “diameter” to the “thickness” of the particles. Here, the “diameter” indicates a diameter of a circle having an area equal to the projected area of the particles when the alumina hydrate is observed with a microscope or an electron microscope. The aspect ratio of the flat plate surface is the ratio of the diameter indicating the minimum value and the maximum value of the flat plate surface when the particles are observed with a microscope, similarly to the aspect ratio. When alumina hydrate having an average aspect ratio not satisfying the above range is used, the pore distribution range of the formed ink receiving layer may be narrowed. Moreover, when using what exceeds the said range, there exists a possibility that it may become difficult to arrange | equalize the particle diameter of an alumina hydrate and to manufacture. When using a material whose aspect ratio does not satisfy the above range, the pore size distribution of the ink receiving layer is similarly narrowed. As described in the literature (Rocek J., et al., Applied Catalysis, Vol. 74, p29-36, 1991), some alumina hydrates have cilia and other shapes. It is generally known that there is. According to the knowledge of the present inventors, even with the same alumina hydrate, the plate-like alumina hydrate has better dispersibility than the cilia-like one. Further, in the case of ciliated alumina hydrate, there is a tendency to orient in parallel to the surface of the undercoat layer during coating, and the formed pores may be reduced. Ink absorbability may be reduced. On the other hand, when using a plate-like alumina hydrate, the tendency to be oriented by coating is small, and therefore there is little effect on the size of the pores of the ink receiving layer and the ink absorbency. . From the above, it is preferable to use plate-like alumina hydrate in order to increase the glossiness as a pigment of the ink receiving layer.

  The manufacturing method of the coating liquid of this invention has the addition process which adds the said alumina hydrate as a powder to the said polyvinyl alcohol aqueous solution. In this addition step, the content of the polyvinyl alcohol with respect to the pigment such as alumina hydrate is not particularly limited as long as it is in a viscosity range that can be fed with a pump or the like after the coating liquid is prepared. However, in order to obtain the strength and ink absorbability of the ink receiving layer, the content of polyvinyl alcohol is preferably 5% by mass or more, more preferably 10% by mass or more with respect to 100% by mass of the pigment. . Moreover, it is preferable to set it as 50 mass% or less, and it is more preferable to set it as 30 mass% or less. When the content of polyvinyl alcohol is less than 5% by mass, cracks are likely to occur in the ink receiving layer. In addition, the mechanical strength of the ink receiving layer becomes insufficient, and powder falls off easily. On the other hand, when it exceeds 50% by mass, there is a possibility that the ink absorbability is lowered (for example, ink overflows and bleeding occurs in the image) or the ink dye adsorptivity is lowered. Furthermore, in order to obtain sufficient ink absorbency even under high temperature and high humidity, the content of polyvinyl alcohol in the ink is preferably 5% by mass or more. Moreover, it is preferable to set it as 20 mass% or less. In this way, after the alumina dispersion and the polyvinyl alcohol aqueous solution are prepared in each tank, the amount of water contained in the coating liquid is reduced compared to a method in which both are mixed and fed separately. Cheap. As a result, not only the solid content of the coating solution of alumina hydrate and polyvinyl alcohol can be kept high, but also the surface active effect of polyvinyl alcohol is exhibited, so that the efficiency of dispersion can be increased. Polyvinyl alcohol can be used alone or by mixing a plurality of vinyl alcohols within the above range.

  In the present invention, the saponification degree of polyvinyl alcohol is preferably 80% or more, and more preferably 85% or more from the viewpoint of workability in the process. Moreover, 90% or less is preferable. When the degree of saponification is less than 80%, a large amount of bubbles are generated when the powder is dispersed, and the foamed bubbles are difficult to be removed. On the other hand, a fully saponified polyvinyl alcohol higher than 90% is not preferable because the effect of reducing the viscosity that tends to change rapidly at the time of dispersion is weakened and the viscosity tends to increase. Here, the saponification degree is a value measured by the method of JIS-K6726, and is a ratio of the number of moles of hydroxyl groups generated by the saponification reaction when polyvinyl acetate is obtained by saponifying polyvinyl acetate. .

  In the present invention, the degree of polymerization of polyvinyl alcohol is not particularly limited, but is preferably 4500 or less, and more preferably 2000 or less. Moreover, it is preferable that it is 1000 or more. If the degree of polymerization exceeds 2000, the effect of reducing the viscosity that tends to change rapidly at the time of dispersion is weakened, and viscosity increase at the time of dispersion is liable to occur.

  The viscosity of the coating solution is preferably 4000 mPa · s or less, and more preferably 3000 mPa · s or less. Moreover, it is preferable that it is 500 mPa * s or more, and it is more preferable that it is 2000 mPa * s or more. When the viscosity of the coating liquid is 4000 mPa · s or less, the viscosity of the coating liquid is not too high, and handling properties such as liquid feeding with a pump are improved. In addition, when the viscosity of the coating liquid is 2000 mPa · s or more, the formation of a coating film is good particularly in high-speed coating, and a necessary coating amount is easily obtained.

  The solid content concentration of the coating solution is preferably 20% by mass or more, more preferably 25% by mass or more, and further preferably 30% by mass or more. Moreover, it is preferable that it is 50 mass% or less from a viewpoint of coating suitability. When the solid content concentration is less than 20% by mass, a large amount of wet coating is required to obtain the required dry coating amount, which is not preferable because the drying load after application increases.

  The coating solution is prepared using a polyvinyl alcohol aqueous solution having a pH of 5.0 or less. The pH of polyvinyl alcohol is more preferably 4.9 or less. Moreover, it is preferable that the pH of polyvinyl alcohol is 3.0 or more, and it is more preferable that it is 3.5 or more. When the pH is higher than 5.0, aggregation of alumina hydrate in the coating solution occurs, resulting in a decrease in handling properties such as the coating solution becoming thicker and difficult to pump. Is easy to produce. Moreover, when pH is lower than 3.0, since acidity becomes strong, corrosion of piping etc. of a liquid feeding process generate | occur | produces or the viscosity of a coating liquid tends to increase, and it is unpreferable.

The ink receiving layer to be formed preferably has a physical property satisfying the following conditions in order to achieve the purpose and effect such as high-speed absorbability, high color developability, and high resolution of the ink. . First, it is preferable that the pore diameter distribution of the ink receiving layer has a peak in the range of at least a pore radius of 5 to 20 nm. If it is less than this range, the high-speed absorbability of the ink may be inferior, and if it exceeds this range, sufficient performance may not be obtained in terms of color developability and resolution. The pore volume of the ink receiving layer is preferably in the range of 0.1 to 1.0 cm ³ / g. That is, when the pore volume is less than the above range, sufficient ink absorption performance cannot be obtained, resulting in an ink receiving layer with poor ink absorption, and in some cases, ink overflows and bleeding occurs in the image. There is a fear. On the other hand, when it exceeds the above range, there is a tendency that cracks and powder fall off easily occur in the ink receiving layer. The BET specific surface area of the ink receiving layer is preferably ^{20 to} 450 m ² / g. If it is less than the above range, sufficient gloss may not be obtained, and haze increases (transparency decreases), so the image may appear white and wrinkled. . Furthermore, in this case, not only the color developability of the dye is lowered but also the dye adsorbability in the ink may be lowered, which is not preferable. On the other hand, exceeding the above range is not preferable because cracks are likely to occur in the ink receiving layer. The values of the pore volume and the BET specific surface area are obtained by a nitrogen adsorption / desorption method.

The dry coating amount of the ink receiving layer is preferably 10 to 50 g / m ² . When the above range is not satisfied, the ink absorbability is sufficient particularly when used in a printer in which a plurality of light-color inks are added in addition to black ink in addition to three inks of cyan, magenta, and yellow. Is difficult to obtain. That is, it is not preferable because ink overflow may occur, bleeding may occur, or ink dye may diffuse to the base material, resulting in a decrease in print density. On the other hand, if the above range is exceeded, cracks tend to occur, which is not preferable. Furthermore, when the dry coating amount is more than 30 g / m ^2, it is preferable because an ink receiving layer exhibiting sufficient ink absorbency even in a high temperature and high humidity environment can be obtained. A dry coating amount of 50 g / m ² or less is preferable because uneven coating of the ink receiving layer hardly occurs and an ink receiving layer having a stable thickness can be easily produced.

<Back side forming process>
On the surface opposite to the ink receiving layer on the surface-treated support, a porous curl adjusting layer forming coating solution containing the same pigment and binder as the ink receiving layer is applied to the surface opposite to the ink receiving layer. It is preferable to work. If necessary, the support may be surface-treated before the curl adjusting layer is formed, as in the case of forming the ink receiving layer. As the material for forming the curl adjusting layer, it is preferable to use alumina hydrate as in the ink receiving layer. As the alumina hydrate, those represented by the general formula (X) can be suitably used. . The curl adjusting layer forming coating solution is prepared by a step of preparing a polyvinyl alcohol aqueous solution having a pH of 5 or lower, and a step of adding alumina hydrate as a powder to the polyvinyl alcohol aqueous solution, in the same manner as the ink receiving layer forming coating solution. It is preferable to be prepared. At this time, it is preferable to use the same polyvinyl alcohol as the ink receiving layer forming coating solution. In preparing the coating liquid, the solid content concentration of the pigment in the pigment dispersion used above is preferably 10% by mass or more and 50% by mass or less.

<Other additives>
In the ink receiving layer forming coating solution and the curling adjusting coating solution, for example, formic acid, acetic acid, glycolic acid, oxalic acid, propionic acid, malonic acid, succinic acid, adipic acid, maleic acid, apple Organic acids such as acid, tartaric acid, citric acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, glutaric acid, gluconic acid, lactic acid, aspartic acid, glutamic acid, pimelic acid, suberic acid, hydrochloric acid, nitric acid, phosphoric acid, etc. Inorganic acids and salts thereof may be added as appropriate.

Including at least one selected from the group consisting of boric acid and borate in the ink receiving layer and curl adjusting layer forming material formed as described above is extremely difficult to form the ink receiving layer. It is valid. Examples of boric acid that can be used in this case include orthoboric acid (H ₃ BO ₃ ), metaboric acid, and hypoboric acid. The borate is preferably a water-soluble salt of boric acid, specifically, for example, sodium salt of boric acid (Na ₂ B ₄ O ₇ · 10H ₂ O, NaBO ₂ · 4H ₂ O etc.) and, potassium salt _{(K 2 B 4 O 7 ·} 5H 2 O, alkali metal salts such KBO _2, etc.), an ammonium salt of boric acid _{(NH 4 B 4 O 9 ·} 3H 2 O, NH 4 BO 2 , etc. ), Alkaline earth metal salts such as magnesium salts and calcium salts of boric acid. It is preferable to use orthoboric acid from the viewpoint of the temporal stability of the coating solution and the effect of suppressing the occurrence of cracks. The amount used is preferably in the range of 0.5 to 15.0% by mass of boric acid solid content with respect to polyvinyl alcohol in the ink receiving layer. Even within this range, cracks may occur depending on manufacturing conditions and the like, and selection is required. On the other hand, exceeding the above range is not preferable because the temporal stability of the coating solution is lowered. That is, in the case of production, since the coating liquid is used for a long time, if the content of boric acid is large, the viscosity of the coating liquid increases during that time, and the generation of a gelled product occurs. Changing the coating liquid, cleaning the coater head, and the like are frequently required, and the productivity tends to decrease significantly. Furthermore, when exceeding the said range, in the process, the surface (cast surface) tends to be punctiform, and a homogeneous and good glossy surface may not be obtained.

  A colorant deterioration preventing agent may be added to the material for forming the ink receiving layer and the curl adjusting layer formed as described above. The colorant deterioration preventing material is a compound that, when present together with a dye in the ink receiving layer, protects the dye from factors that deteriorate the dye, such as gas and light, and improves the weather resistance of the dye. General examples include hindered amine compounds, hindered phenol compounds, benzophenone compounds, benzotriazole compounds, thiourea compounds, thiuram compounds, phosphite compounds, and the like. Of these, hindered amine compounds are preferred.

  Other coating liquid additives include pigment dispersants, thickeners, fluidity improvers, antifoaming agents, antifoaming agents, mold release agents, penetrating agents, colored pigments, colored dyes, fluorescent whitening agents, Ultraviolet absorbers, antioxidants, preservatives, antifungal agents, water resistance agents, dye fixing agents, curing agents, weathering materials, and the like may be appropriately contained as necessary.

  The supply method is particularly limited when a crosslinking agent, colorant deterioration preventing agent or other coating liquid additive is added to the coating liquid or curling adjustment coating liquid used to form the ink receiving layer. is not. For example, a method is preferably used in which mixing is performed using a continuous mixing device such as a static mixer, and the mixed coating solution is sent to an on-line coating head and applied. This supply method can be used particularly preferably in order to prevent the occurrence of cracks during coating and drying and to increase the binding strength of the ink receiving layer. The static mixer is configured by housing a mixing unit in a hollow cylindrical frame. In the mixing unit, a plurality of elements are connected in the longitudinal direction, and one element has a shape that is twisted, for example, 180 degrees in the circumferential direction as the plate body is advanced in the longitudinal direction. The twisting directions of adjacent elements are opposite to each other. In this case, the coating liquid as the essential constituent is uniformly mixed by each element while flowing in the frame.

<Coating machine used for coating the front and back surfaces>
The coating of each coating liquid in the front / back surface treatment step is preferably performed so that an appropriate coating amount is obtained. Examples of coating devices include various blade coaters, roll coaters, air knife coaters, bar coaters, rod blade coaters, curtain coaters, gravure coaters, coaters using an extrusion method, coaters using a slide bead method, and size presses. Etc. In addition, it is applied on-machine and off-machine. At the time of coating, the coating solution may be heated or the coater head may be heated for the purpose of adjusting the viscosity of the coating solution. Among these, application by a blade coater is preferable. When using a blade coater to increase the dry coating amount, as shown in the following general formula, increase the line speed, increase the viscosity by increasing the wet coating amount, decrease the blade pressure, or use for coating. It is necessary to increase the solid content concentration. For drying after coating, for example, a straight-air tunnel dryer, an arch dryer, an air loop dryer, a hot air dryer such as a sine curve air float dryer, a dryer using infrared rays, a heated dryer, a microwave, or the like is used. Is preferred.

W∝A ^1/2・ v ^3/2・ p ^−1/2
(W: wet coating amount, A: viscosity, v: coating speed, p: blade pressing pressure)

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to these examples. In the examples, “%” is based on mass unless otherwise specified.

  First, measurement methods of various physical property values used in the present invention will be described.

<Stick human sizing degree>
5 sheets of recording media were cut into A4 size, and each of the 5 sheets was allowed to stand for 2 hours or more at a temperature of 23 ° C. and a humidity of 50%. After that, in accordance with JIS P8122, each one was The sizing degree was measured and obtained as an average value of five values.

<Air permeability>
After leaving it in the same state as in the measurement of the above-mentioned Steecht sizing degree, each sheet was measured according to JIS P8177, and the average value of five values was obtained.

<Beck smoothness>
After leaving it in the same state as in the measurement of the above-mentioned Steecht sizing, each sheet was measured according to JIS P8119, and the average value of the five sheets was obtained.

<Gurley stiffness>
After leaving it in the same state as in the measurement of the above-mentioned Steecht sizing, Tappi No. According to 40, the longitudinal direction was measured for each sheet, and the average value of the five sheets was obtained.

<Underwater elongation>
The underwater elongation was measured using a DDPM dynamic displacement measurement module (emco). The measurement conditions were a clamp type, a spring tension of 20 g, a sample width of 50 mm, a water temperature of 23 ° C., and an immersion time of 10 minutes.

<BET specific surface area, pore volume>
The alumina hydrate was sufficiently degassed by heating, and then measured with an apparatus using a nitrogen adsorption / desorption method (manufactured by Cantachrome, Autosorb 1). The BET specific surface area was calculated using the method of Brunauer et al. (See J. Am. Chem. Soc., 60, 309, 1938). The pore volume was calculated using the method of Barrett et al. (See J. Am. Chem. Soc., 73, 373, 1951).

<Viscosity measurement method>
The viscosity of the coating liquid was allowed to stand for 15 minutes in a low-temperature constant temperature water bath set at 25 ° C., and then measured using a B-type viscometer (BM type, manufactured by Tokyo Keiki Co., Ltd.).

The measurement conditions are as follows.
When using rotor No. 2, the rotation speed is 100 to 500 mPa · s; 60 rpm,
500 to 1000 mPa · s; 30 rpm
1000-2500 mPa · s; 12 rpm.
Rotation speed 2500 ~ 4000mPa · s when using rotor No3; 30rpm
4000 to 10,000 mPa · s; 12 rpm.

[Example 1]
(Production Example 1 of Support)
First, a support was produced as follows. First, a pulp slurry consisting of 80 parts by weight of hardwood bleached kraft pulp (LBKP) having a freeness of 450 ml CSF (Canadian Standard Freeness) and 20 parts by weight of softwood bleached kraft pulp (NBKP) having a freeness of 480 ml CSF was prepared. Next, 0.60 parts by weight of cationized starch, 10 parts by weight of heavy calcium carbonate, 15 parts by weight of light calcium carbonate, 0.10 parts by weight of alkyl ketene dimer, and 0.03 parts by weight of cationic polyacrylamide are added to the pulp slurry. Externally added. After preparing the stock in this way, it was made with a long paper machine, subjected to a three-stage wet press, and dried with a multi-cylinder dryer. Thereafter, the starch starch aqueous solution was impregnated with a size press device so as to have a solid content of 1.0 g / m ² , dried, and machine calendered. As a result, a base paper A having a basis weight of 155 g / m ² , a Steecht size of 100 seconds, an air permeability of 50 seconds, a Beck smoothness of 30 seconds, and a Gurley stiffness of 11.0 mN was obtained.

Next, an undercoat layer was formed on the base paper A obtained above as follows. As a coating solution used for forming the undercoat layer, a coating solution having the following weight ratio of kaolin (Ultra White 90, manufactured by Engelhard) / zinc oxide / aluminum hydroxide having a weight ratio of 65/10/25 is used. A slurry with a solid content concentration of 70% by mass consisting of 100 parts by mass and 0.1 part by mass of a commercially available polyacrylic acid dispersant was prepared. To this slurry, 7 parts by mass of a commercially available styrene-butadiene latex was added to prepare a composition having a solid content of 60% by mass. Next, this composition was coated on both sides of the base paper A with a blade coater so that the dry coating amount was 15 g / m ² and dried. Then, machine calender finishing (linear pressure 150 kgf / cm), basis weight 185 g / m ² , Steecht size degree 300 seconds, air permeability 3,000 seconds, Beck smoothness 200 seconds, Gurley stiffness 11.5 mN undercoat A layered support was obtained.

<Recording Medium Production Example 1>
A surface treatment comprising the following steps was performed on the undercoat layer of the support obtained above. First, a surface treatment liquid having the following composition heated to 30 ° C. is subjected to a wet coating amount of 10 g / m ² with a blade coater (the coating amount when dried is 0.3 g / m ² ). The coating was performed at 200 m per minute.

(Surface treatment liquid)
Sodium tetraborate: 5g
Isopropanol: 0.15g
Add ion-exchanged water to adjust the total amount to 100 g.

  Next, after coating in the surface treatment step, that is, as soon as the coating solution is impregnated in the undercoat layer, the coating solution used for forming the ink receiving layer is applied and dried to form the ink receiving layer. Formed. The preparation method of the coating liquid in that case is as follows.

<Preparation method A>
Ion exchange water and polyvinyl alcohol were added to the tank (A) and dissolved to obtain an aqueous polyvinyl alcohol solution (A). Next, acetic acid was added to the aqueous polyvinyl alcohol solution (A) in the tank (A) and stirred for a while to prepare an aqueous polyvinyl alcohol solution (B). Next, in the polyvinyl alcohol aqueous solution (B) of the tank (A), powdery alumina hydrate is added so that the solid content ratio of alumina hydrate to polyvinyl alcohol is 100: 10, A coating solution was obtained.

<Preparation method B>
Ion exchange water and polyvinyl alcohol were added to the tank (C) and dissolved to obtain an aqueous solution (C) of polyvinyl alcohol. Next, ion-exchanged water and acetic acid were added to another tank (D), and after stirring for a while, alumina hydrate was added as a powder to prepare an alumina dispersion (D). Next, the alumina dispersion (C) in the tank (C) and the polyvinyl alcohol aqueous solution (D) in the tank (D) so that the solid content ratio of the alumina hydrate and polyvinyl alcohol is 100: 10. The solution was added to the tank (E) and mixed while feeding separately to obtain a coating solution.

<Preparation method C>
Ion exchange water and acetic acid were added to the tank (F) and stirred for a while, and then alumina hydrate was added as a powder to prepare an alumina dispersion (F). This alumina dispersion (F) was used as a coating solution. <Example 1>
By the method of Preparation Method A, PVA210 (manufactured by Kuraray Co., Ltd.) was used as the polyvinyl alcohol to obtain a polyvinyl alcohol aqueous solution (A) having a solid content of 3.7% by mass. Next, acetic acid was added to 2% by mass with respect to the alumina hydrate powder, and the mixture was stirred for a while to prepare an aqueous polyvinyl alcohol solution (B) having a pH of 4.1. Next, Dispersal HP14 (manufactured by Sasol) was added as an alumina hydrate so that the ratio of alumina hydrate to polyvinyl alcohol solids was 100: 10 in the aqueous polyvinyl alcohol solution (B). As a result, a coating liquid having a solid content concentration of 30.3% by mass and a viscosity of 2700 mPa · s was obtained.

<Example 2>
The polyvinyl alcohol of the aqueous polyvinyl alcohol solution (A) of Example 1 was changed to PVA217 (manufactured by Kuraray Co., Ltd.), the solid content concentration of the aqueous polyvinyl alcohol solution (B) was changed to 3.5 mass%, and the pH was changed to 4. Adjusted to 1. A coating solution having a solid content concentration of 29.0% by mass and a viscosity of 2800 mPa · s was obtained in the same manner as in Example 1 except for this.

<Example 3>
The polyvinyl alcohol in the aqueous polyvinyl alcohol solution (A) of Example 1 was changed to PVA420 (manufactured by Kuraray Co., Ltd.), the solid content concentration of the aqueous polyvinyl alcohol solution (B) was changed to 3.7% by mass, and the pH was changed to 4.2. Adjusted. Other than this, a coating solution having a solid content concentration of 30.3% by mass and a viscosity of 2400 mPa · s was obtained in the same manner as in Example 1.

<Example 4>
The polyvinyl alcohol of the polyvinyl alcohol aqueous solution (A) of Example 1 was changed to PVA410 (manufactured by Kuraray Co., Ltd.), the solid content concentration of the polyvinyl alcohol aqueous solution (B) was changed to 3.7 mass%, and the pH was 4.1. Adjusted. Other than this, a coating solution having a solid content concentration of 30.2 mass% and a viscosity of 2000 mPa · s was obtained in the same manner as in Example 1.

<Example 5>
The polyvinyl alcohol in the aqueous polyvinyl alcohol solution (A) of Example 1 was changed to PVA235 (manufactured by Kuraray Co., Ltd.), the solid content concentration of the aqueous polyvinyl alcohol solution (B) was changed to 2.4 mass%, and the pH was 4.1. Adjusted. Other than this, a coating solution having a solid content concentration of 22.0 mass% and a viscosity of 3100 mPa · s was obtained in the same manner as in Example 1.

<Example 6>
The polyvinyl alcohol in the aqueous polyvinyl alcohol solution (A) in Example 1 was changed to PVA110 (manufactured by Kuraray Co., Ltd.), the solid content concentration of the polyvinyl alcohol in the aqueous polyvinyl alcohol solution (B) was changed to 2.4% by mass, and the pH was changed. Adjusted to 4.1. Other than this, a coating solution having a solid content concentration of 22.0 mass% and a viscosity of 3300 mPa · s was obtained in the same manner as in Example 1.

<Example 7>
The polyvinyl alcohol in the aqueous polyvinyl alcohol solution (A) of Example 1 was changed to PVA145 (manufactured by Kuraray Co., Ltd.), the solid content concentration of the aqueous polyvinyl alcohol solution (B) was changed to 2.4 mass%, and the pH was 4.1. Adjusted. Other than this, a coating solution having a solid content concentration of 22.0 mass% and a viscosity of 3800 mPa · s was obtained in the same manner as in Example 1.

<Example 8>
The solid content concentration of the aqueous polyvinyl alcohol solution (B) in Example 1 was changed to 2.4% by mass, and the pH was adjusted to 4.1. Other than this, a coating solution having a solid content concentration of 22.0% by weight and a viscosity of 500 mPa · s was obtained in the same manner as in Example 1.

<Example 9>
The alumina hydrate powder of Example 1 was replaced with HP-18 and an aqueous polyvinyl alcohol solution (the solid content concentration of B was changed to 4.6% by mass, and the pH was adjusted to 4.0. Otherwise, Example 1 and A coating solution having a solid content concentration of 35.5% by mass and a viscosity of 3000 mPa · s was obtained by an equivalent method.

<Example 10>
In the alumina hydrate powder of Example 1, the solid content concentration of HP-18 and the polyvinyl alcohol aqueous solution (B) was changed to 3.3% by mass, and the pH was adjusted to 4.1. Other than this, a coating solution having a solid content concentration of 28.0% by mass and a viscosity of 1500 mPa · s was obtained in the same manner as in Example 1.

<Example 11>
In the alumina hydrate powder of Example 1, the solid content concentration of HP-18 and the polyvinyl alcohol aqueous solution (B) was 4.8% by mass, and the amount of acetic acid added was 2.5% by mass with respect to the alumina hydrate. And the pH was adjusted to 3.6. Other than this, a coating solution having a solid content concentration of 36.5% by mass and a viscosity of 2800 mPa · s was obtained in the same manner as in Example 1.

<Example 12>
In the alumina hydrate powder of Example 1, the solid content concentration of HP-18 and the polyvinyl alcohol aqueous solution (B) was 4.2% by mass, and the amount of acetic acid added was 1.5% with respect to the alumina hydrate. And the pH was adjusted to 4.9. Other than this, a coating solution having a solid content concentration of 33.5% by mass and a viscosity of 3000 mPa · s was obtained in the same manner as in Example 1.

<Comparative Example 1>
Dispersal HP14 (manufactured by Sasol Co., Ltd.) was used as the alumina hydrate of the alumina dispersion liquid (F) by the preparation method C, and a coating liquid having a solid content concentration of 22.0 mass% and a viscosity of 4900 mPa · s was obtained. It was.

<Comparative example 2>
Coating with a solid content concentration of 28.0% by mass in the same manner as in Comparative Example 1 except that Dispersal HP18 (manufactured by Sasol) was used as the alumina hydrate of the alumina dispersion liquid (F) of Comparative Example 1. A liquid was obtained.

  However, because of gelation, the viscosity could not be measured.

<Comparative Example 3>
The polyvinyl alcohol aqueous solution (B) of Example 1 was adjusted to a solid content concentration of 2.5 mass%, an acetic acid addition amount of 0.5 mass% with respect to alumina hydrate, and a pH of 6.7. Except for this, a coating solution having a solid content concentration of 22.0% by mass was obtained in the same manner as in Example 1.

  However, because of gelation, the viscosity could not be measured.

<Comparative example 4>
The polyvinyl alcohol aqueous solution (B) in Example 1 was adjusted to a solid content concentration of 4.3 mass%, an acetic acid addition amount of 0.8 mass% with respect to the alumina hydrate, and a pH of 5.5. Other than this, a coating solution having a solid content concentration of 33.5% by mass was obtained in the same manner as in Example 1.

  However, because of gelation, the viscosity could not be measured.

<Comparative Example 5>
By the method of Preparation Method B, an attempt was made to prepare a coating solution having a solid content concentration of 22.0% by mass. First, PVA210 (made by Kuraray Co., Ltd.) was used as polyvinyl alcohol, and a polyvinyl alcohol aqueous solution having a solid content concentration of 16.1% by mass was obtained in a tank (C). Also, Dispersal HP14 (manufactured by Sasol Co., Ltd.) was used as the alumina hydrate, charged with ion exchange water and 2% by mass of acetic acid into another tank (D), stirred for a while, and then the alumina hydrate was added. An alumina dispersion having a solid content concentration of 22.9% by mass was prepared. Next, the alumina dispersion and the polyvinyl alcohol aqueous solution are separately fed to the tank (E), mixed and coated so that the ratio of the polyvinyl alcohol solid content to the alumina hydrate is 100: 10. An attempt was made to produce a working fluid.

  However, since the alumina dispersion became gelled, it became difficult to send the solution, and the coating liquid could not be produced. For this reason, the viscosity could not be measured.

<Comparative Example 6>
The solid content concentration of the aqueous polyvinyl alcohol solution of Comparative Example 5 was 22.0 mass%, and the solid content concentration of the alumina dispersion was 22.0 mass%. Other than this, an attempt was made to produce a coating solution having a solid content concentration of 22.0% by mass in the same manner as in Comparative Example 5.

  However, since the polyvinyl alcohol aqueous solution gelled, it became difficult to send the solution, and the coating solution could not be produced. For this reason, the viscosity could not be measured.

<Comparative Example 7>
HP18 was used as the alumina hydrate of the alumina dispersion liquid of Comparative Example 5, and the solid content concentration was changed to 30.3% by mass. Except for this, an attempt was made to produce a coating solution having a solid content concentration of 28.0% by mass in the same manner as in Comparative Example 5.

However, since the alumina dispersion became gelled, it became difficult to send the solution, and the coating liquid could not be produced. For this reason, the viscosity could not be measured.
<Comparative Example 8>
HP18 was used as the alumina hydrate of the alumina dispersion liquid of Comparative Example 5, the solid content concentration was 27.5% by mass, and the solid content of the polyvinyl alcohol aqueous solution was changed to 34.2% by mass. Except for this, an attempt was made to produce a coating solution having a solid content concentration of 28.0% by mass in the same manner as in Comparative Example 5.

  However, although the alumina dispersion liquid has a limit viscosity of 5000 mPa · s that can be fed and can be fed, the aqueous polyvinyl alcohol solution becomes difficult to feed due to gelation, and the coating liquid cannot be produced. For this reason, the viscosity could not be measured.

  Among the examples and comparative examples described above, with respect to the example in which the coating liquid could be manufactured, the manufactured coating liquid was applied at 200 m / min with a blade coater. And the coating liquid after coating was dried at 170 degreeC, and the ink receiving layer was formed.

  The coating suitability of these coating solutions was evaluated according to the following criteria.

<Evaluation method>
<Coating suitability>
A A coating solution can be fed, and a coating amount of 15 g / m ² or more can be applied.
B Coating liquid can be fed and coating can be applied at a coating amount of 10 g / m ² or more and less than 14 g / m ² .
C coating solution is a possible liquid feed, but less than a coated amount of 5 g / ^{m 2.} Or it is impossible to feed the coating solution.

  Table 1 shows the evaluation results of Examples 1 to 12 and Comparative Examples 1 to 8.

  In Table 1, when Examples 1-12 are compared with Comparative Examples 1, 2, and 5-8, solid content concentration is obtained by adding alumina hydrate as a powder to an aqueous polyvinyl alcohol solution to produce a coating liquid. It can be seen that a coating solution having a high coating suitability can be obtained. Further, when Examples 1 to 12 and Comparative Examples 3 and 4 are compared, the pH of the aqueous polyvinyl alcohol solution is 5 or less, so that a coating liquid having a high solid content concentration and high coating suitability can be obtained. I understand. Moreover, when Examples 1-4 and Examples 1-8 are compared, when the viscosity of a coating liquid is 2000 mPa * S or more and 3000 mPa * S or less, it turns out that coating suitability is favorable.

Claims (3)

A method for producing a coating liquid used for forming an ink receiving layer of an inkjet recording medium,
a preparation step of preparing an aqueous polyvinyl alcohol solution having a pH of 5.0 or less;
The manufacturing method of the coating liquid which has an addition process which adds an alumina hydrate as a powder to this polyvinyl alcohol aqueous solution.   The method for producing a coating liquid according to claim 1, wherein the viscosity of the coating liquid is 500 mPa · s or more and 4000 mPa · s or less. A method for producing an inkjet recording medium having an ink receiving layer,
A method for producing an inkjet recording medium, wherein the ink receiving layer is formed using a coating liquid produced by the production method according to claim 1.