JP2006142553A - Manufacturing method of inkjet recording medium and inkjet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of an inkjet recording medium, to which a coating liquid suitable for high-speed coating can be manufactured highly densely with favorable productivity and then coated so as to reduce crack developing due to the shrinkage of a highly densified coating film layer and, at the same time, which has favorable gloss and is excellent in ink absorbing capacity, and the inkjet recording medium. <P>SOLUTION: In the manufacturing method of the inkjet recording medium formed by coating a coating fluid dispersed with fine inorganic pigment particles on a support, the dispersion fluid of the fine inorganic pigment particles is heated up to at least 45°C and not higher than 55°C for not longer than 5 hr for stagnation processing. Finally, the coating fluid is formed by addingly mixing with at least a hydrophilic binder after the stagnation processing. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet recording medium manufacturing method and an ink jet recording medium.

  Ink-jet recording is a method in which fine droplets of ink are ejected by various operating principles and deposited on a recording medium such as paper, preferably an ink-jet recording medium, to record images and characters. It has advantages such as noise and easy multicoloring, and has been rapidly spreading in recent years. On the other hand, it is also used for high-quality printing such as photographs, so-called photo-like recording media, has high gloss as a recording medium, has a large amount of ink absorption, and has no trouble such as foreign matter or cracks on the medium. Is required. Photo-like recording media are expensive, and lower prices are increasingly required in the future.

  Smaller particle diameters of inorganic pigment fine particles used for a photo-like recording medium are advantageous in terms of gloss and print density, and silica fine particles have been used among the fine particles so far. Silica fine particles can be broadly classified into vapor phase silica fine particles and wet silica fine particles, and wet silica fine particles are further subdivided into silica fine particles produced by the gel method and silica fine particles produced by the precipitation method. Among the silica fine particles, the gas phase method silica fine particles are finer than the wet method silica fine particles, and are considered to be suitable for a photo-like ink jet recording medium.

  In the case of manufacturing an inkjet recording medium, for example, a silica fine particle is mixed and dispersed with a water-soluble medium to prepare a dispersion, and then a binder and various additives (anti-fading agent, fluorescent whitening agent, softening agent, etc.) (Additives are not limited to the timing of addition even before dispersion or before application) and mixed to form a coating solution. Vapor phase silica fine particles have a small particle size and a large number of active silanol groups, so that secondary dispersions are formed (soft agglomeration) in the dispersion, so high concentration dispersion cannot be achieved, or kneading type that gives high energy There are problems such as having to disperse with a disperser, which is not suitable for high-efficiency production. In addition, if the binder is added immediately after dispersion, the viscosity increases rapidly, and when the silica concentration of the dispersion is high, the liquid is difficult to flow, and when it is severe, it becomes a gel and cannot be handled as a liquid. If the dispersion liquid is not stagnated, a stable coating liquid cannot be produced and cannot be applied, so that it is not suitable for high-efficiency production as described above. As described above, the vapor phase silica fine particles have problems in high-efficiency production, and many techniques have been conventionally proposed to solve these problems.

  It is disclosed that the time from the end of dispersion of the solid fine particles to the application of the coating liquid is at least 5 hours, or the heat treatment is performed at 50 ° C. or higher between the dispersion and application (for example, Patent Documents). 1). This method mainly has the effect of shortening the time from the end of dispersion to coating, and it is described that the heat treatment step of 50 ° C. or higher may be either a dispersion or a coating solution. When the concentration of silica fine particles is high, adding a binder as described above has a problem that the fluidity of the liquid is significantly lowered and deteriorated, making it difficult to handle. Is not suitable.

  Further, there is a description that 10% is the limit of the coating solution silica fine particle concentration in the vapor phase method silica fine particles, and that the coating speed (coating speed, hereinafter also referred to as CS) is 150 m / min. (For example, refer to Patent Document 1). Considering the technology so far, the conditions described here are considered to be excellent, however, however, the market tends to expand in the future, and the productivity is no longer a high-efficiency production under these conditions. Is coming.

In addition, since the wet method silica fine particles have fewer active silanol groups than the gas phase method silica fine particles, high concentration dispersion is possible, and a coating solution can be prepared without requiring a stagnation time after preparation of the dispersion. However, there are limits to the concentration of wet method silica fine particles, and it is possible to apply high CS at a higher concentration than gas phase method silica fine particles. However, in order to improve productivity, higher efficiency production is required. Is coming.
JP 2001-149856 A

  The present invention has been made in view of the above problems, and an object of the present invention is to produce and apply a coating solution suitable for high-speed coating with high concentration and high productivity. An object of the present invention is to provide an ink jet recording medium manufacturing method and an ink jet recording medium which have few cracks generated due to shrinkage of a film layer, etc., which have a good gloss and an excellent ink absorption capacity.

  The above object of the present invention can be achieved by the following constitution.

(Claim 1)
In a method for producing an ink jet recording medium in which a coating liquid in which inorganic pigment fine particles are dispersed is coated on a support, the dispersion of inorganic pigment fine particles is heated and subjected to a stagnation treatment at 45 to 55 ° C. for 5 hours or less, and then at least A method for producing an inkjet recording medium, comprising adding and mixing a hydrophilic binder to produce a coating solution.

(Claim 2)
In a method for producing an inkjet recording medium in which a coating liquid in which inorganic pigment fine particles are dispersed is coated on a support, a coating liquid obtained by adding and mixing at least a hydrophilic binder to a dispersion of inorganic pigment fine particles is subjected to a shearing treatment at least once. A method for producing an ink jet recording medium, comprising coating on a support.

(Claim 3)
In a method for producing an ink jet recording medium in which a coating liquid in which inorganic pigment fine particles are dispersed is coated on a support, the dispersion of inorganic pigment fine particles is heated and subjected to a stagnation treatment at 45 to 55 ° C. for 5 hours or less, and then at least A method for producing an ink jet recording medium, comprising applying a coating solution mixed with a hydrophilic binder to a support after being subjected to a shearing treatment at least once.

(Claim 4)
4. The method for producing an ink jet recording medium according to claim 2, wherein the time until the coating is applied is 1 hour or less after the shearing treatment.

(Claim 5)
The method for producing an ink jet recording medium according to any one of claims 1 to 4, wherein the inorganic pigment fine particles are silica fine particles.

(Claim 6)
6. The method for producing an ink jet recording medium according to claim 5, wherein the coating liquid is applied at a silica fine particle concentration of 10% by mass or more and a coating speed CS of 200 m / min or more.

(Claim 7)
7. The method for producing an ink jet recording medium according to claim 5, wherein the silica fine particles are gas phase method silica fine particles.

(Claim 8)
An ink jet recording medium produced by the method for producing an ink jet recording medium according to claim 1.

  According to the present invention, it is possible to produce and apply a coating solution suitable for high-speed coating at a high concentration with high productivity, and there are few cracks generated due to shrinkage of the coating layer due to the high concentration, and gloss. And a method for producing an ink jet recording medium excellent in ink absorption capacity and an ink jet recording medium can be provided.

  Hereinafter, although the best mode for carrying out the present invention will be described, the present invention is not limited to these.

  The method for producing an ink jet recording medium of the present invention is a method for producing an ink jet recording material by applying a coating liquid in which inorganic pigment fine particles are dispersed on a support. One feature is that a stagnation treatment is carried out at 5 ° C. or less for 5 hours or less, and then at least a hydrophilic polymer (a hydrophilic polymer of a binder) is added and mixed to prepare a coating solution.

  Further, the method for producing an inkjet recording medium of the present invention is a method for producing an inkjet recording material by applying a coating liquid in which inorganic pigment fine particles are dispersed on a support, and at least a hydrophilic binder is added to the dispersion of inorganic pigment fine particles. One feature is that the coating solution in which is added and mixed is subjected to a shearing treatment at least once and coated on a support.

  The method for producing an ink jet recording medium of the present invention is a method for producing an ink jet recording material by applying a coating liquid in which inorganic pigment fine particles are dispersed on a support, and heating the dispersion of inorganic pigment fine particles to 45 ° C. One feature is that a stagnation treatment is carried out at 55 ° C. or less for 5 hours or less, and then a coating solution to which at least a hydrophilic binder is added and mixed is applied to the support by shearing at least once.

  In the present invention, the stagnation treatment is 45 ° C. or more and 55 ° C. or less for 5 hours or less (that is, 0 to 5 hours), preferably 0.5 to 4.5 hours, and 0.5 to 3 hours. More preferably. If it exceeds 5 hours, the inorganic pigment fine particles may be aggregated. If it is less than 45 degreeC, there exists a possibility that adsorption | suction to the inorganic pigment fine particle of a hydrophilic binder may become difficult to advance. On the other hand, when the temperature exceeds 55 ° C., there is a concern that aggregation of inorganic pigment fine particles occurs.

  The present inventors have dispersed inorganic pigment fine particle dispersions dispersed in an aqueous medium and then heated, thereby promoting the promotion of adsorption and soft aggregation of the cationic polymer to the inorganic pigment fine particles, whereby the inorganic pigment fine particles in the dispersion are First, a high-concentration dispersion is first prepared using vapor phase silica fine particles as inorganic pigment fine particles, and stirred and heated to a predetermined temperature (45 ° C. to 55 ° C.). The dispersion liquid was subjected to a stagnation treatment in the present invention (in the present invention, stagnation treatment means that the stagnation treatment is allowed to stand still at a predetermined temperature), and then a binder was added to prepare a coating liquid. It was found that the viscosity of the coating liquid was lower than that of the dispersion liquid in which the dispersion liquid was stagnation processed. In addition, even in the case of a dispersion subjected to stagnation treatment while heating, if the stagnation time is short, the fluidity is remarkably deteriorated when the binder is added, however, the phenomenon of gelation does not occur (stagnation treatment without heating). It has also been found that gelation occurs when it is made to occur. This phenomenon is because the inorganic pigment fine particles in the dispersion are not stabilized (in a stabilized state), the adsorption of the cationic polymer is not completely completed, and active silanol groups are emitted. It is presumed that the fluidity is not deteriorated because it is bonded to the binder. Also, if the stagnation time is short, the viscosity difference after preparation of the coating liquid is large without heating the dispersion, and if the stagnation is long, the dispersion is heated and after preparation of the coating liquid without There is a tendency that the difference in viscosity is small. The viscosity difference after preparing the coating solution after stagnation of the dispersion liquid is considerably smaller than that of a short stagnation time (about 30 minutes), and the viscosity with and without heating during stagnation is proportional to the stagnation time. It was found that the difference was reduced. This phenomenon (effect) was observed in the vapor-phase method silica fine particles, but not so much in the wet method silica fine particles.

Further, even in the case of a coating solution prepared from a dispersion that has been heat-treated during the stagnation treatment, when the silica concentration is high, the viscosity of the coating solution becomes several hundreds × 10 ⁻³ to several tens of thousands × 10 ⁻³ Pa · s. It is difficult to apply at high speed. Therefore, the present inventors have focused on the thixotropy of the liquid, thought that the viscosity can be reduced by shearing the liquid, and found that the viscosity decreased when the coating liquid was sheared. It was also found that the viscosity decreases in proportion to the amount of shearing force. However, after the shearing treatment, in a state where static stagnation or gentle shearing is applied, the original viscosity may be higher than the original viscosity when the original viscosity is high in several minutes to several tens of minutes. found. Therefore, it is necessary to control the time until the coating liquid is applied after the shearing treatment, and the viscosity. Examples of control means include shearing machine position, viscosity monitoring, shearing force control, etc., preliminarily investigating shearing force, the relationship between shearing time and viscosity, etc. with a lab scale, etc. However, it is not limited to these methods and means.

  In the present invention, it is preferable that the time until coating after the shearing treatment of the coating solution is 1 hour or less.

  In this invention, it is preferable to apply | coat with the silica fine particle density | concentration of a coating liquid being 10 mass% or more and the coating speed CS being 200 m / min or more. The silica fine particle concentration in the coating solution is preferably 8 to 20% by mass, and more preferably 10 to 14% by mass. The coating speed CS is preferably 200 m / min or more for improving productivity.

  Next, inorganic pigment fine particles will be described.

[Inorganic pigment fine particles]
Silica fine particles are preferable as the inorganic pigment fine particles used in the present invention. Silica fine particles can be broadly classified into gas phase method silica fine particles and wet method silica fine particles, and wet method silica fine particles are classified into silica fine particles produced by gel method (hereinafter referred to as gel method silica fine particles) and sedimentation method. It is subdivided into manufactured silica fine particles (hereinafter referred to as precipitated silica fine particles).

  Vapor phase silica fine particles are spherical anhydrous silica fine particles having an average primary particle size of 5 to 50 nm, produced by burning silicon tetrachloride with oxygen and hydrogen. Vapor phase silica fine particles have a small apparent specific gravity and a high specific surface area, but spherical particles tend to agglomerate in a network, making it difficult to disperse in water at a high concentration, and stabilizing the dispersion over time. However, it is advantageous for producing gloss and color density, although cracks are likely to occur when it is formed into a coating film.

  Gel silica fine particles are particles in which high-purity silica sand is mixed with sodium silicate and sulfuric acid to form a silicate sol, which is gradually polymerized to form primary particles, and three-dimensional aggregates are formed. Is pulverized by a general method such as airflow pulverization. That is, in the gel method, reaction polymerization is performed on the acidic side, and the gel method is allowed to stand until it is gelled, washed with water and dried to produce silica gel particles. Precipitated silica fine particles can be prepared by reaction polymerization on the alkali side, as it is, and then precipitated and dried.

  Since wet method silica fine particles have internal pores in primary particles, they are advantageous in terms of ink absorption capacity compared to gas phase method silica fine particles having no internal pores. Further, since the wet process silica fine particles contain a larger amount of water than the vapor phase process silica fine particles, there is an advantage that a high-concentration dispersion liquid can be easily obtained in an aqueous medium.

  The difference between the gel method and the precipitated silica fine particles is the primary particle size in addition to the synthesis conditions. Generally, the gel method silica fine particles have a smaller primary particle size than the precipitated silica. When the primary particle size is small, the color density is increased and gloss is easily generated.

  In addition, since the wet process silica fine particles can be dispersed at a high concentration, the water content in the coating solution during coating can be reduced, which is advantageous for drying and as a result, the coating speed can be increased. Furthermore, since the shrinkage rate of the film during drying is small, the stress applied to the film is reduced, and coating failures such as cracks can be reduced.

  The average particle diameter of the silica fine particles used in the present invention is preferably 3 to 50 nm (gas phase method) and 1.0 to 10 μm (wet method). These silica fine particles are not particularly limited, but specific examples include “AEROSIL” (manufactured by Nippon Aerosil Co., Ltd.), “Leolo Seal”, “Fine Seal”, “Toku Seal” (manufactured by Tokuyama Co., Ltd.), and the like. Can be mentioned.

  Next, a method for dispersing the dispersion will be described.

[Distributor]
The inkjet recording medium dispersion according to the present invention is prepared by preliminarily dispersing inorganic fine particles in an aqueous medium (for example, predispersion 1, and further by using a predisperser (for example, disperser 1 and further disperser 2)). After dispersion 2), it is preferable that the dispersion is further dispersed using the present disperser.

  Examples of the preliminary disperser (disperser 1) used in the preliminary dispersion 1 include a roller mill type disperser, a kneader type disperser, and a pin mixer type disperser which are centrifugal dispersers. These dispersers are continuous stirring type dispersers, which can be continuously produced, and are preferable because a wide dispersion space is not required to obtain a dispersion.

  The number of preliminary dispersers is preferably smaller if the target dispersion can be obtained. However, in practice, in order to obtain a high-quality ink jet recording medium by reducing the particle size of the inorganic pigment fine particles, a single spare disperser is required. One unit may be used if possible with a disperser. However, when a target dispersion liquid cannot be obtained, several preliminary dispersers are connected and used.

  Depending on the concentration and type of inorganic pigment fine particles in the aqueous medium and the quality of the target ink jet recording medium, there are several preliminary dispersers (for example, disperser 1, disperser, etc.). 2) are preferably used connected in series.

  As the pre-dispersing machine (dispersing machine 1), there can be mentioned a centrifugal type dispersing machine capable of dispersing at a high concentration continuously. Specifically, a pin mixer type “spiral pin mixer” (manufactured by Taiheiyo Kiko Co., Ltd.). And “Flow Jet Mixer” (manufactured by Flourken Powtex Co., Ltd.) are preferred.

  Examples of the preliminary disperser (disperser 2) include a centrifugal disperser of a continuous centrifugal disperser. Specifically, a neater type capable of reducing the particle size by applying high shear. “Fine Flow Mill” (manufactured by Taiheiyo Kiko Co., Ltd.) is preferable.

  The purpose of the main dispersion using the present dispersing machine is to eliminate the coarse particle size in the pre-dispersed liquid produced by the pre-dispersing machine and to make the particle size distribution uniform.

  Examples of the present disperser (disperser 3) used in the present dispersion include a pressure type and a media type disperser. Among these dispersers, a media-type disperser is preferable, and among them, a sand mill disperser is suitable for pulverizing coarse particle diameters and controlling particle size distribution uniformly, and efficiently producing a uniform dispersion liquid with high concentration. It can be manufactured well and is preferable.

  Since the inorganic pigment is a hard substance, it is preferable to use a hard material or a part coated with a material that is difficult to scrape as the part of the sand mill machine that comes into contact with the liquid.

  The bead diameter used in the sand mill disperser is preferably 0.1 to 1.0 mm, and more preferably 0.3 to 0.5 mm. The bead material is preferably made of zirconia which is hard and has a large specific gravity. The filling rate of the beads into the vessel is preferably 50 to 90% by mass. The residence time in the vessel is preferably 1 to 30 minutes, and more preferably 3 to 15 minutes. The peripheral speed of the disk is preferably 5 to 15 m / sec, and more preferably 8 to 11 m / sec.

  When preparing the dispersion with each disperser, it is preferable to cool the dispersion because the dispersion efficiency deteriorates and it becomes difficult to obtain a dispersion having a preferable particle size when the temperature of the dispersion rises. The apparatus for cooling the dispersion is not particularly limited, but a method of cooling the dispersion by attaching a cooling water circulation device to the dispersion or cooling the dispersion through a heat exchanger is preferable.

  In particular, when producing a high-gloss ink-jet recording medium, coarse particles that cause deterioration in glossiness must be reduced. Therefore, several dispersers can be connected in series to further improve the grindability. Alternatively, it is preferable to remove coarse particles from the dispersion using an apparatus for removing coarse particles.

[Heating processor]
The dispersion liquid after the completion of the dispersion is stored in the stock tank and stagnated. During the stagnation, the dispersion is heated to promote adsorption of the cationic polymer and promote soft aggregation, and the inorganic pigment fine particles in the liquid are stabilized. The heating method may be a method using a jacket with a jacket or a heating method such as online heating through a heat exchanger when sending the liquid from the disperser. For example, it is not limited to this method. The heated liquid is added and mixed with an additive, a hydrophilic binder resin, pure water and the like after several hours from the end of dispersion to form a coating liquid, which is sent to a coating apparatus and coated on a support. Here, if the viscosity is high (several hundreds × 10 ⁻³ to several tens of thousands × 10 ⁻³ Pa · s), the load on the coating liquid preparation device and the load on the coating device are large, and it is difficult to apply at high speed. Become.

[Shearing machine]
As described above, when the viscosity of the coating liquid is high, high-speed coating becomes difficult. Therefore, a shearing machine is provided between the coating liquid preparation pot and the coating apparatus for the purpose of reducing the viscosity of the coating liquid.

  Examples of shearing machines include high-speed rotary type and ultrasonic type, and high-speed rotary type equipment is likely to entrap bubbles when off-line, and there is a concern about coating failure due to bubbles. The method is preferred. In the case of ultrasonic waves, it is not particularly necessary to be a sealed type, but on the other hand, since a heat is generated as compared with a high-speed rotation type, a cooling device is required.

  FIG. 1 is a process diagram showing an example of a method for producing an ink jet recording medium of the present invention.

  The method for producing an inkjet recording medium of the present invention is performed as follows. First, inorganic pigment fine particles from the inorganic pigment fine particle charging device 1 and the aqueous medium from the aqueous medium charging device 2 are charged into the pre-dispersing machine 3 (dispersing machine 1), and then further dispersed by the pre-dispersing machine 4 (dispersing machine 2). I do. The preliminary dispersion machines 3 and 4 are provided with a cooling water circulation device to suppress the temperature rise of the dispersion liquid. In the main dispersion in the present dispersion machine 5 (dispersion machine 3), the temperature rise of the dispersion liquid is large. Therefore, the temperature of the preliminary dispersion liquid is lowered using the heat exchanger 6 and then the dispersion liquid 5 (dispersion machine 3) is charged. Perform this distribution.

  The dispersion liquid which has been dispersed is sequentially sent to the stagnation pot 7. The stagnation pot 7 is provided with a heating facility (a jacket or the like), and heats the dispersion. As another heating method, it is also possible to install a heat exchanger between the disperser 5 and the stagnation pot 7 and heat it online when the dispersion liquid is fed to the stagnation pot 7. After the stagnation in the stagnation pot 7, the dispersion is transferred to the coating liquid preparation pot 8 and added and mixed with an additive, a hydrophilic binder, pure water and the like to obtain a coating liquid. (Other devices are not shown, but a method of using a stagnation pot and a coating liquid preparation pot in common. Examples include addition and a method of adding a hydrophilic binder in-line, and the like, and are not limited to those shown in the figure). The coating liquid is then sent to the coating apparatus 11, and a shearing machine 10 is installed between the coating liquid preparation pot 8 (liquid feeding pot) and the coating apparatus 11 so that the sheared coating liquid is applied. It is applied with the device 11. The sheared coating liquid has a lower viscosity than the viscosity of the coating liquid preparation pot 8 (liquid feeding pot), and is applied to the support at high speed. If necessary, a filter, a defoaming machine, an in-line mixer for adding additives and the like are installed between the coating liquid preparation tank 8 (liquid feeding tank) and the coating apparatus 11.

[Dispersion]
The inkjet recording medium dispersion according to the present invention comprises at least inorganic pigment fine particles and an aqueous medium, and if necessary, a hydrophilic binder, a hardener, a cationic polymer, and other additives are added. be able to.

《Aqueous medium》
The aqueous medium used in the present invention is preferably a medium containing water as a main component and further added with a hardener (for example, boric acid), a lower alcohol (for example, ethyl alcohol), nitric acid and the like.

  Examples of the lower alcohol preferably used in the aqueous medium include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, and butyl alcohol. Among them, ethyl alcohol is preferable.

<< Hydrophilic binder >>
As the hydrophilic binder used in combination with the inorganic pigment fine particles, polyvinyl alcohol and derivatives thereof, polyalkylene oxide, polyvinyl pyrrolidone, polyacrylamide, gelatin, hydroxyl ethyl cellulose, carboxyl methyl cellulose, pullulan, casein, dextran, and the like can be used. However, it is preferable from the viewpoint of film strength immediately after printing to use a high-boiling organic solvent contained in the ink or a hydrophilic binder having low swellability and solubility in water.

  In the present invention, polyvinyl alcohol or a derivative thereof is particularly preferable from the viewpoint of film-forming properties. Among them, those having an average degree of polymerization of 1000 or more are preferable, and those having an average degree of polymerization of 2000 or more are more preferable. Moreover, 70-100% is preferable and, as for the saponification degree of polyvinyl alcohol or its derivative (s), 80-100% is more preferable.

  Two or more hydrophilic binders can be used in combination, but even in this case, it is preferable to contain at least 50% by mass of polyvinyl alcohol or a derivative thereof.

  Examples of the polyvinyl alcohol derivative include cation-modified polyvinyl alcohol, anion-modified polyvinyl alcohol, and nonionic-modified polyvinyl alcohol.

  The cation-modified polyvinyl alcohol can be obtained by saponifying a copolymer of an ethylenically unsaturated monomer having a cationic group and a vinyl acetate group.

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

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

  The degree of polymerization of the cation-modified polyvinyl alcohol is usually 500 to 4000, preferably 1000 to 4000.

  Moreover, the saponification degree of a vinyl acetate group is 60-100 mol% normally, Preferably it is 70-99 mol%.

  Anion-modified polyvinyl alcohol is described in, for example, polyvinyl alcohol having an anionic group as described in JP-A-1-2060888, JP-A-61-237681, and JP-A-63-307979. Examples thereof include a copolymer of vinyl alcohol and a vinyl compound having a water-soluble group, and a modified polyvinyl alcohol having a water-soluble group as described in JP-A-7-285265.

  Nonionic modified polyvinyl alcohol includes, for example, a polyvinyl alcohol derivative in which a polyalkylene oxide group as described in JP-A-7-9758 is added to a part of vinyl alcohol, and JP-A-8-25795. The block copolymer of the vinyl compound and vinyl alcohol which have the described hydrophobic group is mentioned.

  The ratio of the inorganic pigment fine particles to the hydrophilic binder is preferably 3 times or more in terms of mass ratio in order to obtain a high porosity and high film strength. From the same viewpoint, the ratio of the inorganic pigment fine particles to the hydrophilic binder is more preferably 6 times or more.

  The upper limit of the ratio of the inorganic pigment fine particles to the hydrophilic binder is preferably about 8 times or less from the viewpoint of the cracking performance of the film.

《Hardener》
The addition of a hardener capable of crosslinking with the hydrophilic binder in the dispersion improves the film-forming property of the coating film, the water resistance of the coating film, and the occurrence of cracks, which is the object of the present invention. Is preferable. Examples of such hardeners include organic hardeners containing epoxy groups, ethyleneimino groups, active vinyl groups, and the like, and inorganic hardeners such as chromium alum, boric acid, or borax.

  In particular, when the hydrophilic binder is polyvinyl alcohol, an epoxy hardener having at least two epoxy groups in the molecule, boric acid or a salt thereof, and borax are preferable. As boric acid, not only orthoboric acid but also metaboric acid and tetraboric acid can be used.

  The amount of the hardener added is usually 1 to 200 mg, preferably 2 to 100 mg per 1 g of the hydrophilic binder.

  As an example in which no hardener is used, any known method such as a method of curing with an electron beam or a method of curing with ultraviolet or infrared irradiation can be used.

<Cationic polymer>
A cationic polymer is preferably added to the dispersion for the purpose of improving the water resistance and bleeding resistance of the image. As the cationic polymer, for example, a cationic polymer having a primary to tertiary amino group and a quaternary ammonium base can be used. However, there is little discoloration and deterioration of light resistance with time, and dye fixing property is high. Therefore, a cationic polymer having a quaternary ammonium base is preferable.

  Specific examples of preferred cationic polymers are listed below, but the present invention is not limited to these, and dispersion may be carried out by containing other known cationizable substances.

  These cationic polymers having a quaternary ammonium base are generally highly water-soluble due to the quaternary ammonium base, but depending on the composition and ratio of the monomer that does not contain the quaternary ammonium base to be copolymerized, the cationic polymer is sufficiently water-soluble. May not dissolve. However, any solvent that can be dissolved by dissolving in a mixed solvent of water-miscible organic solvent and water can be used.

  Further, if necessary, a basic latex polymer disclosed in JP-A-57-36692, a polyallylamine described in JP-B-4-15744, JP-A-61-58788, and JP-A-62-174184, Alkali metal weak acid salts described in JP-A-61-47290 can be used in combination.

[recoding media]
The ink jet recording medium of the present invention is obtained by applying a coating liquid containing the dispersion onto a support and drying to form a coating film (ink absorbing layer).

<Support>
A well-known thing can be used suitably as a support body of an inkjet recording medium. Examples of the transparent support include films and plates made of materials such as polyester resin, diacetate resin, triacetate resin, acrylic resin, polycarbonate resin, polyvinyl chloride resin, polyimide resin, cellophane, and celluloid. And a glass plate. Among them, those having the property of resisting radiant heat when used as OHP are preferable, and polyethylene terephthalate is particularly preferable. The thickness of such a transparent support is preferably 10 to 200 μm.

  In addition, as a support used when it is not necessary to be transparent, for example, a sheet or plate made of general paper, synthetic paper, resin-coated paper, cloth, wood, metal, etc., and the above translucent support The thing etc. which made the opacification process by a well-known means can be mentioned. As the opaque support, a resin-coated paper (so-called RC paper) having a polyolefin resin coating layer in which a white pigment or the like is added to at least one of the base papers, or a so-called white pet formed by adding a white pigment to polyethylene terephthalate is preferable. For the purpose of increasing the adhesive strength between the support and the ink absorbing layer, the support is preferably subjected to corona discharge treatment, subbing treatment or the like prior to application of the ink absorbing layer. Furthermore, the ink jet recording medium of the present invention is not necessarily colorless, and a colored support may be used.

  In the ink jet recording medium of the present invention, it is preferable to use a paper support in which both sides of the paper support are laminated with polyethylene because the recorded image is close to photographic image quality and a high quality image can be obtained at low cost.

[Coating solution]
In order to improve the brittleness of the coating film when dried, the coating liquid for forming the ink receiving layer of the ink jet recording medium of the present invention is prepared by adding various droplets or polymer latex to the dispersion liquid. It is preferable. Examples of the various droplets include hydrophobic high-boiling organic solvents having a solubility in water of about 0.01% by mass or less at room temperature, such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, and silicone oil. it can. The polymer latex may be obtained, for example, by emulsion polymerization of one or more monomers such as styrene, methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, divinylbenzene, and hydroxyethyl methacrylate, or emulsion dispersion after polymerization. The polymer latex can be mentioned. Such droplets and latex particles can be preferably used in an amount of 10 to 50% by mass based on the hydrophilic binder. It is also preferable to contain polyols having a molecular weight of 300 or less for preventing cracks and film brittleness. Examples of such polyols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, glycerin, 1,6-hexanediol, and polyethylene glycol having a molecular weight of 300 or less.

  Various additives can be added to the arbitrary layer on the ink absorbing layer side of the ink jet recording medium of the present invention as required.

  For example, the ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988 and JP-A-62-261476, JP-A-57-74192, JP-A-57-87989, JP-A-60- Japanese Patent Application Laid-Open Nos. 72785, 61-146591, JP-A-1-95091 and 3-13376, various surfactants of anion, cation or nonion, JP-A-59 No. 42993, 59-52689, 62-280069, 61-242871, and JP-A 4-219266, etc., whitening agent, sulfuric acid, phosphoric acid, acetic acid , PH adjusters such as citric acid, sodium hydroxide, potassium hydroxide, potassium carbonate, lubricants such as diethylene glycol, preservatives, thickening , Antistatic agent, it is preferable to add various known additives such as a matting agent.

<Formation of ink absorption layer>
Solid content of the coating applied to a support (including the ink absorption layer) is preferably ^{5~40g / m 2, 10~30g / m} 2 is more preferable.

  The dry film thickness of the coating film is determined by the porosity of the ink absorbing layer and the required void volume, but is generally 15 μm or more, preferably 20 μm or more.

The gap capacity of the ink absorbing layer is preferably 10 to 40 g per 1 m ² of the ink jet recording medium, and more preferably 15 to 30 g.

However, the void volume is J.P. TAPPI Paper Pulp Test Method No. 51-87 “Liquid absorbency test method for paper and paperboard” (Bristow method), the amount of liquid transfer at an absorption time of 2 seconds when the ink absorption layer side of an inkjet recording medium was measured (g / m ² ).

  The ink jet recording medium of the present invention has at least one ink absorbing layer, preferably two or more. In this case, the ratio of the inorganic pigment fine particles to the hydrophilic binder in the two or more ink absorbing layers is mutually different. May be different.

  In addition to the ink absorbing layer, a swellable layer that does not have voids or is swellable with respect to ink may be included together with the ink absorbing layer.

  Such a swellable layer may be provided in the lower layer (side closer to the support) of the ink absorption layer or the upper layer (side away from the support) of the ink absorption layer. Furthermore, when there are two or more ink absorption layers May be provided between the ink absorbing layers. A hydrophilic binder is usually used for the swellable layer, and examples of the hydrophilic binder used here include the hydrophilic binder used for the ink absorbing layer.

<Formation of back layer>
Various types of back layers are provided on the opposite side of the ink jet recording medium of the present invention from the side having the ink absorbing layer in order to further improve the prevention of curling, sticking when superimposed immediately after printing, and prevention of ink transfer. It is preferable.

  The configuration of the back layer varies depending on the type and thickness of the support and the configuration and thickness of the ink-absorbing layer, but generally a hydrophilic binder or a hydrophobic binder is used. The thickness of the back layer is usually in the range of 0.1 to 10 μm.

  Further, the back layer can be roughened to prevent sticking to other ink jet recording media, improve writing performance, and improve transportability in the ink jet recording apparatus. Organic or inorganic fine particles having a particle diameter of 2 to 20 μm are preferably used for this purpose.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

Example 1
<< Preliminary dispersion (Preparation of dispersion-1) >>
In an aqueous medium, silica fine particles “AEROSILA300” (manufactured by Nippon Aerosil Co., Ltd.) as inorganic pigment fine particles are dispersed at the concentrations shown in Table 1 as a predisperser (disperser 1) “Flow Jet Mixer” (Gakken Powtex Co., Ltd.) The dispersion is performed by using a dispersion machine “Fine Flow Mill” (manufactured by Taiheiyo Kiko Co., Ltd.) as a preliminary dispersion machine (dispersing machine 2) to prepare dispersion-1. did.

  In the dispersion of the preliminary disperser (disperser 1 and disperser 2), cold water was passed through the cooling device (jacket) to prevent the temperature of the dispersion from rising.

  As the aqueous medium, water containing a cationic polymer (Exemplary Compound P13) and a hardening agent (boric acid, borax) was used. The cationic polymer was added at 4% by mass with respect to the silica fine particles, and the hardener was added at 0.3% by mass with respect to the silica fine particles.

<< Main Dispersion (Preparation of Dispersion-2) >>
Then, after cooling through a heat exchanger, this dispersion is further dispersed using a continuous processing type sand mill disperser “Sand Mill RL 12.5” (manufactured by Ashizawa Co., Ltd.) as Disperser 3 (Dispersion-2). Were prepared (Table 1) and fed to a stagnation kettle.

  In the dispersion of this disperser (disperser 3), cold water was passed through a cooling device (jacket) to prevent the temperature of the dispersion from rising.

《Stagnation processing》
Dispersion liquid-2 was heated in a stagnation pot, and the stagnation time until preparation of the coating liquid was changed (described in Tables 1, 2 and 3) to stagnate.

<Preparation of coating solution>
After the stagnation treatment, when preparing the coating liquid, the dispersion was adjusted to 40 ° C., and polyvinyl alcohol “PVA235” (manufactured by Kuraray Industries Co., Ltd.) as a binder was added while stirring. The addition amount of polyvinyl alcohol was set to 5.5% by mass with respect to the silica fine particles.

  After adding the polyvinyl alcohol, pure water was further added (the concentration of silica fine particles was adjusted) to prepare a coating solution.

<< Liquid feeding, shearing, coating, ink jet recording medium preparation >>
After that, when the coating solution is fed to the coating device, it is sheared (US dispersion (ultrasonic dispersion), ultrasonic dispersion machine UH-1200SR, ultrasonic dispersion frequency: 20 KHz) while being fed. An ink-absorbing layer is formed by coating (wire bar) and drying on a support (RC paper) at a coating speed (CS) of 200 m / min so that the amount of silica fine particles is 18 g / m ^2. Was made.

  Although the dispersion | distribution conditions and the shearing process conditions are also implementing other levels, typical levels are shown in Tables 1 to 8.

  The application results are also carried out at various levels. Tables 6 to 8 show typical levels.

  Table 1 shows the silica fine particle concentrations of the preliminary dispersion (dispersion-1) and the main dispersion (dispersion-2); the stagnation treatment (heating, time); and the shearing treatment (presence / absence, time). In addition, the heating at the time of a stagnation process was implemented, stirring at 55 degreeC.

  Tables 2 and 3 show the viscosities of coating liquids obtained by subjecting the dispersion (silica fine particle concentration: 10% by mass, 12% by mass) to stagnation treatment (heating, time); shearing treatment (presence / absence, time (min)).

(Measurement of viscosity)
The viscosity was measured using a B-type viscometer.

  Tables 4 and 5 show a list of the stagnation time (hr) of the dispersion liquid necessary for the coating liquid (silica fine particle concentration: 10%, 12%) to reach the viscosity (300 cp, 600 cp), which is a coatable region.

(Viscosity evaluation)
The viscosity was measured using a B-type viscometer.

  Examples of coating solutions obtained by subjecting a dispersion (silica fine particle concentration: 10% by mass) to a stagnation treatment (heating, time); shearing treatment (presence / absence, time (min)), and an ink jet recording medium obtained by coating the dispersion Tables 6 to 8 show the results of measurement and evaluation of the absorption capacity, gloss, and cracks.

(Measurement of particle size)
The particle diameter is a value measured by a photon correlation method “Zetasizer 1000HS” (manufactured by Malvern).

(Measurement of absorption capacity)
The mass (A (g)) of a sample obtained by cutting an inkjet recording medium into A4 size is measured. Thereafter, the sample is immersed in ion-exchanged water at 25 ° C. for 1 min, taken out, wiped off moisture on the surface, and then the mass (B (g)) is measured. The value of B (g) −A (g) is obtained and converted to a value corresponding to a size (unit) of 1 m ² to obtain an absorption capacity (g / m ² ).

(Measurement and evaluation of cracks)
The number of cracks per 0.3 m ^{2 on the} coated surface was visually counted and evaluated according to the following criteria. In addition, there is no practical problem if the number of cracks is usually 10 or less.

×: The number of cracked parts is 100 or more. Δ: The number of cracked parts is 10 or more and 99 or less. ○: The number of cracked parts is 9 or less (glossiness measurement and evaluation).
The glossiness of 75 ° was measured using a variable angle photometer (VGS-1001DP) manufactured by Nippon Denshoku Industries Co., Ltd. If this value is 45 or more, it is effective as a photo-like image recording medium.

  Even when the silica fine particles were changed to Fine Seal (manufactured by Tokuyama Corporation, X-37, gas phase method silica fine particles) and the cationic polymer was changed to Exemplified Compound P9, almost equivalent results were obtained.

  As apparent from Tables 1 to 8, the ink jet recording medium manufacturing method and the ink jet recording medium according to the present invention can produce a good coating solution with high concentration and high productivity. It can be seen that there can be obtained an ink jet recording medium having little gloss caused by shrinkage of the film layer, good gloss and excellent ink absorption capacity.

It is process drawing which shows an example of the manufacturing method of the inkjet recording medium which concerns on this invention.

Explanation of symbols

1 Inorganic pigment charging device 2 Aqueous medium charging device 3 Preliminary disperser (disperser 1)
4 Preliminary disperser (Disperser 2)
5 Disperser (Disperser 3)
6 Heat exchanger 7 Stagnant pot (with heating device)
8 Coating liquid preparation pot 9 Additive feeding device 10 Shearing machine 11 Coating device

Claims (8)

In a method for producing an ink jet recording medium in which a coating liquid in which inorganic pigment fine particles are dispersed is coated on a support, the dispersion of inorganic pigment fine particles is heated and subjected to a stagnation treatment at 45 to 55 ° C. for 5 hours or less, and then at least A method for producing an inkjet recording medium, comprising adding and mixing a hydrophilic binder to produce a coating solution. In a method for producing an inkjet recording medium in which a coating liquid in which inorganic pigment fine particles are dispersed is coated on a support, a coating liquid obtained by adding and mixing at least a hydrophilic binder to a dispersion of inorganic pigment fine particles is subjected to a shearing treatment at least once. A method for producing an ink jet recording medium, comprising coating on a support. In a method for producing an ink jet recording medium in which a coating liquid in which inorganic pigment fine particles are dispersed is coated on a support, the dispersion of inorganic pigment fine particles is heated and subjected to a stagnation treatment at 45 to 55 ° C. for 5 hours or less, and then at least A method for producing an ink jet recording medium, comprising applying a coating solution mixed with a hydrophilic binder to a support after being subjected to a shearing treatment at least once. 4. The method for producing an ink jet recording medium according to claim 2, wherein the time until the coating is applied is 1 hour or less after the shearing treatment. The method for producing an ink jet recording medium according to any one of claims 1 to 4, wherein the inorganic pigment fine particles are silica fine particles. 6. The method for producing an ink jet recording medium according to claim 5, wherein the coating liquid is applied at a silica fine particle concentration of 10% by mass or more and a coating speed CS of 200 m / min or more. 7. The method for producing an ink jet recording medium according to claim 5, wherein the silica fine particles are gas phase method silica fine particles. An ink jet recording medium produced by the method for producing an ink jet recording medium according to claim 1.

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