JP2006346960A - Method for manufacturing inkjet recording sheet and inkjet recording sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a void-type inkjet recording sheet which can inhibit coating streaks and cracks during rapidly applying a coating liquid containing an inorganic fine particle by a slide coating process, and has excellent production efficiency and no coating trouble, and an inkjet recording sheet. <P>SOLUTION: The method for manufacturing an inkjet recording sheet reduces the viscosity and wet film thickness of a coating liquid of a bottom layer formed adjacent to a support, compared with those of a higher layer, when not less than two coating layers are simultaneously formed on a continuously traveling support in a multi-layer fashion and dried. In this method, a drying process is provided which adds to the coating liquid a water-soluble polymer compound which is crosslinkable by a solvent, an inorganic fine particle and ionizing radiations, then crosslinks the polymer compound by irradiating with the ionizing radiations after applying the coating liquid, and vaporizes the solvent. The dissolved oxygen content of the coating liquid is set to not less than 0.3 and not more than 0.8 times the saturation level at a coating liquid temperature and also to not less than 2.5 mg/L. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording paper, and more particularly to a method for manufacturing an ink jet recording paper that has high productivity and can reduce coating failure, and an ink jet recording paper produced thereby.

  Inkjet recording is a method in which fine droplets of ink are ejected by various operating principles and deposited on recording materials such as paper to record images and characters. In recent years, it has been rapidly spreading.

  Of course, it is also used for high-quality printing such as photographs, and as inkjet recording paper (recording material, sometimes simply recording paper) 1) High ink absorption, fast absorption speed 2) No blurring, 3) High color density, 4) High water resistance, light resistance, ozone resistance, 5) Glossiness, 6) No failure such as foreign matter and cracks on the sheet, 7) High productivity, etc. It is requested.

  In recent years, an ink jet recording sheet having a porous structure in an ink absorbing layer has been developed and put into practical use for the purpose of improving the various properties described above. Since such a recording paper has a porous structure, it has excellent ink absorption (quick drying) and high gloss.

  By the way, an ink jet recording sheet is usually manufactured by applying and drying an ink absorbing layer coating liquid on a support. From the viewpoint of productivity, it is required that a plurality of layers can be simultaneously applied and dried at a high speed, and that the solid content in the coating solution can be increased.

  The coating liquid is produced by adding a hydrophilic resin to inorganic fine particles or a dispersion obtained by dispersing inorganic fine particles in an aqueous medium. Silica is often used as the inorganic fine particles. In particular, silica produced by a vapor phase method is used because of the large porosity when formed into a coating film. However, since the porosity is increased, there is a possibility that a coating failure such as cracking during drying may occur.

  Also, the curtain method and slide method are generally used as a method for simultaneously laminating coating liquids. However, when coating is performed at a high speed or the solid content of the coating liquid is increased more than currently used, the coating properties deteriorate, especially. A streak-like failure occurs. On the other hand, Patent Document 1 proposes a method in which the lowermost coating solution viscosity, film thickness, and binder ratio are the same as or lower than that of the upper layer. Although this method is effective for high-speed coating, the coating solution becomes less viscous in the subsequent drying process, so that the coating film is disturbed (blown) by the drying air, and particularly the coating speed is 200 m / min or more. And the countermeasures are not sufficient at present.

  On the other hand, in Patent Document 2, as a method of gelling a coating film before drying, it is applied using a coating liquid mainly composed of an inorganic sol and an ionizing radiation curable monomer / oligomer, and ionizing radiation is applied after coating. Has proposed a method of forming an ink-receiving layer by drying the coating film after passing through a step of curing the compound by irradiation.

However, since this method forms a film having a relatively high density and a dense three-dimensional cross-linking, a new problem arises that the coating film has poor crack resistance and conversely deteriorates crack resistance. In general, ionizing radiation curable monomers / oligomers have a relatively low molecular weight and many have strong skin irritation, and there are concerns about adverse effects on printing quality due to unreacted components and safety. is there. Furthermore, since most of the compounds on the market are low in hydrophilicity, they are not suitable for general water-based coating used for coating an ink-jet receiving layer, and the range of material selection is naturally narrow.
JP 2000-250171 A (Claims) JP-A-9-263038 (Claims)

  The present invention has been made in view of the above-mentioned actual situation, and the problem to be solved by the present invention is that coating stripes and cracks that are likely to occur when applying a coating liquid containing inorganic fine particles at a high speed by a slide coating method. An object of the present invention is to provide a void-type ink jet recording paper manufacturing method and an ink jet recording paper that are excellent in production efficiency and free of coating failure.

  The object of the present invention has been achieved by adopting the following configuration.

(Claim 1)
When two or more coating layers are simultaneously coated and dried on a continuously running support, the viscosity of the lowermost coating solution provided in contact with the support, the wet film thickness, the viscosity of the upper coating solution, In the method for producing an inkjet recording paper in which the film thickness is lower than the wet film thickness, the coating solution contains at least a solvent, inorganic fine particles, and a water-soluble polymer compound that crosslinks with ionizing radiation, and is irradiated with ionizing radiation after coating. After passing through the step of crosslinking the polymer compound, the method has a drying step of evaporating the solvent, and the amount of dissolved oxygen in the coating solution is 0.3 to 0.8 times the saturation amount at the coating solution temperature. And 2.5 mg / L (liter) or more.

(Claim 2)
2. The method for producing an inkjet recording paper according to claim 1, wherein the inorganic fine particles are silica fine particles and are silica produced by a vapor phase method.

(Claim 3)
3. The method of manufacturing an ink jet recording paper according to claim 1, wherein the simultaneous multilayer coating is a slide coating method.

(Claim 4)
An ink jet recording paper produced by the method for producing an ink jet recording paper according to claim 1.

  According to the results of various studies by the inventors of the present application, it has been found that cracks are greatly affected by bubbles in the coating liquid in the ink jet recording paper as in the present invention. That is, it was found that cracking occurred during the drying process due to the presence of bubbles. As a result of intensive studies, a good correlation is obtained when the dissolved oxygen amount is used as an index of bubbles. In the present invention, 0.3 to 0.8 times the saturated dissolved oxygen amount at the coating solution temperature, and 2. It has been found that setting it to 5 ppm or more is effective in preventing cracks. In particular, the influence of the dissolved oxygen amount on the upper layer side is large.

  If there are bubbles in the coating, it is not evenly irradiated into the film when ionizing radiation is applied, causing cross-linking unevenness, which causes uneven stress during drying, leading to cracking. We found that streaks also deteriorated.

  INDUSTRIAL APPLICABILITY According to the present invention, there is provided a method for producing a void-type ink jet recording paper, which suppresses coating streaks and cracks, which is likely to occur when applying a coating liquid containing inorganic fine particles at a high speed by slide coating, has excellent production efficiency, and has no coating failure. Recording paper could be provided.

  Hereinafter, the compound, the coating solution composition, the coating method and the like used for the coating solution of the inkjet recording paper of the present invention will be further described.

[Inorganic fine particles]
As the inorganic fine particles used in the present invention, those having a low refractive index are preferably used for forming an ink absorption layer (hereinafter also referred to as a void layer) of ink jet recording paper requiring transparency, and silica fine particles are particularly preferable.

  As silica, silica synthesized by an ordinary wet method, colloidal silica, silica synthesized by a gas phase method, or the like is preferably used. Colloidal silica or silica synthesized by a gas phase method is more preferable, and silica synthesized by a gas phase method can obtain a high porosity. The average primary particle size of the silica particles is preferably 3 to 100 nm, more preferably 4 to 50 nm, and most preferably 4 to 20 nm.

  Silica synthesized by a gas phase method having an average primary particle size of 4 to 20 nm, which is most preferably used, is commercially available, for example, with an Aerosil-based product name from Nippon Aerosil.

  Usually, silica is dispersed in an aqueous medium, and a hydrophilic polymer or the like is added and mixed as a dispersion to prepare a coating solution. At that time, silica is present in a state where secondary agglomerated particles are formed.

  As a method of dispersing silica, a known method can be used. For example, a high-pressure homogenizer, a sand mill, an ultrasonic wave, a high-speed stirring type disperser and the like can be mentioned.

  In the present invention, the average particle size is preferably 200 nm or less from the viewpoint of obtaining a high density and preferable image quality during printing. The average particle diameter is obtained as a simple average value (number average) by observing the cross section or surface of the void layer itself or the surface with an electron microscope, determining the particle diameter using 100 arbitrary particles. Here, each particle size is represented by a diameter assuming a circle equal to the projected area.

[Polymer compound that crosslinks with ionizing radiation]
The polymer compound that is cross-linked by water-soluble ionizing radiation used in the ink demand layer of the present invention is a water-soluble resin that undergoes a cross-linking reaction by causing a reaction by irradiation with ionizing radiation such as ultraviolet rays and electron beams, A resin that is water-soluble before the cross-linking reaction, but becomes substantially water-insoluble after the cross-linking reaction. Such a resin is hydrophilic even after the cross-linking reaction and maintains sufficient affinity with ink. Is.

  Examples of such resins include saponified polyvinyl acetate, polyvinyl acetal, polyethylene oxide, polyalkylene oxide, polyvinyl pyrrolidone, polyacrylamide, hydroxyethyl cellulose, methyl cellulose, hydroxypropyl cellulose, or derivatives of the above hydrophilic resins, and these It is at least one selected from the group consisting of copolymers, or a hydrophilic resin modified with a modifying group such as a photodimerization type, a photodecomposition type, a photopolymerization type, a photomodification type, or a photodepolymerization type It is.

  Among these, a resin modified with a photodimerization type or photopolymerization type modification group is preferable from the viewpoint of sensitivity or stability of the resin itself.

  As the photodimerization type modifying group, those having a diazo group, a cinnamoyl group, a styrylpyridinium group, or a styrylquinolium group introduced are preferable, and a resin dyed with a water-soluble dye such as an anionic dye after photodimerization is preferable. Examples of such resins include resins having a cationic group such as a primary amino group or a quaternary ammonium group, such as JP-A Nos. 62-283339, 1-198615, and 60-252341. Photosensitive resins (compositions) described in Japanese Laid-Open Patent Publication Nos. 56-67309 and 60-129742, resins that become cationic after curing, such as azide groups that become amino groups by curing treatment, Examples thereof include photosensitive resins (compositions) described in JP-A-56-67309.

  Specifically, for example, the following can be listed.

  The photosensitive resin described in JP-A-56-67309 is represented by a 2-azido-5-nitrophenylcarbonyloxyethylene structure represented by formula (I) or a formula (II) in a polyvinyl alcohol structure. The resin composition having a 4-azido-3-nitrophenylcarbonyloxyethylene structure.

  Specific examples of the resin are described in Examples 1 and 2 in the official gazette, and the constituent components of the resin and the use ratio thereof are described on page 2 of the official gazette.

  The photosensitive resin described in JP-A-60-129742 describes a compound represented by the general formula (III) in a polyvinyl alcohol structure.

(Wherein R is a phenyl group)
As the photopolymerization type modifying group, for example, a resin disclosed in JP-A No. 2000-181062 is preferable from the viewpoint of reactivity.

Wherein R ₁ is a hydrogen atom or methyl, n is 1 or 2, X is —CO— (CH ₂ ) _m —, —O—CO—CH ₂ —, —O—, and Y is a single bond or aromatic. Ring, m is an integer of 0-6.)
[Photoinitiator / Photosensitizer]
In the present invention, it is also preferable to add a photoinitiator or a photosensitizer to the coating solution. These compounds may be dissolved or dispersed in a solvent, or may be chemically bonded to the photosensitive resin.

  There is no restriction | limiting in particular about the photoinitiator and photosensitizer which are applied, A conventionally well-known thing can be used.

  For example, benzophenones such as benzophenone, hydroxybenzophenone, bis-N, N-dimethylaminobenzophenone, bis-N, N-diethylaminobenzophenone, 4-methoxy-4′-dimethylaminobenzophenone, thioxatone, 2,4-diethylthioxanthone, Thioxanthones such as isopropylthioxanthone, chlorothioxanthone, isopropoxychlorothioxanthone, anthraquinones such as ethyl anthraquinone, benzanthraquinone, aminoanthraquinone, chloroanthraquinone, benzoin ethers such as acetophenone, benzoin methyl ether, 2,4,6-trihalo Methyl triazines, 1-hydroxycyclohexyl phenyl ketone, 2- (o-chlorophenyl) -4,5-diphenyl Midazole dimer, 2- (o-chlorophenyl) -4,5-di (m-methoxyphenyl) imidazole dimer, 2- (o-fluorophenyl) -4,5-phenylimidazole dimer, 2- (O-methoxyphenyl) -4,5-phenylimidazole dimer, 2- (p-methoxyphenyl) -4,5-diphenylimidazole dimer, 2, -di (p-methoxyphenyl) -5-phenyl Imidazole dimer, 2,4,5-triarylimidazole dimer of 2- (2,4-dimethoxyphenyl) -4,5-diphenylimidazole dimer, benzyldimethyl ketal, 2-benzyl-2-dimethyl Amino-1- (4-morpholinophenyl) -butan-1-one, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-1-propyl Panone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one , Phenanthrenequinone, 9,10-phenanthrenequinone, benzoins such as methylbenzoin and ethylbenzoin, 9-phenylacridine, acridine derivatives such as 1,7-bis (9,9'-acridinyl) heptane, bisacylphosphine Examples thereof include oxides and mixtures thereof, and the above may be used alone or in combination.

  In particular, water-soluble 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 4- (2-hydroxyethoxy) -phenyl- (2- Water-soluble photoinitiators such as hydroxy-2-propyl) ketone, thioxanthone ammonium salt, and benzophenone ammonium salt are preferable from the viewpoint of crosslink efficiency because of excellent mixing properties.

  In addition to these photoinitiators, accelerators and the like can also be added. Examples of these include ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, ethanolamine, diethanolamine, triethanolamine and the like.

[Water-insoluble water-soluble resin]
In the present invention, the definition of the water-insoluble and water-affinity resin or the definition of water resistance is as follows.

  This refers to those having a mass residual rate of 85% or more when immersed in warm water of 80 degrees for 5 minutes.

[Ionizing radiation and its irradiation method]
Examples of the ionizing radiation in the present invention include electron beams, ultraviolet rays, α rays, β rays, γ rays, X-rays, etc., which are easy to handle and are widely used industrially, Ultraviolet light is preferred.

  Examples of the electron beam irradiation method include a scanning method, a curtain beam method, and a broad beam method. The curtain beam method is preferable from the viewpoint of processing capability.

  The acceleration voltage of the electron beam can be changed as appropriate depending on the specific gravity and film pressure of the coating film, but 20 to 300 kV is appropriate. The irradiation amount of the electron beam is preferably in the range of 0.1 to 20 Mrad.

In the case of ultraviolet irradiation, a low pressure, medium pressure, high pressure mercury lamp, metal halide lamp or the like having an operating pressure of several 0.1 mkPa to 1000 kPa is used as a light source, but high pressure mercury lamps and metal halide lamps are used from the viewpoint of wavelength distribution of the light source. Preferably, a metal halide lamp is more preferable. It is preferable to provide a filter that cuts light having a wavelength of 300 nm or less. The output of the lamp ^{400W~30kW, 10mW / cm 2 ~1W /} cm 2 as illuminance, preferably 0.1~800mJ / cm ² as irradiation energy, 1 to 100 mJ / cm ² is more preferable.

[Hydrophilic polymer]
In addition to the polymer compound that is cross-linked by the water-soluble ionizing radiation, a known hydrophilic polymer may be used in combination. A preferred hydrophilic polymer is polyvinyl alcohol.

  The polyvinyl alcohol includes, in addition to general polyvinyl alcohol obtained by hydrolysis of polyvinyl acetate, modified polyvinyl alcohol such as cation-modified polyvinyl alcohol and anion-modified polyvinyl alcohol having an anionic group. .

  Polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate preferably has an average polymerization degree of 300 or more, and particularly preferably has an average polymerization degree of 1000 to 5000.

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

  When polyvinyl alcohol is contained as the hydrophilic polymer, it is preferable to add a hardening agent in order to improve the film forming property of the film and increase the strength of the film. When polyvinyl alcohol is used as the hydrophilic binder, it is preferable to use an epoxy hardener or a borate as the hardener.

  As borate, oxygen acid having a boron atom as a central atom and its salt are shown. Specifically, orthoboric acid, metaboric acid, hypoboric acid, tetraboric acid, pentaboric acid and salts thereof. Is included.

  The amount of boric acid or a salt thereof can vary widely depending on the amount of inorganic fine particles and hydrophilic polymer in the coating solution, but is generally 1 to 60% by mass, preferably 5 to 40% by mass with respect to the hydrophilic polymer. .

[Ink absorbing layer]
The ink absorbing layer is preferably porous, and in order to make it porous, it is obtained by using a small amount of a hydrophilic binder with respect to the inorganic fine particles, but the ratio of the inorganic fine particles to the hydrophilic binder is 3 to 3 by mass ratio. 10 times, preferably 4 to 8 times.

  The hydrophilic binder here refers to the total mass of the polymer compound cross-linked by the water-soluble ionizing radiation and the hydrophilic polymer.

  Various additives other than those described above can be added to the ink absorbing layer. 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- No. 72785, 61-146591, JP-A-1-95091 and 3-13376, etc., various anionic, cationic or nonionic surfactants; No. 59-42993, 59-52689, 62-280069, 61-242871, JP-A 4-219266, and the like. Various known additives such as lubricants, preservatives, thickeners, antistatic agents, matting agents and the like can also be contained.

  The dry film thickness of the porous ink absorbing layer is determined in relation to the ink absorption amount, and is generally 20 to 70 μm, but 30 to 50 μm is preferable from the viewpoint that all of the ink solvent must be temporarily retained. . A particularly preferable dry film thickness is 35 to 50 μm.

  In the present invention, when the viscosity of the lowermost coating solution and the wet film thickness are not more than the viscosity of the upper layer and the wet film thickness, high-speed coating is possible. In particular, the slide coating method is effective. The coating speed is preferably 200 m / min or more and 400 m / min or less.

  The viscosity of the lowermost layer is preferably 5 to 20 mPa. The wet film thickness is preferably 3 to 20 μm. The viscosity on the upper layer side may be higher than that of the lowermost layer, but is preferably 300 mPa or less for handling.

  As the lowermost coating solution, it is preferable to adjust the viscosity by diluting the coating solution used for the adjacent upper layer.

[Amount of dissolved oxygen]
As a means for bringing the amount of dissolved oxygen within the range of the present invention, a method of removing air dissolved in the coating solution by defoaming the coating solution is effective. As a method for defoaming the coating liquid, a conventionally known stationary method, a decompression method, a stationary decompression method, a disk that rotates at high speed in a decompression tank, and a liquid droplet to be defoamed is ejected from the disk. In addition to the method of destroying bubbles by colliding with the wall of the tank (dispersion plate type defoaming method), the liquid is stretched to a thin film in a decompressed chamber to promote the bubble outflow, and the gas contained in the bubbles A method of breaking bubbles with pressure (vacuum thin film method), a method of inflating and floating bubbles in a liquid in a vacuum tank, and then jetting pressurized air toward the bubbles that floated, destroying bubbles, and using ultrasonic waves Methods and the like. The coating solution can be defoamed alone or in combination.

  It is also effective to increase the amount of saturated dissolved oxygen by lowering the temperature of the coating solution immediately before coating from the temperature at which the coating solution was produced. Examples of means in this case include a method of cooling a pipe for supplying the coating liquid to the coating machine after preparing the coating liquid in batch, a method using a heat exchanger, a method of cooling the coating machine, and the like.

  The temperature difference at the time of preparing the coating solution and immediately before coating is preferably 1 ° C. or more and 10 ° C. or less.

  In addition, as a means for adjusting the dissolved oxygen amount, it is effective to use deaerated water when dispersing silica or dissolving the hydrophilic binder.

  Moreover, in order to make dissolved oxygen amount 2.5 mg / L or less, an apparatus becomes large and it takes time, and it is unpreferable on production efficiency. Further, when the concentration is 2.5 mg / L or less, the silica particles may be promoted to agglomerate, and on the contrary, the cracks are worsened or the gloss is lowered.

  The temperature immediately before application of the coating solution is preferably 30 ° C or higher and 55 ° C or lower. When it is lower than 30 ° C., the viscosity of the coating solution increases and the handling property is deteriorated. On the other hand, when the temperature is higher than 55 ° C., the silica particles are aggregated, so that cracks are deteriorated.

  The silica mass concentration in the coating solution is preferably in the range of 8 to 30%, particularly preferably in the range of 10 to 20%. If it is 8% or less, the drying load becomes large, and if it is higher than 30%, the fluidity of the coating solution becomes poor, and problems are likely to occur in terms of handling.

  It is preferable to remove foreign matters and coarse particles by applying filtration before applying the coating solution.

In order to efficiently perform the defoaming treatment, it is also preferable to apply shear to the coating solution to reduce the viscosity. As the shear rate, 10 ⁻³ to 10 ⁻⁵ (1 / S) can be preferably used.

[Support]
As a support for the ink jet recording paper of the present invention, a paper support, a plastic support (transparent support), a composite support and the like known as conventional ink jet recording paper can be used as appropriate, but a clear image can be obtained at a higher density. Therefore, it is preferable to use a hydrophobic support that does not allow ink liquid to penetrate into the support.

  Examples of the transparent support include films made of materials such as polyester resins, diacetate resins, triacetate resins, acrylic resins, polycarbonate resins, polyvinyl chloride resins, polyimide resins, cellophane, and celluloid. Among them, those having a property to withstand 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. It is preferable to provide a known undercoat layer on the ink receiving layer side and the backing layer side of the transparent support from the viewpoint of adhesion between the ink receiving layer and the back layer and the support.

  The support used when it is not necessary to be transparent includes, for example, 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 paper, polyethylene terephthalate and white pigment. A so-called white pet obtained by adding the is preferred.

[Preparation of inkjet recording paper]
The ink receiving layer of the ink jet recording paper of the present invention can be obtained, for example, by applying and drying a coating liquid containing at least an inorganic fine particle dispersion and a hydrophilic binder on the support surface. A plurality of different coating solutions can be applied sequentially or simultaneously as required.

  In the case of using a plurality of coating liquids, it is preferable to apply the coating layers in layers at the same time. Further, it is also possible to apply by adding in-line necessary additives just before coating in the coating solution.

The ink absorption layer needs to absorb all ink droplets, and preferably has an absorption capacity of 10 ml / m ² or more, more preferably 15 ml / m ² or more.

The amount of inorganic fine particles attached to the ink receiving layer is preferably 10 to 25 g / m ² . The thickness of the receiving layer is preferably 10 to 50 μm.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the embodiments of the present invention are not limited to these examples. In Examples, “%” indicates absolutely dry mass% unless otherwise specified.

(Preparation of preliminary dispersion)
As an aqueous medium (hereinafter referred to as A liquid),
800L of water
Boric acid 5.8kg
6.4kg of borax
5% nitric acid 3.4L
Ethanol 16.0L
P-1 (10% solution) 440L
(P-1: Compound described in paragraph No. 0072 “Chemical Formula 1” of JP-A-2001-10207 below)
Were mixed and dissolved.

  As the inorganic fine particles, gas phase method silica having an average primary particle diameter of about 7 nm (manufactured by Nippon Aerosil Co., Ltd., A300: hereinafter referred to as A300) was stored at a temperature of 25 ° C.

  Liquid A was supplied to a flow jet mixer (manufactured by Ganken, hereinafter referred to as FJM) separately and continuously at a rate of 8.3 kg / min and A300 at a rate of 3.56 kg / min. The dispersion continuously discharged from the FJM was continuously passed through a fine flow mill (manufactured by Taiheiyo Kiko Co., Ltd., hereinafter referred to as FFM) to obtain a preliminary dispersion. The temperature of the preliminary dispersion was 40 ° C. The conditions of FJM and FFM were performed at a peripheral speed of 30 m / sec.

Example 1
(Preparation of inorganic fine particle dispersion: Main dispersion)
The preliminary dispersion was supplied to RL125V (continuous wet media type pulverizer, manufactured by Ashizawa Co., Ltd., hereinafter referred to as RL) at 10 kg / min to perform main dispersion, thereby obtaining an inorganic fine particle dispersion. The RL conditions were a bead diameter of 0.3 mm zirconia, a bead filling rate of 80%, a residence time of 3 minutes, a rotor rotating peripheral speed of 10 m / sec, and the vessel and rotor made of urethane resin.

(Preparation of coating solution 1 for ink receiving layer: coating solution for upper layer, hereinafter referred to as coating solution 1)
A photocrosslinkable polyvinyl alcohol derivative aqueous solution having a styrylpyridinium group introduced into the inorganic fine particle dispersion and adjusted to a concentration of 10% (Toyo Gosei Kogyo Co., Ltd .: SPP-SHR, main chain PVA polymerization degree 2300, fighting degree 88% ) Water was added, stirred and mixed to obtain a coating solution. The temperature of the coating solution was adjusted to 40 ° C. The viscosity was 200 mPa · s. The dissolved oxygen amount was 7 mg / L and was the saturated dissolved oxygen amount. The amount of dissolved oxygen was measured by Yellow springs instrument Co. Inc. The dissolved oxygen meter model 52 was used, and the probe was measured using a 5905 type.

  The mass ratio between the silica fine particles and the water-soluble resin was 6: 1. The mass concentration of silica fine particles in the coating solution was adjusted with water so as to be 17%.

(Preparation of coating solution 2 for ink receiving layer: coating solution for the bottom layer)
The coating solution 1 was diluted with deaerated water and adjusted to 5 mPa · s. The amount of dissolved oxygen at this time was 5.6 mg / L. The silica concentration was 5.64%.

(Preparation of inkjet recording paper)
The coating solution 1 was defoamed so that the dissolved oxygen amount was 5.6 mg / L (0.8 times the saturation). The coating liquids 1 (upper layer) and 2 (lower layer) were simultaneously coated on the support using a slide type coating apparatus. The coating speed was 300 m / min. The upper layer wet film thickness was 100 μm, and the lower layer was 15 μm. Thereafter, a metal halide lamp having a dominant wavelength at 365 nm was irradiated with ultraviolet rays having an energy amount of 50 mJ / cm ² and dried to obtain a recording paper 1. The coating solution temperature immediately before coating was 40 ° C.

  The support used was a paper support coated with polyethylene on both sides (thickness is 220 μm, and the polyethylene on the ink absorption layer surface contains 13% by mass of anatase-type titanium oxide based on polyethylene). Recording sheets 2 to 23 were prepared by changing the dissolved oxygen amount in the upper layer coating solution 1, the dissolved oxygen amount in the lower layer coating solution 2, the upper and lower layer wet film thicknesses, the viscosity, the coating speed, and the coating solution temperature as shown in Table 1. .

Table 1 shows the results of evaluation of cracks and coating stripes on recording sheets 1 to 23. The viscosity of the coating solution was adjusted by diluting with water. The amount of silica fine particles applied was set to 16.15 g / m ² .

(Evaluation of recording paper)
Cracks The number of cracks per 0.3 m ^{2 on the} coated surface was visually counted. If the number of cracks is usually 10 or less, it is considered that there is no practical problem.

Coating stripe The coating surface was visually evaluated.

○: None △: Slightly occurring but no practical problem ×: Frequent occurrence and practical problem

  It is understood that any of the characteristics within the present invention may have any characteristics, but those outside the present invention have problems with at least any of the characteristics.

Claims (4)

When two or more coating layers are simultaneously coated and dried on a continuously running support, the viscosity of the lowermost coating solution provided in contact with the support, the wet film thickness, the viscosity of the upper coating solution, In the method for producing an inkjet recording paper in which the film thickness is lower than the wet film thickness, the coating solution contains at least a solvent, inorganic fine particles, and a water-soluble polymer compound that crosslinks with ionizing radiation, and is irradiated with ionizing radiation after coating. After passing through the step of crosslinking the polymer compound, the method has a drying step of evaporating the solvent, and the amount of dissolved oxygen in the coating solution is 0.3 to 0.8 times the saturation amount at the coating solution temperature. And 2.5 mg / L (liter) or more. 2. The method for producing an inkjet recording paper according to claim 1, wherein the inorganic fine particles are silica fine particles and are silica produced by a vapor phase method. 3. The method of manufacturing an ink jet recording paper according to claim 1, wherein the simultaneous multilayer coating is a slide coating method. An ink jet recording paper produced by the method for producing an ink jet recording paper according to claim 1.