JP2005119110A - Ink jet recording paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ink jet recording paper which is excellent in ink absorbing properties and high-speed recording suitability, has a high weather resistance, reduces nonuniformity in gloss and provides an ink jet print having a protective film having few surface defects, and particularly to provide the ink jet recording paper which is capable of providing a uniform feel of gloss (glossiness, image clarity) without depending on an image density. <P>SOLUTION: The ink jet recording paper is used in an ink jet recording method wherein the protective film having a dry solid content of 0.05-0.3 g per 1 m<SP>2</SP>is formed on the ink jet recording paper having an image formed with ink containing a colorant, by using colorless ink which contains a polymer having a film forming function, but contains no colorant substantially. The paper has at least one porous ink absorbing layer on a non-water-absorbing substrate and this layer contains a compound of which the molecular weight is 200 or less and which is expressed by general formula (I). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink jet recording paper used for ink jet recording with a colorant-containing ink. More specifically, the present invention relates to an ink jet recording paper excellent in high-speed printing suitability and capable of obtaining a high-gloss and high-quality ink jet print having high weather resistance. About.

  In recent years, ink jet recording materials have been rapidly improved in image quality and approaching photographic image quality. In particular, in order to achieve image quality comparable to photographic image quality by ink jet recording, improvements have been made from the aspect of ink jet recording paper (hereinafter simply referred to as recording paper). A void-type recording paper provided with a porous layer made of a hydrophilic polymer has a high gloss, shows a vivid color, or has an excellent ink absorption and drying property. It is becoming one. In particular, when a non-water-absorbing support is used, there is no occurrence of cockling after printing, as seen on a water-absorbing support, so-called “wrinkles”, and a high smooth surface can be maintained. Prints can be obtained and gradually become the mainstream of photographic prints created by inkjet recording.

  Inkjet recording is generally divided into ink using water and a water-soluble solvent as an ink solvent, and ink using a non-aqueous oil-based solvent, and each has a type using a dye and a type using a pigment. In order to obtain a recorded image, dedicated paper suitable for each type is required. Of these, water-based inks are mainly used from the viewpoint of environment and safety.

  Inkjet prints using water-soluble dye inks have high image sharpness, uniform surface gloss, and color prints comparable to photographic image quality. However, prints using this water-soluble dye have poor storage stability compared to pigment inks, are susceptible to fading due to sunlight, ozone, or other oxidizing gases, and have a large image blur. It has become. In particular, in a void-type recording paper provided with a fine porous layer, the contact area between the dye and the indoor air is widened, and therefore, fading due to the oxidizing gas in the air is large, and improvement thereof is desired.

  In order to improve the deterioration due to such storage, it has been proposed to add various antioxidants as anti-fading agents. For example, JP-A-57-87989, JP-A-57-74192 and JP-A-60-72785 discloses an ink-jet recording paper containing various compounds as an antioxidant, and JP-A-57-74193 discloses an ink-jet recording paper containing an ultraviolet absorber. Hydrazides are added to No. 61-14659, hindered amine antioxidants are added to JP-A 61-14659, and nitrogen-containing heterocyclic mercapto compounds are added to JP-A 61-177279. However, Japanese Patent Laid-Open Nos. 1-115677 and 1-335479 may be added with a thioether-based antioxidant. Hindered phenol antioxidants having a specific structure are added to No. 3, and JP-A-3-13376 includes adding a hindered phenol antioxidant and a hindered amine antioxidant in combination. Ascorbic acids are added to 7-195824 and 8-150773, zinc sulfate is added to JP-A-7-149037, and thiocyanate is contained in JP-A-7-314882. Japanese Patent Application Laid-Open No. 8-318792 discloses that thiourea derivatives and the like are added, and that Japanese Patent Application Laid-Open Nos. 7-276790 and 8-108617 contain saccharides. Can be added with a phosphoric acid antioxidant, and nitrite, sulfite, thiosulfate, etc. are added to JP-A-8-300807. But the Japanese Patent Laid-Open No. 9-267544 discloses that the addition of hydroxylamine derivative.

  However, the effect of ink jet recording paper having fine pores is not always sufficient, and when these various anti-fading agents are added in a large amount in order to obtain a sufficient anti-fading effect, the ink absorption of the porous layer There are many disadvantages such as lowering the performance.

  Further, when water-soluble dye ink is used, there is a weak point that bleeding occurs due to high hydrophilicity and water resistance is inferior. That is, the dye is likely to bleed when stored for a long time under high humidity after image recording or when water droplets adhere to the printed surface. In order to solve this problem, it is a common practice to add a dye-fixing substance such as a cationic substance to the porous layer. For example, a method of binding to an anionic ink dye using a cationic polymer and immobilizing it firmly is preferably used. Examples of such a cationic polymer include a polymer having a quaternary ammonium group. For example, “Inkjet printer technology and materials” (issued by CMC, July 1998) and JP-A-9-193532 [ [0008] is described in the literature. Also proposed is a method in which water-soluble polyvalent metal ions are added in advance to an ink jet recording paper, and the dye is solidified and fixed during ink jet recording. Although the use of a cationic polymer or polyvalent metal ion improves bleeding and water resistance, the dye is unevenly dyed in the ink absorption layer due to binding with the cationic polymer or polyvalent metal. For this reason, even if the anti-fading agent described above is added, if the diffusibility is small in the ink absorbing layer, the effect may not be sufficiently exhibited.

  On the other hand, the pigment ink has high durability of the image such as light resistance, gas resistance, and bleeding of the image, but it has a weak point that the gloss is easily changed to an image shape, and as a result, it is difficult to obtain a print close to photographic quality.

  Various techniques have been proposed to compensate for such weak points. However, it is difficult to obtain an ink jet print having high gloss and no change in gloss in an image state by a normal recording method for the basic reason. That is, the pigment particles used in the pigment ink generally have a size of about 0.1 μm (100 nm). The size of the dye molecule is on the order of 1 nm. When the ink is made of pigment particles much smaller than 0.1 μm, the characteristics approach that of the dye ink, and the high durability characteristic of the pigment ink is lowered. .

  On the other hand, in order to obtain a highly glossy and highly colored recording paper, the size of the inorganic fine particles used for making the ink absorbing layer of the recording paper porous should be 0.1 μm or less. It is necessary because of the relationship.

  Therefore, in order for the pigment particles of the ink to land on the recording paper composed of particles of the same size in order to achieve high gloss and high color, the pigment ink particles do not penetrate into the ink absorbing layer and the surface is uneven. Will form. At this time, the pigment particles of the ink are oriented on the surface of the receiving layer, and the gloss increases from the white background (becomes metallic glossy), or the pigment particles randomly coalesce on the surface to make the surface unevenness coarser This causes problems such as causing irregular reflection and reducing gloss. Such behavior is largely dependent on the characteristics of the pigment ink, but when a normal image is printed, it is common that a very unnatural gloss change occurs in the image and a high-quality print cannot be obtained. .

  The present applicant has made various studies in order to improve the unnaturalness of an image formed with the pigment ink as described above. For example, there has been proposed a recording sheet that improves the unnaturalness of the image by using a recording sheet having a surface roughness (Ra) in a specific range (see, for example, Patent Document 1). According to this technique, although the unnaturalness that the gloss changes to an image is improved, a recording sheet having a sufficiently high gloss cannot be obtained. Further, in Japanese Patent Application Nos. 2001-240509, 2002-352196, 2003-27191, and 2003-77673, a polymer is contained in an area where an image is recorded with pigment ink or an area where no image is recorded with pigment ink. Ink jet recording methods have been proposed in which gloss uniformity is improved by spraying colorless ink.

  In addition, an inkjet recording method is disclosed in which a protective film layer is formed with a polymer-containing colorless ink on an image surface printed with pigment ink (see, for example, Patent Documents 2 to 8).

  It has been found that there is a new problem when forming a protective coating layer by spraying colorless ink over the entire image recording area as described in the above publications. That is, when colorless ink is sprayed onto the area printed with pigment ink, if the ink is not discharged below the ink absorption capacity of the porous ink absorption layer, the colorless ink overflows in the image area and forms a patchy protective film layer. . When the protective coating layer is formed in a patchy shape, a local change in the thickness of the protective coating layer occurs, which causes a slight point-like gloss unevenness or a rainbow unevenness phenomenon due to light diffraction. Therefore, in order to avoid this phenomenon, the droplet forming the protective film layer and the film thickness to be formed are important.

In general, the ejection amount of pigment ink necessary for forming an image is approximately 15 to 25 ml per 1 m ^{2 of} recording paper, and ink absorption of an ink jet recording paper provided with a porous ink absorbing layer on a non-water-absorbing support. The volume is generally 20-30 ml. Therefore, in order to form a protective film layer with colorless ink, it is necessary to carry out the discharge amount of this colorless ink at about 10 ml or less per 1 m ^{2 of} recording paper. If a measure for further increasing the porous ink absorption capacity of the recording paper is taken, this limitation is eased, but it is not preferable because of a significant increase in cost and curl.

By the way, the film-forming polymer concentration contained in the colorless ink cannot be extremely increased due to the restriction that it should have an appropriate viscosity (usually about several mPa · s) as the ink. Therefore, the range that can be normally used is about 10% or less. Due to such restrictions, in practice, the thickness of the protective coating layer formed of colorless ink is about 1 g / m ² as a polymer, and the thickness is about 1 μm or less.

In this regard, Japanese Patent Application Laid-Open No. 2002-301428 describes the thickness of the coating layer as 0.1 to 100 μm, preferably 0.5 to 20 μm as the thickness after drying. Japanese Patent Application Laid-Open No. 2003-53942 discloses that the amount of coating layer is 0.77 to 7.7 g / m ² in terms of wet film thickness, and the solid content concentration of the coating liquid is 0.5 to 20% by mass. Therefore, the dry solid content of the coat layer is 0.0039 to 1.54 g / m ² . Japanese Patent Laid-Open No. 2002-264465 has a description of coating in the range of 0.1 to 5 g / m ² . When the dry solid mass is 1 g / m ² and the solid density is 1, the dry film thickness of the coat layer is 1 μm.

  According to the study by the present inventors, when a protective film having a film thickness of about 0.5 to 1 μm is formed, a change in color tone or a slight change in film thickness that is considered to be caused by rainbow-like interference fringes in the coat layer. It has been found that minute glaring easily occurs. The rainbow-like interference fringe is a phenomenon that changes the color tone when the viewing angle of the recording paper is changed, and is a phenomenon that gives a different color tone depending on the viewing angle of the white background portion or the image recording portion. As a result of studies for solving these problems, it has been found that it is effective to set the film thickness to about 0.3 μm or less. Furthermore, the present inventors can obtain a relatively thin protective film by sufficiently adjusting the thickness of the protective film in order to sufficiently reduce the difference in glossiness between the image area and the non-image area. First, in Japanese Patent Application No. 2003-320882, it was found that it was necessary to adjust the surface characteristics of the inkjet recording paper.

As a result of further investigation on the above problems, in order to obtain a uniform glossiness (expressed by numerical values of glossiness and image clarity) over the entire region of images having different densities with a protective film of 0.3 μm or less. Requires extremely fine and uniform thickness control. However, the realization thereof is not easy, and there is a problem that fine point defects are easily generated. In addition, when stored for a long period of time, the protective film is likely to be peeled off from the recording material, centering on defects, and there has been a problem that non-uniformity of glossiness is further increased.
JP 2001-341409 A International Patent Publication WO00 / 06390 Pamphlet JP 2000-225695 A JP 2001-270217 A JP 2001-277488 A Japanese Patent Laid-Open No. 2002-201428 JP 2002-264465 A JP 2002-307755 A

  The present invention has been made in view of the above-mentioned problems, and its purpose is to reduce gloss unevenness, which is a weak point of pigment ink, having good ink absorbability, excellent high-speed recording suitability, high weather resistance, An object of the present invention is to provide an ink jet recording paper that provides a high gloss, high quality ink jet print having a protective film with few surface defects. In particular, an object of the present invention is to provide an ink jet recording paper that can give a uniform gloss (glossiness, image clarity) regardless of image density.

The above object of the present invention is achieved by the following configurations.
(Claim 1)
0.05 to 0.3 g per m ² using a colorless ink containing a polymer having a film-forming ability and substantially free of a colorant on an ink jet recording paper image-formed with a colorant-containing ink. An ink jet recording paper for use in an ink jet recording method for forming a protective film having a dry solid content of at least one porous ink absorbing layer on a non-water-absorbing support, the porous ink absorbing layer comprising: An inkjet recording paper comprising a compound represented by the following general formula (I) having a molecular weight of 200 or less.

[Wherein, R ₁ represents a hydrogen atom, a substituted or unsubstituted alkyl group, an alkenyl group, an aryl group, an acyl group, a heteroaryl group, a heterocyclic group, NR ₄ R ₅ , or OR ₆ . R _{2 to} R ₆ each have the same meaning as R ₁ . R ₁ and R ₂ , R ₁ and R ₃ may be bonded to each other to form a ring. X represents an oxygen atom or NH. ]
(Claim 2)
The inkjet recording paper according to claim 1, wherein the compound represented by the general formula (I) is urea or a urea derivative.
(Claim 3)
The inkjet recording paper according to claim 1 or 2, wherein the protective film is formed by the colorless ink substantially over the entire surface of the inkjet recording paper.
(Claim 4)
The discharge of the colorless ink droplets forming the protective film is performed immediately after the image formation with the colorant-containing ink is performed while the water is not substantially evaporated. The inkjet recording paper of any one of Claims.
(Claim 5)
The inkjet recording paper according to any one of claims 1 to 4, wherein the colorant-containing ink is a pigment ink.
(Claim 6)
The porous ink absorption layer located on the surface of the porous ink absorption layer contains inorganic fine particles having an average particle diameter of 10 to 100 nm and polyvinyl alcohol. The inkjet recording paper of any one of Claims.
(Claim 7)
The center line average roughness (Ra) when measured with a reference length of 2.5 mm as defined in JIS-B-0601 and a cutoff value of 0.8 mm on the surface of the porous ink absorbing layer is 0.08 to 0.20 μm. The inkjet recording paper according to claim 1, wherein

  According to the present invention, the ink absorption is good, the high-speed recording suitability is high, the weather resistance is high, the gloss unevenness, which is a weak point of the pigment ink, is reduced, and the protective film with a small surface defect is provided. An object of the present invention is to provide an ink jet recording paper that provides high-quality ink jet printing. In particular, it is possible to provide an ink jet recording paper that can give a uniform gloss (glossiness, image clarity) regardless of image density.

  Hereinafter, the best mode for carrying out the present invention will be described in detail, but the present invention is not limited thereto.

  The recording paper of the present invention is particularly suitable for an ink jet recording system in which an image is recorded using a pigment ink, but can also be applied to a system in which an ink jet image is recorded using a dye ink. When ink-jet image recording is performed using pigment ink, the effect of improving the image-like gloss unevenness and the scratch resistance of the pigment particle layer formed on the recording paper is particularly remarkable. In particular, the effect of improving the resistance to discoloration of the oxidizing gas by ozone gas or the like is great for the image recorded matter.

  The present invention is described in detail below.

  The recording paper of the present invention is a recording paper suitable for an ink jet recording system, and has a porous ink absorbing layer on at least one surface on a non-water-absorbing support.

  Non-water-absorbing supports that can be preferably used in the present invention include transparent supports and opaque supports. Examples of the transparent support include polyester resins, diacetate resins, triatesate resins, acrylic resins, polycarbonate resins, polyvinyl chloride resins, polyimide resins, cellophane, celluloid, and other films. 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 50 to 200 μm.

  As the opaque support, for example, resin-coated 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, so-called RC paper, polyolefin (polyethylene, polypropylene, etc.), polyethylene terephthalate, barium sulfate, An opaque resin film to which a white pigment such as titanium oxide is added or a film support obtained by bonding two or more of them can be used.

  The thickness of these various opaque supports can vary widely depending on the application, but is generally in the range of 60 to 300 μm.

  Prior to application of the ink absorbing layer, the support is subjected to corona discharge treatment or subbing treatment with gelatin, other hydrophilic polymer or hydrophobic polymer for the purpose of increasing the adhesive strength between the various supports and the ink absorbing layer. Etc. are preferably performed. Furthermore, the ink jet recording paper of the present invention does not necessarily need to be transparent or white, and may be a colored recording sheet.

  In the ink jet recording paper of the present invention, using a paper support in which both sides of the base paper support are laminated with polyethylene, the recorded image is close to photographic image quality, and a high quality image can be obtained at a relatively low cost. Particularly preferred.

  Such a paper support laminated with polyethylene will be described below.

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

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

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

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

  The basis weight of the base paper is preferably 40 to 250 g, particularly preferably 60 to 220 g. The thickness of the base paper is preferably 40 to 250 μm.

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

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

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

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

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

  As the polyethylene-coated paper surface, a surface that has been finely roughened for the purpose of improving the adhesion to the ink receiving layer and the coating property can also be used. In this case, it is preferable that the fine rough surface is formed in a range of Ra = 0.10 to 0.25 μm. In the polyethylene-coated paper, it is particularly preferable to keep the moisture content in the paper at 3% by mass to 10% by mass.

  The stiffness of these supports mainly depends mainly on the thickness of the base paper, and the desired stiffness can be obtained by appropriately selecting the thickness of the base paper. In addition, curling of the support is an important characteristic that determines the curling characteristics provided with the ink absorbing layer, and an optimal curl balance is achieved in combination with the ink absorbing layer, but the ink absorbing layer is a porous ink absorbing layer. In the recording paper of the present invention, it is generally preferable to design a minus curl (a curl in which the four corners are lifted when left on a horizontal board with the ink-absorbing layer-coated side on the bottom). Although the curl design of the base paper is determined by the relationship with the ink receiving layer, it is generally -5 to -50 mm (the A4 size base paper is lifted at the four corners when left at a temperature of 23 ° C and a relative humidity of 20 to 80% for 1 hour. (Average height) is preferable.

  Next, the porous ink absorbing layer provided on the support will be described.

  The porous ink absorbing layer (hereinafter also simply referred to as the ink absorbing layer) may be provided on only one side of the support or on both sides. When providing on both surfaces, each may have the same structure and thickness, or may differ. The ink absorption layer may be a single layer or may be composed of a plurality of layers.

  The porous ink absorbing layer of the recording paper of the present invention preferably comprises at least a hydrophilic binder and inorganic fine particles.

  Examples of inorganic fine particles include light calcium carbonate, heavy calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc hydroxide, zinc sulfide, zinc carbonate, hydrotalcite, Examples include white inorganic pigments such as aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, alumina, colloidal alumina, pseudoboehmite, aluminum hydroxide, lithopone, zeolite, and magnesium hydroxide. . The inorganic fine particles can be used as primary particles or in a state where secondary agglomerated particles are formed.

  In the present invention, from the viewpoint of obtaining high-quality prints on inkjet recording paper, silica-based inorganic fine particles have a low refractive index and an average particle size of about 0.1 μm or less can be obtained relatively inexpensively. Particles or alumina diameter particles are preferable, and alumina, pseudoboehmite, colloidal silica, fine particle silica synthesized by a gas phase method, and the like are preferable, and fine particle silica synthesized by a gas phase method is particularly preferable.

  The silica synthesized by this vapor phase method may have a surface modified with aluminum. The aluminum content of vapor-phase process silica whose surface is modified with aluminum is preferably 0.05 to 5% by mass with respect to silica.

  The particle diameter of the inorganic fine particles is preferably 200 nm or less, particularly preferably 100 nm or less, from the viewpoint of glossiness and color density. Although the minimum of a particle size is not specifically limited, From a viewpoint on manufacture of inorganic fine particles, about 10 nm or more is preferable.

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

  The inorganic fine particles may be present in the porous coating as primary particles or as secondary particles or higher-order aggregated particles, but the average particle size is determined by the porous layer when observed with an electron microscope. Among them, the particle size of the particles forming independent particles.

  When the inorganic fine particles are secondary or higher aggregated particles, the average primary particle size is equal to or less than the average particle size observed in the porous film, and the primary particle size of the inorganic fine particles is 50 nm or less. Are preferable, more preferably 30 nm or less, and most preferably 4 to 20 nm.

The content of the inorganic fine particles in the water-soluble coating solution is 5 to 40% by mass, and particularly preferably 7 to 30% by mass. The inorganic fine particles need to form an ink-absorbing layer having sufficient ink absorptivity and less cracking of the film, and the amount of 5 to 50 g / m ² is preferable in the ink-receiving layer. . Furthermore, it is especially preferable that it is 10-30 g / m < ² >.

  The hydrophilic binder contained in the porous layer is not particularly limited, and conventionally known hydrophilic binders can be used. For example, gelatin, polyvinyl pyrrolidone, polyethylene oxide, polyacrylamide, polyvinyl alcohol, and the like can be used. However, polyvinyl alcohol is particularly preferable from the viewpoint of relatively small moisture absorption characteristics of the binder and less curling of the recording paper and from the viewpoint of high binder capacity of inorganic fine particles and excellent cracking and film-forming properties when used in a small amount.

  As polyvinyl alcohol preferably used in the present invention, in addition to ordinary polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate, modified polyvinyl alcohol such as polyvinyl alcohol having a cation-modified terminal or anion-modified polyvinyl alcohol having an anionic group. Alcohol is also included.

  The polyvinyl alcohol obtained by hydrolyzing vinyl acetate preferably has an average degree of polymerization of 300 or more, particularly preferably an average degree of polymerization of 1,000 to 5,000, and a saponification degree of 70. -100% is preferable, and 80-99.8% is particularly preferable.

  Examples of the cation-modified polyvinyl alcohol include polyvinyl having a primary to tertiary amino group or a quaternary amino group in the main chain or side chain of the polyvinyl alcohol as described in JP-A No. 61-10383. These are alcohols, which are obtained by saponifying a copolymer of an ethylenically unsaturated monomer having a cationic group and vinyl acetate.

  Examples of the ethylenically unsaturated monomer having a cationic group include trimethyl- (2-acrylamido-2,2-dimethylethyl) ammonium chloride and trimethyl- (3-acrylamido-3,3-dimethylpropyl) ammonium chloride. N-vinylimidazole, N-methylvinylimidazole, N- (3-dimethylaminopropyl) methacrylamide, hydroxyethyltrimethylammonium chloride, trimethyl- (3-methacrylamidopropyl) ammonium chloride, and the like.

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

  Examples of the anion-modified polyvinyl alcohol include polyvinyl alcohol having an anionic group described in JP-A-1-206088, vinyl alcohol described in JP-A-61-237681 and JP-A-63-330779, and water-soluble. And a copolymer with a vinyl compound having a functional group, and a modified polyvinyl alcohol having a water-soluble group described in JP-A-7-285265.

  Nonionic modified polyvinyl alcohol is, for example, a polyvinyl alcohol derivative obtained by adding a polyalkylene oxide group described in JP-A-7-9758 to a part of vinyl alcohol, and described in JP-A-8-25795. And a block copolymer of a vinyl compound having a hydrophobic group and vinyl alcohol.

  Polyvinyl alcohol can be used in combination of two or more, such as the degree of polymerization and the type of modification. In particular, when using polyvinyl alcohol having a degree of polymerization of 2,000 or more, the degree of polymerization is from 0.05 to 10% by weight, preferably 0.1 to 5% by weight, based on the inorganic fine particles. Addition of 2,000 or more polyvinyl alcohol is preferred because there is no significant thickening.

  The ratio of the inorganic fine particles to the hydrophilic binder of the porous layer is preferably 2 to 20 by mass ratio. If the mass ratio is 2 times or more, a porous film having a sufficient porosity can be obtained, it becomes easy to obtain a sufficient void volume, and does not cause a situation where the voids are blocked by swelling during ink jet recording with a hydrophilic binder that can be maintained. As a result, a high ink absorption speed can be maintained. On the other hand, if this ratio is 20 times or less, cracks are less likely to occur when the porous layer is applied as a thick film. The ratio of the inorganic fine particles to the particularly preferred hydrophilic binder is 2.5 to 12 times, most preferably 3 to 10 times.

  In addition to inorganic fine particles and binders, various additives can be used for the porous ink absorbing layer. Among these, cationic polymers, crosslinking agents, and polyvalent metal compounds are ink absorbent and improve ink ink bleeding. It plays an important role.

  In the inkjet recording paper of the present invention, a cationic polymer is preferably used for the purpose of preventing bleeding of the image during long-term storage after image recording with a dye ink.

Examples of cationic polymers include polyethyleneimine, polyallylamine, polyvinylamine, dicyandiamide polyalkylene polyamine condensate, polyalkylene polyamine dicyandiamide ammonium salt condensate, dicyandiamide formalin condensate, epichlorohydrin-dialkylamine addition polymer, diallyldimethylammonium chloride Polymer, diallyldimethylammonium chloride / SO ₂ copolymer, polyvinyl imidazole, vinyl pyrrolidone / vinyl imidazole copolymer, polyvinyl pyridine, polyamidine, chitosan, cationized starch, vinyl benzyl trimethyl ammonium chloride polymer, (2-methacryloyl) Oxyethyl) trimethylammonium chloride polymer, dimethylaminoethyl methacrylate And the like, such as over preparative polymer.

  Examples include the cationic polymers described in Chemical Industry Times, August 15 and 25, 1998, and polymer dye fixing agents described in “Introduction to Polymer Drugs” issued by Sanyo Chemical Industries, Ltd.

  The inkjet recording paper of the present invention is characterized by containing a compound represented by the above general formula (I) having a molecular weight of 200 or less.

In the general formula (I), R ₁ is a hydrogen atom, a substituted or unsubstituted alkyl group (for example, methyl group, ethyl group, isopropyl group, t-butyl group, hexyl group, dodecyl group, cycloalkyl group, etc.), A substituted or unsubstituted alkenyl group (eg, propenyl group, butenyl group, nonenyl group), a substituted or unsubstituted aryl group (eg, phenyl group), a substituted or unsubstituted acyl group (eg, acetyl group, propionyl) Group, butanoyl group, hexanoyl group, cyclohexanoyl group, benzoyl group, pyridinoyl group, etc.), substituted or unsubstituted heteroaryl group (eg triazole group, imidazole group, pyridine group, furan group, thiophene group, etc.), substituted Or an unsubstituted heterocyclic group (eg, pyridyl group, thiazolyl group, oxazolyl group) Imidazolyl group, a furyl group, a pyrrolyl group, pyrazinyl group, pyrimidinyl group, pyridazinyl group, selenazolyl group, Surihoraniru group, a piperidinyl group, a pyrazolyl group, etc. tetrazolyl group), represents a NR ₄ R ₅ or OR _6,. R ₁ and R ₂ , R ₁ and R ₃ may be bonded to each other to form a ring. X represents an oxygen atom or NH.

  In the present invention, the compound represented by the general formula (I) preferably has no alcoholic hydroxyl group from the viewpoint of exhibiting the object effect of the present invention.

  In the general formula (I), the molecular weight is characterized by 200 or less, the number of atoms excluding hydrogen atoms is preferably 15 or less, and it is water-soluble from the viewpoint of easy addition. preferable.

  Examples of the compound represented by the general formula (I) according to the present invention are listed below, but the present invention is not limited to these.

  The compound represented by the general formula (I) according to the present invention can be easily synthesized by a person skilled in the art according to a known method, or can be obtained as a commercial product.

  In the inkjet recording paper of the present invention, among the compounds represented by the general formula (I), urea or a derivative thereof is preferable, and urea is particularly preferable.

  In order to improve the water resistance and moisture resistance of the image, the ink jet recording paper of the present invention preferably contains a polyvalent metal ion. The polyvalent metal ion is not particularly limited as long as it is a divalent or higher-valent metal ion, but preferable polyvalent metal ions include aluminum ions, zirconium ions, titanium ions, and the like.

  These polyvalent metal ions can be contained in the ink receiving layer in the form of a water-soluble or water-insoluble salt. Specific examples of the salt containing aluminum ions include aluminum fluoride, hexafluoroaluminic acid (for example, potassium salt), aluminum chloride, basic aluminum chloride (for example, polyaluminum chloride), and tetrachloroaluminate (for example, sodium). Salt), aluminum bromide, tetrabromoaluminate (eg potassium salt), aluminum iodide, aluminate (eg sodium salt, potassium salt, calcium salt), aluminum chlorate, aluminum perchlorate, thiocyanic acid Aluminum, aluminum sulfate, basic aluminum sulfate, potassium aluminum sulfate (alum), ammonium aluminum sulfate (ammonium alum), sodium aluminum sulfate, aluminum phosphate, aluminum nitrate, hydrogen phosphate Aluminum, Aluminum carbonate, Aluminum polysulfate silicate, Aluminum formate, Aluminum acetate, Aluminum lactate, Aluminum oxalate, Aluminum isopropylate, Aluminum butyrate, Ethyl acetate Aluminum diisopropylate, Aluminum tris (acetylacetonate), Aluminum tris (ethylacetate) Acetate), aluminum monoacetylacetonate bis (ethylacetoacetonate) and the like.

  Among these, aluminum chloride, basic aluminum chloride, aluminum sulfate, basic aluminum sulfate, and basic aluminum sulfate silicate are preferable, and basic aluminum chloride and basic aluminum sulfate are most preferable.

  Specific examples of the salt containing zirconium ions include zirconium difluoride, zirconium trifluoride, zirconium tetrafluoride, hexafluorozirconium salt (for example, potassium salt), heptafluorozirconium salt (for example, sodium salt). Potassium salts and ammonium salts), octafluorozirconium salts (for example, lithium salts), zirconium fluoride oxide, zirconium dichloride, zirconium trichloride, zirconium tetrachloride, hexachlorozirconium salts (for example, sodium salts and potassium salts) , Zirconium oxychloride (zirconyl chloride), zirconium dibromide, zirconium tribromide, zirconium tetrabromide, zirconium bromide oxide, zirconium triiodide, zirconium tetraiodide, zirconium peroxide, zirconium hydroxide, sulfide Luconium, zirconium sulfate, zirconium p-toluenesulfonate, zirconyl sulfate, sodium zirconyl sulfate, acidic zirconyl sulfate trihydrate, zirconium potassium sulfate, zirconium selenate, zirconium nitrate, zirconyl nitrate, zirconium phosphate, zirconyl carbonate, zirconyl carbonate Ammonium, zirconium acetate, zirconyl acetate, zirconyl ammonium acetate, zirconyl lactate, zirconyl citrate, zirconyl stearate, zirconyl phosphate, zirconium oxalate, zirconium isopropylate, zirconium butyrate, zirconium acetylacetonate, acetylacetone zirconium butyrate, stearin Zirconate butyrate, zirconium acetate, bis (acetylacetonato) dichroic acid Zirconium tris (acetylacetonato) chloro zirconium, and the like.

  Among these compounds, zirconyl carbonate, zirconyl ammonium carbonate, zirconyl acetate, zirconyl nitrate, zirconyl chloride, zirconyl lactate, zirconyl citrate are used in the viewpoint of further prominently preventing bleeding after printing, which is the object of the present invention. Particularly preferred are zirconyl ammonium carbonate, zirconyl chloride and zirconyl acetate.

  These polyvalent metal ions may be used alone or in combination of two or more different kinds. The compound containing a polyvalent metal ion may be added to the coating solution for forming the ink receiving layer, or after the porous layer is applied once, in particular, after the porous layer is applied and dried, the compound is added to the ink receiving layer. You may supply by an overcoat method. When adding a compound containing polyvalent metal ions to the coating solution for forming the ink absorbing layer as in the former, a method of uniformly dissolving in water, an organic solvent or a mixed solvent thereof, or wet grinding such as a sand mill A method of dispersing and adding to fine particles by a method such as a method or emulsification dispersion can be used. When the ink receiving layer is composed of a plurality of layers, only one layer may be added, or it may be added to the coating liquid of two or more layers or all the constituent layers. In addition, when the porous ink receiving layer is once formed and then added by the overcoat method as in the latter case, the compound containing polyvalent metal ions is uniformly dissolved in a solvent and then supplied to the ink receiving layer. Is preferred.

These polyvalent metal ions are generally used in an amount of 0.05 to 20 mmol, preferably 0.1 to 10 mmol, per 1 m ^{2 of} recording paper.

  In the ink jet recording paper of the present invention, it is preferable to add a hardener of a water-soluble binder that forms a porous ink receiving layer.

  The curing agent that can be used in the present invention is not particularly limited as long as it causes a curing reaction with a water-soluble binder, but boric acid and its salts are preferable, but other known ones can be used. Specifically, it is a compound having a group capable of reacting with a water-soluble binder or a compound that promotes the reaction between different groups of the water-soluble binder, and is appropriately selected depending on the type of the water-soluble binder. Specific examples of the curing agent include, for example, epoxy curing agents (diglycidyl ethyl ether, ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-diglycidyl cyclohexane, N, N-diglycidyl- 4-glycidyloxyaniline, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, etc.), aldehyde curing agents (formaldehyde, glioxal, etc.), active halogen curing agents (2,4-dichloro-4-hydroxy-1,3,5) -S-triazine, etc.), active vinyl compounds (1,3,5-trisacryloyl-hexahydro-s-triazine, bisvinylsulfonylmethyl ether, etc.), aluminum alum and the like.

  Boric acid or a salt thereof refers to an oxygen acid having a boron atom as a central atom and a salt thereof, specifically, orthoboric acid, diboric acid, metaboric acid, tetraboric acid, pentaboric acid, and octaboron. Examples include acids and their salts.

  Boric acid having a boron atom and a salt thereof as a curing agent may be used as a single aqueous solution or as a mixture of two or more. Particularly preferred is a mixed aqueous solution of boric acid and borax. The aqueous solutions of boric acid and borax can be added only in relatively dilute aqueous solutions, respectively, but by mixing them both can be made into a concentrated aqueous solution and the coating solution can be concentrated. Further, there is an advantage that the pH of the aqueous solution to be added can be controlled relatively freely. The total amount of the curing agent used is preferably 1 to 600 mg per 1 g of the water-soluble binder.

  Various additives other than those described above can be added to the porous ink absorbing layer of the present invention. For example, organic latex fine particles such as polystyrene, polyacrylic acid esters, polymethacrylic acid esters, polyacrylamides, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, or a copolymer thereof, urea resin, or melamine resin , Various cationic or nonionic surfactants, 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-60-27285, JP-A-61-146591, JP-A-1-95091 and JP-A-3-13376, etc., and JP-A-59-42993, JP-A-59-52689, JP-A-62. -280069, 61-242871 and JP-A-4-219266. Brighteners, sulfuric acid, phosphoric acid, citric acid, sodium hydroxide, potassium hydroxide, potassium carbonate and other pH adjusters, antifoaming agents, preservatives, thickeners, antistatic agents, mats Various known additives such as an agent can also be contained.

  Next, the manufacturing method of the inkjet recording paper of this invention is demonstrated.

  As a method for producing the ink jet recording paper of the present invention, each constituent layer including an ink absorbing layer is selected from a known coating method, either individually or simultaneously, and coated and dried on a support. Can do. Examples of the coating method include a roll coating method, a rod bar coating method, an air knife coating method, a spray coating method, a curtain coating method, and U.S. Pat. Nos. 2,761,419 and 2,761,791. A slide bead coating method using a hopper, an extrusion coating method or the like is preferably used.

  When the slide bead coating method is used, the viscosity of each coating solution at the time of simultaneous multilayer coating is preferably in the range of 5 to 100 mPa · s, more preferably in the range of 10 to 70 mPa · s. Moreover, when using a curtain application | coating system, the range of 5-1200 mPa * s is preferable, More preferably, it is the range of 25-500 mPa * s.

  Further, the viscosity at 15 ° C. of the coating solution is preferably 100 mPa · s or more, more preferably 100 to 30,000 mPa · s, further preferably 3,000 to 30,000 mPa · s, and most preferably 10 , 30,000 to 30,000 mPa · s.

  As a coating and drying method, the coating liquid is heated to 30 ° C. or higher, and after simultaneous multilayer coating is performed, the temperature of the formed coating film is once cooled to 1 to 15 ° C. and dried at 10 ° C. or higher. Is preferred. More preferably, the drying conditions are a wet bulb temperature of 5 to 50 ° C. and a film surface temperature of 10 to 50 ° C. Moreover, as a cooling method immediately after application | coating, it is preferable to carry out by a horizontal set system from a viewpoint of the formed coating-film uniformity.

  In addition, after applying and drying the ink-receiving layer as patented by the present applicant in Japanese Patent Application No. 2002-258715, it is overcoated with another water-soluble additive online before winding up into a roll. A method of producing by drying can also be applied to the present invention.

  Further, it is preferable to have a step of storing for 24 hours or more and 60 days or less under conditions of 35 ° C. or more and 70 ° C. or less in the manufacturing process of the recording paper. The heating condition is not particularly limited as long as it is stored at a temperature of 35 ° C. or more and 70 ° C. or less for 24 hours or more and 60 days or less, but a preferable example is 36 ° C. for 3 days to 4 weeks, 40 ° C. 2 days to 2 weeks, or 1 to 7 days at 55 ° C. By performing this heat treatment, the curing reaction of the water-soluble binder can be promoted, or the crystallization of the water-soluble binder can be promoted, and as a result, preferable ink absorbability can be achieved.

In the recording paper of the present invention, since a non-water-absorbing support is used as the support, the ink absorption capacity that can absorb almost all of the ink for forming the image and the ink for forming the protective film is maintained. is required. If there is not a sufficient amount of ink absorption, ink overflows when colorless ink forming a protective film is ejected, causing glare due to point-like thickness changes. The absorption capacity of the ink absorption layer is preferably about 20 ml / m ² or more. The upper limit is not particularly limited. Increasing the ink absorption amount not only increases the thickness of the layer, but also greatly increases the curling problem. It becomes a big cause. The upper limit of the preferred ink absorption is approximately 30 ml / m ² .

When recording an image, it is necessary to design so that the sum of the ink for forming the image and the colorless ink for forming the protective film is equal to or less than the ink absorption amount of the recording paper. The sum total of the image forming ink is approximately 15 to 25 ml / m ² , and the sum total of the colorless ink is 3 to 10 ml / m ² .

  Next, the surface characteristics of the recording paper of the present invention will be described.

  In the ink jet recording paper of the present invention, the center line average roughness (Ra) when measured on the surface of the porous ink absorbing layer at a reference length of 2.5 mm as defined in JIS-B-0601 and a cutoff value of 0.8 mm. Is preferably 0.08 to 0.20 μm, more preferably 0.10 to 0.18 μm.

When Ra on the surface of the porous ink absorbing layer is less than 0.08 μm, when a protective film having a dry solid content of 0.05 to 0.3 g / m ² is formed on a white background portion, the viewing angle caused by interference fringes It is easy to change the color of the white background due to the difference. This is because the smoothness of the surface of the ink absorption layer is too high, and the smoothness of the interface between the protective film layer and the surface of the ink absorption layer is too high, so that the specular reflection light becomes larger and interference fringes tend to occur. This is considered to be because the specular reflection of the light by suppressing the regular reflection of the light by slightly roughening the surface can suppress the spot-like glare derived from the interference fringes.

  On the other hand, when Ra exceeds 0.20 μm, the glaring becomes more conspicuous in a high density portion, particularly a black solid portion. Originally, if the surface quality of the mold is good, this point is not much of a concern. However, in the white background area and low density area, this point-like glare in the high density area is obtained only by having a more glossy and uniform recording surface. Adhesion is not preferable because it has a large effect on print quality.

  As a method for adjusting the Ra of the ink absorbing layer surface to the range defined in the present invention, various methods can be appropriately selected and used. Examples of specific methods are shown below, but the present invention is not limited to these methods.

1: A method of adjusting the smoothness of the middle paper surface of the support. Specifically, there is a method of adjusting the fiber length of the pulp, adjusting the pressure when calendering, adjusting the amount of the surface sizing agent, etc. 2: of the polyolefin resin that covers the inner paper Method for adjusting thickness 3: Method for adjusting the surface shape of the cooling roll used for cooling when the polyolefin resin is melt-extruded onto a paper support. Specifically, a method using a mirror surface roller, a fine surface processing roller, a mat surface processing roller, etc. 4: A method of adjusting the composition and thickness of the undercoat layer 5: Inorganic contained in the surface layer of the porous ink absorption layer Method of adjusting particle diameter of fine particles 6: Method of adding various additives to the surface layer of the porous ink absorbing layer 7: Method of adjusting drying conditions after applying the porous ink absorbing layer 8: Porous This can be achieved by appropriately selecting or combining methods of drying by applying water or another solvent again after the ink absorption layer is applied and dried.

  Ra of the white background after providing the protective film layer depends on the discharge conditions of the colorless ink, but generally it is lower than before providing the protective film layer, and Ra is generally 0.05 to 0.15 μm. .

  Further, the 60-degree specular gloss by S-Z8741 of the porous ink-absorbing surface is generally 30 to 70%. The gloss level itself does not necessarily correspond completely to Ra, but generally the higher the Ra, the lower the gloss level.

  The glossiness of the white background portion after providing the protective coating layer is also changed by providing the protective coating layer in the same manner as Ra, and usually increases by 5 to 40% from before the protective coating layer is provided.

  Further, the 10-point average roughness (Rz) when measured at a reference length of 2.5 mm and a cut-off value of 0.8 mm defined in JIS-B-0601 on the surface of the porous ink absorbing layer is 0.5 to 5. A filtered waviness curve derived from a cross-sectional curve measured in accordance with JIS-B-0610 at 0 μm and a cut-off value of 0.8 mm, with a reference length of 2.5 mm, a maximum waviness of filtration of 0.5 to 5 μm, and JIS K7105 The 60 degree C value specified is in the range of 30-90%.

  The membrane surface pH of the porous ink absorbing layer is preferably from 3 to 7, and particularly preferably from 4 to 6.5.

  Next, an ink jet recording method using the ink jet recording paper of the present invention will be described.

  The recording paper of the present invention is suitably used as a recording paper for water-based pigment ink or water-based dye ink which is a colorant-containing ink.

  The water-based dye ink is an ink using a water-soluble dye as a colorant, and is an ink obtained by mixing water or an organic solvent having high miscibility with water as an ink solvent. Examples of the dye include conventionally known azo dyes, xanthene dyes, phthalocyanine dyes, quinone dyes, anthraquinone dyes, etc., which are improved in water solubility by introducing a sulfo group or a carboxy group. Basic dyes are typically used.

  On the other hand, as the pigment used in the pigment ink, various inorganic or organic pigment inks conventionally known by inkjet can be used. Examples of the inorganic pigment ink include carbon black, titanium oxide, and iron oxide. Examples of organic pigments include various azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, indigo pigments, or lake pigments obtained by reacting water-soluble dyes with polyvalent metal ions. Can do.

  These pigment particles are preferably used together with various dispersants and dispersion stabilizers such as hydrophilic polymers and surfactants. The pigment particles are preferably used in which the average particle size is dispersed to about 70 to 150 μm with these dispersed local dispersion stabilizers.

  The concentration of the colorant dye and pigment in the ink depends on the type of the dye or pigment, the type of ink used (whether or not the dark ink is used), and the type of recording paper. It is 0.2-10 mass%.

  Various solvents are used in the colorant-containing ink. As such an ink solvent, water or an organic solvent highly miscible with water can be used alone or mixed with water. Specifically, alcohol solvents such as ethanol, 2-propanol, ethylene glycol, propylene glycol, glycerin, 1,2-hexanediol, 1,6-hexanediol, diethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, 2- Amides such as pyrrolidinone, N-methylpyrrolidone, N, N-dimethylacetamide, amines such as triethanolamine, N-ethylmorpholine, triethylenetetramine, sulfolane, dimethyl sulfoxide, urea, acetonitrile, acetone, etc. These solvents may be used alone or in combination.

  In addition, various surfactants for the purpose of enhancing the permeability of the ink solvent and other purposes can be used for the colorant-containing ink. As such a surfactant, an anionic or nonionic surfactant is preferably used. Of these, acetylene glycol surfactants are particularly preferred.

  Next, the colorless ink for forming the protective film layer will be described.

  Colorless ink basically does not contain a colorant, but a slight amount of dye or pigment used to make the colorant as an impurity or the white background of the recording paper close to the white background of the printing paper, for example, or fluorescent A brightener can also be added.

  The colorless ink contains a polymer capable of forming a protective film.

  This polymer can be used in a state in which it is completely dissolved in the solvent of the colorless ink, or it can be used in a state where it is present in a fine particle state in the colorless ink.

Suitable polymers used for the former purpose include, for example, polyvinyl alcohol, polyacrylamide, water-soluble polyester, polyvinyl pyrrolidone, and polyethylene oxide. However, use a water-soluble polymer to cover the white background and the recorded colorant layer sufficiently with a very small amount of the solid content of the protective coating layer of 0.05 to 0.3 g / m ² . Then, a part of the recording paper penetrates into the recording paper and the colorant layer, and it is difficult to obtain a sufficient covering effect. For the polymer contained in the colorless ink, it is preferable to use such polymer fine particles having low permeability.

  As such polymer fine particles, for example, those described in JP-A Nos. 2002-264465, 2014428, and International Application Publication No. WO00 / 06390 can be used. An emulsion polymerization dispersion obtained by emulsion polymerization of monomers is particularly preferably used.

  Examples of such vinyl monomers include ethylene, propylene, isoprene, butadiene, pentadiene, vinyl chloride, vinylidene chloride, styrene, divinylbenzene, vinyl toluene, acrylic acid and its salts, methacrylic acid and its salts, acrylamide, itacone Acids and salts thereof, maleic acid and salts thereof, methyl vinyl ether, acrylic acid or methacrylic acid derivatives (for example, methyl ester, ethyl ester, benzyl ester, butyl ester), N-substituted acrylamide or N-substituted methacrylamide derivative, acetic acid Vinyl, N-vinylpyrrolidone, 2-vinyloxazoline and the like can be mentioned, but are not limited thereto. These monomers can be used alone or in combination of two or more.

  A preferred polymer dispersion is obtained by emulsion polymerization of one or more of the above monomers in the presence of a polymerization initiator. At this time, it is preferable to carry out in the presence of a surfactant or a hydrophilic polymer in order to control the particle size of the emulsified dispersion and to improve the stability.

  When emulsion polymerization is performed using a surfactant, relatively fine particles can be obtained. However, when used as a colorless ink, the surface tension required for the ink must be selected so as not to be adversely affected.

  On the other hand, a polymer dispersion emulsified and dispersed in the presence of a hydrophilic polymer is particularly advantageous for the recording paper of the present invention from the viewpoint of stability of the emulsion polymerization dispersion and formation of a protective film with a colorless ink. As the hydrophilic polymer used here, any water-soluble polymer capable of forming a film can be used, but polyvinyl alcohol is particularly preferred from the viewpoint of ink stability and coating performance. The polyvinyl alcohol preferably used here has an average polymerization degree of 300 to 2000 and a saponification degree of 70 to 100, preferably 80 to 90.

  The amount of the hydrophilic polymer used at the time of emulsion polymerization is generally from 0.1 to 40% by mass, particularly preferably from 0.5 to 20% by mass, based on the monomer. In this case, a surfactant can be used in combination with the hydrophilic polymer during emulsion polymerization. The usage-amount of surfactant is 0.1-20 mass% with respect to a monomer, Preferably it is 0.2-10 mass%.

  On the other hand, these hydrophilic polymers may be added after the emulsion polymerization of the polymer dispersion.

  The average particle diameter of the polymer dispersion is approximately 0.02 to 1 μm, preferably 0.03 to 0.3 μm. The glass transition temperature (Tg) of the polymer dispersion is advantageously from 0 to 80 ° C. from the formed film properties. When Tg is less than 0 ° C., the stickiness of the surface is increased, and fingerprints are easily attached or sheets are easily adhered to each other. Moreover, when Tg exceeds 80 degreeC, it will become difficult to form a uniform membrane | film | coat on the surface. Tg is most preferably 10 to 70 ° C.

  The colorless ink may contain a compound having an ultraviolet absorbing ability, a compound having an antioxidant function, or the like, if necessary. Further, a polymer dispersion emulsified and dispersed using a monomer having these functions can also be used.

  The colorless ink can contain various additives such as a water-miscible organic solvent, a surfactant, a viscosity modifier, a pH adjuster, and an antifungal agent similar to those of the colorant-containing ink described above.

  Next, a method for recording an inkjet image on the recording paper of the present invention using a colorant-containing ink and a colorless ink will be described.

  The recording paper of the present invention forms a protective film on substantially the entire area of the recording paper after the image is recorded with the colorant-containing ink or at the same time, preferably by discharging colorless ink onto substantially the entire area of the recording paper. To do.

  “Forming a protective film over substantially the entire area of the recording paper” as used herein refers to a state where it can be recognized that the protective film is formed over the entire area of the recording paper in normal observation. For example, even if the protective film is not formed in the minute range of the end portion of the recording paper, the influence on the print quality is small, and the observer recognizes that the protective film is present in the entire region. Usually, a protective film may be formed on the remaining area excluding the area of about 1 mm, preferably about 0.5 mm or less from the edge of the recording paper. As another example, an area not recorded with colorless ink may be cut off or covered with a frame after printing. It is not necessary to discharge colorless ink in an area that is not valuable as an image. That is, in a normal image print, the recording applied to the recording paper of the present invention is to cover all areas of the white area observed as an image and the area where the colorant-containing ink is discharged, with the colorless ink. Is the method.

  According to the study by the present inventors, in order to form a thin and uniform protective film, the composition of the colorless ink to be applied and the application method are of course important, but since the amount of the colorless ink applied is small, it is colorless. It has been found that the uniformity of the surface of the recording material to which ink is applied is extremely important. That is, if there are fine point defects or cracks on the surface of the recording material, non-uniformity occurs in the protective film formed on that portion (for example, thicker, thinner, not formed, etc.), appearing as point defects, The print quality is degraded.

  The recording material of the present invention is characterized by containing the compound represented by the general formula (I), and it is conceivable that the surface defects and cracks of the recording material are reduced as an effect thereof. In addition, as an effect of adding the compound represented by the general formula (1), it is known that the ink absorbability is improved, and the amount of the ink solvent remaining on the surface of the recording material is rapidly reduced. Subsequently, when colorless ink is applied, it is considered that a uniform protective film can be obtained without causing repelling or unevenness. These are beyond the scope of speculation, and future work must be awaited for the mechanism of action that provides the effects of the present invention.

  When the recording material of the present invention is used, glossiness (glossiness, image clarity) after applying a colorless ink to form a protective film is brought about. In particular, the image clarity is improved at a high density portion when an image is formed with pigment ink. It is considered that the effect is obtained by obtaining a uniform protective film, but the mechanism of action is not clear.

  The time for discharging the colorless ink is preferably the same as or immediately after the image formation with the colorant-containing ink from the viewpoint of obtaining the effect of improving the image clarity. In particular, it is preferably performed immediately after the image formation with the colorant-containing ink is performed while the water is not substantially evaporated.

  When colorless ink is ejected after a time has elapsed after an image is formed with a colorant-containing ink, the ink solvent of the colorant-containing ink evaporates. This is not preferable because a clear interface is formed between the surface and the colorless ink forming film. Particularly preferably, both are discharged almost simultaneously in the same printer.

The protective film is formed with colorless ink so that the dry solid content is 0.05 to 0.3 g per 1 m ^{2 of} recording paper. If the dry solid content exceeds 0.3 g, a rainbow-like color tone is formed on the white background portion. Changes are likely to occur. On the other hand, if it is less than 0.05 g, the formation of the film becomes insufficient, and in particular, the effect of preventing fading on a dye ink-formed image or the like is rapidly reduced, or in the case of pigment ink, the effect of improving the change in glossiness of the image area is improved. Get smaller. The dry solid content of the film formed with a preferred colorless ink is 0.07 to 0.25 g.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In the examples, “%” and “part” represent “% by mass” and “part by mass” unless otherwise specified.

Example 1
<Production of recording paper>
[Preparation of recording paper 1]
(Production of support)
1 part of polyacrylamide, 4 parts of ash (talc), 2 parts of cationized starch, 0.5 part of polyamide epichlorohydrin resin and 100 parts of wood pulp (LBKP / NBSP = 50/50) Slurry liquids containing various addition amounts of alkyl ketene dimer (sizing agent) were prepared, and base paper was made using a long paper machine so that the basis weight was 170 g / m ² . After calendering the base paper, a low-density polyethylene resin having a density of 0.92 containing 7% anatase-type titanium oxide and a small amount of a color tone adjusting agent is melt-extruded and coated at 320 ° C. to a thickness of 28 μm. Then, one side of the base paper was covered with and cooled immediately with a mirror cooling roller. Then, the opposite surface was coated with a melt obtained by mixing high density polyethylene with a density of 0.96 / low density polyethylene with a density of 0.92 = 70/30 to a thickness of 32 μm by the melt extrusion method. .

  The 60 ° glossiness on the surface side on which the ink absorbing layer was provided was 56%, and the centerline average roughness Ra was 0.12 μm.

The support was subjected to corona discharge on the titanium oxide-containing layer side, and then coated to give 0.05 g / m ^{2 of} gelatin to provide an undercoat layer.

  On the other hand, on the opposite side, a dry film thickness of about 0.5 μm of styrene / acrylic emulsion containing silica fine particles (matting agent) with an average particle size of about 1.0 μm and a small amount of cationic polymer (conductive agent) is used. Then, a support for applying the ink absorbing layer was prepared.

  On the back surface side, the 60 ° gloss was about 18%, Ra was about 4.5 μm, and the Beck smoothness was 160 to 200 seconds.

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

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

[Preparation of ink absorbing layer coating solution]
A front side coating solution was prepared according to the following procedure.

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

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

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

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

(Preparation of coating solution)
Each coating solution of the first layer, the second layer, the third layer, and the fourth layer was prepared by the following procedure.

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

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

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

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

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

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

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

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

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

(Application)
Each coating solution thus obtained was coated on the front side of the support coated on both sides with the above prepared polyolefin, on the first layer (35 μm), the second layer (45 μm), the third layer (45 μm), and the fourth layer. Each layer was applied simultaneously so as to be in the order of layers (40 μm). In addition, the numerical value in the parenthesis of each layer shows each wet film thickness. The coating was carried out simultaneously at a coating width of about 1.5 m and a coating speed of 100 m / min using a four-layer curtain coater at 40 ° C. for each coating solution.

Immediately after coating, the film is cooled for 20 seconds in a cooling zone maintained at 8 ° C., then 20 to 30 ° C., relative humidity 20% or less for 30 seconds, 60 ° C., relative humidity 20% or less for 120 seconds, 55 ° C., relative humidity 20%. It dried by blowing each drying wind for 60 seconds below. The film temperature in the constant rate drying area is 8-30 ° C., and after the film temperature gradually rises in the decreasing rate drying area, the film is conditioned in a humidity adjustment zone of 23 ° C. and relative humidity 40-60% to form a roll. The recording paper 1 was obtained by winding. The obtained recording paper 1 was then heated and stored at 40 ° C. for 5 days in the form of a roll, and then cut into a predetermined size. The ink absorption capacity of the recording paper 1 was 25 ml / m ² as a result of measurement by Bristow measurement.

[Preparation of recording sheets 2-9]
In the production of the recording paper 1, the recording paper 2 was produced in the same manner except that 10 ml of 10% urea aqueous solution was added to each of the first to fourth coating solutions.

<Preparation of ink>
(Preparation of pigment dispersion)
<Preparation of yellow pigment dispersion>
C. I. Pigment Yellow 74 20% by mass
Styrene-acrylic acid copolymer (molecular weight 10,000, acid value 120) 12% by mass
Diethylene glycol 15% by mass
Remaining amount of ion-exchanged water The above additives were mixed and dispersed using a horizontal bead mill (System Zeta Mini manufactured by Ashizawa Co., Ltd.) filled with 0.3 mm zirconia beads by volume ratio to obtain a yellow pigment dispersion. . The average particle size of the obtained yellow pigment was 112 nm.

<Preparation of magenta pigment dispersion>
C. I. Pigment Red 122 25% by mass
Jonkrill 61 (acrylic-styrene resin, manufactured by Johnson)
18% by mass in solid content
Diethylene glycol 15% by mass
Remaining amount of ion-exchanged water The above additives were mixed and dispersed using a horizontal bead mill (System Zetamini manufactured by Ashizawa Co., Ltd.) filled with 0.3 mm zirconia beads at a volume ratio of 60% to obtain a magenta pigment dispersion. . The average particle size of the obtained magenta pigment was 105 nm.

<Preparation of cyan pigment dispersion>
C. I. Pigment Blue 15: 3 25% by mass
Jonkrill 61 (acrylic-styrene resin, manufactured by Johnson)
15% by mass as solid content
Glycerin 10% by mass
Remaining amount of ion-exchanged water The above additives were mixed and dispersed using a horizontal bead mill (System Zetamini manufactured by Ashizawa Co., Ltd.) filled with 0.3 mm zirconia beads at a volume ratio of 60% to obtain a cyan pigment dispersion. . The average particle diameter of the obtained cyan pigment was 87 nm.

<Preparation of black pigment dispersion>
Carbon black 20% by mass
Styrene-acrylic acid copolymer (molecular weight 7000, acid value 150) 10% by mass
Glycerin 10% by mass
Remaining amount of ion-exchanged water The above additives were mixed and dispersed using a horizontal bead mill (System Zetamini manufactured by Ashizawa Co., Ltd.) filled with 0.3 mm zirconia beads by volume ratio to obtain a black pigment dispersion. . The average particle size of the obtained black pigment was 75 nm.

(Preparation of pigment ink set)
<Preparation of yellow ink>
Yellow pigment dispersion 15% by mass
20% by mass of ethylene glycol
Diethylene glycol 10% by mass
Surfactant (Surfinol 465 manufactured by Nissin Chemical Industry Co., Ltd.) 0.1% by mass
Remaining amount of ion-exchanged water The above compositions were mixed, stirred, and filtered through a 1 μm filter to prepare a yellow ink which is an aqueous pigment ink. The average particle diameter of the pigment in the ink was 120 nm, and the surface tension γ was 36 mN / m.

<Preparation of magenta ink>
Magenta pigment dispersion 15% by mass
20% by mass of ethylene glycol
Diethylene glycol 10% by mass
Surfactant (Surfinol 465 manufactured by Nissin Chemical Industry Co., Ltd.) 1% by mass
Remaining amount of ion-exchanged water The above compositions were mixed, stirred, and filtered through a 1 μm filter to prepare a magenta ink that was an aqueous pigment ink. The average particle size of the pigment in the ink was 113 nm, and the surface tension γ was 35 mN / m.

<Preparation of cyan ink>
Cyan pigment dispersion 10% by mass
20% by mass of ethylene glycol
Diethylene glycol 10% by mass
Surfactant (Surfinol 465 manufactured by Nissin Chemical Industry Co., Ltd.) 1% by mass
Remaining amount of ion-exchanged water The above compositions were mixed, stirred, and filtered through a 1 μm filter to prepare a cyan ink that was an aqueous pigment ink. The average particle size of the pigment in the ink was 95 nm, and the surface tension γ was 36 mN / m.

<Preparation of black ink>
Black pigment dispersion 10% by mass
20% by mass of ethylene glycol
Diethylene glycol 10% by mass
Surfactant (Surfinol 465 manufactured by Nissin Chemical Industry Co., Ltd.) 1% by mass
Remaining amount of ion-exchanged water The above compositions were mixed, stirred, and filtered through a 1 μm filter to prepare a black ink that was an aqueous pigment ink. The average particle diameter of the pigment in the ink was 85 nm, and the surface tension γ was 35 mN / m.

<< Preparation of colorless ink >>
Polymer dispersion [copolymer (styrene / methyl methacrylate / ethyl methacrylate = 50/30/20, Tg≈40 ° C., emulsion-polymerized in polyvinyl alcohol having an average polymerization degree of 300 and a saponification degree of 88% in the presence of a surfactant) , Average particle size ≒ 0.08μm)]
2.4% by mass as solid content
20% by mass of ethylene glycol
Diethylene glycol 10% by mass
Surfactant (Surfinol 465 manufactured by Nissin Chemical Industry Co., Ltd.) 1% by mass
Remaining amount of ion-exchanged water The above compositions were mixed and stirred, filtered through a 1 μm filter, and a colorless ink dispersed in the aqueous system of the present invention was prepared. The surface tension γ of the colorless ink was 35 mN / m.

  Further, it was confirmed that even when the same amount of the colorless ink and each pigment ink was mixed, the average particle diameter of the pigment particles did not change and aggregation did not occur.

<Inkjet image recording>
The above ink set (colorant-containing ink) and colorless ink cartridge were accommodated, and an ink jet printer equipped with a piezo head was used to print an image on the prepared recording papers 1 and 2 to obtain prints 2 and 4. .

  As an image forming method, a cartridge of the type described in FIG. 1 of Japanese Patent Application Laid-Open No. 2000-225695 is used so that colorless ink is discharged immediately after image recording with an ink set (colorant-containing ink). I went.

The maximum total amount of ink ejected at the image recording site was 17 ml / m ² , and the colorless ink was ejected uniformly at 4 ml / m ² over the entire recording paper. At this time, the dry solid content of the colorless ink was about 0.1 g / m ² .

  In the following evaluation, as a comparative sample, an image in which colorless ink was not ejected was simultaneously printed on recording sheets 1 and 2, and these were designated as prints 1 and 3.

<Evaluation of recorded images>
The evaluation of the image was performed on the glossiness (60 degrees) and image clarity of the white background portion and the black solid image portion (reflection density≈2.0).

(Glossiness measurement)
60 degree specular gloss using a gloss meter (VGS-1001DP) manufactured by Nippon Denshoku Industries Co., Ltd. according to the method defined in JIS Z 8741 for the white background portion and the black solid image portion (reflection density≈2.0). The degree was measured, and this was defined as the glossiness.

(Measurement of image clarity C value)
According to the method specified in JIS K 7105, the white background portion and the black solid image portion (reflection density ≒ 2.0) are reflected at 60 degrees by the image clarity measuring device ICM-1DP (manufactured by Suga Test Machine Co., Ltd.), optical The image clarity C% (C value) at a comb of 2 mm was measured. The measurement was performed five times on the same sample, and the average value of the five measurements was taken.

(Evaluation of resistance to point defects)
A black solid image portion after 1 hour (condition 1) after image formation by the above method and a black solid image after image formation by the above method and storage for 7 days in an environment of 85 ° C. and 60% RH (condition 2) About the image part, the state of occurrence of point defects was observed with a loupe over the surface of each image over 0.1 m ² , and the point defect resistance was evaluated according to the following criteria.

A: Most point-like defects are not observed. B: A few point defects of less than 0.5 mm are observed. C: Some coarse point defects of 0.5 mm or more are observed. D: Point defects. Is observed on the entire surface (evaluation of rainbow unevenness resistance)
The rainbow-like unevenness was evaluated by visually observing whether or not the color tone changes by changing the viewing angle of the recording paper, and evaluating the rainbow unevenness resistance according to the following criteria.

1: No rainbow unevenness is observed 2: Very little rainbow unevenness is observed, but there is no problem in practice. 3: Irregular rainbow unevenness is observed, and it is anxious at the time of appreciation. 4: Severe rainbow unevenness and glare. The results obtained as described above are shown in Table 1.

  As is clear from the results in Table 1, the print 4 in which the recording material 2 containing the compound according to the present invention (urea = Exemplary Compound 13) is imaged with a colored ink and then a protective film is formed with a colorless ink has a solid black color. It can be seen that the image clarity C value of the portion is improved and the difference from the C value of the white background portion is small, and uniform image clarity is obtained in the entire image region. Further, the print 4 has almost no point defects on the surface, and a uniform protective film is obtained. This protective film does not increase defects even under severe storage conditions of 85 ° C. and 60% RH.

  As described above, it was confirmed that the use of the recording material of the present invention and the colorless ink is effective in obtaining a uniform glossy image.

Example 2
<< Preparation of recording sheets 3-7 >>
In the recording paper 2 produced in Example 1, in place of urea, 1 g of Exemplified Compound 2, which is a compound represented by the general formula (I), was added to each of the first to fourth coating liquids per liter. A recording paper 3 was produced in the same manner except for the above.

  Further, recording papers 4 to 7 were prepared in the same manner as in the production of the recording paper 3 except that the exemplified compounds 25, 28, 39, and 50 were used in place of the exemplified compound 2, respectively.

<< Inkjet image recording and evaluation of recorded images >>
About the produced recording papers 3-7, it carried out similarly to the method of Example 1, the image formation by the colored ink and the protective film formation by a colorless ink were performed, and the prints 5-9 were created. With respect to each of these obtained prints, the glossiness, image clarity C value, dot defect resistance, and rainbow unevenness resistance were evaluated in the same manner as in Example 1. Table 2 shows the results obtained.

  As is clear from the results in Table 2, the print of the present invention using each compound represented by the general formula (I) in place of urea obtains the same result as the print 4 described in Example 1. I was able to.

Example 3
<< Creation of prints 10-12 >>
In the production of the print 4 described in the first embodiment, the prints 10 to 12 were performed in the same manner except that the density of the colorless ink was changed from 2.5% to 1.0% using the recording papers 1, 2, and 3. It was created. The dry solid content of the film formed with this colorless ink is 0.04 g / m ² .

<< Creation of prints 13-15 >>
Prints 13 to 15 were made in the same manner except that the density of the colorless ink was changed from 2.5% to 5.0% using the recording papers 1, 2, and 3 in the production of the print 4 described in Example 1. It was created. The dry solid content of the film formed with this colorless ink is 0.20 g / m ² .

<< Creation of prints 16-18 >>
Prints 16 to 18 were produced in the same manner as in the production of prints 13 to 15 except that the discharge amount of the colorless ink was changed from 4 ml / m ² to 7 ml / m ² . The dry solid content of the film formed with this colorless ink is 0.35 g / m ² .

<Evaluation of recorded images>
About each created said print, it carries out similarly to the method of Example 1, and evaluates point-like defect tolerance and rainbow nonuniformity tolerance, and Table 3 shows the obtained result.

As is apparent from the results in Table 3, when the comparative recording paper 1 is used, the occurrence of point defects can be prevented by increasing the film thickness (solid content) of the protective film (print 16). However, when the protective film layer is 0.3 g / m ² or more, the rainbow unevenness of the white background portion is significantly deteriorated, and thus the two characteristics cannot be made compatible. On the other hand, in the recording papers 2 and 3 of the present invention, even when the protective film layer is 0.3 g / m ² or less, point defects are not likely to occur. It can be compatible and is excellent. However, even with the recording sheets 2 and 3 of the present invention, when the protective film layer is less than 0.05 g / m ² , the effect of preventing the occurrence of point defects is insufficient. (Print 11, 12).

Therefore, in this invention, it turns out that it is preferable that it is the range of 0.05-0.3 g / m < ² > as dry solid content of a protective film.

Example 4
<< Preparation of recording paper 8-10 >>
In the same manner as in the recording paper 2 produced in Example 1, except that the inorganic fine particles used in the ink absorbing layer were changed to vapor phase silica having average particles of 7 nm, 20 nm, and 30 nm, respectively, the recording papers 8 to 10 were formed. Produced.

<< Preparation of recording paper 11 >>
In the recording paper 2 prepared in Example 1, a copoly (styrene / hydroxylethyl methacrylate / methyl methacrylate / ethyl methacrylate = 55/5/20/20) dispersion having an average particle size of about 0.2 μm was solidified in the fourth layer. Recording paper 11 was produced in the same manner except that the amount was added so that the amount was 0.5 g per 1 m ^{2 of} recording paper.

<< Preparation of recording paper 12 >>
20 ml / m ² of a mixed solvent of ethanol / water = 50/50 was applied to the ink absorption layer coating surface side of the recording paper 2 produced in Example 1, and then dried to produce a recording paper 12.

<< Preparation of recording paper 13 >>
A recording paper 13 was produced in the same manner as in the recording paper 2 produced in Example 1, except that the coating and drying conditions were changed as follows.

  The first layer to the fourth layer were simultaneously applied at a coating speed of 50 m / min, and after cooling for 40 seconds in a cooling zone maintained at 8 ° C. immediately after the application, after 20 to 30 ° C. and a relative humidity of 20% or less for 60 seconds, Drying was performed at 45 ° C. and a relative humidity of 20% or less for 240 seconds, and at 40 ° C. and a relative humidity of 20% or less for 120 seconds.

<< Measurement of centerline average roughness (Ra) of recording paper >>
The center line average roughness Ra (μm) of the outermost surface of the ink absorbing layer of the recording paper is measured under the conditions of a reference length of 2.5 mm and a cut-off value of 0.8 mm in accordance with the method specified in JIS B 0601. Table 4 shows the obtained results.

<< Inkjet image recording and evaluation of recorded images >>
For the recording papers 8 to 13 produced above and the recording paper 2 produced in Example 1, image formation with colored ink and protective film formation with colorless ink were performed in the same manner as the production method of the print 4 described in Example 1. Prints 19-24 were made. The obtained prints were evaluated for glossiness, image clarity C value, and rainbow unevenness resistance in the same manner as in Example 1, and the results obtained are shown in Table 4.

  As is clear from the results in Table 4, the recording papers 2, 8, 9, and 13 in which the center line average roughness Ra of the outermost surface of the ink absorbing layer of the recording paper is in the range of 0.08 to 0.20 μm are good. It can be seen that it has glossiness and no rainbow unevenness or glare occurs. In the recording paper 10 in which the center line average roughness Ra of the outermost surface of the ink absorbing layer of the recording paper is 0.20 or more, the glossiness and image clarity of the black solid portion tend to decrease. On the other hand, when Ra is 0.08 or less, the rainbow unevenness in the white background portion becomes conspicuous, which is not preferable. Therefore, it can be seen that Ra is preferably 0.20 or less.

Example 5
Using the recording paper prepared in Example 1 and Example 2, the polymer dispersion used in the colorless ink described in Example 1 is used as a thermoplastic resin (urethane resin, Tg 30 ° C., average particle size 80 nm). Except for the change, a print was made in the same manner as in Example 1 and the recorded image was evaluated according to the method described in Example 1. As a result, even if the type of the polymer having film-forming ability was changed, the present invention The image formed using this recording paper showed good glossiness and image clarity, and it was confirmed that there were few surface defects.

Example 6
After recording an image with a commercially available pigment ink using the recording papers 1 and 2 produced in Example 1, the moisture was dried at room temperature for about 1 hour, and then a protective film was formed with a colorless ink. 26, and together with the prints 2 and 4 created in Example 1, the image clarity C value was evaluated in the same manner as in Example 1, and the obtained results are shown in Table 5.

  As is apparent from the results in Table 5, the image clarity C value of the black solid image portion is slightly deteriorated when the moisture is sufficiently dried after image recording with the pigment ink. This is presumably because the interface of the pigment particle layer and the interface of the protective coating layer have become clearer. The degree of deterioration is larger in the comparative recording paper 1 not containing the compound of the present invention.

Example 7
In the same manner as in Example 1, except that printing was performed by adjusting the amount of colorless ink applied (Pml / m ² ) in a reverse image manner according to the amount of colored ink applied (Qml / m ² ). Prints 1 and 2 were made to produce prints 27 and 28. In prints 27 and 28, the amount of colorless ink applied (Pml / m ² ) was changed according to P = (25−Q) ^1/2 . Incidentally, dry solids of the colorless ink is in the range of about 0.07~0.12g / m ^2.

  Each of the created prints was evaluated for glossiness, image clarity C value, dot defect resistance and rainbow unevenness resistance in the same manner as in Example 1. Table 6 shows the results obtained.

  As is clear from the results in Table 6, when the amount of colorless ink applied is changed in an inverse image-like manner, the glossiness and image clarity of the black solid portion tend to be slightly lowered, but the effect of the present invention is reduced. It turns out that it is obtained. Further, even when the colorless ink was ejected almost simultaneously with the colored ink in accordance with the above method, the results close to the prints 27 and 28 were obtained, and the effect of the present invention was confirmed.

Claims (7)

0.05 to 0.3 g per m ² using a colorless ink containing a polymer having a film-forming ability and substantially free of a colorant on an ink jet recording paper image-formed with a colorant-containing ink. An ink jet recording paper for use in an ink jet recording method for forming a protective film having a dry solid content of at least one porous ink absorbing layer on a non-water-absorbing support, the porous ink absorbing layer comprising: An inkjet recording paper comprising a compound represented by the following general formula (I) having a molecular weight of 200 or less.

[Wherein, R ₁ represents a hydrogen atom, a substituted or unsubstituted alkyl group, an alkenyl group, an aryl group, an acyl group, a heteroaryl group, a heterocyclic group, NR ₄ R ₅ , or OR ₆ . R _{2 to} R ₆ each have the same meaning as R ₁ . R ₁ and R ₂ , R ₁ and R ₃ may be bonded to each other to form a ring. X represents an oxygen atom or NH. ] The inkjet recording paper according to claim 1, wherein the compound represented by the general formula (I) is urea or a urea derivative. The inkjet recording paper according to claim 1 or 2, wherein the protective film is formed by the colorless ink substantially over the entire surface of the inkjet recording paper. The discharge of the colorless ink droplets forming the protective film is performed immediately after the image formation with the colorant-containing ink is performed while the water is not substantially evaporated. The inkjet recording paper of any one of Claims. The inkjet recording paper according to any one of claims 1 to 4, wherein the colorant-containing ink is a pigment ink. The porous ink absorption layer located on the surface of the porous ink absorption layer contains inorganic fine particles having an average particle diameter of 10 to 100 nm and polyvinyl alcohol. The inkjet recording paper of any one of Claims. The center line average roughness (Ra) when measured with a reference length of 2.5 mm as defined in JIS-B-0601 and a cutoff value of 0.8 mm on the surface of the porous ink absorbing layer is 0.08 to 0.20 μm. The inkjet recording paper according to claim 1, wherein