JP2007050580A - Sheet for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet for inkjet recording which has a high gloss and a high printing density and reduces uneven agglomeration of ink on the occasion of printing and moreover which has a high surface strength and is hardly damaged in carrying in a printer, no matter which of a dye ink and a pigment ink is used. <P>SOLUTION: The sheet 1 for inkjet recording has an air-permeable base 10 and an ink accepting layer 20 containing particulates and an adhesive, and the surface of the ink accepting layer 20 is subjected to casting. At least in the outermost surface part 21 of the ink accepting layer 20, polyoxylene-group-containing polyvinyl alcohol is contained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inkjet recording sheet applied to inkjet recording.

The ink jet recording method that forms images by ejecting water-based ink from fine nozzles is easy to make full color, can be recorded at high speed, and can be cheaper than other printing devices when printing a small number of copies. And so on. Therefore, it is widely used in terminal printers, facsimiles, plotters, form printing, and the like.
In recent years, rapid spread of printers and higher definition and speed have been advanced, and accordingly, ink-jet recording sheets are required to have higher ink absorption speed and higher surface strength than ever before. Furthermore, there is a strong demand for printing a recorded image taken with a digital camera with a high image quality comparable to a silver salt photograph, and more specifically, there is a need for further improvements in print density and gloss.

Therefore, in order to increase the gloss, a method has been proposed in which the glossy layer is pressed against a heated mirror drum while it is wet and the mirror surface is copied (see Patent Document 1).
In addition, for the purpose of improving gloss, print density, ink absorbability, etc., the outermost part using two or more ink-receiving layers on a substrate and using an aggregate pigment having an average particle diameter of 1 μm or less Has been proposed to be formed by pressure bonding to a heated mirror drum while in a wet state (see Patent Document 2).
In addition, for the purpose of improving ink acceptability, bleeding resistance, glossiness, and weather resistance, a composition for forming an ink receiving layer containing an oxyalkylene group-containing polyvinyl alcohol and a cationic group-containing polyvinyl alcohol has been proposed. (See Patent Document 3).
Japanese Unexamined Patent Publication No. 7-117335 JP 2001-10220 A JP 2003-26885 A

However, in the method described in Patent Document 1, since the crack is easily formed in the glossy expression layer, the print density is low.
In the method described in Patent Document 2, since the outermost surface portion of the ink receiving layer is easily cracked, the printing density is insufficient, and a large amount of colored pigment is absorbed in the cracked portion, resulting in uneven printing. In addition, the surface strength was insufficient, and it was easily damaged when transported by a printer.
The ink receiving layer formed from the composition described in Patent Document 3 has insufficient print density and surface strength, and cannot be said to have a sufficiently high gloss.

In recent years, not only dye inks, but also pigment inks with excellent water resistance and light resistance have been used in an increasing amount, and therefore for ink jet recording capable of printing with high quality for both dye inks and pigment inks. A sheet is required. However, it is difficult to form an ink receiving layer excellent in printability of both dye ink and pigment ink by the methods of Patent Documents 1 to 3.
The present invention has been made in view of the above circumstances, and even if the ink is dye ink or pigment ink, the gloss and the print density are high, and the uneven aggregation of the ink at the time of printing is suppressed. Another object of the present invention is to provide an ink jet recording sheet that has high surface strength and is hardly damaged when conveyed by a printer.

The inkjet recording sheet of the present invention is an inkjet recording sheet having a gas-permeable substrate and an ink receiving layer containing fine particles and an adhesive, and the surface of the ink receiving layer is cast.
Polyoxylene group-containing polyvinyl alcohol is contained in at least the outermost portion of the ink receiving layer.
In the inkjet recording sheet of the present invention, the ink receiving layer preferably contains polyvinyl alcohol having no substituent and having an average degree of polymerization of 3500 or more.
In the ink jet recording sheet of the present invention, it is preferable that a cationic group-containing polyvinyl alcohol is further contained in the outermost portion of the ink receiving layer.
It is preferable that the casting process in the ink jet recording sheet of the present invention is a rewet casting method using a rewet liquid, and the rewet liquid contains polyoxylene group-containing polyvinyl alcohol.

  The ink jet recording sheet of the present invention has high gloss and printing density regardless of whether the ink is dye ink or pigment ink, suppresses uneven aggregation of the ink when printed, and has high surface strength. It is hard to be damaged when transported by a printer.

One embodiment of the ink jet recording sheet of the present invention will be described.
FIG. 1 shows an ink jet recording sheet according to this embodiment. The inkjet recording sheet 1 includes a gas-permeable substrate 10, an ink receiving layer 20, and an undercoat layer 30 provided between the gas-permeable substrate 10 and the ink receiving layer 20.

<Air-permeable substrate>
Examples of the air permeable substrate 10 include a paper substrate and resin film sheets having air permeability.
The paper base material includes, for example, wood pulp as a main component, and fillers, various auxiliaries and the like added as necessary. Here, as the wood pulp, various chemical pulps, mechanical pulps, regenerated pulps and the like can be used.
These pulps can be adjusted in degree of beating (freeness) by a beating machine in order to adjust paper strength, papermaking suitability, and the like. Specifically, in order to increase the smoothness of the paper substrate surface, it is preferable to increase the freeness of the pulp, and in order to prevent blurring of the sheet and bleeding of the recorded image caused by moisture in the ink, It is preferable to reduce the freeness of the. From these, the freeness of the pulp is preferably 250 to 550 ml (CSF: JIS-P-8121), more preferably 300 to 500 ml.

The filler added to the paper base material is blended for imparting opacity and adjusting the ink absorbability, and examples thereof include calcium carbonate, calcined kaolin, silica, and titanium oxide. Among them, use of calcium carbonate is preferable because a paper base material having high whiteness can be obtained and glossiness of the ink jet recording sheet is enhanced.
As for the content rate (ash content) of the filler in a paper base material, about 1-20 mass% is preferable. If the filler content is 1% by mass or more, the air permeability of the paper substrate is good, and if the filler content is 20% by mass or less, sufficient paper strength is obtained.
A more preferable filler content is 7 to 20% by mass. Within this range, smoothness, air permeability, and paper strength are balanced, and an inkjet recording sheet excellent in glossiness and image sharpness can be easily obtained.

Examples of the auxiliary agent added to the paper substrate include a sizing agent, a fixing agent, a paper strength enhancer, a cationizing agent, a yield improver, a dye, and a fluorescent brightening agent.
As the paper strength enhancer, polyamide / epichlorohydrin resin, N-vinylformamide / vinylamine copolymer and the like are preferably used. Among these, polyamide epichlorohydrin resin is preferably used because it has an effect of improving the dimensional stability of paper when wet. The paper strength enhancer can be added to the paper substrate by a process such as internal addition, coating, or impregnation.
Furthermore, in the size press process of the paper machine, the surface strength, sizing degree, etc. can be adjusted by applying and impregnating starch, polyvinyl alcohols, cationic resins and the like to the paper substrate.

  Specific examples of the paper substrate as described above include fine paper, art paper, coated paper, cast coated paper, foil paper, craft paper, baryta paper, paperboard, impregnated paper, vapor-deposited paper, water-soluble paper, or Examples include acid paper and neutral paper used for general coated paper.

Moreover, as a steech human sizing degree (100 g / m < ² > paper) of a paper base material, about 1 to 400 second is preferable and 4 to 350 second is more preferable.
If the Steecht sizing degree is 1 second or more, operational problems such as wrinkling during coating are unlikely to occur, and if the Steecht sizing degree is 400 seconds or less, it exhibits good ink absorption and printing. Later curling and cockling are suppressed.
Although the basic weight of a paper base material is not specifically limited, About 20-400 g / m < ² > is preferable.

  The Oken type air permeability of the paper substrate is preferably 10 to 350 seconds, more preferably 10 to 200 seconds, and particularly preferably 20 to 100 seconds. If the air permeability is 10 seconds or more, the coating liquid can be prevented from penetrating into the paper substrate. If the air permeability is 350 seconds or less, the operability at the time of press-contact finishing on the cast drum can be improved.

<Ink receiving layer>
The ink receiving layer 20 is a layer that is disposed on the surface of the inkjet recording sheet 1, includes fine particles and an adhesive, and is subjected to a cast treatment on the surface.

Examples of the fine particles contained in the ink receiving layer 20 include amorphous silica, alumina, colloidal silica, and the like. These fine particles may be used alone or in combination of two or more.
Among these, amorphous silica is preferable, and the average secondary particle diameter of amorphous silica is preferably 90 to 700 nm. If the average secondary particle diameter of the amorphous silica is 90 nm or more, the ink absorbability is higher, and if the average secondary particle diameter of the amorphous silica is 700 nm or less, the print density and surface gloss are higher.
As the amorphous silica, wet method silica, gas phase method silica and the like are preferably used.

  The adhesive contained in the ink receiving layer 20 is not particularly limited, but it is preferable that at least one ink receiving layer contains polyvinyl alcohol having no substituent. Here, the polyvinyl alcohol having no substituent is a polymer of 1-hydroxyethylene. The average degree of polymerization of the polyvinyl alcohol having no substituent is preferably 3500 or more, and more preferably 4000 to 7000. When the average degree of polymerization is 3500 or more, particularly 4000 or more, the strength of the ink receiving layer 20 is increased and cracks are suppressed, and a sufficient print density can be obtained in a pigment printer. When the average degree of polymerization is 7000 or less, sufficient ink absorbability can be obtained, and handling during preparation of the coating liquid is good.

The ink receiving layer 20 has a low molecular weight cationic compound (hereinafter referred to as a cationic resin or a cationic surfactant) in order to improve the color developability and storage stability of the dye ink, the ink absorbability, and the water resistance of the printed image. It is preferable to add a general name of a cationic compound. In addition, a cationic compound, particularly a cationic resin, may play a role as an adhesive.
In order to improve the printing density, it is preferable to add a cationic resin. The cationic resin can be used in the form of an aqueous solution or an emulsion.
Moreover, a cationic resin can be used as a cationic organic pigment which is a particulate form.
The cationic organic pigment is a crosslinked resin obtained by copolymerizing a polyfunctional monomer when polymerizing a cationic resin. Alternatively, a crosslinking resin is added to a cationic resin having a reactive functional group (hydroxyl group, carboxyl group, amino group, acetoacetyl group, etc.) as necessary to obtain a crosslinked resin by means of heat, radiation, etc. It is.

Examples of the cationic resin include polyalkylene polyamines such as polyethylene polyamine and polypropylene polyamine or derivatives thereof, acrylic polymers having secondary or tertiary amino groups or quaternary ammonium groups, or co-polymerization of those acrylamides. Polymers, polyvinylamine and polyvinylamidines, dicyandiamide-cationic compounds represented by dicyandiamide / formalin copolymer, polyamine-based cationic compounds represented by dicyandiamide / polyethyleneamine copolymer, epichlorohydrin / dimethylamine copolymer, diallyldimethylammonium -SO ₂ double condensates, diallylamine salt -SO ₂ double condensates, diallyl dimethyl ammonium chloride polymer, diallyl dimethyl ammonium chloride - acrylamide copolymerization Things, a copolymer of allylamine salt, dialkylaminoethyl (meth) acrylate 4 Kyushiotomo polymers, acrylamide diallylamine copolymers, dimethylaminopropyl acrylamide polymers, and the like. These cationic resins may be used alone or in combination of two or more.

  The content of the cationic compound is preferably 1 to 100 parts by mass and more preferably 5 to 50 parts by mass with respect to 100 parts by mass of the fine particles. If the content of the cationic compound is less than 1 part by mass, the effect of improving the print density is small, and if it exceeds 100 parts by mass, the print density may be lowered or image blurring may occur.

  In the ink receiving layer 20, a commonly used dispersant, crosslinking agent, thickener, antifoaming agent, antistatic agent, preservative, ultraviolet absorber, preservability improving agent are used within a range not impairing the effects of the present invention. Various additives such as a fluorescent brightening agent and a coloring agent can be appropriately added.

In the ink receiving layer 20 of the present invention, at least the outermost portion 21 contains polyoxylene group-containing polyvinyl alcohol as an adhesive.
Polyoxylene group-containing polyvinyl alcohol is obtained by saponifying a copolymer of an unsaturated monomer having an oxyalkylene group and a vinyl ester compound. Examples of the unsaturated monomer having an oxyalkylene group include (meth) acrylic acid ester type monomers, but the present invention is not limited to these.
The oxyalkylene group-containing polyvinyl alcohol preferably has 0.1 to 30 mol% of oxyalkylene groups. If the oxyalkylene group is less than 0.1 mol%, the ink acceptability tends to decrease or tends to bleed, and if it exceeds 30 mol%, the weather resistance and water resistance tend to decrease.
The saponification degree of the oxyalkylene group-containing polyvinyl alcohol is not particularly limited, but is preferably 50 mol% or more. If the degree of saponification is less than 50 mol%, ink acceptability and weather resistance tend to be lowered.
Although it does not specifically limit about average polymerization degree, It is preferable that it is 50-3000, and it is more preferable that it is 1000-2500. If the average degree of polymerization is less than 50, the film-forming property is low, stickiness or the like remains on the surface, and the inkjet recording sheet 1 may cause blocking. On the other hand, if it exceeds 3000, the viscosity of the coating liquid used for forming the ink receiving layer may increase, and the operability may be lowered.

Furthermore, it is preferable that the outermost surface portion 21 of the ink receiving layer 20 further contains a cationic group-containing polyvinyl alcohol as an adhesive. If the outermost surface portion 21 contains a cationic group-containing polyvinyl alcohol, the surface strength, transportability, and print density are further improved.
The saponification degree of the cationic group-containing polyvinyl alcohol is not particularly limited, but is preferably 50 to 100 mol%, more preferably 70 to 100 mol% from the viewpoint of ink absorbability and weather resistance. Moreover, although it does not specifically limit about average polymerization degree, It is preferable that it is 50-3000 for the same reason as the case of the said polyoxylene group containing polyvinyl alcohol.

The polyoxylene group-containing polyvinyl alcohol and the cationic group-containing polyvinyl alcohol may be contained in the inner portion 22.
Further, the ink receiving layer 20 may be a uniform layer.

<Undercoat layer>
The undercoat layer 30 includes, for example, fine particles and an adhesive.
Examples of the fine particles contained in the undercoat layer 30 include amorphous silica, kaolin, clay, calcined clay, zinc oxide, aluminum oxide, titanium oxide, aluminum hydroxide, calcium carbonate, satin white, aluminum silicate, alumina, colloidal silica, Zeolite, synthetic zeolite, sepiolite, smectite, synthetic smectite, magnesium silicate, magnesium carbonate, magnesium oxide, diatomaceous earth, styrene plastic pigment, hydrotalcite, urea resin plastic pigment, benzoguanamine plastic pigment, and the like. These fine particles may be used alone or in combination of two or more. Among these, amorphous silica is preferable.

The average secondary particle diameter of the amorphous silica is preferably 10 μm or less, and more preferably 3 to 5 μm. In addition, the average secondary particle diameter of amorphous silica is a particle diameter obtained by observing an aqueous silica dispersion with an electron microscope (SEM, TEM) (taken an electron micrograph of 10,000 to 400,000 times, 5 cm square) The average particle diameter of the dispersed silica particles was measured and averaged (see “Fine Particle Handbook”, Asakura Shoten, p. 52, 1991)).
If the average secondary particle diameter of the amorphous silica is 3 μm or more, the ink absorptivity becomes higher and the strength of the undercoat layer 30 is increased, and if it is 5 μm or less, the surface of the ink receiving layer 20 is cast. Glossiness and ink absorption are higher.

  Examples of the adhesive contained in the undercoat layer 30 include proteins such as casein, soybean protein, and synthetic protein, various starches such as starch and oxidized starch, polyvinyl alcohol having no substituent, and cationic group-containing polyvinyl alcohol. , Polyvinyl alcohols containing modified polyvinyl alcohol such as silyl modified polyvinyl alcohol, cellulose derivatives such as carboxymethylcellulose and methylcellulose, styrene-butadiene copolymer, conjugated diene polymer latex of methylmethacrylate-butadiene copolymer, acrylic polymer Examples thereof include a polymer latex, a vinyl polymer latex such as an ethylene-vinyl acetate copolymer, an aqueous polyurethane, and an aqueous polyester. These adhesives may be used alone or in combination of two or more.

  The content of the adhesive in the undercoat layer 30 is preferably 20 to 100 parts by mass with respect to 100 parts by mass of the fine particles. If the amount is less than 20 parts by mass, the generation of paper dust may not be sufficiently suppressed. If the amount exceeds 100 parts by mass, the ink absorbability may be impaired.

  In addition, the undercoat layer 30 may contain a cationic compound that may be contained in the ink receiving layer 20, a known dispersant, thickener, antifoaming agent, antistatic agent, preservative, fluorescent dye, if necessary. Various auxiliary agents such as a colorant can be added as appropriate.

<Manufacturing method>
A method for producing the ink jet recording sheet of this embodiment will be described.
First, a coating solution for forming an undercoat layer containing fine particles and an adhesive is applied onto the air-permeable substrate 10 and dried to form the undercoat layer 30. Thereafter, a supercalender, brush is used as necessary. A smoothing process such as multiplication is performed.
Here, the solid content concentration of the coating liquid for forming the undercoat layer is preferably 5 to 50% by mass.

Coating methods for the undercoat layer forming coating solution include blade coaters, air knife coaters, roll coaters, brush coaters, Champlex coaters, bar coaters, lip coaters, gravure coaters, curtain coaters, slot die coaters, slide coaters, sprays, etc. A coating method using various known coating apparatuses can be employed.
The dry coating amount of the undercoat layer forming coating solution is preferably 6 to 12 g / m ² . If the dry coating amount of the coating liquid for forming the undercoat layer is 6 g / m ² or more, the ink absorbability can be increased, and if the dry coating amount is 12 g / m ² or less, the print gloss becomes higher.

In order to further prevent the ink receiving layer 20 from cracking, the undercoat layer forming coating solution preferably contains a crosslinking agent.
As a crosslinking agent, the well-known crosslinking agent which has the crosslinking | crosslinked property with respect to an adhesive agent, and the various well-known gelatinizers which gelatinize an adhesive agent can be used.
For example, as a compound having a crosslinking property to polyvinyl alcohol, an aldehyde crosslinking agent such as glyoxal, an epoxy crosslinking agent such as ethylene glycol diglycidyl ether, a vinyl crosslinking agent such as bisvinylsulfonylmethyl ether, boric acid and borax And boron-containing compounds, zirconium compounds, aluminum compounds, chromium compounds and the like. Among these, a boron-containing compound is preferable because thickening or gelation is fast.

Here, the boron-containing compound is an oxygen acid having a boron atom as a central atom and a salt thereof. Specific examples include orthoboric acid, metaboric acid, hypoboric acid, tetraboric acid, pentaboric acid, and sodium, potassium and ammonium salts thereof. Among these, orthoboric acid and disodium tetraborate are preferably used because they have an effect of increasing the viscosity of the coating solution to an appropriate degree.
The content of the boron-containing compound depends on the type of the boron-containing compound and the average degree of polymerization of the polyvinyl alcohol, and is preferably an amount contained in the undercoat layer 30 by 0.01 to 2.0 g / m ² . If the content of the boron-containing compound is 0.01 g / m ² or more in the undercoat layer 30, the crosslinkability with the adhesive and the gelation of the coating solution will be good, and the undercoat layer 30 will crack. Is suppressed. If the content of the boron-containing compound is 2.0 g / m ² or less in the undercoat layer 30, it is possible to prevent excessive crosslinking of the adhesive.

  Furthermore, various auxiliary agents such as a crosslinking agent, a dispersant, an antifoaming agent, a colorant, a fluorescent dye, an antistatic agent, and an antiseptic can be appropriately added to the coating solution for forming the undercoat layer.

  Next, the ink receiving layer 20 is formed by applying an ink receiving layer forming coating solution containing fine particles and an adhesive on the undercoat layer 30. Here, as an adhesive, polyoxylene group-containing polyvinyl alcohol may be included. The solid content concentration of the ink receiving layer forming coating solution is preferably 5 to 50% by mass, and more preferably 5 to 20% by mass. If the solid content concentration is 5% by mass or more, the drying efficiency of the ink receiving layer 20 is improved. Moreover, if it is 50 mass% or less, the crack of the ink receiving layer 20 can be prevented more.

As necessary, the ink receiving layer forming coating liquid may be a synthetic resin latex such as styrene-butadiene latex or methyl methacrylate-butadiene copolymer latex, or proteins such as casein, soy protein, synthetic protein, starch or oxidized starch. Various starches such as polyvinyl alcohol, cellulose derivatives such as carboxymethylcellulose and methylcellulose, various thickeners such as polycarboxylic acid, polyacrylic acid, acrylic emulsion, polyamide, polyester, alkali thickener and nonionic surfactant And flow modifiers, sodium chloride, ammonium chloride, zinc chloride, magnesium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, zinc sulfate, magnesium sulfate, ferrous sulfate, sodium nitrate, ammonium nitrate, monobasic sodium phosphate, phosphoric acid Numonium, calcium phosphate, sodium polyphosphate, sodium hexametaphosphate, sodium formate, ammonium formate, sodium acetate, potassium acetate, sodium monochloroacetate, sodium malonate, sodium tartrate, potassium tartrate, potassium citrate, sodium lactate, sodium gluconate , Ammonium salts and metal salts of inorganic and organic acids such as sodium adipate, sodium dioctylsulfosuccinate, sodium aluminate, and methylamine, diethanolamine, diethylenetriamine, diisopropylamine, triethanolamine, ethanolamine, ethanolamine, etc. Amines, phosphates, polyoxyethylene alkylphenol ether phosphates, polyoxyethylene ethers Phosphate esters such as acid ester salt, alkylphenol ether phosphate ester salt, polyoxyethylene, alkyl ether, polyoxyethylene and ammonia water, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, polyethylene glycol diglycyl ether, polypropylene glycol Contains various additives such as polyfunctional epoxy compounds such as diglycidyl ether and adipic acid diglycidyl ester, various water-proofing agents such as urea-formaldehyde, polyamide-epichlorohydrin, and glyoxal, and printing suitability improvers. be able to. In particular, if a surfactant derived from acetylene alcohol or acetylene glycol is contained, the defoaming property and wettability of the ink-receiving layer-forming coating solution are enhanced.
The content of various additives in the ink-receiving layer-forming coating solution is preferably 0.05 to 10% by mass, and more preferably 0.1 to 5% by mass.

  Furthermore, various auxiliary agents such as a crosslinking agent, a dispersant, an antifoaming agent, a colorant, a fluorescent dye, an antistatic agent, and an antiseptic can be appropriately added to the ink receiving layer forming coating solution.

As the coating method of the ink receiving layer forming coating solution, the same method as the undercoat layer forming coating solution can be employed.
The dry coating amount of the ink receiving layer forming coating solution is preferably 10 to ²⁰ g / m ² . When the dry coating amount is 10 g / m ² or more, the glossiness and the ink absorbency are further increased, and when the dry coating amount is 20 g / m ² or less, cracking of the ink receiving layer 20 can be further suppressed. Good dot roundness can be obtained, and the printing density of pigment ink and dye ink is sufficient.

Thereafter, the surface of the ink receiving layer 20 is cast. The casting process is a process of obtaining a smooth and glossy ink receiving layer 20 surface by drying the surface of the ink receiving layer 20 on a smooth surface and copying the smooth surface onto the ink receiving layer 20.
Examples of the cast treatment include a cast drum system using a smooth cast drum (mirror finished metal drum or the like), a mirror finished metal plate, a planar transfer system using a plastic sheet, film, glass plate, or the like.

As the cast drum system, for example, wet casting is performed by pressing the ink receiving layer 20 against a heated cast drum and drying it while the ink receiving layer 20 formed from the ink receiving layer forming coating liquid is in a wet state. Rewetting cast method, gelation casting method, heating method wherein ink receiving layer 20 formed from a coating solution for forming an ink receiving layer is once dried and then re-wetted with a rewet solution, pressed against a heated cast drum and dried. Examples include a precast method in which an ink receiving layer forming coating solution is applied to the cast drum, and then the surface of the undercoat layer is pressed and dried to finish.
In the cast drum system, the temperature of the heated cast drum is preferably 50 to 150 ° C, and more preferably 70 to 120 ° C.

  In addition, as the planar transfer method, (a) a coating film for forming an ink receiving layer is applied onto the undercoat layer 30 and a smooth film or a film is applied to the ink receiving layer 20 while the ink receiving layer 20 is in a wet state. A method of peeling and finishing a smooth film or sheet after the sheets are stacked and dried. (B) The ink receiving layer 20 is wetted by applying a coating solution for forming an ink receiving layer on the smooth film or sheet. Examples thereof include a method in which the ink receiving layer 20 is pressed against the undercoat layer 30 while it is in a state and dried, and then a smooth film or sheet is peeled off and finished. In this case, it is preferable to use a polyethylene terephthalate (PET) film.

Among cast processes, it is excellent in surface smoothness, and is advantageous in terms of productivity and cost. Therefore, a cast drum system is preferable, and among the cast drum systems, a uniform ink receiving layer 20 is easily formed. In addition, the rewet cast method is preferable because of high printing density and excellent gloss.
The coating amount of the rewet liquid in the rewet cast method is preferably 0.1 to 30 g / m ² in terms of dry solid content. If it is less than 0.1 g / m ² , the print density and gloss may be insufficient. If it exceeds 30 g / m ² , drying may be burdened and operability may be reduced.
As the rewetting liquid coating method, the same method as the coating method of the undercoat layer forming coating liquid can be employed. The rewetting liquid is not particularly limited as long as the surface of the ink receiving layer 20 can be rewet, and examples thereof include water containing fine particles and an adhesive. The rewetting liquid preferably contains polyoxylene group-containing polyvinyl alcohol. If the rewetting liquid contains polyoxylene group-containing polyvinyl alcohol, the polyoxylene group-containing polyvinyl alcohol can be easily contained in the outermost surface portion 21 of the ink receiving layer 20.

When performing the cast treatment, it is preferable to use a release agent in order to improve the peelability of the cast drum. Examples of the method of using the release agent include a method of adding to the ink receiving layer forming coating solution, a method of applying to the cast drum surface, and a method of adding to the rewetting solution.
Examples of mold release agents include higher fatty acid amides such as stearic acid amide and oleic acid amide, polyolefin waxes such as polyethylene wax, oxidized polyethylene wax and polypropylene wax, calcium stearate, zinc stearate, potassium oleate, and ammonium oleate. Examples include higher fatty acid alkali salts, silicone compounds such as lecithin, silicone oil and silicone wax, and fluorine compounds such as polytetrafluoroethylene. Of these, cationic release agents are preferred.

  In the above production method, the crosslinking agent is contained in the undercoat layer forming coating solution, but the crosslinking agent may be applied onto the undercoat layer not containing the crosslinking agent.

  In the ink jet recording sheet in which the polyoxylene group-containing polyvinyl alcohol is contained in at least the outermost portion 21 of the ink receiving layer 20 as described above, the printing density is high regardless of whether the ink is a dye ink or a pigment ink. In addition, unevenness of ink aggregation during printing is suppressed. Further, as a result of the cast treatment being performed on the surface of the outermost surface portion 21 containing the polyoxylene group-containing polyvinyl alcohol, the gloss becomes sufficiently high. In addition, the surface strength is high and scratches are less likely to occur when transported by a printer. On the other hand, the above effect is not exhibited in the ink jet recording sheet in which the polyoxylene-containing polyvinyl alcohol is contained only in the inner layer 22 of the ink receiving layer 20.

  In addition, this invention is not limited to the said embodiment. In the above embodiment, the undercoat layer is provided, but the undercoat layer may be omitted. However, if it has an undercoat layer, the ink absorption capacity and absorption speed of the ink jet recording sheet can be increased, and the absorption speed of the ink receiving layer on the undercoat layer can be increased, and the print density can be further improved. You can make it. For this reason, the ink jet recording sheet of the present invention preferably has an undercoat layer.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the following examples, “parts” and “%” represent “parts by mass” and “% by mass”, respectively, unless otherwise specified, and are solid contents excluding water.

Example 1
<Preparation of paper substrate>
Wood pulp (LBKP: freeness 440 ml CSF) 100 parts, filler (calcium carbonate 3: talc 1 ratio) 15 parts, commercially available sizing agent (trade name: Fibran 81K, manufactured by NSC Japan) 0.05 part Then, a papermaking material containing 0.45 part of sulfuric acid band, 0.45 part of starch, 0.4 part of polyamide / epichlorohydrin resin (paper strength enhancer) and a little yield improver was prepared. Then, after obtaining a paper having a basis weight of 188 g / m ² from the papermaking material by a long paper machine, a super calender treatment is performed at a linear pressure of 150 kg / cm to obtain a paper base material which is a gas permeable base material. Produced. The resulting paper substrate had a thickness of 210 μm and an air permeability of 30 seconds.

<Formation of undercoat layer>
100 parts of synthetic amorphous silica (trade name: Fine Seal X-45, manufactured by Tokuyama Corporation, average secondary particle size 4.5 μm), 80 parts of silyl-modified polyvinyl alcohol (trade name: R1130, manufactured by Kuraray Co., Ltd.), fluorescent dye (Product name: Whitetex BPS (H), manufactured by Sumitomo Chemical Co., Ltd.) 2 parts, 5 parts of a cationic compound composed of diallyldimethylammonium chloride polymer (Product name: Unisense CP-102, manufactured by Senka Co., Ltd., ink fixing agent) were mixed. A coating solution for forming an undercoat layer having a solid content concentration of 15% was prepared.
Then, this undercoat layer forming coating solution was coated on the paper substrate with an air knife coater so that the dry coating amount was 8 g / m ² and dried to form an undercoat layer.

<Formation of ink receiving layer>
Using commercially available gas phase silica (trade name: Leolosil QS-30, manufactured by Tokuyama Corporation, average primary particle size 9 nm, specific surface area 300 m ² / g), repeated crushing and dispersion with a high-speed collision type homogenizer, and after classification, A 10% silica dispersion having an average secondary particle size of 200 nm was prepared. To 100 parts (solid content) of this silica dispersion, 10 parts by mass of a cationic compound having a 5-membered ring amidine structure (trade name; SC-700M, molecular weight; 30,000, manufactured by Hymo Co., Ltd.) is added, and high-speed flow collision Further dispersion was performed with a type homogenizer to prepare a 10% by mass cationic polymer-silica composite particle dispersion having an average secondary particle size of 0.15 μm. The pore volume of this composite particle by BET was 1.1 ml / g, and 100 parts by mass (solid content) of this cationic polymer-silica composite particle dispersion (solid name) : PVA145, manufactured by Kuraray Co., Ltd., average polymerization degree 4500) 15 parts were mixed to prepare a coating solution for forming an ink receiving layer.
Thereafter, a 3% by mass borax aqueous solution is applied onto the undercoat layer so that the dry coating amount is 1.5 g / m ² , and the dry mass is 17 g / m ² without drying. The ink receiving layer forming coating solution was applied by a die coater. Then, the ink receiving layer was formed by drying with hot air at 150 ° C. so that the equilibrium water content was 8%.
Next, 50 parts of polyoxylene group-containing polyvinyl alcohol (trade name: Ecomati WO320R, manufactured by Nippon Synthetic Chemical Co., Ltd.) and 1 part of a release agent (polyethylene wax, nonionic) were mixed to prepare a rewetting liquid.
Then, after the rewetting liquid was applied to the surface of the ink receiving layer, the surface was pressed against a cast drum having a surface temperature of 100 ° C. at a linear pressure of 200 kg / cm to perform a rewetting cast treatment. As a result, the outermost portion containing the polyoxylene group-containing polyvinyl alcohol was formed in the ink receiving layer to obtain an ink jet recording sheet.

(Example 2)
An ink jet recording sheet was obtained in the same manner as in Example 1 except that 50 parts of cationic group-containing polyvinyl alcohol (trade name: CM318, manufactured by Kuraray Co., Ltd.) was added to the rewetting liquid in Example 1.

(Example 3)
An ink receiving layer forming coating solution containing 200 parts of vapor phase silica (trade name: Leolosil QS-30) with respect to 100 parts of polyoxylene group-containing polyvinyl alcohol (trade name: Ecomati WO320R) was prepared. Then, after coating the ink receiving layer forming coating solution on the surface of the undercoat layer formed in the same manner as in Example 1, the surface was pressed against a cast drum having a surface temperature of 100 ° C. at a linear pressure of 200 kg / cm. Then, a wet casting process was performed to obtain an ink jet recording sheet.

(Comparative Example 1)
Example 1 except that instead of the polyoxylene group-containing polyvinyl alcohol, 50 parts of polyvinyl alcohol having no substituent (trade name: PVA117, manufactured by Kuraray Co., Ltd., average degree of polymerization 1700) was prepared to prepare a rewet liquid. Similarly, an ink jet recording sheet was obtained.

(Comparative Example 2)
Inkjet recording was carried out in the same manner as in Comparative Example 1 except that 50 parts of low-saponified cationic group-containing polyvinyl alcohol (trade name LM-10HD, manufactured by Kuraray Co., Ltd.) was added to the rewet cast coating liquid of Comparative Example 1. A sheet was obtained.

(Evaluation method and evaluation criteria)
The inkjet recording sheets obtained in the above examples and comparative examples were evaluated by the following methods. The results are shown in Table 1.

[Printability in inkjet recording]
Evaluation of printability was carried out with respect to print density, ink absorbability, glossiness of the printed part, glossiness, surface strength, and printer transportability using both dye ink and pigment ink type printers.

Evaluation printer printer A: Commercially available dye ink type ink jet printer (trade name: PM-G800, manufactured by Seiko Epson Corporation)
Printer B: Commercially available pigment ink type ink jet printer (trade name: PM-G900, manufactured by Seiko Epson Corporation)

Printing density Black solid printing was performed using printer A (dye ink type) and printer B (pigment ink type), and the printing density was measured with an X-Rite reflection densitometer (938 Spectrodensitometer).

・ Ink absorbability Using printer A (dye ink type), black, cyan, magenta, yellow, red, green, and blue solid colors are printed in a grid pattern so as to touch each other. The ink bleeding at the boundary between them was visually evaluated according to the following criteria.
(Double-circle): The blur of printing is not recognized at all and it is an excellent level.
○: Slight bleeding is observed, but there is no practical problem.
Δ: Slightly blurring of printing and slightly problematic in practical use.
X: The level at which printing blur is remarkable and becomes a serious problem in practical use.

・ Glossiness of printed part Using a printer A (dye ink type), a photographic image (JIS X 9204 compliant “high-definition color digital standard image (XYZ / SCID) data”), image identification code: N1, image name: Glass and female) were printed, and the uniformity of the printed portion was visually observed and evaluated according to the following criteria.
A: Excellent level with no unevenness in printed gloss on the entire image.
○: A level where the glossiness of printing is slightly lowered in a portion having a dark printing color development property, but does not cause a problem as a whole.
×: Level at which printing gloss partially disappears and becomes a serious problem in practical use.
In addition, in the evaluation of ◎, the most excellent one was designated as ◎ +.

[Glossiness]
The surface of the blank inkjet recording sheet was visually observed from an oblique direction, and glossiness was evaluated according to the following criteria.
A: Extremely high gloss.
○: Glossy.
X: The glossiness is inferior.
In addition, in the evaluation of ◎, the most excellent one was designated as ◎ +.

[Surface strength]
Using a friction tester type II (Gakushoku type) described in JIS L 0849, the test piece was mounted on the test piece base and the tip of the friction element so that the outermost ink receiving layers were opposed to each other. Then, with a load of 2 N (the mass of the friction element is 200 g), 100 mm of the test piece surface was rubbed back and forth 100 times at a speed of 30 times per minute. From this, the surface strength was evaluated from the presence or absence of removal of the outermost surface and the degree of generation of paper dust.
(Evaluation criteria)
○: Good △: Slightly inferior ×: Impractical

[Transportability]
Using the printer (A), solid printing was continuously performed, and the transportability of the inkjet recording sheet was evaluated.
○: Good △: Slightly inferior ×: Impractical

[Ink aggregation unevenness]
Using the printer (B), solid printing was performed, and the degree of ink aggregation unevenness was visually evaluated.
○: Good △: Slightly inferior ×: Impractical

The inkjet recording sheets of Examples 1 to 3, in which the outermost surface portion 21 of the ink receiving layer contains polyoxylene-containing polyvinyl alcohol and the surface of the ink receiving layer was cast, the print density, ink absorptivity, Gloss and surface strength were high, and scratches and ink agglomeration unevenness were prevented when transported by a printer. Moreover, it had the printability of both dye ink and pigment ink.
In contrast, the ink-jet recording sheets of Comparative Examples 1 and 2 in which the ink-receiving layer does not contain polyoxylene-containing polyvinyl alcohol have low print density and surface strength, and are damaged when transported by a printer. Insufficient prevention. In Comparative Example 2, the outermost surface portion of the ink receiving layer contained the cationic group-containing polyvinyl alcohol, but the surface strength and ink aggregation unevenness were not improved. From this, it is understood that it is important that the polyoxylene group-containing polyvinyl alcohol is contained in the outermost portion of the ink receiving layer.

It is sectional drawing which shows one Embodiment of the sheet | seat for inkjet recording of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet recording sheet, 10 Air-permeable base material, 20 Ink receiving layer, 21 Outermost part, 30 Undercoat layer

Claims (4)

An ink-jet recording sheet having a gas-permeable substrate, an ink receiving layer containing fine particles and an adhesive, and having a cast treatment on the surface of the ink receiving layer,
An ink jet recording sheet comprising a polyoxylene group-containing polyvinyl alcohol at least on the outermost surface of the ink receiving layer.   The ink jet recording sheet according to claim 1, wherein the ink receiving layer contains polyvinyl alcohol having no substituent and an average degree of polymerization of 3500 or more.   The inkjet recording sheet according to claim 1, wherein the outermost surface portion of the ink receiving layer further contains a cationic group-containing polyvinyl alcohol. The inkjet recording sheet according to any one of claims 1 to 3, wherein the casting treatment is a rewetting casting method using a rewetting liquid, and the rewetting liquid contains polyoxylene group-containing polyvinyl alcohol.

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