JP2008074099A - Glossy inkjet recording sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glossy inkjet recording sheet which has high ink absorption/white paper glossiness/print density and excellent inkjet recording suitability. <P>SOLUTION: This glossy inkjet recording sheet includes a base and a plurality of coating layers including at least, one ink receptive layer, formed on the base. In addition, a gloss development layer containing a pigment and a binder holding the pigment, is formed on the top part of the coating layers. The pigment contains a primary particle colloidal silica with 10 to 60 nm particle diameter and a secondary particle colloidal silica which forms a linkage of straight-line shape or branched shape by associating with a plurality of primary particles, and also has 60 to 160 nm particle diameter. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a glossy ink jet recording sheet, and more particularly to a glossy ink jet recording sheet excellent in ink absorbability and glossiness, and excellent in ink jet recording suitability and coating layer strength.

The ink jet recording method that forms an image by ejecting water-based ink from fine nozzles is easy to make full color, enables high-speed recording, and in the case of printing a small number of copies, the printing cost is higher than other printing devices. It has the advantage that it can be made inexpensive.
For this reason, this ink jet recording method is widely used in terminal printers, facsimiles, plotters, form printing, and the like.
In recent years, ink jet printers have been rapidly spread and have high definition and high speed, and accordingly, ink jet recording sheets are required to have higher ink absorption speed and surface strength than ever before.
In addition, with the widespread use of digital cameras, inkjet recording sheets are strongly required to be able to print recorded images taken with digital cameras with high image quality comparable to silver halide photography. Further improvement of sex is required.

  Since digital camera image printing requires a large amount of ink compared to printing, the recording sheet is required to have a large capacity of ink absorption and rapid ink absorption speed. In a sheet, generally, two or more coating layers including a solvent absorption layer and an ink fixing layer are provided on a substrate to improve ink absorption and ink absorption speed (Patent Document 1). .

In order for this recording sheet to exhibit a high gloss comparable to a silver salt photograph, the gloss of the surface must be further improved.
Therefore, in order to improve the glossiness of the sheet, a glossy expression layer containing colloidal particles as a pigment and polyvinyl alcohol as a binder is formed.
The gloss developing layer is formed by applying a gloss developing coating liquid onto a paper substrate, and performs a casting process in which the coating liquid is pressed against a heated mirror drum while the coating liquid is in a wet state. As a result, the mirror surface of the drum is copied onto the developing layer so that gloss is developed (Patent Document 2).
However, even in this glossy layer, the gloss is not sufficient as compared with the silver salt photograph, and there is a problem in the absorption performance, and further improvement is necessary.

Focusing on pigments and binders that are excellent in glossiness and ink absorbability as a technique for improving glossiness and recordability, colloidal silica having a particle diameter of 0.01 to 0.15 μm as a pigment, and particle diameter as a binder Is applied to a paper base material to form a coating layer for casting, and the coating layer is in a wet state. In addition, the cast coated paper for inkjet recording, which is excellent in glossiness, print density, ink absorbency, recording image quality, etc. of the blank paper portion and the print portion, by performing press processing on the heated mirror drum and drying and finishing. There is also known a technique for obtaining (Patent Document 3).
Although this cast coated paper for inkjet recording has gloss and recording image quality superior to conventional ones, inkjet recording such as ink absorptivity and print density as the recent printers become more precise and faster. It has become impossible to deal with aptitude sufficiently.

JP 2000-355163 A JP 2000-319715 A JP 2000-238419 A

The present invention has been made in view of the above circumstances, and as a result of extensive studies, the present inventors have optimized the colloidal silica used in the glossy expression layer, and thereby have solved the above problem. As a result, the present invention has been completed.
The technical problem of the present invention is to provide a glossy inkjet recording sheet having high ink absorbability and white paper glossiness, high printing density, excellent ink jet recording suitability, and high coating layer strength.

  The gloss ink jet recording sheet of the present invention for solving the above-described problems has a base material and a plurality of coating layers including at least one ink-receiving layer provided on the base material. In the inkjet recording sheet having a glossy expression layer containing a pigment and a binder holding the pigment at the outermost part of the layer, the pigment has primary particle colloidal silica having a particle diameter of 10 to 60 nm, and primary A plurality of particles are associated to form a linked body linked linearly or branchedly, and contains secondary particle colloidal silica having a particle diameter of 60 to 160 nm. .

  According to the preferable structure aspect of this invention, the compounding ratio of said primary particle colloidal silica and secondary particle colloidal silica is 20 / 80-80 / 20.

According to another preferred configuration of the present invention, the binder contains an acrylic polymer or contains an acrylic polymer-silica composite.
Further, the binder preferably contains an acrylic polymer-silica composite and casein from the viewpoint of improving the coating layer strength.

  According to the other preferable structure aspect of this invention, it is preferable that the said glossiness expression layer is glossed by the cast process.

  The ink jet recording sheet of the present invention has high ink absorbability and white paper gloss, high print density, and excellent ink jet recording suitability and coating layer strength.

The glossy ink jet recording sheet according to the present invention will be described in detail based on the following embodiments.
The glossy inkjet recording sheet of the present embodiment has a substrate and a plurality of coating layers including at least one ink-receiving layer provided on the substrate, and the outermost portion of the coating layer And a glossy layer including a pigment and a binder for holding the pigment.
The pigment has a primary particle colloidal silica having a particle diameter of 10 to 60 nm (hereinafter, this primary particle colloidal silica is referred to as colloidal silica A) and a plurality of primary particles are associated with each other in a linear or In addition to forming a branched connected body, it contains secondary particle colloidal silica having a particle size of 60 to 160 nm (hereinafter, this secondary particle colloidal silica is referred to as colloidal silica B). .

<Base material>
Although the base material used for the inkjet recording sheet of the present embodiment is not particularly limited, a paper base material, a resin film having air permeability, or a sheet material that is a gas permeable base material is used. Is preferred.
In particular, it is preferable to use a paper substrate from the viewpoints of excellent air permeability, ease of handling as a recording sheet, and ease of disposal.
As the paper substrate, a known paper substrate that is usually used can be used as long as the effects of the present invention are not impaired. For example, fine paper, art paper, coated paper, cast coated paper, craft paper , Baryta paper, paperboard, impregnated paper, and vapor-deposited paper.
Further, acid paper, neutral paper, etc. used for general coated paper can be used as appropriate.

[Paper base]
The outline | summary of these paper base materials is demonstrated.
The paper base material contains wood pulp as a main component, and fillers, various auxiliaries and the like are added as necessary.
As the wood pulp, various chemical pulps, mechanical pulps, recycled pulps and the like can be used.
In particular, softwood and hardwood kraft pulp, or softwood bleached kraft pulp bleached from these kraft pulp (referred to as NBKP) and hardwood bleached kraft pulp (referred to as LBKP) are preferable.
In addition, in these pulps, chlorine-free pulp in which the influence of chlorine has been removed in the bleaching process, for example, ECF (Elemental, which uses chlorine compounds for pulp bleaching without using chlorine itself)
Chlorine Free) and TCF (Total Chlorine Free) pulp using a bleaching agent that does not contain any chlorine element for pulp bleaching are preferably used.

  These pulps can be adjusted by a beating machine to adjust paper strength, papermaking suitability, etc., and the beating degree (CSF: Canadian Standard Freeness) is not particularly limited, but 250 to 550 ml (JIS) -P8121) is preferred.

As the filler added to the paper substrate, for example, calcium carbonate, calcined kaolin, silica, titanium oxide, talc and the like are preferably used. Of these, calcium carbonate is preferred because it provides a paper substrate with high whiteness and increases the glossiness of the ink jet recording sheet.
The filler content (ash content) in the paper substrate is preferably about 1 to 20% by mass. Within this range, smoothness, air permeability, paper strength, and rigidity are balanced, and a glossy inkjet recording sheet excellent in balance of glossiness, image clarity, and rigidity is 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 sizing agent, known sizing agents such as reinforced rosin and alkenyl succinic anhydride are used.
In addition, a sulfuric acid band is used as a fixing agent for this sizing agent, and starch is used as a fixing yield improving agent in combination with the sizing agent.

  About 1 to 300 seconds are preferable, and the Stecchito sizing degree (JIS-P8122) of the paper base material is more preferably 4 to 200 seconds. If the sizing degree is less than 1 second, there is a risk of operational problems such as wrinkling during coating, and if it exceeds 300 seconds, the ink absorbability may decrease, and curling and cockling after printing. There is a possibility that (absorption wrinkles) may be remarkable, which is not preferable.

Although the basic weight of a paper base material is not specifically limited, About 20-400 g / m < ² > is preferable.
10-350 seconds are preferable, as for the Oken type air permeability (Japan TAPPI No. 5) of a paper base material, 10-200 seconds are more preferable, and 20-100 seconds are further more preferable.
If the air permeability is less than 10 seconds, the ink receiving layer coating liquid may permeate excessively into the paper substrate, and if it exceeds 350 seconds, it may occur when press-contacting the cast drum. There is a possibility that the operability is lowered, which is not preferable.
The paper substrate is manufactured by a long net paper machine or the like, and the thickness thereof is not particularly limited, but is appropriately selected in the range of 20 μm to 500 μm depending on the application.

<Coating layer>
The glossy ink jet recording sheet of the present embodiment includes a single ink receiving layer provided on a base material, a gloss developing layer provided on the ink receiving layer, and forming the outermost part of the recording sheet. It has two coating layers consisting of
The ink receiving layer is a layer for fixing ink and improving the ink absorption capacity and the absorption speed. The ink receiving layer is not limited to one layer, and two or more layers may be provided as necessary.
When three or more coating layers are provided, one layer may be provided on the base material as an undercoat layer that absorbs the ink solvent, and an ink receiving layer may be provided thereon.

(Ink receiving layer)
The ink receiving layer contains a pigment and a binder that holds the pigment as main components, and further contains an ink fixing agent for fixing the ink.
A polymer is used as the binder, and generally an adhesive as a polymer is used.

(Pigment)
As the pigment, a pigment generally used in the coated paper manufacturing field is used.
Examples of these pigments include zeolite, light calcium carbonate, heavy calcium carbonate, magnesium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium oxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, and aluminum silicate. Diatomaceous earth, calcium silicate, magnesium silicate, silica, aluminum hydroxide, alumina, alumina hydrate, aluminosilicate, boehmite, pseudoboehmite, etc. Alternatively, two or more kinds can be used in combination.
Among these, the use of a pigment containing at least one selected from silica, alumina, alumina hydrate, and aluminosilicate is preferable from the viewpoint of ink absorbability, and amorphous silica is particularly preferable. Mesoporous silica is preferable in terms of ink absorbability and recording density.

The gas phase method silica is also called fumed silica and is generally produced by a flame hydrolysis method.
Specifically, a method of making silicon tetrachloride by burning with hydrogen and oxygen is generally known, but silanes such as methyltrichlorosilane and trichlorosilane are used alone or with silicon tetrachloride instead of silicon tetrachloride. It can be used in a mixed state.
Vapor phase silica is commercially available from Nippon Aerosil Co., Ltd. under the product name Aerosil, and from Tokuyama Corp. under the QS type.
Vapor phase silica is agglomerated in a solution to form secondary particles having appropriate voids, and it is preferable to add this to the ink receiving layer because the surface glossiness of this layer becomes high.

This gas phase method silica is a primary particle having a particle size of 3 to 40 nm. This particle size is obtained by first adjusting 200 g of a 3% silica dispersion, followed by a commercially available homomixer at 1000 rpm for 30 minutes. After stirring and dispersing, the particle diameter was immediately observed with an electron microscope (SEM and TEM), and the martin diameter of silica dispersed particles was measured and averaged (“Fine Particle Handbook”, Asakura Shoten, p. 52, 1991). See year).
As a result of measurement by the present inventors, when the vapor phase method silica is in the form of a slurry, the particle diameter varies greatly depending on the agglomeration state of the silica, but almost the same value can be obtained under the above measurement conditions.

The mesoporous silica is a porous silica having an average pore diameter of 1.5 to 100 nm.
In addition, mesoporous silica into which aluminum, titanium, vanadium, boron, manganese atoms or the like are introduced can also be used.
The physical properties of the mesoporous silica are not particularly limited, but the BET specific surface area (nitrogen adsorption specific surface area) is preferably 200 to 1500 m ² / g, and the pore volume is preferably 0.5 to 4 ml / g.

A method for synthesizing mesoporous silica is not particularly limited, but a method for synthesizing a quaternary ammonium salt containing a long-chain alkyl with a alkoxide of silica described in US Pat. No. 3,556,725 as a silica source, and a special table A hydrothermal synthesis method using amorphous silica powder or alkaline silicate aqueous solution described in JP-A-5-503499 as a silica source and using a quaternary ammonium salt having a long-chain alkyl group or a phosphonium salt as a template; As a silica source described in Japanese Patent Publication No. 4-238810 or the like, a layered silicate such as kanemite or a method of synthesizing by a long chain alkylammonium cation or the like by an ion exchange method, further, dodecylamine, hexadecylamine or the like Amine and nonionic surface activity As the like template, and a method of synthesis using an active silica as a silica source to form a water glass or the like by ion exchange.
And as a removal method of the template from a nanoporous silica precursor, the method of baking at high temperature and the method of extracting with an organic solvent are mentioned.

  Further, the vapor phase silica is preferably added as fine particles combined with a cationic compound as an ink fixing agent described later, instead of being added as a simple substance to the ink receiving layer coating solution. Details will be described in the section of the ink fixing agent.

(Polymer)
As the binder, an adhesive is generally used. However, the binder is not limited to the adhesive, and other polymers may be used as long as they have a pigment holding function.
As this adhesive, known adhesives used for coated paper are used, for example, (b) proteins such as casein, soy protein, synthetic protein, (b) various types of starch, oxidized starch, etc. Starches, (c) polyvinyl alcohol (hereinafter referred to as PVA), cationic PVA, PVA containing various modified PVA such as silyl modified PVA, (d) cellulose derivatives such as carboxymethyl cellulose, methyl cellulose, (e) styrene-butadiene Vinyl polymers such as copolymers and conjugated diene polymers of methyl methacrylate-butadiene copolymer, (f) acrylic polymers, ethylene-vinyl acetate copolymers, styrene-acrylic copolymers, ) Acrylic polymer-silica composite with silica held in acrylic polymer, (h) water-based polyurethane resin, (li) water Polyester resins, and the like.
The water-based polyurethane resin is also commonly referred to as urethane emulsion, urethane latex, polyurethane latex, etc., and is obtained from a reaction between a polyisocyanate compound and an active hydrogen-containing compound, and contains a relatively large number of urethane bonds and urea bonds. It is a molecular compound.
These adhesives may be used alone or in combination of two or more.

Among these adhesives, PVA is preferably used from the viewpoint of coating layer strength.
The properties of PVA used for the ink receiving layer differ depending on the saponification degree, and it is preferable to select the saponification degree according to the purpose.
When PVA having a saponification degree of 95% or more, more preferably 98% or more is used, the strength of the coating layer is increased and foaming does not occur during the preparation of the coating solution, resulting in very good workability during production. It is.
In addition, when partially saponified PVA having a saponification degree of 75 to 90% is used, the coating layer has excellent flexibility and is very effective in preventing its cracking.
These PVA having different saponification degrees may be used alone or in combination depending on the purpose.

  Further, the degree of polymerization of the PVA is preferably 3500 or more, particularly preferably 3500 to 5000. If the degree of polymerization is less than 3500, the strength of the ink receiving layer is weak, cracks are likely to occur, and paper dust may be generated during cutting, and if it exceeds 5000, sufficient ink absorbability is difficult to obtain. At the same time, the solution viscosity is high and the handling surface in preparing the coating solution may be difficult, which is not preferable.

  The blending ratio of the pigment and the adhesive is generally adjusted in the range of 1 to 100 parts by weight, preferably 2 to 50 parts by weight with respect to 100 parts by weight of the pigment, although it depends on the type.

(Ink fixing agent)
The ink fixing agent has a function of fixing a dye pigment in the ink for ink jet recording, thereby imparting water resistance to the printed image.
As the ink fixing agent, a cationic compound is used, and examples thereof include a cationic resin and a low molecular weight cationic compound (for example, a cationic surfactant).
Cationic resins are preferred from the standpoint of improving the printing density, and various known cationic resins that are generally used in inkjet recording sheets can be used.

Examples of these cationic resins include (a) polyalkylene polyamines such as polyethylene polyamine and polypropylene polyamine or derivatives thereof, and (b) an acrylic heavy group having a secondary or tertiary amino group or a quaternary ammonium group. Or acrylamide copolymers thereof, (c) polyvinylamine and polyvinylamidines, (d) dicyan-based cationic compounds represented by dicyandiamide-formalin copolymer, (e) dicyandiamide-polyethyleneamine copolymer (E) epichlorohydrin-dimethylamine copolymer, (to) diallyldimethylammonium-SO ₂ polycondensate, (thi) diallylamine salt-SO ₂ polycondensate, (li) diallyl Dimethylammonium black (U) allylamine salt copolymer, (l) dialkylaminoethyl (meth) acrylate quaternary salt copolymer, (e) acrylamide-diallylamine copolymer, (wa) 5-membered ring amidine structure. And a cationic resin.
In the embodiment of the present invention, these fixing agents are used alone or in combination of two or more.

(Silica-cationic compound aggregate)
The cationic compound aggregates with the gas phase method silica in a mixed solution with the gas phase method silica to form a silica-cationic compound aggregate.
For this reason, this cationic compound is preferably used in the form of an aggregate with vapor phase silica in advance rather than being used alone.
By the way, since the silica-cationic compound aggregate forms relatively large particles in this mixed solution, the large aggregate particles are pulverized and dispersed to obtain silica-cationic particles having a particle diameter of 90 to 500 nm. The compound aggregate fine particles are used in an ink-receiving layer coating solution.
The single-phase gas phase method silica used for forming the silica-cationic compound aggregated fine particles is a primary particle having a particle diameter of 3 to 40 nm. The aggregated fine particles are substantially composed of primary particles. Made of secondary particles.

An outline of a method for producing silica-cationic compound aggregate fine particles will be described.
The addition amount of the cationic compound is adjusted in the range of 1 to 30 parts by mass, preferably 5 to 20 parts by mass with respect to 100 parts by mass of the vapor phase method silica.
When a cationic compound is added to and mixed with the vapor phase silica dispersion, a thickened aggregate dispersion is obtained.
As a method of pulverizing / dispersing the silica-cationic compound aggregate particles into fine particles, a breaking down method (a method of subdividing the bulk material) that gives a strong force by mechanical means is employed.
Examples of the mechanical means include an ultrasonic wave, a high-speed rotating mill, a roller mill, a container driving medium mill, a medium stirring mill, a jet mill, a crusher, a sand grinder, a nanomizer (trade name), and a homomixer.

  The silica-cationic compound aggregated fine particles as a pigment and an ink fixing agent are used singly or in combination of two or more. By using this, the transparency of the ink receiving layer and the strength of the coating layer are used. In addition, the ink absorptivity, color developability, weather resistance, water resistance, and the like can be improved.

  Further, various auxiliary agents such as a dispersant, a thickener, an antifoaming agent, an antistatic agent, and an antiseptic used in the production of general coated paper are appropriately added to the ink receiving layer. In addition, a fluorescent dye or a colorant can be added to the ink receiving layer.

In addition, a single cationic compound may be blended in the ink receiving layer in order to further improve the ink fixing property and improve the water resistance.
Examples of the cationic compound include those used in the silica-cationic compound aggregate, and among these, water-soluble resins or emulsions are preferably used.
In addition, a cationic compound, particularly a cationic resin, blended as a simple substance is often used when a role as an adhesive is also given.

(Method for forming ink receiving layer)
The ink receiving layer is formed by applying an ink receiving layer coating liquid composed of the above-described material onto a paper substrate.
The ink receiving layer coating liquid is generally adjusted to a solid content concentration of about 5 to 50% by mass.
If the solid content concentration is less than 5% by mass, the drying efficiency of the ink receiving layer may be lowered, and if it exceeds 50% by mass, the coating layer may be cracked.

The coating amount of the ink receiving layer coating solution, by dry weight, 2~100g / ^{m 2,} preferably from 5 to 50 g / ^{m 2} approximately.
If the coating amount is less than 2 g / m ² , the glossiness and ink absorbability may not be sufficient, and if it exceeds 100 g / m ² , cracks in the coating layer tend to occur and good dot trueness is likely to occur. It is difficult to obtain circularity and the print density may be insufficient, which is not preferable.

Two or more ink receiving layers can be formed. When two or more ink receiving layers are formed as described above, the silica and the adhesive constituting each layer may be the same or different.
In addition, two or more types of silica and adhesive may be mixed in the same layer, or a combination thereof may be used.
As the coating method of the ink receiving layer coating solution, various known and publicly available methods such as blade coaters, air knife coaters, roll coaters, brush coaters, Champex coaters, bar coaters, lip coaters, die coaters, gravure coaters, curtain coaters, sprays, etc. A coating method using any one of the coating apparatuses can be mentioned.
Further, the coated ink receiving layer may be subjected to a smoothing process such as super calendering or brushing as necessary.

(Crosslinking agent)
In order to prevent cracking of the ink receiving layer, the ink receiving layer may contain a cross-linking agent that cross-links the adhesive, or a gelling agent that cross-links and gels the adhesive, if necessary. It is preferred to crosslink the agent.
Whether these cross-linking agents (including gelling agents) are added to the ink receiving layer coating solution, or are previously applied to the surface of the base material before applying the ink receiving layer as an aqueous coating solution. The ink-receiving layer is applied on the surface after coating, or when a plurality of ink-receiving layers are provided, any one of various methods such as coating between the ink-receiving layers is used. It can be included.
By these methods, the contained cross-linking agent cross-links the adhesive contained in the site where it is added or in contact with the coating site.
The layer containing the crosslinking agent (gelling agent) may be any one of the layers described above, or may be a plurality of layers.

As the crosslinking agent, known crosslinking agents and gelling agents used in the production of this type of recording sheet can be used.
As the crosslinking agent, for example, as a compound having crosslinkability to PVA, an aldehyde crosslinking agent such as glyoxal, an epoxy crosslinking agent such as ethylene glycol diglycidyl ether, and a vinyl crosslinking agent such as bisvinylsulfonylmethyl ether, Examples of the gelling agent that crosslinks PVA and gels include boron-containing compounds such as boric acid and borax, zirconium compounds, aluminum compounds, and chromium compounds.
In the present embodiment, among these, a boron-containing compound which is a gelling agent is particularly preferably used because thickening or gelation occurs early.

Here, the boron-containing compound is an oxygen acid having a boron atom as a central atom and a salt thereof, and specific examples thereof include orthoboric acid, metaboric acid, hypoboric acid, tetraboric acid, pentaboric acid, And their sodium, potassium and ammonium salts.
Of 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 compounding amount of the boron-containing compound depends on the kind of the boron-containing compound and the degree of polymerization of PVA, and is applied to either surface of the ink receiving layer as a dry coating amount of 0.01 to 2.0 g / m ^2. It is preferable.
When the coating amount of the boron-containing compound is less than 0.01 g / m ² , the crosslinking property with the hydrophilic adhesive and the gelation of the coating solution are not sufficient, and the coating layer is cracked. If it exceeds 2.0 g / m ² , the high crosslinking density with the adhesive is saturated, and it is not desirable to further improve the crack prevention effect of the coating layer. .

(Glossy expression layer)
In the recording sheet of the present embodiment, a gloss developing layer that expresses gloss is formed on the ink receiving layer. This gloss developing layer has a gloss developing property that becomes a glossy surface after being casted as described later.
This gloss developing layer develops a certain level of gloss even when subjected to a smoothing process such as super calendering or brushing, but exhibits an excellent gloss when casted.
The glossy layer is the outermost part of the recording sheet that exhibits gloss because the pigment constituting the main component and the binder that holds the pigment have a predetermined composition.

(Pigment)
As the pigment, colloidal silica A composed of spherical primary particles having a particle diameter of 10 to 60 nm and a plurality of the primary particles are associated to form a connected body, and the particle diameter is 2 to 60 to 160 nm. Colloidal silica B composed of secondary particles is used.
The particle size of the colloidal silica B conjugate is measured by a dynamic light scattering method, and specific examples include Snowtex PS series manufactured by Nissan Chemical Industries.
If the particle diameter of colloidal silica A is less than 10 nm, the ink absorbability may be lowered, and if it exceeds 60 nm, the glossiness may be lowered and the print density may be lowered.
If the particle diameter of colloidal silica B is less than 60 nm, the ink absorbability may decrease, and if it exceeds 160 nm, the glossiness may decrease and the print density may decrease, such being undesirable.

That is, when these colloidal silica A and colloidal silica B are compared, the small particle colloidal silica A has the characteristics that it is excellent in gloss and is slightly inferior in ink absorbability. It has excellent absorbency and slightly inferior glossiness.
In addition, colloidal silica B may be called pearl necklace-like colloidal silica from the connection body structure, and it is preferable that the particle diameter of the primary particle which comprises this connection body is 10-40 nm.

These colloidal silicas A and B include an alkaline type and an acidic type, both of which can be used, but it is necessary to use them appropriately according to the physical properties such as pH of the coating solution.
The blending ratio of these colloidal silica A and colloidal silica B is preferably 20/80 to 80/20 by mass ratio.
A recording sheet having a gloss developing layer with this blending ratio has the best balance between sheet physical properties such as gloss and ink jet recording suitability such as ink absorbency and printing density.
If the colloidal silica A is less than 20 and the colloidal silica B exceeds 80, the gloss may be lowered. If the colloidal silica A exceeds 80 and the colloidal silica B is less than 20, the absorbency is lowered. This is not preferable.
And within this range of the blending ratio, the blending ratio of colloidal silica A and B can be appropriately determined according to the application.
The coating liquid used for the glossy layer is generally used as aqueous dispersion colloidal particles having a solid content concentration of about 5 to 20%.

(adhesive)
As the binder, an adhesive is used, and the same adhesive as the above-described adhesive used for the ink receiving layer is used.
The adhesive selected and used from them may be used alone or in combination of two or more.
In addition, when an ink fixing agent is blended in the glossy layer coating liquid, a cationically modified adhesive is particularly preferable.

Among the adhesives that can be used for the glossy layer, the use of casein is preferable because of its excellent releasability from the cast drum when the glossy layer is formed.
In addition, the acrylic polymer in the adhesive, an acrylic polymer-silica composite emulsion in which silica is held in the acrylic polymer, an acrylic copolymer emulsion that is a vinyl polymer, and a styrene-acrylic copolymer. The polymer emulsion is preferable because the recorded image has excellent clarity and gloss.
Further, these preferable adhesives can be used in combination.
In the recording sheet of the present embodiment, this adhesive is preferably an acrylic polymer-silica composite.
The acrylic polymer-silica composite is obtained by holding a silica compound such as colloidal silica in an acrylic polymer, and an acrylic emulsion commercially available from Daicel under the trade name Aquabrid 906 and a particle size of 20 to Examples thereof include a mixture of 30 nm colloidal silica at a weight ratio of 20:80 and Aquabrid 914 (trade name), which is an improved product and has a high glass transition point.
By using an acrylic polymer-silica composite, ink absorbability can be increased and ink concentration can be improved.
In addition, the acrylic polymer-silica composite is preferably used together with casein because powder falling is prevented and the coating layer strength is increased.

When using an emulsion as an adhesive for the glossy layer, the preferred average molecular weight is 1000 to 10 million, more preferably 5000 to 5 million.
If the average molecular weight is less than 1000, the glossy layer may have insufficient strength, and if it exceeds 10 million, the stability of the emulsion may be insufficient.

It is preferable that the compounding quantity of an adhesive agent is adjusted in 40-100 mass parts with respect to 100 mass parts of pigments.
If the blending amount of the adhesive is less than 40 parts by mass, the strength of the coating layer is weakened and the surface is liable to be damaged, and there is a risk of powder falling off. If the amount exceeds 100 parts by mass, the ink absorbability decreases. There is a possibility that desired ink jet recording suitability may not be obtained.

(Other additives)
In addition, the glossy layer includes an ink fixing agent, a dispersant, a cross-linking agent, a thickener (flow modifier), an antifoaming agent, a water-resistant agent (printability improver), an antistatic agent, as necessary. Various additives such as preservatives, ultraviolet absorbers, preservability improvers, fluorescent brighteners, and colorants can be appropriately added.

  As the ink fixing agent, the same cationic compounds as those used in the ink receiving layer are used.

  Examples of the thickener and flow modifier include (a) synthetic resin copolymers such as styrene-butadiene copolymer and methyl methacrylate-butadiene copolymer, (b) casein, (c) soybean protein, and synthetic protein. Proteins, (d) various starches such as starch and oxidized starch, (e) PVA, (f) cellulose derivatives such as carboxymethylcellulose and methylcellulose, (g) polycarboxylic acid, polyacrylic acid, acrylic resin emulsion, Polyamide, polyester synthetic resin polymer, (h) nonionic surfactant, and the like are appropriately used.

  Examples of the water-resistant agent and printability improver include sodium chloride, ammonium chloride, zinc chloride, magnesium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, zinc sulfate, magnesium sulfate, ferrous sulfate, sodium nitrate, ammonium nitrate, first Sodium phosphate, ammonium phosphate, calcium phosphate, sodium polyphosphate, sodium hexametaphosphate, sodium formate, ammonium formate, sodium acetate, potassium acetate, sodium monochloroacetate, sodium malonate, sodium tartrate, potassium tartrate, potassium citrate, Ammonium and metal salts of inorganic and organic acids such as sodium lactate, sodium gluconate, sodium adipate, sodium dioctylsulfosuccinate, sodium aluminate, Methylamine, diethanolamine, diethylenetriamine, diisopropylamine, triethanolamine, methanolamine, ethanolamine and other amines, phosphate esters, polyoxyethylene alkylphenol ether phosphate ester salts, polyoxyethylene ether phosphate ester salts, alkylphenol ether phosphorus Phosphate esters such as acid ester salts, polyoxymethylene, alkyl ether, polyoxyethylene and aqueous ammonia, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether and adipic acid di Polyfunctional epoxy compounds such as glycidyl ester, urea-formaldehyde compounds, poly De - epichlorohydrin compounds, glyoxal, and the like are used as appropriate.

The above-mentioned various additives are added to the glossy layer coating liquid in a range of 0.05 to 10% by mass, preferably 0.1 to 5% by mass as the solid content concentration.
Furthermore, pigments such as alumina, colloidal silica, fine silica, clay and calcium carbonate can also be added to the glossy layer coating liquid as other additives.
In addition, when performing the rewetting process mentioned later, the dispersing agent, antifoaming agent, coloring agent, fluorescent dye, antistatic agent, preservative, etc. in the above additives may be added to the wetting liquid used for the rewetting process. good.

<Glossing treatment>
The gloss-developing layer is preferably subjected to various glossing treatments after coating and drying a coating solution containing the above components.
The glossing treatment can be performed by a super calendar as long as it is glossy to some extent, but it is preferable to perform a casting process in order to obtain a high gloss.

In general, cast processing means that the coating layer is pressed onto a cast drum having a mirror surface (drum made of mirror-finished metal, plastic, glass, etc.), mirror-finished metal plate, plastic sheet, film, glass plate, etc., and dried. The mirror surface is copied onto the coating layer to obtain a smooth and glossy coating layer surface.
In this method, the gloss is developed by casting using a heated mirror drum. (A) The outermost coating layer coating solution is applied onto the substrate so that the coating solution is in a wet state. A method of pressing and drying on a mirror drum heated for a while and then finishing (wet casting method)
(B) A method in which the outermost coating layer coated on the substrate is once dried, then the outermost coating layer is rewet, and then heated to a heated mirror drum and dried to finish (rewet casting method). ,
(C) The outermost coating layer on the substrate is gelled to form a gel-like coating layer, which is pressed onto a heated mirror drum and dried to finish (gelation cast method).
(2) Apply the coating solution for the outermost coating layer directly on the heated mirror drum, and after drying to form the outermost coating layer on the mirror drum, the mirror drum is placed on the substrate. Pressing and finishing the above outermost coating layer by transferring (precast method),
Is mentioned.
In these casting processes, the temperature of the heated mirror drum is, for example, 50 to 150 ° C, preferably 70 to 120 ° C.

Furthermore, a film transfer method can also be adopted as the casting process.
What is film transfer system?
(A) The above-mentioned coating solution for the outermost coating layer is applied onto a substrate, and a smooth film or sheet is stacked while the coating solution is in a wet state, dried, and then smooth. And the method of peeling and finishing the sheet,
(B) Applying the coating solution for the outermost coating layer on a smooth film or sheet, with the substrate surface to be bonded in a wet state to some extent, press against the substrate surface, A method of peeling and finishing a smooth film or sheet after drying,
It is.
Compared to the film transfer method, the cast method using a heated mirror drum tends to be superior in surface smoothness and is more advantageous in terms of productivity and cost.

Any of the above methods may be used for casting, but in the recording sheet of the present embodiment, the above-described ink-receiving layer coating solution is applied on a paper substrate and dried. It is preferable to use a wet casting method in which after the coating liquid for the glossy layer is applied, it is immediately pressed onto a heated mirror surface metal drum and dried.
In this wet casting method, a uniform coating layer is easily formed, and a glossy expression layer having a high printing density and excellent gloss is easily obtained.
Moreover, in the said cast process, it is preferable that the coating amount of a glossiness expression layer shall be 0.1-3.0 g / m < ² > by dry solid content.
If it is less than 0.1 g / m ² , the print density and gloss may not be sufficiently obtained. If it exceeds 3.0 g / m ² , the effect is almost saturated, and an increase in coating amount places a burden on drying, This is not preferable because the operability is lowered and the effect of the ink receiving layer may not be sufficiently exhibited.

  In each of the above-described casting processes, when applying the coating liquid for the glossy layer, various known coating methods are used, for example, for coating apparatuses such as blades, brush coaters, Champlex coaters, bar coaters, and gravure coaters. The coating method of coating using either can be used.

In performing the casting treatment, it is preferable to use a release agent in order to smoothly peel off the layer from the cast drum or the like.
The mold release agent can be appropriately used by any one of a method of adding to the gloss developing layer coating solution, a method of applying to the surface of a cast drum or the like, and a method of adding to the wet solution of the rewet cast method.
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. Among these, a cationic release agent is particularly preferably used.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.
Further, “parts” and “%” in the following examples and comparative examples represent “parts by mass” and “% by mass” of solids excluding water, respectively, unless otherwise specified.

<Example 1>
[Preparation of paper substrate]
Wood pulp (LBKP, freeness (JIS-P8121): 500 ml CSF) 100 parts, filler (calcium carbonate 3: talc 1 ratio) 15 parts, sizing agent (trade name: Fibran 81K, manufactured by NSC Japan) 0 .05 parts, 0.45 parts of sulfuric acid band, 0.45 parts of starch, 0.4 parts of polyamide / epichlorohydrin resin (paper strength enhancer), a paper making material consisting of a little yield improver, and a long net paper machine A paper substrate having a basis weight of 188 g / m ² was obtained. This paper had a steecht degree of sizing of 60 seconds, a thickness of 210 μm, and a Oken air permeability of 30 seconds.

[Coating liquid for ink receiving layer]
(Adjustment of silica dispersion)
Using a homogenizer to pulverize and disperse silica (trade name: Leolosil QS-30, primary particles, manufactured by Tokuyama Corporation) with an average particle size of 9 nm in ion-exchanged water, and then use Nanomizer (trade name) The combination with the step of pulverizing and dispersing was repeated to prepare a 10% dispersion. To 100 parts of silica (in terms of solid content) of this dispersion, 8 parts of polyvinylamine copolymer ammonium hydrochloride (trade name: Himax SC-700, manufactured by Hymo) having a 5-membered ring amidine structure as a cationic compound ( Solid content conversion) was added to obtain a thickened aggregate dispersion. This thickened aggregate dispersion was dispersed again with a homomixer, and pulverization and dispersion were repeated using a nanomizer (trade name) to prepare 10% silica dispersion A.

(Adjustment of ink receiving layer coating solution)
15 parts of PVA (trade name: PVA-145, polymerization degree 4500, saponification degree 99%, manufactured by Kuraray Co., Ltd.) as a binder is mixed with 100 parts of silica dispersion A, and the coating liquid for ink receiving layer having a solid content concentration of 15%. Was prepared.

(Adjustment of coating liquid for glossy layer)
Colloidal silica A (trade name: Snowtex 50, particle size: 20-30 nm, primary particles, manufactured by Nissan Chemical Co., Ltd.) 20 parts, colloidal silica B (trade name: Snowtex PS-S, particle size 80-120 nm) 80 parts of secondary particles (manufactured by Nissan Chemical Co., Ltd.), a composition liquid containing 20 parts of an acrylic polymer-silica composite emulsion (trade name: Aquabrid 906, manufactured by Daicel) as a binder and 5 parts of casein are mixed. To this, 1 part of potassium stearyl phosphate (trade name: Wopol 1800, manufactured by Matsumoto Yushi Co., Ltd.) was added as a release agent and further mixed to prepare a coating solution for glossy expression layer having a solid content concentration of 10%. .

[Preparation of glossy inkjet recording sheet]
A 3% borax aqueous solution having a dry coating amount of 1.0 g / m ² is applied onto the paper substrate, and the dry coating amount is 10 g when the ink receiving layer coating solution prepared separately is dried. After coating with a die coater so as to be / m ² and drying, the above-described glossy layer coating solution separately prepared on the surface is coated with a die coater so that the dry coating amount is 1 g / m ^2. Then, a wet cast finish was performed to obtain a glossy inkjet recording sheet.

<Example 2>
Colloidal silica A80 parts (trade name: Snowtex 20L, average particle diameter 40 nm, primary particles, manufactured by Nissan Chemical Industries, Ltd.), colloidal silica B (trade name: Snowtex PS-S) as pigments in the coating liquid for glossy layer ) A glossy inkjet recording sheet was obtained in the same manner as in Example 1 except that 20 parts were used.

<Example 3>
Example 1 was used except that 50 parts of colloidal silica A (trade name: SNOWTEX 20L) and 50 parts of colloidal silica B (trade name: SNOWTEX PS-S) were used as pigments in the coating liquid for the glossy layer. Thus, a glossy inkjet recording sheet was obtained.

<Example 4>
As a binder in the glossy layer coating liquid, 20 parts of an acrylic polymer-silica composite emulsion (trade name: Aquabrid 906, manufactured by Daicel), 5 parts of casein, and an acrylic ester resin (trade name: X506) A glossy ink jet recording sheet was obtained in the same manner as in Example 2 except that a composition solution containing 25 parts of -526E-67, manufactured by Seiden Chemical Co., Ltd.) was mixed.

<Example 5>
A glossy inkjet recording sheet was obtained in the same manner as in Example 4 except that casein was not used as the binder in the glossy layer coating liquid.

<Comparative Example 1>
A glossy inkjet recording sheet was obtained in the same manner as in Example 1 except that only 80 parts of colloidal silica A (trade name: Snowtex 20L) was used as a pigment in the coating liquid for glossy layer.

<Comparative example 2>
A glossy inkjet recording sheet was obtained in the same manner as in Example 1 except that only 80 parts of colloidal silica B (trade name: Snowtex PS-S) was used as the pigment in the coating liquid for glossy layer.

<Evaluation method and evaluation criteria>
The glossy inkjet recording sheets obtained in the above Examples and Comparative Examples were evaluated for the glossiness of sheet physical properties and printability in inkjet recording by the following methods.
The results are shown in Table 1.

[Coating layer strength]
After the ink jet recording body was conditioned at 23 ° C. and a relative humidity of 50% RH for 24 hours, when the recording surface was bent outward, the coating layer was observed as a powdery fine piece and peeled off. Evaluation was made according to the following criteria.
A: Very good level with no powder falling off.
○: Almost no powder fall off, excellent level.
○-: Slightly powdered, but at a level that is not a problem for practical use.
X: A level of about 0.5 mm other than the powder is peeled off and cannot be practically used.

[Glossiness]
The glossiness was evaluated by visually observing glossiness and smoothness from the lateral direction with respect to the surface of the blank recording sheet, and evaluated according to the following criteria.
◎: Very high glossiness ○: Glossy feeling, excellent level △: Inferior glossiness, slightly problematic level in practical use ×: Inferior glossiness, level that causes serious practical problems

[Printability in inkjet recording]
The evaluation of printability was evaluated for each item of print density (black solid print) and ink absorbency using a commercially available printer.

(Evaluation printer)
Commercially available inkjet printer (trade name: PIXUS iP4200, manufactured by Canon)

(Print density)
Black solid printing was performed, and each printing density was measured with an X-light reflection densitometer (trade name: 938 Spectrodensitometer).

(Ink absorption)
For black, solid printing arranged on the grid so as to be in contact with each other was performed, and ink bleeding at the boundary was visually observed and evaluated according to the following criteria.
◎: Very good level with no blurring of printing ○: Almost no blurring of printing and excellent level △: Level of slight blurring of printing and slightly problematic for practical use ×: Printing Level of significant blurring and a serious problem in practical use

As is apparent from Table 1, the glossy ink jet recording sheet of this example is excellent in balance between glossiness and various printability.
On the other hand, the comparative example was a practically problematic level for any of the evaluation items.

Claims (6)

A substrate and a plurality of coating layers including at least one ink-receiving layer provided on the substrate; and a pigment and a binder for holding the pigment on the outermost surface of the coating layer In the inkjet recording sheet having a gloss developing layer,
The pigment has a primary particle colloidal silica having a particle size of 10 to 60 nm and a plurality of primary particles associated with each other to form a linked body that is linearly or branched, and the particle size thereof. And a secondary particle colloidal silica having a particle size of 60 to 160 nm.   2. The glossy ink jet recording sheet according to claim 1, wherein a mixing ratio of the primary particle colloidal silica and the secondary particle colloidal silica is 20/80 to 80/20.   The glossy ink jet recording sheet according to claim 1, wherein the binder contains an acrylic polymer.   The glossy ink jet recording sheet according to claim 1, wherein the binder contains an acrylic polymer-silica composite.   The glossy ink jet recording sheet according to claim 1, wherein the binder contains an acrylic polymer-silica composite and casein.   The glossy ink jet recording sheet according to claim 1, wherein the glossy expression layer is glossed by casting.