JP6827872B2 - Recording sheet for inkjet - Google Patents

Description

The present invention relates to a recording sheet for an inkjet.

The information recording method using inkjet ink is widely used because it is possible to easily obtain a high-quality image in full color and to realize a high image quality close to that of silver halide photography due to recent technological advances.
The inks are water-based inks containing various coloring materials in a solvent such as water or a mixed solvent of water and a hydrophilic organic solvent, and oil-based inks containing an oil-soluble coloring material in a hydrophobic organic solvent. Ink can be mentioned and used properly according to the purpose.

A recording sheet for an inkjet is configured by providing an ink receiving layer for absorbing ink to form a print or an image on a base material such as paper. The ink receiving layer is required to have good ink drying property and to suppress ink bleeding, which is particularly important when performing high-speed printing. Further, in consideration of mass production, it is desirable that the recording sheet for an inkjet can perform a so-called high-speed super calendar processing in which the surface is smoothed while being heated and pressed at high speed, and the ink receiving layer withstands such processing. It is desirable to be. The ink receiving layer can be formed by applying and drying a composition containing components necessary for fixing ink and a dispersion medium for dispersing them.

On the other hand, the recording sheet for an inkjet may be used in an environment wet with water due to the expansion of applications. In this case, it is desired that the recording sheet for an inkjet device fully exerts its function even in the presence of water. For example, a recording sheet for an inkjet may be used as a label for a frozen parcel delivery service. In this case, water may adhere to the recording sheet for the inkjet due to dew condensation, and it is conceivable that the sheets in such a state rub against each other, making it impossible to read the print or the image. , It is expected that the occurrence of such a problem can be suppressed.

As a recording sheet for inkjet having improved water resistance, an ink receiving layer containing a pigment, an adhesive, a cationic sizing agent, and two or more kinds of cationic resins having a specific range of cationization degree and molecular weight ( A binder provided with a receiving layer) (see Patent Document 1), containing a pigment and a binder, and the binder contains polyvinyl alcohol having a specific degree of saponification and polyurethane, and the binder is based on the pigment content. A material having an ink receiving layer having an content in a specific range (see Patent Document 2) is disclosed.

Japanese Patent No. 4042970 Japanese Unexamined Patent Publication No. 2016-182818

However, although the inkjet recording sheet disclosed in Patent Document 1 has a high effect of suppressing bleeding due to the adhesion of moisture for printing and images, the water resistance of the ink receiving layer itself is insufficient and the ink receiving layer itself gets wet with water. When used in an environment, there is a problem that the ink receiving layer is likely to be broken or peeled off.
Further, the inkjet recording sheet disclosed in Patent Document 2 also has a high effect of suppressing bleeding due to the adhesion of water on prints and images, and although the ink receiving layer itself has a certain level of water resistance, water There is a problem that the ink receiving layer is liable to be broken or peeled off when it is immersed in the ink or rubbed with water attached.

The present invention has been made in view of the above circumstances, and is an ink acceptor having good ink drying property, suppression of ink bleeding, strength sufficient to withstand high-speed super calendar processing, and water resistance. An object of the present invention is to provide a recording sheet for an inkjet having a layer.

The present invention is an inkjet recording sheet including a base material and an ink receiving layer formed on at least one surface of the base material, wherein the ink receiving layer is an average secondary particle as a pigment. The ink receiving layer contains a cationic styrene resin and polyvinyl alcohol as a binder, and the ink receiving layer contains the first and second aggregated light calcium carbonates having different diameters, and the ink receiving layer serves as an ink fixing agent. It contains a cationic resin other than the cationic styrene resin, and the total content of the cationic styrene resin and the polyvinyl alcohol in the ink receiving layer with respect to the total content of the first and second aggregated light calcium carbonates. The ratio of the content of the polyvinyl alcohol to the total content of the first and second aggregated light calcium carbonates in the ink receiving layer is 7% by mass or less. A certain ink recording sheet is provided.

In the recording sheet for inkjet of the present invention, the average secondary particle size of the first aggregated light calcium carbonate is less than 1 μm, and the average secondary particle size of the second aggregated light calcium carbonate is 2 to 5 μm. In the ink receiving layer, the ratio of [content of first aggregated light calcium carbonate (mass)]: [content of second aggregated light calcium carbonate (mass)] is 22:78 to 78:22. It is preferable to have.

According to the present invention, an inkjet recording sheet provided with an ink receiving layer having good ink drying property, suppressing ink bleeding, strength enough to withstand high-speed super calendar processing, and water resistance. Is provided.

It is sectional drawing which shows typically one Embodiment of the recording sheet for an inkjet of this invention. It is sectional drawing which shows typically the other embodiment of the recording sheet for an inkjet of this invention.

<< Recording Sheet for Inkjet >>
The recording sheet for an inkjet of the present invention is an inkjet recording sheet including a base material and an ink receiving layer formed on at least one surface of the base material, and the ink receiving layer is used as a pigment. The ink receiving layer contains a cationic styrene resin and polyvinyl alcohol as a binder, and the ink receiving layer contains ink, and the ink receiving layer contains first and second aggregated light calcium carbonates having different average secondary particle diameters. As the fixing agent, a cationic resin other than the cationic styrene resin is contained, and the cationic styrene resin and polyvinyl are contained in the ink receiving layer with respect to the total content of the first and second aggregated light calcium carbonates. The ratio of the total content of alcohol is 11 to 25% by mass, and the ratio of the content of polyvinyl alcohol to the total content of the first and second aggregated light calcium carbonates in the ink receiving layer is It is 7% by mass or less.

In the recording sheet for an inkjet of the present invention, since the ink receiving layer has the above-mentioned limited composition, the drying property of the ink is good, the ink bleeding can be suppressed, and the ink receiving layer has a high-speed super calendar. By having enough strength to withstand processing and water resistance, printing and images can be stably retained.
That is, the recording sheet for an inkjet of the present invention may be calendar-processed (smoothed).

The calendar process is a process of smoothing the surface of the sheet by pressurizing the surface of the sheet, and the surface of the sheet may be heated at the same time. The high-speed super calendar processing is to perform this calendar processing (smoothing processing) at high speed.
The processing speed at the time of high-speed super calendar processing is, for example, 300 m / min or more.
The recording sheet for an inkjet of the present invention is particularly suitable for mass production because the ink receiving layer can withstand high-speed super calendar processing.

<Ink receiving layer>
The ink receiving layer can be formed by using a composition for an ink receiving layer containing a component for constituting the ink receiving layer. More specifically, the ink receiving layer can be formed by applying the composition for an ink receiving layer on a substrate and drying it.

The ratio of the contents of the components that do not vaporize at room temperature in the composition for the ink receiving layer is usually the same as the ratio of the contents of the components of the ink receiving layer. In addition, in this specification, "room temperature" means a temperature which is not particularly cooled or heated, that is, a normal temperature, and examples thereof include a temperature of 15 to 25 ° C.

The coating of the composition for the ink receiving layer on the substrate may be performed once or may be performed in a plurality of times. When the coating is performed in a plurality of times, the method of further coating the composition for the ink receiving layer on the dried coating layer and the method of further applying the ink receiving on the undried coating layer. It may be any method of coating the layer composition.
The coating amount of the composition for the ink receiving layer may be appropriately adjusted in consideration of the solid content concentration of the composition for the ink receiving layer, the thickness of the ink receiving layer, and the like.

The coating method of the composition for the ink receiving layer is not particularly limited, and any method can be used as long as it can coat a liquid substance. Specific coating methods include, for example, various coaters such as air knife coaters, curtain coaters, die coaters, blade coaters, roll coaters, gate roll coaters, bar coaters, rod coaters, gravure coaters, and gravure offset coaters; wire bars. A known method using a device such as a coater can be mentioned.

The coated composition for the ink receiving layer may be dried by a known method such as blast drying and heating blast drying. Conditions such as drying temperature and drying time may be appropriately set according to the drying method.

The amount of the ink receiving layer formed on the substrate is preferably 4 g / m ² or more, more preferably 4.5 g / m ² or more, and particularly preferably 5 g / m ² or more. When the amount of the ink receiving layer formed is equal to or more than the lower limit, for example, the effect of suppressing ink bleeding becomes higher, and in particular, when at least the surface of the ink receiving layer is smoothed using a calendar device. In addition, such an effect becomes higher.
On the other hand, the upper limit of the amount of the ink receiving layer formed on the substrate is not particularly limited, and may be, for example, 30 g / m ² .
The amount of the ink receiving layer formed is preferably within a range set by appropriately combining any of the above lower limit values and upper limit values.

The amount of the ink receiving layer formed can be adjusted, for example, by adjusting the amount of the ink receiving layer composition coated on the substrate, the amount of each compounding component of the ink receiving layer composition, and the like. ..

The recording sheet for an inkjet of the present invention may be provided with an ink receiving layer on at least one surface of the base material, may be provided on only one side, or may be provided on both sides.
When the recording sheet for an inkjet of the present invention has ink receiving layers on both sides of a base material, these two ink receiving layers may be the same as each other or may be different from each other.

<Composition for ink receiving layer>
Examples of the composition for the ink receiving layer include the pigment, the binder, the ink fixing agent, and, if necessary, other components that do not fall under any of these.
Hereinafter, each component will be described.

[Pigment]
The pigment is a component that retains the pigment in the ink in the ink receiving layer and affects the absorption and permeation of water.
The composition for the ink receiving layer and the ink receiving layer contain the first aggregated light calcium carbonate and the second aggregated light calcium carbonate having different average secondary particle diameters as the pigment.

Calcium carbonate includes heavy calcium carbonate and light calcium carbonate.
Heavy calcium carbonate is a crushed classification of natural limestone.
Light calcium carbonate is chemically synthesized, and the shape and size of its particles can be chemically controlled. The shape of the particles of light calcium carbonate is usually cubic, spindle-shaped, pillar-shaped, or the like. Light calcium carbonate includes those in which primary particles exist as single particles and those in which primary particles aggregate to form secondary particles.
Light calcium carbonate in which primary particles aggregate to form secondary particles is called aggregated light calcium carbonate. The average particle size of the primary particles (average primary particle size) can be obtained from, for example, observation results with a scanning electron microscope. The average particle size of the secondary particles is determined by, for example, measurement by a laser diffraction method.
In the present invention, as the pigment, first aggregated light calcium carbonate and second aggregated light calcium carbonate having at least different average secondary particle diameters are used.

The average secondary particle size of the first aggregated light calcium carbonate is preferably less than 1 μm, more preferably 0.9 μm or less, for example, 0.8 μm or less, 0.7 μm or less, and 0.6 μm or less. These may be any of the above, but these are examples.
On the other hand, the lower limit of the average secondary particle size of the first aggregated light calcium carbonate is not particularly limited and may be, for example, 0.2 μm.
Since the ink receiving layer contains the first aggregated light calcium carbonate, the effect of suppressing ink bleeding becomes higher when the ink receiving layer is subjected to inkjet printing on an inkjet recording sheet.

The average secondary particle size of the second aggregated light calcium carbonate is preferably 2 to 5 μm, more preferably 2.3 to 4.7 μm, and for example, 2.6 to 4.4 μm. It may be, but this is just an example.
Since the ink receiving layer contains the second aggregated light calcium carbonate, the drying property of the ink becomes higher when the ink is printed on the recording sheet for inkjet. Here, "highly dry ink" means "short time required for drying ink".

The ink receiving layer preferably contains, as the first aggregated light calcium carbonate and the second aggregated light calcium carbonate, any of the above-mentioned average secondary particle diameters in an appropriate combination. For example, a preferred combination of the first aggregated light calcium carbonate and the second aggregated light calcium carbonate in the ink receiving layer is the first having an average secondary particle size of less than 1 μm (for example, 0.2 μm or more and less than 1 μm). Examples include a combination of aggregated light calcium carbonate and a second aggregated light calcium carbonate having an average secondary particle size of 2 to 5 μm, which is an example.
As described above, since the ink receiving layer contains both the first aggregated light calcium carbonate and the second aggregated light calcium carbonate, the recording sheet for an inkjet can be printed in color by a high-speed inkjet printer. The dryness of the ink is improved.

In the composition for the ink receiving layer and the ink receiving layer, the ratio of [content of first aggregated light calcium carbonate (mass)]: [content of second aggregated light calcium carbonate (mass)] is not particularly limited. Is preferably 10:90 to 90:10, more preferably 16:84 to 84:16, and particularly preferably 22:78 to 78:22. The content of the first aggregated light calcium carbonate is preferably high in that the effect of suppressing ink bleeding is higher, and the content of the second aggregated light calcium carbonate is higher in that the ink is more dry. Is preferable. Then, the ratio of [content (mass) of first aggregated light calcium carbonate]: [content (mass) of second aggregated light calcium carbonate] is within the above range, so that the recording sheet for an inkjet can be used. , Both the improvement of the effect of suppressing ink bleeding and the improvement of dryness can be achieved in a more balanced manner, and the recording sheet for inkjet has better dryness of ink even when color printing is performed with a high-speed inkjet printer. It will be good.

The composition for the ink receiving layer and the ink receiving layer do not fall under any of the first aggregated light calcium carbonate and the second aggregated light calcium carbonate, as long as the effects of the present invention are not impaired. It may contain a pigment.
Examples of the other pigment include non-aggregated light calcium carbonate (that is, light calcium carbonate in which primary particles are not aggregated to form secondary particles); the first and first heavy calcium carbonate and the like. Calcium carbonate other than the aggregated light calcium carbonate of 2 can be mentioned.

The first and second aggregated light calcium carbonates and the other pigments may be used alone or in combination of two or more, and when two or more are used in combination, they may be used alone. The combination and ratio of the above may be appropriately selected according to the purpose.

In the composition for the ink receiving layer and the ink receiving layer, the ratio of the total content of the first and second aggregated light calcium carbonate to the total content of the pigment is preferably 92% by mass or more, preferably 94% by mass. The above is more preferable, 96% by mass or more is further preferable, 98% by mass or more is particularly preferable, and 100% by mass may be used.

The ratio of the pigment content (that is, the pigment content of the ink receiving layer) to the total content of the components other than the solvent described later in the composition for the ink receiving layer is preferably 70 to 95% by mass. It is more preferably 74 to 92% by mass, and particularly preferably 78 to 89% by mass. When the ratio is at least the lower limit value, the effect of using the pigment can be obtained more remarkably. Further, when the ratio is not more than the upper limit value, the strength of the ink receiving layer becomes higher.
In the present specification, "pigment content" refers to all pigments used, including not only the first and second aggregated light calcium carbonates but also other pigments, unless otherwise specified. It means the content (that is, the total content of the pigment).

[binder]
The binder is a component for retaining the pigment (first and second aggregated light calcium carbonate, etc.) contained therein in the ink receiving layer.
The composition for the ink receiving layer and the ink receiving layer contain a cationic styrene resin and polyvinyl alcohol as the binder.
The cationic styrene resin is a component that mainly affects the water resistance of the ink receiving layer and also affects the drying property and bleeding of the ink in the ink receiving layer.
Polyvinyl alcohol is a component that mainly affects the strength of the ink receiving layer.

Cationic styrene-based resins have structural units derived from styrene and exhibit cationic properties when dissolved or dispersed in water.
The cationic styrene resin is not particularly limited as long as it is such a resin, and may have, for example, only a structural unit derived from styrene or a derivative thereof, or a configuration derived from styrene or a derivative thereof. It may have a unit and other structural units other than these.
Further, the cationic styrene resin may be a copolymer of a resin having a structural unit derived from styrene or a derivative thereof and another resin other than the resin, and such a copolymer may be used. For example, a copolymer of a resin having a structural unit derived from styrene or a derivative thereof and an acrylic resin (a resin having a (meth) acryloyl group) can be mentioned.

In addition, the description of "derivative" and "class" in this specification means that one or more hydrogen atoms of the original compound are substituted with a group other than a hydrogen atom, unless otherwise specified. Here, the "group" includes not only an atomic group formed by bonding a plurality of atoms but also one atom.
Further, the "(meth) acryloyl group" is a concept including both "acryloyl group" and "methacryloyl group". The same applies to terms similar to the (meth) acryloyl group. For example, "(meth) acrylic acid" is a concept that includes both "acrylic acid" and "methacrylic acid", and "(meth) acrylate". "" Is a concept that includes both "acrylate" and "methacrylate".

The weight average molecular weight of the cationic styrene resin is preferably 5000 to 110,000.
In the present specification, the weight average molecular weight is a polystyrene-equivalent value measured by a gel permeation chromatography (GPC) method unless otherwise specified.

Examples of polyvinyl alcohol include fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol.

The degree of saponification of polyvinyl alcohol is preferably 90 mol% or more, more preferably 93 mol% or more, and particularly preferably 96 mol% or more. When the degree of saponification of polyvinyl alcohol is at least the above lower limit value, the effect of suppressing ink bleeding in the ink receiving layer becomes higher, and the strength of the ink receiving layer becomes higher. The upper limit of the degree of saponification of polyvinyl alcohol is not particularly limited, and may be, for example, 99.5 mol% or 100 mol%.
The degree of saponification of polyvinyl alcohol is preferably within a range set by appropriately combining any of the above lower limit values and upper limit values.

The degree of polymerization of polyvinyl alcohol is preferably 500 to 2500, more preferably 750 to 2350, further preferably 1000 to 2200, and particularly preferably 1250 to 2000. When the degree of polymerization of polyvinyl alcohol is not more than the above upper limit value, the drying property of the ink becomes higher. Further, when the degree of polymerization of polyvinyl alcohol is at least the above lower limit value, the strength of the ink receiving layer becomes higher.

The composition for the ink receiving layer and the ink receiving layer may contain other binders other than the cationic styrene resin and polyvinyl alcohol as long as the effects of the present invention are not impaired.
Examples of the other binder include cationic styrene resins and water-soluble polymers other than polyvinyl alcohol.

Examples of the water-soluble polymer include modified polyvinyl alcohols such as cation-modified polyvinyl alcohols, anion-modified polyvinyl alcohols, and silanol-modified polyvinyl alcohols; oxidized starch; phosphoric acid esterified starch; locons; casein; carboxymethyl cellulose (CMC); esters. Examples thereof include polyurethanes such as polyurethanes and carbonates.
The polyurethane may be, for example, cationic, anionic or nonionic.

The cationic styrene resin, polyvinyl alcohol, and the other binder may be used alone or in combination of two or more, and when two or more are used in combination, they may be used alone. The combination and ratio may be appropriately selected according to the purpose.

The ratio of the total content of the cationic styrene resin and polyvinyl alcohol to the total content of the binder in the composition for the ink receiving layer and the ink receiving layer is preferably 65% by mass or more, preferably 75% by mass or more. It is more preferable, and it is particularly preferable that it is 85% by mass or more, and for example, it may be either 90% by mass or more, 95% by mass or more, or 100% by mass.

The ratio of the total content of the cationic styrene resin and polyvinyl alcohol to the total content of the first and second aggregated light calcium carbonates in the composition for the ink receiving layer and the ink receiving layer is 11 to 25 mass by mass. %, More preferably 12.5 to 23% by mass, and more preferably 14 to 21% by mass. When the ratio is not more than the lower limit value, the water resistance of the ink receiving layer becomes higher, and when the ratio is not more than the upper limit value, the drying property of the ink in the ink receiving layer becomes higher.

In the composition for the ink receiving layer and the ink receiving layer, the ratio of the content of the polyvinyl alcohol to the total content of the first and second aggregated light calcium carbonate is 7% by mass or less, and is 0.5 to 0.5. It is preferably 7% by mass, more preferably 0.5 to 6.5% by mass, further preferably 0.5 to 6% by mass, and 0.5 to 5.5% by mass. Is particularly preferred. When the ratio is not more than the upper limit value, the water resistance of the ink receiving layer is increased, and when the ratio is not more than the lower limit value, the strength of the ink receiving layer is further increased. In particular, the high strength of the ink receiving layer makes the recording sheet for an inkjet suitable for performing high-speed super calendar processing.

The ratio of the content of the cationic styrene resin to the total content of the first and second aggregated light calcium carbonates in the composition for the ink receiving layer and the ink receiving layer is 4 to 24.5% by mass. It is preferably 6 to 22.5% by mass, more preferably 8 to 20.5% by mass, and particularly preferably 8 to 20.5% by mass.

[Ink fixer]
The ink fixing agent is a component for fixing ink in the ink receiving layer.
In the composition for the ink receiving layer and the ink receiving layer, as the ink fixing agent, a cationic resin other than the cationic styrene resin (in the present specification, it may be referred to as a "cationic resin fixing agent") is used. contains.

The cationic resin fixing agent exhibits cationic properties when dissolved or dispersed in water.
The cationic resin fixing agent is preferably, for example, a monomer, oligomer or polymer of a primary amine, a secondary amine, a tertiary amine or a quaternary ammonium salt, and is preferably the oligomer or polymer. More preferred.

More preferred cationic resin fixers are, for example, alkylamine-epicrolhydrin copolymers; acrylic polymers having a secondary amino group, a tertiary amino group or a quaternary ammonium group; polyvinylamine; polyvinylamidine. 5-membered ring amidines; dicyan cationic resins such as dicyandiamide-formalin copolymers; polyamine-based cationic resins such as dicyandiamide-polyethyleneamine copolymers; polyalkylene polyamines such as polyethylene polyamines and polypropylene polyamines and derivatives thereof. ; diallyldimethylammonium -SO ₂ copolymer; diallylamine salt -SO ₂ copolymer; dimethyldiallylammonium chloride polymer; polymer of allylamine salt, a homopolymer of vinylbenzyl triallyl ammonium salts or copolymers; dialkylamino Ethyl (meth) acrylate quaternary salt copolymer; acrylamide-diallylamine salt copolymer; aluminum salts such as polyaluminum chloride and polyaluminum acetate, and alkylamine-epichlorohydrin copolymer is particularly preferable, and dimethyl Most preferably, it is an amine-epicrolhydrin copolymer.

In the present specification, the polymer also includes a polycondensate.

As the cationic resin fixing agent, one type may be used alone, two or more types may be used in combination, and when two or more types are used in combination, the combination and ratio thereof should be appropriately selected according to the purpose. Just do it.

In the composition for the ink receiving layer and the ink receiving layer, the ratio of the content of the cationic resin fixing agent to the content of the pigment is preferably 1 to 40% by mass, and preferably 1 to 25% by mass. More preferably, for example, it may be any one of 1 to 15% by mass, 1 to 10% by mass, 1 to 6% by mass and 1 to 4% by mass, but these are examples.

[Other ingredients]
Examples of the other components include a solvent, a polyvalent metal salt, a pH adjuster, an antifoaming agent, an antifoaming agent, a mold release agent, a foaming agent, an antioxidant, an antiseptic agent, a water resistant agent, and a paper strength enhancer. , Color dyes, color pigments, pigment fixers, pigment dispersants, fluorescent whitening agents, ultraviolet absorbers and the like, which are components usually used in the ink receiving layer of recording sheets for inkjet.
As the other components, one type may be used alone, two or more types may be used in combination, and when two or more types are used in combination, the combination and ratio thereof may be appropriately selected according to the purpose. Good.

(solvent)
In the composition for the ink receiving layer, the solvent other than the pigment, the binder, the ink fixing agent, or the other component other than the solvent is blended as a dispersion or a solution and used as the dispersion medium or the solvent at that time. When not used, the solvent means the dispersion medium used to prepare the dispersion or the solvent used to prepare the solution.
Further, when a solvent is separately blended in addition to the dispersion medium used for preparing the dispersion or the solvent used for preparing the solution, the solvent is the dispersion medium or solvent and this separately blended. Means both solvent and. When all of the pigment, the binder, the ink fixing agent, and the other components other than the solvent are blended as a solid substance, the solvent means a solvent blended separately from these.
Examples of the solvent include water, alcohol and the like.

As the solvent, one type may be used alone, two or more types may be used in combination, and when two or more types are used in combination, the combination and ratio thereof may be appropriately selected according to the purpose.

The content of the solvent in the composition for the ink receiving layer may be appropriately selected depending on the intended purpose, and is not particularly limited, but is preferably 35 to 90% by mass, for example.

(Multivalent metal salt)
The polyvalent metal salt is a component for improving the drying property of the ink in the ink receiving layer, and is not particularly limited as long as it contains a metal cation having a valence of 2 or more as a constituent component.

Examples of the polyvalent metal salt include calcium chloride (CaCl ₂ ), magnesium chloride (MgCl ₂ ), aluminum chloride (AlCl ₃ ), barium chloride (BaCl ₂ ), zinc chloride (ZnCl ₂ ), and calcium sulfate (CaSO ₄ ). , Magnesium Sulfate (sulfonyl ₄ ), Calcium Nitrate (Ca (NO ₃ ) ₂ ), Magnesium Acetate ((CH ₃ COO) ₂ Mg), Calcium Acetate ((CH ₃ COO) ₂ Ca), Potassium Aluminum Sulfate (Karimyoban, AlK (SO ₄ ) ₂ ) and the like can be mentioned.
The polyvalent metal salt may be a hydrate or a non-hydrate.

Among them, the polyvalent metal salt can improve the drying property and color density of the ink in the ink receiving layer, and the water resistance and scratch resistance of the ink receiving layer in a well-balanced manner, and has high safety. In that respect, calcium chloride, magnesium chloride or potassium aluminum sulfate is preferable, and potassium aluminum sulfate is particularly preferable in that the drying property of the ink becomes higher.

As the polyvalent metal salt, one type may be used alone, two or more types may be used in combination, and when two or more types are used in combination, the combination and ratio thereof may be appropriately selected according to the purpose. Good.

When the composition for the ink receiving layer and the ink receiving layer contain a polyvalent metal salt, it is preferable that the composition contains one or more selected from the group consisting of calcium chloride, magnesium chloride and potassium aluminum sulfate, and potassium aluminum sulfate. Is more preferable, and when potassium aluminum sulfate is contained, one containing either or both of calcium chloride and magnesium chloride is more preferable. By containing at least potassium aluminum sulfate in the ink receiving layer, the drying property of the ink becomes higher.

When the composition for the ink receiving layer and the ink receiving layer contain a polyvalent metal salt, the ratio of the content of the polyvalent metal salt to the content of the pigment in the composition for the ink receiving layer and the ink receiving layer is It is preferably 3 to 55% by mass, more preferably 3 to 25% by mass, further preferably 3 to 15% by mass, and particularly preferably 3 to 10% by mass. When the ratio is at least the lower limit value, the effect of using the polyvalent metal salt can be obtained more remarkably. Further, when the ratio is not more than the upper limit value, excessive use of the polyvalent metal salt is suppressed.

(Defoamer)
The defoaming agent is not particularly limited and may be a known one.
As the defoaming agent, one type may be used alone, two or more types may be used in combination, and when two or more types are used in combination, the combination and ratio thereof may be appropriately selected according to the purpose. ..

The total content of the other components in the composition for the ink receiving layer may be appropriately adjusted according to the intended purpose.

Examples of particularly preferable compositions for the ink receiving layer and the ink receiving layer are a first aggregated light calcium carbonate having an average secondary particle size of less than 1 μm and a second aggregated light calcium carbonate having an average secondary particle size of 2 to 5 μm. The ratio of [content of first aggregated light calcium carbonate (mass)] to [content of second aggregated light calcium carbonate (mass)] is 22:78 to Those that are 78:22 can be mentioned.

<Manufacturing method of composition for ink receiving layer>
The composition for the ink receiving layer can be produced by blending the pigment, the binder, the ink fixing agent, and other components as necessary, and sufficiently stirring these blending components. In the composition for the ink receiving layer, the pigment is preferably dispersed, and the binder and the ink fixing agent are preferably dissolved or dispersed.

The blending order of each component is not particularly limited.
Further, when blending each component, all the components may be added and then mixed, or some components may be sequentially added and mixed, or all the components may be sequentially added and mixed. You may.
As described above, the solvent may be used by being mixed in advance with the pigment, the binder, the ink fixing agent, or the other components other than the solvent, or may be used alone without being mixed with these components in advance. You may use it.

The temperature at the time of blending each component is not particularly limited and may be appropriately adjusted according to the type of the blended component and the like, but is usually preferably 15 to 30 ° C.
Stirring may be performed by a known method for preparing a dispersion, such as a method using a mixer. The stirring time may be appropriately adjusted according to the total amount of the composition for the ink receiving layer to be produced, the stirring method, and the like, and is preferably 10 minutes to 24 hours, for example.

<Base material>
The material of the base material is not particularly limited, and it may be selected from those capable of forming a coating layer according to the purpose. For example, the base material may be a water resistant base material or a non-water resistant base material.
Examples of the water-resistant base material include a base material having a residual ratio of either vertical grain or horizontal grain of 10% or more in a wet tensile strength test based on JIS P8135: 1998.

Specifically, as the material of the base material, for example, papers such as water resistant paper, high quality paper, art paper, coated paper, cast coated paper, resin coated paper, synthetic paper; polyethylene, polypropylene, polyvinyl chloride, polystyrene, etc. Polyvinyl acetate, acrylic resin, AS resin, ABS resin, polyamide, polyacetal, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyphenylensulfide, polysulfone, polycarbonate, epoxy resin, melamine Examples thereof include resins, phenol resins, urea resins, polyurethanes, synthetic resins such as polyethylene, and the like.

The thickness of the base material is not particularly limited as long as the shape of the base material is sheet-like or film-like, but is preferably 20 to 1000 μm, more preferably 35 to 500 μm, and 50 to 200 μm. Is particularly preferred. When the thickness of the base material is at least the above lower limit value, the structure of the ink receiving layer can be held more stably, and when the thickness of the base material is at least the above upper limit value, the handleability as a recording sheet is improved. It will be better.

The base material may be composed of a single layer, may be composed of a plurality of layers of two or more layers, and when composed of a plurality of layers, the plurality of layers may be the same or different from each other. That is, all layers may be the same, all layers may be different, or only some layers may be different. When the plurality of layers are different from each other, the combination of the plurality of layers is not particularly limited. Here, when a plurality of layers are different from each other, it means that at least one of the material and the thickness of each layer is different from each other.
When the base material is composed of a plurality of layers, the total thickness of each layer may be set to the above-mentioned preferable thickness of the base material.

As the base material, a commercially available product may be used, or a material produced by a known method may be used.

<< Manufacturing method of recording sheet for inkjet >>
The recording sheet for an inkjet of the present invention can be produced by forming an ink receiving layer on at least one surface of a base material.
The method of forming the ink receiving layer is as described above.

When the recording sheet for an inkjet of the present invention is subjected to calendar processing (smoothing processing), the calendar processing may be performed on at least the surface of the ink receiving layer after the ink receiving layer is formed.

The calendar processing (smoothing processing) of the recording sheet for inkjet (the surface of the ink receiving layer) is known as, for example, a machine calendar, a TG calendar, a super calendar, a soft calendar, a gloss calendar, a compact calendar, a mat super calendar, a mat calendar and the like. It can be done using the calendar device of.

The calendar device may be either an off-type separated from the coater or an on-type integrated with the coater.
Among the calendar devices, the rolls include, for example, a rigid roll and an elastic roll.
Examples of the rigid roll include a metal roll, a roll whose metal surface is mirror-treated with hard chrome plating, and the like.
Examples of the elastic roll include a roll made of a resin such as polyurethane, epoxy resin, polyamide, phenol resin or polyacrylate; and a roll obtained by molding cotton, nylon, asbestos, aramid fiber or the like.

The conditions for the calendar processing are appropriately selected according to the required quality, such as the temperature of the rigid roll, the calendar pressure, the number of nip, the roll speed, and the paper moisture before the calendar processing.

The processing temperature during the calendar processing is not particularly limited, but can be, for example, 10 to 50 ° C.

The pressure during calendar processing is not particularly limited, but can be, for example, 50 to 400 kN / m.
The pressure during calendar processing is adjusted by, for example, adjusting the pressure when pressing a pair of rolls in the calendar device against the recording sheet for inkjet to be processed and the distance between the roll surfaces of the pair of rolls. it can. The method of adjusting the distance between the roll surfaces to adjust the pressure during calendar processing is suitable for calendar processing on a small scale. As an example, the pressure during calendar processing can be easily adjusted by setting the distance between the roll surfaces to preferably 10 to 400 μm according to the thickness of the recording sheet for inkjet to be processed.

Next, the overall configuration of the recording sheet for an inkjet of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing an embodiment of a recording sheet for an inkjet of the present invention. Further, FIG. 2 is a cross-sectional view schematically showing another embodiment of the recording sheet for an inkjet of the present invention.
In FIG. 2, the same components as those shown in FIG. 1 are designated by the same reference numerals as those shown in FIG.
In addition, the drawings used in the following description may be shown by enlarging the main parts for convenience in order to make the features of the present invention easy to understand, and the dimensional ratios and the like of each component are the same as the actual ones. Is not always the case.

The recording sheet 1 for an inkjet shown in FIG. 1 is provided with an ink receiving layer 12 only on one surface (sometimes referred to as a “first surface” in the present specification) 11a of the base material 11.
The inkjet recording sheet 2 shown in FIG. 2 is on the first surface 11a of the base material 11 and on the other surface (sometimes referred to as the “second surface” in the present specification) 11b (that is, on both sides). Both of them are provided with an ink receiving layer 12. Regarding the two ink receiving layers 12 and 12 in the recording sheet 2 for inkjet, those provided on the first surface 11a of the base material 11 are shown as the first ink receiving layer 121 as needed, and the base material is shown. Those provided on the second surface 11b of 11 are shown as the second ink receiving layer 122 to distinguish them from each other.

In FIG. 1, reference numeral 12a indicates a surface of the ink receiving layer 12 opposite to the base material 11 side (sometimes referred to as “first surface” in the present specification), and reference numeral 12b is ink. The surface of the receiving layer 12 on the base material 11 side (sometimes referred to as “second surface” in the present specification) is shown.
Further, in FIG. 2, reference numerals 12a, 121a, and 122a are surfaces (first surface) of the ink receiving layer 12, the first ink receiving layer 121, and the second ink receiving layer 122, which are opposite to the base material 11 side, respectively. 12b, 121b, and 122b indicate the surfaces (second surface) of the ink receiving layer 12, the first ink receiving layer 121, and the second ink receiving layer 122 on the base material 11 side, respectively.

In FIGS. 1 and 2, the base material 11 and the ink receiving layer 12 (the first ink receiving layer 121 and the second ink receiving layer 122) are those described above, respectively.

However, the inkjet recording sheet shown in FIGS. 1 and 2 is only an example of the present invention, and the inkjet recording sheet of the present invention is not limited thereto.

In the recording sheet for an inkjet of the present invention, the ink receiving layer may be provided on the entire surface of the surface to be formed on the base material, or may be provided only in a part of the region.
When the recording sheet for an inkjet of the present invention is viewed in a plan view from above the side where the ink receiving layer is provided, the surface area of the ink receiving layer may be equal to or less than the surface area of the base material. As long as the conditions are met, there is no particular limitation. The shapes of the ink receiving layer and the base material when viewed in a plane in this way can also be arbitrarily set according to the purpose and are not particularly limited.

The recording sheet for an inkjet of the present invention may include a layer other than the ink receiving layer on the substrate, depending on the purpose.
Examples of the other layer include an adhesive layer, an adhesive layer, a release film, and the like.

Examples of the pressure-sensitive adhesive layer and the pressure-sensitive adhesive layer include those for attaching and fixing an inkjet recording sheet to an object. When the recording sheet for an inkjet is provided with such an adhesive layer or an adhesive layer, it is preferable that a release film is further provided on these layers and the adhesive layer or the adhesive layer is not exposed.

As the adhesive layer, for example, the overlapping surfaces of the sheets are bonded to each other and then peeled off, so that the overlapping surfaces of the sheets can be peeled off again without being damaged, so-called. There is also a pressure-sensitive adhesive layer that adheres the sheets to each other so that they can be peeled off again.
The pressure-sensitive adhesive layer may be provided on the ink receiving layer.

The recording sheet for inkjet provided with the pressure-sensitive adhesive layer may be in a state in which the sheet to be bonded is removably bonded to the pressure-sensitive adhesive layer, or the sheet to be bonded is bonded. It may not be necessary, and one inkjet recording sheet may be folded and removably adhered by a pressure-sensitive adhesive layer.

Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the examples shown below.

<Base material>
In the following examples and comparative examples, the following materials were used as the base material.

<Raw materials>
In the following Examples and Comparative Examples, the pigments and binders shown below were used.

In the following Examples and Comparative Examples, the raw materials other than the pigment and the binder were used as shown below.
[Cationic resin fixing agent]
(C) -1: Alkylamine-epichlorohydrin polycondensate (“Jetfix 260” manufactured by Satoda Kako Co., Ltd.)
[Multivalent metal salt]
(D) -1: Calcium chloride (d) -2: Potassium aluminum sulfate (potassium alum)

<< Manufacturing of Recording Sheets for Inkjet >>
[Example 1]
Pigment (a) -1 (25 parts by mass) and pigment (a) -2 (75 parts by mass), binder (b) -1 (12.5 parts by mass (solid content)), binder (b) -2 ( 2.5 parts by mass (solid content)) and the cationic resin fixing agent (c) -1 (2.78 parts by mass (solid content)) are added, and these components are sufficiently stirred at room temperature to remove these components. The mixture was dispersed to obtain a composition for an ink receiving layer, which is a dispersion liquid.
Next, using a wire bar coater, the composition for the ink receiving layer obtained above is coated on the base material (z) -1 with a coating amount such that the amount of the ink receiving layer formed is 9 g / m ^2. Then, it was dried at 105 ° C. to form an ink receiving layer having a thickness of about 10 μm, which was used as a recording sheet for an inkjet.
Further, this inkjet recording sheet was subjected to calendar processing at room temperature to obtain a target inkjet recording sheet. At the time of calendar processing, the distance between the roll surfaces of the pair of metal rolls was set to 25 μm, and the distance between the roll surfaces was set to 25 μm, and the inkjet recording sheet was pressed by passing the inkjet recording sheet between the roll surfaces.

[Examples 2 to 8 and Comparative Examples 1 to 7]
Same as Example 1 except that any one or more of the type of the base material, the type and the amount of the compounding component of the composition for the ink receiving layer, and the amount of forming the ink receiving layer are set as shown in Table 4. A recording sheet for an inkjet was produced by the method.
In addition, the description of "-" in the column of the compounding component in Table 4 means that the component is not compounded.

<< Evaluation of Recording Sheet for Inkjet >>
The following items were evaluated for the above-mentioned recording sheet for inkjet. The results are shown in Table 5.

[Dot bleeding]
Dot bleeding was evaluated by the dot shape coefficient. The evaluation sample was printed (single color printing) on the ink receiving layer of the recording sheet for inkjet using a desktop inkjet printer with a size of 2 cm x 2 cm and a density of 10% so that the dots do not overlap. Made. Next, a microscope image of the surface of the recording sheet for an inkjet was taken and analyzed using a dot analyzer (“DA6000” manufactured by Oji Measuring Instruments Co., Ltd.). Specifically, the peripheral length and area of the dots were measured, and the dot shape coefficient was calculated by the following formula.
Dot shape coefficient = (peripheral length) ² / (4π x area)

The dot shape coefficient becomes 1 when the dots are perfect circles, and becomes a larger value as the shape of the dots deviates from the perfect circle, that is, the dots are blurred. The dot shape coefficient measured by a desktop inkjet printer (printing speed 250 f (76.2 m) / min) has a sufficient correlation with the dot shape coefficient measured by a high-speed inkjet printer (printing speed 500 f (152.4 m) / min). I confirmed in advance that there is.

By the above method, the dot shape coefficient was calculated for about 30 dots to obtain the average value, and the dot bleeding was evaluated according to the following evaluation criteria. The results are shown in Table 5. The numerical value in parentheses in the column of "dot bleeding" in Table 5 is the average value of the dot shape coefficients.
(Evaluation criteria)
A: The average value of the dot shape coefficients is 1.8 or less, and the bleeding of dots is completely or highly suppressed.
B: The average value of the dot shape coefficients exceeds 1.8 and is 2.0 or less, and dot bleeding is suppressed.
C: The average value of the dot shape coefficients exceeds 2.0, and dot bleeding is not suppressed.

[Ink drying property]
Using an inkjet printer, printing was performed on the ink receiving layer of the recording sheet for inkjet with four color inks of cyan, magenta, yellow, and black. More specifically, the printing was performed by changing the printing density for each color from 100% to 400% in units of 10%.
Then, immediately after the completion of printing, a transparent polyethylene terephthalate film (thickness 100 μm) was superposed on the printed surface of the recording sheet for an inkjet and firmly pressed against the printed surface to bring them into close contact with each other.
Next, with the film in close contact with the printing surface, visually observing from the side opposite to the contact surface with the printing surface, the maximum print density of the ink not transferred from the printing surface to the contact surface is confirmed. Then, the dryness of the ink was evaluated according to the following evaluation criteria. The results are shown in Table 5. The numerical value in parentheses in the column of "dryness of ink" in Table 5 is the maximum print density. In this evaluation method, it was confirmed in advance that the evaluation results would not vary as long as the film was in close contact with the printed surface.
(Evaluation criteria)
A: The maximum print density of the ink is 300% or more, the drying property is excellent, and the ink has high-speed printing suitability.
B: The maximum print density of the ink is 190% or more and less than 300%, the drying property is good, and the ink has high-speed printing suitability.
C: The maximum print density of the ink is less than 190%, the drying property is inferior, and the ink does not have high-speed printing suitability.

[Strength of ink receiving layer]
A recording sheet for an inkjet was cut into a size of 70 mm × 40 mm to prepare a test piece. Further, a polyethylene terephthalate (PET) film having a size of 20 mm × 40 mm and a thickness of 75 μm was prepared. The test piece and the PET film are laminated so that the entire surface of one surface of the PET film overlaps one surface of the test piece and the surface of the test piece on the side provided with the ink receiving layer is an exposed surface. The first laminate was obtained. Further, the first laminate was sandwiched between two stainless steel mirror plates having a size larger than that of the first laminate and a thickness of 1 mm to form a second laminate. At this time, the first laminated product was arranged so that the entire surfaces of both of the first laminated products overlap with the mirror surface plate. As a result, in the second laminate, the ink receiving layer of the test piece is in direct contact with the mirror plate. Next, using a heat pressurizing device (laminator) capable of pressurizing and heating at the same time, the second laminate is sandwiched between the two heat and pressurizing treatment surfaces, and the temperature is 50 ° C. and the pressure is 10 kN. The second laminate was heat-pressurized under the condition of a treatment time of 30 seconds. At this time, the second laminate was arranged so that the entire surfaces of both surfaces of the second laminate overlap with the heat-pressurized surface. As a result, the pressure during the heat and pressurization treatment was evenly applied to the entire surface of the test piece that overlaps with the PET film.
After the completion of the heat and pressurization treatment, the surface of the mirror plate that was in direct contact with the test piece was visually observed, and the presence or absence of transfer of the ink receiving layer to the mirror plate, and if there was transfer, the degree of transfer. From the viewpoint, the strength of the ink receiving layer was evaluated according to the following evaluation criteria. The results are shown in Table 5.
(Evaluation criteria)
A: No transfer of the ink receiving layer to the mirror plate is observed, and the ink receiving layer has sufficient strength to withstand high-speed super calendar processing.
B: Although some transfer of the ink receiving layer to the mirror surface plate is observed, the ink receiving layer has enough strength to withstand high-speed super calendar processing.
C: The transfer of the ink receiving layer to the mirror plate is clearly observed, and the ink receiving layer is not strong enough to withstand the high-speed super calendar processing.

[Water resistance of ink receiving layer]
Using the same desktop inkjet printer used in the evaluation of dot bleeding described above, printing (solid printing) was performed on the entire surface of the ink receiving layer of the recording sheet for inkjet with black ink at a density of 100%. Then, the ink after printing was completely dried.
Next, the printed inkjet recording sheet was immersed in a sufficient amount of tap water for 1 minute, and the ink receiving layer was rubbed with a finger in the tap water in that state. Next, the state of the ink receiving layer was visually observed, and the water resistance of the ink receiving layer was evaluated according to the following evaluation criteria from the viewpoint of the presence or absence of breakage and peeling of the ink receiving layer and the degree of breakage or peeling. The results are shown in Table 5. As described above, the reason why the black ink is used for printing on the recording sheet for an inkjet is to make it possible to clearly see whether or not the ink receiving layer is broken or peeled off.
(Evaluation criteria)
A: No breakage or peeling of the ink receiving layer was observed, and the ink receiving layer has excellent water resistance.
B: The ink receiving layer is slightly broken or peeled off, but there is no problem in actual use, and the ink receiving layer has good water resistance.
C: The ink receiving layer is clearly broken or peeled off, there is a problem in actual use, and the ink receiving layer is inferior in water resistance.

As is clear from the above results, the inkjet recording sheets of Examples 1 to 8 had a good effect of suppressing dot bleeding and good ink drying properties, and had good characteristics as an inkjet recording sheet. All of these inkjet recording sheets had good strength and water resistance of the ink receiving layer.

On the other hand, in the recording sheet for an inkjet of Comparative Example 1, the strength of the ink receiving layer was insufficient because polyvinyl alcohol was not used as a binder.
In the recording sheet for inkjet of Comparative Example 2, the ratio of the total content of the cationic styrene resin and polyvinyl alcohol to 100 parts by mass of the total content of the first and second aggregated light calcium carbonate was too low. The water resistance of the ink receiving layer was insufficient.
In the recording sheets for inkjet of Comparative Examples 3 and 4, the ratio of the content of polyvinyl alcohol to 100 parts by mass of the total content of the first and second aggregated light calcium carbonate was too high, so that the ink receiving layer was water resistant. The sex was inadequate.

In the recording sheet for an inkjet of Comparative Example 5, dot bleeding was not suppressed because a cationic resin other than the cationic styrene resin was not used as the ink fixing agent.
The recording sheets for inkjet of Comparative Examples 6 and 7 did not use a cationic styrene resin as a binder, and the content of polyvinyl alcohol was based on 100 parts by mass of the total content of the first and second aggregated light calcium carbonates. The water resistance of the ink receiving layer was insufficient because the ratio was too high.

INDUSTRIAL APPLICABILITY The present invention has excellent inkjet printability and can be used as an inkjet recording sheet for performing high-speed supercalender processing.

1, 2, ... Ink recording sheet, 11 ... Base material, 11a ... First surface of base material, 11b ... Second surface of base material, 12 ... Ink receiving layer, 12a ... The first surface of the ink receiving layer, 12b ... the second surface of the ink receiving layer, 121 ... the first ink receiving layer, 121a ... the first surface of the first ink receiving layer, 121b ... 2nd surface of the 1st ink receiving layer, 122 ... 2nd ink receiving layer, 122a ... 1st surface of the 2nd ink receiving layer, 122b ... 2nd surface of the 2nd ink receiving layer

Claims (1)

A recording sheet for an inkjet that includes a base material and an ink receiving layer formed on at least one surface of the base material.
The ink receiving layer contains first and second aggregated light calcium carbonates having different average secondary particle diameters as pigments.
The ink receiving layer contains a cationic styrene resin and polyvinyl alcohol as a binder, and contains
The ink receiving layer contains a cationic resin other than the cationic styrene resin as an ink fixing agent.
In the ink receiving layer, the ratio of the total content of the cationic styrene resin and polyvinyl alcohol to the total content of the first and second aggregated light calcium carbonate is 11 to 25% by mass.
In the ink receiving layer, to the total content of the first and second aggregation precipitated calcium carbonate, the percentage content of the polyvinyl alcohol is state, and are 7% or less,
The average secondary particle size of the first aggregated light calcium carbonate is less than 1 μm, and the average secondary particle size of the second aggregated light calcium carbonate is 2 to 5 μm.
In the ink receiving layer, the ratio of [content (mass) of first aggregated light calcium carbonate]: [content (mass) of second aggregated light calcium carbonate] is 22:78 to 78:22. Ink recording sheet.

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