JP6974079B2 - Inkjet recording sheet - Google Patents

Description

The present invention relates to an inkjet recording sheet.

The information recording method using inkjet ink is widely used because it can easily obtain high-quality images in full color and can achieve high image quality close to that of silver halide photography due to recent technological advances.
The inks include 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. Examples include ink, and these inks are used properly according to the purpose.

The inkjet recording sheet is configured to include an ink receiving layer for absorbing ink to form a print or an image on a substrate such as paper. 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 a substrate.
The ink receiving layer is required to have good drying properties of the ink, and is further required to have other characteristics depending on the application. For example, an inkjet recording sheet in which ink bleeding is suppressed is advantageous for forming a clear image, has high versatility, and is important.

Such an inkjet recording sheet in which ink bleeding is suppressed includes a base material and an ink receiving layer formed on at least one surface of the base material, and the receiving layer is a pigment and a binder. (See Patent Document 1) is disclosed, wherein the pigment contains first and second aggregated light calcium carbonates having different average secondary particle sizes.

Japanese Unexamined Patent Publication No. 2015-193250

The inkjet recording sheet disclosed in Patent Document 1 can reduce the dot shape coefficient, which is an index of the degree of dot bleeding, to a minimum of 1.50, and can be reduced to an average of about 1.6. Therefore, it has an excellent effect of suppressing ink bleeding. When the dots are perfect circles, the dot shape coefficient is 1, and the closer the dot shape coefficient is to 1, the closer the dot shape is to a perfect circle, and the higher the effect of suppressing bleeding. As described above, the inkjet recording sheet disclosed in Patent Document 1 has a high effect of suppressing ink bleeding and can form a relatively clear image, but the effect of suppressing ink bleeding is further improved. , Can be expected to be used for different purposes.

For example, the image formed by the inkjet printing method may exhibit characteristics unique to the inkjet printer used. That is, the image formed by the inkjet printer may show a difference in the model of the inkjet printer. However, this model difference is extremely small and cannot be recognized unless the effect of suppressing ink bleeding on the inkjet recording sheet is remarkably high. In other words, an inkjet recording sheet that can recognize such a minute model difference is extremely useful as an evaluation sheet for evaluating the performance of ink or the performance of an inkjet printer, for example.

Therefore, it is an object of the present invention to provide an inkjet recording sheet capable of highly suppressing ink bleeding.

The present invention is an inkjet recording sheet comprising a substrate and an ink receiving layer formed on the surface of at least one of the substrates, wherein the ink receiving layer is an average secondary particle as a pigment. The ink receiving layer contains hollow particles and polyvinyl alcohol as a binder, respectively, and contains the first and second aggregated light calcium carbonates having different diameters. In the ink receiving layer, the first and second ink receiving layers are contained. The ratio of the content of the polyvinyl alcohol to the total content of the aggregated light calcium carbonate is 4 to 17% by mass, and the total content of the first and second aggregated light calcium carbonate in the ink receiving layer. Provided is an ink recording sheet in which the ratio of the content of the hollow particles to the ink is 23% by mass or less.

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 (mass) of first aggregated light calcium carbonate]: [content (mass) of second aggregated light calcium carbonate] is 22:78 to 78:22. It is preferable to have.

According to the present invention, there is provided an inkjet recording sheet capable of highly suppressing ink bleeding.

It is sectional drawing which shows typically one Embodiment of the inkjet recording sheet of this invention. It is sectional drawing which shows typically the other embodiment of the ink jet recording sheet of this invention. It is the microscope image data of the surface of the ink jet recording sheet at the time of the evaluation of Example 1. It is the microscope image data of the surface of the ink jet recording sheet at the time of the evaluation of Example 2. It is the microscope image data of the surface of the ink jet recording sheet at the time of the evaluation of Example 3. It is the microscope image data of the surface of the ink jet recording sheet at the time of evaluation of Example 4. 6 is microscopic image data of the surface of the inkjet recording sheet at the time of evaluation of Example 5. 6 is microscopic image data of the surface of the inkjet recording sheet at the time of evaluation of Example 6. It is the microscope image data of the surface of the ink jet recording sheet at the time of evaluation of Example 7. 8 is microscopic image data of the surface of the inkjet recording sheet at the time of evaluation of Example 8. 9 is microscopic image data of the surface of the inkjet recording sheet at the time of evaluation of Example 9. It is the microscope image data of the surface of the ink jet recording sheet at the time of evaluation of Example 10. It is the microscope image data of the surface of the ink jet recording sheet at the time of evaluation of Example 11. It is the microscope image data of the surface of the ink jet recording sheet at the time of evaluation of Example 12. It is the microscope image data of the surface of the ink jet recording sheet at the time of evaluation of Example 13. It is the microscope image data of the surface of the ink jet recording sheet at the time of evaluation of Example 14. It is the microscope image data of the surface of the ink jet recording sheet at the time of evaluation of Example 15. It is the microscope image data of the surface of the ink jet recording sheet at the time of evaluation of the comparative example 1. It is the microscope image data of the surface of the ink jet recording sheet at the time of evaluation of the comparative example 2.

<< Inkjet recording sheet >>
The ink-receiving recording sheet of the present invention is an ink-inking recording sheet comprising 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 hollow particles and polyvinyl alcohol as a binder, respectively, and contains the first and second aggregated light calcium carbonates having different average secondary particle diameters. The ratio of the content of the polyvinyl alcohol to the total content of the first and second aggregated light calcium carbonate is 4 to 17% by mass, and in the ink receiving layer, the first and second aggregated light calcium carbonate The ratio of the content of the hollow particles to the total content of calcium is 23% by mass or less.

The ink jet recording sheet of the present invention has good ink drying property and can highly suppress ink bleeding because the ink receiving layer has the above-mentioned limited composition.
The inkjet recording sheet of the present invention can highly suppress ink bleeding, and its effect is significantly higher than that of the conventional inkjet recording sheet, so that an extremely clear and high-quality image can be formed.

For example, in the image formed by the inkjet printing method, there may be a difference in the model of the inkjet printer, reflecting the characteristics peculiar to the inkjet printer used. This model difference is extremely small, and it is difficult to recognize when the conventional inkjet recording sheet is used. On the other hand, the inkjet recording sheet of the present invention can form a clear and high-quality image as described above, so that such a model difference can be easily detected. Therefore, the inkjet recording sheet of the present invention is extremely suitable as an evaluation sheet for evaluating the performance of ink and the performance of an inkjet printer.

The advanced ink bleeding suppressing effect of the inkjet recording sheet of the present invention can be confirmed, for example, by calculating the dot shape coefficient of the printed dots. The dot shape coefficient becomes 1 when the dot is a perfect circle, and becomes a value closer to 1 as the dot shape approaches the perfect circle, that is, the higher the dot bleeding suppressing effect. In other words, the dot shape coefficient becomes larger as the shape of the dots is farther from the perfect circle, that is, as the dots are blurred.

The dot shape coefficient can be calculated by measuring the perimeter and area of the printed dots and using these measured values by the following formula. The perimeter and area of the dots can be determined, for example, by observing the dots with a microscope and, if necessary, using an image analysis device in combination to analyze the acquired microscope image data.
Dot shape coefficient = (perimeter) ² / (4π x area)

When 20 to 40 (for example, 30) dots are printed on the inkjet recording sheet of the present invention in a size of, for example, 2 cm × 2 cm, the average value of the dot shape coefficients calculated for these dots is preferably. It is less than 1.5, more preferably 1.48 or less, still more preferably 1.46 or less, and may be, for example, either 1.37 or less and 1.3 or less.
On the other hand, the lower limit of the average value of the dot shape coefficients is 1. The average value is preferably 1.15 or more in that the inkjet recording sheet can be manufactured more easily.

In the inkjet recording sheet of the present invention, the average value of the dot shape coefficients can be appropriately adjusted so as to be within a range set by arbitrarily combining any of the above-mentioned preferable lower limit values and upper limit values. For example, the average value of the dot shape coefficients is preferably 1 or more and less than 1.5, more preferably 1-1.48, still more preferably 1-1.46, and for example, 1-1.37 and 1 to 1. It may be any one of 1.3. However, these are just examples.

The inkjet recording sheet of the present invention is not particularly limited as long as it includes the base material and the ink receiving layer. For example, the inkjet recording sheet may be one that has been subjected to calendar processing (smoothing processing) or one that has undergone high-speed super calendar processing.

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.

In the calendar-processed inkjet recording sheet, the surface of the ink receiving layer is smoothed. Therefore, such an inkjet recording sheet usually has worse ink drying properties in the ink receiving layer than an inkjet recording sheet that has not been calendared.
On the other hand, the inkjet recording sheet of the present invention is provided with the ink receiving layer having the above-mentioned limited composition, so that the ink drying property in the ink receiving layer is good even if the ink receiving layer is subjected to calendar processing. Is.

<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, "normal 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, a method of further coating the composition for the ink receiving layer on the dried coating layer and further ink receiving on the undried coating layer. Any method of applying the layer composition may be used.
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 method for applying the composition for the ink receiving layer is not particularly limited, and any method may be used as long as it can apply a liquid material. 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 the drying temperature and the drying time may be appropriately set according to the drying method.

Formation of the ink receiving layer on the substrate is preferably 2 g / ^{m 2} or more, more preferably 3.5 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 greater 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. For example, the amount of the ink receiving layer formed on the substrate may be any of ^{30 g / m 2} or less, 25 g / m ² or less, and 20 g / m ^{2 or less.}

The amount of the ink receiving layer formed can be appropriately adjusted within a range set by arbitrarily combining any of the above-mentioned preferable lower limit values and upper limit values. For example, the amount of the ink receiving layer formed may be preferably ^{2 to} 30 g / m 2, more preferably 3.5 to 25 g / m ² , and particularly preferably 5 to 20 g / m ^2. This is just one example.

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

In the inkjet recording sheet of the present invention, the value of the amount of the ink receiving layer formed on the substrate (g / m ² ) is the value of the thickness (μm) of the formed ink receiving layer, and the value of the ink receiving layer is the same as the value of the thickness (μm). It will be the same.

The ink jet recording sheet of the present invention may be provided with the ink receiving layer on at least one surface of the substrate, may be provided on only one side, or may be provided on both sides.
When the ink jet recording sheet of the present invention has ink receiving layers on both sides of a substrate, the 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 an ink receiving layer include the pigment, a binder, hollow particles, 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 transmission of water.
The composition for the ink receiving layer and the ink receiving layer contain, as the pigment (inorganic pigment), a first aggregated light calcium carbonate and a second aggregated light calcium carbonate having different average secondary particle sizes.

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, columnar, 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 (average primary particle size) of the primary particles can be obtained from, for example, observation results with a scanning electron microscope. The average particle size of the secondary particles can be determined, for example, by 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 average secondary particle sizes different from each other 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. For example, the average secondary particle size may be 0.2 μm or more.
Since the ink receiving layer contains the first aggregated light calcium carbonate, the effect of suppressing ink bleeding becomes higher when inkjet printing is performed 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 and 3 to 3. It may be any of 4 μm, but this is an example.
Since the ink receiving layer contains the second aggregated light calcium carbonate, the drying property of the ink becomes higher when inkjet printing is performed on the ink jet recording sheet. Here, "high drying property of 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, those having an average secondary particle size of any of the above 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 (eg, 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 2-5 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 ink jet recording sheet can be printed in color even when printed by a high-speed inkjet printer. The dryness of the ink is good.

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. When the ratio of [content (mass) of first aggregated light calcium carbonate]: [content (mass) of second aggregated light calcium carbonate] is within the above range, the ink in the inkjet recording sheet It is possible to achieve both the improvement of the effect of suppressing bleeding and the improvement of dryness in a more balanced manner, and the ink jet recording sheet has better ink dryness even when color printing is performed with a high-speed inkjet printer. Become.

In the composition for the ink receiving layer and the ink receiving layer, it is preferable that the content of the first aggregated light calcium carbonate is high in that the effect of suppressing the bleeding of the ink is higher. As described above, when the content of the first aggregated light calcium carbonate is high, [content of first aggregated light calcium carbonate (mass)]: [content of second aggregated light calcium carbonate (mass)] The ratio may be, for example, 53:47 to 90:10, 58:42 to 84:16, and 63:37 to 78:22, but these are examples.

On the other hand, in the composition for the ink receiving layer and the ink receiving layer, it is preferable that the content of the second aggregated light calcium carbonate is large in that the drying property of the ink becomes higher. As described above, when the content of the second aggregated light calcium carbonate is high, [content of first aggregated light calcium carbonate (mass)]: [content of second aggregated light calcium carbonate (mass)] The ratio may be, for example, 47:53 to 10:90, 42:58 to 16:84, and 37:63 to 22:78, but these are examples.

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 inorganic pigments, and more specifically, non-aggregated light calcium carbonate (that is, light calcium carbonate in which primary particles are not aggregated to form secondary particles); Calcium carbonate other than the first and second aggregated light calcium carbonates such as the heavy calcium carbonate 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.

In the composition for the ink receiving layer, 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 is preferably 60 to 92% by mass. , 65-89% by mass, more preferably 70-86% 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, the term "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).

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 having an average secondary particle size of 2 to 5 μm. The ratio of [content of first aggregated light calcium carbonate (mass)]: [content of second aggregated light calcium carbonate (mass)] is 22:78 to The one that is 78:22 is mentioned.

[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 polyvinyl alcohol as the binder.
Polyvinyl alcohol is a component that has a great influence on the drying property and the bleeding suppressing effect of the ink mainly in the ink receiving layer. Polyvinyl alcohol is also a component that can affect the strength of the ink receiving layer.

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, further preferably 96 mol% or more, and particularly preferably 97 mol% or more. For example, it may be any of 97.3 mol% or more, 97.6 mol% or more, and 97.8 mol% or more. When the saponification degree of polyvinyl alcohol is at least the above lower limit value, the drying property and the bleeding suppressing effect of the ink in the ink receiving layer are further enhanced.
The upper limit of the saponification degree of polyvinyl alcohol is not particularly limited. For example, the degree of saponification of polyvinyl alcohol may be any of 100 mol% or less, 99.8 mol% or less, 99.6 mol% or less, and 99.3 mol% or less.

The degree of saponification of polyvinyl alcohol can be appropriately adjusted within a range set by arbitrarily combining any of the above-mentioned preferable lower limit values and upper limit values. For example, the degree of saponification of polyvinyl alcohol is preferably 90 to 100 mol%, more preferably 93 to 99.8 mol%, still more preferably 96 to 99.6 mol%, and particularly preferably 97 to 99.3 mol%. It may be any of 97.3 to 99.3 mol%, 97.6 to 99.3 mol%, and 97.8 to 99.3 mol%, but these are examples. be.

The degree of polymerization of polyvinyl alcohol is preferably 300 to 3000, more preferably 350 to 2800, further preferably 400 to 2600, and particularly preferably 450 to 2450. 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. Further, when the degree of polymerization of polyvinyl alcohol is not more than the above upper limit value, the drying property of the ink in the ink receiving layer becomes higher.

The composition for the ink receiving layer and the ink receiving layer may contain a binder other than the polyvinyl alcohol as long as the effect of the present invention is not impaired.
Examples of the other binder include water-soluble polymers other than the polyvinyl alcohol.

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

As for the polyvinyl alcohol and other binders, 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 determined according to the purpose. It may be selected as appropriate.

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 binder is preferably 80% by mass or more, more preferably 85% by mass or more. It is more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be, for example, 98% by mass or 100% by mass.

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 4 to 17% by mass, and 4.2. It is preferably ~ 16.5% by mass, more preferably 4.5 to 16% by mass, and particularly preferably 4.8 to 15.5% by mass. When the ratio is equal to or higher than the lower limit, the strength of the ink receiving layer is increased. Further, when the ratio is not more than the upper limit value, the effect of suppressing ink bleeding in the ink receiving layer becomes higher.

[Hollow particles]
The hollow particles are components for improving the effect of suppressing ink bleeding in the ink receiving layer.
The constituent material of the hollow particles may be either an organic material or an inorganic material.
The constituent materials constituting one hollow particle may be only one kind or two or more kinds, and when there are two or more kinds, the combination and the ratio thereof depend on the purpose. Can be selected as appropriate.

The hollow particles are not particularly limited as long as the whole shape is particulate and the hollow particles have a hollow portion. For example, the number of hollow portions contained in one hollow particle may be only one, or may be two or more.
Further, the hollow particles may have an opening connecting the inside and the outside of the hollow particles in a part of the outer shell thereof. It is important that the hollow particles have voids inside, and the shape of the outer shell is not particularly limited as long as the presence of the voids inside can be maintained.

Examples of the hollow particles having only one hollow portion per particle include those in which microcapsules known in the fields of medicine, pesticides and the like do not contain a solvent or a core substance. Such hollow particles can also be said to be, for example, particles formed so as to have only one hollow portion by the film-forming component forming the outer shell of the microcapsule.

Examples of the hollow particles having two or more hollow portions per particle include known porous particles.

The constituent material of the hollow particles is preferably an organic material, more preferably a resin.
Examples of the resin include latex containing natural rubber as a main component (natural rubber latex), modified latex containing modified rubber modified from natural rubber as a main component, synthetic resin and the like.

The synthetic resin may be a homopolymer in which one kind of monomer is polymerized, or may be a copolymer in which two or more kinds of monomers are copolymerized.
Examples of the copolymer include a styrene / (meth) acrylic acid ester copolymer, a styrene / (meth) acrylic acid copolymer, and the like. The styrene / (meth) acrylic acid ester copolymer is preferably, for example, a styrene / methyl (meth) acrylate copolymer, and more preferably a styrene / methyl methacrylate copolymer.

In addition, in this specification, "(meth) acrylic acid" is a concept including both "acrylic acid" and "methacrylic acid". The same applies to terms similar to "(meth) acrylic acid", for example, "(meth) acrylate" is a concept that includes both "acrylate" and "methacrylate", and is a "(meth) acryloyl group". "" Is a concept that includes both "acryloyl group" and "methacryloyl group".

The average particle size of the hollow particles is not particularly limited, but is preferably 0.35 to 3 μm, more preferably 0.4 to 2.7 μm, and preferably 0.45 to 2.4 μm. Especially preferable. When the average particle size of the hollow particles is at least the above lower limit value, the glossiness of the surface of the ink receiving layer becomes higher, and the effect of suppressing ink bleeding in the ink receiving layer becomes higher. When the average particle size of the hollow particles is not more than the upper limit value, the drying property of the ink in the ink receiving layer becomes higher.

The average particle size of the hollow particles is the particle size at 50% accumulation (D) obtained from the volume-based cumulative particle size distribution curve obtained by measuring the particle size distribution of the hollow particles using a Coulter counter. ₅₀ , median diameter).

The hollow ratio of the hollow particles is not particularly limited, but is preferably 40 to 85%, more preferably 50 to 80%. When the hollow ratio of the hollow particles is in such a range, the effect of using the hollow particles can be obtained more remarkably.
The hollow ratio (%) of the hollow particles is calculated from the theoretical value D ₁ of the density of the hollow particles and the measured value D ₂ of the density of the hollow particles by the formula “(D ₁ − D ₂ ) / D ₁ × 100”. ,Desired.

The thickness of the outer shell of the hollow particles is preferably 5 to 10% of the particle size of the hollow particles. When the thickness of the outer shell of the hollow particles is in such a range, the effect of using the hollow particles can be obtained more remarkably.

The shape of the hollow particles is not particularly limited as long as they are particulate and have a hollow portion in the ink receiving layer. For example, the shapes of the hollow particles do not have to match when the production of the hollow particles is completed and when the production of the inkjet recording sheet is completed. When a force is applied to the hollow particles during the manufacture of the inkjet recording sheet, the shape of the hollow particles may be deformed. In the present invention, even if the shape is different from the original shape due to the deformation, if the original shape before the deformation can be recognized as a particle shape and the hollow portion is provided even after the deformation. Such things are also treated as hollow particles. As described above, the inkjet recording sheet of the present invention exhibits the above-mentioned excellent effects by using the hollow particles whose shape is maintained in the form of particles and having a hollow portion.

In the composition for the ink receiving layer and the ink receiving layer, the ratio of the content of the hollow particles to the total content of the first and second aggregated light calcium carbonate is 23% by mass or less, and 22.3% by mass. % Or less, more preferably 21.6% by mass or less, and particularly preferably 21% by mass or less. When the ratio is not more than the upper limit value, the effect of suppressing ink bleeding in the ink receiving layer is high, and the drying property of the ink is further improved.
The lower limit of the ratio is not particularly limited as long as it is larger than 0% by mass. For example, the ratio may be any of 0.2% by mass or more, 0.4% by mass or more, 0.6% by mass or more, and 0.8% by mass or more. When the ratio is at least the lower limit value, the effect of suppressing ink bleeding 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 hollow particles to the total content of the first and second aggregated light calcium carbonates is a preferable lower limit value and upper limit value of any one of the above. Can be appropriately adjusted so as to be within the range set by any combination of. For example, the ratio is preferably greater than 0% by mass and 23% by mass or less, more preferably 0.2 to 23% by mass, still more preferably 0.4 to 22.3% by mass, and particularly preferably 0.6 to 21. It is 6.6% by mass, most preferably 0.8 to 21% by mass. However, these are just examples.

[Other ingredients]
Examples of the other components include a solvent, an ink fixing agent, a polyvalent metal salt, a pH adjusting agent, an antifoaming agent, a defoaming agent, a mold release agent, a foaming agent, an antioxidant, an antiseptic agent, and a water resistant agent. Examples thereof include components usually used in the ink receiving layer of a recording sheet for inkjet, such as a paper strength enhancer, a coloring dye, a coloring pigment, a dye fixing agent, a pigment dispersant, a fluorescent whitening agent, and an ultraviolet absorber.
As the other components, one type may be used alone, or 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)
To prepare the dispersion or solution when the pigment, binder, hollow particles, or other components other than the solvent are blended as a dispersion or solution to produce a composition for an ink receiving layer. When no solvent is blended in addition to the solvent used, the solvent means the solvent used to prepare the dispersion or solution.
On the other hand, when a solvent is separately blended in addition to the solvent used for preparing the dispersion or solution, the solvent is the solvent used for preparing the dispersion or solution and the solvent separately. It means both the compounded solvent and.
When the pigment, the binder, the hollow particles, or the other components other than the solvent are all 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.

(Ink fixing agent)
The ink fixing agent is a component for fixing ink in the ink receiving layer.
Examples of the ink fixing agent include a cationic resin that exhibits cationic properties when dissolved or dispersed in water.

The cationic resin is preferably a monomer, oligomer or polymer of a primary amine, a secondary amine, a tertiary amine or a quaternary ammonium salt, and more preferably the oligomer or polymer.

Further preferred of the cationic resin are, for example, an alkylamine-epichlorohydrin copolymer; an acrylic polymer having a secondary amino group, a tertiary amino group or a quaternary ammonium group; polyvinylamine; polyvinylamidine; 5-membered ring amidins; 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; diallyldimethylammonium chloride polymer; polymer of allylamine salt, a homopolymer of vinylbenzyl triallyl ammonium salts or copolymers; dialkylaminoethyl Examples thereof include (meth) acrylate quaternary salt copolymers; acrylamide-diallylamine salt copolymers; aluminum salts such as polyaluminum chloride and polyaluminum acetate.
Among them, the cationic resin is particularly preferably an alkylamine-epichlorohydrin copolymer, and most preferably a dimethylamine-epichlorohydrin copolymer.

In the present specification, the polymer also includes a polycondensate.
Further, the description of "derivative" and "class" means that one or more hydrogen atoms of the original compound are substituted with a group other than the 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.

As the ink 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 may be appropriately selected according to the purpose. ..

When the composition for the ink receiving layer and the ink receiving layer contain an ink fixing agent, the ratio of the content of the ink fixing agent to the content of the pigment in the composition for the ink receiving layer and the ink receiving layer is 1 to 1. It is preferably 40% by mass, more preferably 1 to 25% by mass, for example, 1 to 15% by mass, 1 to 10% by mass, 1 to 6% by mass, or 1 to 4% by mass. There may be. However, these ratios are just one example of what is preferable. When the ratio is at least the lower limit value, the effect of using the ink fixing agent can be obtained more remarkably. Further, when the ratio is not more than the upper limit value, excessive use of the ink fixing agent is suppressed.

(Multivalent metal salt)
The polyvalent metal salt is a component for improving the drying property of the ink in the ink receiving layer.
The polyvalent metal salt 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 (ו 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 dryness and color density of the ink in the ink receiving layer, and the ink jet printability such as water resistance and scratch resistance of the ink receiving layer in a well-balanced manner, and is highly safe. 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.

One type of polyvalent metal salt may be used alone, or two or more types may be used in combination. 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, those containing one or more selected from the group consisting of calcium chloride, magnesium chloride and potassium aluminum sulfate are preferable. Those containing potassium aluminum sulfate are more preferable, and when potassium aluminum sulfate is contained, those containing either or both of calcium chloride and magnesium chloride are 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, 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, the 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.

<Manufacturing method of composition for ink receiving layer>
The composition for an ink receiving layer can be produced by blending the pigment, the binder, the hollow particles, and, if necessary, the other components, and sufficiently stirring these blending components. In the composition for the ink receiving layer, the pigment and the hollow particles are preferably dispersed, and the binder is 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 hollow particles, or the other components other than the solvent, or may be used alone without being mixed with these components in advance. You may.

However, at the time of producing the composition for the ink receiving layer, the surface gloss of the ink receiving layer tends to be higher by blending the pigment before the binder (the pigment and the binder are blended in this order).

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 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 according to 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 synthetic resins such as resins, phenol resins, urea resins, polyurethanes and polyimides.

The base material may be composed of a single layer, may be composed of two or more layers, or may be composed of a plurality of layers, and 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 the 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.

The thickness of the base material is not particularly limited as long as the shape of the base material is in the form of a sheet or a film, 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, it is handled as an inkjet recording sheet. The sex becomes better.
When the base material is composed of a plurality of layers, the total thickness of each layer may be set to be the above-mentioned preferable thickness of the base material.

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

<< Manufacturing method of inkjet recording sheet >>
The inkjet recording sheet of the present invention can be manufactured 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 inkjet recording sheet 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 matte super calendar, a matte calendar, and the like. It can be done using the calendar device of.

The calender device may be either an off type separated from the coater or an on type integrated with the coater.
Among the calender devices, the rolls include, for example, rigid rolls and elastic rolls.
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 calender processing conditions are appropriately selected according to the required quality, such as the temperature of the rigid roll, the calender pressure, the number of nip, the roll speed, and the paper moisture before the calender processing.

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

The pressure during calender processing is not particularly limited, but can be, for example, 50 to 400 kN / m.
The pressure during calendar processing is adjusted, for example, by adjusting the pressure when a pair of rolls in the calendar device is pressed against the inkjet recording sheet to be processed and the distance between the roll surfaces of the pair of rolls. 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 inkjet recording sheet to be processed.

Next, the overall configuration of the inkjet recording sheet of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing an embodiment of an inkjet recording sheet of the present invention. Further, FIG. 2 is a cross-sectional view schematically showing another embodiment of the inkjet recording sheet 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 in FIG. 1.
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. It is not always the case.

The inkjet recording sheet 1 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.
Further, the ink jet recording sheet 2 shown in FIG. 2 is on the first surface 11a and the other surface (sometimes referred to as “second surface” in the present specification) 11b (that is, on both sides) of the base material 11. Both are provided with an ink receiving layer 12. Regarding the two ink receiving layers 12 and 12 in the inkjet recording sheet 2, those provided on the first surface 11a of the base material 11 are shown as the first ink receiving layer 121 as necessary, 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 surface (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 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 ink jet recording sheet of the present invention, the ink receiving layer may be provided on the entire surface of the surface to be formed on the substrate, or may be provided only in a part of the region.
When the inkjet recording sheet of the present invention is viewed from above on the side where the ink receiving layer is provided and viewed in a plan view, 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 as described above can be arbitrarily set according to the purpose, and are not particularly limited. For example, the shapes of the ink receiving layer and the base material when viewed in a plan view may be similar to each other or dissimilar to each other.

The inkjet recording sheet of the present invention may be provided with 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 adhesive layer include those for attaching and fixing an inkjet recording sheet to an object. When the recording sheet for inkjet is provided with such an adhesive layer or an adhesive layer, it is preferable that the 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, by laminating the overlapped surfaces of the sheets and then peeling them off, it is possible to make the laminated surfaces of the sheets peeled off again without damaging them. 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 inkjet recording sheet 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 to the pressure-sensitive adhesive layer. It does not have to be. Further, the inkjet recording sheet provided with the pressure-sensitive adhesive layer may be in a state in which one inkjet recording sheet is folded and removably bonded by the 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, binders and hollow particles shown below were used.

In the following Examples and Comparative Examples, the raw materials shown below were used as raw materials other than the pigment, the binder and the hollow particles.
[Ink fixer]
(C) -1: Alkylamine-epichlorohydrin polycondensate (“Jetfix 260” manufactured by Satoda Kako Co., Ltd., molecular weight 710)
[Multivalent metal salt]
(D) -1: Calcium chloride (d) -2: Potassium aluminum sulfate (potassium alum)

<< Manufacturing of Inkjet Recording Sheets >>
[Example 1]
Ink (a) -1 (25 parts by mass), pigment (a) -2 (75 parts by mass), binder (b) -2 (8.3 parts by mass (solid content)), hollow particles (Y) -1 (1 part by mass), ink fixing agent (c) -1 (2.78 parts by mass (solid content)), polyvalent metal salt (d) -1 (4.29 parts by mass) and polyvalent metal salt (d). -2 (2.14 parts by mass) is added, and the mixture is stirred at 1400 rpm for 1 hour at room temperature using a stirrer to disperse these components to obtain a composition for an ink receiving layer which is a dispersion liquid. rice field.
Then, using a wire bar coater, the composition for the ink receiving layer obtained above is applied onto the base material (z) -1 and dried at 105 ° C. to receive ink having a thickness of about 10 μm. The layer was formed at an amount of 10 g / m ² to form an inkjet recording sheet.
Further, the 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 ink jet recording sheet was pressed twice by passing the ink jet recording sheet between the roll surfaces.

[Examples 2 to 14, Comparative Examples 1 to 2]
An inkjet recording sheet was produced by the same method as in Example 1 except that one or both of the types and amounts of the components of the composition for the ink receiving layer were set as shown in Table 5.
In addition, the description of "-" in the column of the compounding component in the following table means that the component is not compounded.

[Example 15]
An inkjet recording sheet was manufactured by the same method as in Example 3 except that the distance between the roll surfaces of the pair of metal rolls was set to 100 μm instead of 25 μm during the calendar processing at room temperature.

<< Evaluation of inkjet recording sheet >>
The following items were evaluated for the inkjet recording sheet obtained above. The results are shown in Table 5.

[Dot bleeding]
Dot bleeding was evaluated by the dot shape coefficient. The evaluation sample is printed (single color printing) on the ink receiving layer of the inkjet recording sheet 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 inkjet recording sheet was taken, and the image was analyzed using a dot analyzer (“DA6000” manufactured by Oji Measuring Instruments Co., Ltd.). Specifically, the perimeter and area of the dots were measured, and the dot shape coefficient was calculated by the following formula.
Dot shape coefficient = (perimeter) ² / (4π x area)

In this evaluation, the dot shape coefficient measured by a desktop inkjet printer (printing speed 250 f (76.2 m) / min) is the dot measured by a high-speed inkjet printer (printing speed 500 f (152.4 m) / min). It was confirmed in advance that there was a sufficient correlation with the shape coefficient.

The dot shape coefficient was calculated for about 30 dots by the above method to obtain an average value, and dot bleeding was evaluated according to the following evaluation criteria. The results are shown in Table 6. The numerical value in parentheses in the column of "dot bleeding" in Table 6 is the average value of the dot shape coefficients.
(Evaluation criteria)
A: The average value of the dot shape coefficients is less than 1.3, the dots are extremely close to a perfect circle, and the bleeding of the dots is extremely suppressed.
B: The average value of the dot shape coefficients is 1.3 or more and less than 1.5, the dots are fairly close to a perfect circle, and the bleeding of the dots is highly suppressed.
C: The average value of the dot shape coefficients is 1.5 or more and less than 1.8, the dots are close to a perfect circle, and the bleeding of the dots is appropriately suppressed.
D: The average value of the dot shape coefficients is 1.8 or more and less than 2.0, and dot bleeding is suppressed.
E: The average value of the dot shape coefficients is 2.0 or more, and the bleeding of dots is not suppressed.

Further, the microscope image data of the surface of the inkjet recording sheet obtained at this time is shown in FIGS. 3 to 19 for each Example and Comparative Example. FIG. 3 is the microscopic image data in Example 1, FIG. 4 is the microscopic image data in Example 2, and thereafter, corresponding to the numerical order of the examples, FIGS. 17 to 17 are the microscopic image data of Examples 3 to 15. 18 is the microscopic image data in Comparative Example 1, and FIG. 19 is the microscopic image data in Comparative Example 2.

[Drying of ink]
Using an inkjet printer, printing was performed on the ink receiving layer of the inkjet recording sheet 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 inkjet recording sheet and firmly pressed against the printed surface to bring them into close contact with each other.
Next, while the film is in close contact with the printing surface, visually observe from the side opposite to the contact surface with the printing surface to confirm the maximum printing density of the ink not transferred from the printing surface to the contact surface. Then, the dryness of the ink was evaluated according to the following evaluation criteria. The results are shown in Table 6. The numerical value in parentheses in the column of "dryness of ink" in Table 6 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.

As is clear from the above results, the inkjet recording sheets of Examples 1 to 15 had good ink drying properties and had excellent basic characteristics as an inkjet recording sheet. In the inkjet recording sheets of Examples 1 to 15, dot bleeding was highly suppressed. The inkjet recording sheet of Example 15 differs from the inkjet recording sheet of other examples in that the pressure during calendar processing is low, but has good characteristics like the inkjet recording sheet of other examples. Had.

On the other hand, the inkjet recording sheet of Comparative Example 1 moderately suppressed the dot bleeding, but this suppressing effect was inferior to that of the inkjet recording sheets of Examples 1 to 15. This was because the ink receiving layer of the inkjet recording sheet of Comparative Example 1 did not contain hollow particles. On the other hand, the inkjet recording sheet of Comparative Example 1 had good ink drying properties.

The inkjet recording sheet of Comparative Example 2 was inferior in the drying property of the ink, although the dot bleeding was highly suppressed. This was because the ratio of the content of the hollow particles to the total content of the first and second aggregated light calcium carbonates in the ink receiving layer of the inkjet recording sheet of Comparative Example 2 was too high.

The present invention can be used as an inkjet recording sheet for the purpose of forming a clear image, and can also be used as an inkjet recording sheet for performing calendar processing. The present invention can also be used as an ink performance evaluation paper and an inkjet printer performance evaluation paper.

1, 2, ... Inkjet recording sheet, 11 ... Base material, 11a ... First surface of the base material, 11b ... Second surface of the 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 ... Second surface of the first ink receiving layer, 122 ... Second ink receiving layer, 122a ... First surface of the second ink receiving layer, 122b ... Second surface of the second ink receiving layer

Claims (1)

An inkjet recording sheet comprising a substrate and an ink receiving layer formed on at least one surface of the substrate.
The ink receiving layer contains first and second aggregated light calcium carbonates having different average secondary particle sizes as pigments.
The ink receiving layer contains hollow particles and polyvinyl alcohol as a binder, respectively.
In the ink receiving layer, the ratio of the content of polyvinyl alcohol to the total content of the first and second aggregated light calcium carbonate is 4 to 17% by mass.
In the ink receiving layer, to the total content of the first and second aggregation precipitated calcium carbonate, the percentage of the content of the hollow particles is state, and are than 23% by weight,
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. Inkjet recording sheet.

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