JP2000225767A - Recording sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a recording sheet of high ink absorbability and high color density provided when recording is carried out. SOLUTION: A recording sheet contains silica gel as an ink absorption material, and silica gel is provided with the 1.5-3.5 ml/g pore volume in the range of 1-100 nm pore radius based on the nitrogen absorption process, 500-1000 m2/g specific surface area and 300 ml/100 g or more oil absorption amount, and the recording sheet is provided with a feature of not changing substantially its pore volume and oil absorption amount after being dispersed in water, separated and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a recording sheet, and more particularly to a recording sheet for an ink jet recording system.

[0002]

2. Description of the Related Art The ink jet recording method is applied to various printers, plotters, facsimile machines and the like because of low noise, high speed recording and easy colorization. The inkjet recording method is
Since an ink containing a large amount of solvent is used, the recording sheet needs to have a property of absorbing and adsorbing the solvent and dye in the ink.

In order to satisfy such demands, for example, Japanese Patent Application Laid-Open No. 62-282966 and Japanese Patent Application Laid-Open
Japanese Patent Laid-Open Publication No. HEI 9-214605 proposes applying porous silica to a substrate such as paper. Further, Japanese Patent Application Laid-Open No. 9-176988
In the publication, paper containing silica internally having an oil absorption of 250 to 350 ml / 100 g is proposed.

Conventionally, silica having a large ink absorption capacity has a small specific surface area, and silica used for a recording sheet has a small specific surface area.
Conversely, those having a large specific surface area had a small ink absorption capacity. For this reason, in a recording sheet containing silica, there is a tendency that the higher the ink absorptivity, the lower the color density at the time of recording, and conversely, the higher the color absorptivity, the lower the ink absorptivity.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a recording sheet having a high ink absorbency and a high color density upon recording.

[0006]

The present invention is a recording sheet containing silica gel as an ink absorbing material, wherein the silica gel has a pore radius of 1 to 100 nm by a nitrogen adsorption method.
Pore volume 1.5 to 3.5 ml / g, specific surface area 5
00-1000m ² / g, oil absorption 300ml / 100g
Nitrogen adsorption of silica gel obtained by dispersing 1% by weight of the silica gel in water having an electric conductivity of 1 μS / cm or less, separating and drying at 120 ° C. for 5 hours using a stationary dryer. The recording sheet is characterized in that the pore volume and the oil absorption in the pore radius range of 1 to 100 nm by the method are respectively 90% or more of the values before being dispersed in water.

The silica gel used in the recording sheet of the present invention has a pore volume of 1.5 to 3.5 ml / g in a pore radius range of 1 to 100 nm by a nitrogen adsorption method. Hereinafter, when simply referred to as the pore volume, the pore radius is 1 to 3 according to the nitrogen adsorption method.
It shall mean a pore volume in the range of 100 nm. The pore volume is determined by analyzing the result of measurement at a nitrogen relative pressure of 0 to 0.99 by the nitrogen adsorption method using the BJH method. For the measurement, for example, Kantachrome Autosorb manufactured by Kantachrome Co., Ltd. can be adopted.

If the pore volume is less than 1.5 ml / g, it is not appropriate because the ink absorbency of the recording sheet is insufficient. If the pore volume exceeds 3.5 ml / g,
This is unsuitable because silica gel having a high specific surface area cannot be practically obtained. The pore volume of silica gel is 1.8-3.5 ml
/ G is more preferable.

The specific surface area of the silica gel used in the present invention is
500-1000m^Two/ G. Larger specific surface area
However, because the number of adsorption sites on the surface increases,
The color density increases. Specific surface area is 600-1000
m^Two/ G is more preferable. Conventional sedimentation
Rica has a specific surface area of approximately 400 m as described above.^Two/
g or less, but the silica gel used in the present invention is
It has a higher specific surface area. Primary particles of this silica gel
The diameter is 2.2 g / cm of the true specific gravity of silica gel. ^ThreeSphere
It is 4-7 nm when calculated assuming non-porous particles of
Can be distinguished from precipitated silica with a primary particle size of 15 nm or more
You. The specific surface area is also determined by the nitrogen adsorption method as in the case of the pore volume.
The results measured at a relative nitrogen pressure of 0 to 0.99 were determined by the BET method.
Analyze with.

The silica gel used in the present invention has an oil absorption of 300 ml / 100 g or more. Oil absorption 300ml
When the weight is less than / 100 g, the ink absorbency of the recording sheet is insufficient, which is inappropriate. Oil absorption 350ml /
It is more preferable that the weight is 100 g or more. Oil absorption is
It is measured according to JIS K5101. That is, boiled linseed oil is added to the sample while kneading until the whole sample becomes one lump. The oil absorption is represented by the volume of boiled linseed oil per 100 g of the sample. In this specification, the amount of oil absorption by this measurement method is simply referred to as the amount of oil absorption.

The silica gel used in the present invention is separated by dispersing 1% by weight of the silica gel in water having an electric conductivity of 1 μS / cm or less and separating it by using a stationary drier.
The silica gel obtained by drying at 5 ° C. for 5 hours has a pore volume and an oil absorption of 90% or more of the values before being dispersed in water, respectively.

Conventionally, silica having a high oil absorption has been obtained by supercritical drying. However, when this silica is placed in a solvent such as water and dried again, its pore volume and oil absorption become extremely small. The silica gel used in the present invention has a high oil absorption. Even if the silica gel is dried again in a solvent such as water, its pore volume and oil absorption hardly change. Therefore, during the production of the recording sheet, there is no decrease in the pore volume or apparent contraction of the volume, and the oil absorption can be maintained large, so that the absorbability of the recording sheet is not impaired.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The average particle size of the silica gel used in the present invention can be arbitrarily selected depending on the method of use.
It is preferably 30 μm. Average particle size is 1-2
It is more preferable that the thickness be 0 μm. Furthermore, when the particle shape of the silica gel is spherical, it is easy to improve the dispersibility when blended into paper or the like, and to form a uniform coating layer when forming a coating layer on the substrate surface. It is preferred. Here, the spherical shape includes not only a true spherical shape but also a slightly distorted shape. In this case, the ratio of the minor axis to the major axis is 0.
It is preferably from 8 to 1.0.

[0014] Spherical silica gel, when converted to silicic acid component of alkali silicate aqueous solution to SiO _2, the SiO ₂
Aqueous alkali silicate solution containing at least one anion selected from the group consisting of chloride ions, sulfate ions, nitrate ions and fluoride ions in a proportion of 0.1 to 0.5 equivalent per 1 mol Can be produced by emulsifying in an organic solvent and gelling with carbon dioxide gas. A more preferable range of the content of the anion is 0.2 to 0.4.
Is equivalent.

As the alkali silicate, sodium silicate, potassium silicate and the like can be used. Sodium silicate is preferred in that it is economical. Hereinafter, a description will be given of sodium silicate as an example, but the same applies to the case of using potassium silicate.

The content of the silicic acid component in the aqueous sodium silicate solution is preferably 3 to 20% by weight in terms of SiO ₂ . A more preferable range of the silicic acid component in an aqueous sodium silicate solution is 5 to 15% by weight in terms of SiO _2. The SiO ₂ / Na ₂ O ratio of the aqueous sodium silicate solution is preferably 1 to 4. A more preferred range of the SiO ₂ / Na ₂ O ratio is 2.5 to 3.5.

The above anion is preferably contained in the aqueous solution of sodium silicate by adding a water-soluble salt. Such salts include metal chlorides,
Metal sulfates, metal nitrates and metal fluorides are preferred. Specifically, alkali metal chloride, alkali metal sulfate,
Alkali metal nitrates, alkali metal fluorides, alkaline earth metal chlorides and alkaline earth metal nitrates are preferred.
Particularly, alkali metal chlorides such as sodium chloride and potassium chloride, and alkali metal sulfates such as sodium sulfate are preferable.

As the organic solvent for emulsifying the aqueous solution of sodium silicate, a substance capable of dissolving carbon dioxide gas is preferable.
Such organic solvents include, for example, aliphatic hydrocarbons such as hexane and octane, aromatic hydrocarbons such as xylene and toluene, chlorinated hydrocarbons such as chloroform, trichloroethylene and tetrachloroethylene, trichlorotrifluoroethane, and dichlorotrifluoroethane. And chlorinated fluorinated hydrocarbons such as dichlorofluoroethane and dichloropentafluoropropane.

It is preferable that a surfactant is dissolved and used in the organic solvent. As the surfactant, polyethylene glycol fatty acid ester, polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, sorbitan fatty acid ester, and polyoxyethylene sorbitan fatty acid ester are preferable. Its usage is
0.05 to 10% by weight based on the organic solvent is preferred.

When an aqueous solution of sodium silicate is added to an organic solvent and emulsified, an aqueous solution of sodium silicate with respect to the organic solvent in a volume ratio of 0.1 to 1 is formed so as to form a W / O type emulsion. It is preferable to add them. The emulsification is preferably performed by means such as a turbine type stirrer or a high-speed shearing type emulsifier. In the emulsion, the droplets of the aqueous sodium silicate solution preferably have an average particle diameter of 1 to 30 μm.

Next, the aqueous alkali silicate solution is gelled by introducing carbon dioxide gas into the emulsion. Since the gel is formed in an emulsified state, spherical silica gel is obtained. The partial pressure and flow rate of the carbon dioxide gas can be appropriately selected.

After completion of the gelation, the organic solvent is removed, and a heat treatment or a chemical treatment is appropriately performed, followed by washing and drying. At the end of gelation, silica gel with high oil absorption and high specific surface area has already been generated, so heat treatment and hydrothermal treatment under alkaline conditions conventionally performed to obtain silica with high oil absorption are not performed here. .

As the drying method, known methods can be used, but in order to prevent shrinkage of pores during drying, flash drying, spray drying, freeze drying, supercritical drying and the like can be preferably used. In addition, before drying, the water can be replaced with an organic solvent having a low surface tension, which is compatible with water, and then dried. This can prevent the pores from shrinking during drying.

After the silica gel used in the present invention is produced by the above-mentioned method, it is treated with an aqueous solution of an aluminate, calcium salt, magnesium salt, or the like, whereby the dye in the ink is fixed well. For example, when treated with an aqueous solution of aluminate, silica gel whose surface is modified with alumina is obtained. Further, by bringing a cationic resin containing a quaternary ammonium base into contact with silica gel, the fixability of the dye can be similarly improved.

The present invention is a recording sheet containing silica gel as an ink absorbing material. A first layer in which a coating layer containing the silica gel and the binder is formed on a substrate;
The recording sheet of the second aspect and the recording sheet of the second aspect containing the silica gel in a dispersed state inside the substrate can be preferably exemplified.

In the recording sheet of the first embodiment, when forming a coating layer containing the silica gel and the binder, it is preferable to prepare a coating liquid containing the silica gel and the binder and apply it to a substrate. .

As the binder, a natural or synthetic polymer can be used. For example, polyvinyl alcohol, silanol-modified polyvinyl alcohol, polyvinyl acetate,
Starch, carboxymethyl cellulose, gelatin, casein, chitosan and the like can be used. The amount of the binder used is preferably 5 to 50% by weight based on the silica gel. The total amount of the silica gel and the binder in the coating liquid is preferably 5 to 30% by weight.

The coating amount is preferably from 0.1 to 50 g / m ² . A more preferable coating amount is 5 to 40 g / m ² .
As a coating method, bar coating, die coating, blade coating, roll coating, air knife coating, dip coating, spin coating and the like can be used.

The coating layer thus obtained can be further glossed by subjecting it to a calender treatment or the like. Further, another layer can be formed on the coating layer. As the upper layer, specifically, a porous layer containing alumina hydrate is exemplified.

In the recording sheet of the second embodiment, the silica gel is preferably mixed with a resin such as pulp or polyethylene to form a sheet. The content of the silica gel can be arbitrarily selected in consideration of the purpose of use, the strength of the recording sheet, and the like. When the silica gel is added to the pulp, the content of the silica gel is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight of the recording sheet. When added to the resin, the content of the silica gel is preferably 1 to 70% by weight of the recording sheet.

[0031]

EXAMPLES [Synthesis Example 1] SiO ₂ concentration 10.0 wt%,
In 240 ml of an aqueous solution of sodium silicate having a SiO ₂ / Na ₂ O molar ratio of 2.7, sodium chloride
It was dissolved in 0.36 equivalent with respect to O ₂ 1 mol. This aqueous solution is mixed with trichlorotrifluoroethane 96
3.36 g of sorbitan monooleate in 0 ml
Was added to the solution in which was dissolved, and emulsified by a homomixer.

Carbon dioxide gas (CO ₂ concentration: 30% by volume) diluted with air was blown into the emulsion to gel at 15 ° C. After blowing carbon dioxide gas for 15 minutes, trichlorotrifluoroethane was separated to obtain a slurry composed of spherical silica gel and water. The pH of this slurry was 9.0. Sulfuric acid was added to the slurry, the pH was adjusted to 2.5, and the slurry was heated at 60 ° C. for 1 hour.

This slurry was filtered, and the cake was washed with ion-exchanged water having a solid content of 100 times by weight and dried with a spray drier to obtain spherical silica gel. The pore volume was 2.8 ml / g, the specific surface area was 758 m ² / g, the oil absorption was 550 ml / 100 g, and the average particle size was 4.8 μm.

1 g of this spherical silica gel was dispersed in 99 g of ion-exchanged water having an electric conductivity of 0.5 μS / cm, and dried at 120 ° C. for 5 hours using a stationary dryer to obtain silica gel. When the pore characteristics of the silica gel after this treatment were similarly evaluated, the pore volume was 2.8 ml /
g, specific surface area: 760 m ² / g, oil absorption: 553 ml / g
100 g.

[Synthesis Example 2] Silica gel 100 of Synthesis Example 1
g was dispersed in ion-exchanged water, and a polyaluminum chloride aqueous solution (aluminum concentration was 23.6% by weight in terms of Al ₂ O ₃ , Cl was 8.1% by weight, basicity was 84%, manufactured by Taki Chemical Co., Ltd.) (Takibain # 1500) (22 g) was added over 10 minutes. Thereafter, the pH of the dispersion was adjusted to 8.1 by adding 43 g of a 5N aqueous sodium hydroxide solution, and the dispersion was further washed with pure water and dried.

As a result, spherical silica gel whose surface was modified with alumina (average particle diameter: 5.1 μm) was obtained. The pore volume of this silica gel was 2.5 ml / g, the specific surface area was 630 m ² / g, and the oil absorption was 450 ml / 100 g. 1 g of this silica gel has an electric conductivity of 0.5 μS / c.
m of ion-exchanged water (99 g), and further dried at 120 ° C. for 5 hours using a stationary dryer to obtain silica gel.
When the pore volume, specific surface area, and oil absorption of the silica gel after this treatment were evaluated in the same manner, the silica gel did not substantially change as compared to before dispersing in ion-exchanged water.

Example 1 100 g of the silica gel of Synthesis Example 1 and polyvinyl alcohol (Poval M manufactured by Kuraray Co., Ltd.)
A-26) 300 g of a 10% by weight aqueous solution was mixed to prepare a coating liquid. The coating liquid was applied to a high-quality paper having a basis weight of 175 g / m ² using a bar coater, and then dried at 60 ° C. to obtain a recording sheet. Coating amount after drying is 20 g / m
^{Was 2} . When printing was performed on this recording sheet with a commercially available color inkjet printer, sufficient ink absorbency and color density were achieved.

Example 2 100 g of the silica gel of Synthesis Example 2 and polyvinyl alcohol (Poval M, manufactured by Kuraray Co., Ltd.)
A-26) 300 g of a 10% by weight aqueous solution was mixed to prepare a coating liquid. After applying this coating solution to a polyethylene terephthalate film using a bar coater,
After drying at 40 ° C., a recording sheet was obtained. The coating amount after drying was 20 g / m ² . When printing was performed on this recording sheet with a commercially available color inkjet printer, sufficient ink absorbency and color density were achieved. The color density was higher than for the recording sheet of Example 1.

Example 3 The silica gel of Synthesis Example 2 was mixed with a pulp slurry, and papermaking was performed according to a conventional method to obtain a recording sheet. This recording sheet had a basis weight of 50 g / m ² and a silica gel content of 10% by weight. When printing was performed on this recording sheet with a commercially available color inkjet printer, sufficient ink absorbency and color density were achieved.

Example 4 40 parts by weight of the silica gel of Synthesis Example 1, 40 parts by weight of polyethylene powder, and 20 parts by weight of process oil were mixed by a mixer, extruded into a sheet, and molded. The obtained sheet-like molded body was cut, the process oil was extracted with hexane, and dried to obtain a recording sheet in which silica gel was dispersed inside porous polyethylene. When printing was performed on this recording sheet with a commercially available color inkjet printer, sufficient ink absorbency and color density were achieved.

[0041]

The recording sheet of the present invention has a high ink absorption speed and a high color density upon recording. The recording sheet of the present invention is suitable for an ink jet printer.

Claims (4)

[Claims] 1. A recording sheet containing silica gel as an ink absorbing material, wherein said silica gel has a pore volume of 1.5 to 100 nm having a pore radius of 1 to 100 nm by a nitrogen adsorption method.
3.5 ml / g, specific surface area 500 to 1000 m ² / g,
1% by weight of the silica gel is dispersed in water having an oil absorption of 300 ml / 100 g or more and an electric conductivity of 1 μS / cm or less, then separated, and further dried at 120 ° C. using a stationary dryer.
A record characterized in that the silica gel obtained by drying for a time has a pore volume and an oil absorption in a range of pore radius of 1 to 100 nm by a nitrogen adsorption method of 90% or more of values before being dispersed in water, respectively. Sheet. 2. The recording sheet according to claim 1, wherein a coating layer containing said silica gel and a binder is formed on a base material. 3. The recording sheet according to claim 1, wherein the silica gel is dispersed in a base material. 4. The silica gel has an average particle diameter of 1 to 30.
The recording sheet according to claim 1, 2 or 3, wherein the particle size is spherical and the particle shape is spherical.