JPH0227941B2 - EKITAIKYUSHUSEINOSHIITO - Google Patents

Description

[Detailed description of the invention]

A: Technical Field of the Invention The present invention relates to a liquid-absorbing sheet, and more particularly to a liquid-absorbing sheet for inkjet recording, which has excellent absorption speed of aqueous ink for inkjet recording and has high transparency. B. Prior Art and its Problems In recent years, inkjet recording systems have come to be used in a variety of applications including information equipment due to their various excellent features. The ink used in the inkjet recording method is generally water-soluble, and the solvent used is a mixed solvent with a slow drying rate, such as a mixture of water and high-boiling point glycols. Therefore, it is necessary to use a recording sheet that has an excellent absorption speed and has the ability to rapidly absorb the ink deposited on the recording sheet into the sheet. Conventional sheets with this kind of performance include:
Recording paper with low transparency is used, whose surface is coated with pigments that have high liquid absorption ability. However, as the applications of the inkjet recording system expanded, there was a need for recording sheets with excellent ink absorption speed and transparency that could be used as base paper for diazo copies or overhead projectors. ing. Currently, for this purpose, tracing paper or transparent film is coated with a coating layer consisting of inorganic pigments and water-soluble polymers (Japanese Patent Application Laid-Open No.
57-107880), or a liquid-absorbing lower layer made of polyvinylpyrrolidone, a copolymer of methyl vinyl ether and maleic anhydride, etc., and a liquid-permeable layer made of cellulose acetate, etc. are provided on a transparent polymer film such as polyester. Attempts have been made to use materials such as those with a high ink absorption speed (Japanese Patent Application Laid-Open No. 1989-89954) as recording sheets, but in both cases, if the ink absorption speed is excellent, the transparency is low; conversely, if the transparency is good, the ink absorption speed is low. is slow,
At present, there is a strong desire for an inkjet recording sheet that satisfies both ink absorption speed and transparency. C. Structure, Objectives, and Effects of the Present Invention In view of the above-mentioned current situation, the present inventors conducted intensive research on a liquid absorbent sheet for inkjet recording that can simultaneously satisfy ink absorption speed and transparency. The inventors discovered that both the above-mentioned ink absorption speed and transparency can be satisfied by forming a liquid-absorbing coating layer containing polyvinyl alcohol and polyacrylic acid-based water-soluble polymer, and completed the present invention. I reached it. D More detailed description of the present invention As for the mixing ratio of polyvinyl alcohol and polyacrylic acid-based water-soluble polymer used in the present invention, on a weight basis, the former/latter = 1/9 to
9/1, more preferably 3/7 to 7/3. If the amount of polyvinyl alcohol is less than the above ratio, the resulting coating layer may be easily cracked.
Moisture absorption tends to cause deterioration in physical properties such as stickiness, and on the other hand, if the amount of polyvinyl alcohol is greater than the above ratio, the liquid absorption rate decreases. There is no particular restriction on the degree of polymerization of the polyvinyl alcohol used in the present invention, and it is usually 100 to 100.
Selected from a range of 3000. The saponification degree may be 70 to 99 mol % as long as it is water-soluble, but 75 to 88 mol % is preferably used from the viewpoint of liquid absorption rate for glycol solvents. The polyacrylic acid-based water-soluble polymer used in the present invention includes poly(meth)acrylic acid,
Copolymers of (meth)acrylic acid and methyl, ethyl or butyl esters of (meth)acrylic acid, copolymers of (meth)acrylic acid and (meth)acrylamide, or alkali metal or ammonium salts thereof; etc. can be used, but
From the viewpoint of compatibility with polyvinyl alcohol, poly(meth)acrylic acid or a copolymer of (meth)acrylic acid and an ester of (meth)acrylic acid is preferably used. The (meth)acrylic acid unit in the above-mentioned polyacrylic acid-based water-soluble polymer is at least 5 mol%.
It is preferably at least 10 mol%, and more preferably at least 10 mol%.
The degree of polymerization is not particularly limited, but from the viewpoint of coatability, it is preferably 100,000 or less, and more preferably 10,000 or less. Regarding the transparency of the liquid-absorbing sheet obtained by the present invention, when used as a base paper for diazo copies or a base paper for overhead projectors, the transparency determined by the measuring method described below is as follows:
80% or more is preferable, especially when used as a base paper for overhead projectors, transparency is 95%.
The above are particularly desirable. In addition, the supporting substrate used in the present invention includes:
There are no particular restrictions as long as the sheet is highly transparent and water-insoluble; transparent synthetic resin sheets such as polyester, polystyrene, polyvinyl chloride, polymethyl methacrylate, cellulose acetate, and highly transparent paper can be used. Of course, since it is essential that the transparency of the liquid absorbent sheet obtained using such a support substrate be 80% or more as mentioned above, the transparency of these support substrates must also be 80% or more. The higher the transparency, the better. Further, the liquid absorbent sheet obtained by the present invention is particularly excellent in absorption speed of water-soluble ink for inkjet recording. The liquid used in the liquid-absorbent sheet of the present invention generally includes a mixed liquid of water and glycols such as ethylene glycol, glycerin, and diethylene glycol, and the weight ratio of the former/latter is 10/90 to 10/90. 90／
10, preferably 15/85 to 80/20 may be used. The liquid-absorbing coating layer of the present invention containing polyvinyl alcohol and polyacrylic acid-based water-soluble polymer may contain a small amount of surfactant or a small amount of pigment that does not reduce transparency depending on the purpose. I can't hold back in any way. As a method for forming the liquid-absorbing coating layer containing polyvinyl alcohol and polyacrylic acid-based water-soluble polymer according to the present invention, a conventional coating method such as an air knife coater, a roll coater, a bar coater, etc. is used. It is possible. The thickness of the coating layer is not particularly limited, but the thickness after drying is usually 0.5 to 100μ, preferably 1 to 100μ.
50μ is adopted. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto. In the examples, unless otherwise specified, "%" and "part" represent weight basis. In addition, methods for measuring various physical property values in Examples are shown below. (1) Liquid absorption rate After coating an acetone solution of phenolphthalene on a supporting substrate and drying it, a liquid-absorbing coating layer is provided on the support substrate, and 1μ of a mixed solution of water/glycerin in which sodium hydroxide is dissolved is applied to the surface of the coating layer. dripping,
Time until red color develops due to reaction between sodium hydroxide and phenolphthalene (sec)
was measured. The shorter the time (sec), the higher the absorption rate. (2) Ink absorption speed After a 0.5μ ink droplet of water-based ink for inkjet is attached to the surface of a liquid absorbent sheet, the time it takes for the ink to stop adhering to the paper even if the top is rubbed with paper (sec) was measured.
The shorter the time (sec), the higher the ink absorption speed. (3) Transparency Visible light transmittance of liquid absorbent sheet (%)
was measured with a spectrophotometer using visible light with a wavelength of 500 nm. This transmittance is defined as transparency. The higher the transmittance, the higher the transparency. Examples 1 to 3 An acetone solution of phenolphthalein was applied onto a polyester sheet having a thickness of 100μ and a transparency of 99.8%, and polyvinyl alcohol with a degree of saponification of 88 mol% and a degree of polymerization of 1750 was placed on the dried sheet. Apply a 10% aqueous solution of an equal amount of a polyacrylic acid-based water-soluble polymer as shown below, dry it, and measure the dry thickness.
A polyester sheet with a 5μ liquid-absorbing coating layer was obtained. Table 1 shows the liquid absorption rate and transparency of this sheet. Polyacrylic acid-based water-soluble polymer Example 1: Polyacrylic acid with a degree of polymerization of 2000. Example 2: Containing 10 mol% of acrylic acid units,
A copolymer of acrylic acid, ethyl acrylate, and butyl acrylate with a degree of polymerization of approximately 1000. Example 3: Contains 30 mol% of acrylic acid units,
A copolymer of acrylic acid and acrylamide with a polymerization degree of 3000.

[Table] As is clear from Table 1, the liquid absorbent sheet obtained according to the present invention has an extremely high absorption rate of a mixed liquid of water and glycols such as glycerin, diethylene glycol, etc., and has a low transparency. It is a liquid-absorbing sheet with extremely good transparency, having a content of 95.0% or more. Comparative Example 1 Thickness 100μ and transparency 99.8% used in Example 1
An acetone solution of phenolphthalein was applied onto a polyester sheet, and a 10% aqueous solution of polyvinyl alcohol with a degree of polymerization of 1750 and a degree of saponification of 88 mol% was applied onto the dried sheet to a dry thickness of 5μ. , dried. The measurement results of the liquid absorption rate and transparency of the obtained sheet are shown in Table 1. Although the transparency was good, the liquid absorption rate was extremely slow and the sheet was poor in practical use. Comparative Example 2 Thickness 100μ and transparency 99.8% used in Example 1
An acetone solution of phenolphthalein is applied onto a polyester sheet, and 70 parts of synthetic silica, colloidal silica (refractive index
1.46) 30 parts, polyvinyl alcohol (degree of polymerization 550,
A coating solution consisting of 15 parts (saponification degree: 98.5 mol%) and 460 parts of water was applied to a dry thickness of 5 μm and dried. The liquid absorption rate and transparency of the obtained sheet were
Write it down according to the table. Although the liquid absorption rate was quite good, the transparency was extremely low at 70%, making it unsuitable as a base paper for diazo copies or overhead projectors. Comparative Example 3 Thickness 100μ and transparency 99.8% used in Example 1
An acetone solution of phenolphthalein was applied onto a polyester sheet, and on the dried sheet, a 10% aqueous solution of polyacrylic acid with a degree of polymerization of 2000 was applied to a dry thickness of 5μ, and dried.
The coating layer of the obtained sheet became extremely sticky due to moisture absorption, resulting in the inconvenience that it adhered to other sheets when the sheets were laminated. Examples 4 to 6 On a polyester sheet with a thickness of 100μ and a transparency of 99.8%, 100 parts of polyvinyl alcohol with a degree of saponification of 80 mol% and a degree of polymerization of 2000 and 200 parts of a polyacrylic acid-based water-soluble polymer as shown below were prepared. A 10% aqueous solution of the mixture was applied and dried to obtain a polyester sheet having a liquid absorbent coating layer with a dry thickness of 5 μm. Table 2 shows the ink absorption speed and transparency of this sheet. Polyacrylic acid-based water-soluble polymer Example 4: Polyacrylic acid used in Example 1 with a degree of polymerization of 2000. Example 5: The acrylic acid unit used in Example 2
The degree of polymerization of acrylic acid, ethyl acrylate, and butyl acrylate containing 10 mol%
1000 copolymers. Example 6: The acrylic acid unit used in Example 3
A copolymer of acrylic acid and acrylamide with a polymerization degree of 3000, containing 30 mol%.

[Table] As is clear from Table 2, the liquid absorbent sheet obtained by the present invention has an extremely fast absorption rate of water-based ink for inkjet recording, and is extremely transparent with a transparency of 95.0% or more. It is a liquid-absorbing sheet with good properties, and is excellent as a base paper for diazo copies or overhead projectors. Comparative Example 4 70 parts of synthetic silica, 30 parts of colloidal silica (refractive index 1.46), polyvinyl alcohol (polymerization degree
A coating solution consisting of 15 parts of 550 (Saponification degree: 98.5 mol%) and 460 parts of water was applied to a dry thickness of 5 μm and dried. The ink absorption speed and transparency of the obtained sheet are shown in Table 2, and the transparency was only 70%, which was extremely low. Comparative Example 5 A methanol solution of a copolymer of methyl vinyl ether and maleic anhydride was coated on a polyester sheet with a thickness of 100μ and a transparency of 99.8% so that the dry thickness was 3μ, and after drying, A methyl ethyl ketone solution of cellulose acetate/butyrate was applied to a dry thickness of 2 μm and dried to obtain a sheet. The ink absorption speed and transparency of this sheet are shown in Table 2, and it is clear that the ink absorption speed is extremely slow and is not practical.

Claims (1)

[Scope of Claims] 1. A liquid-absorbing sheet characterized by having a coating layer containing polyvinyl alcohol and a water-soluble polyacrylic acid polymer on the surface of a supporting substrate. 2. The liquid absorbent sheet according to claim 1, wherein the polyacrylic acid-based water-soluble polymer is poly(meth)acrylic acid. 3. The liquid-absorbing sheet according to claim 1, wherein the water-soluble polyacrylic acid polymer is a copolymer of (meth)acrylic acid and (meth)acrylic acid ester. 4 The mixing ratio of polyvinyl alcohol and polyacrylic acid-based water-soluble polymer is the former /
Claim 1 in which the latter = 1/9 to 9/1
Liquid absorbent sheet as described in section. 5 The mixing ratio of polyvinyl alcohol and polyacrylic acid-based water-soluble polymer is the former /
Claim 1 in which the latter = 3/7 to 7/3
Liquid absorbent sheet as described in section. 6. The liquid absorbent sheet according to claim 1, wherein the liquid absorbent sheet is a liquid absorbent sheet for inkjet recording. 7 Claim 1 with transparency of 80% or more
Liquid absorbent sheet as described in section. 8 Claim 1 with transparency of 95% or more
Liquid absorbent sheet as described in section.