JPH0338375A - Ink jet recording sheet - Google Patents

Abstract

PURPOSE:To obtain ink jet paper printable at a high speed by providing an aqueous ink receptive coating layer based on highly water-absorbing pigment and a water-soluble polymer adhesive on a paper sheet, which is based on cellulose pulp and humidified to specific moisture or more after dried to specific moisture or less and placed under tension, in a specific ratio. CONSTITUTION:A paper sheet based on cellulose pulp is dried to moisture of 6% or less as a humidifying condition and humidified by 1% or more as moisture and placed under tension. An aqueous ink receptive coating layer based on highly water-absorbing pigment and a water-soluble polymer adhesive is provided on the paper sheet reduced in irregular shrinkage, contraction or curling to a moisture change in a ration of 0.5 - 15g/m<2> to prepare base paper absorbing type ink jet paper. The water absorbing speed of paper being a base material is fast and the uneven distribution of roughness or dimensional change due to the absorption of aqueous ink is reduced and the optimum ink image receptivity is achieved and an excellent ink jet recording sheet is obtained.

Description

[Detailed Description of the Invention] [Industrial Applications] The present invention relates to a water-based ink recording material, and more particularly to an inkjet printer paper having excellent dimensional stability and improved appearance after printing, that is, a recording sheet. It is related to.

[Prior art and problems to be solved by the invention] Improvements in inkjet printers and inks that use water-based inks have made it possible to use plain paper as inkjet paper and obtain clear images and prints. However, in order to make the quality, saturation, appearance, and images of prints more attractive, there has been a demand for paper with more advanced characteristics, that is, recording sheets.

Conventionally, inkjet paper has been made using sizeless paper to improve ink absorption, or paper with an absorbent coating layer such as silica on virtually sizeless paper (
(Japanese Patent Publication No. 60-27588), or paper in which an absorbent coating layer containing silica as a main component is provided on a non-water-absorbing base material such as high-size paper or plastic film in order to improve the color density (Japanese Patent Publication No. 60-27588). -65037) has been proposed.

Among these papers, base paper absorption type inkjet paper has a good balance of cost, texture, and performance and is expected to be used as conventional inkjet paper. The base paper of this type of paper has good ink absorption properties, and the ink is absorbed inside the paper layer, leaving the paper with an appearance of dryness. Both are required to hold back. Since paper with high ink absorbency is likely to be deformed greatly by water-based ink, these two conditions generally cause problems. For example, if the absorption speed is increased by using a small paper size, the ink will penetrate faster and deeper, causing curling and bumpiness.

On the other hand, by providing an absorbent coating layer on a high-sized base paper, the absorption speed of only the absorbent coating layer can be increased, and ink absorption into the base paper can be suppressed. However, if the ink absorption limit of the absorbent coating layer is exceeded, it may cause bleeding, and ink absorption often increases the curl of the paper as a whole. It also becomes more expensive.

In Japanese Patent Publication No. 6:3-52588, a proposal has been made to weaken the bonds between fibers of pulp and reduce curling and unevenness by incorporating glass fibers and a large amount of water-absorbing pigment. However, its practicality as printer paper is questionable because of various problems in use due to the addition of glass fibers and the loss of paper strength.

BACKGROUND ART Papers that have good dimensional stability against changes in moisture and humidity have been known so far, and are used as OCR paper, NIP paper, and the like. However, there are still no known techniques or properties that can reduce or improve the cause of paper blurring and curl caused by water-based ink.

[Purpose of the invention]

The present invention is a recording material for multi-color or single-color inkjet printers using water-based ink, which has a fast ink absorption speed, a large absorption capacity, minimal dusting and curling, and can print at high speed. It is an object of the present invention to provide an inkjet paper, that is, a recording material, which can overcome the drawbacks of the prior art.

[Structure of the invention]

The inkjet recording sheet of the present invention is mainly composed of cellulose pulp, and the residual stress inside the paper, which causes variations in elongation in ice and curl within a unit sheet, which is the cause of lumpiness, is moisturized. Then, by leaving the ink still under tension, the problem is resolved and the smudge caused by the water-based ink is improved.

In the present invention, a highly water-absorbent pigment and an aqueous polymer adhesive are applied onto a paper sheet that has been dried to a moisture content of 6% or less, then humidified with a moisture content of 1% or more, and placed under tension to eliminate residual stress. 0.5 to 15 g/m of the aqueous ink receptive coating layer as a component
It is characterized in that it is provided at a ratio of 2.

Inkjet paper is typically used in cut sheets such as A4 or fanfold.

The present inventors have discovered that the unevenness caused by water-based ink is caused by curling and/or variation in elongation in ice within these unit sheets.

In particular, as a result of observing the bumping phenomenon caused by water-based ink on high-quality paper made using a regular fourdrinier multi-tube paper machine, we found that the bumping caused by water-based ink, which causes problems in appearance, occurs with a period of several mm to several centimeters. It was found that this was due to variations in underwater elongation and curl. In order to solve such problems caused by variations in the physical behavior of paper, we believe that it is important to alleviate the residual stress inside the paper sheet that causes the problem. Although the absolute value of the underwater elongation of paper made from cellulose pulp cannot be reduced below a certain level, its variation can be reduced by stress relaxation.

When we observed the kokkuri phenomenon caused by water-based ink on a sample sheet, we found that it was made using a normal Fourdrinier multi-tube paper machine, and then placed on a dry base paper, containing a highly water-absorbing pigment and a water-soluble polymer adhesive as the main ingredients. When printing was performed using an aqueous inkjet printer on an inkjet paper provided with an aqueous ink receptive coating layer, noticeable curling was observed.

However, in order to evaluate the aesthetic appearance, similar paper was made using a regular Fourdrinier multitubular paper machine, dried, humidified, rolled up under tension, and stored to relieve stress. When we made a prototype of inkjet paper and printed it on a water-based inkjet printer, we found that the scratching was reduced.

From the viewpoint of aesthetic evaluation, it is preferable to dry the material to a moisture content of 6% or less, then humidify it with moisture of 1% or more, and place it under tension.

In this way, a water-based ink-receptive coating layer containing a highly water-absorbing pigment and a water-soluble polymer adhesive as main components is applied to a paper sheet that has reduced irregular expansion/contraction and curling due to moisture changes.
When a base paper absorption type ink genie/t paper was manufactured by applying the water-based ink at a ratio of 0.5 to 15 g/m2, the water absorption rate of the base paper was still high, but there were no lumps or dimensional changes due to water-based ink absorption. This achieved optimal ink image receptivity.

In order to eliminate the drawbacks of the prior art described above, the present inventors have
As a result of various studies, we applied a coating liquid containing super-absorbent fine particles and a water-soluble polymer adhesive as main components to a sheet-like support that has been paper-formed or post-processed to minimize deviations in elongation in water of the above-mentioned paper. The inventors have discovered that an excellent inkjet recording sheet free from unevenness can be obtained by coating and drying to form an ink-receptive coating layer.

The recording sheet of the present invention may have a configuration in which a sheet-like support is used as an absorbent body, but other configurations are not excluded as long as the requirements of the present invention are met.

In the present invention, by using highly water-absorbing fine particles such as synthetic silicic acid and a water-soluble polymer adhesive as components of the ink-receptive coating layer, permeability is imparted to the ink-receptive coating layer, and the shape of the ink dots is By controlling the spread, clear images are achieved. Adding a cationic vinyl acetate copolymer emulsion to the ink-receptive coating layer improves permeability, shape of ink dots,
This is one of the preferred means of achieving the objectives of the present invention, which further improves spread control.

The materials used in the present invention will be explained.

・Papermaking sheet The papermaking sheet of the present invention, that is, the base paper, is mainly composed of cellulose pulp made from wood, usually bleached rough pulp, but it also contains fibers such as glass fiber, polyester fiber, polyvinyl alcohol fiber, etc. Anything that can be dispersed can be used as a component. The base paper is made by forming a wet paper using a Fourdrinier paper machine or the like and drying it using a dryer.

As the dryer, a Yankee dryer, a multi-barrel dryer, etc. are used.

In the present invention, since a paper sheet is also used as an absorbent material, it has a basis weight of 64 g/m2 and a Steckigt sizing degree of 1 to 15.
Preferably, the sheet has a water absorption rate of seconds, especially 3 to 10 seconds.

The thickness of the recording sheet is determined by the final use of the print, but it is 10 to 200 μm and the tsubo weight is 20 to 200 g/
m2, and those with good surface smoothness are usually used.

- Pigment The pigment used in the ink-receptive coating layer of the present invention is a highly liquid-absorbing and color-developing white pigment.

Preferably, the main component is fine particle synthetic silicic acid.

In order to ensure voids between particles for absorption in a short time, it is preferable that particles having a somewhat large secondary particle diameter of 1 to 5 μm be the main component. Examples of white pigments that can be used or used in combination with fine-particle synthetic silicic acid include, for example, kaolin clay, talc, zeolite, precipitated calcium carbonate, ground calcium carbonate, aluminum hydroxide, white carbon, and organic pigments (
plastic pigments), etc.

・Water-soluble polymer adhesive The adhesive of the present invention is a natural water-soluble polymer such as polyvinyl alcohol, a protein such as casein, a starch derivative, or a base water-soluble polymer such as polyvinyl alcohol that has adhesive properties with a super water-absorbing pigment. It is preferable because it has good compatibility with aqueous ink and improves liquid absorption in a short time.

Polymer latex adhesives such as polyvinyl acetate and styrene butadiene can also be used.

The blending ratio of components such as pigments and adhesives is determined based on the absorption behavior and strength requirements of the aqueous ink-receptive coating layer, but it also depends on the operational characteristics of the coating solution (e.g. viscosity, fluidity, drying properties of the coating film). It is also limited by the request of The amount of water-soluble polymer adhesive is 10 to 50% by weight, especially 2% by weight of the solid content of the coating layer.
0 to 40% by weight is preferred. Cationic vinyl acetate copolymer microspheres (for use in emulsion polymers)
is preferably 2 to 25% by weight of the solid content of the coating layer, particularly 5% by weight of the solid content of the coating layer.
~15% by weight is preferred.

By adding cationic polymer emulsions, especially vinyl acetate microspheres, the ink-receiving layer can be made permeable and the ink absorption can be improved.

A cationic water-soluble polymer such as polyethyleneimine used for making water-based ink images waterproof is added to the coating layer with a solid content of 2 to 2%.
It is preferable to add 5% by weight.

The thickness of the coating layer is determined by the required amount of water absorption by the coating layer, but if it is too thick, the coating layer will lack strength and cause various problems when used in printers, such as paper dust, so it should not exceed 15 g/m2. It is desirable that

If the tl is too high, the initial absorption and initial permeation of the ink will be insufficient and it will be difficult to obtain a uniform coating layer.
It is preferably 5 g/m2 or more, particularly 2 to 10 g/m2.

Hereinafter, the present invention will be explained in more detail with reference to Examples. In the examples, parts indicate parts by weight of solid content.

Example 1 100 kg of bleached kraft pulp, 25 kg of light calcium carbonate
kg, cationic starch 200 g, paper strength enhancer 100 g,
200g of alkyl ketendermer sizing agent and 500g of water
After mixing 0 kg, wet paper was formed using a long steel paper machine, dried to a moisture content of 5% using a multi-barrel dryer, and then increased to 7.5% using an electrostatic humidifier. The paper was wound up at the bottom to obtain high-quality paper with a basis weight of 65 g/m2. The Beck smoothness of the produced paper was 35 seconds for the felt surface and 28 seconds for the wire surface.

To this base material, 100 parts of fine silicic acid (Fine Seal: Fi Sansoda), silanated polyvinyl alcohol (R
-1130: Kuraray) 20 parts, cationic vinyl acetate copolymer (Yodozol 1E502) -4: Kanebo N5C
) was applied on one side at a solid content of 7 g/m'', smoothed with a spark calender, and the recording sheet was prepared. Manufactured.

The smoothness of the coated surface was 120 seconds, and the Steckigt size degree of the entire sheet was 8 seconds.

Example 2 A high-quality paper base material having a basis weight of 65 g/m' was produced in the same manner as in Example 1 except that it was dried to a moisture content of 4%. Using a gravure coater, the moisture content was increased to 8.5% to obtain high-quality paper. The Beck smoothness of the produced paper was 35 seconds on the felt surface and 28 seconds on the wire surface.

On this base material, apply the same paint as in Example 1 on one side with a solid content.
A recording sheet was produced by coating at a rate of 5 g/m', drying, and smoothing with a super calendar. The smoothness of the coated surface was 100 seconds, and the Steckigt size degree of the entire sheet was 7 seconds.

Comparative Example 1 A base paper of 4 g/m2 was obtained by winding the paper in the same manner as in Example 1, except that it was dried to a moisture content of 4%.The resulting paper had a felt surface with a solid smoothness of 55 seconds and a wire surface. The smoothness was 45 seconds.

On this base material, apply the same paint as in Example 1 on one side with a solid content.
A recording sheet was prepared by coating at a rate of 5 g/m2, drying, and smoothing with a super calendar. The smoothness of the coated surface was 100 seconds, and the Steckigt size degree of the entire sheet was 8 seconds.

Comparative Example 2 A base paper of 66 g/m 2 was obtained in the same manner as in Example 1 except that the paper was dried to a moisture content of 8%. The resulting paper had a felt surface with a solid smoothness of 70 seconds and a wire surface with a smoothness of 65 seconds.

On this base material, apply the same paint as in Example 1 on one side with a solid content.
A recording sheet was produced by coating at a rate of 5 g/m2, drying, and smoothing with a super calendar. The smoothness of the coated surface is 140 seconds, and the Steckicht size of the entire sheet is 7.
It was seconds.

Table 1 shows the evaluation results for each of these recording sheets.

The inkjet recording properties were evaluated using an inkjet printer (Paintjet, manufactured by HP) regarding ink absorbency, color density, dot shape, and unevenness after printing.

Ink absorbency was evaluated by measuring the number of seconds it took for the printed ink to appear to be completely dry, and the drying performance was evaluated by sensory evaluation.

The vividness of color development was evaluated visually by the color development of yellow, magenta, and cyan color inks, and sensory evaluated in the order of brightness.

The shape of the dots was determined by sensory evaluation from those closest to perfect circles.

The unevenness was evaluated visually after the printed ink had apparently dried, and the prints were visually evaluated and observed, and the level of unevenness was evaluated by sensory evaluation based on the degree of lightness.

〔Effect of the invention〕

The recording material for inkjet printers of the present invention has a high ink absorption speed and amount, and the dot shape is close to a perfect circle.Although it is excellent, it eliminates the unevenness that is a drawback of conventional methods, and allows for excellent high-speed inkjet printing.・It makes full-color printing possible and will greatly contribute to industry.

Claims (1)

[Claims] 1. Cellulose pulp is the main component, and after drying to a moisture content of 6% or less, it is humidified with water of 1% or more, and a super absorbent pigment and a water-soluble polymer adhesive are mainly added onto a paper sheet that is placed under tension. 0.5 to 15 g of the aqueous ink receptive coating layer as a component
An inkjet recording sheet characterized in that the inkjet recording sheet is provided at a ratio of m^2.