JP3074128B2 - Inkjet recording paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink-jet recording paper, and more particularly, to high print quality and image density in characters and ruled lines when printing with an ink-jet color printer, as well as uniformity in image density in a solid print area. The present invention relates to an inexpensive inkjet recording paper having an excellent plain paper feeling.

[0002]

2. Description of the Related Art Ink-jet recording systems have the advantages of high speed, low noise, and easy colorization. In addition, extremely low-cost color ink-jet printers can reproduce high-quality images similar to prints and photographs at low cost. And has been rapidly spreading in recent years. Further, inexpensive and high-precision inkjet heads are being used for copiers, word processors, facsimile machines and the like.

[0003] With the spread of such inexpensive color ink jet printers, color information can be easily placed in sentences even in office documents and personal use, which conventionally used mainly monochrome printers. As a result, the paper used therein has been required to have characteristics as color ink jet printer paper in addition to the characteristics provided by the conventional monochrome ink jet printer paper. At the same time, in order to use as ordinary office paper, as in the case of PPC paper, there is a demand for a feeling of plain paper, which is excellent in writability and easy handling with a pencil.

In the case of a monochrome printer,
Since characters and tables are mainly printed, sharpness of characters and ruled lines is required, so that low feathering property is regarded as important. Feathering is a phenomenon in which ink spreads in the horizontal direction, blurs dots, and ink bleeds along the fibers in a whisker-like manner, losing the clarity of characters and ruled lines. It becomes difficult.

[0005] In order to improve such feathering, an internal sizing agent in the base paper and an external sizing agent in the ink receiving layer are added to enhance the sizing properties of the entire paper to improve the ink quality. It is necessary to reduce the wetting of the paper. However, if the size is made too high, ink droplets do not permeate into the paper layer forever and remain on the paper surface, and after printing, other parts of the printer or the hand touches, or the next page of paper is printed. When superimposed, the printed portion is rubbed and stains occur.

Therefore, after printing, it is necessary that the ink droplets quickly permeate into the paper layer and become apparently dry. This is called ink drying property. To improve the ink drying property, it is necessary to reduce the size. As described above, the feathering and the ink drying property are in a contradictory relationship, but how much the sizing property is determined from this balance is one of the important issues in designing the ink jet recording paper.

Also, in the case of monochrome printing, it is necessary to increase the image density in the same way as in the case of color printing in order to make characters clearly visible. In a color print having many halftone or solid print portions, it is more important that the dot density or the image density of the solid print portion is high than in the case of monochrome print. Therefore, in the case of recording paper for a color ink jet printer, a method of providing an ink receiving layer mainly composed of a highly absorbent pigment such as silica and a binder has been devised (for example, Japanese Patent Application Laid-Open No. Sho 55-51583). ,
JP-A-62-158084, JP-A-5-96844, etc.).

In color ink-jet printing, as in the case of other color image reproduction techniques, all three colors or four colors of ink are reproduced, so that a maximum of four colors of ink are printed in the same place. Sometimes. Such a portion where several colors of ink are overprinted is referred to as a mixed color portion. In the mixed color portion, since the amount of ink is 2 to 4 times that of the single color portion, a high ink absorption capacity is naturally required.

Further, if another color ink is printed before the already printed ink is absorbed, the inks flow into each other at the boundary between the colors, causing bleeding (this is called bleeding). From the viewpoint of preventing such bleeding, color inkjet printer paper is required to have a higher ink absorption capacity and ink absorption speed than monochrome recording paper.

By the way, as the ink jet recording paper, fine paper type that does not perform pigment coating, fine coating type 0.5 to 5 g / m ² provided an ink-receiving layer, 10 g / m ²
There is a light coat type before and after, and a heavy coat type around 20 g / m ² . However, among these, the light coat type and heavy coat type have the drawback that the coating layer is shaved when writing with a pencil, and the paper is stiff and the handling is poor, so that it has the drawback of giving a plain paper feeling. there were.

On the other hand, in the case of a high quality paper type which is not coated with a pigment, there is a disadvantage that it is difficult to obtain a sufficient image density as a color ink jet recording paper. Therefore, in recent years, many finely coated ink jet recording papers have been proposed as full color ink jet recording papers having a feeling of plain paper. For example, Japanese Unexamined Patent Publication
JP-A-312572 discloses a recording paper in which the surface of a pulp fiber of a base paper is coated with at least 70% using an ultrafine inorganic pigment, and JP-A-6-158893 discloses a pigment area ratio. There is disclosed a recording paper in which an ink receiving layer is provided on the surface of a base paper having a larger size.

However, as described in Japanese Patent Application Laid-Open No. 6-312572, in order to cover 70% or more of the pulp fiber with a small coating amount, extremely fine inorganic pigments such as expensive colloidal silica such as colloidal silica are required. The use of such a pigment increases the cost, and it is difficult to obtain sufficient ink absorbency with an ink receiving layer of 5 g / m ² or less even if such a pigment is used. Was.

Further, when the ink receiving layer is provided on the surface having a high yield of the internal filler as in the invention disclosed in Japanese Patent Application Laid-Open No. H6-155893, the amount of filler in the base paper is increased ( JP-A-6-143796).
Even if sufficient ink absorbency is obtained, there is a disadvantage that the image density is reduced because the internal filler optically shields the ink absorbed in the paper layer.

That is, in the case of a finely coated recording paper having an ink receiving layer of 5 g / m ² or less, the ink cannot be absorbed by the ink absorbing layer alone. However, if the amount of internal filler used is increased to increase the voids in the base paper and thereby increase the ink absorbency, the filler optically shields the ink that has penetrated into the paper layer, and the This results in a decrease in concentration.

Further, the mere use of a method using a base paper having a low size (for example, JP-A-52-5301) cannot prevent the deterioration of feathering as described above. Therefore, a coating layer made of a water-soluble polymer is provided as an ink receiving layer (JP-A-55-144172).
And JP-A-55-146786), but it is difficult to obtain a sufficient ink absorption capacity by this method.

Apart from the development of these recording papers, as one of the methods for solving these problems, an attempt has been made to improve the absorbency of the ink by lowering the surface tension of the ink (Japanese Patent Application Laid-Open (JP-A) no. (Showa 59-20366, and JP-A-3-41171). As a result, the ink of the conventional inkjet printer has a surface tension of 50 dyne / c.
m, but now 30-45 dyne
/ Cm having a surface tension in the range of / cm.

Nevertheless, it is still difficult to satisfy both feathering and ink absorptivity with a finely coated ink jet recording paper having a plain paper feeling, and measures must be taken from the paper side. The present inventors have conducted intensive studies to solve the above problems, and as a result, by adjusting the porosity of the wood pulp used for the base paper, it is possible to obtain a plain paper feeling excellent not only in characters but also in color image reproducibility. The present inventors have found that an inkjet recording paper having the same can be manufactured, and have reached the present invention.

[0018]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a plain paper feel in terms of writing and handling with a pencil, and to reduce blurring of characters and ruled lines, and to improve character quality and quality. An object of the present invention is to provide an inexpensive fine-coating type ink jet recording paper excellent in color image reproducibility.

[0019]

SUMMARY OF THE INVENTION The object of the present invention is to provide at least one surface of a base paper mainly composed of wood pulp and filler.
An ink jet recording paper provided with an ink receiving layer containing a superabsorbent pigment and a binder as main components in an amount of 0.5 to 5.0 g / m ^{2 on} one side, wherein the content of the filler is 100 parts by weight of wood pulp. 0 to 10 parts by weight, and the contact angle of the ink receiving layer measured using a liquid having a surface tension of 40 dyne / cm is in the range of 85 to 100 degrees. 25-100%
Was achieved by an ink jet recording sheet characterized by L-BKP having a Runkel ratio of 1.0 to 3.0.

Hereinafter, the ink jet recording paper of the present invention will be described in detail. The raw material of the wood pulp used in the present invention can be appropriately selected from L-BKP, N-BKP, recycled pulp, mechanical pulp and the like.
-BKP has a tendency to reduce image quality due to feathering and the like because the fibers are thicker and longer than L-BKP, and mechanical pulp tends to affect the texture of paper and lose the feeling of plain paper. 75% of the pulp fiber
It is necessary that the above is L-BKP, and in the present invention, particularly, the Runkel ratio of this L-BKP is 1.0 to 3.0.
It is necessary to

The Runkel ratio R is one of the indices for characterizing the morphology of the pulp fiber, and as shown in FIG. 1, a value determined by the width L of the lumen (lumen) of the fiber and the thickness t of the cell wall. And is represented by R = 2 · t / L.
The Runkel ratio is measured in "On the Morphological Properties of Wood Fibers and the Properties of Paper" by Masao Moriya, Journal of the Japan Pulp and Paper Technology, No. 2.
The method may be performed by the method described in Vol. 1, No. 3, page 20.

When paper is made using pulp fibers having a large Runkel ratio, a porous paper having a small bonding area between the fibers is obtained, and the ink absorbency is improved. If the Runkel ratio is too large, the bonding area between the fibers becomes very small, so that the strength and the stiffness are reduced, not only impairing the feeling of plain paper, but also the surface properties are reduced, so that the printing suitability is also reduced.

By the way, pulp is usually used after being beaten. However, since the progress of beating increases the bond between fibers and makes the paper denser, the pulp having a Runkel ratio larger than that usually used is used. This is in a direction to offset the effect of the present invention by using fibers. Therefore, in the present invention, the freeness is 450 to 60 without much beating.
0 ml C.I. S. F. In particular, it is preferable to make the range as high as 500 to 600.

As described above, the Runkel ratio is 1.0 to 3.0.
By keeping the L-BKP pulp fiber content of at least 25% of the total pulp fiber and maintaining a high freeness as required, sufficient ink absorbency can be maintained without deteriorating feathering. However, even in this case, if the contact angle with ink having a surface tension of the recording paper surface of 40 dyne / cm exceeds 100 degrees, the ink absorbency becomes insufficient.

In order to improve feathering, the contact angle is preferably 85 degrees or more.
In addition, the measurement of the contact angle is based on TAPPI standard.
d Value measured according to T458 OM-84.
However, when a solution of 40 dyne / cm is used as the test solution, the change in the contact angle is large, so that the measurement needs to be performed within 0.1 second after dropping.

Therefore, the contact angle is adjusted by adding a filler or a sizing agent to the base paper in the present invention. The internal filler is
While improving the ink absorption capacity, if too much, as described above, the opacity increases and the image density decreases,
It is preferable that the content be 10 parts by weight or less per 100 parts by weight of the pulp fiber. Such a filler can be appropriately selected from known fillers such as calcium carbonate, talc, and kaolin.

On the other hand, the internal sizing agent has a contact angle of 85 to 1 with a liquid having a surface tension of 40 dyne / cm.
It is necessary to adjust the size together with the (externally added) sizing agent of the ink receiving layer so as to be 00 degrees. However, from the viewpoint of coatability and permeability of the coating solution, the Stighit sizing degree of the base paper is 5 seconds or more. It is preferable to adjust so that As the internal sizing agent used in the present invention, any of an acidic sizing agent and a neutral sizing agent may be used, but a neutral sizing agent such as AKD, ASA or neutral rosin is preferable from the viewpoint of color development. In the present invention, other internal chemicals such as a paper strength enhancer can also be used as appropriate.

Next, as the pigment for the ink receiving layer provided on at least one side of the base paper, various known white pigments such as kaolin and calcium carbonate can be used in combination. It is necessary to use a highly absorbent pigment as a main component in order to obtain a high image density. The high-absorbing pigment is a pigment having a specific surface area of 100 cm ² / g or more according to the BET method, and a large amount of voids are formed in a coating layer when the coating is performed using the pigment.

As the binder used in the ink receiving layer, various modified starches and latexes can be used, but it is particularly preferable to use polyvinyl alcohol (PVA) from the viewpoint of image clarity and the like.
In particular, it is preferable to use PVA having a degree of polymerization of 1,000 or less. If the ink receiving layer is provided on one side of the base paper, it becomes a single-sided recording paper, and if it is provided on both sides, it is possible to obtain a double-sided recording paper capable of providing substantially the same quality of recorded images on both sides.

In the present invention, from the viewpoint of obtaining a high image density with a color ink jet printer and providing a feeling of plain paper, the coating amount of the ink receiving layer is set to 0.5 to 5.0 g / side per side. and m ^2. 0.5
g / m ² or less, a sufficient image density cannot be obtained and 5.0 g
If it is more than / m ² , the pencil writing property and the feel of plain paper will be lost.

The coating method for providing the ink receiving layer is as follows.
Air knife coating or bar coating or various blade coatings can also be used, but using a coating device installed in a paper machine such as a size press or gate roll,
You may provide by performing what is called on-machine coating.

[0032]

According to the ink jet recording paper of the present invention, 75% or more of the wood pulp has a Runkel ratio of 1.0 to 3.0.
-Since it is BKP, both feathering and ink absorption are good. Further, since an extremely thin ink receiving layer is provided, the feeling of plain paper is sufficient, the image density is high, and a sufficiently high quality recorded image can be obtained even for color ink jet recording.

[0033]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In the examples,% indicates% by weight, and part indicates parts by weight.
The measurements in the examples were performed as follows.

(1) Runkel ratio: According to the method described in "On the Morphological Properties of Wood Fibers and the Properties of Paper", by Masao Moriya, Journal of the Japan Institute of Paper and Pulp, Vol. 21, No. 3, page 20. Thin sections were collected from the wood chips before cooking, stained, photographed at a magnification of 500 times with a microscope, and the average value of 1000 fibers was determined.

(2) Contact angle: The measurement liquid was a wetting index standard liquid No. manufactured by Wako Pure Chemical Industries, Ltd. 40 (Surface tension 40d
yne / cm), the contact angle of the measurement liquid 0.1 seconds after the dropping was measured using an automatic contact angle meter CA-Z manufactured by Kyowa Interface Chemical Co., Ltd. (3) Recording density: A predetermined recording pattern is printed using an ink jet recording apparatus (DeskJet 505J: trade name) manufactured by Hewlett-Packard Company, and the solid black portion is measured using a Macbeth densitometer (RD514: trade name). did.

(4) Feathering: an ink jet recording apparatus manufactured by Hewlett-Packard Company (Desk Jet 505J:
Using the product name), a predetermined recording pattern was printed, and the bleeding of the whisker-like ink in the ruled line portion was visually observed, and evaluated as follows. ：: good △: slight whisker bleed ×: severe whisker bleed (5) Ink drying time: a predetermined recording pattern was printed using an inkjet recording device (Desk Jet 505J: trade name) manufactured by Hewlett-Packard Company. Thereafter, the printed portion was rubbed with a hand, and the time required for the ink to apparently dry and no longer stain was measured.

(6) Bleeding: an ink jet recording apparatus (Desk Jet 505J, manufactured by Hewlett-Packard Company)
: Product name), print a predetermined recording pattern,
The boundary between red (a mixed part of magenta and yellow) and green (a mixed part of cyan and yellow) was magnified and observed, and the width of the bleeding at the boundary was measured. .

Embodiment 1 A mixture of 50 parts of L-BKP produced from eucalyptus from Newcastle, Australia (runkel ratio of 2.35) and 50 parts of L-BKP produced from eucalyptus from Tasmania (runkel ratio of 0.66), and having a freeness of 500 ml
C. S. F. The pulp slurry was adjusted beaten in, then ground calcium carbonate to the pulp slurry,琉酸aluminum 1.0 parts 1 part of cationized starch, sizing agent (alkyl ketene dimer) 0.1 parts of a retention aid 0 .
A stock to which 02 parts was added was prepared. From the obtained stock,
Using a fourdrinier paper machine, paper was made so that the basis weight was 78 g / m ² and the amount of filler in the paper was 5.8%, and the following coating solution 1 was applied to both sides using a size press.

Coating liquid 1 Synthetic silica: Fine seal (trade name, manufactured by Tokuyama Soda Co., Ltd.): 100 parts Binder: PVA117 (trade name, manufactured by Kuraray Co., Ltd.): 20 parts Sizing agent: Vasoplast 250D (trade name, manufactured by Basof) ): 10 parts Antifoam: Formaster AP (trade name, manufactured by San Nopco): 0.05 parts

Embodiment 2 FIG. A mixture of 70 parts of L-BKP produced from Acacia from South Africa (runkel ratio 1.49) and 30 parts of L-BKP from Hokkaido (runkel ratio 0.46) was mixed with a freeness of 450 ml C.I. S. F. An internal chemical was added to the pulp slurry beaten in the same manner as in Example 1 to prepare a stock. From the obtained stock, paper is made using a fourdrinier paper machine so that the basis weight is 61 g / m ² and the amount of filler in the paper is 7.5%, and the following coating liquid is used using a gate roll coater. 2 was coated on both sides.

Coating Solution 2 Synthetic silica: Mizuka Seal (trade name, manufactured by Mizusawa Chemical): 100 parts Binder: PVA117 (manufactured by Kuraray): 10 parts Sizing agent: NC size C-40 (manufactured by Nichika Chemical Co., Ltd.) Name): 12 parts Antifoam: Formaster AP (manufactured by San Nopco): 0.05 parts

Embodiment 3 FIG. A mixture of 50 parts of L-BKP produced from eucalyptus (Runkel ratio 2.35) from Newcastle, Australia and 50 parts of L-BKP produced from acacia (Runkel ratio 1.49) from South Africa was mixed to give a freeness of 520 ml. S. F. An internal chemical was added to the pulp slurry beaten in the same manner as in Example 1 to prepare a stock. From the obtained paper stock, using a fourdrinier paper machine,
Paper was made so that the basis weight was 125 g / m ² and the amount of filler in the paper was 3.2%, and the following coating solution 2 was applied to both sides using a size press.

Coating liquid 3 Synthetic silica: Aerosil (trade name, manufactured by Nippon Aerosil Co.): 100 parts Binder: PVA105 (trade name, manufactured by Kuraray): 10 parts Sizing agent: BLS-720 (trade name, manufactured by Misawa Ceramics): 10 parts Antifoam: Formaster AP (manufactured by San Nopco): 0.05 parts

Comparative Example 1 100 parts of L-BKP produced from eucalyptus from Tasmania (Runkel ratio: 0.66) was filtered at a freeness of 500 ml. S. F. An internal chemical was added to the pulp slurry beaten in the same manner as in Example 1 to prepare a stock. From the obtained paper stock, paper is made using a fourdrinier paper machine so that the basis weight is 78 g / m ² and the amount of filler in the paper is 5.5%. Was coated on both sides.

Comparative Example 2 100 parts of L-BKP from Hokkaido (Runkel ratio 0.46) was drained at a freeness of 400 ml. S. F. An internal chemical was added to the pulp slurry beaten in the same manner as in Example 1 to prepare a stock. From the obtained paper stock, paper is made using a fourdrinier paper machine so that the basis weight is 61 g / m ² and the amount of filler in the paper is 7.5%, and the above coating liquid is used using a gate roll coater. 2 was coated on both sides.

Comparative Example 3 A stock was prepared exactly as in Example 3. From the obtained stock, paper was made using a fourdrinier paper machine so that the basis weight was 125 g / m ² and the amount of filler in the paper was 3.3%. Was coated on both sides.

Coating liquid 4 Synthetic silica: Aerosil (manufactured by Nippon Aerosil Co., Ltd.): 100 parts Binder: PVA105 (manufactured by Kuraray Co., Ltd.): 10 parts Antifoaming agent: Formaster AP (manufactured by San Nopco): 0.05 part

Comparative Example 4 100 parts of L-BKP produced from eucalyptus produced in Tasmania (Runkel ratio 0.66) was dried at 400 ml C.I. S. F. An internal chemical was added to the pulp slurry beaten in the same manner as in Example 1 to prepare a stock. From the obtained stock, paper was made using a fourdrinier paper machine so that the basis weight was 78 g / m ² and the amount of filler in the paper was 5.5%. Was coated on both sides.

Coating liquid 5 Synthetic silica: Fine seal (manufactured by Tokuyama Soda Co.): 100 parts Binder: PVA117 (manufactured by Kuraray): 20 parts Sizing agent: BLS-720 (manufactured by Misawa Ceramics): 30 parts Antifoaming agent : For Master AP (manufactured by San Nopco): 0.05 parts

Comparative Example 5 L-BKP70 manufactured from Indonesian mangrove (Runkel ratio 3.35)
And L-BK manufactured from Tasmanian eucalyptus
P30 mixed with 500 ml of freeness: C.I. S. F. An internal chemical was added to the pulp slurry beaten in the same manner as in Example 1 to prepare a stock. Using a fourdrinier machine from the obtained paper stock, the basis weight is 78 g / m ² and the amount of filler in paper is 5.
The paper was made so as to be 6%, and the above-mentioned coating solution 1 was coated on both sides using a size press.

Embodiment 4 FIG. From the paper stock obtained in exactly the same manner as in Example 1, paper was made using a Fourdrinier paper machine so that the basis weight was 78 g / m ² and the amount of filler in the paper was 5.2%, and the size was pressed using a size press. A 3% solution of oxidized starch was applied to both sides. Coating solution 1 was applied to one side of the obtained paper with a Meyer bar coater, and a 3% solution of PVA105 was applied to the opposite side for curl adjustment.

The pulp material type, Runkel ratio, blending ratio and freeness used in each of the examples and comparative examples are as shown in Table 1. In addition, in each of Examples and Comparative Examples, the measurement results of the coating amount of the ink receiving layer, the contact angle, and the recording density of the recorded image, feathering, ink drying time, and bleeding are as shown in Table 2. .

[0053]

[Table 1]

[0054]

[Table 2]

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross-sectional shape of a pulp fiber for explaining a Runkel ratio.

[Explanation of symbols]

 L Width of fiber lumen (lumen) t Fiber wall thickness

──────────────────────────────────────────────────続 き Continuing on the front page (72) Michiko Okamoto, Inventor 1-30-6 Kamiochiai, Shinjuku-ku, Tokyo Nihon Paper Industries Co., Ltd. Product Development Laboratory (72) Inventor Yoshihiro Kuroyama 1-30, Kamiochiai, Shinjuku-ku, Tokyo No. 6 Nihon Paper Industries Co., Ltd. Product Development Laboratory (56) References JP-A-7-61112 (JP, A) JP-A-62-177299 (JP, A) JP-A-3-41171 (JP, A) JP-A-5-254239 (JP, A) JP-A-4-341885 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/00 D21H 15/00

Claims (2)

(57) [Claims] 1. An ink receiving layer containing a highly absorbent pigment and a binder as a main component is provided on at least one surface of a base paper mainly composed of wood pulp and a filler in an amount of 0.5 to 5.0 g / m 2 per surface.
^{2. An} ink jet recording paper provided, wherein the content of the filler is 0 to 10 with respect to 100 parts by weight of wood pulp.
Parts by weight, and the contact angle of the ink receiving layer measured using a liquid having a surface tension of 40 dyne / cm is 85.
An ink jet recording paper having a range of 100 to 100 degrees and 25 to 100% of the wood pulp in the base paper is L-BKP having a Runkel ratio of 1.0 to 3.0. 2. The average freeness of all wood pulp in the base paper is 4
50-600 ml C.I. S. F. The inkjet recording paper according to claim 1, wherein