JP2000062309A - Ink jet recording sheet and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an ink jet recording sheet of superior ink absorbability provided with dots of small diameter and almost of the round shape and generating no powder dropping. SOLUTION: An ink jet recording sheet is formed of pulp as a main raw material, and the corona discharge treatment is applied with the 70-150 W/m2/ minute power to be treated on the surface of a base paper containing a sizing agent of 0.1% or more to pulp and then an ink acceptive layer is applied on a corona discharge treated surface of the base paper within 60 minutes after the treatment. The corona discharge treatment is carried out just before the coating of the ink acceptive layer by an on-coater corona discharge treatment device. Also the wetting properties of the surface of the base paper on which the sizing agent is destroyed by the corona discharge treatment is improved by 3-5 dyne/cm2 more than the wetting properties of an untreated base paper.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an ink jet recording sheet. More specifically, the ink absorbency is good, the dot diameter is small, and the shape is close to a perfect circle.
The present invention also relates to an inkjet recording sheet with less powder falling off and a manufacturing method thereof.

[0002]

2. Description of the Related Art An ink jet recording system is a system in which minute droplets of ink are ejected by various operating principles and adhered to a recording sheet such as paper to record images, characters, etc. It has features such as easy multicoloring, great flexibility in recording patterns, and no need for development-fixing.
As a recording device for various figures and color images including kanji, it is rapidly spreading for various purposes.

As a recording sheet used in this ink jet recording system, various efforts have been made in terms of devices and inks so that high quality paper or coated paper used in ordinary printing and writing can be used. It was However, as the performance of inkjet recording devices such as faster printing, full-color printing, and higher definition of photo-like has been improved and the applications have been expanded, high quality image quality has been demanded. Inkjet recording sheets having both characteristics have been required. (1) High image density. (2) Good ink absorption. (3) The dot diameter is small and the shape is close to a perfect circle. (4) In the coat type recording sheet, the ink receiving layer has high adhesiveness and less powder is removed.

Among the characteristics required for an ink jet recording sheet, it is most important that the image quality is good and there is no bleeding. For that purpose, it is necessary to increase the absorbency and reduce the dot diameter. As the inkjet recording sheet, the one in which a white inorganic pigment having excellent absorbability such as porous synthetic amorphous silica is coated as a main component in the ink receiving layer on a base paper made from pulp as a main raw material is mainstream. Is. If the average particle diameter of the synthetic amorphous silica in the ink receiving layer is reduced, the dot diameter can be reduced and excellent image quality can be obtained. However, the adhesiveness between the base paper and the ink receiving layer deteriorates, and the powder drops more frequently.

Further, as in JP-A-58-132586 or JP-A-59-35977, by increasing the size of the base paper, the ink receiving layer is not absorbed by the base paper, so that the print density is high. , A clear image is obtained,
It is described that since the water-soluble binder in the ink receiving layer is not absorbed by the base paper, it is possible to reduce powder falling. In order to create a high-definition and clear image, there is a method of reducing the bleeding and reducing the dot diameter by absorbing a part of the ink with the base paper because the amount of ink is large. In that case, it was disadvantageous to give the base paper sizeability.

[0006] In order to improve properties such as adhesiveness of the barrier between the base paper and the ink receiving layer, a method of performing corona discharge treatment on the base paper has already been reported. Japanese Unexamined Patent Publication No. 4-345883 describes that corona discharge treatment may be performed on the pulp-processed base paper in order to improve the adhesion to the ink receiving layer. However, nothing is described about the effect of corona discharge treatment on the sizing agent contained in the base paper.

There is a method of increasing the adhesiveness and lowering the absorptivity of the ink-receiving layer of the ink jet recording sheet by adding a water-soluble binder, a water-proofing agent and the like to suppress powder drop. Cannot be made smaller. There was no means other than the investigation of the base paper and the coating composition for suppressing the powder drop of the inkjet recording sheet, improving the absorbability, and reducing the dot diameter.

[0008]

SUMMARY OF THE INVENTION The present invention provides a base paper for an ink jet recording sheet and an ink receiving layer,
Examination of the base paper and coating composition by increasing the size of the base paper made from pulp as the main raw material to prevent the ink receiving layer from penetrating into the base paper and increasing the adhesiveness between the base paper and the ink receiving layer. By the method other than, the ink absorption is good,
An object of the present invention is to provide an inkjet recording sheet having a small dot diameter, a shape close to a perfect circle, and less powder falling off, and a manufacturing method thereof.

[0009]

As a result of various studies on the relationship between the base paper of an ink jet recording sheet and the ink receiving layer, the inventors have invented the ink jet recording sheet of the present invention and a method for producing the same. That is, according to the method for producing an inkjet recording sheet of the present invention, a corona discharge treatment is applied to the surface of a base paper containing pulp as a main raw material and containing a sizing agent in an amount of 0.1% or more with a treatability of 70 to 150 W / m ² / min. It is characterized in that the ink receiving layer is applied to the corona discharge treated surface within 60 minutes after the application.

Further, the method for producing an ink jet recording sheet of the present invention is characterized by an on-coater corona discharge treatment in which the corona discharge treatment is carried out immediately before the coating of the ink receiving layer.

The ink jet recording sheet of the present invention is an ink jet recording medium sheet in which an ink receiving layer is provided on the surface of a raw paper, and the wettability of the surface of the raw paper obtained by corona discharge treatment to destroy the sizing agent is untreated. 3-5 compared to
It is characterized by improving dyne / cm ² .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The ink jet recording sheet of the present invention will be described in detail below. The base paper in the present invention comprises various pulps and various fillers, sizing agents, fixing agents, dyes, retention aids and other auxiliary materials, and may be coated with starch and a water resistant agent by a size press or the like. The various pulps may be wood pulp such as LBKP, NBKP, NBSP, GP, etc., non-wood pulp such as hemp, bagasse, bamboo, etc., and may also include deinked pulp of used paper. Further, synthetic fibers, synthetic pulp, etc. may be used. The various fillers may include talc, heavy calcium carbonate, light calcium carbonate kaolin, titanium and the like, and are not particularly limited. The sizing agent may be an acidic sizing agent or an alkaline sizing agent such as rosin size, alkyl ketene dimer, and alkenyl succinic anhydride. Various fillers in size press
The pigment, surface sizing agent, and binder may be applied, and the presence or absence of size press is not limited.

The base paper in the present invention may be acidic papermaking or alkaline papermaking, and the pH of white water at the time of papermaking is not particularly limited, but the sizing agent is at least 0.1% based on the pulp.
The above is included. If the sizing agent is less than 0.1% of the pulp, the water repellency of the base paper is insufficient, and when the coating liquid of the ink receiving layer is smeared on the base paper, the water-soluble binder contained in the coating liquid penetrates into the base paper, Since the amount of the water-soluble binder contained in the receiving layer is reduced, the adhesiveness between the base paper and the ink receiving layer is weakened, and the disadvantages such as powder falling off as an inkjet recording sheet occur, which is not preferable. In addition, the effect of corona discharge treatment, which will be described later, cannot be obtained, which is not preferable.

The corona discharge treatment in the present invention will be described. 5-30 by high frequency impulse electron irradiation method
It was carried out under the condition of a frequency of 20 to 100 kHz at a voltage of kV. First, a firing voltage of 1.0 microsecond or less, which is close to 30 kV, is applied to make the first contact with the surface of the base paper, and then 6
The relatively low voltage of -10 kV continues, which makes it possible to form a constant high-frequency current inside the base paper. With this system, a small number of millions of times per second, but effective sparks are generated, and the current beam penetrates to approximately 0.001 mm below the surface of the base paper, and there is a change in the molecular structure of the composition that constitutes the base paper. The sizing agent contained in the waking base paper is destroyed. Uniform size and density on the surface of the base paper with a depth of 0.0
Since the pinhole of about 01 mm is formed and the sizing agent in that part is destroyed, the wetting property of the surface of the base paper is improved. When the sizing agent for the base paper containing pulp as the main raw material is contained in the pulp in an amount of 0.1% or more, corona discharge treatment improves the wettability of the surface of the base paper. If it is less than 0.1%, the improvement of the wetting property of the base paper is insufficient, which is not preferable.

In the present invention, the reason why the wetting property of the surface of the base paper which has been subjected to the corona discharge treatment to destroy the sizing agent is improved by 3 to 5 dyne / cm ² as compared with the untreated base paper will be described. In the present invention, it was considered necessary to improve the wetting property of the base paper in order for the ink to be absorbed on a part of the surface of the base paper. Generally, the wetting property of the ink is 30 to 37 dynes / cm ² , while that of the base paper made from pulp as the main raw material is 30 to 37 dynes / cm ² .
It is 60 dynes / cm ² , and the higher the wettability of the base paper compared to the wettability of the ink, the better the ink absorbability. When the improvement of the wettability of the surface of the base paper exceeds 5 dyne / cm ² as compared with the untreated base paper, the absorptivity is improved, but the adhesiveness between the base paper and the ink receiving layer is decreased, and powder falling off is more preferable. Absent. If it is less than 3 dynes / cm ² , the improvement of ink absorption is insufficient and the dot diameter does not become so small.
Bleeding does not improve, which is not preferable.

In the present invention, the wetting property of the surface of the base paper which has been subjected to corona discharge treatment to destroy the sizing agent is 3 to 3 as compared with the untreated base paper.
The treatability of the corona discharge treatment was determined so that it would be improved by 5 dynes / cm ² . Under the conditions of corona discharge treatment, the intensity of the current beam irradiation affects the number, depth and density of pinholes on the surface of the base paper, the degree of destruction of the sizing agent, and the wettability. Therefore, that is, since this is the wattage per unit area per hour, it is determined by the power, the processing width and the processing speed, and the base paper containing pulp as the main raw material and the sizing agent in an amount of 0.1% or more of the pulp is When the corona discharge treatment is performed so that the treatment capacity is 70 to 150 W / m ² / min, the wetting property of the surface of the base paper is 3 to
It was found that the improvement was 5 dynes / cm ² . Processing capacity is 7
If it is less than 0 W / m ² / min, the size will not be sufficiently destroyed and absorption will be insufficiently improved. Therefore, the dot diameter after printing will not be small and bleeding will not be improved, which is not preferable. When the processability exceeds 150 W / m ² / min, the absorption is sufficiently improved, but the sizing agent is excessively destroyed, and the water-soluble binder of the ink receiving layer penetrates into the base paper. Adhesion is weakened and powder is often removed, which is not preferable.

After the corona discharge treatment is applied to the surface of the base paper, the effect of the corona discharge treatment is attenuated over time and the wetting property is lowered. Therefore, it is necessary to apply the ink receiving layer as soon as possible. . In the present invention, it has been found that if the ink receiving layer is coated within 60 minutes after the corona discharge treatment on the surface of the base paper, the wettability is not lowered and there is no problem. The on-coater corona discharge treatment, which is performed immediately before the coating of the ink receiving layer, is most preferable. The corona discharge treatment and the coating of the ink receiving layer may be performed by different machines, but the ink receiving layer needs to be coated within 60 minutes after the corona discharging treatment. After a lapse of 60 minutes or more, moisture is absorbed from the surface of the stencil having a wettability, the effect of the corona discharge treatment is attenuated, the wettability is lowered, and the ink absorptivity is lowered, which is not preferable.

In the present invention, the ink receiving layer is applied within 60 minutes after the corona discharge treatment is applied to the surface of the base paper. Here, the ink receiving layer is at least one layer and is composed of a white inorganic pigment, a water-soluble polymer binder, a cationic dye fixing agent, acidic colloidal silica, a hydroxide of an alkaline earth metal, and the like. The number of layers and the coating composition are not particularly limited as long as the absorbency and the adhesiveness to the base paper are balanced. The coating method is air knife, blade coater,
A method using a curtain coater or the like can be considered, but the method is not particularly limited. In the coating composition, the surface tension of the coating liquid is high when the absorption is prioritized, and the surface tension of the coating liquid is low when the adhesiveness is prioritized.

Examples of white inorganic pigments used in the ink receiving layer of the ink jet recording sheet of the present invention include calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white. , White silicate pigments such as aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, synthetic amorphous silica, pseudo-boehmite, aluminum hydroxide, alumina, lithopone, zeolite, hydrohaloysite, magnesium carbonate, magnesium hydroxide, styrene plastic pigment , Polyethylene, microcapsules, urea resins, melamine resins, and other organic pigments. Among these, a porous inorganic pigment is preferable as a main component in the ink receiving layer, and examples thereof include porous synthetic amorphous silica, porous magnesium carbonate, and porous alumina.
In particular, porous synthetic amorphous silica having a large pore volume is preferable.

Examples of the water-soluble polymer binder used in the ink receiving layer of the present invention include starch derivatives such as oxidized starch, etherified starch and phosphoric esterified starch; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; casein. , Polyvinyl alcohol derivatives such as gelatin, soybean protein, polyvinyl alcohol, or silyl-modified polyvinyl alcohol; polyvinylpyrrolidone, maleic anhydride resin, styrene-
Conjugated diene copolymer latex such as butadiene copolymer and methyl methacrylate-butadiene copolymer; Acrylic (co) polymer latex such as polymer or copolymer of acrylic acid ester and methacrylic acid ester; Ethylene vinyl acetate Vinyl-based copolymer latex such as copolymer; or functional group-modified (co) polymer latex with functional group-containing monomer such as carboxy group of these various (co) polymers; melamine resin, urea resin, etc. Water-based adhesive such as thermosetting synthetic resin; polymer or copolymer resin of acrylic acid ester or methacrylic acid ester such as polymethylmethacrylate; polyurethane resin,
Mention may be made of unsaturated polyester resins, vinyl chloride-vinyl acetate copolymers, polyvinyl butyral, alkyd resins. Among these aqueous polymer binders, polyvinyl alcohol or a polyvinyl alcohol derivative such as silanol-modified polyvinyl alcohol is preferable from the viewpoint of adhesive strength.

The cationic dye fixing agent used in the ink receiving layer of the present invention is a monomer, oligomer or polymer of a primary to tertiary amine or quaternary ammonium salt which dissociates and exhibits a cationic property when dissolved in water. Of these, oligomers and polymers are preferable. Especially, the cation charge amount by colloid titration is 1
-10 meq. / G of cationic dye fixing agent. 1
meq. If it is less than / g, the fixing performance of the water-soluble dye in the ink is poor, and the water resistance of the recorded image is reduced. 10m
eq. If it exceeds / g, the water resistance of the recorded image can be improved with a small amount, but the light resistance and ozone resistance of the recorded image are inferior, and the inkjet recording sheet tends to yellow.

The acidic colloidal silica used in the ink receiving layer in the present invention is preferably contained in an amount of 10 to 50 parts by weight, more preferably 20 to 50 parts by weight, based on 100 parts by weight of the white inorganic pigment. . It is preferable that the water-soluble polymer binder is contained in an amount of 10 to 100 parts by weight, the cationic dye fixing agent is included in an amount of 0.1 to 5 g / m ² , and the cationic charge amount is included in an amount of 0.1 to 50 meq / m ² .

In the ink jet recording sheet of the present invention, after the ink receiving layer is coated, calendering is performed, and the water-soluble binder and the cationic fixing agent / white pigment are pressure-bonded to make the printed surface smooth and to remove powder. So that it doesn't come out.

In the present invention, the coating amount of the ink receiving layer is not particularly limited, but the dry coating amount is preferably in the range of 5 to 15 g / m ² . When the coating amount of the ink receiving layer is less than 5 g / m ² , the image density, color and sharpness are low, and feathering may occur. When the coating amount exceeds 15 g / m ² , the drying load after coating increases, not only the productivity decreases due to the decrease in coating speed, but also the binder in the ink receiving layer evaporates at high load drying. It moves to the surface of the ink receiving layer together with the solvent, reduces the amount of voids on the surface, hinders ink absorption during recording, and causes scumming, which is not preferable.

Other additives may be added to the support and the ink receiving layer in the ink jet recording sheet of the present invention.
Pigment dispersant, thickener, fluidity improver, defoamer, foam suppressor,
A release agent, a foaming agent, a penetrating agent, an anti-bacterial agent, a waterproofing agent, a wet paper strength enhancer, a dry paper strength enhancer, a dye and the like can be appropriately added.

The ink used in the present invention is a colorant, a solvent,
It is a recording liquid containing other additives. Examples of the colorant include direct dyes, acid dyes, basic dyes, reactive dyes, water-soluble dyes such as food dyes, and color pigments. Other additives include, for example, a pH adjusting agent, a sequestering agent, an antifungal agent, a viscosity adjusting agent, a surface tension adjusting agent, a wetting agent, a surfactant and a rust preventive agent. In the inkjet recording sheet of the present invention, oil-based ink, that is, dye or pigment ink containing a so-called hydrophobic organic solvent may be used for recording.

[0027]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. Further, “parts” and “%” shown in the examples represent parts by weight and% by weight, unless otherwise specified.

<Preparation of Base Paper 1> Base paper 1 was prepared as a support for the ink jet recording sheet of the present invention. Freeness 470 ml LBKP 50 parts of CSF, Freeness 480 ml
A pulp slurry consisting of 50 parts of NBKP of CSF was beaten to a final freeness of 380 mlcsf, 5 parts of heavy calcium carbonate and 5 parts of talc were added, and after stirring, cationic starch 0.6
Parts, alkyl ketene dimer 0.15 parts, and retention aid 0.002 parts were sequentially added to adjust the pH of the pulp slurry to 8.2, papermaking dried with a Fourdrinier paper machine, and continuously dissolved tapioca An aqueous solution of oxidized starch was impregnated with a size press to a solid content of 5 g / m ² on both sides, dried, and machine calendered to obtain base paper 1 having a basis weight of 75 g / m ² . The thus obtained base paper 1 had a Steckigt sizing degree of 40 seconds and a wettability of 53 dynes / cm ² .

<Preparation of Base Papers 2 to 7> Base papers 2 to 7 were prepared as supports for the ink jet recording sheet of the present invention. Base papers 2 to 6 were prepared in the same manner as the base paper 1 except that the conditions such as the blending / freeness of pulp, the kind and ratio of the filler, and the kind and ratio of the sizing agent were changed. Base papers 1 to 4 are alkaline papers and are shown in Table 1. The base papers 5 to 7 are acidic paper base papers and are shown in Table 2.

<Preparation of Coating Liquid 1> The coating liquid 1 to be the ink receiving layer of the ink jet recording sheet of the present invention was prepared by the following procedure. 25% caustic soda solution 2 in 500 parts of water
After adding 100 parts (solid 0.5 part), 100 parts of amorphous silica (Mizukasil P78D, manufactured by Mizusawa Chemical Co., Ltd.) was added and stirred and dispersed to prepare a silica dispersion slurry having a concentration of 16.6%. To this, polyvinyl alcohol (R polymer 113
0, 200 parts of a 10% aqueous solution of Kuraray Co. (solid 20
10 parts (solid 5 parts) of an ethylene vinyl acetate copolymer aqueous emulsion (OM6000, manufactured by Kuraray Co., Ltd.), an acrylic acid sialylamine hydrochloride copolymer (Smilet's resin 1001, (Sumitomo Chemical Co., Ltd.)
100 parts (solid 30 parts), styrene-acrylic acid ester copolymer dispersion (VasoPlast 265D, B
ASF Co., Ltd.) 25 parts (solid 5 parts) and polyoxyethylene (Olfin E1010, Nisshin Chemical Co., Ltd.) 0.05 parts were added and stirred gently, concentration 15%, PH 5.6, viscosity 100.
A coating liquid 1 having a cps (15 ° C.) was prepared. The surface tension of the coating liquid 1 was measured and found to be 39 dynes / cm ² .

<Preparation of Coating Liquid 2> The coating liquid 2 to be the ink receiving layer of the ink jet recording sheet of the present invention was prepared by the following procedure. With the formulation shown in Table 3, the concentration was 19%, PH6.
2. A coating liquid 2 having a viscosity of 190 cps (15 ° C.) was prepared.
The mixing method and the concentration were different, but the stirring method was the same as that of the coating liquid 1. Fine Seal X-60 (manufactured by Tokuyama Corp.) was used as the amorphous silica, and Kycor BBL (manufactured by Nippon Soda Co., Ltd.) was used as the fluorescent dye. When the surface tension of coating liquid 2 is measured, it is 44
It was dynes / cm ² .

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

Comparative Example 1 Coating liquid 1 was coated on the surface of base paper 1 by air knife coating at a coating solid content of 7 g / m ² to form an ink receiving layer, and dried.
Then, it was passed through a calendar at 10 kg / cm ² to obtain an inkjet recording sheet of Comparative Example 1.

Comparative Example 2 An on-coater corona discharge treatment device having a width of 0.7 m and a distance from the corona discharge treatment device to the air knife coating portion of 4 m on the surface of the base paper 1 was subjected to high frequency impulse electron irradiation of 100 kHz at a voltage of 2. Corona discharge treatment was performed at 0.2 kV, current 0.8 A, machine speed 50 m / min, and immediately after that, coating liquid 1
Was coated with an air knife coating at a coating solid content of 7 g / m ² , an ink receiving layer was provided, and the coating was dried. The corona discharge treatment capacity at this time is calculated by the following mathematical formula 1.

[0037]

## EQU1 ## Corona discharge treatment capacity (W / m ² / min) = (voltage V) × (current A) ÷ (width m) ÷ (machine speed m / min) (Formula 1) Ink after corona discharge treatment The time until coating the receiving layer is calculated by the following mathematical formula 2.

[0038]

## EQU00002 ## T = D / S (Equation 2) where T is the time from the corona discharge treatment until the ink receiving layer is applied, and D is the time from the corona discharge treatment device to the ink receiving layer coating portion. Distance, S represents machine speed.

The corona discharge treatment capacity is 50 W according to Equation 1.
/ M ² / min, the time from the corona discharge treatment to the coating of the ink receiving layer was 4.8 seconds according to Formula 2.
After that, pass it through a super calendar at 10 kg / cm ² ,
An inkjet recording sheet of Comparative Example 2 was obtained.

Examples 1 to 3 and Comparative Example 3 The voltage of the on-coater corona discharge treatment device was 3.1 kV,
Inkjet recording sheets of Examples 1 to 3 and Comparative Example 3 were obtained in exactly the same manner as Comparative Example 2 except that the voltage was set to 4.4 kV, 6.5 kV, and 7.5 kV. The corona discharge treatability at this time was calculated in the same manner as in Comparative Example 2, and was 71 and 10 respectively.
It was 1,149,171 W / m < ² > / min.

Comparative Examples 4 to 12 and Examples 4 to 10 The combination of the base paper and the coating liquid for the ink receiving layer was changed,
Further, the presence / absence of corona discharge treatment, the ability to be subjected to corona discharge treatment, and the time from the corona discharge treatment to the coating of the ink receiving layer were changed, and Comparative Examples 4 to 12 and Examples 4 to 10 were changed.
To obtain an inkjet recording sheet. Among these, among the inkjet recording sheets to be subjected to corona discharge treatment, in Example 10 and Comparative Example 8, the corona discharge treatment and the coating of the ink receiving layer were performed by different machines, and the others were all on-coater corona discharge treatment devices. I went there. The condition of the corona discharge treatment device was that only the voltage was changed, and the other conditions were exactly the same as in Comparative Example 2.

Table 4 shows Comparative Examples 1-12 and Examples 1-10.
Of the base paper, corona discharge treatment ability, elapsed time from corona discharge to coating of the ink receiving layer, and coating liquid of the ink receiving layer. The coating solid content of the ink receiving layer of the ink jet recording sheets of Comparative Examples 1 to 12 and Examples 1 to 10 is 7
g / m ² and calender pressure were all 10 kg / cm ² .

[0043]

[Table 4]

The above-mentioned ink jet recording sheet was tested for the following evaluation items, and the results are shown in Table 5.

<Evaluation items> (1) Wetting property The wetting property of the surface of the base paper of the ink jet recording sheet was measured. The raw paper was measured before and after the corona discharge treatment. First, a water-wetting reagent prepared by changing only the concentration with an aqueous solution of ethylene glycol monoethyl ether.
Prepare No30 to No60. For example, water wetness reagent No3
0 means that the wettability is 30 dynes / cm ² . Wet the tip of the cotton swab with the water-removing reagent No. 30 and trace the surface of the paper with the tip of the cotton swab. At this time, the reagent does not repel, and when soaked, it shows that the wettability exceeds 30 dynes / cm ^2. Therefore, the same test is performed with a water wettability reagent of No. 31 or higher. If the reagent repels, lower the water-retaining reagent number and perform the same procedure. The reagent does not repel and is the most soaked
The wettability of the water-removing reagent having a large No. was regarded as the same value as the wettability of the paper, and this value was defined as the wettability of the paper. Regarding wettability, (A) was shown before corona discharge treatment of the base paper of the ink jet recording sheet and (B) after corona discharge treatment, and (BA) was shown as improved wettability.

(2) Printing Density BJC610J inkjet printer (manufactured by Canon Inc.) was used for printing, and the black solid printing portion was measured using a Macbeth RD-918 type densitometer. When the optical density is 1.5 or more, there is no practical problem, and more preferably 1.7 or more. If it is less than 1.5, it is a problem in practical use.

(3) Absorbency Using a BJC610J ink jet printer, black characters were printed on the solid yellow printing portion, and the degree of character bleeding was evaluated according to the following three grades. A: Almost no bleeding is seen and the characters are sharp. B: Some bleeding is seen, but no crushed characters are seen. C: Some characters are blurred due to bleeding. If it is A or B, there is no problem in practical use. In C, this is a practical problem.

(4) Dot diameter BJC610J Inkjet printer was used to print, and 36 black dots (6 vertical x 6 horizontal) were printed so that adjacent dots would not overlap.
(C) was observed with an optical microscope and the average value of equivalent circle diameters measured with an image analyzer was used as the dot diameter.

(5) Roundness While observing 36 dots (6 vertical × 6 horizontal) of the printing portion of the above-mentioned black monochromatic dot with an optical microscope, the perimeter L of each dot and The area A is measured, and the shape factor C defined by the following formula 3 is calculated,
The average value was used as the roundness. Roundness is away from 1.0,
The larger the value, the worse the dot shape due to dot bleeding and the like, and the worse the image quality.

[0050]

Equation 3] ^{C = L 2 / (4π ×} A) ( Equation 3) where, C is the dot shape factor, L is the peripheral length of dots, A
Represents the area of a dot. Evaluation criteria; A: Roundness is less than 1.2. B: The average value is 1.2 or more. If it is A, there is no problem in practical use. B has a problem in practical use.

(6) A black cloth was placed on the surface of the powder-falling ink jet recording sheet, and a weight with a load of 20 g / cm ² was placed on the black cloth, and the cloth was moved at a constant speed for 6 minutes.
The amount of powder adhering to the black cloth when pulled by 0 cm was evaluated. Evaluation criteria; A: Almost no powder adhesion is observed. B: Adhesion of powder is recognized in part of the portion where the weight was placed. C: Adhesion of powder is recognized on the entire portion where the weight was placed. If it is A or B, there is no problem in practical use. C has a practical problem.

[0052]

[Table 5]

[0053]

From Tables 1 to 5, when corona discharge treatment is applied to the surface of the base paper to which the sizing property is given according to the present invention, the wetting property of the surface of the base paper is improved, and the ink receiving layer is formed on the surface of the base paper. When an inkjet recording sheet is manufactured by coating
The dot diameter after printing becomes smaller and the absorbability is improved.
Since the adhesion between the base paper and the ink receiving layer is reduced, the powder drop is a little worse, but the processability of corona discharge treatment is 150 W /
There is no problem if it is adjusted to m ² / min or less. The effect of improving the absorbability by corona discharge treatment is that the treated capacity is 70 W / m ² /
You can get it in minutes or more. Further, since the corona discharge treatment has a damping effect over time, the best method is to perform the corona discharge treatment immediately before the ink receiving layer coating with an on-coater corona discharge treatment device. If there is no on-coater corona discharge treatment device, it is necessary to apply the ink receiving layer within 60 minutes after the corona discharge treatment. In the prior art, the formulation of the coating liquid for the ink receiving layer may cause a bias such that the ink-jet recording sheet has weak absorption and strong adhesiveness, but according to the production method of the present invention, corona discharge treatment is performed. The effect of destroys the sizing agent on the surface of the base paper,
Since the wetting property can be modified so that the ink is absorbed by a part of the surface of the base paper, it is easy to adjust the dot size, absorption and adhesiveness in a well-balanced manner.

Claims (3)

[Claims] 1. A corona discharge treatment is applied to the surface of a base paper containing pulp as a main raw material and containing a sizing agent in an amount of 0.1% or more with respect to pulp at a treatability of 70 to 150 W / m ² / min, and then 60 minutes. A method for producing an ink jet recording sheet, characterized in that an ink receiving layer is coated on the corona discharge treated surface of the base paper. 2. The method for producing an ink jet recording sheet according to claim 1, wherein the on-coater corona discharge treatment is carried out immediately before coating the ink receiving layer. 3. An ink jet recording sheet having an ink receiving layer on the surface of a base paper, wherein the wetting property of the surface of the base paper treated with corona discharge to destroy the sizing agent is 3 to 5 dyne / cm as compared with the untreated base paper. ² An inkjet recording sheet that is improved.