JPH05331395A - Water-base recording ink - Google Patents

Abstract

PURPOSE:To obtain a water-base for ink jet recording which forms, in printing, characters having water resistance and does not bleed at the time of printing, and which is less likely to suffer from nozzle clogging and exhibits excellent pigment particle dispersion stability when a pigment is used as a colorant. CONSTITUTION:The ink comprises at least water, a colorant and a water-soluble polymer composed of at least tow members having different solubilities in water, one of them having a solubility at 20 deg.C in water of 2wt.% or less, preferably polyvinyl alcohol.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based recording ink used in an ink jet printer for recording using liquid ink.

[0002]

2. Description of the Related Art Conventionally, as an ink composition for ink jet recording, a liquid ink composition based on water or the like has been used, and one containing a resin is disclosed in JP-A-55-6.
0477, JP-A-58-13675 and the like. According to this, by adding the water-soluble resin to the water-based ink, the water-soluble resin acts as a fixing agent, so that the bleeding of characters on the recording paper can be prevented, and it is highly effective for any recording paper as well as designated paper. Printing with high quality and high resolution is possible. Further, since the water-soluble resin has a moisturizing effect, it is difficult for the ink to solidify in the nozzles of a fine inkjet head, and it has an effect of preventing clogging.

On the other hand, conventional ink jet recording inks are mainly those in which a dye is dissolved as a coloring agent, but the recorded matter is poor in light resistance and water resistance due to the characteristics of the dye. .. In order to solve the problem, an ink using a pigment such as carbon black or aniline black as a colorant has been devised. JP-A-61-283875, JP-A-64-6074, and JP-A-1-3188.
No. 1 publication and the like. Since the ink using a pigment as a colorant is a dispersion system in which fine pigment particles are dispersed in an aqueous medium, addition of a water-soluble resin to the pigment ink not only prevents bleeding, but also the resin is a pigment particle in the dispersion medium. It is widely known that they have the effect of adsorbing to and protecting the particles and stabilizing the dispersion of the particles.

[0004]

However, as described above, when a water-soluble resin having a high solubility in water is added to the ink, when water adheres to the characters printed on the paper, the solidified and fixed ink is dissolved again. However, there is a drawback that the characters are blurred and difficult to read.

The present invention has been made in view of the above problems, and an object of the present invention is that a character or the like once printed has water resistance and does not cause bleeding during printing.
It is an object of the present invention to provide an aqueous recording ink for inkjet recording, which is less likely to cause nozzle clogging and, when the colorant is a pigment, has excellent dispersion stability of pigment particles.

[0006]

In order to solve such problems, the aqueous recording ink of the present invention is composed of at least water, a colorant and a water-soluble polymer, and has a solubility in water as a water-soluble polymer. The polymer is characterized by containing at least two different kinds, one kind of which has a solubility in water at 20 ° C. of not more than 2% by weight. Desirably, polyvinyl alcohols are used as the water-soluble polymer having a solubility in water at 20 ° C. of 2% by weight or less.

When a polymer having a solubility in water at 20 ° C. of 2% by weight or more is used, the ink once fixed on the paper is easily redissolved when water adheres, so that the printed matter is significantly stained. The present invention prevents the redissolution of ink by using a water-soluble resin having a solubility of less than that,
The water resistance of the printed matter is greatly improved.

Materials which can be used in the aqueous recording ink composition used in the present invention will be described in detail below.

First, as the colorant which can be used in the water-based ink composition used in the present invention, direct dyes, acid dyes, basic dyes, food dyes, reactive dyes, disperse dyes, vat dyes,
Soluble vat dyes, reactive dyes, oil dyes, organic pigments, inorganic pigments and the like can be mentioned. The addition amount of these colorants is determined depending on the type of colorant, the type of solvent component, the properties required for the ink, etc., but generally 0.2 to 20% by weight based on the total weight of the ink. , Preferably 0.5 to 10
It is set in the range of wt%.

The solvent for the ink composition has a low viscosity, is excellent in safety, and is easy to handle.
Water is mainly used for reasons such as low cost and no odor. However, ion-exchanged water is used to prevent unwanted ions from being mixed in the ink.

A water-soluble resin is added to fix the ink on the paper. The water-soluble resin is used by mixing two or more kinds having different solubilities. One of them has a solubility in water at 20 ° C. of not more than 2% by weight and is used for the purpose of improving the water resistance of the printed matter. Generally, the solubility of the water-soluble resin decreases as the molecular weight increases, so that any kind of water-soluble resin can be used if the molecular weight is controlled. However, since the viscosity of the aqueous solution increases at the same time as the molecular weight increases, it is necessary to select a water-soluble resin that does not cause a large increase in viscosity. Preferred water-soluble resins include polyvinyl alcohol, polyvinyl butyral, polypropylene glycol and the like.

In addition to the low-solubility water-soluble resin, one or more water-soluble resins are added. Examples of the water-soluble resin include proteins such as gelatin and casein,
Natural rubber such as gum arabic, glucooxide such as savonine, methyl cellulose, carboxymethyl cellulose,
Cellulose derivatives such as hydroxymethyl cellulose, natural polymers such as lignin sulfonate, shellac, polyacrylate, polyacrylamide, styrene-acrylic acid copolymer salt, vinylnaphthalene-acrylic acid copolymer salt, styrene-maleic acid Copolymer salt, vinylnaphthalene-maleic acid copolymer salt, sodium salt of β-naphthalenesulfonic acid formalin condensate, ionic polymer such as polyphosphoric acid, polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, polypropylene glycol, polyethylene oxide A nonionic polymer such as polyvinyl methyl ether can be used.

Further, water or water and a water-soluble organic solvent can be added to the ink. Examples of the water-soluble organic solvent include alcohols and glycols. For example, alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, monoethylene glycol, diethylene glycol,
Propylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, glycerin,
Examples thereof include glycols such as polyethylene glycol, but are not limited thereto. In addition, a dispersion liquid in which a water-insoluble polymer is dispersed in a medium containing water as a main component, for example, acrylic acid ester type, methacrylic acid ester type, styrene type, styrene-acrylic copolymer, olefin type and amino group, amide group , Homopolymerization or copolymerization resin monomers, microemulsions of monomers having hydrophilic functional groups such as carboxyl groups and hydroxyl groups,
Internal three-dimensional crosslinked organic fine particles, paraffin wax,
Natural and synthetic wax emulsions such as polyethylene wax, carnauba wax, latex, colloidal solution,
A suspension or the like can be added to the ink.

When a pigment is used as a colorant, it is preferable to add a dispersant in order to disperse the pigment better. As the dispersant, an anionic or nonionic surfactant, a polymer dispersant, or the like may be used, or a soap-free dispersant may be used. For example, acrylic acid, methacrylic acid, maleic acid, etc., and salts thereof, acrylic acid esters, styrene or its derivatives, vinyl ethers, ethylenically unsaturated monomers such as vinyl esters, etc., alone or in combination of two or more. Can be used by mixing and polymerizing.

In addition, if necessary, an antifungal agent, a rust preventive agent,
Urea, thiourea, ethylene urea and the like can be added as a defoaming agent, a viscosity adjusting agent, a penetrating agent, a pH adjusting agent, and a nozzle drying inhibitor.

In the method for preparing the aqueous recording ink composition used in the present invention, in the case of a dissolving ink using a dye or the like as a colorant, water is heated to 40 to 80 ° C. and stirred and mixed with a screw or the like. , Can be easily prepared by dissolving. Further, the dispersion method in the case of a dispersion ink using a pigment or the like is a fine pigment dispersion method which has been conventionally used, for example, ball mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill. It can also be easily manufactured by a wet jet mill or the like.

Further, in order to remove dusts, coarse particles, and blended materials after dissolution or dispersion, pressurization or vacuum filtration is performed in one or more steps using a filter, or a centrifuge is used. It is preferable to perform the centrifugal separation treatment alone or in combination with the filtration treatment.

[0018]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The composition ratios in the text are all by weight of each component with respect to the total weight of the ink.

(Example 1) After mixing the above ingredients and stirring and dissolving at 60 ° C. for 2 hours,
Using a 0.8 μm diameter membrane filter (registered trademark of Advantech), pressure filtration was performed at a pressure of ² kg / cm ² to obtain the ink of the present invention. Polyvinylpyrrolidone (K-30) used as a water-soluble resin is polyvinylpyrrolidone having an average molecular weight of about 40,000 manufactured by Tokyo Kasei, and polyvinyl alcohol (K-17E) is Denka Poval (registered trademark of Denki Kagaku Kogyo Co., Ltd.). , Solubility 0.7%)
Is.

Further, a trial production was carried out in which the ejection nozzle diameter was 40 μm, the piezoelectric element drive voltage was 80 V, the drive frequency was 6 kHz, the resolution was 360 dots / inch, and the ink ejection amount was 0.1 μg.
Using a nozzle ink jet evaluation machine, PPC paper (PPC paper registered by Xerox Co., Ltd.), recycled paper (Yamayuri registered by Honshu Paper Co., Ltd.), bond paper (Gilbert bond 25% cotton paper registered by Mead Co., Ltd.), fine paper (Oji Paper Registration A solid alphabet letter or the like was printed on the trademark OK high-quality paper L), and the following tests 1 to 7 were evaluated. The evaluation results are shown in Table 1.

[0021]

[Table 1]

(Test 1) Character print sample Visual evaluation of print quality.

The evaluation results are classified as follows.

Bleeding is not observed with the naked eye ... ◎ Bleeding is seen but characters are recognizable △ △ Characters are not recognizable ・ ・ ・ ・-(Test 2) Density evaluation of the solid printed portion by Macbeth TR-927 type (registered trademark of Kollomorgan) optical densitometer (aperture size 4 mm).

The evaluation results are classified as follows.

O. D. Value 1.3 or more ... D. Value 1.1 or more and less than 1.3 ... D. Value less than 1.1 -------- (Test 3) Drop a drop of water on the area where normal characters are printed, leave it as it is until it dries, and observe the bleeding of the printed characters. Water resistance evaluation.

The evaluation results are classified as follows.

No bleeding is observed ..... ◎ Slight bleeding occurs, but characters can be distinguished. △ △ Significant bleeding occurs and characters cannot be distinguished. × (Test 4 ) Water rubbing resistance evaluation is conducted by rubbing the part where the ruled lines are printed with a wet cotton cloth at a pressure of 300 g / cm ² to investigate the occurrence of print stains.

The evaluation results are classified as follows.

Almost no stain is observed ..... ◎ There is some stain, but the density of the ruled line does not decrease much ..
・ ・ △ There is stain and the density of the ruled line is obviously reduced. ・ × (Test 5) The character printed part is rubbed with a finger 5 minutes after the printing is finished, and the print stain is visually observed.

The evaluation results are classified as follows.

No stains on the printed matter are observed. ◎ Some stains on the printed matter occur, but the characters can be distinguished.
・ ・ △ Characters cannot be discerned due to stains on the printed matter .... × (Test 6) Continuous ejection stability evaluation to check for missing dots during continuous printing at room temperature for 36 hours.

The evaluation results are classified as follows.

Dot omission 10 times or less within 36 hours ・ ・ ・ ◎ Dot omission 10 times or less within 24 hours ・ ・ ・ △ Dot omission 10 times or more within 1 hour ・ ・ ・ × Evaluation result is All of the tests 1 to 6 were excellent.

(Comparative Example 1-1) This is obtained by removing polyvinyl alcohol from Example 1 and supplementing it with ion-exchanged water. The preparation was performed in the same manner as in Example 1.

In this example, since the water-soluble resin contained was only polyvinylpyrrolidone having a high solubility, the ink solidified and fixed was likely to be redissolved, and the test 3
The water resistance / water rub resistance evaluation of No. 4 was greatly deteriorated.

(Comparative Example 1-2) This is obtained by removing polyvinylpyrrolidone from Example 1 and supplementing it with ion-exchanged water. The preparation method was the same as in Example 1.

In this example, the moisturizing effect of polyvinylpyrrolidone was impaired, so that the ink jet head was clogged and the ejection stability in Test 6 deteriorated.

(Comparative Example 1-3) This is the same as Example 1 except that polyvinyl alcohol added is Denka Poval K.
-05 (registered trademark of Denki Kagaku Kogyo Co., Ltd., solubility 2.5)
%). The preparation method was the same as in Example 1.

[0040] In this example, since both polyvinylpyrrolidone and polyvinyl alcohol have high solubilities, the solidified and fixed ink was easily redissolved, and the water resistance / water rub resistance evaluations of Tests 3 and 4 were greatly deteriorated.

(Example 2) This is compared with Example 1 in that
One kind of water-soluble resin to be added from polyvinyl alcohol to polypropylene glycol (Daiichi Kogyo Seiyaku
The solubility was changed to 1.7%). The preparation method was the same as in Example 1.

[0042] In this example as well, good ink characteristics were obtained as in Example 1. Similar to Comparative Examples 1-1 to 1-3, those without polypropylene glycol, those without polyvinylpyrrolidone, and polypropylene with high solubility (solubility 2.9%) were prepared and tested. However, the same results as those of the corresponding comparative examples were obtained.

(Third Embodiment) This is compared with the first embodiment.
One of the water-soluble resins to be added is changed from polyvinyl alcohol to polyvinyl butyral (Denka Butyral # 2000-L, registered by Denki Kagaku Kogyo KK, solubility 0.6%). The preparation method was the same as in Example 1.

[0044] In this example as well, good ink characteristics were obtained as in Example 1. Similar to Comparative Examples 1-1 to 1-3, those without polyvinyl butyral, those without polyvinyl pyrrolidone, and those with highly soluble polyvinyl butyral added (solubility 2.3%) were prepared and tested. However, the same results as those of the corresponding comparative examples were obtained.

(Example 4) This is compared with Example 1 in that
A water-soluble resin, carboxymethyl cellulose (Serogen 5A, registered trademark of Daiichi Kogyo Seiyaku Co., Ltd.) was added as a thickening agent to contain three kinds of water-soluble resins.

[0046] Also in this example, good printing characteristics were obtained as in Example 1.

(Example 5) The carbon black used here is MA-100 (registered trademark of Mitsubishi Kasei Co., Ltd.).

The ink was manufactured by the following procedure, but the invention is not limited to this. First, carbon black and a dispersant were stirred and mixed in ion-exchanged water using a paint shaker for 30 minutes or more, and it was confirmed by microscopic observation that the particle size became about 1 μm or less, and polyvinylpyrrolidone and polyvinyl alcohol were added thereto. Then, mix and stir for another 30 minutes to completely dissolve. Glycerin and ethanol were added to the dispersion and the mixture was stirred for 5 minutes, and filtered with a stainless mesh filter having a pore size of 5 μm and a filter diameter of 47 mm at a pressure of 1 kg / cm ² to remove dust and coarse particles. An aqueous recording ink having an average particle size of 0.15 μm and pH 6 was obtained. Further, it is preferable to perform pre-filtration with a filter having a large pore size in order to increase the collection efficiency of coarse particles.

Since it is difficult to achieve the same degree of ejection stability as the dye ink which is a complete solution at the time of the pigment particle dispersion type ink, the evaluation standard of the ejection stability test of Test 6 was changed. did.

(Test 6 ") Continuous ejection stability evaluation for investigating the presence or absence of missing dots during continuous printing at room temperature for 12 hours.

The evaluation results are classified as follows.

Dot omission 10 times or less within 12 hours ... ◎ Dot omission 10 times or less within 6 hours ... △ Δ Dot omission 10 times or more within 1 hour ... × Multiple pigments When the particles agglomerate, they become coarse particles, and the nozzles of the inkjet head may be clogged.
Therefore, a storage stability evaluation test of pigment particles was performed.

(Test 7) Evaluation of storage stability by observing a particle size change of carbon black particles in a glass sample bottle sealed at an environmental temperature of 70 ° C. and a humidity of 85% for 30 days with a 400 × transmission microscope.

The evaluation results were classified as follows.

No change in particle size after 30 days ... ◎ A slight change in particle size was observed after 30 days ... △ Particle size clearly increased after 30 days ... -× The evaluation result was ⊚ in all Tests 1-7.

(Comparative Example 5-1) This is the same as Comparative Example 1-1 except that polyvinyl alcohol was removed from Example 5 and that portion was supplemented with ion-exchanged water. Preparation is in Example 5
I went the same way.

In this example, as in Comparative Example 1-1, the water-soluble resin contained only polyvinylpyrrolidone,
Water resistance and water rub resistance deteriorated.

(Comparative Example 5-2) This is the same as Comparative Example 1-2 except that polyvinylpyrrolidone was removed from Example 5 and that portion was supplemented with ion-exchanged water. Preparation Example 2
I went the same way.

In this example, similarly to Comparative Example 1-2, the ejection stability deteriorated, and the dispersion stability of the pigment particles in the ink also deteriorated.

Comparative Example 5-3 In the same manner as in Comparative Example 1-3, polyvinyl alcohol added in comparison with Example 5 was added to Denka Poval K-05 (registered trademark of Denki Kagaku Kogyo KK, solubility 2). .5%). The preparation was performed in the same manner as in Example 5.

[0061] In this example as well, as in Comparative Example 1-3, the solidified and fixed ink was likely to be redissolved, and the water resistance / rubbing resistance evaluations of Tests 3 and 4 were significantly deteriorated.

(Example 6) This is compared with Example 5 in that
One kind of water-soluble resin to be added from polyvinyl alcohol to polypropylene glycol (Daiichi Kogyo Seiyaku
The solubility was changed to 1.7%). The preparation was performed in the same manner as in Example 5.

[0063] In this example as well, good ink characteristics were obtained as in Example 5. Similar to Comparative Examples 5-1 to 5-3, those without polypropylene glycol, those without polyvinylpyrrolidone, and those with highly soluble polypropylene glycol added (solubility 2.9%) were prepared and tested. However, the same results as those of the corresponding comparative examples were obtained.

(Example 7) This is compared with Example 5 in that
One of the water-soluble resins to be added is changed from polyvinyl alcohol to polyvinyl butyral (Denka Butyral # 2000-L, registered by Denki Kagaku Kogyo KK, solubility 0.6%). The preparation was performed in the same manner as in Example 5.

[0065] In this example, the print density was slightly reduced,
The other properties were good. Comparative Examples 5-1 to 5-3
In the same manner as the above, the test was carried out by preparing and removing polyvinyl butyral, removing polyvinylpyrrolidone, and adding highly soluble polyvinyl butyral (solubility 2.3%). Similar results were obtained.

(Embodiment 8) This is compared with Embodiment 5 in that
Acrylic acid-acrylonitrile copolymer, which is a water-soluble resin, was added as a pigment dispersant to contain three kinds of water-soluble resins.

[0067] Also in this example, good printing characteristics were obtained as in Example 5.

As can be seen from the above Examples and Comparative Examples,
In an aqueous recording ink containing at least two or more types of water-soluble polymers, one of the water-soluble polymers has a solubility in water at 20 ° C. of not more than 2% by weight, The water resistance, water rub resistance, and finger touch are improved, and the nozzle clogging resistance of the inkjet head and the dispersion stability of the pigment particles can be kept good.

On the other hand, in an ink containing only a polymer whose solubility in water at 20 ° C. is 2% by weight or less, clogging of nozzles and aggregation of pigment particles occur. In addition, inks not containing it are inferior in water resistance and water rub resistance, and both are unsuitable as water-based recording inks for inkjet recording.

[0070]

As described above, according to the present invention, in an aqueous recording ink containing at least water, a colorant, and two or more kinds of water-soluble polymers, one of the water-soluble polymers is water at 20 ° C. Since the polymer has a solubility of 2% by weight or less in water, the water resistance and finger touch of printed characters can be greatly improved without causing clogging of nozzles of ink-jet heads or agglomeration of pigment particles in ink. It has the effect of improving.

Claims (2)

[Claims] 1. An aqueous recording ink comprising at least water, a colorant, and a water-soluble polymer, containing at least two or more water-soluble polymers having different solubilities in water, one of which is at 20 ° C. Solubility in water is 2
A water-based recording ink characterized by using a polymer in an amount of less than or equal to wt%. 2. The aqueous recording ink according to claim 1, wherein the water-soluble polymer is polyvinyl alcohol.