JPH07145335A - Ink for ink jet recording and its production - Google Patents

Abstract

PURPOSE:To obtain the subject ink which can give a high-quality print without detriment to nozzle clogging prevention and storage stability by mixing the essential components with a saccharide and optionally urea and adjusting the amount of the water-soluble resin in an eluted stage to a specified percentage based on the pigment. CONSTITUTION:This ink is an ink for ink jet recording comprising a pigment, a water-soluble resin, a saccharide, water and optionally urea, wherein the amount of the water-soluble resin in an eluted state in the ink is 5wt.% or below based on the pigment. This ink is produced by a combination of a step of dispersing the pigment in an aqueous solution of the water-soluble resin with a step of removing the water-soluble resin in the eluted state from the ink. This ink can provide a print of high print quality without detriment to nozzle clogging prevention and storage stability. When the amount of the water- soluble resin in an eluted state is higher than the above value, the ink too deeply penetrates into paper to lose its sufficient color density and to tend to cause blotting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous pigment ink used in an ink jet printer and a method for manufacturing the same.

[0002]

2. Description of the Related Art The characteristics of ink jet recording inks are that the physical property values do not change during storage, the fine ink ejection nozzles are not clogged, the color density of the printed matter is high, and the printed matter is clear. High storage stability (water resistance, light resistance), etc. are required.

Conventionally, inks used in ink jet printers have basically been composed of a dye and an aqueous medium. However, due to the nature of the dye, there is a problem that the light resistance and water resistance of the printed matter are poor. Therefore, in order to solve this problem, an ink using a pigment instead of a dye has been proposed.

In the field of ink jet recording inks that use pigments, many efforts have been made to ensure reliability. In the case of a pigment ink, the solid content is likely to agglomerate because an insoluble component is contained in the medium, and if the agglomeration occurs, the recovery is extremely difficult. In particular, clogging of nozzles and securing of ejection stability are major problems, and some proposals have been made to solve these problems. For example, Japanese Patent Application Laid-Open No. 2-255875 proposes that the concentration of the dispersant (water-soluble resin) dissolved in the medium is 2% by weight or less in order to ensure ejection stability, and is related to the application. Japanese Patent Laid-Open No. 3-210373,
JP-A-4-18461, JP-A-4-18462, JP-A-4-18467, JP-A-4-59880, JP-A-4-126780, JP-A-4-126781, and JP-A-4-132775 In the publication, an attempt has been made to improve various problems that are a problem with water-based pigment inks, such as color density and abrasion resistance of printed matter, by optimizing the type or density of ink constituents. There is.

Further, in Japanese Patent Laid-Open No. 18472/1990, it is proposed to add inositol as a drying / aggregation preventing agent to prevent clogging.

[0006]

However, the water-based pigment inks of the prior art are aimed at preventing nozzle clogging, ensuring storage stability, improving discharge stability, and the like, so that the respective objectives have been achieved. However, the print quality was not practically satisfactory. That is, the color density of the printed matter was low and the outline of the character was unclear (so-called "bleeding" phenomenon).

As a problem peculiar to the pigment ink, there is printing unevenness. The print unevenness is the disturbance of the color density of the printed matter due to the deviation of the pigment particles on the paper. Print unevenness is also one of the parameters that determine print quality, and is a problem that must be solved in order to achieve high print quality, similar to the color density or bleeding of printed matter mentioned above.

[0008] Therefore, an object of the present invention is to provide an ink jet recording ink capable of providing a printed matter having high printing quality without impairing reliability such as nozzle clogging and storage stability, and a method for producing the same. It is to be.

[0009]

The present invention is an ink jet recording ink containing a pigment, a water-soluble resin, a saccharide and water, wherein the amount of the water-soluble resin eluted in the ink is relative to the pigment. And 5% by weight or less, and a step of dispersing the pigment in an aqueous solution of a water-soluble resin, and a step of removing the water-soluble resin eluted in the ink. And a method for producing the ink jet recording ink.

The amount of the water-soluble resin eluted in the ink of the present invention is 5% by weight or less, preferably 3% by weight or less based on the pigment. When the content is higher than 5% by weight, the ink penetrates deeply into the paper at the time of printing, a sufficient color density cannot be obtained, and bleeding easily occurs. Note that "water-soluble resin that is eluted in the ink" means when the water-soluble resin that is dissolved in the ink without being adsorbed to the pigment is used, and specifically when the pigment component is settled by an ultracentrifuge. , Refers to a water-soluble resin contained in ink water.

The saccharides used in the ink of the present invention include:
Monosaccharides such as pentose, hexose, heptose, and octose, or polysaccharides such as disaccharides, trisaccharides, and tetrasaccharides, or their derivative sugar alcohols, reduced derivatives such as deoxyacids, oxidized derivatives such as aldonic acid and uronic acid, and glycoceen. Such as dehydrated derivatives, amino acids, thiosugars and the like. Polysaccharides refers to sugars in a broad sense, and also includes substances widely existing in the natural world such as alginic acid, dextrin, and cellulose. The saccharides mentioned above may be used alone or in combination of two or more to be added to the aqueous pigment ink of the present invention.

The content of these saccharides is in the range of 0.1 to 40% by weight, preferably 0.5 to 30% by weight. 0.
If it is less than 1% by weight, the effect of adding saccharides cannot be obtained, and if it exceeds 40% by weight, dissolution in water becomes difficult, so that favorable results cannot be obtained.

When urea is used in addition to saccharides, it effectively prevents clogging of the nozzle. When the dispersion stability of the pigment is low and the nozzle clogging cannot be sufficiently prevented by only adding the saccharide, or when higher reliability is required, the reliability of the ink is remarkably improved by adding urea.

The pigment used in the ink of the present invention includes:
Various conventionally known inorganic pigments and organic pigments can be used. Examples thereof include inorganic pigments such as carbon black and titanium oxide, organic pigments such as azo pigments, phthalocyanine pigments, quinacridone pigments, anthraquinone pigments and dioxazine pigments. In addition to the various pigments listed above,
Any pigment that can be dispersed in water can be used, and a processed pigment such as graft carbon whose pigment surface is treated with a resin can also be used.

The pigment particles can be used if the particle size is 10 μm or less, but it is preferably 1 μm or less. This is because if the particle size exceeds 10 μm, the sedimentation speed of the particles increases and the dispersed state cannot be kept stable.

The content of these pigments varies depending on the kind, but is generally 1 to 20% by weight, preferably 2 to 10%.
It is in the range of% by weight.

As the dispersant, a polymer dispersant used for pigment dispersion can be used, and a resin soluble in an aqueous solution in which an amine is dissolved is preferable. For example, acrylic resin,
Specifically, styrene-acrylic acid copolymer, acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic Acid alkyl ester copolymer, styrene-α
-Methylstyrene-acrylic acid copolymer, styrene-α
-Methylstyrene-acrylic acid-acrylic acid alkyl ester copolymer, and salts thereof, polyacrylic acid salts,
Polymethacrylate, vinylnaphthalene-acrylic acid copolymer, styrene-maleic acid copolymer, maleic acid-
Examples thereof include maleic anhydride copolymers, vinylnaphthalene-maleic acid copolymers and salts thereof. Further, proteins such as gelatin, albumin and casein, natural polymers such as gum arabic, sodium salts of β-naphthalenesulfonic acid formalin condensate, anionic polymers such as phosphates, further, acrylonitrile, vinyl acetate, Polymers such as vinylidene chloride, ethylene, hydroxyethyl acrylate and glycidyl methacrylate may be copolymerized. These are used alone or in combination of two or more.

The weight average molecular weight of the water-soluble resin is 300.
It is preferably 0 to 50,000, and more preferably 7,000 to 15,000. Further, the content of the water-soluble resin varies depending on the combination of the pigment used and the water-soluble resin,
The amount eluted in the ink may be 5% by weight or less with respect to the pigment, and generally 2 to 50% by weight with respect to the pigment.
It is desirable to use.

Although the main components constituting the water-based pigment ink of the present invention have been described above, other water-insoluble resin emulsions, water-soluble organic solvents, pH adjusters, preservatives, antifungal agents, etc. may be used as required. May be added.

The water-insoluble resin emulsion usable in the present invention includes polyacrylic ester emulsion, polymethacrylic ester emulsion, acrylic emulsion, vinyl acetate emulsion, styrene-butadiene emulsion, vinyl chloride emulsion. And an internal three-dimensionally cross-linked microemulsion and its intermediate, and the content thereof is 0.1 in terms of solid content.
It is in the range of 1 to 40% by weight, preferably 1 to 25% by weight. The print density can be improved by adding a resin emulsion insoluble in water.

As the water-soluble organic solvent, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-
Examples thereof include nitrogen-containing compounds such as 2-imidazolidinone and amides such as dimethylformamide and dimethylacetamide.

Examples of the pH adjusting agent include organic amines such as diethanolamine and triethanolamine, inorganic bases such as sodium hydroxide and potassium hydroxide, organic acids and mineral acids.

Next, a method for manufacturing the ink jet recording ink of the present invention will be described.

First, a dispersant (water-soluble resin) is dissolved in water containing an amine to prepare an aqueous solution of the dispersant. The amine used here is preferably an organic amine such as monoethanolamine, diethanolamine, aminomethylpropanol, or ammonia.

Subsequently, a pigment is added to the above aqueous dispersant solution,
Disperse after stirring well. To disperse the pigment, a commonly used disperser such as a ball mill, a sand mill, an attritor, a roll mill, an agitator mill, a Henschel Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a jet mill and an ong mill is used.

After the dispersion, the eluted water-soluble resin is removed from the dispersion. Specific means includes ultrafiltration, extraction and the like, which is repeatedly performed until the amount of the water-soluble resin eluted in the dispersion becomes 5% by weight or less based on the pigment.

As a method for measuring the amount of unadsorbed resin,
The pigment component and the dispersant adsorbed to the pigment are precipitated using an ultracentrifuge (80,000 rpm, 2 hours), and the visible-UV absorption spectrum of the supernatant is measured. The water-soluble resin concentration in the supernatant can be identified by comparing with the absorption spectrum of a standard sample of known concentration.

[0028]

The aqueous pigment ink of the present invention can solve the problem of print quality, which has been a problem in the prior art, without degrading the reliability of the ink. That is,
When the aqueous pigment ink of the present invention is used in an inkjet recording system, the obtained printed matter has high color density and is clear,
Also, printing unevenness hardly occurs.

According to the present invention, each phenomenon can be explained without contradiction by considering as follows. Among the components contained in the water-based pigment ink, it is considered that the dispersant has the most bad influence on the print quality. The dispersant has both a hydrophilic structure part and a hydrophobic structure part in order to stably disperse the pigment in water, which is the medium of the ink. As a result, the dispersant eluted in the ink, that is, the dispersant not adsorbed to the pigment, acts as a surfactant, promoting the penetration of the ink into the paper, lowering the color density, or causing bleeding, etc. cause. Therefore, the aqueous pigment ink of the present invention realizes high printing quality by suppressing the amount of the dispersant eluted in the ink to a low level.

However, there is an equilibrium relationship between the components adsorbed on the pigment of the dispersant and the components eluted in water, and when the amount of the dispersant eluted in the ink is small, the pigment is dispersed. Therefore, the dispersant is desorbed and the dispersion system cannot be kept stable. Therefore, sugar or urea is added to the ink to prevent clogging at the nozzle. It is not clear why sugar and urea are effective in preventing clogging, but nozzle clogging may be caused by the moisturizing effect, the effect of preventing film formation during aggregation, or the interaction with pigment particles in the ink. It is considered to be effectively prevented.

[0031]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples of the present invention.

Example 1 (Preparation of Pigment Dispersion) Styrene-acrylic acid copolymer 3 parts Triethanolamine 7 parts Ion-exchanged water Remaining amount The above components are mixed and heated to about 70 ° C. to remove the resin component. It was completely dissolved. Add carbon black (MA7,
15 parts (manufactured by Mitsubishi Kasei) was added, and the dispersion treatment was performed under the following conditions.

Dispersing machine: Sand mill (Yasukawa Seisakusho) Grinding media: Glass beads (1.7 mm diameter) Media filling rate: 1.5 times (weight) Dispersion time: 2 hours After dispersion, the glass beads were removed and a 5 μm membrane was used. Coarse particles and dust were removed with a filter to obtain a pigment dispersion liquid. The pigment dispersion liquid was subjected to ultrafiltration to remove the water-soluble resin eluted in the dispersion liquid. The filtration conditions are shown below.

Ultrafiltration device: Ultrafiltration system Minitan (Millipore) Molecular partition amount: 50,000 When ultrafiltration is performed under the above conditions, the pigment and the water-soluble resin adsorbed on the pigment are all in the concentrated liquid. On the other hand, the water-soluble resin eluting in the dispersion liquid is divided into both a filtrate and a concentrate. Therefore, the concentration of the water-soluble resin eluted in the dispersion liquid can be lowered by repeating the operation of adding the amine aqueous solution to the concentrated liquid in an amount corresponding to the decrease in the volume during filtration and again performing ultrafiltration. The amount of the resin eluted in the dispersion was monitored by the method described above, and the ultrafiltration was terminated when the amount of the resin was 3% by weight or less based on the pigment.

(Preparation of Ink) Dispersion 33 parts Sucrose 0.7 part Maltitol 6.3 parts Urea 10 parts Ion-exchanged water Remaining amount The above components were mixed and stirred at room temperature for 20 minutes to obtain an ink.

Example 2 (Preparation of Pigment Dispersion) Styrene-maleic anhydride copolymer 4 parts Triethanolamine 10 parts Ion-exchanged water Remaining amount The above components are mixed and heated to about 70 ° C. to give a resin component. Was completely dissolved. Carbon black (MA10
20 parts (manufactured by Mitsubishi Kasei Co., Ltd.) were added and dispersed. The conditions of dispersion or the conditions of ultrafiltration performed after dispersion are the same as in Example 1.

(Preparation of ink) Dispersion 20 parts Polymethacrylate emulsion (solid content 40%) 3 parts Sucrose 0.7 parts Maltitol 6.3 parts Urea 10 parts Ion-exchanged water Remaining amount The above components are mixed. Then, the ink was obtained by stirring at room temperature for 20 minutes.

Example 3 The same pigment dispersion as in Example 1 was used, and 4 parts of xylose was added instead of sucrose and maltitol at the time of ink preparation.

Example 4 (Preparation of Pigment Dispersion) Styrene-acrylic acid copolymer 2.5 parts Triethanolamine 5 parts Ion-exchanged water Remaining amount The above components are mixed and heated to about 70 ° C. to form a resin. The minutes were completely dissolved. Add carbon black (MA7,
25 parts of Mitsubishi Kasei Co., Ltd. was added, and dispersion treatment was performed under the following conditions.

Dispersing machine: Sand mill (manufactured by Yasukawa Seisakusho) Crushing media: Glass beads (1.7 mm diameter) Media filling rate: 1.5 times (weight) Dispersion time: 2 hours After dispersion, the glass beads were removed to 5 μm. Coarse particles and dust were removed with a membrane filter to obtain a pigment dispersion. Subsequently, extraction was performed with methylene chloride to remove the water-soluble resin eluted in the dispersion liquid.

(Preparation of ink) 20 parts of the above dispersion liquid 3 parts of α-cyclodextrin Ion-exchanged water Remaining amount The above components were mixed and stirred at room temperature for 20 minutes to obtain an ink.

(Comparative Example 1) The ink in which the ultrafiltration was omitted in the manufacturing process of Example 1, and the other formulation was the same as that of Example 1.

(Comparative Example 2) An ink in which ultrafiltration was omitted in the manufacturing process of Example 2 and the other formulation was the same as that of Example 2.

(Comparative Example 3) Glycerin 1 was used as sucrose, maltitol and urea contained in the ink of Example 1.
The ink was manufactured with the same formulation except for 0 part.

Using the inks obtained above, the following evaluations were carried out.

(Evaluation 1) Clogging property The ink cartridge of the ink jet printer MJ-500 (manufactured by Seiko Epson Corp.) is filled with a predetermined ink, and after printing the alphanumeric characters continuously for 10 minutes, the printer is stopped. Then, it was left for 2 weeks in an environment of 40 ° C. and 25% RH without a cap. After leaving it, print alphanumeric characters again,
The number of times of the clogging recovery operation required until the print equivalent to that before leaving was obtained was examined.

◯: Printing equivalent to the initial printing is possible with the returning operation 0 to 2 times Δ: Printing equivalent to the initial printing is possible with the returning operation 3 to 5 times ×: Equivalent to the initial printing even with the returning operation 6 times or more Printing is not possible (Evaluation 2) Storage stability 50 cc of ink is collected in a Laborin screw bottle,
It was left at 50 ° C. for 2 months. The average particle size before and after standing was compared, and the storage stability was evaluated according to the following criteria.

◯: Increase in average particle size is 10% or less Δ: Increase in average particle size is 10 to 20% ×: Increase in average particle size exceeds 20% (Evaluation 3) Printing quality (bleeding) The paper was printed with MJ-500, and the presence or absence of bleeding was evaluated according to the following criteria.

Evaluation Paper (1) Xerox P (Fuji Xerox Co., Ltd.) (2) Riccopy 6200 (Ricoh Co., Ltd.) (3) EPP (Seiko Epson Co., Ltd.) (4) Xerox R (Fuji Xerox Co., Ltd.) , Recycled paper) (5) Yamayuri (Recycled paper from Honshu Paper Co., Ltd.) (6) Conqueror Laid (European paper) (7) Rapid Copy (European paper) (8) Modo Copy (European paper) (9) Neenah Bond (American paper) (10) Xerox 4024 3R721 (American paper) Evaluation ◯: No bleeding and clear printing Δ: Scratch-like bleeding occurs X: Blurring to the extent that the outline of characters is not clear (Evaluation 4) Printing quality (OD) Value) Printed on the above 10 papers with MJ-500, and
The OD value of 10 points was measured by h PCMII, and the average value was evaluated according to the following criteria.

◯: OD value of 1.4 or more Δ: OD value of 1.2 or more ×: OD value of less than 1.2 (Evaluation 5) Printing unevenness The above 10 papers were printed with MJ-500 and manufactured by Konica Corporation. Using a Sakura Micro Densitometer, 1 mm of the filled and printed portion is measured with a slit width of 200 μm × 20 μm. The difference between the maximum and minimum OD values at that time was evaluated according to the following criteria.

◯: No printing unevenness (less than 0.2) Δ: Slight printing unevenness (0.5 or less) ×: Printing unevenness is noticeable (0.5 or more)

[0052]

[Table 1]

The evaluation result will be described.

First, Example 1 and Comparative Example 1 having the same ink constituents will be compared. Regarding the clogging and storage stability, both Example 1 and Comparative Example 1 satisfy the actual use level. On the other hand, the print quality of the printed matter is ◯ in all of the items in Example 1, and is evaluated as Δ or X in Comparative Example 1. The difference between Example 1 and Comparative Example 1 is whether or not ultrafiltration is performed. As a result of ultrafiltration, the amount of water-soluble resin eluted in the ink is 8% by weight (Comparative Example 1 , The concentration relative to the pigment) to 3% by weight (Example 1, the same). Therefore, it can be confirmed that the print quality is improved by suppressing the concentration of the eluted water-soluble resin in the ink to a low level.

The same applies to Example 2 and Comparative Example 2, and the same experiment was conducted using different pigment-dispersant (water-soluble resin) systems. The results obtained here are the same as those in Example 1 and Comparative Example 1. That is, the print quality is improved by keeping the concentration of the eluted water-soluble resin in the ink low.

Example 3 is an example in which the type of sugar added to the ink is changed, and Example 4 is an example in which the type of sugar is changed and urea is not added. In all of Examples 3 and 4, the print quality of the printed matter was evaluated as ◯ in all items. On the other hand, we have secured a level that can withstand actual use in terms of clogging and storage stability.

Comparative Example 3 is an example in which glycerin which is generally used as a moisturizer is added without adding sugar and urea. The print quality is rated as O because the concentration of the water-soluble resin is low, but clogging and storage stability are rated as X.

As is clear from the above description, the inks of the respective examples of the present invention have a high print quality while having the ability to withstand practical use in terms of prevention of nozzle clogging and storage stability. It is realized at the same time. On the other hand, the inks given as the comparative examples show that the printing quality is poor although the clogging characteristics and the storage stability are at the actual use level, or vice versa, and it is not possible to achieve both reliability and high printing quality.

[0059]

According to the present invention, it is possible to provide an ink having a high color density of printed matter and little print unevenness without preventing nozzle clogging and impairing storage stability.

Claims (5)

[Claims] 1. An ink-jet recording ink containing a pigment, a water-soluble resin, a saccharide, and water, wherein the amount of the water-soluble resin eluted in the ink is 5% by weight or less based on the pigment. An ink for inkjet recording characterized by: 2. An inkjet recording ink comprising a pigment, a water-soluble resin, a saccharide, urea, and water, wherein the amount of the water-soluble resin eluted in the ink is 5% by weight or less based on the pigment. An inkjet recording ink characterized by the above. 3. The saccharide is one kind or a mixture of two or more kinds selected from monosaccharides, disaccharides, polysaccharides, and derivatives thereof, and the content thereof is in the range of 0.1 to 40% by weight. The ink for ink jet recording according to claim 1 or 2, wherein 4. The water-soluble resin is a polymer having both a hydrophilic structure portion and a hydrophobic structure portion in the molecule, and the molecular weight thereof is in the range of 3,000 to 50,000. 2. The ink jet recording ink according to 2 and 3. 5. The method for manufacturing an ink jet recording ink according to claim 1, wherein at least a step of dispersing a pigment in an aqueous solution of a water-soluble resin and removing the water-soluble resin eluted in the ink. A method for producing an ink for inkjet recording, comprising the steps of: