JP3056664B2 - Recording liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording liquid, and more particularly to a recording liquid used for ink jet recording.

[0002]

2. Description of the Related Art Ink jet recording is a recording method capable of high-speed printing with low noise, and is a recording method that has been rapidly spreading recently. In such ink jet recording, recording is performed by discharging a recording liquid as small droplets by a method such as heating or pressurization and attaching the recording liquid to a recording material such as paper.

[0003] Dyes have been used as coloring materials for recording liquids. However, from the viewpoint of water resistance and weather resistance of the recorded matter, it is more advantageous to use a pigment than a dye. As the liquid medium, an aqueous liquid medium is more advantageous than a non-aqueous liquid medium from the viewpoint of bleeding on plain paper.

Therefore, an attempt has been made to prepare a recording liquid by using a pigment as a coloring material of the recording liquid and dispersing the pigment in an aqueous liquid medium (Japanese Patent Publication No. 1-15542).

[0005]

However, a recording liquid in which a pigment is dispersed in an aqueous liquid medium is less likely to bleed than a recording liquid using a non-aqueous liquid medium, but has low permeability to paper because of its low permeability to paper. May remain on the paper fibers. At this time, when the solubility of the dispersant used in water is large, water resistance after printing becomes a problem, and when the paper is exposed to running water, the pigment remaining on the fibers flows down, and when the paper is rubbed with a wet hand, There were problems such as stains on the recorded matter.

On the other hand, when the solubility of the dispersant in water is low, the dispersion of the pigment becomes poor, causing the aggregation and clogging of the pigment.

Further, even when the recording liquid is well-dispersed, when the recording liquid is mounted on an ink jet printer head, the dispersion state changes due to the evaporation of water from the nozzle holes of the head, and the pigment aggregates to cause clogging. It's easy to do. In order to solve this problem, it is necessary to add a humectant to the recording liquid. However, the addition of a large amount of the humectant causes an increase in the viscosity of the recording liquid, which causes a discharge failure.

Further, since the conventional recording liquid in which a pigment is dispersed in an aqueous liquid medium is a non-uniform system, aggregation of the pigment during long-term storage causes a problem, and also causes a problem such as clogging.

The viscosity of the recording liquid must be adjusted according to the characteristics of the recording head, the driving method, and the like. In order to reduce the viscosity of the recording liquid, not only the type of the humectant but also the function of the dispersant must be imparted. preferable.

Accordingly, an object of the present invention is to provide a recording liquid comprising at least a dispersant, an aqueous liquid medium and a pigment,
An object of the present invention is to provide an excellent recording liquid which is excellent in dispersibility of a pigment in an aqueous liquid medium and storage stability thereafter, and is also excellent in water resistance and dischargeability and does not cause clogging.

[0011]

According to the present invention, there is provided a recording liquid comprising at least a dispersant, an aqueous liquid medium, and a pigment, wherein the dispersant comprises at least an aromatic ring, a carboxylic acid group, and a copolymer having a carboxylic acid long-chain alkyl ester group represented by the following chemical formula 2, an anionic polymer dispersant comprising a compound forming a carboxylic acid group and a salt of the copolymer, the copolymer It is characterized in that the molecular weight is from 7,000 to 100,000.

[0012]

Embedded image

(In the formula, n represents an integer of 4 or more.)

Alternatively, in the recording liquid of the present invention, the long-chain carboxylic acid alkyl ester group may be an acrylate ester or a methacrylate ester having an alkyl group having 5 or more carbon atoms.
It is characterized by being introduced from crotonic esters, itaconic esters, maleic esters, fumaric esters and the like.

The recording liquid of the present invention is characterized in that the aromatic ring in the copolymer of the dispersant is introduced from styrene, a styrene derivative, vinylnaphthalene or a vinylnaphthalene derivative. is there.

In the recording liquid of the present invention, the carboxylic acid group in the copolymer of the dispersant may be acrylic acid, methacrylic acid,
It is characterized by being introduced from crotonic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester and the like.

In the recording liquid of the present invention, when the number of aromatic rings in the copolymer of the dispersant is A, the number of carboxylic acid groups is B, and the number of ester groups is C, the value of A satisfies the following expression (2). And the value of the number of carboxylic acid groups is 10% or more and 30% or less of the number of carbon atoms in the main chain of the copolymer.

[0018]

## EQU2 ## 40 ≦ 100A / (A + B + C) ≦ 7
5

Hereinafter, the configuration of the present invention will be specifically described.
Examples of the compound that gives an aromatic ring to the copolymer used in the recording liquid of the present invention include styrene, a styrene derivative, vinyl naphthalene, and a vinyl naphthalene derivative, as described above.

Examples of the compound that gives a carboxylic acid group to the copolymer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, itaconic acid monoester, maleic acid, and maleic acid monoester.

Further, the compound which gives the copolymer a long-chain carboxylic acid alkyl ester group may be an unsaturated carboxylic acid ester having the structure shown in Chemical formula 2 , but such an ester may be acrylic Long-chain alkyl esters having an alkyl group of 5 or more such as acid esters, methacrylic esters, crotonic esters, itaconic esters, maleic esters, and fumaric esters are exemplified.

Here, the above-mentioned monoesters of itaconic acid, maleic acid, fumaric acid and the like also have a carboxylic acid group, which alone contains a carboxylic acid group and a carboxylic acid long-chain alkyl ester group or a carboxylic acid oxyalkylene ester. It can be used as a compound giving both groups.

Examples of the compound forming a salt with the copolymer used in the present invention include salts or hydroxides of alkali metals such as sodium and potassium, aliphatic amines such as monomethylamine, dimethylamine and triethylamine, and monoamines. Examples thereof include alcoholamines such as methanolamine, diethanolamine, and triethanolamine.

As the aqueous liquid medium used for the recording liquid of the present invention, water or a mixture of water and a water-soluble organic solvent can be used. Examples of the water-soluble organic solvent include alcohols such as n-propyl alcohol and cyclohexyl alcohol, alkanolamines such as monoethanolamine, diethanolamine and triethanolamine,
Amides such as dimethylacetamide, ethers such as dioxane, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol,
Examples include polyhydric alcohols such as tripropylene glycol, polypropylene glycol, and glycerin; glycol ethers such as ethylene glycol monomethyl ether and tripropylene glycol monomethyl ether; and nitrogen-containing cyclic compounds such as N-methyl-2-pyrrolidone.

The pigments used in the recording liquid of the present invention include azo, phthalocyanine, quinacridone, anthraquinone, dioxazine, indigo, thioindigo, perylene, perinone, isoindolinone, and quinophthalone. Organic pigments such as organic pigments or carbon black can be used.

The aqueous liquid medium, the pigment, the copolymer, and the compound forming a salt with the copolymer are selected so as to satisfy desired properties such as mutual affinity, dispersion stability and viscosity of the pigment. Is used.

The recording liquid of the present invention comprises at least an aqueous liquid medium, a pigment, the above-mentioned copolymer as a dispersant, and a compound which forms a salt with the copolymer. If necessary, various additives may be used. Etc. may be added. These various additives are appropriately added to the recording liquid to be prepared, if necessary. Examples of such additives include a surface tension adjuster, an antioxidant, an ultraviolet absorber, and a stabilizer. Can be

By preparing a recording liquid in the combination as described above, it is possible to obtain a recording liquid which is excellent in dispersibility, storage stability and water resistance, and which gives a recorded matter excellent in ejection property. Further, the recording liquid of the present invention using a copolymer having a carboxylic acid oxyalkylene ester group as a dispersant has excellent moisture retention.

[0029]

Since the dispersant used in the present invention has a carboxyl group, it can be dissolved in an aqueous liquid medium by forming a salt. The aromatic ring in the copolymer and the long-chain alkyl group constituting the ester group shown in Chemical formula 2 are the basic units of condensed polycyclic aromatic organic pigments such as carbon black, phthalocyanine pigment, perylene pigment and quinacridone pigment. It has an affinity with the aromatic ring to contribute to the improvement of the dispersibility of these pigments. Furthermore, the dispersant of the present invention, which has an aromatic ring and further has an ester group shown in Chemical formula 2 , has a long-chain alkyl group, so that it is not so soluble in water as a general water-soluble polymer. For this reason, the copolymer not only functions as a dispersant for the pigment, but also functions as a binder for the pigment remaining on the fibers of the paper, so that a recorded matter having excellent water resistance due to friction can be obtained.

The above effect can be further enhanced by adjusting the ratio of each functional group in the copolymer of the dispersant used in the present invention.

If the proportion of the number of aromatic rings in the copolymer is too small, the ability to adsorb to the pigment will be reduced, causing a reduction in dispersibility and storage stability of the recording liquid. Conversely, if the proportion is too large, the solubility in water will be poor. Gets worse. Therefore, as described above, when the number of aromatic rings in the copolymer is A, the number of carboxylic acid groups is B, and the number of ester groups of carboxylic acid long-chain alkyl ester or carboxylic acid oxyalkylene ester is C, the value of A Is preferably in a range that satisfies the expression (2).

On the other hand, if the proportion of the number of carboxylic acid groups in the copolymer is too small, the solubility in water deteriorates. If the proportion is too large, the dispersibility of the pigment in an aqueous liquid medium and the water resistance of the recording liquid are reduced. Cause. Therefore, the ratio of the number of carboxylic acid groups is 10% to 30% of the number of carbon atoms in the main chain of the copolymer.
It is preferred that

Further, the molecular weight of the copolymer in the dispersant is
Too small dispersibility and storage stability of the pigment is lowered, the viscosity of the recording liquid too large increases, when having only carboxylic acid long-chain alkyl ester group represented by the formula 2, more than 7,000 100,000 It must be:

If the dispersibility of the pigment is poor, the pigment particles become large particles. Also, even if the initial dispersibility is good,
If the dispersibility is reduced in a short time with the passage of time and the pigment particles become large, the storage stability is poor. When used as a recording liquid for an ink jet printer, the pigment particles need to be smaller than 200 nm, and when the particle size is 200 nm or more, problems such as clogging occur.

[0035]

Next, the present invention will be described in more detail with reference to examples.

Example 1 A dispersant comprising a copolymer and a compound forming a salt with the copolymer was dissolved in an aqueous liquid medium comprising water and a water-soluble organic solvent to prepare a dispersion medium. Thereafter, the dispersion medium and the pigment were dispersed for 10 hours using a paint shaker, and then the precipitate was separated and removed by a centrifugal separator to prepare a recording liquid. The mixing ratio is shown below. The parentheses in the following copolymers indicate the polymerization ratio of each monomer, and the same applies to the following Examples and Comparative Examples.

Water 73% by weight Diethylene glycol 20% by weight Styrene-acrylic acid-dodecyl acrylate copolymer 1.5% by weight (65/20/15); molecular weight about 60,000 Triethylamine 0.5% by weight Carbon black 5% by weight

Evaluations shown in the following a to f were performed on the prepared recording liquid.

A. Dispersibility: At the time of preparation of the recording liquid, the separated sediment was collected by a centrifugal separator, dried, weighed, and the weight ratio of the sediment to the recording liquid was determined. When the value was less than 0.3%, it was judged to be good. b. Initial particle size: The average particle size of the pigment in the recording liquid was determined using a particle size distribution analyzer. When the value was less than 200 nm, it was judged to be good. c. Ejectability: The recording liquid was mounted on an on-demand type piezoelectric inkjet printer head, and printing was performed on plain paper, and the ejectability was investigated. d. Water resistance: The recorded matter obtained by printing the recording liquid on plain paper was examined for a decrease in print density when exposed to running water for 5 minutes, and for the presence or absence of stains when the recorded matter was rubbed with a cotton swab wetted with water. . e. Preservability: After recording the recording liquid at 50 ° C. for 2 months, the liquid properties and the average particle size of the pigment were examined. When the average particle size of the pigment was less than 200 nm, it was judged to be good. f. Clogging property: The recording liquid was mounted on an on-demand type piezoelectric ink jet printer head, and after confirming good initial printing, the recording liquid was left for 1 hour in a no-cap state. Printing was performed after standing, and the recording liquid was ejected from all the nozzles without disturbance of the landing accuracy, and a printed matter that was not different from the initial printing was obtained.

Example 2 A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 75.6% by weight Glycerin 20% by weight Styrene-methacrylic acid-octyl acrylate copolymer 1.0% by weight (60/25/15); molecular weight about 8,500 Triethanolamine 0.4% by weight Phthalocyanine 3% by weight pigment

Example 3 A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 73% by weight Glycerin 20% by weight Styrene-maleic acid monohexyl ester copolymer 1.5% by weight (60/40); molecular weight about 65,000 Triethanolamine 0.5% by weight Carbon black 5% by weight Here, the monohexyl maleate used in the copolymer has a carboxylic acid group and a carboxylic acid long-chain alkyl ester group at the same time as described above, and has both roles. Play.

Example 4 A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 67.3% by weight Propylene glycol 25% by weight Styrene-acrylic acid-dodecyl methacrylate copolymer 2% by weight (50/20/30); molecular weight of about 15,000 0.7% by weight of triethylamine 5% by weight of carbon black %

Example 5 A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 78% by weight Diethylene glycol 15% by weight Styrene-acrylic acid-ethoxytripropylene glycol acrylate copolymer 1.5% by weight (55/30/15); molecular weight about 8,000 Triethylamine 0.5% by weight Carbon black 5 % By weight The recording liquid obtained here had a lower viscosity than the recording liquid prepared in Example 1.

(Example 6) A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 80.6% by weight Glycerin 15% by weight Styrene-methacrylic acid-propoxytriethylene glycol acrylate copolymer 1.0% by weight (60/20/20); molecular weight about 10,000 Triethanolamine 0.4% by weight % Phthalocyanine pigment 3% by weight The recording liquid obtained here had a lower viscosity than the recording liquid prepared in Example 2.

(Example 7) A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 78% by weight Glycerin 15% by weight Styrene-acrylic acid-ethoxydiethylene glycol acrylate copolymer 1.5% by weight (50/40/10); molecular weight about 4,000 Triethanolamine 0.5% by weight Carbon black 5% by weight The recording liquid obtained here had a lower viscosity than the recording liquid prepared in Example 2.

Comparative Example 1 A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 75% by weight Diethylene glycol 20% by weight Acrylic acid-octyl methacrylate copolymer 1.5% by weight (20/80); molecular weight about 10,000 Triethylamine 0.5% by weight Phthalocyanine pigment 3% by weight

(Comparative Example 2) A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 72.7% by weight Diethylene glycol 20% by weight Styrene-maleic acid-diisobutylene copolymer 1.5% by weight (50/40/10); molecular weight about 30,000 Diethanolamine 0.8% by weight Carbon black 5% by weight %

Comparative Example 3 A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 72.9% by weight Glycerin 20% by weight Styrene-maleic acid monomethyl ester copolymer 1.5% by weight (50/50); molecular weight about 25,000 Triethylamine 0.6% by weight Phthalocyanine pigment 5% by weight

(Comparative Example 4) A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 75% by weight Glycerin 20% by weight Vinyl naphthalene-acrylate-octyl methacrylate copolymer 1.5% by weight (50/20/30); molecular weight about 5000 Triethylamine 0.5% by weight Phthalocyanine pigment 3% by weight

(Comparative Example 5) A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 76% by weight Diethylene glycol 15% by weight Styrene-methacrylic acid-methyl methacrylate copolymer 3% by weight (20/35/45); molecular weight about 40,000 Triethylamine 1% by weight Carbon black 5% by weight

(Comparative Example 6) A recording liquid was prepared in the same manner as in Example 1 with the following compounding ratio.
Thereafter, evaluation was made for items a to f in the same manner as in Example 1.

Water 76% by weight Glycerin 15% by weight Styrene-acrylic acid-propyl methacrylate copolymer 2% by weight (30/30/40); molecular weight about 70,000 Dimethylethanolamine 1% by weight Carbon black 6% by weight

Example 8 The results of the above evaluations in Examples 1 to 7 and Comparative Examples 1 to 6 are shown in Table 1 below. The recording liquid of each Example is dispersibility, initial particle size, dischargeability, water resistance, storage stability,
All of the clogging resistances were good. Comparative Example 1 contained no aromatic ring in the copolymer and had the worst pigment dispersibility.
All items were poor. Comparative Example 2 does not contain ester groups indicated in the copolymer in Formula 2, also, since the proportion of carboxylic acid groups is large, poor water resistance, also those discharge characteristics become high viscosity recording liquid is lowered It is. In Comparative Example 3, the copolymer did not contain the ester group shown in Chemical formula 2, and the dispersibility of the pigment was poor and the storage stability was poor. Comparative Example 4 has a carboxylic acid long-chain alkyl ester group shown in Chemical formula 2 , but has a molecular weight of about 50
Since it was as low as 00, the dispersibility, storage stability and clogging resistance of the pigment were poor, and the pigment did not function as a binder on a recording material such as paper, and the water resistance was poor.
Comparative Examples 5 and 6 both show that the copolymer
Since it does not contain the ester group shown in Chemical formula 2 and has a small number of aromatic rings, the dispersibility decreases over time even though the initial dispersibility is good, the storage stability is poor, and clogging has occurred.

[0065]

[Table 1]

As can be seen from the results of the examples and comparative examples, the dispersant used in the recording liquid of the present invention has a high pigment dispersing ability, and the recording liquid of the present invention using such a dispersant has excellent dischargeability and water resistance. It can be seen that they have excellent storage stability and clogging resistance. Further, in the recording liquid of the present invention, the one in which the copolymer in the dispersant has a carboxylic acid oxyalkylene ester group was also excellent in moisture retention.

[0067]

As described above, at least a dispersant,
Aqueous liquid medium, in a recording liquid composed of a pigment, at least an aromatic ring in the dispersant, at the same time as a carboxylic acid group, a copolymer having a carboxylic acid long-chain alkyl ester group, and a carboxylic acid group of the copolymer The recording liquid of the present invention using an anionic polymer dispersant comprising a compound forming a salt,
It has excellent dischargeability, water resistance, storage stability and clogging resistance.

Thus, according to the present invention, a pigment is used as a coloring material to provide excellent water resistance and weather resistance, and the use of an aqueous liquid medium causes less bleeding, prevents stains of recorded matter even when wet with water, and provides long-term storage stability. It is possible to provide a recording liquid having good dispersibility and good clogging without dispersion.

(56) References JP-A-6-322306 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09D 11/00-11/20

Claims (5)

(57) [Claims] 1. A recording liquid comprising at least a dispersant, an aqueous liquid medium, and a pigment, wherein the dispersant has at least an aromatic ring, a carboxylic acid group, and a carboxylic acid long-chain alkyl ester group represented by the following formula 1. A recording liquid, which is an anionic polymer dispersant comprising a polymer and a compound that forms a salt with a carboxylic acid group of the copolymer, wherein the copolymer has a molecular weight of 7,000 to 100,000. . Embedded image (In the formula, n represents an integer of 4 or more.) 2. The carboxylic acid long-chain alkyl ester group is introduced from an acrylate, a methacrylate, a crotonic ester, an itaconic ester, a maleic ester or a fumaric ester. The recording liquid according to claim 1. Wherein the aromatic ring in the copolymer of the dispersing agent is styrene or a styrene derivative or of claim 1 or claim 2, wherein it is intended to be introduced from a vinyl naphthalene or vinyl naphthalene derivatives, Recording liquid. 4. The carboxylic acid group in the copolymer of the dispersant is acrylic acid, methacrylic acid, crotonic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid or fumaric acid monoester. claim 1, claim 2 or claim 3 recording liquid, wherein it is intended to be introduced from. 5. When the number of aromatic rings in the copolymer of the dispersant is A, the number of carboxylic acid groups is B, and the number of ester groups is C,
2. The method according to claim 1, wherein the value of A is within a range satisfying the following expression 1, and the value of the number of carboxylic acid groups is 10% to 30% of the number of carbon atoms in the main chain of the copolymer. The recording liquid according to claim 2, 3, or 4 . 40 ≦ 100A / (A + B + C) ≦ 7
5