JPH03134073A - Inkjet recording liquid - Google Patents

Abstract

PURPOSE:To stabilize the ejection behavior of the title fluid even when driving condition fluctuates or the fluid is used for a long time and to improve fastness and long-term storage stability of a print by compounding a neutral or basic carbon black and a water-soluble resin and an aq. lig. medium. CONSTITUTION:3-20 wt.% neutral or basic carbon black (A) obtd. by the furnace black method, a water-soluble resin (B) wherein the wt. ratio of the ingredient A to the ingredient B is 3-10:1 and which is in an amount of 0.1-5 wt.% based on the total wt. of a recording fluid and is used as a dispersing agent, an aq. liq. medium (C) which is a solvent mixture of 10-90 wt.% water based on the total wt. of the obtd. recording fluid and 13-50 wt.% water-soluble org. solvent wherein org. amines are incorporated as essential ingredients based on the total wt. of the obtd. recording fluid and, if necessary, a pH modifier, a surface active agent, an anti-foaming agent, an antiseptic agent, a water-soluble dye, etc., (D) are compounded to obtain the title recording fluid with a surface tension of 30 dyne/cm.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a recording liquid suitable for an inkjet printer, and further relates to a recording method in which recording is performed by ejecting a recording liquid from an orifice of a recording head by the action of thermal energy. In particular it concerns a suitable recording liquid.

[Conventional technology]

The infusiera recording method has the advantage that it generates less noise during recording and that high-resolution recorded images can be obtained at high speed by using a highly integrated head.

In this type of inkjet recording method, various water-soluble dyes dissolved in water or a mixture of water and an organic solvent are used as inks. Since the water-soluble dyes originally have poor light resistance, the light resistance of recorded images is often a problem, and since the ink is water-soluble, the water resistance of recorded images is often a problem. That is, if a recorded image is exposed to rain, sweat, or drinking water, the recorded image may smudge or disappear.

On the other hand, similar problems exist in stationery using dyes such as ballpoint pens, and various water-based pigment inks for stationery have been proposed to solve the problems of light resistance and water resistance.

In order to put water-based pigment ink into practical use, examples of studies investigating dispersion stability, prevention of solidification of ink at the pen tip, and prevention of wear on the ball of a ballpoint pen include JP-A-58-80388 and JP-A-61-200182. Publication, JP-A No. 61-2477
74, JP 61-272278, JP 62-568, JP 62-101671゜10
1672, etc., and recently, ballpoint pens and markers using water-based pigment inks have come on the market as products.

[Problem that the invention seeks to solve]

However, when conventional water-based pigment ink for stationery is used in an inkjet recording device that performs recording by jetting the recording liquid from the orifice of the recording head, it has the disadvantage that it causes significant problems in ejection stability and causes printing defects. was there.

In particular, in the inkjet method that performs recording by ejecting droplets by applying thermal energy, when conventional pigment ink is used, when a pulse is applied to the ink, the heat causes deposits to form on the thin film resistor. Incomplete bubbling of the ink may cause ejection disturbances or non-ejection, or even if no deposits are formed on the thin film resistor, the ejection of droplets may not respond to the applied pulse due to incomplete bubbling. Non-discharge may occur.

In other words, in order to stably eject ink from the nozzle tip, the ink must have the ability to foam on the thin film resistor to a desired volume, and also to be able to repeat foaming and defoaming in a desired amount of time. However, conventional inks for stationery do not satisfy these performance requirements, so when an inkjet recording device is filled with the ink and used for recording, various inconveniences such as those described above occur.

Therefore, the purpose of the present invention is to solve the problems of the prior art described above, and to improve the robustness of printed matter.
An object of the present invention is to provide an inkjet recording liquid that can always perform stable ejection even when driving conditions change or are used for a long time, and has excellent long-term storage stability.

[Means for solving problems]

That is, the present invention is an inkjet recording liquid characterized by containing neutral or basic carbon black and a water-soluble resin in an aqueous liquid medium.

The present invention will be explained in detail below.

Although the recording liquid of the present invention contains a pigment dispersion liquid,
It has the thermal stability practically required for inkjet recording.

That is, an inkjet recording device ejects ink from an ejection opening of 50 μm or less, and when a dispersion system such as pigment ink is used, its viscosity and the particle size of the dispersion have a large influence on the ejection characteristics.

The inventors of the present invention have intensively investigated methods for improving the dispersion stability of aqueous pigment inks using carbon black, and have found that the pH of carbon black affects the dispersion stability. When the ink was adjusted using a pigment with a neutral or alkaline black pH, no change occurred over time even after storage at room temperature and 60° C. for 3 months.

The reason why the dispersion stability is better when the pH of carbon black is neutral or alkaline is not clear, but it is speculated that the surface of carbon black is neutral or alkaline, so it can be used in the present invention. This is thought to be because the carboxyl group added to the dispersant is easily adsorbed. Further, since the particle size of such a dispersion is small regardless of the type of dispersant, it has excellent discharge properties and does not cause sedimentation or sedimentation even during long-term storage.

The carbon black contained in the recording liquid of the present invention preferably has a pH of 7 to 10, for example, N02300. N0900゜MCF8
8. NO33, NO4000B, NO40, NO4
5°N052. CF9. N0IOB (manufactured by Mitsubishi Kasei),
Commercial products such as Rega166OR, Regat 330R (manufactured by Capot), and PRINTEX35 (manufactured by Tegutsusa), as well as those newly manufactured for this purpose can also be used.

The carbon black used in the present invention is produced by the furnace black method.

The Furnace Black process uses natural gas or petroleum fraction as a raw material, and sprays the raw material into a closed reactor kept in a high-temperature atmosphere to thermally decompose the raw material.

Here, the pH of carbon black as used in the present invention means a value obtained by the following measuring method.

That is, weigh out a carbon black sample l~Log into a beaker, add water at a ratio of 10 ml per 1 g of sample, cover with a watch glass, and boil for 15 minutes (to make the sample wet).
You may add a few drops of ethanol to do this. ). After boiling, cool to room temperature and remove the supernatant liquid by decanting or centrifugation, leaving a slurry.

Place the electrode of a glass electrode pH meter into this slurry, and
2. Measure the pH using 8802 (pH measurement method).

In this case, the measured value may change depending on the insertion position of the electrode, so move the beaker to change the position of the electrode and weigh carefully so that the electrode surface and the mud surface are in sufficient contact.
Read the value when the H value becomes constant.

The amount of carbon black used in the present invention is 3 to 3 by weight.
It is preferable to use it in a range of 20% by weight.

As the dispersant contained in the recording liquid of the present invention, a water-soluble resin used for pigment dispersion can be used, and as the water-soluble resin, any material can be used as long as it is soluble in an aqueous solution in which an amine is dissolved. , styrene-acrylic acid copolymer, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid copolymer, styrene-
Maleic acid-acrylic acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-
Examples include maleic acid half ester copolymer, vinylnaphthalene-acrylic acid copolymer, vinylnaphthalene-maleic acid copolymer, or salts thereof. Various methods can be used to measure the weight average molecular weight of the dispersion resin, but it is generally measured by GPC (gel permeation chromatography) or the like. The water-soluble resin is preferably contained in an amount of 0.1 to 5% by weight based on the total weight of the recording liquid.

In addition, the properties generally required of inkjet recording liquids include the above-mentioned physical properties such as viscosity, surface tension, and pH, but in dispersion systems such as aqueous pigment inks,
Even if these physical properties are satisfied, ink foaming may become unstable, especially in an inkjet method in which recording is performed by applying thermal energy to eject droplets.

Therefore, the present inventors conducted extensive research on the performance of an aqueous pigment ink that is thermally stable and capable of optimal foaming, and found that it is preferable that the ratio of carbon black and water-soluble resin in the recording liquid be 3:1. It has been found that when the ratio is between 10:1 and 10:1 (weight ratio), the ink foams accurately on the resistor under any driving conditions, and furthermore, no deposits are generated on the thin film resistor even over a long period of time. .

In other words, if there is a large amount of excess water-soluble resin in the ink relative to the carbon black, the ink may not foam even if a certain amount of thermal energy is applied to the thin film resistor, or the heat generated during pulse application may cause these ink to foam. Excess water-soluble resin becomes an insoluble substance and accumulates on the thin film resistor, causing non-discharge and irregular printing.

Further, the total amount of carbon black and water-soluble resin in the dispersion is preferably 10% or more. The reason for this is that unless a certain concentration or higher of carbon black and water-soluble resin are present in the dispersion liquid, dispersion cannot be carried out efficiently and an optimum dispersion state cannot be obtained.

Further, in the recording liquid of the present invention, preferably, the entire recording liquid is adjusted to be neutral or alkaline, so that the solubility of the water-soluble resin is improved, and - the recording liquid has excellent long-term storage stability of the layer. This is desirable because it can be done as follows. Since the recording liquid of the present invention uses neutral or basic carbon black, it becomes a highly alkaline recording liquid, but depending on the type of carbon black, it may exhibit strong alkalinity. In such a case, it may cause corrosion of various members used in the inkjet recording apparatus, so it is desirable that the pH range is preferably 7 to 1O.

Examples of the pH adjuster include various organic amines such as jetanolamine and triethanolamine, and inorganic alkaline agents such as alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide.

The above carbon black and water-soluble resin are dispersed or dissolved in an aqueous liquid medium.

A suitable aqueous liquid medium in the recording liquid of the present invention is a mixed solvent of water and a water-soluble organic solvent, and the water is not ordinary water containing various ions, but ion exchange water (deionized water). It is preferable to use

Examples of water-soluble organic solvents used in combination with water include organic amines such as monoethanolamine, jetanolamine, triethanolamine, and aminomethylpropanol, methyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, 5
Alkyl alcohols having 1 to 4 carbon atoms such as ec-butyl alcohol, tert-butyl alcohol, and isobutyl alcohol; Amides such as dimethylformamide and dimethylacetamide; Ketone or keto alcohols such as acetone and diacetone alcohol; tetrahydrofuran and dioxane Ethers such as: polyalkylene glycols such as polyethylene glycol and polypropylene glycol; ethylene glycol, propylene glycol,
Butylene glycol, triethylene glycol, 1.2
．． Alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms, such as 6-hexandriol, thiodiglycol, hexylene glycol, diethylene glycol; Glycerin: ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) Lower alkyl ethers of polyhydric alcohols such as ether, triethylene glycol monomethyl (or ethyl) ether; N-methyl-2-pyrrolidone, 1
．． Examples include 3-dimethyl-2-imidazolidinone.

Among these many water-soluble organic solvents, organic amines are contained as essential components in the recording liquid of the present invention, preferably in an amount of 0.001 to 10% by weight based on the total weight of the recording liquid.

In addition, the above-mentioned water-soluble organic solvents other than organic amines are selected as desired and are contained in appropriate amounts, but among them, polyhydric alcohols such as diethylene glycol, polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether, etc. Lower alkyl ethers of alcohols are preferred.

It has been found that it is effective to add 3% or more of ethanol or isopropyl alcohol in order to stabilize the discharge. This is thought to be because the addition of ethanol or isopropyl alcohol solvent allows the recording liquid to foam more stably on the thin film resistor. However, adding too much ethanol or isopropyl alcohol solvent has the disadvantage of impairing the quality of printed matter, so it has been found that the appropriate concentration of ethanol or isopropyl alcohol solvent is 3 to 10%. Furthermore, the effect of ethanol and isopropyl alcohol solvents is that by adding these solvents to the dispersion liquid, the generation of bubbles during dispersion can be suppressed and efficient dispersion can be achieved.

The content of the water-soluble organic solvent in the recording liquid of the present invention is generally in the range of 13 to 50% by weight of the total weight of the recording liquid,
The amount of water used is 10 to 90% by weight of the total weight of the recording liquid.

In addition to the above-mentioned components, the recording liquid of the present invention may optionally contain a surfactant,
Antifoaming agents, preservatives, etc. can be added, and it is also possible to add commercially available water-soluble dyes.

Examples of surfactants include fatty acid salts, higher alcohol sulfate ester salts, liquid fatty oil sulfate ester salts, anionic surfactants such as alkylaryl sulfonates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, polyoxy There are nonionic surfactants such as ethylene sorbitan alkyl esters, and one or more of these can be appropriately selected and used.

The amount used varies depending on the dispersant, but it is preferably 0.01 to 5% by weight based on the total amount of the ink.

At this time, the surface tension of the recording liquid is 30 d y n e /
It is preferable to determine the amount of the activator to be added so that it is at least cm. This is because if the surface tension of the recording liquid is smaller than this, in a recording method such as the present invention, undesirable situations such as print distortion due to wetting of the nozzle tip will occur.

The method for preparing the recording liquid of the present invention described above is to mix the carbon black described above into an aqueous solution made alkaline by adding a predetermined amount of amines to a dispersant, and then perform a dispersion treatment using the means described below. The above-mentioned water-soluble solvent, water, etc. are added to this dispersion liquid, and the pH of the recording liquid is adjusted to a range of 7 or more using the above-mentioned pH adjuster to obtain a recording liquid. Further, a water-soluble solvent, an antifoaming agent, etc. may be added to this dispersion liquid as necessary, or the dispersion liquid itself may be used as a recording liquid. Furthermore, a centrifugal separation process may be performed as necessary.

The dispersing machine used in the present invention may be any commonly used dispersing machine, such as a ball mill,
Examples include roll mills and sand mills. Among them, high-speed sand mills are preferable, such as super mill,
Sand grinders, bead mills, agitator mills, grain mills, guino mills, pearl mills, cobol mills (all trade names), and the like can be mentioned.

In the present invention, methods for obtaining a pigment with a desired particle size distribution include reducing the size of the grinding media of the dispersion machine, increasing the filling rate of the grinding media, lengthening the processing time, and slowing the discharge speed. Methods such as crushing, classification using a filter, centrifugal separation, etc. are used. Alternatively, a combination of these methods may be used.

〔effect〕

As explained above, the inkjet recording liquid G of the present invention not only has excellent durability of printed matter, but also enables stable ejection even under fluctuations in driving conditions and long-term use, and can be used for a long period of time. It has the effect of having excellent storage stability.

Next, the present invention will be explained with reference to Examples.

[Example 1] (Preparation of pigment dispersion) Styrene-acrylic acid-ethyl acrylate copolymer 1 part (acid value 17)
4. Average molecular weight 18000) Monoethanolamine
0.5 part ion exchange water
78.5 parts ethylene glycol 5
The above ingredients were mixed and heated to 70°C in a water bath to completely dissolve the resin. At this time, if the concentration of the resin to be dissolved is low, it may not be completely dissolved, so when dissolving the resin, a high concentration solution may be prepared in advance and diluted to prepare the desired resin solution. To this solution, 10 parts of carbon black (MCF-88, pH 8.0, manufactured by Mitsubishi Kasei) and 5 parts of ethanol were added, and after premixing for 30 minutes, dispersion treatment was performed under the following conditions.

Dispersion machine Sand grinder (manufactured by Igarashi Kikai) Grinding media Filling rate of zirconium beads 1mm diameter grinding media 50% (volume) Grinding time
Centrifugation treatment (12,000 RPM, 20 minutes) was further performed for 3 hours to remove coarse particles and obtain a dispersion.

(Preparation of ink) Above dispersion 50 parts glycerin 8 parts ethylene glycol
10 parts ethanol
4 parts ion exchange water, pH adjuster 1N-HCl
! 28 part dispersion, glycerin, ethylene glycol, ethanol, and ion exchange water (15 parts) were mixed, and IN-H
(After adjusting the pH to 7 to 9 with J', add ion exchange water,
The total amount was 100 parts.

The above components were mixed and stirred for 1 hour to obtain an ink (A) having a pH of 7.3.

[Example 2] An ink was prepared using the same components as in Example 1, except that IN acetic acid was used as the pH adjuster, and an ink (B) with a pH of 8.0 was obtained.

[Example 3] (Preparation of pigment dispersion) Acrylic acid-butyl acrylate-methyl methacrylate copolymer 5 parts (acid value 80, average molecular weight 6700) Monoethanolamine 2 parts Ion exchange water 68 parts Ethylene glycol 5 parts Mix the above ingredients and heat to 70°C in a water bath.
Completely dissolve the resin. To this solution, 15 parts of carbon black (#45. pH 8.0, manufactured by Mitsubishi Kasei) and 5 parts of ethanol were added, and after premixing for 30 minutes, dispersion treatment was performed under the following conditions.

Dispersion machine Sand grinder (manufactured by Igarashi Kikai) Glass beads 1 mm Diameter 60% (volume) 3 hours Grinding media Filling rate of grinding media Grinding time Further centrifugation treatment (20000 RPM, 20 minutes) was performed to remove coarse particles. It was made into a dispersion liquid.

(Preparation of ink) Above dispersion 40 parts thiodiglycol 10 parts ethylene glycol 10 parts ethanol
4 parts ion exchange water, pH adjuster
36 parts dispersion, thiodiglycol, ethylene glycol, ethanol, and 15 parts of ion-exchanged water were added, and after adjusting the pH to 7 to 9 with IN lithium acetate, ion-exchanged water was added to bring the total amount to 100 parts.

The above components were mixed and stirred for 1 hour to obtain an ink (C) having a pH of 8.3.

[Example 4] Example 3 except that 1N phosphoric acid was used as the pH adjuster.
An ink (D) was prepared using the same ingredients. pH is 7.8
Met.

[Example 5] (Preparation of pigment dispersion) Styrene-maleic ester-maleic anhydride copolymer 2 parts (acid value 15
5. Average molecular weight 13000) Aminomethyl propatool 1 part ion exchange water
67 parts diethylene glycol 5 parts The above ingredients were mixed and heated to 70°C in a water bath to completely dissolve the resin. Carbon black (
Saugal 660RSpH 5. After adding 15 parts (manufactured by Kabot) and 7 parts of ethanol and performing premixing for 30 minutes, dispersion treatment was performed under the following conditions.

Disperser Pearl mill (manufactured by Ashizawa) Grinding media Glass beads 1 mm Filling rate of milling media 50% (volume) Discharge speed
100 mjl! / min.

Further centrifugation treatment (12000 RPM, 20 minutes)
to remove coarse particles and prepare a dispersion.

(Preparation of ink) Above dispersion 40 parts glycerin 10 parts ethylene glycol
5 parts ethanol
5 parts ion exchange water, pH adjuster 4
0 part dispersion, glycerin, ethylene glycol, ethanol, and 20 parts of ion-exchanged water were added, and the solution was purified with sodium acetate.
After adjusting to H7~9, add ion exchange water and bring the total amount to 1
00 copies.

The above components □ were mixed and stirred for 1 hour to obtain an ink (E) with a pH of 8.5.

[Example 6] Ink (F) was prepared with the same composition as in Example 5, except that the pH was adjusted using a mixed solution of potassium hydrogen phosphate and phosphoric acid. The pH of the ink was 8.1.

Samples (A) to (F) prepared in Examples and Comparative Examples were evaluated according to the following method, and the evaluation results are summarized in Table 1.

Printing was performed using a BJ130 printer (Canon ■).

TI<Driving conditions and ejection stability> The driving conditions were set to 25V and 30V, and printing was performed at room temperature under two conditions of frequency 2KHz and 4KHz at each voltage, and it was confirmed that irregularities in printing, chipping, non-ejection, etc. The presence or absence was observed and the ejection stability was evaluated.

A; - Clear discharge from the first character, no irregularities in printing, chipping, or non-discharge during continuous printing.

B: Letters were ejected neatly, but ejection failure occurred in several areas with solid printing.

C: Even in the character part, when a few characters are printed, non-ejection occurs and the printing is disturbed to the extent that the characters are impossible to read. T2 <Ink storage test> After storing each ink at 60°C for 4 weeks, The viscosity and the amount of precipitate attached to the bottom of the storage layer were visually observed.

A: No precipitate was observed.

B: A slight amount of sediment is seen at the bottom of the bottle, but there is no problem in practical use.

C: A large amount of precipitate was formed.

The evaluation results are shown in Table 1.

table

Claims (2)

[Claims] (1) An inkjet recording liquid characterized by containing neutral or basic carbon black and a water-soluble resin in an aqueous liquid medium. (2) The inkjet recording liquid according to claim 1, wherein the content ratio of the neutral or basic carbon black to the water-soluble resin is in the range of 3:1 to 10:1 (weight ratio).