JPH0418467A - Ink and method for ink jet recording with the same - Google Patents

Abstract

PURPOSE:To provide an ink giving printed products having excellent fastness and high concentration, capable of being stably jetted and having excellent preservability for a long period by adding a specific carbon black and a water- soluble resin having a specified mol.wt. to an aqueous medium. CONSTITUTION:A neutral or basic carbon black having a BET surface ratio of >=150m<2>/g, preferable <=300m<2>/g, and a water-soluble resin having a weight- average mol.wt. of 3000-7000 (preferably having an acid value of >=100, e.g. styrene-acrylic acid copolymer) to an aqueous medium [preferably comprising water and a water-soluble organic solvent including a polyhydric alcohol (alkyl ether) and an aliphatic monohydric alcohol] to provide the objective ink.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ink particularly suitable for inkjet printers, and furthermore, the present invention relates to ink suitable for inkjet printers, and furthermore, the present invention relates to an ink that is particularly suitable for inkjet printers, and furthermore, ink droplets are ejected and blown from an orifice of a recording head by the action of thermal energy to print on uncoated paper. , relates to an inkjet recording method for recording on so-called plain paper.

[Conventional technology]

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

In such an inkjet recording method, ink prepared by dissolving various water-soluble dyes in water or a mixture of water and an organic solvent is used.

However, when water-soluble dyes are used, the light resistance of recorded images often becomes a problem because these water-soluble dyes inherently have poor light resistance.

Furthermore, since the ink is water-soluble, water resistance of recorded images often becomes 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. For the practical application of water-based pigment ink, examples of studies investigating dispersion stability, prevention of solidification of ink at the pen tip, and prevention of wear of the ball of a hole pen include JP-A-58-80368 and JP-A-61200182. , Japanese Patent Publication No. 61-247
774, JP 61-272278, JP 62-568, JP 62-101671.1
Publication No. 01672, JP 1-249869.1-30
For example, Publication No. 1760 is cited. Recently, hole pens and markers using water-based pigment inks have come onto 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 ejecting and flying ink droplets from the orifice of the recording head by the action of thermal energy, the ejection stability is significantly impaired. There was a drawback that printing defects occurred. In particular, when conventional pigment ink is used for recording by ejecting droplets by applying thermal energy, when a pulse is applied to the ink, the heat causes deposits to form on the thin film resistor, causing the ink to eject. Foaming may be incomplete and droplet ejection may not respond to the applied pulse, resulting in non-ejection. In other words,
In order for ink to be stably ejected from the nozzle tip, the ink must have the ability to foam to the desired volume on the thin film resistor and also have the ability to repeat foaming and defoaming in the desired time. However, since conventional inks for stationery do not satisfy these performance requirements, various inconveniences as described above occur when an inkjet recording device is filled with the ink and used for recording.

Furthermore, as mentioned above, when pigment ink using carbon black, as proposed in the past, is used for inkjet recording, the fastness of printed matter is significantly improved compared to that using dye ink. Subsequent research revealed that one of the characteristics of inkjet recording was that the density of printed matter was inferior to that printed using dye ink. Furthermore, in order to increase the print density, it is possible to increase the pigment concentration, but when a pigment ink with a high concentration is used in an inkjet printer, there is a drawback that it causes a significant problem in ejection stability.

In general, printing ink can be used at a much higher density than the inkjet recording device used in the present invention, so the printing density can be increased relatively easily. Also,
High density can also be obtained by increasing the thickness of the applied ink layer, but when performing inkjet recording, especially high-density recording, the size of the nozzle is extremely small, and the amount of ink that can be ejected is limited. . Furthermore, as described above, when the pigment concentration in the ink is increased, undesirable situations such as precipitation occurring during long-term storage or solidification of the ink due to drying at the nozzle tip may occur, resulting in non-ejection.

Furthermore, although some conventional water-based pigment inks have excellent ejection properties in a relatively short period of time, ejection becomes unstable when the driving conditions of the print head are changed or continuous ejection is performed for a long period of time. Eventually, the problem arises that it stops being discharged.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an ink that provides high density printed matter when printed on uncoated paper. Another object of the present invention is to provide an ink that can always be stably ejected even when driving conditions vary or when used for a long time, and has excellent long-term storage stability.

A further object of the present invention is to provide an inkjet recording method that enables stable high-speed recording at all times and provides printed matter with excellent durability such as water resistance and light resistance.

[Means and effects for solving the problems] The above objects are achieved by the present invention as described below.

That is, the present invention has a BET specific surface area of 150r in an aqueous medium.
r? / g or more of neutral or basic carbon black and a water-soluble resin having a weight average molecular weight in the range of 3,000 to 7,000.

In addition, the present invention provides a weight average molecular weight of 3000 to 7 in an aqueous medium.
BE with a water-soluble resin in the range of 000 adsorbed on the surface
The ink is characterized by containing neutral or basic carbon black having a T specific surface area of 150rd/g or more.

Furthermore, the present invention is an inkjet recording method characterized in that recording is performed by ejecting the ink as droplets from micropores by applying thermal energy to the ink according to a recording signal.

The present invention will be explained in detail below.

The present inventors have intensively studied methods for increasing the density of printed matter by inkjet recording using aqueous pigment ink using carbon black, and found that, among others, 1) carbon black has a BET specific surface area of 150 rr;
? /g or more, preferably 300 m2/g or less, neutral or basic carbon black, 2) The water-soluble resin contained as a dispersant for carbon black preferably has a weight average molecular weight of 3000 to 7000. The inventors have discovered that by using an ink having an acid value of 100 or more, it is possible to create an ink with a high density of printed matter and good dispersion stability, leading to the present invention.

In other words, if the above-mentioned carbon black is dispersed using a water-soluble resin having a weight average molecular weight of 7000 or less and the ink is prepared, the ink is equivalent to or equal to that of a dye ink. ,
This means that a printed matter with an even higher print density can be obtained.

Generally, the specific surface area of carbon black is an indicator of the blackness of carbon black. However, when ink is actually created by dispersing pigments with a high specific surface area in order to increase print density and ejected from an inkjet recording device, the ejection condition changes significantly depending on the dispersion preparation conditions, and the surface area does not necessarily change. It has been found that printed matter with high print density cannot be obtained in proportion to the above.

Therefore, the present inventors discovered that there is some correlation between ejection stability and the combination of carbon black and dispersion resin, and after intensive study, they found that a dispersant with an average molecular weight of 3.
It has been found that good printing characteristics can be obtained under a wide range of driving conditions by creating an ink by dispersing a resin having a molecular weight of 000 to 7000, leading to the present invention. Moreover, even if such a dispersion resin that can provide stable discharge is used, the desired print density cannot be obtained due to the blackness of the carbon black itself.

The inventors of the present invention conducted intensive research and found that the preferable range of the specific surface area of carphone black required to obtain a preferable print density is 150 rrr/g or more. However, when dispersion is performed with the composition of the pigment dispersion used in the present invention, if the specific surface area exceeds 300 rrr/g, the dispersion becomes unstable and tends to cause significant thickening during dispersion. This is thought to be because the amount of dispersion resin used in the present invention is relatively small compared to carbon black for reasons described later, and therefore pigments with a specific surface area exceeding 300 g/g cannot be dispersed.

The reason why neutral or basic carbon black is preferable in the present invention is that acidic carbon lowers the pH of the dispersion compared to neutral or basic carbon, and it is difficult to obtain a stable dispersion over a long period of time. can be mentioned.

The amount of carbon black used in the present invention is 3 by weight.
It is preferable to use it in a range of 20% by weight, preferably 3 to 12% by weight.

Any carbon black can be used in the present invention as long as it satisfies the above performance, but #23
00. #950. #900. #850. MCF
88 (manufactured by Mitsubishi Chemical), RAVEN2000, 150
0 (] Roronpia), BLACK PEARLS
MONARCKlloo, 900.880 (made by Cabot), Pr1n tex95°90, 85.80
Commercially available products such as (manufactured by Degussa), and even products newly manufactured for this purpose can also be used.

The carbon black contained in the ink of the present invention is produced by the Furnace Black method.

The Furnace Black process uses natural gas or petroleum fractions as raw materials and thermally decomposes them by spraying them into a closed reactor kept at a constant temperature.

Here, the pH of carbon black according to the present invention means a value obtained by the following measuring method.

That is, weigh 1 to 10 g of a carphone black sample into a beaker, add water at a ratio of lomβ per 1 g of sample,
Cover and boil for 15 minutes (a few drops of ethanol may be added to help wet the sample).

The boiling liquid is cooled to room temperature and the supernatant liquid is removed by decanting or centrifugation, leaving a slurry. A glass electrode pH electrode is placed in this slurry, and JISZ 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 carbon black used in the present invention has a pH of 6 to 6.
A value in the range of 10 is particularly preferred from the viewpoint of storage stability over time of the pigment ink.

The EET specific surface area of carbon black is Brunaur
Nitrogen adsorption method by Emmett-Teller method (BE
T method).

Furthermore, in the present invention, the weight average molecular weight of the water-soluble resin (dispersion resin) used to disperse carbon black is 3.
Must be in the range 000 to 7000.

In other words, an inkjet recording device uses thermal energy to eject ink from an ejection port with a side of 50 μm or less, and when using a dispersion system such as pigment ink, the viscosity and particle size of the dispersion affect the ejection characteristics. have a big impact,
In order to perform stable discharge, it is desirable that the viscosity and particle size of the dispersion be as small as possible.

Generally, as the average molecular weight of a polymer dispersed resin increases, the viscosity increases when the same amount is dissolved in an aqueous solution. Further, the dispersion resin has the role of adsorbing around carbon black when carbon black is dispersed and stably dispersing the carbon black through steric hindrance. Therefore, an increase in the molecular weight of the dispersion resin means that the adsorption layer becomes thicker and the particle size of the dispersion becomes larger.

In particular, since the carbon black used in the present invention has a large specific surface area, it is necessary to adsorb a large amount of the dispersed resin on the surface.To do this, it is necessary to increase the amount of the dispersed resin or reduce the molecular weight of the dispersed resin. , it is possible to increase the number of molecules.

However, in the inkjet recording apparatus in which the present invention is used, the amount of dispersed resin cannot be increased for reasons described later.

Therefore, a stable dispersion could be obtained by decreasing the molecular weight of the dispersing resin and increasing the number of dispersed resins as in the present invention. Furthermore, the inkjet recording apparatus used is required to have long-term storage stability over several years.

Therefore, when the acid value of the dispersion resin is set to 100 or more, long-term stability can be obtained even in a system disadvantageous in terms of steric hindrance because the molecular weight is small and the amount added is small. This is achieved by increasing the acid value of the resin.
This is thought to be due to increased stability in aqueous media.

The water-soluble resin contained in the ink of the present invention as a dispersant for carbon black is soluble in an aqueous solution containing an alkali and has a weight average molecular weight in the range of 3000 to 7000.
Any material with an acid value of 100 or more can be used, including styrene-acrylic acid copolymer, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid copolymer, and styrene-maleic acid-acrylic acid. Acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid half-nisel copolymer, vinylnaphthalene-acrylic acid copolymer, vinylnaphthalene-maleic acid Copolymer or
These salts and the like can be mentioned.

Various methods can be used to measure the weight average molecular weight of the dispersed resin, but it is generally measured by GPC (gel verminion chromatography) or the like.

The water-soluble resin is 0.1 to 5% by weight based on the total amount of ink,
It is preferably contained in a range of 0.3 to 2% by weight.

The acid value of the water-soluble resin is a measured value of the acid equivalent contained in the sample, and is expressed in mg of potassium hydroxide required to neutralize 1 g of the sample. For detailed measurement methods, refer to "Analysis and Testing Methods for Coloring Materials," Coloring Materials Association, Maruzen, page 86.

Furthermore, in the ink of the present invention, preferably the entire ink is adjusted to be neutral or alkaline, which improves the solubility of the water-soluble resin and provides an ink with excellent long-term storage stability of the layer. It is desirable because it can be done. However, in this case, it may cause corrosion of various members used in the inkjet recording device, so preferably 7 to 10
It is desirable that the pH is within the range of .

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

As described above, the carbon black and the water-soluble resin are dispersed or dissolved in the water-soluble medium.

A suitable aqueous medium for the ink of the present invention is a mixed solvent of water and a water-soluble organic solvent, and as water, ion-exchanged water (deionized water) is used instead of ordinary water containing various ions. is preferred.

Examples of water-soluble organic solvents used in combination with water include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, 5ec-butyl alcohol, tert-butyl alcohol, and isobutyl alcohol. Carbon number 1-4
Alkyl alcohols; amides such as dimethylformamide and dimethylacetamide; ketone or keto alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; ethylene glycol , propylene glycol, butylene glycol, triethylene glycol, ], 2. Alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms, such as 6-hexandriol, thiodiglycol, hexylene glycol, diethylene glycol; glycerin: Lower alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether; N-methyl-2=
Examples include pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and the like. Among these many water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether are preferred.

Among these water-soluble organic solvents, organic amine water is contained as an essential component in the recording liquid of the present invention, preferably in an amount of 0.001 to 10% by weight based on the entire 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.

Further, in order to prevent the ink from solidifying at the tip of the nozzle during use and storage of the head, the content of polyhydric alcohol is preferably 10% or more. moreover,
It has been found that it is effective to add 3% by weight or more of an aliphatic monohydric alcohol, such as ethanol or isopropyl alcohol, in order to achieve discharge stability. This is thought to be because the addition of these solvents allows the ink to foam on the thin film resistor more stably. However, if excessive amounts of these solvents are added, the quality of the printed matter will be impaired, so a more suitable concentration of these solvents is 3 to 10% by weight. Further, as an effect of these solvents, by adding these solvents to the dispersion liquid, generation of bubbles can be suppressed during dispersion, and efficient dispersion can be performed.

The content of the water-soluble organic solvent in the ink of the present invention is 10 to 50% by weight, preferably 10 to 40% by weight of the total weight of the ink.
% by weight, and the water used is 10% of the total weight of the ink.
-90% by weight, preferably 30-70% by weight.

In addition to the above-mentioned components, the ink of the present invention may contain surfactants, antifoaming agents, preservatives, etc., if necessary, in order to make the ink have desired physical properties. It is also possible to add 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 0% based on the total amount of ink.
．． 5% by weight from Ol is desirable. At this time, it is preferable to determine the amount of the activator added so that the surface tension of the ink is 30 dyne/cm or more. This is because if the surface tension of the ink exhibits a value smaller than this, in a recording method such as the present invention, undesirable situations such as print distortion (deviation of the landing point of ink droplets) due to wetting of the nozzle tip will occur. It is. On the other hand, in order to obtain ink with desired physical properties, water-soluble organic solvents,
A pH adjuster, an antifoaming agent, a preservative, etc. can be added. Furthermore, it is also possible to add commercially available water-soluble dyes.

Performance required for inkjet inks generally includes 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 occur. was often unstable.

Therefore, the present inventors conducted extensive research on the performance of water-based pigment inks that are thermally stable and capable of optimal foaming. It has been found that by setting the amount to 2% by weight or less, preferably 1% by weight or less, the ink foams accurately on the resistor under various 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.

The dissolved water-soluble resin refers to a resin that is not adsorbed to the pigment in the ink but is dissolved in the liquid medium.

One way to reduce the amount of dissolved water-soluble resin is to increase the ratio of pigment to water-soluble resin by weight to 3 when creating ink.
:1 to 10:1, preferably 1O:3 to 10:1.

Further, the total amount of carbon black and water-soluble resin in the dispersion is preferably 10% or more, preferably 30% or less on a weight basis. 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.

The method for producing the ink of the present invention is to first add a pigment to an aqueous solution containing at least a dispersion resin, an amine, and water, stir it, then disperse it using the dispersion means described below, and if necessary, centrifuge it. Treatment is carried out to obtain the desired dispersion. Next, the components listed above are added to this dispersion liquid and stirred to obtain a recording liquid.

In particular, in order to reduce the amount of unadsorbed resin to 2% or less, in the preparation method, an aqueous solution containing resin, amine, and water must be
It is necessary to completely dissolve the resin in advance by stirring at a temperature of at least 30°C for 3 minutes or more.

Further, it is necessary to add the amount of amine that dissolves the resin at least 1.2 times the amount of amine calculated from the acid value of the resin. The amount of this amine is determined by the following formula.

Furthermore, it is also necessary to perform premixing for 30 minutes or more before dispersing the aqueous solution containing the pigment.

This premixing operation improves the wettability of the pigment surface and promotes adsorption of the resin onto the pigment surface.

The amines added to the dispersion include monoethanolamine, jetanolamine, triethanolamine,
Organic amines such as aminomethylpropertool and ammonia are preferred.

On the other hand, the dispersing machine used in the present invention may be any commonly used dispersing machine, and examples thereof include a ball mill, a roll mill, and a sand mill.

Among these, high-speed sand mills are preferred, and examples include super mills, sand grinders, bead mills, agitator mills, grain mills, dyno mills, pearl mills, and cobol mills (all trade names).

In the present invention, methods for obtaining a pigment having 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 down the discharge speed. , pulverization followed by classification using a filter, centrifugal separation, etc. Or a combination of these methods may be used.

The method of measuring the amount of unadsorbed resin according to the present invention is to precipitate the pigment bones and the resin adsorbed to the pigment using an ultracentrifuge or the like, and then calculate the amount of residual resin contained in the supernatant liquid. TOC (Total Organic Car
on % total organic carbon meter), gravimetric method (method of evaporating the supernatant to dryness and measuring the amount of resin), etc. are preferably used.

The recording liquid of the present invention is particularly suitable for use in an inkjet recording system in which recording is performed by ejecting droplets under the action of thermal energy, but it goes without saying that it can also be used for general writing instruments.

A suitable recording device for recording using the ink of the present invention includes a device that applies thermal energy corresponding to a recording signal to a recording liquid in a chamber of a recording head and generates droplets using the energy.

An example of the configuration of the head, which is the main part, is shown in FIG. 1(a).

(b), shown in FIG.

The head 13 includes a glass, ceramic, or plastic plate having grooves 14 through which ink passes, and a heat generating head 15 (a thin film head is shown in the figure, but is not limited to this) used for thermal recording. Obtained by gluing. The heating head 15 includes a protective film 16 made of silicon oxide or the like, aluminum electrodes 17-1, 17-2, a heating resistor layer 18 made of nichrome or the like, a heat storage layer 19, and a substrate 20 with good heat dissipation properties such as alumina. It consists of

The ink 21 has reached an ejection orifice (micropore) 22, and a meniscus 23 is formed by the pressure P.

Now, electrode 17-1. When an electrical signal is applied to 17-2,
The area indicated by n of the heat generating head 15 suddenly generates heat, bubbles are generated in the ink 21 in contact with this area, the meniscus 23 protrudes due to the pressure, the ink 21 is ejected, and it becomes a recording droplet 24 from the orifice 22. , fly toward the recording medium 25. FIG. 2 shows an external view of a multi-head in which a large number of heads shown in FIG. 1(a) are arranged. The multi-head includes a glass plate 27 having multi-grooves 26, and a glass plate 27 as shown in FIG. 1(a).
It is made by bonding a heat generating head 28 similar to that described in .

Note that FIG. 1(a) shows the head 13 along the ink flow path.
FIG. 1(b) is a sectional view taken along A-B in FIG. 1(a).
This is a cut plane along a line.

An example of an ink jet recording apparatus incorporating the head according to FIG. 3 is shown.

In FIG. 3, 61 is a blade as a wiping member, one end of which is held by a blade holding member and becomes a fixed end in the form of a cantilever. The blade 61 is disposed adjacent to the recording area of the recording head, and in this example, is held in a protruding form in the movement path of the recording head. A cap 62 is disposed at a home position adjacent to the blade 61, and is configured to move in a direction perpendicular to the direction of movement of the recording head and come into contact with the ejection port surface to perform capping. Furthermore, 63 is an ink absorber provided adjacent to the blade 61;
Like the blade 61, it is held in a protruding form in the movement path of the recording head. The blade 61 and cap 62
The absorber 63 constitutes an ejection recovery section 64, and the blade 61 and the absorber 63 remove moisture, dust, etc. from the ink ejection orifice surface.

Reference numeral 65 is a recording head that has an ejection energy generating means and performs recording by ejecting ink onto a recording material facing the ejection orifice surface on which ejection ports are arranged, and 66 is a recording head that mounts the print head 65 and moves the print head 65. It is a carriage for carrying out. The carriage 66 is slidably engaged with a guide shaft 67, and a portion of the carriage 66 is connected to a belt 69 (not shown) driven by a motor 68. This allows the carriage 66 to move along the guide shaft 67, allowing the recording head 65 to move the recording area and its adjacent area.

Reference numeral 51 denotes a paper feeding section for inserting a recording material, and 52 a paper feed roller driven by a motor (not shown). With these configurations, the recording material is fed to a position facing the ejection opening surface of the recording head, and as recording progresses, the recording material is discharged to a paper discharge section provided with a paper discharge roller 53.

In the above configuration, when the recording head 65 returns to the home position after recording ends, etc., the cap 6 of the head recovery section 64
2 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. As a result, the ejection port surface of the recording head 65 is wiped. Note that when the cap 62 contacts the ejection surface of the recording head 65 to perform capping, the cap 62 moves so as to protrude into the movement path of the recording head.

When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are in the same position as the wiping position described above. As a result, even during this movement, the ejection orifice surface of the recording head 65 is wiped.

The above-mentioned movement of the print head to the home position is not limited to the end of printing or recovery of ejection, but also the movement of the print head to the home position adjacent to the print area at predetermined intervals while moving the print area for printing. However, along with this movement, the above-mentioned wiping is performed.

FIG. 4 is a diagram showing an example of an ink cartridge containing ink supplied to the head via an ink supply tube. Here, 40 is an ink bag containing supply ink, and a rubber stopper 42 is provided at the tip of the ink bag. By inserting a needle (not shown) into this plug 42,
The ink in the ink bag 40 can be supplied to the head. 44 is an ink absorber that receives waste ink.

The inkjet recording device used in the present invention includes:
The head and ink cartridge are not limited to separate units as described above, but a unit in which they are integrated as shown in FIG. 5 may also be suitably used.

In FIG. 5, 70 is an inkjet cartridge, which houses an ink absorber impregnated with ink. It is configured to be discharged as

Reference numeral 72 denotes an atmosphere communication port for communicating the inside of the cartridge with the atmosphere.

This inkjet cartridge 70 is used in place of the recording head 65 shown in FIG. 3, and is detachable from the carriage 66.

〔Example〕

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

Example 1 (Preparation of pigment dispersion) Styrene-acrylic acid-butyl acrylate copolymer
2 parts (acid value 116, weight average molecular weight 3700) monoethanolamine 1 part ion exchange water
73 parts diethylene glycol
Mix 5 parts of the above bones and water bath 7
Heat to 0°C to completely dissolve the resin. To this solution, 14 parts of carbon black (MCF88 manufactured by Mitsubishi Kasei),
After adding 5 parts of isopropyl alcohol and performing premixing for 30 minutes, dispersion treatment was performed under the following conditions.

Dispersion machine Sand grinder (manufactured by Igarashi Kikai) Grinding media Zirconium beads l m Filling rate of m-diameter grinding media 50% (volume) Grinding time
Further centrifugation treatment for 3 hours (1200 ORPM, 20 minutes)
to remove coarse particles and prepare a dispersion.

(Preparation of ink) Above dispersion 30 parts diethylene glycol 15 parts isopropyl alcohol 5 parts ion exchange water
50 parts of the above components were mixed, and the pH was adjusted from 8 to 10 with monoethanolamine to prepare ink (A).

Example 2 (Preparation of pigment dispersion) Styrene-acrylic acid-butyl acrylate copolymer
5 parts (acid value 120, weight average molecular weight 6100) triethanolamine 2 parts ion exchange water
66 parts diethylene glycol
Mix 5 parts of the above ingredients and soak in a water bath for 70 min.
Heat to ℃ to completely dissolve the resin. Carbon black (Printex 95. manufactured by Degutsusa) 1 is added to this solution.
After adding 5 parts and 7 parts of ethanol and performing premixing for 30 minutes, dispersion treatment was performed under the following conditions.

Disperser Pearl mill (Pearl mill) Grinding media Filling rate of grinding media after glass beads 1mm 50% (volume) Discharge speed 100mj! /
min.

Further, centrifugation treatment (1200 ORPM, 20 minutes) was performed to remove coarse particles and obtain a dispersion.

(Preparation of ink) Above dispersion 30 parts diethylene glycol 10 parts ethylene glycol 10 parts ethanol
5 parts ion exchange water
45 parts The above components were mixed, the pH was adjusted to 8 to 10 with triethanolamine, and the mixture was mixed with ink (B) and Example 3 (Preparation of pigment dispersion) Styrene-acrylic acid-ethyl acrylate copolymer
4 parts (acid value 138, weight average molecular weight 5600) aminomethyl propatool 2 parts ion exchange water
69 parts diethylene glycol
Mix 5 parts of the above ingredients and soak in a water bath for 70 min.
Heat to ℃ to completely dissolve the resin. To this solution, 15 parts of carbon black (MCF88, manufactured by Mitsubishi Kasei) and 5 parts of ethanol were added, premixing was performed for 30 minutes, and then dispersion treatment was performed under the following conditions.

Dispersion machine Pearl mill (Pearl mill) Grinding media Filling rate of grinding media after glass beads 1mm 50% (volume) Discharge speed 100 m1/m
in.

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

(Preparation of ink) Above dispersion 50 parts triethylene glycol 15 parts ethylene glycol 5 parts ethanol
5 parts ion exchange water
25 parts The above ingredients were mixed, the pH was adjusted from 8 to 1O with aminomethyl propatool, and the ink (C
) was obtained.

Example 4 (Preparation of pigment dispersion) Styrene-maleic acid half ester maleic anhydride copolymer 3
1 part (acid value 188, weight average molecular weight 5600) monoethanolamine 1 part ion exchange water
71 parts ethylene glycol
Mix 5 parts of the above ingredients and soak in a water bath for 70 min.
Warm to °C to completely dissolve the resin. Carbon black (Mona r ch 90
Add 15 parts of
After premixing for a minute, dispersion treatment was performed under the following conditions.

Dispersion machine Sand grinder (manufactured by Igarashi Kikai) Grinding media Zirconium beads 0, 5 mm Filling rate of milling media 40% (volume) Grinding time
Centrifugation treatment (12,000 RPM, 20 minutes) was further carried out for 3 hours to remove coarse particles and obtain a dispersion liquid (D).

(Preparation of ink) Above dispersion 30 parts thiodiglycol 20 parts ethylene glycol 5 parts ethanol
4 parts ion exchange water 4
One part of the above components were mixed and stirred for 1 hour to obtain ink (D).

Reference Example 1 A dispersion liquid was prepared using the ink of Example 1 using the following dispersion resin, and an ink was prepared in the same manner as above, and the ink (
E).

Styrene-maleic acid half ester copolymer (acid value 1
80, weight average molecular weight 10000) Reference Example 2 The carbon black contained in the dispersion of Example 2 was
Ink (F) was prepared by using the same recipe instead of using GAL660R (manufactured by Cabot).

Reference Example 3 A dispersion liquid was prepared using the following dispersion resin in the ink of Example 4, and an ink was prepared in the same manner as above, and the ink (
G) was obtained.

Styrene-acrylic acid-butyl acrylate copolymer (
Acid value 88, weight average molecular weight 13000) Using each of the above inks, the following was performed using an inkjet recording device having an on-demand multi-recording head that ejects ink by applying thermal energy to the ink according to a recording signal. A test was conducted.

TI = Driving conditions and ejection stability The driving voltage is set to 25V, and the frequency is 2KH at each voltage.
Printing is performed at room temperature under two conditions: z and 4KHz.
The ejection stability was evaluated by observing the presence or absence of irregularities in printing, chipping, and non-ejection.

A: Clean ejection from the first character, no ejection failure, chipping, or irregular printing at all during continuous printing.

B: Letters were ejected clearly, but ejection failure occurred at several locations in solid print areas.

Even in the C character part, when several characters are printed, non-ejection occurs, and the printing becomes disordered to the point that the characters are impossible to read.

T2: Optical density of printed matter NP-DK paper and XEROX4024 paper A printed matter printed using a J-BJ130 printer (manufactured by Canon) was measured using a Maches densitometer (RD918). The evaluation was based on the average value of the two papers.

T3 Long-term ink storage test After storing each ink at 40°C for 4 weeks, visually observe the amount of precipitate attached to the bottom of the storage bottle.

A: No precipitate was observed.

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

A very large amount of C0 precipitate is present.

TO = amount of dissolved water-soluble resin The obtained ink is centrifuged at 55,000 rpm for 5 hours using an ultra-high-speed refrigerated centrifuge (manufactured by Beckman) to sediment the resin adsorbed on the pigment needles and pigment. A certain amount of the supernatant liquid is collected and dried and solidified in a vacuum dryer (60'C, 124 hours). The percentage of this resin amount to the charged ink is calculated and determined as the residual resin concentration.

Note that Table 1 describes the performance of the carbon black used in this experiment. Furthermore, the evaluation results are shown in Table 2. Regarding the evaluations in the table, the results based on the above-mentioned criteria were listed for the ejection stability at T1, the reflection density of the printed matter at T2, and the visual results at T3.

Carbon black performance evaluation results 64... Ejection recovery section 65... Recording head 66... Carriage [Effect] As explained above, the ink of the present invention improves the robustness of printed matter when applied to an inkjet printer. Not only does it have excellent print density, but it also has the advantage of being able to consistently eject stably even when driving conditions fluctuate or over long periods of use, and has excellent long-term storage stability.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are a longitudinal cross-sectional view and a cross-sectional view of a head section of an inkjet recording apparatus. FIG. 2 is an external perspective view of a multi-head head shown in FIG. 1. FIG. 3 is a perspective view showing an example of an inkjet recording apparatus. FIG. 4 is a longitudinal sectional view of the ink cartridge. FIG. 5 is a perspective view of the inkjet cartridge. 61... Wiping member 62... Cap 63... Ink absorber (Fig. 1) (Fig. (b))

Claims (20)

[Claims] (1) BET specific surface area in aqueous medium is 150 m^2/g
An ink comprising the above neutral or basic carbon black and a water-soluble resin having a weight average molecular weight in the range of 3,000 to 7,000. (2) The ink according to claim (1), wherein the water-soluble resin has an acid value of 100 or more. (3) The amount of the water-soluble resin dissolved in the ink is 2
The ink according to claim 1, wherein the amount is not more than % by weight. (4) The ink according to claim (1), wherein the aqueous medium contains water and a water-soluble organic solvent. (5) The ink according to (4), wherein the water-soluble organic solvent contains a polyhydric alcohol and/or an alkyl ether thereof and an aliphatic monohydric alcohol. (6) In an aqueous medium, weight average molecular weight 3000-700
An ink characterized by containing neutral or basic carbon black having a BET specific surface area of 150 m^2/g or more, on which a water-soluble resin in the range of 0.0 is adsorbed. (7) The amount of the water-soluble resin dissolved in the ink is 2
The ink according to claim 6, wherein the amount is not more than % by weight. (8) The ink according to item (6), wherein the water-soluble resin has an acid value of 100 or more. (9) The ink according to (6), wherein the aqueous medium contains water and a water-soluble organic solvent. (10) The ink according to (9), wherein the water-soluble organic solvent contains a polyhydric alcohol and/or an alkyl ether thereof and an aliphatic monohydric alcohol. (11) In an inkjet recording method in which recording is performed by ejecting ink as droplets from micropores by applying thermal energy to the ink according to a recording signal, the ink has a BET specific surface area of 150 m in an aqueous medium. ^2/g
An inkjet recording method comprising the above neutral or basic carbon black and a water-soluble resin having a weight average molecular weight in the range of 3,000 to 7,000. (12) The inkjet recording method according to item (11), wherein the water-soluble resin has an acid value of 100 or more. (13) The inkjet recording method according to item (11), wherein the amount of the water-soluble resin dissolved in the ink is 2% by weight or less. (14) The inkjet recording method according to (11), wherein the aqueous medium in the ink contains water and a water-soluble organic solvent. (15) The inkjet recording method according to (14), wherein the water-soluble organic solvent contains a polyhydric alcohol and/or an alkyl ether thereof and an aliphatic monohydric alcohol. (16) In an inkjet recording method in which recording is performed by ejecting ink as droplets from micropores by applying thermal energy to the ink according to a recording signal, the ink is placed in an aqueous medium with a weight average molecular weight of 3000 to 3000. 7000
An inkjet recording method, characterized in that a water-soluble resin in the range of 100 to 100% contains neutral or basic carbon black having a BET specific surface area of 150 m^2/g or more adsorbed on the surface. (17) The inkjet recording method according to item (16), wherein the water-soluble resin has an acid value of 100 or more. (18) The inkjet recording method according to item (16), wherein the amount of water-soluble resin dissolved in the ink is 2% by weight or less. (19) The inkjet recording method according to (16), wherein the aqueous medium in the ink contains water and a water-soluble organic solvent. (20) The inkjet recording method according to (19), wherein the water-soluble organic solvent contains a polyhydric alcohol and/or an alkyl ether thereof and an aliphatic monohydric alcohol.