JPH04325574A - Ink for ink jet recording - Google Patents

Abstract

PURPOSE:To provide the title ink which gives a distinct color image with a high definition on plain paper, such as a reporting paper, a copying paper, a bond paper, and a high-quality paper, causes no clogging at a nozzle tip, can be stored for a long time, and is suitable for thermal ink jet printing and ink jet printing using a piezo system, supersonic wave, or electric field, and esp. to provide the title ink which can stably reproduce a distinct full-color image on the plain paper. CONSTITUTION:The title compsn. consists mainly of a dye dissolved or dispersed in a mixture of water with a water-sol. org. solvent, contains 0.8-5wt.% propylene oxide-ethylene oxide block copolymer having an average mol. wt. of 1000-5000 and an ethylene oxide content in the range of 5-60wt.% of the average mol.wt., and has a surface tension at 20 deg.C of 30-40dyne/cm and a viscosity of 1-10cP at 20 deg.C.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel inkjet recording ink.

0002

[Prior Art] So-called inkjet printers, which eject liquid or solid ink from nozzles, slits, or porous films to record on paper, cloth, film, etc., are small, inexpensive, quiet, etc. The advantages of this technology have been extensively investigated, and printers that can produce good print quality on so-called plain paper such as report paper and copy paper are now commercially available, especially black monochrome printers.

The following points are required for ink used in inkjet printers. (1) A high-resolution, high-density, uniform image with no bleeding or fogging can be obtained on paper. (2) There is no clogging caused by ink drying at the nozzle tip, and ejection responsiveness and ejection stability are maintained at all times. (3) the ink dries quickly on paper; (4) the image fastness is good;
5) Good long-term storage stability.

[0004] In order to satisfy these demands, many studies have been made in the past, including studies on various additives and various water-soluble organic solvents.
2-11781 describes the use of a surfactant, and JP-A-62-89776 and JP-A-1-25789 describe the use of a block copolymer of ethylene oxide and propylene oxide. It is stated that it is used.

[0005]

[Problems to be Solved by the Invention] However, among the inkjet recording inks that have been proposed hitherto, no one has been obtained that satisfies all of the above five requirements. On the other hand, inkjet printers that can produce full-color images are also commercially available, but these do not dry well when printed on plain paper, which not only hinders the printer's high-speed output, but also prints on ink of different tones. The images are mixed together, and faithful image reproduction cannot be obtained. therefore,
Usually, it is necessary to use special paper with surface treatment, which increases the cost of printing per sheet, making it difficult to popularize it as a general-purpose printer.

The present invention has been made with the aim of solving the above-mentioned problems in the prior art, and includes:
To provide an ink that enables the creation of clear, high-resolution color images on plain paper, satisfies all required conditions, prevents clogging at the nozzle tip, and can be stored for a long period of time. That is, the purpose of the present invention is to
For thermal inkjet, it can form clear, high-resolution color images on plain paper such as paper, copy paper, bond paper, and high-quality paper, and can be stored for a long time without clogging at the nozzle tip. Another object of the present invention is to provide an inkjet recording ink using a piezo system, ultrasonic waves, electric field, or the like. In particular, the object of the present invention is to provide an inkjet recording ink that can clearly and stably reproduce full-color images on plain paper.

[0007] Regardless of the type of paper, the drying properties of ink on paper are largely determined by its permeability into the paper. That is, in order to speed up the drying of ink on plain paper, it is sufficient to promote the wettability of the ink to the paper surface and its penetration into the paper. Therefore, attempts have been made to add 1.3 to 25% by weight of a surfactant to the ink, as shown in Japanese Patent Publication No. 11781/1981, but this ink foams and has poor wettability with the ink head. If the ink is too good, ink drips from the head, and stable ejection cannot be achieved due to thickening of the ink. In addition, there are many bleed-throughs where the ink penetrates to the back side of the paper, making it difficult to obtain good image quality when mixing full colors. Furthermore, in the so-called thermal inkjet method that utilizes thermal energy, problems such as burning of the head portion may occur depending on the type of surfactant. Inks using a block copolymer of propylene oxide and ethylene oxide have been proposed in Japanese Patent Publication No. 1-25789 and Japanese Patent Application Laid-Open No. 62-89776, but these inks suffer from bleeding of monochrome images and problems with the ink. Although drying properties and initial ejection properties are improved, there are still problems with ejection stability and full-color image quality.

[0008]

[Means for Solving the Problems] As a result of intensive studies, the present inventors have developed a block copolymer of propylene oxide and ethylene oxide in order to obtain an ink that can produce clear color images without bleeding, especially on plain paper. with an average molecular weight of about 1000-5
000, and contains about 0.8 to 5% by weight of a specific block copolymer in which the content of ethylene oxide groups is within the range of about 5 to 60% by weight of the average molecular weight, and the surface tension at 20°C is 3.
Only inkjet inks with a viscosity of 0 to 40 dyne/cm and a viscosity of 1 to 10 cp, preferably 1 to 5 cp, can avoid the above-mentioned troubles, and in particular can significantly accelerate the penetration into plain paper and prevent the ink from drying on the paper. The present invention was completed based on the discovery that not only the properties could be greatly improved, but also no foaming or dripping from the head occurred, and at the same time it satisfied all the required properties and made it possible to reproduce good full color. I ended up doing it.

Therefore, the present invention provides an inkjet ink composed of a dye, water and a water-soluble organic solvent for dissolving or dispersing the dye, and an average molecular weight of 100.
A block copolymer of propylene oxide and ethylene oxide (hereinafter simply referred to as "block copolymer") having a molecular weight of 0 to 5,000 and a content of ethylene oxide groups of 5 to 60% by weight of the average molecular weight. Contains 0.8 to 5% by weight, 2
It is characterized by a surface tension of 30 to 40 dyne/cm and a viscosity of 1 to 10 centipoise at 0°C.

In the present invention, the molecular weight of the block copolymer is determined from the amount of OH groups, and the content of ethylene oxide groups is determined from the difference between the amount charged during polymerization and the amount unpolymerized.

The present invention will be explained in detail below. Further, the inkjet recording ink of the present invention can be a full-color ink consisting of a combination of three colors, cyan, magenta, and yellow, or a combination of four colors including black.

The block copolymer used in the present invention has an average molecular weight of 1,000 to 5,000, preferably 200
0 to 5000, and the content of ethylene oxide groups is 5 to 60% by weight of the average molecular weight, preferably 20 to 5%.
Those within the range of 0% by weight are used. When the molecular weight of the block copolymer is higher than 5,000, the viscosity of the ink tends to increase extremely, which is unfavorable for ejection and also tends to cause clogging. Furthermore, images with uneven image quality tend to be formed. On the other hand, the molecular weight is 1000
If it is lower than , it tends to bleed very easily,
An image with blur is formed. Therefore, the average molecular weight of the block copolymer in the present invention needs to be within the above range.

Furthermore, when the content of ethylene oxide groups in the block copolymer exceeds 60% by weight, the solubility in water or water-soluble organic solvents becomes too good, and the block copolymer on the surface of the ink droplet becomes Good results cannot be obtained, probably because the surface layer formation becomes unstable. On the other hand, when the content of ethylene oxide groups is less than 5% by weight, the ink structure becomes non-uniform due to poor solubility in water or water-soluble organic solvents, and similarly good results cannot be obtained.

In the present invention, two or more of the above block copolymers may be used in combination. In that case, the ethylene oxide content of each individual copolymer does not necessarily need to be 5 to 60% by weight with respect to the average molecular weight of each copolymer, and even if the ethylene oxide content in the mixture is 5 to 60% by weight. Bye. In the present invention, the block copolymer needs to be contained in the ink in an amount of 0.8 to 5% by weight, preferably 1.0 to 4.0% by weight.
Contain within the range of . The amount of block copolymer added is 0.
If it is less than 8% by weight, sufficient effects will not be exhibited. Moreover, when the amount exceeds 5% by weight, the viscosity of the ink increases significantly, ejection becomes unstable, and image quality deteriorates.

The inkjet ink of the present invention has 20
It is necessary that the surface tension at °C be in the range of 30 to 40 dyne/cm and the viscosity be in the range of 1 to 10 cp. 20℃
If the surface tension at the ink droplet is less than about 30 dyne/cm, ink drips from the head and dots significantly expand, making it impossible to obtain good image quality. On the other hand, 2
If the surface tension at 0° C. is greater than about 40 dyne/cm, the wettability of the ink to paper will be poor, and drying will take a long time, making it impossible to improve the drying time. Further, if the viscosity is lower than 1 cp at 20° C., excessive ink flows out from the nozzle and blurring and scattering of the image become noticeable, which is not desirable. Moreover, if it becomes higher than 10 cp, the fluidity of the ink will not be good, and the stability of ejection will not be obtained. A more preferred viscosity range is 1 to 5 cp.

Examples of the water-soluble organic solvent used in the present invention include ethylene glycol, diethylene glycol, propylene glycol, butylene glycol,
triethylene glycol, tetraethylene glycol,
polyethylene glycol, polypropylene glycol,
Polyhydric alcohols such as glycerin, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,
Examples include glycol ethers such as diethylene glycol monobutyl ether and propylene glycol monomethyl ether, basic solvents such as N-methylpyrrolidone and triethanolamine, and alcohols such as ethyl alcohol, methyl alcohol, isopropyl alcohol and benzyl alcohol. These may be used in combination of two or more types. The content of these water-soluble organic solvents is preferably about 5 to 50% by weight based on the total weight of the ink.

The dye may be any of acid dyes, direct dyes, basic dyes, disperse dyes, etc., but acid dyes and direct dyes are more preferably used. For example, C. I
．． Direct black -17, -19, -32, -80
, -151, -154, -168, C. I. Direct Blue-86, -112, -199, C. I. Direct Red-80, C. I. Direct Yellow-86,
-142,C. I. Food Black-2, C. I. Acid Black-2,-24,-26,-48,-52,
-63, -172, -194, -208, C. I. Acid Blue-9, -185, -249, -254, C.
I. Acid Red-8,-35,-37,-249,
-257, Acid Yellow-23, etc. The content of these dyes is 0.3 to 1 based on the total amount of ink.
It is in the range of 5% by weight, more preferably 1-8% by weight. These dyes can be used alone, or two or more of them may be mixed, or they may be toned to custom colors such as red, blue, and green in addition to the four primary colors of cyan, magenta, yellow, and black.

In the ink of the present invention, a so-called surfactant may be added in order to further stabilize the dissolution and dispersion state of the block copolymer in the ink. The surfactant may be nonionic, anionic, cationic, or amphoteric surfactant. For example, nonionic surfactants include polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene Examples include ethylene sorbitan fatty acid ester and fatty acid alkylolamide. Examples of anionic surfactants include alkylbenzene sulfonates, alkylphenol sulfonates, alkylnaphthalene sulfonates, formalin condensates of alkylnaphthalene sulfonates, higher fatty acid salts, sulfuric ester salts of higher fatty acid esters, and sulfones of higher fatty acid esters. Examples include acid salts, sulfate ester salts of higher alcohols and ethers, sulfonate salts, alkyl carboxylate salts of higher alkylsulfonamides, and salts of dialkyl sulfosuccinates. As cationic surfactants, 1 to 3
Examples include quaternary amine salts and quaternary ammonium salts. Examples of amphoteric surfactants include betaine, sulfoobetaine, and sulfate betaine. Among these, anionic surfactants can be used favorably. However, from the viewpoint of image quality and ejection stability, it is preferable that the amount of these surfactants added is about 1% by weight or less in the ink.

The ink of the present invention may contain a pH adjuster, a fungicide, a water-soluble polymer such as a polyethyleneimine, a polyvinylpyrrolidone, a cellulose derivative, a polyacrylate, a cyclodextrin, a crown ether, etc. as necessary. It is also possible to contain compounds, viscosity modifiers, conductive agents, etc.

[0020]

[Operation] The ink prepared as described above satisfies all the conditions required for forming clear, high-resolution color images on plain paper, and has no clogging at the nozzle tip and can be stored for a long time. It is possible. In the present invention, the mechanism of why adding a predetermined amount of the block copolymer to the ink greatly improves the image quality and drying properties on plain paper is not necessarily clear, but the propylene oxide moiety Because the block copolymer is a hydrophobic group with appropriate affinity and has an appropriate high molecular weight, when ink is ejected from a nozzle to form an ink droplet, near the surface of the ink droplet, It is thought that it forms a stable surface layer and promotes ink penetration into the paper, but prevents excessive dot size spreading and bleeding. This phenomenon occurs only when the composition and molecular weight of the block copolymer in the present invention are within the above-mentioned specific ranges, and when the concentration of the block copolymer added in the ink is within the above-mentioned specific ranges. This is extremely effective when controlling a mixed color image during full color image formation.

[0021]

[Examples] The present invention will be explained in more detail below with reference to Examples and Comparative Examples. Examples 1 and 2, Comparative Examples 1 to 5 C. I. acid blue 249
3 parts ion exchange water
70 parts diethylene glycol
25 parts block copolymer a, b, c, d, e
, f, g parts (average molecular weight 1,700, ethylene oxide group content 30%) The above components were thoroughly mixed and dissolved, filtered under pressure using a Teflon filter with a pore size of 1 μm, and then degassed using a vacuum pump. , an ink was prepared.

(Ink evaluation test) (1) Ink surface tension Measured using a Wilhelmy surface tension meter in an environment of 20° C. and 50% RH. (2) Ink viscosity 20°C, 50% RH environment, shear rate 1.4
Measured at 00/sec.

(3) Image quality test Using the obtained ink, a prototype ink jet printer (300 spi, 192 nozzles) and a modified desk jet printer (manufactured by Hewlett-Packard) were used to print FX as a typical plain paper. A printing test was conducted using -L paper (manufactured by Fuji Xerox) and coated paper for inkjet (manufactured by Xerox). Evaluation items include density and uniformity of solid images, blurring of line images,
Check for thickening or ink scattering around the image. 10
Human sensory tests were used to compare and evaluate newspaper color printing and print quality, and a relative ranking was given. Evaluation was performed based on the following criteria. ○...Good, △...Acceptable, ×...Poor.

(4) Mixed color image quality In each ink, dye is mixed with C.I. I. Acid Red 257 and C. I. Inks were prepared in the same manner except for Acid Yellow 86 to create a three-color ink set. Using these, a full color image was created on the same paper as in (1) using a prototype full color inkjet printer. Evaluation was performed based on the following criteria. ○...Good, △...Acceptable, ×...Poor.

(5) Drying time test The plain papers used were FX-L paper (manufactured by Fuji Xerox Co., Ltd.), 4024 paper (manufactured by Xerox Corporation), report paper (manufactured by Lion Office Co., Ltd.), and coated paper for inkjet (manufactured by Lion Office Co., Ltd.). (manufactured by Xerox Corporation), 51 mm x 10 m
A solid image of m was printed, overlaid with inkjet coated paper (manufactured by Xerox Corporation), and pressure was applied from above. The time until the ink was no longer transferred to the inkjet coated paper side was defined as the drying time.

(6) Discharge stability test desk jet modified machine (manufactured by Hewlett-Packard)
Printing tests were conducted in the atmospheres of 10° C., 15% RH, and 30° C., 85% RH, respectively, and the presence or absence of image omissions and changes in dot diameter on paper were observed. Evaluation was performed based on the following criteria. ○…No problems occurred during 100 prints. Dot diameter change: ±10% or less △…During 100 sheets printed, 10 problems occurred and dot diameter change: ±15% or less×…During 100 sheets printed, 11 or more problems occurred, or dot diameter change: ±15% or more

The above results are shown in Table 1. In addition, Example 1
FIG. 1 shows the relationship between the content of ethylene oxide groups and the drying time for the composition.

[0028]

[Table 1]

Example 3 C. I. direct black 168
5 parts ion exchange water

83 parts glycerin

10 parts block copolymer (average molecular weight 2,500, 2 parts ethylene oxide group content 20%) Using the above components, an ink was prepared in the same manner as in the above example. The surface tension of this ink at 20°C is 37 dyne/cm
The viscosity was 2.4 cp. When tests similar to those above were conducted, good results were obtained in all cases.

Example 4 C. I. hood black 2
3 parts ion exchange water
80 parts diethylene glycol
10 parts block copolymer (average molecular weight 4,000, 3 parts
(Ethylene oxide group content: 50%) An ink was prepared in the same manner as in the above example using the above components. The surface tension of this ink at 20° C. was 35 dyne/cm, and the viscosity was 2.8 cp. When tests similar to those above were conducted, good results were obtained in all cases.

Example 5 C. I. acid blue 249
3 parts ion exchange water

80 parts diethylene glycol
10 parts triethanolamine

5-part block copolymer (average molecular weight 3,00
0.3 parts Ethylene oxide group content 40%) An ink was prepared using the above components in the same manner as in the above example. The surface tension of this ink at 20° C. was 35 dyne/cm, and the viscosity was 2.8 cp. When tests similar to those above were conducted, good results were obtained in all cases.

Example 6 C. I. acid red
3 parts ion exchange water
90 parts diethylene glycol
10 parts alkylbenzenesulfonic acid
0.2 part sodium
Block copolymer (average molecular weight 4,000
3 parts Ethylene oxide group content: 30%) Using the above components, an ink was prepared in the same manner as in the above example. The surface tension of this ink at 20°C is 35
dyne/cm, and the viscosity was 2.9 cp. When tests similar to those above were conducted, good results were obtained in all cases.

Example 7 C. I. direct blue 199
3 parts ion exchange water

70 parts diethylene glycol
10 parts isopropyl alcohol

5-part block copolymer (average molecular weight 2,500,
3 parts Ethylene oxide group content: 30%) An ink was prepared using the above components in the same manner as in the above example. The surface tension of this ink at 20°C is 34 dyne/cm, and the viscosity is 3.
It was 1 cp. When I conducted a test similar to the above, I found that
Good results were obtained in all cases.

[0034]

[Effects of the Invention] Since the inkjet ink of the present invention has the above-mentioned structure, it satisfies all the conditions required when forming a clear, high-resolution color image on plain paper, and also has a It does not clog and can be stored for a long time. In other words, it is possible to form clear, high-resolution color images on plain paper such as report paper, copy paper, bond paper, and high-quality paper. It is suitable as an inkjet recording ink. The inkjet recording ink of the present invention is particularly suitable as an ink capable of clearly and stably reproducing full-color images on plain paper.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the content of ethylene oxide groups and drying time in Example 1.

Claims (2)

[Claims] Claim 1: An inkjet ink composed of a dye, water and a water-soluble organic solvent for dissolving or dispersing the dye, which has an average molecular weight of 1000 to 5000, and an ethylene oxide group content of 5 to 60% of the average molecular weight. weight%
Contains 0.8 to 5% by weight of a block copolymer of propylene oxide and ethylene oxide within the range of
An inkjet recording ink characterized by centipoise. 2. The inkjet recording method according to claim 1, wherein the ink is a full-color ink consisting of a combination of three colors, cyan, magenta, and yellow, or a combination of four colors including black. ink.