JPH04372669A - Ink for ink jet printer - Google Patents

Abstract

PURPOSE:To uniformly wet a nozzle surface of a plastic head, used as an ink jet head of an on-demand type, with ink. CONSTITUTION:This ink has a surface tension not higher than the critical surface tension and is prepd. by adding a surfactant and a low-surface-tension org. solvent to a water-sol. ink at least contg. a wetting agent, a dye, and water to reduce the surface tension to a value below the critical surface tension. Such a low surface tension assures good wetting of a nozzle surface of a head with the ink, prevents ink drops from flying along an extremely curved route to the surface of paper, and enables high-quality printing.

Description

Description: FIELD OF INDUSTRIAL APPLICATION This invention relates to printing inks, and more particularly to the composition of printing inks used in on-demand inkjet printers. [0002] Conventionally, the end face of a head including an integrated nozzle array is provided with a groove so as to be a symmetrical surface with respect to the nozzle array, and the nozzle end face is made of Ni, Ti, SiO2, TiO2, etc.
JP-A No. 1-123752 proposes a method in which the surface is treated by a coating method such as plating, vapor deposition, or sputtering. This method has the advantage that the nozzle surface of the recording head is wetted with ink, and that good print quality can be obtained without causing the ink droplets ejected from the nozzles to be significantly bent. [0003] However, with the above-mentioned conventional technology, the number of steps for forming the head increases, and the unit cost increases, and furthermore, with the above-mentioned coating method, the nozzle surface of the head cannot be completely uniformly coated. This is difficult, and there are areas where the ink wets the nozzle surface and areas where it does not, causing problems such as the ejection direction of ink droplets becoming unspecified and the print quality worsening. The present invention has been made to solve these drawbacks, and the surface tension of the ink allows the ink to move against the plastic nozzle surface of the head without processing or surface treating the nozzle surface of the head. The purpose is to uniformly wet the paper, stabilize the ejection direction, and improve print quality. Means for Solving the Problems The ink for an inkjet printer of the present invention is a water-soluble ink comprising at least a wetting agent, a dye, and water, and the ink is applied to a nozzle surface made of plastic of a recording head of an inkjet printer. It is characterized in that the surface tension is less than or equal to the critical surface tension. Furthermore, the method is characterized in that a surfactant or a low surface tension organic solvent is added as a means for lowering the surface tension of the ink to below the critical surface tension. EXAMPLES The present invention will be explained based on examples. The basic composition of the inkjet printer ink used in the present invention is firstly a water-soluble dye and secondly a solvent. As the solvent, the main liquid medium components are water (deionized water or pure water) and a mixture of a wetting agent and a surface tension modifier. As water-soluble dyes, C.I. Examples include I Direct Black 154 and 168. Examples of wetting agents include water-soluble organic solvents that have low vapor pressure and are difficult to evaporate to dryness, such as diethylene glycol, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl (ethyl) ether, tetraethylene glycol, dipropylene glycol, and glycerin. . [0010] As a surface tension adjusting agent for lowering the surface tension of ink to a critical surface tension or less, an acetylene glycol surfactant represented by chemical structural formula 1, polyoxyethylene alkyl allyl ether, polyoxyethylene alkyl ether, polyoxyethylene can be used. Nonionic surfactants such as nonylphenyl ether and polyoxyethylene derivatives, anionic surfactants such as sodium dioctyl sulfosuccinate and sodium lauryl sulfate, sec- ond (tertiary) butanol, isopropanol, n-propanol, ethanol,
Examples include water-soluble organic solvents with low surface tension such as methanol, propylene glycol monomethyl (ethyl) ether, and dipropylene glycol monomethyl (ethyl) ether. The above chemical structural formula is as follows. ##STR1## The content of the above dye in the ink is within the range of 0.5 to 20% by weight, more preferably 1 to 10% by weight based on the total weight of the water-soluble ink. The content of the wetting agent in the ink is in the range of 0 to 70% by weight, more preferably 5 to 40% by weight, based on the total weight of the water-soluble ink. [0015] Furthermore, the water content is 10 to 90% by weight, more preferably 40 to 8% by weight, based on the total weight of the water-soluble ink.
The content is preferably 5% by weight. The content of the above-mentioned surfactant in the ink is within the range of 0.01 to 30% by weight, more preferably 0.1 to 20% by weight based on the total weight of the water-soluble ink. The content of the organic solvent for tension is in the range of 5 to 60% by weight, more preferably 10 to 50% by weight, but in any case it is necessary that the surface tension of the ink is below the critical surface tension. The ink is manufactured by mixing the above-mentioned wetting agent, water, water-soluble dye, and surface tension adjusting agent, and stirring and dissolving the mixture while heating it to 70° C. to 80° C. for 30 minutes. If the surface tension of the ink thus obtained is less than the critical surface tension, the nozzle surface made of plastic of the inkjet recording head can be uniformly wetted with the ink, and good print quality can be obtained. Can be done. The present invention will now be explained in more detail by specifically showing the ink components. [0020] Critical surface tension is the surface tension of various inks and the contact angle (θ) of the ink to the plastic.
was measured, and the relationship between COSθ and surface tension was graphed,
It is obtained by reading the surface tension value of the liquid corresponding to COS θ=1. The critical surface tension of plastic polycarbonate is 29 mN/m. The compositions and surface tension values of inks of Examples manufactured so as to have a surface tension of 29 mN/m or less are shown below, but these Examples do not limit the present invention. The ink is prepared by mixing a wetting agent, pure water, water-soluble dye, and a surface tension adjuster at 70℃~
The product was produced by stirring and dissolving while heating to 80° C. and naturally cooling to room temperature. Surface tension was measured using a Wilhelmy surface tension meter. [Example 1]

Weight% glycerin
20C
．． I Direct Black 168
2 Polyoxyethylene alkyl ether 5
Pure water

73 Surface tension
29.0 mN/m [Example 2]

Weight% glycerin
20C
．． I Direct Black 168
1 Polyoxyethylene alkyl ether 7
Pure water

72 Surface tension
28.8 mN/m [Example 3]

Weight% glycerin
20C
．． I Direct Black 168
2 Polyethyleneoxyalkyl allyl ether 1
Pure water

77 Surface tension 28.0m
N/m [Example 4]

Weight% glycerin
20
C. I Direct Black 154
2 Polyoxyethylene alkyl ether 4
Pure water

74 Surface tension 29.0 mN/m [Example 5]

Weight% polyethylene glycol
10 C. I Direct Black 154
1 Tertiary butanol

25 Pure water

64 Surface tension 28.2 mN/m [Example 6]

Weight% triethylene glycol
15 C. I Direct Black 154
2 Dipropylene glycol monomethyl ether 20
Pure water
63
Surface tension 28.5mN/m
Below, as a comparative example of the present invention, the surface tension is 29 mN/
The composition and surface tension value of an ink manufactured so as to be larger than m are shown. The method for producing ink and the method for measuring surface tension are the same as in Examples. [Comparative Example 1]

Weight% glycerin
20C
．． I Direct Black 154
2 pure
water
78
Surface tension 58.0mN/m [Comparative example 2]




weight%
glycerin
30
C. I Direct Black 168
2
Polyethyleneoxyalkyl allyl ether
0.05 Pure water

67.95 Surface tension: 49.5mN
/m [Comparative Example 3]

Weight% glycerin
20C
．． I Direct Black 154
10 Butanol

5 Pure
water
65 Surface tension: 54.1mN
/m [Comparative Example 4]

Weight part Glycerin
5
C. I Direct Black 154
2 Ethanol

1 pure
water
72 Surface tension: 58.6mN
/mThe above ink is laminated and bonded onto a first substrate having a nozzle, a pressure chamber, a supply port and a common ink chamber, a second substrate bonded to the surface of this substrate, and a second substrate bonded to the surface of the first substrate. Wetting was evaluated on the nozzle surface of an on-demand inkjet head made of polycarbonate and consisting of a diaphragm and a piezoelectric element laminated and bonded on the diaphragm. [0023] The voltage applied to the piezoelectric element is changed from 60V to 150V.
The driving frequency was changed from 300 Hz to 3 kHz, and the wetting of the nozzle surface of the head was observed using a microscope. As a result, the inks of Examples 1 to 6 with a surface tension of 29 mN/m or less wet the nozzle surface uniformly, whereas the inks of Comparative Examples 1 to 4 with a surface tension of more than 29 mN/m wetted the nozzle surface uniformly. resulted in uneven wetting. Furthermore, when ink produced with the above composition was printed using a printer using the above head, the inks of Examples 1 to 6 uniformly wetted the nozzle surface, and the ink droplets flew perpendicular to the paper surface, resulting in good results. However, since the inks of Comparative Examples 1 to 4, which wet the nozzle surface non-uniformly, flew in an unspecified manner onto the paper surface, characters could not be formed correctly. Above, the critical surface tension of the ink has been determined for plastic polycarbonate, and examples have been given. However, if the surface tension of the ink is less than the critical surface tension for other plastic materials, , similar effects can be obtained. For example, 35 mN/m or less for polysulfone, 39 mN/m or less for polymethyl methacrylate, and 33 mN/m for polystyrene.
By adjusting the surface tension of the ink to 46 mN/m or less for polyamide, the ink uniformly wets the nozzle surface of the head, and the ink droplets fly perpendicular to the paper surface, resulting in good printing. You can get quality. [0027] As described above, according to the present invention, the surface tension of water-soluble ink consisting of at least a wetting agent, dye, and water can be reduced with respect to plastic, which is the head material of an on-demand inkjet printer. By keeping the surface tension below the critical surface tension, good wetting can be ensured, and good print quality can be obtained without ink droplets being greatly bent and flying onto the paper surface.

Claims (3)

[Claims] 1. An inkjet inkjet device, characterized in that, in a water-soluble ink comprising at least a wetting agent, a dye, and water, the surface tension of the ink with respect to a nozzle surface made of plastic of a recording head of an inkjet printer is equal to or less than a critical surface tension. Ink for printers. 2. The ink for an inkjet printer according to claim 1, wherein a surfactant is used as the material for lowering the surface tension to below the critical surface tension. 3. The ink for an inkjet printer according to claim 1, wherein a low surface tension organic solvent is used as the material for lowering the surface tension to below the critical surface tension.