JPS6270464A - Ink for ink jet printer - Google Patents

Abstract

PURPOSE:To obtain the titled ink which will not entrap air bubbles therein on cooling and whose degree of volume expansion can be controlled so that higher reliability in printing can be realized, by using as ink component a solid or a high-viscosity liquid which becomes a low-viscosity liquid when melted by heating and increases its volume when solidified by cooling. CONSTITUTION:For example, 100g of nitrobenzene is mixed with 5g of n-(C26)paraffin, 1g of a black dye, and 20g of myristic acid to give an ink which is solid at ordinary temperatures and increases its volume when solidified by cooling. This ink 18 is placed in an ink reservoir 17 in the head of an ink jet printer, melted by heating with a heater block 19, a power source 20 and a switch 21, and kept in a low-viscosity state. A switch 14 is turned on to heat a heater plate 13, with which the melted ink 22 is heated. The melted ink 22 is introduced into the passage in the head, thus completing the preparation for printing. Then, a switch 10 is turned on to apply a voltage on a piezo vibrator 7, causing a vibrating plate 2 to form a recessed part by the interaction of a metal plate 6 which is bonded to the vibrator 7, thus pushing down the low-viscosity melted ink 22, and an ink drop 23 is sprayed in the spraying direction 24, thus effecting printing. When the operation is stopped and the ink is cooled, the ink increases its volume; therefore, it will not entrap air bubbles therein.

Description

Detailed Description of the Invention [Technical field to which the invention pertains] The present invention provides a stable inkjet printer that prints by using a solid or high viscosity liquid as an ink component, melting it by heating and ejecting it from a nozzle as a low viscosity liquid. It relates to ink for operation.

[Prior Art] Conventional ink for solid inkjet printers undergoes volumetric contraction when it cools from a molten state and solidifies.
When the solid ink is heated and melted to print, then stopped and cooled, the ink in the flow path contracts and air bubbles are drawn into the ink from the ink jet port. These bubbles remain in the flow path or expand when reheating and reprinting, so
Unable to reprint, reducing reliability as a printer.

FIG. 12 shows the temperature characteristics of volume change of an ink using paraffin wax as an example of a conventional ink for solid inkjet printers.

[Problems to be Solved by the Invention] A drawback of the conventional solid-state Infusier I printer is that the ink undergoes volumetric contraction when the ink is cooled from a heated molten state. That is, conventional inks for solid inkjet printers have a fatal drawback that air bubbles are taken in from the ink surface of the ink ejection nozzle due to the volumetric contraction, making printing impossible after reheating.

[Means for Solving the Problems] The present invention relates to an ink that generates volumetric expansion when cooled from a heated molten state to prevent the incorporation of air bubbles, which is the critical size of the conventional ink.

Furthermore, the ink of the present invention is characterized in that, for example, by changing the amount of constituent components, the degree of volumetric expansion can be arbitrarily controlled, thereby further improving the reliability of printing.

[Example] First, the configuration of a head for a solid inkjet printer used in the present invention will be described using FIG. 1.

A substrate 1 having a groove for an ink flow path and a diaphragm 2 are bonded together, an ink flow path 3, a nozzle 4, and an ink supply hole 5 are formed. A plate 6, a piezo vibrator 7, and a thin film electrode 8 are bonded and installed. Solder bumps 9 are formed on the thin film electrode 8 , and a drive power source 11 is connected between the metal plate 6 and the solder bumps 9 via a switch 10 . Heater plate sandwiched between sheet electrodes 12 to heat and melt the solid ink] 3 is the substrate 1
The seal electrode 12 is connected to a power source 15 via a switch 14. Ink is supplied to the head from an ink supply hole 5 in a direction 16.

Next, an example of the operation of the solid inkjet printer used in the present invention will be explained using FIG. An ink reservoir 17 is installed on the ink supply side of the head, and ink 18, which has been solid at room temperature, is heated to a temperature of 1-2 by a heater block, a power supply 20, and a switch 21 installed at the bottom of the ink reservoir 17. Melt and maintain low viscosity. Next, when the switch 14 is closed and the heater plate 13 is heated, the entire head is heated to a temperature T1, and since the molten ink 22 has a low viscosity, it uniformly enters the head flow path, completing preparation for printing. . When the switch 10 is closed and a voltage is applied to the piezo vibrator 7, the diaphragm 2 is deformed into a concave shape by the interaction between the piezo vibrator 7 and the metal plate 6, which pushes the ink 22, which has a low viscosity. Printing is performed by jetting ink droplets 23 in a jetting direction 24. For ink that is insufficient after ejection, molten ink 18 is supplied from the supply port in the supply direction 25.

To make the purpose of the present invention more clear, FIG. 13 shows the unstable filling of ink on the nozzle surface that occurs at the start and stop of printer operation, which is a serious problem with conventional ink for solid inkjet printers. explain.

In FIG. 13(a), when the printer operation is stopped, the switch 10.14.21 is opened, the head is cooled, and the ink 22 in the flow path is lowered from the melting temperature T1 to T'1.
The ink in the ink reservoir 17 is also cooled from the temperature TZ to T'z and solidified, but at this time, since the coefficient of thermal expansion of the ink material is positive and large, the ink contracts as it cools.
At the same time, the ink 22 in the flow path is also cooled and solidified and is not supplied from the supply port 5, so the ink surface 22 of the nozzle part when melted
is drawn into the flow path and becomes an ink surface 27 during assimilation. Similarly, the ink in the ink reservoir 17 also melts, and the ink surface 18 changes to the ink surface 2 as the ink cools and assimilates.
It becomes 8. FIGS. 13(b) and 13(C) show the situation around 7 failures after each head has been cooled and reheated.

In FIG. 13(b), the ink surface 26 at the time of melting retreats toward the inside direction 29 of the flow path while being cooled to a temperature T/,
Although the ink is solidified on the ink surface 27, the ink surface 27 usually forms a non-uniform surface with many irregularities, or an ink residue 30 is formed inside the nozzle. When the ink that has solidified at the start of printer operation is reheated to the melting temperature T1, these inks nonuniformly stick to each other and entrap air bubbles 32, as shown in FIG. 13(C). After melting, the ink surface 31 returns to normal due to the surface tension of the ink, but bubbles 32
does not disappear, and for this reason, when printing starts, ink droplets may not be ejected or the amount of ink ejected may be small, resulting in extremely unstable printing.

FIG. 3 shows the state of the ink surface at the nozzle section for explaining the present invention in detail. (a) is the ink temperature T/1
The viscosity of the ink is high and the ink has a low viscosity, and the ink surface 33-1 of the nozzle also forms a normal meniscus and is in a printable state. (b) is a state in which the printer is stopped, and the ink is cooled to a temperature Ti and solidified. The ink surface 33-2 of the nozzle part solidifies so as to protrude from the nozzle when the ink is cooled due to volumetric expansion of the ink.
(c) exhibiting a convex shape is obtained by reheating (b) and increasing the ink temperature T.
'1. Ink surface 33-2 during cooling
Since the ink surface 33-3 has a moderate convexity, even during reheating, the ink surface 33-3 is not drawn into the nozzle to a large extent, forming a normal meniscus, and stable printing is possible without air bubbles being taken in at the nozzle.

Some embodiments of the present invention that meet the key points of solving the above problems will be described below.

(Example 1) Nitrobenzene 100gn-paraffin (carbon number 26) 5g black dye (Black
5) 1g myristic acid
20g Ink was prepared with the composition shown in Table 1, and the volume change due to temperature was measured. The results are shown in FIG.

In the figure, curve A shows the dissolution curve of myristic acid with respect to the solvent component (nitrobenzene) in the ink, and curve B shows the volume change of the ink. As a result, the solubility of myristic acid in the ink decreases significantly as the temperature decreases,
Approximately 15% between 40°C and around 106°C to precipitate
It was found that the volumetric expansion of At temperatures below 20°C, myristic acid was uniformly dispersed in the ink in the form of fine particles, and the ink had a very high viscosity and did not flow. When the amount of myristic acid mixed in was increased, the volumetric expansion due to cooling became larger, resulting in a solid state.

The present invention will be explained in detail using FIG. While heating the ink to about 60°C, it is injected into the ink reservoir 17 of the Infusiera I printer head, which has been previously heated to about 60°C by the heater plate 13 and heater 19, and is pressurized to melt the inside of the flow path. Fill with the ink 22 of the state. In this state, a voltage was applied to the piezo vibrator 7, and the ink droplets 23 were ejected to print. Since the ink 22 has a low viscosity, after the ink droplets 23 are ejected, the ink can be continuously supplied from the ink reservoir 17 in the direction 25 from the supply port. At this time, when no voltage was applied to the piezo vibrator 7, the ink surface 26 of the nozzle portion formed a normal meniscus similar to that shown in FIG. 3(a). When the printer is stopped and the head is cooled, the ink 22 begins to expand and the ink surface at the nozzle becomes convex, but at the same time, the viscosity of the ink 22 increases significantly, so the ink 22 does not spill out from the nozzle, and the ink 22 starts to expand. The surface 26 is the ink surface 33-2 in FIG. 3(b).
It was fixed in a moderate convex state equivalent to.

Next, the temperature of the ink is T2 by the heater plate 13 and the heater 19 again.
≧T1, and even if the temperature rises to about 6°C, the shape of the ink surface 26 remains the same as that of the ink surface 3 in FIG. 3(c).
A normal meniscus similar to that of 3-3 was formed, and stable printing was performed when voltage was applied to the piezoelectric vibrator 7 without entrapment of air bubbles.

This is because the surface tension of ink is large on the ink surface 26 of the nozzle portion, and because ink is supplied from the supply hole in the direction 25 by an amount corresponding to the decrease in ink volume due to temperature rise.

In order to investigate the effects of the present invention, the head shown in FIG. 1 used was made of borosilicate glass having a thermal expansion coefficient of about 8 x 10-6/deg for the substrate 1 and diaphragm 2 that constitute the flow path 3. Since the temperature is changed between 10°C and 60°C, the volume change of the flow path is at most 0.15%, which is negligible compared to the 15% volume change of the ink. Just think about it.

As a result of this experiment, it was found that by using ink that expands in volume upon cooling, it is possible to manufacture a solid inkjet printer that can perform stable printing without introducing air bubbles into the nozzle during cooling. Furthermore, in the present invention, the solute n
- By adjusting the amount of paraffin and myristic acid, the temperature dependence of the volume change rate and viscosity can be adjusted, so the characteristics of the ink can be changed relatively freely. Similar characteristics could also be obtained by changing nitrobenzene to 0-xylene.

(Other Examples) Nitrobenzene 100gn-paraffin (carbon number 26) 3g black dye (Black
5) Igbenzoic acid
30g Table 2 Nitrobenzene 100gn-Paraffin (26 carbon atoms) Ig black dye (Black
5) 1g resorcinol
30g Table 3 Nitrobenzene 100gn-paraffin (24 carbon atoms) 3g Palmitic acid
Log black dye (Black 5)
1. gTable 4 Dioxane 100gn-Paraffin (26 carbon atoms) 1g Stearic acid
50g black dye (Black 5)
Ig Table 5 Toluene 100gn-Paraffin (24 carbon atoms) 1g Fluorene
50g black dye (Black 5)
Ig Table 6 0-xylene 100gn-paraffin (24 carbon atoms) 0.5g lauric acid
100g black dye (Black 5)
Ig Table 7 Toluene 100gn-Paraffin (24 carbons) 1g Phenanthrene
70g black dye (Black 5)
The temperature characteristics of volume changes of inks prepared with the compositions shown in Tables 2 to 8 of Table 8 are shown in FIGS. 6 to 11, respectively. When printing was performed using these inks in the same manner as in Example 1, good results similar to those in Example 1 were obtained without air intake from the nozzle. Also, benzoic acid in Table 2, resorcinol in Table 3, palmitic acid in Table 4, stearic acid in Table 5, fluorene in Table 6, lauric acid in Table 7, and By adjusting the concentration of each phenanthrene in the table, the temperature dependence of the volume change rate and the viscosity could be adjusted, and the same effects as in Example could be obtained.

[Effects of the Invention] As described above, it is essential for solid inkjet printers to operate at high temperatures, and they are always cooled down when stopped. In general, ordinary substances have a positive coefficient of thermal expansion, so even if ink is made of ordinary materials, air will always be taken in from the ink jet holes during cooling, causing a fatal defect that makes printing impossible.However, with the ink of the present invention, Volumetric expansion occurred during cooling and assimilation, and because no air was taken in, extremely stable printing was possible.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a solid inkjet printer head using the ink of the present invention. FIG. 2 is an explanatory diagram of the operation of the head. FIG. 3 is an explanatory diagram of the state of the ink surface of the nozzle section using the ink of the present invention. FIGS. 4 to 11 are explanatory diagrams of examples of the temperature characteristics of the ink of the present invention, respectively. FIG. 12 is a temperature characteristic diagram of conventional ink. FIG. 13 is an explanatory diagram of a stopping state of an inkjet head using conventional ink. 1... Substrate 2... Vibration plate 3... Channel 4... Nozzle 5... Ink supply hole 6... Metal plate 7... Piezo vibrator 8... Thin film electrode 9. ... Solder bumps 10.14.21 ... Switch 11 ... Drive power supply 12 ... Sheet electrode 13 ... Heater plate 15.20 ... Power supply 16 ... Supply direction 17 ... Middle ink reservoir 18...Ink when melted 19...Heater block 22...Ink 23...Ink droplets 24...Ejection direction 25...Supply direction 26...Ink surface 27.28.31.33 -1 33-2.33-3...Ink surface 29...Inner direction of flow path 30...Ink remaining 32...Bubble or more

Claims (1)

[Claims] Heat and melt solids or high viscosity liquids to make them low viscosity liquids,
An ink for an inkjet printer using the low viscosity liquid as an ink component, characterized in that the volume increases when the low viscosity liquid is cooled.