JPS61211046A - Ink jet printer - Google Patents

Abstract

PURPOSE:To prevent the clogging of a printing head nozzle and the overloading of ink to a tank side by making an expansion chamber continuous to a cap member which is abutted on a printing head under a hermetically sealed design. CONSTITUTION:In a condition where a printing head 4 is abutted on a cap member 5 under a hermetically sealed design after the completion of printing, a narrow space S where ink C in the tip of a nozzle N is sealed immediately reaches a saturated vapor pressure level of ink solvent, so that the hardening of ink at the tip of the nozzle does not occur. If an ambient temperature increases to allow a gas in the space S to expand, a thin membrane 14 provided on the surface of an expansion chamber swells outward to hold the soaring of pressure in the space S, and the ink C stays at the tip of the nozzle under its own surfacial tension. In addition, if an ambient temperature drops to allow the gas contained in the space S to contract, the thin membrane 14 of the expansion chamber 15 protrudes inward to allow the inner pressure to reach a near atmospheric pressure level. Thus the leak of ink C from the tip of the nozzle does not occur.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to on-demand inkjet printers, and more particularly to technology for preventing clogging of print heads.

(Prior art) An on-demand inkjet print head has a nozzle forming an ink jetting port formed on the negative side, and a pressure generating means such as a piezo element or a heating element provided in a thin tube that communicates with an ink supply tank on the other side. The pressure generating means is configured to be driven by a print signal to eject ink droplets toward the paper.

However, since the nozzle tip of this print head is open to the atmosphere, there is a major problem in that liquid components in the ink evaporate and cause clogging.

- For this reason, when the ink is not in operation, a plate-like body A made of an elastic material is brought into contact with the nozzle tip of the print head B to prevent the liquid component in the ink from evaporating, as shown in FIG. 8 (a). is proposed.

However, when the ink is not ejected, the ink contracts inside the nozzle due to its own surface tension, so air is trapped between the plate-like body A and the nozzle tip. This trapped air expands as the surrounding temperature rises and pushes the ink C from the nozzle back toward the tank, making it impossible to eject ink during use.

In order to solve this problem, a space E is formed on the nozzle side of the ink head, and this space is connected to a negative pressure generation mechanism, so that ink is sucked out to the nozzle tip by the negative pressure generation mechanism prior to the start of operation. A cap member F has also been proposed that enables this, but at the installation stage E, it is blocked from the atmosphere to prevent clogging, so the ink C at the tip of the nozzle is exposed to atmospheric pressure due to thermal expansion in the space E. They still have the problem of being pushed back to the tank side.

(Objective) In view of these problems, an object of the present invention is to provide an on-demand inkjet print head in which the amount of ink pushed back by the clogging prevention member is minimized.

(Structure) Therefore, details of the present invention will be described below based on illustrated embodiments.

FIG. 1 shows an embodiment of an on-demand inkjet printer to which the present invention is applied, and the reference numeral 1 in the figure is guided by guide members 2, 2 to move in the axial direction of a platen 3. The carriage is configured to mount a rad 4 for on-demand printing and move it in the width direction of the printing paper P. A cap member 5, which will be described later, is swingably attached to an actuator 6 disposed at the home position of the print head 4 via a rotation shaft 7, and is configured to be pressed against the front surface of the print head. There is. Note that group number 8 in Figure 1 indicates an ink tank.

FIG. 2 shows an embodiment of a cap member which is a characteristic part of the present invention. Group number 5 in FIG. The cap 11 is lined with a cover 12 made of a hard polymer material. A recess 13 is formed on the other surface of the cap member 9, and a thin film 14 impermeable to vapor molecules, such as a film 14 made of nylon or fluororesin, is adhered to the upper surface of the recess 13 to form an expansion chamber 15. , through a through hole 16 to communicate with a recess 10 formed on the nozzle surface side.

In this embodiment, when the printing operation is completed and the print head returns to the home position, the actuator 6 is actuated by a signal from a home position sensor (not shown). Due to this.

The cap member 5 moves toward the nozzle body side of the print head 4, and comes into airtight contact with the head surface while compensating for any misalignment with the front surface of the head using the rotating shaft 7 (FIG. 3).

In this state, since the ink C at the tip of the nozzle N is confined within the narrow space S formed by the cap member 5 and the front surface of the nozzle, the inside of this space S immediately reaches the saturated vapor pressure of the ink solvent. However, the ink C does not solidify at the nozzle tip, and no clogging occurs at the nozzle tip.

When the ambient temperature rises and the gas in the space S begins to expand, the thin If! J14 expands outward and absorbs the expansion, thereby suppressing the pressure in the space S surrounding the nozzle tip from increasing. As a result, the ink C on the head nozzle surface stops at the nozzle tip due to its own surface tension.

Furthermore, when the ambient temperature drops and the gas trapped in the space S formed by the cap member 5 and the nozzle surface begins to contract, the thin film 14 of the expansion chamber 15 protrudes inward, bringing the internal pressure closer to atmospheric pressure. . This prevents the ink C at the nozzle tip from leaking from the nozzle tip.

FIG. 4 shows a second embodiment of the present invention,
In this embodiment, an expansion chamber 20 is separately formed by stretching a thin film 19 on the surface of the base material 18 on the concave side in which the concave part 17 is formed, and is communicated with the cap member 5 through a tube 22. According to the above, not only can the size of the cap member 5 be reduced to simplify attachment to the home position, but also the size of the expansion chamber 20 can be increased as much as possible to effectively reduce the inflation pressure. .

FIG. 5 shows a third embodiment of the present invention,
An expansion chamber 20 is connected in the middle of a conduit 23 that connects the cap member 5 and the suction pump, and the expansion chamber 20 compensates for gas expansion between the cap member 5 and the print head. When the nozzle tip becomes clogged, the pump is activated to forcefully discharge ink to the nozzle tip.

6(a) and 6(b) show a fourth embodiment of the present invention, in which an elongated capillary tube 24 is bent and arranged on the front surface of the cap member 5, and one end thereof is communicated with the recess 10. According to this embodiment, the expanded gas is quickly discharged to the atmosphere via the capillary tube 24 due to the pressure difference generated.
This prevents the air pressure from increasing inside the ink solvent vapor.

Since diffusion within the capillary tube 24 becomes slower,
Evaporation of the ink at the tip of the nozzle, which is sufficiently far away from the atmosphere-opening end, is suppressed and the nozzle is prevented from clogging.

FIG. 7 shows a fifth embodiment of the present invention,
The concave portion 10 of the cap member 5 is communicated with the atmosphere through a check valve 25 that allows circulation to the atmosphere, and is also connected to a suction pump. This can be done by means of valve 25.

(Effects) As explained above, according to the present invention, since the expansion chamber is communicated with the cap member that airtightly contacts the print head, the evaporation of the ink solvent is suppressed and the clogging of the print head nozzle is prevented. In addition, the inflation pressure of the cap member can be reduced as much as possible to prevent ink from being pushed into the tank.

Further, according to the present invention, since the orifice member is communicated with the cap member, the air in the cap member can be quickly discharged, while the discharge of the ink solvent component can be suppressed, thereby preventing clogging of the print head nozzle. This makes it possible to prevent ink from being pushed in with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an outline of an on-demand inkjet printer to which a clogging prevention member according to the present invention is applied, and FIG. 2 is a diagram (jt) and (g) of the present invention, respectively. It is a sectional view showing an example of a clogging prevention member. 1・Rei・・Carriage

Claims (2)

[Claims] (1) An inkjet print head body comprising a thin tube having an ink ejection port formed on one side and communicating with an ink tank on the other side, and means for applying ejection pressure to the ink in the thin tube, and contact with the print head body. An inkjet printer comprising: a cap member having a recess formed on its side and detachable from the print head body; and an expansion chamber communicating with the recess of the member and having an expansion membrane at least in part. (2) an inkjet print head body comprising a thin tube having an ink ejection port formed on one side and communicating with an ink tank on the other side, and means for applying ejection pressure to the ink inside the thin tube;
An inkjet printer comprising: a cap member having a concave portion formed on a side that contacts the print head body and detachable from the print head body; and an orifice member communicating with the concave portion of the cap member.