JP3262864B2 - On-demand printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an on-demand type printing apparatus, and more particularly to an on-demand type printing apparatus for printing large dots on a large article such as a steel material.

[0002]

2. Description of the Related Art A conventional printing apparatus of this type has a discharge nozzle suitable for dot printing at the tip thereof, and a discharge control valve comprising a valve seat and a spherical valve body is formed inside the discharge nozzle. You. The spherical valve body is integrally connected to a movable iron core of a vibration mechanism, for example, an electromagnetic solenoid, via a rod. Around the valve seat and the spherical valve element, there is a chamber filled with pressurized paint. The discharge control valve is opened and closed by the reciprocating motion of the movable iron core, and the dot-shaped liquid paint is intermittently discharged from the discharge nozzle. When the control valve is closed, the paint remains in the discharge nozzle, and at the nozzle tip, the paint forms a convex meniscus due to interfacial tension. Paints used for steel materials, etc. require quick drying with a drying time of 30 seconds or less.
If the control valve remains closed for a considerable period of time (eg, 0.5 minutes), the paint in the meniscus will dry and stick to the nozzle. Then, this becomes an obstacle for the paint to be discharged next, and the paint cannot be discharged straight.

In order to prevent the solidification of the paint near the tip of the nozzle, conventionally, the paint near the tip of the nozzle is removed by washing with a detergent or a solvent, or a mist of the solvent is generated to bring the paint into contact with air. Was to be shut off.

[0004] However, the above solution is structurally complicated and bulky, and is unsuitable especially when the print head is made movable. The costs and labor required for installation and maintenance of ancillary equipment such as a circulation device for cleaning agents or solvents cannot be neglected.

[0005]

DISCLOSURE OF THE INVENTION The present invention is directed to a printing apparatus capable of preventing the solidification of paint at the tip of a nozzle and the trouble due to the coating, while having the above-mentioned disadvantages improved and having a very simple structure. The purpose is to provide.

[0006]

Means for Solving the Problems The present inventor has achieved the above object by utilizing the expansion and contraction of a paint due to a temperature change.

That is, the present invention provides a discharge nozzle for discharging a dot-like liquid paint, a discharge control valve comprising a valve seat and a valve body provided in a flow path of the discharge nozzle, and opening and closing the discharge control valve. An on-demand type printing apparatus having a mechanism for discharging a dot-shaped liquid paint by means of a means for reducing the volume of the liquid paint remaining in the discharge nozzle after closing the control valve, whereby the tip of the discharge nozzle is The on-demand type printing device is characterized in that the liquid paint interface in the above-mentioned is receded.

As means for reducing the volume of the liquid paint remaining in the nozzle, (1) a mechanism for cooling the discharge nozzle is provided, and (2) before the discharge on the rear side (the side opposite to the discharge nozzle) of the control valve. A mechanism for heating the liquid paint may be combined.

[0009] Unlike an office printer that prints on paper, an on-demand printer that prints on a steel pipe or the like has a relatively large inner volume of a discharge nozzle (preferably 1 mm ³ or more). Therefore, the effects of the present invention are particularly remarkably exhibited.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 1 is a partial sectional view of the vicinity of a discharge nozzle of a printing apparatus. This printing apparatus has a head 2 fixed to the tip of a main body 1, a valve seat 3 is mounted on the bottom of a hole of the head 2, and a nozzle holder having a discharge nozzle 4 adjacent to the valve seat 3. A cooling air guide 7 having concentric holes forming an annular cooling air passage 6 around the discharge nozzle 4 according to the invention is then screwed into the head 2. It is preferable that the tip of the discharge nozzle 4 protrudes from the outlet 6 'of the cooling air passage 6 by, for example, 1 to 5 mm. The cooling air passage 6 is connected to a cooling air connection port 10 via a radial hole 8 of the cooling air guide 7 and a radial hole 9 of the head 2. On the other hand, the valve seat 3 has a spherical valve body 11.
Is integrally connected to a movable iron core 13 of a vibration mechanism via a rod 12, for example, an electromagnetic solenoid, a fixed iron core 15 is adjacent to the movable iron core 13, and a solenoid coil 16 is arranged around these iron cores. I have. The pressurized paint is fed into the chamber 14 around the valve seat 3 and the spherical valve element 11 from the paint connection port 15 and is filled under pressure.

When the solenoid coil of the vibration mechanism is not energized, the spherical valve body 11 is pressed against the valve seat 3 by a spring. When energized, the movable iron core 13 is sucked in the direction opposite to the discharge nozzle 4, the spherical valve body 11 is separated from the valve seat 3 and opened, and the pressurized paint is discharged from the discharge nozzle as dot-like liquid fine particles. You. When the current to the solenoid coil is cut off, the valve is closed, and the paint 21 remains in the nozzle 4 as shown in FIG. 2A, and the paint forms a convex meniscus 22 at the tip of the nozzle.

When the valve is closed for a considerable period of time, cooling air is flowed around the discharge nozzle 4 to cool the residual paint 21 according to the present invention (or cooling air may be constantly flowed). Then, the residual paint 21 contracts, and the paint interface at the tip of the discharge nozzle recedes as shown in FIG. 2 (b). In this state, drying and solidification at the interface of the paint is slow. Even if drying and solidification occurs, the next time the valve is opened and the discharge pressure is applied, the paint film is easily discharged together with the liquid paint, and there is no foreign matter (fixed paint) at the nozzle tip.
The paint discharge direction is not bent.

In the present invention, the discharge nozzle has a larger internal volume (V) and a smaller cross-sectional area (S) at the front end portion.
This is preferable because the effect that the paint is drawn into the nozzle is large. Therefore, as shown in FIG. 3, only the tip of the nozzle has a predetermined nozzle diameter l ₁ , after a distance l ₃ from the nozzle tip, a larger inner diameter l ₂ , and this inner diameter l ₂
And the length l _{4 of the} part to be cooled is preferably as long as possible.

As an example, l ₁ = 0.15 mm, l ₂ = 0.3 m
m, l ₃ = 5 mm, l ₄ = 50 mm, as a liquid forming a paint, ethanol (volume expansion β at 20 ° C.)
Taking the case where the paint using _t = 1.08 × 10 ⁻³ ) is cooled at 10 ° C. in the nozzle as an example, calculate the length at which the liquid level is drawn by the temperature change. β _t × V × 10 / S = (1.08 × 10 ^-3 ) × {5 × π × (0.15 / 2)
² + 50 × π × (0.3 / 2) ² ｝ × 10 / ｛π × (0.15 / 2) ² ｝ =
2.21 In other words, paint is drawn about 2.2mm from the nozzle tip. In actual tests, the length of the paint drawn into the nozzle was about 0.5 to 1 mm. It is considered that the deviation from the theoretical value is due to the fact that the seal between the valve seat and the valve element is not perfect and the meniscus portion that originally existed. In any case, the retraction of 0.5 to 1 mm in the test was sufficient to obtain the effect of the present invention. Although an example of cooling at 10 ° C. has been described above, a temperature difference of 5 to 20 ° C. is generally sufficient.

Another aspect of the means for reducing the volume of the liquid paint remaining in the discharge nozzle is a mechanism for heating the liquid paint before discharge at a position rearward of the control valve (opposite to the discharge nozzle). This is shown in FIG.
In addition, it can be performed by raising the temperature of the movable iron core 13 by a mechanism for flowing a current that does not move the movable iron core 13. The movable iron core 13 continues to the paint chamber 14, where the paint is warmed. As mentioned above, a temperature difference of 5 to 20 ° C. is sufficient for the temperature of the paint to decrease after the valve is closed, so in this embodiment it is sufficient that the paint in the chamber 14 is 5 to 20 ° C. above room temperature. Alternatively, a conventional heat exchange means such as a hot hose may be provided between the paint tank (not shown) and the connection port 15 to heat the paint. In this case, the paint is sufficiently heated so that the temperature of the paint in the chamber 14 becomes higher than the room temperature by, for example, 5 to 20 ° C. in consideration of the temperature of the paint falling in the chamber 14. Preferably, the chamber 14 is kept warm with heat insulating material.

By combining the above two aspects, namely, (1) cooling of the discharge nozzle and (2) heating of the paint, the respective loads of cooling and heating can be reduced, and the object can be easily realized.

A plurality of on-demand printers according to the present invention can be arranged to perform matrix printing.

[0019]

In the printing apparatus according to the present invention, the paint does not dry and solidify at the nozzle tip. Therefore, the paint is discharged straight and printing can be performed quickly and reliably.

[Brief description of the drawings]

FIG. 1 is a sectional view of an example of an on-demand type printing apparatus according to the present invention.

FIG. 2 is a cross-sectional view showing a state of a paint at a nozzle tip.

FIG. 3 is a sectional view of an example of a preferred nozzle that can be used in the printing apparatus of the present invention.

[Explanation of symbols]

 4 Discharge nozzle 3 Valve seat 6 Cooling air passage 7 Cooling air guide 11 Spherical valve 13 Moving core 14 Chamber (filled with pressurized paint) 16 Solenoid coil 21 Paint 22 Convex meniscus

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/015 B41J 2/165 B05B 1/24

Claims (3)

(57) [Claims] 1. A discharge nozzle for discharging a dot-shaped liquid paint, a discharge control valve including a valve seat and a valve body provided in a flow path of the discharge nozzle, and a dot-shaped by opening and closing the discharge control valve. In an on-demand printing apparatus having a mechanism for discharging the liquid paint, a mechanism for cooling the discharge nozzle is provided, and after the control valve is closed, the volume of the liquid paint remaining in the discharge nozzle is contracted. An on-demand type printing apparatus characterized in that the liquid paint interface at the tip of the discharge nozzle recedes. 2. Rearward of the control valve (on the side opposite to the discharge nozzle)
The apparatus according to claim 1, further comprising a mechanism for heating the liquid paint before discharging. 3. The discharge nozzle has an inner volume of at least 1 mm ^3.
The device according to claim 1, wherein