JPH01195054A - Ink jet recording apparatus - Google Patents

Abstract

PURPOSE:To obtain uniform recording density by making it possible to keep the diameter of an emitted ink droplet constant even when the temp. of a recording head is changed, by forming the orifice plate of a recording head from a shape memory alloy and automatically making an orifice small when the temp. of the head becomes set temp. or more. CONSTITUTION:An orifice plate 7 has orifices 2 communicating with respective nozzles (respective grooves 6) formed thereto and an ink emitting orifice is formed by each of the orifices 2. The orifice plate 7 is formed from a shape memory alloy storing the shape (the shape dimension of each of the orifices 2) at predetermined head temp. during recording and set so that the opening area of each of the orifices is contracted to a preliminarily stored small opening (the original opening before deformation) within a range exceeding predetermined head temp. Therefore, when head temp. is low at the start time of recording, each of the orifices 2 has a large enlarged and deformed opening but, when head temp. rises by the continuation of recording to exceed set temp., each of the orifices 2 becomes a small opening before deformation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a recording head of an inkjet recording apparatus.

[Conventional technology]

One of the recording methods used in recording devices such as printers and facsimiles is inkjet recording devices, which eject ink droplets from an orifice formed in a head and form an image with a pattern of dots adhered to by the ink droplets. .

There are two types of inkjet recording devices: one is the hubble type, which heats the ink in the nozzle passage to generate bubbles, and uses the pressure of the bubbles to eject ink droplets, and the other is the hubble type, which uses piezo elements to generate kinetic energy when voltage is applied. There is an electromechanical energy conversion method that uses a piezoelectric element to eject ink droplets.

By the way, in an inkjet recording device, the recording density is determined by the droplet diameter (the size of the ink droplet), but the size of the ink droplet ejected from the orifice of the head changes depending on the head temperature, and the higher the head temperature, the larger the trotube diameter. When the head temperature is low, the trotube diameter becomes smaller and becomes lighter.

The reason for this is that when the head temperature rises, the bubbles generated become larger and the ejection pressure increases even if the same amount of heat is applied, and the ink viscosity decreases. This is because the ejected ink droplets become larger.

[Problem that the invention seeks to solve]

In conventional ink sheet recording devices, even if the temperature of the print head is low when printing starts, the temperature of the print head gradually rises while printing continues, resulting in a difference in print density between when printing starts and after printing continues. There was a problem with print quality.

[F stage to solve the problem]

The present invention was made in view of the problems of the prior art described above, and provides an inkjet recording device that can maintain the diameter of ejected ink droplets constant even when the temperature of the recording head changes, and can obtain uniform recording density. The purpose is to provide.

In the present invention, the orifice plate of the recording head is formed of a shape memory alloy that memorizes the shape at a predetermined head temperature during recording, and each orifice has a small opening area memorized in advance in a range exceeding the predetermined head temperature. By shrinking, the above purpose is achieved.

〔Example〕 The present invention will be specifically described below with reference to the drawings.

FIG. 1 is an exploded perspective view of a recording heel 1 of an inkjet recording apparatus according to an embodiment of the present invention.

In FIG. 1, an electrode pattern 3 for ejecting ink droplets from each orifice (ink ejection port) 2 is formed on the upper surface of a substrate 1, and a heater (heater for generating bubbles) is provided in front of each electrode pattern 3. Resistor) 4 is connected.

By bonding the cover 5 to the upper surface of the substrate 1, nozzles communicating with each orinois (ink ejection port) 2 are formed. A plurality of vertical grooves 6 are formed on the bonding surface of the cover 5 at predetermined intervals (same as the spacing between the electrode patterns 3), and when the cover 5 is bonded onto the substrate 1, each vertical groove 6 is formed. A corresponding electrode pattern 3 and a heater 4 are arranged in each nozzle formed by the method.

After the cover 5 is bonded to the substrate 1 to form a nozzle, the orifice plate 7 is bonded to the front surface thereof.

This orifice plate 7 is formed with an orifice 2 communicating with each nozzle (trough 6), and the orifice 2 forms an ink ejection opening.

Note that a common liquid chamber is formed between the rear half of the substrate 1 and the rear half of the cover 5 by joining these together, which communicates with each nozzle in common.

Further, an ink supply port 8 communicating with the common liquid chamber is provided in the rear half of the cover 5. ) However, the orifice plate 7 is formed of a shape memory alloy that memorizes the shape (the shape and dimensions of the orifice 2) at a predetermined head temperature during recording, and the opening area of each orifice changes in the range exceeding the predetermined head temperature. Pre-memorized (original before transformation)
It is set to contract into a small opening.

As the shape memory alloy, for example, a titanium-nickel alloy can be used.

Therefore, when the head temperature is low at the start of recording, each orifice 2 is expanded and deformed to have a large opening, but as recording continues and the head temperature rises and exceeds the set temperature,
Each orifice 2 becomes its original small opening before deformation.

FIGS. 2A to 2F are explanatory diagrams schematically showing the state in which flying ink droplets are formed in the recording head of FIG. 1.

In FIG. 2, (A> shows the state before the heater 4 is driven, and the inside of the nozzle is filled with only the ink 10.

Therefore, when the heater 4 is energized, the ink 10 in the area in contact with the heater 4 is rapidly heated, and a plurality of small bubbles 11 are generated as shown in (B), and these bubbles quickly coalesce as shown in (C). When the bubble 12 becomes one bubble 12 and expands from (C) to (D), the pressure inside the nozzle increases and ink is forced out from the orifice 2.

The extruded ink becomes a droplet 15 as shown in (E), and at this time, the pressure inside the nozzle causes air bubbles 15 to form.
2 becomes smaller.

As shown in (F), when the ink droplet 15 is completely pushed out, the bubble 12 in the nozzle disappears and the ink 10 is supplied from the rear.

In the above ink droplet formation, if the opening of the orifice 2 is the same, as the recording operation continues and the temperature of the nozzle part of the recording head increases, the size of the bubbles and the pressure generated by the bubbles increase, causing bubble formation. The force increases, and in addition to this, the ink viscosity decreases, so the diameter of the ink droplet 15 ejected from the orifice 2 increases, and the recording density increases.

However, according to the present invention, the orifice plate 7 on which the orifice 2 is formed is made of a shape memory alloy that memorizes the shape at a predetermined head temperature during recording. Orifice 2 or pre-recorded 1. a and is configured to shrink to a small opening area.

Therefore, when the head temperature rises above a predetermined value during recording and the ink droplets become too large, the orifice 2 is made smaller in diameter to increase the ejection resistance. Even if the amount of ink increases, the ink droplets (ink amount) 15 ejected from the orifice 2 can be reduced accordingly.

In this way, even if the head temperature changes, the change in the size of the ink droplets (drop diameter) can be kept small and almost uniform, resulting in uniform recording density and stable printing quality. is obtained.

The graph in FIG. 3 shows a comparative test of the ink droplet diameter μm with respect to the recording head temperature T'C between a conventional inkjet head (shown by a chain line) and an Ink Geno 1 to head of the present invention (shown by a solid line). This shows the results.

In FIG. 3, T1 indicates the head temperature at low temperatures such as when recording begins, T2 indicates the head temperature at high temperatures such as when recording continues for a long time, and dl and d2 represent these temperatures T1, T
The ink droplet diameter at No. 2 is shown.

Further, Ts indicates the temperature at which the orifice plate 7 made of a shape memory alloy returns to its original shape, that is, the temperature at which each orifice 2 returns to its original small opening area.

It is clear from the graph in FIG. 3 that according to the present invention, when the head temperature rises and the ink droplets become large, the orifice 2 is narrowed down to make it smaller. An inkjet recording device was obtained in which the diameter of the ink droplets can be controlled to be approximately constant, thereby forming prints (images) with uniform and stable density.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the orifice spray 1- of the recording head is made of a shape memory alloy,
Since the orifice is configured to automatically shrink when the head temperature exceeds the set temperature, the size of the ejected ink droplets can be kept almost constant even if the head temperature changes, resulting in stable and uniform recording density. An inkjet printer capable of producing high-quality images is obtained.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view of a recording head of an ink sheet recording apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic diagram showing over time the state in which ink droplets are formed in the recording nozzle of FIG. 1.
FIG. 3 is a graph showing changes in ink droplet diameter with respect to printhead temperature for a conventional printhead and a printhead according to the present invention. 2 ---- Orifice (ink discharge port), 4 ----
--Heater, 7-=-==-orifice plate,
TI, TSXT2 ------- Head temperature.

Claims (1)

[Claims] (1) By forming the orifice plate of the recording head with a shape memory alloy that memorizes the shape at a predetermined head temperature during recording, the core orifice has a small opening area memorized in advance in a range exceeding the predetermined head temperature. An inkjet recording device characterized by shrinking.