JPH03132354A - Ink jet recording head - Google Patents

Abstract

PURPOSE:To hold an ink free surface form at an ink discharge opening constant by a simple structure by a method wherein a magnetic field generating means is provided to the ink discharge part of a substrate and besides, an ink chamber and the ink discharge part are filled by magnetic ink, which are used. CONSTITUTION:An ink jet recording head is composed of a head body 1 which has a slit like ink discharge part 15 and an ink chamber 17, a heat energy applicating means 3 which applies heat energy to ink 2 held with an ink discharge part 16 of the head body 1, and an electrostatic energy applicating means 5 which forms a specified positive charge between the ink discharge part 16 and a recording sheet 4 and further, a magnetic field generating means 7 is arranged by complying with the ink discharge part 16. A magnetic field formed by the magnetic field generating means 7 generates ink holding force in an ink chamber 17 direction, ink supply force in an ink discharge opening 15 direction, and ink uniform distributing force along a head body 1 longitudinal direction to the magnetic ink 2 held with the ink discharge part 16, and an ink holding state at the ink discharge part 16 is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an inkjet recording head, and in particular,
The present invention relates to an improvement in an inkjet recording head in which ink is ejected from a strip-shaped opening using an energy signal containing electrostatic energy.

[Prior Art] The inkjet recording method performs recording by flying small droplets of ink onto a recording member such as a recording sheet.
It is considered to be an extremely useful recording method for various reasons, including the fact that it generates little noise and can form color images with a small and simple mechanical configuration.

This inkjet recording method is classified into several types depending on the shape of the ink ejection opening that ejects the ink droplets or the method of applying energy to eject the ink droplets and make them fly. There is a so-called slit jet method in which ink is ejected from a recording head having ink ejection ports using electrostatic energy.

Conventionally, an inkjet recording head using this slit jet 1 type has, for example, formed a slit-shaped ink ejection opening communicating with an ink chamber by a pair of opposing substrates, and an ink ejection port facing this ink ejection opening has been used. An electrode array consisting of a group of electrodes arranged according to the pixel density is provided on one side of the part, while an electrode for static induction is provided in a part facing the ink ejection port, and each electrode of the electrode array is connected to the electrode array for static N induction. By applying a control signal according to image information between the electrodes, an electrostatic field according to the image pattern is formed between the ink ejection part holding ink and the electrostatic induction electrode,
An electric field control type is known that uses electrostatic attraction to cause ink to fly toward a recording sheet placed in front of an electrostatic induction electrode (Japanese Patent Laid-Open No. 56-6716
No. 3).

Another example is a thermal control type in which the flight of ink is controlled by thermal energy applied to the ink; specifically, a slit-shaped ink ejection port is formed from a pair of substrates, similar to the electric field 1110 type described above. A heating resistor array consisting of a group of heating resistors arranged according to the pixel density is provided on one side of the ink jetting portion facing the ink jetting port, while a static resistor array consisting of a group of heating resistors arranged according to the pixel density is provided. An electrostatic energy applying means is provided to apply electrostatic energy to the ink to form an electric field, and heat energy is applied to each unit area of the ink according to image information by the heating resistor 7 lay, and the electrostatic energy is applied to each unit area of the ink. Japanese Patent Laid-Open No. 62-225388) is already known in which each unit area of ink heated by a predetermined electrostatic attraction force from an applying means is caused to fly toward the recording sheet side according to an image pattern. .

[Problems to be Solved by the Invention] By the way, to explain in more detail the principle of ink flying by electrostatic energy in such a slit-jet type inkjet recording head, the ink ejection part of the recording head and the static N induction electrode The electrostatic field formed during this process generates an induced charge on the ink free surface of the ink ejection port, and the ink held in the ejection portion is It can be said that it rises from the ejection port and flies toward the recording sheet.

Therefore, in order to make the image recording characteristics of the head constant, in addition to forming the electrostatic field with a constant intensity, it is also necessary to keep the 1lli charge generated on the free surface constant. However, the generated induced charge depends on the shape of the ink free surface, so it is important to always maintain the ink free surface in a constant shape for stabilizing image recording characteristics.

Conventionally, for this purpose, ink was supplied to the ink chamber at a constant supply pressure using a precisely controlled pump, or In order to keep the static pressure constant, methods such as connecting an ink tank with an accurately controlled height to the ink chamber have been adopted.

However, in either method, ink retention in the ink ejection section is unstable, and when the printing speed increases and pressure fluctuations in the ejection section become large, the ink tends to flow out from the ejection port. This method was accompanied by a complicated configuration and was not satisfactory in terms of reliability, production efficiency, etc.

In addition, in particular, in the thermal type slit jet method, by applying thermal energy to lower the viscosity of the ink, it is possible to control the ink corresponding to the recording pixels, and in the ink area where thermal energy is not applied, the ink is It has a high viscosity. Therefore,
After the ink flies, it takes a certain amount of time for new ink to be replenished into the ψ position region. In addition, since the fluid motion accompanying the ink flying propagates to the high viscosity ink in the adjacent unit area to which no thermal energy is applied, it takes time for the ink retention in the adjacent unit area to return to the initial state before the flying operation. It takes. Therefore, in the heat-controlled slit jet method, a problem arises in that the printing speed has to be extremely slow due to the fluidity of the high viscosity ink.

The present invention has been made in view of these problems,
The purpose is to provide a highly reliable slit-jet type inkjet recording head that can maintain a constant shape of the ink free surface at the ink ejection port with a simple configuration.

Another object of the present invention is to provide an inkjet recording head capable of increasing printing speed in a thermally controlled slitjet system using high viscosity ink.

[Means for Solving the Problems] In order to achieve the above object, an inkjet recording head of the present invention has an ink chamber and a slit-shaped ink ejection opening continuous with the ink chamber formed by a pair of substrates facing each other. comprising a head main body and an energy applying means for applying an energy signal including at least electrostatic energy according to image information to each unit area of ink held in the ink ejection part facing the ink ejection port, The present invention is characterized in that a magnetic field generating means for forming a magnetic field in the ink discharge section is provided on the substrate, and the ink chamber and the ink discharge section are filled with magnetic ink.

In such technical means, as long as the head body has an ink chamber and a slit-shaped ink discharge port continuous to the ink chamber, the design of the constituent members of the head body and the shape of the ink chamber may be changed as appropriate. do not have.

Further, the energy applying means may be appropriately selected depending on the type of recording head, for example, if it is a thermal control type, it will be a combination of a thermal energy applying means and an electrostatic energy applying means, In this case, as a thermal energy application means, the ink may be indirectly heated using a heat generating resistor array in which a plurality of heat generating resistors are arranged according to the pixel density, or the ink may be heated indirectly using radiation. As a source, the ink may be heated for each pixel density, or the ink itself having a predetermined resistivity may be heated by direct energization.On the other hand, regarding the electrostatic energy applying means, The design may be changed as appropriate as long as it generates an electrostatic attraction force to the extent that the unit area of the ink, which has been heated by the thermal energy applying means and whose viscosity has been reduced, flies toward the recording sheet side. Regarding electric field control type,
If the ink ejection section is capable of selectively ejecting unit areas of ink corresponding to the pixel density according to image information, control electrodes are arranged in the ink ejection section according to the pixel density, and each The design may be changed as appropriate, such as applying electrostatic energy according to image information to a corresponding unit area of ink via an electrode.

Furthermore, if the magnetic field generating means is to form a -like magnetic field in the longitudinal direction of the head main body in the ink ejecting section and exert a magnetic force on the magnetic ink held in the ejecting section, it is possible to create a permanent magnetic field. The structure may be modified as appropriate, such as by magnets, electromagnets, or both. Furthermore, the arrangement on the substrates can be changed as appropriate depending on the strength of the magnetic field, such as providing it only on one substrate or providing it on both substrates.

Furthermore, the saturation magnetization value of the magnetic ink used may be appropriately selected in relation to the strength of the magnetic field generated by the magnetic field generating means. However, if an excessively large magnetic force is applied to the ink, the flight of the ink may be inhibited, so care must be taken in selecting the ink.

[Function] The inventor of the present invention has devised three magnet arrangements as shown in Fig. 5 as a manner of arranging the magnetic field generating means for forming a magnetic field in the ink discharge portion on the substrate. Detailed description of the invention.

FIG. 5(a) shows an example in which a pair of magnets a and b are arranged on one substrate C of the head body. In this case, both magnets a
, b are arranged with mutually different magnetic poles facing the substrate C side, and thereby a magnetic field having lines of magnetic force as shown by broken lines is formed in the ink discharge portion d. Therefore,
Forces f1 and f2 directed toward the center P of the pair of magnets a and b act on the magnetic ink held in the ink discharge portion d.

Also, regarding the longitudinal direction of the head body (direction perpendicular to the page) -
As a result of the occurrence of fl and f2, it can be considered that a force f3 is acting on the magnetic ink within the magnetic field to restrict movement along the longitudinal direction of the head.

Further, in FIG. 5(b), a pair of magnets a and b are arranged on respective substrates c and e so that different magnetic poles face each other.

In this case, a magnetic field having magnetic lines of force directed from the substrate e toward the substrate C is formed in the ink discharge portion d, and fl, f2, and f3 act on the magnetic ink held in the ink discharge portion d.

Further, FIG. 5(C) shows an example in which - number of magnets a are arranged on one substrate C. In this case, the magnetic field is formed symmetrically on both sides of magnet a, and for magnetic ink fl, f
2. In addition to f3, a force directed toward point P' is also acting.

These forces f1, f2, and f3 act as forces (hereinafter referred to as ink retention force) to pull back the ink held near the ink discharge port toward the ink chamber, and prevent the ink from flowing out from the ink discharge port. prevent, f2: act as a force (hereinafter referred to as ink supply force) to suck ink held in the vicinity of the ink chamber to the ink ejection section and improve ink supply performance, f3: move ink along the longitudinal direction of the head body. This acts as a force for uniformly distributing the ink (hereinafter referred to as an ink distribution force), and improves the ability to restore the ink retention state after the ink flies.

As a result, the withstand pressure fluctuation in the ink ejecting section is improved, and the time required for the ink retention after the ink flying operation to return to the initial state before the flying operation is shortened.

[Example] Hereinafter, the inkjet recording head of the present invention will be described in detail based on the accompanying drawings.

In this embodiment, the present invention is applied to a thermally controlled inkjet recording head, and as shown in FIGS. 1 and 2, a slit-shaped ink discharge port 15 and an ink chamber 1
1, a thermal energy applying means 3 for applying thermal energy to the ink 2 held in the ink ejecting section 16 of the head main body 1, and a predetermined gap between the ink ejecting section and the recording sheet 4. The electrostatic energy applying means 5 forms an electrostatic field.

First, the head body 1 is made of glass and has a thickness of about 5 mm.
The heating resistor substrate 12 has a thickness of about 0.35M and is made of alumina ceramics on which a glaze layer (SiO2) is laminated to ensure flatness and heat storage. A concave portion 14 with a depth of approximately one inch is formed on the wall surface of the insulating substrate 11 by sandblasting, while a polyester film coating is formed on the heating resistor substrate 12 along the outer periphery except for the tip side. A letter-shaped spacer (not shown) is provided, and these insulating substrates 1
1 and the heating resistor substrate 12 are bonded together via the spacer, and the slit-shaped ink discharge port 15 and the ink discharge portion 1 are bonded to each other through the spacer.
6, and an ink chamber 17 continuous thereto. The head main body 1 configured in this way has a heating resistor substrate 12 mounted on an aluminum base 6 having a thickness of 5 InM.
It is held in place by gluing it to. In this embodiment, the slit width of the ink ejection part 16 is 50 μm, the depth of the ink ejection part 16 from the ink ejection port 15 to the ink chamber is 1M, and the length of the head main body 1 (in the direction perpendicular to the plane of the paper) is 2M.
The length of the ink discharge port 15 was 210 m.

Further, in the head main body 1 constructed in this manner, a magnetic field generating means 7 consisting of a pair of ferrite magnets as shown in FIG. 3 is disposed corresponding to the ink ejecting section 16 thereof.

The first magnet 11 has 11 pole width [1-1 threshold, thickness ul=5
It has a thin plate shape with mIRx length (perpendicular to the plane of the paper) of 220M, and is bonded to the tip end surface of the base so that the S pole is in contact with the back surface of the heating resistor substrate 12.

At this time, the heating resistor substrate 1 facing the ink discharge section 16
The magnetic flux density on the two surfaces was 200 Gauss (no opposing magnet). Moreover, the second magnet 72 has a magnetic pole width t2=20#I
#l, thickness u2 = 5M1 length is 2, same as first magnet 71
It has a rod shape of 20 mm, and is bonded to the insulating substrate 11 so that the N pole is in contact with the insulating substrate 11. The magnetic flux density was 10 Gauss on the surface of the insulating substrate 11 facing the ink discharge section 16 (no opposing magnet).

On the other hand, the thermal energy applying means 3 includes a heating resistor 31 made of a Ta2N thin film with a thickness of about 300 mm for each pixel density (for example, 8 dots/layer), which is deposited by reactive sputtering and formed by photolithography. Each heating resistor 31 is arranged along the edge of one side of the ink ejecting section 16, and each heating resistor 31 has a N 1-Cr Approximately 500 people, A
A pair of current-carrying electrodes 32 are formed by sequentially and continuously uniformly depositing L + about 1 μm, and by photolithography edge leg method.
is connected. A switching element 33 that opens and closes in response to an image control signal is connected between each of the current-carrying electrodes 32. Incidentally, reference numeral 34 denotes an Si film having a thickness of approximately 2 μm, which is formed by high-frequency sputtering and insulatingly covers the heating resistor 31 and each current-carrying electrode 32.
Insulating layers such as 02 and 35 are power sources for supplying current to each heating resistor 31.

Further, the electrostatic energy applying means 5 is shown in FIGS. 1 and 2.
As shown in the figure, on the insulating layer 34, approximately 500 Cr and C
A head side electrode 51 formed by depositing about 10,000 U and about 500 Cr, and the ink ejection port 1.
A roll-shaped electrostatic induction electrode 52 arranged at an appropriate distance from the ink discharge part 16 is interposed between the head side electrode 51 and the static N induction electrode 52, and is directed from the ink ejection part 16 to the electrostatic induction electrode 52 side. The electrostatic induction power source 53 forms an electrostatic field. Note that the head side electrode 51 is grounded.

The ink 2 accommodated in the ink chamber 17 and the ink discharge section 16 has a viscosity of 320CP at room temperature (20°C).
A magnetic ink with a saturation magnetization of 305 Gauss (Ferricolloid LS-40, manufactured by Taihohe Gyo Co., Ltd.) was used.

In the inkjet recording head of this embodiment configured as described above, the printing operation is the same as the conventional one, that is, a drive pulse corresponding to image information is applied to the heating resistor 31 to heat the corresponding ink unit area. At the same time, an electrostatic control pulse synchronized with the application timing of the drive pulse is applied to the electrostatic induction electrode 52 to form an electrostatic field between the head side electrode 51 and the electrostatic induction mold [i52]. The ink unit amount 1tf corresponding to the recording pixel of the ink 2 held over the entire length of the slit-shaped ink ejection section 16
It is performed by making the ij fly.

At this time, according to this embodiment, the magnetic field generated by the magnetic field generating means 7 exerts an ink holding force on the magnetic ink 2 held in the ink ejection portion 16 in the direction of the ink chamber 17 and in the direction of the ink ejection port 15. Ink supply power to and head body 1
A force for uniformly distributing the ink along the longitudinal direction is applied to stabilize the state of ink retention in the ink discharge section 16.

Next, regarding the effectiveness of this example, the results of experiments conducted by the inventor of the present application will be reported.

In this experiment, as a comparative example, a recording head having the same head structure as the present example but without the magnetic field generating means 1 was prepared, and a non-magnetic ink containing C/B pigment dispersed in a mineral oil base was used. The ink chamber 17 was filled. For both the present example and the comparative example, the ink chamber 1
Experiments were conducted when a pump was used and when it was not used to supply ink to No. 7, and the experimental results were compared for each of the following items.

In addition, when using a pump, conduct the experiment by connecting a low pulsation bimorph pump (manufactured by Misuzu Erie Co., Ltd.) to the ink chamber 17.
By adjusting the AC applied voltage of 50H2, the ink 2 is sent to the ejection port 1.
-10 mtnH○± IJ from the supply pressure flowing out from 5
Feed pressure was set at IIIH20.

When the pump was not used, the ink tank 8 was connected to the ink chamber 11, and the ink pressure in the ink chamber was adjusted by adjusting the height of the ink tank 8 (see FIG. 4).

Experimental item ■ Maximum printable frequency f IIla × ■ Print frequency f
Printing condition when f > f max■Printing energy E required for ink flying in a unit area■Change value p of ink pressure from ink retention state to ink outflow during non-operation ■Ink dot diameter at each recording pixel Uniformity d Also, experiments were conducted for the case where magnetic ink was used in the recording head of the comparative example, and the results were compared with the experimental results of the present example.

A table summarizing the experimental results is shown on the next page.

According to this experimental result, even when the recording head of the comparative example is connected to a pump, the maximum printable frequency f wa
When x = 15011z was exceeded, printing became impossible due to ink leakage, whereas in the inkjet recording head of this example, the maximum printable frequency fIlax, that is, the maximum printing speed, was higher than that of the comparative example, regardless of the presence or absence of a pump. This has more than doubled. This is because the ink holding force caused by the magnetic field prevents ink from flowing out against pressure fluctuations in the ink ejection section 16 during high-speed printing, while the ink supply force caused by the magnetic field accelerates the ink supply speed to the ink ejection section 16. It is presumed that this is because of this, and the effectiveness of this example was confirmed. Furthermore, since similar experimental results were obtained regardless of whether a pump was used or not, it was found that the recording head of this example could eliminate the pump and adopt a simpler configuration.

In addition, in this embodiment, the pressure fluctuation la until the ink flows out is
p was about 4 times that of the comparative example, and in this respect as well, the effectiveness of the ink retention force by the magnetic field could be confirmed.

Furthermore, the uniformity of ink dots for each recording pixel, that is, the variation in dot diameter, in the recording head of this embodiment is less than half that of the comparative example.

This is presumed to be because the ink distribution force acting along the longitudinal direction of the ink ejection section 16 regulates the ink flow in that direction and equalizes the amount of ink flying in each unit area. Ru.

The reason why the ink dot diameter in this example is smaller than the ink dot diameter in the comparative example is considered to be because the ink flow in the longitudinal direction of the ink ejection portion is regulated by the ink uniform distribution force. It is also believed that the reason why the printing energy is large is because the ink is ejected against the ink retention force due to the magnetic field.

In this way, in the inkjet recording head of this embodiment, the magnetic field generating means 7 disposed in the head body 1 applies a magnetic force to the magnetic ink 2, so that the ink ejection portion 16
The ink retention in the printer is stabilized, and the printing speed is improved and the ink dots are made uniform with a simple structure.

[Effects of the Invention] As described above, according to the inkjet recording head of the present invention, magnetic ink can be firmly held within the ink ejection section by the magnetic field formed in the ink ejection section, and the ink pressure can be reduced. It becomes possible to increase the limit of ink outflow due to fluctuations.

In addition, the ink supply is promoted and the ink flow along the longitudinal direction of the head body is regulated, thereby improving the resiliency of the ink retention state in the ink ejection section.
It becomes possible to improve printing speed.

Furthermore, by regulating the flow of ink along the longitudinal direction of the head body, the ink m flying from each ink unit area becomes uniform, so it is possible to obtain a good recorded image with uniform ink dot diameters. It becomes possible.

Furthermore, since it is no longer necessary to precisely control the pressure inside the ink chamber, the apparatus configuration is simplified and it becomes possible to obtain an inkjet recording head with improved productivity.

[Brief explanation of the drawing]

FIG. 1 is a perspective view (partially cut away) schematically showing a first embodiment of an inkjet recording head according to the present invention, and FIG. 2 is a sectional view of the inkjet recording head according to the first embodiment.
FIG. 3 is an enlarged cross-sectional view showing the main parts of the inkjet recording head according to the first embodiment, FIG. 4 is a cross-sectional view schematically showing a comparative example that does not use a pump, and FIGS. 5 (aHb) and (c) are respectively It is a schematic diagram showing an example of composition of a magnetic field generation means of the present invention. [Description of symbols 1 1: Head main body 2: Magnetic ink 3: Thermal energy application means 4: Recording sheet 5: Electrostatic energy application means 7: Magnetic field generation means 15: Ink discharge port 16: Ink discharge section 17: Ink chamber

Claims (1)

[Claims] A head main body in which an ink chamber and a slit-shaped ink discharge port continuous with the ink chamber are formed by a pair of opposing substrates, and each unit area of ink held in the ink discharge portion facing the ink discharge port. An inkjet recording head comprising an energy applying means for applying an energy signal including at least electrostatic energy according to image information,
An inkjet recording head characterized in that a magnetic field generating means for forming a magnetic field in the ink discharge section is provided on the substrate, and the ink chamber and the ink discharge section are filled with magnetic ink.