JPH0987559A - Ink composition for inkjet recording device - Google Patents

Abstract

(57) [Summary] [Structure] Distilled water applied evenly and thinly on a smooth dry coating film formed on a smooth glass plate breaks the liquid film within 0.9 seconds, leaving it in a non-wet state. In addition to having the properties, the contact angle of water droplets of distilled water on the dried coating film was set to 50 degrees or less. [Effect] According to the present invention, it is possible to obtain a new finding that the retention time of water wetness is 0.9, not the contact angle of water which is an index for evaluating the hydrophilicity of a coating film.
If you use an ink that has coating properties that are less than a second, you can ensure sufficient straightness stability of the ink column 24, and even with ink using a highly hydrophilic material, the ink column will not wobble and printing quality will improve. To do.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an ink composition used in an ink jet recording apparatus. Timing of particle cutting and charge application by stabilizing the ejection direction by preventing the phenomenon that the ink column ejected from the ink ejection port and vibrates or suddenly shakes before being made into particles Is constant, and as a result, the accuracy of the landing position of the ink particles is improved, and the surface characteristics of the ink dry coating film for obtaining high quality printing quality are concerned.

[0002]

2. Description of the Related Art The principle of a conventional ink jet recording apparatus will be described with reference to FIGS. During the recording operation of the inkjet recording apparatus, the ink sent from the ink container 9 by the ink supply pump 10 is adjusted to a predetermined liquid pressure by the pressure regulating valve 11. After that, the ink flow is supplied to the nozzle 1. Here, an appropriate frequency and voltage are applied to the electrostrictive element 2 from the excitation power supply 3, and the ink is atomized. A predetermined charge is given to each ink particle 6 by the charging electrode 4 provided at a position where the ink is made into particles, and when the ink passes through the deflection electric field 7 part generated by the deflection electrode 5, each ink particle 6 is given. Receives a biasing force according to the amount of charge of the. After that, the ink particles 6 fly linearly and come into contact with the object to be printed 12 to form the printing dots 13. Ink particles that have not been charged by the charging electrode 4 are collected in the ink container 9 from the gutter 8.

FIG. 2 is an enlarged view of a portion near the nozzle 1.
An orifice 23 is formed at the tip of the nozzle 1, and an ink ejection port 25 having a diameter of about 30 to 120 × 10 ⁻⁶ m is provided at the center of the orifice 23. The ink pressurized by the ink supply pump 10 is ejected from the ink ejection port 25 at a flow rate of 5 to 50 m / sec while forming an ink column, and the electrostrictive element 2 imparts an appropriate frequency and voltage to the ink. Therefore, the ink column 24 is gradually constricted, and is eventually cut into particles. In a state where the ink column 24 is on the verge of being cut into the ink particles 6, a predetermined charge is applied to each particle by the charging electrode 4.

Various conditions are required for ideal flight control of the ink particles 6. Regarding the environment in which the inkjet recording apparatus itself is installed, it is needless to say that if strong wind blows or there is a disturbance in the electromagnetic field such as strong static electricity, control becomes difficult and print quality deteriorates. Various mechanisms for stabilizing the turbulent air flow and the electrostatic field have been proposed as countermeasures on the device side for these conditions. On the other hand, as the characteristics required for the ink liquid itself. It is essential that basic physical properties such as viscosity, surface tension, and electrical conductivity meet the specifications of the inkjet recording device, and those physical property values are uniform, and there is no significant physical property deterioration during long-term running. Is required.
In addition to the ink specification values that can be simply quantified as described above, there are three detailed ink characteristics required for stable printing. First, the first point is that the ink ejection port 25 is not clogged. The second point is the orifice 23
It is required that the ink column 24 rising from above always keeps a constant direction and the central axis does not swing. Thirdly, it is required that the ink column 24 be smoothly cut so that fine particles that adversely affect the stringing and the charging of the ink particles 6 do not occur. Regarding the first problem of ink clogging, there is a high awareness of the problem, and by adding a component such as a glycol system having a relatively high boiling point to the ink,
Many techniques have been proposed to prevent the ink ejection port 25 from drying. Known examples of actual applications corresponding to this include, for example, JP-A-60-229969, JP-A-62-121776 and JP-A-62-169875. Regarding the problem of the third generation of fine particles, the molecular weight of the resin component, which is the binder component in the ink, may be adjusted, or the generated fine particles may be physically removed.
The techniques described in JP-A-55-61478 and JP-A-58-185270 are known. On the other hand, the second problem, which is the directional stability of the ink column 24, has not been emphasized so far, and therefore, no publicly known examples of countermeasure techniques have been found. In particular, in the charge control type inkjet recording device, there is no known technique relating to countermeasures based on ink formulation. Orifice 2
3 Regarding the technology for stabilizing the ink ejection direction by surface treatment of the periphery, the water repellency and oil repellency can be improved by applying a coating agent based on a fluorine-based material to the very surfaces of the orifice 23 and the ink ejection port 25. Examples of those which are stabilized by adding are Japanese Patent Application Laid-Open No. 57-29465, Japanese Patent Application Laid-Open No. 57-107848 and Japanese Patent Application Laid-Open No. 6-320733. On the contrary, there is an idea of stabilizing the flight direction of ink particles by improving the liquid wettability of the surface by forming a SiO ₂ film on the surface of the orifice 23 or the ink ejection port 25. It is described in Japanese Patent No. 123752 and the like and is publicly known. Further, Japanese Patent Application Laid-Open No. 5-124198 and Japanese Patent Application Laid-Open No. 6-286129 disclose a method of stabilizing the ink jet port 25 by providing a concave portion or a gradient of the liquid pool.

However, there is a limit to the method of improving the shape and material of the ink jet recording apparatus itself for stabilizing the ink ejection direction. This is because, in the peripheral parts of the nozzle 1, particularly in the vicinity of the ink ejection port 25, the solvent component volatilizes after the ejected ink exudes or scatters and a dry coating film of the ink is formed. This is because the most surface layer is not the material of these components or the surface-treated material for improving the wettability, but the coating layer of dried ink.

The recording method of the ink jet recording apparatus to which these conventional inventions are applied is called an on-demand method. In the case of the on-demand system, the ink ejected from the ink ejection port 25 is the amount of one ink particle 6, that is, the ink which has already been made into particles is ejected. Further, a mechanism is provided in which ink particles are ejected from each of the plurality of ink ejection ports 25 only at a necessary timing. However, in the present invention, in the case of a target charge control type inkjet recording device, the ink liquid is ejected in a beam form from one ink ejection port 25, and then the beam is constricted to cut.
The particles are made into particles, and only the necessary particles are deflected by electrostatic force, selected, and used for printing. Therefore, the ink ejection port 2
From 5, the ink liquid is constantly ejected in the form of a beam without interruption. In the case of such a structure, the pressurized ink liquid is continuously ejected from the minute nozzles at a high speed, and the temperature in the vicinity of the ink ejection port 25 of the orifice 23 is slightly lowered.
If the temperature lower than the ambient temperature continues for a certain period of time or longer, dew condensation occurs on the surface of the member. That is, the water in the air becomes supersaturated on the surface of the member having a low temperature and is condensed to form water droplets. When the minute water droplets are generated on the dried ink coating film on the orifice 23 and the generation rate is higher than the water droplet drying rate,
The water droplets gradually become larger and finally come into contact with the root portion of the ink column 24. When the grown water droplet comes into contact with the ink column 24, the axial direction of the ink column 24 is instantly inclined at the contact angle. For this reason, the flight direction of the ink particles 6 is not fixed, and the print quality is degraded.

As described above, this is a phenomenon that occurs remarkably in the charge control system in which ink is continuously ejected in the form of a beam, and is a phenomenon that occurs according to the above principle.
The effect cannot be obtained by the conventional techniques such as the surface treatment of the parts such as the orifice itself. Further, in the prior art, there has not been found a technique of solving this problem by devising the surface characteristics of the ink coating film.

[0008]

As described above, even if the shape and material of parts of the ink jet recording apparatus itself are improved as a means for stabilizing the ink ejection direction, the fundamental problem cannot be solved. . Therefore, the problem to be solved by the present invention is to pay attention to the characteristics of the ink, in particular, the property of the dry coating film which remains after evaporation of the solvent, and to solve this problem by improving the ink compounding material. The factor that disturbs the straight running stability of the ink column 24 is due to the dew condensation of the moisture in the air as described above. It was found that there is a close correlation between the stability of the ink and the wettability of the dried ink film. That is, the higher the hydrophilicity of the ink dry coating film, the lower the stability of the ink column 24, and the higher the hydrophobicity of the ink dry coating film, the more stable the axis of the ink column 24 does not swing.

On the other hand, the charge control type ink jet recording apparatus is required to print at high speed on indiscriminate materials and various surface shapes for lot management of mass-produced products. Unlike the case where the solvent of the target on-demand type ink is mainly water-based, an organic solvent having a fast drying property is often used as the solvent of the ink. For example, ketones such as cyclohexanone, methyl ethyl ketone, and acetone, aromatic solvents such as toluene and xylene, aliphatic solvents such as hexane, and alcohols such as ethyl alcohol, methyl alcohol, and propyl alcohol may be used alone or Used as a mixture. In recent years, recognition of global environmental problems and occupational health environmental problems is increasing, and alcohol solvents are often used from the viewpoint of odor and toxicity. Among them, ethyl alcohol, which is particularly low in toxicity, is used as the main solvent. There is an increasing demand for ink. Among the organic solvents, ethyl alcohol is a highly polar solvent, and the resins, dyes, and various additives to be mixed are highly polar and soluble in ethyl alcohol, unlike the materials used in conventional inks. This is a hydrophilic material that is close to water, which is a highly polar solvent. Naturally, the dry coating film of ink made of highly hydrophilic material has a high hydrophilicity, and it has a low contact angle when contacted with water droplets, and it does not become water droplets when exposed to steam or placed in a humid environment to cause condensation. It exhibits surface characteristics that form a thin water film. As described above, in the case of the charge control type inkjet printer, when the ink circulation is started, the surface temperature of the orifice 23 becomes low, which is a condition in which dew condensation easily occurs. The area around the ink ejection port 25 is soiled with ink, and the wettability of the ink dried coating film determines the shape of the dew condensation water. However, on the coating film made of a relatively hydrophilic material soluble in ethyl alcohol. The water condensed at is a water droplet with a low contact angle and tends to become a large water droplet. In the case of a coating film with low water wettability, that is, an ink made of a general material that is soluble in a low-polarity organic solvent, the condensed water droplet forms a water droplet once because it has a high contact angle and is close to a sphere, and has a large surface area. Even so, it easily re-evaporates into the air, and drops or rolls before it grows into large water droplets. On the other hand, when a water droplet with a small contact angle is formed, the contact area is large and the water droplet is easily retained on the surface, so that the water droplet grows and remains as a large water droplet. When the grown water drops come into contact with the root of the ink column 24, the advancing direction of the water drops is changed to deteriorate the printing quality. However, the larger the weight of the water drops, the greater the effect. As described above, in general ink of a solvent having a relatively low polarity, the weight of water droplets condensed on the surface of the orifice 23 is small, and even if the ink droplet 24 comes into contact with the ink column 24, there is almost no adverse effect. When the ink dry coating film has high hydrophilicity like the ink using, the weight of the condensed water droplets tends to be large, and as a result, the problem of impeding the straight running stability of the ink particles 6 remarkably occurs.

In the case of an ink using a resin having a relatively low hydrophilicity which is soluble in alcohols, the destabilizing factor due to the condensation is improved, but the solubility in ethyl alcohol is reduced. This is a problem that the re-dissolvability of ink in the nozzle portion is lowered, that is, a problem that directly results in nozzle clogging, and from this viewpoint, it is preferable to blend a resin that is easily dissolved in a solvent.

As is clear from the explanation of this phenomenon, the problem to be solved by the present invention is such that the solid content in the ink is easily soluble in the solvent to the extent that nozzle clogging does not occur, and the ink particles 6 are This is to obtain an ink that does not form a condensed water droplet having a size that affects the flight direction on the ink dry coating film on the surface of the orifice 23.

[0012]

As is apparent from the above description, the object of the present invention is to wet the components constituting the dry coating film other than the volatile components such as the solvent among the components to be blended in the ink. Can be solved by adjusting the wettability to an appropriate wettability.

When a polar solvent such as alcohol is not used, a dry coating film having sufficiently high hydrophobicity is usually obtained. Specifically, it has hydrophobicity such that the contact angle of water droplets is 50 degrees or more, and the size of water droplets that condense is large enough to tilt the propelling direction of ink even if it contacts an ink column. Does not grow. Therefore, the problem of instability of the ink column, which is the object of the present invention, does not occur.

However, in the case of an ink using an alcohol solvent as a solvent, the ink dry coating film 2 is used because of its solubility.
Since 6 is relatively hydrophilic, the condensed water droplet grows and has a large mass. For this reason, when the water droplet contacts the ink column, the propelling direction of the ink is affected, and the print quality is degraded. This phenomenon becomes remarkable when the contact angle of water drops of the dried coating film is 50 degrees or less. In particular, when ethyl alcohol, which is particularly safe, is used as a solvent, a resin that dissolves easily is blended, and when this is used as a dry coating film, the contact angle of water is 50 degrees or less in most cases. When the printing operation is performed by using the ink, the flight direction of the ink particles becomes unstable. There is a relatively hydrophobic resin component having a contact angle of 50 degrees or more, but since it does not dissolve easily, once a dry film is formed near the ink ejection port 25, it becomes difficult to re-dissolve, causing so-called ink clogging. Resulting in.

Polyethylene and polypropylene films described in JIS K6768, as will be described later, using a dry coating film component such as a resin that is easily dissolved, that is, even if the ink composition has a water contact angle of 50 degrees or less. If the surface property showing a certain degree of water repellency is obtained by a water wetting test according to the wetting test method described above, it is effective in preventing the condensation water droplets from enlarging. In JISK6768, a polyethylene or polypropylene film is used for the test piece, but here it is 30
A smooth glass plate having a size of 20 mm and a width of 20 mm is used, and a test body is prepared by coating the target ink with the glass plate. In JIS K6768, a mixture of formamide and ethylene glycol monoethyl ether is used as the wetting index determination liquid, but distilled water is used here. The content of the test method is the same, and the distilled water is uniformly applied by the specified method with the specified cotton swab, and the original state is maintained without causing breakage in the state of the central part of the liquid film. If it is, it is determined that it is wet, and if it is broken, it is determined that it is not wet.

In the case of an ink having surface characteristics such that the water film is broken within 0.9 seconds after applying water in this water wettability test, even if the water contact angle is within 50 degrees. The size of the condensed water changes the direction of the ink column, and the phenomenon that the print quality is deteriorated does not occur.

[0017]

When the surface of the dried coating film has low water wettability, that is, when spherical water droplets having a contact angle of 50 degrees or more are formed, the surface area per weight is large and evaporation is promoted, so that large water droplets are difficult to grow. Further, when it grows, it tends to move in the lateral direction, and the ink pillar comes into contact with the ink column until it grows or moves to the end portion on the orifice so as to affect the inclination of the ink column. However, when the contact angle is 50 degrees or less and the hydrophilic surface is such that it keeps wet for 1.0 second or longer in the above-mentioned water wettability test, the formed dew condensation water gradually merges with each other and becomes large. Eventually, it contacts the ink column and changes its driving direction. Even with a contact angle of 50 degrees or less, if the water-repellent surface is such that the water film is broken within 0.9 seconds in the above-mentioned water-wettability test and cannot keep wet, the initial stage of dew condensation The water droplet gradually grows and merges with the water droplet next to it to grow to a certain size, but before the water droplet grows large enough to affect the direction of the ink column, the water film breaks and moves laterally. Begins. As a result, although some of them also come into contact with the ink columns, they do not change the driving direction.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. Although there is a description about the composition of some inks in the content of the examples described below, the present invention relates to the correlation between the water wetting property of the dried coating film of the ink for an inkjet recording apparatus and the flight direction stability of the ink particles. It does not refer to the content of the ink composition. The content regarding the ink composition is only an example.

FIG. 1 shows the principle of a conventional charge control type ink jet recording apparatus. 2 and 3 show enlarged views of the nozzle portion of the conventional example. FIG. 4 shows the principle of the embodiment of the present invention in an enlarged view of the nozzle portion.

First, the basic configuration of a charge control type ink jet recording apparatus common to the conventional configuration and the present invention will be described with reference to the conventional example of FIG. In FIG. 1, the ink container 9, the ink supply pump 10, the pressure regulating valve 11, and the nozzle 1 are connected in series. The ink flowing in the nozzle 1 is atomized by applying a predetermined voltage and frequency to the electrostrictive element 2 from the excitation power source 3. A predetermined charge is applied to each ink particle 6 by the charging electrode 4 provided at the position where the ink is made into particles, and this is the deflection electrode 5
Is deflected when passing through the deflection electric field 7 formed by The gutter 8 is located at a position where the ink particles 6 that do not contribute to the printing without the charge can be received. The gutter 8 and the ink container 9 are also connected in series, and the recovered ink returns to the ink container 9.

FIG. 2 shows an enlarged view of the nozzle portion. The orifice 23 is made of artificial ruby, is cut into a spherical shape from the inside, and the ink ejection port 25 is provided at the portion where the wall pressure is thinnest. The ink liquid to which the internal pressure is applied is ejected from the ink ejection port to form the ink column 24. Since the ink column 24 has been ultrasonically excited in advance, the ink column 24 gradually becomes constricted after being ejected, and the ink column is cut at a timing just passing through the charging electrode 4 to become the ink particles 6. Pressure and excitation frequency are adjusted.

[0022]

[Table 1]

On the surface of the orifice 23, at the same time when the ejection of ink is started, the ink liquid is wetted and the solvent of the ink is dried to form an ink dried coating film 26 unless the solvent is a solvent which is hard to volatilize such as water. . Alternatively, it is in a state where it is repeatedly dried and redissolved by the ink liquid oozing out from the root of the ink column 24. When the solvent vaporizes, it takes heat, so the temperature of the ink dry coating film 26 becomes lower than the ambient temperature. Then, water in the air starts to form dew on the surface of the ink dry coating film 26. The ink dry coating film 26 is not necessarily in a completely dry state, but in many cases, the solvent component is always supplied from the ink column 24 and is in a semi-dry state. The condensed water thus formed grows with time. The conventional example shown in FIG. 2 is an ink having a composition as shown in the conventional example 1 of Table 1 and using ethyl alcohol as a main solvent. The contact angle of water droplets is as low as 35 degrees, and the result of the water-wettability test according to JIS K6768 described above shows that the wet retention time is 15 seconds, which retains wetness for a considerable time, and has a highly hydrophilic coating property. . When such an ink is used, the grown dew condensation water droplets 27 gradually merge with adjacent water droplets and become larger, but the wetness of the ink dry coating film 26 of the base becomes too high to form a continuous water film, and thus water droplets are formed. The weight of 27 is very large. And finally, it contacts the root part of the ink column 24. The dew condensation water contact portion 28 has a sufficient weight to incline the propelling direction of the ink column 24, and the flying direction of the ink particles 6 is disturbed at the moment of contact, and the printing accuracy deteriorates. Actually, the condensed water droplets 27 continuously grow one after another and come into contact with the ink column 24, so that the direction of the ink column 24 becomes a phenomenon that the direction of the ink column 24 sways without interruption.

FIG. 3 is an enlarged view of a nozzle portion in the case of an ink in which a highly hydrophobic resin is dissolved in a highly hydrophobic solvent as another conventional example. The ink composition is shown in Table 1.
In the conventional example 2, the dry coating film has a high water drop contact angle of 85 degrees and a very short water retention time of 0.2 seconds, which is a highly water-repellent coating film. In the case of the ink having such characteristics, the condensed water grows from a hemisphere to a nearly spherical shape as shown in FIG. The higher the contact angle, the larger the contact area per unit weight of water that comes into contact with the atmosphere. Therefore, it is difficult for large water droplets to form. Further, since the water wettability is very low, when water droplets of a certain size are formed, they start rolling on the ink dry coating film 26,
Although some of them contact the ink column 24 (condensation water contact portion 28), the ink column 24 cannot be tilted. Therefore, the quality of the printed matter is not adversely affected. As in the case of Conventional Example 2, when the ink composition components, particularly the toxicity and odor of the solvent are not restricted and the ink can be composed of a hydrophobic material, there is no problem in the straightness stability of the ink column, and the present invention is concerned. There is no place to do it.

FIG. 4 is an enlarged view of the nozzle portion when inks of the ink formulations of Examples 1 and 2 of the present invention are printed. The ink formulation is as shown in Examples 1 and 2 of Table 1, and the feature is that Example 1 has almost the same composition as that of Conventional Example 1 based on an ethyl alcohol solvent. The only difference is the addition of 1.0 part by weight of a silicone surfactant. By the addition of this silicone-based surfactant, the contact angle of water droplets was 35 degrees, which was not changed at all from the case of Conventional Example 1, while the water wetting retention time was very short at 0.6 seconds. It has a characteristic that it is hard to change. In addition, in the case of Example 2, the composition was similar to that of Example 1, but the resin component having a low molecular weight was used, and as a result, the ink dried coating film obtained became more hydrophilic in nature. The contact angle of water droplets is 26 degrees, which is lower than that in Example 1. If this formulation does not contain a silicone-based surfactant, the water-wettability is further enhanced, and the water-wet retention time is about 6
It becomes 0 second, and the straightness of the ink column also decreases. In the normal case, the lower the contact angle of water droplets, the longer the water wetting retention time. However, also in this case, since the silicone-based surfactant is blended as in Example 1, the water wetting retention time is as short as 0.7 seconds, and it has the feature that it does not form a water film as in Conventional Example 1.

When the printing operation is performed using the ink having the surface characteristics as in these examples, water droplets having a low contact angle are gradually formed as in the case of the conventional example 1, and the droplets continue to grow. When it becomes a certain size by fusing with water droplets, it becomes impossible to keep it wet and the water film breaks off. Although some of them contact the ink column 24,
The size of the dew condensation water contact portion 28 does not affect the ink direction. Therefore, the ink column 24 is stable,
It does not reduce the printing accuracy.

In this embodiment, ethyl alcohol or the like is blended as a solvent, but the material of the solvent is not particularly limited. However, alcohol solvents are preferable in consideration of odor, toxicity, drying performance and the like. Particularly, lower alcohols having 6 or less carbon atoms are preferable, and it is desirable that these lower alcohols, alone or mixed, account for 80% or more of the total solvent weight. Suitable alcohols include, for example, methyl alcohol,
Examples thereof include ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, isobutyl alcohol and the like. Of these, ethyl alcohol, which is the safest, is preferable, and it is preferable that the amount is 50% or more of the total solvent weight.

Further, in this embodiment, an acrylic resin is blended as a binder component, but various natural and synthetic resins can be used as long as they are resins soluble in the solvent. Suitable resins include, for example, rosin ester resins, rosin fumaric acid resins, rosin maleic acid resins, styrene / maleic acid copolymer resins, ketone resins, phenolic resins, styrene / acrylic copolymer resins, acrylic resins. Resin, polyvinyl butyral resin, cellulose resin, polyester resin, alkyd resin, etc. can be used. The characteristics required of the resin component are, of course, not only the robustness and adhesion as an ink film, but also a problem peculiar to the charge control type inkjet recording device is water dissolution stability. In the case of the charge control type, the structure is such that the ink is made into particles and then collected, and at this time, moisture in the air is gradually absorbed in the ink. The absorbed water content is also consumed for printing, so the water content in the ink converges at a certain value, but if the solid components such as resin do not have hydrophilicity to some extent, the effect of this absorbed water content Problems such as precipitation will occur. In particular, when a hydrophilic solvent such as alcohol is used, this water absorption rate tends to increase. Therefore, it is preferable to select a resin having as high hydrophilicity as possible, that is, a resin having a contact angle of water as low as possible.

In this embodiment, carbon black pigment is blended as a coloring agent, but not limited to this, various oil-soluble dyes, solvent-soluble dyes and alcohol-soluble dyes can be used. . For example, alcohol-soluble dyes such as monoazo type, disazo type, ketone / imine type, phthalocyanine type, xanthene type, triphenylmethane type and various metal complex salt type are suitable. Further, as the dispersion pigment, a carbon-based pigment, a titanium oxide-based pigment, or the like can be used.

Further, in this embodiment, a silicone-based surfactant is added as an additive for shortening the retention time of the ink dry coating film with water. This is an organic silicone material that is soluble in water or the solvent of ink, and various materials can be used as long as they do not adversely affect the stability of dyes, conductive agents, and the like. Specifically, polyoxyethylene / methylpolysiloxane copolymer and poly (oxyethylene /
Oxypropylene) methylpolysiloxane copolymer and the like are preferable. Here, as an example, a silicone-based material is used, but other fluorine-based surfactants and hydrocarbon-based surfactants also have some of the same effects. Further, the same effect can be obtained by using a resin modified with silicone or fluorine as the resin component to be blended as described above.

[0031]

EFFECTS OF THE INVENTION Conventionally, in inks using a polar solvent having a relatively high safety such as alcohol, it is necessary to mix resins and dyes having a sufficient solubility. The surface property of the film becomes hydrophilic, and the retention time for water wetting becomes long. As a result, the water droplets of the dew condensation water near the ink ejection port 25 become too large to contact the ink column 24 and print quality. There was a phenomenon of dropping. According to the present invention, it is possible to obtain a new finding that it is a water wetting retention time, not a water contact angle that is an index for evaluating hydrophilicity of a coating film, and the water wetting retention time is 0.9 seconds or less. The use of an ink having such coating film characteristics has the effect of sufficiently ensuring the straight-line stability of the ink column 24.

As a result, even if the ink is made of a material having high hydrophilicity, the ink column does not fluctuate, and the printing quality is improved.

[Brief description of drawings]

FIG. 1 shows a principle diagram of a conventional inkjet recording apparatus.

FIG. 2 is an enlarged view showing a nozzle portion of a conventional inkjet recording apparatus.

FIG. 3 is an enlarged view showing a nozzle portion of a conventional inkjet recording apparatus.

FIG. 4 is a view showing the principle of enlarging the nozzle portion according to the embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Nozzle, 2 ... Electrostrictive element, 3 ... Excitation power supply, 4 ... Charging electrode, 5 ... Deflection electrode, 6 ... Ink particle, 7 ... Deflection electric field, 8
… Gutter, 9… Ink container, 10… Ink supply pump,
11 ... Pressure regulating valve, 12 ... Printed object, 13 ... Print dot, 2
2 ... Conveyor, 23 ... Orifice, 24 ... Ink column, 25 ... Ink ejection port, 26 ... Ink dry coating film, 27
... condensation water drop, 28 ... condensation water contact part.

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[Procedure amendment]

[Submission date] October 25, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

On the other hand, the charge control type ink jet recording apparatus is required to print at high speed on indiscriminate materials and various surface shapes for lot management of mass-produced products. Unlike the solvent of the target on-demant type ink being mainly water-based, an organic solvent having a fast drying property is often used as the solvent of the ink. For example, ketones such as cyclohexanone, methyl ethyl ketone, and acetone, and esters such as ethyl acetate
-Based solvents, aromatic solvents such as toluene and xylene, aliphatic solvents such as hexane, ethyl alcohol,
Alcohols such as methyl alcohol and propyl alcohol may be used alone or in combination. in recent years,
Awareness of global environmental problems and occupational health environmental problems is increasing, and alcohol solvents are often used from the viewpoint of odor and toxicity. Demand is rising. Among the organic solvents, ethyl alcohol is a highly polar solvent, and the resins, dyes, and various additives to be mixed are highly polar and soluble in ethyl alcohol, unlike the materials used in conventional inks. This means
Closer to the water is a highly polar solvent, a hydrophilic material.
Drying of the ink consisting of highly hydrophilic material coating naturally high hydrophilicity, is brought into contact with water droplets becomes low contact angle, also when the dew condensation in have your humid environment or against steam, without being waterdrop shape It exhibits surface characteristics that form a thin water film. As described above, in the case of the charge control type inkjet printer, when the ink circulation is started, the surface temperature of the orifice 23 becomes low, which is a condition in which dew condensation easily occurs. The area around the ink ejection port 25 is soiled with ink, and the wettability of the ink dried coating film determines the shape of the dew condensation water. However, on the coating film made of a relatively hydrophilic material soluble in ethyl alcohol. The water condensed at is a water droplet with a low contact angle and tends to become a large water droplet. Coating film with low water wettability,
That is, in the case of an ink made of a general material that is soluble in a low-polarity organic solvent, the condensed water droplet has a high contact angle and is close to a sphere, and the surface area is large, so even if a water droplet is formed once, it re-evaporates in the air. It is easy to do, and drops or rolls before it grows into large water droplets. On the other hand, when a water droplet with a small contact angle is formed, the contact area is large and the water droplet is easily retained on the surface, so that the water droplet grows and remains as a large water droplet.
When the water droplet ink column 24 which has grown grows in contact with the root of the ink droplet, the traveling direction is changed to deteriorate the printing quality. However, the larger the weight of the water droplet, the greater the influence. As described above, in general ink of a solvent having a relatively low polarity, the weight of water droplets condensed on the surface of the orifice 23 is small, and even if the ink droplet 24 comes into contact with the ink column 24, there is almost no adverse effect. In the case where the ink dry coating film has high hydrophilicity, such as the ink using, the weight of the condensed water droplets tends to be large, and as a result, the problem of impeding the straight running stability of the ink particles 6 remarkably occurs.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayuki Kanari, 1-1 1-1 Higashitaga-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Electric Appliances Division, Hitachi Ltd. 1-1-1 Taga-cho, Electric Appliances Division, Hitachi, Ltd. (72) Inventor Ichiro Hashimoto 1-1-1, Higashi-Tagacho, Hitachi City, Ibaraki Hitachi Ltd., Electric Appliances Division, Hitachi Ltd. (72) Inventor Yuka Hirota 1-1-1, Higashi-Taga-cho, Hitachi City, Ibaraki Prefecture Hitachi Electric Co., Ltd. Electrical Equipment Division Taga Headquarters (72) Inventor, Mitsuo Inokari 1-1-1, Higashi-Tagacho, Hitachi City, Ibaraki Prefecture No. Incorporated company Hitachi Ltd. Electric Appliances Division Taga Headquarters (72) Inventor Tetsuo Ishikawa 1-1-1 Higashitagacho, Hitachi City, Ibaraki Prefecture Co., Ltd., Hitachi Home Appliances Division Taga within headquarters

Claims (9)

[Claims] 1. Distilled water uniformly thinly applied on a smooth dry coating film formed on a smooth glass plate has the property of breaking the liquid film within 0.9 seconds and leaving it in a non-wet state. At the same time, the contact angle of water droplets of distilled water on the dried coating film is 50.
An ink composition for an ink jet recording apparatus, which is less than or equal to 100 degrees. 2. The structure according to claim 1, wherein the structure of the ink jet recording apparatus supplies pressurized ink to an exciting nozzle, atomizes an ink jet flow ejected from the exciting nozzle, and imparts electric charges to the flying particles. An ink composition for an ink jet recording apparatus, which is of a charge control type in which the amount is controlled and deflected by passing through a constant electric field. 3. The ink composition according to claim 1, wherein when the total amount of the solvent of the ink composition is 100 parts by weight, 80 parts by weight or more of the solvent is a lower alcohol having 6 or less carbon atoms. An ink composition for an inkjet recording device. 4. The ink for an ink jet recording apparatus according to claim 1, wherein when the total solvent of the ink composition is 100 parts by weight, 50 parts by weight or more of the solvent is ethyl alcohol. Composition. 5. An ink jet system according to claim 1, characterized in that, when the total amount of the ink composition is 100 parts by weight, no solid precipitate is generated even if 10 parts by weight of distilled water is added. Ink composition for recording device. 6. The ink composition for an ink jet recording apparatus according to claim 1, which contains an organic silicone resin as one component of the ink composition. 7. The inkjet printer according to claim 6, wherein the organosilicone resin is dissolved in distilled water or one or more of the lower alcohols having 6 or less carbon atoms. Ink composition for recording device. 8. An ink jet recording apparatus according to claim 6, wherein the compounding ratio of the organic silicone resin is 5 parts by weight or less when the total amount of the ink composition is 100 parts by weight. Ink composition for use. 9. The ink composition for an inkjet recording device according to claim 6, wherein the organic silicone resin does not undergo ion dissociation in the solvent.