JPH1036737A - ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the feathering of printed ink image without increasing the viscosity of the ink or preparatorily applying a substance such as oil and fat to the surface of the printing object. SOLUTION: A substance having a liquid-repelling part and a lyophilic part in the molecular structure is used as a component of the objective ink. The substance is usually called as a surfactant and has a liquid repelling part and a lyophilic part in one molecular structure. The molecular structure of the liquid-repelling part often contains silicon atoms or fluorine atoms and the molecular structure of the lyophilic part often has an ether or amide structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an ink for an apparatus for printing an identification character on the surface of an object to be printed.

[0002]

2. Description of the Related Art Ink jet printers form particles of ink and fly the ink onto a printing object to form characters and the like. As a means of flying, there is a method of changing the particleized ink by electrostatic force, a method of giving pressure fluctuation (fluctuation due to a boiling phenomenon of a solvent in a minute area or a change in volume due to a piezo element) to the ink, and discharging the ink from a nozzle. is there. The former is a charge control type. The latter is called on-demand type.

A charge control type ink-jet printer creates charged ink particles by applying a charge while discharging ink under pressure from a nozzle to which vibration is applied, and the ink particles are directed by an electrostatic deflection system. To record character information. The principle is shown in FIG.

The ink in the ink bottle 8 is supplied by a supply pump 7
Is suctioned and pressurized. The pressure is controlled by the pressure regulating valve 1. The pressure is adjusted to 0.28 MPa as an example of the pressure. The ink whose pressure is controlled is supplied to the nozzle 3.
The nozzle 3 is provided with an electrostrictive element 2, and by applying an electric signal to the electrostrictive element 2, vibration can be applied to the ink. Frequency 68.2 as an example of an electric signal
kHz 200V is applied. A discharge port 18 is provided at the tip of the nozzle. The diameter of the discharge port 18 is, for example, 65 μm. The vibrated ink is discharged from the outlet 18 and forms ink particles 10 in the charging electrode 4. At this time, a charge can be applied to the ink particles 10 formed by applying a voltage to the charging electrode 4.
200 V is applied as an example of the voltage. The ink particles 10 discharged from the nozzle 3 pass between the deflection electrodes 9. A voltage is applied to the deflection electrode 9. For example, 5.
A voltage of 4 kV is applied. The ink particles 10 passing between the deflecting electrodes 9 are deflected by electrostatic force and fly to the printing object 5 to form characters. The ink not involved in the characters is first stored in the gutter 11, and further collected by the collection pump 6 and returned to the ink container 8.

[0005] A feature of the ink jet printer is that ink is jetted for printing. Therefore, printing can be performed by separating the nozzle from the printing object, and printing can be performed even on an uneven surface or a curved surface of the printing object. In addition, since the charge amount can be electrically changed, there is a feature that character information can be easily changed. Taking advantage of these features, steel, paper,
It is often printed on aluminum, plastic, glass, etc. Conventionally, methyl ethyl ketone, methanol, or ethanol has been mainly used as a solvent in order to use a resin having an adhesive force to these as a material of the ink. Water may be used as a solvent for printing on printed matter or food that does not require strong adhesive force. In particular, in order to reduce the influence on the working environment, the main solvent tends to shift from methyl ethyl ketone to ethanol and water. In addition, as a dye that gives a color to the ink, a dye that is soluble in these solvents and a pigment that has a property of being insoluble in a medium but dispersed in a medium are used. Conventionally, dyes having a metal such as chromium have been mainly used because they are soluble in a medium and have excellent light resistance. However, it becomes difficult to use chromium or the like due to environmental issues, and pigments having excellent light resistance tend to be used instead.

[0006] Since these solvents all have a certain amount of vapor pressure at atmospheric pressure, as shown in FIG.
When it comes out of the nozzle 3 as 0 and contacts the atmosphere while being collected in the ink container 8 via the gutter 11,
Some of them are vaporized into the atmosphere as vapor. as a result,
The composition ratio of the solvent in the recovered ink decreases from the initial state. Therefore, the ink concentration and the ink viscosity increase. When the ink jet printer discharges from the nozzle 3 as described above, the ink is deformed by the vibration given from the electrostrictive element 2 to form ink particles 10. for that reason,
When the viscosity of the ink increases, the deformation of the ink is hindered and the ink particles 1
0 may not be formed promptly. In order to prevent this, it has a function of replenishing the solvent volatilized by a mechanism not shown in the figure. Therefore, a liquid level sensor for managing the liquid level of the ink is provided. In general, the ink is obtained by dissolving a resin that gives an adhesive force and a dye that gives a color tone in a medium such as a solvent. When the ink flies over the print object and the medium volatilizes, the remaining resin and dye are solidified to form a film and adhere to the print object to form characters and the like. In normal printing, this performance alone is sufficient for use. However, since the resin or the like is originally dissolved in the medium, there is a problem that the printed material is dissolved when the printed material is brought into contact with a solvent or the like again. That is, if the object to be printed is washed with a solvent or the like after the printing, the printing is removed and a flowing state occurs. For this reason, an ink having a function of solidifying by applying some kind of stimulus without solidifying even if the solvent volatilizes after printing is used for an object to be printed on which a process such as washing is performed after printing. As an example, there is an ink that uses a low-molecular-weight acrylic oligomer that is an incomplete polymer as a resin, and includes a substance that generates a radical such as benzofienone as a component by light stimulation. Even if the solvent volatilizes after printing, the ink does not solidify because the resin remaining on the surface is the incomplete polymer described above.However, radical polymerization is started by irradiating ultraviolet light that is high energy light after printing, A polymer acrylic resin film is formed. Since this film is insoluble in a solvent, it does not dissolve after irradiation with ultraviolet light. That is, it has the performance of withstanding the subsequent cleaning process. As another example, there is an ink containing a resin having an epoxy group in a molecular structure and a resin having an amino group as constituent resins. This ink does not form a film even when the solvent is volatilized, but when heated, the epoxy group and the amino group react and polymerize to form a film. As a result, it is possible to endure the washing in the subsequent step.

[0007]

The ink has an excellent property of being resistant to washing in a post-process, but does not cure even if it is not stimulated from outside even after printing, and remains in a liquid state. There is a problem. That is, when a liquid substance is attached to the surface of a printed matter, the liquid spreads (bleeds) unless resistance to the spread occurs. The drying time of an ink that solidifies by the evaporation of a normal solvent can be changed by controlling the evaporation rate of the solvent after printing. That is, the time required to change from the liquid state to the solid state can be adjusted. For example, it is possible to improve the volatilization speed of the medium by heating the printing object before printing and volatilizing the medium by the residual heat, or applying hot air after printing. Therefore, even if the spread of the ink changes due to a change in the surface condition of the printing object, the spread (bleeding) can be adjusted by these external means. However, since the ink that does not solidify after printing is always in a liquid state, it is not possible to prevent the spread (bleeding) by controlling the volatilization speed of the medium. In particular, when the surface of the printing object is not in a uniform state, there is a problem that partial bleeding and bleeding occur and stable printing cannot be obtained.

[0008] For this reason, conventionally, a response using ink and a response using an object to be printed have been made.

The ink after printing is in a liquid state of an uncured resin on the surface of the printing object. Means for controlling the speed of spreading (smearing) by reducing the fluidity of the resin is taken. As a means for this, there is a method of increasing the viscosity of the ink. For example, when printing on non-water-absorbing plastic and the ink viscosity is 3.0 mPa · s, the diameter of the printing particles is 0.4 mm. By changing this to 4.0 mPa · s, the diameter is 0.3 mm. Can be suppressed. However, when the viscosity is increased, the driving capability of the electrostrictive element necessary for the ink ejected from the nozzle 3 to become the ink particles 10 is insufficient, so that normal ink particles 10 cannot be formed and it is difficult to form regular characters. The problem arises. In particular, when printing is performed at a low temperature (for example, 5 ° C.), there is a problem that the viscosity of a high-viscosity ink is remarkably increased at a low temperature, making it difficult to form particles. Therefore, there is a problem that the printable temperature range is limited.

[0010] In response to the printing object, the surface state of the printing object is kept constant. For example, a state in which the difference between the maximum height and the minimum height of the stainless steel plate is 1.2 μm is 0.9 μm.
The occurrence of bleeding can be prevented by holding down to m. Also,
Even when the unevenness is different, it is possible to control the bleeding of the surface by applying a dilute resin, oil or fat, or a release agent to the surface. It is also possible to control by attaching not a substance on a liquid but a minute solid or the like. However, each of these means has a problem in that ink other than the ink that should be applied must be applied. That is, the process of attaching,
An additional mechanism is required. In addition, there is a possibility that the printed object may be damaged by the attachment. For example, when fats and oils are adhered, there is a problem in that the adhesion to the print target is reduced.

An object of the present invention is to provide an ink capable of preventing ink bleeding after printing without increasing the viscosity of the ink and without previously adhering a substance such as oil or fat to the surface of a printing object. To give.

[0012]

The object is achieved by including a substance having a lyophobic part and a lyophilic part in its molecular structure in the ink component. This material is commonly called a surfactant. FIG. 3 shows an example of the structure. The surfactant shown in FIG. 3 includes a lyophobic part 14 and a lyophilic part 15 in one molecular structure.
Exists. The molecular structure of the liquid-repellent part is often a structure containing silicon-based or fluorine-based atoms. In addition, the molecular structure of the lyophilic portion often has an ether-based or amide-based molecular structure. The present invention is not limited to these structures.

FIG. 2 shows a state in which the ink particles 10 have landed on the printing object 5. The added surfactant 12 has a property of collecting at the interface of the substance. That is, ink particle 1
In the case of 0, this surfactant is disposed on the boundary surface between the liquid ink particles and the atmosphere, that is, on the surface of the ink particles 10. In that case, the repellent portion 14 of the surfactant is located on the air side,
The lyophilic part 15 is arranged on the ink particle side. Ink particles 10
Is attached to the printing object 5, the surfactant is also arranged on the boundary surface with the printing object 5. In FIG. 2, the notation of this state is omitted. The attached ink particles 10 tend to spread while wetting the surface of the printing object 5. This spreading point is a point where the ink, which is a liquid, the object to be printed, which is a solid, and the atmosphere, which is a gas, form a boundary. Therefore, surfactant 12 is concentrated at the dense points of these interfaces. At this dense point, the surfactant 12 causes the lyophobic portion 14 to
Therefore, the surface of the printing object 5 is opposed to the lyophobic portion 14 because it is arranged in a state of being disposed on the surface of the printing object 5. The molecular structure of the liquid repellent portion 14 of the surfactant 12 has an element that repels the surface of the printing object 5. Therefore, when the ink particles 10 spread on the surface of the printing object 5, the repulsive force 1
It will spread while receiving 3. As a result, it becomes resistant to the spreading movement, and the spreading is suppressed. That is,
While the ink itself spreads, the surface of the printing object is changed to a lyophobic state. Therefore, it is not necessary to perform a pre-processing on the surface of the printing object. Further, when the amount of the added surfactant is very small, the viscosity of the ink does not increase. Also,
If the surface tension of the ink is also added in a small amount, there is no change, and there is no effect on the ink particle formation.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is an explanatory view showing the principle of a charge control type ink jet printer. The ink in the ink container 8 is suction-pressed by the supply pump 7. The pressure is controlled by the pressure regulating valve 1. 0.28Mpa as an example of pressure
Is regulated. The ink whose pressure is controlled is supplied to the nozzle 3. The nozzle 3 is provided with the electrostrictive element 2,
By giving an electric signal to the electrostrictive element 2, vibration can be given to the ink. A frequency of 68.2 kHz 200 V is applied as an example of the electric signal. An orifice is provided at the tip of the nozzle. The diameter of the orifice is, for example, 65 μm. The vibrated ink is ejected from the orifice, and the ink particles 1
0 is formed. At this time, a charge can be applied to the ink particles 10 formed by applying a voltage to the charging electrode 4. 200 V is applied as an example of the voltage. The ink particles 10 discharged from the nozzle 3 pass between the deflection electrodes 9. A voltage is applied to the deflection electrode 9. As an example, a voltage of 5.4 kV is applied. The ink particles 10 passing between the deflecting electrodes 9 are deflected by electrostatic force and fly to the printing object 5 to form characters. The ink not involved in the characters is first stored in the gutter 11, and further collected by the collection pump 6 and returned to the ink container 8.

The ink is pressurized by the supply pump 7 and discharged from the nozzle 3. The structure is shown in FIG. Nozzle 3
Is provided with a nozzle tube 12. A discharge plate 14 is provided at the tip of the nozzle tube 12. Discharge plate 1
As an example of the material No. 4, a hard material such as ruby, ceramic or the like is used to prevent abrasion by ink. The discharge plate 14 is provided with a discharge port 18. The pressurized ink passes through the inside of the nozzle pipe 12 and
To form an ink column 13. Since the ultrasonic wave is applied to this ink by the electrostrictive element 2 as described above, the ink column 1 ejected from the ejection port 18 of the nozzle 3
3 forms ink particles 10 by vibration of the ink.

An outline of an example of a material constituting the ink is shown below. This ink cures when irradiated with ultraviolet light.

Solvent Methyl ethyl ketone 60% Resin Acrylic oligomer 30% Dye Chromium complex dye 5% Conductive agent Lithium nitrate 2% Photoinitiator Benzophenone 3% Surfactant Perfluoroalkylethylene oxide 0.2% Another example Is shown below. This ink is cured by heating at 120 ° C. for 10 minutes after printing.

Solvent Methyl ethyl ketone 70% Resin Epoxy resin 12% Modified amine resin 12% Pigment Chromium complex dye 4% Conductive agent Lithium nitrate 2% Surfactant Perfluoroalkyl ethylene oxide 0.2% The behavior of these inks is described below. Show. FIG. 2 shows the state of the ink particles 10 flying on the surface of the printing object 5. The added surfactant 12 has a property of collecting at the interface of the substance. That is, in the ink particles 10, the surfactant is disposed on the boundary surface between the liquid ink particles and the atmosphere, that is, on the surface of the ink particles 10. In this case, the repellent portion 14 of the surfactant is arranged on the air side, and the lyophilic portion 15 is arranged on the ink particle side. When the ink particles 10 adhere to the printing object 5, the surfactant is also arranged on the boundary surface with the printing object 5. In FIG. 2, the notation of this state is omitted. The attached ink particles 10 tend to spread while wetting the surface of the printing object 5. This spreading point is a point where the ink, which is a liquid, the object to be printed, which is a solid, and the atmosphere, which is a gas, form a boundary. Therefore, surfactant 12 is concentrated at the dense points of these interfaces. At this dense point, the surfactant 12 gathers in a state where the liquid-repellent portions 14 are arranged on the surface of the ink particles 10, so that the surface of the printing object 5 faces the liquid-repellent portions 14. The molecular structure of the liquid repellent portion 14 of the surfactant 12 has an element that repels the surface of the printing object 5. Therefore, when the ink particles 10 spread on the surface of the printing object 5, they spread while receiving the repulsive force 13. As a result, it becomes resistant to the spreading movement, and the spreading is suppressed. That is, the surface of the printing object is changed to a lyophobic state while the ink itself spreads.

The surfactant that can be used is preferably a nonionic surfactant. In an electrification control type ink jet printer, the ink needs to have conductivity in order to charge the ink. Therefore, a conductive agent is added to the ink. Therefore, if an ionic substance is added, these may be affected. On-demand type ink jet printers do not have this problem. The surfactant to be added is silicon-based, that is, silicon-based dimethylpolysiloxane whose main chain is epoxy-modified, polyether-modified, alcohol-modified, epoxy-modified.
Examples thereof include those subjected to polyether modification and alkyl aralkyl polyether modification. Further, as the fluorine type, perfluoroalkyl betaine, perfluoroalkylamine oxide, perfluoroalkylethylene oxide and the like can be mentioned. The present invention is not limited to these substances. The amount of these additives varies depending on the type of polar medium and surfactant, but is usually 0.05.
% Is often appropriate. Since the amount of addition is very small, the viscosity of the ink does not increase. Also, the surface tension of the ink does not change, and does not affect the particle formation of the ink.

Thus, it is possible to prevent the bleeding of the ink without pre-treating the surface of the printing object or increasing the viscosity of the ink.

[0022]

According to the present invention, since the influence of bleeding due to the surface condition of the printing object can be reduced, stable printing quality can be obtained. Further, there is no need to provide a means for controlling the surface state, and the peripheral device can be simplified.

[Brief description of the drawings]

FIG. 1 is a perspective view of a printing apparatus using ink according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a contact state between ink and a print target according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a surfactant used in the ink of one embodiment of the present invention.

[Explanation of symbols]

5 to be printed, 10 to ink particles, 12 to surfactant,
13 ... Repulsive force.

Claims (1)

[Claims] 1. An ink which does not solidify even when a constituent medium is volatilized, wherein the component contains at least one substance having a lyophobic part and a lyophilic part in a molecular structure. ink.