JP2005262775A - Inkjet recording apparatus and ink set for inkjet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording apparatus capable of realizing not only a storing quality of a recorded article but also an image quality of the recorded article, especially a smooth gradation expression in a low color density region without using a light-colored ink, and to provide an ink set for inkjet recording used in the inkjet recording apparatus. <P>SOLUTION: In the inkjet recording apparatus provided with a colored ink containing a coloring material, and a clear ink containing no coloring material, the inkjet recording apparatus characterized by having a mechanism adjusting a color density on a body to be recorded in accordance with the usage, and making the surface tension of the clear ink lower than the surface tension of the colored ink, is used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink jet recording apparatus that realizes not only the storage quality of a recorded matter but also the image quality of the recorded matter, particularly a smooth gradation expression in a low color density region, and an ink set for ink jet recording used in the ink jet recording device. .

  Ink jet recording is performed by applying heat or mechanical energy to ink, ejecting ink droplets from a recording portion having fine nozzles, and depositing the ink droplets on the surface of a recording medium. Specifically, as an ink jet recording method, an electric signal is converted into a mechanical signal using an electrostrictive element, and ink and ink stored in the nozzle head portion are intermittently ejected to record characters and symbols on the surface of the recording medium. Method: The ink stored in the nozzle head part is rapidly heated at a part close to the ejection part to generate bubbles, and ejected intermittently by volume expansion due to the bubbles, and characters and symbols on the surface of the recording medium Has been put to practical use, and according to this recording method, recording can be performed without direct contact between the recording portion and the recording medium, and application to various recording applications has been performed. .

Accompanied by technological advances in ink jet recording apparatuses, high resolution and high quality recording using fine ink droplets has been put into practical use, but the ink used for recording on the recording medium depends on the recording medium. It is required to provide recording quality. In particular, recording on glossy recording media may require recording quality equivalent to a silver salt photograph. From the viewpoint of improving the storage quality of recorded materials such as weather resistance, gas resistance, and water resistance, it is better than dyes. It is also effective to use a pigment as a coloring material with a small degree of fading. On the other hand, various studies have been made so far on improvement of image quality of recorded matter such as improvement of glossiness, color development and reduction of graininess.
For example, in order to improve color developability, Japanese Patent Application Laid-Open No. 9-124986 adds a compound exhibiting thermoreversible type thickening to obtain an ink composition having an addition amount of 0.05 to 20% by weight. A water-based ink that eliminates image feathering and bleeding and realizes high color development is described.

  Japanese Patent Application Laid-Open No. 2003-220758 discloses an ink for ink jet recording characterized by containing at least one kind of carbohydrazide and its derivative and at least one kind of hydrazine and its derivative other than carbohydrazide and its derivative. It is described that it becomes a photo-like ink composition for ink jet recording having ink absorbability, high water resistance, and high glossiness and improved storage stability.

On the other hand, Japanese Patent Application Laid-Open No. 6-270411 describes an ink jet recording apparatus that includes a plurality of dye inks and clear inks, and can select an optimal ink composition according to the purpose of use so that inks having different compositions can be prepared in the recording apparatus. ing.
However, in the above-mentioned Japanese Patent Application Laid-Open No. 9-124986, the color developability is improved, but the granularity of the pigment ink becomes remarkable at the time of recording in a low color density region, and the image quality on the glossy recording material is insufficient. A dot is seen.

  In Japanese Patent Laid-Open No. 2003-220758, although improvement in glossiness can be confirmed, it is necessary to provide light ink in order to realize gradation expression in a low color density region. As a result, the number of colors required for recording increases, and the number of verification items regarding the suitability of each ink as ink for inkjet recording, such as ejection reliability and aggregation unevenness when recording secondary colors, increases. There is a possibility that the reliability between the ink jet recording apparatus and the ink composition becomes an obstacle.

  Further, in JP-A-6-270411, an area for separately mixing an ink composition must be secured in the recording apparatus, and when a pigment ink and a clear ink are prepared using the recording apparatus, the ink is used. This is not preferable because the mixing of the resin may become uneven and clogging is likely to occur.

  As described above, it is not preferable to ensure the smoothness of gradation expression by increasing the number of colors in order to ensure the reliability of the ink jet recording apparatus, and an optimal ink composition is prepared by mixing colored ink and clear ink. Even in the case of selection, it is necessary to improve clogging and improve the apparatus when blending the pigment ink and the clear ink.

JP-A-9-124986 JP 2003-220758 A JP-A-6-270411

  In view of the above, the problem to be solved by the present invention is to realize not only the storage quality of a recorded matter but also the image quality of the recorded matter, particularly smooth gradation expression in a low color density region without using light ink. The present invention provides an ink jet recording apparatus capable of satisfying the requirements and an ink set for ink jet recording used therefor.

  In an ink jet recording apparatus having a colored ink containing a color material and a clear ink not containing a color material, the ink jet recording apparatus has a mechanism for adjusting the color density on the recording medium according to the application, and the surface tension of the clear ink is An ink jet recording apparatus having a lower surface tension than the colored ink is used.

  The present invention provides an ink jet recording apparatus comprising a colored ink containing a color material and a clear ink not containing a color material, and has a mechanism for adjusting a color density on a recording medium in accordance with an application, The ink jet recording apparatus is characterized in that the surface tension of the ink is lower than the surface tension of the colored ink. The color density is adjusted by overlaying colored ink and clear ink on the surface of the recording medium. At this time, by setting the surface tension of the clear ink lower than the surface tension of the colored ink, dots are formed on the surface of the recording medium. The effect of spreading the color ink and diffusing the color ink discharged in the same region to lower the color density can be obtained. In addition, additives for improving the recording quality such as glossiness, color development, bleeding, etc. can be added to the above-mentioned clear ink, and the color density can be adjusted by combining multiple clear inks. It is.

  The color ink and the clear ink are both ink jet recording apparatuses in which the surface tension is 18 mN / m or more and 35 mN / m or less. If the surface tension of the ink exceeds 35 mN / m, when using plain paper, which is normal paper, the ink is difficult to soak up and takes time to dry. There is a problem that a mark of previous printing remains (a show-through phenomenon), and there is a problem that printing cannot be performed at high speed. On the other hand, when the surface tension is less than 18 mN / m, wetting and bending occur on the nozzle end face of the nozzle plate of the inkjet head, and accurate recording cannot be performed on the surface of the recording medium. Therefore, the surface tension of the colored ink is preferably about 22 mN / m to 32 mN / m, and preferably 30 mN / m. On the other hand, since the surface tension of the clear ink is lower than the surface tension of the colored ink, it is preferably about 20 mN / m to 30 mN / m, and preferably 28 mN / m.

  As the coloring material of the colored ink, any of a dye and a pigment can be used, but a pigment is preferable from the viewpoint of excellent weather resistance, gas resistance, water resistance and the like of the image on the surface of the recording material. Further, the pigment ink may be an ink jet recording apparatus using a pigment coated with a polymer. As for the dispersion form of the pigment used as the ink, there is a method in which the surface of the pigment is chemically treated to give a hydrophilic group and dispersed, or the pigment is coated with a polymer and dispersed due to the hydrophilicity and physical steric hindrance of the polymer. For example, a method of adding an emulsion, a method of adding an emulsion, or a combination thereof. From the viewpoint of supporting the development of fixability and glossiness on a recording medium, a dispersion method including a pigment with a polymer may be adopted. Desirably, the addition of a resin emulsion with additional functionality can improve the printing quality, particularly the color development and abrasion resistance. Specifically, the polymer that coats the pigment includes polyacrylic acid, polyvinyl acetate, polyvinyl chloride, polybutadiene, polyacrylonitrile, polyacrylic ester, styrene-acrylic acid copolymer, polystyrene, polyester, polyamide, polyimide, It is preferable that at least one selected from the group consisting of a silicon polymer and a sulfur-containing polymer is used as a component. Since the substance consisting of one or more selected from acetylene glycol surfactants, glycol ethers and 1,2-alkylene glycols used in the present invention is likely to cause an adsorption / desorption reaction with a dispersant used for normal dispersant dispersion, The phenomenon that the printing is disturbed by the detached dispersant is likely to occur. However, it is preferable to use the above-mentioned polymer because the polymer stably contains a colorant and hardly absorbs and desorbs. Further, the printing quality with the resin emulsion and the ink physical properties are desirable because of their small interaction. Further, since the pigment ink directly adheres to the surface of the recording material and develops color, the pigment ink should be small in order to reduce the granularity of the pigment particles, and the particle size is 100 nm or less, more preferably 80 nm or less.

  Further, the ink set is a combination of the above-described colored ink and clear ink. When recording an image including a gradation with a smooth gradation, by providing a light ink in each colored ink, the fineness in a region having a low color density is improved, but the number of ink sets increases accordingly, and the inkjet head In the case where the ink storage tank is mounted on the carriage portion including the ink, the load on the carriage due to the inertia resulting from the increase in the weight of the carriage is large, and the energy consumed in recording is also large. For this reason, when recording is performed by adjusting the discharge amount of the colored ink and the clear ink and performing the recording with a low density when the ink set is composed of the minimum combination of the colored ink and the clear ink, and the recording is performed, This is preferable because the score can be reduced.

  Further, the color ink and the clear ink are an ink jet recording apparatus containing 0.01 to 5% by weight of an acetylene glycol surfactant. By adding an acetylene glycol surfactant, the printing quality can be improved and the permeability of the ink composition can be adjusted. The addition amount is 0.01 to 5% by weight, but if it exceeds 5% by weight, even if it is added, the print quality is not further improved, and adverse effects such as an increase in viscosity occur. A more preferable addition amount is 0.1 to 3.0% by weight. Examples of acetylene glycol surfactants include the Surfynol series from Air Products. The ratio of (addition amount of acetylene glycol to the colored ink) / (addition amount of acetylene glycol to the clear ink) is 0 in order to reduce the surface tension of the clear ink, although both the color ink and the clear ink may be in the above-mentioned addition range. .3 to 0.5 is preferable.

  Furthermore, it is an ink set for ink jet recording used in the ink jet recording apparatus.

  As the recording head of the ink jet recording apparatus, one having discharge nozzles arranged in a straight line parallel to the paper feeding direction in the order of clear, Y, M, C, Bk from the left in the paper feeding direction is used. In order to discharge the ink composition for inkjet recording described above, recording is performed according to the arrangement shown in FIG.

  Here, FIG. 2 is a view of the print head 9 as viewed from the front side of the discharge surface. The direction of the arrow 11 is the paper feed direction. In the discharge nozzles 1 to 8, the black ink from the nozzle 1 and the cyan ink from the nozzle 2. It is assumed that magenta ink is ejected from nozzle 3, yellow ink is ejected from nozzle 4, and clear ink having a composition ratio based on Examples 7 and 8 and Comparative Examples 1 and 2 is ejected from nozzles 5-8.

  When recording with low color density, the density can be controlled by driving the clear ink or colored ink before the colored ink or clear ink is completely fixed on the recording medium. After ink has been ejected, it is better to eject clear ink into the same area without interruption. More preferably, colored ink and clear ink are ejected within the same scan of the carriage.

In addition, with respect to the amount of colored ink and clear ink applied to the recording medium, the ink composition to be applied based on the upper limit value of the amount of ink applied to each recording medium when the colored ink is applied to the recording medium and subsequently the clear ink is applied. Recording shall be performed in a range where the total sum of the amounts does not exceed the upper limit.
Here, the upper limit value of the hit amount is specifically colored ink or clear ink necessary to cover the recording surface when the dots ejected on the recording surface are recorded so as not to overlap each other. The sum of

  When ejecting the above-described ink onto a recording medium, it is preferable to have a recording setting in which the above-described ink ejection amount can be adjusted by various recording media. For example, a plurality of recording settings are prepared according to the type of glossy or non-glossy recording medium, and gloss or color suitable for the recording medium can be obtained from the recording settings, and subtle gradations can be obtained. It is better to execute the setting that enables expression. In addition, regardless of the type of recording medium, a setting may be provided in which the setting of the ink discharge amount described above can be used arbitrarily.

  Further, the contact portion of the apparatus used in the present invention with the ink has a mechanism that holds the above-described ink and does not leak out of the apparatus. Specific properties required for this mechanism include, specifically, addition polymerization of a monomer in which a halogen group or a nonpolar group substituent is introduced into a vinyl skeleton such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, or polyvinylidene chloride. The polymer obtained by (1) is mentioned, Preferably polystyrene is good. It is desirable to use the same material for the container for storing the ink.

  Examples of the present invention will be described in detail below. However, various modifications are included and are not limited to the following examples without departing from the spirit of the present invention.

  FIG. 1 is a schematic view of an ink jet recording apparatus embodying the present invention. The carriage 31 can be mounted with a black (Bk) ink jet recording cartridge 71 and an ink jet recording cartridge 72 containing clear (CL), yellow (Y), magenta (M), and cyan (C) inks. The cartridge of each ink composition was provided, and the effect was confirmed for each color according to the arrangement shown in FIG.

  Here, FIG. 2 is a view of the print head 9 as viewed from the front side of the discharge surface. The direction of the arrow 11 is the paper feed direction, and the following <Ink set embodiment> and <Clear are set for the discharge nozzles 1 to 8. It is assumed that the recording liquid shown in the ink embodiment> is discharged. Further, nozzles for discharging each ink composition are formed in the recording head 28 below the carriage 31 in FIG. 1, and an introduction tube for guiding each ink composition is erected at the bottom of the carriage 31. Has been. When the black ink cartridge 71 and the color ink cartridge 72 are mounted on the carriage 31 from above, an introduction tube is inserted into a connection hole provided in each cartridge, and ink can be supplied from each cartridge to the recording head 28. .

Further, the recording body 22 is conveyed along the platen 26, and the carriage 31 is reciprocated in the axial direction (main scanning direction) of the platen 26 by the carriage motor 24, thereby driving the recording head 28 mounted on the carriage 31. Ink ejection and dot formation are performed.
Further, the mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 is an endless arrangement between the carriage motor 24 and a slide shaft 34 that is laid in parallel with the axis of the platen 26 and slidably holds the carriage 31. A pulley 38 that stretches the drive belt 36, a position detection sensor 39 that detects the origin position of the carriage 31, and the like.
These series of recording commands are executed by a control circuit 40 that controls the exchange of signals with the operation panel 32 and a piezo element drive circuit 50 that receives a signal from the control circuit 40 and generates a drive signal for driving the piezo element.

  In the present invention, PM-970C (manufactured by Seiko Epson Corporation) is used as an ink jet recording apparatus using, as an example of an ink jet mechanism, a mechanical deflection due to electric energy of a piezo element as an ejection unit.

Next, the ink used in the examples will be described.
A colorant obtained by coating a pigment with a polymer (hereinafter abbreviated as a polymer-coated pigment) is prepared by the following method.

<Production of polymer-coated pigments 1 to 4>
First, the dispersion 1 uses MA100 (manufactured by Mitsubishi Chemical), which is carbon black. The reaction vessel equipped with a stirrer, thermometer, reflux tube and dropping funnel was purged with nitrogen, and then 20 parts of styrene, 5 parts of α-methylstyrene, 15 parts of butyl methacrylate, 10 parts of lauryl methacrylate, 2 parts of acrylic acid, t-dodecyl Add 0.3 part of mercaptan and heat to 70 ° C., separately prepared 150 parts of styrene, 15 parts of acrylic acid, 50 parts of butyl methacrylate, 1 part of t-dodecyl mercaptan, 20 parts of methyl ethyl ketone and 3 parts of azobisisobutyronitrile. Is placed in a dropping funnel and the dispersion polymer is polymerized while being dropped into the reaction vessel over 4 hours. Next, methyl ethyl ketone is added to the reaction vessel to prepare a dispersed polymer solution having a concentration of 40%.

  40 parts of the dispersion polymer solution and a jet mill (manufactured by Sanko Shoji Co., Ltd.) for 1 hour, 30 parts of MA100 (manufactured by Mitsubishi Chemical) as carbon black, 100 parts of a 0.1 mol / L aqueous sodium hydroxide solution, 30 parts of methyl ethyl ketone is mixed and stirred with a homogenizer for 30 minutes. Thereafter, 300 parts of ion-exchanged water is added and further stirred for 1 hour. Then, the whole amount of methyl ethyl ketone and a part of water were distilled off using a rotary evaporator, neutralized with 0.1 mol / L sodium hydroxide, adjusted to pH 9, and filtered through a 0.3 μm membrane filter. Thus, Dispersion 1 having a solid content (dispersion polymer and carbon black) of 20% is obtained.

  Dispersions 2 to 4 are obtained in the same manner as above. As the dispersion 2, Pigment Blue 15: 3 (manufactured by Clariant) is used. As the dispersion 3, Pigment Red 202 (manufactured by Clariant) is used. As the dispersion 4, Pigment Yellow 180 (manufactured by Clariant) is used.

<Manufacture of ink set>
The composition of the ink constituting the ink set is shown below. The numerical unit is wt%. The pigment composition refers to a value including the polymer after dispersion, and the weight ratio of the polymer to the pigment is shown immediately before the composition ratio in the order of (polymer) :( pigment).

Black ink <Composition ratio> wt%
(Pigment 1) [30:70] /7.5
1,2-pentanediol 5
Triethylene glycol monobutyl ether 5
Olphine STG
(Acetylene glycol surfactant: manufactured by Nissin Chemical Industry Co., Ltd.) 0.8
Glycerin 10
Benzotriazole: Corrosion inhibitor (manufactured by Kanto Chemical Co., Ltd.) 0.05
Pure water remaining

Cyan ink <Composition ratio> wt%
(Pigment 2) [45:55] /4.5
1,2-hexanediol 4.5
Diethylene glycol monobutyl ether 2.5
Surfinol 465
(Acetylene glycol surfactant: manufactured by Air Products) 1.2
Glycerin 9
Benzotriazole: Corrosion inhibitor (manufactured by Kanto Chemical Co., Ltd.) 0.05
Pure water remaining

Magenta ink <Composition ratio> wt%
(Pigment 3) [50:50] /5.5
1,2-hexanediol 1
Diethylene glycol monobutyl ether 5
Dipropylene glycol monobutyl ether 2.5
Olphin E1010
(Acetylene glycol surfactant: manufactured by Nissin Chemical Industry Co., Ltd.) 1
Glycerin 7
Benzotriazole: Corrosion inhibitor (manufactured by Kanto Chemical Co., Ltd.) 0.05
Pure water remaining

Yellow ink <Composition ratio> wt%
(Pigment 4) [45:55] / 5
1,2-pentanediol 5
Triethylene glycol monobutyl ether 3
Surfinol 61
(Acetylene glycol surfactant: manufactured by Nissin Chemical Industry Co., Ltd.) 0.8
Glycerin 9
Benzotriazole: Corrosion inhibitor (manufactured by Kanto Chemical Co., Ltd.) 0.05
Pure water remaining

Clear ink 1
<Composition ratio> wt%
Cybinol SK-200
(Acrylic resin emulsion, made by Seiden Chemical Co., Ltd.) 5
1,2-hexanediol 4.5
Diethylene glycol monobutyl ether 3
Olphine STG
(Acetylene glycol surfactant: manufactured by Nissin Chemical Industry Co., Ltd.) 2.5
Glycerin 8
Benzotriazole: Corrosion inhibitor (manufactured by Kanto Chemical Co., Ltd.) 0.05
Pure water remaining

Clear ink 2
<Composition ratio> wt%
Cybinol SK-200
(Acrylic resin emulsion, made by Seiden Chemical Co., Ltd.) 5
1,2-hexanediol 5
Diethylene glycol monobutyl ether 2
Surfinol 465
(Acetylene glycol surfactant: manufactured by Air Products) 2.5
Glycerin 8
Benzotriazole: Corrosion inhibitor (manufactured by Kanto Chemical Co., Ltd.) 0.05
Pure water remaining

Clear ink 1 for comparison (comparative example)
<Composition ratio> wt%
Cybinol SK-200
(Acrylic resin emulsion, made by Seiden Chemical Co., Ltd.) 5
1,2-hexanediol 4.5
Diethylene glycol monobutyl ether 3
Glycerin 9.5
Benzotriazole: Corrosion inhibitor (manufactured by Kanto Chemical Co., Ltd.) 0.05
Pure water remaining

Clear ink 2 for comparison (comparative example)
<Composition ratio> wt%
Cybinol SK-200
(Acrylic resin emulsion, made by Seiden Chemical Co., Ltd.) 5
1,2-hexanediol 5
Diethylene glycol monobutyl ether 2
Glycerin 9
Benzotriazole: Corrosion inhibitor (manufactured by Kanto Chemical Co., Ltd.) 0.05
The remaining amount of pure water The ink composition for ink jet recording was prepared and carried out.

  Next, a recording method in the embodiment will be described below. In the implementation, recording was performed according to the arrangement shown in FIG. 2 in order to discharge the ink composition for ink jet recording described above using an ink jet printer PM-970C manufactured by Seiko Epson Corporation. Here, FIG. 2 is a view of the print head 9 as seen from the front side of the discharge surface. The direction of the arrow 11 is the paper feed direction, and the recording liquid is discharged based on the arrangement shown in Table 1. The symbols in Table 1 are Bk: black ink, C: cyan ink, M: magenta ink, Y: yellow ink, CL1: clear ink 1, CL2: clear ink 2, Rf1: comparison clear ink 1, Rf2. : Clear ink 2 for comparison.

<Evaluation on glossy recording medium>
For the recording material used for glossiness evaluation, “Photo paper (silk tone); A4 size”, “Photo Gloss” manufactured by Seiko Epson Corporation having a specular glossiness of 10 or more based on a test method in JIS standard (JIS P 8741). Paper (only for pigment); A4 size "and" photographic paper (gloss); A4 size "were used, and recording was performed with a solid color with the following <Recording condition 1> setting as the recording condition. Further, in order to compare the scratch resistance, rubbing with a finger was evaluated for the printed matter. Further, whether or not the gradation expression at a low color density is smooth was determined by measuring several points of the OD of a single solid color with a low color density and calculating the standard deviation of the degree of variation in the values.

<Recording condition 1>
Record type: Photo paper (glossy)
Mode settings: Advanced settings Print quality: Photo-Super Bidirectional printing: None Color adjustment: No color correction As a combination of colored ink and clear ink used for recording,
(1) Recording with colored ink only (Comparative Example 1)
(2) Recording with colored ink and clear ink 1 (Example 1)
(3) Recording with colored ink and clear ink 2 (Example 2)
(4) Recording with colored ink and comparative clear ink 1 (Comparative Example 2)
(5) Recording with colored ink and comparative clear ink 2 (Comparative Example 3)
In these five cases, measurement was performed after recording single color solids of Bk, C, M, and Y under <Recording condition 1>.

<Specular gloss measurement on glossy recording medium>
The specular glossiness of the recording surface at an incident angle of 60 degrees was measured with a gloss checker (IG-320: manufactured by HORIBA, Ltd.), and Table 2 shows values obtained by averaging five times for each recording paper.

  Although the rate of increase differs depending on the recording medium, it has been confirmed that the glossiness is the same or improved by recording with the combination of the clear ink and the colored ink of the present invention in any recording medium.

<Evaluation of abrasion resistance of glossy recording medium>
The cases (1) to (5) described above were evaluated according to the following four levels.
A: No trace of rubbing with a finger is left.
B: When observing carefully, rubbing marks are seen.
C: A trace of rubbing with a finger remains.
D: After rubbing with a finger, it remains clear and does not fix.

Although a difference was observed depending on the recording medium, it was confirmed that in any recording medium, the abrasion resistance was equal or improved by recording with the combination of the clear ink and the colored ink of the present invention.
<Comparison evaluation of smoothness of gradation expression in low color density area in glossy recording medium>
After recording solids of 50%, 30%, and 10% in each single color when the upper limit value of the amount of each ink composition to be shot is 100%, the OD value is recorded as a Gretag spectrophotometer (GRETAG SPM50: GRETAG). The standard deviation of the OD values measured by changing the location at 10 points for each driving amount condition was calculated and compared.

<Evaluation on a glossy recording medium>
<Measurement of reflection optical density (OD) on plain paper>
Recording paper (plain paper): OD on Reymat paper, Hammermill Copy Plus paper, and Xerox 4024 paper was measured with a Gretag spectrophotometer (GRETAG SPM50: manufactured by GRETAG). Table 5 shows the results of solid-color recording performed under <Recording condition 2> shown below as the recording conditions.

<Recording condition 2>
Paper type: Plain paper-Color Mode setting: Recommended setting-Fast

<Bleed measurement on plain paper>
Recording paper (plain paper): The degree of bleeding on Reymat paper, Hammermill Copy Plus paper, and Xerox 4024 paper was measured. Table 6 shows the results of evaluating whether or not the roundness of the dots has decreased due to the uneven penetration of the ink based on the following criteria.
A: The roundness is very good.
B: Although the degree of roundness is slightly reduced, there is no practical problem.
C: A decrease in roundness is observed, and there is a problem in practical use.
D: The roundness is remarkably lowered and is not suitable for practical use.

1 is a schematic diagram of an ink jet recording apparatus embodying the present invention. FIG. 5 is a nozzle arrangement diagram for discharging the color material ink used in the embodiment.

Explanation of symbols

1. 1. Ink and emulsion added solution discharge nozzle 2. Ink and emulsion added solution discharge nozzle 3. Ink discharge nozzle 4. Ink discharge nozzle 5. Ink discharge nozzle 6. Ink discharge nozzle Ink discharge nozzle 8. Ink discharge nozzle 9. 10. Outline of head Cover head 11. Paper feeding direction 22. Recording medium 23. Paper feed motor 24. Carriage motor 26. Platen 28. Recording head 31. Carriage 32. Operation panel 34. Sliding shaft 36. Drive belt 38. Pulley 39. Position detection sensor 40. Control circuit 50. Piezo element driving circuit 61. Black discharge nozzle 62-66. Color discharge nozzle 71. Black ink cartridge 72. Color ink cartridge

Claims (5)

  In an ink jet recording apparatus comprising a colored ink containing a color material and a clear ink not containing a color material, the ink jet recording apparatus has a mechanism for adjusting the color density on the recording medium according to the application, and the surface of the clear ink An ink jet recording apparatus, wherein a tension is lower than a surface tension of the colored ink.   2. The ink jet recording apparatus according to claim 1, wherein surface tensions of the colored ink and the clear ink are both 18 mN / m and 35 mN / m.   An ink set for ink-jet recording comprising a colored ink and a clear ink for use in the ink-jet recording apparatus according to claim 1 or 2.   The inkjet recording apparatus according to claim 1, wherein the colored ink and the clear ink contain 0.01 to 5% by weight of an acetylene glycol surfactant. The ink set for inkjet recording according to claim 3, wherein the colored ink and the clear ink contain 0.01 to 5% by weight of an acetylene glycol surfactant.

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