JP5146041B2 - Inkjet printer and inkjet head cleaning liquid - Google Patents

Description

  The present invention relates to an inkjet printer having an inkjet head cleaning mechanism and an inkjet head cleaning liquid used therefor.

  The ink jet recording method is a method in which minute ink droplets are ejected by various operating principles and adhered to a recording medium such as paper to record images / characters. It has advantages such as being easy to make. In the ink jet recording system, various improvements have been made in each field of ink, ink jet recording medium, and ink jet recording apparatus, and now, they are rapidly spreading in various fields such as various printers, facsimiles, computer terminals and the like. In particular, recently, the image quality of printers has been improved and the image quality has been reached.

  As an ink jet printer used in the ink jet recording method, a plurality of ink discharge ports (nozzle portions) and a plurality of ink liquid paths are used as a recording head (hereinafter also referred to as a multi-head) in which a plurality of recording elements are arranged in order to improve printing speed. A collection is used. Furthermore, a printer equipped with a plurality of recording heads having the above-described configuration is often used for color correspondence. In that case, the heads that eject ink of each color are generally arranged in parallel in the main scanning direction.

  In ink jet recording in which micro droplets are ejected, an ink liquid containing a color material is ejected from a thin nozzle onto a recording medium to form an image. Therefore, as one of the color materials, water-soluble water-soluble A dye is used. Such a water-based dye ink has a sharp absorption spectrum and shows a clear color with high purity. Further, since it has no particle property and does not generate scattered light or reflected light, it has characteristics such as high transparency and clear hue. However, an image formed with a dye has a problem that an image that requires high image storage stability cannot be obtained because the durability of the dye itself is low.

  On the other hand, from the viewpoint of obtaining high image storability, an ink jet recording method using a pigment ink using a pigment as a coloring material is known. Aqueous pigment inks are prepared by dispersing pigments in an aqueous medium in the form of fine particles, and the pigments themselves have high light resistance and ozone fading resistance. Can be significantly increased as compared to those using dyes. Water-based pigment inks having such characteristics are widely used mainly in large-format ink jet prints. However, in the case of using the ink with the pigment, since the pigment particles are not soaked into the recording medium and are deposited on the surface, there is a problem that the scratch resistance of the formed image surface is inferior. However, the usable period is limited, or it is unavoidable that the surface is further laminated and used.

  As means for improving the scratch resistance of an image formed with such an aqueous pigment ink, a method of adding a water-soluble resin or a fixing resin to the aqueous pigment ink is disclosed (for example, Patent Document 1, Patent Document). 2). By adding each of these resins into the ink, it is possible to improve the scratch resistance of the formed image, but the liquid properties of the ink change greatly, especially in the vicinity of the ejection port (nozzle part) of the inkjet head. From the viewpoint of ejection stability, the ink attached to the ink dries to form a resin film, or dust or the like further adheres to the formed resin film, which causes ejection bending or nozzle missing during ink ejection. A large impact.

  On the other hand, from the viewpoint of imparting high-speed printability and obtaining a high-density image, studies have been made on inks that have a smaller ink droplet amount to be ejected and a higher pigment concentration. However, the ink with an increased pigment concentration, like the above, causes the ink from adhering to the vicinity of the ejection port of the ink jet head to dry, which causes the bending of the ink and the lack of nozzles when ejecting the ink. A large impact.

  In order to remove the ink adhering to the vicinity of the discharge port of the inkjet head, an inkjet printer having an alkaline aqueous cleaning solution containing a specific surfactant and having a pH of less than 11 has been proposed (for example, , See Patent Document 3).

However, the current situation is that the inkjet head cannot be sufficiently cleaned within the scope of the technique disclosed in Patent Document 3. In particular, the aqueous pigment ink with an increased amount of the fixing resin or the like for the purpose of improving the scratch resistance as described above or the aqueous pigment ink with an increased pigment concentration adheres to the ejection surface of the inkjet head and solidifies. As a result, the developed ink has not been sufficiently washed, and an immediate technical development is desired.
Japanese Patent Laid-Open No. 10-316907 JP 2007-23161 A Japanese Patent Laid-Open No. 11-263022

  The present invention has been made in view of the above problems, and its purpose is to remove ink stains near the ejection head of an inkjet head with a simple mechanism and to increase the amount of fixing resin added, and to increase the pigment concentration. It is an object of the present invention to provide an ink jet printer capable of maintaining stable emission characteristics over a long period of time even with a water-based pigment ink with improved water resistance and an ink jet head cleaning liquid used therefor.

  The above object of the present invention is achieved by the following configurations.

1. An inkjet printer comprising an inkjet head that discharges an aqueous pigment ink to form an image on a recording medium, and a cleaning mechanism that cleans an ejection port of the inkjet head,
The cleaning mechanism is a mechanism for wiping the discharge port of the inkjet head using a cleaning member to which an inkjet head cleaning liquid containing at least a solvent having a surface tension of less than 35 mN / m and a basic compound is attached.
The content of the solvent is 2 to 20% by mass with respect to the total mass of the inkjet head cleaning liquid,
The water-based pigment ink is a non-polymerization type ink, and has a pigment solid content of 6.0% by mass or more and a total resin solid content of 6.0% by mass or more with respect to the total mass of the ink.

2. 2. The ink jet printer as described in 1 above, wherein the solvent having a surface tension of less than 35 mN / m contained in the ink jet head cleaning liquid is at least one organic solvent selected from alkylene glycol monoethers and alkanediols. .

3. An ink set composed of the aqueous pigment ink is composed of at least a yellow pigment ink, a magenta pigment ink, a cyan pigment ink, and a black pigment ink, and the aqueous pigment ink of at least one color has a pigment solid content of 6 with respect to the total mass of the ink. 3. The ink jet printer as described in 1 or 2 above, wherein the content is 0.0% by mass or more and the total resin solid content is 6.0% by mass or more.

4). 4. The inkjet printer according to any one of items 1 to 3 , further comprising a heating mechanism that heats the recording medium during image formation.

5. 5. An ink jet head cleaning liquid for use in the ink jet printer according to any one of 1 to 4 , comprising at least a solvent having a surface tension of less than 35 mN / m and a basic compound.

  According to the present invention, it is possible to remove ink stains near the ejection port of an inkjet head with a simple mechanism, and even a water-based pigment ink with an increased amount of fixing resin added or a water-based pigment ink with an increased pigment concentration is stable over a long period of time. Ink jet printer capable of maintaining the emission characteristics and an ink jet head cleaning liquid used therefor can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  As a result of intensive studies in view of the above problems, the present inventor has an inkjet head that discharges aqueous pigment ink to form an image on a recording medium, and a cleaning mechanism that cleans the discharge port of the inkjet recording head. In the inkjet printer, the cleaning mechanism has a mechanism for cleaning using an inkjet head cleaning liquid containing at least a solvent having a surface tension of less than 35 mN / m and a basic compound. Ink jet printer that can remove ink stains near the ejection port of the ink jet head and maintain stable emission characteristics over a long period, even with aqueous pigment inks with an increased amount of fixing resin added or water pigment inks with increased pigment concentration As a result, the present invention has been found.

  Details of the present invention will be described below.

<Inkjet printer>
First, the configuration of the inkjet printer of the present invention and the details of the cleaning mechanism will be described.

[Inkjet printer]
In the inkjet printer of the present invention, when forming an image by ejecting water-based pigment ink (hereinafter also simply referred to as ink), the inkjet head (hereinafter also simply referred to as head) to be used is an on-demand system or a continuous system. But it can be applied.

  In addition, as a discharge method, an electro-mechanical conversion method (single cavity type, double cavity type, bender type, piston type, shear mode type, shared wall type, etc.), electro-thermal conversion method (thermal ink jet type, bubble jet ( (Registered Trademark) type, etc.) may be used. In a preferred embodiment of the present invention, an ink having a high concentration and high fixability is obtained using an ink having a high pigment solid content and a resin solid content. In order to form, the piezo method is preferable.

  The ink jet printer of the present invention is an ink jet printer mainly comprising an ink jet head for discharging an aqueous pigment ink to form an image and a cleaning mechanism for cleaning an ink discharge port of the ink jet head, the cleaning mechanism comprising: An inkjet printer comprising a cleaning process using an inkjet cleaning liquid (hereinafter also simply referred to as a cleaning liquid) containing at least a solvent having a surface tension of less than 35 mN / m and a basic compound.

  The so-called shuttle type in which the inkjet head is mounted on a carriage and the carriage moves on a rail is preferable because it can be applied to recording media of various sizes. In a preferred embodiment, at least a portion where a cap is disposed, a printing portion where a recording medium is disposed and printing, and an inkjet head cleaning mechanism are disposed within a range in which the inkjet head can move. Furthermore, it is preferable to provide a maintenance portion for performing head replacement or the like.

  Hereinafter, the details of the ink jet printer of the present invention will be described with reference to the drawings. However, the present invention is not limited only to the configurations described in the drawings.

  FIG. 1 is a schematic perspective view illustrating an example of a main configuration of an inkjet printer.

  The ink jet printer 1 performs printing by ejecting ink onto a recording medium 2. As shown in FIG. 1, as a main configuration of a portion that performs the printing, a conveying means (for conveying the recording medium 2 forward during printing) (Not shown), an inkjet head (head) 3 that ejects ink onto the recording medium 2, a carriage 4 that houses the inkjet heads 3 for each of a plurality of colors, a suction cap 5A that performs maintenance of the inkjet head 3, and the present invention. A maintenance unit 5 having such a cleaning mechanism 5B, a guide rail 6 for guiding the carriage 4 along the main scanning direction (arrow A) at the time of printing or maintenance, and a moisture retention cap 8 serving as a waiting place for the carriage 4 are provided. And a control unit (not shown) for controlling these units. C is an ink cartridge, and each ink sent from the ink cartridge C is once stored in the sub-tank T and then sent to the recording head through the supply valve V and the ink supply path P.

  The recording medium conveying means conveys the recording medium 2 on the printing area 9 in synchronization with the operation of the carriage 4 at the time of printing, and the recording medium 2 moves downward (arrows) from the printing area in accordance with the end of printing. B) is conveyed.

  The home position 7 is provided with the same number of moisturizing caps 8 as the recording head 3 for moisturizing the nozzle surface of the recording head, and covers and seals the nozzle surface of the recording head 3 while the carriage 4 is on standby. .

  In addition, the ink jet printer of the present invention includes a mechanism for heating a recording medium to be printed in advance or heating the recording medium at the time of printing for the purpose of suppressing ink mixing with respect to the recording medium having various characteristics. This is one of the preferred embodiments.

  FIG. 2 is a schematic diagram illustrating an example of a maintenance process and a printing process of the inkjet printer.

  In FIG. 2 a), the inkjet head 3 mounted on the carriage 4 in the resting state is in a state in which the suction cap 5A on the maintenance unit 5 is attached. The suction cap 5A caps the inkjet head 3, This is a mechanism for preventing the ink at the discharge port in contact with the outside air from drying out. In addition, the suction cap 5A has a suction function, and can also suck out a certain amount of ink from the inkjet head 3 through the ejection port.

  The maintenance unit 5 is provided with a cleaning mechanism 5B at a position adjacent to the plurality of suction caps 5A, and as shown in FIG. 2B, the inkjet head 3 before printing is made of, for example, rubber warping. The discharge port is cleaned using the blade while holding the inkjet cleaning liquid according to the present invention. A detailed cleaning method will be described later.

  The carriage 4 that has completed the above-described cleaning operation of the ejection port is moved to the printing position by the guide rail 6 and then ejects ink onto the recording medium 2 to form an image as shown in FIG. Do. At this time, in the present invention, it is preferable to install a heater H for heating the recording medium at the lower part of the recording medium transport unit, and perform heat treatment from the back side of the recording medium as necessary.

[Cleaning mechanism]
The ink jet printer of the present invention is a printer having a cleaning mechanism for cleaning an ejection port of an ink jet head, and the cleaning mechanism includes an ink jet cleaning liquid containing at least a solvent having a surface tension of less than 35 mN / m and a basic compound. It includes a process of cleaning using.

  Although the mechanism by which the effect of the present invention is manifested by using a cleaning mechanism having a configuration defined in the present invention has not been clarified, it is presumed as follows.

  In the case of using an aqueous pigment ink, particularly an aqueous pigment ink having a high pigment concentration or an aqueous pigment ink having a lot of resin components, it is considered that two functions are necessary to remove the ink film adhered to the ink jet head and dried. . One is the role of acting on the interface between the ink jet head member and the ink film to float the ink film. Usually, the vicinity of the ejection port of the inkjet head is provided with a water-repellent coating for facilitating ink repelling, and therefore, the vicinity of the ejection port is in a state where ink is difficult to adhere, but once the ink is adhered and dried. The cleaning liquid is difficult to enter the interface between the ink jet head member and the ink film, or is difficult to remove. The reason why the cleaning effect of the inkjet cleaning liquid of the present invention is large is that a solvent having a surface tension of less than 35 mN / m is used, so that it can effectively penetrate into the interface between the inkjet head member and the ink film even in a short time contact. ing. The same effect can be expected by using a surfactant, but the effect is not sufficient, and the surfactant in the cleaning liquid tends to remain on the head and after the ink film is removed from the ejection port. , Which may affect the injection properties and the like.

  Another function is a function of redissolving or redispersing the resin in the ink. When removing ink stains from the ink jet head member, it is preferable to dissolve or disperse the ink film components at the same time because the effect of preventing reattachment to the ink jet head can be expected. Further, even when wiping is performed, it may be possible to completely remove the dirt by returning it to a liquid state by a dissolving power without applying a force enough to remove the solid content as it is. In that sense, the function of re-dissolving or re-dispersing the resin in the ink is important.

  In the cleaning mechanism according to the present invention, the process of cleaning the inkjet head using the inkjet cleaning liquid is not particularly limited, but 1) the process of applying the cleaning liquid to the head discharge port, and 2) removing the ink component adhering to the head discharge port. It is preferred to include both processes. In particular, the method of wiping the head with a member to which an inkjet cleaning liquid is attached is preferable because the apparatus is simple and the cleaning effect is large. As the wiping member, a resin member such as rubber can be preferably used. For example, acrylic rubber, acrylonitrile butadiene rubber, isoprene rubber, urethane rubber, ethylene propylene rubber (EPM, EPDM), epichlorohydrin rubber, chloroprene rubber, silicone rubber, styrene Butadiene rubber, butadiene rubber, fluorine rubber, polyisobutylene rubber and the like can be used, and EPDM is particularly preferable.

  FIG. 3 is a schematic view showing an example of a discharge port cleaning process by the cleaning mechanism of the present invention.

  In the present invention, the inkjet head 3 moved to the position b) in FIG. 2 using the cleaning mechanism shown in FIG. 3 is used to wipe the ink discharge surface using the cleaning blade by the cleaning mechanism according to the present invention. It is one of the preferred embodiments that washing is performed.

  In FIG. 3, the inkjet head 3 has an ink reservoir 10 and a discharge port 11 for discharging it, and a water repellent plate 12 is provided on the discharge surface. On the other hand, in the cleaning mechanism 5B, the cleaning liquid container 13 is filled with the inkjet cleaning liquid 16 according to the present invention, and a blade-like wiping member 15 attached to the rotary shaft 14 is installed in the inkjet cleaning liquid 16. .

  The wiping member 15 moves while rotating from the positions P1 to P7 by the rotation of the rotating shaft 14. Positions P1 and P2 move in the inkjet cleaning liquid 16, rotate while accompanying the inkjet cleaning liquid 13 when moving out of the liquid, and start contact with the lower part of the inkjet head at position P3 and adhere to the water repellent blade 12. Is peeled or dissolved to clean the surface of the water-repellent plate 12. The wiping member 15 that has been cleaned is immersed again in the liquid at position P7, and the ink film or the like adhering to the wiping member 15 is dissolved and removed by the inkjet cleaning liquid 16, and then returns to position P1.

  In FIG. 3, an example in which one blade-like wiping member 15 of the rotating shaft 14 is attached is shown. However, a configuration in which a plurality of two, three, four, etc., are installed at regular intervals. You may take it.

(Inkjet head cleaning solution)
Next, an inkjet cleaning liquid applied to the cleaning mechanism according to the present invention will be described.

  The cleaning liquid according to the present invention contains a base component and is effective for redissolving or redispersing the acid component-containing resin used in the ink.

  It is an essential requirement that the cleaning liquid according to the present invention contains at least a solvent having a surface tension of less than 35 mN / m and a basic compound.

  As a function required for the cleaning liquid applied to the ink jet printer, it is important to stably maintain the cleaning ability for a long period of time and not to affect the ejection characteristics of the ink jet head after the cleaning.

  The cleaning liquid according to the present invention is characterized by containing a solvent having a surface tension of less than 35 mN / m. Examples of the solvent having a surface tension of less than 35 mN / m include alkylene glycol monoethers or alkanediols. Is preferred.

  Examples of alkylene glycol monoethers that can be suitably used in the cleaning liquid according to the present invention include ethylene glycol monoethyl ether (28.2), ethylene glycol monobutyl ether (27.4), and diethylene glycol monoethyl ether (31. 8), diethylene glycol monobutyl ether (33.6), triethylene glycol monobutyl ether (32.1), propylene glycol monopropyl ether (25.9), dipropylene glycol monomethyl ether (28.8), tripropylene glycol monomethyl ether (30.0). The numerical value in the parenthesis represents the surface tension value (mN / m).

  In addition, as the alkanediols that can be suitably used in the cleaning liquid according to the present invention, 1,2-alkanediols are preferable. For example, 1,2-butanediol, 1,2-pentanediol, 1,2- Examples include hexanediol (28.1) and 1,2-heptanediol.

  Among the above solvents, diethylene glycol monoalkyl ethers are preferable, and diethylene glycol monobutyl ether is particularly preferable.

  In the present invention, the method for measuring the surface tension of a solvent is described in a reference book on general surface chemistry, colloid chemistry, and the like. Edited by Maruzen Co., Ltd. 68-117 can be referred to, and specifically, it can be determined by using a ring method (Dunoi method) or a vertical plate method (Wilhelmy method). In the present invention, specifically, the surface tension was measured using a surface tension meter CBVP type A-3 type (Kyowa Science Co., Ltd.).

  In addition, the cleaning liquid according to the present invention is characterized by containing a basic compound together with a solvent having a surface tension of less than 35 mN / m.

  The basic compound applicable to the present invention may be an inorganic basic compound or an organic basic compound, but it is more preferable to use an organic basic compound.

  As inorganic base compounds, use hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide, carbonates such as potassium carbonate and sodium carbonate, potassium hydrogen carbonate and bicarbonates such as sodium hydrogen carbonate. Can do.

  As the organic base compound, ammonia, alkanolamines, alkylamines and the like can be used.

  Organic base compounds include ammonia, triethylamine, N, N, -dimethylaminoethanol, N, N-dibutylaminoethanol, N-methyl-diethanolamine, 2-amino-2-methylpropanol, diethanolamine, triethanolamine, N- Methylaminoethanol, N, N-diethylaminoethanol or the like can be used.

  Among these, ammonia, N, N, -dimethylaminoethanol, N, N-dibutylaminoethanol, N-methyl-diethanolamine, 2-amino-2-methylpropanol, and N, N-diethylaminoethanol can be preferably used.

  If necessary, other additives such as a surfactant, a humectant, a culture medium and the like may be added to the cleaning liquid according to the present invention.

<Water-based pigment ink>
Next, the configuration of the aqueous pigment ink applied to the ink jet printer of the present invention will be described.

  The aqueous pigment ink applied to the inkjet printer of the present invention is not particularly limited, but at least a yellow pigment ink, a magenta pigment ink, a cyan pigment ink, and a black pigment can be used from the viewpoint that the effect of the cleaning mechanism according to the present invention can be sufficiently exerted. Using an ink set composed of four color pigment inks, at least one aqueous pigment ink has a pigment solid content of 6.0% by mass or more and a total resin solid content of 6.0% with respect to the total mass of the ink. It is preferable that it is mass% or more. Among these, the pigment solid content of the black pigment ink is particularly preferably 6.0% or more.

(Pigment)
The pigment that can be used in the present invention is not particularly limited as long as it can be stably dispersed in an aqueous system. For example, in addition to a pigment alone, a pigment dispersion dispersed with a polymer resin, or a water-insoluble resin is coated. Examples thereof include capsule pigments, self-dispersing pigments that can be dispersed without modifying the pigment surface and using a dispersing resin. In particular, when emphasizing the storability of the ink, it is preferable to select a capsule pigment coated with a water-insoluble resin.

  When a pigment dispersion dispersed with a polymer resin is used, a water-soluble one can be used as the polymer resin. For example, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid copolymer, styrene-maleic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester are preferably used as the water-soluble resin. Copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer Examples thereof include water-soluble resins such as polymers.

  Various methods such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker can be used as a method for dispersing the pigment.

  For the purpose of removing coarse particles of the pigment dispersion according to the present invention, it is also preferable to use a centrifugal separator or a filter.

  In the case of using a capsule pigment coated with a water-insoluble resin, the water-insoluble resin is a resin that is insoluble in water in a weakly acidic to weakly basic range, and preferably has a solubility of 2 in an aqueous solution having a pH of 4 to 10. % Resin.

  Such resins include acrylic, styrene-acrylic, acrylonitrile-acrylic, vinyl acetate, vinyl acetate-acrylic, vinyl acetate-vinyl chloride, polyurethane, silicon-acrylic, acrylic silicon, polyester Examples thereof include epoxy resins and epoxy resins.

  Further, a resin obtained by copolymerizing a hydrophobic monomer and a hydrophilic monomer can be used as the resin.

  Examples of hydrophobic monomers include acrylic acid esters (such as n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate), methacrylic acid esters (such as ethyl methacrylate, butyl methacrylate, glycidyl methacrylate), and styrene. Etc.

  Examples of the hydrophilic monomer include acrylic acid, methacrylic acid, acrylamide and the like, and those having an acidic group such as acrylic acid can preferably be those neutralized with a base after polymerization.

  As the molecular weight of the resin, an average molecular weight of 3000 to 500,000 can be used. Preferably, 7,000 to 200,000 can be used. Resin having a Tg of about -30 ° C to 100 ° C can be used. Preferably, a temperature of about −10 ° C. to 80 ° C. can be used.

  As the polymerization method, solution polymerization or emulsion polymerization can be used. The polymerization may be separately synthesized with the pigment in advance, or may be performed by supplying a monomer without dispersing the pigment.

  Various known methods can be used as a method for coating the pigment with the resin. Preferably, in addition to the phase-emulsification method and the acid precipitation method, the pigment is dispersed using a polymerizable surfactant, and the monomer is then dispersed therein. It is preferable to select from a method of coating while polymerizing. As a more preferred method, the water-insoluble resin is dissolved in an organic solvent such as methyl ethyl ketone, and the acidic group in the resin is partially or completely neutralized with a base, and then the pigment and ion-exchanged water are added and dispersed. Thereafter, a production method is preferred in which the organic solvent is removed, and water is added if necessary.

  The mass ratio of the pigment to the resin can be selected in the range of 100/40 to 100/150 as the pigment / resin ratio. In particular, the range of 100/60 to 100/110 has good image durability, injection stability, and ink storage stability.

  The average particle size of the pigment particles coated with the water-insoluble resin is preferably about 80 to 150 nm from the viewpoint of ink storage stability and color development.

  Moreover, as the self-dispersing pigment, a surface-treated commercial product can be used, and examples thereof include CABO-JET200, CABO-JET300 (manufactured by Cabot Corporation), Bonjet CW1 (manufactured by Orient Chemical Industry Co., Ltd.) and the like. Can do.

  As the pigment that can be used in the present invention, conventionally known organic and inorganic pigments can be used. For example, azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. Examples include cyclic pigments, dye lakes such as basic dye lakes and acid dye lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black and daylight fluorescent pigments, and inorganic pigments such as carbon black.

  Specific organic pigments are exemplified below.

  Examples of pigments for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the orange or yellow pigment include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 128, C.I. I. And CI Pigment Yellow 138.

  Examples of pigments for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

(Resin component)
The water-based pigment ink according to the present invention preferably contains a resin component in order to improve fixability to a recording medium and to improve abrasion resistance, adhesion, water resistance, and the like.

  As a resin component, it may be used as a conventionally used pigment dispersion resin, or may be added additionally during ink preparation.

  In the present invention, it is preferable that at least one color aqueous pigment ink is contained in the ink in an amount of 6.0% by mass or more as a solid component of the resin component in order to improve the fixing property.

  The resin component referred to in the present invention may be a water-soluble resin or a water-dispersible resin, or both may be used in combination.

  As the water-soluble resin, a resin having a hydrophobic component and a hydrophilic component in a certain balance is designed and used. At this time, as the hydrophilic component, either an ionic component or a nonionic component may be used, but an ionic component is more preferable, and an anionic component is more preferable. In particular, those that are rendered water-soluble by neutralizing anionic substances with a volatile base component are preferred. In particular, at least one of the ink-soluble resins has a carboxyl group or a sulfonic acid group as an acidic group, and a resin having an acid value of 80 mgKOH / g or more and less than 300 mgKOH / g is preferable. An acid value of about 90 mgKOH / g to 200 mgKOH / g is used.

  The acid value is the number of milligrams of potassium hydroxide required to neutralize the acidic component contained in 1 g of resin.

  Examples of such resins include acrylic resins, styrene-acrylic resins, acrylonitrile-acrylic resins, vinyl acetate-acrylic resins, polyurethane resins, and polyester resins. Particularly, acrylic copolymers and styrene resins can be used. -Acrylic is preferred.

  Examples of the hydrophobic monomer include acrylic acid esters (for example, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, etc.), methacrylic acid esters (for example, ethyl methacrylate, butyl methacrylate, methacrylic acid). Glycidyl acid), styrene and the like.

  Examples of the hydrophilic monomer include acrylic acid, methacrylic acid, acrylamide and the like, and those having an acidic group such as acrylic acid can preferably be those neutralized with a base after polymerization.

  As the molecular weight of the resin, an average molecular weight of 3000 to 30000 can be used. Preferably, 7000 to 20000 can be used.

  Resin having a Tg of about -30 ° C to 100 ° C can be used. Preferably, a temperature of about −10 ° C. to 80 ° C. can be used.

  As the polymerization method, it is preferable to use solution polymerization.

  The acidic group derived from the acidic monomer of the resin is preferably partially or completely neutralized with a base component. As the neutralizing base in this case, an alkali metal-containing base such as sodium hydroxide or potassium hydroxide, or an amine (ammonia, alkanolamine, alkylamine, etc. can be used) can be used. In particular, neutralization with amines having a boiling point of less than 200 ° C. is particularly preferable from the viewpoint of improving image durability.

  The ink of the present invention may use a water-dispersible resin in addition to the water-soluble resin. In particular, it is preferable to add a water-dispersible resin having a Tg of 20 to 80 ° C. in an amount smaller than that of the water-soluble resin in order to further improve the abrasion resistance.

  The water-based pigment ink is preferably one that can be printed not only on plain paper and exclusive inkjet paper having an ink absorbing layer, but also on resin materials such as coated paper and films, fabrics, leather materials, etc. without an ink absorbing layer. In order to have such a function, it is preferable to contain 6.0% by mass or more in the ink as the solid content of the resin component.

(Ink surface tension)
The ink according to the present invention preferably contains 10 to 30% by mass of an organic solvent having a surface tension of less than 35 mN / m. When printing on various media such as coated paper for printing, film base materials, resin materials, and fabrics, it is preferable that ink mixing can be sufficiently prevented, and fabrics can further suppress bleeding along fibers.

  The surface tension of the ink according to the present invention is preferably adjusted to a range of 23 to 30 mN / m. As a means for adjusting the surface tension of the ink to the above range, it is adjusted by adding 10 to 30% of an organic solvent having a surface tension of less than 35 mN / m, and further adding a silicon-based or fluorine-based surfactant. can do. By using such a surface tension value, it is possible to print on a recording medium such as a plastic film while suppressing ink mixing. The silicon surfactant is preferably a polyether-modified polysiloxane compound, and examples thereof include KF-351A and KF-642 manufactured by Shin-Etsu Chemical Co., and BYK347 and BYK348 manufactured by Big Chemie.

  The fluorosurfactant means a compound in which a part or all of the fluorosurfactant is substituted with fluorine in place of hydrogen bonded to carbon of a hydrophobic group of a normal surfactant. Of these, those having a perfluoroalkyl group in the molecule are preferred.

  Among the fluorine-based surfactants, certain types are traded under the trade name Megafac F from Dainippon Ink & Chemicals, and Surflon from Asahi Glass, Minnesota Mining and Under the trade name Fluorad FC from Manufacturing Company, under the trade name Monflor from Imperial Chemical Industry, and Zonyls from EI Dupont Nemeras & Company. It is commercially available under the trade name and also under the trade name Licobet VPF from Farbeberke Hoechst.

(Other additives)
The water-based pigment ink according to the present invention includes various known additions depending on the purpose of improving ejection stability, compatibility with recording heads and ink cartridges, storage stability, image storage stability, and other various performances as necessary. An agent such as a viscosity modifier, a surface tension modifier, a specific resistance modifier, a film forming agent, an ultraviolet absorber, an antioxidant, a fading inhibitor, an antifungal agent, and a rust inhibitor may be appropriately selected and used. it can.

"recoding media"
The aqueous pigment ink according to the present invention is suitable for printing on a non-absorbent recording medium such as a polyvinyl chloride sheet, plain paper, coated paper, inkjet dedicated paper, and the like.

  Examples of non-absorbable recording media include polymer sheets, boards (soft vinyl chloride, hard vinyl chloride, acrylic plates, polyolefins, etc.), glass, tiles, rubber, synthetic paper, and the like.

  As a low-absorption or absorbent recording medium, various fabrics (cotton, silk, hair, polyester, etc.), plain paper (copy paper, plain paper for printing), coated paper, art paper, inkjet paper, inkjet glossy paper, Examples include cardboard and wood.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<< Preparation of pigment dispersion >>
[Preparation of Pigment Dispersion 1]
(Preparation of Cyan Pigment Dispersion 1)
As a pigment dispersant, a styrene-acrylic acid copolymer (Johncrill 678, molecular weight: 8500, acid value: 215 mgKOH / g) 4.5 parts, dimethylaminoethanol 1.3 parts, ion-exchanged water 80.7 parts at 70 ° C. The mixture was dissolved by stirring.

  Next, C.I. I. After 15 parts of Pigment Blue 15: 3 was added and premixed, the mixture was dispersed using a sand grinder filled with 50% by volume of 0.5 mm zirconia beads, and the cyan pigment content was 15%. Body 1 was prepared.

(Preparation of yellow pigment dispersion 1, magenta pigment dispersion 1, black pigment dispersion 1)
In preparing the cyan pigment dispersion, cyan pigment C.I. I. Instead of CI Pigment Blue 15: 3, C.I. I. Pigment Yellow-74, C.I. I. A yellow pigment dispersion 1, a magenta pigment dispersion 1, and a black pigment dispersion 1 were prepared in the same manner except that Pigment Red 122 and carbon black were used as the black pigment.

[Preparation of Pigment Dispersion 2]
In the preparation of the cyan pigment dispersion 1, the yellow pigment dispersion 1, the magenta pigment dispersion 1, and the black pigment dispersion 1, the same applies except that the amount of each pigment added was changed to 18 parts. Cyan pigment dispersion 2, yellow pigment dispersion 2, magenta pigment dispersion 2, and black pigment dispersion 2) were prepared.

[Preparation of Pigment Dispersion 3]
In the preparation of the above-mentioned cyan pigment dispersion 1, yellow pigment dispersion 1, magenta pigment dispersion 1, and black pigment dispersion 1, a completed dispersion was obtained in the same manner except that the amount of each pigment added was changed to 15.8 parts. 3 (cyan pigment dispersion 3, yellow pigment dispersion 3, magenta pigment dispersion 3, black pigment dispersion 3) was prepared.

<< Preparation of water-soluble resin >>
[Preparation of water-soluble resin 1]
50 g of methyl ethyl ketone was added to a flask equipped with a dropping funnel, a nitrogen introducer, a reflux condenser, a thermometer and a stirrer, and heated to 75 ° C. while bubbling nitrogen.

  Thereto, a mixture of 80 g of n-butyl methacrylate, 20 g of acrylic acid, 50 g of methyl ethyl ketone, and 500 mg of a polymerization initiator (azobisisobutyronitrile, AIBN) was dropped from a dropping funnel over 3 hours. It heated and refluxed for 6 hours after dripping. After allowing to cool, the mixture was heated under reduced pressure to distill off methyl ethyl ketone to obtain a polymer residue.

  Sodium hydroxide equivalent to 1.05 moles of acrylic acid added as a monomer was dissolved in 450 ml of ion-exchanged water, and the polymer residue was dissolved therein. The concentration was adjusted with ion-exchanged water to obtain an aqueous solution of water-soluble resin 1 (acid value: 117 mgKOH / g, weight average molecular weight: 60,000) having a water-soluble resin content of 20%.

[Preparation of water-soluble resin 2]
50 g of methyl ethyl ketone was added to a flask equipped with a dropping funnel, a nitrogen introducer, a reflux condenser, a thermometer and a stirrer, and heated to 75 ° C. while bubbling nitrogen.

  Thereto, a mixture composed of 80 g of n-butyl methacrylate, 20 g of acrylic acid, 50 g of methyl ethyl ketone, and 500 mg of a polymerization initiator (AIBN) was added dropwise from a dropping funnel over 3 hours. After the dropwise addition, the mixture was further heated to reflux for 6 hours. After allowing to cool, the mixture was heated under reduced pressure, and methyl ethyl ketone was distilled off to obtain a polymer residue.

  In 450 ml of ion-exchanged water, dimethylaminoethanol corresponding to 1.05 moles of acrylic acid added as a monomer was dissolved, and the polymer residue was added and dissolved therein. Subsequently, the concentration was adjusted with ion-exchanged water to obtain an aqueous solution of water-soluble resin 2 (acid value: 117 mgKOH / g, weight average molecular weight: 60,000) having a water-soluble resin content of 20%.

<Preparation of ink set>
[Preparation of ink set 1]
The following additives were sequentially mixed to prepare an ink set 1 comprising a yellow pigment ink 1, a magenta pigment ink 1, a cyan pigment ink 1, and a black pigment ink 1.

(Preparation of each color aqueous pigment ink)
Each pigment dispersion 1
Pigment Solid content 5.0% by mass
Pigment dispersant resin (styrene-acrylic acid copolymer) 1.5 mass% solid content
Water-soluble resin 1 solid content 1.0% by mass
Propylene glycol (PG) 10.0% by mass
Glycerin (Gly) 15.0% by mass
Orphine E1010 (acetylene glycol surfactant, manufactured by Nissin Chemical)
0.5% by mass
Ion exchange water was added to prepare a total amount of 100 parts, and filtration was performed with a 5 μm filter.

[Preparation of ink set 2]
The following additives were sequentially mixed to prepare an ink set 2 composed of a yellow pigment ink 2, a magenta pigment ink 2, a cyan pigment ink 2, and a black pigment ink 2.

(Preparation of each color aqueous pigment ink)
Each pigment dispersion 2
Pigment Solid content 6.0% by mass
Pigment dispersant resin (styrene-acrylic acid copolymer) 1.5 mass% solid content
Water-soluble resin 1 solid content 3.5% by mass
Propylene glycol (PG) 10.0% by mass
Glycerin (Gly) 15.0% by mass
Orphine E1010 (acetylene glycol surfactant, manufactured by Nissin Chemical)
0.5% by mass
Ion exchange water was added to prepare 100 parts in total.

[Preparation of ink set 3]
The following additives were sequentially mixed to prepare an ink set 3 comprising a yellow pigment ink 3, a magenta pigment ink 3, a cyan pigment ink 3, and a black pigment ink 3.

(Preparation of each color aqueous pigment ink)
Each pigment dispersion 2
Pigment Solid content 6.0% by mass
Pigment dispersant resin (styrene-acrylic acid copolymer) 1.5 mass% solid content
Water-soluble resin 1 Solid content 4.5% by mass
Propylene glycol (PG) 10.0% by mass
Glycerin (Gly) 15.0% by mass
Orphine E1010 (acetylene glycol surfactant, manufactured by Nissin Chemical)
0.5% by mass
Ion exchange water was added to prepare 100 parts in total.

[Preparation of ink set 4]
The following additives were sequentially mixed to prepare an ink set 4 comprising a yellow pigment ink 4, a magenta pigment ink 4, a cyan pigment ink 4, and a black pigment ink 4.

(Preparation of each color aqueous pigment ink)
Each pigment dispersion 2
Pigment Solid content 6.0% by mass
Pigment dispersant resin (styrene-acrylic acid copolymer) 1.5 mass% solid content
Water-soluble resin 2 Solid content 4.5% by mass
Propylene glycol (PG) 10.0% by mass
Diethylene glycol monobutyl ether (DEBE) 15.0% by mass
BYK347 (polyether-modified polysiloxane compound, manufactured by Big Chemie)
0.5% by mass
Ion exchange water was added to prepare 100 parts in total.

[Preparation of ink set 5]
The following additives were sequentially mixed to prepare an ink set 5 comprising a yellow pigment ink 5, a magenta pigment ink 5, a cyan pigment ink 5, and a black pigment ink 5.

(Preparation of each color aqueous pigment ink)
Each pigment dispersion 3
Pigment Solid content 7.0% by mass
Pigment dispersant resin (styrene-acrylic acid copolymer) Solid content 2.0% by mass
Water-soluble resin 2 Solid content 8.0% by mass
Propylene glycol (PG) 5.0% by mass
Glycerin (Gly) 2.0% by mass
Diethylene glycol monobutyl ether (DEBE) 15.0% by mass
BYK347 (polyether-modified polysiloxane compound, manufactured by Big Chemie)
0.5% by mass
Ion exchange water was added to prepare 100 parts in total.

<< Preparation of cleaning liquid >>
[Preparation of cleaning solution 1]
DEGBE and ion-exchanged water were mixed at the following ratio to prepare cleaning liquid 1.

Diethylene glycol monobutyl ether (DEBE) 5.0% by mass
95.0% by weight of water
[Preparation of cleaning solutions 2-14]
Solvents and basic compounds listed in Table 2 were mixed and finished to 100% by mass with ion-exchanged water to prepare cleaning solutions 2-14.

  In addition, the detail of each additive described by the abbreviation in Table 2 is as follows.

<solvent>
DEGBE: Diethylene glycol monobutyl ether TEGBE: Triethylene glycol monobutyl ether DEGEE: Diethylene glycol monoethyl ether 1,2-HD: 1,2-hexanediol <Basic compound>
DMAE: Dimethylaminoethanol <Surfactant>
E1010: Olfine E1010, acetylene glycol surfactant, manufactured by Nissin Chemical Co., Ltd. << Inkjet printer >>
[Preparation of inkjet printer 1]
Equipped with four inkjet heads with a driving frequency of 10 kHz, ink droplet volume of 14 pl, 128 nozzles per color, nozzle density of 180 dpi (dpi indicates the number of dots per 2.54 cm), and a maximum recording density of 720 x 720 dpi. The ink jet printer shown in FIG. 1 was used, which was filled with each of the four color aqueous pigment inks 1 constituting the ink set 1.

  The ink jet printer 1 has a head cap at one end of a carriage mounted with an ink jet head, and has a mechanism for preventing drying by capping the ink jet head when printing is suspended. The part adjacent to the cap part is provided with the cleaning mechanism shown in FIG. The cleaning mechanism is equipped with one blade made of ethylene propylene rubber (EPDM) as a wiping member on the rotating shaft, and is filled with cleaning liquid 1 as shown in FIG.

[Production of inkjet printers 2 to 23]
Inkjet printers 2 to 23 were prepared in the same manner as in the inkjet printer 1 except that the combination of the ink set type and the cleaning liquid type was changed as shown in Table 3.

<Evaluation of inkjet printer>
[Evaluation of cleanability]
Using the inkjet printers 1 to 23, after confirming that all nozzles are ejected normally by nozzle check pattern printing, full color of 100cm width x 100cm width on Superfine exclusive paper (manufactured by Seiko Epson Corporation) Five images were continuously printed (720 dpi × 720 dpi). During this period, cleaning and maintenance were not performed. Next, the inkjet head is placed on standby at the cap position, left for 10 minutes without being capped, and after printing a full color image of 100 cm width × 100 cm width, immediately after the nozzle check pattern is printed, each inkjet printer is Several missing patterns were observed, and when the vicinity of the discharge port of the inkjet head was observed, ink marks were observed in various places.

  Next, wiping of each cleaning solution was performed using a cleaning mechanism. Wiping was performed 5 times for each inkjet head. Thereafter, nozzle check pattern printing was performed to confirm the presence or absence of missing patterns. After confirmation, if there was a missing pattern, ink suction was performed using the suction function of the cap, and then wiping was performed again.

  The cleaning result by the wiping operation was evaluated according to the following criteria, and this was used as a measure of cleaning performance.

5: 1 wiping eliminates missing nozzles 4: 1 wiping eliminates missing nozzles, but second wiping eliminates missing nozzles 3: Second wiping does not eliminate missing nozzles Nozzle missing after the third wiping 2: No nozzle missing after the third wiping, but no nozzle missing after the fourth wiping 1: No nozzle missing after the fourth wiping It was made to adhere to a polyurethane resin (trade name: Rubycell, manufactured by Toyo Polymer Co., Ltd.), and the ejection surface of the ink jet head was directly washed by hand, so that there was no missing nozzle.

[Evaluation of printed image]
(Evaluation of scratch resistance)
In the same manner as in the evaluation of the cleaning property, after forming a 100 cm wide × 100 cm wide full-color image, each color image surface was reciprocated 20 times while applying a 9N load using a cotton cloth (Kanakin No. 3). The image was transferred to a cotton cloth by rubbing and visually observed, and the scratch resistance was evaluated according to the following criteria.

5:20 Reciprocating rubbing shows almost no coloration of the cotton cloth. 4:20 Reciprocating rubbing reveals the color of the cotton cloth. It is very slight at 10 reciprocations, and the cotton fabric is colored when rubbing 2:10 reciprocations, but it is very slight at 5 reciprocations. Coloring of the cotton fabric is recognized even at 1: 5 reciprocations (evaluation of water resistance).
In the same manner as the evaluation of the cleaning property, after forming a full color image of 100 cm width × 100 cm width, each color image sample is immersed in ion exchange water at 25 ° C. for 1 hour, and then lifted from the ion exchange water and suspended. It dried in the state which carried out. The bleeding state of the formed image in each step was visually observed, and water resistance was evaluated according to the following criteria.

5: Immediately after immersion in ion-exchanged water at 25 ° C. for 1 hour, even if the formed image surface is rubbed with a cotton cloth (Kanakin No. 3), coloring of the cotton cloth is not recognized. 4: Immerse in ion-exchanged water at 25 ° C. for 1 hour However, there is no blurring of the image, and no ink marks remain in the process of hanging and drying, but the cotton cloth is colored when rubbed with cotton cloth (Kanakin No. 3) before drying 3: Ion exchange at 25 ° C There is no occurrence of image blur when immersed in water for 1 hour, but traces of ink flow occur in the process of hanging and drying 2: Bleeding occurs when immersed in ion exchange water at 25 ° C for 10 minutes or more Yes 1: Bleeding occurs when immersed in deionized water at 25 ° C. for less than 10 minutes Table 3 shows the results obtained.

  As is apparent from the results shown in Table 3, the ink jet printer having the cleaning mechanism defined in the present invention is different from the comparative example in that an ink jet head is used even when an ink having a high pigment concentration or an ink having a high resin content is used. It was possible to stably form an image having excellent cleaning properties on the ejection surface and excellent scratch resistance and water resistance.

  Further, in the same manner as in the above printing method, printing is performed while heating Superfine paper (manufactured by Seiko Epson), which is a recording medium, to 50 ° C. with a heater H provided at the lower part of the recording medium conveyance section of the ink jet printer. As a result, excellent detergency, scratch resistance and water resistance of the formed image were obtained, and a clear image with no image blur could be obtained.

It is a schematic perspective view which shows an example of the main structures of an inkjet printer. It is the schematic which shows an example of the maintenance process and printing process of an inkjet printer. It is a schematic diagram which shows an example of the cleaning process of the discharge outlet by the cleaning mechanism of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet printer 2 Recording medium 3 Inkjet head 4 Carriage 5 Maintenance unit 5A Suction cap 5B Cleaning mechanism 6 Guide rail 12 Water repellent plate 13 Cleaning liquid container 14 Rotating shaft 15 Wiping member 16 Inkjet cleaning liquid P1 to P7 Position of wiping member

Claims (5)

An inkjet printer comprising an inkjet head that discharges an aqueous pigment ink to form an image on a recording medium, and a cleaning mechanism that cleans an ejection port of the inkjet head,
The cleaning mechanism is a mechanism for wiping the discharge port of the inkjet head using a cleaning member to which an inkjet head cleaning liquid containing at least a solvent having a surface tension of less than 35 mN / m and a basic compound is attached.
The content of the solvent is 2 to 20% by mass with respect to the total mass of the inkjet head cleaning liquid,
The water-based pigment ink is a non-polymerization type ink, and has a pigment solid content of 6.0% by mass or more and a total resin solid content of 6.0% by mass or more with respect to the total mass of the ink. 2. The inkjet according to claim 1, wherein the solvent having a surface tension of less than 35 mN / m contained in the inkjet head cleaning liquid is at least one organic solvent selected from alkylene glycol monoethers and alkanediols. Printer. An ink set composed of the aqueous pigment ink is composed of at least a yellow pigment ink, a magenta pigment ink, a cyan pigment ink, and a black pigment ink, and the aqueous pigment ink of at least one color has a pigment solid content of 6 with respect to the total mass of the ink. The ink jet printer according to claim 1 or 2, wherein the total amount of resin solids is 0.0% by mass or more and 6.0% by mass or more. During image formation, the ink-jet printer according to any one of claims 1 to 3, characterized in that it has a heating mechanism for heating the recording medium. An inkjet head cleaning liquid used in the ink jet printer according to any one of claims 1-4, ink jet head cleaning liquid, wherein at least the surface tension contains a solvent and a basic compound of less than 35 mN / m .

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