JP6115020B2 - Inkjet image forming method - Google Patents

Description

  The present invention relates to an inkjet image forming method.

  Currently, the mainstream printing methods are screen printing and roller printing. On the other hand, as a method for producing a small amount of various products, an ink-jet printing system (ink-jet printing method) is becoming widespread. The types of color materials used in inkjet printing inks are mainly acid dyes, disperse dyes, reactive dyes or pigments. Of these, printing inks containing reactive dyes are widely applied to cotton, silk, and the like, and consume much.

  The reactive dyes used in inkjet printing inks are roughly classified into two types, mainly vinyl sulfone type and monochlorotriazine type. In general, the monochlorotriazine type is excellent in hue and image fastness but has low reactivity. On the other hand, the vinyl sulfone type has high reactivity and color density (see Patent Documents 1 to 5).

  Ink-jet textile printing ink needs to have a low viscosity in order to be ejected from an ink-jet recording head. Therefore, it is desirable that the amount of the dye contained in the inkjet printing ink is small. In this respect, it is preferable to perform ink jet printing using a vinyl sulfone type reactive dye having high reactivity and color density.

  On the other hand, the ink jet recording apparatus is required to be increased in size and speed (see Patent Document 6).

Special table 2003-521572 gazette Japanese Patent Laid-Open No. 2002-241539 JP 2010-116566 A Special Table 2002-520498 Japanese Patent No. 4601605 JP 2005-518974 A

  However, when the amount of ink droplets ejected from the ink jet recording head varies, the amount of dye that lands on the recording medium also varies. When a vinyl sulfone type reactive dye is used, the image density on the recording medium varies and becomes conspicuous when the ink ejection varies as compared with the monochlorotriazine type reactive dye. As described above, techniques for increasing the size of the ink jet recording apparatus have been proposed, but there are cases in which variations in the discharge amount increase due to the increase in size.

  The present invention has been made in view of the above circumstances, and suppresses a decrease in ejection properties when a printing ink containing a vinyl sulfone-type reactive dye is ejected from an ink jet recording head, in particular, suppresses variations in image density. With the goal.

The above object of the present invention is achieved by the following configurations.
[1] A step of discharging an inkjet ink containing a reactive dye having a vinyl sulfone group, an organic acid buffer, a humectant, and an aqueous solvent onto a recording medium using an inkjet recording apparatus including an inkjet recording head. An image forming method comprising:
The ink jet recording head includes a head chip including a pressure chamber including a piezoelectric material that converts electrical energy into mechanical energy for ink ejection, and an ink supply channel for supplying the ink jet ink to the head chip. A manifold member to be configured,
The image forming method, wherein the head chip and the manifold are bonded with an adhesive containing an epoxy compound.
[2] The image forming method according to [1], wherein the humectant is alkylene urea.
[3] The image forming method according to [1] or [2], wherein the printing speed is 100 square meters or more per hour.

  According to the image forming method of the present invention, even when high-speed printing is performed, it is possible to provide an image with less ink jetting drop, particularly an image with little variation in image density.

It is a perspective view which shows an example of an inkjet recording device. It is a disassembled perspective view which shows an example of an inkjet recording head.

1. Ink-jet printing ink The printing ink contains at least a reactive dye having a vinyl sulfone group, an organic acid buffer, a humectant, and an aqueous solvent.

<Vinyl sulfone type reactive dye>
The dye contained in the textile printing ink used in the present invention is a reactive dye having a vinyl sulfone group (vinyl sulfone type). A vinylsulfone type reactive dye is characterized by high reactivity and color density compared to a monochlorotriazine type reactive dye.

The vinyl sulfone-type reactive dye is a compound having an equilibrium relationship between the following general formula (1) and the structure of the following general formula (1 ′).
D—SO ₂ —CH ₂ CH ₂ —O—SO ₃ Na (1) ⇔ D—SO ₂ CH═CH ₂ + HO—SO ₃ Na (1 ′)
[Wherein D represents a pigment matrix]

  The vinyl sulfone type reactive dye reacts with the recording medium. For example, the hydroxyl group of the recording medium undergoes a nucleophilic addition reaction with the vinyl group of the vinyl sulfone type reactive dye, and the vinyl sulfone type reactive dye is dyed onto the recording medium.

  The vinyl sulfone type reactive dye used in the present invention may have one or two or more vinyl sulfone groups.

Examples of vinyl sulfone type reactive dyes include, but are not limited to:
C. I. Reactive Yellow 13, 14, 17, 57, 174, 184,
C. I. Reactive Orange 7, 16, 72, 125,
C. I. Reactive Red22, 22: 1, 23, 49, 111, 180, 194, 195, 198, 222, 223, 227, 240, 241, 261,
C. I. Reactive Violet 4, 5,
C. I. Reactive Blue 6, 19, 21, 27, 36, 194, 221, 222, 225, 231, 238,
C. I. Reactive Brown 9, 31,
C. I. Reactive Black 2, 5, 31

  Although not particularly limited, the content of the vinyl sulfone reactive dye is preferably 3% by mass or more and less than 20% by mass with respect to the entire ink. In particular, when a plurality of printing inks of the same color are used, the content of the vinylsulfone reactive dye in the printing ink having the highest dye concentration is preferably 10% by mass or more and less than 20% by mass. When the content of the vinyl sulfone type reactive dye is less than 3% by mass, the color density on the recording medium is low. On the other hand, when the reactive dye is 20% by mass or more, the ink viscosity is increased and the ejection property is decreased.

<Organic acid buffer>
The organic acid buffer is a solution having a property (buffering action) that the pH does not change greatly even when an acid or a base is added from the outside. As a method of keeping the pH of the buffer solution constant (to some extent), it is common to make a weak acid (such as acetic acid) and its salt (such as sodium acetate) coexist. Even when some acid or base is added to the solution, or when the solution concentration changes due to evaporation or dilution of the solution, the pH hardly changes. Further, the pH of the buffer solution can be freely determined to some extent by the combination of contained substances and the content ratio.

  It is preferable to adjust the pH of the printing ink mainly composed of the vinylsulfone type reactive dye used in the present invention to 3-7. The organic acid buffer for adjusting the pH of the ink to the above range preferably contains citric acid, phthalic acid, succinic acid, or phosphoric acid and its metal salt.

  The content of the organic acid buffer is preferably 0.1 to 2.0% by mass with respect to the entire ink. When the content of the organic acid buffer is less than 0.1% by mass, it is difficult to make the pH of the printing ink constant. On the other hand, when the content of the organic acid buffer is more than 2.0% by mass, the ink viscosity increases, and the ejectability from the ink jet recording head decreases.

  When the printing ink containing the vinylsulfone type reactive dye is used and the ejection from the ink jet recording head is continued, the ejection stability may be lowered. When the cause was analyzed, it was found that the adhesive inside the ink jet recording head was swollen. Since the volume of the pressure chamber fluctuates due to swelling of the adhesive inside the ink jet recording head, it is considered that the amount of ink droplets varies when ejection from the ink jet recording head is continued. On the other hand, since the textile printing ink used in the present invention contains an organic acid buffer, swelling of the adhesive can be suppressed. Furthermore, the decomposition of the ink itself can be suppressed.

<About moisturizer>
By including a moisturizing agent in the textile printing ink used in the present invention, evaporation of moisture in the ink can be suppressed.

  Examples of humectants include urea, alkylene urea, polyhydric alcohols (eg, ethylene glycol, diethylene glycol, triethylene glycol or tetraethylene glycol, 1,2-propylene glycol, dipropylene glycol, glycerin, etc.) or N-methyl-2 -Pyrrolidone and the like are included. Among these, urea or alkylene urea is preferable, and alkylene urea is more preferable. When urea is used as a humectant, urea is decomposed into ammonia and carbon dioxide when stored over time to generate gas. This is because if the gas is absorbed by the ink, the ink ejection property is likely to be lowered.

  Examples of alkylene urea include methylene urea, ethylene urea, 1,3-propylene urea, hydantoin, 1,3-tetramethylene urea and the like. Among these, ethylene urea is preferable.

  The content of the humectant is preferably 0.1 to 10% by mass with respect to the whole ink. By setting the content of the humectant within the above range, it is possible to prevent the nozzle surface of the ink jet recording head from being dried and to suppress a decrease in the ink ejection property.

<Aqueous solvent>
The aqueous solvent used in the present invention contains at least water, and is preferably a mixture of water and a water-soluble organic solvent.

Examples of water-soluble organic solvents are
Alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, t-butanol),
Polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol),
Amines (e.g., ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyl Diethylenetriamine, tetramethylpropylenediamine),
Amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.),
Heterocycles (for example, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, etc.), sulfoxides (for example, dimethyl sulfoxide), etc. It is.

  The content of the water-soluble organic solvent is preferably 5 to 50% by mass with respect to the whole ink. By setting the content of the water-soluble organic solvent in the above range, clogging due to drying on the ink jet recording head nozzle surface can be suppressed.

  The inkjet ink used in the present invention contains water as a main component. The total content of the aqueous solvent, which is a mixture of water and a water-soluble organic solvent as a main component, is preferably 50 to 96.8% by mass with respect to the entire ink, for example.

<Surfactant>
The textile printing ink used in the present invention preferably further contains a surfactant.

  Examples of surfactants that can be used in the present invention include dialkyl sulfosuccinates, alkyl naphthalene sulfonates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene Examples include, but are not limited to, polyoxypropylene block copolymers, alkylamine salts, quaternary ammonium salts, silicon surfactants, or fluorine surfactants. Among these, anionic or nonionic surfactants are preferable; among nonionic surfactants, acetylene glycol-based surfactants have low foaming properties and can adjust surface tension. This is preferable. Examples of commercially available nonionic surfactants include Olphine E1010 (manufactured by Nisshin Chemical Co., Ltd.) and the like.

  The content of the surfactant is preferably adjusted so that the surface tension of the ink is 30 to 60 mN / m. Specifically, it is preferably 0.0001 to 5% by mass with respect to the entire ink.

  The method for measuring the surface tension is described in reference books on general surface chemistry and colloid chemistry. For example, New Experimental Chemistry Course Volume 18 (Interface and Colloid), The Chemical Society of Japan, published by Maruzen Co., Ltd. 68-117 can be referred to. More specifically, it can be determined using a ring method (Dunoi method) or a vertical plate method (Wilhelmy method). The surface tension of the textile printing ink used in the present invention can be measured using a surface tension meter CBVP type A-3 type (Kyowa Kagaku Co., Ltd.).

<Other additives>
In the textile printing ink used in the present invention, an antiseptic and an antifungal agent can be added to the ink in order to maintain long-term storage stability of the ink. The preservative and the antifungal agent are not particularly limited, and for example, aromatic halogen compounds (for example, Preventol CMK), methylene dithiocyanate, halogen-containing nitrogen sulfur compounds, 1,2-benzisothiazolin-3-one (for example, PROXEL) GXL).

<Physical properties of textile printing ink>
The textile printing ink used in the present invention is preferably used for inkjet.

  The textile printing ink used in the present invention preferably has an ink viscosity at 25 ° C. of 1 to 40 mPa · s, more preferably 4 to 40 mPa · s, and more preferably 4 to 20 mPa · s from the viewpoint of ejection properties. More preferably.

  The surface tension of the ink at 25 ° C. is preferably 30 to 60 mN / m. When the surface tension is less than 30 mN / m, the wettability of the ink with respect to the recording medium is too high, so that the ink droplets that have landed on the recording medium are coalesced and the image is likely to bleed. On the other hand, when the surface tension is more than 60 mN / m, the wettability of the ink with respect to the recording medium is lowered, and the ink penetration force is likely to be lowered.

  The textile printing ink used in the present invention is preferably adjusted to a pH of 3 to 7 in order not to swell the adhesive inside the ink jet recording head as described above.

2. Manufacturing method of textile printing ink The textile printing ink used in the present invention is a mixture of the above-mentioned reactive dye having a vinyl sulfone group, an organic acid buffer, a humectant, an aqueous solvent, and other components as required. Manufactured through steps.

3. Inkjet recording apparatus The image forming method of the present invention can be performed using an inkjet recording apparatus. Hereinafter, each recording apparatus will be described with reference to the drawings, but the ink jet recording apparatus is not limited thereto.

<Whole inkjet recording apparatus>
FIG. 1 is a perspective view of the ink jet recording apparatus 1. The ink jet recording apparatus 1 includes a head carriage 4 on which a plurality of ink jet recording heads 3 (see FIG. 2) are mounted, and a main carriage 4 that moves along a horizontal direction orthogonal to the recording medium conveyance direction (arrow F direction). It has a scanning device 5, a transport device 20 that transports the recording medium in the direction of arrow F, and a frame 100 that supports the entire device. The horizontal direction along the conveyance direction of the recording medium is defined as the Y-axis direction, the horizontal direction along the conveyance direction of the head carriage 4 is defined as the X-axis direction, and the vertical vertical direction is defined as the Z-axis direction.

(flame)
As shown in FIG. 1, the frame 100 includes a rectangular main body portion 101 installed along the X-axis direction, a first base portion 102 that supports one end portion in the X-axis direction of the main body portion 101, and the X-axis direction and the like. It is comprised from the 2nd base part 103 which supports an edge part. The first base portion 102 and the second base portion 103 are disposed on both sides in the X-axis direction with the above-described transport device 20 interposed therebetween, and the main body portion 101 is installed above the transport device 20.

(Transport device)
The transport device 20 includes a drive roller 21, a driven roller (not shown), a drive motor 22, and a transport belt 23. The axial direction of the driving roller 21 is arranged in the X-axis direction, and a driving motor 22 is attached to one end of the driving roller 21. The drive motor 22 is a drive source for rotating the drive roller 21. The conveyance belt 23 circulates between the driving roller 21 and the driven roller, and conveys the recording medium disposed on the upper surface of the conveyance belt 23 in the direction of arrow F. The drive motor 22 is driven according to control of a control device (not shown).

(Main scanning device)
The main scanning device 5 includes a pair of carriage rails 51 inside the main body 101. These carriage rails 51 are stored along the X-axis direction, and are installed so as to pass above the conveyor belt 23. The carriage rail 51 supports the head carriage 4 so as to reciprocate along the X-axis direction.

(carriage)
The head carriage 4 is a substantially rectangular casing having an open top, and a plurality of inkjet recording heads 3 are mounted on the bottom plate. The arm part 42 at the upper part of the head carriage 4 extends toward both sides in the Y-axis direction, and is installed at the upper part of the carriage rail 51 via a linear guide (not shown).

(Inkjet recording device for high-speed printing)
A plurality of inkjet recording heads 3 are mounted on the head carriage 4. Normally, the head carriage 4 has a separate ink jet recording head 3 corresponding to each color. The number of inkjet recording heads 3 corresponding to each color may be one, or two or more. In order to form an image by inkjet printing at a speed similar to the printing speed of screen printing or roller printing, it is required to increase the number of inkjet recording heads 3 to be mounted.

  However, when a large number of ink jet recording heads 3 are mounted on the head carriage 4, the amount of heat generated from the ink jet recording head 3 or the ink jet recording apparatus 1 increases. Furthermore, since a large number of ink jet recording heads 3 are arranged densely, the generated heat is difficult to escape to the outside, and the ink jet recording head 3 is brought to a high temperature state. When the ink jet recording head 3 reaches a high temperature state, the swelling and dissolution of the adhesive inside the ink jet recording head 3 by the vinyl sulfone reactive dye contained in the printing ink is further promoted. As a result, the volume variation of the pressure chamber becomes larger, and the variation in the amount of ejected ink droplets also becomes larger. As a result, as compared with the case where a large number of ink jet recording heads 3 are not mounted on the head carriage 4, the variation in image density on the recording medium becomes remarkable.

  On the other hand, in the inkjet image forming method of the present invention, a head chip having a pressure chamber and a manifold member are bonded with an adhesive containing an epoxy compound. Therefore, even when a large number of ink jet recording heads 3 are mounted on the head carriage 4 and an image is formed at a high speed, the adhesive inside the ink jet recording head 3 is hardly decomposed and swollen. Therefore, even if the printing ink containing the vinyl sulfone reactive dye is ejected from the heated ink jet recording head 3, the remarkable variation in the image density on the recording medium can be suppressed.

(Image forming method)
The ink jet recording apparatus 1 scans the head carriage 4 from one end portion in the X-axis direction (for example, the side where the head carriage 4 is located in FIG. 1) to the other end portion in the X-axis direction. When this scanning is completed, the driving roller 21 is rotated by a predetermined amount, the recording medium is conveyed by a predetermined distance in the direction of arrow F, and the driving of the driving roller 21 is stopped. Next, the inkjet recording apparatus 1 scans the head carriage 4 from the other end in the X-axis direction to one end in the X-axis direction. When this scanning is completed, the driving roller 21 is rotated again by a predetermined amount, and the recording medium is conveyed by a predetermined distance in the direction of arrow F. Thereafter, the driving of the driving roller 21 is stopped. This operation is repeated and the recording medium is conveyed intermittently. Then, while the head carriage 4 is scanned in both directions of the X axis, ink is ejected from each inkjet recording head 3 mounted on the head carriage 4 to form an image.

<Inkjet recording head>
FIG. 2 is an exploded perspective view of the ink jet recording head. The inkjet recording head 3 includes a head chip 41 in which two inkjet recording head units (hereinafter referred to as “head units”) are stacked, two sets of manifolds 48 a and 48 b that supply ink to the head chip 41, Two sets of head drive substrates 46 that transmit control signals from the control unit to each actuator, and a casing 54 to which the components of the inkjet recording head 3 are attached and fixed.

  The head chip 41 has a long outer shape, and includes an ink supply port 43, an ink flow path (not shown), a pressure chamber (not shown), an actuator (not shown), and a nozzle port (not shown). ,have.

  A large number of nozzle openings are arranged on a nozzle surface (not shown) on the lower end surface of the head chip 41. Ink droplets are ejected from the nozzle opening to form an image on a recording medium.

  The ink supply port 43 has a substantially rectangular shape, and is provided on the outer surface of each of the two head units. The ink supply port 43 and the nozzle port communicate with each other via an ink flow path, and a part of the ink flow path forms a pressure chamber.

  The pressure chamber includes an actuator that converts electrical energy into mechanical energy for ink ejection. By the action of the actuator, the pressure in the pressure chamber is changed, and ink droplets are ejected from the nozzle openings.

  The actuator includes a piezoelectric material. More specifically, it is a piezo element.

  Two sets of manifolds 48 a and 48 b are bonded to both side surfaces of the head chip 41. Ink supplied from a supply ink channel 59 to be described later is supplied to the head chip 41 through a manifold.

  Bonding between the head chip 41 and the manifolds 48a and 48b may be performed at a portion where both are in contact. For example, any part (shaded part A) of the surface of the head chip 41 except the ink supply port 43, the nozzle surface, and the upper end surface on the opposite side of the nozzle surface may be bonded. Alternatively, the manifolds 48a, 48b and the housing 54 may be bonded to a portion (shaded portion B).

  Two sets of head drive substrates 46 are connected to each actuator via a flexible wiring board 47. Thereby, a control signal from a control unit (not shown) is transmitted to each actuator of the head chip 41.

  The components of the inkjet recording head 3, such as the head chip 41, the manifolds 48a and 48b, and the head drive substrate 46, are attached to the housing 54 and fixed. The housing 54 is covered with a cover (not shown). Further, the casing 54 includes a supply ink channel 59 for supplying ink to the manifolds 48a and 48b, a first communication channel 61 for communicating the manifolds 48a and 48b with the atmosphere, and manifolds 48a and 48b. A second communication channel 64 is provided for communicating 48b with the atmosphere.

  In the present invention, the adhesive used for bonding the head chip 41 and the manifolds 48a and 48b is an adhesive containing an epoxy compound. The adhesive containing an epoxy-based compound includes an epoxy resin (main agent) and a curing agent, and may be a one-component type or a two-component type in which both are separated.

  Examples of the main agent include bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, triazine skeleton epoxy resin, or glycidylamine type epoxy resin. Examples of the curing agent include an amine curing agent, a polyaminoamide curing agent, an acid anhydride curing agent, a dicyandiamide curing agent, a polymercaptan curing agent, or an imidazole curing agent. The details of these materials are described in detail in “New Epoxy Resin Handbook I” published by Masaki Shinbo and are widely used.

  As a result of studies by the present inventor, a printing ink containing a vinylsulfone reactive dye can form a good image in the initial stage of use, but gradually forms a normal image when image formation is continued with an inkjet recording apparatus over a long period of time. It turned out to be impossible. This is presumed that if image formation is continued for a long time using the textile printing ink, the pH of the ink is low, so that the adhesive inside the ink jet recording head easily swells and dissolves, and the volume of the pressure chamber fluctuates. . If the amount of ejected ink droplets varies due to the volume variation of the pressure chamber, the amount of dye that lands on the recording medium also varies. When the ink discharge amount varies, the variation in image density on the recording medium becomes remarkable. In particular, when a large inkjet recording apparatus is used, the variation in the discharge amount tends to increase.

  By adjusting the pH of the printing ink containing the vinylsulfone type reactive dye to weak acidity (pH 3 to 7), swelling and dissolution of the adhesive can be suppressed to some extent. However, when the textile printing ink is used over a long period of time, the ink discharge amount still tends to vary.

  The ink jet recording apparatus used in the present invention uses an adhesive containing an epoxy compound as an adhesive inside the ink jet recording head. As a result, the structure of the adhesive hardly changes even when the low pH ink and the adhesive come into contact with each other, so that the ink does not easily swell or dissolve. Therefore, the volume fluctuation of the pressure chamber in the ink jet recording head is small, and variations in the ink ejection amount can be suppressed. Further, even when a large-sized ink jet apparatus is used, variations in the discharge amount can be suppressed.

4). INKJET IMAGE FORMING METHOD The present invention is an image forming method using an inkjet printing ink containing a vinyl sulfone type reactive dye and the like, and is performed in the following steps.

<Pretreatment process>
The image forming method of the present invention preferably includes a pretreatment step of applying a pretreatment agent to the recording medium to be used. Examples of the method for applying the pretreatment agent to the recording medium include a pad method, a coating method, and a spray method. With these coating methods, the pretreatment agent can be coated on the recording medium.

  The pretreatment agent may be appropriately selected according to the printing ink and recording medium to be used, and is not particularly limited, but is preferably a printing paste, and more preferably an alkaline printing paste. This is because the presence of an appropriate alkaline substance is necessary for reliably printing the printing ink containing the reactive dye on the recording medium.

  Examples of printing pastes include natural gums such as guar and locust bean, starches, seaweeds such as sodium alginate, funari, plant skins such as pectic acid, methyl fibrin, ethyl fibrin, hydroxyethylcellulose, carboxymethylcellulose, etc. Fibrin derivatives, roasted starch, alpha starch, carboxymethyl starch, carboxyethyl starch, hydroxyethyl starch, and other processed starches, processed natural gums such as shiraz gum and roast bean gum, algin derivatives, polyvinyl alcohol, polyacrylic acid Synthetic pastes such as esters, emulsions and the like are included.

  The coating amount (squeezing ratio) of the pretreatment agent or the amount of printing paste contained in the pretreatment agent is appropriately set according to the type of recording medium and its use.

  The recording medium is preferably a fabric. The fabric includes woven fabric made of fibers that can be dyed with reactive dyes such as cotton, hemp, viscose, wool, silk, and nylon; nonwoven fabric; these fibers and polyester fibers, acetate fibers, polypropylene fibers, A blended woven fabric made of synthetic fibers such as vinylon fibers; a blended nonwoven fabric and the like are included. In the image forming method of the present invention, these woven fabrics or non-woven fabrics may be conventionally known or pretreated.

  The pretreatment agent may further contain a hydrotropic agent. Examples of hydrotropic agents include ureas, dimethylureas, thioureas, monomethylthioureas, or alkylureas such as dimethylthiourea. By adding the hydrotropic agent, the image density is improved. Moreover, the addition amount can be reduced by adding urea, alkylurea, and thiourea to the pretreatment agent in combination. From the viewpoint of uniform dyeing, it is preferable to add thiourea.

  Although the addition amount of the hydrotropic agent to the pretreatment agent is not particularly limited, it is preferably 15% by mass or less, more preferably 10% by mass or less based on the entire pretreatment agent. By adding the hydrotropic agent, the stability of the pretreatment agent is improved, and cracks of the recording medium coated with the pretreatment agent can be prevented. When the hydrotropic agent is contained in the printing ink, the addition of the hydrotropic agent to the pretreatment agent can be reduced or eliminated. The pretreatment agent may further contain a pH adjuster. Preferable examples of the pH adjuster include acid ammonium salt, ammonium sulfate, ammonium tartrate, dibasic sodium phosphate, sodium carbonate and the like. By adding a pH adjuster, it is possible to improve hue stabilization and dyeability. The amount of the pH adjuster added to the pretreatment agent is not particularly limited, but is preferably about 0.2 to 5.0% by mass, and more preferably about 0.5 to 3.0% by mass.

<Image formation process before color development reaction>
The image forming method of the present invention ejects ink droplets of textile printing ink from an inkjet recording head toward a recording medium using an inkjet recording apparatus. The droplets of the inkjet ink ejected from the nozzle surface of the inkjet recording head land on a certain area (landable area) of the recording medium coated with the pretreatment agent.

  The ink jet recording head is scanned as many times as necessary to eject the ink jet ink to one landable area, and then the recording medium is appropriately conveyed. Again, an ink jet ink droplet is ejected and landed on the landable area adjacent to the one landable area by the ink jet recording head. By repeating the above operation, a pre-color-reaction image composed of an aggregate of ink-jet ink droplets is formed on a recording medium coated with a pretreatment agent.

<Coloring process>
The image forming method of the present invention preferably further includes a coloring step. The color development step is a step in which the dye in the pre-coloration reaction image that is not sufficiently adsorbed and fixed in the recording medium is adsorbed and fixed on the recording medium to develop the original hue of the ink. The method may be a conventionally known method, and includes, for example, a steaming method, an HT steaming method, a thermofix method, an alkali pad steam method, an alkali blotch steam method, an alkali shock method, or an alkali cold fix method. These are appropriately selected depending on the printing ink, the recording medium, and the like. The recording medium on which the pre-coloring reaction image has been formed may be colored immediately or after a lapse of time.

<Washing process>
The image forming method of the present invention may further include a cleaning step. By washing, the dye that could not be dyed on the recording medium after the color development step of the recording medium can be removed. The method is appropriately selected depending on the textile printing ink or the recording medium. For example, the cellulose fiber is generally washed with water and hot water, then treated with a soaping bath containing a nonionic detergent, and then washed with hot water and water.

<Drying process>
The image forming method of the present invention may further include a drying step. The drying process is performed after the washing process. The drying method is not particularly limited, and the washed recording medium is squeezed, dried, or dried using a dryer (heat roll, iron, etc.).

  In the following, the invention will be described in more detail with reference to examples. These examples do not limit the scope of the present invention.

<Preparation of materials>
(Reactive dye)
C. I. Reactive Blue 21 (Vinylsulfone type)
C. I. Reactive Blue 72 (monochlorotriazine type)
(Water-soluble organic solvent)
Ethylene glycol Propylene glycol Glycerin (Organic acid buffer)
Citric acid Citric acid 3Na dihydrate Sodium dihydrogen phosphate Disodium hydrogen phosphate (humectant)
Urea Ethyleneurea 1,3-propyleneurea (surfactant)
Olphine E1010 (manufactured by Nissin Chemical)
(water)
Ion exchange water

<Preparation of blue ink>
(Preparation of ink B-1)
As a reactive dye, C.I. I. 15 parts by weight of reactive blue 72, 15 parts by weight of ethylene glycol, 10 parts by weight of propylene glycol, 4.5 parts by weight of glycerin, 0.05 parts by weight of citric acid as an organic acid buffer Parts, 0.5 parts by mass of citric acid 3Na dihydrate, 1.5 parts by mass of ethylene urea as urea, and 0.05 parts by mass of Orphine E1010 as a surfactant are mixed together with ion-exchanged water. Was prepared to be 100 parts by mass to obtain Ink B-1.

(Preparation of inks B-2 to B-13)
Inks B-2 to B-13 were prepared in the same manner as ink B-1, except that the ink composition was changed as shown in Table 1.

<Ink physical properties>
The viscosity, surface tension, and pH at 25 ° C. of inks B-1 to B-13 prepared by the above method were measured by the following methods.

(Measurement of viscosity)
For the measurement of the viscosity, the thermostatic bath was set to 25 ° C. using a rotary viscometer with a thermostatic bath (manufactured by Toki Sangyo Co., Ltd .: VISCOMETER TV-33, VISCOMATE VM-150III). The viscosity of the ink before heating (initial stage) at 25 ° C. after 1 minute from the start of measurement was measured. The measurement results are shown in Table 1.

(Measurement of surface tension)
The surface tension of the ink was measured at 25 ° C. using a CBVP type A-3 type manufactured by Kyowa Interface Science Co., Ltd. The measurement results are shown in Table 1.

(Measurement of pH)
The pH of the ink was measured using pH METER HM-20S manufactured by Toa Denpa Kogyo. The measurement results are shown in Table 1.

<Evaluation of ink storage stability>
The ink prepared above was placed in a constant temperature bath at 60 ° C., and the ink viscosity after one week was measured. The rate of change was evaluated according to the following criteria, compared to the viscosity before entering the thermostatic bath in advance. The obtained evaluation results are shown in Table 1.
○: Change rate is within 5% △: Change rate is over 5% to within 10% ×: Change rate is over 10%

<Inkjet recording head>
An ink jet recording head (heads a, b, c) was manufactured by bonding a polyethyleneimide manifold member used for manufacturing the ink jet recording head shown in FIG. 2 and a head chip. The types of adhesive used for bonding and the bonding conditions are as follows.

(Head a)
<Adhesive type: Epoxy adhesive>
Epicoat 807 (bisphenol F: epoxy equivalent 165, manufactured by Japan Epoxy Resin Co., Ltd.): 100 parts by mass 1-benzyl-2-methylimidazole: 10 parts by mass << Adhesion conditions >>
Heating temperature during bonding: 45 ° C
Heating time: 13 hours

(Head b)
<< Type of adhesive: Acrylate adhesive >>
Butyl acrylate: 90 parts by mass 2-hydroxyethyl acrylate: 10 parts by mass These were solution polymerized in a mixed solvent of toluene and butyl acetate (1: 1) at 85 ° C. for 8 hours using benzoin peroxide as a catalyst.
<Adhesion conditions>
Heating temperature during bonding: 45 ° C
Heating time: 16 hours

(Head c)
<Adhesive type: Urethane adhesive>
UM700S (solvent-free urethane adhesive manufactured by Cemedine Co., Ltd.)
<Adhesion conditions>
Heating temperature during bonding: 35 ° C
Heating time: 3 hours

The head unit has a nozzle diameter of 28 μm, a number of nozzles of 256, a minimum liquid amount of 14 pl, and a nozzle density of 180 dpi (where dpi represents the number of dots per 2.54 cm). The heads a, b, and c are ink jet recording heads including a head chip in which two head units are bonded to each other while being shifted by half the dot pitch (360 dpi). The produced heads a, b, and c all have a resolution of 360 dpi and a driving frequency of 12 kHz. As shown in the following formula 1, an ink jet printer equipped with this ink jet recording head can print at a printing speed of 110.1 square meters per head.
Formula 1: Drive frequency 12 kHz × 3600 seconds × 512 nozzles × area per dot (70.6 μm 2) = 110.1 m ² / hour

<Printer>
A 4-color printer (16 total number of ink jet recording heads) equipped with four heads a per color and a textile printing ink jet printer (printer 1) having a printing width of 1.6 m were prepared. A printing ink jet printer (printer 2) in which the ink jet recording head of the printer 1 was changed from the head a to the head b was prepared. A textile inkjet printer (printer 3) was prepared by changing the inkjet recording head of the printer 1 from head a to head c.

Example 1
<Pretreatment>
A pretreatment agent containing 20 g / L sodium alginate, 30 g / L sodium carbonate and 100 g / L urea was applied to a cotton cloth processed with mercerization (cotton 200, manufactured by Tokai Denko Co., Ltd.) by a pad method (squeezing ratio: 70%). )did. Thereafter, the cotton cloth was dried.

<Image formation processing before color development>
Using the above three types of printers, one of the four blue ink heads was filled with ink B-1 to B-13. Inks B-1 to B-13 were discharged to perform pre-color image formation. The printing area per hour is 110.1 square meters.

<Coloring treatment>
The cotton fabric on which an image was formed before color development was left for 24 hours in an environment of a temperature of 25 ° C. and a relative humidity of 50%. Then, the coloring process for 12 minutes was performed in the saturated steam of 103 degreeC.

<Cleaning process>
The developed cotton fabric was washed with cold water for 5 minutes and with warm water at 65 ° C. for 5 minutes. Thereafter, it was washed by boiling at 85 ° C. using a soaping agent, rinsed again with warm water at 65 ° C. for 5 minutes and with cold water for 5 minutes, and then dried.

<Image evaluation>
(Image density evaluation)
A color development process similar to that of a cotton cloth on which an unprinted cotton cloth was printed was performed, a printed cloth was placed on 20 sheets, the image density in status T was measured using an X-Rite 938 Spectrodensitometer, and evaluation was performed according to the following criteria. The obtained evaluation results are shown in Table 2.
○: Image density is 1.0 or more Δ: Image density is 0.5 or more and less than 1.0 ×: Image density is less than 0.4

(Evaluation of variation in image density)
Printing with an area of 10 square meters was performed using the printer. Using an X-Rite 938 Spectrodensitometer, the image density in status T was measured at 1 meter intervals (10 points in total). Evaluation was made according to the following criteria from the variation of the measured 10 points of the average value. The obtained evaluation results are shown in Table 2.
◎: Image density variation ± 2% or less ○: Image density variation more than ± 2% ± 5% or less Δ: Image density variation more than ± 5% ± 10% or less ×: Image density variation ± 10% % Over 20% or less

(Continuous injection property evaluation)
Using the printer, solid images were printed continuously for 1 hour. After the printing was completed, a nozzle check pattern was printed to confirm the number of missing nozzles and evaluated according to the following criteria. The obtained evaluation results are shown in Table 2.
◎: No nozzle missing ○: Nozzle missing △: Nozzle missing 2-5 ×: Nozzle missing 6 or more

(Intermittent injection evaluation)
Each of the prepared inks was allowed to stand for 16 hours in an ink jet recording head in an environment of 23 ° C. and 20% RH. Thereafter, ink was ejected, and the flying state of the ink droplets was observed and evaluated according to the following criteria. The obtained evaluation results are shown in Table 2.
◎: All 512 nozzles were ejected ○: Flying bend occurred at 1 to 5 nozzles, but wiping operation of inkjet recording head was performed once to restore normal ejection state △: Flying bend at 1 to 5 nozzles The ink jet recording head suction and wiping operations were performed once, and the normal ejection state was restored. X: Flying bending occurred at 6 nozzles or more, but the ink jet recording head suction and wiping operations were performed twice. To restore normal injection

(Color variation)
Each ink prepared above was filled in an ink jet recording head. Thereafter, a solid image was printed on a cotton cloth every 1 square meter for 5 consecutive days, and color development was performed. La * b * measurement was performed on the five cotton fabrics thus prepared. With reference to the values of L, a *, b * of the cotton fabric created on the first day, the color difference (ΔE: difference of L, difference of a *, difference of b *, respectively) for the cotton fabric on and after the second day Squared and taking the square root thereof) was calculated, and the maximum value was evaluated according to the following criteria. The obtained evaluation results are shown in Table 2.
◎: ΔE (color difference) is within 1 ○: ΔE (color difference) is more than 1 and less than 2 △: ΔE (color difference) is 2 or more and less than 5 ×: ΔE (color difference) is 5 or more

  Comparative Example 1-1 contains a monochlorotriazine type reactive dye as a dye, citric acid and citric acid 3Na dihydrate as an organic acid buffer, and ethylene urea as a moisturizing agent. In addition, an epoxy adhesive is used for manufacturing the ink jet recording head. Looking at the evaluation results, “image density” and “image density variation” are somewhat low and inferior to “intermittent ejection”, but other evaluation items show good results.

  Example 1-2 contains a vinyl sulfone type reactive dye and an organic acid buffer. In contrast to Example 1-2, Comparative Example 1-2 contains a vinyl sulfone-type reactive dye, but no organic acid buffer is added. For this reason, the pH of the ink during storage is lowered, and the reactivity of the vinyl sulfone type reactive dye is lowered, so that “ink storage stability” is lowered and “image density” is slightly lowered. In addition, the reactivity of the dye landed on the cotton cloth varies locally, “image density variation” in the same plane decreases, and “color variation” greatly deteriorates. On the other hand, Example 1-2 has good evaluation results of “ink storage stability”, “image density”, “image density variation”, and “color variation”. From this result, it can be seen that by including an organic acid buffer in the ink, good results can be obtained even when a vinyl sulfone reactive dye is used.

  In Comparative Example 1-3, the dye was changed to a monochlorotriazine type reactive dye and the humectant was changed from 1,3-propylene urea to urea. Although the “continuous injection property” was slightly improved as compared with Comparative Example 1-2, other evaluation results were not improved. Rather, “intermittent injection” is slightly reduced. Urea has a moisturizing action, but is decomposed by storage over time to generate gas. Therefore, it is considered that “intermittent injection” is lowered.

  Since Comparative Example 1-4 contains a vinyl sulfone reactive dye, the “image density” is good. However, since the organic acid buffer and the humectant are not contained, evaluation results other than “image density” are low. On the other hand, Examples 1-1 to 1-3 containing an organic acid buffer and a humectant have good evaluation results other than “image density”. For this reason, it is very effective to add an organic acid buffer solution and a humectant to an ink containing a vinyl sulfone type reactive dye.

  Comparative Example 1-9 has the same ink composition as Comparative Example 1-4. However, Comparative Example 1-9 is different in that the adhesive used for manufacturing the ink jet recording head is urethane, and Comparative Example 1-4 is epoxy. Similar to Comparative Example 1-4, Comparative Example 1-9 has a low evaluation result other than “image density”. Even when the results of Comparative Example 1-4 and Comparative Example 1-9 are compared, only by changing the adhesive used for manufacturing the ink jet recording head to an epoxy system, “variation in image density”, “continuous injection”, It can also be seen that “intermittent ejection” is not improved.

  Compared with Comparative Example 1-2, Comparative Example 1-5 changed the moisturizer from 1,3-propylene urea to ethylene urea. In addition, the adhesive used for producing the ink jet recording head was changed from an epoxy type to an acrylic type. Thereby, in Comparative Example 1-5, the “continuous injection property” is lowered. This is presumably because stable injection properties could not be secured due to the penetration and swelling of the ink with respect to the acrylic adhesive.

  In contrast to Comparative Example 1-5, Comparative Example 1-6 contained an organic acid buffer in the ink, but the adhesive used to fabricate the ink jet recording head remained acrylic. As a result, the “ink storage stability” of Comparative Example 1-6 is good, but the adhesive swells and the “continuous injection property” is still not good.

  Further, as in Comparative Examples 1-6 and 1-7, even when an ink containing a vinyl sulfone-type reactive dye, an organic acid buffer, and a humectant is used, the adhesive used for manufacturing the ink jet recording head is different. In the case of an acrylic or urethane type, the adhesive swells and the “continuous injection property” remains lowered.

  Furthermore, if the moisturizer is not added from the ink of Comparative Example 1-7, the evaluation result of “intermittent ejection” is also lowered (Comparative Example 1-8).

  In comparison with these comparative examples, Examples 1-1 to 1-3 are all good in evaluation results.

(Example 2)
Four blue ink heads of the printer used in Example 1 were filled with inks B-1 to B-13, respectively, and the same evaluation as in Example 1 was performed. The obtained evaluation results are shown in Table 3. The printing area per hour is four times that of the first embodiment.

  In Example 2, the evaluation results are generally lowered, and the evaluation results of “continuous injection” and “intermittent injection” are particularly low. Further, since the number of ink jet recording heads is increased, the evaluation results of “image density” and “image density variation” are markedly lowered as compared with the first embodiment.

(Example 3)
Ink B-1 to B-13 were respectively filled in 4 heads for yellow, red, blue, and black ink of the printer used in Example 1, and a total of 16 heads, and the same evaluation as in Example 1 was performed. The obtained evaluation results are shown in Table 4. The printing area per hour is 16 times that of the first embodiment.

  In contrast to the second embodiment, the third embodiment further increases the number of ink jet recording heads and increases the printing speed per hour. Although the “image density” of Comparative Examples 3-1 to 3-10 is better than the other evaluation items from the evaluation results, “image variation”, “continuous ejection” and “intermittent ejection” are examples. Compared to 2, it is generally lower. Further, “color variation” is also decreasing.

  As the number of ink jet recording heads increases, the amount of heat generated by the ink jet recording head due to ejection increases. Since the ink jet recording heads are closely arranged, the heat on the nozzle surface is difficult to escape and the ink on the nozzle surface is likely to dry. Furthermore, the adhesive used for manufacturing the ink jet recording head is decomposed and swollen, thereby varying the amount of ink discharged. For this reason, the emissivity is lowered, and the image density varies.

  In contrast, Examples 3-1 to 3-3 are inferior to Examples 1-1 to 1-3 and Examples 2-1 to 2-3, but “image density” and “image variation”. ”,“ Continuous ejection ”,“ intermittent ejection ”and“ color fluctuation ”are excellent. From this result, it was confirmed that the effect of the present invention that can suppress the decrease in the ejection property and the variation in the image density can be confirmed even when high-speed printing is performed using the inkjet printing ink.

  According to the present invention, it is possible to provide ink jet image formation that can suppress a drop in ejection properties, particularly a variation in image density.

DESCRIPTION OF SYMBOLS 1 Inkjet recording device 3 Inkjet recording head 4 Head carriage 5 Main scanning device 20 Conveyance device 21 Drive roller 22 Drive motor 23 Conveyance belt 41 Head chip 42 Arm part 43 Ink supply port 46 Head drive substrate 47 Flexible wiring board 48a, 48b Manifold 51 Carriage rail 54 Housing 59 Supply ink flow path 61 First communication flow path 64 Second communication flow path 100 Frame 101 Main body section 102 First base section 103 Second base section

Claims (3)

An image including a step of discharging an inkjet ink containing a reactive dye having a vinyl sulfone group, an organic acid buffer, a humectant, and an aqueous solvent to a recording medium using an inkjet recording apparatus including an inkjet recording head. A forming method comprising:
The pH of the inkjet ink is 3 or more and less than 6,
The ink jet recording head includes a head chip including a pressure chamber including a piezoelectric material that converts electrical energy into mechanical energy for ink ejection, and an ink supply channel for supplying the ink jet ink to the head chip. A manifold member to be configured,
The image forming method, wherein the head chip and the manifold are bonded with an adhesive containing an epoxy compound.   The image forming method according to claim 1, wherein the humectant is alkylene urea.   3. The image forming method according to claim 1, wherein the printing speed is 100 square meters or more per hour.

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