JP5804713B2 - Ink for inkjet recording apparatus and inkjet recording method - Google Patents

Description

  The present invention relates to an ink for an ink jet recording apparatus and an ink jet recording method.

  In recent years, rapid progress in recording technology has made it possible to obtain high-definition image quality comparable to silver halide photography, so inkjet recording apparatuses that form images by the inkjet recording method have been widely used as image forming apparatuses. ing.

  For such an ink jet recording apparatus, it is strongly desired to increase the speed of image formation. However, when image formation is performed at high speed in an ink jet recording apparatus, the recording medium is discharged through the discharge roller before the ink penetrates the recording medium such as paper, and the ink adheres to the discharge roller (offset). Image defects are likely to occur.

  In order to solve the problem of offset when printing at high speed, it is conceivable to improve the drying property of the ink. However, it is difficult to stably discharge ink droplets from the ink discharge port of the ink jet recording apparatus when the drying property of the ink is increased, when recording is interrupted or when recording is not performed for a long period of time. It becomes difficult to form.

  Thus, there is a need for an ink that can suppress the occurrence of offset due to poor drying and has good intermittent ejection properties that can be stably ejected even when recording is interrupted or recording is not performed for a long period of time.

  Under such circumstances, as an ink in which the problems relating to the suppression of the offset and the intermittent ejection property are solved, for example, a polyhydric alcohol monoalkyl ether containing a colorant and having a vapor pressure at 20 ° C. of 0.1 mmHg or less is 5 There has been proposed an aqueous ink for an ink jet recording apparatus characterized by containing ˜15% by weight and containing 5˜50% by weight of a polyhydric alcohol (Patent Document 1).

JP 09-012945 A

  However, in the ink jet recording apparatus, further speeding up of image formation is required. In such a case, the ink for the ink jet recording apparatus described in Patent Document 1 cannot necessarily solve the problems related to the suppression of offset and the intermittent ejection property. Further, the ink for an ink jet recording apparatus described in Patent Document 1 has a problem that an image appears on the back surface of the recording medium due to the permeation of the ink, and the image is easily exposed.

  The present invention has been made in view of the above circumstances, and can form a good image without see-through, can suppress the occurrence of offset even in the case of forming an image at high speed, and can stably produce ink droplets. It is an object of the present invention to provide an ink for an ink jet recording apparatus having an intermittent ejection property capable of ejecting water. In addition, the present invention is capable of forming a good image with no show-through, capable of forming an image at a high speed while suppressing the occurrence of offset, excellent in the intermittent ejection of ink droplets, and capable of forming a good image. An object of the present invention is to provide an image forming method using a recording apparatus.

  The present inventors have disclosed an ink for an ink jet recording apparatus comprising at least water, a pigment dispersion, and glycol monomethyl ether selected from the group consisting of triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether, and mixtures thereof. In Example 1, a pigment dispersion containing a resin having a molecular weight of 30,000 to 150,000 is used, and the content of glycol monomethyl ether is set to 15% by mass or more based on the mass of the ink. The present inventors have found that the above-mentioned problems can be solved by forming an image using an image, and have completed the present invention. Specifically, the present invention provides the following.

  (1) At least water, a pigment dispersion, and a glycol monomethyl ether selected from the group consisting of triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether, and mixtures thereof, and the pigment dispersion has a molecular weight of 30 Ink for an ink jet recording apparatus, comprising a resin of 1,000,000 to 150,000, wherein the content of the glycol monomethyl ether is 15% by mass or more based on the mass of the ink.

  (2) An image forming method of forming an image by an ink jet recording apparatus using the ink for an ink jet recording apparatus according to (1).

  (3) In the ink jet recording apparatus, the time from when the ink droplets land on the recording medium until the ink landing position of the recording medium reaches the discharge portion for discharging the recording medium The image forming method according to (2), wherein the image forming method is within 1 second.

(4) The image is formed by ejecting the ink droplets onto a recording medium so that the total amount of the ink of one color or a plurality of colors is 30 g / m ² or less. Image forming method.

  (5) The inkjet recording apparatus includes a recording head that discharges the ink droplets using pressure generated in the liquid chamber by voltage control to the piezoelectric element, and the recording method is a line head type recording method. The image forming method according to any one of (2) to (4).

  (6) The image forming method according to any one of (2) to (5), wherein the surface of a member that contacts the printing surface of the inkjet recording apparatus is formed of a water repellent material.

  According to the present invention, it is possible to form a good image without show-through, and even in the case of forming an image at high speed, the occurrence of offset can be suppressed, and the intermittent ejection property can stably eject ink droplets. An ink for an ink jet recording apparatus can be provided. In addition, according to the present invention, it is possible to form a good image without show-through, to form an image at a high speed while suppressing the occurrence of offset, and to form a good image with excellent intermittent ink droplet ejection properties. An ink jet recording method can be provided.

FIG. 1 is a side sectional view showing a schematic configuration of a line head type ink jet recording apparatus. FIG. 2 is a plan view of the conveyance belt of the ink jet recording apparatus shown in FIG. 1 as viewed from above. FIG. 3 is a block diagram showing a configuration of a line head type ink jet recording apparatus. FIG. 4 is an enlarged plan view showing a part of a dot head formed on a line head and recording paper used in an ink jet recording apparatus of a line head type recording system.

  Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. In addition, although description may be abbreviate | omitted suitably about the location where description overlaps, the summary of invention is not limited.

[First Embodiment]
The first embodiment includes at least water, a pigment dispersion, and a glycol monomethyl ether selected from the group consisting of triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether, and mixtures thereof. Relates to an ink for an ink jet recording apparatus, comprising a resin having a molecular weight of 30,000 to 150,000, and having a glycol monomethyl ether content of 15% by mass or more based on the mass of the ink.

  The ink for an ink jet recording apparatus according to the first embodiment (hereinafter also simply referred to as ink) essentially contains water, a pigment dispersion containing a resin having a specific molecular weight, and a specific type of glycol monomethyl ether. Further, the ink for an ink jet recording apparatus of the present invention includes a penetrant that increases the penetrability of the ink into the recording medium, a dissolution stabilizer that stabilizes the dissolved state of the components contained in the ink, and a liquid from the ink, if necessary. It may contain other liquid components of one or more glycol monomethyl ether selected from the group consisting of humectants that suppress the volatilization of the components and stabilize the properties of the ink. Hereinafter, water, pigment dispersion, glycol monomethyl ether, and other liquid components that are essential or optional components included in the ink for an ink jet recording apparatus, and a method for producing the ink for the ink jet recording apparatus are sequentially described. explain.

〔water〕
The ink for an inkjet recording apparatus of the present invention is a water-based ink and essentially contains water. The water contained in the ink is not particularly limited as long as it does not impair the object of the present invention, and water having a desired purity can be appropriately selected from water conventionally used for producing water-based inks. The water content in the ink for an ink jet recording apparatus of the present invention is not particularly limited as long as the object of the present invention is not impaired. The content of water is appropriately changed according to the amount of other components to be described later. The typical water content in the ink is preferably 20 to 70% by mass, more preferably 30 to 60% by mass with respect to the total mass of the ink.

(Pigment dispersion)
The ink for an ink jet recording apparatus of the present invention includes a pigment dispersion containing a pigment as a colorant. The pigment that can be contained in the pigment dispersion is not particularly limited as long as the object of the present invention is not impaired, and can be appropriately selected from pigments that have been conventionally used as colorants in inks for inkjet recording apparatuses. . Specific examples of suitable pigments include C.I. I. Pigment Yellow 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, 193 and the like, C.I. I. Pigment Orange 34, 36, 43, 61, 63, 71 and other orange pigments, C.I. I. Red pigments such as CI Pigment Red 122 and 202, C.I. I. Blue pigments such as CI Pigment Blue 15; I. Purple pigments such as C.I. Pigment Violet 19, 23 and 33; I. And black pigments such as CI Pigment Black 7.

The pigment dispersion contained in the ink for an ink jet recording apparatus of the present invention contains a resin having a molecular weight of 30,000 to 150,000. The molecular weight of the resin contained in the pigment dispersion is a weight average molecular weight ( Mw ) and can be measured by gel filtration chromatography. If the molecular weight of the resin is too small, the back-through tends to occur when an image is formed on the recording medium. If the molecular weight is too large, it is difficult to obtain an ink having excellent intermittent ejection properties.

  A method for producing a pigment dispersion containing a pigment and a resin is not particularly limited as long as the object of the present invention is not impaired, and can be appropriately selected from conventionally known methods. As a suitable method, for example, using a media type wet disperser such as Nano Glen Mill (manufactured by Asada Tekko Co., Ltd.), MSC Mill (manufactured by Mitsui Mining Co., Ltd.), Dino Mill (manufactured by Shinmaru Enterprises Co., Ltd.) In a suitable liquid medium, a pigment and a resin are kneaded to form a pigment dispersion. In the processing by the media type wet disperser, beads having a small particle diameter are used. The particle diameter of the beads is not particularly limited and is typically a particle diameter of 0.5 to 1.0 mm. The material of the beads is not particularly limited, and beads made of a hard material such as zirconia beads are used.

  The amount of the liquid medium used in producing the pigment dispersion is not particularly limited as long as the pigment can be favorably kneaded with the resin. Typically, the use amount of the liquid medium is preferably 1 to 10 times, more preferably 3 to 7 times, the total mass of the pigment and the resin.

  The volume average particle diameter of the pigment contained in the pigment dispersion is preferably from 50 to 200 nm, more preferably from 70 to 150 nm, from the viewpoints of ink color density, hue, ink stability, and the like. The volume average particle diameter of the pigment can be adjusted by adjusting the particle diameter of beads and the treatment time when the pigment and the resin are kneaded. If the volume average particle size is too small, the image density may decrease. If the volume average particle size is too large, clogging of nozzles that discharge ink may occur, or ink discharge performance may deteriorate. There is a case. The volume average particle diameter of the pigment can be measured, for example, using a sample obtained by diluting the pigment dispersion 300 times with ion-exchanged water, using a dynamic light scattering particle size distribution measuring device (manufactured by Sysmex Corporation).

  The resin contained in the pigment dispersion is not particularly limited as long as it has a predetermined molecular weight, and can be appropriately selected from various resins conventionally used in the production of pigment dispersions. Specific examples of suitable resins include styrene-acrylic acid-acrylic acid alkyl ester copolymers, styrene-acrylic acid copolymers, styrene-maleic acid copolymers, and styrene-maleic acid-acrylic acid alkyl ester copolymers. Styrene-methacrylic acid copolymer, styrene-methacrylic acid alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, and the like. . Among these resins, since they are easy to prepare and have excellent pigment dispersion effects, styrene-acrylic acid-alkyl acrylate ester copolymers, styrene-acrylic acid copolymers, styrene-maleic acid-alkyl acrylates. Units derived from styrene, such as ester copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid alkyl ester copolymers, and units derived from acrylic acid, methacrylic acid, acrylic esters, or methacrylic esters A styrene-acrylic resin containing The above resin is obtained by radical polymerization. The molecular weight of the resin can be adjusted according to a known method of adjusting the amount of polymerization initiator used, the polymerization temperature, the polymerization time, or the like.

  The amount of the pigment used is not particularly limited as long as the object of the present invention is not impaired, but typically 1 to 40% by mass is preferable and 5 to 30% by mass is more preferable with respect to the total mass of the ink. If the amount of pigment used is too small, the color density of the ink tends to decrease, and if the amount of pigment used is excessive, the fluidity of the ink is impaired and it may be difficult to form a good image.

[Glycol monomethyl ether]
The ink for an ink jet recording apparatus of the present invention contains glycol monomethyl ether selected from the group consisting of triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether, and mixtures thereof. The amount of glycol monomethyl ether is 15% by mass or more and more preferably 15 to 25% by mass with respect to the total mass of the ink. When the amount of glycol monomethyl ether is excessive, the penetration of the ink may cause an image to appear on the back surface of the recording medium, resulting in image see-through.

  Triethylene glycol monomethyl ether and tripropylene glycol monomethyl ether are excellent in permeability to a recording medium such as paper and excellent in moisture retention of ink. For this reason, the ink for an ink jet recording apparatus of the present invention is less likely to cause an offset because the liquid component in the ink that has landed on the recording medium such as paper quickly penetrates into the recording medium. Since the change hardly occurs, it has a good intermittent ejection property.

[Other liquid components of glycol monomethyl ether]
The ink for an inkjet recording apparatus of the present invention includes, as another liquid component of glycol monomethyl ether, a penetrant that enhances the permeability of the ink into the recording medium, a dissolution stabilizer that stabilizes the dissolved state of the components contained in the ink, And one or more components selected from the group consisting of humectants that suppress the volatilization of the liquid component from the ink and stabilize the viscosity of the ink.

  The penetrant is a liquid component that enhances the permeability of ink into the recording medium. Specific examples of the penetrant include 1,2-hexylene glycol, 1,2-octanediol, 2,4-diethyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol. And diols such as triethylene glycol monobutyl ether and diethylene glycol monobutyl ether. Two or more penetrants can be used in combination. When the ink contains a penetrant, the content of the penetrant is appropriately adjusted according to the type of penetrant. The typical penetrant content is preferably 0.5 to 20% by mass relative to the total mass of the ink.

  The humectant is a component that stabilizes the viscosity of the ink by suppressing the volatilization of the liquid component from the ink. Specific examples of the humectant include polyalkylene glycols such as polyethylene glycol and polypropylene glycol; ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 1,2,6-hexanetriol. Alkylene glycols such as thiodiglycol, 1,3-butanediol and 1,5-pentanediol; glycerin. Among these humectants, glycerin is more preferable because of its excellent effect of suppressing volatilization of liquid components such as water. Two or more kinds of humectants can be used in combination. When the ink contains a humectant, the content of the humectant is preferably 5 to 50% by mass and more preferably 10 to 40% by mass with respect to the total mass of the ink.

  The dissolution stabilizer is a component that compatibilizes the components contained in the ink and stabilizes the dissolved state of the ink. Specific examples of the dissolution stabilizer include 2-pyrrolidone, N-methyl-2-pyrrolidone, and γ-butyrolactone. These dissolution stabilizers can be used in combination of two or more. When the ink contains a dissolution stabilizer, the content of the dissolution stabilizer is preferably 1 to 20% by mass and more preferably 3 to 15% by mass with respect to the total mass of the ink.

  In the ink containing other liquid components of these glycol monomethyl ethers, 1 to 20% by mass of 1,2-hexylene glycol and / or triethylene glycol monobutyl ether as a penetrating agent with respect to the total mass of the ink. An ink containing 1 to 20% by mass of 2-pyrrolidone as a dissolution stabilizer and 2 to 30% by mass of glycerin as a humectant is preferable. In such a case, it is easy to suppress the occurrence of offset, and it is easy to obtain an ink excellent in intermittent discharge performance.

[Method for producing ink for inkjet recording apparatus]
The method for producing an ink for an ink jet recording apparatus according to the present invention comprises adding water, a pigment dispersion, and glycol monomethyl ether to other liquid components of glycol monomethyl ether as necessary, and then uniformly dispersing these ink components. If it can mix, it will not specifically limit. As a specific example of the method for producing the ink for an ink jet recording apparatus, there is a method in which each component of the ink is uniformly mixed by a mixer and then foreign matters and coarse particles are removed by a filter having a pore diameter of 10 μm or less. When manufacturing ink for an ink jet recording apparatus, other than glycol monomethyl ether such as a penetrant, a dissolution stabilizer, and a humectant, if necessary, with respect to water, pigment dispersion, and glycol monomethyl ether. Various additives conventionally added to inks for ink jet recording apparatuses, such as liquid components, surfactants, antioxidants, viscosity modifiers, pH adjusters, antiseptics and fungicides, can be added.

  The ink for an ink jet recording apparatus according to the first embodiment described above can form a good image without back-through, can suppress the occurrence of offset even in the case of image formation at high speed, and can stably produce ink. Since it has intermittent ejection properties capable of ejecting liquid droplets, it can be suitably used in various ink jet recording apparatuses.

[Second Embodiment]
The second embodiment relates to an image forming method for forming an image by an ink jet recording apparatus using the ink for the ink jet recording apparatus according to the first embodiment. The recording method of the ink jet recording apparatus used in the image forming method according to the second embodiment is not particularly limited, and even if the recording type is a serial type in which recording is performed while scanning the recording medium, the recording is fixed to the apparatus main body. A line head type in which recording is performed by a head may be used. The recording system of the ink jet recording apparatus used in the image forming method according to the second embodiment is preferably a line head type from the viewpoint of high speed image formation.

  Hereinafter, the image forming method according to the second embodiment will be described with reference to the drawings in the case of using a line head type ink jet recording apparatus and recording paper as a recording medium. FIG. 1 is a side sectional view showing a schematic configuration of an ink jet recording apparatus of a line head type recording system, and FIG. 2 is a plan view of a transport belt of the ink jet recording apparatus shown in FIG.

  As shown in FIG. 1, a paper feed tray 2 that stores recording paper P is provided on the left side of the inkjet recording apparatus 100, and the recording paper P that is stored at one end of the paper feed tray 2 is A feeding roller 3 for feeding and feeding one sheet at a time in order from the uppermost recording sheet P and a driven roller 4 that is in pressure contact with the feeding roller 3 and driven to rotate are provided.

  A transport belt 5 is rotatably disposed on the downstream side (right side in FIG. 1) of the paper feed roller 3 and the driven roller 4 in the paper transport direction. The conveying belt 5 is stretched between a belt driving roller 6 disposed on the downstream side in the sheet conveying direction and a belt roller 7 disposed on the upstream side and rotated by the belt driving roller 6 via the conveying belt 5. As the belt driving roller 6 is driven to rotate clockwise, the recording paper P is conveyed in the arrow X direction.

  Here, since the belt driving roller 6 is arranged on the downstream side in the paper transport direction X, the paper feeding side (upper side in FIG. 1) of the transport belt 5 is pulled by the belt driving roller 6, so that belt tension is applied. Therefore, the recording paper P can be stably conveyed. In addition, a sheet made of dielectric resin is used for the conveyance belt 5, and a (seamless) belt or the like having no seam is preferably used.

  Further, on the downstream side of the conveyance belt 5 in the sheet conveyance direction, the recording sheet P on which an image is recorded by being driven clockwise in the drawing is discharged to the outside of the apparatus main body, and is pressed against the upper portion of the discharge roller 8a. A driven roller 8b that is driven to rotate is provided, and a discharge tray 10 on which the recording paper P discharged outside the apparatus main body is stacked is provided on the downstream side of the discharge roller 8a and the driven roller 8b.

  Since the driven roller 8b directly touches the printing surface, the material forming the surface of the driven roller 8b is preferably a water repellent material. By forming the surface of the driven roller 8b with a water-repellent material, it is possible to suppress the ink that has not penetrated the recording paper P from adhering to the roller and easily suppress the occurrence of offset. Suitable water repellent materials include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, tetrafluoro Ethylene-vinylidene fluoride copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer, polychlorotrifluoroethylene, chlorotrifluoroethylene-ethylene copolymer, chlorotrifluoroethylene-vinylidene fluoride copolymer Examples thereof include fluororesins such as polymers, polyvinylidene fluoride, and polyvinyl fluoride. Similar to the driven roller 8b, the surface of the member in contact with the printing surface is preferably formed of a water repellent material.

  An image is recorded on the recording paper P that is supported above the conveying belt 5 at a height that forms a predetermined interval with respect to the upper surface of the conveying belt 5. Line heads 11C, 11M, 11Y and 11K to be performed are arranged. These line heads 11C to 11K are filled with colored inks of four different colors (cyan, magenta, yellow and black), and recording is performed by ejecting the respective colored inks from the line heads 11C to 11K. A color image is formed on the paper P.

  After the ink droplets discharged from the line heads 11C to 11K have landed on the recording paper P, the ink landing location on the recording paper P discharges the recording paper P composed of the discharge roller 8a and the driven roller 8b. The time required to reach the discharge unit 8 is preferably within 1 second in order to reduce the size of the apparatus. Even when the time is within 1 second, by using the ink of the first embodiment, the effect of suppressing the occurrence of offset at the time of image formation at high speed can be sufficiently obtained.

Also, ejected from the line head 11C~11K the recording paper P, the total amount of color or multiple colors of ink is driven into the recording paper P is preferably 40 g / ^{m 2} or less, 30 g / ^{m 2} or less is more preferable. By setting the ink discharge amount to such an amount, it is easy to form an image at high speed while suppressing the occurrence of offset. In the case where the ink of four or more colors on the recording paper P is driven also, the total amount of a plurality of colors of ink is preferably from 40 g / m ² or less, which are discharged to the recording paper P, 30 g / m ² or less is more preferable.

  As shown in FIG. 2, these line heads 11 </ b> C to 11 </ b> K include a nozzle row in which a plurality of nozzles are arranged in a direction orthogonal to the transport direction (vertical direction in FIG. 2), and the width of the transported recording paper P Having the above recording area, the image of one line can be collectively recorded on the recording paper P conveyed on the conveying belt 5.

  In the line head type ink jet recording apparatus, a plurality of nozzles are arranged in the longitudinal direction of a long head body formed to have a width dimension larger than that of the transport belt 5, thereby increasing the width of the recording paper P. However, the recording paper is conveyed by arranging a plurality of short head units each having a plurality of nozzles in the width direction of the conveying belt 5, for example. A line head that can record an image over the entire width in the P width direction may be used.

  In addition, as an ink ejection method of the line heads 11C to 11K, for example, ink droplets are ejected using a pressure generated in the liquid chambers of the line heads 11C to 11K using a piezoelectric element (piezo element) (not shown). Various methods such as a piezoelectric element method and a thermal ink jet method in which bubbles are generated by a heating element and ink is ejected under pressure can be applied. The ink ejection method is preferably a piezoelectric element method because the ejection amount can be easily controlled.

  FIG. 3 is a block diagram showing a configuration of a line head type ink jet recording apparatus. Portions common to FIGS. 1 and 2 are denoted by the same reference numerals and description thereof is omitted. The inkjet recording apparatus 100 includes a control unit 20. An interface 21, ROM 22, RAM 23, encoder 24, motor control circuit 25, line head control circuit 26, voltage control circuit 27, and the like are connected to the control unit 20. Has been.

  The interface 21 transmits / receives data to / from a host device such as a personal computer (not shown). The control unit 20 converts the image signal received via the interface 21 into image data by performing scaling processing or gradation processing as necessary. And a control signal is output to the various control circuits mentioned later.

  The ROM 22 stores a control program or the like for recording the image by driving the line heads 11C to 11K. The RAM 23 stores the image data subjected to scaling processing or gradation processing by the control unit 20 in a predetermined area.

  The encoder 24 is connected to a belt driving roller 6 on the paper discharge side that drives the conveyance belt 5, and outputs a pulse train according to the rotational displacement amount of the rotating shaft of the belt driving roller 6. The control unit 20 calculates the rotation amount by counting the number of pulses transmitted from the encoder 24, and grasps the paper feed amount (paper position). Then, the control unit 20 outputs a control signal to the motor control circuit 25 and the line head control circuit 26 based on the signal from the encoder 24.

  The motor control circuit 25 drives the recording medium transport motor 28 by an output signal from the control unit 20. The recording medium conveying motor 28 is driven to rotate the belt driving roller 6 and rotate the conveying belt 5 clockwise in FIG. 1 to convey the sheet in the direction of the arrow X.

  The line head control circuit 26 transfers the image data stored in the RAM 23 to the line heads 11C to 11K based on the output signal from the control unit 20, and the line heads 11C to 11K receive the image data based on the transferred image data. Controls ink ejection. By this control and the control of the conveyance of the sheet by the conveyance belt 5 driven by the recording medium conveyance motor 28, the recording process on the sheet is performed.

  The voltage control circuit 27 generates an alternating electric field by applying a voltage to the belt roller 7 on the paper feeding side based on an output signal from the control unit 20, and electrostatically attracts the sheet to the transport belt 5. The electrostatic adsorption is released by grounding the belt roller 7 or the belt driving roller 6 based on an output signal from the control unit 20. Here, the voltage is applied to the belt roller 7 on the paper feed side, but the voltage may be applied to the belt drive roller 6 on the paper discharge side.

  A method of forming dots using a line head type ink jet recording apparatus will be described in detail with reference to FIG. In FIG. 4, the line head 11C is described as an example among the line heads 11C to 11K shown in FIGS. 1 and 2, but the other line heads 11M to 11K are also described in the same manner.

  As shown in FIG. 4, the line head 11C has nozzle rows N1 and N2 made up of a plurality of nozzles arranged in parallel in the transport direction (arrow X direction). That is, as the nozzles for forming each dot row in the transport direction, each of the nozzle rows N1 and N2 (for example, the nozzles 12a and 12a 'in the dot row L1) is provided with a total of two nozzles. For convenience of explanation, only 16 nozzles of 12a to 12p and 12a ′ to 12p ′ corresponding to the dot rows L1 to L16 are shown in the nozzles constituting the nozzle rows N1 and N2. However, in actuality, it is assumed that a larger number of nozzles are arranged in a direction orthogonal to the transport direction.

  Then, an image is formed on the recording medium using the nozzle rows N1 and N2 in sequence. For example, after forming the dot column D1 for one row in the width direction (left and right direction in the figure) of the recording medium by ejecting ink from the nozzle row N1 (solid line arrow in the figure) while moving the recording medium in the transport direction. The next dot row D2 for one row is formed by ink ejection from the nozzle row N2 (broken arrows in the figure), and the next dot row D3 for the next row is again formed by ink ejection from the nozzle row N1. . Hereinafter, the dot rows D4 and thereafter are similarly formed by alternately using the nozzle rows N1 and N2.

  In the image forming method according to the second embodiment described above, since the ink according to the first embodiment is used, it is possible to form a good image without back-through and to form an image at high speed while suppressing the occurrence of offset. It is possible, and it is excellent in the intermittent discharge property of ink droplets and can form a good image.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited at all by the Example.

[Production of styrene-acrylic resin]
The styrene-acrylic resin used for the preparation of the pigment dispersion was produced by a macromonomer synthesis method. Specifically, an oligomer (AS-6, manufactured by Toa Gosei Co., Ltd., number average molecular weight (Mn) 6,000) having a (meth) acryloyl group bonded to one of molecular ends of polystyrene, and a copolymerization monomer, Resin 1 to Resin 6 having different molecular weights were produced by changing the polymerization conditions in methyl ethyl ketone in the presence of a polymerization initiator. The weight average molecular weight (Mw) of the obtained resin was confirmed by gel filtration chromatography. Table 1 shows the weight average molecular weights of Resin 1 to Resin 6. Moreover, when the acid value of the obtained resin was confirmed by titration, the acid values of Resin 1 to Resin 6 were all 30 to 60 mgKOH.

(Preparation of pigment dispersion)
Pigment dispersion A was prepared using resin 1, and similarly pigment dispersions B to F were prepared using resins 2 to 6, respectively. Specifically, water, a pigment, and a styrene-acrylic resin are charged into a nano glen mill (manufactured by Asada Iron Works Co., Ltd.) so that the water becomes 75% by mass, the pigment is 20% by mass, and the styrene-acrylic resin is 5% by mass. A nanograin mill was filled with 0.5 mm zirconia beads as a medium, and the pigment was dispersed while cooling with water to obtain a pigment dispersion. The obtained pigment dispersion was diluted 300 times with ion-exchanged water, and the volume average particle diameter D50 of the pigment was measured with a dynamic light scattering particle size distribution device (Zetasizer Nano, manufactured by Sysmex Corporation). It was confirmed that the volume average particle diameter of the pigment was in the range of 70 to 150 nm.

[Examples 1-12 and Comparative Examples 1-12]
Using pigment dispersions A to F, each component was uniformly mixed by a stirrer in the ratios a to d shown in Table 2, and then filtered through a filter having a pore size of 5 μm. 12 and Comparative Examples 1-12 were prepared. In addition, the amount described in Table 2 is mass% of each component with respect to the total mass of the ink.

  The composition of the inks a to d is set so that the total amount of glycerin and glycol monomethyl ether is constant. However, since glycol monomethyl ether is slightly better in moisture retention than glycerin, the amount of glycol monomethyl ether used As the ink increases, the moisture retention of the ink improves. Further, glycerin hardly affects the permeability of the ink into the recording medium. For this reason, according to the ink of composition of ad, the influence on the performance of the ink by the improvement in the moisture retention property and permeability of an ink accompanying the increase in the amount of glycol monomethyl ether can be confirmed. In addition, in the ink of composition of ad, although the mixture of triethylene glycol monomethyl ether and tripropylene glycol monomethyl ether is used as glycol monomethyl ether, only one of triethylene glycol monomethyl ether or tripropylene glycol is used. Can be used to obtain ink having the same performance.

＊１：オルフィンＥ１０１０（アセチレンジオールのエチレンオキシド付加物、日信化学工業株式会社製）
＊２：トリエチレングリコールモノメチルエーテルの含有量と、トリプロピレングリコールモノメチルエーテル含有量との合計量。

* 1: Olfine E1010 (ethylene oxide adduct of acetylene diol, manufactured by Nissin Chemical Industry Co., Ltd.)
* 2: Total amount of triethylene glycol monomethyl ether content and tripropylene glycol monomethyl ether content.

[Intermittent discharge evaluation]
Using the inks obtained in Examples and Comparative Examples, intermittent ejection properties were evaluated according to the following methods. Table 4 shows the evaluation results of the intermittent discharge performance.

<Intermittent ejection evaluation method>
Using a line head type ink jet recording apparatus having a heater capable of keeping heat inside and a temperature detection unit, and having a recording head that discharges ink by controlling the voltage to the piezoelectric element, a heat retention set temperature of 25 ° C., The intermittent discharge performance was evaluated in an environment of 10 ° C. and 15% RH. Intermittent ejection evaluation is performed by printing a line image in the longitudinal direction of the head on glossy paper, passing through any non-printing section, then printing again on horizontal line glossy paper, and checking the state of the printed line image with a microscope. Observed and evaluated in three stages, ◎, ○, and ×. The evaluation criteria are as follows.
A: The line image is not disturbed even if it exceeds the vertical non-printing section of A3 size paper.
◯: The line image is not disturbed up to the non-printing section corresponding to the length of A3 size paper.
X: Disturbance occurs in the line image until the non-printing section corresponding to the length of A3 size paper.

  From Table 4, in Comparative Examples 1 and 5 to 9 in which the content of glycol monomethyl ether is less than 15% by mass, the moisture retention of the ink is not sufficient, which is caused by changes in ink properties such as viscosity during intermittent ejection. Thus, it can be seen that it is difficult to eject the droplets at a constant speed and direction, and the line image is likely to be disturbed. Further, in Comparative Examples 9 to 12 in which the average molecular weight of the resin used for preparing the pigment dispersion exceeds 150,000, ink ejection failure from the nozzle tends to occur as the ink viscosity increases due to drying, and the line image is disturbed. Is likely to occur.

  On the other hand, in Examples 1 to 12 and Comparative Examples 2 to 4 in which the content of glycol monomethyl ether is 15% by mass or more and the average molecular weight of the resin used for preparing the pigment dispersion is 150,000 or less, intermittent The ink properties are unlikely to change during ejection, and ink ejection defects from the nozzles are less likely to occur, so that the line image is less likely to be disturbed.

[Offset evaluation]
Using the inks obtained in the examples and comparative examples, the offset property was evaluated according to the following method. Tables 5 and 6 show the evaluation results of the offset property.

<Evaluation of offset property>
Using a line head type ink jet recording apparatus having a heater capable of keeping heat inside and a temperature detection unit, and having a recording head that discharges ink by controlling the voltage to the piezoelectric element, a heat retention set temperature of 25 ° C., The offset property was evaluated in an environment of 32.5 ° C. and 85% RH. The ejection amount is set so that the amount of ink applied to the recording medium per color is 15 g / m ² , the ink is ejected from the recording head of cyan ink and magenta ink, and the total amount of ink ejection is The surface material is polytetrafluoroethylene resin (PTFE) provided in a discharge unit that continuously forms solid images on three recording media so as to be 30 g / m ² and discharges the recording media. The offset property was evaluated by observing the state of the printed matter on the recording medium after coming into contact with the driven roller. The criteria for evaluating the offset property are as follows.
A: All three sheets are not stained in the white portion (non-image portion) on the rear end side of the image.
○: In the white portion (non-image portion) on the rear end side of the image, the first two sheets are not stained, and the third sheet is stained.
Δ: In the white portion (non-image portion) on the rear end side of the image, the first sheet is not stained, and the second sheet and the third sheet are stained.
X: All three sheets are dirty in the white portion (non-image portion) on the rear end side of the image.
The conveyance speed of the recording medium of the ink jet recording apparatus was 846.7 mm / second. Further, the time from the landing of the ink on the recording medium to the arrival of the driven roller was 0.5 seconds. As a recording medium, a sheet (IJW, manufactured by Oji Paper Co., Ltd.) cut into A4 size was used. The size of the image formed on the recording medium was 10 × 10 cm.

Also, the ejection amount is set so that the amount of ink applied to the recording medium per color is 20 g / m ^2, and the total amount of ink ejected from the cyan and magenta ink recording heads is set. The offset property was evaluated in the same manner as in the test in which the total amount of ink was 30 g / m ² except that three solid images were continuously printed so that the amount was 40 g / m ² .

  From Tables 5 and 6, in Comparative Examples 1 to 4, in which the average molecular weight of the resin used for the preparation of the pigment dispersion is less than 30,000, the ink tends to adhere to the driven roller, and offset is likely to occur. I understand. Further, in Comparative Examples 1 and 5 to 8, in which the content of glycol monomethyl ether is less than 15% by mass, the ink hardly adheres to the recording medium, so that the ink easily adheres to the driven roller, and offset occurs. I understand that it is easy. In Comparative Example 9, even if the content of glycol monomethyl ether is less than 15% by mass, the average molecular weight of the resin used for the preparation of the pigment dispersion is as large as 200,000, so that offset is unlikely to occur. I understand.

  On the other hand, the inks of Examples 1 to 12 and Comparative Examples 10 to 12 in which the content of glycol monomethyl ether is 15% by mass or more and the average molecular weight of the resin used for preparing the pigment dispersion is 30,000 or more. Then, it can be seen that the occurrence of offset is suppressed.

[Confirmation test of influence of driven roller material]
In addition to changing the material of the driven roller from PTFE to polyoxymethylene resin (POM), the offset property is evaluated in the same manner as the offset property evaluation when the total amount of ink applied to the recording medium is 30 g / m ^2. did. Table 7 shows the evaluation results of the offset property.

  Comparison between Table 5 and Table 7 shows that the occurrence of offset is suppressed when the material of the driven roller is not POM which is a non-water-repellent material but PTFE which is a water-repellent material. In addition, from Table 7, the average molecular weight of the resin used for the preparation of the pigment dispersion is less than 30,000, or the inks of Comparative Examples 1 to 9 in which the content of glycol monomethyl ether is less than 15% by mass are offset. It can be seen that the occurrence of is remarkable. On the other hand, the average molecular weight of the resin used for the preparation of the pigment dispersion is 30,000 or more, and the contents of glycol monomethyl ether are 15% by mass or more, and inks of Examples 1 to 12 and Comparative Examples 10 to 12 Thus, it can be seen that even when an ink jet recording apparatus including a POM driven roller that is likely to generate an offset is used, the occurrence of the offset is suppressed.

(Permeability evaluation)
Using the inks obtained in Examples and Comparative Examples, the penetrability (ease of occurrence of back-through) of the printed back surface when printing was evaluated according to the following method. The evaluation results of permeability are shown in Table 8 and Table 9.

<Permeability evaluation method>
Using a line head type ink jet recording apparatus having a heater capable of keeping heat inside and a temperature detection unit, and having a recording head that discharges ink by controlling the voltage to the piezoelectric element, a heat retention set temperature of 25 ° C., The permeability was evaluated in an environment of 25 ° C. and 60% RH. The penetrability was evaluated by ejecting ink from a cyan ink recording head at an ejection amount of 15 g / m ² and 20 g / m ² to form a solid image having the highest density in one color on a recording medium. Thereafter, the image density on the back side of the image after the obtained solid image was left overnight was measured by a portable reflection densitometer RD-19 (manufactured by Gretag Macbeth). The conveyance speed from the recording medium feeding to the discharging section when forming a solid image was 846.7 mm / sec. As a recording medium, A4 size paper (ribbon friendly, manufactured by Nippon Paper Industries Co., Ltd.) was used. The size of the image formed on the recording medium was 10 × 10 cm. The penetrability was evaluated in three stages of ◎, ○, and × according to the following criteria based on the image density on the back side of the print.
A: The image density on the back side of the image is less than 0.16.
A: The image density on the back side of the image is 0.16 or more and less than 0.18.
X: The image density on the back side of the image is 0.18 or more.
The evaluation results at a discharge amount of 15 g / m ² are shown in Table 8, and the evaluation results at a discharge amount of 20 g / m ² are shown in Table 9.

  In Comparative Examples 1 and 5 to 9 in which the content of glycol monomethyl ether is less than 15% by mass, it can be seen that the ink hardly permeates the paper and the problem of show-through is unlikely to occur. From Comparative Examples 2 to 4, even when the content of glycol monomethyl ether is 15% by mass or more, when the average molecular weight of the resin used for preparing the pigment dispersion is less than 30,000, the amount of ink discharged is large. It can be seen that the show-through tends to occur.

  On the other hand, from Examples 1-12 and Comparative Examples 10-12, when the content dragon of glycol monomethyl ether is 15% by mass or more and the average molecular weight of the resin used for preparing the pigment dispersion is 30,000 or more, It turns out that the strikethrough is unlikely to occur.

  From the above evaluation results, the pigment is treated with a resin having a molecular weight of 30,000 to 150,000, and is selected from the group consisting of triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether, and mixtures thereof. Only in the case of using the ink according to claim 1, wherein the content of glycol monomethyl ether is 15% by mass or more, a good image without back-through can be formed, and even when the image is formed at high speed, the offset It can be seen that it is possible to suppress the occurrence of ink droplets and to realize intermittent ejection that can stably eject ink droplets.

2 Feeding tray 3 Feeding roller 4 Driven roller 5 Conveyor belt 6 Belt drive roller 7 Belt roller 8 Ejector 8a Ejection roller 8b Follower roller 10 Ejection tray 11C, 11M, 11Y, 11K Line heads 12a to 12p, 12a ′ to 12p 'nozzle 20 control unit 30 detection means 100 inkjet recording apparatus D1 to D4 dot row (row direction)
L1 to L16 dot row (transport direction)
N1, N2 Nozzle array P Recording paper

Claims (6)

Glycol monomethyl selected from the group consisting of at least water, a pigment dispersion comprising styrene-acrylic resin, pigment and water , a surfactant, triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether, and mixtures thereof Ether , 1,2-hexylene glycol, 2-pyrrolidone, glycerin, and triethylene glycol monobutyl ether ,
The pigment dispersion includes the styrene-acrylic resin having a weight average molecular weight of 100,000 or 150,000 ,
When the weight average molecular weight of the styrene-acrylic resin is 100,000, the glycol monomethyl ether content is 25% by mass with respect to the mass of the ink, and the glycerin content is 5 mass with respect to the mass of the ink. %
When the weight average molecular weight of the styrene-acrylic resin is 150,000, the content of the glycol monomethyl ether is 20% by mass with respect to the mass of the ink , and the content of glycerin is 10 % with respect to the mass of the ink. % in either said glycol Ri 25% by mass content relative to the weight of the ink monomethyl ether, and Ru 5% by mass relative to the mass content of the ink glycerin, ink-jet recording apparatus .   An image forming method for forming an image by an ink jet recording apparatus using the ink for an ink jet recording apparatus according to claim 1.   In the ink jet recording apparatus, the time from when the ink droplets land on the recording medium to when the ink landing position of the recording medium reaches the discharge portion for discharging the recording medium is within one second. The image forming method according to claim 2, wherein   4. The image forming method according to claim 2, wherein an image is formed by ejecting ink droplets onto a recording medium so that a total amount of the ink of one color or a plurality of colors is 30 g / m 2 or less.   3. The ink jet recording apparatus includes a recording head that discharges the ink droplets using pressure generated in a liquid chamber by voltage control to a piezoelectric element, and the recording method is a line head type recording method. 5. The image forming method according to any one of 4 to 4.   The image forming method according to claim 2, wherein a surface of a member that contacts the print surface of the inkjet recording apparatus is formed of a water repellent material.

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