JP2011213057A - Inkjet recording method and recorded matter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet recording method capable of suppressing all of deterioration in fixing properties of an ink composition onto a medium to be recorded, clogging in an inkjet head, and unevenness of density of an image formed on the medium to be recorded.SOLUTION: The inkjet recording method includes a process for forming images by hitting the ink composition on the medium to be recorded while the medium to be recorded is sucked and attracted onto a conveying belt by vacuum suction through an opening part 130A formed on the conveying belt 130. The ink composition includes a pigment, a humectant, and a specified amount of water. The humectant is a mixture of (A) glycerin or the like, (B) trimethylolpropane or the like, and a compound such as (C) betaines, and a mass ratio of the contents is (A):(B):(C)=(1.0):(0.1-1.0):(1.0-3.0).

Description

  The present invention relates to an inkjet recording method and a recorded matter.

The ink jet recording method is a recording method in which printing is performed by ejecting ink droplets from an ink jet head and landing on a recording medium such as paper. Due to recent advances in ink jet recording technology, the ink jet recording method has come to be used for high-definition image recording (printing), which has been the field of photography and offset printing.
The ink (ink composition) used in this ink jet recording method must have proper ink physical properties for ejecting and controlling fine ink droplets from the ink jet head. The ink composition preferably has a lower viscosity than the ink composition. As one of the methods, ink having a high water content (water-based ink) is widely used.

As such a water-based ink composition, for example, Patent Document 1 includes a colorant, water, a water-soluble organic solvent, and at least one carbazide compound and / or hydrazide compound. The organic solvent is a liquid in a temperature range of at least 0 to 40 ° C., has a solubility in water at a temperature of 20 ° C. of 1% by weight or more, has a saturated vapor pressure at a temperature of 20 ° C. of 1.7 Pa or less, and An ink composition is disclosed in which the organic solvent is contained in an ink composition in an amount of 10 wt% to 35 wt%.
Patent Document 2 discloses an unsaturated monomer having a carboxyl group and an unsaturated monomer having an aliphatic hydrocarbon group having 14 to 20 carbon atoms and having an aromatic ring of 5% by mass or more. Contains a self-water-dispersible copolymer resin having an acid value of 70 to 130 mgKOH / g, copolymerized with a monomer component containing 15% by mass or more of a body, pigment, trimethylglycine, glycerin, basic compound and water An aqueous pigment-type inkjet ink composition, wherein the amount of trimethylglycine added is in the range of 0.1 to 15% by mass relative to the total amount of the aqueous pigment-type inkjet ink composition, and the amount of glycerin added and trimethyl The total amount of trimethylglycine and glycerin added to the total amount of the aqueous pigment-type inkjet ink composition in a ratio of 1: 1 to 100: 1 with respect to the amount of glycine added. The aqueous pigmented ink jet ink composition, wherein the Te in the range of 10 to 30% by weight is disclosed.
Furthermore, Patent Document 3 discloses an ink set comprising two or more ink compositions including at least a black ink composition and a color ink composition, wherein the black ink composition has a hydrophilic group on its surface. And the color ink composition comprises a self-dispersing pigment having a hydrophilic group on its surface via a phenyl group, and all the ink compositions are An ink set comprising a resin emulsion is disclosed.

JP 2002-294117 A JP 2003-238853 A JP 2009-256606 A

  By the way, as a recording method using a copying machine or the like, there is a method in which a recording medium is transported and printing is performed in a state where the recording head is fixed with respect to the transporting direction. A belt may be used. Further, in order to transport the recording medium in a state where the recording medium is detachably fixed to the transport belt, there is a method of transporting the recording medium by sucking and adsorbing the recording medium to the transport belt by vacuum suction through an opening formed in the transport belt. is there. According to this method, by operating a suction means such as a suction fan installed on one side via the conveyor belt, by suction from the other side to the one side through the opening of the conveyor belt, The recording medium on the other side is sucked and sucked onto the transport belt. As a result, the recording medium can be transported while being fixed to the transport belt. If the recording medium is transported by the transport belt and moved to a place where it is not sucked by the suction means, the recording medium can be detached from the transport belt, and the process can proceed to the next step.

  However, the present inventors have examined in detail the application of the recording method to the ink jet recording method. When the conventional ink compositions disclosed in Patent Documents 1 to 3 are used, the following problems occur. It turned out that. That is, even if these ink compositions are appropriately adjusted within the disclosure range, the fixability of the ink composition on the recording medium is reduced, clogging in the vicinity of the nozzles in the inkjet head, and the recording medium. It has become clear that any one or more of the density unevenness of the formed image cannot be suppressed.

  Therefore, the present invention has been made in view of the above circumstances, such as a decrease in fixability of the ink composition to the recording medium, clogging in the inkjet head, and density unevenness of the image formed on the recording medium. An object of the present invention is to provide an ink jet recording method and recorded matter that can suppress all of them.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the uneven density of the image formed on the recording medium (hereinafter also simply referred to as “image density unevenness”) is the above-described suction. It was found that this is due to the method of adsorbing and transporting. As a result of further investigation by the present inventors, even if the composition is appropriately adjusted within the disclosure range of the conventional ink composition so as to eliminate the uneven image density, the fixing property of the ink composition on the recording medium is reduced ( In the following, it has been found that at least one of “clogging of the fixing property” and clogging in the ink jet head (hereinafter also simply referred to as “clogging”) cannot be suppressed. As a result of detailed studies on the ink composition for suppressing all of these problems, the present invention has been completed.

  That is, the present invention is an ink jet recording method including a step of forming an image on a recording medium while sucking and adsorbing the recording medium to the conveying belt by vacuum suction through an opening formed in the conveying belt. In the forming step, the image is formed by landing the ink composition on a printing surface opposite to the conveyance belt side of the recording medium. The ink composition includes at least a pigment, a humectant, and the like. The ink composition contains 60% by mass to 10% by mass of water in the total amount of the ink composition, and the humectant is a mixture of the following compounds (A), (B) and (C), and the mass ratio of the contents thereof Provides an ink jet recording method wherein (A) :( B) :( C) = (1.0) :( 0.1-1.0) :( 1.0-3.0). Here, the compound (A) is at least one compound selected from the group consisting of glycerin, 1,2,6-hexanetriol, diethylene glycol, triethylene glycol, tetraethylene glycol, and dipropylene glycol. The compound (B) is at least one compound selected from the group consisting of trimethylolpropane and trimethylolethane. Further, the compound (C) is at least one compound selected from the group consisting of betaines, saccharides and ureas and having a molecular weight in the range of 100 to 200.

  According to such an ink jet recording method, the solid content in the ink composition and the solid content aggregation are mainly attributed to the water content, the type of humectant and the mass ratio of the content. Since it can prevent, clogging can be suppressed. In addition, it is possible to suppress a decrease in fixability mainly due to the water content. Furthermore, image density unevenness can be suppressed mainly due to the type of humectant and the mass ratio of its content. The property suitable for suppressing clogging is also referred to as “clogging suitability” hereinafter.

  In the inkjet recording method of the present invention, the compound (C) preferably contains betaines. Thereby, image density unevenness can be particularly effectively suppressed. In addition, it is preferable that the ink composition further contains a resin emulsion since it can more effectively prevent a decrease in fixing property. From the same viewpoint, the resin emulsion is preferably a resin emulsion having a minimum film forming temperature of less than 20 ° C. In addition, it is preferable that the ink composition contains 6% by mass or more of the pigment with respect to the total amount because the color developability in the image is improved.

  The present invention provides a recorded matter recorded by the above-described ink jet recording method. Such a recorded matter is one in which both image density unevenness and fixing property decrease are suppressed, and clogging is also suppressed, so that the ink composition lands on the recording medium as desired, and dot missing. Thus, a recorded material on which a small amount of image is formed.

1 is a schematic view schematically showing an ink jet recording apparatus according to an example of the present invention. 1 is a perspective view schematically showing a part of an ink jet recording apparatus according to an example of the present invention. FIG. 4 is a cross-sectional view schematically showing a cross section appearing by cutting along line IV-IV in FIG. 2.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary. However, the present invention is limited to the following embodiment. It is not a thing. The present invention can be variously modified without departing from the gist thereof. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  The inkjet recording method according to the present embodiment includes a process of forming an image on a recording medium while sucking and adsorbing the recording medium to the conveyance belt by vacuum suction through an opening formed in the conveyance belt. In the recording method, in the forming step, the image is formed by landing the ink composition on a printing surface opposite to the conveyance belt side of the recording medium, and the ink composition includes at least a pigment, The humectant and the ink composition contain 60% by mass to 10% by mass of water, and the humectant is a mixture of the following compounds (A), (B) and (C), and its content The mass ratio of (A) :( B) :( C) = (1.0) :( 0.1-1.0): 1.0-3.0).

  The ink jet recording apparatus used in the ink jet recording method of the present embodiment has, for example, the structure shown in FIGS. FIG. 1 is a schematic view schematically showing, in particular, a paper transport portion of the ink jet recording apparatus, and FIG. 2 is a perspective view schematically showing a part of the recording apparatus. FIG. 3 is a cross-sectional view schematically showing a cross section appearing by cutting along line IV-IV in FIG. 2, and shows a state in which a recording medium such as plain paper is conveyed.

  First, a description will be given with reference to FIG. In general, the line-type inkjet recording apparatus 100 capable of high-speed and high-density printing ejects ink composition droplets (hereinafter also referred to as “ink droplets”) onto a recording medium 101 such as plain paper to form an image. An inkjet head unit 190 for recording, a conveyance belt 130 for conveying the recording medium 101 below the inkjet head unit 190, a storage cassette 104 storing the recording medium 101 before printing, and a recording medium from the storage cassette 104 Via a paper feed roller 105 that feeds 101, a pair of transport rollers (gate rollers) 140 for transporting the recording medium 101, and an opening 130 </ b> A (not shown in FIG. 1) of the transport belt 130. Then, a vacuum suction unit 210 for vacuum suction of the recording medium 101 and a pair of discharges for discharging the recording medium 101 And over La 150, a sheet discharge cassette 106 for accommodating the recording medium 101 printed, a control unit 111, and a position detection sensor 109 for detecting the position of the recording medium 101 to be fed.

  The inkjet head unit 190 includes a plurality of inkjet heads 110 corresponding to the types of ink, and each inkjet head has a plurality of ink discharge nozzles corresponding to the entire width in the width direction of the recording medium 101, so-called. It consists of a line head.

  The annular conveyance belt 130 conveys the recording medium 101 to the inkjet head unit 190 (printing area). The driving roller 180 drives the conveyor belt 130, and the driven roller 170 is driven while the conveyor belt 130 faces the ejection port of the inkjet head unit 190. The driving roller 180 is driven by a motor 115 that is driven and controlled by the control unit 111. The paper feed roller 105 is a roller for sending the recording medium 101 inside the storage cassette 104 to the transport roller 140 and is driven by a motor 118 that is driven and controlled by the control unit 111.

  The transport roller 140 includes a driving roller 140A as a roller unit that is driven by a motor 116 that is driven and controlled by the control unit 111, and a driven roller 140B that is driven in contact with the driving roller 140A. The discharge roller 150 forms a discharge roller pair with a drive roller 150A driven by a motor 117 driven and controlled by the control unit 111 and a driven roller 150B driven in contact with the drive roller 150A.

  The reduced pressure suction unit 210 includes a suction fan 210A and a casing 210B surrounding the suction fan 210A. The suction fan 210 </ b> A is driven by a motor 211 that is driven and controlled by the control unit 111, and sucks the recording medium 101 on the conveyance belt 130 under reduced pressure.

  The control unit 111 stores print data (record data) input via a interface (IF) from a CPU (Central Processing Unit), a host computer, or the like that executes print processing (record processing) and various processes in a data storage area. A RAM (Random Access Memory) for storing or temporarily storing various data, a PROM for storing a control program for controlling each unit, an EEPROM (Electrically Erasable Programmable Read-Only Memory), and the like are provided.

  As the position detection sensor 109, for example, a reflection type photosensor in which an infrared light emitting diode as a light emitting element and a phototransistor as a light receiving element are combined is used. The position detection sensor 109 is disposed in a paper conveyance unit between the paper feed roller 105 and the conveyance roller 140, detects the leading end position of the recording medium 101 being conveyed (the presence or absence of the recording medium 101), and a detection signal thereof. Is input to the control unit 111. In the control unit 111, drive control processing of the transport roller 140 is performed based on the detection signal of the leading end position of the recording medium 101.

  The recording medium 101 reaches a conveying roller 140 that rotates when the motor 116 is driven by a drive signal from the control unit 111, and the leading end surface of the recording medium 101 comes into contact with the leading end of the recording medium 101. In addition, the direction is adjusted, the paper is fed between the driving roller 140A and the driven roller 140B, and the paper is fed onto the conveying belt 130. The recording medium 101 conveyed to the printing area below the inkjet head unit 190 by the conveyance belt 130 is ejected from the nozzles of the inkjet head unit 190 while being conveyed to the conveyance belt 130, and based on the print data. Printing is performed.

  For printing on the recording medium 101, the control unit 111 obtains from the host computer via the IF, the print data stored in the RAM is subjected to predetermined processing in the CPU, and the head is based on this processing data. A drive signal is output to the driver, the drive signal is input to the inkjet head unit 190 via the head driver, and the electrostatic actuator to which the drive signal is input drives the ink from the corresponding nozzle to the recording medium 101. Drops are ejected, and an image is printed (recorded) based on the print data.

  The recording medium 101 on which printing has been performed is transported to the discharge unit (discharge roller 150) by the transport belt 130. When the transported recording medium 101 reaches the discharge roller 150, the motor 117 is driven by the drive signal from the control unit 111 to rotate the drive roller 150A, and the driven roller 150B that is driven by contacting the drive roller 150A. The paper is fed between the sheets and is stored in the paper discharge cassette 106.

  Next, a description will be given with reference to FIGS. The ink jet recording apparatus 100 is a line printer, and an ink jet head unit 190, a platen unit 120 provided below and opposite to the ink jet head unit 190, and a recording target to be used for printing on the upstream side in the transport direction of the platen unit 120. A medium supply unit (not shown) for supplying the medium 101, a medium receiving unit (not shown) for storing the recording medium 101 printed on the downstream side in the transport direction of the platen unit 120, and recording from the medium supply unit Conveying means 160 for conveying the medium 101 onto the platen unit 120 and conveying the recording medium 101 after printing to the medium receiving unit.

The inkjet head unit 190 is capable of line printing by arranging a plurality of inkjet heads 110 in a staggered manner in a direction intersecting the conveyance direction of the recording medium 101.
The platen unit 120 includes a conveyance belt 130 that conveys the recording medium 101, and the conveyance belt 130 also serves as a platen belt. The conveyance belt 130 has an opening 130A that can be arranged to face the plurality of inkjet heads 110 during the operation, and the opening 130A penetrates the conveyance belt 130 in the thickness direction. The plurality of openings 130 </ b> A are arranged in a staggered manner in the same manner as the plurality of inkjet heads 110. Further, the transport unit 160 includes a pair of transport rollers 140 and a discharge roller 150 which are opposed to sandwich the recording medium 101 from above and below on the upstream side and the downstream side of the transport belt 130 in the transport direction, respectively. A conveying means 160 is configured together with the belt 130. The transport belt 130 operates by the rotation of the driven roller 170 and the drive roller 180 so as to transport the recording medium 101 placed thereon in the transport direction.

  Below the portion of the transport belt 130 on which the recording medium 101 is placed, a reduced pressure suction unit 210 that sucks the recording medium 101 through the opening 130A of the transport belt 130 is provided. The vacuum suction unit 210 includes a suction fan 210A and a casing 210B surrounding the suction fan 210A. The upper part of the housing 210B has a flat shape so as to serve also as a platen plate, and has a plurality of openings 210C to enable suction by the suction fan 210A.

  The configuration other than the above provided in the inkjet recording apparatus 100 may be a conventionally known configuration.

  The operation of the ink jet recording apparatus 100, that is, the ink jet recording method is as follows. First, the transport unit 160, that is, the transport belt 130, the transport roller 140, and the discharge roller 150 are operated to transport the recording medium 101 from the medium supply unit toward the platen unit 120 in the transport direction. When the recording medium 101 is placed on the transport belt, the suction fan 210A is operated to suck the recording medium 101 under reduced pressure through the openings 130A and 210C. As a result, the recording medium 101 is sucked and adsorbed from the lower surface (back surface) side to the conveyor belt 130 and placed on the conveyor belt 130 in a fixed state. When the recording medium 101 is conveyed below the ink jet head 110, ink composition droplets are ejected from the nozzles of the ink jet head 110, and are ejected to land on the printing surface (upper surface) of the recording medium 101. Thus, an image is formed on the recording medium 101. Then, the recording medium 101 on which an image has been formed (printed) is further conveyed to a medium receiving portion downstream of the inkjet head unit 190.

  As is apparent from the drawing, the ink jet recording apparatus 100 has a configuration in which the recording medium 101 is sucked and sucked onto the transport belt 130 only above the decompression suction unit 210. Therefore, since the recording medium 101 is not sucked and adsorbed by the conveyance belt 130 in the upstream and downstream of the conveyance direction of the vacuum suction unit 210, the recording medium 101 is not wound around the conveyance belt 130 on the outer periphery of the driven roller 170 and the driving roller 180, and the smooth conveyance is performed. It becomes possible.

  The ink jet recording method in the present embodiment is a method in which an ink composition is ejected as droplets (ink droplets) from a fine nozzle, and the droplets are landed and attached to a recording medium. This will be specifically described below.

As a first method, there is an electrostatic suction method, which applies a strong electric field between the nozzle and the acceleration electrode placed in front of the nozzle, and continuously ejects ink from the nozzle in the form of droplets. In this method, a printing information signal is supplied to the deflection electrode while the droplet is flying between the deflection electrodes and recorded, or a droplet of ink is ejected in response to the printing information signal without being deflected.
The second method is a method in which ink droplets are forcibly ejected by applying pressure to the liquid ink composition with a small pump and mechanically vibrating the nozzle with a quartz vibrator or the like. The ejected droplets are charged simultaneously with the ejection, and a printing information signal is applied to the deflection electrodes and recorded while the droplets fly between the deflection electrodes.
The third method is a method using a piezoelectric element, in which a pressure and a print information signal are simultaneously applied to a liquid ink composition by a piezoelectric element to eject and record ink droplets.
The fourth method is a method in which the liquid ink composition is rapidly expanded in volume by the action of thermal energy, and the ink composition is heated and foamed with a microelectrode in accordance with a print information signal, and the droplets are ejected and recorded. is there.
Any of the above methods can be employed in the ink jet recording method of the present embodiment.

  When the above-described transport belt 130 is used, the suction fan 210A is operated, and the recording medium 101 placed on the transport belt 130 is sucked downward through the opening 130A, whereby the recording medium 101 is recorded. Is in close contact with the conveyor belt 130. Therefore, if the recording medium 101 such as plain paper has some air permeability, the ink composition attached to the recording medium 101 in the portion of the recording medium 101 on the opening 130A of the conveyance belt 130. Objects are easily sucked toward the back side (bottom side). On the other hand, the adhering ink composition is difficult to be sucked into the portion of the recording medium 101 other than the opening 130A. Conventionally, the former ink composition permeates quickly by being sucked into the recording medium 101 and dries quickly by the generation of an air flow accompanying suction. In contrast, the latter ink composition is slow to penetrate and dry. Conventionally, the permeation speed and the drying speed of the ink composition adhering to the recording medium 101 are not uniform over the entire recording medium 101 placed on the conveyance belt 130. Image density unevenness occurs. The property suitable for suppressing the ink composition from penetrating excessively into the recording medium and hereinafter referred to as “throughthrough suitability” is hereinafter referred to as “throughout suitability”.

  In this embodiment, “plain paper” generally refers to paper that uses pulp as a main raw material and is used in a printer or the like, and is defined by JIS P 0001 number 6139. Specific examples include high-quality paper, PPC copy paper, and non-coated printing paper. As the plain paper, those commercially available from various companies can be used. For example, various papers such as Xerox 4200 (manufactured by Xerox) and GeoCycle (manufactured by Gerogia-Pacific) can be used.

  Next, the ink composition used in the ink jet recording method of this embodiment will be described in detail.

  The ink composition according to this embodiment is preferably an aqueous ink composition in which the main solvent of the ink is water from the viewpoint of safety and handling, and the water is ion-exchanged water, ultrafiltered water, reverse osmosis. It is preferable to use pure water or ultrapure water such as water or distilled water. In particular, it is preferable to use water sterilized by ultraviolet irradiation or addition of hydrogen peroxide in order to prevent the generation of mold and bacteria and to enable long-term storage of the ink. From the viewpoint of ensuring appropriate physical properties (such as viscosity) of the ink and ensuring the stability and reliability of the ink, water is preferably contained in the ink composition in an amount of 60% by mass to 10% by mass.

  By defining the content of water contained in the ink composition within the above range, the amount of water absorbed by cellulose in plain paper is less than that of conventional ink compositions, resulting in cockling and curling. The thought swelling of cellulose can be suppressed. Hereinafter, properties suitable for suppressing cockling or curling are also referred to as “cockling suitability” and “curl suitability”, respectively.

  When the water content is less than 10% by mass, the fixability to the recording medium may be lowered. On the other hand, when the water content exceeds 60% by mass, like a conventional aqueous ink composition, when printing on a recording medium having an absorption layer of a paper support with poor ink absorbability, Curling is likely to occur.

  The viscosity of the ink in the temperature range of 10 ° C. to 40 ° C. is affected by the temperature characteristics of the colorant, humectant, solvent, etc. contained in the ink. Among these, the influence of the humectant is particularly great, and the viscosity at 10 ° C. is likely to increase and the viscosity at 40 ° C. is likely to decrease depending on the type, addition amount, and content ratio of the humectant. In the present specification, the fact that the difference in viscosity at 10 ° C. to 40 ° C. is smaller is described as being excellent in the viscosity characteristics depending on the temperature of the ink.

  The moisturizing agent used in the present embodiment is (A) glycerin, 1, 2, 6 from the viewpoint of maintaining an appropriate balance of curling, cockling suitability, suitability for back-through, clogging suitability, and viscosity characteristics depending on ink temperature. -At least one compound selected from the group consisting of hexanetriol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, (B) at least one compound selected from the group consisting of trimethylolpropane and trimethylolethane (C) A mixture of at least one compound selected from the group consisting of betaines, sugars and ureas and having a molecular weight in the range of 100 to 200.

The moisturizing agent (A) is particularly effective for suppressing clogging and also has an effect for suppressing curling and cockling. However, the material is inferior in penetrability due to its excellent permeability to a recording medium. Glycerin and triethylene glycol are preferred as the humectant of (A) from the viewpoint of more effectively and surely achieving the above effects.
The moisturizing agent (B) is particularly effective for suppressing clogging, and is a substance having excellent penetration-throughability since it has a permeation suppressing effect. From the viewpoint of more effectively and surely achieving these effects, trimethylolpropane is preferred as the humectant of (B).
The humectants of (A) and (B) have a large viscosity difference between 10 ° C. and 40 ° C. of the substance, so that as the content in the ink composition increases, the viscosity characteristics due to temperature are greatly affected. The ink composition also has a large viscosity difference at 10 ° C to 40 ° C.

  The humectant (C) is a substance that has a particularly high effect of suppressing uneven image density and is excellent in curling and cockling suitability. Further, this humectant is a substance having excellent viscosity characteristics depending on temperature. Specifically, as the humectant of (C), glycine betaine (molecular weight 117, also referred to as “trimethylglycine”), γ-butyrobetaine (145), homarine (137), trigonelline (137), carnitine ( 161), homoserine betaine (161), valine betaine (159), lysine betaine (188), ornithine betaine (176), alanine betaine (117), stachydrin (185) and glutamate betaine (189) ) Betaines which are N-trialkyl-substituted amino acids such as glucose (180), mannose (180), fructose (180), ribose (150), xylose (150), arabinose (150) ), Galactose (180) and sorbitol (182) Sugars such as allyl urea (100), N, N-dimethylolurea (120), malonyl urea (128), carbamylurea (103), 1,1-diethylurea (116), n-butyl Examples include ureas (116), creatinine (113), and benzylurea (150). Moreover, the tendency for the viscosity difference in 10 to 40 degreeC to become large that the molecular weight is less than 100 becomes strong. On the other hand, when the molecular weight is 200 or more, the viscosity of the ink composition tends to increase with respect to the amount of the humectant added to the ink composition. Therefore, the molecular weight of the humectant (C) is preferably in the range of 100 to 200. Among these, betaines and saccharides are preferable, and betaines are more preferable because the effect of suppressing unevenness in image density is particularly high. From the same viewpoint, as the betaines, glycine betaine is more preferable, and as the saccharide, sorbitol is more preferable. Among these, glycine betaine is particularly preferable. As the glycine betaine, for example, a commercially available product such as amino coat (manufactured by Asahi Kasei Chemicals Corporation) can also be used.

  By using the humectants (A) and (C) in combination, image density unevenness can be effectively suppressed. The reason for this is currently unknown in detail. However, the inventors of the present invention, as one of the factors, use the humectant of (A) and (C) alone and examine the moisturizing property, respectively. However, it is higher than the moisturizing property by the humectant of (A), in other words, the evaporation rate of water by the humectant of (C) is slower than the evaporation rate of water by the humectant of (A). I believe that In particular, the humectant (C) such as glycine betaine is a liquid phase (coating film) and a gas phase on the surface (interface) of the ink coating formed immediately after the ink composition has landed on the recording medium. It is presumed to have a molecular density gradient that has a buffering effect and exerts a barrier function against rapid drying. Then, it is presumed that rapid moisture evaporation is suppressed by the increase in the molecular density in the vicinity of the interface due to the molecular density gradient.

These humectants are contained in the ink composition in a total amount of (A), (B) and (C) from the viewpoints of suppression of image density unevenness, curl suitability, cockling suitability, showthrough suitability and clogging suitability. It is preferable that 40 mass% is contained.
Moreover, about those moisturizers, the mass ratio of the contents is (A) :( B) :( C) = (1.0) :( 0) from the viewpoint of exerting the above-described effects of the moisturizer in a balanced manner. .1-1.0) :( 1.0-3.0). From the same viewpoint, (A) :( B) is preferably (1.0) :( 0.2-0.5), more preferably (1.0) :( 0.3-0.45). From the same viewpoint, (A) :( C) is preferably (1.0) :( 1.0-2.0), and (1.0) :( 1.0-1.5) is more preferable. preferable. When the mass ratio of the humectant of (B) to the humectant selected from the group of (A) (referred to as “(A) humectant” hereinafter the same) is larger than the above, curl suitability and cockling. The suitability decreases, and if it is decreased, the strike-through aptitude decreases. When the mass ratio of the humectant of (C) is larger than the above with respect to the humectant of (A), the clogging suitability is lowered, and when it is reduced, it is particularly difficult to suppress unevenness in image density. Cockling suitability decreases.

  In addition, the ink composition according to the present embodiment prevents clogging in the vicinity of the nozzles of the inkjet head, moderately controls the penetration and bleeding of the ink into the recording medium, suppresses image density unevenness, For the purpose of imparting the drying property, it is preferable to contain a water-soluble organic solvent. From the above viewpoint, the water-soluble organic solvent preferably contains 1,2-alkanediol and / or glycol ether. Specific examples of 1,2-alkanediol include 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol, and 4-methyl-1,2-pentanediol. Specific examples of the glycol ether include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether. Ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol mono-n-butyl ether, 1-methyl-1-methoxybutanol, propylene Recall monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, di Examples include propylene glycol mono-n-propyl ether and dipropylene glycol mono-iso-propyl ether. In addition to the above, 2-pyrrolidone, N-methyl-2-pyrrolidone and the like can also be used as the water-soluble organic solvent. These water-soluble organic solvents can be used singly or in combination of two or more, and 1 mass in the ink composition from the viewpoint of ensuring appropriate physical properties (such as viscosity) of the ink, ensuring print quality, and reliability. % To 50% by mass is preferable.

  Furthermore, the ink composition preferably contains a surface tension adjusting agent in order to control the wettability of the ink to the recording medium and to obtain the permeability to the recording medium and the printing stability in the ink jet recording method. As the surface tension adjusting agent, acetylene glycol surfactants and polyether-modified siloxanes are preferable. Examples of acetylene glycol-based surfactants include Surfynol 420, 440, 465, 485, 104, STG (above, Air Products, product name), Olfine PD-001, SPC, E1004, E1010 (above, day). Shinken Chemical Co., Ltd., product name), acetylenol E00, E40, E100, LH (above, Kawaken Fine Chemicals Co., Ltd., product name). Examples of the polyether-modified siloxanes include BYK-346, 347, 348, and UV3530 (Bic Chemie product). These may be used alone or in combination of two or more in the ink composition, and are included so that the surface tension of the ink composition is preferably adjusted to 20 mN / m to 40 mN / m, preferably 0 in the ink composition. .1% by mass to 3.0% by mass.

  If necessary, a pH adjuster, a complexing agent, an antifoaming agent, an antioxidant, an ultraviolet absorber, an antiseptic / antifungal agent, and the like can be added to the ink composition. As the pH adjuster, for example, an alkali hydroxide such as lithium hydroxide, potassium hydroxide, or sodium hydroxide and / or an alkanolamine such as ammonia, triethanolamine, tripropanolamine, diethanolamine, or monoethanolamine can be used. it can. In particular, it is preferably adjusted to pH 6 to 10 including at least one pH adjusting agent selected from alkali metal hydroxide, ammonia, triethanolamine, and tripropanolamine. When the pH is out of this range, there is an adverse effect on the material constituting the ink head printer, and the clogging recovery property tends to deteriorate. Examples of the complexing agent include aminopolycarboxylic acids such as ethylenediaminetetraacetic acid and salts thereof (for example, sodium salt and ammonium salt) and salts thereof.

  As the pigment used in the present embodiment, any of known inorganic pigments and organic pigments can be used. Examples of such pigments include pigment yellow, pigment red, pigment violet, pigment blue, and pigment black described in the Color Index, as well as phthalocyanine, azo, anthraquinone, azomethine, and condensed rings. Examples thereof include pigments of the type. Further, organic pigments such as yellow No. 4, No. 5, 205, 401; orange No. 228, 405; blue No. 1, 404, carbon black, titanium oxide, zinc oxide, zirconium oxide, iron oxide, ultramarine , Inorganic pigments such as bitumen and chrome oxide. Examples of the color index of the pigment include C.I. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42, 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 128, 138, 150, 153, 155, 174, 180, 198, C.I. I. Pigment Red 1,3,5,8,9,16,17,19,22,38,57: 1,90,112,122,123,127,146,184,202, C.I. I. Pigment Bio Red 1,3,5: 1, 16, 19, 23, 38, C.I. I. Pigment Blue 1, 2, 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, C.I. I. Pigment Black 1 and 7 may be mentioned, and one or more pigments may be included in the ink composition.

  The pigment used in the present embodiment may be a resin dispersion type. The pigment of such an embodiment is a pigment dispersion liquid dispersed in an aqueous medium using a ball mill, a roll mill, a bead mill, a high-pressure homogenizer, a high-speed stirring disperser, and the like, together with a dispersant such as a polymer dispersant and a surfactant. Alternatively, a dispersibility-imparting group (hydrophilic functional group and / or salt thereof) is directly or indirectly bonded to the pigment surface via an alkyl group, an alkyl ether group, an aryl group, etc., and an aqueous medium without a dispersant The pigment composition is preferably blended in the ink composition as a pigment dispersion which is processed as a self-dispersing pigment dispersed and / or dissolved therein and dispersed in an aqueous medium.

  Examples of dispersants include polymer dispersants such as natural polymer compounds such as glue, gelatin and saponin, polyvinyl alcohols, polypyrrolidones, acrylic resins (polyacrylic acid, acrylic acid-acrylonitrile copolymer, Vinyl acetate-acrylic acid copolymer, vinyl acetate-acrylic acid ester copolymer, etc.), styrene-acrylic acid resins (styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid- Acrylic acid alkyl ester copolymer, styrene-α-methylstyrene-acrylic acid copolymer, styrene-α-methylstyrene-acrylic acid-alkyl acrylate copolymer, styrene-vinyl acetate-acrylic acid copolymer, etc. ), Styrene-maleic acid resins, vinyl acetate-fatty acid vinyl-ethylene Synthetic polymer compounds such as resins of tyrene copolymer and their salts, and the like, and the constitution of the copolymer may be any of random type, block type and graft type.

  Examples of surfactants used as dispersants include anionic surfactants such as fatty acid salts, higher alkyl dicarboxylates, higher alcohol sulfate esters, higher alkyl sulfonates, fatty acid amine salts, and fatty acid ammonium salts. Nonionic surfactants such as cationic surfactants, polyoxyalkyl ethers, polyoxyalkyl esters, sorbitan alkyl esters and the like can be mentioned.

  Of these dispersants, water-insoluble resins are particularly preferable. Specifically, the water-insoluble resin is composed of a block copolymer resin of a monomer having a hydrophobic group and a monomer having a hydrophilic group, and contains at least a monomer having a salt-forming group. A resin having a solubility in 100 g of water at 25 ° C. of less than 1 g later is preferred. Examples of the monomer having a hydrophobic group include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl. Methacrylic acid esters such as methacrylate, dodecyl methacrylate, octadecyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, glycidyl methacrylate, vinyl esters such as vinyl acetate, vinylcyan compounds such as acrylonitrile and methacrylonitrile, styrene, α- Methylstyrene, vinyltoluene, 4-t-butylstyrene Emissions, chlorostyrene, vinyl anisole, aromatic vinyl monomers such as vinyl naphthalene. These can be used individually by 1 type or in mixture of 2 or more types. Examples of the monomer having a hydrophilic group include polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, and ethylene glycol / propylene glycol monomethacrylate. These may be used alone or in combination of two or more. be able to. Examples of the monomer having a salt-forming group include acrylic acid, methacrylic acid, styrene carboxylic acid, and maleic acid, and these can be used alone or in combination of two or more. Furthermore, a macromonomer such as a styrene macromonomer or a silicone macromonomer having a polymerizable functional group at one end, or other monomers can be used in combination.

  This water-insoluble resin is preferably used as a salt neutralized with a tertiary amine such as ethylamine or trimethylamine, or an alkali neutralizer such as lithium hydroxide, sodium hydroxide, potassium hydroxide or ammonia, and has a weight average molecular weight of 10,000. About ˜150,000 is preferable from the viewpoint of stably dispersing the pigment.

  A self-dispersing pigment that can be dispersed and / or dissolved in water without a dispersant is, for example, an active species having a dispersibility-imparting group or a dispersibility-imparting group by applying a physical treatment or a chemical treatment to the pigment. It is produced by bonding (grafting) to the surface of the pigment. Examples of the physical treatment include vacuum plasma treatment. Examples of the chemical treatment include a wet oxidation method in which the pigment surface is oxidized with an oxidizing agent in water, and a method in which a carboxyl group is bonded via a phenyl group by bonding p-aminobenzoic acid to the pigment surface. it can. Since the ink composition containing the self-dispersing pigment does not need to contain the above-mentioned dispersant to be contained for dispersing a normal pigment, there is almost no foaming due to the reduction of the defoaming property caused by the dispersant. It is easy to prepare an ink having excellent ejection stability. In addition, since a significant increase in viscosity due to the dispersant can be suppressed, a larger amount of pigment can be contained, the printing density can be sufficiently increased, or handling becomes easy. Because of these advantages, the self-dispersing pigment is particularly effective for black ink compositions that require a high concentration, and the black ink composition used as the ink composition of the present embodiment has no dispersant. It is preferable that at least a self-dispersing pigment that can be dispersed and / or dissolved in water is contained.

  In the present embodiment, a self-dispersing pigment that is surface-treated by oxidation treatment with hypohalous acid and / or hypohalite or ozone is preferable from the viewpoint of high color development. Commercially available products can also be used as self-dispersing pigments. Examples of such commercially available products include Microjet CW-1 (trade name; manufactured by Orient Chemical Industry Co., Ltd.), CAB-O-JET200, CAB. -O-JET300 (the above-mentioned brand name; Cabot company make) can be illustrated.

  These pigments preferably have a volume average particle diameter in the range of 50 nm to 200 nm from the viewpoint of storage stability of the ink and prevention of nozzle clogging. These volume average particle diameters can be obtained by particle diameter measurement using a Microtrac UPA150 (manufactured by Microtrac) or a particle size distribution analyzer LPA3100 (manufactured by Otsuka Electronics Co., Ltd.).

  These pigments are preferably contained in the ink composition in a range of 6% by mass or more. If the content is less than 6% by mass, the print density (color developability) may be insufficient. Moreover, the upper limit of the content is not specifically limited, For example, content may be 25 mass% or less. When the content is larger than 25% by mass, there may be a problem in reliability such as nozzle clogging or unstable discharge.

The ink composition used in the present embodiment preferably contains a resin emulsion from the viewpoint of securing fixability to a recorded matter. Also, from the viewpoint of suppressing the image density unevenness to some extent, it is preferable that the ink composition contains a resin emulsion. Originally, as the ink composition landed on the surface of the recording medium is dried, the resin emulsion associates with the pigment particles and deforms and forms a film, thereby fixing the pigment on the surface of the recording medium. The However, in the mixed system with the humectant (C) such as glycine betaine as in the present embodiment, the humectant of (C) starts from the resin emulsion on the coating film surface (interface) of the ink composition. Since the molecular density is likely to increase, abrupt moisture evaporation is suppressed in combination with the progress of film formation by the resin emulsion, so that it is estimated that the image density unevenness is suppressed to some extent.

The resin emulsion preferably contains resin fine particles having a minimum film forming temperature of less than 20 ° C. By using a resin emulsion containing resin fine particles having a minimum film-forming temperature of less than 20 ° C., the resin fine particles are formed into a film at an ambient temperature under a use environment that is usually 20 ° C. or higher. Improves fixing properties and abrasion resistance on recording media.
Here, the minimum film-forming temperature is measured as follows. First, a resin emulsion is applied to a thickness of 0.3 mm on a stainless steel plate of a temperature gradient test apparatus. Immediately after application, the basket containing silica gel is placed on a plate and covered with a transparent plastic lid. After the coating film has dried, the temperature at the boundary between the uniform continuous film portion and the cloudy portion is read to obtain the minimum film forming temperature.

  These resin emulsions contain one or more resin fine particles selected from the group consisting of acrylic resins, methacrylic resins, vinyl acetate resins, vinyl chloride resins, and styrene-acrylic resins. Is preferred. These resins may be used as a homopolymer or may be used as a copolymer, and any of a single-phase structure and a multiphase structure (core-shell type) can be used.

Furthermore, at least one of the resin emulsions contained in the ink composition used in the present embodiment is blended in the ink composition in the form of an emulsion of resin fine particles obtained by emulsion polymerization of unsaturated monomers. It is preferable. Even if the resin fine particles are added alone to the ink composition, the dispersion of the resin fine particles may be insufficient. Therefore, in the production of the ink composition, the emulsion form is preferable. The emulsion is preferably an emulsion of acrylic resin fine particles, that is, an acrylic emulsion, from the viewpoint of the storage stability of the ink composition.
An emulsion of resin fine particles (such as an acrylic emulsion) can be obtained by a known emulsion polymerization method. For example, an unsaturated monomer (such as an unsaturated vinyl monomer) can be obtained by emulsion polymerization in water in which a polymerization initiator and a surfactant are present.

  Examples of unsaturated monomers include acrylic acid ester monomers, methacrylic acid ester monomers, aromatic vinyl monomers, vinyl ester monomers, vinyl cyanide monomer monomers that are generally used in emulsion polymerization. , Halogenated monomers, olefin monomers, and diene monomers.

  More specifically, as an unsaturated monomer, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate Acrylates such as octyl acrylate, decyl acrylate, dodecyl acrylate, octadecyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, glycidyl acrylate; methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n -Amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate , Methacrylates such as 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, glycidyl methacrylate; vinyl esters such as vinyl acetate; vinyl such as acrylonitrile, methacrylonitrile Cyanide compounds; halogenated monomers such as vinylidene chloride and vinyl chloride; aromatic vinyl monomers such as styrene, α-til styrene, vinyl toluene, 4-t-butyl styrene, chlorostyrene, vinyl anisole, vinyl naphthalene; ethylene Olefins such as propylene; dienes such as butadiene and chloroprene; vinyls such as vinyl ether, vinyl ketone and vinyl pyrrolidone. Nyl monomer; unsaturated carboxylic acid such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid and maleic acid; acrylamides such as acrylamide, methacrylamide and N, N′-dimethylacrylamide; 2-hydroxyethyl acrylate, 2 -Hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, hydroxyl group-containing monomers such as 2-hydroxypropyl methacrylate. These may be used alone or in combination of two or more.

  A crosslinkable monomer having two or more polymerizable double bonds can also be used as the unsaturated monomer. Examples of the crosslinkable monomer having two or more polymerizable double bonds include polyethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, 1,9-nonanediol diacrylate, polypropylene glycol diacrylate, 2,2′-bis (4-acryloxypropyloxyphenyl) propane, 2,2 ′ -Diacrylate compounds such as bis (4-acryloxydiethoxyphenyl) propane; Triacrylate compounds such as trimethylolpropane triacrylate, trimethylolethane triacrylate, tetramethylolmethane triacrylate Tetraacrylate compounds such as ditrimethylol tetraacrylate, tetramethylol methane tetraacrylate, pentaerythritol tetraacrylate; hexaacrylate compounds such as dipentaerythritol hexaacrylate; ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol di Methacrylate, 1,3-butylene glycol dimethacrylate, 1,4 butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, polybutylene glycol dimethacrylate , 2, 2 Dimethacrylate compounds such as' -bis (4-methacryloxydiethoxyphenyl) propane; trimethacrylate compounds such as trimethylolpropane trimethacrylate and trimethylolethane trimethacrylate; methylenebisacrylamide; divinylbenzene. These may be used alone or in combination of two or more.

  In addition to the polymerization initiator and surfactant used in emulsion polymerization, a chain transfer agent, further a neutralizing agent, and the like may be used according to a conventional method. In particular, the neutralizing agent is preferably ammonia or an inorganic alkali hydroxide such as sodium hydroxide or potassium hydroxide.

In the present embodiment, the resin emulsion contains 1 fine resin particles in the ink composition from the viewpoint of more effectively obtaining the ink-appropriate properties of the ink composition, reliability (clogging, ejection stability, etc.), fixability, and the like. It is preferable to contain so that it may become the range of 10 mass%-10 mass%.
The volume average particle size of the resin emulsion contained in the ink composition is preferably 5 nm to 400 nm, and preferably 50 nm to 200 nm, from the viewpoints of dispersion stability of the resin fine particles in the ink composition and fixing properties. Is more preferable. The volume average particle diameter is measured using, for example, a Coulter counter N4 (trade name, manufactured by Coulter Inc.).

  The recorded matter of the present embodiment is obtained by recording by the above ink jet recording method. Since the recorded matter is obtained by the ink jet recording method according to the present embodiment, both the image density unevenness and the fixing property are suppressed, and clogging is also suppressed, so that the ink composition Is landed on the recording medium as desired, resulting in a recorded matter on which an image with little dot missing is formed. In addition, this recorded matter is excellent in the safety and stability of the ink, and always achieves the same recording quality for various recording media regardless of the operating temperature. Has ring suitability, back-through suitability, and duplex printing suitability.

  Unlike the prior art, according to the ink jet recording method of the present embodiment, the solid content in the ink composition is mainly due to the water content, the type of humectant, and the mass ratio (content ratio) of the content. Clogging can be suppressed because precipitation of solids and aggregation of solids can be prevented. That is, mainly, the content of water in the ink composition is set to 10% by mass or more, the type of the humectant is as described above, and the content ratio of the humectant (C) to the humectant (A) is 3. By setting it to 0 or less, it is possible to prevent clogging by preventing precipitation and aggregation of solids in the vicinity of the nozzle of the inkjet head. In addition, mainly by using the humectant and at the same time reducing the water content to 60% by mass or less, the drying rate of the ink composition landed on the recording medium is controlled to suppress a decrease in fixability. Is possible. And the ink composition with respect to the recording medium on the opening part of the conveyance belt and other parts mainly by making the content ratio of the humectant of (C) to the humectant of (A) 1.0 or more. Since the difference between the penetrability and the drying property can be reduced, it is possible to suppress image density unevenness.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the said this embodiment. The present invention can be variously modified without departing from the gist thereof. For example, in the above-described embodiment, a line printer including a suction fan has been described as an example. However, the recording apparatus used in the present invention can transfer a recording medium to the transport belt by vacuum suction through an opening formed in the transport belt. As long as it can form an image on a recording medium while being sucked and sucked and conveyed, a known recording device may be used, a suction fan may not be provided, and a line printer may not be used. Good. Further, when the ink composition includes a resin emulsion, the above-described ink jet recording apparatus 100 may include a heating unit and a hot air blowing unit so that printing can be performed at a temperature higher than the minimum film forming temperature of the resin emulsion.

  Hereinafter, although this embodiment is described in more detail using examples, the present embodiment is not limited to these examples.

[Preparation of colorant]
(Pigment dispersion B1)
100 g of commercially available carbon black Color Black S170 (trade name: manufactured by Degussa Huls) was mixed with 1 kg of water and pulverized by a ball mill using zirconia beads. 1400 g of sodium hypochlorite (effective chlorine concentration 12%) was added dropwise to the pulverized stock solution, reacted for 5 hours while pulverizing with a ball mill, and further boiled for 4 hours with stirring to perform wet oxidation. The obtained dispersion stock solution was filtered with glass fiber filter paper GA-100 (trade name: manufactured by Advantech Toyo Co., Ltd.) and further washed with water. The obtained wet cake was redispersed in 5 kg of water, desalted and purified with a reverse osmosis membrane until the electric conductivity reached 2 mS / cm, and further concentrated until the pigment concentration reached 20% by mass to obtain pigment dispersion B1 Was prepared.
The volume average particle size of the pigment in this dispersion was measured by particle size distribution measurement using Microtrac UPA150 (manufactured by Microtrac), and found to be 110 nm.

(Pigment dispersion B2)
The pigment dispersion B1 obtained above was dried under reduced pressure at 40 ° C. for 3 days to remove moisture. The obtained paste was weighed into a round bottom flask, triethylene glycol-mono-n-butyl ether was added so that the solid content concentration was 20% by mass, and the mixture was stirred for 24 hours using a magnetic stirrer. Subsequently, a round bottom flask containing the triethylene glycol-mono-n-butyl ether dispersion was placed in the ultrasonic cleaning tank, and the dispersion was subjected to vacuum degassing for 8 hours with an aspirator while performing ultrasonic dispersion. The inside air was completely replaced with triethylene glycol mono-n-butyl ether to obtain a pigment dispersion B2.

(Pigment dispersion Y1)
In a reaction vessel sufficiently substituted with nitrogen gas using 20 parts by mass of an organic solvent (methyl ethyl ketone), 0.03 parts by mass of a polymerization chain transfer agent (2-mercaptoethanol), a polymerization initiator, and each monomer shown in Table 1. The mixture was polymerized under stirring at 75 ° C., 0.9 part by mass of 2,2′-azobis (2,4-dimethylvaleronitrile dissolved in 40 parts by mass of methyl ethyl ketone was added to 100 parts by mass of the monomer component, and 80 ° C. For 1 hour to obtain a polymer solution.

5 parts by mass of the polymer solution obtained by drying the obtained polymer solution under reduced pressure was dissolved in 15 parts by mass of methyl ethyl ketone, and the polymer was neutralized with an aqueous sodium hydroxide solution. Furthermore, C.I. I. 15 parts by weight of Pigment Yellow 74 was added, and further kneaded with a disperser while adding water. After adding 100 parts by mass of ion-exchanged water to the obtained kneaded product and stirring, the yellow ethyl pigment having a solid content concentration of 20% by mass is removed by removing methyl ethyl ketone at 60 ° C. under reduced pressure and further removing a part of the water. An aqueous dispersion (pigment dispersion Y1) was obtained.
The volume average particle size of the pigment in this dispersion was measured by measuring the particle size distribution of Microtrac UPA150 (manufactured by Microtrac) and found to be 100 nm.

(Pigment dispersion M1)
C. I. Instead of CI Pigment Yellow 74, C.I. I. A pigment dispersion M1 was obtained in the same manner as in the preparation of the pigment dispersion Y1 except that CI Pigment Red 122 was used.
The volume average particle diameter of the pigment of this dispersion was measured by particle size distribution measurement of Microtrac UPA150 (manufactured by Microtrac), and it was 140 nm.

(Pigment dispersion C1)
C. I. Instead of CI Pigment Yellow 74, C.I. I. A pigment dispersion C1 was obtained in the same manner as in the preparation of the pigment dispersion Y1, except that CI Pigment Blue 15: 4 was used.
The volume average particle size of the pigment in this dispersion was measured by measuring the particle size distribution of Microtrac UPA150 (manufactured by Microtrac), and found to be 80 nm.

(dye)
Acid Red 249 was used.

[Preparation of resin emulsion]
A resin emulsion (polymer 1) having a minimum film forming temperature of less than 20 ° C. is produced by emulsion polymerization of 20 g of acrylamide with 600 g of methyl methacrylate, 125 g of n-butyl acrylate, 30 g of methacrylic acid, and 5 g of triethylene glycol diacrylate in water. did. The volume average particle diameter of resin fine particles in the emulsion was 50 nm, and the minimum film forming temperature was 10 ° C. The volume average particle diameter of the resin fine particles was measured using a Coulter Counter N4 (trade name, manufactured by Coulter Inc.), and the minimum film forming temperature was measured as described above.

  A resin emulsion (polymer 2) having a minimum film forming temperature of 20 ° C. or higher was produced by emulsion polymerization of 20 g of acrylamide with 600 g of styrene, 200 g of n-butyl acrylate, and 30 g of methacrylic acid in water. The volume average particle diameter of resin fine particles in the emulsion was 130 nm, and the minimum film forming temperature was 36 ° C. The volume average particle diameter of the resin fine particles was measured using a Coulter Counter N4 (trade name, manufactured by Coulter Inc.), and the minimum film forming temperature was measured as described above.

[Preparation of ink composition]
After mixing each component in the ratio shown in Table 2 and stirring at room temperature for 2 hours, the mixture was filtered with a membrane filter having a pore size of 5 μm, and the ink compositions of Production Examples 1 to 9 and Comparative Production Examples 1 to 5 were used. Prepared. However, the addition amounts shown in Table 2 are all expressed as mass% concentrations, the numbers in () of the pigment dispersion indicate the solid content concentration (mass%) of the pigment, and the numbers in () of the resin emulsion. Indicates the resin fine particle concentration (% by mass). The “remaining amount” of ion-exchanged water means adding ion-exchanged water so that the total amount of the ink composition becomes 100% by mass.

<Evaluation of ink composition>
(Test 1) Back-through of ink About each of the obtained ink compositions, as shown in FIG. 2, using a line-type ink jet printer provided with a transport belt having an opening, the following three types of plain paper were used: A solid image was printed at% duty, 600 × 600 dpi. As plain paper, Xerox P (manufactured by Fuji Xerox), Xerox 4024 (manufactured by Xerox Co.), and recycle cut R-100 (manufactured by Oji Paper Co., Ltd.) were used. The printed matter was allowed to stand for 24 hours in an environment of 24 ° C., and then the through-through state of the ink on the back side of the printed surface was visually evaluated. The evaluation criteria were as follows.
A: Almost no ink breakthrough is observed.
B: Back-through of ink is recognized, but there is no problem in reprinting on the back side.
C: There was considerable ink back-through, which hindered reprinting on the back side.
The evaluation results are shown in Table 3.

(Test 2) Image density unevenness Using an ink jet printer similar to the above, a half density image was printed on the following three types of plain paper at 25% duty and 600 × 600 dpi. As plain paper, Xerox P (manufactured by Fuji Xerox), Xerox 4024 (manufactured by Xerox Co.), and recycle cut R-100 (manufactured by Oji Paper Co., Ltd.) were used. After the printed matter was left for 24 hours in an environment of 24 ° C., image density unevenness corresponding to the belt suction opening on the printed surface was visually evaluated. The evaluation criteria were as follows.
A: Image density unevenness is not recognized at all.
B: Image density unevenness is slightly observed, but is within an allowable range.
C: Image density unevenness is clearly recognized and is outside the allowable range.
The evaluation results are shown in Table 3.

(Test 3) Fixability immediately after printing A solid image was printed at 600 × 600 dpi on Epson photographic paper <Glossy> (manufactured by Seiko Epson Corporation), which is glossy paper, using an ink jet printer similar to the above. Immediately after printing, the printed surface was strongly rubbed with a finger, and the state of the printed surface was visually observed. The evaluation criteria were as follows.
A: Ink cannot be taken at all.
B: Some ink is removed, but the fingers are not soiled.
C: Ink is removed and the finger is soiled.
The evaluation results are shown in Table 3.

(Test 4) Color development (optical density (OD value))
The OD value of the solid image printed in Test 1 was measured 5 times (at 5 locations) using a Gretag densitometer (manufactured by Gretag Macbeth). Then, an arithmetic average value for each ink composition was obtained, and an optical density value (OD value) was evaluated based on the following determination criteria for the calculated average OD value.
A: 1.2 or more B: 1.1 or more and less than 1.2 C: less than 1.1 Table 3 shows the evaluation results.

(Test 5) Clogging recovery property Using an ink jet printer similar to the above, printing was continued for 10 minutes, and after confirming that ink was normally discharged from all nozzles, the ink cartridge was removed and recording was performed. With the head removed from the head cap, it was left in an environment of 40 ° C. for 1 week. After leaving, the cleaning operation (the same cleaning operation as PX-B500 (manufactured by Seiko Epson)) is repeated until all the nozzles discharge to the same level as the initial stage, and it is easy to recover the discharge performance from the clogged state according to the following criteria. Was evaluated.
A: It recovered to the same level as the initial stage by cleaning operation less than 6 times.
B: It recovered to the same level as the initial stage after 6 to 12 cleaning operations.
C: It recovered to the same level as the initial stage after cleaning 12 times or more.
The evaluation results are shown in Table 3.

  As is apparent from Table 3, according to the ink jet recording method of the present invention, the fixing property of the ink composition on the recording medium is reduced, the ink jet head is clogged, and the density of the image formed on the recording medium is uneven. All of can be suppressed.

  DESCRIPTION OF SYMBOLS 100 ... Inkjet recording apparatus, 101 ... Recording medium, 110 ... Inkjet head, 120 ... Platen part, 130 ... Conveyance belt, 130A ... Opening part, 140 ... Conveyance roller, 150 ... Discharge roller, 160 ... Conveyance means, 170 ... Follow-up Roller, 180 ... driving roller, 190 ... inkjet head unit, 210 ... vacuum suction unit, 210A ... suction fan, 210B ... housing, 210C ... opening.

Claims (5)

An ink jet recording method comprising a step of forming an image on the recording medium while sucking and adsorbing the recording medium to the conveying belt by vacuum suction via an opening formed in the conveying belt,
In the forming step, the image is formed by landing an ink composition on a printing surface opposite to the conveying belt side of the recording medium,
The ink composition contains at least 60% by mass to 10% by mass of water in the total amount of the pigment, the humectant, and the ink composition,
The humectant is a mixture of the following compounds (A), (B) and (C), and the mass ratio of the contents thereof is (A) :( B) :( C) = (1. 0): (0.1-1.0): (1.0-3.0),
Inkjet recording method.
(A) At least one compound selected from the group consisting of glycerin, 1,2,6-hexanetriol, diethylene glycol, triethylene glycol, tetraethylene glycol and dipropylene glycol.
(B) At least one compound selected from the group consisting of trimethylolpropane and trimethylolethane.
(C) At least one compound selected from the group consisting of betaines, sugars and ureas and having a molecular weight in the range of 100 to 200.   The inkjet recording method according to claim 1, wherein the compound (C) contains betaines.   The ink jet recording method according to claim 1, wherein the ink composition further contains a resin emulsion.   The inkjet recording method according to claim 3, wherein the resin emulsion includes resin fine particles having a minimum film forming temperature of less than 20 ° C. 5.   The recorded matter recorded by the inkjet recording method as described in any one of Claims 1-4.

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