JP2015150694A - Image recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image recording method capable of obtaining an image with high ink fixability and suppressed graininess. To provide a clear ink for applying a clear ink containing resin particles to a recording medium. And an ink application process for applying an ink containing a pigment so as to at least partially overlap a region of the recording medium to which the clear ink is applied, the method comprising: The absorption coefficient Ka is 0.3 mL / m 2 · ms 1/2 or less, and the viscosity of the clear ink applied to the recording medium is 1.0 to 102 mPa · s or more when the ink is applied in the ink application step. An image recording method, which is performed when the pressure is less than 6.0 to 103 mPa · s. [Selection figure] None

Description

  The present invention relates to an image recording method.

  In recent years, an image recording method for recording an image using water-based ink on printing paper, which is a poorly permeable recording medium, and glass, plastic, film, etc., which are non-permeable recording media, has been studied. In such an image recording method, the water-based ink is hardly absorbed or not absorbed by the recording medium, so that the water-based ink is difficult to spread on the recording medium, and an image having a graininess may be obtained. . Further, the fixability of the ink on the recording medium was also low. In order to solve such a technical problem, Patent Document 1 describes a method for hydrophilizing the surface of a recording medium by applying a clear ink containing a specific resin prior to the ink to the recording medium. Has been.

JP 2011-98540 A

  However, according to the study by the present inventors, even with the method described in Patent Document 1, the graininess cannot be sufficiently suppressed. Further, the ink fixing property was not sufficient.

  Accordingly, an object of the present invention is to provide an image recording method capable of obtaining an image having high ink fixability and suppressed graininess even on a hardly permeable or non-permeable recording medium. is there.

The above object is achieved by the present invention described below. That is, the image recording method according to the present invention overlaps at least partly with a clear ink applying step for applying a clear ink containing resin particles to a recording medium, and a region of the recording medium to which the clear ink is applied. An ink application step of applying an ink containing a pigment to the ink, and the water absorption coefficient Ka of the recording medium is 0.3 mL / m ² · ms ^1/2 or less, and the ink in the ink application step Is applied when the viscosity of the clear ink applied to the recording medium is 1.0 × 10 ² mPa · s or more and less than 6.0 × 10 ³ mPa · s.

  According to the present invention, it is possible to provide an image recording method capable of obtaining an image having high ink fixability and suppressed graininess.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments.

<Image recording method>
The image recording method of the present invention includes a clear ink applying step for applying a clear ink containing resin particles to a recording medium, and an ink containing a pigment so as to at least partially overlap a region to which the clear ink of the recording medium is applied. And an ink applying step for applying the ink. Furthermore, it is preferable to have a heating and drying step for heating and drying the recording medium between the clear ink applying step and the ink applying step. Hereinafter, each step will be described in detail.

(Clear ink application process)
The clear ink applied in the clear ink application process contains resin particles. In addition, you may have an aqueous medium and surfactant.

(Ink application process)
As a result of the study by the present inventors, in the preceding clear ink application step, the viscosity of the clear ink applied to the recording medium is 1.0 × 10 ² mPa · s or more and less than 6.0 × 10 ³ mPa · s. At some point, it has been found that by applying ink to the recording medium, the ink is buried in the clear ink layer, so that the fixability of the ink is improved. Furthermore, since the clear ink layer acts like an ink receiving layer, it is possible to suppress the graininess of the image, rather than directly applying ink to a hardly permeable or non-permeable recording medium.

(Heat drying process)
Examples of the heat drying method include a method of heating the recording medium and a method of applying heated air (warm air) to the recording medium. At this time, the heating temperature of the recording medium and the temperature of the hot air are preferably set to 50 ° C. or higher so that only water of the ink applied to the recording medium is efficiently evaporated.

<Clear ink>
In the present invention, the clear ink means that the ratio A _max / A _min between the maximum absorbance A _max and the minimum absorbance A _min in the wavelength range of 400 nm to 780 nm, which is the wavelength range of visible light, is 1.0 or more and 2.0 or less. Ink. This means that in the wavelength range of visible light, there is substantially no absorbance peak, or even if it has, the intensity of the peak is extremely small. The clear ink preferably contains no color material. In the examples of the present invention to be described later, the above absorbance was measured with a Hitachi double beam spectrophotometer U-2900 (manufactured by Hitachi High-Technologies) using undiluted clear ink. The absorbance may be measured by diluting the clear ink. This is because the values of the maximum absorbance A _max and the minimum absorbance A _min of the clear ink are both proportional to the dilution factor, and the value of A _max / A _min does not depend on the dilution factor.

(Resin particles)
In the present invention, the “resin particle” means a resin dispersed in water in a state having a particle size. Specifically, acrylic particles synthesized by emulsion polymerization of monomers such as (meth) acrylic acid alkyl ester and (meth) acrylic acid alkylamide; (meth) acrylic acid alkyl ester and (meth) acrylic acid alkylamide And styrene-acrylic particles synthesized by emulsion polymerization of styrene monomers; polyethylene particles, polypropylene particles, polyurethane particles, styrene-butadiene particles, and the like. In addition, core-shell type resin particles with different polymer compositions between the core part and the shell part constituting the resin particles, and acrylic fine particles synthesized in advance to control the particle diameter are used as seed particles, and emulsion polymerization is performed around them. The resulting particles may be used. Furthermore, hybrid resin particles in which different resin particles such as acrylic resin particles and urethane resin particles are chemically bonded may be used.

  The monomer constituting the resin particles is synthesized from (meth) acrylic acid; alkyl alcohol such as methyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and (meth) acrylic acid. (Meth) acrylic acid alkyl ester; (meth) acrylamide, dimethyl (meth) acrylamide, N, N-dimethylethyl (meth) acrylamide, N, N-dimethylpropyl (meth) acrylamide, isopropyl (meth) acrylamide, diethyl (meth) ) (Meth) acrylic acid alkylamides such as acrylamide (meth) acryloylmorpholine. In the present invention, from the viewpoint of affinity with the A block, it is preferable to synthesize the resin particles using the same type of unit as the A block.

  The resin particles used in the ink of the present invention have a polystyrene-equivalent number average molecular weight (Mn) obtained by GPC of 100,000 to 3,000,000, and more preferably 300,000 to 2,000,000. The following is preferable.

  The average particle size of the resin particles used in the ink of the present invention is preferably 50 nm or more and 250 nm or less. When the average particle size is less than 50 nm, the surface area of the resin particles per unit volume increases, and the cohesive force between the particles increases, so that the effect of improving storage stability may not be sufficiently obtained. On the other hand, if the average particle size is larger than 250 nm, the sedimentation rate of the resin particles in the ink is increased, so that the effect of improving the ink ejection stability and storage stability may not be sufficiently obtained.

  The content (% by mass) of the resin particles used in the ink of the present invention is preferably 1% by mass or more and 10% by mass or less based on the total mass of the clear ink. Furthermore, 3 mass% or more and 8 mass% or less are more preferable.

(Aqueous medium)
The clear ink of the present invention preferably contains an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As water, ion exchange water (deionized water) is preferably used. Examples of the water-soluble organic solvent include alkyl alcohols having 1 to 4 carbon atoms, amides, polyalkylene glycols, glycols, alkylene glycols having 2 to 6 carbon atoms in the alkylene group, and polyhydric alcohols. , Alkyl ethers of polyhydric alcohols, nitrogen-containing compounds, and the like. These water-soluble organic solvents can be used alone or in combination of two or more. The content (% by mass) of water in the clear ink is 10.0% by mass or more and 90.0% by mass or less, and further 30.0% by mass or more and 80.0% by mass or less based on the total mass of the clear ink. Preferably there is. The content (% by mass) of the water-soluble organic solvent in the clear ink is 8.0% by mass or more and 60.0% by mass or less, and further 10.0% by mass or more and 50. It is preferable that it is 0 mass% or less.

(Other ingredients)
In addition to the above components, the clear ink of the present invention includes a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, and a chelate as necessary. Various additives such as an agent and a resin other than the above triblock polymer may be contained. The content (% by mass) of such an additive in the clear ink is 0.05% by mass or more and 10.0% by mass or less, and further 0.2% by mass or more and 5.0% by mass based on the total mass of the clear ink. It is preferable that it is below mass%.

  In particular, in the present invention, it is preferable to contain a silicone-based surfactant or a fluorine-based surfactant.

<Ink>
(Pigment)
In the present invention, any known inorganic pigment or organic pigment can be used as the ink. As a method for dispersing the pigment, a resin dispersion type pigment using a resin as a dispersant (a resin dispersed pigment using a polymer dispersant, a microcapsule pigment in which the surface of pigment particles is coated with a resin, a polymer on the surface of pigment particles) Polymer-bonded self-dispersing pigments in which organic groups containing are chemically bonded) and self-dispersing type pigments (self-dispersing pigments) in which hydrophilic groups are introduced on the surface of pigment particles. Of course, it is also possible to use pigments having different dispersion methods in combination. The content of the pigment is suitably 0.1% by mass or more and 20.0% by mass or less based on the total mass of the ink, and more preferably 1.0% by mass or more and 12.0% by mass or less. preferable.

(Aqueous medium and other components)
For the ink, water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent can be used. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.0 mass% or more and 50.0 mass% or less based on the total mass of the ink. As the water-soluble organic solvent, those similar to the water-soluble organic solvents listed as usable for clear ink can be used. It is preferable to use deionized water (ion exchange water) as the water. The content (% by mass) of water in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. In addition, as the ink, the same components as those described above that can be used for the clear ink can be used.

<Recording medium>
The recording medium used in the present invention has an absorption coefficient Ka for water of 0.3 mL / m ² · ms ^1/2 or less. Specific examples include printing paper that is a hardly permeable recording medium; glass, plastic, and film that are non-permeable recording media. More specifically, “OK Top Coat +” made by Oji Paper, “Aurora Coat” made by Nippon Paper Industries, “Recycle Coat T-6”, “Tokuhishi Art” made by Mitsubishi Paper Industries, etc.

In the present invention, as a method for deriving the absorption coefficient Ka of the recording medium, the JAPAN TAPPI paper pulp test method No. The Bristow method described in “Liquid absorbability test method for paper and paperboard” 51 is used. Since the Bristow method is described in many commercial books, detailed description is omitted, but wetting time Tw, absorption coefficient Ka (mL / m ² · ms ^1/2 ) and roughness index Vr (mL / m ²⁾ ). In the present invention, 25 ° C. water is used as the liquid that penetrates the recording medium. That is, Ka in the present invention is an absorption coefficient for water at 25 ° C.

  Note that the recording medium used in the inkjet recording method of the present invention may be cut into a desired size or may be cut into a desired size after image formation using a recording medium wound in a roll shape. It may be a thing.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited in any way by the following examples as long as the gist thereof is not exceeded. In the description of the following examples, “part” is based on mass unless otherwise specified.

(Measurement of semi-dry film viscosity)
An inkjet printer iPF5100 manufactured by Canon Inc. was used, and the resolution during recording was set to 1200 dpi (dots / inch) in the sub-scanning direction and 2400 dpi in the main scanning direction. The amount of ink ejected from one nozzle in one ejection operation is 4.5 pl.

  Using the printer, 100% duty of colorless ink was recorded in one pass on white glossy PVC KSM-VS (manufactured by Kimoto). After a certain period of time under a desired temperature environment, the colorless ink layer was quickly scraped with a squeegee, and the viscosity was measured with a viscoelasticity measuring device MCR-300 (manufactured by Anton Paar). At that time, the temperature was adjusted as necessary.

  “Duty” is a value calculated by the equation: duty (%) = actual printing dot number / (vertical pixel number × horizontal pixel number) × 100. In the equation, “actual print dot count” is the actual print dot count per unit area. “Number of vertical pixels” and “Number of horizontal pixels” are the number of vertical pixels and the number of horizontal pixels per unit area, respectively.

[Preparation of clear ink]
The following materials are mixed, sufficiently stirred and dispersed, filtered through a glass filter AP20 (MILLIPORE), and further added with an aqueous potassium hydroxide solution to adjust the pH to 9.5. Obtained.
(Clear ink 1)
・ Jonkrill 537J (manufactured by BASF) 5 parts ・ 2-pyrrolidone 20 parts ・ 2-methyl-1,3-propanediol 5 parts ・ Nonionic surfactant FS-3100 (manufactured by DuPont) 1 part ・ Ion-exchanged water 69 parts (Clear ink 2)
・ Jonkrill 537J (made by BASF) 5 parts ・ Diethylene glycol monoethyl ether 20 parts ・ 2-methyl-1,3-propanediol 5 parts ・ Nonionic surfactant FS-3100 (made by DuPont) 1 part ・ Ion-exchanged water 69 (Clear ink 3)
・ Jonkrill 537J (manufactured by BASF) 5 parts ・ 2-pyrrolidone 5 parts ・ 2-methyl-1,3-propanediol 10 parts ・ Nonionic surfactant FS-3100 (manufactured by DuPont) 1 part ・ Ion-exchanged water 79 parts (Clear ink 4)
・ Johncrill 537J (BASF) 5 parts ・ Glycerin 20 parts ・ 2-Methyl-1,3-propanediol 5 parts ・ Nonionic surfactant FS-3100 (DuPont) 1 part ・ Ion-exchanged water 69 parts (Clear) Ink 5)
・ Jonkrill 678 (manufactured by BASF) 5 parts ・ 2-pyrrolidone 20 parts ・ 2-methyl-1,3-propanediol 5 parts ・ Nonionic surfactant FS-3100 (manufactured by DuPont) 1 part ・ Ion-exchanged water 69 parts

[Preparation of ink]
The following materials are mixed, sufficiently stirred and dispersed, filtered through a glass filter AP20 (manufactured by MILLIPORE), and inks 1 and 2 having pH adjusted to 9.5 by appropriately adding an aqueous potassium hydroxide solution are prepared. did.
(Ink 1)
・ CAB-O-JET265M (manufactured by Cabot) 5 parts ・ Johncrill 537J (manufactured by BASF) 5 parts ・ 2-pyrrolidone 20 parts ・ 2-methyl-1,3-propanediol 5 parts ・ Nonionic surfactant FS-3100 (DuPont) 1 part ・ Ion-exchanged water 64 parts (Ink 2)
・ CAB-O-JET265M (manufactured by Cabot) 5 parts ・ Johncrill 678 (manufactured by BASF) 5 parts ・ Diethylene glycol 15 parts ・ 2-methyl-1,3-propanediol 5 parts ・ Nonionic surfactant FS-3100 (DuPont) (Made) 1 part ・ 69 parts of ion-exchanged water

[Production of image]
Inkjet printer iPF5100 (manufactured by Canon Inc.) was filled with the combination of clear ink and ink described in Table 1. Using the printer, clear ink was printed on white glossy vinyl chloride KSM-VS (manufactured by Kimoto) with a 100% duty area of 20 mm × 100 mm. A 640 W sheathed heater (manufactured by Sakaguchi Electric Heat Co., Ltd.) for heating the recording medium during and after recording was installed on the top of the head. The surface temperature of the recording medium during the clear ink application step was adjusted to the value shown in Table 1, and left for the drying time shown in Table 1. The surface temperature of the recording medium was measured with a digital radiation temperature sensor FT-H20 (manufactured by Keyence) with a real time meter. Next, the clear ink image obtained above was set in the printer, and the recording duty was recorded in 10% increments from 10% to 100% so as to overlap the clear ink application region. The “clean” mode was used as the ink recording method. Then, it heat-dried at 50 degreeC for 3 minutes. The viscosity of the clear ink at the time of ink application was measured by collecting the clear ink at the time of ink application and using a viscoelasticity measuring device MCR-300 (manufactured by Anton Paar). The evaluation method is shown below. The evaluation results are shown in Table 1.

<Image graininess>
The graininess of the image was visually observed and evaluated according to the following evaluation criteria.
A: No graininess B: Some graininess, but inconspicuous level C: Graininess was conspicuous.

<Ink fixability>
The obtained image was subjected to a scratch test with a scratch evaluation apparatus HEIDON (manufactured by Shinto Kagaku Co., Ltd.) immediately after recording, and evaluated according to the following criteria. The scratch test was performed using a sapphire scratch needle (φ = 0.5 mmR) at a scraping speed of 3.0 m / min.
A: The substrate was not visible even when the load was 500 g or more. B: The substrate was not visible when the load was 300 g or more and less than 500. C: The substrate was visible when the load was less than 500 g.

Claims (2)

A clear ink application step for applying a clear ink containing resin particles to a recording medium, and an ink application for applying an ink containing a pigment so as to at least partially overlap the area of the recording medium to which the clear ink is applied. An image recording method comprising the steps of:
The recording medium has an absorption coefficient Ka for water of 0.3 mL / m ² · ms ^1/2 or less,
The ink application in the ink application step is performed when the viscosity of the clear ink applied to the recording medium is 1.0 × 10 ² mPa · s or more and less than 6.0 × 10 ³ mPa · s. An image recording method characterized by the above. The image recording method according to claim 1, further comprising a step of heating and drying the recording medium between the clear ink application step and the ink application step.