Inkjet recording device

Abstract

To provide an inkjet recording apparatus capable of forming images that are free from smudging and highly scratch-resistant. [Solution] An inkjet recording device forms an image using a first ink and a second ink. The first minimum film-forming temperature of the first binder contained in the first ink is equal to or greater than the second minimum film-forming temperature of the second binder contained in the second ink. The inkjet recording device comprises a first ejection head, a first drying unit, a second ejection head, and a second drying unit. The first ejection head ejects the first ink onto the recording medium. The first drying unit dries the first ink ejected onto the recording medium by the first ejection head at a first drying temperature that is equal to or greater than the second minimum film-forming temperature and less than or equal to the first minimum film-forming temperature. The second ejection head ejects the second ink onto the first ink that has been dried by the first drying unit. The second drying unit dries the second ink ejected onto the first ink by the second ejection head at a second drying temperature that is equal to or greater than the first minimum film-forming temperature and less than or equal to 80°C.

Description

Technical Field

[0001] The present invention relates to an inkjet recording apparatus.

Background Art

[0002] In an inkjet recording apparatus for forming an image on a resin-made non-absorbent medium, a technique is known in which two types of inks are laminated to form an image, thereby enhancing the adhesion of the image to the non-absorbent medium (see, for example, Patent Documents 1 to 3). In such two types of inks in an inkjet recording apparatus, resin fine particles are blended as a binder for enhancing the adhesion of the image to the non-absorbent medium.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an ink containing a binder, if the formation of the binder film occurs at an early stage after landing on the non-absorbent medium, the binder film becomes a lid and the surface is closed, preventing internal drying. If the internal drying of the first ink that lands on the non-absorbent medium first is insufficient, the pinning property of the second ink that lands on the first ink is impaired, and bleeding is likely to occur in the image formed on the non-absorbent medium. On the other hand, if the formation of the binder film in the first ink and the second ink is insufficient, it becomes difficult to obtain scratch resistance in the image formed on the non-absorbent medium.

[0005] In view of the above circumstances, the object of the present invention is to provide an inkjet recording apparatus capable of forming images that are free from bleeding and have high scratch resistance. [Means for solving the problem]

[0006] To achieve the above objective, an inkjet recording apparatus according to one embodiment of the present invention is of the line type and forms an image on a recording medium by an ink set including a first ink and a second ink. The first ink and the second ink each contain a binder with a minimum film-forming temperature of 40°C to 80°C, a water-soluble organic solvent, a surfactant, and water. The first minimum film-forming temperature of the first binder contained in the first ink is equal to or greater than the second minimum film-forming temperature of the second binder contained in the second ink. The inkjet recording apparatus comprises a first ejection head, a first drying unit, a second ejection head, a second drying unit, and a control unit. The first ejection head ejects the first ink onto the recording medium. The first drying unit dries the first ink ejected onto the recording medium by the first ejection head at a first drying temperature that is above the second minimum film formation temperature and below the first minimum film formation temperature. The second ejection head ejects the second ink onto the first ink which has been dried by the first drying unit. The second drying unit dries the second ink ejected onto the first ink by the second ejection head at a second drying temperature that is between a first minimum film-forming temperature and 80°C. The control unit controls the first discharge head, the first drying unit, the second discharge head, and the second drying unit.

[0007] In this inkjet recording device, by setting the first drying temperature of the first drying section to below the first minimum film-forming temperature of the first ink, the film formation of the first ink is delayed, allowing the first ink to dry thoroughly to the interior. Furthermore, by setting the first drying temperature of the first drying section to above the second minimum film-forming temperature of the second ink, a good preheating effect is obtained on the surface of the dried first ink where the second ink lands. As a result, in this inkjet recording device, the pinning properties of the second ink on the dried first ink are improved, and blurring of the image formed on the recording medium is less likely to occur. In addition, by setting the second drying temperature of the second drying section to above the first minimum film-forming temperature of the first ink, the first binder of the first ink and the second binder of the second ink can be sufficiently film-formed, resulting in high abrasion resistance of the image formed on the recording medium.

[0008] The first ink may be clear ink or white ink. The difference between the first minimum film formation temperature and the second minimum film formation temperature may be 10°C or more.

[0009] The recording medium may be a non-absorbent medium made of resin. In this case, the inkjet recording apparatus may further include a surface treatment unit that performs surface treatment on the recording medium before the first ejection head ejects the first ink. [Effects of the Invention]

[0010] As described above, the present invention provides an inkjet recording apparatus capable of forming images that are free from bleeding and have high scratch resistance. [Brief explanation of the drawing]

[0011] [Figure 1] This is a block diagram showing the schematic configuration of an inkjet recording device according to one embodiment of the present invention. [Figure 2] This diagram shows the evaluation criteria for text smudging. [Figure 3] This diagram shows the evaluation criteria for text smudging.

Best Mode for Carrying Out the Invention

[0012] Embodiments of the present invention will be described.

[0013] [Ink Set] (Schematic Explanation) An ink set according to an embodiment of the present invention has a first ink and a second ink. The recording medium for forming an image by the ink set according to this embodiment is mainly a resin-made non-absorbent medium having a low-polarity recording surface with low ink permeability and poor ink adhesion. Examples of the resin constituting such a non-absorbent medium include polyester, polypropylene, polyethylene, polystyrene, polyvinyl chloride, and the like. The recording surface of the non-absorbent medium may be subjected to surface treatments such as corona treatment, UV treatment, plasma treatment, primer, and the like. In the following description, an example using a non-absorbent medium as the recording medium will be described, but the recording medium for forming an image by the ink set according to this embodiment may be an absorbent medium having ink permeability.

[0014] The ink set according to this embodiment is configured to be able to form an image with high rub resistance and is particularly useful for surface printing on non-absorbent media. For this reason, in the ink set according to this embodiment, typically, the first ink is a clear ink or a white ink, and the second ink is a color ink. However, in the ink set according to this embodiment, its use is not limited, and it may be used for reverse printing on a transparent non-absorbent medium, etc. When used for reverse printing, the first ink may be a color ink and the second ink may be a white ink.

[0015] (First Ink) The first ink according to this embodiment contains a first binder, a water-soluble organic solvent, a surfactant, and water. The first ink according to this embodiment is applied to the recording surface of the non-absorbent medium and dried to form a first ink layer on the non-absorbent medium.

[0016] In the first ink according to this embodiment, a first binder is blended to improve the adhesion of the image formed by the ink set to a non-absorbent medium. The first binder is configured as resin fine particles. The first minimum film-forming temperature of the first binder is 40°C or higher and 80°C or lower. In the first ink according to this embodiment, it is preferable that the content of the first binder is 3% by mass or more and 20% by mass or less.

[0017] The water-soluble organic solvent blended in the first ink according to this embodiment is not particularly limited as long as it is compatible with other components. In the first ink according to this embodiment, the drying property can be adjusted by the water-soluble organic solvent. Examples of the water-soluble organic solvent that can be used in the first ink according to this embodiment include propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, triethylene glycol monobutyl ether, 1,2-propanediol, 3-methyl-1,3-butanediol, 1,2-pentanediol, 2-methyl-1,3-propanediol, 1,3-propanediol, dipropylene glycol, butyl triglycol, 1,5-pentanediol, and 3-methyl-1,5-pentanediol. In the first ink according to this embodiment, it is preferable that the content of the water-soluble organic solvent is 1.0% by mass or more and 35% by mass or less.

[0018] The type and composition of the surfactant are not limited to those described below or in the examples, but a silicone-based surfactant is preferred as the surfactant to be incorporated into the first ink according to this embodiment. A silicone-based surfactant is a surfactant that has a siloxane bond in its molecule. In the first ink according to this embodiment, incorporating a silicone-based surfactant can improve the wettability on the recording surface of a non-absorbent media. Examples of commercially available silicone-based surfactants include Silface® SAG002 and Silface SAG503A, manufactured by Nisshin Chemical Industry Co., Ltd. In the first ink according to this embodiment, the surfactant content is preferably 0.05% by mass or more and 0.5% by mass or less.

[0019] The first ink according to this embodiment contains a white pigment in the case of a white ink. For example, titanium dioxide fine particles can be used as the white pigment. As a result, the first ink according to this embodiment can form a high-quality white image with high whiteness and opacity. The primary particle size of the titanium dioxide fine particles used as the white pigment is preferably 100 nm to 500 nm, and more preferably 150 nm to 400 nm. The titanium dioxide fine particles used as the white pigment may also be surface-treated with, for example, silica or alumina. In the first ink according to this embodiment, the content of the white pigment is preferably 3.0% by mass to 15.0% by mass.

[0020] In the first ink according to this embodiment, for example, ion-exchanged water, purified water, or distilled water can be used as water. In the first ink according to this embodiment, from the viewpoint of drying properties and ejection reliability, it is preferable that the water content is 40% by mass or more and 80% by mass or less.

[0021] (Second ink) The second ink according to this embodiment contains a second binder, a water-soluble organic solvent, a surfactant, and water. The second ink according to this embodiment is applied to a first ink layer formed on the recording surface of a non-absorbent medium and dried to form a second ink layer on the first ink layer.

[0022] The second ink according to this embodiment is formulated with a second binder to improve adhesion to non-absorbent media in the image formed by the ink set. The second binder is composed of resin fine particles. The second minimum film-forming temperature of the second binder is 40°C to 80°C. In the second ink according to this embodiment, it is preferable that the content of the second binder is 3% by mass to 20% by mass.

[0023] The water-soluble organic solvent to be incorporated into the second ink according to this embodiment is not particularly limited as long as it is compatible with other components. In the second ink according to this embodiment, the drying properties can be adjusted by the water-soluble organic solvent. Examples of water-soluble organic solvents that can be used in the second ink according to this embodiment include propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, triethylene glycol monobutyl ether, 1,2-propanediol, 3-methyl-1,3-butanediol, 1,2-pentanediol, 2-methyl-1,3-propanediol, 1,3-propanediol, dipropylene glycol, butyl triglyceride, 1,5-pentanediol, and 3-methyl-1,5-pentanediol. In the second ink according to this embodiment, the content of the water-soluble organic solvent is preferably 1.0% by mass or more and 35% by mass or less.

[0024] A silicone-based surfactant is preferred as the surfactant to be incorporated into the second ink according to this embodiment. A silicone-based surfactant is a surfactant that has a siloxane bond in its molecule. In the second ink according to this embodiment, the wetting spreadability on the first ink layer can be improved by incorporating a silicone-based surfactant. Examples of commercially available silicone-based surfactants include Silface® SAG002 and Silface SAG503A, manufactured by Nisshin Chemical Industry Co., Ltd. In the second ink according to this embodiment, the surfactant content is preferably 0.05% by mass or more and 0.5% by mass or less.

[0025] The second ink according to this embodiment contains a pigment as a coloring agent, from the viewpoint of improving the ability to prevent color mixing and the water resistance of images formed on a non-absorbent medium. The pigment may be either an inorganic pigment or an organic pigment. In addition, if necessary, these may be used in combination with an extender pigment.

[0026] Specific examples of inorganic pigments usable in the second ink according to this embodiment include, for example, carbon black and metal oxides, with carbon black being particularly preferred for black inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.

[0027] Specific examples of organic pigments that can be used in the second ink according to this embodiment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.

[0028] In the second ink according to this embodiment, the hue is not particularly limited, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of preferred chromatic pigments include CI pigment yellow, CI pigment red, CI pigment orange, CI pigment violet, CI pigment blue, and CI pigment green. The second ink according to this embodiment can use one or more selected from these chromatic pigments as the pigment.

[0029] In the second ink according to this embodiment, for example, ion-exchanged water, purified water, or distilled water can be used as water. In the second ink according to this embodiment, from the viewpoint of drying properties and ejection reliability, it is preferable that the water content is 40% by mass or more and 80% by mass or less.

[0030] (Relationship between the first lowest film formation temperature and the second lowest film formation temperature) In the ink set according to this embodiment, the first minimum film-forming temperature of the first binder contained in the first ink is equal to or greater than the second minimum film-forming temperature of the second binder contained in the second ink. This makes it easier to obtain high pinning properties of the second ink on the first ink after drying. Furthermore, in the ink set according to this embodiment, it is preferable that the difference between the first minimum film-forming temperature of the first binder contained in the first ink and the second minimum film-forming temperature of the second binder contained in the second ink is 10°C or more. This makes it even easier to obtain high pinning properties of the second ink on the first ink after drying.

[0031] (Other ingredients) The ink according to this embodiment (at least one of the first ink and the second ink) may contain components other than those mentioned above, as needed. For example, the ink according to this embodiment may contain a pigment dispersion resin that enhances the dispersibility of the pigment in a solvent. The pigment dispersion resin adsorbs onto the surface of the pigment in the pigment dispersion liquid, thereby forming a pigment dispersion together with the pigment. Examples of pigment dispersion resins include copolymers of at least one monomer from alkyl (meth)acrylate, styrene, and vinylnaphthalene, and at least one monomer from (meth)acrylic acid and maleic acid.

[0032] As the pigment dispersion resin, a resin having repeating units derived from (meth)acrylic acid ((meth)acrylic acid units), repeating units derived from (meth)acrylate alkyl ester ((meth)acrylate alkyl ester units), and styrene units is preferred. In this case, the proportion of (meth)acrylic acid units among the total repeating units of the pigment dispersion resin is preferably 4.5% by mass or more and 8.0% by mass or less. The proportion of (meth)acrylate alkyl ester units among the total repeating units of the pigment dispersion resin is preferably 35% by mass or more and 70% by mass or less. The proportion of styrene units among the total repeating units of the pigment dispersion resin is preferably 27% by mass or more and 60% by mass or less. As the pigment dispersion resin, a resin having repeating units derived from methacrylic acid, repeating units derived from methyl methacrylate, repeating units derived from butyl acrylate, and styrene units is more preferred.

[0033] In the ink according to this embodiment, the pigment dispersion resin content is preferably 0.5% by mass or more and 8.0% by mass or less, and more preferably 1.5% by mass or more and 4.0% by mass or less. In the ink according to this embodiment, by setting the pigment dispersion resin content to 0.5% by mass or more, pigment aggregation can be suppressed more effectively. In the ink according to this embodiment, by setting the pigment dispersion resin content to 8.0% by mass or less, the occurrence of ejection defects can be suppressed.

[0034] In a pigment dispersion liquid containing a pigment dispersion composed of a pigment and a pigment dispersion resin, prior to its preparation as an ink, it is preferable to use water as the dispersion medium. The pigment dispersion liquid preferably further contains a low molecular weight surfactant to improve the dispersibility of the pigment dispersion. The D50 of the pigment dispersion composed of the pigment and the pigment dispersion resin is preferably 50 nm to 200 nm, and more preferably 70 nm to 130 nm. The D50 of the pigment dispersion can be measured, for example, using a dynamic light scattering particle size distribution analyzer (e.g., Malvern's "Zetasizer Nano ZS") as a sample, using a solution obtained by diluting the pigment dispersion liquid 300 times with deionized water. In the pigment dispersion liquid, the pigment content is preferably 5.0% by mass to 25.0% by mass, and more preferably 10.0% by mass to 20.0% by mass. In the pigment dispersion liquid, the pigment dispersion resin content is preferably 2.0% by mass to 10.0% by mass, and more preferably 4.0% by mass to 8.0% by mass. In the pigment dispersion, the content of low molecular weight surfactant is preferably 0.1% by mass or more and 2.0% by mass or less, and more preferably 0.3% by mass or more and 1.0% by mass or less.

[0035] Furthermore, in addition to the pigment dispersion resin, the ink according to this embodiment may also contain various additives as needed, such as dissolution stabilizers, antioxidants, viscosity modifiers, pH adjusters, and neutralizing agents.

[0036] [Inkjet recording device] The inkjet recording apparatus 1 according to this embodiment is configured to form an image on a non-absorbent medium using the ink set according to this embodiment. Figure 1 is a block diagram showing the schematic configuration of the inkjet recording apparatus 1. The inkjet recording apparatus 1 includes a surface processing unit 2, a first ejection head 3, a first drying unit 4, a second ejection head 5, a second drying unit 6, and a control unit 7.

[0037] The inkjet recording apparatus 1 is of the line type, and the first ejection head 3 and the second ejection head 5 are configured as line heads. In the inkjet recording apparatus 1 according to this embodiment, it is preferable that the surface treatment section 2, the first ejection head 3, the first drying section 4, the second ejection head 5, and the second drying section 6 are arranged in the order from upstream to downstream in the transport direction of the non-absorbent media.

[0038] The surface treatment unit 2 applies surface treatments such as corona treatment or UV treatment to the recording surface of the non-absorbent media. As a result, the surface energy and polarity of the recording surface of the non-absorbent media are improved, leading to more uniform ink wetting and improved image adhesion.

[0039] The first ejection head 3 ejects the first ink onto the recording surface of the non-absorbent media. The first drying unit 4 dries the first ink ejected onto the recording surface of the non-absorbent media by the first ejection head 3 at a first drying temperature that is above the second minimum film-forming temperature and below the first minimum film-forming temperature. By setting the first drying temperature of the first drying unit 4 to be below the first minimum film-forming temperature of the first ink, the film formation of the first ink is delayed, and the first ink can be thoroughly dried to the interior, thereby improving the pinning properties of the second ink on the first ink after drying. Furthermore, by setting the first drying temperature of the first drying unit 4 to be above the second minimum film-forming temperature of the second ink, a preheating effect is obtained on the surface of the first ink where the second ink will land, further improving the pinning properties of the second ink on the first ink after drying.

[0040] The second discharge head 5 discharges the second ink onto the first ink which has been dried by the first drying unit 4. The second drying unit 6 dries the second ink discharged onto the first ink by the second discharge head 5 at a second drying temperature between a first minimum film-forming temperature and 80°C. By setting the second drying temperature of the second drying unit 6 to be above the second minimum film-forming temperature of the second ink, the first binder and the second binder in the first and second inks can be sufficiently film-formed, resulting in high abrasion resistance in the image formed on the non-absorbent media. Furthermore, by setting the second drying temperature of the second drying unit 6 to 80°C or lower, it is possible to prevent damage to the quality of the non-absorbent media made of heat-sensitive resin.

[0041] The control unit 7 controls the operation of the surface processing unit 2, the first discharge head 3, the first drying unit 4, the second discharge head 5, and the second drying unit 6, as well as the first drying temperature of the first drying unit 4 and the second drying temperature of the second drying unit 6.

[0042] The inkjet recording device 1 is not limited to the above configuration and can be modified as needed. For example, the inkjet recording device 1 does not need to have a surface treatment unit 2 if it is not necessary to apply a surface treatment to the recording surface of the non-absorbent media, such as when using a non-absorbent media with a surface treatment applied to the recording surface in advance.

[0043] [Examples and Comparative Examples] As examples and comparative examples of the present invention, an ink set was prepared and an inkjet recording device was evaluated. Note that the following examples merely illustrate one example of the present invention, and the present invention is not limited to the configurations of the following examples.

[0044] (Explanation of ink components) In both the first and second inks used in the ink sets of the examples and comparative examples, 1,3-propanediol and butyl triglycol were used as water-soluble organic solvents, and Silface® SAG503A (manufactured by Nisshin Chemical Industry Co., Ltd.), a silicone-based surfactant, was used as the surfactant. In addition, one of the following commercially available products was used as the binder for both the first and second inks. • Superflex 820 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., minimum film formation temperature: 40℃) • Superflex 130 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., minimum film formation temperature: 55℃) • Superflex 420NS (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., minimum film formation temperature: 65℃) • Superflex 870 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., minimum film formation temperature: 70℃) ·UC-6600 (manufactured by Saiden Chemical Co., Ltd., minimum film forming temperature: 85℃) • Sepolsion NE205 (manufactured by Sumitomo Seika Co., Ltd., minimum film formation temperature: 140℃)

[0045] (Preparation of the first ink) First, a pigment dispersion was prepared in which white pigment was dispersed in water. 75g of pigment dispersion resin (manufactured by BIC Chemie Japan Co., Ltd., product name: DISPERBYK-190, non-volatile content: 40% by mass, dispersion medium: water) was diluted with 775g of deionized water, and 150g of white pigment (manufactured by Teika Co., Ltd., "JR-804") was added. The mixture was then premixed using a homodisper at a rotation speed of 5000 rpm for 1 hour. Subsequently, a white pigment dispersion was obtained by dispersion treatment using a bead mill (manufactured by Nippon Coke Co., Ltd.). Zirconia beads (0.2 mmφ) were packed into the vessel at a filling rate of 80% of the volume. The pigment and pigment dispersion resin contained in the pigment dispersion constitute the components of the pigment dispersion in each ink. The water contained in the pigment dispersion constitutes the water component in each ink.

[0046] Next, ink was prepared using the pigment dispersion described above. The pigment dispersion, first binder, water-soluble organic solvent, surfactant, and water were measured and placed in a beaker. The contents of the beaker were stirred at a rotation speed of 400 rpm using a stirrer (Shinto Kagaku Co., Ltd. "Three One Motor BL-600") to uniformly mix the contents of the beaker and obtain ink. The ink was filtered using a filter (pore size 5 μm) to remove foreign matter and coarse particles contained in the mixture. White ink was obtained as a result. Clear ink was prepared without using the pigment dispersion. Table 1 shows the types and contents (mass %) of the components of the first ink p1 to p7 used in the ink sets of the examples and comparative examples. The first inks p1 to p6 are white inks, and the first ink p7 is a clear ink.

[0047] [Table 1]

[0048] (Preparation of the second ink) First, a pigment dispersion was prepared in which color pigments were dispersed in water. 75g of pigment dispersion resin (manufactured by BIC Chemie Japan Co., Ltd., product name: DISPERBYK-190, non-volatile content: 40% by mass, dispersion medium: water) was diluted with 775g of deionized water, and 150g of either Pigment Blue 15:03 or Pigment Yellow 155 was added. The mixture was then premixed using a homodisper at a rotation speed of 5000 rpm for 1 hour. Subsequently, the mixture was dispersed using a bead mill (manufactured by Nippon Coke Co., Ltd.) to obtain cyan and yellow pigment dispersions. Zirconia beads (0.2 mmφ) were packed into the vessel at a filling rate of 80% of the volume. The pigments and pigment dispersion resin contained in the pigment dispersion constitute the components of the pigment dispersion in each ink. The water contained in the pigment dispersion constitutes the water component in each ink.

[0049] Next, ink was prepared using the pigment dispersion described above. The pigment dispersion, second binder, water-soluble organic solvent, surfactant, and water were measured and placed in a beaker. The contents of the beaker were stirred at a rotation speed of 400 rpm using a stirrer (Shinto Kagaku Co., Ltd. "Three One Motor BL-600") to uniformly mix the contents of the beaker and obtain the ink. The ink was filtered using a filter (pore size 5 μm) to remove foreign matter and coarse particles contained in the mixture. Cyan and yellow inks were obtained as a result. Table 2 shows the types and content (mass %) of the components of the second ink q1 to q6 used in the ink sets of the examples and comparative examples.

[0050] [Table 2]

[0051] (Evaluation of inkjet recording devices) Inkjet recording devices using various ink sets consisting of combinations of first inks p1-p7 and second inks q1-q6 were evaluated for ink bleeding, character bleeding, abrasion resistance, and media quality.

[0052] • Method for evaluating ink bleeding Each ink set was loaded into a one-pass printing evaluation device equipped with an inkjet head (piezoelectric, 1200 dpi). The printing conditions for each ink were set to an appropriate amount of ejected liquid (2 pl) and a print head resolution of 1200 dpi. A non-absorbent media (OPP (biaxially oriented polypropylene) film "Trefan" (manufactured by Toray Industries, Inc.)) was used as the recording medium. The first and second drying sections were configured using dryers. The airflow velocity in the first and second drying sections was set to between 0.5 m / s and 1 m / s.

[0053] For each example and comparative example, a band-shaped solid image was formed on the recording surface of a non-absorbent media by performing the following operations in order: ejection of the first ink, drying of the first ink, ejection of the second ink (cyan and yellow), and drying of the second ink. Furthermore, for each example and comparative example, a band-shaped solid image was formed in the same manner on a PET film "GT703" (manufactured by Toyobo Co., Ltd.), which has been specially processed to prevent bleeding as a recording medium, as a reference. For each example and comparative example, the increase rate of the width of the band-shaped solid image relative to the reference was used as the ink bleeding evaluation value. The ink bleeding evaluation value was assessed according to the following criteria A to C. For ink bleeding, a solid image with an evaluation of A was considered acceptable, while solid images with evaluations of B and C were considered unacceptable. A: Less than 3% B: 3% or more but less than 5% C: 5% or more

[0054] • Method for evaluating text smudging Each ink set was loaded into a one-pass printing evaluation device equipped with an inkjet head (piezoelectric, 1200 dpi). The printing conditions for each ink were: head applied voltage 21V, drive frequency 36kHz, appropriate liquid ejection volume 2pl, and print head resolution 1200 dpi. A non-absorbent media (OPP (biaxially oriented polypropylene) film "Trefan" (manufactured by Toray Industries, Inc.)) was used as the recording medium. The first and second drying sections were configured using dryers. The airflow velocity in the first and second drying sections was set to between 0.5 m / s and 1 m / s.

[0055] For each example and comparative example, a 3pt character string image was formed on the recording surface of a non-absorbent media by performing the following operations in order: ejection of the first ink, drying of the first ink, ejection of the second ink (cyan), and drying of the second ink. Character bleeding was evaluated according to the following criteria A and B. For character bleeding, a character string image with an evaluation of A is considered acceptable, and a character string image with an evaluation of B is considered unacceptable. A: No text distortion (see Figure 2) B: Text is distorted (see Figure 3)

[0056] • Method for evaluating abrasion resistance For each example and comparative example, a 100% solid image was formed on the recording surface of a non-absorbent media by performing the following operations in order: ejection of the first ink, drying of the first ink, ejection of the second ink (cyan), and drying of the second ink. The image was then held at 110°C for 20 minutes and left for 1 day. Subsequently, a dry friction test was performed on the solid image according to the Japan Society for the Promotion of Science (JSPS) testing method, and the solid image was observed visually after 100 friction cycles. Scratch resistance was evaluated according to the following criteria A and B. A solid image with an evaluation of A was considered acceptable, and a solid image with an evaluation of B was considered unacceptable. A: No exposure of non-absorbent media due to peeling of solid image. B: Non-absorbent media exposed due to peeling of solid image.

[0057] • Methods for evaluating media quality The condition of the non-absorbent media was visually observed before and after the ink bleeding evaluation described above. Media quality was evaluated according to the following A and B criteria. Non-absorbent media with an A rating are considered acceptable, and non-absorbent media with a B rating are considered unacceptable. A: There is no change in non-absorbed media. B: Wrinkling has occurred in the non-absorbent media after the ink bleeding evaluation.

[0058] (Examples 1-5) In Examples 1 to 5, the ink set was constructed using the combinations of first and second inks shown in Table 3. Table 3 shows the first minimum film formation temperature (MFT1) of the first binder for each first ink, and the second minimum film formation temperature (MFT2) of the second binder for each second ink. In Examples 1 to 5, the first and second drying temperatures were also as shown in Table 3. In Examples 1 to 5, both the ink set and the first and second drying temperatures are configured as in the above embodiment. Table 3 shows the evaluation results for ink bleeding, character bleeding, scratch resistance, and media quality for Examples 1 to 5. In all of Examples 1 to 5, the results were satisfactory for ink bleeding, character bleeding, scratch resistance, and media quality.

[0059] [Table 3]

[0060] (Comparative Examples 1-9) In Comparative Examples 1 to 9, the ink set was composed of the first and second inks in the combinations shown in Table 4. Table 4 shows the first minimum film formation temperature (MFT1) of the first binder for each first ink, and the second minimum film formation temperature (MFT2) of the second binder for each second ink. In addition, the first and second drying temperatures for Comparative Examples 1 to 9 were as shown in Table 4. Comparative Examples 2 to 4 and 9 differ from the configuration of the above embodiment in that the first minimum film formation temperature is less than the second minimum film formation temperature. Comparative Examples 7 and 8 differ from the configuration of the above embodiment in that the first minimum film formation temperature exceeds 80°C. Comparative Examples 1 and 6 differ from the configuration of the above embodiment in that the first drying temperature exceeds the first minimum film formation temperature. Comparative Examples 4, 5, 8, and 9 differ from the configuration of the above embodiment in that the second drying temperature exceeds 80°C. Table 4 shows the evaluation results for ink bleeding, text bleeding, abrasion resistance, and media quality for Comparative Examples 1 to 9. In Comparative Examples 1-9, each product failed in at least one of the following areas: ink bleeding, text bleeding, scratch resistance, and media quality.

[0061] [Table 4] [Explanation of Symbols]

[0062] 1… Inkjet recording device 2…Surface treatment 3…First discharge head 4…First drying section 5…Second discharge head 6…Second drying section 7…Control Unit

Claims

1. A line-type inkjet recording apparatus that forms an image on a recording medium using an ink set including a first ink and a second ink, The first ink and the second ink each contain a binder with a minimum film-forming temperature of 40°C to 80°C, a water-soluble organic solvent, a surfactant, and water. The first minimum film-forming temperature of the first binder contained in the first ink is equal to or greater than the second minimum film-forming temperature of the second binder contained in the second ink. The aforementioned inkjet recording device is A first ejection head for ejecting the first ink onto the recording medium, A first drying unit that dries the first ink ejected onto the recording medium by the first ejection head at a first drying temperature that is above the second minimum film formation temperature and below the first minimum film formation temperature, A second discharge head discharges the second ink onto the first ink which has been dried by the first drying unit, A second drying unit that dries the second ink ejected onto the first ink by the second ejection head at a second drying temperature of a first minimum film-forming temperature or higher and 80°C or lower, The system comprises the first discharge head, the first drying unit, the second discharge head, and the second drying unit, and a control unit that controls these units. Inkjet recording device.

2. An inkjet recording apparatus according to claim 1, The first ink is clear ink or white ink. Inkjet recording device.

3. An inkjet recording apparatus according to claim 1 or 2, The difference between the first minimum film formation temperature and the second minimum film formation temperature is 10°C or more. Inkjet recording device.

4. An inkjet recording apparatus according to claim 1 or 2, The recording medium is a non-absorbent medium made of resin. The inkjet recording apparatus further comprises a surface treatment unit that performs surface treatment on the recording medium before the first ejection head ejects the first ink. Inkjet recording device.

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