Ink, inkjet recording method, and inkjet recording apparatus

Abstract

To improve the wettability and spreadability of binder-based inks on non-absorbent recording media. [Solution] The ink is an ink for non-absorbent recording media. The ink contains a silicone-based surfactant, a binder, and water. The pH of the ink at 25°C is 6.5 to 9.0. By incorporating a binder into this ink, it is possible to form an image with high adhesion to the non-absorbent recording media, and high scratch resistance is obtained in the image formed on the non-absorbent recording media. Furthermore, by incorporating a silicone-based surfactant into this ink and setting the pH at 25°C to 6.5 to 9.0, high wettability and spreadability are obtained on the non-absorbent recording media.

Description

Technical Field

[0001] The present invention relates to ink, an inkjet recording method, and an inkjet recording apparatus.

Background Art

[0002] Patent Documents 1 and 2 disclose aqueous inks for forming an image on a recording medium by an inkjet recording apparatus. In such an aqueous ink, when forming an image on a non-absorbent recording medium with low water permeability, it is essential to have high adhesion to the non-absorbent recording medium. On the other hand, in the aqueous ink described in Patent Document 2, fine particles of urethane resin are blended as a binder so as to obtain high adhesion to a non-absorbent recording medium.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an aqueous ink, in order to form a high-quality image without unevenness on a non-absorbent recording medium, a certain degree of wet spreading property on the non-absorbent recording medium is required. On the other hand, in an aqueous ink containing a binder, the binder exhibits an action of quickly fixing on the non-absorbent recording medium and at the same time an action of inhibiting wet spreading on the non-absorbent recording medium, so the wet spreading property on the non-absorbent recording medium tends to be insufficient.

[0005] In view of the above circumstances, an object of the present invention is to improve the wet spreading property on a non-absorbent recording medium in an ink using a binder. [Means for solving the problem]

[0006] To achieve the above objective, an ink according to one embodiment of the present invention is an ink for a non-absorbent recording medium. The above ink contains a silicone-based surfactant, a binder, and water. The pH of the above ink at 25°C is between 6.5 and 9.0.

[0007] This ink, by incorporating a binder, enables the formation of images with high adhesion to non-absorbent recording media, and also provides high scratch resistance to the images formed on the non-absorbent recording media. Furthermore, by maintaining a pH of 6.5 to 9.0 at 25°C and incorporating a silicone-based surfactant, this ink achieves high wettability and spreadability on non-absorbent recording media.

[0008] The binder may be at least one of urethane resin, polyolefin resin, and acrylic resin. The pH of the above ink at 25°C is less than 8.5.

[0009] In one embodiment of the present invention, an image is formed on the recording surface of a non-absorbent recording medium. The above recording surface is subjected to corona treatment. An ink containing a silicone-based surfactant, a binder, and water, with a pH of 6.5 to 9.0 at 25°C, is ejected onto the recording surface that has undergone the corona treatment described above. The above non-absorbent recording medium may be a polyethylene terephthalate film.

[0010] In this configuration, by combining the above-mentioned ink with corona treatment of the non-absorbent recording medium, it is possible to further improve the adhesion of the image to the non-absorbent recording medium and the wetting and spreading properties of the ink on the non-absorbent recording medium.

[0011] An inkjet recording apparatus according to one embodiment of the present invention is an apparatus that performs a recording operation to form an image on the recording surface of a non-absorbent recording medium. The above-mentioned inkjet recording device comprises a surface treatment unit, a recording head, and a control unit. The above surface treatment device applies corona treatment to the recording surface. The recording head ejects ink onto the recording surface, which contains a silicone-based surfactant, a binder, and water, and has a pH of 6.5 to 9.0 at 25°C. The control unit controls the surface treatment unit and the recording head so that the surface treatment unit performs the corona treatment on the recording surface, and then the recording head ejects the ink onto the recording surface. The above non-absorbent recording medium may be a polyethylene terephthalate film. [Effects of the Invention]

[0012] As described above, the present invention makes it possible to improve the wettability and spreadability of an ink using a binder on a non-absorbent recording medium. [Brief explanation of the drawing]

[0013] [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 is a diagram illustrating a method for evaluating the wettability and spreadability of ink. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will now be described. In this invention, "acrylic" and "methacrylic" are collectively referred to as "(meth)acrylic," meaning that "(meth)acrylic" includes both "acrylic" and "methacrylic."

[0015] [Ink composition] (Schematic configuration) The ink according to one embodiment of the present invention contains a pigment a, a binder b, a surfactant c, and water. The ink according to the present embodiment is an aqueous ink that is ejected from a recording head of an inkjet recording apparatus onto a recording medium to form an image on the recording medium. The recording medium on which an image is formed by the ink according to the present embodiment is a non-absorbent recording medium having low absorbency of the ink. Note that the ink according to the present embodiment may be a clear ink that does not contain the pigment a.

[0016] Examples of the non-absorbent recording medium include foil paper, overhead projector (OHP) sheets, and plastic recording media. Examples of the plastic constituting the recording medium include polyethylene terephthalate (PET), polyester, polypropylene, polyethylene, polystyrene, and polyvinyl chloride. The non-absorbent recording medium on which an image is formed by the ink according to the present embodiment is preferably a polyethylene terephthalate film or a polypropylene film, and more preferably a polyethylene terephthalate film surface-modified by corona treatment or the like or a polypropylene film surface-modified by corona treatment or the like.

[0017] In the ink according to the present embodiment, by blending the binder b, it becomes possible to form an image with high adhesion to the non-absorbent recording medium, and high abrasion resistance can be obtained in the image formed on the non-absorbent recording medium.

[0018] Further, in the ink according to the present embodiment, by using a silicone-based surfactant as the surfactant c, high wet spreading property on the non-absorbent recording medium can be obtained. Further, in the ink according to the present embodiment, from the viewpoint of sufficiently obtaining the action of the silicone-based surfactant, the pH at 25°C is preferably 6.5 or more and 9.0 or less, and more preferably 7.5 or more and less than 8.5.

[0019] Furthermore, it is preferable that the recording surface on which an image is formed with the ink according to this embodiment in a non-absorbent recording medium is subjected to corona treatment. On the recording surface of a non-absorbent recording medium that has been corona-treated, the surface energy and polarity are improved, resulting in more uniform ink wetting and spreading, and improved image adhesion. With the ink according to this embodiment, the wetting and spreading properties and adhesion are further enhanced on the recording surface of a non-absorbent recording medium that has been corona-treated, making it possible to more effectively prevent color unevenness and peeling of the image. It is more preferable that the non-absorbent recording medium on which an image is formed with the ink according to this embodiment is a polyethylene terephthalate film that has been corona-treated.

[0020] The details of each component of the ink according to this embodiment will be described below.

[0021] (Pigment a) In the ink according to this embodiment, examples of pigment a include yellow pigment, orange pigment, red pigment, blue pigment, purple pigment, black pigment, and white pigment. Examples of yellow pigments include CI Pigment Yellow (74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, and 193). Examples of orange pigments include CI Pigment Orange (34, 36, 43, 61, 63, and 71). Examples of red pigments include CI Pigment Red (122 and 202). Examples of blue pigments include CI Pigment Blue (15, more specifically 15:3). Examples of purple pigments include CI Pigment Violet (19, 23, and 33). Examples of black pigments include CI Pigment Black (7). Examples of white pigments include titanium dioxide. Among these, surface-treated titanium dioxide is preferred because it exhibits relatively good dispersibility in aqueous media. For example, titanium dioxide surface-treated with silica and alumina is preferred. Furthermore, it is even more preferable to use titanium dioxide that has been surface-treated with a silane coupling agent after being surface-treated with silica and alumina.

[0022] In the ink according to this embodiment, in the case of color ink (other than white ink and clear ink), the content of pigment a is preferably 0.5% by mass or more and 11.0% by mass or less, and more preferably 1.5% by mass or more and 10.0% by mass or less. In the case of white ink according to this embodiment, the content of pigment a is preferably 5.0% by mass or more and 15.0% by mass or less.

[0023] (Binder b) In the ink according to this embodiment, a binder b is incorporated to improve the adhesion of the image to a non-absorbent recording medium and the scratch resistance of the image formed on the non-absorbent recording medium. Binder b is fine particles formed of resin. Examples of resins constituting binder b include urethane resin, polyolefin resin, (meth)acrylic resin, styrene resin, polyvinyl resin, polyester resin, amino resin, epoxy resin, polyether resin, polyamide resin, phenolic resin, silicone resin, fluororesin, and copolymers containing monomers of these resins. In the ink according to this embodiment, in order to more effectively obtain the effect of binder b, it is preferable that binder b is composed of at least one of urethane resin, polyolefin resin, and acrylic resin.

[0024] In the ink according to this embodiment, it is preferable that the binder b content be 3% by mass or more, from the viewpoint of obtaining high adhesion of the image to the recording medium and high scratch resistance of the image formed on a non-absorbent recording medium. Furthermore, in the ink according to this embodiment, it is preferable that the binder b content be 20% by mass or less, from the viewpoint of obtaining high ejection performance from the recording head.

[0025] (Surfactant c) The surfactant c incorporated into the ink according to this embodiment is a silicone-based surfactant. A silicone-based surfactant is a surfactant containing a silicone compound. Silicone-based surfactants have a strong effect of lowering the surface tension of the ink. In the ink according to this embodiment, by setting the pH at 25°C to 6.5 or higher and 9.0 or lower, the effect of the silicone-based surfactant in lowering the surface tension of the ink is effectively obtained, and high wettability on a non-absorbent recording medium can be obtained even in a configuration using binder b.

[0026] In the ink according to this embodiment, from the viewpoint of obtaining high wettability on a non-absorbent recording medium, it is preferable that the content of surfactant c is 0.03% by mass or more. Furthermore, in the ink according to this embodiment, from the viewpoint of discharge performance, it is preferable that the content of surfactant c is 0.5% by mass or less.

[0027] (water) In the ink according to this embodiment, for example, ion-exchanged water, purified water, or distilled water can be used as water. In the ink according to this embodiment, from the viewpoint of drying properties and ejection reliability, it is preferable that the water content is 50% by mass or more and 80% by mass or less.

[0028] (Other ingredients) The ink according to this embodiment may contain components other than those mentioned above, as needed. For example, the ink according to this embodiment may contain a dispersant that enhances the dispersibility of pigment a in a solvent. Examples of dispersants include pigment dispersing resins and surfactants.

[0029] The pigment dispersion resin is a fine particle of resin that adsorbs onto the surface of pigment a, thereby improving the dispersibility of pigment a in the solvent. Styrene-(meth)acrylic resin is preferred as the pigment dispersion resin. The styrene-(meth)acrylic resin has repeating units derived from at least one monomer selected from alkyl (meth)acrylate and (meth)acrylic acid, and styrene units. Examples of alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate. A copolymer of styrene, methyl methacrylate, methacrylic acid, and butyl acrylate is preferred as the styrene-(meth)acrylic resin.

[0030] In inks containing a pigment dispersion resin, the pigment a and the pigment dispersion resin together constitute a pigment dispersion (pigment particles). The pigment dispersion is composed of, for example, a core containing the pigment and a pigment dispersion resin coating the core. The pigment dispersion resin may be partially dispersed in the solvent. In pigment dispersions composed of pigment a other than white, from the viewpoint of optimizing color density, hue, and stability, the median volume diameter is preferably 30 nm to 200 nm, and more preferably 70 nm to 130 nm. In pigment dispersions composed of white pigment a, from the viewpoint of optimizing color density, hue, and stability, the median volume diameter is preferably 100 nm to 500 nm, and more preferably 150 nm to 400 nm.

[0031] The surfactant added as a dispersant is added separately from surfactant c and improves the dispersibility of pigment a in the solvent by reducing the interfacial tension between pigment a and the solvent. Examples of such surfactants include nonionic surfactants and anionic surfactants.

[0032] Furthermore, in addition to the dispersant, the ink according to this embodiment may contain various additives as needed, such as water-soluble organic solvents, dissolution stabilizers, drying inhibitors, antioxidants, viscosity modifiers, pH adjusters, neutralizing agents, and antifungal agents.

[0033] [Inkjet recording method] The inkjet recording method according to this embodiment is a method of forming an image on the recording surface of a non-absorbent recording medium that has not been subjected to corona treatment using the ink according to this embodiment. In the inkjet recording method according to this embodiment, the recording surface of the non-absorbent recording medium is subjected to corona treatment, and then the ink according to this embodiment is ejected onto the corona-treated recording surface of the non-absorbent recording medium to form an image. The inkjet recording method according to this embodiment provides higher wettability and spreadability of the ink according to this embodiment on the recording surface of the non-absorbent recording medium, and higher adhesion of the image formed with the ink according to this embodiment to the recording surface of the non-absorbent recording medium.

[0034] [Inkjet recording device] The inkjet recording apparatus 1 according to this embodiment is configured to enable the inkjet recording method 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 recording head 3, and a control unit 4.

[0035] The surface treatment unit 2 performs corona treatment on the recording surface of the non-absorbent recording medium. The recording head 3 ejects the ink according to this embodiment onto the recording surface of the non-absorbent recording medium. The control unit 4 controls the surface treatment unit 2 and the recording head 3 so that the surface treatment unit 2 performs corona treatment on the recording surface of the non-absorbent recording medium, and then the recording head 3 ejects the ink according to this embodiment onto the recording surface of the non-absorbent recording medium.

[0036] [Examples and Comparative Examples] Ink preparation and evaluation were performed as examples and comparative examples of the present invention.

[0037] (Ink preparation) First, a pigment dispersion was prepared by dispersing pigment a in water. 75g of pigment dispersion resin (SOLSPERSE® W100, manufactured by Lubrizol, non-volatile content: 40% by mass) was diluted with 425g of deionized water, and 500g of pigment (CI Pigment Blue 15:3) was added. The mixture was then premixed in a homodisperser at a rotation speed of 5000 rpm for 1 hour. Afterward, the mixture was dispersed using a bead mill (manufactured by Nippon Coke Co., Ltd.) to obtain the pigment dispersion. During the dispersion process, zirconia beads (0.2mmφ) were packed into the vessel at a filling rate of 80% of the volume. The pigment a 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.

[0038] Next, inks according to the examples and comparative examples were prepared. Pigment dispersion, binder b, surfactant c, water-soluble organic solvent d, 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.

[0039] In this example and comparative example, binders b1 to b3 shown in Table 1 were used as binder b, surfactants c1 to c4 shown in Table 2 were used as surfactant c, and water-soluble organic solvents d1 and d2 shown in Table 3 were used as water-soluble organic solvents d. Binder b1 is composed of urethane resin, binder b2 is composed of polyolefin resin, and binder b3 is composed of acrylic resin. Surfactants c1 and c2 are silicone-based surfactants, while surfactants c3 and c4 are not silicone-based surfactants. The products shown as binders b1 to b3 are emulsions in which binders b1 to b3 are dispersed in water. The water contained in this emulsion constitutes the water component in each ink.

[0040] [Table 1]

[0041] [Table 2]

[0042] [Table 3]

[0043] (Evaluation method) The inks used in the examples and comparative examples were evaluated for image scratch resistance, adhesion, and wetting spread properties.

[0044] • Method for evaluating the scratch resistance of images Each ink was applied to a non-absorbent recording medium (Futamura Chemical Co., Ltd. PET film "FE2001") using a bar coater (#02 grit), and then dried at 80°C for 2 minutes to form an image 6 μm thick. The image formed on the recording medium was rubbed once with a weight of 1000 g. The peeling rate, which is the percentage of the image that peeled off out of the entire area rubbed by the weight, was observed visually. The peeling rate of each image was evaluated according to the following criteria A to D. For abrasion resistance, images with evaluations of A and B were considered acceptable, and images with evaluations of C and D were considered unacceptable. A: 0% B: More than 0% and less than 5% C: More than 5% and less than 10% D: More than 10%

[0045] • Method for evaluating image adhesion Each ink was applied to a non-absorbent recording medium (Futamura Chemical Co., Ltd. PET film "FE2001") using a bar coater (#02 grit), and then dried at 80°C for 2 minutes to form an image 6 μm thick. A 5x5 grid pattern was cut into the image formed on the recording medium at 1 mm intervals using a cutter, and a tape peel test was performed using the cross-cut method. The number of peeled squares in the 25 grid-like image squares after the tape peel test was counted. The number of peeled squares in each image was evaluated according to the following criteria A to D. Regarding adhesion, images with evaluations of A and B were considered acceptable, while images with evaluations of C and D were considered unacceptable. A:0 pieces B: 1 or more and 3 or less C: 4 or more and 6 or less D:7 or more

[0046] • Wetting properties Each ink was used to form an image of a pattern of straight lines, as shown in Figure 2, on a non-absorbent recording medium (PET film "FE2001" manufactured by Futamura Chemical Co., Ltd.) using a test machine. The image was then dried by holding it in a hot air dryer at 80°C for 120 seconds. The test machine used for evaluation was equipped with a piezo-type inkjet head (KJ4B-1200, manufactured by Kyocera Corporation) that ejects pigment ink and pretreatment liquid. The test machine settings were: head applied voltage 20V, drive frequency 18kHz, appropriate amount of ejected liquid 3pl, print head resolution 1200dpi, and pre-ejection flushing count 100 times. For the image formed on the non-absorbent recording medium with each ink, the width of 14 lines was measured, and the average value of the 14 line widths was calculated. The average value of the line width and the presence or absence of droplet unification in each image were evaluated according to the following criteria A to C. For wetting spreadability, images with evaluations of A and B were considered acceptable, and images with evaluations of C were considered unacceptable. A: No droplet coalescence, and the average line width is 70 μm or more. B: No droplet cohesion, and the average line width is between 50 μm and 70 μm. C: Droplet unification is present, or the average line width is less than 50 μm.

[0047] (Examples 1-7) In Examples 1-6, inks were prepared using the above method by varying the type and amount of binder b and surfactant c. In Example 7, a clear ink was prepared without using pigment a and pigment dispersion. Table 4 shows the composition of the inks in Examples 1-7. The type and amount of water-soluble organic solvent d were the same for all inks in Examples 1-7.

[0048] [Table 4]

[0049] The inks from Examples 1 to 7 were evaluated for image abrasion resistance, adhesion, and wetting spread. Table 5 shows the evaluation results for image abrasion resistance, adhesion, and wetting spread of the inks from Examples 1 to 7. All of the inks from Examples 1 to 7 passed the evaluations for image abrasion resistance, adhesion, and wetting spread.

[0050] [Table 5]

[0051] (Examples 8, 9) In Examples 8 and 9, the ink from Example 1 was used, and the type of non-absorbent recording medium was changed to evaluate the scratch resistance, adhesion, and wetting spread of the image. Specifically, in Example 8, a corona-treated PET film was used as the non-absorbent recording medium. In Example 9, a corona-treated biaxially oriented polypropylene (OPP) film was used as the non-absorbent recording medium.

[0052] Table 6 shows the evaluation results for image abrasion resistance, adhesion, and wetting spread for Examples 8 and 9. All inks used in Examples 8 and 9 passed the evaluations for image abrasion resistance, adhesion, and wetting spread. In particular, Example 8, which used a corona-treated PET film, showed especially good results in terms of abrasion resistance and adhesion.

[0053] [Table 6]

[0054] (Comparative Examples 1-4) In Comparative Examples 1 to 4, inks were prepared using the above method, but with different compositions of binder b and surfactant c compared to the above examples. Table 7 shows the compositions of the inks for Comparative Examples 1 to 4. In all of the inks for Comparative Examples 1 to 4, the type and amount of water-soluble organic solvent d were the same as those for the inks for Examples 1 to 6. The ink for Comparative Example 1 differs from the ink for the above examples in that its pH at 25°C is greater than 9.0. The ink for Comparative Example 2 differs from the ink for the above examples in that binder b is not included. The inks for Comparative Examples 3 and 4 differ from the inks for the above examples in that they do not contain a silicone-based surfactant, or instead do not use a silicone-based surfactant.

[0055] [Table 7]

[0056] The inks related to Comparative Examples 1 to 4 were evaluated for image abrasion resistance, adhesion, and wetting spread. Table 8 shows the evaluation results for image abrasion resistance, adhesion, and wetting spread for the inks related to Comparative Examples 1 to 4. The ink related to Comparative Example 1 failed the wetting spread test. This is thought to be because the effect of surfactant c in reducing surface tension was not sufficiently obtained in the ink related to Comparative Example 1, which has a pH of more than 9.0 at 25°C. The ink related to Comparative Example 2 failed the image abrasion resistance and adhesion test. This is thought to be because the ink related to Comparative Example 2, which does not contain binder b, had insufficient adhesion strength of the image to the recording medium. The inks related to Comparative Examples 3 and 4 failed the wetting spread test. This is thought to be because the inks related to Comparative Examples 3 and 4, which do not contain silicone-based surfactants, did not sufficiently reduce surface tension.

[0057] [Table 8] [Explanation of Symbols]

[0058] 1… Inkjet recording device 2…Surface treatment 3…Recording head 4…Control Unit

Claims

1. An ink for non-absorbent recording media, It contains a silicone-based surfactant, a binder, and water. The pH at 25°C is between 6.5 and 9.

0. ink.

2. The ink according to claim 1, The binder is composed of at least one of urethane resin, polyolefin resin, and acrylic resin. ink.

3. The ink according to claim 1 or 2, The pH at 25°C is less than 8.

5. ink.

4. The ink according to claim 1 or 2, The non-absorbent recording medium is a polyethylene terephthalate film or a polypropylene film. ink.

5. An inkjet recording method for forming an image on the recording surface of a non-absorbent recording medium, The recording surface is subjected to corona treatment, An ink comprising a silicone-based surfactant, a binder, and water, with a pH of 6.5 to 9.0 at 25°C, is ejected onto the corona-treated recording surface. Inkjet recording method.

6. The inkjet recording method according to claim 4, The non-absorbent recording medium is a polyethylene terephthalate film or a polypropylene film. Inkjet recording method.

7. An inkjet recording apparatus for forming an image on the recording surface of a non-absorbent recording medium, A surface treatment unit that performs corona treatment on the recording surface, A recording head that ejects ink containing a silicone-based surfactant, a binder, and water, with a pH of 6.5 to 9.0 at 25°C, onto the recording surface. A control unit controls the surface treatment unit and the recording head so that the surface treatment unit performs the corona treatment on the recording surface, and then the recording head ejects the ink onto the recording surface. An inkjet recording device equipped with the following.

8. An inkjet recording apparatus according to claim 7, An inkjet recording apparatus in which the non-absorbent recording medium is a polyethylene terephthalate film or a polypropylene film.

Images