Water-based ink for non-penetrating media

Abstract

To provide a water-based ink that ensures ejection stability while forming images with high adhesion and abrasion resistance on non-penetrating media. [Solution] The water-based ink for non-penetrating media contains a pigment, a urethane resin, polyethylene wax, triethylene glycol monobutyl ether, and water. The urethane resin has a glass transition temperature of 40°C to 110°C and an elongation at break of 50% or less at 25°C. The polyethylene wax has a melting point of 100°C to 140°C. The urethane resin content is 3% to 8% by mass on a solid content basis. The polyethylene wax content is 2% to 5% by mass on a solid content basis. The triethylene glycol monobutyl ether content is 3% to 6% by mass.

Description

Technical Field

[0001] The present invention relates to an aqueous ink for non-permeable media.

Background Art

[0002] Patent Document 1 discloses an aqueous ink for forming an image on a medium by an inkjet recording apparatus. In such an aqueous ink, when forming an image on a non-permeable medium with low water permeability, it is essential to have high adhesion to the non-permeable medium. On the other hand, in the aqueous ink described in Patent Document 1, a polyolefin resin is blended as a binder so as to obtain high adhesion to the non-permeable medium.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the aqueous ink according to Patent Document 1, since the hardness of the polyolefin resin as the main component is low, it is difficult to obtain sufficient rub resistance in the image formed on the non-permeable medium. Also, there is a problem that it is difficult to obtain ejection stability in an aqueous ink containing a binder.

[0005] In view of the above circumstances, an object of the present invention is to provide an aqueous ink capable of forming an image with high adhesion and rub resistance on a non-permeable medium while ensuring ejection stability.

Means for Solving the Problems

[0006] To achieve the above objective, a water-based ink for non-penetrating media according to one embodiment of the present invention contains a pigment, a urethane resin, polyethylene wax, triethylene glycol monobutyl ether, and water. The above-mentioned urethane resin has a glass transition temperature of 40°C to 110°C and an elongation at break of 50% or less at 25°C. The polyethylene wax mentioned above has a melting point between 100°C and 140°C. The urethane resin content is between 3% and 8% by mass, calculated on a solids basis. The polyethylene wax content is between 2% and 5% by mass, calculated on a solids basis. The content of the above-mentioned triethylene glycol monobutyl ether is 3% by mass or more and 6% by mass or less. The above-mentioned water-based ink for non-penetrating media can be used for surface printing.

[0007] In this water-based ink for non-permeable media, while the incorporation of a rigid urethane resin provides high abrasion resistance and ejection stability, it also makes it more difficult to achieve the inherent adhesion-enhancing effect of the urethane resin. To compensate for this reduction in adhesion, this water-based ink for non-permeable media incorporates polyethylene wax, which has a composition similar to that of the non-permeable media material, thereby ensuring ejection stability while simultaneously achieving both adhesion and abrasion resistance. Furthermore, by incorporating triethylene glycol monobutyl ether into this water-based ink for non-permeable media, the effect of improving adhesion and abrasion resistance provided by the urethane resin can be more effectively achieved. [Effects of the Invention]

[0008] As described above, the present invention provides a water-based ink that can form images with high adhesion and abrasion resistance on non-penetrating media while ensuring discharge stability. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows the evaluation criteria for abrasion resistance in the examples and comparative examples. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below.

[0011] [Overall structure] The water-based ink for non-penetrating media according to this embodiment (hereinafter also simply referred to as "ink") contains pigment a, urethane resin b, polyethylene wax c, triethylene glycol monobutyl ether d, and water. The recording medium on which images are formed using the ink according to this embodiment is a non-penetrating media with low ink permeability.

[0012] The urethane resin b incorporated into the ink according to this embodiment has a glass transition temperature of 40°C to 110°C and an elongation at break of 50% or less at 25°C, and is relatively hard. By using the hard urethane resin b in the ink according to this embodiment, high abrasion resistance and ejection stability can be obtained. Furthermore, by incorporating triethylene glycol monobutyl ether d in the ink according to this embodiment, the molecular chains of the urethane resin b can be sufficiently extended after impact with the non-penetrating media, making the urethane resin b form a uniform film. As a result, in the ink according to this embodiment, the effect of improving adhesion and abrasion resistance by the urethane resin b is obtained uniformly along the in-plane direction.

[0013] In the ink according to this embodiment, while the use of a hard urethane resin b improves scratch resistance and discharge stability, it becomes more difficult to obtain the inherent effect of improving the adhesion of the urethane resin b. In the ink according to this embodiment, polyethylene wax c, which has a composition similar to that of the non-permeable media material, is blended to compensate for this decrease in adhesion. The polyethylene wax c blended in the ink according to this embodiment has a melting point of 100°C to 140°C and is relatively hard. In the ink according to this embodiment, by using polyethylene wax c, which is relatively hard like urethane resin b, the compatibility between urethane resin b and polyethylene wax c is improved, and thus the adhesion to the non-permeable media is further enhanced.

[0014] As described above, the ink according to this embodiment is configured to form an image on a non-permeable medium that possesses both adhesion and abrasion resistance. Therefore, even when the ink according to this embodiment is used to form an image on the front surface of a non-permeable medium that is exposed to the viewer, for example, in front printing on a transparent non-permeable medium, the ink is configured to form an image that possesses both adhesion and abrasion resistance, so peeling and abrasion of the image are unlikely to occur without the need for protective treatment such as lamination. Accordingly, the ink according to this embodiment is particularly suitable for producing printed materials in which the recording surface of the non-permeable medium is visible from the front and no protective treatment is applied to the image. However, the ink according to this embodiment is not limited to the above-mentioned uses, and may be used, for example, in back printing on a transparent non-permeable medium.

[0015] [Detailed Configuration] (Pigment a) The ink according to this embodiment contains pigment a as a coloring agent, from the viewpoint of improving the ability to prevent color mixing and the water resistance of images recorded on a recording medium. Pigment a may be either an inorganic pigment or an organic pigment. In addition, if necessary, these may be used in combination with an extender pigment.

[0016] Specific examples of inorganic pigments usable in the 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.

[0017] Specific examples of organic pigments that can be used in the 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.

[0018] In the ink according to this embodiment, the hue is not particularly limited, and any of the chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of preferred chromatic pigments include C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green. In the ink according to this embodiment, as the pigment a, one or more selected from these chromatic pigments can be used.

[0019] (Urethane resin b) In the ink according to this embodiment, the urethane resin b is blended as a binder. The urethane resin b is fine particles composed of polyurethane. In the ink according to this embodiment, in order to sufficiently obtain the above-described action of the urethane resin b, the content of the urethane resin b is 3% by mass or more in terms of solid content. Further, in the ink according to this embodiment, in order to avoid ejection failure due to contamination of the nozzle surface and thickening in the recording head, the content of the urethane resin b is 8% by mass or less in terms of solid content. Furthermore, in the ink according to this embodiment, in order to more effectively obtain the above-described action of the urethane resin b, it is preferable that the particle size (D50) of the urethane resin b is 10 nm or more and 100 nm or less.

[0020] (Polyethylene wax c) In the ink according to this embodiment, the polyethylene wax c is blended as a binder. The polyethylene wax c is fine particles composed of low molecular weight polyethylene. In the ink according to this embodiment, in order to sufficiently obtain the above-described action of the polyethylene wax c, the content of the polyethylene wax c is 2% by mass or more in terms of solid content. Further, in the ink according to this embodiment, in order to avoid ejection failure due to contamination of the nozzle surface and thickening in the recording head, the content of the polyethylene wax c is 5% by mass or less in terms of solid content.

[0021] (Triethylene glycol monobutyl ether d) In the ink according to this embodiment, triethylene glycol monobutyl ether d is incorporated as a film-forming aid. Triethylene glycol monobutyl ether d is a highly safe water-soluble organic solvent and has properties (SP value, boiling point, etc.) that are particularly good with urethane resin b. In the ink according to this embodiment, the content of triethylene glycol monobutyl ether d is 3% by mass or more in order to fully obtain the effect of the above-mentioned triethylene glycol monobutyl ether d. Furthermore, in the ink according to this embodiment, the content of triethylene glycol monobutyl ether d is 6% by mass or less in order to avoid deterioration of adhesion and abrasion resistance due to high solubility and deterioration of discharge stability due to low viscosity.

[0022] (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 40% by mass or more and 80% by mass or less.

[0023] (Other ingredients) The ink according to this embodiment may contain other components as needed. For example, it is preferable to include a surfactant in the ink according to this embodiment. A silicone-based surfactant is preferred as the surfactant to be included in the ink according to this embodiment. By including a silicone-based surfactant in the ink according to this embodiment, the wetting spread on the surface of a non-penetrating media can be improved. A silicone-based surfactant is a surfactant that has a siloxane bond in its molecule. Examples of commercially available silicone-based surfactants include Silface® SAG002 and Silface SAG503A, manufactured by Nisshin Chemical Industry Co., Ltd.

[0024] Furthermore, the ink according to this embodiment may contain a dispersant that enhances the dispersibility of pigment a in a solvent. A pigment dispersion resin can be used as the dispersant. The pigment dispersion resin is a fine particle of resin that is water-soluble and adheres to the surface of pigment a, thereby suppressing the aggregation of pigment a and constituting a pigment dispersion together with the pigment a. 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.

[0025] 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.

[0026] 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. By setting the pigment dispersion resin content to 0.5% by mass or more, aggregation of pigment a can be more effectively suppressed. By setting the pigment dispersion resin content to 8.0% by mass or less, nozzle clogging of the recording head can be suppressed.

[0027] Furthermore, in addition to surfactants and pigment dispersion resins, the ink according to this embodiment may also contain various additives such as dissolution stabilizers, antioxidants, viscosity modifiers, pH adjusters, and neutralizing agents, as needed.

[0028] [Examples and Comparative Examples] Ink preparation and evaluation were performed as examples and comparative examples of the present invention.

[0029] (Ink preparation) First, a pigment dispersion was prepared by dispersing pigment a in water. The pigment dispersion was prepared by wet dispersion of pigment a, a pigment dispersion resin, and water using a media-type wet dispersion machine. In wet dispersion using a media-type wet dispersion machine, for example, small-particle beads (for example, beads with a D50 of 0.5 mm or more and 1.0 mm or less) can be used as the media. The material of the beads is not particularly limited, but hard materials (for example, glass and zirconia) are preferred.

[0030] In both the examples and comparative examples, carbon black was used as pigment a, styrene-acrylic resin as the pigment dispersion resin, and deionized water was used as the water. In addition, in both the examples and comparative examples, the pigment a content was 3% by mass, the pigment dispersion resin content was 1.5% by mass, and the remainder was water.

[0031] Next, inks for the Examples and Comparative Examples were prepared. For the inks for the Examples and Comparative Examples, one of the urethane resins b1, b2, b3, b4, b5, and b6 shown in Table 1 was used as urethane resin b, and one of the polyethylene waxes c1, c2, and c3 shown in Table 2 was used as polyethylene wax c. The inks for the Examples and Comparative Examples were prepared by blending urethane resin b, polyethylene wax c, pigment dispersion, propylene glycol, triethylene glycol monobutyl ether d, Silface SAG503A, and water. In both the Examples and Comparative Examples, deionized water was used as the water.

[0032] [Table 1]

[0033] [Table 2]

[0034] (Ink evaluation) For the examples and comparative examples, image adhesion, image scratch resistance, and ink ejection stability were evaluated.

[0035] • Method for evaluating image adhesion In evaluating image adhesion, a solid image was formed by first applying a pretreatment solution to a non-permeable medium and then dispensing ink. Corona-treated polyethylene terephthalate (PET) and corona-treated biaxially oriented polypropylene (OPP) film from Futamura Chemical Co., Ltd. were used as the non-permeable medium. Tape (Nichiban Co., Ltd., Cellotape®, 18mm width, CT-18S) was applied to the solid image formed on the non-permeable medium, and the surface condition of the solid image after peeling was observed. The ratio of the area where the image was peeled off to the total area where the tape was applied was measured. The obtained measurement value was used as the evaluation value for image adhesion. Image adhesion was evaluated according to the following criteria A to C. 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 10% B: 10% or more but less than 50% C: 50% or more

[0036] • Method for evaluating the scratch resistance of images The abrasion resistance of the images was tested in accordance with JIS L 0849, with a load of 200g, using cotton friction cloth (cotton cloth) and 100 back-and-forth cycles. For the evaluation of image abrasion resistance, solid images with a wet film thickness of approximately 6 μm were first formed on non-permeable media coated with each pretreatment solution using each ink with a bar coater (K303S Multi Coater, manufactured by Matsuo Sangyo Co., Ltd.) at bar number 1. Corona-treated polyethylene terephthalate (PET) and corona-treated biaxially oriented polypropylene (OPP) film manufactured by Futamura Chemical Co., Ltd. were used as non-permeable media. The solid images formed on the non-permeable media were dried at 100°C for 10 minutes, and then left to stand in the air for half a day before being subjected to an abrasion resistance test using a JSPS-type friction tester. The solid images after the test were visually observed and evaluated according to the following criteria A to C. For abrasion resistance, solid images with an evaluation of A were considered acceptable, while solid images with evaluations of B and C were considered unacceptable. A: No streaks or abrasions are observed. (See Photo A in Figure 1) B: Fewer than 10 streaks are observed. (See photo B in Figure 1) C: More than 10 streaks are observed. (See photo C in Figure 1)

[0037] ·Discharge stability Ink ejection stability was evaluated based on the degree of waviness in the non-printed area. In other words, the lower the ink ejection stability, the more likely the tail of the ejected ink droplet is to ripple, which causes waviness in the non-printed area. Therefore, it can be seen that the greater the waviness in the non-printed area, the lower the ejection stability.

[0038] The degree of distortion in the non-printed area was evaluated under normal temperature and high humidity conditions (temperature 25°C and humidity 80%RH) to minimize the effect of drying of the line head nozzles. An inkjet recording device (prototype, 600dpi, manufactured by Kyocera Document Solutions Inc.) was used as the evaluation machine. For this evaluation machine, the pretreatment liquid or ink was purged from the line head and the line head was wiped (purge-wipe process). One minute after the purge-wipe process, a single horizontal line (a line along the main scanning direction) was formed on A4 glossy paper (Seiko Epson Corporation's "Super Fine Paper") using the evaluation machine. At this time, the line width of the horizontal line was set to 1 dot (equivalent to 1 drop of pretreatment liquid or ink). The volume of pretreatment liquid or ink ejected per dot (volume per drop) from each nozzle of the line head was set to 3 pL.

[0039] Next, the amount of misalignment of the aforementioned horizontal lines was determined using an optical microscope (Nikon Corporation "MM-800"). Specifically, the maximum distance (amount of misalignment) in the sub-scanning direction of each dot constituting the aforementioned horizontal lines was measured using the application software included with the optical microscope. A larger amount of misalignment indicates that distortion occurred in the aforementioned horizontal lines due to warping in the non-printed area. For ejection stability, the amount of misalignment obtained for each pretreatment solution or ink was used as the evaluation value. The evaluation value of the ejection stability of each pretreatment solution or ink was evaluated according to the following A and B criteria. For image density, a pretreatment solution or ink with an evaluation of A is considered acceptable, and a pretreatment solution or ink with an evaluation of B is considered unacceptable. A: 20μm or less B: More than 20μm

[0040] (Examples 1-9) In Examples 1 to 9, inks with the compositions shown in Table 3 were prepared. In Table 3, the numerical values ​​listed for each component indicate the content (mass %) of each component. The inks in Examples 1 to 9 have the same composition as the inks according to the above embodiments.

[0041] [Table 3]

[0042] Table 4 shows the evaluation results for image adhesion, image scratch resistance, and ejection stability for the inks of Examples 1 to 9. As shown in Table 4, all of the inks of Examples 1 to 9 passed the evaluations for image adhesion, image scratch resistance, and ink ejection stability.

[0043] [Table 4]

[0044] (Comparative Examples 1-8) In Comparative Examples 1 to 8, inks with the compositions shown in Table 5 were prepared. In Table 4, the numerical values ​​listed for each component indicate the content (mass%) of each component. The ink according to Comparative Example 1 differs from the ink according to the above embodiment in that it has a low content of triethylene glycol monobutyl ether d. The ink according to Comparative Example 2 differs from the ink according to the above embodiment in that it has a high content of triethylene glycol monobutyl ether d. The inks according to Comparative Examples 3 to 5 differ from the ink according to the above embodiment in that the elongation at break of the urethane resin b is high. The inks according to Comparative Examples 4 and 6 differ from the ink according to the above embodiment in that the glass transition temperature Tg of the urethane resin b is low. The ink according to Comparative Example 7 differs from the ink according to the above embodiment in that dipropylene glycol methyl ether is used instead of triethylene glycol monobutyl ether d. The ink according to Comparative Example 8 differs from the ink according to the above embodiment in that the melting point of polyethylene wax c is low.

[0045] [Table 5]

[0046] Table 6 shows the evaluation results for image adhesion, image abrasion resistance, and ejection stability for the inks related to Comparative Examples 1 to 8. As shown in Table 6, all of the inks related to Comparative Examples 1 to 8 failed to meet at least one of the following criteria: image adhesion, image abrasion resistance, and ink ejection stability.

[0047] [Table 6]

Claims

1. Pigments and A urethane resin having a glass transition temperature of 40°C to 110°C and an elongation at break of 50% or less at 25°C, A polyethylene wax having a melting point of 100°C or higher and 140°C or lower, Triethylene glycol monobutyl ether and Water and, It contains, The urethane resin content is 3% by mass or more and 8% by mass or less in terms of solid content. The polyethylene wax content is 2% by mass or more and 5% by mass or less on a solid content basis. The content of the aforementioned triethylene glycol monobutyl ether is 3% by mass or more and 6% by mass or less. Water-based ink for non-penetrating media.

2. A water-based ink for non-penetrating media according to claim 1, Used in surface printing Water-based ink for non-penetrating media.

Images