ink

Abstract

The present invention provides an ink that can suppress the occurrence of curl and offset, while ensuring intermittent ejection and image density. [Solution] The ink contains a pigment, a pigment dispersion resin, polyethylene glycol with a molecular weight of 200 to 600 in an amount of 7% to 20% by mass, 3-methyl-1,5-pentanediol in an amount of 1% to 15% by mass, triethylene glycol monobutyl ether in an amount of 1% to 10% by mass, and water.

Description

Technical Field

[0001] The present invention relates to an ink for forming an image by an inkjet method.

Background Art

[0002] An inkjet recording apparatus forms an image on a recording medium such as paper by repeatedly ejecting small droplets of ink from nozzles. In a recording medium such as paper composed of fibers, a phenomenon (curl) in which the shape is bent due to partial stretching and contraction of the fibers is likely to occur due to the formation of an image by ink. Patent Document 1 discloses a technique of blending polyethylene glycol into ink in order to suppress the occurrence of curl.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the ink containing polyethylene glycol, since the viscosity increases, drying progresses in the nozzles of the recording head, and it is likely to become unable to eject, that is, it is difficult to ensure intermittent ejection property. Further, in the ink containing polyethylene glycol, the density of the image formed on the recording medium tends to be low, and it is likely to adhere to the paper discharge roller of the inkjet recording apparatus, so that a phenomenon (offset) of soiling the subsequent recording medium through the paper discharge roller is likely to occur.

[0005] In view of the above circumstances, an object of the present invention is to provide an ink capable of suppressing the occurrence of curl and offset and ensuring intermittent ejection property and image density.

Means for Solving the Problems

[0006] To achieve the above objective, an ink according to one embodiment of the present invention contains a pigment, a pigment dispersion resin, polyethylene glycol with a molecular weight of 200 to 600 in an amount of 7% to 20% by mass, 3-methyl-1,5-pentanediol in an amount of 1% to 15% by mass, triethylene glycol monobutyl ether in an amount of 1% to 10% by mass, and water.

[0007] This ink suppresses curling of the recording medium by incorporating 7% or more by mass of polyethylene glycol with a molecular weight of 200 or more. Furthermore, by keeping the molecular weight of the polyethylene glycol below 600, intermittent ejection is ensured. Additionally, by incorporating 1% or more by mass of 3-methyl-1,5-pentanediol, image density is ensured. Moreover, by incorporating 1% or more by mass of triethylene glycol monobutyl ether, offset is suppressed.

[0008] In the above ink, the dynamic surface tension at a surface life of 10 milliseconds may be 40.0 mN / m or less. In the above ink, the content of the pigment dispersion resin may be 4% by mass or less. The above ink may further contain an acetylene glycol-based surfactant. [Effects of the Invention]

[0009] As described above, the present invention provides an ink that can suppress the occurrence of curl and offset, and can ensure intermittent ejection and image density. [Modes for carrying out the invention]

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

[0011] [Ink composition] (Schematic configuration) An ink according to one embodiment of the present invention contains a pigment a, a pigment dispersion resin b, a water-soluble solvent c, and water. The ink according to this embodiment is typically a water-based ink that is ejected from the recording head of an inkjet recording device onto a recording medium to form an image on the recording medium. The recording medium on which the image is formed with the ink according to this embodiment is made of fibers such as cellulose fibers, and examples include plain paper, copy paper, recycled paper, thin paper, and thick paper.

[0012] In the ink according to this embodiment, by blending three types of organic solvents as the water-soluble solvent c, it is possible to suppress the occurrence of curl and offset, and to realize a configuration that ensures intermittent ejection and image density. Furthermore, in the ink according to this embodiment, in order to ensure penetration into the recording medium and suppress offset, it is preferable that the dynamic surface tension at a surface life of 10 milliseconds is 40.0 mN / m or less. In the ink according to this embodiment, in order to ensure image density, it is preferable that the dynamic surface tension at a surface life of 10 milliseconds is 25 mN / m or more. The details of each component of the ink according to this embodiment will be described below.

[0013] (Pigment a) In the ink according to this embodiment, pigment a can be, for example, a yellow pigment, an orange pigment, a red pigment, a blue pigment, a purple pigment, or a black pigment. Examples of yellow pigments include CI Pigment Yellow 74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, or 193. Examples of orange pigments include CI Pigment Orange 34, 36, 43, 61, 63, or 71. Examples of red pigments include CI Pigment Red 122 or 202. Examples of blue pigments include CI Pigment Blue 15 or 15:3. Examples of purple pigments include CI Pigment Violet 19, 23, or 33. Examples of black pigments include CI Pigment Black 7.

[0014] In the ink according to this embodiment, the content of pigment a is preferably 4% by mass or more and 8% by mass or less. This makes it easier to obtain a high image density in the image formed on the recording medium and to ensure penetration into the recording medium. If the content of pigment a is less than 4% by mass, it becomes difficult to obtain a high image density in the image formed on the recording medium. On the other hand, if the content of pigment a exceeds 8% by mass, it becomes difficult to obtain penetration into the recording medium and it may be difficult to ensure the fluidity of the pigment particles in the solvent, making it difficult to obtain a high image density in the image formed on the recording medium.

[0015] (Pigment-dispersed resin b) The ink according to this embodiment is formulated with a pigment dispersion resin b to enhance the dispersibility of pigment a in the solvent. The pigment dispersion resin b is made up of fine resin particles and suppresses the aggregation of pigment a by adsorbing onto the surface of pigment a. In an ink formulated with pigment dispersion resin b, pigment a and pigment dispersion resin b together constitute pigment particles (pigment dispersion). The pigment particles are composed of, for example, a core containing pigment a and a pigment dispersion resin b that coats the core. In the case of pigment dispersion resin b, a portion may be dispersed in the solvent without adsorbing onto the surface of pigment a.

[0016] Pigment dispersion resin b can be appropriately selected from known pigment dispersion resins. Specific examples of pigment dispersion resin b include styrene-acrylic resin, styrene-maleic acid copolymer, styrene-maleic acid half-ester copolymer, vinylnaphthalene-acrylic acid copolymer, or vinylnaphthalene-maleic acid copolymer. Styrene-acrylic resin is a resin containing units derived from styrene and units derived from acrylic acid, methacrylic acid, acrylic acid ester, or methacrylic acid ester. Examples of styrene-acrylic resin include styrene-acrylic acid-alkyl acrylate copolymer, styrene-methacrylic acid-alkyl methacrylate-alkyl acrylate copolymer, styrene-acrylic acid copolymer, styrene-maleic acid-alkyl acrylate copolymer, styrene-methacrylic acid copolymer, or styrene-alkyl methacrylate copolymer. Among these pigment dispersion resins b, styrene-acrylic resin is preferred because it is easy to prepare and has excellent dispersion effect on pigment a, styrene-methacrylic acid-alkyl methacrylate-alkyl acrylate copolymer is more preferred, and methacrylic acid-methyl methacrylate-butyl acrylate-styrene copolymer is particularly preferred.

[0017] In the ink according to this embodiment, it is preferable that the content of pigment dispersion resin b is 0.4% by mass or more and 8% by mass or less. Furthermore, in the ink according to this embodiment, it is preferable that 10 parts by mass or more and 100 parts by mass of pigment dispersion resin b is blended with 100 parts by mass of pigment a.

[0018] (Water-soluble solvent c) The ink according to this embodiment contains polyethylene glycol, 3-methyl-1,5-pentanediol, and triethylene glycol monobutyl ether as the water-soluble solvent c. In the ink according to this embodiment, the molecular weight of polyethylene glycol is 200 to 600. Furthermore, in the ink according to this embodiment, the polyethylene glycol content is 7% to 20% by mass, the 3-methyl-1,5-pentanediol content is 1% to 15% by mass, and the triethylene glycol monobutyl ether content is 1% to 10% by mass.

[0019] In the ink according to this embodiment, curling can be suppressed by incorporating 7% by mass or more of polyethylene glycol with a molecular weight of 200 or more. Furthermore, intermittent discharge can be ensured by keeping the molecular weight of polyethylene glycol at 600 or less. In addition, image density can be ensured by incorporating 1% by mass or more of 3-methyl-1,5-pentanediol while keeping the content of triethylene glycol monobutyl ether at 10% by mass or less. Moreover, offset can be suppressed by incorporating 1% by mass or more of triethylene glycol monobutyl ether while keeping the content of polyethylene glycol at 20% by mass or less. Furthermore, the redispersibility of pigment particles in the solvent can be improved by keeping the content of 3-methyl-1,5-pentanediol at 15% by mass or less and the content of triethylene glycol monobutyl ether at 10% by mass or less.

[0020] (Surfactant d) The ink according to this embodiment preferably contains surfactant d. Surfactant d has the effect of enhancing the wettability of the ink with respect to the storage medium and the effect of enhancing the compatibility and dispersion stability of each component contained in the ink. Examples of surfactant d to be blended in the ink according to this embodiment include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants. As the surfactant to be blended in the ink according to this embodiment, a nonionic surfactant is preferable, and among them, an acetylene glycol-based surfactant is particularly preferable.

[0021] (Water) In the ink according to this embodiment, for example, ion-exchanged water, purified water, distilled water, etc. can be used as water. In the ink according to this embodiment, from the viewpoints of drying property and ejection reliability, the water content is preferably 25.0 mass% or more and 80.0 mass% or less, and more preferably 35.0 mass% or more and 60.0 mass% or less.

[0022] (Other components) In the ink according to this embodiment, components other than the above may be blended as necessary. For example, in the ink according to this embodiment, a surfactant different from surfactant d may be blended as a dispersant for enhancing the dispersibility of pigment a in the solvent. The surfactant blended as a dispersant enhances the dispersibility of pigment a in the solvent by reducing the interfacial tension between pigment a and the solvent. As such a surfactant, for example, a nonionic surfactant or an anionic surfactant can be used.

[0023] Also, in the ink according to this embodiment, various additives such as a dissolution stabilizer, an anti-drying agent, an antioxidant, a viscosity modifier, a pH adjuster, a neutralizing agent, and a fungicide may be blended as necessary in addition to the above.

[0024] [Examples and Comparative Examples] As examples and comparative examples of the present invention, the ink was prepared and evaluated.

[0025] (Preparation of Ink) First, a pigment dispersion was prepared by dispersing pigment a in water. Pigment dispersion resin b was diluted with deionized water, pigment a was added, and then a preliminary dispersion treatment was performed using a homodisper. Subsequently, the main dispersion treatment was performed using a bead mill (manufactured by Nippon Coke Co., Ltd.) until the average particle size of the pigment particles reached 110 nm, thereby obtaining the pigment dispersion. In both the examples and comparative examples, CABOT's "Black Pearls 800" was used as pigment a. In both the examples and comparative examples, Bic Chemie's "DISPERBYK-190" was used as pigment dispersion resin b. The water contained in the pigment dispersion constitutes the water component in each ink.

[0026] Next, inks according to the examples and comparative examples were prepared. Pigment dispersion, water-soluble solvent c, surfactant 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 ink.

[0027] In the examples and comparative examples, the following water-soluble solvents c were used: polyethylene glycol 400 (PEG400, average molecular weight: approximately 400, manufactured by Tokyo Chemical Industry Co., Ltd.), polyethylene glycol 1000 (PEG1000, average molecular weight: approximately 1000, manufactured by Tokyo Chemical Industry Co., Ltd.), diethylene glycol (DEG, molecular weight: 106.12, manufactured by Tokyo Chemical Industry Co., Ltd.), 3-methyl-1,5-pentanediol (manufactured by Tokyo Chemical Industry Co., Ltd.), and triethylene glycol monobutyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.). In addition, in both the examples and comparative examples, the surfactant d was Surfinol 420 (manufactured by Nisshin Chemical Industry Co., Ltd.), an acetylene glycol-based surfactant.

[0028] (Evaluation method) The inks used in the examples and comparative examples were evaluated for intermittent ejection, image density, redispersibility, and resistance to offset and curling.

[0029] • Evaluation unit For the evaluation of intermittent ejection, image density, and resistance to offset and curl, a prototype evaluation unit manufactured by Kyocera Document Solutions Inc. was used as the inkjet recording device, and the "KJ4B-QA" recording head manufactured by Kyocera Document Solutions Inc. was used.

[0030] • Method for evaluating intermittent discharge The recording head was kept at 25°C, and intermittent ejection performance was evaluated under a 10°C, 15% RH environment. Specifically, for each ink, the recording head formed a first line image on the recording medium, then passed through a non-image-forming region where no image was formed, and then the first line... A second line image similar to the image was formed. Then, it was determined by microscopic observation whether or not there was any distortion in the second line image. For each ink, the maximum value M (mm) of the transport direction dimension of the non-image-forming region where no distortion occurred in the second line image was determined, and the value corresponding to the maximum value M (=100 × (M / 420)), with the dimension corresponding to the longitudinal dimension of A3 size (420 mm) set to 100, was used as the evaluation value for intermittent ejection performance. The evaluation value was evaluated according to the following criteria A and B. For intermittent ejection performance, inks with an evaluation of A were considered acceptable, and inks with an evaluation of B were considered unacceptable. A: 100 or more B: Less than 100

[0031] • Method for evaluating image density A 10cm x 10cm solid image was formed on a recording medium (Fujifilm Business Innovation Co., Ltd. "C2" (A4 size)) by setting the ink ejection amount per nozzle of the recording head to 11 pL. The recording medium with the formed solid image was kept overnight in a normal temperature and humidity environment. Subsequently, the image density of each solid image was measured at 10 locations using a portable reflectivity densitometer RD-19 (Gretag Macbeth Corporation), and the average of the image densities at the 10 locations was used as the image density evaluation value. The evaluation value was assessed according to the following A and B criteria. For image density, ink with an evaluation of A was considered acceptable, and ink with an evaluation of B was considered unacceptable. A: 1.1 or higher B: Less than 1.1

[0032] ·Redispersibility Petri dishes containing 2g of each ink were placed in an incubator and maintained at 40°C for 72 hours. After maintenance, deionized water was added to each ink at a rate of 5ml / second, and after 10 seconds, the pigment particles in each ink were visually observed to see if they were dispersed in the solvent. The observation results were evaluated according to the following criteria A and B. In terms of redispersibility, inks with an evaluation of A were considered acceptable, and inks with an evaluation of B were considered unacceptable. A: Pigment particles are dispersed in water. B: Pigment particles are not dispersed in water.

[0033] • Evaluation method for the likelihood of offset occurrence First, ink was filled into the recording head closest to the paper output roller in the evaluation machine, and excess liquid flowing onto the nozzle surface was scraped off with a wipe blade. In the evaluation machine, the distance between the nozzle surface of the recording head and the recording medium was fixed at 1 mm, and the transport speed of the recording medium from the paper feed roller to the paper output roller was set to 846.7 mm / second. As the recording medium, Oji Paper Co., Ltd.'s "IJW" cut to A4 size was used. The amount of ink impregnated from the recording head to the recording medium in the evaluation machine was 15 g / m². 2 Ten consecutive 10cm x 10cm solid images were formed on recording media. For the tenth recording media, the area prone to smudging due to ink adhering to the paper output roller (offset area) was scanned using an image scanner (Seiko Epson Corporation's "GT-X820") and binarized with a threshold of 220. The offset area ratio (%) (=100 x number of black pixels / total number of pixels) was calculated from the number of black pixels and the total number of pixels in the binarized image, and the offset area ratio was used as an evaluation value for the likelihood of offset occurring. For the evaluation value, the following A and B criteria were used to determine whether or not smudging on the recording paper P due to offset could be confirmed by visual inspection. In terms of likelihood of offset occurring, ink with an evaluation of A is considered acceptable, and ink with an evaluation of B is considered unacceptable. A: 0.030% or less B: More than 0.030%

[0034] • Evaluation method for resistance to curl formation A 10cm x 10cm solid image was formed on a recording medium (Fujifilm Business Innovation Co., Ltd. "C2" (A4 size)) by setting the ink ejection amount per stroke at each nozzle of the recording head to 11 pL. Immediately afterward, the recording medium with the formed solid image was placed on the top surface of a horizontal table so that the solid image on the recording medium faced the top surface of the horizontal table. The height of the four corners of the recording medium from the top surface of the horizontal table was measured, and the average height of the four corners of the recording medium was used as the evaluation value for resistance to curling. For the evaluation value, when using a 0.8 kPa suction fan, suction adsorption by a conveyor belt, and correction of the recording medium using a decal mechanism, the following A and B criteria were used to evaluate whether or not the recording medium could be adsorbed for the formation of an image on the second side (back side) of double-sided printing. For resistance to curling, inks with an evaluation of A were considered acceptable, and inks with an evaluation of B were considered unacceptable. A: 20mm or less B: More than 20mm

[0035] (Examples 1-14) In Examples 1 to 14, inks were prepared using the method described above to achieve the compositions shown in Table 1. Note that all values ​​in Table 1 are in "mass%". In Examples 1 to 14, the amounts of pigment dispersion resin b, polyethylene glycol, 3-methyl-1,5-pentanediol, triethylene glycol monobutyl ether, and surfactant d were varied.

[0036] [Table 1]

[0037] The inks from Examples 1 to 14 were evaluated for intermittent ejection, image density, redispersibility, and resistance to offset and curl. Table 2 shows the evaluation results for intermittent ejection, image density, redispersibility, and resistance to offset and curl for the inks from Examples 1 to 14. All of the inks from Examples 1 to 14 passed the evaluations for intermittent ejection, image density, redispersibility, and resistance to offset and curl.

[0038] [Table 2]

[0039] Furthermore, the inks in Examples 2, 12 to 14 differ in the amount of surfactant d, and therefore in their surface tension. Figure 3 shows the dynamic surface tension at a surface life of 10 milliseconds for the inks in Examples 2, 12 to 14. A bubble pressure dynamic surface tensile meter (KRUSS BP-100) was used to measure the dynamic surface tension at a surface life of 10 milliseconds for each ink. The evaluation results for the inks in Examples 2, 12 to 14 confirmed that good results were obtained in terms of intermittent ejection, image density, redispersibility, and resistance to offset and curl when the dynamic surface tension at a surface life of 10 milliseconds was 40.0 mN / m or less.

[0040] [Table 3]

[0041] (Comparative Examples 1-8) In Comparative Examples 1 to 8, inks were prepared by the method described above to have the compositions shown in Table 4. Note that all values ​​in Table 4 are in "mass%". In Comparative Examples 1 to 8, the composition of the water-soluble solvent c differed from that of the above examples. Specifically, the ink in Comparative Example 1 differs from the ink in the above examples in that it does not contain 3-methyl-1,5-pentanediol. The ink in Comparative Example 2 differs from the ink in the above examples in that the content of 3-methyl-1,5-pentanediol exceeds 15% by mass. The ink in Comparative Example 3 differs from the ink in the above examples in that the content of polyethylene glycol is less than 8% by mass. The ink in Comparative Example 4 differs from the ink in the above examples in that the content of polyethylene glycol exceeds 20% by mass. The ink in Comparative Example 5 differs from the ink in the above examples in that it does not contain triethylene glycol monobutyl ether. The ink in Comparative Example 6 differs from the ink in the above examples in that the content of triethylene glycol monobutyl ether exceeds 10% by mass. The ink according to Comparative Example 7 differs from the ink according to the above example in that it does not use polyethylene glycol 400, but instead uses polyethylene glycol 1000. The ink according to Comparative Example 7 differs from the ink according to the above example in that it does not use polyethylene glycol 400, but instead uses diethylene glycol.

[0042] [Table 4]

[0043] The inks related to Comparative Examples 1 to 8 were evaluated for intermittent ejection, image density, redispersibility, and resistance to offset and curl. Table 5 shows the evaluation results for intermittent ejection, image density, redispersibility, and resistance to offset and curl for the inks related to Comparative Examples 1 to 8.

[0044] [Table 5]

[0045] The ink according to Comparative Example 1 failed to meet the requirements for image density. This is thought to be because the ink according to Comparative Example 1, which does not contain 3-methyl-1,5-pentanediol, lacked sufficient aggregation of pigment particles. Furthermore, the ink according to Comparative Example 2 failed to meet the requirements for redispersibility. This is thought to be because the ink according to Comparative Example 2, which has a high content of 3-methyl-1,5-pentanediol, exhibited excessive aggregation of pigment particles.

[0046] The ink in Comparative Example 3 failed to meet the requirements for redispersibility and resistance to curling. This is thought to be because the ink in Comparative Example 3, which had a low polyethylene glycol content, exhibited excessive aggregation of pigment particles and increased penetration into the recording medium. Furthermore, the ink in Comparative Example 4 failed to meet the requirements for resistance to offsetting. This is thought to be because the ink in Comparative Example 4, which had a high polyethylene glycol content, became more prone to adhesion to the paper discharge roller due to increased viscosity.

[0047] The ink in Comparative Example 5 failed to meet the requirements for resistance to offset. This is thought to be because the ink in Comparative Example 5, which does not contain triethylene glycol monobutyl ether, was unable to suppress the increase in viscosity due to polyethylene glycol, making it prone to sticking to the paper output roller. Furthermore, the ink in Comparative Example 6 failed to meet the requirements for image density and redispersibility. This is thought to be because the ink in Comparative Example 6, which has a high content of triethylene glycol monobutyl ether, lacked sufficient viscosity.

[0048] The ink in Comparative Example 7 failed to meet the requirements for intermittent ejection. This is thought to be because the larger molecular weight of polyethylene glycol in the ink in Comparative Example 7 increased viscosity, making it more prone to sticking to the paper discharge roller. Furthermore, the ink in Comparative Example 8 failed to meet the requirements for resistance to curling. This is thought to be because the ink in Comparative Example 8, which contains diethylene glycol with a smaller molecular weight than polyethylene glycol, had higher penetration into the recording medium.

Claims

1. Pigments and Pigment dispersion resin and Polyethylene glycol with a molecular weight of 200 to 600, comprising 7% to 20% by mass, 1% by mass to 15% by mass of 3-methyl-1,5-pentanediol, 1% by mass to 10% by mass of triethylene glycol monobutyl ether, Water and, Ink containing [a specific ingredient / material].

2. The ink according to claim 1, The dynamic surface tension at a surface lifetime of 10 milliseconds is 40.0 mN / m or less. ink.

3. The ink according to claim 1 or 2, The content of the pigment dispersion resin is 4% by mass or less. ink.

4. The ink according to claim 1 or 2, It further contains an acetylene glycol-based surfactant. ink.

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